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1. Basis for selection of printed wire width:
The minimum width of the printed wire is related to the current flowing through the wire:
If the line width is too small, the resistance of the printed wire is large, and the voltage drop on the line will also be large, which affects the performance of the circuit. If the current load is calculated at 20A/mm2, when the thickness of the copper clad foil is 0.5MM, (usually so much), the current load of the 1MM (about 40MIL) line width is 1A, so the line width is 1-- 2.54MM (40-100MIL) can meet the general application requirements. The ground wire and power supply on the high-power device board can be appropriately increased according to the power level. On the low-power digital circuit, in order to increase the wiring density, The minimum line width is 0.254--1.27MM (10--15MIL) to meet. In the same circuit board, the power line. The ground line is thicker than the signal line.
2. Line spacing: When it is 1.5MM (about 60MIL), the insulation resistance between lines is greater than 20M ohms, and the maximum withstand voltage between lines can reach 300V. When the line spacing is 1MM (40MIL), the maximum withstand voltage between lines is 200V. Therefore, on the PCB board of medium and low voltage (the line voltage is not greater than 200V), the line spacing is 1.0--1.5MM (40-60MIL). In low-voltage circuits, such as digital circuit systems, it is not necessary to consider the breakdown voltage, as long as The production process allows it, and it can be small.
3. Pad: For a 1/8W resistor, a pad lead diameter of 28MIL is sufficient.
For 1/2W, the diameter is 32MIL, the lead hole is too large, and the width of the copper ring of the pad is relatively reduced, resulting in a decrease in the adhesion of the pad. It is easy to fall off, the lead hole is too small, and it is difficult to install components.
4. Draw the circuit border: The shortest distance between the border line and the component pin pad should not be less than 2MM, (generally 5MM is more reasonable), otherwise it will be difficult to blank the material.
5. Component layout principle:
A General principle: In PCB design, if the circuit system has both digital circuits and analog circuits, as well as high-current circuits, they must be laid out separately to minimize the coupling between the systems. In the same type of circuit, according to the signal flow direction and function, Divide into blocks, and place components in divisions.
B: Input signal processing unit, output signal driving components should be close to the edge of the circuit board, and the input and output signal lines should be as short as possible to reduce the interference of input and output.
C: Component placement direction: Components can only be arranged in two directions, horizontal and vertical. Otherwise, they cannot be used in plug-ins.
D: Component spacing. For medium-density boards, small components, such as low-power resistors, capacitors, diodes, and other discrete components, the spacing between each other 2.54MM) manual can be larger, such as taking 100MIL, integrated circuit chip, component spacing is generally 100-150MIL
E: When the potential difference between the components is large, the component spacing should be large enough to prevent discharge.
F: Before entering the IC, the capacitor should be close to the power supply and ground pin of the chip. Otherwise, the filtering effect will be worse. In the digital circuit, in order to ensure the reliable operation of the digital circuit system, the power supply of each digital integrated circuit chip IC decoupling capacitors are placed between the ground. Decoupling capacitors generally use ceramic capacitors, with a capacity of 0.01 ~ 0.1UF. A 10UF capacitor and a 0.01UF ceramic capacitor should also be added between the power line and the ground line.
G: The hour hand circuit components are as close as possible to the clock signal pins of the microcontroller chip to reduce the length of the clock circuit. And it is best not to route the wires below.
The above is an introduction to some small principles of PCB technology. Ipcb is also provided to PCB manufacturers and PCB manufacturing technology.
