Introduction to the basic knowledge of printed circuit board PCB


Ⅰ. Printed circuit board (PCB)

 

PCB is the abbreviation of Printed Circuit Board. Also known as printed circuit boards, printed circuit boards, because it is made by electronic printing, it is called "printing" circuit board. A printed circuit board is a substrate for assembling electronic components, and is a printed board on which a point-to-point connection and a printed component are formed on a general-purpose substrate in a predetermined design. The main function of this product is to make various electronic components form the connection of the 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". PCBs are used as substrates and critical interconnects for electronic component loading, and are required for any electronic device or product.

Ⅱ. The principle of PCB manufacturing

 

When we open the keyboard of a general-purpose computer, we can see a soft film (flexible insulating substrate) printed with silver-white (silver paste) conductive patterns and graphic patterns. Since the universal screen printing method obtains such a pattern, we call this printed wiring 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 home appliances that we see in Computer City are different. The substrate used is paper-based (usually used for single-sided) or glass-based (usually used for double-sided and multi-layer), pre-impregnated with phenolic or epoxy resin, and coated on one or both sides of the surface. Made. This kind of circuit board copper-clad sheet, we call it a rigid board. To make a printed circuit board, we call it a rigid printed circuit board. Printed circuit graphics on one side We call a single-sided printed circuit board, printed circuit patterns on both sides, and printed circuit boards formed by double-sided interconnection through metallization of holes. We call it a double-sided board. If a double-sided inner layer, two single-sided outer layers or two double-sided inner layers and two single-sided outer printed circuit boards are used, the positioning system and the insulating bonding material are alternately The printed circuit boards in which the conductive patterns are interconnected according to the design requirements become four-layer and six-layer printed circuit boards, which are also called multi-layer printed circuit boards. There are now more than 100 layers of practical printed circuit boards.

Ⅲ. The PCB production process

PCB production process is more complicated, it involves a wide range of processes, from simple machining to complex machining, common chemical reactions and photochemical electrochemical thermochemistry, computer-aided design CAM and other aspects of knowledge . Moreover, there are many technical problems in the production process and new problems will be encountered from time to time. Some problems will disappear if the cause is not found out. Because the production process is a non-continuous pipeline form, any problem will cause the whole line to be discontinued. Or the consequences of a large number of scraps, if the printed circuit board can not be recycled and reused, the work pressure of the process engineer is large, so many engineers left the industry to transfer to the printed circuit board equipment or materials business to do sales and technical services. .

 

The substrate of the board itself is made of insulating and heat-insulating materials that are not easily bent. The thin circuit material that can be seen on the surface is copper foil. The original copper foil covers the entire board, and part of the manufacturing process. It is etched away, and the remaining part becomes a mesh-like fine line. These lines are called conductor patterns or wires and are used to provide circuit connections for parts on the PCB.

 

In order to fix the parts on the PCB, we soldered their pins directly to the wiring. On the most basic PCB (single panel), 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 Side and Solder Side.

If there are some parts on the PCB, you need to remove or replace it after the production is completed. Then the socket will be installed when the part is installed. Since the socket is directly welded to the board, the parts can be disassembled arbitrarily. .

 

If you want to connect two PCBs to each other, we usually use the edge connector. The Edge connector contains a lot of bare copper pads, which are actually part of the PCB layout. Usually when we connect, we will A gold finger on a piece of PCB is inserted into a suitable slot on another PCB. In a computer, such as a display card, sound card or other similar interface card, it is connected to the motherboard by a gold finger.

 

The green or brown color on the PCB is the color of the solder mask. This layer is an insulating protective layer that protects the copper wire and prevents the parts from being soldered to the wrong place. A layer of silk screen will be printed. Usually the text and symbols (mostly white) will be printed on it to indicate the position of each part on the board. The screen printing surface is also called Legend.

 

The printed circuit board traverses the complex copper wire between the part and the part, and then etches it on a board to provide the main support for the installation and interconnection of electronic components. It is indispensable for all electronic products. Basic parts.

 

A printed circuit board is a flat plate made of a non-conductive material on which a pre-drilled hole is typically designed to mount the chip and other electronic components. The holes of the component help to electronically connect the metal paths pre-defined on the board surface, pass the pins of the electronic components through the PCB, and then adhere to the PCB with conductive metal electrodes to form a circuit.

Ⅳ. A brief history and development direction of PCB development

 

A brief history of development: China began the development of single-sided printed boards from the mid-1950s, first applied to semiconductor radios. In the 1960s, China developed its own foil-clad substrate, making the copper foil etching method the leading technology in China's PCB production. In the 1960s, it was able to produce single-panel in large quantities. Small-volume production of double-sided metallized holes, and the development of multi-layer boards in a few units. In the 1970s, the pattern electroplating etching process was promoted in China. However, due to various interferences, printed circuit materials and special equipment did not keep up in time, and the entire production technology level lags behind the advanced level in foreign countries. In the 1980s, due to the approval of the reform and opening up policy, not only a large number of single-sided, double-sided, multi-layer printed board production lines with advanced levels in the 1980s were introduced, but also improved and absorbed faster after more than ten years of digestion. China'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 computers, communication equipment, consumer electronics and automobile industry, the PCB industry has also achieved rapid development. With the development of printed circuit products, new materials, new process technologies and new equipment are required. China's printed electrical materials industry should focus on improving performance and quality while expanding production; the printed circuit equipment industry is no longer a low-level counterfeit, but a development of production automation, precision, multi-function, modern equipment. . PCB production integrates world high-tech technology, and printed circuit production technology adopts new technologies such as liquid photosensitive imaging, direct electroplating, pulse plating, and multi-layer laminate.

Ⅴ. The characteristics and classification of PCB and upstream and downstream

  

PCB features high density, high reliability, designability, productivity, assemblability and maintainability.

  

In general, the more complex the functions of electronic products, the longer the loop distance, the more the number of contacts, the more layers the PCB requires, such as high-end consumer electronics, information and communication products, and the soft board is mainly used in needs. Among the products that are bent: such as notebook computers, cameras, car instruments, etc. PCB classification is divided into single panel (SSB), double panel (DSB) and multilayer board (MLB); according to softness, it can be divided into rigid printed circuit board (RPC) and flexible printed circuit. Board (FPC). In industrial research, the PCB industry is generally subdivided into six main subdivisions: single-panel, double-panel, conventional multi-layer board, flexible board, HDI (high-density sintered) board, and package substrate according to the basic classification of the above PCB products industry.

 

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

Fiberglass cloth: Fiberglass cloth is one of the raw materials for copper clad laminates. It is made of fiberglass yarn, accounting for about 40% (thick plate) and 25% (thin plate) of CCL. The glass fiber yarn is calcined into a liquid state by a raw material such as silica sand in a kiln, and is drawn into a very fine glass fiber through a very fine alloy nozzle, and then several hundred glass fibers are twisted into a glass fiber yarn.

 

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

 

CCL: CCL is a product of pressing glass fiber and copper foil together with epoxy resin as a fusion agent. It is a direct raw material for PCB. It is made into a printed circuit after being etched, plated, and laminated. board.