With the rapid development of mobile phones, electronics, communication industries, and other industries, the PCB circuit board industry is also constantly growing and growing rapidly. The requirements for the number of layers, weight, precision, materials, line width, line spacing, reliability, and other aspects of circuit boards are becoming increasingly high.

　　1 Selection criteria for printed wire width: The minimum width of printed wire is related to the current flowing through the wire. If the wire width is too small, the resistance of the newly printed wire will be high, and the voltage drop on the wire will also be large, affecting the performance of the circuit. If the wire width is too wide, the wiring density will not be high, and the board area will increase. In addition to increasing costs, it is also not conducive to miniaturization If the current load is calculated at 20A/square millimeter, when the thickness of the copper foil is 0.5MM (usually so much), the current load for a 1MM (about 40MIL) line width is 1A. Therefore, a line width of 1-2.54MM (40-100MIL) can meet the general application requirements. The ground wire and power supply on high-power equipment boards can increase the line width appropriately according to the power size. In low-power digital circuits, to improve wiring density, the minimum line width is 0.254-1.27MM (10-15MIL) to meet the requirements. In the same circuit board, the power and ground wires are thicker than the signal wires.

　　2、 Line spacing: When the line spacing 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 medium and low voltage (line to line voltage not exceeding 200V) circuit boards, the line spacing is taken as 1.0-1.5mm (40-60MIL). In low-voltage circuits, such as digital circuit systems, breakdown voltage does not need to be considered, as long as the production process allows, it can be very small.

　　III Pad: For a 1/8W resistor, a pad lead diameter of 28MIL is sufficient, while for a 1/2W resistor, a diameter of 32MIL results in larger lead holes and a relatively smaller copper ring width, leading to a decrease in pad adhesion. Easy to fall off, the lead hole is too small, and it is difficult to install the components.