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Principles That Must Be Known About PCB Board Technology

Principles That Must Be Known About PCB Board Technology

1. Width selection criteria of printed conductors for custom circuit board China: The minimum width of printed conductors is related to the current flowing through the conductors: the line width is too small, the resistance of the newly printed conductors is too large, and the voltage drop on the line is also large, which affects the performance of the circuit. If the line width is too wide, the wiring density is not high and the board area increases, which is not conducive to miniaturization in addition to increasing costs. If the current load is calculated by 20A/square millimeter, when the thickness of copper foil is 0.5MM, the current load of 1MM (about 40MIL) line width is 1A. Therefore, the line width of 1-2.54MM (40-100MIL) can meet the general application requirements. The ground wire and power supply on the high-power equipment floor can increase the line width appropriately according to the power size. In low-power digital circuits, in order to improve the wiring density, the minimum line width of 0.254-1.27MM (10-15MIL) can be satisfied. In the same circuit board, the ground wire is thicker than the signal line.


2. Line spacing of custom circuit board China: When the line spacing is 1.5MM (about 60MIL), the insulation resistance between wires is greater than 20MO, and the maximum withstand voltage between wires can reach 300V. When the line spacing is 1MM (40MIL), the maximum withstand voltage between wires is 200V. Therefore, in the medium and low voltage (line voltage is less than 200V), the line spacing is 1.0-1.5MM (40-60MIL). In low voltage circuit, such as digital circuit system, breakdown voltage need not be considered, as long as the production process permits, it can be very small.


3. Custom circuit board China: For 1/8W resistance, the diameter of pad lead is 28 MIL, while for 1/2W, the diameter of pad lead is 32 MIL, the lead hole is too large, the width of pad copper ring is relatively reduced, resulting in the decrease of pad adhesion. It is easy to fall off, and lead hole is too small, so component installation is difficult.


4. Circuit Borders of Custom circuit board China:

The shortest distance between the frame line and the pin pad of the components should not be less than 2MM (generally 5MM is more reasonable), otherwise it is difficult to cut.


5.The component layout principles of Custom circuit board China:


1. General Principles: In the design of PCB board, if there are both digital circuit and analog circuit in the circuit system, and high current circuit, it must be separately laid out, so that the coupling between the systems can be minimized in the same type of circuit, according to the direction and function of the signal, the components are divided into blocks and placed in zones.


2. In the input signal processing unit, the driver of output signal should be close to the edge of the circuit board to make the input and output signal lines as short as possible to reduce the interference of input and output.


3. Component placement direction: Components can only be arranged horizontally and vertically. Otherwise, plug-ins are not allowed.


4. Spacing of components. For medium density plates, small components, such as small power resistors, capacitors, diodes, and other discrete components, the spacing between each other is related to plug-ins and welding process. When wave soldering, the spacing between components can be taken 50-100MIL (1.27-2.54MM) manually, such as 100MIL, integrated circuit chips, and the spacing between components is generally 100-150MIL.


5. When the potential difference between components is large, the spacing between components should be large enough to prevent discharge.


6. In the digital circuit, in order to ensure the reliable operation of the digital circuit system, the IC decoupling capacitor is placed between the power supply and the ground of each digital integrated circuit chip. The decoupling capacitor generally adopts the ceramic capacitor, with the capacity of 0.01-0.1UF. In addition, a capacitor of 10 UF and a ceramic chip capacitor of 0.01 UF should be added between the power supply line and the ground line at the entrance of the circuit power supply.


7. Clock circuit elements should be as close as possible to the clock signal pins of MCU chips in order to reduce the connection length of clock circuit. And it is better not to go down below.


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