PCB Tech - Basic knowledge of printed circuit board PCB

1.Printed circuit board(PCB)

PCB is the abbreviation for Printed Circuit Board. Also known as printed circuit board, printed circuit board, because it is made by electronic printing, it is called "printed" circuit board. The printed circuit board is a substrate for assembling electronic parts. It is a printed board that connects dots and prints components on a common base material according to a predetermined design. The main function of this product is to make various electronic components form a predetermined circuit connection, which plays the role of relay transmission. It is the key electronic interconnection of electronic products and is known as the "mother of electronic products". PCB is used as a substrate and key interconnection for electronic parts, and any electronic equipment or product needs to be equipped.

2, the manufacturing principle of PCB

When we open the keyboard of a general-purpose computer, we can see a flexible film (flexible insulating substrate), printed with silver-white (silver paste) conductive graphics and healthy bit graphics. Because the general screen printing method obtains this kind of pattern, we call this kind of printed circuit board a flexible silver paste printed circuit board. The printed circuit boards on the various computer motherboards, graphics cards, network cards, modems, sound cards and household appliances that we saw in the Computer City were different. The substrate used in it is made of paper base (usually used for single-sided) or glass cloth base (usually used for double-sided and multilayer), pre-impregnated with phenolic or epoxy resin, and the surface layer is laminated with copper-clad film on one or both sides and then laminated to cure Become. This kind of circuit board copper clad sheet material, we call it rigid board. And then make a printed circuit board, we call it a rigid printed circuit board. We call single-sided printed circuit boards with printed circuit patterns on one side, and printed circuit boards on both sides with printed circuit patterns on both sides. The printed circuit boards formed by double-sided interconnection through hole metallization are called double-sided boards. If 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 alternate together and The printed circuit board with the conductive pattern interconnected according to the design requirements becomes a four-layer or six-layer printed circuit board, also called a multilayer printed circuit board. Now there are more than 100 layers of practical printed circuit boards.

3, the production process of PCB

The production process of PCB is relatively complex, and it involves a wide range of processes, from simple mechanical processing to complex mechanical processing, common chemical reactions, photochemical, electrochemical, thermochemical and other processes, computer-aided design CAM, and many 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 of the problems disappear without finding out the cause. Because the production process is a non-continuous assembly line form, any problem in any link will cause the entire line to stop production. Or as a result of a large number of scraps, if printed circuit boards are scrapped, they cannot be recycled and reused. The work pressure of process engineers is relatively high, so many engineers have left the industry and turned to printed circuit board equipment or material vendors to do sales and technical services. .

The substrate of the board itself is made of insulating and non-flexible material. The small circuit material that can be seen on the surface is copper foil. The copper foil is originally covered on the entire board, and part of it during the manufacturing process After being etched away, the remaining part becomes a network of fine lines. These lines are called conductors (conductor
pattern) or wiring, and is used to provide circuit connections for parts on the PCB.

In order to fix the parts on the PCB, we solder their pins directly on the wiring. On the most basic PCB (single-sided board), the parts are concentrated on one side, and the wires are concentrated on the other side. So we It is necessary to make holes in the board so that the pins can pass through the board to the other side, so the pins of the parts are soldered on the other side. Because of this, the front and back sides of the PCB are called component sides (Component
Side) and Solder Side.

If there are some parts on the PCB that need to be removed or reinstalled after the production is completed, then the socket (Socket) will be used when the part is installed. Since the socket is directly soldered on the board, the parts can be disassembled and assembled at will .

If you want to connect two PCBs to each other, we generally use edge connectors commonly known as "golden fingers" (edge
connector). The gold finger contains a lot of exposed copper pads, which are actually part of the PCB wiring. Usually, when connecting, we insert the gold finger on one PCB into the appropriate slot on the other PCB. On (usually called expansion slot Slot). In the computer, such as display card, sound card or other similar interface cards, are connected to the motherboard by golden fingers.

The green or brown on the PCB is solder mask (solder
mask) color. This layer is an insulating protective layer, which can protect the copper wire and prevent the parts from being soldered to the incorrect place. In addition, a layer of silk screen printing surface will be printed on the solder mask.

screen). Usually, text and symbols (mostly white) are printed on this to indicate the position of each part on the board. The screen printing surface is also called the icon surface (legend).

The printed circuit board etches the complex circuit copper wires between parts and parts on a board after careful and neat planning, and provides the main support for the installation and interconnection of electronic components. It is indispensable for all electronic products. The basic parts.

A printed circuit board is a flat plate made of non-conductive materials. The flat plate is usually designed with pre-drilled holes to install chips and other electronic components. The hole of the component helps to electronically connect the pre-defined metal paths printed on the board. After the pins of the electronic component are passed through the PCB, the conductive metal welding rod is attached to the PCB to form a circuit.

4, the development history and development direction of PCB

A brief history of development: my country began the development of single-sided printed boards in the mid-1950s, which were first used in semiconductor radios. In the mid-1960s, my country's foil-clad laminate substrates were independently developed, making copper foil etching the dominant process in my country's PCB production. In the 1960s, single-sided panels could be produced in large quantities. Small batch production of double-sided metallized hole printing, and the development of multilayer boards in a few units. In the 1970s, the pattern electroplating etching process was promoted in China, but due to various interferences, the special materials and special equipment for printed circuits did not keep up in time, and the overall production technology level lags behind the foreign advanced level. In the 1980s, due to the introduction of the reform and opening policy, not only a large number of single-sided, double-sided, and multi-layer printed circuit board production lines with the advanced level of foreign countries in the 1980s were introduced, but also after more than ten years of digestion and absorption, they have increased rapidly. my country's printed circuit production technology level.

Development direction: In recent years, China’s electronics industry has become one of the main pillars driving domestic economic growth. With the rapid development of computer, communication equipment, consumer electronics and automobile industries,
The PCB industry has also achieved rapid development. With the development of printed circuit products, new materials, new technology and new equipment are required. While expanding output, my country's printed electrical materials industry must pay more attention to improving performance and quality; the printed circuit special equipment industry is no longer a low-level imitation, but is developing toward production automation, precision, multi-function, and modern equipment. . PCB production integrates the world's high-tech technologies. The printed circuit production technology will adopt new technologies such as liquid photosensitive imaging, direct electroplating, pulse electroplating, and multilayer multilayer boards.

5, the characteristics and classification of PCB and upstream and downstream

PCB features six aspects: high density, high reliability, designability, manufacturability, assemblability and maintainability.

Generally speaking, the more complex the functions of electronic products, the longer the loop distance, and the greater the number of contact pins, the more layers the PCB requires, such as high-end consumer electronics, information and communication products, etc.; and soft boards are mainly used for needs. Among the winding products: such as notebook computers, cameras, car meters, etc. PCB classification is divided according to the number of layers, which can be divided into single-sided board (SSB), double-sided board (DSB) and multi-layer board (MLB); according to flexibility, it can be divided into rigid printed circuit board (RPC) and flexible printed circuit Board (FPC). In industry research, the PCB industry is generally subdivided into six major subdivisions: single-sided, double-sided, conventional multilayer, flexible, HDI (high-density sintered) board, and package substrate according to the basic classification of the above-mentioned PCB products. industry.

PCB upstream industry includes PCB substrate board raw material suppliers and PCB production equipment suppliers, downstream industries include consumer electronics, computers and peripheral products, automobile industry and mobile phone industry. According to the industry chain, it can be divided into raw materials-copper clad laminates-printed circuit boards-electronic product applications. The specific analysis is as follows:

Glass fiber cloth: Fiberglass cloth is one of the raw materials of copper clad laminates. It is woven from glass fiber yarn and accounts for about 40% (thick board) and 25% (thin board) of the cost of the copper clad laminate. The glass fiber yarn is calcined into a liquid state from raw materials such as silica sand in a kiln. It is drawn into a very fine glass fiber through a very small alloy nozzle, and then hundreds of glass fibers are twisted into a glass fiber yarn.

Copper foil: Copper foil is the raw material that accounts for the largest proportion of the cost of copper clad laminates, accounting for about 30% (thick plate) and 50% (thin plate) of the cost of copper clad laminates. Therefore, the price increase of copper foil is the main driving force for the price increase of copper clad laminates.

Copper clad laminate: The copper clad laminate is a product made by pressing glass fiber cloth and copper foil together with epoxy resin as a fusion agent. It is the direct raw material of PCB and is made into a printed circuit after etching, electroplating, and multi-layer board pressing. plate.