Design Improvements for Selective Soldering Assemblies

Soldering requirements for PCB assembly have become ever more critical. The automotive industry tends to eliminate repair of soldering defects, which makes it even more important to understand the soldering process and material characteristics in order to avoid excessive waste and costs. Many designs have their roots in wave soldering and defects can be dramatically reduced when some simple improvements are made to enhance compatibility with selective soldering applications. Many defects can be eliminated in the design phase of the assemblies when specific rules for a robust selective soldering process are applied. This includes material selection as well as board design-related properties. This paper details methods of defect prevention through the application of design rules that are made for selective soldering processes using different methods of soldering. These rules includes recommendations for handling the board (placement accuracy, warpage, etc.), dimensions of pads, distances to surrounding SMDs or other components, improving heat transfer to the board by designing special via holes or modified pad structure, and more. The rules are identical for leaded or lead-free applications, although lead-free is more difficult due to the alloy’s higher melting point, increased copper leaching, solder contamination, and the greater difficulty in achieving sufficient hole fill.

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