When designing PCB soldering plates in the design of PCB, it is necessary to design strictly according to the relevant requirements. Because in the process of SMT patch, the design of PCB pad is very important. The design of pad will directly affect the weldability, stability and heat transfer of components, which is related to the quality of patch processing. What is the design standard of PCB pad?
1. Design criteria for shape and size of PCB welds:
1, call the PCB standard package library.
2, the minimum of the single side of the weld plate is not less than 0.25mm, and the maximum diameter of the plate is not more than 3 times the diameter of the element.
3, try to ensure that the distance between the edges of the two pads is greater than 0.4mm.
4. A plate with a diameter of more than 1.2mm or the diameter of a weld plate over 3.0mm should be designed to be a diamond or a plum shaped pad.
5, when the wiring is more dense, the elliptical and long circular connection plates are recommended. The diameter or the minimum width of the single panel pad is 1.6mm, and the weak electric line pad of the double side plate only needs the diameter of the hole plus 0.5mm. Too large pad is easy to cause unnecessary continuous welding.
Two, PCB welding disc hole size standard:
The pad hole is generally not less than 0.6mm, because of less than 0.6mm hole punching mold is not easy to process, usually with metal pin diameter value plus 0.2mm as the pad hole diameter, such as metal resistance pin diameter is 0.5mm, the pad diameter corresponding to the 0.7mm, the pad diameter depends on the inside hole diameter.
Three, PCB welding disk reliability design key points:
1. symmetry, in order to ensure the balance of the surface tension of the molten solder, the welded plates at both ends must be symmetrical.
2. welding disc spacing, too large or too small plate spacing will cause welding defects, so to ensure that the end of the end of the element or pin and weld plate is appropriate.
3. the remaining dimensions of the weld plate, the remaining size of the end or pin of the element, must ensure that the solder joint can form a meniscus.
4. the width of the weld plate should be basically the same as the width of the end or pin of the element.
The correct PCB pad design, if there is a slight skew in the patch processing, can be corrected due to the effect of molten solder surface tension during reflow soldering. If the design of PCB pad is incorrect, even if the placement is very accurate, the location deviation and suspension bridge will easily appear after reflow. Therefore, the design of PCB pad should be paid attention to when designing PCB.