Summary： Printed circuit is a conductive pattern attached to the insulating substrate surface to connect electronic components. The finished boards of printed circuit become printed circuit boards, namely PCBs.
Classification and Features of PCB
Printed circuit is a conductive pattern attached to the insulating substrate surface to connect electronic components. The finished boards of printed circuit become printed circuit boards, namely PCBs. A printed circuit board (PCB) mechanically supports and electrically connects electronic components or electrical components using conductive tracks, pads and other features etched from one or more sheet layers of copper laminated onto and/or between sheet layers of a non-conductive substrate. Components are generally soldered onto the PCB to both electrically connect and mechanically fasten them to it. Printed circuit boards are used in all but the simplest electronic products. They are also used in some electrical products, such as passive switch boxes. Alternatives to PCBs include wire wrap and point-to-point construction, both once popular but now rarely used. PCBs require additional design effort to lay out the circuit, but manufacturing and assembly can be automated. Specialized CAD software is available to do much of the work of layout. Mass-producing circuits with PCBs is cheaper and faster than with other wiring methods, as components are mounted and wired in one operation. Large numbers of PCBs can be fabricated at the same time, and the layout only has to be done once. PCBs can also be made manually in small quantities, with reduced benefits. PCBs can be single-sided (one copper layer), double-sided (two copper layers on both sides of one substrate layer), or multi-layer (outer and inner layers of copper, alternating with layers of substrate). Multi-layer PCBs allow for much higher component density, because circuit traces on the inner layers would otherwise take up surface space between components. The rise in popularity of multilayer PCBs with more than two, and especially with more than four, copper planes was concurrent with the adoption of surface mount technology. However, multilayer PCBs make repair, analysis, and field modification of circuits much more difficult and usually impractical.
1. Rigid PCB: The rigid PCB has a certain mechanical strength, and the parts installed with it have a certain ability of resistance to bending, and it is usually at a state of flat when used. Generally, the rigid PCBs are always popular with the electronic devices because of its good flatness and excellent performance of resistance to bending.
2. Flexible PCB: Flexible PCBs are made of soft laminated plastics or other soft insulating materials. The boards made by the flexible PCBs can easily be bent and stretched, which means that people can bend optionally them when using the flexible PCBs according to the installation requirements. Flexible printing plate is used for special occasions. For example, the display screen of some digital multimeter can be rotated just because of the popularity and application of the flexible PCBs.
3. Single-side PCB: Single sided PCB is the basic simple PCB, parts is layouted on one side and the circuit is on the other side. As there is only layer conductor, it is called single sided PCB (Single-sided PCB or one layer PCB). Single-side PCB is usually made of the laminate or the glass cloth and the conductive pattern of it is relatively simple, so most of them are made by silkscreen printing or wet film process. In addition, some small amount of various products usually use photoresist to pattern circuit.
4. Double-side PCB: Double Sided PCBs (also known as Double-Sided Plated Thru or DSPT, which is usually made of the epoxy board or the glass cloth.) circuits are the gateway to higher technology applications. They allow for closer (and perhaps more) routing traces by alternating between a top and bottom layer using vias.
5. Multi-layer PCB: A multilayer PCB is a printed circuit board with three or more layers of conductive graphics. The conductive graphic of the inner layer of the multi-layer board is superimposed with the insulating bonding sheet, and the outer layers are covered with foils, which are compressed into a whole multi-layer board. The holes of multi-layer board must be metallized in order to lead out and connect the printed circuits sandwiched between the insulating substrates, which is also namely PTH (Plate Through Hole).
I. General characteristics:
1) Higher density: Over the past 100 years, the high density of PCB can be developed with the improvement of integrated circuit and the progress of installation technology.
2) Higher reliability: A series of inspections, tests, and aging tests will ensure that the PCB will work reliably for a long period of time (generally 20 years).
3) Good designability: The requirements for various properties (electrical, physical, chemical, mechanical, etc.) of PCB can be achieved through normalization and standardization of design, with short time and high efficiency.
4) Good Producibility: Adopting modern management can carry out standardization, scale, automation and other production, guaranteing product quality consistency.
5) Easily testability analysis: A relatively complete test method, test standard, various test equipment and instruments were established to test and evaluate the PCB product's qualification and service life.
6) Assembly ability: PCB products not only facilitate the standardized assembly of various components, but also can be automated and mass production. At the same time, PCB and various components can be assembled into larger components, systems and even whole machines.
7) Great Maintainability: As PCB products and components are assembled into parts that are designed and manufactured in a standardized way, they are also standardized. In case of system failure, the system can be replaced quickly, conveniently and flexibly and the system can be restored quickly.
II. Features of Multi-layer PCB:
1) Used with integrated circuit can make the whole machine miniaturization, reducing the weight of the whole machine.
2) It improves the wiring density, reduces the spacing of components and shortens the signal transmission path.
3) It reduces the component welding points which results in the reduction of the failure rate.
4) The signal distortion of the circuit is reduced because of the application of the shielding layer.
5) The grounding thermal plane is introduced to reduce the local overheating, improving the reliability of the whole machine.
