The actual printed circuit board is composed of copper foil layer, printed data layer and silk screen layer. The copper foil layer includes the signal layer and internal electrical layer in the software design, which mainly completes the electrical connection characteristics of the circuit. Generally, the number of layers of copper foil is defined as the number of layers of printed circuit board (single panel, double-sided board and multilayer board). The printed data layer, also known as insulation layer or copper clad laminate, is mainly used to block the power supply layer and wiring layer and support the whole printed circuit board. The silk screen layer is located at the top layer of the printed board to protect the copper foil layer and record some logo patterns and text symbols (generally white) to facilitate installation and repair.
Design methods and skills of printed circuit board
When selecting the layer of printed circuit board, we should consider the electrical function, reliability, processing technology requirements and economic indicators. Common copper clad laminates include phenolic paper laminate, epoxy paper laminate, polyester glass cloth laminate and epoxy glass cloth laminate. Epoxy paper laminate is generally used in the laboratory. It is better to use polyester glass cloth laminate for UHF printed circuit board. For electronic equipment requiring flame retardant, laminated flame retardant printed circuit board immersed in flame retardant resin is also required. The thickness of printed circuit board shall be determined according to the function of printed circuit board, the component installed, the standard of printed circuit board socket, the overall dimension of printed circuit board and the accepted mechanical load. The most important thing is to ensure the stiffness and strength of the. The thickness of common printed circuit boards is 0.5mm, 1.0mm, 1.5mm and 2.0mm.
Mainly manual layout, generally following the following rules:
1) Layout according to the circuit function: layout the components according to the schematic diagram as far as possible. The signals enter the right output from the left, input from the top and output from the bottom. According to the circuit flow, arrange the orientation of each functional circuit unit to maintain smooth signal flow and common direction.
2) Layout around the central circuit: the arrangement of components should be uniform, regular and compact. The digital circuit part shall be separated from the analog circuit part.
3) The shorter the connection between high-frequency elements, the better, so as to reduce electromagnetic disturbance; The easily disturbed elements shall not be too close, and the elements with high potential difference shall meet the specified safety requirements.
4) The conditioning elements are placed on the printed circuit board in an easy conditioning position; For external conditioning, its orientation should correspond to the orientation of the conditioning knob on the chassis panel; The distance between components and the edge of printed circuit board shall be more than 3mm. Components with too large weight should not be installed on the printed circuit board; Heating elements should be kept away from heat sensitive elements.
5) Order of component placement: first place components with fixed orientation closely matched with the structure. For example, power socket, indicator light, switch and connector, etc; Then place special components, such as heating elements, transformers, integrated circuits, etc; Finally, place small components, such as resistors, capacitors, diodes, etc.