Introduction For Several Key-points Decide The PCB Copy Board Quality

In PCB board copying, PCB modification and PCB design, the width of the printed wire, line spacing, circuit frame and component layout will affect the quality and performance of the circuit board.

1. Selection basis of printed wire width

The minimum width of a printed wire is related to the current flowing through the wire. Line width is too small, the resistance of just printed wire is large, and the voltage drop on the line is large,  affecting the circuit’s performance.If the wire 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/ MM square, the current load of 1MM(about 40MIL) wireline is 1A when the thickness of the copper clad foil is 0.5mm (generally this much). 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, according to the power size, can be appropriately increased line width, and in the low-power digital circuit, to improve the wiring density, the minimum line width of 0.254-1.27mm (10–15MIL) can be full The foot. In the same circuit board, the power cord. The ground wire is thicker than the signal wire.

2. Line spacing:

When it is 1.5mm (about 60MIL), the insulation resistance between wires is greater than 20M ohms, and the maximum voltage between wires can reach 300V. When the line spacing is 1MM(40MIL), the maximum voltage between the lines is 200V, therefore, in the low and medium voltage (the voltage between the lines is not greater than 200V) on the circuit board, the line spacing is 1.0- 1.5mm (40- 60MIL) in the low voltage circuit, such as digital circuit system, do not have to consider the breakdown voltage, as long as the production process allows, can be very small.

3. Pad:

Pad lead diameter of 28MIL is sufficient for 1/8W resistance, For 1/2W, with a diameter of 32MIL, the lead hole is too large, and the width of the copper ring of the pad is relatively reduced, which leads to the decrease of the adhesion of the pad. Easy to fall off, lead hole is too small, component seeding is difficult.

4. PCB border:

The shortest distance between the frame line and the component pin pad should not be less than 2MM (generally 5MM is more reasonable), otherwise it is difficult to blanching.

5. Principle of component layout:

• General rule: In PCB design, if the circuit system exists both digital and analog circuits.And large current circuit, must be separated layout, so that the coupling between the systems to a minimum, in the same type of circuit, according to the signal flow direction and function, block, partition placed components.
• The input signal processing unit and the output signal driving element should be close to the circuit board edge to make the input and output signal lines as short as possible to reduce the interference of input and output.
• Element placement direction: the element can only be arranged in two directions: horizontal and vertical.Otherwise not in the plug-in.
• Component spacing. The spacing between small components, such as small power resistors, capacitors, diodes, etc., is related to plug-in and welding process for medium density board.When wave soldering, element spacing can be 50-100mil (1.27– 2.54mm) manual can be larger, such as 100MIL, integrated circuit chips, element spacing is generally 100-150mil
• When the potential difference between the elements is large, the distance between the elements should be large enough to prevent discharge.
• The coupling capacitance of the IC should be close to the ground pin of the chip’s power supply.Otherwise the filtering effect will be poor. In the digital circuit, to ensure the reliable work of the digital circuit system, the IC decoupling capacitor is placed between the power supply and the ground of each digital integrated circuit chip. The capacitance of lotus root is generally made of porcelain chip capacitance, and the capacity of which is 0.01~ 0.1uF. The capacitance of lotus root is generally chosen by the reciprocal of the system operating frequency F. In addition, a 10uF capacitor and a 0.01uF ceramic chip capacitor are also required between the power line at the entrance of the circuit power supply and the ground wire.
• The hour hand circuit element should be as close as possible to the clock signal pin of the single chip to reduce the connection length of the clock circuit.And you’d better not run the wires underneath.