PCB Technical - Line width design of PCB circuit board

1: Selection basis for printed wire width:

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

The line width is too small, and the resistance of the printed wire is 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.In addition to increasing the cost, it is also not conducive to miniaturization.

If the current load is calculated at 20A/square millimeter, when the thickness of the copper clad foil is 0.5MM, (usually so much), 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 line and power supply on the high-power equipment board can be appropriately increased according to the power level. On the circuit, in order to improve the wiring density, the minimum line width is 0.254--1.27MM (10--15MIL) to meet. (Manual welding: 20-30MIL power line and ground line should be wider)

In the same circuit board, the power line and the ground line are thicker than the signal line. The silk-screen layer has a line width of 10--30MIL (15MIL).

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, in the middle On low-voltage (line-to-line voltage not greater than 200V) circuit boards, 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. Very small. (Hand welding 25-30MIL)

3: Pad

For a resistor of 1/8W, a diameter of 28MIL of the pad lead 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 the component placement is difficult. (Manual Welding: inner diameter 35MIL, outer diameter: 70MIL)

4: Draw the circuit border

The shortest distance between the border line and the component pin pad cannot be less than 2MM, (generally 5MM is more reasonable) otherwise it is 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. And 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, place components in divisions.

B: Input signal processing unit and output signal drive 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 is related to the plug-in and welding process. During wave soldering, the component spacing can be 50-100MIL (1.27-- 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: In the IC, the decoupling 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. The selection of decoupling capacitor capacity is generally selected according to the reciprocal of the system operating frequency F. In addition, at the entrance of the circuit power supply A 10UF capacitor and a 0.01UF ceramic capacitor are also required between the power line and the ground line.

G: The clock 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.