when the size is too small, the heat dissipation is decreased, the welding is not easy to control, and adjacent lines easily appear. Mutual interference, such as the electromagnetic interference of the circuit board. 

Therefore, PCB design must be optimized: 

1. Shorten the connection between high-frequency components and reduce EMI interference. 

2. Components with a large weight (eg more than 20g) should be fixed with brackets and then welded. 

3. The heat-generating component should consider the heat dissipation problem to prevent the component surface from having a large defect and rework, and the heat-sensitive component should be far away from the heat source. 

4. The arrangement of the components is as parallel as possible, which is not only aesthetic but also easy to solder, and mass production is preferred. The circuit board is designed to have a 4:3 rectangle best. Do not change the width of the wire to avoid wiring discontinuities. When the circuit board is heated for a long time, the copper foil is likely to swell and fall off. Therefore, large-area copper foil should be avoided.