Some problems shouldbe paid attention to when designing PCBA, such as PCBA assembly process design,component layout design, assembly process design, automatic production lineveneer transmission and positioning element design.

1. Automaticproduction line board transmission and positioning elements design, automaticproduction line assembly, PCB must have the ability to transmit edge andoptical positioning symbols, which is the prerequisite for production.

2.PCBA assemblyprocess design, PCBA assembly process design, that is, components on the frontand back of the PCB components layout structure. It determines the process PCBplant method and path for assembly, so it is also called process path design.

3. Component layoutdesign, namely, the position, direction and spacing design of components on theassembly surface. The layout of components depends on the welding method used.Each welding method has specific requirements on the placement position,direction and spacing of components. Therefore, this book introduces the layoutdesign requirements according to the welding process used in packaging. Itshould be pointed out that  sometimes twoor more welding processes are used for an assembly surface, such as"reflow welding 10 wave welding", for such cases, PCBA layout shouldbe designed according to the welding process used for each package.

4. Assembly processdesign, assembly process design, design for welding rty (namely, through thewelding plate, resistance welding and the matching design of stencil, solderpaste quantitative, the stability of the fixed point distribution, through thedesign of the layout, to achieve a single synchronous melting and solidification,encapsulate all welds by installing hole reasonable wiring design, achieve 75%tin penetration rate, etc., These e design goals are ultimately to improve theyield of welding.

There are manycontents of PCBA thermal design, and the specific requirements of each PCBboard content will have some differences. For example, if there is less tin inthe thermal design of the heat sink pad, we can use some methods to solve theproblem. The most common one is to increase the heat dissipation hole. So we don'thave to panic when we encounter some problems, find some professional peoplecan solve all our problems.

(1) Thermal designof heat sink pad. In the welding of heat sink elements, tin loss on the heatsink pad is encountered, which is a typical application that can be improved byheat sink design.

For the abovesituation, chip factory can adopt the method of increasing the heat capacity ofthe cooling hole to design. Connect the heat dissipation hole with the innerground layer, if the ground layer is less than 6 layers. Part of the signallayer can be isolated as a heat dissipation layer while reducing the apertureto the minimum available aperture size.

(2) thermal designof high-power grounding jack.

In some specialproduct designs, plug holes are sometimes required to be connected to multipleground/level surfaces. Because the contact time of the soldering pin and tinwave is very short, often for 2~3s, if the heat capacity of the jack isrelatively large, the temperature of the lead may not meet the requirements ofwelding, the formation of cold -welding  point.