What material are printed circuit boards made of? Basic materials for the production of printed circuit boards. Visual representation of the material

Base material – the main carrier of the mounting device and electronic circuits of the printed circuit board. The base material is supplied to the PCB manufacturer in the form of a "panel" and cut to the required size to produce a specific board. There are many base materials for printed circuit boards with different thicknesses and coatings, as well as different electrical and mechanical properties that affect functionality electronic circuit. See also PP Materials. Often the base material is fiberglass with epoxy resin (FR4), available as copper foil or prepreg.

Getinax foil - compressed layers of electrical insulating paper impregnated with phenolic or epoxyphenolic resin as a binder, lined on one or both sides with copper foil.

Flexibility insulating material – is specified by the number of bending cycles around the mandrel, the diameter of which is equal to several values ​​of the thickness of the flexible section.

Hard gilding - Electrolytic hard gold plating is a friction-resistant surface used for gold leads. We electroplate nickel onto the copper trace. Gold is then applied to the nickel.

Rolled copper foil – has a relative elongation 5-6 times greater than that of electrolytic foil, therefore it has greater flexibility, bending ability, and the ability to be machined without delamination. Is expensive. Used in the production of flexible printed circuit boards.

PCB base material – material (dielectric) on which the printed circuit board design is made.

Unreinforced base materials - copper foil coated with resin with state B - partially polymerized resin or with state C - fully polymerized resin, as well as liquid dielectrics and dielectrics coated with a dry film.

Non-foil dielectrics There are two types. 1. With an adhesive layer, which is applied to increase the adhesion strength of copper deposited during the manufacturing process of PP by a chemical method; 2. With a catalyst introduced into the volume of the dielectric, which promotes the deposition of chemical copper.

PCB with thick copper - usually called a board with thick copper printed circuit board with copper thickness >105µm. Such boards are used for high switching currents in automotive and industrial electronics and for specific client requests. Copper offers the highest thermal conductivity after silver.
Boards with a thick layer of copper allow you to:
High switching currents
Optimal heat transfer with local heating
Increased life, reliability and level of integration
However, when designing the board, special precautions must be taken regarding the etching process; only wider conductor structures are acceptable.

Prepregs – insulating cushioning material used for gluing layers of MPP. They are made of fiberglass impregnated with under-polymerized thermosetting epoxy or other resins.

SAF (prepreg with low viscosity, low flow prepreg) - an adhesive material with controlled fluidity, which is used in the manufacture of GZhP, has adhesion to both fiberglass and polyimide.

Gold connection - PCB surface Bond gold is a collective term for surfaces capable of bonding, usually gold surfaces. For connection the following are used: immersion gold plating over a nickel sublayer (ENIG) for connection aluminum wires(Al), electroplated soft gold for bonding gold wires (Au) and ENEPIG (nickel-palladium immersion gilding), which is suitable for both bonding methods.
The thickness of the gold layer for chemical (immersion) gilding is about 0.3-0.6µm, for electrolytic (soft) gilding about 1.0-2.0µm and about 0.05-0.1µm gold plus 0.05-0.15µm palladium for ENEPIG. The gold layers are based on approximately 3.0-6.0µm of nickel.

Foil fiberglass laminate – compressed layers of fiberglass impregnated with epoxyphenol or epoxy resin. Compared to getinax, it has better mechanical and electrical properties, higher heat resistance, and less moisture absorption.

Technological (consumable) materials for the manufacture of PP – photoresists, special screen paints, protective masks, copper plating electrolytes, etching, etc.

Strengthened base materials and prepregs – non-woven glass materials developed specifically for laser technology with a given filament geometry and a given filament distribution (flat side in the Z-axis direction), organic materials with a non-oriented arrangement of fibers (aramid), prepreg for laser technology, standard structures based on glass fabric, etc.

Foil dielectrics – consist of fiberglass made from threads; resin used to impregnate fiberglass; foil used as a metal coating for foil materials.

Foil and non-foil polyimide – used in electronic equipment responsible appointment, operating at high temperatures, for the production of flexible printed circuit boards, GPCs, rigid-flex printed circuit boards, as well as multilayer printed circuit boards, integrated circuit carrier tapes, and large hybrid integrated circuits with up to 1000 pins.

Electrolytic Copper Foil – inexpensive; used in the manufacture of GPCs with a high density of conductor patterns. It has a higher resolution when etching copper from gaps compared to a katana.

CEM 1 is a base material for printed circuit boards made from multi-layer paper. CEM 1 has a core of epoxy resin impregnated paper and one outer layer of fiberglass. Due to the paper base, this material is not suitable for metallization through holes. The material specification is contained in document IPC-4101.

IMDS – International Material Data System . IMDS (www.mdsystem.com) was developed by automobile manufacturers to capture the composition of materials used in automobiles, parts, devices, and systems to identify the individual material components of each vehicle or sub-group (eg, engine).
Since the entry into force of the ELV Directive (06/21/2003), automotive suppliers have been required to provide data on the ingredients of their products as part of the IMDS in order to determine the recovery rates available.
Must be registered in IMDS:
Printed circuit boards
Mounted PCBs
Components
ZVEI and the Automotive Industry have signed the document Assembly Material Data – Cooperation on Material Data Declaration:
Division Electronic Components and Systems and Division Printed Circuit Boards and Electronic Systems at ZVEI – the German Association for Electronic and electrical manufacturers developed an effective concept for declaring data on materials electronic components and printed circuit boards. Data on materials should be obtained by forming cross-corporate product groups and standard values. These material data tables, called “umbrella” specifications, greatly simplify declarations without noticeable loss of accuracy. This concept has been successfully applied in the automotive industry since 2004.
To apply the Umbrella Specifications with the IMDS system, IMDS has issued Guideline 019, Printed Circuit Boards. These guidelines describe the method for entering the material content of printed circuit boards assembled.
Excerpt from Item 5: Standard Rules and Guidelines for E/E (PCB Component) from IMDS Recommendation 019: “PCB component data in IMDS, Umbrella Spec, IPC1752 or similar format is accepted if agreed between business partners.”
Umbrella specifications for IMDS developed by ZVEI with PCB manufacturers.
The dynamic program makes it easy to count the substances contained in a printed circuit board of any size. The surface and number of layers are freely selectable. Standard technologies are stored in a database.

RoHS - directive on the prohibition of harmful substances. This provision of European Union legislation states that electronic devices cannot contain lead or other harmful substances. For printed circuit boards, RoHS compliance is controlled by two components: the base material and the surface.

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 impregnating the 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

Metal coatings are used as the material for printed pattern elements (conductors, contact pads, end contacts, etc.). 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 environmentally friendly.

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 of 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.

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 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 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 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 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 circuit 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), there are usually 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. 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 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 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

Getting the correct and reliable solder connections V electronic equipment depends on many design and technological 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 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 that provides 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.

An electronic printed circuit board (Russian abbreviation - PP, English - PCB) is sheet panel, where interconnected microelectronic components are located. 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 screw terminal blocks. The wooden base was also modernized, giving preference to metal.

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

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

American engineer suggested unique way organizing electrical connections on an insulated plate. He used electrically conductive ink and a stencil to transfer the circuit diagram onto a 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 connecting lines, the new era PCB design.

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 software format of the computer that controls the 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, the negative image of the circuit (mask) is transferred to transparent sheet 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. The atmosphere and objects of production premises are controlled automatically for the presence of contaminants.

Many electronic printed circuit board manufacturing companies practice unique manufacturing. And in standard form production of double-sided printing electronic 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. Epoxy resin hardens, the copper foil is bonded under pressure to the substrate 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 a 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