Five principles of PCB copy board

Printed wire width selection basis

The minimum width of the printed wire is related to the current flowing through the wire: the line width is too small, the resistance of the printed wire is large, and the voltage drop on the wire is large, which affects the performance of the circuit. If the line width is too wide, the wiring density is not high. The increase in board area, in addition to increasing costs, is also not conducive to miniaturization. If the current load is calculated at 20 A/mm 2 , when the thickness of the copper clad is 0.5 MM (generally so much), the current load of 1 MM (about 40 mil) line width is 1 A, so the line width is 1 - 2.54. MM (40-100MIL) can meet the general application requirements. The ground wire and power supply on the high-power equipment board can increase the line width according to the power. On the low-power digital circuit, in order to improve the wiring density, the minimum The line width is 0.254 - 1.27MM (10 - 15MIL). In the same board, the power cord. The ground line is thicker than the signal line.

Line spacing

When it is 1.5MM (about 60MIL), the insulation resistance between wires is greater than 20M ohms, 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 middle For low voltage (line voltage not greater than 200V), the line spacing is 1.0 - 1.5MM (40 - 60MIL) in low voltage circuits, such as digital circuit systems, regardless of the breakdown voltage, as long as the production process allows, Very small.

Pad

For a 1/8W resistor, a pad lead diameter of 28 MIL is sufficient, while for a 1/2 W, the diameter is 32 MIL, the lead hole is too large, and the pad copper ring width is relatively reduced, resulting in a pad The adhesion is reduced. It is easy to fall off, the lead hole is too small, and component mounting is difficult.

Draw circuit border

The shortest distance between the border line and the component pin pad can't be less than 2MM (usually 5MM is reasonable), otherwise it is difficult to cut.

Component layout principle

General Principle: In PCB design, if there are digital circuits and analog circuits in the circuit system. As well as high-current circuits, they must be laid out separately, so that the matching between the systems can be minimized in the same type of circuit, and the components are placed in the direction of signal flow and function, partitioning, and partitioning.