PCB board should pay attention to the five processes, whether
PCB proofing or mass production, we should pay attention to the following 5 points.
1: Line spacing: When 1.5MM (about 60MIL), the insulation resistance between lines is greater than 20M Euro, the maximum voltage withstand between lines can reach 300V, when the line spacing is 1MM (40MIL), the maximum voltage withstand between lines is 200V, therefore, in the low-voltage circuit board (the voltage between lines is less than 200V), the line spacing is 1.0-1.5MM (40-60MIL) in the low-voltage circuit, such as digital circuit system, no The breakdown voltage must be taken into consideration, so long as the production process permits, it can be very small.
2: Pad: For 1/8W resistance, the lead diameter of the pad is 28 MIL is enough, and for 1/2W, the diameter of the lead hole is 32 MIL, the lead hole is bigger, the width of the copper ring of the pad is relatively reduced, resulting in the reduction of the adhesion of the pad. It is easy to fall off, the lead hole is too small, and the components are difficult to sow.
3: Width selection of printed wire: The minimum width of printed wire is related to the current flowing through the wire: the line width is too small, the resistance of the printed wire is too large, the voltage drop on the line is too large, affecting the performance of the circuit, the line width is too wide, the wiring density is not high, the board area is increased, in addition to increasing the cost, it is not conducive to miniaturization. The load is 20A/square millimeter. When the copper foil thickness is 0.5MM, the current load of 1MM (about 40MIL) linewidth is 1A. Therefore, the linewidth of 1-2.54MM (40-100MIL) can meet the general application requirements. The ground wire and power supply on the high-power equipment board can be increased appropriately according to the power level, while the number of low-power devices can be increased appropriately. In order to increase the wiring density, the minimum line width can be satisfied by 0.254--1.27MM (10--15MIL). In the same circuit board, the power line is larger than the signal line.
4: Draw the circuit frame: The shortest distance between the frame line and the pad of the element pin can not be less than 2MM, otherwise cutting is difficult.
5: element layout principle:
(1) General Principle: In the design of PCB board, if there are both digital and analog circuits in the circuit system, and high-current circuits, it must be separately arranged, so that the coupling between the systems can be minimized in the same type of circuit, according to the signal flow direction and function, the components are divided into blocks and placed in different areas.
(2): Input signal processing unit, the output signal driving element should be close to the circuit board, so that the input and output signal lines as short as possible, in order to reduce input and output interference.
(3): Component placement direction: Components can only be arranged horizontally and vertically. Otherwise, they must not be in the plug-in.
(4): Spacing between components. For medium density board, small components, such as low power resistance, capacitance, diodes, and other discrete components, the spacing between each other and plug-in, welding process, peak welding, component spacing can be taken 50-100 MIL (1.27-2.54 MM) manual can be larger, such as 100 MIL, integrated circuit chips, component spacing is generally 100-150 MIL.
(5) when the potential difference between components is large, the spacing between components should be large enough to prevent discharge.
(6): In order to ensure the reliability of the digital circuit system, IC decoupling capacitor is placed between the power supply and the ground of each digital integrated circuit chip. The decoupling capacitor is usually ceramic capacitor with a capacity of 0.01-0.1UF. In addition, a 10UF capacitor and a 0.01UF ceramic chip capacitor are added between the power cord and the ground wire at the entrance of the circuit power supply.
(7): Clockwise circuit elements as close as possible to the clock signal pins of the microcontroller chip, to reduce the length of the clock circuit connection. And the following is best not to line.
Pay attention to the above 5 points
PCB proofing or mass production is qualified products.
