The printed circuit boards used in actual electronic products are very different, and there are different classifications according to different standard printed circuit boards.

1. Classified by the distribution of printed circuits

According to the approximate distribution of the printed circuit, the printed circuit board can be divided into three types: single panel, double panel and multi-layer board

• Single sided PCB

The single-sided board is on an insulating substrate with a thickness of 0.2-5mm, only one surface is covered with copper foil, and a printed circuit is formed on the substrate by printing and etching. The single panel is simple to manufacture and easy to assemble. It is suitable for the requirements of a circuit, such as radios, televisions, etc.; it is not suitable for occasions requiring high assembly density or complex circuits.

• Double sided PCB

Double-sided boards are printed circuits on both sides of an insulating substrate with a thickness of 0.2-5mm. It is suitable for electronic products with general requirements, such as electronic computers, electronic instruments and meters. Since the wiring density of the double-sided printed circuit is higher than that of the single-sided printed circuit, the volume of the device can be reduced.

• Multilayer PCB board

 

Printed boards with more than 3 layers of printed circuits printed on an insulating substrate are called multilayer boards. It is a combination of several thin single or double panels, and its thickness is generally 1.2-2.5mm. In order to lead out the circuit sandwiched between the insulating substrate, the holes for mounting components on the multilayer board need to be metalized, that is, a metal layer is applied to the inner surface of the small holes to connect them with the printed circuit sandwiched between the insulating substrate.

 

The following figure is a schematic diagram of the structure of the multilayer board. The components used in the multilayer board are mostly SMD components. Its characteristics are:

 

1. Used in conjunction with integrated circuits, the whole machine can be miniaturized and the weight of the whole machine reduced;

 

2. Improve the wiring density, reduce the spacing of components, and shorten the signal transmission path;

 

3. Reduce the welding points of components and reduce the failure rate;

 

4. The shielding layer is added to reduce the signal distortion of the circuit;

 

5. The introduction of a grounded heat dissipation layer can reduce local overheating and improve the reliability of the whole machine;

2. Classification according to the nature of the substrate

 

According to the nature of the substrate, printed circuit boards can be divided into rigid and flexible.

 

Rigid PCB

 

The rigid printed board has a certain mechanical strength, and the parts assembled with it have a flat state. Rigid printed boards are used in general electronic products.

 

Flexible printed board

The flexible printed board is made of soft layered plastic or other soft insulating materials as the base material. The parts made of it can be bent and stretched, and can be bent according to the installation requirements during use. Flexible printed boards are generally used in special occasions. For example, the display screen of some digital multimeters can be rotated, and flexible printed boards are often used inside; the display screens and buttons of mobile phones.

The picture below shows a mobile phone flexible printed board. Its base material is polyimide, and the surface is treated with anti-oxidation. The minimum line width and line spacing are set to 0.1mm. The outstanding feature of the flexible printed board is that it can be bent, curled, folded, and can be connected to rigid printed boards and movable parts, so as to enable three-dimensional wiring and realize three-dimensional spatial interconnection. It is small in size, light in weight, easy to assemble, and suitable for space Small, high-density electronic products.

 

Three, according to the scope of application

 

According to the scope of application, printed circuit boards can be divided into low-frequency and high-frequency printed circuit boards.

 

The high frequency of electronic equipment is the development trend, especially in today's wireless network and satellite communication, information products are moving towards high speed and high frequency, and communication products are moving towards the standardization of voice, video and data for wireless transmission with large capacity and speed. Therefore, the development of a new generation of products requires high-frequency printed boards, and the foil substrate can be composed of materials with low dielectric loss and dielectric constant such as polytetrane ethylene, polyvinyl ethylene, polystyrene, polytetrafluoroethylene glass cloth, etc.

 

Fourth, the types of special printed boards

 

At present, some special printed boards such as metal core printed boards, surface mounted printed boards, and carbon film printed boards have also appeared.

 

Metal core printed board

 

The metal core printed board is to replace the epoxy glass cloth board with a metal plate of equivalent thickness. After special treatment, the conductor circuits on both sides of the gold board are connected to each other, and the metal part is highly insulated. The advantage of the metal core printed board is good heat dissipation and dimensional stability. This is because magnetic materials such as aluminum and iron have a shielding effect and can prevent mutual interference.

Surface mount printed board

 

The surface mount printed board is a printed board developed to meet the needs of electronic products for "light, thin, short, and small" and to match the mounting process of surface mount devices with pin density and low cost. The printed board has the characteristics of small aperture, small line width and spacing, high precision, and high substrate requirements.

 

Carbon film printed board

 

The carbon film printed board is a printed board in which a layer of carbon film is printed to form a contact or jumper (resistance value meets the specified requirements) after the conductor pattern is made on the copper-plated board. It is characterized by simple production process, low cost, short cycle, good wear resistance, electrical conductivity, can achieve high-density single panel, product miniaturization, light weight, suitable for televisions, telephones, video recorders and electronic organs And other products.