Design standards for pads in PCB design
Pad, the basic unit of surface mount assembly, is used to form the land pattern of the circuit board, that is, various combinations of pads designed for special component types.
1) Design standards for the shape and size of the PCB pads:
1. Call the PCB standard package library.
2. The minimum single side of the pad is not less than 0.25mm, and the maximum diameter of the entire pad is not more than 3 times the diameter of the component.
3. Try to ensure that the distance between the edges of the two pads is greater than 0.4mm.
4. Pads with a diameter of more than 1.2mm or a pad diameter of more than 3.0mm should be designed as diamond-shaped or plum-shaped pads.
5. In the case of dense wiring, it is recommended to use oval and oval connection pads. The diameter or minimum width of the single-sided pad is 1.6mm; the double-sided weak current circuit pad only needs to add 0.5mm to the hole diameter, and the pad is too large to cause unnecessary continuous welding.
2), PCB pad via hole size standard:
The inner hole of the pad is generally not less than 0.6mm, because the hole smaller than 0.6mm is not easy to process when punching. Usually, the diameter of the metal pin plus 0.2mm is used as the diameter of the inner hole of the pad, such as the diameter of the metal pin of a resistor. When it is 0.5mm, the diameter of the inner hole of the pad corresponds to 0.7mm, and the diameter of the pad depends on the diameter of the inner hole.
3) Key points of reliability design of PCB pads:
1. Symmetry, in order to ensure the balance of the surface tension of the molten solder, the pads at both ends must be symmetrical.
2. Pad spacing, too large or too small pad spacing will cause soldering defects, so make sure that the distance between component ends or pins and pads is appropriate.
3. The remaining size of the pad, the remaining size of the component end or pin after overlapping the pad must ensure that the solder joint can form a meniscus.
4. The width of the pad should be basically the same as the width of the component end or pin.
