Abstract: The use of semiconductor devices. Rules for the installation and operation of semiconductor devices 1 Rules for the operation of semiconductor devices

Usage: in the field of manufacturing semiconductor devices by flux-free soldering in air without the use of protective media, it can be used in the assembly of Schottky diodes and bipolar transistors by soldering semiconductor crystals to housings with lead-based solders. Essence of the invention: a method for assembling semiconductor devices consists in placing a filtering and alloying element on the base of the housing, on which a solder sample and a crystal are placed, and a cassette with assembled devices is loaded into a conveyor hydrogen furnace at a soldering temperature of 370°C. New in the method is that semiconductor crystals with solder on the collector side are fixed in an inverted position in the cells of the vacuum suction cup and combined with the contact pads of the device cases, and heating to the soldering temperature is carried out in air by a current pulse through V-shaped electrodes, which are rigidly fixed in bracket, electrically connected in series with each other and located differentially above each crystal, and at the moment of solder melting, the vacuum suction cup with crystals is subjected to ultrasonic vibrations in the direction parallel to the solder seam, while pressure on each crystal is carried out by the mass of the device body and the bracket with electrodes. The technical result of the invention is to increase the reliability of semiconductor devices by reducing the heating temperature when soldering the surface of a crystal with structures, improving the wetting of the joined surfaces with solder, increasing the productivity of assembly operations due to group soldering of crystals to cases. 2 ill.

The invention relates to the manufacture of semiconductor devices by flux-free soldering in air without the use of protective media. It can be used in the assembly of Schottky diodes and bipolar transistors by soldering semiconductor chips to packages with lead-based solders. There are various ways to solder semiconductor chips to the package. There is a known method for assembling powerful transistors by the cassette method, according to which the leg of the transistor is placed on guides in the cassette, and a solder charge is placed between the crystal and the case, while soldering is carried out in a conveyor furnace with a reducing medium without the use of fluxes. The cassette ensures the exact orientation of the crystal relative to the device leg and prevents its displacement during the soldering process. The disadvantage of this method is the relatively high complexity of manufacturing semiconductor devices. In addition, the presence of oxide films on the surfaces to be joined impairs the wetting and capillary flow of the solder in the joint gap. A method is known for soldering microstrip devices with low-temperature solders without the use of fluxes, in which the soldered surfaces are pre-coated with metals or alloys with a melting temperature close to the melting point of the solder, but above it, and at the moment the solder is melted, low-frequency vibrations are reported to one of the parts to be soldered. The main disadvantage of this method is the low productivity of this assembly operation, because soldering is carried out discretely. The closest to the claimed method in terms of technical essence is the method of assembling semiconductor devices, which consists in the fact that a filter and alloying element is placed on the base of the housing, on which a solder sample and a crystal are then placed. The disadvantage of this method is the high complexity of the assembly operations and the low percentage of yield of suitable devices. In addition, this method does not provide preliminary orientation and fixation of the crystal relative to the body, as a result of which the crystal can be turned and displaced even before the soldering process begins. Moreover, soldering requires a high heating temperature, which imposes certain requirements on the crystal. Particularly noteworthy is the presence of non-solders in the soldered seam, which contributes to an increase in the thermal and electrical resistance of the contact between the semiconductor crystal and the case. Therefore, this method of assembling semiconductor devices is inefficient (or inefficient), especially when soldering semiconductor chips to cases of power electronics products. The task to be solved by the claimed solution is to increase the reliability of semiconductor devices by reducing the heating temperature when soldering the surface of a crystal with structures, improving the wetting of the joined surfaces with solder, increasing the productivity of assembly operations due to group soldering of crystals to cases. This task is achieved by the fact that in the method of assembling semiconductor devices, which consists in the fact that a filter and alloying element is placed on the base of the housing, on which a solder sample and a crystal are placed, and the cassette with the assembled devices is loaded into a conveyor hydrogen furnace at a soldering temperature of 370 o C , in order to increase the reliability of semiconductor devices by reducing the heating temperature when soldering the surface of crystals with structures, improving the wetting of the joined surfaces with solder and increasing the productivity of assembly operations due to group soldering of crystals to cases, semiconductor crystals with solder on the collector side are fixed in an inverted position in the cells vacuum suction cup and combined with the pads of the housings, and heating to the soldering temperature is carried out in air by a current pulse through V-shaped electrodes, which are rigidly fixed in the bracket, electrically connected in series with each other and located differentially bath above each crystal, and at the moment of solder melting, the vacuum suction cup with crystals is subjected to ultrasonic vibrations in the direction parallel to the soldered seam, while pressure on each crystal is carried out by the mass of the device body and the bracket with electrodes. A comparable analysis with the prototype shows that the claimed method differs from the known one in that in order to increase the reliability of semiconductor devices by reducing the heating temperature when soldering the surface of the crystal with structures, improving the wetting of the joined surfaces with solder and increasing the productivity of assembly operations due to group soldering of crystals to cases semiconductor crystals with solder on the collector side are fixed in an inverted position in the cells of the vacuum suction cup and combined with the contact pads of the housings, and heating to the soldering temperature is carried out in air by a current pulse through V-shaped electrodes, which are rigidly fixed in the bracket, electrically connected in series with each other and are located differentially above each crystal, and at the moment of solder melting, the vacuum suction cup with crystals is subjected to ultrasonic vibrations in the direction parallel to the solder seam, while pressure on each crystal carried out by the mass of the body of the device and the bracket with electrodes. Thus, the claimed method of assembly of semiconductor devices meets the criterion of "novelty". Comparison of the proposed method with other known methods from the prior art also did not allow us to identify in them the features claimed in the distinctive part of the formula. The essence of the invention is illustrated by drawings, which schematically show: in Fig. 1 - scheme of assembly and soldering of semiconductor crystals to cases, side view; in fig. 2 - a fragment of the assembly and soldering of one crystal to the case, side view. The method of assembling semiconductor devices (FIGS. 1 and 2) is implemented according to a circuit containing base 1 connected to a vacuum pump. A vacuum suction cup 2 is fixed on the base, in the cells of which semiconductor crystals 3 with solder 4 are fixed with the collector surface upwards on the soldered surface. Device cases 5 are placed on the crystals. V-shaped electrodes 6 are rigidly fixed in the bracket 7, are electrically connected in series with each other and are differentially located above each crystal. For uniform heating of the entire area of ​​the crystal during soldering, the dimensions of the working area of ​​the electrode should be 0.6-1.0 mm larger than each side of the crystal. The case, crystal and solder are heated to the soldering temperature due to the heat generated by the working platform of the V-shaped electrode when a current pulse passes through it. To destroy the oxide films and activate the surfaces of the crystal and body to be joined at the moment of solder melting, the crystals 3 through the vacuum suction cup 2 and the base 1 are exposed to ultrasonic vibrations in the direction parallel to the solder seam from the ultrasonic concentrator 8. The pressure on each crystal is carried out by the mass of the body and the bracket with electrodes . An example of an assembly of semiconductor devices is the assembly of Schottky diodes. The following films are sequentially applied to the collector surface of a semiconductor crystal as part of a wafer according to known technology: aluminum - 0.2 μm, titanium - 0.2-0.4 μm, nickel - 0.4 μm, and for soldering - solder, for example PSr2, 5 with a thickness of 40-60 microns. Then the semiconductor wafer is divided into crystals. Metal plate, consisting of 10 cases 5 type TO-220, covered by known technology with electroplated Nickel with a thickness of 6 microns. The assembly process of Schottky diodes is as follows: the crystals 3 are fixed with the collector surface upwards in the cells of the vacuum suction cup 2, the vacuum pump is turned on, and due to the pressure difference, the crystals are pressed against the walls of the vacuum suction cup; a plate with instrument cases 5 is placed on crystals; bracket 7 with electrodes 6 is combined with the contact pads of the housings in the places of their soldering with crystals 3. When soldering, the bracket 7 with electrodes 6 presses the plate from the housing 5 to the crystals 3. A current pulse is passed through the electrodes connected electrically in series with each other. The heat from the working platform of the electrode is transferred to the cases and further to the crystals, heating the solder to the soldering temperature. At this time, the crystals are exposed to ultrasonic vibrations in the direction parallel to the solder seam from the ultrasonic concentrator 8. This contributes to the destruction of oxide films and improves the wetting of the joined surfaces of the crystal and the body with solder. After a specified time, the current is turned off, and after the crystallization of the solder, a high-quality solder joint is formed. The compressive force of the crystal to the case during soldering is set by the mass of the case and the bracket with electrodes. Since during pulse soldering the crystal is heated through the case, the collector surface is heated to the soldering temperature, and the opposite surface of the crystal with structures has a heating temperature much lower than the collector surface. This factor improves the reliability of semiconductor devices. Thus, the use of the proposed method for assembling semiconductor devices provides the following advantages over existing methods. 1. The reliability of semiconductor devices is increased by lowering the heating temperature when soldering the surface of a crystal with structures. 2. Wetting of the surfaces to be joined with solder is improved. 3. The productivity of assembly operations is increased due to the group soldering of crystals to cases. Sources of information 1. Assembly of powerful transistors by the cassette method /P.K. Vorobyevsky, V.V. Zenin, A.I. Shevtsov, M.M. Ipatova//Electronic technology. Ser. 7. Technology, organization of production and equipment. - 1979.- Issue. 4.- S. 29-32. 2. Soldering microstrip devices with low-temperature solders without the use of fluxes / V.I. Bayle, F.N. Krokhmalnik, E.M. Lyubimov, N.G. Otmakhova//Electronic engineering. Ser.7. Microwave Electronics.- 1982.- Issue. 5 (341).- P. 40. 3. Yakovlev G.A. Soldering materials with lead-based solders: Review. - M .: TsNII "Electronics". Ser. 7. Technology, organization of production and equipment. Issue. 9 (556), 1978, p. 58 (prototype).

Claim

A method for assembling semiconductor devices, which consists in placing a filter and alloying element on the base of the housing, on which a solder sample and a crystal are placed, and the cassette with assembled devices is loaded into a conveyor hydrogen furnace at a soldering temperature of 370 ° C, characterized in that semiconductor crystals with solder on the collector side is fixed in an inverted position in the cells of the vacuum suction cup and combined with the contact pads of the instrument cases, and heating to the soldering temperature is carried out in air by a current pulse through V-shaped electrodes, which are rigidly fixed in the bracket, electrically connected in series with each other and located differentially above each crystal, and at the moment of solder melting, the vacuum suction cup with crystals is subjected to ultrasonic vibrations in the direction parallel to the soldered seam, while pressure on each crystal is carried out by the mass of the device body and the bracket with electrodes.

The electrical installation of radio components must ensure the reliable operation of equipment, devices and systems under the conditions of mechanical and climatic influences specified in the specifications for this type of electronic equipment. Therefore, when mounting semiconductor devices (SS), integrated circuits (ICs) of radio components on printed circuit boards or equipment chassis, the following conditions must be met:

• reliable contact between the body of a powerful PP and a heat sink (radiator) or chassis;
• necessary air convection at radiators and elements that release a large amount of heat;

• removal of semiconductor elements from circuit elements that emit a significant amount of heat during operation;
• protection of the installation, located near the removable elements, from mechanical damage during operation;
• in the process of preparing and conducting the electrical installation of the PCB and IC, mechanical and climatic effects on them should not exceed the values ​​specified in the specifications;
• when straightening, forming and trimming PCB and IC leads, the lead section near the case must be fixed so that bending or tensile forces do not occur in the conductor. Equipment and fixtures for forming leads must be grounded;
• the distance from the PCB or IC body to the beginning of the lead bend must be at least 2 mm, and the bending radius with a lead diameter of up to 0.5 mm - at least 0.5 mm, with a diameter of 0.6-1 mm - at least 1 mm, with a diameter of more than 1 mm - not less than 1.5 mm.

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

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

When installing an IC with rigid radial leads in the metallized holes of the printed circuit board, the protruding part of the leads above the surface of the board at the soldering points should be 0.5-1.5 mm. The IC is mounted in this way after trimming the leads (Fig. 55). To facilitate dismantling, it is recommended to install the IC 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 the contact pads of the board without mounting holes. In this case, their location on the board is determined by the shape of the pads (Fig. 56).

Rice. 56. Mounting ICs with flat (planar) leads on a printed circuit board:
1 - contact pad with a key, 2 - case, 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 PCBs and ICs, as well as mounted radio components on printed circuit boards, should provide access to them and the possibility of replacing them. To cool ICs, they should be placed on printed circuit boards, taking into account the movement of 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 leads are mechanically fixed on it. For soldering the field joint, an acid-free flux is used, the remnants of which are removed after soldering.

The 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. At the same time, the radio components are fixed so that they do not move during vibration and shock (shaking). Recommended types of fastening of radio components (resistances, capacitors, diodes, transistors) are shown in fig. 58.

Rice. 58. Installation of radio components on mounting fittings:
a, b - resistors (capacitors) with flat and round leads; 1 - housing, 2 - petal, 3 - output, 4 - radiator, 5 - wires, 6 - insulating tube

The mechanical fastening of the leads of the radio components on the mounting fittings is carried out by bending or twisting them around the fittings, followed by compression. In this case, a break in the output during compression is not allowed. If there is a hole in the contact post or petal, the radio component output is mechanically fixed before soldering by passing it through the hole and bending half or a full turn around the petal or post, followed by crimping. At the same time, 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 leads are specified in the assembly drawing for the product.

To reduce the distance between the radio component and the chassis, insulating tubes are put on their cases or terminals, the diameter of which is equal to or somewhat smaller than the diameter of the radio component. In this case, the radio components are located close to each other or to the chassis. Insulating tubes put on the leads of the radio components exclude the possibility of a short circuit with neighboring conductive elements.

The length of the mounting leads from the soldering point to the body of the radio component is given in the technical specifications and, as a rule, is specified in the drawing: for discrete radio components, it must be at least 8 mm, and for PP - at least 15 mm. The lead length from the housing to the bend of the radio component is also specified in the drawing: it must be at least 3 mm. The conclusions of the radio components are bent with a template, fixture or a special tool. Moreover, the inner radius of the bend must be at least twice the diameter or thickness of the output. Rigid terminals of radio components (PEV resistances, etc.) are not allowed to be bent during installation.

The 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 ratings and adjusting the device, the radio components must be soldered to the reference points with mechanical fastening of the leads.

ASSEMBLY OF SEMICONDUCTOR DEVICES

AND INTEGRATED MICROCIRCUIT

Features of the assembly process

The assembly of semiconductor devices and integrated circuits is the most time-consuming and responsible technological stage in the overall cycle of their manufacture. The stability of electrical parameters and the reliability of finished products largely depend on the quality of assembly operations.

The assembly stage begins after the completion of the group processing of semiconductor wafers using planar technology and their separation into individual elements (crystals). These crystals can have the simplest (diode or transistor) structure or include a complex integrated circuit (with a large number of active and passive elements) and come to the assembly of discrete, hybrid or monolithic compositions.

The difficulty of the assembly process lies in the fact that each class of discrete devices and ICs has its own design features that require well-defined assembly operations and modes of their implementation.

The assembly process includes three main technological operations: attaching a crystal to the base of the case; connection of current-carrying leads to active and passive elements of the semiconductor crystal to the internal elements of the case; sealing the crystal from the external environment.

Attaching the Crystal to the Case Base

Attaching a semiconductor device crystal or IC to the base of the package is carried out using the processes of soldering, fusion using eutectic alloys and gluing.

The main requirement for the operation of attaching a crystal is the creation of a connection between the crystal and the base of the body, which has high mechanical strength, good electrical and thermal conductivity.

Soldering- the process of connecting two different parts without melting them using a third component called solder. A feature of the soldering process is that the solder during the formation of a solder joint is in a liquid state, and the parts to be joined are in a solid state.

On fig. 1a shows a variant of attaching an IC chip having tinned copper contact protrusions to a substrate. This design of the leads is not afraid of solder spreading over the substrate. The presence of a high mushroom-shaped protrusion provides the necessary gap between the semiconductor crystal and the substrate during solder melting. This allows the attachment of the crystal to the substrate with a high degree of accuracy.

On fig. 1c shows a variant of the assembly of crystals having soft bumps made of tin-lead solder.

P
The connection of such a crystal to the base of the housing is carried out by conventional heating without additional pressure on the crystal. The solder of the contact protrusions during heating and melting does not spread over the surface of the tinned sections of the body base due to surface tension forces. This, moreover, provides a certain gap between the crystal and the substrate.

The considered method of attaching IC crystals to the base of the case or to any board makes it possible to mechanize and automate the assembly process to a large extent.

Surfacing using eutectic alloys. This method of attaching semiconductor chips to the package base is based on the formation of a molten zone in which the surface layer of the semiconductor material and the metal layer of the package base are dissolved.

Two eutectic alloys are widely used in industry: gold-silicon (melting point 370°C) and gold-germanium (melting point 356°C). The process of eutectic attachment of the crystal to the base of the housing has two varieties. The first type is based on the use of a gasket made of eutectic alloy, which is located between the connected elements: the crystal and the case. In this type of connection, the surface of the housing base must be gold-plated in the form of a thin film, and the surface of the semiconductor chip may not be gold-plated (for silicon and germanium) or be covered with a thin layer of gold (in the case of other semiconductor materials being attached). When such a composition is heated to the melting temperature of the eutectic alloy, a liquid zone is formed between the connected elements (the crystal-base of the body). In this liquid zone, on the one hand, the dissolution of the layer of the semiconductor material of the crystal (or the layer of gold deposited on the surface of the crystal).

After the entire system is cooled (the body base is a eutectic melt-semiconductor crystal), the liquid zone of the eutectic alloy solidifies, and a solid solution forms at the semiconductor-eutectic alloy boundary. As a result of this process, a mechanically strong connection of the semiconductor material with the base of the package is created.

The second type of eutectic attachment of the crystal to the base of the housing is usually implemented for silicon or germanium crystals. Unlike the first type, a eutectic alloy gasket is not used to attach the crystal. In this case, the liquid zone of the eutectic melt is formed as a result of heating the composition of the gold-plated base of the body-silicon (or germanium) crystal. Let's take a closer look at this process. If a silicon crystal without a gold coating is placed on the surface of the base of the case, which has a thin layer of gold coating, and the entire system is heated to a temperature of 40-50 ° C higher than the temperature of the gold-silicon eutectic, then a liquid phase of the eutectic composition is formed between the connected elements. Since the process of alloying the layer of gold with silicon is non-equilibrium, the amount of silicon and gold dissolved in the liquid zone will be determined by the thickness of the gold coating, the temperature and time of the alloying process. At sufficiently long exposures and a constant temperature, the process of alloying gold with silicon approaches equilibrium and is characterized by a constant volume of the gold-silicon liquid phase. The presence of a large amount of the liquid phase can lead to its outflow from under the silicon crystal to its periphery. During solidification, the leaked eutectic leads to the formation of sufficiently large mechanical stresses and shells in the silicon crystal structure, which sharply reduce the strength of the alloy structure and worsen its electrical parameters.

At the minimum values ​​of time and temperature, the fusion of gold with silicon does not occur uniformly over the entire area of ​​contact between the crystal and the case base, but only at its individual points.

As a result, the strength of the alloy joint decreases, the electrical and thermal resistance of the contact increases, and the reliability of the resulting reinforcement decreases.

The state of the surfaces of the original joined elements has a significant impact on the process of eutectic fusion. The presence of contaminants on these surfaces leads to a deterioration in the wetting of the contacting surfaces with the liquid phase and uneven dissolution.

gluing is a process of connecting elements to each other, based on the adhesive properties of certain materials, which make it possible to obtain mechanically strong connections between semiconductor crystals and housing bases (metal, glass or ceramic). Bonding strength is determined by the adhesive force between the adhesive and the bonded surfaces of the elements.

Bonding various elements of integrated circuits makes it possible to connect a wide variety of materials in various combinations, simplify the design of the assembly, reduce its mass, reduce the consumption of expensive materials, avoid the use of solders and eutectic alloys, and greatly simplify the technological processes of assembling the most complex semiconductor devices and ICs.

As a result of gluing, it is possible to obtain fittings and complex compositions with electrical insulating, optical and conductive properties. Attaching the dies to the base of the package using the gluing process is indispensable for the assembly and installation of hybrid, monolithic and optoelectronic circuit elements.

When gluing crystals to the base of the housings, various types of adhesives are used: insulating, conductive, light-conducting and heat-conducting. According to the activity of interaction between the adhesive and the surfaces to be glued, polar (based on epoxy resins) and non-polar (based on polyethylene) are distinguished.

The quality of the gluing process largely depends not only on the properties of the adhesive, but also on the state of the surfaces of the elements to be glued. To obtain a strong connection, it is necessary to carefully process and clean the surfaces to be glued. Temperature plays an important role in the bonding process. So, when gluing structural elements that are not exposed to high temperatures in subsequent technological operations, epoxy-based cold curing adhesives can be used. For gluing silicon crystals to metal or ceramic bases of housings, VK-2 glue is usually used, which is a solution of organosilicon resin in an organic solvent with finely dispersed asbestos as an active filler or VK-32-200, in which glass or quartz is used as a filler. .

The technological process of gluing semiconductor crystals is carried out in special assembly cassettes that provide the desired orientation of the crystal on the base of the case and the necessary pressing it to the base. The assembled cassettes, depending on the adhesive material used, are subjected to a certain heat treatment or kept at room temperature.

Special groups are electrically conductive and optical adhesives used for gluing elements and assemblies of hybrid and optoelectronic ICs. Conductive adhesives are compositions based on epoxy and organosilicon resins with the addition of silver or nickel powders. Among them, the most widely used adhesives are AC-40V, EK-A, EK-B, K-3, EVT and KN-1, which are pasty liquids with a specific electrical resistance of 0.01-0.001 ohm-cm and a range of operating temperatures from -60 to +150°С. Optical adhesives are subject to additional requirements for the value of the refractive index and light transmission. The most widely used optical adhesives OK.-72 F, OP-429, OP-430, OP-ZM.

The main parameters of the thermocompression welding mode are specific pressure, heating temperature and welding time. The specific pressure is selected depending on the allowable compression stress of the semiconductor crystal and the allowable deformation of the material of the welded lead. The welding time is chosen experimentally.

Relative deformation during thermocompression welding

,

where d is the wire diameter, microns; b-connection width, microns.

The pressure on the tool is determined based on the distribution of stresses at the stage of deformation completion:

,

G

de A-coefficient characterizing the change in stress during wire deformation; f is the reduced coefficient of friction, which characterizes the friction between the tool, wire and substrate; - relative deformation; - Yield strength of wire material at deformation temperature; d is the diameter of the wire; D is the diameter of the pressing tool, usually equal to (2h3)d.

Rice. 2. Nomogram for selecting modes of thermocompression welding:

a - gold wire with an aluminum film; b- aluminum wire with an aluminum film

On fig. Figure 2 shows the nomograms of the modes of thermocompression welding of gold (a) and aluminum (b) wire with aluminum contact pads. These nomograms enable the optimum selection of the relationship between pressure, temperature and time.

Thermocompression welding has quite a few varieties that can be classified by the method of heating, by the method of attachment, by the shape of the tool. According to the heating method, thermocompression welding is distinguished with separate heating of the needle, crystal or punch, as well as with simultaneous heating of two of these elements. According to the method of connection, thermocompression welding can be butt and overlap. According to the shape of the instrument, a “bird's beak”, “wedge”, “capillary” and “needle” are distinguished (Fig. 14.3).

When welding with the "bird's beak" tool, the same device feeds the wire, attaches it to the contact pads of the integrated circuit and automatically breaks without releasing it from the "beak". The tool in the form of a "wedge" presses the end of the wire to the substrate, while not the entire wire is pressed in, but only its central part. When welding with a "capillary tool", the wire passes through it. The capillary tip simultaneously serves as a tool that transmits pressure to the wire. When welding with a “needle”, the end of the wire lead is brought into the welding zone by a special mechanism and placed on the contact pad, and then pressed with a needle with a certain force.

R

is. 3. Types of tools for thermocompression welding:

a- "bird's beak"; b- "wedge"; c- "capillary"; Mr. "needle"

To carry out the process of thermocompression welding, various installations are used, the main components of which are: a working table with or without a heating column, a mechanism for creating pressure on the attached terminal, a working tool, a mechanism for feeding and breaking wire for terminals, a mechanism for feeding crystals or parts with attached to them crystal; a mechanism for combining the connected elements, an optical system for visual observation of the welding process, power and control units. All of the listed nodes can have a different design, but the principle of their design and the nature of the work performed is the same.

Currently, two methods of electric resistance welding are used to connect leads to contact pads of integrated circuit crystals: with one-sided arrangement of two electrodes and with one-sided arrangement of one double electrode. The second method differs from the first one in that the working electrodes are made in the form of two current-carrying elements separated from each other by an insulating spacer. At the moment of pressing such an electrode to the wire lead and passing the electrode current through the formed system, a large amount of heat is released at the point of contact. External pressure in combination with heating the parts to the temperature of plasticity or melting leads to their strong connection.

The crystal feed mechanism includes a set of cassettes, and the alignment mechanism includes a system of manipulators that allow you to place the crystal in the desired position. An optical visual observation system consists of a microscope or a projector. The power supply and control unit allows you to set the operating mode of welding and to rebuild and adjust it when changing the type of crystal and output material.

Cold welding. The cold sealing method is widely used in the electronics industry. In those cases when, when sealing the original parts of the hulls, their heating is unacceptable and a high purity of the process is required, cold pressure welding is used. In addition, cold welding provides a strong hermetic connection of the most commonly used dissimilar metals (copper, nickel, kovar and steel).

The disadvantages of this method include the presence of significant deformation of the body parts at the junction, which leads to a significant change in the shape and overall dimensions of the finished products.

The change in the outer diameter of the body of the device depends on the thickness of the original welded parts. Change in the outer diameter of the finished device after the cold welding process

where is the thickness of the shoulder of the upper part before welding; - thickness of the shoulder of the lower part before welding.

Of great importance for the cold welding process is the presence of an oxide film on the surface of the parts to be joined. If this film is ductile and softer than the base metal, then under pressure it spreads in all directions and thins, thereby separating clean metal surfaces, as a result of which welding does not occur. If the oxide film is more brittle and harder than the metal it covers, then under pressure it cracks, and cracking occurs equally on both parts to be joined. Contaminants present on the surface of the film are packed on both sides in a kind of packages, firmly clamped at the edges. A further increase in pressure leads to the spreading of pure metal to the peripheral areas. The greatest spreading occurs in the middle plane of the formed seam, due to which all packages with impurities are forced out, and clean metal surfaces, entering into interatomic interactions, firmly adhere to each other.

Thus, brittleness and hardness are the main qualities of the oxide film, providing a tight connection. Since for most metals the thickness of the coating with oxide films does not exceed 10-7 cm, parts made of such metals are nickel-plated or chrome-plated before welding. Nickel and chromium films have sufficient hardness and brittleness and, therefore, significantly improve the welded joint.

Before carrying out the cold welding process, all parts are degreased, washed and dried. To form a high-quality connection of two metal parts, it is necessary to ensure sufficient deformation, plasticity and cleanliness of the parts to be welded.

The degree of deformation K during cold welding should be in the range of 75-85%:

,

where 2H is the total thickness of the parts to be welded; t is the thickness of the weld.

Weld strength

where P is the breaking force; D is the diameter of the imprint of the protrusion of the punch; H is the thickness of one of the parts to be welded with the smallest size; - tensile strength with the smallest value.

For body parts during cold welding, the following combinations of materials are recommended: copper MB-copper MB, copper MB-copper M1, copper MB-steel 10, alloy N29K18 (kovar)-copper MB, kovar-copper M1.

The critical pressures required for plastic deformation and cold welding, for example, for a combination of copper-copper, are 1.5 * 109 N / m2, for a combination of copper - kovar they are 2 * 109 N / m2.

Plastic sealing. Expensive sealing of glass, glass-to-metal, cermet and metal cases is now being successfully replaced by plastic sealing. ) In some cases, this increases the reliability of devices and ICs, since the contact of the semiconductor crystal with the gaseous medium inside the case is eliminated.

Plastic sealing allows you to reliably isolate the crystal from external influences and provides high mechanical and electrical strength of the structure. For sealing ICs, plastics based on epoxy, organosilicon, and polyester resins are widely used.

The main methods of sealing are pouring, enveloping and pressing under pressure. When sealing by pouring, hollow molds are used, in which semiconductor crystals with soldered external leads are placed. The molds are filled with plastic.

When sealing devices by enveloping, two (or more) leads made of tape or wire material are taken, they are connected to each other with a glass or plastic bead, and a semiconductor crystal is soldered to one of the leads, and electrical contact conductors are connected to the other (other) lead. The assembly thus obtained is sealed by plastic wrapping.

The most promising way to solve the problem of assembling and sealing devices is to seal crystals with active elements on a metal tape, followed by sealing with plastic. The advantage of this sealing method is the possibility of mechanization and automation of assembly processes of various types of ICs. The main structural element of the plastic case is a metal band. To select the profile of a metal tape, it is necessary to proceed from the size of the crystals, the thermal characteristics of the devices, the possibility of mounting the finished devices on the printed circuit board of the electronic circuit, the maximum tear strength from the case, and the simplicity of the design.

The technological scheme of plastic sealing of the device includes the main stages of planar technology. Semiconductor crystals with active elements are attached to a metal tape coated with gold, by eutectic alloying of gold with silicon, or by conventional soldering. Metal tape is made from kovar, copper, molybdenum, steel, nickel.

Applications

R

is. 3. Scheme of the fan-type assembly

R
is. 4. Assembly diagram with base part

R

is. 5. Assembly diagram (a) and IC section (b) in a round case:

1 balloon; 2-connecting conductors; 3-crystal; 4-pin pads; 5-solder; 6-leg cap; 7-glass; 8-conclusions; 9-split leads with glass; 10-connection by electrocontact welding of a cylinder and a leg; 11-plating layer (tire)

Rice. 6. Scheme of connection (assembly) of a crystal with ball leads and a substrate by soldering:

1
-crystal; 2-pin pad; 3-glass; 4-ball copper; 5-copper pillow; 6-solder (high temperature); 7-solder (low temperature); 8-lead from AgPb alloy; 9-substrate.

Rice. 7. Scheme of connection (assembly) of a crystal with beam leads and a substrate by soldering:

1-gold beam lead; 2-silicide plate; 3-crystal; 4-silicon nitride; 5-platinum; 6-titanium; 7-substrate; 8-gold pad.

Rice. 8. Diagram of the integrated circuit assembly line

Transfer tapes are used on the assembly line. Assembly and transportation are carried out on a kovar tape, which is subjected to photolithography in sections L and B to obtain conclusions 2 (Fig. 10, a). In sections C, D and D, on the basis of a tape with lead frames, instrument cases with gilded leads are made. Pieces of tape with housings are sent for assembly. Tape 2, unwinding from reel 1, is washed and degreased in bath 3 and applied with a photoresist in bath 4, exposed in unit 5 with an ultraviolet lamp 7. The role of the mask in the unit is performed by tape 6 continuously moving synchronously with tape 2. Then the tapes are washed in baths 8 and 9. Frame 2 leads (Fig. 10, a) and perforations are etched in bath 10. The photoresist layer is removed in bath 11, and the tape is dried at the exit. The resulting perforations are used to tension and move the tape with the help of an asterisk 12. In the installation 13, a transfer tape with a layer of solder glass is glued on both sides of the lead tape. The resulting system is fired, the adhesive layer burns out, and the glass is soldered to the metal of the main tape (Fig. 10, b). Cooling to room temperature is carried out in chamber 14. Using device 15, masking tapes with windows are glued onto the glass layers, through which cavities are etched in the bath 16 until internal leads are detected (Fig. 10, f).

P
the body blocks obtained in this way from metal and glass tapes are fed into the bath 17 for gilding the leads. On the device 18, the tape is cut into segments with cases, which are fed through the conveyor 19 to the assembly. A crystal with ready-made structures is connected with the help of ball protrusions to the terminal system inside the resulting package using the inverted mounting method, face down (Fig. 10, d). The casing is sealed in a protective environment with pieces of kovar tape 7, which are soldered to the base using glass heated by the tool (Fig. 10, e). The resulting microcircuit is shown in Fig. 10, e

Rice. 9. Transfer Ribbon:

1-carrier layer; 2-transfer layer; 3-adhesive layer; 4-release paper

R

is. 10. Scheme of automated assembly of ICs on tape:

1-carrier tape; 2- conclusions (after etching); 3- perforation for tape movement; 4-glass solder tape; 5-cavity IC package; 6-crystal with finished structures; 7 - body; 8-lid; 9-heating tool

Semiconductor devices have in most cases flexible leads. Therefore, they are included in the circuit by soldering. The soldering of the leads is carried out at a distance of at least 10 mm from the body of the semiconductor device (from the top of the insulator) using low-temperature solder. Bending of the leads is allowed at a distance of at least 3 - 5 mm from the body (Fig. 90). The soldering process should be short (no more than 10 seconds). The power of the soldering iron should not exceed 50-60 watts. The soldered terminal is tightly clamped with pliers. Pliers in this case play the role of a heat sink. It is necessary to ensure that the heated soldering iron does not touch the body of the semiconductor device even for a short time. Drops of solder should also not fall on it.

To avoid overheating of semiconductor devices, do not place them near power transformers, electronic lamps and other parts of the equipment that emit heat. It is desirable to reduce the operating temperature of the device. If it is 10°C below the limit, then the number of failures is halved. Mounting semiconductor devices on leads is not recommended, especially if the equipment may be subject to vibration. Operating voltages, currents and powers must be below the limit values.

The service life of diodes is extended if they are operated at reverse voltages not exceeding 80% of the maximum allowable.

Do not allow a short circuit of the rectifier on semiconductor diodes (test "spark"). This can damage the diodes. A semiconductor diode can be damaged if a voltage is applied to it in the forward direction (even from one battery cell) without a limiting resistor connected in series.

Transistors should not even work for a short time with the base turned off. When power supplies are turned on, the base terminal of the transistor must be connected first (when turned off, last).

Transistors cannot be used in a mode where two limiting parameters are simultaneously reached (for example, the maximum allowable collector voltage and at the same time the maximum allowable power dissipated by it).

The service life of the transistor is extended and the reliability of its operation increases if during its operation the collector voltage does not exceed 80% of the maximum permissible value.

When the transistor operates at elevated temperatures, it is necessary to reduce the dissipated power and the voltage on the collector.

It is necessary to ensure that the supply voltage applied to the transistor is of the correct polarity (for example, you cannot connect the positive pole of the voltage to the collector of a p-n-p-type transistor or the negative pole of the voltage to the collector of an n-p-n-type transistor). So that for this reason the transistor does not become unusable when it is installed in the circuit, you need to know for sure what type it is: p-n-p or n-p-n.

If you need to remove the transistor from the circuit (or include it in the circuit), you must first turn off the power to the circuit.

Semiconductor devices, information about which is given in the handbook, are devices for general use. They can operate in a variety of conditions and modes typical for various classes of electronic equipment for wide, industrial and special applications.

General technical requirements for devices intended for equipment of a certain class are contained in the general technical specifications (GTU) for these devices. Specific standards for the values ​​of electrical parameters and specific requirements for this type of device are set out in private specifications (ChTU) and GOST for devices.

High reliability of electronic equipment based on semiconductor devices can be ensured only if the following features of devices are taken into account at the stage of its design, manufacture and operation:

• scatter of parameter values, their dependence on the mode and operating conditions;
• changes in parameter values ​​during storage or operation;
• the need for good heat dissipation or instrument housings;
• the need to provide reserves for electrical, mechanical and other loads on devices in radio-electronic equipment;
• the need to take measures to ensure that there is no overload of devices during the installation and assembly of radio-electronic equipment.

The values ​​of the parameters of devices of the same type are not the same, but lie in a certain interval. This interval is limited by the minimum or maximum values ​​specified in the directory. Some parameters have a two-way value limit. The current-voltage characteristics given in the reference book, the dependences of parameters on the mode and temperature are averaged for a large number of instances of devices of this type. These dependences can be used when choosing the type of device for a given circuit and its approximate calculation.

Most of the parameters of semiconductor devices change significantly depending on the operating mode and temperature. For example, the recovery time of the reverse resistance of switching diodes depends on the value of the forward current, the switching voltage, and the load resistance; the conversion loss and noise figure of microwave diodes depend on the input power level. Significantly varies in the temperature range specified in the technical specifications, the reverse current of the diode. The reference book contains the values ​​of the parameters guaranteed by the specifications for the corresponding optimal or limiting modes of use.

The use and operation of devices must be carried out in accordance with the requirements of technical specifications and standards - guidelines for use. When designing radio-electronic equipment, it is necessary to strive to ensure its performance in the widest possible ranges of changes in the most important parameters of the devices. The scatter of device parameters and the change in their values ​​over time when designing equipment are taken into account by calculation methods or experimentally, for example, by the method of boundary tests.

The time during which semiconductor devices can operate in equipment (their service life) is practically unlimited. Regulatory and technical documentation for the supply of devices (GOST. TU), as a rule, guarantees a minimum operating time of at least 15,000 hours, and in light modes and conditions operation - up to 30,000 hours. However, theory and experiments show that after 50 - 70 thousand hours of operation, an increase in the failure rate is not observed. However, changes in instrument parameter values ​​may occur during storage and operation. In some instances, these changes are so significant that the equipment fails. To control the level of reliability of manufactured devices, indicators such as gamma-percentage resource, gamma-percentage retention, minimum operating time (warranty operating time), failure rate during special short-term tests in forced mode are used. The norms for these indicators are established in the technical specifications for devices.

To calculate the reliability of radio-electronic equipment, quantitative indicators of reliability should be used, which are established by conducting special tests, processing a large amount of statistical data on various tests and "operation of devices in various equipment.

It has been experimentally established that the intensity (probability) of device failures increases with an increase in the operating temperature of the junctions, the voltage on the electrodes, and the current. Due to the increase in temperature, I am accelerating (with almost all types of failures: short circuits, breaks and significant changes in parameters. An increase in voltage significantly accelerates the failures of devices with MIS structures and with low-voltage transitions. An increase in current leads mainly to accelerated destruction of contact connections and current-carrying metallization tracks on crystals.

The approximate dependence of the failure rate on the load has the form:

where λ(T p,max, Umax, Imax) is the failure rate at maximum load (can be taken from the results of short-term tests in forced mode). The value of B is approximately 6000 K.

To increase the reliability of the operation of devices in equipment, it is necessary to reduce, mainly, the temperature of junctions and crystals, as well as operating voltages and currents, which should be significantly lower than the maximum permissible ones. It is recommended to set voltages and currents (power) at the level of 0.5-0.7 limit (maximum) values. Operation of semiconductor devices at a temperature, voltage or current equal to the limit value is prohibited. Even a short-term (impulse) excess of the maximum permissible mode during operation is not allowed. Therefore, it is necessary to take measures to protect devices from electrical overloads that occur during transient processes (when turning the equipment on and off, when changing its operating mode, connecting loads, random changes in the voltage of power supplies).

The operating modes of the devices should be controlled taking into account possible unfavorable combinations of equipment operating conditions (high ambient temperature, low ambient pressure, etc.).

If the required value of current or voltage exceeds the maximum allowable value for this device, it is recommended to use a more powerful or high-voltage device, and in the case of diodes, their parallel or series connection. When connected in parallel, it is necessary to equalize the currents through the diodes using low-resistance resistors connected in series with each diode. When the diodes are connected in series, the reverse voltages across them are equalized using shunt resistors or capacitors. The recommended resistances and capacitances of the shunts are usually specified in the specifications for the diodes. There must be a good thermal connection between devices connected in series or in parallel (for example, all devices are installed on the same radiator). Otherwise, the load distribution between the devices will be unstable.

Under the influence of various factors (temperature, moisture, chemical, mechanical and other influences), the parameters, characteristics and some properties of semiconductor devices may change. To protect the structures of semiconductor devices from external influences, instrument cases are used. The housings of powerful devices simultaneously provide the necessary conditions for heat removal, and the housings of microwave devices - the optimal connection of the electrodes of the devices with the circuit. It should be borne in mind that the cases of devices have limitations in terms of tightness and corrosion resistance, therefore, when operating devices in conditions of high humidity, it is recommended to cover them with special varnishes (for example, such as UR-231 or EP-730).

Providing heat removal from semiconductor devices is one and; main tasks in the design of electronic equipment. It is necessary to adhere to the principle of the maximum possible decrease in the temperature of junctions and instrument cases. To cool powerful diodes or thyristors, heat sinks are used that operate under conditions of natural convection or forced airflow, as well as structural elements of units and equipment blocks that have a sufficient surface or good heat dissipation. Fixing devices to the radiator should provide case thermal contact. If the device case must be insulated, then in order to reduce the overall thermal resistance, it is better to isolate the radiator from the equipment case than a diode or thyristor from the radiator.

Heat dissipation is improved with a vertical arrangement of the active surfaces of the radiator, since convection conditions are better in this case. Approximate dimensions of heat sinks in the form of vertically oriented aluminum plates (square or rectangular), depending on the power dissipated by them, can be determined using the formula

where S is the area of ​​one side of the plate, cm 2 ; P is the power dissipated in the device, W. Plates with an area of ​​up to 25 cm 2 can have a thickness of 1-2 mm, with an area of ​​25 to 100 cm 2 2-3 mm. over 100 cm 2 - 3 - 4 mm.

When casting boards with semiconductor devices with compounds, foam plastics, foam rubber, it is necessary to take into account the change in thermal resistance between the device case and the environment, as well as the possibility of increasing additional heating of devices from nearby circuit elements with high heat release. The temperature during pouring should not exceed the maximum temperature of the device body specified in the specifications. When pouring, no mechanical loads should occur on the leads that violate the integrity of the glass insulators or instrument cases.

In the process of preparation and installation of semiconductor devices in equipment, mechanical and climatic effects on them should not exceed the values ​​specified in the specifications.

When straightening, forming and cutting the leads, the lead section near the body must be fixed in a hook. so that bending or tensile forces do not occur in the conductor. Equipment and fixtures for forming leads must be grounded. The distance from the body of the device to the beginning of the lead bend must be at least 2 mm. The bending radius with a lead diameter of up to 0.5 mm must be at least 0.5 mm, with a diameter of 0.6-1 mm - at least 1 mm. with a diameter of more than 1 mm - not less than 1.5 mm.

Soldering irons used for soldering device leads must be low-voltage. The distance from the case or insulator to the place of tinning or soldering of the output must be at least 3 mm. To remove heat, the output section between the body and the soldering point is clamped with tweezers with red copper sponges. The soldering iron tip must be properly grounded. If the solder temperature does not exceed 533 + 5 K, and the soldering time is not more than 3 s. then it is possible to perform soldering without a heat sink or by a group method (wave, immersion in solder, etc.).

Cleaning of printed circuit boards from flux is done with liquids. which do not affect the coating, markings or body material (for example, an alcohol-petrol mixture).

In the process of installation, transportation, storage of microwave devices, it is necessary to protect them from the effects of static electricity. For the logo, all measuring, testing, mounting equipment and tools are reliably grounded: grounding bracelets or rings are used to remove the charge from the operator's body. antistatic clothing, footwear, table coverings of workplaces are used.

Microwave diodes must be protected from the effects of external electric pillows and electromagnetic fields. Microwave diodes should not be stored or even briefly left without special shielding packaging. Before installing microwave diodes in equipment, the latter must be grounded. The inputs and outputs of the microwave path in a non-working or stored unit of equipment using microwave diodes must be covered with metal plugs.

During the operation of the equipment, measures must be taken to protect the microwave diodes from electrical microwave overloads, which can either lead to an irreversible deterioration of the parameters. or to a complete failure (burnout) of the diodes. To protect against microwave overloads, resonant arresters, ferrite limiters, and gas-discharge attenuators are used in the equipment.