Cosa sono i materiali PCB?Pubblicato il 10/07/2020
Esistono tre tipi principali di schede PCB:
Single-sided boards are on the most basic PCB . The parts are concentrated on one side, and the wires are concentrated on the other side (when there are chip components and the wire are on the same side, the plug-in device is on the other side). Because the wires only appear on one side, this PCB is called a single-sided (Single-sided). Because the single panel has many strict restrictions on the design of the circuit (because there is only one side, the wiring between can not cross and must be around a separate path), so only early circuits use this type of board.
Double panel board
The double-sided circuit board has wiring on both sides, but to use the wires on both sides. It is necessary to have an appropriate circuit connection between the two sides. This “bridge” between circuits is called a via. The via hole is a small hole filled or coated with metal on the PCB, which can be connected to 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 connected to the other side through the hole), and it is more suitable for use in more complicated circuits than the single-sided board.
In order to increase the wiring area of the multilayer board, the multilayer board uses more single or double-sided wiring boards. A printed circuit board with one double-sided as inner layer, two single-sided as outer layers or two double-sided as inner layers and two single-sided as outer layers. Printed circuit boards that are interconnected by positioning systems and insulating adhesive materials and whose conductive patterns are interconnected according to design requirements become four-layer and 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, an empty layer will be added to control the thickness of the board. Usually, the number of layers is even, and it includes the two outermost layers. Most of the motherboards are 4 to 8-layer structure, but technically, the theory can achieve nearly 100-layer PCB board. Most large-scale supercomputers use quite multiple layers of motherboards, but because such computers can be replaced by clusters of many ordinary computers, ultra-multilayer boards have gradually been discontinued. Because the various layers in the PCB are tightly combined, it is generally not easy to see the actual number, but if you look closely at the motherboard, you can still see it.
In terms of materials, PCB material can be divided into organic materials and inorganic materials:
- Organic materials: Phenolic resin, glass fiber/epoxy resin, polyimide, BT/Epoxy, etc. all belong to it.
- Inorganic material: Aluminum, copper-invar-copper, ceramic, etc. belong to it.
The choice of PCB sheet must strike a balance between meeting design requirements and mass production and cost. Design requirements include electrical and institutional components. This material problem is usually more important when designing very high-speed PCB boards (frequency greater than GHz).
PCB material type:
94HB: ordinary cardboard, not fireproof (the lowest grade material, die punching, can not be a power board);94V0: flame retardant cardboard (die punching);
22F: single-sided half-glass fiber board (die punching);
CEM-1: single-sided glass fiber board (must be computer drilled, not die punching);
CEM-3: double-sided half-glass fiber board (except for double-sided cardboard, which belongs to the lowest end of the double-sided board, simple double-sided board can use this material);
FR-4: double-sided glass fiber board;
The classification of flame retardant properties can be divided into 94V-0/V-1/V-2, 94-HB four.
94V-0 and 94V-2 belong to a class of flame retardant grade materials. And among these two types, 94V-0 belongs to the highest flame retardant grade material. PCB board is generally divided into several colors, green is the most common, and black, red, blue, yellow. Color and quality are irrelevant, just a personalized performance.
Advantages of PCB
After the electronic equipment adopts the printed board, due to the consistency of similar printed boards, the error of manual wiring is avoided. And can realize automatic insertion or placement of electronic components, automatic soldering, automatic detection. Ensure the quality of electronic equipment, improve labor productivity, reduce costs, and facilitate maintenance.
The reason why PCB can be more and more widely used, because it has many unique advantages, the outline is as follows.
High-density: For decades, the high-density of printed boards can develop with the improvement of integrated circuit integration and advancement of mounting technology.
High reliability: Through a series of inspections, tests and aging tests, the PCB can be guaranteed to work reliably for a long time (usage period, generally 20 years).
Designability: For various PCB performance (electrical, physical, chemical, mechanical, etc.) requirements, printed board design can be achieved through design standardization and standardization, with short time and high efficiency.
Manufacturability: With modern management, standardization, scale (quantity), automation and other production can be carried out to ensure product quality consistency.
Testability: Established a relatively complete test method, test standards, various test equipment and instruments, etc. to test and identify the qualification and service life of PCB products.
Assemblability: PCB products are not only convenient for standardized assembly of various components, but also can be automated and large-scale mass production. At the same time, PCB and various component assembly parts can also be assembled to form larger parts and systems to the whole machine.
Maintainability: Because PCB products and various component assembly parts are standardized design and mass production, these parts are also standardized. Therefore, once the system fails, it can be replaced quickly, conveniently and flexibly, and the system can be quickly restored to work. Of course, there are more examples. Such as miniaturizing and lightening the system, and speeding up signal transmission.
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