PCB is the abbreviation of printed circuit board in English (Printed Circuit Board). Generally, a conductive pattern made of a printed circuit, a printed component or a combination of the two is called a printed circuit board on the insulating material according to the predetermined preset. The conductive pattern that supplies electrical connection between components on an insulating substrate is called a printed circuit. In this way, the printed circuit or the finished board of the printed circuit is called a printed circuit board, also known as a printed board or a printed circuit.
PCB is inseparable from almost all the facilities we can see, ranging from watches, calculators, general-purpose computers on electronic wrists, to computers, communications, and military weapon systems. As long as there are electronic components such as integrated circuits, their All electrical interconnections are made using the PCB. It provides mechanical support for various fixed assemblies such as integrated circuits, successfully realizes wiring and electrical connection or electrical insulation between various electronic components such as integrated circuits, and provides required electrical special properties, such as special properties impedance, etc. . At the same time, it provides solder mask graphics for semi-automatic soldering; it provides identification of wrong characters and graphics for component insertion, inspection and maintenance.
How is PCB made? When we open the keyboard of the general-purpose computer, we can see a flexible film (flexible insulating substrate) printed with conductive graphics and positioning graphics in silver-white color (silver paste). Because of the general screen printing method to obtain this kind of pattern, we call this printed circuit board flexible silver paste printed circuit board. And the printed circuit boards on various computer motherboards, graphics cards, video cards, sound cards and home appliances that we see in the computer city are different. The base material it uses is made of paper base (usually used for single-sided) or glass cloth base (usually used for double-sided and multi-layered), pre-impregnated phenolic or epoxy natural resin, and the surface layer is pasted with copper cladding on one or both sides. Press cured. This kind of circuit board copper clad sheet, we call it rigid board. After making a printed circuit board, we call it a rigid printed circuit board. A printed circuit board with printed circuit patterns on one side is called a single-sided printed circuit board, a printed circuit board with printed circuit patterns on both sides, and a printed circuit board formed by metallization of holes and double-sided interconnection, we call it a double-sided board. If a printed circuit board with double-sided as inner layer, two single-sided as outer layer, or two double-sided as inner layer and two single-sided as outer layer are used, they are alternately placed together through positioning system and insulating bonding material. And printed circuit boards with conductive patterns interconnected according to preset requirements become four-layer and six-layer printed circuit boards, also known as multi-layer printed circuit boards. Today there are 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. Simple methods are used to handle single machining to complex machining, including ordinary chemical reactions and photochemical electrochemical thermochemical processes. Computer assistance Knowledge of various aspects such as preset CAM. And in the production process, there are many process problems and new problems will be encountered from time to time, and local problems will disappear without finding out the root cause, because the production process is a non-continuous pass-through plane contact line method, no matter what link If there is a problem, it will lead to the shutdown of the entire line or the consequences of a large number of discarded printed circuit boards. There is no way to recycle and reuse the printed circuit boards if they are scrapped. The process engineers are under great office pressure, so many engineers leave the industry and turn to printed circuit board facilities. Or material suppliers to do sales and technical services.
In order to further understand the PCB, we must understand the manufacturing process of ordinary single-sided and ordinary multi-layer boards, so as to increase our understanding of it.
Single-sided rigid printed board: → single-sided copper clad laminate → blanking → (scrubbing, drying) → drilling or punching → screen printed circuit anti-corrosion engraving pattern or using dry film → curing inspection repair board → etched copper → remove Anti-corrosion printing material, drying → scrubbing, drying → screen printing solder mask pattern (commonly used green oil), UV curing → screen printing character mark graphics, UV curing → preheating, punching and shape → electrical open, short circuit test → scrubbing, Drying → pre-coating with anti-oxidant for soldering (drying) or spraying with tin and hot air for leveling → checking and inspecting the packaging → finished product leaving the factory.
Double-sided rigid printed board: → double-sided copper clad laminate → blanking → stacking → digitally controlled drilling through holes → inspection, deburring and scrubbing → chemical plating (through hole metallization) → (full board electroplating of thin copper) →Inspect, check and scrub → screen print negative circuit pattern, cure (dry or wet film, exposure, development) → check, check, repair board → circuit pattern plating → electroplating tin (resist nickel/gold) → remove printing material (photosensitive Film) → etching copper → (tin stripping) → cleaning and scrubbing → screen printing solder mask pattern commonly used heat-curing green oil (photosensitive dry film or wet film, exposure, development, heat curing, commonly used photosensitive heat-curing green oil) → cleaning , drying → screen printing mark character graphics, curing → (spray tin or organic solder protection film) → shape processing → cleaning, drying → electrical continuity inspection and determination → inspection and inspection of packaging → finished product delivery.
Through hole metallization method to make multi-layer board process → inner copper clad laminate double-sided cutting → scrubbing → drilling positioning hole → paste photoresist dry film or coating photoresist → exposure → development → etching and Removal of film → roughening of inner layer, deoxidation and oxidation of inner layer → inspection of inner layer → (manufacturing of single-sided copper clad laminate on outer layer, B-stage bonding sheet, inspection of sheet bonding sheet, drilling of positioning holes) → lamination → digital control Drilling → hole inspection → hole pretreatment and chemical copper plating → thin copper plating on the whole board → coating inspection → paste photoresist electroplating dry film or coating photoresist electroplating agent → surface layer base plate exposure → development, repair plate → Circuit pattern plating → electroplating tin-lead alloy or nickel/gold plating → film removal and etching → search → screen printing solder mask pattern or photoresist pattern → printing character pattern → (hot air leveling or organic solder protection film) → Digital control washing shape → cleaning, drying → electrical continuity inspection and determination → finished product inspection → packaging and delivery.
It can be seen from the process flow chart that the multi-layer board process is developed from the basic progress of the double-face metallization process. In addition to the double-sided process, it has several unique and special internal meanings: metallized hole inner layer interconnection, drilling and de-ringing oxygen drilling, positioning system, lamination, special materials.
Our common computer boards are basically epoxy-oxygen natural resin glass cloth-based double-sided printed circuit boards. One side is the plug-in component and the other side is the component foot welding surface. It can be seen that the solder joints are very regular. We call it the pad for the discrete welding surface of the component feet of these solder joints. Why are other copper wire patterns not tinned? Except for the parts such as the pads that need to be soldered, there is a layer of solder mask resistant to wave soldering on the surface of the remaining parts. Most of the external solder mask is green, and a small amount of yellow, black, blue, etc. is used as appropriate, so the solder mask oil is often called green oil in the PCB industry. Its effect is to avoid the bridging phenomenon during wave soldering, improve the welding quality and save solder. It is also the long-term best care layer of the printed board, which can prevent moisture, corrosion, mildew and mechanical scratches. From the outside, the green color solder mask with a smooth and bright appearance is a green oil for film-to-board photosensitive heat curing. Not only is the appearance more pleasing to the eye, but also the pads are very accurate, thus increasing the reliability of the solder joints.
We can see from the computer board that there are three forms of component installation. A plug-in installation process for transmission, inserting electronic components into the through holes of the printed circuit board. In this way, it is easy to see that the via holes of the double-sided printed circuit board are as follows: one is the naive component insertion hole; the second is the component insertion and double-sided interconnection via holes; the third is the naive Double-sided via holes; the fourth is the substrate mounting and positioning holes. The other two installation forms are surface installation and chip direct installation. In fact, the direct chip mounting technology can be considered as a branch of the surface mounting technology. It directly sticks the chip on the printed board, and then uses the wire bonding method or the tape carrier method, the flip chip method, the beam lead method and other packaging technologies to interconnect the printed board. The welding surface is on the component surface.
Surface installation technology has advantages as described below:
1. Because of the large number of printed boards, the large through-hole or buried-hole interconnection technology is eliminated, the density of wiring on the printed board is increased, and the size of the plane or surface of the printed board is reduced (usually plug-in type). It can also reduce the preset number of layers and cost of the printed board.
2. The weight has been reduced, the shock resistance has been increased, and the jelly solder has been used as appropriate, and the new welding technology has been thought of, which has increased the quality and reliability.
3. Due to the increase in wiring density and the reduction in lead length, the parasitic capacitance and parasitic inductance are reduced, which is more helpful to increase the electrical parameters of the printed board.
4. It is easier to successfully realize semi-automation than the plug-in installation, which increases the installation speed and labor productivity, and reduces the assembly cost accordingly.
It can be seen from the above surface mounting technology that the growth of circuit board technology increases with the growth of chip packaging technology and surface mounting technology. Today, the appearance of the computer boards we look at is constantly rising. In fact, this kind of circuit board cannot meet the technical requirements by using the screen printing circuit graphics of the transmission. Therefore, the circuit pattern and solder mask pattern of the usual high-precision circuit board are basically considered appropriate, and the photosensitive circuit and the photosensitive green oil manufacturing process are used.
With the development direction of high density of circuit boards, the production requirements of circuit boards are getting higher and higher, and more and more new technologies are applied to the production of circuit boards, such as laser technology, photosensitive natural resin and so on. The above is just an in-depth introduction on the surface. There are still many items in the production of circuit boards that are not explained due to space limitations, such as blind buried vias, winding boards, Teflon boards, lithography technology and so on. If you want to deepen the research, you need to try your best.
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