With the rapid development of electronic technology, printed circuit board is widely used in various fields, almost all electronic equipment contains the corresponding printed circuit board. Today, I’d like to introduce the composition of PCB and its advantages.
What is PCB?
The Chinese name of PCB is printed circuit board, which is an important electronic component and the support of electronic components. It will appear in almost every electronic equipment. If there are electronic parts in a certain device, they are also embedded in PCB of different sizes. In addition to fixing various small parts, the main function of PCB is to provide the mutual electrical connection of various parts on the top.
Printed circuit board is composed of insulating base board, connecting wire and soldering pad for assembling soldering electronic components, which has double functions of conducting circuit and insulating base board. It can replace the complex wiring and realize the electrical connection between the components in the circuit. It not only simplifies the assembly and soldering of electronic products, reduces the wiring workload in the traditional way and greatly reduces the labor intensity of workers, but also reduces the volume of the whole machine, reduces the product cost and improves the quality and reliability of electronic equipment.
The current circuit board is mainly composed of the following
- Circuit and pattern: circuit is a tool for conducting between components. In design, large copper surface will be designed as the grounding and power layer. Lines and drawings are made at the same time.
- Dielectric layer: used to maintain the insulation between lines and layers, commonly known as substrate.
- Through hole / via: the through hole can make the lines above two levels open to each other, the larger through hole is used as the part plug-in, in addition, the non through hole is usually used as the surface mounting location, and the screws are fixed during assembly.
- Solder resist / solder mask: not all copper surfaces need to eat tin parts, so don’t eating tin areas will be printed with a layer of substance (usually epoxy resin) to prevent the short circuit between non tin eating lines. According to different processes, it can be divided into green oil, red oil and blue oil.
- Legend / marking / silk screen: This is an unnecessary component. Its main function is to mark the name and position box of each part on the circuit board, which is convenient for maintenance and identification after assembly.
- Surface finish: because the copper surface is easy to oxidize in general environment, so it can’t be tinned (poor solder tin ability), so it will be protected on the copper surface to be tinned.
According to the number of layers: divided into single board, double-sided board and multilayer board. The common multi-layer board is generally 3-6-layer board, and the complex multi-layer board can reach more than 10 layers.
Single side board
On the most basic PCB, the parts are concentrated on one side and the wires on the other. Because the wire only appears on one side, this kind of printed circuit board is called single board. Because there are many strict restrictions on the design circuit of single board (because there is only one side, the wiring can’t cross and it has to go around its own path), the early circuit uses this kind of circuit board
Double sided board
This kind of circuit board has wiring on both sides. In order to connect the wires on both sides, there must be a proper circuit connection between the two sides, which is called a pilot hole. A pilot hole is a small hole filled with or coated with metal on a printed circuit board, which can be connected with wires on both sides. Because the area of the double-sided board is twice larger than that of the single board, and the wiring can be staggered (can be wound to the other side), the double sided board can be used on more complex circuits than the single board.
In order to increase the area that can be wired, 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 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 represents that there are several independent wiring layers. Generally, the number of layers is even and includes the outermost two layers. Most of the motherboards are 4 to 8-layer structures, but the technology can achieve nearly 100 layers of PCB. Most of the large supercomputers use quite a number of multi-layer mother boards, 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 not easy to see the actual number, but if you carefully observe the main board, you may see it.
According to the hardware and software of circuit board: flexible pcb, rigid pcb and rigid-flex pcb board.