Selection basis of printed circuit width

The minimum width of the printed wire is related to the amount of current flowing through the wire:

 1: The line width is too small, the resistance of the printed wire is large, and the voltage drop on the wire 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 is increased, which is not conducive to miniaturization besides increasing cost

If the current load is calculated as 20A / mm2, when the concentration of copper clad 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 board can appropriately increase the line width according to the power size. On the low-power digital circuit, in order to improve the wiring density, the minimum line width of 0.254-1.27mm (10-15mil) can meet the requirements

 In the same circuit board, the power line and ground line are thicker than the signal line


Wire spacing: when the wire spacing is 1.5mm (about 60mil), the insulation resistance between wires is greater than 20mohm, and the maximum withstand voltage between wires can reach 300V. When the wire spacing is 1mm (40mil), the maximum withstand voltage between wires is 200V. Therefore, on the circuit board of medium and low voltage (the voltage between wires is not greater than 200V), the wire spacing is 1.0-1.5mm (40-60mil) in the low-voltage circuit, such as the digital circuit system, the breakdown voltage does not need to be considered, as long as the production process allows, it can Very small.

 3: Pad: for a 1 / 8W resistance, a pad lead diameter of 28mil is sufficient,

 For 1 / 2W, the diameter is 32mil, the lead hole is too large, the width of the copper ring of the pad is relatively reduced, which leads to the decrease of the adhesion force of the pad. It is easy to fall off, the lead hole is too small, and it is difficult to plant the components

 4: Draw circuit border:

The shortest distance between frame wire and component pin pad shall not be less than 2 mm (it is reasonable to take 5 mm generally), otherwise it is difficult to cut

 5: Principle of component layout:

A general principle: in PCB design, if the circuit system has both digital circuit and analog circuit, as well as large current circuit, it must be arranged separately, so that the coupling between each system can be minimized in the same type of circuit, and components can be placed in blocks and zones according to signal flow direction and function

 B: The input signal processing unit and output signal driving element shall be close to the circuit board to make the input and output signal lines as short as possible to reduce the input and output interference

 C: Component placement direction: components can only be arranged in horizontal and vertical directions. Otherwise, they cannot be placed in plug-ins

 D: Component spacing. For medium density boards, the spacing between small components, such as small power resistors, capacitors, diodes, and bisectors, is related to plug-ins and welding processes. When wave soldering, the component spacing can be 50-100mil (1.27-2.54mm) or larger manually, such as 100mil, integrated circuit chip, and component spacing is generally 100-150mil

 E: When the potential difference between components is large, the distance between components should be large enough to prevent discharge

 F: In the digital circuit, in order to ensure the reliable operation of the digital circuit system, IC decoupling capacitor is placed between the power supply and the ground of each digital integrated circuit chip. Generally, porcelain chip capacitor is used for decoupling capacitor with a capacity of 0.01 ~ 0.1uF. The selection of decoupling capacitor capacity is generally based on the operating frequency f of the system In addition, a 10uF capacitor and a 0.01uF ceramic chip capacitor should be added between the power line and the ground wire at the entrance of the circuit power supply

 G: The clock circuit component should be close to the clock signal pin of the single chip as far as possible, so as to reduce the connection length of the clock circuit. And it is better not to run the wire below