一、Printed circuit board (PCB)
PCB is the abbreviation of Printed Circuit Board (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. A printed circuit board is a substrate for assembling electronic components, and is a printed board that forms point-to-point connections and printed components on a general-purpose substrate according to a predetermined design. The main function of this product is to make various electronic components form a predetermined circuit connection 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". As the substrate and key interconnection of electronic parts, PCB is required for any electronic equipment or products.
二、The manufacturing principle of PCB
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 graphics and graphics. Because this kind of pattern is obtained by the general screen printing method, we call this printed circuit board a flexible silver paste printed circuit board. However, the various computer motherboards, graphics cards, network cards, modems, sound cards and printed circuit boards on household appliances that we saw in the computer city are different. The base material it uses is made of paper base (usually used on one side) or glass cloth base (usually used on double sides and multi-layers), pre-impregnated with phenolic or epoxy resin, and one or both sides of the surface layer are glued with copper clad film and then laminated and cured. made. This kind of circuit board copper clad sheet, we call it a rigid board. 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 with printed circuit patterns on both sides and then double-sided interconnection through hole metallization, we call it double-sided boards. If a printed circuit board with one double-sided inner layer and two single-sided outer layers or two double-sided inner layers and two single-sided outer layers is used alternately through the positioning system and insulating bonding materials and 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, also known as multilayer printed circuit boards. Now there are more than 100 layers of practical printed circuit boards.
三、PCB production process
The production process of PCB is relatively complicated; 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 other knowledge. Moreover, there are many technological problems in the production process and new problems will be encountered from time to time, and some problems will disappear without finding out the cause. Since the production process is a discontinuous assembly line, any problem in any link will cause the entire line to stop production or The consequences of a large number of scrapping, if the printed circuit board is scrapped, it cannot be recycled and reused, and the work pressure of process engineers is relatively high, so many engineers leave this industry and go to printed circuit board equipment or material suppliers to do sales and technical services.
The substrate of the board itself is made of insulating and heat-insulating materials that are not easy to bend. The small circuit material that can be seen on the surface is copper foil. Originally, the copper foil covered the entire board and was partially covered in the manufacturing process. After etching, the remaining part becomes a network of fine lines. These lines are called conductors.
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 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. In this way, we can Holes need to be punched on 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 the component side (Componentside) and welding surface (Solder Side).
If there are some parts on the PCB; it can be removed or put back after the production is completed, then the socket (Socket) will be used when installing the part. Since the socket is directly welded on the board, the parts can be disassembled arbitrarily Pack.
If two PCBs are to be connected to each other, generally we will use edge joints commonly known as "golden fingers".
Connector), the gold finger contains many exposed copper pads, these copper pads are actually part of the PCB wiring. Usually when connecting, we insert the gold finger on one of the PCBs into the appropriate socket on the other PCB On the slot (commonly called the expansion slot Slot). In the computer, such as a 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 resist
mask). This layer is an insulating protective layer that protects copper wires and prevents parts from being soldered to incorrect places. A layer of silkscreen is printed on the solder mask. Usually Text and symbols (mostly white) will be printed on this to mark the position of each part on the board. The screen printing surface is also called the legend surface (legend).
The printed circuit board etches the complex circuit copper wires between parts and parts on a board after careful and neat planning, providing the main support for electronic components during installation and interconnection, and is indispensable for all electronic products base parts.
A printed circuit board is a flat plate made of non-conductive material, usually with pre-drilled holes designed to mount chips and other electronic components. The holes of the components help to electronically connect the pre-defined gold house paths printed on the board. After the pins of the electronic components pass through the PCB, they are adhered to the PCB with conductive metal electrodes to form a circuit.
四、Brief 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 board base material was self-reliantly developed; the copper foil etching method became the leading process of PCB production in my country. In the 1960s, single-sided boards could be produced in large quantities. Production of double-sided metallized hole printing in small batches, and development of multi-layer boards in a few units. In the 1970s, the graphic electroplating and etching process was promoted in China, but due to various interferences, the special materials and special equipment for printed circuits did not keep up with the overall production technology level and fell behind the advanced foreign level. In the 1980s, due to the introduction of the reform and opening up 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. 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 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 material industry must focus on improving performance and quality; the printed circuit special equipment industry is no longer a low-level imitation. It is developing towards production automation, precision, multi-function, and modern equipment . PCB production integrates the world's high and new technologies. The printed circuit production technology will adopt new technologies such as liquid photosensitive imaging, direct electroplating, pulse electroplating, and laminated multi-layer boards.
五、the characteristics and classification of PCB and upstream and downstream
PCB features six aspects: high density, high reliability, designability, manufacturability, assembleability and maintainability.
Generally speaking, the more complex the functions of electronic products, the longer the loop distance, and the more contact pins, the more layers the PCB requires; such as high-end consumer electronics, information and communication products, etc., and flexible boards are mainly used Around the products: such as notebook computers, cameras, automotive instrumentation and so on. According to the number of layers, PCB classification can be divided into single-sided board (SSB), double-sided board (DSB) and multi-layer board (MLB); according to softness, 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 types: single-sided boards, double-sided boards, conventional multilayer boards, flexible boards, HDI (high-density sintered) boards, and packaging substrates according to the basic classification of the above-mentioned PCB products. Main subdivided industries.
The PCB upstream industry includes PCB substrate board raw material suppliers and PCB production equipment suppliers, and the downstream industry includes consumer electronics computers and peripheral products, automobile industry and mobile phone industry. According to the industrial 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: Glass fiber cloth is one of the raw materials of copper clad laminates. It is spun from glass fiber yarn and accounts for about 40% (thick plate) and 25% (thin plate) of the cost of copper clad laminates. The glass fiber yarn is calcined into a liquid state by calcining silica sand and other raw materials in a kiln, and 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: Copper-clad laminate is the product of bonding glass fiber cloth and copper foil together with epoxy resin as a fusion agent. It is the direct raw material of PCB. After etching, electroplating, and lamination of multi-layer boards, printed circuits are made. plate.
