PCB manufacturing is a process that involves fields such as electrical engineering, chemistry, and physics. In this article, we will summarize some key principles of the PCB manufacturing process that help ensure the quality and performance of PCBs.
1. Selecting the Width of Printed Conductors
The width of the printed conductors must be determined based on the amount of current flowing through them.
If the line width is too small, it will cause an increase in resistance and a higher voltage drop, which will affect circuit performance.
If the line width is too wide, it will increase costs and hinder miniaturization.
Generally, a line width of 1 to 2.54 millimeters (40 to 100 mil) is sufficient for most applications.
For ground and power traces on high-power device boards, the trace width can be slightly wider, whereas in low-power digital circuits, the minimum trace width can range from 0.254 to 1.27 millimeters (10 to 15 mil) to increase routing density.
2. Line Spacing
The choice of trace spacing depends on the voltage between traces; generally, a trace spacing of 1.0 to 1.5 millimeters (40 to 60 MIL) is sufficient to meet the requirements of low- and medium-voltage circuits.
In low-voltage circuits, such as digital circuit systems, there is no need to give excessive consideration to breakdown voltage, so a smaller trace spacing can be selected to increase routing density.
3. Pad Design
The design of pads also requires careful consideration for components with different power ratings. For example, for a 1/8-watt resistor, the pad lead diameter can be 28 mil, while for a 1/2-watt resistor, the diameter can be 32 mil.
Excessively large lead holes can result in narrower copper rings on the pads, which may reduce the pads' adhesion, while excessively small lead holes can make it more difficult to mount the components.
4. Draw the circuit outline
When designing a PCB, the minimum distance between the border and the component pin pads must not be less than 2 millimeters (5 millimeters is generally considered a reasonable value). This ensures that no problems arise during the cutting process.
5. Principles of Component Layout
In PCB design, component placement is crucial. Here are some common principles for component placement:
- Separate digital circuits from analog circuits and high-current circuits to minimize interference.
- The input signal processing unit and output signal driver should be placed as close to the edge of the circuit board as possible to minimize the length of the input and output lines.
- Components can only be arranged horizontally or vertically; they cannot be tilted.
- The spacing between components depends on their size and the soldering process; it is generally between 50 and 100 mils.
- When there is a large potential difference, the spacing between components should be sufficient to prevent discharge.
- For clock circuits, place them as close as possible to the microcontroller chip's clock signal pins to minimize the length of the clock circuit's wiring.
By following the small design principles outlined above, you can better design and manufacture high-quality PCBs. In PCB design, a well-thought-out and reasonable layout is key to ensuring circuit performance.
