Printed circuit board introduction knowledge and production process

Printed circuit board, English abbreviation PCB (abbreviation for Printed Circuit Board), because the printed circuit board is basically based on epoxy resin, so the industry does not mention its full name epoxy printed circuit board, usually only print Circuit board, or English abbreviation PCB. According to experts from the China Epoxy Resin Industry Association, conductive patterns, which are usually printed on printed circuit boards, printed components, or a combination of the two on an insulating material, are called printed circuits. A conductive pattern that provides electrical connection between components on an insulating substrate is called a printed circuit. In this way, a printed circuit board or a printed circuit board is called a printed circuit board, which is also called a printed board or a printed circuit board. And this insulating substrate is epoxy resin.
Epoxy printed circuit boards, almost we can see the electronic equipment can not do without it, from small electronic watches, calculators, general-purpose computers, to computers, communications electronic equipment, military weapons systems, as long as there is integrated circuits and other electronic No devices, they are used for electrical interconnections between them. It provides mechanical support for the assembly of various electronic components such as integrated circuits, wiring and electrical connection between various electronic components such as integrated circuits, or electrical insulation, and provides required electrical characteristics such as characteristic impedance. At the same time, it provides solder resist patterns for automatic soldering; it provides identification characters and graphics for component insertion, inspection and maintenance.

How is it made? When we open the keyboard of a general-purpose computer, we can see a flexible film (flexible insulating substrate) with a silver-white (silver paste) conductive pattern and a healthy image. Because the universal screen printing method obtains this pattern, we call this printed circuit board a flexible silver paste printed circuit board. The various kinds of computer motherboards, graphics cards, network cards, modems, sound cards, and home appliances that we see at Computer City are different. The substrates used are paper-based (usually used for single-sided) or glass-based (usually used for double-sided and multi-layered), pre-impregnated phenolic or epoxy resin, with one or both sides of the surface coated with copper, and then laminated and cured. Made. This kind of circuit board copper plate, we call it a rigid board. Then we made the printed circuit board, we call it a rigid printed circuit board.

Single-sided printed circuit patterns, we call single-sided printed circuit board; double-sided printed circuit patterns, and then through the hole metallization for double-sided interconnection of the printed circuit board, we call it a double panel. If a double-sided inner layer, two single-sided outer layers or two double-sided inner layers and two single-sided printed wiring boards are used, the positioning system and the insulating bonding material are alternated and Printed circuit boards whose conductive patterns are interconnected according to design requirements have become four-layer and six-layer printed circuit boards, also called multilayer printed circuit boards. There are now more than 100 layers of practical epoxy printed circuit boards.

The production process of epoxy printed circuit boards is relatively complex. It involves a wide range of processes, from simple mechanical processing to complex mechanical processing, common chemical reactions, photochemical electrochemical thermochemistry, and computer-aided design CAM. And so much knowledge. Moreover, there are many process problems in the production process and they may encounter new problems from time to time. Some problems disappear when the cause is not clearly identified. Because the production process is a discontinuous assembly line, any problems in one of the links will cause a complete shutdown. Or the consequences of a lot of scrap, if the printed circuit board cannot be recycled for reuse, the work pressure of process engineers is high, so many engineers have left the industry to go to the work of printing circuit board equipment or materials vendors for sales and technical services. .

In order to further understand epoxy printed circuit boards, it is necessary to understand the manufacturing processes of common single-sided, double-sided printed circuit boards and common multi-layer boards to deepen understanding of them.

Single-sided rigid printed boards: → single-sided copper clad laminates → blanking → (brushing, drying) → drilling or punching → screen printing circuit etching patterns or using dry film → curing check plate → etching copper → resisting corrosion Printing material, drying, brushing, drying, screen printing solder mask pattern (used in green oil), UV curing, screen printing character marking pattern, UV curing, preheating, punching and appearance, electrical opening, short circuit testing, brushing, drying Pre-painted welding anti-oxidant (dry) or spray hot air leveling → inspection packaging → finished products.

Double-sided rigid printed boards: → double-sided copper clad → cutting → lamination → CNC drilling through holes → inspection, deburring and brushing → electroless plating (metallization of vias) → (full-plate copper plating) → inspection Brushing → screen printing negative circuit pattern, curing (dry film or wet film, exposure, development) → inspection, repair plate → circuit pattern plating → electroplating tin (anti-corrosion nickel / gold) → to print material (photosensitive film) → etching Copper → (retreat tin) → cleaning brush → screen printing solder mask pattern commonly used thermal curing green oil (paste sensitive dry film or wet film, exposure, development, thermal curing, commonly used photographic heat curing green oil) → cleaning, drying → screen printing Marked character graphics, curing → (spray or organic solder mask) → shape processing → cleaning, drying → electrical continuity testing → inspection packaging → finished products.

Through-hole metallurgy method to manufacture multi-layered plates → Inner-layer copper clad plate double-sided cutting → brushing → drilling positioning holes → photo-resist dry film or photoresist coating → exposure → development → etching and removal Membrane → Inner Coarsening, Deoxidation → Inner Inspection → (External Single-sided CCL Production, B-stage Bonding, Plate Bonding Inspection, Drilling Positioning) → Lamination → Number Controlled Drilling→ Hole Inspection → Pre-hole Treatment and Electroless Copper Plating → Full Plate Copper Plating → Plating Inspection → Laminate Plating Resistant Electroplating Dry Film or Coating Photoresist Plating Agent → Surface Backplane Exposure → Development, Plate Repair → Circuit Pattern Plating → Plating tin-lead alloy or nickel/gold plating → film removal and etching → inspection → screen printing solder resist pattern or photo-resistance solder pattern → printed character pattern → (hot air leveling or organic solder mask) → numerical control wash shape → cleaning , Drying → Electrical continuity test → Finished product inspection → Packing and shipping.

From the process flow chart, it can be seen that the multilayer board process is developed based on the two-face metallization process. According to experts from the China Epoxy Resin Industry Association, apart from the double-sided process, it has several unique features: metallized hole interconnections, drilling and epoxy drilling, positioning systems, lamination, and special applications. material. Our common computer board is basically an epoxy glass cloth based double-sided printed circuit board. One side of the board is a component foot soldering surface on the other side. We can see that the solder joints are very regular. These solder joints are The discrete soldering surface of the component leg is called a pad.

Why are other copper wire patterns not tinned? Because in addition to solder pads and other parts, the rest of the surface has a wave solder mask. The surface of the solder mask is mostly green, and a few are yellow, black, blue, etc. So in the PCB industry, the solder resist oil is often called green oil. Its role is to prevent bridging during wave soldering, improve soldering quality and save solder. It is also a permanent protective layer of the printed board, can play a role in moisture, corrosion, mold and mechanical abrasion. From the outside, the surface is smooth and bright green solder mask, which is a photo-sensitive heat-cured green oil film for the film. Not only does the appearance look better, what is important is the high accuracy of its pads, which improves the reliability of solder joints.

Reproduced from: China's epoxy industry online