Surface mount semiconductor device package. Semiconductor devices - types, overview and use Operation of semiconductor devices

Electrical installation of radio components must ensure reliable operation of equipment, devices and systems under the conditions of mechanical and climatic influences specified in the technical specifications for this type REA. Therefore, when installing semiconductor devices (SD), integrated circuits (IC) radio components on printed circuit boards or equipment chassis, the following conditions must be met:

reliable contact of the powerful PCB case with the heat sink (radiator) or chassis;
necessary air convection near radiators and elements that generate large amounts of heat;
removal of semiconductor elements from circuit elements that emit a significant amount of heat during operation;
protection of installations located near removable elements from mechanical damage during operation;
in the process of preparing and carrying out electrical installation of PP and IS, mechanical and climatic influences on them should not exceed the values specified in the technical specifications;
When straightening, forming and cutting PP and IC leads, the lead area near the housing must be secured so that no bending or tensile forces arise in the conductor. Equipment and devices for forming leads must be grounded;
the distance from the PCB or IC body to the start of bending of the lead must be at least 2 mm, and the bending radius for a lead diameter of up to 0.5 mm should be at least 0.5 mm, with a diameter of 0.6-1 mm - at least 1 mm, with a diameter over 1 mm - at least 1.5 mm.

During installation, transportation and storage of PCBs and ICs (especially microwave semiconductor devices), it is necessary to ensure their protection from the effects of static electricity. To do this, all installation equipment, tools, control and measuring equipment are reliably grounded. To remove static electricity from the electrician’s body, they use grounding bracelets and special clothing.

To remove heat, the output section between the PCB (or IC) body and the soldering point is clamped with special tweezers (heat sink). If the solder temperature does not exceed 533 K ± 5 K (270 °C), and the soldering time does not exceed 3 s, soldering of the PP (or IC) leads is carried out without a heat sink or group soldering is used (wave solder, immersion in molten solder, etc.) .

Cleaning of printed circuit boards (or panels) from flux residues after soldering is carried out with solvents that do not affect the markings and material of PCB (or IC) housings.

When installing ICs with rigid radial leads into metallized holes of a printed circuit board, the protruding part of the leads above the board surface at the soldering points should be 0.5-1.5 mm. Installation of the IC in this way is carried out after trimming the leads (Fig. 55). To facilitate dismantling, it is recommended to install ICs on printed circuit boards with gaps between their cases.

Rice. 55. Forming rigid radial IC leads:
1 - molded leads, 2 - leads before molding

Integrated circuits in packages with soft planar leads are installed on board pads without mounting holes. In this case, their location on the board is determined by the shape of the contact pads (Fig. 56).

Rice. 56. Installation of ICs with flat (planar) leads on printed circuit board:
1 - contact pad with key, 2 - housing, 3 - board, 4 - output

Examples of molding ICs with planar leads are shown in Fig. 57.

Rice. 57. Forming flat (planar) IC leads when installed on a board without a gap (i), with a gap (b)

Installation and fastening of PP and IC, as well as mounted radio components on printed circuit boards must provide access to them and the possibility of their replacement. To cool the ICs, they should be placed on printed circuit boards, taking into account the air flow along their cases.

For electrical installation of PCBs and small-sized radio components, they are first installed on mounting fittings (petals, pins, etc.) and the terminals are mechanically secured to it. To solder the field connection, acid-free flux is used, the residues of which are removed after soldering.

Radio components are attached to the mounting fittings either mechanically on their own terminals, or additionally with a clamp, bracket, holder, filling with compound, mastic, glue, etc. In this case, the radio components are fixed so that they do not move due to vibration and shock (shaking). Recommended types of fastening of radio components (resistors, capacitors, diodes, transistors) are shown in Fig. 58.

Rice. 58. Installation of radio components on mounting fixtures:
a, b - resistors (capacitors) with flat and round leads, c - capacitor ETO, d - diodes D219, D220, d - powerful diode D202, f - triodes MP-14, MP-16, g - powerful triode P4; 1 - body, 2 - petal, 3 - output, 4 - radiator, 5 - wires, 6 - insulating tube

Mechanical fastening of the terminals of radio components to the mounting fittings is carried out by bending or twisting them around the fittings and then crimping them. In this case, breaking the terminal during compression is not allowed. If there is a hole in the contact post or petal, the lead of the radio component is mechanically secured before soldering by threading it through the hole and bending it half or a full turn around the petal or post, followed by crimping. The excess output is removed with side cutters, and the attachment point is crimped with pliers.

As a rule, methods for installing radio components and fastening their terminals are specified in the assembly drawing for the product.

To reduce the distance between the radio component and the chassis, insulating tubes are placed on their housings or terminals, the diameter of which is equal to or slightly less than the diameter of the radio component. In this case, the radio components are placed close to each other or to the chassis. Insulating tubes placed on the terminals of radio components eliminate the possibility of short circuits with adjacent conductive elements.

The length of the mounting leads from the soldering point to the body of the radio component is given in the specifications and, as a rule, specified in the drawing: for discrete radio components it must be at least 8 mm, and for PCBs - at least 15 mm. The length of the lead from the housing to the bend of the radio component is also specified in the drawing: it must be at least 3 mm. The leads of radio components are bent using a template, fixture or special tool. Moreover inner radius the bend must be no less than twice the diameter or thickness of the lead. Rigid terminals of radio components (PEV resistances, etc.) are not allowed to be bent during installation.

Radio components selected when setting up or adjusting the device should be soldered without mechanical fastening to the full length of their leads. After selecting their values and adjusting the device, the radio components must be soldered to the reference points with the pins mechanically secured.

Analysis of failures of semiconductor devices and microcircuits shows that in most cases they are associated with an increase in the maximum permissible voltages and currents, as well as with mechanical damage. To ensure that semiconductor devices and microcircuits do not fail during repairs and adjustments, precautions must be taken. Arbitrary replacement of radioelements that determine the circuit mode is unacceptable even for a short time, as this can lead to overload of transistors, microcircuits and their failure. Particular care must be taken to ensure that the probes of the measuring instruments do not accidentally short-circuit the circuit circuits. Do not connect a signal source with a small signal to semiconductor devices. internal resistance, because large currents can flow through them, exceeding the maximum permissible values.

Serviceability semiconductor diodes can be checked using an ohmmeter. The degree of their suitability is determined by measuring forward and reverse resistance. In the event of a breakdown of the diode, the indicated resistances will be equal and amount to several Ohms, and in the event of a break they will be infinitely large. Serviceable diodes have direct resistance in the range: germanium point - 50-100 Ohms; silicon point - 150-500 Ohm and planar (germanium and silicon) - 20-50 Ohm.

When measuring the resistance of a diode that has a leak, the arrow reading of the device slowly decreases and, having reached a certain value, the arrow of the device stops. When re-measuring, the process is repeated again. Diodes with such defects should be replaced. To replace the failed ones, diodes of the same type or analogues are selected, checked and the polarity of the connection is determined.

Checking the serviceability of transistors and measuring their main parameters can be done using a special transistor parameter tester type L2-23. Using the tester, you can quickly determine the current transfer coefficient "alpha", the reverse collector current, the presence or absence of a breakdown between the emitter and the collector, etc. Measuring such important operational parameters allows us to judge the possibilities of further use of the transistor in BREA circuits.

In the absence of a special device, the health of the transistors can be determined by measuring the resistance of the pn junctions using an ohmmeter. It is recommended to carry out the measurement at the highest measuring range of the ohmmeter, where the current flow is minimal.

Checking the serviceability of microcircuits begins with measuring constants and impulse voltage on their findings. If the measurement results differ from the required ones, then the reason should be established: defects in the radio elements connected to the IC, deviation of their values from the nominal values, the source from which the necessary pulses and constant voltages, or a malfunction of the IC itself.

You cannot check the serviceability of an IC by replacement if for this purpose it must be soldered from the printed circuit board. It is not recommended to install the soldered IC again, even if the test showed its serviceability. This requirement is explained by the fact that due to repeated overheating of the terminals, failure-free operation is not guaranteed.

If it is necessary to replace semiconductor devices and microcircuits, you must adhere to the following rules:

1. Installation and fastening of semiconductor devices must be carried out while maintaining the tightness of the device housing. To prevent cracks from appearing in them, it is recommended to bend the leads at a distance of at least 10 mm from the device body. To do this, it is necessary to firmly fix the leads between the bending point and the glass insulator using pliers.

2. Replacement of semiconductor devices, microcircuits and microassemblies is carried out only when the power supply to the device is turned off. When removing the transistor from the circuit, the collector circuit is first desoldered. The base terminals of the transistor are disconnected last, and during installation the base terminal is connected first. You cannot apply voltage to a transistor whose base terminal is disconnected.

3. Soldering of leads of semiconductor devices is carried out at a distance of at least 10 mm from the device body, with the exception of transistors (for example, KT315, KT361, etc.), for which this distance is 5 mm. A heat sink should be used between the housing and the soldering area. During installation, the microcircuit is installed on a printed circuit board with a gap that is provided by the design of the pins (pins are not formed).

4. The electric soldering iron should be small in size, with a power of no more than 40 W, powered by a voltage source of 12-42 V. The temperature of the soldering iron tip should not exceed 190 degrees. Celsius. An alloy with a low melting point (POS-61, POSK-50-18, POSV-33) must be used as solder. Soldering time for each pin is no more than 3 seconds. The interval between soldering adjacent pins of microcircuits is at least 10 seconds. In order to save time, it is recommended to solder microcircuits through one pin. The soldering iron tip and the body (common bus) of the radio device should be grounded or the electric soldering iron should be connected to the network through a transformer, since during soldering the occurrence of leakage currents between the tip of the soldering iron connected to the network and the terminals of the IC can lead to its failure.

5. For better cooling powerful transistors and the microcircuits are installed on radiators. To avoid failure of these devices due to overheating, you must follow the rules when installing them.

6. Contact surfaces must be clean, without any roughness that would interfere with their tight fit.

7. Contact surfaces must be lubricated with paste on both sides (KPT-8 paste).

8. The screws securing the transistor must be tightened firmly. If the screws are not tightened sufficiently, the thermal resistance of the contact increases, which can lead to failure of the transistor.

9. To replace the micro-assembly, it must be removed from the panel. To do this, you need to pull one edge of the microassembly out of the panel by 1-2 mm, and then the other. Then repeat the operation and finally remove the microassembly without distortions. It is forbidden to take the microassembly by the plane on which all the elements are located. All operations should be performed while holding the microassembly by its end parts. The microassembly is first inserted into the guide side grooves of the panel. Then press it on one side until the lower edge of this side penetrates the panel contacts by 1-2 mm. After this, press the microassembly in the middle and insert it into the panel all the way without distortion.

To avoid damage to semiconductor devices during installation, it is necessary to ensure that their terminals are stationary near the housing. To do this, bend the leads at a distance of at least 3...5 mm from the body and perform soldering with low-temperature POS-61 solder at a distance of at least 5 mm from the device body, ensuring heat removal between the body and the soldering point. If the distance from the soldering point to the body is 8...10 mm or more, it can be done without additional heat sink (within 2...3 s).

Re-soldering during installation and replacement of individual parts in circuits with semiconductor devices should be carried out with the power turned off using a soldering iron with a grounded tip. When connecting a transistor to a circuit under voltage, you must first connect the base, then the emitter, and then the collector. Disconnecting the transistor from the circuit without removing the voltage is performed in the reverse order.

To ensure normal operation of semiconductor devices at full power, it is necessary to use additional heat sinks. Finned radiators made of red copper or aluminum are used as heat sinks, which are placed on the devices. When designing circuits with a wide temperature range of operation, it should be taken into account that as the temperature increases, not only the permissible power dissipation of many types of semiconductor devices decreases, but also the permissible voltages and current strength of the transitions.

Operation of semiconductor devices should be carried out only within the range of required operating temperatures, and the relative humidity should be up to 98% at a temperature of 40 ° C; atmospheric pressure - from 6.7 10 2 to 3 10 5 Pa; vibration with acceleration up to 7.5 g in the frequency range 10...600 Hz; repeated impacts with acceleration up to 75g; linear accelerations up to 25g.

Increasing or decreasing the above parameters negatively affects the performance of semiconductor devices. Thus, a change in the operating temperature range causes cracking of semiconductor crystals and changes in the electrical characteristics of devices. In addition, under the influence of high temperatures, drying and deformation of the protective coatings, release of gases and melting of the solder occur. High humidity promotes corrosion of housings and terminals due to electrolysis. Low pressure causes a decrease in breakdown voltage and a deterioration in heat transfer. Changes in the acceleration of impacts and vibration lead to the appearance of mechanical stress and fatigue in structural elements, as well as mechanical damage (up to separation of leads), etc.

To protect against the effects of vibrations and acceleration, the structure with semiconductor devices must have shock absorption, and to improve moisture resistance it must be coated with a protective varnish.

Assembly and sealing of microcircuits and semiconductor devices includes 3 main operations: attaching the crystal to the base of the package, connecting the leads, and protecting the crystal from the external environment. Stability depends on the quality of assembly operations electrical parameters and reliability of the final product. In addition, the choice of assembly method affects the total cost of the product.

Attaching the crystal to the base of the case

The main requirements when connecting a semiconductor crystal to the base of the package are high reliability of the connection, mechanical strength and, in some cases, a high level of heat transfer from the crystal to the substrate. The connection operation is carried out using soldering or gluing.

Adhesives for mounting crystals can be divided into two categories: electrically conductive and dielectric. Adhesives consist of an adhesive binder and a filler. To ensure electrical and thermal conductivity, silver is usually added to the adhesive in the form of powder or flakes. To create heat-conducting dielectric adhesives, glass or ceramic powders are used as filler.

Soldering is carried out using conductive glass or metal solders.

Glass solders are materials composed of metal oxides. They have good adhesion to a wide range of ceramics, oxides, semiconductor materials, metals and are characterized by high corrosion resistance.

Soldering with metal solders is carried out using solder samples or pads of a given shape and size (pre-forms) placed between the crystal and the substrate. In mass production, specialized solder paste is used for mounting crystals.

Connecting leads

The process of connecting the leads of the crystal to the base of the package is carried out using wire, tape or rigid leads in the form of balls or beams.

Wire installation is carried out by thermocompression, electric contact or ultrasonic welding using gold, aluminum or copper wire/tapes.

Wireless installation is carried out using the “inverted crystal” technology (Flip-Chip). Hard contacts in the form of beams or solder balls are formed on the chip during the metallization process.

Before applying solder, the surface of the crystal is passivated. After lithography and etching, the contact pads of the crystal are additionally metalized. This operation is carried out to create a barrier layer, prevent oxidation and improve wettability and adhesion. After this, conclusions are formed.

Beams or solder balls are formed by electrolytic or vacuum deposition, filling with ready-made microspheres, or screen printing. The crystal with the formed leads is turned over and mounted on the substrate.

Protecting the crystal from environmental influences

The characteristics of a semiconductor device are largely determined by the state of its surface. The external environment has a significant impact on the surface quality and, accordingly, on the stability of device parameters. this effect changes during operation, so it is very important to protect the surface of the device to increase its reliability and service life.

Protection of the semiconductor crystal from the influence of the external environment is carried out at the final stage of assembling microcircuits and semiconductor devices.

Sealing can be carried out using a housing or in an open-frame design.

Housing sealing is carried out by attaching the housing cover to its base using soldering or welding. Metal, metal-glass and ceramic cases provide vacuum-tight sealing.

The cover, depending on the type of case, can be soldered using glass solders, metal solders or glued with glue. Each of these materials has its own advantages and is selected depending on the tasks being solved.

For unpackaged protection of semiconductor crystals from external influences, plastics and special casting compounds are used, which can be soft or hard after polymerization, depending on the tasks and materials used.

Modern industry offers two options for filling crystals with liquid compounds:

Filling with medium viscosity compound (glob-top, Blob-top)
Creating a frame from a high-viscosity compound and filling the crystal with a low-viscosity compound (Dam-and-Fill).

The main advantage of liquid compounds over other methods of crystal sealing is the flexibility of the dosing system, which allows the use of the same materials and equipment for various types and crystal sizes.

Polymer adhesives are distinguished by the type of binder and the type of filler material.

Binding material

Organic polymers used as adhesives can be divided into two main categories: thermosets and thermoplastics. All of them are organic materials, but

differ significantly in chemical and physical properties.

In thermosets, when heated, polymer chains are irreversibly cross-linked into a rigid three-dimensional network structure. The bonds that arise in this case make it possible to obtain high adhesive ability of the material, but at the same time maintainability is limited.

Thermoplastic polymers do not cure. They retain the ability to soften and melt when heated, creating strong elastic bonds. This property allows thermoplastics to be used in applications where maintainability is required. The adhesive ability of thermoplastic plastics is lower than that of thermosets, but in most cases it is quite sufficient.

The third type of binder is a mixture of thermoplastics and thermosets, combining

advantages of two types of materials. Their polymer composition is an interpenetrating network of thermoplastic and thermoplastic structures, which allows them to be used to create high-strength repairable joints at relatively low temperatures (150 o C - 200 o C).

Each system has its own advantages and disadvantages. One of the limitations of using thermoplastic pastes is the slow removal of solvent during the reflow process. Previously, joining components using thermoplastic materials required a process of applying paste (maintaining flatness), drying to remove solvent, and then mounting the die onto the substrate. This process eliminated the formation of voids in the adhesive material, but increased the cost and made it difficult to use this technology in mass production.

Modern thermoplastic pastes have the ability to evaporate the solvent very quickly. This property allows them to be applied by dosing using standard equipment, and the crystal to be installed on the paste that has not yet dried. This is followed by a rapid low-temperature heating step, during which the solvent is removed and adhesive bonds are created after reflow.

For a long time, there have been difficulties in creating highly thermally conductive adhesives based on thermoplastics and thermosets. These polymers did not allow increasing the content of thermally conductive filler in the paste, since good adhesion required a high level of binder (60-75%). For comparison: in inorganic materials the proportion of binder could be reduced to 15-20%. Modern polymer adhesives (Diemat DM4130, DM4030, DM6030) do not have this drawback, and the content of thermally conductive filler reaches 80-90%.

Filler

The type, shape, size and amount of filler play a major role in creating a thermally and electrically conductive adhesive. Silver (Ag) is used as a filler as a chemically resistant material with the highest thermal conductivity coefficient. Modern pastes contain

silver in the form of powder (microspheres) and flakes (scales). The exact composition, quantity and size of particles are experimentally selected by each manufacturer and largely determine the thermal, electrically conductive and adhesive properties of materials. In applications where a dielectric with heat-conducting properties is required, ceramic powder is used as a filler.

When choosing an electrically conductive adhesive, consider the following factors:

Thermal and electrical conductivity of the glue or solder used
Permissible technological installation temperatures
Temperatures of subsequent technological operations
Mechanical strength of the connection
Automation of the installation process
Maintainability
Cost of installation operation

In addition, when choosing an adhesive for installation, you should pay attention to the elastic modulus of the polymer, the area and difference in the thermal expansion coefficient of the components being connected, as well as the thickness of the adhesive seam. The lower the elastic modulus (the softer the material), the larger the areas of the components and the greater the difference in the CTE of the components being connected and the thinner the adhesive seam is permissible. A high elastic modulus limits the minimum thickness of the adhesive joint and the dimensions of the components to be connected due to the possibility of large thermomechanical stresses.

When deciding on the use of polymer adhesives, it is necessary to take into account some technological features of these materials and the components being connected, namely:

die (or component) length determines the load on the adhesive joint after cooling the system. During soldering, the crystal and substrate expand in accordance with their CTE. For larger crystals, it is necessary to use soft (low modulus) adhesives or CTE-matched crystal/substrate materials. If the CTE difference is too great for a given chip size, the bond may be broken, causing the chip to delaminate from the substrate. For each type of paste, the manufacturer usually gives recommendations on maximum sizes crystal for certain values of the crystal/substrate CTE difference;

width of the die (or components to be connected) determines the distance that the solvent contained in the adhesive travels before leaving the adhesive line. Therefore, the crystal size must also be taken into account for proper solvent removal;

metallization of the crystal and substrate (or components to be connected) not required. Typically, polymer adhesives have good adhesion to many non-metallized surfaces. Surfaces must be cleaned of organic contaminants;

thickness of the adhesive seam. For all adhesives containing a thermally conductive filler, there is a minimum adhesive joint thickness dx (see figure). A joint that is too thin will not have enough bonding agent to cover all of the filler and form bonds to the surfaces being joined. In addition, for materials with a high elastic modulus, the thickness of the seam may be limited by different CTE for the materials being joined. Typically, for adhesives with a low elastic modulus, the recommended minimum seam thickness is 20-50 µm, for adhesives with a high elastic modulus 50-100 µm;

the lifetime of the adhesive before installing the component. After applying the adhesive, the solvent from the paste begins to gradually evaporate. If the glue dries, the materials being joined will not be wetted or bonded. For small components, where the ratio of surface area to volume of adhesive applied is large, the solvent evaporates quickly and the time after application before installing the component must be minimized. As a rule, the lifetime before component installation for various adhesives varies from tens of minutes to several hours;

lifetime before thermal curing of the adhesive is counted from the moment the component is installed until the entire system is placed in the oven. With a long delay, delamination and spreading of the glue may occur, which negatively affects the adhesion and thermal conductivity of the material. The smaller the component size and the amount of glue applied, the faster it can dry. The lifetime before thermal curing of the adhesive can vary from tens of minutes to several hours.

Selection of wire, tapes

The reliability of a wire/tape connection greatly depends on the correct choice of wire/tape. The main factors determining the conditions for using a particular type of wire are:

Type of shell. Sealed enclosures use only aluminum or copper wire because gold and aluminum form brittle intermetallic compounds at high sealing temperatures. However, for non-sealed housings, only gold wire/tape is used because this type the housing does not provide complete insulation from moisture, which leads to corrosion of aluminum and copper wire.

Wire/Ribbon Sizes(diameter, width, thickness) thinner conductors are required for circuits with small pads. On the other hand, the higher the current flowing through the connection, the larger the cross-section of the conductors must be provided

Tensile strength. Wire/strips are subject to external mechanical stress during subsequent stages and during use, so the higher the tensile strength, the better.

Relative extension. Important characteristic when choosing wire. Too high elongation values make it difficult to control loop formation when creating a wire connection.

Choosing a crystal protection method

Sealing of microcircuits can be carried out using a housing or in an open-frame design.

When choosing the technology and materials to be used at the sealing stage, the following factors should be taken into account:

Required level of housing tightness
Permissible technological sealing temperatures
Chip operating temperatures
Presence of metallization of connected surfaces
Possibility of using flux and special installation atmosphere
Automation of the sealing process
Cost of sealing operation

The article provides an overview of the technologies and materials used to form pin leads on semiconductor wafers in the production of microcircuits.

Analysis of failures of semiconductor devices and microcircuits shows that in most cases they are associated with an increase in the maximum permissible voltages and currents, as well as with mechanical damage. To ensure that semiconductor devices and microcircuits do not fail during repairs and adjustments, precautions must be taken. Arbitrary replacement of radioelements that determine the circuit mode is unacceptable even for a short time, as this can lead to overload of transistors, microcircuits and their failure. Particular care must be taken to ensure that the probes of the measuring instruments do not accidentally short-circuit the circuit circuits. Semiconductor devices should not be connected to a signal source with low internal resistance because they can carry large currents that exceed the maximum permissible values.

The health of semiconductor diodes can be checked using an ohmmeter. The degree of their suitability is determined by measuring forward and reverse resistance. In the event of a breakdown of the diode, the indicated resistances will be equal and amount to several Ohms, and in the event of a break they will be infinitely large. Serviceable diodes have direct resistance in the range: germanium point - 50-100 Ohms; silicon point - 150-500 Ohm and planar (germanium and silicon) - 20-50 Ohm.

Checking the serviceability of microcircuits begins with measuring direct and pulse voltages at their terminals. If the measurement results differ from the required ones, then the cause should be established: defects in the radio elements connected to the IC, deviation of their values from the nominal values, the source from which the necessary pulse and direct voltages come, or a malfunction of the IC itself.

If it is necessary to replace semiconductor devices and microcircuits, you must adhere to the following rules:

5. For better cooling, powerful transistors and microcircuits are installed on radiators. To avoid failure of these devices due to overheating, you must follow the rules when installing them.

6. Contact surfaces must be clean, without any roughness that would interfere with their tight fit.

7. Contact surfaces must be lubricated with paste on both sides (KPT-8 paste).