The physical and mechanical properties of materials must satisfy the established specifications and ensure high-quality production of PCBs in accordance with standard technical specifications. For the manufacture of boards, layered plastics are used - foil dielectrics clad with electrolytic copper foil with a thickness of 5, 20, 35, 50, 70 and 105 microns with a copper purity of at least 99.5%, surface roughness of at least 0.4–0.5 microns, which are supplied in the form of sheets with dimensions of 500×700 mm and a thickness of 0.06–3 mm. Laminated plastics must have high chemical and thermal resistance, moisture absorption of no more than 0.2–0.8%, and withstand thermal shock (260°C) for 5–20 s. Surface resistance of dielectrics at 40°C and relative humidity 93% for 4 days. must be at least 10 4 MOhm. The specific volume resistance of the dielectric is not less than 5·10 11 Ohm·cm. The adhesion strength of the foil to the base (3mm wide strip) is from 12 to 15 MPa. Used as a base in laminated plastics getinaks , which is compressed layers of electrical insulating paper impregnated with phenolic resin; fiberglass laminates are compressed layers of fiberglass impregnated with epoxyphenolic resin, and other materials (Table 2.1).

Table 2.1. Basic materials for making circuit boards.

Material	Brand	Thickness	Application area
Foils, microns	Material, mm
Getinax: foil-coated fire-resistant moisture-resistant Fiberglass: foil-coated fire-resistant heat-resistant etching with an adhesive layer with thin foil Foil dielectric: thin for MPP for microelectronics Fiberglass cushioning Lavsan foiled Fluoroplastic: foil-reinforced polyamide foiled Steel enameled Aluminum anodized Aluminum oxide ceramics	GF-1(2) GPF-2-50G GOFV-2-35 SF-1(2) SFO-1(2) STF-1(2) FTS-1(2) STEC STPA-1 FDP-1 FDM-1 (2) FDME-1(2) SP-1-0.0025 LF-1 LF-2 FF-4 FAF-4D PF-1 PF-2 – – –	35, 50 35, 50 18, 35 18, 35 – – – – –	1-3 1-3 1-3 0,8-3 0,9-3 0,1-3 0,08-0,5 1,0-1,5 0,1-3 0,5 0,2-0,35 0,1-0,3 0,0025 0,05 0,1 1,5-3 0,5-3 0,05 0,1 1-5 0,5-3 2-4	OPP DPP DPP OPP, DPP OPP, DPP OPP, DPP MPP, DPP DPP OPP, DPP MPP MPP MPP MPP GPP GPP DPP GPP GPP GPP DPP DPP, GIMS DPP, MPP

Getinax, having satisfactory electrical insulating properties in normal climatic conditions, good processability and low cost, has found application in the production of household electronic equipment. For PCBs operated in difficult climatic conditions with a wide range of operating temperatures (–60...+180°C) as part of electronic computing equipment, communications equipment, and measuring equipment, more expensive glass textolites are used. They are distinguished by a wide range of operating temperatures, low (0.2 - 0.8 %) water absorption, high values ​​of volumetric and surface resistance, resistance to warping. Disadvantages - the possibility of peeling off the foil due to thermal shocks, enveloping the resin when drilling holes. Increasing the fire resistance of dielectrics (GPF, GPFV, SPNF, STNF) used in power supplies is achieved by introducing fire retardants into their composition (for example, tetrabromodiphenylpropane).

For the manufacture of foil dielectrics, electrolytic copper foil is mainly used, one side of which must have a smooth surface (not lower than the eighth class of cleanliness) to ensure accurate reproduction of the printed circuit, and the other must be rough with a microroughness height of at least 3 microns for good adhesion to the dielectric. To do this, the foil is subjected to oxidation electrochemically in a solution of sodium hydroxide. The foiling of dielectrics is carried out by pressing at a temperature of 160–180°C and a pressure of 5–15 MPa.

Ceramic materials are characterized by high mechanical strength, which varies slightly in the temperature range of 20–700°C, stability of electrical and geometric parameters, low (up to 0.2%) water absorption and gas release when heated in a vacuum, but are fragile and have a high cost.

Steel and aluminum are used as the metal base of the boards. On steel bases, insulation of current-carrying areas is carried out using special enamels, which include oxides of magnesium, calcium, silicon, boron, aluminum or mixtures thereof, a binder (polyvinyl chloride, polyvinyl acetate or methyl methacrylate) and a plasticizer. The film is applied to the base by rolling between rollers followed by burning. An insulating layer with a thickness of several tens to hundreds of micrometers with an insulation resistance of 10 2 – 10 3 MOhm on the aluminum surface is obtained by anodic oxidation. The thermal conductivity of anodized aluminum is 200 W/(m K), and that of steel is 40 W/(m K). Non-polar (fluoroplastic, polyethylene, polypropylene) and polar (polystyrene, polyphenylene oxide) polymers are used as the basis for microwave PP. For the manufacture of microboards and microassemblies in the microwave range, ceramic materials with stable properties are also used. electrical characteristics and geometric parameters.

Polyamide film is used for the manufacture of flexible circuit boards with high tensile strength, chemical resistance, and fire resistance. It has the highest temperature stability among polymers, since it does not lose flexibility from the temperatures of liquid nitrogen to the temperatures of eutectic soldering of silicon with gold (400°C). In addition, it is characterized by low gas evolution in a vacuum, radiation resistance, and no envelopment during drilling. Disadvantages: increased water absorption and high cost.

Formation of a diagram drawing.

Drawing a pattern or protective relief of the required configuration is necessary when carrying out metallization and etching processes. The drawing must have clear boundaries with accurate reproduction of fine lines, be resistant to etching solutions, not contaminate circuit boards and electrolytes, and be easy to remove after performing its functions. The transfer of a printed circuit design onto a foil dielectric is carried out using gridography, offset printing and photo printing. The choice of method depends on the design of the board, the required accuracy and density of installation, and the serial production.

Gridographic method drawing a circuit diagram is the most cost-effective for mass and large-scale production of circuit boards with a minimum width of conductors and a distance between them > 0.5 mm, image reproduction accuracy ± 0.1 mm. The idea is to apply special acid-resistant paint to the board by pressing it with a rubber spatula (squeegee) through a mesh stencil, in which the required pattern is formed by open mesh cells (Fig. 2.4).

To make the stencil, metal mesh is used from stainless steel with a wire thickness of 30–50 microns and a weaving frequency of 60–160 threads per 1 cm, metallized nylon fiber, which has better elasticity, with a thread thickness of 40 microns and a weaving frequency of up to 200 threads per 1 cm, as well as from polyester fibers and nylon

One of the disadvantages of mesh is that it stretches with repeated use. The most durable are meshes made of stainless steel (up to 20 thousand prints), metallized plastics (12 thousand), polyester fibers (up to 10 thousand), nylon (5 thousand).

Rice. 2.4. The principle of screen printing.

1 – squeegee; 2 – stencil; 3 – paint; 4 – base.

The image on the grid is obtained by exposing liquid or dry (film) photoresist, after development of which open (pattern-free) grid cells are formed. The stencil in the mesh frame is installed with a gap of 0.5–2 mm from the surface of the board so that the contact of the mesh with the surface of the board is only in the area where the mesh is pressed with a squeegee. The squeegee is a rectangular sharpened strip of rubber installed in relation to the substrate at an angle of 60–70°.

To obtain a PP pattern, thermosetting paints ST 3.5 are used;

ST 3.12, which are dried either in a heating cabinet at a temperature of 60°C for 40 minutes, or in air for 6 hours, which lengthens the screenography process. More technologically advanced are the photopolymer compositions EP-918 and FKP-TZ with ultraviolet curing for 10–15 s, which is a decisive factor in automating the process. When applied once, the green coating has a thickness of 15–25 microns, reproduces a pattern with a line width and gaps of up to 0.25 mm, withstands immersion in molten POS-61 solder at a temperature of 260°C for up to 10 s, exposure to an alcohol-gasoline mixture for up to 5 min and thermal cycling in the temperature range from – 60 to +120 °C. After applying the design, the board is dried at a temperature of 60 ° C for 5–8 minutes, the quality is controlled and, if necessary, retouched. Removal of the protective mask after etching or metallization is carried out using a chemical method in a 5% solution of caustic soda for 10–20 s.

Table 2.2. Equipment for screen printing.

For screen printing, semi-automatic and automatic equipment is used, differing in print format and productivity (Table 2.2). Automatic screen printing lines from Chemcut (USA), Resco (Italy) have automatic systems for feeding and installing boards, squeegee movement and resist supply. To dry the resist, an IR-tunnel type oven is used.

Offset printing used for large-scale production of PCBs with a small range of circuits. Resolution is 0.5–1 mm, the accuracy of the resulting image is ±0.2 mm. The essence of the method is that paint is rolled into the cliche that carries the image of the circuit (printed conductors, contact pads). Then it is removed with a rubber-coated offset roller, transferred to an insulating base and dried. The cliche and the board base are located one behind the other on the base of the offset printing machine (Fig. 2.5)

Fig.2.5. Offset printing scheme.

1 – offset roller; 2 – cliche; 3 – board;

4 – roller for applying paint; 5 – pressure roller.

The accuracy of printing and the sharpness of the contours are determined by the parallelism of the roller and the base, the type and consistency of the paint. With one cliche you can make an unlimited number of prints. The productivity of the method is limited by the duration of the oscillatory cycle (paint application - transfer) and does not exceed 200–300 impressions per hour. Disadvantages of the method: the duration of the cliche manufacturing process, the difficulty of changing the pattern of the circuit, the difficulty of obtaining non-porous layers, the high cost of the equipment.

Photographic method drawing a pattern allows you to obtain a minimum width of conductors and distances between them of 0.1–0.15 mm with a reproduction accuracy of up to 0.01 mm. From an economic point of view, this method is less cost-effective, but allows for maximum pattern resolution and is therefore used in small-scale and mass production in the manufacture of high-density and precision boards. The method is based on the use of photosensitive compositions called photoresists , which must have: high sensitivity; high resolution; a homogeneous, non-porous layer over the entire surface with high adhesion to the board material; resistance to chemical influences; ease of preparation, reliability and safety of use.

Photoresists are divided into negative and positive. Negative photoresists under the influence of radiation they form protective relief areas as a result of photopolymerization and hardening. The illuminated areas stop dissolving and remain on the surface of the substrate. Positive photoresists transmit the photomask image without changes. During light processing, the exposed areas are destroyed and washed out.

To obtain a pattern of a circuit when using a negative photoresist, exposure is made through a negative, and a positive photoresist is exposed through a positive. Positive photoresists have a higher resolution, which is explained by differences in the absorption of radiation by the photosensitive layer. The resolution of the layer is affected by the diffraction bending of light at the edge of the opaque element of the template and the reflection of light from the substrate (Fig. 2.6, A).

Fig.2.6. Exposure of the photosensitive layer:

a – exposure; b – negative photoresist; c – positive photoresist;

1 – diffraction; 2 – scattering; 3 – reflection; 4 – template; 5 – resist; 6 – substrate.

In negative photoresist, diffraction does not play a noticeable role, since the template is tightly pressed to the resist, but as a result of reflection, a halo appears around the protective areas, which reduces the resolution (Fig. 2.6, b). In the positive resist layer, under the influence of diffraction, only the upper area of ​​the resist under the opaque areas of the photomask will be destroyed and washed out during development, which will have little effect on the protective properties of the layer. Light reflected from the substrate may cause some destruction of the area adjacent to it, but the developer does not wash out this area, since under the influence of adhesive forces the layer will move down, again forming a clear edge of the image without a halo (Fig. 2.6, V).

Currently, liquid and dry (film) photoresists are used in industry. Liquid photoresists– colloidal solutions of synthetic polymers, in particular polyvinyl alcohol (PVA). The presence of the hydroxyl group OH in each chain link determines the high hygroscopicity and polarity of polyvinyl alcohol. When ammonium dichromate is added to an aqueous solution of PVA, the latter is “sensitized.” A PVA-based photoresist is applied to the pre-prepared surface of the board by dipping the workpiece, pouring, and then centrifuging. Then the photoresist layers are dried in a heating cabinet with air circulation at a temperature of 40°C for 30–40 minutes. After exposure, the photoresist is developed in warm water. To increase the chemical resistance of PVA-based photoresist, chemical tanning of the PP pattern in a solution of chromic anhydride is used, and then thermal tanning at a temperature of 120°C for 45–50 minutes. Tanning (removal) of the photoresist is carried out for 3–6 s in a solution of the following composition:

– 200–250 g/l oxalic acid,

– 50–80 g/l sodium chloride,

– up to 1000 ml of water at a temperature of 20 °C.

The advantages of PVA-based photoresist are low toxicity and fire hazard, development using water. Its disadvantages include the effect of dark tanning (therefore, the shelf life of blanks with applied photoresist should not exceed 3–6 hours), low acid and alkali resistance, the difficulty of automating the process of obtaining a pattern, the complexity of preparing photoresist, and low sensitivity.

Improved properties of liquid photoresists (elimination of tanning, increased acid resistance) are achieved in photoresist based on cinnamate. The photosensitive component of this type of photoresist is polyvinyl cinnamate (PVC), a product of the reaction of polyvinyl alcohol and cinnamic acid chloride. Its resolution is approximately 500 lines/mm, development is carried out in organic solvents - trichloroethane, toluene, chlorobenzene. To intensify the process of developing and removing PVC photoresist, ultrasonic vibrations are used. Diffusion in an ultrasonic field is greatly accelerated due to acoustic microflows, and the resulting cavitation bubbles, when collapsed, tear off sections of the photoresist from the board. The development time is reduced to 10 s, i.e. 5–8 times compared to conventional technology. The disadvantages of PVC photoresist include its high cost and the use of toxic organic solvents. Therefore, PVC resists have not found wide application in the manufacture of PCBs, but are used mainly in the manufacture of ICs.

Photoresists based on diazo compounds are used mainly as positive ones. The photosensitivity of diazo compounds is due to the presence in them of groups consisting of two nitrogen atoms N2 (Fig. 2.7).

Fig.2.7. Molecular bonds in the structure of diazo compounds.

Drying of the photoresist layer is carried out in two stages:

– at a temperature of 20°C for 15–20 minutes to evaporate volatile components;

– in a thermostat with air circulation at a temperature of 80 ° C for 30–40 minutes.

Developers are solutions of trisodium phosphate, soda, and weak alkalis. Photoresists FP-383, FN-11 based on diazo compounds have a resolution of 350–400 lines/mm, high chemical resistance, but their cost is high.

Dry film photoresists Riston brands were first developed in 1968 by Du Pont (USA) and have a thickness of 18 microns (red), 45 microns (blue) and 72 microns (ruby). Dry film photoresist SPF-2 has been produced since 1975 in thicknesses of 20, 40 and 60 microns and is a polymer based on polymethyl methacrylate 2 (Fig. 2.8), located between the polyethylene 3 and lavsan / films with a thickness of 25 microns each.

Fig.2.8. Structure of dry photoresist.

The following types of dry film photoresists are produced in the CIS:

– manifested in organic substances – SPF-2, SPF-AS-1, SRF-P;

– water-alkaline – SPF-VShch2, TFPC;

– increased reliability – SPF-PNShch;

– protective – SPF-Z-VShch.

Before rolling onto the surface of the PCB base, the protective film of polyethylene is removed and dry photoresist is applied to the board using the roller method (cladding, lamination) when heated to 100°C at a speed of up to 1 m/min using a special device called a laminator. Dry resist polymerizes under the influence of ultraviolet radiation, the maximum of its spectral sensitivity is in the region of 350 nm, therefore mercury lamps are used for exposure. Development is carried out in jet-type machines in solutions of methyl chloride and dimethylformamide.

SPF-2 is a dry film photoresist, similar in properties to Riston photoresist, can be processed in both acidic and alkaline environments and is used in all methods of manufacturing DPP. When using it, it is necessary to seal the developing equipment. SPF-VShch has a higher resolution (100–150 lines/mm), is resistant in an acidic environment, and can be processed in alkaline solutions. The composition of the TFPC photoresist (in the polymerizing composition) includes methacrylic acid, which improves performance characteristics. It does not require heat treatment of the protective relief before electroplating. SPF-AS-1 allows you to obtain a PP pattern using both subtractive and additive technologies, since it is resistant in both acidic and alkaline environments. To improve the adhesion of the photosensitive layer to the copper substrate, benzotriazole was introduced into the composition.

The use of dry photoresist significantly simplifies the PCB manufacturing process and increases the yield of suitable products from 60 to 90%. Wherein:

– the operations of drying, tanning and retouching, as well as contamination and instability of layers are excluded;

– protection of metallized holes from photoresist leakage is provided;

– high automation and mechanization of the PCB manufacturing process and image control is achieved.

Installation for applying dry film photoresist - laminator (Fig. 2.9) consists of rollers 2, submitting fees 6 and pressing the photoresist to the surface of the workpieces, rollers 3 And 4 for removing the protective polyethylene film, reel with photoresist 5, heater 1 with thermostat.

Fig.2.9. Laminator diagram.

The speed of movement of the board blank reaches 0.1 m/s, the heater temperature is (105 ±5) °C. The design of the ARSM 3.289.006 NPO Raton (Belarus) installation provides a constant pressing force regardless of the gap installed between the heater rollers. The maximum width of the PP workpiece is 560 mm. A feature of rolling is the danger of dust getting under the photoresist layer, so the installation must operate in a hermetic zone. The rolled photoresist film is kept for at least 30 minutes before exposure to complete shrinkage processes, which can cause distortion of the pattern and reduce adhesion.

The development of the pattern is carried out as a result of the chemical and mechanical action of methyl chloroform. The optimal development time is taken to be 1.5 times longer than necessary for complete removal untanned SPF. The quality of the development operation depends on five factors: development time, development temperature, developer pressure in the chamber, contamination of the developing gel, and the degree of final rinsing. As dissolved photoresist accumulates in the developer, the development speed slows down. After development, the board must be washed with water until all solvent residues are completely removed. The duration of the SPF-2 development operation at a developer temperature of 14–18°C, a solution pressure in the chambers of 0.15 MPa and a conveyor speed of 2.2 m/min is 40–42 s.

Removal and development of photoresist is carried out in inkjet machines (GGMZ.254.001, ARSMZ.249.000) in methylene chloride. This is a strong solvent, so the photoresist removal operation must be performed quickly (within 20–30 s). The installations provide a closed cycle for the use of solvents; after irrigating the boards, the solvents enter the distiller, and then the pure solvents are switched to reuse.

Exposure of a photoresist is intended to initiate photochemical reactions in it and is carried out in installations that have light sources (scanning or stationary) and operate in the ultraviolet region. To ensure a tight fit of the photomasks to the board blanks, frames are used where a vacuum is created. The exposure installation SKTSI.442152.0001 NPO "Raton" with a working field of loading frames of 600×600 mm provides a productivity of 15 boards/hour. Exposure time mercury lamp DRSh-1000 1–5 min. After exposure, to complete the dark photochemical reaction, exposure at room temperature for 30 minutes is required before removing the Mylar protective film.

The disadvantages of dry photoresist are the need to apply mechanical force during rolling, which is unacceptable for glass-ceramic substrates, and the problem of recycling solid and liquid waste. For every 1000 m 2 of material, up to 40 kg of solid and 21 kg of liquid waste are generated, the disposal of which is an environmental problem.

To obtain a conductive pattern on an insulating base, both by gridographic and photochemical methods, it is necessary to use photomasks, which are a graphic image of the pattern on a 1:1 scale on photographic plates or film. Photomasks are made in a positive image when building up conductive areas on the tapes and in a negative image when conductive areas are obtained by etching copper from gap areas.

The geometric accuracy and quality of the PP pattern are ensured primarily by the accuracy and quality of the photomask, which must have:

– a contrasting black and white image of elements with clear and even boundaries with an optical density of black fields of at least 2.5 units, transparent areas of no more than 0.2 units, measured on a DFE-10 type densitometer;

– minimal image defects (dark dots in white spaces, transparent dots in black fields), which do not exceed 10–30 µm;

– accuracy of the design elements ±0.025 mm.

To a greater extent, the listed requirements are met by high-contrast photographic plates and films “Mikrat-N” (USSR), photographic plates such as FT-41P (USSR), RT-100 (Japan) and Agfalit (Germany).

Currently, two main methods of obtaining photomasks are used: photographing them from photographic originals and drawing them with a light beam on photographic film using program-controlled coordinateographs or a laser beam. When making photo originals, the PP design is made on an enlarged scale (10:1, 4:1, 2:1) on low-shrink material by drawing, making appliqués or cutting into enamel. The application method involves gluing pre-prepared standard elements onto a transparent base (lavsan, glass, etc.). The first method is characterized by low accuracy and high labor intensity, therefore it is used mainly for prototype boards.

Enamel cutting is used for PP with high installation density. To do this, polished sheet glass is covered with an opaque layer of enamel, and the cutting of the circuit design is carried out using a manually controlled coordinateograph. The accuracy of the pattern is 0.03–0.05 mm.

The produced photographic original is photographed with the necessary reduction on a high-contrast photographic plate using photoreproduction printing cameras such as PP-12, EM-513, Klimsch (Germany) and photomasks are obtained, which can be control and working. For replication and production of working, single, and group photo masks, the contact printing method is used from a negative copy of the control photo mask. The operation is performed on a multiplier model ARSM 3.843.000 with an accuracy of ±0.02 mm.

The disadvantages of this method are the high labor intensity of obtaining a photographic original, which requires highly skilled labor, and the difficulty of uniformly illuminating photographic originals of a large area, which reduces the quality of photomasks.

The increasing complexity and density of PP patterns and the need to increase labor productivity led to the development of a method for producing photomasks using a scanning beam directly on photographic film. Coordinate machines with program control have been developed to produce a photomask using a light beam. With the transition to machine design of boards, the need to draw a drawing disappears, since the punched paper tape with the coordinates of the conductors obtained from the computer is entered into the reading device of the coordinateograph, on which the photomask is automatically created.

The coordinateograph (Fig. 2.10) consists of a vacuum table 8, on which the film, photo heads and control unit are mounted /. The table moves with high precision in two mutually perpendicular directions using precision lead screws 9 and 3, which are driven by stepper motors 2 And 10. The photo head turns on the illuminator 4, focusing system 5, circular diaphragm 6 and photo shutter 7. The diaphragm has a set of holes (25–70), forming a certain element of the PP pattern, and is fixed on the shaft of the stepper motor. In accordance with the operating program, signals from the control unit are supplied to the stepper motors of the table drive, diaphragm and to the illuminator. Modern coordinateographs (Table 5.4) are equipped with systems for automatically maintaining a constant light mode, outputting information about photomasks from the computer onto film at a scale of 1:2; 1:1; 2:1; 4:1.

Rice. 5.10. Coordinateograph diagram.

Tahiti!.. Tahiti!..
We have not been to any Tahiti!
They feed us well here too!
© Cartoon cat

Introduction with digression

How were boards made in the past in domestic and laboratory conditions? There were several ways, for example:

1. future conductors drew drawings;
2. engraved and cut with cutters;
3. they glued it with adhesive tape or tape, then cut out the design with a scalpel;
4. They made simple stencils and then applied the design using an airbrush.

The missing elements were completed with drawing pens and retouched with a scalpel.

It was a long and laborious process, requiring the “drawer” to have remarkable artistic abilities and accuracy. The thickness of the lines hardly fit into 0.8 mm, there was no repetition accuracy, each board had to be drawn separately, which greatly limited the production of even a very small batch printed circuit boards(further PP).

What do we have today?

Progress does not stand still. The times when radio amateurs painted PP with stone axes on mammoth skins have sunk into oblivion. The appearance on the market of publicly available chemistry for photolithography opens up completely different prospects for the production of PCB without metallization of holes at home.

Let's take a quick look at the chemistry used today to produce PP.

Photoresist

You can use liquid or film. We will not consider film in this article due to its scarcity, difficulties in rolling onto PCBs and the lower quality of the resulting printed circuit boards.

After analyzing market offers, I settled on POSITIV 20 as the optimal photoresist for home PCB production.

Purpose:
POSITIV 20 photosensitive varnish. Used in small-scale production of printed circuit boards, copper engravings, and when carrying out work related to transferring images to various materials.
Properties:
High exposure characteristics provide good contrast of transferred images.
Application:
It is used in areas related to the transfer of images onto glass, plastics, metals, etc. in small-scale production. Directions for use are indicated on the bottle.
Characteristics:
Color: blue
Density: at 20°C 0.87 g/cm 3
Drying time: at 70°C 15 min.
Consumption: 15 l/m2
Maximum photosensitivity: 310-440 nm

The instructions for the photoresist say that it can be stored at room temperature and is not subject to aging. I strongly disagree! It should be stored in a cool place, for example, on the bottom shelf of the refrigerator, where the temperature is usually maintained at +2+6°C. But under no circumstances allow negative temperatures!

If you use photoresists that are sold by the glass and do not have lightproof packaging, you need to take care of protection from light. It should be stored in complete darkness and at a temperature of +2+6°C.

Enlightener

Likewise, I consider TRANSPARENT 21, which I constantly use, to be the most suitable educational tool.

Purpose:
Allows direct transfer of images onto surfaces coated with photosensitive emulsion POSITIV 20 or other photoresist.
Properties:
Gives transparency to paper. Provides transmission of ultraviolet rays.
Application:
For quick transfer contours of drawings and diagrams onto the substrate. Allows you to significantly simplify the reproduction process and reduce time s e costs.
Characteristics:
Color: transparent
Density: at 20°C 0.79 g/cm 3
Drying time: at 20°C 30 min.
Note:
Instead of regular paper with transparency, you can use transparent film for inkjet or laser printers, depending on what we will print the photomask on.

Photoresist developer

There are many different solutions for developing photoresist.

It is recommended to develop using a “liquid glass” solution. Its chemical composition: Na 2 SiO 3 * 5H 2 O. This substance has a huge number of advantages. The most important thing is that it is very difficult to overexpose the PP in it; you can leave the PP for a non-fixed exact time. The solution almost does not change its properties with temperature changes (there is no risk of decay when the temperature increases), and also has a very long shelf life - its concentration remains constant for at least a couple of years. The absence of the problem of overexposure in the solution will allow increasing its concentration to reduce the time of development of PP. It is recommended to mix 1 part concentrate with 180 parts water (just over 1.7 g of silicate in 200 ml of water), but it is possible to make a more concentrated mixture so that the image develops in about 5 seconds without the risk of surface damage due to overexposure. If it is impossible to purchase sodium silicate, use sodium carbonate (Na 2 CO 3) or potassium carbonate (K 2 CO 3).

I haven’t tried either the first or the second, so I’ll tell you what I’ve been using without any problems for several years now. I use a water solution of caustic soda. For 1 liter of cold water 7 grams of caustic soda. If there is no NaOH, I use a KOH solution, doubling the concentration of alkali in the solution. Development time 30-60 seconds with correct exposure. If after 2 minutes the pattern does not appear (or appears weakly), and the photoresist begins to wash off from the workpiece, this means that the exposure time was chosen incorrectly: you need to increase it. If, on the contrary, it quickly appears, but both exposed and unexposed areas are washed away; either the concentration of the solution is too high, or the quality of the photomask is low (ultraviolet light passes freely through the “black”): you need to increase the print density of the template.

Copper etching solutions

Excess copper is removed from printed circuit boards using various etchants. Among people doing this at home, ammonium persulfate, hydrogen peroxide + hydrochloric acid, copper sulfate solution + table salt are often common.

I always poison with ferric chloride in a glass container. When working with the solution, you need to be careful and attentive: if it gets on clothes and objects, it leaves rusty stains that are difficult to remove with a weak solution of citric (lemon juice) or oxalic acid.

We heat a concentrated solution of ferric chloride to 50-60°C, immerse the workpiece in it, and carefully and effortlessly move a glass rod with a cotton swab at the end over areas where copper is etched less easily, this achieves a more even etching over the entire area of ​​the PP. If you do not force the speed to equalize, the required etching duration increases, and this eventually leads to the fact that in areas where copper has already been etched, etching of the tracks begins. As a result, we don’t get what we wanted at all. It is highly desirable to ensure continuous stirring of the etching solution.

Chemicals for removing photoresist

What is the easiest way to wash off unnecessary photoresist after etching? After repeated trial and error, I settled on ordinary acetone. When it’s not there, I wash it off with any solvent for nitro paints.

So, let's make a printed circuit board

Where does a high quality PCB start? Right:

Create a high-quality photo template

To make it, you can use almost any modern laser or inkjet printer. Considering that we are using positive photoresist in this article, the printer should draw black where copper should remain on the PCB. Where there should be no copper the printer should not draw anything. Very important point when printing a photomask: you need to set the maximum dye flow (in the printer driver settings). The blacker the painted areas, the greater the chances of getting a great result. No color is needed, a black cartridge is enough. From the program (we will not consider programs: everyone is free to choose for themselves - from PCAD to Paintbrush) in which the photo template was drawn, we print it on a regular sheet of paper. The higher the printing resolution and the higher quality the paper, the higher the quality of the photomask. I recommend no lower than 600 dpi; the paper should not be very thick. When printing, we take into account that with the side of the sheet on which the paint is applied, the template will be placed on the PP blank. If done differently, the edges of the PP conductors will be blurred and indistinct. Let the paint dry, if it was jet printer. Next, we impregnate the paper with TRANSPARENT 21, let it dry and the photo template is ready.

Instead of paper and enlightenment, it is possible and even very desirable to use transparent film for laser (when printing on a laser printer) or inkjet (for inkjet printing) printers. Please note that these films have unequal sides: only one working side. If you use laser printing, I highly recommend dry running a sheet of film before printing - simply run the sheet through the printer, simulating printing, but not printing anything. Why is this necessary? When printing, the fuser (oven) will heat the sheet, which will inevitably lead to its deformation. As a consequence, there is an error in the geometry of the output PCB. When producing double-sided PCBs, this is fraught with a mismatch of layers with all the consequences And with the help of a “dry” run, we will warm up the sheet, it will be deformed and will be ready for printing the template. When printing, the sheet will pass through the oven a second time, but the deformation will be much less significant checked several times.

If the PP is simple, you can draw it manually in a very convenient program with Russified interface Sprint Layout 3.0R (~650 KB).

At the preparatory stage, draw not too bulky electrical circuits very convenient in the also Russified program sPlan 4.0 (~450 KB).

This is what ready-made photo templates look like, printed on Epson printer Stylus Color 740:

We print only in black, with maximum dye addition. Material transparent film for inkjet printers.

Preparing the PP surface for applying photoresist

For the production of PP, sheet materials coated with copper foil are used. The most common options are with copper thickness of 18 and 35 microns. Most often, for the production of PP at home, sheet textolite (fabric pressed with glue in several layers), fiberglass (the same, but epoxy compounds are used as glue) and getinax (pressed paper with glue) are used. Less commonly, sittal and polycor (high-frequency ceramics are used extremely rarely at home), fluoroplastic (organic plastic). The latter is also used for the manufacture of high-frequency devices and, having very good electrical characteristics, can be used anywhere and everywhere, but its use is limited by its high price.

First of all, you need to make sure that the workpiece does not have deep scratches, burrs or corroded areas. Next, it is advisable to polish the copper to a mirror. We polish without being particularly zealous, otherwise we will erase the already thin layer of copper (35 microns) or, in any case, we will achieve different thicknesses of copper on the surface of the workpiece. And this, in turn, will lead to different speeds etching: it will etch faster where it is thinner. And a thinner conductor on the board is not always good. Especially if it is long and a decent current will flow through it. If the copper on the workpiece is of high quality, without sins, then it is enough to degrease the surface.

Applying photoresist to the surface of the workpiece

We place the board on a horizontal or slightly inclined surface and apply the composition from an aerosol package from a distance of about 20 cm. We remember that the most important enemy in this case is dust. Every particle of dust on the surface of the workpiece is a source of problems. To create a uniform coating, spray the aerosol in a continuous zigzag motion, starting from the upper left corner. Do not use the aerosol in excess quantities, as this will cause unwanted smudges and lead to the formation of a non-uniform coating thickness, requiring a longer exposure time. In summer, when ambient temperatures are high, re-treatment may be necessary, or the aerosol may need to be sprayed from a shorter distance to reduce evaporation losses. When spraying, do not tilt the can too much; this leads to increased consumption of propellant gas and, as a result, the aerosol can stops working, although there is still photoresist in it. If you are getting unsatisfactory results when spray coating photoresist, use spin coating. In this case, photoresist is applied to a board mounted on a rotating table with a 300-1000 rpm drive. After finishing coating, the board should not be exposed to strong light. Based on the color of the coating, you can approximately determine the thickness of the applied layer:

• light gray blue 1-3 microns;
• dark gray blue 3-6 microns;
• blue 6-8 microns;
• dark blue more than 8 microns.

On copper, the coating color may have a greenish tint.

The thinner the coating on the workpiece, the better the result.

I always spin coat the photoresist. My centrifuge has a rotation speed of 500-600 rpm. Fastening should be simple, clamping is carried out only at the ends of the workpiece. We fix the workpiece, start the centrifuge, spray it on the center of the workpiece and watch how the photoresist spreads over the surface in a thin layer. Centrifugal forces will throw off excess photoresist from the future PCB, so I highly recommend providing a protective wall so as not to turn the workplace into a pigsty. I use an ordinary saucepan with a hole in the bottom in the center. The axis of the electric motor passes through this hole, on which a mounting platform is installed in the form of a cross of two aluminum slats, along which the workpiece clamping ears “run”. The ears are made of aluminum angles, clamped to the rail with a wing nut. Why aluminum? Low specific gravity and, as a result, less runout when the center of mass of rotation deviates from the center of rotation of the centrifuge axis. The more accurately the workpiece is centered, the less beating will occur due to the eccentricity of the mass and the less effort will be required to rigidly attach the centrifuge to the base.

Photoresist is applied. Let it dry for 15-20 minutes, turn the workpiece over, apply a layer on the other side. Give another 15-20 minutes to dry. Do not forget that direct sunlight and fingers on the working sides of the workpiece are unacceptable.

Tanning photoresist on the surface of the workpiece

Place the workpiece in the oven, gradually bring the temperature to 60-70°C. Maintain at this temperature for 20-40 minutes. It is important that nothing touches the surfaces of the workpiece; only touching the ends is permissible.

Aligning the top and bottom photomasks on the workpiece surfaces

Each of the photo masks (top and bottom) should have marks along which 2 holes need to be made on the workpiece to align the layers. The farther the marks are from each other, the higher the alignment accuracy. I usually place them diagonally on the templates. Using a drilling machine, using these marks on the workpiece, we drill two holes strictly at 90° (the thinner the holes, the more accurate the alignment; I use a 0.3 mm drill) and align the templates along them, not forgetting that the template must be applied to the photoresist the side on which the print was made. We press the templates to the workpiece with thin glasses. It is preferable to use quartz glass as it transmits ultraviolet radiation better. Plexiglas (plexiglass) gives even better results, but it has the unpleasant property of scratching, which will inevitably affect the quality of the PP. For small PCB sizes, you can use a transparent cover from a CD package. In the absence of such glass, you can use ordinary window glass, increasing the exposure time. It is important that the glass is smooth, ensuring an even fit of the photomasks to the workpiece, otherwise it will be impossible to obtain high-quality edges of the tracks on the finished PCB.

A blank with a photomask under plexiglass. We use a CD box.

Exposure (light exposure)

The time required for exposure depends on the thickness of the photoresist layer and the intensity of the light source. Photoresist varnish POSITIV 20 is sensitive to ultraviolet rays, the maximum sensitivity occurs in the area with a wavelength of 360-410 nm.

It is best to expose under lamps whose radiation range is in the ultraviolet region of the spectrum, but if you do not have such a lamp, you can also use ordinary powerful incandescent lamps, increasing the exposure time. Do not start illumination until the lighting from the source has stabilized; it is necessary for the lamp to warm up for 2-3 minutes. The exposure time depends on the thickness of the coating and is usually 60-120 seconds when the light source is located at a distance of 25-30 cm. The glass plates used can absorb up to 65% of ultraviolet radiation, so in such cases it is necessary to increase the exposure time. The best results are achieved when using transparent plexiglass plates. When using photoresist with a long shelf life, the exposure time may need to be doubled remember: Photoresists are subject to aging!

Examples of using different light sources:

UV lamps

We expose each side in turn, after exposure we let the workpiece stand for 20-30 minutes in a dark place.

Development of the exposed workpiece

We develop it in a solution of NaOH (caustic soda) see the beginning of the article for more details at a solution temperature of 20-25°C. If there is no manifestation within 2 minutes small O exposure time. If it appears well, but useful areas are also washed away you are too clever with the solution (the concentration is too high) or the exposure time is too long this source radiation or low-quality photomask insufficiently saturated printed black color allows ultraviolet light to illuminate the workpiece.

When developing, I always very carefully, effortlessly “roll” a cotton swab on a glass rod over the places where the exposed photoresist should be washed off; this speeds up the process.

Washing the workpiece from alkali and residues of exfoliated exposed photoresist

I do this under the tap with regular tap water.

Re-tanning photoresist

We place the workpiece in the oven, gradually raise the temperature and hold it at a temperature of 60-100°C for 60-120 minutes; the pattern becomes strong and hard.

Checking the development quality

Briefly (for 5-15 seconds) immerse the workpiece in a ferric chloride solution heated to a temperature of 50-60°C. Rinse quickly with running water. In places where there is no photoresist, intensive etching of the copper begins. If photoresist accidentally remains somewhere, carefully remove it mechanically. It is convenient to do this with a regular or ophthalmic scalpel, armed with optics (soldering glasses, magnifying glass A watchmaker, loupe A on a tripod, microscope).

Etching

We poison in a concentrated solution of ferric chloride at a temperature of 50-60°C. It is advisable to ensure continuous circulation of the etching solution. We carefully “massage” poorly bleeding areas with a cotton swab on a glass rod. If ferric chloride is freshly prepared, the etching time usually does not exceed 5-6 minutes. We rinse the workpiece with running water.

Board etched

How to prepare a concentrated solution of ferric chloride? Dissolve FeCl 3 in slightly (up to 40°C) heated water until it stops dissolving. Filter the solution. It should be stored in a cool, dark place in sealed non-metallic packaging in glass bottles, for example.

Removing unnecessary photoresist

We wash off the photoresist from the tracks with acetone or a solvent for nitro paints and nitro enamels.

Drilling holes

It is advisable to select the diameter of the point of the future hole on the photomask such that it will be convenient to drill later. For example, with a required hole diameter of 0.6-0.8 mm, the diameter of the point on the photomask should be about 0.4-0.5 mm in this case the drill will be well centered.

It is advisable to use drills coated with tungsten carbide: drills made of high-speed steels wear out very quickly, although steel can be used for drilling single holes of large diameter (more than 2 mm), since drills coated with tungsten carbide of this diameter are too expensive. When drilling holes with a diameter of less than 1 mm, it is better to use a vertical machine, otherwise your drill bits will break quickly. If you drill with a hand drill, distortions are inevitable, leading to inaccurate joining of holes between layers. The top-down movement on a vertical drilling machine is the most optimal in terms of the load on the tool. Carbide drills are made with a rigid (i.e. the drill fits exactly to the hole diameter) or a thick (sometimes called "turbo") shank that has a standard size (usually 3.5 mm). When drilling with carbide-coated drills, it is important to firmly secure the PCB, since such a drill, when moving upward, can lift the PCB, skew the perpendicularity and tear out a fragment of the board.

Small diameter drills are usually fitted into either a collet chuck (various sizes) or a three-jaw chuck. For precise clamping, clamping in a three-jaw chuck is not the best option, and the small drill size (less than 1 mm) quickly makes grooves in the clamps, losing good clamping. Therefore, for drills with a diameter less than 1 mm, it is better to use a collet chuck. To be on the safe side, purchase an extra set containing spare collets for each size. Some inexpensive drills come with plastic collets; throw them away and buy metal ones.

To obtain acceptable accuracy, it is necessary to properly organize the workplace, that is, firstly, to ensure good lighting of the board when drilling. To do this, you can use a halogen lamp, attaching it to a tripod to be able to choose a position (illuminate the right side). Secondly, raise the work surface about 15 cm above the tabletop for better visual control over the process. It would be a good idea to remove dust and chips while drilling (you can use a regular vacuum cleaner), but this is not necessary. It should be noted that the dust from fiberglass generated during drilling is very caustic and, if it comes into contact with the skin, causes skin irritation. And finally, when working, it is very convenient to use the foot switch of the drilling machine.

Typical hole sizes:

• vias 0.8 mm or less;
• integrated circuits, resistors, etc. 0.7-0.8 mm;
• large diodes (1N4001) 1.0 mm;
• contact blocks, trimmers up to 1.5 mm.

Try to avoid holes with a diameter of less than 0.7 mm. Always keep at least two spare drills of 0.8 mm or smaller, as they always break just at the moment when you urgently need to order. Drills 1 mm and larger are much more reliable, although it would be nice to have spare ones for them. When you need to make two identical boards, you can drill them simultaneously to save time. In this case, it is necessary to very carefully drill holes in the center of the contact pad near each corner of the PCB, and for large boards, holes located close to the center. Lay the boards on top of each other and, using 0.3mm centering holes in two opposite corners and pins as pegs, secure the boards to each other.

If necessary, you can countersink the holes with larger diameter drills.

Copper tinning on PP

If you need to tin the tracks on the PCB, you can use a soldering iron, soft low-melting solder, alcohol-rosin flux and coaxial cable braid. For large volumes, they tin in baths filled with low-temperature solders with the addition of fluxes.

The most popular and simple melt for tinning is the low-melting alloy “Rose” (tin 25%, lead 25%, bismuth 50%), the melting point of which is 93-96°C. Using tongs, place the board under the level of the liquid melt for 5-10 seconds and, after removing it, check whether the entire copper surface is evenly covered. If necessary, the operation is repeated. Immediately after removing the board from the melt, its remains are removed either using a rubber squeegee or by sharp shaking in a direction perpendicular to the plane of the board, holding it in the clamp. Another way to remove residual Rose alloy is to heat the board in a heating cabinet and shake it. The operation can be repeated to achieve a mono-thickness coating. To prevent oxidation of the hot melt, glycerin is added to the tinning container so that its level covers the melt by 10 mm. After the process is completed, the board is washed from glycerin in running water. Attention! These operations involve working with installations and materials exposed to high temperatures, therefore, to prevent burns, it is necessary to use protective gloves, goggles and aprons.

The operation of tinning with a tin-lead alloy is similar, but the higher melt temperature limits the scope of application this method in conditions of artisanal production.

After tinning, do not forget to clean the board from flux and thoroughly degrease it.

If you have a large production, you can use chemical tinning.

Applying a protective mask

The operations with applying a protective mask exactly repeat everything that was written above: we apply photoresist, dry it, tan it, center the mask photomasks, expose it, develop it, wash it and tan it again. Of course, we skip the steps of checking the quality of development, etching, removing photoresist, tinning and drilling. At the very end, tan the mask for 2 hours at a temperature of about 90-100°C - it will become strong and hard, like glass. The formed mask protects the surface of the PP from external influences and protects against theoretically possible short circuits during operation. It also plays an important role in automatic soldering: it prevents the solder from “sitting” on adjacent areas, short-circuiting them.

That's it, the double-sided printed circuit board with mask is ready

I had to make a PP in this way with the width of the tracks and the step between them up to 0.05 mm (!). But this is already jewelry work. And without much effort, you can make PP with a track width and a step between them of 0.15-0.2 mm.

I did not apply a mask to the board shown in the photographs; there was no such need.

Printed circuit board in the process of installing components on it

And here is the device itself for which the PP was made:

This is a cellular telephone bridge that allows you to reduce the cost of mobile communication services by 2-10 times for this it was worth bothering with the PP;). The PCB with soldered components is located in the stand. Previously, there was an ordinary charger for mobile phone batteries.

Additional Information

Metallization of holes

You can even metallize holes at home. To do this, the inner surface of the holes is treated with a 20-30% solution of silver nitrate (lapis). Then the surface is cleaned with a squeegee and the board is dried in the light (you can use a UV lamp). The essence of this operation is that under the influence of light, silver nitrate decomposes, and silver inclusions remain on the board. Next, the chemical precipitation of copper from the solution is carried out: copper sulfate (copper sulfate) 2 g, caustic soda 4 g, ammonia 25 percent 1 ml, glycerin 3.5 ml, formaldehyde 10 percent 8-15 ml, water 100 ml. The shelf life of the prepared solution is very short; it must be prepared immediately before use. After the copper is deposited, the board is washed and dried. The layer turns out to be very thin; its thickness must be increased to 50 microns by galvanic means.

Solution for applying copper plating by electroplating:
For 1 liter of water, 250 g of copper sulfate (copper sulfate) and 50-80 g of concentrated sulfuric acid. The anode is a copper plate suspended parallel to the part being coated. The voltage should be 3-4 V, current density 0.02-0.3 A/cm 2, temperature 18-30°C. The lower the current, the slower the metallization process, but the better the resulting coating.

A fragment of a printed circuit board showing metallization in the hole

Homemade photoresists

Photoresist based on gelatin and potassium bichromate:
First solution: pour 15 g of gelatin into 60 ml of boiled water and leave to swell for 2-3 hours. After the gelatin swells, place the container in a water bath at a temperature of 30-40°C until the gelatin is completely dissolved.
Second solution: dissolve 5 g of potassium dichromate (chrompic, bright orange powder) in 40 ml of boiled water. Dissolve in low, diffused light.
Pour the second into the first solution with vigorous stirring. Using a pipette, add a few drops of ammonia to the resulting mixture until it becomes straw-colored. The emulsion is applied to the prepared board under very low light. The board is dried until it is tack-free at room temperature in complete darkness. After exposure, rinse the board under low ambient light in warm running water until the untanned gelatin is removed. To better evaluate the result, you can paint areas with unremoved gelatin with a solution of potassium permanganate.

Improved homemade photoresist:
First solution: 17 g of wood glue, 3 ml of ammonia aqueous solution, 100 ml of water, leave to swell for a day, then heat in a water bath at 80°C until completely dissolved.
Second solution: 2.5 g potassium dichromate, 2.5 g ammonium dichromate, 3 ml aqueous ammonia solution, 30 ml water, 6 ml alcohol.
When the first solution has cooled to 50°C, pour the second solution into it with vigorous stirring and filter the resulting mixture ( This and subsequent operations must be carried out in a darkened room, sunlight is not allowed!). The emulsion is applied at a temperature of 30-40°C. Continue as in the first recipe.

Photoresist based on ammonium dichromate and polyvinyl alcohol:
Prepare a solution: polyvinyl alcohol 70-120 g/l, ammonium bichromate 8-10 g/l, ethyl alcohol 100-120 g/l. Avoid bright light! Apply in 2 layers: first layer drying 20-30 minutes at 30-45°C second layer drying 60 minutes at 35-45°C. Developer 40% ethyl alcohol solution.

Chemical tinning

First of all, the board must be picked out to remove the formed copper oxide: 2-3 seconds in a 5% solution of hydrochloric acid, followed by rinsing in running water.

It is enough to simply carry out chemical tinning by immersing the board in an aqueous solution containing tin chloride. The release of tin on the surface of a copper coating occurs when immersed in a tin salt solution in which the potential of the copper is more electronegative than the coating material. The change in potential in the desired direction is facilitated by the introduction of a complexing additive, thiocarbamide (thiourea), into the tin salt solution. This type of solution has the following composition (g/l):

Among the listed solutions, solutions 1 and 2 are the most common. Sometimes, the use of Progress detergent in an amount of 1 ml/l is suggested as a surfactant for the 1st solution. Adding 2-3 g/l bismuth nitrate to the 2nd solution leads to the precipitation of an alloy containing up to 1.5% bismuth, which improves the solderability of the coating (prevents aging) and greatly increases the shelf life of the finished PCB before soldering components.

To preserve the surface, aerosol sprays based on fluxing compositions are used. After drying, the varnish applied to the surface of the workpiece forms a strong, smooth film that prevents oxidation. One of the popular substances is “SOLDERLAC” from Cramolin. Subsequent soldering is carried out directly on the treated surface without additional varnish removal. In particularly critical cases of soldering, the varnish can be removed with an alcohol solution.

Artificial tinning solutions deteriorate over time, especially when exposed to air. Therefore, if you have large orders infrequently, then try to prepare a small amount of solution at once, sufficient to tinning the required amount of PP, and store the remaining solution in a closed container (bottles of the type used in photography that do not allow air to pass through are ideal). It is also necessary to protect the solution from contamination, which can greatly degrade the quality of the substance.

In conclusion, I want to say that it is still better to use ready-made photoresists and not bother with metalizing holes at home; you still won’t get great results.

Many thanks to the candidate of chemical sciences Filatov Igor Evgenievich for consultations on issues related to chemistry.
I also want to express my gratitude Igor Chudakov."

A printed circuit board is a dielectric plate on the surface of which conductive tracks are applied and places are prepared for mounting electronic components. Electrical radio components are usually installed on the board using soldering.

PCB device

The electrically conductive tracks of the board are made of foil. The thickness of the conductors is, as a rule, 18 or 35 microns, less often 70, 105, 140 microns. The board has holes and contact pads for mounting radio elements.

Separate holes are used to connect conductors located on different sides of the board. A special protective coating and markings are applied to the outer sides of the board.

Stages of creating a printed circuit board

In amateur radio practice, one often has to deal with the development, creation and manufacture of various electronic devices. Moreover, any device can be built on a printed circuit board or a regular board with surface mounting. The PCB works much better, is more reliable and looks more attractive. Creating it involves performing a number of operations:

Preparation of the layout;

Drawing on textolite;

Etching;

Tinning;

Installation of radio elements.

Manufacturing printed circuit boards is a complex, labor-intensive, and interesting process.

Development and production of a layout

The board drawing can be done manually or on a computer using one of the special programs.

It is best to draw the board manually on recorder paper on a 1:1 scale. Graph paper is also suitable. Installed electronic components must be displayed in mirror image. The tracks on one side of the board are shown as solid lines, and on the other side as dotted lines. The dots mark the places where radio elements are attached. Soldering areas are drawn around these places. All drawings are usually made using a drawing board. As a rule, simple drawings are made by hand, more complex circuits printed circuit boards are developed on a computer in special applications.

Most often used a simple program Sprint Layout. Only a laser printer is suitable for printing. The paper should be glossy. The main thing is that the toner does not eat into it, but remains on top. The printer must be adjusted so that the toner thickness of the drawing is maximum.

Industrial production of printed circuit boards begins with entering the circuit diagram of the device into a computer-aided design system, which creates a drawing of the future board.

Preparing the workpiece and drilling holes

First of all, you need to cut a piece of PCB with the given dimensions. File the edges. Attach the drawing to the board. Prepare the tool for drilling. Drill directly according to the drawing. The drill must be good quality and correspond to the diameter of the smallest hole. If possible, you should use a drilling machine.

Having made all the necessary holes, remove the drawing and drill out each hole to the specified diameter. Clean the surface of the board with fine sandpaper. This is necessary to eliminate burrs and improve the adhesion of paint to the board. To remove traces of grease, treat the board with alcohol.

Drawing on fiberglass laminate

The board drawing can be applied to the PCB manually or using one of many technologies. Laser ironing technology is the most popular.

Manual drawing begins by marking the mounting areas around the holes. They are applied using a drawing pen or a match. The holes are connected with tracks in accordance with the drawing. It is better to draw with nitro paint in which rosin is dissolved. This solution provides strong adhesion to the board and good resistance to high-temperature etching. Asphalt bitumen varnish can be used as paint.

Manufacturing printed circuit boards using laser-iron technology gives good results. It is important to perform all operations correctly and carefully. The degreased board must be placed on a flat surface with the copper facing up. Carefully place the design on top with the toner facing down. Additionally, add a few more sheets of paper. Iron the resulting structure with a hot iron for about 30-40 seconds. When exposed to temperature, the toner should change from a solid to a viscous state, but not to a liquid. Let the board cool and place it in warm water for a few minutes.

The paper will become limp and tear off easily. You should carefully examine the resulting drawing. Absence separate tracks indicates that the iron temperature is insufficient; wide tracks are obtained when the iron is too hot or the board is heated for an excessively long time.

Small defects can be corrected with a marker, paint or nail polish. If you don’t like the workpiece, then you need to wash everything off with a solvent and clean it sandpaper and repeat the process again.

Etching

A grease-free printed circuit board is placed in a plastic container with the solution. At home, ferric chloride is usually used as a solution. The bath with it needs to be rocked periodically. After 25-30 minutes, the copper will completely dissolve. Etching can be accelerated by using a heated ferric chloride solution. At the end of the process, the printed circuit board is removed from the bath and thoroughly washed with water. Then the paint is removed from the conductive paths.

Tinning

There are many methods of tinning. We have a prepared printed circuit board. At home, as a rule, there are no special devices and alloys. Therefore, they use a simple, reliable method. The board is coated with flux and tinned with a soldering iron with regular solder using copper braiding.

Installation of radio elements

At the final stage, the radio components are inserted one by one into the places intended for them and soldered. Before soldering, the legs of the parts must be treated with flux and, if necessary, shortened.

The soldering iron should be used carefully: if there is excess heat, the copper foil may begin to peel off and the printed circuit board will be damaged. Remove any remaining rosin with alcohol or acetone. The finished board can be varnished.

Industrial development

It is impossible to design and manufacture a printed circuit board for high-end equipment at home. For example, the printed circuit board of an amplifier for High-End equipment is multi-layered, copper conductors are coated with gold and palladium, conductive tracks have different thicknesses, etc. Achieving this level of technology is not easy even in an industrial enterprise. Therefore, in some cases it is advisable to purchase a ready-made high-quality board or place an order to carry out work according to your own scheme. Currently, the production of printed circuit boards is established at many domestic enterprises and abroad.

What is a printed circuit board

Printed circuit board (English: printed circuit board, PCB, or printed wiring board, PWB) - a plate made of dielectric, on the surface and/or in the volume of which electrically conductive circuits are formed electronic circuit. A printed circuit board is designed to electrically and mechanically connect various electronic components. Electronic components on a printed circuit board are connected by their terminals to elements of a conductive pattern, usually by soldering.

Unlike surface mounting, on a printed circuit board the electrically conductive pattern is made of foil, located entirely on a solid insulating base. The printed circuit board contains mounting holes and pads for mounting leaded or planar components. In addition, printed circuit boards have vias for electrically connecting sections of foil located on different layers of the board. On the outside of the board, a protective coating (“solder mask”) and markings (supporting drawing and text according to the design documentation) are usually applied.

Depending on the number of layers with an electrically conductive pattern, printed circuit boards are divided into:

single-sided (OSP): there is only one layer of foil glued to one side of the dielectric sheet.

double-sided (DPP): two layers of foil.

multilayer (MLP): foil not only on two sides of the board, but also in the inner layers of the dielectric. Multilayer printed circuit boards are made by gluing together several single-sided or double-sided boards.

As the complexity of the designed devices and installation density increases, the number of layers on the boards increases.

The basis of the printed circuit board is a dielectric; the most commonly used materials are fiberglass and getinax. Also, the basis of printed circuit boards can be a metal base coated with a dielectric (for example, anodized aluminum); copper foil of the tracks is applied on top of the dielectric. Such printed circuit boards are used in power electronics for efficient heat removal from electronic components. In this case, the metal base of the board is attached to the radiator. The materials used for printed circuit boards operating in the microwave range and at temperatures up to 260 °C are fluoroplastic reinforced with glass fabric (for example, FAF-4D) and ceramics. Flexible circuit boards are made from polyimide materials such as Kapton.

What material will we use to make the boards?

The most common, affordable materials for making boards are Getinax and Fiberglass. Getinax paper impregnated with bakelite varnish, fiberglass textolite with epoxy. We will definitely use fiberglass!

Foil fiberglass laminate is sheets made from glass fabrics, impregnated with a binder based on epoxy resins and lined on both sides with copper electrolytic galvanic resistant foil 35 microns thick. Maximum permissible temperature from -60ºС to +105ºС. It has very high mechanical and electrical insulating properties and can be easily machined by cutting, drilling, stamping.

Fiberglass is mainly used single or double-sided with a thickness of 1.5 mm and with copper foil with a thickness of 35 microns or 18 microns. We will use one-sided fiberglass laminate with a thickness of 0.8 mm with a foil with a thickness of 35 microns (why will be discussed in detail below).

Methods for making printed circuit boards at home

Boards can be produced chemically and mechanically.

With the chemical method, in those places where there should be tracks (pattern) on the board, a protective composition (varnish, toner, paint, etc.) is applied to the foil. Next, the board is immersed in a special solution (ferric chloride, hydrogen peroxide and others) which “corrodes” the copper foil, but does not affect the protective composition. As a result, copper remains under the protective composition. The protective composition is subsequently removed with a solvent and the finished board remains.

The mechanical method uses a scalpel (for manual production) or a milling machine. A special cutter makes grooves on the foil, ultimately leaving islands with foil - the necessary pattern.

Milling machines are quite expensive, and the milling machines themselves are expensive and have a short resource. So we won't use this method.

The simplest chemical method is manual. Using a risograph varnish, we draw tracks on the board and then etch them with a solution. This method does not allow making complex boards with very thin traces - so this is not our case either.

The next method of making circuit boards is using photoresist. This is a very common technology (boards are made using this method at the factory) and is often used at home. There are a lot of articles and methods for making boards using this technology on the Internet. It gives very good and repeatable results. However, this is also not our option. The main reason is rather expensive materials (photoresist, which also deteriorates over time), as well as additional tools(UV illumination lamp, laminator). Of course, if you have a large-scale production of circuit boards at home - then photoresist is unrivaled - we recommend mastering it. It is also worth noting that the equipment and photoresist technology allows us to produce silk-screen printing and protective masks on circuit boards.

With the advent of laser printers, radio amateurs began to actively use them for the manufacture of circuit boards. As you know, a laser printer uses “toner” to print. This is a special powder that sinteres under temperature and sticks to the paper - the result is a drawing. The toner is resistant to various chemicals, which allows it to be used as a protective coating on the surface of copper.

So, our method is to transfer toner from paper to the surface of copper foil and then etch the board with a special solution to create a pattern.

Due to ease of use this method has earned a very wide distribution in amateur radio. If you type in Yandex or Google how to transfer toner from paper to a board, you will immediately find a term such as “LUT” - laser ironing technology. Boards using this technology are made like this: the pattern of the tracks is printed in a mirror version, the paper is applied to the board with the pattern on the copper, the top of this paper is ironed, the toner softens and sticks to the board. The paper is then soaked in water and the board is ready.

There are “a million” articles on the Internet about how to make a board using this technology. But this technology has many disadvantages that require direct hands and a very long time to adapt yourself to it. That is, you need to feel it. The payments don't come out the first time, they come out every other time. There are many improvements - using a laminator (with modification - the usual one does not have enough temperature), which allows you to achieve very good results. There are even methods for constructing special heat presses, but all this again requires special equipment. The main disadvantages of LUT technology:

overheating - the tracks spread out - become wider

underheating - the tracks remain on the paper

the paper is “fried” to the board - even when wet it is difficult to come off - as a result, the toner may be damaged. There is a lot of information on the Internet about what paper to choose.

Porous toner - after removing the paper, micropores remain in the toner - through them the board is also etched - corroded tracks are obtained

repeatability of the result - excellent today, bad tomorrow, then good - it is very difficult to achieve a stable result - you need a strictly constant temperature for warming up the toner, you need stable contact pressure on the board.

By the way, I was unable to make a board using this method. I tried to do it both on magazines and on coated paper. As a result, I even spoiled the boards - the copper swelled due to overheating.

For some reason, there is unfairly little information on the Internet about another method of toner transfer - the cold chemical transfer method. It is based on the fact that toner is not soluble in alcohol, but is soluble in acetone. As a result, if you choose a mixture of acetone and alcohol that will only soften the toner, then it can be “re-glued” onto the board from paper. I really liked this method and immediately bore fruit - the first board was ready. However, as it turned out later, I could not find anywhere detailed information, which would give 100% results. We need a method that even a child could make the board with. But the second time it didn’t work out to make the board, then again it took a long time to select the necessary ingredients.

As a result, after much effort, a sequence of actions was developed, all components were selected that give, if not 100%, then 95% of a good result. And most importantly, the process is so simple that the child can make the board completely independently. This is the method we will use. (of course, you can continue to bring it to the ideal - if you do better, then write). The advantages of this method:

all reagents are inexpensive, accessible and safe

no additional tools needed (irons, lamps, laminators - nothing, although not - you need a saucepan)

there is no way to damage the board - the board does not heat up at all

the paper comes off on its own - you can see the result of the toner transfer - where the transfer did not come out

there are no pores in the toner (they are sealed with paper) - therefore, there are no mordants

we do 1-2-3-4-5 and we always get the same result - almost 100% repeatability

Before we start, let's see what boards we need and what we can do at home using this method.

Basic requirements for manufactured boards

We will make devices on microcontrollers, using modern sensors and microcircuits. Microchips are getting smaller and smaller. Accordingly, the following requirements for boards must be met:

the boards must be double-sided (as a rule, it is very difficult to wire a single-sided board, making four-layer boards at home is quite difficult, microcontrollers need a ground layer to protect against interference)

the tracks should be 0.2mm thick - this size is quite enough - 0.1mm would be even better - but there is a possibility of etching and the tracks coming off during soldering

the gaps between tracks are 0.2mm - this is enough for almost all circuits. Reducing the gap to 0.1mm is fraught with merging of tracks and difficulty in monitoring the board for short circuits.

We will not use protective masks, nor will we do silk-screen printing - this will complicate production, and if you are making the board for yourself, then there is no need for this. Again, there is a lot of information on this topic on the Internet, and if you wish, you can do the “marathon” yourself.

We will not tin the boards, this is also not necessary (unless you are making a device for 100 years). For protection we will use varnish. Our main goal is to quickly, efficiently, and cheaply make a board for the device at home.

This is what the finished board looks like. made by our method - tracks 0.25 and 0.3, distances 0.2

How to make a double-sided board from 2 single-sided ones

One of the challenges of making double-sided boards is aligning the sides so that the vias line up. Usually a “sandwich” is made for this. Two sides are printed on a sheet of paper at once. The sheet is folded in half, and the sides are accurately aligned using special marks. Double-sided textolite is placed inside. With the LUT method, such a sandwich is ironed and a double-sided board is obtained.

However, with the cold toner transfer method, the transfer itself is carried out using a liquid. And therefore it is very difficult to organize the process of wetting one side at the same time as the other side. This, of course, can also be done, but with the help of a special device - a mini press (vice). Thick sheets of paper are taken - which absorb the liquid to transfer toner. The sheets are wetted so that the liquid does not drip and the sheet holds its shape. And then a “sandwich” is made - a moistened sheet, a sheet of toilet paper to absorb excess liquid, a sheet with a picture, a double-sided board, a sheet with a picture, a sheet of toilet paper, a moistened sheet again. All this is clamped vertically in a vice. But we won’t do that, we’ll do it simpler.

A very good idea came up on board manufacturing forums - what a problem it is to make a double-sided board - take a knife and cut the PCB in half. Since fiberglass is a layered material, this is not difficult to do with a certain skill:

As a result, from one double-sided board with a thickness of 1.5 mm we get two single-sided halves.

Next we make two boards, drill them and that’s it - they are perfectly aligned. It was not always possible to cut the PCB evenly, and in the end the idea came to use a thin one-sided PCB with a thickness of 0.8 mm. The two halves then do not need to be glued together; they will be held in place by soldered jumpers in the vias, buttons, and connectors. But if necessary, you can glue it with epoxy glue without any problems.

The main advantages of this hike:

Textolite with a thickness of 0.8 mm is easy to cut with paper scissors! In any shape, that is, it is very easy to cut to fit the body.

Thin PCB - transparent - by shining a flashlight from below you can easily check the correctness of all tracks, short circuits, breaks.

Soldering one side is easier - the components on the other side do not interfere and you can easily control the soldering of the microcircuit pins - you can connect the sides at the very end

You need to drill twice as many holes and the holes may slightly mismatch

The rigidity of the structure is slightly lost if you do not glue the boards together, but gluing is not very convenient

Single-sided fiberglass laminate with a thickness of 0.8mm is difficult to buy; most people sell 1.5mm, but if you can’t get it, you can cut thicker textolite with a knife.

Let's move on to the details.

Necessary tools and chemistry

We will need the following ingredients:

Now that we have all this, let’s take it step by step.

1. Layout of board layers on a sheet of paper for printing using InkScape

Automatic collet set:

We recommend the first option - it is cheaper. Next, you need to solder wires and a switch (preferably a button) to the motor. It is better to place the button on the body to make it more convenient to quickly turn the motor on and off. All that remains is to choose a power supply, you can take any power supply with 7-12V current 1A (less is possible), if there is no such power supply, then USB charging at 1-2A or a Krona battery may be suitable (you just have to try it - not everyone likes charging motors, the motor may not start).

The drill is ready, you can drill. But you just need to drill strictly at an angle of 90 degrees. You can build a mini machine - there are various schemes on the Internet:

But there is a simpler solution.

Drilling jig

To drill exactly 90 degrees, it is enough to make a drilling jig. We will do something like this:

It is very easy to make. Take a square of any plastic. We place our drill on a table or other flat surface. And drill a hole in the plastic using the required drill. It is important to ensure an even horizontal movement of the drill. You can lean the motor against the wall or rail and the plastic too. Next, use a large drill to drill a hole for the collet. From the reverse side, drill out or cut off a piece of plastic so that the drill is visible. You can glue a non-slip surface to the bottom - paper or rubber band. Such a jig must be made for each drill. This will ensure perfectly accurate drilling!

This option is also suitable, cut off part of the plastic on top and cut off a corner from the bottom.

Here's how to drill with it:

We clamp the drill so that it sticks out 2-3mm when the collet is fully immersed. We put the drill in the place where we need to drill (when etching the board, we will have a mark where to drill in the form of a mini hole in the copper - in Kicad we specially put a checkmark for this, so that the drill will stand there on its own), press the jig and turn on the motor - hole ready. For illumination, you can use a flashlight by placing it on the table.

As we wrote earlier, you can only drill holes on one side - where the tracks fit - the second half can be drilled without a jig along the first guide hole. This saves a little effort.

8. Tinning the board

Why tin the boards - mainly to protect copper from corrosion. The main disadvantage of tinning is overheating of the board and possible damage to the tracks. If you don’t have a soldering station, definitely don’t tin the board! If it is, then the risk is minimal.

You can tin a board with ROSE alloy in boiling water, but it is expensive and difficult to obtain. It is better to tin with ordinary solder. To do this efficiently, you need to make a simple device with a very thin layer. We take a piece of braid for soldering parts and put it on the tip, screw it to the tip with wire so that it does not come off:

We cover the board with flux - for example LTI120 and the braid too. Now we put tin into the braid and move it along the board (paint it) - we get an excellent result. But as you use the braid, it comes apart and copper fluff begins to remain on the board - they must be removed, otherwise there will be a short circuit! You can see this very easily by shining a flashlight on the back of the board. With this method, it is good to use either a powerful soldering iron (60 watt) or ROSE alloy.

As a result, it is better not to tin the boards, but to varnish them at the very end - for example, PLASTIC 70, or simple acrylic varnish purchased from auto parts KU-9004:

Fine tuning of the toner transfer method

There are two points in the method that can be tuned and may not work right away. To configure them, you need to make a test board in Kicad, tracks in a square spiral of different thicknesses, from 0.3 to 0.1 mm and with different intervals, from 0.3 to 0.1 mm. It is better to immediately print several such samples on one sheet and make adjustments.

Possible problems that we will fix:

1) tracks can change geometry - spread out, become wider, usually very little, up to 0.1mm - but this is not good

2) the toner may not stick well to the board, come off when the paper is removed, or stick poorly to the board

The first and second problems are interconnected. I solve the first one, you come to the second one. We need to find a compromise.

The tracks can spread for two reasons - too much pressure, too much acetone in the resulting liquid. First of all, you need to try to reduce the load. The minimum load is about 800g, it is not worth reducing below. Accordingly, we place the load without any pressure - we just put it on top and that’s it. There must be 2-3 layers of toilet paper to ensure good absorption of excess solution. You must ensure that after removing the weight, the paper should be white, without purple smudges. Such smudges indicate severe melting of the toner. If you can’t adjust it with a weight and the tracks still blur, then increase the proportion of nail polish remover in the solution. You can increase to 3 parts liquid and 1 part acetone.

The second problem, if there is no violation of the geometry, indicates insufficient weight of the load or a small amount of acetone. Again, it’s worth starting with the load. More than 3 kg does not make sense. If the toner still does not stick well to the board, then you need to increase the amount of acetone.

This problem mainly occurs when you change your nail polish remover. Unfortunately, this is not a permanent or pure component, but it was not possible to replace it with another. I tried to replace it with alcohol, but apparently the mixture is not homogeneous and the toner sticks in some patches. Also, nail polish remover may contain acetone, then less of it will be needed. In general, you will need to carry out such tuning once until the liquid runs out.

The board is ready

If you do not immediately solder the board, it must be protected. The easiest way to do this is to coat it with alcohol rosin flux. Before soldering, this coating will need to be removed, for example, with isopropyl alcohol.

Alternative options

You can also make a board:

Additionally, custom board manufacturing services are now gaining popularity - for example Easy EDA. If you need a more complex board (for example, a 4-layer board), then this is the only way out.

Any electronic device requires connecting together a bunch of parts. Of course, you can solder the device on a circuit board, but there is a high risk of making a lot of mistakes, and the device itself will look very ugly. Only lovers of trash design will appreciate the wires sticking out in all directions. Therefore, we will make a printed circuit board!

And to make it easier for you, I made a video lesson on the topic of making printed circuit boards using the Laser Iron aka LUT method.

Full cycle, from preparing the board from a piece of PCB to drilling and tinning.

Printed circuit boards made of foil insulating material (getinax, fiberglass, fluoroplastic). Metal foil is firmly glued to one side of the sheet of insulating material, which makes it possible to obtain printed conductors of any shape in the future. They are a strip of foil connecting the leads of two or more parts installed on a printed circuit board in accordance with circuit diagram radio device.

What is required to make printed circuit boards?

0) Drawing of a printed circuit board in electronic form.

1) Laser printer, for printing a print of the future board. It is desirable that the printer has the ability to have a straight path - printing with minimal bending of the paper. I have a Samsung ML1520. Print to the maximum, without any toner savings!

2) Foil PCB.

3) Photo paper for inkjet printing Lomond 120gsm, glossy, single-sided with improved coating. Also good results on Lomond 230gsm glossy paper.

4) Suede brush with metal + plastic bristles (optional)

5) Acetone

6) Nulevka skin

The shape of the conductors, their number and relative position are determined by the device diagram, the elements used, as well as the experience of the radio amateur developing the printed circuit board drawing.

It must be remembered that the drawings are developed for the installation of very specific types of elements. If the types of some elements are different (for example, instead of capacitors of the K50-6 type, capacitors of the K53-4 type with a different pin arrangement are used), then the board drawing will have to be changed accordingly.

Most often, for the manufacture of printed circuit boards, radio amateurs use foil-clad fiberglass laminate of the STF brand or foil-coated getinaks of the GF brand. Getinax has slightly worse characteristics compared to fiberglass, but it is quite suitable for the vast majority of amateur radio designs. When working with getinax, use low-melting solders (POSK-50, POS-40, POS-61), since the foil can easily peel off when the printed conductors overheat during soldering.

Foil materials produced by industry have different thicknesses. Usually a material with a thickness of 1.5 mm is used. But in cases where the board is large and massive elements need to be installed on it, material with a thickness of 2-2.5 mm is used.

If you don’t have ready-made foil material at your disposal, you can make it yourself.

Cut a blank to the size of the future board from getinax 1.5-2 mm thick, and from sheet copper foil (its thickness should be in the range of 0.05 - 0.1 mm) - a plate of the same size. Sand the surfaces to be glued with fine-grained sandpaper, clean them of dust and degrease with acetone or gasoline. Apply a thin layer of BF-2 glue to the getinax and foil and dry it for an hour at room temperature, then apply a second layer of glue and dry for about 30 minutes. After this, place the foil on the getinax and roll it out with a hard roller from the middle to the edges. Place the workpiece processed in this way under a press or in a vice and leave for 2-3 days.

Place the workpiece between two metal plates (additionally place cardboard on the foil side) and squeeze the entire bag tightly.

Drawing a printed circuit board

Prepare an auxiliary drawing of the printed circuit board from the side of the printed conductors on a scale of 1:1, marking the centers of future holes with dots.

Glue the design to the foil with a few drops of rubber cement. Using a punch, with light blows of a small hammer, alternately transfer the centers of all future holes onto the foil,

Keep the center punch perpendicular to the surface of the board, otherwise the markings will be inaccurate. Do not sand the foil before this operation so that the marks left by the punch are more noticeable.

Remove the design from the workpiece and drill holes. It is best to do this on a drilling machine, since the holes for the leads of the parts have 0 0.8 -1 mm. You can also use an electric drill. To do this, clamp the workpiece in a vice through cardboard or getinaks gaskets with foil towards you. Sitting on a chair, place your left elbow on the workbench, place an electric drill on your palm, and hold the drill handle with your right hand.

Adjust the feed of the drill in the horizontal plane with coordinated movements of both hands. As you drill holes, change the position of the workpiece; at the end of the work, check that all the holes are drilled.

Sand the foil with fine sandpaper, remove dust and remaining rubber glue, and degrease the surface with acetone. Now try not to touch the foil with your hands until the processing of the printed circuit board is completed.

To ensure that printed conductors remain on the board after etching, paint the corresponding areas of the foil with some acid-resistant varnish or paint. Most often, radio amateurs use nitro enamel; it dries quickly and adheres well to the surface of the foil. For ease of use, paint should be poured in small portions into small glass or metal containers and scooped up from there. You can transfer an image from paper to foil using. a regular or glass drawing pen, a modified medical syringe, a pen refill from which the ball has been removed, or an ordinary pointed match. It is advisable that the holes are also covered with paint, this will protect their walls from being soaked with solutions during etching. As soon as stretching “threads” appear on the match, change the portion of paint, otherwise they can form thin bridges between the conductors on the board, which will make the device impossible to operate.

To transfer the design, you can also use asphalt-bitumen varnish, colored tsaponvark, BF glue, some types of ink and ink.

After all the conductors are depicted, check the quality of the drawing, correct the appearance of the “conductors” if necessary, remove jumpers, and work out the gaps between the contact pads (they must be at least 1 mm). When examining the drawing, it is advisable to use a magnifying glass.

Some radio amateurs, instead of paint or varnish, use adhesive tape - skoch, cutting “conductors” and “contact pads” from it and gluing them on foil in accordance with the drawing. For those who want to use this method of preparing a board for etching, we advise you to very carefully monitor the quality of the tape sections, otherwise there may be breaks in the conductors. More high quality The drawing can be obtained using special drawing devices. You can get acquainted with the description of the design of one of them by reading the book by Yu. V. Bezdelev “Flat and volumetric modules in amateur designs” (published by the publishing house “Energy” in 1977).

Remove areas of foil not protected by paint, varnish or adhesive tape by etching the board in one of the recommended solutions. The main material for etching is a solution of ferric chloride - it is sold in chemical stores in powder or granules. To obtain a solution, you need to pour about 3/4 of ferric chloride powder into a glass and add warm water.

Board etching

For etching, use glass or plastic containers, such as a photographic cuvette. Place the board in the solution with the pattern facing up; the entire surface of the board should be filled with the solution. The etching process is accelerated if the vessel is shaken or heated. Etching produces toxic fumes, so work either in a well-ventilated area or in outdoors. Periodically check the condition of the board by lifting it for inspection with wooden or plastic sticks; metal tools and devices should not be used for this purpose. Once you are sure that the foil in unprotected areas has completely disappeared, stop the etching process,

For example, use a clothespin to transfer the board under running water and rinse thoroughly, then dry it at room temperature.

If you intend to reuse the solution, pour it into a tightly sealed container and store it in a cool, dark place. Please note that the effectiveness of the solution decreases with repeated use.

When working with ferric chloride solution, remember that it should not get on your hands or other exposed parts of the body, as well as on the surfaces of bathtubs and sinks, since the latter may leave yellow stains that are difficult to wash off.

You can make your own ferric chloride solution by treating iron filings with hydrochloric acid. Take 25 parts by weight of 10 percent hydrochloric acid and mix with one part by weight of iron filings. Keep the mixture in a tightly sealed container for 5 days in a dark place, after which it can be used. When pouring the solution into a vessel for etching, do not shake it: the sediment should remain in the container in which the solution was prepared.

The duration of the board etching process in a ferric chloride solution depends on the concentration of the solution, its temperature, the thickness of the foil and is usually 40 - 50 minutes.

Solutions for etching boards can be prepared not only based on ferric chloride. An aqueous solution of copper sulfate and table salt may be more affordable for many radio amateurs. It is not difficult to prepare - dissolve 4 tablespoons of table salt and 2 tablespoons of copper sulfate crushed into powder in 500 ml of hot water (t about 80°C). If the solution is used immediately, its effectiveness will be low; it increases significantly after keeping the solution for two to three weeks.

The etching time of the board in such a solution is three hours or more.

A significant reduction in etching time can be achieved by using acid-based solutions. The process of etching a board, for example, in a concentrated solution of nitric acid lasts only 5-7 minutes.

In this case, the design is applied with bakelite varnish of medium viscosity using a glass pen and the writing unit of a fountain pen with the ball removed. When filling the tool, lower its working end into the varnish, and create a vacuum at the other end by sucking air through a vinyl chloride tube. After etching, wash the board thoroughly with soap and water.

Good results are obtained by using a solution of hydrochloric acid and hydrogen peroxide. To prepare, take 20 parts (by volume) of hydrochloric acid with a density of 1.19 g/cm3, 4 parts of pharmaceutical hydrogen peroxide, 40 parts of water. First mix water with hydrogen peroxide, then carefully add acid. In this case, the drawing is done with nitro paint.

Pour acid-based solutions into glass or ceramic containers; work with them only in well-ventilated areas.

Method of galvanic etching of boards

This will require a source. direct current voltage 25-30 V and a concentrated solution of table salt. Using an alligator clip, connect the positive pole of the source to the unpainted areas of the board foil, and attach a cotton swab to the exposed and looped end of the wire coming from the negative pole of the source. Soak the latter generously in the salt solution and, lightly pressing it against the foil, move it along the surface of the board; the movement of the swab should resemble drawing the number 8. The foil will be “washed off” in this case. Change the tampon whenever it gets dirty.

In all cases, after completing the etching process, the boards are thoroughly washed in running water (for example, under a water tap, dried, and only after that the paint is removed with acetone, white spirit and other similar solvents. The paint remaining in the holes is removed with a thin awl or needle.

Now sand the conductors to a shine with the finest sandpaper or ink eraser, remove all foreign particles from the board and tin the conductors in the following way: lubricate them with alcohol-rosin flux (15% rosin and 15% ethyl alcohol), take a piece of braided wire from a shielded cable and saturate it with the same flux, put a little POS-61 solder on the soldering iron tip and “rub” the solder into the foil through the braid. The speed of the soldering iron should be such that the conductors are well tinned, but do not peel off from the board material. When performing this work, it is advisable to secure the board motionless. You can limit yourself to tinning only the contact pads.

Having finished tinning the conductors, remove any remaining flux and excess solder (including from the holes), check the quality of the board and begin installing radio elements on it.