PCB News - smt factory sharing: small principles in PCB copying process

smt factory sharing: small principles in PCB copying process
Today, the smt factory will share with you the small principles in the PCB copying process. For details, please see the following small principles.
smt factory sharing: small principles in PCB copying process
1. Selection basis for printed wire width
The minimum width of the printed wires in the smt factory is related to the size of the current flowing through the wires: the wire width is too small, and the resistance of the printed wires is large, and the voltage drop on the wire will also be large, which will affect the performance of the circuit. If the wire width is too wide, the wiring density will not be High, the PCB board area increases, in addition to increasing the cost, it is also not conducive to miniaturization. If the current load is calculated at 20A/mm2, when the thickness of the copper clad foil is 0.5MM, (usually so much), the current load of the 1MM (about 40MIL) line width is 1A, 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 be appropriately increased according to the power level. In the low-power digital circuit, in order to increase the wiring density, the minimum The line width is 0.254-1.27MM (10-15MIL) can be satisfied. 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 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, the breakdown voltage does not need to be considered, as long as the production process allows it. Very small.

3. Pad

For 1/8W resistors, a diameter of 28MIL of the pad lead is sufficient, while for 1/2W, 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 size of the pad. Adhesion drops. It is easy to fall off, the lead hole is too small, and it is difficult to install the components.

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 will be difficult to blank.

5. Component layout principle

A: General principle: In PCB design, if there are digital circuits and analog circuits in the circuit system. As well as high-current circuits, the layout must be separated to minimize the coupling between systems. In the same type of circuit, components are placed in blocks and partitions according to signal flow and function.

6. The input signal processing unit and output signal drive components should be close to the side 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.

7. Component placement direction

Components can only be arranged in two directions, horizontal and vertical. Otherwise it must not be used for plug-ins.

8. Component spacing.

For medium-density boards, the spacing of small components such as low-power resistors, capacitors, diodes, and other discrete components is related to the plug-in and soldering process. During wave soldering, the component spacing can be 50-100MIL (1.27-2.54MM). Manually. Larger, such as 100MIL, integrated circuit chip, the component spacing is generally 100-150MIL.

9. When the potential difference between the components is large, the component spacing should be large enough to prevent discharge.

10. Before entering the IC, the lotus coupling 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, an IC decoupling capacitor is placed between the power supply and the ground of each digital integrated circuit chip. Decoupling capacitors generally use ceramic capacitors, and the capacity of the decoupling capacitor is 0.01~0.1UF. The selection of the decoupling capacitor capacity is generally selected according to the reciprocal of the system operating frequency F. In addition, a 10UF capacitor and a 0.01UF ceramic capacitor should be added between the power line and the ground line at the entrance of the circuit power supply.

11. The clock circuit components are as close as possible to the clock signal pins of the single-chip microcomputer chip to reduce the wiring length of the clock circuit. And it is best not to run the wires below.

The above selection basis of printed wire width, line spacing, pads, drawing circuit borders and component layout principles are some of the principles in the PCB copying process. Although it may be some small principles, we still need to follow them. This is the end for Baiqian smt factories to share the small principles in the PCB copying process. If you want to know more about the information shared by smt factories, you can follow us.