What Is PCB(printed circuit board)

2021-02-20 11:46:14 Edward Qin 42

Overview

PCB (printed circuit board) is abbreviated as printed circuit board, which is one of the important parts of the electronics industry. Almost every kind of electronic equipment, from electronic watches, calculators, to computers, communication electronic equipment, military weapon systems, as long as there are electronic components such as integrated circuits, in order to make the electrical interconnection between the various components must be printed board. The printed circuit board is composed of an insulating bottom plate, connecting wires and pads for assembling and welding electronic components, and has the dual functions of conductive lines and insulating bottom plates. It can replace complex wiring and realize the electrical connection between the components in the circuit. It not only simplifies the assembly and welding of electronic products, reduces the workload of wiring in the traditional way, and greatly reduces the labor intensity of workers; but also reduces the overall machine Volume, reduce product cost, improve the quality and reliability of electronic equipment. The printed circuit board has good product consistency, and it can adopt standardized design, which is conducive to the realization of mechanization and automation in the production process. At the same time, the whole printed circuit board that has been assembled and debugged can be used as an independent spare part to facilitate the interchange and maintenance of the entire product. At present, printed circuit boards have been extremely widely used in the manufacture of electronic products.

The earliest printed circuit boards used paper-based copper-clad printed boards. Since semiconductor transistors appeared in the 1950s, the demand for printed boards has risen sharply. In particular, the rapid development and widespread application of integrated circuits have made electronic equipment smaller and smaller, and circuit wiring density and difficulty increasing, which requires continuous updating of printed boards. At present, the variety of printed boards has developed from single-sided boards to double-sided boards, multilayer boards and flexible boards; structure and quality have also developed to ultra-high density, miniaturization and high reliability; new design methods, design supplies and Board-making materials and board-making techniques continue to emerge. In recent years, various computer-aided design (CAD) printed circuit board application software has been popularized and promoted in the industry. In specialized printed circuit board manufacturers, mechanized and automated production has completely replaced manual operations.

Origin

The creator of PCB is Austrian Paul Eisler (Paul Eisler), in 1936, he first used a printed circuit board in the radio. In 1943, Americans mostly used this technology for military radios. In 1948, the United States officially approved this invention for commercial use. Since the mid-1950s, printed circuit boards have been widely used. Printed circuit boards appear in almost every electronic device. If there are electronic parts in a certain device, they are all mounted on PCBs of different sizes. The main function of PCB is to connect various electronic components to a predetermined circuit, and play the role of relay transmission. It is the key electronic interconnection of electronic products and is known as the "mother of electronic products".

High density possible

Over the years, the high density of printed boards has been able to develop correspondingly with the improvement of integrated circuit integration and the advancement of mounting technology. The printed circuit board actually belongs to the integrated circuit industry, but the accuracy is only one ten thousandth of the current mainstream integrated circuit.

Classified by layer

According to the number of circuit layers: divided into single-sided, double-sided and multi-layer boards. Common multilayer boards are generally 4-layer boards or 6-layer boards, and complex multilayer boards can reach dozens of layers. PCB board has the following three main types of division:

Single panel

Single-Sided Boards On the most basic PCB, the parts are concentrated on one side, and the wires are concentrated on the other side (when there are SMD components and the wires are on the same side, the plug-in devices are on the other side). Because the wires only appear on one side, this kind of PCB is called a single-sided (Single-sided). Because single-sided boards have many strict restrictions on the design of the circuit (because there is only one side, the wiring cannot cross and must be around a separate path), so only early circuits use this type of board.

Double panel

Double-Sided Boards (Double-Sided Boards) This type of circuit board has wiring on both sides, but to use two-sided wires, there must be a proper circuit connection between the two sides. The "bridge" between such circuits is called a via. A via 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 as large as that of the single-sided board, the double-sided board solves the difficulty of interleaving wiring in the single-sided board (it can be conducted to the other side through holes), and it is more suitable for use in circuits that are more complicated than the single-sided board.

Multilayer board

Multi-Layer Boards In order to increase the area that can be wired, multi-layer boards use more single or double-sided wiring boards. Use one double-sided as the inner layer, two single-sided as the outer layer or two double-sided as the inner layer and two single-sided as the outer layer of the printed circuit board. The positioning system and the insulating bonding material alternately together and the conductive pattern Printed circuit boards that are interconnected according to design requirements become four-layer or six-layer printed circuit boards, also known as multilayer printed circuit boards. The number of layers of the board does not mean that there are several independent wiring layers. In special cases, empty layers are added to control the thickness of the board. Usually, the number of layers is even and includes the two outermost layers. Most motherboards have a 4 to 8 layer structure, but technically it can be a PCB board with nearly 100 layers. Most large supercomputers use fairly multi-layered motherboards, but because these types of computers can already be replaced by clusters of many ordinary computers, super-multilayered boards are gradually not being used. Because the layers in the PCB are tightly integrated, it is generally not easy to see the actual number, but if you look closely at the motherboard, you can still see it.

Edit by soft and hard classification

Divided into rigid circuit boards and flexible circuit boards, flexible and rigid boards. The intuitive 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. The common thickness of a flexible PCB is 0.2mm, and a thick layer is added to the back where the parts are to be welded. The thickness of the thick layer varies from 0.2mm to 0.4mm. The purpose of understanding these is to provide structural engineers with a spatial reference when designing. Common materials for rigid PCB include: phenolic paper laminate, epoxy paper laminate, polyester glass mat laminate, epoxy glass cloth laminate; flexible PCB materials common include: polyester film, polyimide Amine film, fluorinated ethylene propylene film.