Materials used for the manufacture of printed circuit boards. Materials for the manufacture of printed circuit boards. Types of Electronic Component Housings

Our company produces printed circuit boards from high-quality domestic and imported materials, ranging from standard FR4 to FAF microwave materials.

Typical designs printed circuit boards are based on the use of standard fiberglass laminate type FR4, with an operating temperature from -50 to +110 °C, and a glass transition temperature Tg (softening) of about 135 °C.

For increased requirements for heat resistance or when mounting boards in an oven using lead-free technology (t up to 260 °C), high-temperature FR4 High Tg or FR5 is used.

Basic materials for printed circuit boards:

"+" - Typically in stock

"+/-" - On request (not always available)

Prepreg ("tie" layer) for multilayer printed circuit boards

FR-4

Foil-coated fiberglass with nominal thickness 1.6 mm, lined with copper foil 35 microns thick on one or both sides. Standard FR-4 is 1.6 mm thick and consists of eight layers (“prepregs”) of fiberglass. The central layer usually contains the manufacturer's logo; its color reflects the flammability class of this material (red - UL94-VO, blue - UL94-HB). Typically, FR-4 is transparent, standard green color determined by the color of the solder mask applied to the finished PCB

• volumetric electrical resistance after conditioning and restoration (Ohm x m): 9.2 x 1013;
• surface electrical resistance (Ohm): 1.4 x1012;
• peeling strength of foil after exposure to galvanic solution (N/mm): 2.2;
• flammability (vertical test method): class Vо.

MI 1222

is a layered pressed material based on fiberglass impregnated with an epoxy binder, lined on one or both sides with copper electrolytic foil.

• surface electrical resistance (Ohm): 7 x 1011;
• specific volumetric electrical resistance (Ohm): 1 x 1012;
• dielectric constant (Ohm x m): 4.8;
• foil peel strength (N/mm): 1.8.

FAF-4D

They are glass fiber reinforced fluoroplastic, lined on both sides with copper foil. Application: - as bases printed circuit boards operating in the microwave range; - electrical insulation for printed elements of receiving and transmitting equipment; - capable of long-term operation in the temperature range from +60 to +250° C.

• Adhesion strength of foil to base per 10 mm strip, N (kgf), not less than 17.6(1.8)
• Dielectric loss tangent at a frequency of 106 Hz, no more than 7 x 10-4
• Dielectric constant at frequency 1 MHz 2.5 ± 0.1
• Available sheet sizes, mm (maximum deviation in sheet width and length 10 mm) 500x500

T111

material made from a thermally conductive polymer based on ceramics with an aluminum base, are used when it is intended to use components that generate significant thermal power (for example, ultra-bright LEDs, laser emitters, etc.). The main properties of the material are excellent heat dissipation and increased dielectric strength when exposed to high voltages:

• Aluminum base thickness - 1.5 mm
• Dielectric thickness - 100 microns
• Copper foil thickness - 35 microns
• Thermal conductivity of the dielectric - 2.2 W/mK
• Dielectric thermal resistance - 0.7°C/W
• Thermal conductivity of aluminum substrate (5052 - analogue of AMg2.5) - 138 W/mK
• Breakdown voltage - 3 KV
• Glass transition temperature (Tg) - 130
• Volume resistance - 108 MΩ×cm
• Surface resistance - 106 MΩ
• Highest operating voltage (CTI) - 600V

Protective solder masks used in the production of printed circuit boards

Solder mask (also known as brilliant green) - layer durable material, designed to protect conductors from ingress of solder and flux during soldering, as well as from overheating. The mask covers the conductors and leaves the pads and blade connectors exposed. The method of applying a solder mask is similar to applying photoresist - using a photomask with a pattern of pads, the mask material applied to the PCB is illuminated and polymerized, the areas with soldering pads are unexposed and the mask is washed off from them after development. Most often, the solder mask is applied to the copper layer. Therefore, before its formation, the protective layer of tin is removed - otherwise the tin under the mask will swell from the heating of the board during soldering.

PSR-4000 H85

Green color, liquid photosensitive heat-hardening, 15-30 microns thick, TAIYO INK (Japan).

Has approval for use by the following organizations and end product manufacturers: NASA, IBM, Compaq, Lucent, Apple, AT&T, General Electric, Honeywell, General Motors, Ford, Daimler-Chrysler, Motorola, Intel, Micron, Ericsson, Thomson, Visteon, Alcatel , Sony, ABB, Nokia, Bosch, Epson, Airbus, Philips, Siemens, HP, Samsung, LG, NEC, Matsushita(Panasonic), Toshiba, Fujitsu, Mitsubishi, Hitachi, Toyota, Honda, Nissan and many, many others;

IMAGECURE XV-501

Colored (red, black, blue, white), liquid two-component solder mask, Coates Electrografics Ltd (England), thickness 15-30 microns;

DUNAMASK KM

Dry film mask from DUNACHEM (Germany), thickness 75 microns, provides tenting vias, has high adhesion.

Duration: 2 hours (90 min.)

25.1 Basic questions

PP base materials;

Materials for creating printed design elements;

Technological materials for the manufacture of PP.

25.2 Lecture text

25.2.1 Basic mPP base materials – up to 40 min

Basic materials of printed circuit boards include:

foil-coated (on one or both sides) and non-foil-coated dielectrics (getinax, textolite, fiberglass, fiberglass, lavsan, polyimide, fluoroplastic, etc.), ceramic materials and metal (with a surface dielectric layer) plates from which printed circuit board bases are made;

insulating spacer material (adhesive gaskets - prepregs) used for gluing MPP layers.

To protect the surface of PP from external influences, polymer protective varnishes and protective coating films are used.

When choosing a PP base material, you need to pay attention to the following: expected mechanical effects (vibrations, shocks, linear acceleration, etc.); accuracy class PP (distance between conductors); implemented electrical functions; performance; terms of Use; price.

The base material must adhere well to the metal of the conductors, have high mechanical strength, retain its properties when exposed to climatic factors, and have a similar coefficient of thermal expansion compared to the metal of the conductors.

The choice of material is determined by:

electrical insulating properties;

mechanical strength;

stability of parameters when exposed to aggressive environments and changing conditions;

machinability;

cost.

Foil dielectrics are produced with a conductive coating of copper (less commonly nickel or aluminum) electrolytic foil with a thickness of 5 to 105 microns. To improve adhesion strength, the foil is coated on one side with a layer of chromium 1…3 microns thick. The foil is characterized by purity of composition (impurities no more than 0.05%), ductility. Foiling is carried out by pressing at a temperature of 160...180 0 C and a pressure of 5...15 MPa.

Non-foil dielectrics are produced in two types:

with an adhesive (adhesive) layer with a thickness of 50...100 microns (for example, an epoxy rubber composition), which is applied to increase the adhesion strength of chemical copper deposited during the manufacturing process of PP;

with a catalyst introduced into the volume of the dielectric, which promotes the deposition of chemical copper.

Laminated plastics consisting of a filler (electrical insulating paper, fabric, fiberglass) and a binder (phenolic or phenolic epoxy resin) are used as the dielectric base of rigid PP. Laminated plastics include getinax, textolite and fiberglass.

Getinax is made from paper and is used under normal climatic operating conditions for household equipment. It has low cost, good workability, and high water absorption.

Textolite is made from cotton fabric.

Fiberglass laminates are made from fiberglass. Compared to getinaks, fiberglass laminates have better mechanical and electrical characteristics, higher heat resistance, less moisture absorption. However, they have a number of disadvantages: worse machinability; higher cost; a significant difference (about 30 times) in the coefficient of thermal expansion of copper and fiberglass in the direction of the material thickness, which can lead to rupture of the metallization in the holes during soldering or during operation.

For the manufacture of PCBs used in conditions of increased fire hazard, fire-resistant getinaks and fiberglass laminates are used. Increasing the fire resistance of dielectrics is achieved by introducing fire retardants into their composition.

The introduction of 0.1...0.2% palladium or cuprous oxide into the varnish that impregnates fiberglass improves the quality of metallization, but slightly reduces the insulation resistance.

To manufacture PCBs that provide reliable transmission of nanosecond pulses, it is necessary to use materials with improved dielectric properties (reduced dielectric constant and dielectric loss tangent). Therefore, the use of bases made of organic materials with a relative dielectric constant below 3.5 is considered promising. Non-polar polymers (fluoroplastic, polyethylene, polypropylene) are used as the basis for PP in the microwave range.

To produce GPP and GPC that can withstand repeated bending, dielectrics based on polyester film (lavsan or polyethylene terephthalate), fluoroplastic, polyimide, etc. are used.

Insulating cushioning material (prepregs) is made from fiberglass impregnated with under-polymerized thermosetting epoxy resin (or other resins); made of polyimide with an adhesive coating applied on both sides and other materials.

Ceramics can be used as the base material for the PP.

The advantage of ceramic PP is better heat removal from active elements, high mechanical strength, stability of electrical and geometric parameters, reduced noise levels, low water absorption and gas emission.

The disadvantage of ceramic boards is fragility, large mass and small dimensions (up to 150x150 mm), long manufacturing cycle and large shrinkage of the material, high cost.

PP on metal base used in products with high current loads and at elevated temperatures. Aluminum, titanium, steel, copper, and an alloy of iron and nickel are used as base materials. To obtain an insulating layer on a metal base, special enamels, ceramics, epoxy resins, polymer films, etc. are used; an insulating layer on an aluminum base can be obtained by anodic oxidation.

The disadvantage of metal enameled boards is the high dielectric constant of the enamel, which precludes their use in high-frequency equipment.

The metal base of the PCB is often used as power and ground buses, as a shield.

25.2.2 Materials of printed design elements – up to 35 min

The material used for printed pattern elements (conductors, contact pads, end contacts, etc.) is metal coatings. Copper is most often used to create the main current-carrying layer. Ceramic PCBs use graphite.

The materials used to create metal coatings are presented in Table 25.1.

Table 25.1 – Metal coatings used to create printed design elements

25.2.3 Technological (consumables) mmaterials for the manufacture of PP – up to 15 min

Technological materials for the manufacture of PCB include photoresists, special screen paints, protective masks, copper plating electrolytes, etching, etc.

Requirements for consumables are determined by the design of the PCB and the manufacturing process.

Photoresists must provide the necessary resolution when obtaining a circuit pattern and appropriate chemical resistance. Photoresists can be liquid or dry film (SPF).

Negative and positive photoresists are used. When using negative photoresists, the exposed areas of the PCB blank remain on the board, and the unexposed areas are washed out during development. When using positive photoresistors, the exposed areas are washed out during development.

Etching solutions must be compatible with the resist used for etching, be neutral to insulating materials, and have a high etching rate. Acid and alkaline solutions of copper chloride, solutions based on ferric chloride, solutions based on ammonium persulfate, and iron-copper chloride solutions are widely used as etching electrolytes.

All materials must be economical and safe for environment.

The base used is foil and non-foil dielectrics (getinax, textolite, fiberglass, fiberglass, lavsan, polyamide, fluoroplastic, etc.), ceramic materials, metal plates, insulating cushioning material (prepreg).

Foil dielectrics are electrical insulating bases, usually clad with electrolytic copper foil with an oxidized galvanic-resistant layer adjacent to the electrical insulating base. Depending on the purpose, foil dielectrics can be single-sided or double-sided and have a thickness from 0.06 to 3.0 mm.

Non-foil dielectrics, intended for semi-additive and additive manufacturing methods of boards, have a specially applied adhesive layer on the surface, which serves for better adhesion of chemically deposited copper to the dielectric.

PCB bases are made of a material that can adhere well to the metal of the conductors; have a dielectric constant of no more than 7 and a small dielectric loss tangent; have sufficiently high mechanical and electrical strength; allow the possibility of processing by cutting, stamping and drilling without the formation of chips, cracks and delamination of the dielectric; maintain their properties when exposed to climatic factors, be non-flammable and fire resistant; have low water absorption, low thermal coefficient linear expansion, flatness, and resistance to aggressive environments during circuit design and soldering.

The base materials are layered pressed plates impregnated with artificial resin and possibly lined on one or both sides with copper electrolytic foil. Foil dielectrics are used in subtractive methods of manufacturing PCBs, non-foil dielectrics are used in additive and semi-additive ones. The thickness of the conductive layer can be 5, 9, 12, 18, 35, 50, 70 and 100 microns.

In production, materials are used, for example, for OPP and DPP - foil fiberglass laminate grades SF-1-50 and SF-2-50 with a copper foil thickness of 50 microns and an intrinsic thickness of 0.5 to 3.0 mm; for MPP - foil-etched fiberglass laminate FTS-1-18A and FTS-2-18A with a copper foil thickness of 18 microns and its own thickness from 0.1 to 0.5 mm; for GPP and GPK - foil-coated lavsan LF-1 with a copper foil thickness of 35 or 50 microns and its own thickness from 0.05 to 0.1 mm.

Compared to getinaks, fiberglass laminates have better mechanical and electrical characteristics, higher heat resistance, and lower moisture absorption. However, they have a number of disadvantages, for example, low heat resistance compared to polyamides, which contributes to contamination of the ends of the inner layers with resin when drilling holes.

To manufacture PCBs that provide reliable transmission of nanosecond pulses, it is necessary to use materials with improved dielectric properties, these include PCBs made from organic materials with a relative dielectric constant below 3.5.

For the manufacture of PCBs used in conditions of increased fire hazard, fire-resistant materials are used, for example, fiberglass laminates of the SONF, STNF, SFVN, STF brands.

For the manufacture of GPCs that can withstand repeated bends of 90 in both directions from starting position with a radius of 3 mm, foil-coated lavsan and fluoroplastic are used. Materials with a foil thickness of 5 microns make it possible to produce PCBs of the 4th and 5th accuracy classes.

Insulating cushioning material is used for gluing PP layers. They are made of fiberglass impregnated with under-polymerized thermosetting epoxy resin with an adhesive coating applied on both sides.

To protect the surface of PP and GPC from external influences, polymer protective varnishes and protective coating films are used.

Ceramic materials are characterized by the stability of electrical and geometric parameters; stable high mechanical strength over a wide temperature range; high thermal conductivity; low moisture absorption. The disadvantages are a long manufacturing cycle, large shrinkage of the material, fragility, high price and etc.

Metal bases are used in heat-loaded PCBs to improve heat removal from the IC and ERE in EAs with high current loads operating at high temperatures, as well as to increase the rigidity of PCBs made on thin bases; they are made from aluminum, titanium, steel and copper.

For high-density printed circuit boards with microvias, materials suitable for laser processing are used. These materials can be divided into two groups:

1. Strengthened non-woven glass materials and preprigs ( composite material based on fabrics, paper, continuous fibers, impregnated with resin in an uncured state) with a given geometry and thread distribution; organic materials with a non-oriented arrangement of fibers Preprig for laser technology has a smaller thickness of fiberglass along the Z axis compared to standard fiberglass.

2. Unreinforced materials (resin coated copper foil, polymerized resin), liquid dielectrics and dry film dielectrics.

Of the other materials used in the manufacture of printed circuit boards, the most widely used are nickel and silver as a metal resist for soldering and welding. In addition, a number of other metals and alloys are used (for example, tin - bismuth, tin - indium, tin - nickel, etc.), the purpose of which is to provide selective protection or low contact resistance, improve soldering conditions. Additional coatings that increase the electrical conductivity of printed conductors are in most cases performed by galvanic deposition, less often by vacuum metallization and hot tinning.

Until recently, foil dielectrics based on epoxy-phenolic resins, as well as dielectrics based on polyimide resins used in some cases, satisfied the basic requirements of printed circuit board manufacturers. The need to improve heat dissipation from ICs and LSIs, low requirements dielectric constant board material for high-speed circuits, the importance of matching the coefficients of thermal expansion of the board material, IC packages and crystal carriers, widespread adoption modern methods installation led to the need to develop new materials. Widely used in modern designs In computer hardware, ceramic-based MPPs are found. The use of ceramic substrates for the manufacture of printed circuit boards is primarily due to the use of high-temperature methods for creating a conductive pattern with a minimum line width, but other advantages of ceramics are also used (good thermal conductivity, matching the coefficient of thermal expansion with IC packages and media, etc.). In the manufacture of ceramic MPPs, thick film technology is most widely used.

In ceramic bases, aluminum and beryllium oxides, as well as aluminum nitride and silicon carbide are widely used as starting materials.

The main disadvantage of ceramic boards is their limited size (usually no more than 150x150 mm), which is mainly due to the fragility of ceramics, as well as the difficulty of achieving the required quality.

The formation of a conductive pattern (conductors) is carried out by screen printing. Pastes consisting of metal powders, an organic binder and glass are used as conductor materials in ceramic substrate boards. For conductor pastes, which must have good adhesion, the ability to withstand repeated heat treatment, and low electrical resistivity, powders of noble metals are used: platinum, gold, silver. Economic factors also force the use of pastes based on compositions: palladium - gold, platinum - silver, palladium - silver, etc.

Insulating pastes are made on the basis of crystallizing glasses, glass-crystalline cements, and glass ceramics. Pastes made from powders of refractory metals: tungsten, molybdenum, etc. are used as conductor materials in batch-type ceramic boards. Tapes made from ceramic cheeses based on aluminum and beryllium oxides, silicon carbide, and aluminum nitride are used as the base of the workpiece and insulators.

Rigid metal bases coated with a dielectric are characterized (like ceramic ones) by high-temperature burning of thick-film pastes based on glasses and enamels into the substrate. Features of boards on a metal base are increased thermal conductivity, structural strength and speed limitations due to the strong connection of conductors with the metal base.

Plates made of steel, copper, titanium, coated with resin or fusible glass are widely used. However, the most advanced in terms of a range of indications is anodized aluminum and its alloys with a fairly thick oxide layer. Anodized aluminum is also used for thin-film multilayer PCB layout.

The use of bases with a complex composite structure, including metal spacers, as well as bases made of thermoplastics, in printed circuit boards is promising.

PTFE bases with fiberglass are used in high-speed circuits. Various composite bases from "Kevlar and quartz" as well as copper - Invar - copper are used in cases where it is necessary to have a thermal expansion coefficient close to the expansion coefficient of aluminum oxide, for example, in the case of mounting various ceramic crystal carriers (microcases) on a board. Polyimide-based composite substrates are mainly used in powerful circuits or in high temperature PCB applications.

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 the principle electrical diagram, intended for electrical connection and mechanical fastening of products installed on it electronic technology, quantum electronics and electrical products - 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 two external 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 more low temperature melting than the materials of the parts being joined. The soldered contacts of the parts, as well as 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 liquid state and wets the surfaces of 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 CAD programs 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 various structures layers. 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 case 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 located on 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) 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 extra space for 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 that it is more high price manufacturing 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 each specific case the decision on their use 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

Getting the correct and reliable solder connections in electronic equipment depends on many design and technological factors, including the proper level of solderability of the connected elements, 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 applied chemical methods 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.

The quality of supplied materials complies with the IPC4101B standard, and the manufacturers' quality management system is confirmed by international certificates ISO 9001:2000.

FR4 – fiberglass laminate with fire resistance class 94V-0 is the most common material for the production of printed circuit boards. Our company supplies the following types materials for the production of single- and double-sided printed circuit boards:

• Fiberglass laminate FR4 with a glass transition temperature of 135ºС, 140ºС and 170ºС for the production of single-sided and double-sided printed circuit boards. Thickness 0.5 - 3.0 mm with foil 12, 18, 35, 70, 105 microns.
• Basic FR4 for internal layers of MPP with glass transition temperatures of 135ºС, 140ºС and 170ºС
• FR4 prepregs with glass transition temperatures of 135ºС, 140ºС and 170ºС for pressing MPP
• Materials XPC, FR1, FR2, CEM-1, CEM-3, HA-50
• Materials for boards with controlled heat dissipation:
  • (aluminum, copper, stainless steel) with a dielectric with thermal conductivity from 1 W/m*K to 3 W/m*K produced by Totking and Zhejiang Huazheng New Material Co.
  • Material HA-30 CEM-3 with thermal conductivity 1 W/m*K for the production of single- and double-sided printed circuit boards.

For some purposes, a high-quality non-foil dielectric is required that has all the advantages of FR4 (good dielectric properties, stability of characteristics and dimensions, high resistance to adverse influences). climatic conditions). For these applications we can offer non-foil FR4 fiberglass laminate.

In many cases where fairly simple printed circuit boards are required (in the production of household equipment, various sensors, some components for automobiles, etc.), the excellent properties of fiberglass are redundant, and indicators of manufacturability and cost come to the fore. Here we can offer the following materials:

• XPC, FR1, FR2 - foil getinaks (base made of cellulose paper impregnated with phenolic resin), widely used in the manufacture of printed circuit boards for consumer electronics, audio and video equipment, in the automotive industry (arranged in ascending order of properties, and, accordingly, price ). Excellent stamping.
• CEM-1 is a laminate based on a composition of cellulose paper and fiberglass with epoxy resin. Stamps beautifully.

Our assortment also includes electrodeposited copper foil for pressing MPP produced by Kingboard. Foil is supplied in rolls of various widths, foil thicknesses are 12, 18, 35, 70, 105 microns, foil thicknesses of 18 and 35 microns are almost always available from our warehouse in Russia.

All materials are produced in accordance with the RoHS directive, the content of harmful substances is confirmed by relevant certificates and RoHS test reports. Also, all materials, many items have certificates, etc.