PCB is the abbreviation of Printed Circuie Board in English. Generally, the conductive pattern formed on the insulating material according to a predetermined design to make a printed circuit, a printed element, or a combination of the two is called a printed circuit. A conductive pattern that provides electrical connection between components on an insulating substrate is called a printed circuit. In this way, the finished board of the printed circuit or printed circuit is called a printed circuit board, and is also called a printed board or a printed circuit board.
PCB is almost inseparable from the electronic equipment we can see, ranging from electronic watches, calculators, general-purpose computers, to computers, communication electronic equipment, military weapon systems, as long as there are electronic devices such as integrated circuits, they are PCBs are used for electrical interconnections. It provides mechanical support for the fixed assembly of various electronic components such as integrated circuits, realizes the wiring and electrical connection or electrical insulation between various electronic components such as integrated circuits, and provides the required electrical characteristics, such as characteristic impedance. At the same time, it provides soldering resistance graphics for automatic soldering; and provides identification characters and graphics for component insertion, inspection and maintenance.
How is PCB made? We can see a soft film (flexible insulating substrate) with a silver-white (silver paste) conductive pattern and a healthy pattern printed on the health disk of a general-purpose computer. Because this pattern is obtained by the general screen printing method, we call this printed circuit board a flexible silver paste printed circuit board. The printed circuit boards on various computer motherboards, video cards, network cards, modems, sound cards, and household appliances that we saw in Computer City were different. The base material used is made of paper base (usually used for single-sided) or glass cloth base (usually used for double-sided and multi-layer), prepreg phenolic or epoxy resin, the surface layer is glued on one or both sides and then laminated and cured Made. This kind of circuit board copper clad sheet, we call it rigid board. After making the printed circuit board, we call it rigid printed circuit board. A printed circuit board with a printed circuit pattern on one side is called a single-sided printed circuit board, a printed circuit pattern on both sides, and then double-sided interconnection through metallization of holes, we call it a double-sided board. If a double-sided printed circuit board is used as the inner layer, two single-sided outer layers or two double-sided inner layers and two single-sided outer layers, the positioning system and the insulating bonding material are alternately used together and Printed circuit boards with conductive patterns interconnected according to design requirements become four-layer and six-layer printed circuit boards, also known as multi-layer printed circuit boards. There are now more than 100 layers of practical printed circuit boards.
The production process of PCB is relatively complex, and it involves a wide range of processes, from simple mechanical processing to complex mechanical processing. There are common chemical reactions and photochemical electrochemical thermochemical processes, computer-aided design CAM and other aspects of knowledge . Moreover, there are many process problems in the production process and new problems will be encountered from time to time. Some problems will disappear without clarifying the cause. Since the production process is a discontinuous pipeline form, any problem will cause the entire line to stop production. Or the consequences of a lot of scrapping. If the printed circuit board is scrapped, it cannot be recycled and reused, and the work pressure of the process engineer is relatively large, so many engineers leave this industry and turn to printed circuit board equipment or material vendors to do sales and technical services. .
In order to further understand PCB, we need to understand the manufacturing process of single-sided and double-sided printed circuit boards and ordinary multilayer boards, so as to deepen our understanding of it.
Single-sided rigid printed board: → single-sided copper clad laminate → blanking → (brushing, drying) → drilling or punching → screen printed circuit anti-etching graphics or using dry film → curing inspection repair board → etching copper → anti-corrosion Printing material, drying → brushing, drying → screen printing solder mask pattern (usually green oil), UV curing → screen printing character marking pattern, UV curing → preheating, punching and shape → electrical opening, short circuit test → brushing, drying → Pre-coating welding anti-oxidant (drying) or tin spray hot air leveling → inspection packaging → finished products leave the factory.
Double-sided rigid printed board: → double-sided copper clad laminate → blanking → stacking board → CNC drilling through hole → inspection, deburring and brushing → chemical plating (via hole metallization) → (full plate electroplated thin copper) → inspection Brushing → Screen printing negative circuit pattern, curing (dry film or wet film, exposure, development) → inspection, repair board → circuit pattern plating → tin plating (nickel / gold resist) → printing material (photosensitive film) → etching Copper → (Removal of tin) → Cleaning and scrubbing → Frequently used heat-cured green oil for screen-printed solder mask patterns (paste photosensitive dry film or wet film, exposure, development, thermal curing, commonly used light-sensitive heat-cured green oil) → clean, dry → screen Mark character graphics, curing → (spraying tin or organic solder mask) → shape processing → cleaning, drying → electrical continuity detection → inspection packaging → finished products leave the factory.
Through-hole metallization method for manufacturing multi-layer board → Inner layer copper clad laminate double-sided cutting → Brushing → Drilling positioning hole → Paste photoresist dry film or apply photoresist → Exposure → Development → Etching and removing Membrane → inner layer roughening, deoxidation → inner layer inspection → (outer single-sided copper clad laminate circuit production, B-stage bonding sheet, sheet bonding sheet inspection, drilling positioning holes) → lamination → number control drilling → Hole inspection → hole pre-treatment and chemical copper plating → full-board thin copper plating → plating inspection → paste photoresistance plating dry film or coating photoresistance plating agent → surface layer bottom plate exposure → development, repair board → circuit pattern plating → Electroplated tin-lead alloy or nickel / gold plating → film removal and etching → inspection → screen-printed solder mask pattern or photo-induced solder mask pattern → printed character pattern → (hot air leveling or organic solder mask) → CNC washing shape → cleaning , Drying → Electrical continuity testing → Finished product inspection → Packaging and leaving the factory.
It can be seen from the process flow chart that the multi-layer board process is developed from the double-faced metallization process. In addition to the double-sided process, it also has several unique contents: interconnection of inner layers of metallized holes, drilling and decontamination, positioning systems, lamination, and special materials.
Our common computer board is basically epoxy resin glass cloth double-sided printed circuit board, one side of which is the inserted component and the other side is the component foot welding surface. We can see that the solder joints are very regular. We call it the pad for the discrete soldering surface of the component foot. Why not tin on other copper wire patterns? Because in addition to the pads and other parts that need to be soldered, the rest of the surface has a layer of solder mask that resists wave soldering. The surface of the solder mask is mostly green, and a few use yellow, black, blue, etc., so in the PCB industry, solder resist oil is often called green oil. Its function is to prevent bridging during wave soldering, improve soldering quality and save solder. It is also a permanent protective layer for printed boards, which can prevent moisture, corrosion, mildew and mechanical scratches. Viewed from the outside, the surface is smooth and bright green solder mask, heat-curing green oil for film on the board. Not only does the appearance look better, it is important that its pad accuracy is higher, thereby improving the reliability of the solder joints.
We can see from the computer board that there are three ways to install components. A plug-in installation process for transmission, which inserts electronic components into the through holes of the printed circuit board. In this way, it is easy to see that the through holes of the double-sided printed circuit board are as follows: one is the simple component insertion hole; the second is the component insertion and double-sided interconnection through hole; the third is the simple double-sided guide Through holes; Fourth, the base board installation and positioning holes. The other two mounting methods are surface mounting and chip direct mounting. In fact, the direct chip mounting technology can be regarded as a branch of surface mounting technology, which is to directly stick the chip to the printed board, and then interconnect the printed technology with wire bonding or tape method, flip chip method, beam lead method and other packaging technologies. System board. The soldering surface is on the component surface.
Surface mounting technology has the following advantages:
1) Because the printed circuit board largely eliminates the large via hole or buried via interconnection technology, it improves the wiring density of the printed board and reduces the printed board area (generally one-third of the plug-in installation), while It can also reduce the design layers and cost of printed boards.
2) Reduced weight and improved seismic performance. Adhesive solder and new soldering technology are used to improve product quality and reliability.
3) As the wiring density is increased and the lead length is shortened, the parasitic capacitance and parasitic inductance are reduced, which is more conducive to improving the electrical parameters of the printed board.
4) It is easier to automate than plug-in installation, improve installation speed and labor productivity, and reduce assembly costs accordingly.
As can be seen from the above surface security technology, the improvement of circuit board technology is improved with the improvement of chip packaging technology and surface mounting technology. Now we see that the surface mounting rate of computer boards is constantly rising. In fact, this kind of circuit board reuse transmission screen pattern can not meet the technical requirements. Therefore, the circuit pattern and solder resist pattern of the common high-precision circuit board basically adopt the production process of photosensitive circuit and photosensitive green oil.
With the development trend of high-density circuit boards, the production requirements of circuit boards are getting higher and higher, and more and more new technologies are used in the production of circuit boards, such as laser technology, photosensitive resin and so on. The above is just a superficial introduction to some surfaces. There are still many things in the production of circuit boards that are not explained due to space limitations, such as blind buried holes, winding boards, Teflon boards, lithography technology, etc. If you want in-depth research, you need to work hard.
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