The types of PCB
PCB can be divided into rigid circuit boards, flexible circuit boards, and rigid-flex board.
General PCB is called rigid PCB. The visual difference between rigid PCB and flexible PCB is that flexible PCB can be bent. The common thickness of rigid PCB is 0.2mm, 0.4mm, 0.6mm, 0.8mm, 1.0mm, 1.2mm, 1.6mm, 2.0mm, etc. And the common thickness of flexible PCB is 0.2mm, and the thickness of the thickened layer will be added at the back of the parts to be welded. The thickness of the thickened layer varies from 0.2mm to 0.4mm. The purpose of understanding these is to provide a spatial reference for structural engineers when they design. Common materials of rigid PCB include: phenolic paper laminate, epoxy paper laminate, polyester glass felt laminate, epoxy glass cloth laminate; common materials of flexible PCB include: polyester film, polyimide film, FEP film.
According to the number of circuit layers, PCB can be divided into single panel, double-sided board and multilayer board. The common multi-layer board is a 4-layer board or 6-layer board, and the complex multi-layer board can reach dozens of layers.
Single panel
Single-side boards. On the most simple PCB, parts are concentrated on one side, while wires are concentrated on the other side (when there are chip components, they are the same side as wires, and plug-in devices are on the other side). Because wires only appear on one side, this kind of PCB is called a single side. Because there are many strict restrictions on the design circuit of the single panel (because there is only one side, the wiring can not cross and must be around the independent path), only the early circuits use such boards.
Double-sided board
Double-sided boards have wiring on both sides of the board, but to use wires on both sides, it is necessary to have a proper circuit connection between the two sides. The "bridge" between these circuits is called a pilot hole (via). The guide hole is a small hole filled or coated with metal on the PCB, which can be connected with the wires on both sides. Because the area of the double-sided board is twice larger than that of the single panel, the double panel solves the problem of staggering wiring in the single panel (it can be conducted to the other side through holes), which is more suitable for circuits more complex than the single panel.
Multilayer board
In order to increase the area of wiring, multi-layer boards use more single or double-sided wiring boards. A printed circuit board with one double-sided as inner layer, two single-sided as outer layer or two double-sided as inner layer and two single-sided as the outer layer. The printed circuit board which is alternately connected by positioning system and insulating bonding material and whose conductive graphics are interconnected according to the design requirements becomes a four-layer and six-layer printed circuit board, also known as multi-layer printed circuit board. The number of layers of the board does not mean that there are several independent wiring layers. In special cases, a blank layer will be added to control the board thickness. Generally, the number of layers is even and includes the outermost two layers. Most of the motherboards are 4 to 8-layer structure, but in theory, it can achieve nearly 100 layers of PCB. Most of the large supercomputers use quite a number of multi-layer motherboards, but because this kind of computer can be replaced by a lot of ordinary computer clusters, the ultra multi-layer boards have gradually been out of use. Because the layers in PCB are closely combined, it is generally not easy to see the actual number, but if you carefully observe the mainboard, you can still see it.
Characteristic
The reason why PCB can be more and more widely used is that it has many unique advantages, as follows.
High density. For decades, the high density of PCB has been developing with the improvement of IC integration and installation technology.
High reliability. Through a series of inspections, tests and aging tests, PCB can be guaranteed to work reliably for a long time (generally 20 years).
Designability. For PCB performance (electrical, physical, chemical, mechanical, etc.), PCB design can be realized through design standardization, standardization, etc., with short time and high efficiency.
Producibility. With modern management, standardization, scale (quantity), automation and other production can be carried out to ensure the consistency of product quality.
Testability. A relatively complete test method, test standard, various test equipment, and instruments are established to test and identify PCB product qualification and service life.
Assemblability. Kunshan JINGDING electronic PCB products are not only convenient for standardized assembly of various components, but also for automatic and large-scale mass production. At the same time, PCB and various component assembly parts can also be assembled to form larger parts, systems, and even the whole machine.
Maintainability. Because PCB products and various component assembly parts are produced in standardized design and scale, these parts are also standardized. Therefore, once the system breaks down, it can be replaced quickly, conveniently and flexibly, and the system can be recovered quickly. Of course, there are more examples. Such as miniaturization, lightweight, high-speed signal transmission and so on.
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