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

Table 2.1. Basic materials for making circuit boards.

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

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

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

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

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

Formation of a diagram drawing.

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

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

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

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

Rice. 2.4. The principle of screen printing.

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

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

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

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

Table 2.2. Equipment for screen printing.

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

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

Fig.2.5. Offset printing scheme.

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

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

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

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

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

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

Fig.2.6. Exposure of the photosensitive layer:

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

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

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

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

– 200–250 g/l oxalic acid,

– 50–80 g/l sodium chloride,

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

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

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

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

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

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

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

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

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

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

Fig.2.8. Structure of dry photoresist.

Issued in the CIS following types dry film photoresists:

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

– water-alkaline – SPF-VShch2, TFPC;

– increased reliability – SPF-PNShch;

– protective – SPF-Z-VShch.

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

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

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

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

– protection of metallized holes from photoresist leakage is provided;

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

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

Fig.2.9. Laminator diagram.

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

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

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

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

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

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

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

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

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

– accuracy of the design elements ±0.025 mm.

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

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

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

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

The disadvantages of this method are the high labor intensity of obtaining a photographic original, which requires highly skilled labor, and the difficulty uniform lighting photo originals of a large area, which reduces the quality of photo masks.

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

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

Rice. 5.10. Coordinateograph diagram.

Printed circuit board

A printed circuit board with electronic components mounted on it.

Flexible printed circuit board with installed volumetric and surface mounting parts.

Board drawing in CAD program and finished board

Device

Also, the basis of printed circuit boards can be a metal base coated with a dielectric (for example, anodized aluminum); copper foil of the tracks is applied on top of the dielectric. Such printed circuit boards are used in power electronics for efficient heat removal from electronic components. In this case, the metal base of the board is attached to the radiator.

The material used for printed circuit boards operating in the microwave range and at temperatures up to 260 °C is fluoroplastic, fiberglass reinforced (for example, FAF-4D) and ceramics.

• GOST 2.123-93 Unified system of design documentation. Completeness of design documentation for printed circuit boards in computer-aided design.
• GOST 2.417-91 Unified system of design documentation. Printed circuit boards. Rules for the execution of drawings.

Other PCB standards:

• GOST R 53386-2009 Printed circuit boards. Terms and Definitions.
• GOST R 53429-2009 Printed circuit boards. Basic design parameters. This GOST specifies the accuracy classes of printed circuit boards and the corresponding geometric parameters.

Typical process

Let's look at a typical process for developing a board from a ready-made circuit diagram:

• Translation of a circuit diagram into a CAD database for PCB layout. The drawings of each component, the location and purpose of the pins, etc. are determined in advance. Ready-made libraries of components supplied by CAD developers are usually used.
• Check with the future manufacturer of the printed circuit board about its technological capabilities (available materials, number of layers, accuracy class, permissible hole diameters, possibility of coatings, etc.).
• Determination of the design of the printed circuit board (dimensions, mounting points, permissible heights of components).
  • Drawing the dimensions (edges) of the board, cutouts and holes, areas where the placement of components is prohibited.
  • Location of structurally related parts: connectors, indicators, buttons, etc.
  • Selecting the board material, number of metallization layers, material thickness and foil thickness (the most commonly used is 1.5 mm thick fiberglass with foil 18 or 35 microns thick).
• Perform automatic or manual component placement. Usually they try to place components on one side of the board since mounting parts on both sides is noticeably more expensive to manufacture.
• Launch the tracer. If the result is unsatisfactory, the components are repositioned. These two steps are often performed dozens or hundreds of times in a row. In some cases, PCB tracing (routing tracks) is produced entirely or partially by hand.
• Checking the board for errors ( DRC, Design Rules Check): checking for gaps, short circuits, overlapping components, etc.
• Export the file to a format accepted by the PCB manufacturer, such as Gerber.
• Preparation of an accompanying note which, as a rule, indicates the type of foil material, drilling diameters of all types of holes, type of vias (closed with varnish or open, tinned), areas of galvanic coatings and their type, solder mask color, the need for marking, method of board separation ( milling or scribing), etc.

Manufacturing

PP can be manufactured using additive or subtractive methods. In the additive method, a conductive pattern is formed on a non-foil material by chemical copper plating through a previously applied coating on the material. protective mask. In the subtractive method, a conductive pattern is formed on the foil material by removing unnecessary sections of the foil. In modern industry, exclusively the subtractive method is used.

The entire process of manufacturing printed circuit boards can be divided into four stages:

• Manufacturing of blanks (foil material).
• Processing the workpiece to obtain the desired electrical and mechanical appearance.
• Installation of components.
• Testing.

Often, the manufacture of printed circuit boards refers only to the processing of the workpiece (foil material). A typical process for processing foil material consists of several stages: drilling vias, obtaining a conductor pattern by removing excess copper foil, plating the holes, applying protective coatings and tinning, and applying markings. For multilayer printed circuit boards, pressing of the final board from several blanks is added.

Production of foil material

Foil material is a flat sheet of dielectric with copper foil glued to it. As a rule, fiberglass is used as a dielectric. In old or very cheap equipment, textolite is used on a fabric or paper basis, sometimes called getinax. Microwave devices use fluorine-containing polymers (fluoroplastics). The thickness of the dielectric is determined by the required mechanical and electrical strength; the most common thickness is 1.5 mm.

A continuous sheet of copper foil is glued onto the dielectric on one or both sides. The thickness of the foil is determined by the currents for which the board is designed. The most widely used foils are 18 and 35 microns thick. These values ​​are based on standard copper thicknesses in imported materials, in which the thickness of the copper foil layer is calculated in ounces (oz) per square foot. 18 microns corresponds to ½ oz and 35 microns corresponds to 1 oz.

Aluminum PCBs

A separate group of materials consists of aluminum metal printed circuit boards. They can be divided into two groups.

The first group is solutions in the form of an aluminum sheet with a high-quality oxidized surface, onto which copper foil is glued. Such boards cannot be drilled, so they are usually made only one-sided. The processing of such foil materials is carried out using traditional chemical printing technologies.

The second group involves creating a conductive pattern directly in the aluminum base. For this purpose, the aluminum sheet is oxidized not only on the surface but also throughout the entire depth of the base according to the pattern of conductive areas specified by the photomask.

Workpiece processing

Obtaining a wire pattern

In the manufacture of circuit boards, chemical, electrolytic or mechanical methods are used to reproduce the required conductive pattern, as well as their combinations.

Chemical method

The chemical method for manufacturing printed circuit boards from finished foil material consists of two main stages: applying a protective layer to the foil and etching unprotected areas using chemical methods.

In industry, the protective layer is applied photolithographically using an ultraviolet-sensitive photoresist, a photomask and a source ultraviolet light. The copper foil is completely covered with photoresist, after which the pattern of tracks from the photomask is transferred to the photoresist by illumination. The exposed photoresist is washed off, exposing the copper foil for etching; the unexposed photoresist is fixed on the foil, protecting it from etching.

Photoresist can be liquid or film. Liquid photoresist is applied in industrial conditions as it is sensitive to non-compliance with the application technology. Film photoresist is popular for hand-made circuit boards, but is more expensive. The photomask is a UV-transparent material with a track pattern printed on it. After exposure, the photoresist is developed and fixed as in a conventional photochemical process.

In amateur conditions, a protective layer in the form of varnish or paint can be applied by silk-screening or manually. To form an etching mask on foil, radio amateurs use toner transfer from an image printed on a laser printer (“laser-iron technology”).

Foil etching refers to the chemical process of converting copper into soluble compounds. Unprotected foil is etched, most often, in a solution of ferric chloride or in a solution of other chemicals, such as copper sulfate, ammonium persulfate, ammonia copper chloride, ammonia copper sulfate, chlorite-based, chromic anhydride-based. When using ferric chloride, the board etching process proceeds as follows: FeCl 3 +Cu → FeCl 2 +CuCl. Typical solution concentration is 400 g/l, temperature up to 35°C. When using ammonium persulfate, the board etching process proceeds as follows: (NH 4) 2 S 2 O 8 +Cu → (NH 4) 2 SO 4 +CuSO 4.

After etching, the protective pattern is washed off from the foil.

Mechanical method

The mechanical manufacturing method involves the use of milling and engraving machines or other tools for mechanical removal layer of foil from specified areas.

Laser engraving

Until recently, laser engraving of printed circuit boards was not widespread due to the good reflective properties of copper at the wavelength of the most common high-power gas CO lasers. Due to progress in the field of laser technology, laser-based industrial prototyping installations have now begun to appear.

Metallization of holes

Via and mounting holes can be drilled, punched mechanically (in soft materials such as getinax) or laser (very thin vias). Metallization of holes is usually done chemically or mechanically.

Mechanical metallization of holes is carried out with special rivets, soldered wires or by filling the hole with conductive glue. The mechanical method is expensive to produce and therefore is used extremely rarely, usually in highly reliable one-piece solutions, special high-current equipment or amateur radio conditions.

During chemical metallization, holes are first drilled in a foil blank, then they are metallized, and only then the foil is etched to obtain a print pattern. Chemical metallization of holes - multi-stage difficult process, sensitive to the quality of reagents and adherence to technology. Therefore, it is practically not used in amateur radio conditions. Simplified, it consists of the following steps:

• Applying the walls of the hole of a conductive substrate to the dielectric. This substrate is very thin and fragile. Applied by chemical metal deposition from unstable compounds such as palladium chloride.
• Electrolytic or chemical deposition of copper is performed on the resulting base.
• At the end of the production cycle, either hot tinning is used to protect the rather loose deposited copper or the hole is protected with varnish (solder mask). Poor quality, untinned vias are one of the most common causes of electronic failure.

Pressing of multilayer boards

Multilayer boards (with more than 2 layers of metallization) are assembled from a stack of thin two- or single-layer printed circuit boards made traditional way(except for the outer layers of the bag - they are left with the foil untouched for now). They are assembled in a “sandwich” with special gaskets (prepregs). Next, pressing is carried out in an oven, drilling and metallization of vias. Lastly, the foil of the outer layers is etched.

Via holes in such boards can also be made before pressing. If the holes are made before pressing, then it is possible to obtain boards with so-called blind holes (when there is a hole in only one layer of the sandwich), which allows the layout to be compacted.

Coating

Possible coatings include:

• Protective and decorative varnish coatings (“soldering mask”). Usually has a characteristic green color.
• Tinning. Protects the copper surface, increases the thickness of the conductor, and facilitates the installation of components. Typically performed by immersion in a solder bath or wave of solder.
• Electroplating of foil with inert metals (gold plating, palladizing) and conductive varnishes to improve the contact properties of connectors and membrane keyboards.
• Decorative and information coverings (labeling). Usually applied using silk-screen printing, less often - inkjet or laser.

Mechanical restoration

Many individual boards are often placed on one sheet of workpiece. They go through the entire process of processing the foil blank as one board and only at the end are they prepared for separation. If the boards are rectangular, then non-through grooves are milled, which facilitate the subsequent breaking of the boards (scribing, from the English. scribe to scratch). If the boards have a complex shape, then through milling is done, leaving narrow bridges so that the boards do not crumble. For boards without metallization, instead of milling, a series of holes with small pitches are sometimes drilled. Drilling of mounting (non-metalized) holes also occurs at this stage.

See also: GOST 23665-79 Printed circuit boards. Contour processing. Requirements for standard technological processes.

According to the standard technical process, the separation of boards from the workpiece occurs after the components are installed.

Installation of components

Soldering is the primary method of assembling components onto printed circuit boards. Soldering can be done either manually with a soldering iron or using specially developed specific technologies.

Wave soldering

The main method of automated group soldering for lead components. Using mechanical activators, a long wave of molten solder is created. The board is passed over the wave so that the wave barely touches the bottom surface of the board. In this case, the leads of pre-installed lead components are wetted by a wave and soldered to the board. Flux is applied to the board using a sponge stamp.

Soldering in ovens

The main method of group soldering of planar components. A special solder paste (solder powder in a paste-like flux) is applied to the contact pads of the printed circuit board through a stencil. Then the planar components are installed. The board with the components installed is then fed into a special oven where the solder paste flux is activated and the solder powder melts, soldering the component.

If such installation of components is performed on both sides, then the board undergoes this procedure twice - separately for each side of the installation. Heavy planar components are mounted on beads of adhesive that prevent them from falling off the inverted board during the second soldering. Lightweight components are held on the board by the surface tension of the solder.

After soldering, the board is treated with solvents to remove flux residues and other contaminants, or, when using no-clean solder paste, the board is immediately ready for certain operating conditions.

Installing components

Installation of components can be performed either manually or using special automatic installers. Automatic installation reduces the likelihood of errors and significantly speeds up the process (the best machines install several components per second).

Finish coatings

After soldering, the printed circuit board with components is coated with protective compounds: water repellents, varnishes, means of protecting open contacts.

Similar technologies

Hybrid chip substrates are something similar to a ceramic printed circuit board, but usually use different technical processes:

• silk-screen printing of conductors with metallized paste followed by sintering of the paste in an oven. The technology allows multilayer wiring of conductors due to the possibility of applying an insulator layer to a layer of conductors using the same silk-screen printing methods.
• Metal deposition through a stencil.

An electronic printed circuit board (Russian abbreviation - PP, English - PCB) is a sheet panel that houses interconnected microelectronic components. Printed circuit boards are used as part of various electronic equipment, ranging from simple doorbells, household radios, studio radios and ending with complex radar and computer systems. Technologically, the manufacture of electronics printed circuit boards involves the creation of connections with conductive “film” material. Such material is applied (“printed”) on an insulating plate, which is called a substrate.

Electronic printed circuit boards marked the beginning of the formation and development of electrical interconnection systems developed in the mid-19th century.

Metal strips (rods) were originally used for bulky electrical components mounted on a wood base.

Gradually, metal strips replaced conductors with screws terminal blocks. Wooden base also modernized, giving preference to metal.

This is what the prototype looked like modern production PP. Similar design solutions were used in the mid-19th century

The practice of using compact, small-sized electronic parts required a unique solution on the basic basis. And so, in 1925, a certain Charles Ducasse (USA) found such a solution.

An American engineer proposed a unique way of organizing electrical connections on an insulated plate. He used electrically conductive ink and a transfer stencil schematic diagram onto the plate.

A little later, in 1943, the Englishman Paul Eisler also patented the invention of etching conductive circuits on copper foil. The engineer used an insulator plate laminated with foil material.

However, the active use of Eisler technology was noted only in the period 1950-60, when they invented and mastered the production of microelectronic components - transistors.

The technology for manufacturing through holes on multilayer printed circuit boards was patented by Hazeltyne (USA) in 1961.

Thus, thanks to the increase in the density of electronic parts and the close arrangement of interconnecting lines, a new era of printed circuit board design has opened.

Electronic printed circuit board - manufacturing

A generalized vision of the process: individual electronic parts are distributed over the entire area of ​​the insulating substrate. The installed components are then connected by soldering to the circuit circuits.

The so-called contact “fingers” (pins) are located along the extreme areas of the substrate and act as system connectors.

Through contact “fingers”, communication with peripheral printed circuit boards or connection of external control circuits is organized. The electronic printed circuit board is designed for wiring a circuit that supports one function or several functions simultaneously.

Three types of electronic printed circuit boards are manufactured:

1. One-sided.
2. Double-sided.
3. Multilayer.

Single-sided printed circuit boards are characterized by the placement of parts exclusively on one side. If the complete circuit parts do not fit on a single-sided board, a double-sided option is used.

Substrate material

The substrate traditionally used in printed circuit boards is typically made from fiberglass combined with epoxy resin. The substrate is covered with copper foil on one or two sides.

Electronics printed circuit boards made from phenolic resin paper, also coated with copper film, are considered cost-effective for production. Therefore, more often than other variations, they are used to equip household electronic equipment.

The connections are made by coating or by etching the copper surface of the substrate. Copper tracks are coated with a tin-lead composition to protect against corrosion. Contact pins on printed circuit boards are coated with a layer of tin, then nickel, and finally gold.

Performing strapping operations

Surface mounting technology involves the use of straight (J-shaped) or angled (L-shaped) branches. Due to such branches, each electronic part is directly connected to a printed circuit.

By using a complex paste (glue + flux + solder), electronic parts are temporarily held at the point of contact. The hold continues until the printed circuit board is inserted into the oven. There the solder melts and connects the circuit parts.

Despite the challenges of component placement, surface mount technology has another important advantage.

This technique eliminates the lengthy drilling process and insertion of bonding gaskets, as is practiced with the outdated through-hole method. However, both technologies continue to be actively used.

Electronic PCB Design

Each individual electronics printed circuit board (batch of boards) is designed for unique functionality. Electronic printed circuit board designers turn to design systems and specialized “software” to layout the circuit on a printed circuit board.

The gap between conductive tracks is usually measured in values ​​of no more than 1 mm. Hole locations for component conductors or contact points are calculated.

All this information is translated into the computer software format that controls drilling machine. An automatic machine for the production of electronic printed circuit boards is programmed in the same way.

Once the circuit diagram is laid out, a negative image of the circuit (mask) is transferred to a transparent sheet of plastic. Areas of the negative image that are not included in the circuit image are marked in black, and the circuit itself remains transparent.

Industrial manufacturing of electronics printed circuit boards

Electronics printed circuit board manufacturing technologies provide for production conditions in a clean environment. Atmosphere and objects production premises are automatically controlled for the presence of contamination.

Many electronic printed circuit board manufacturing companies practice unique manufacturing. And in standard form Manufacturing a double-sided printed circuit board traditionally involves the following steps:

Making the base

1. The fiberglass is taken and passed through the process module.
2. Impregnated with epoxy resin (immersion, spraying).
3. The glass fiber is rolled on a machine to the desired thickness of the substrate.
4. Dry the substrate in an oven and place it on large panels.
5. The panels are arranged in stacks, alternating with copper foil and a backing coated with glue.

Finally, the stacks are placed under a press, where at a temperature of 170°C and a pressure of 700 kg/mm ​​2, they are pressed for 1-2 hours. The epoxy resin hardens and the copper foil is bonded under pressure to the backing material.

Drilling and tinning holes

1. Several backing panels are taken, laid one on top of the other, and firmly fixed.
2. The folded stack is placed in a CNC machine, where holes are drilled according to the schematic pattern.
3. The holes made are cleared of excess material.
4. The internal surfaces of the conductive holes are coated with copper.
5. Non-conductive holes are left uncoated.

Producing a drawing of a printed circuit board

A sample PCB circuit is created using an additive or subtractive principle. In the case of the additive option, the substrate is coated with copper according to the desired pattern. In this case, the part outside the scheme remains unprocessed.

The subtractive process primarily covers the overall surface of the substrate. Then individual areas that are not included in the diagram are etched or cut out.

How does the additive process work?

The foil surface of the substrate is pre-degreased. The panels go through a vacuum chamber. Due to the vacuum, the layer of positive photoresist material is tightly compressed over the entire foil area.

The positive material for photoresist is a polymer that has the ability to solubilize under ultraviolet radiation. Vacuum conditions eliminate any possible remaining air between the foil and the photoresist.

The circuit template is laid on top of the photoresist, after which the panels are exposed to intense ultraviolet light. Since the mask leaves areas of the circuit transparent, the photoresist at these points is exposed to UV radiation and dissolves.

Then the mask is removed and the panels are pollinated with an alkaline solution. This, a kind of developer, helps to dissolve the irradiated photoresist along the boundaries of the areas of the circuit design. Thus, the copper foil remains exposed on the surface of the substrate.

Next, the panels are galvanized with copper. Copper foil acts as the cathode during the galvanization process. Exposed areas are galvanized to a thickness of 0.02-0.05 mm. The areas remaining under the photoresist are not galvanized.

Copper traces are additionally coated with a tin-lead composition or other protective coating. These actions prevent oxidation of copper and create a resist for the next stage of production.

Unneeded photoresist is removed from the substrate using an acid solvent. The copper foil between the circuit design and the coating is exposed. Since the copper of the PCB circuit is protected by a tin-lead compound, the conductor here is not affected by acid.

Techniques for industrial manufacturing of electronic circuit boards

What does it represent printed boards A?

Printed boards A or boards A, is a plate or panel consisting of one or two conductive patterns located on the surface of a dielectric base, or a system of conductive patterns located in the volume and on the surface of a dielectric base, interconnected in accordance with a circuit diagram, intended for electrical connection and mechanical fastening of electronic products, quantum electronics and electrical products installed on it - passive and active electronic components.

Simplest printed boards oh is boards A, which contains copper conductors on one side printed boards s and connects the elements of the conductive pattern on only one of its surfaces. Such boards s known as single layer printed boards s or unilateral printed boards s(abbreviated as AKI).

Today, the most popular in production and the most widespread printed boards s, which contain two layers, that is, containing a conductive pattern on both sides boards s– double-sided (double-layer) printed boards s(abbreviated DPP). Through connections are used to connect conductors between layers. installation metalized and transitional holes. However, depending on the physical complexity of the design printed boards s, when the wiring is on both sides boards does not become too complex in production order available multilayer printed boards s(abbreviated MPP), where the conductive pattern is formed not only on the two outer sides boards s, but also in the inner layers of the dielectric. Depending on complexity, multi-layer printed boards s can be made of 4,6,...24 or more layers.

For installation A electronic components on printed boards s, a technological operation is required - soldering, used to obtain a permanent connection of parts made of different metals by introducing molten metal - solder, which has a lower melting point than the materials of the parts being connected - between the contacts of the parts. The soldered contacts of the parts, as well as the solder and flux, are brought into contact and subjected to heating at a temperature above the melting point of the solder, but below the melting temperature of the parts being soldered. As a result, the solder goes into a liquid state and wets the surfaces of the parts. After this, the heating stops and the solder goes into the solid phase, forming a connection. This process can be done manually or using specialized equipment.

Before soldering, components are placed on printed boards e leads of components into through holes boards s and soldered to the contact pads and/or metallized inner surface holes - so-called technology installation A into holes (THT Through Hole Technology - technology installation A into holes or other words - pin installation or DIP installation). Also, more progressive surface technology has become increasingly widespread, especially in mass and large-scale production. installation A- also called TMP (technology installation A to the surface) or SMT(surface mount technology) or SMD technology (from surface mount device - a device mounted on a surface). Its main difference from “traditional” technology installation A into holes is that the components are mounted and soldered onto land pads, which are part of the conductive pattern on the surface printed boards s. In surface technology installation A Typically, two soldering methods are used: solder paste reflow soldering and wave soldering. The main advantage of the wave soldering method is the ability to simultaneously solder both surface-mounted components boards s, and into the holes. At the same time, wave soldering is the most productive soldering method when installation e into the holes. Reflow soldering is based on the use of a special technological material - solder paste. It contains three main components: solder, flux (activators) and organic fillers. Soldering paste applied to the contact pads either using a dispenser or through stencil, then the electronic components are installed with the leads on the solder paste and then, the process of reflowing the solder contained in the solder paste is carried out in special ovens by heating printed boards s with components.

To avoid and/or prevent accidental short-circuiting of conductors from different circuits during the soldering process, manufacturers printed boards a protective solder mask is used (English solder mask; also known as “brilliant”) - a layer of durable polymer material designed to protect conductors from the ingress of solder and flux during soldering, as well as from overheating. Soldering mask covers conductors and leaves pads and blade connectors exposed. The most common solder mask colors used in printed boards A x - green, then red and blue. It should be kept in mind that soldering mask doesn't protect boards from moisture during operation boards s and special organic coatings are used for moisture protection.

In the most popular systems programs computer-aided design printed boards and electronic devices (abbreviated CAD - CAM350, P-CAD, Protel DXP, SPECCTRA, OrCAD, Allegro, Expedition PCB, Genesis), as a rule, there are rules associated with the solder mask. These rules define the distance/setback that must be maintained between the edge of the solder pad and the edge of the solder mask. This concept is illustrated in Figure 2(a).

Silk-screen printing or marking.

Marking (eng. Silkscreen, legend) is a process in which the manufacturer applies information about electronic components and which helps to facilitate the process of assembly, inspection and repair. Typically, markings are applied to indicate reference points and the position, orientation and rating of electronic components. It can also be used for any design purpose printed boards, for example, indicate the company name, setup instructions (this is widely used in old motherboards boards A x personal computers), etc. Marking can be applied to both sides boards s and it is usually applied using screen printing (silk-screen printing) with a special paint (with thermal or UV curing) of white, yellow or black color. Figure 2 (b) shows the designation and area of ​​the components, made with white markings.

Structure of layers in CAD

As noted at the beginning of this article, printed boards s can be made of several layers. When printed boards A designed using CAD, can often be seen in the structure printed boards s several layers that do not correspond to the required layers with wiring of conductive material (copper). For example, the marking and solder mask layers are non-conductive layers. The presence of conductive and non-conductive layers can lead to confusion, as manufacturers use the term layer when they only mean conductive layers. From now on, we will use the term "layers" without "CAD" only when referring to conductive layers. If we use the term "CAD layers" we mean all types of layers, that is, conductive and non-conductive layers.

Structure of layers in CAD:

Figure 3 shows three different layer structures. The orange color highlights the conductive layers in each structure. Structure height or thickness printed boards s may vary depending on the purpose, but the most commonly used thickness is 1.5mm.

Types of Electronic Component Housings

There are a wide variety of electronic component housing types on the market today. Typically, there are several types of housings for one passive or active element. For example, you can find the same microcircuit in both a QFP package (from the English Quad Flat Package - a family of microcircuit packages with planar pins located on all four sides) and in an LCC package (from the English Leadless Chip Carrier - is a low-profile square ceramic housing with contacts located on its bottom).

There are basically 3 large families of electronic enclosures:

Contact pad printed boards s(English land)

Contact pad printed boards s- part of the conductive pattern printed boards s, used for electrical connection of installed electronic products. Contact pad printed boards s It represents parts of the copper conductor exposed from the solder mask, where the component leads are soldered. There are two types of pads - contact pads installation holes for installation A into holes and planar pads for surface installation A- SMD pads. Sometimes, SMD via pads are very similar to via pads. installation A into the holes.

Figure 4 shows the pads for 4 different electronic components. Eight for IC1 and two for R1 SMD pads, respectively, as well as three pads with holes for Q1 and PW electronic components.

Copper conductors

Copper conductors are used to connect two points on printed boards e - for example, for connecting between two SMD pads (Figure 5.), or for connecting an SMD pad to a pad installation hole or to connect two vias.

Conductors can have different calculated widths depending on the currents flowing through them. Also, at high frequencies, it is necessary to calculate the width of the conductors and the gaps between them, since the resistance, capacitance and inductance of the conductor system depends on their length, width and their relative position.

Through plated vias printed boards s

When you need to connect a component that is on the top layer printed boards s with a component located on the bottom layer, through-plated vias are used that connect the elements of the conductive pattern on different layers printed boards s. These holes allow current to pass through printed boards u. Figure 6 shows two wires that start on the pads of a component on the top layer and end on the pads of another component on the bottom layer. Each conductor has its own via hole, which conducts current from the upper layer to the lower layer.

Figure 6. Connection of two microcircuits through conductors and metallized vias on different sides printed boards s

Figure 7 gives a more detailed view of the cross section of 4-layer printed boards. Here the colors indicate the following layers:

On the model printed boards s, Figure 7 shows a conductor (red) that belongs to the upper conductive layer, and which passes through boards y using a through-via, and then continues its path along the bottom layer (blue).

Figure 7. Conductor from the top layer passing through printed boards y and continuing its path on the lower layer.

"Blind" metallized hole printed boards s

In HDI (High Density Interconnect - high density connections) printed boards A x, it is necessary to use more than two layers, as shown in Figure 7. Typically, in multi-layer structures printed boards s On which many ICs are installed, separate layers are used for power and ground (Vcc or GND), and thus the outer signal layers are freed from power rails, which makes it easier to route signal wires. There are also cases where signal conductors must pass from the outer layer (top or bottom) along the shortest path in order to provide the necessary characteristic impedance, galvanic isolation requirements and ending with the requirements for resistance to electrostatic discharge. For these types of connections, blind metallized holes are used (Blind via - “blind” or “blind”). This refers to the holes connecting outer layer with one or more internal ones, which allows you to make the connection minimal in height. A blind hole starts on the outer layer and ends on the inner layer, which is why it is prefixed with "blind".

To find out which hole is present on boards e, you can put printed boards above the light source and look - if you see light coming from the source through the hole, then this is a transition hole, otherwise it is blind.

Blind vias are useful to use in design boards s, when you are limited in size and have too little space for placing components and routing signal wires. You can place electronic components on both sides and maximize space for wiring and other components. If the transitions are made through through holes rather than blind ones, you will need additional space for the holes because the hole takes up space on both sides. At the same time, blind holes can be located under the chip body - for example, for wiring large and complex BGA components.

Figure 8 shows three holes that are part of a four-layer printed boards s. If we look from left to right, the first thing we will see is a through hole through all the layers. The second hole starts at the top layer and ends at the second inner layer - the L1-L2 blind via. Finally, the third hole starts in the bottom layer and ends in the third layer, so we say it is a blind via L3-L4.

The main disadvantage of this type of hole is the higher manufacturing cost printed boards s with blind holes, compared to alternative through holes.

Hidden vias

English Buried via - “hidden”, “buried”, “built-in”. These vias are similar to blind vias, except that they start and end on the inner layers. If we look at Figure 9 from left to right, we can see that the first hole goes through all the layers. The second is a blind via L1-L2, and the last is a hidden via L2-L3, which starts on the second layer and ends on the third layer.

Figure 9. Comparison of via via, blind hole, and buried hole.

Manufacturing technology for blind and hidden vias

The technology for manufacturing such holes can be different, depending on the design that the developer has laid down, and depending on the capabilities factory a-manufacturer. We will distinguish two main types:

The hole is drilled in a double-sided workpiece DPP, metallized, etched and then this workpiece, essentially a finished two-layer printed boards A, pressed through prepreg as part of a multilayer preform printed boards s. If this blank is on top of the “pie” MPP, then we get blind holes, if in the middle, then we get hidden vias.

1. A hole is drilled in a compressed workpiece MPP, the drilling depth is controlled to accurately hit the pads of the inner layers, and then metallization of the hole occurs. This way we only get blind holes.

In complex structures MPP Combinations of the above types of holes can be used - Figure 10.

Figure 10. Example of a typical combination of via types.

Note that the use of blind holes can sometimes lead to a reduction in the cost of the project as a whole, due to savings on the total number of layers, better traceability, and reduction in size printed boards s, as well as the ability to apply components with finer pitches. However, in every specific case the decision to use them should be made individually and reasonably. However, one should not overuse the complexity and variety of types of blind and hidden holes. Experience shows that when choosing between adding another type of blind hole to a design and adding another pair of layers, it is better to add a couple of layers. In any case, the design MPP must be designed taking into account exactly how it will be implemented in production.

Finish metal protective coatings

Achieving correct and reliable solder connections in electronic equipment depends on many design and process factors, including the proper level of solderability of the elements being connected, such as components and printed conductors. To maintain solderability printed boards before installation A electronic components, ensuring the flatness of the coating and for reliable installation A solder joints, the copper surface of the pads must be protected printed boards s from oxidation, the so-called finishing metal protective coating.

When looking at different printed boards s, you can notice that the contact pads almost never have a copper color, often and mostly they are silver, shiny gold or matte gray. These colors determine the types of finishing metal protective coatings.

The most common method of protecting soldered surfaces printed boards is the coating of copper contact pads with a layer of silver tin-lead alloy (POS-63) - HASL. Most manufactured printed boards protected by the HASL method. Hot tinning HASL - hot tinning process boards s, by immersion for a limited time in a bath of molten solder and with rapid removal by blowing a stream of hot air, removing excess solder and leveling the coating. This coating dominates for several recent years, despite its severe technical limitations. Plat s, produced in this way, although they retain solderability well throughout the entire storage period, are unsuitable for some applications. Highly integrated elements used in SMT technologies installation A, require ideal planarity (flatness) of the contact pads printed boards. Traditional HASL coatings do not meet planarity requirements.

Coating technologies that meet planarity requirements are chemically applied coatings:

Immersion gold plating (Electroless Nickel / Immersion Gold - ENIG), which is a thin gold film applied over a nickel sublayer. The function of gold is to provide good solderability and protect nickel from oxidation, and nickel itself serves as a barrier preventing the mutual diffusion of gold and copper. This coating ensures excellent planarity of the contact pads without damage printed boards, ensures sufficient strength of solder joints made with tin-based solders. Their main disadvantage is the high cost of production.

Immersion Tin - ISn - gray matte chemical coating, providing high flatness printed sites boards s and compatible with all soldering methods than ENIG. The process of applying immersion tin is similar to the process of applying immersion gold. Immersion tin provides good solderability after long-term storage, which is ensured by the introduction of an organometal sublayer as a barrier between the copper of the contact pads and the tin itself. However, boards s, coated with immersion tin, require careful handling and should be stored vacuum-packed in dry storage cabinets and boards s with this coating are not suitable for the production of keyboards/touch panels.

When operating computers and devices with blade connectors, the contacts of the blade connectors are subject to friction during operation. boards s Therefore, the end contacts are electroplated with a thicker and more rigid layer of gold. Galvanic gilding of knife connectors (Gold Fingers) - coating of the Ni/Au family, coating thickness: 5 -6 Ni; 1.5 – 3 µm Au. The coating is applied by electrochemical deposition (electroplating) and is used primarily on end contacts and lamellas. Thick, gold coating has high mechanical strength, resistance to abrasion and adverse environmental influences. Indispensable where it is important to ensure reliable and durable electrical contact.

Laminate FR4

You can find a detailed description of the laminate.

Laminates in TePro warehouse

Microwave material ROGERS

NOTE: To use ROGERS material in the production of circuit boards, please indicate this in the order form

Since Rogers material is significantly more expensive than standard FR4, we are forced to introduce an additional markup for boards manufactured using Rogers material. Working fields of used workpieces: 170 × 130; 270 × 180; 370 × 280; 570 × 380.

Metal based laminates

Visual representation of the material

Aluminum laminate ACCL 1060-1 with dielectric thermal conductivity 1 W/(m K)

Description

Aluminum laminate CS-AL88-AD2(AD5) with dielectric thermal conductivity 2(5) W/(m K)

Description

Prepreg

In production we use prepregs 2116, 7628 and 1080 grade A (highest) from ILM.

You can find a detailed description of prepregs.

Solder mask

Properties

You can find a detailed description of the solder mask.

Frequently asked questions and answers on laminates and prepregs

What is XPC?

What's the difference between FR1 and FR2?

What is FR2?

What is FR3?

What is FR4?

What is FR5?

What is CEM-1?

What is CEM-3?

What is G10?

How can laminates be replaced?

What are "prepregs"?

What does FR or CEM stand for?

Is FR4 really green?

Does the color of the logo mean anything?

Does logo orientation mean anything?

What is UV blocking laminate?

What laminates are suitable for plating through holes?

Is there an alternative for plating through holes?

What is "material thickness"?

What is: PF-CP-Cu? IEC-249? GFN?

What is CTI?

What does #7628 mean? What other numbers are there?

What is 94V-0, 94V-1, 94-HB?