Process Challenges for Selective Soldering: Examining parameters for optimal processing

Selective soldering is now an extremely popular methodology for joining through-hole components to PCBs. After its inception in the 1990s, it has established itself as a mainstay production technique for printed circuit board manufacture in both hand-load machines and in-line conveyorized systems. Challenges in selective soldering generally can be attributed to either process requirements such as process speed or complexity of design requiring changes in soldering parameters to achieve good quality. This paper analyses the key process steps and parameters to achieve an optimal selective soldering process. Typical steps in a selective soldering process are fluxing, preheating and finally soldering. There are many variables and different technologies that can be employed in each of these processes that build into a complete soldering process. By analyzing the variables, technologies and challenging factors in selective soldering, this paper will present a methodological consideration on how to minimize errors and increase soldering quality. Selective soldering has now reached a stage of maturity where it can be considered its own processing technology distinct from but still bearing similarly to wave soldering. As such, PCBs should be designed with this processing technology in mind. Designation of through-hole areas late into design can lead to the implementation of difficult-to-achieve selective soldering. This can result from closeness to surface mount components or cycle time pressures due to lack of understanding of the selective soldering method. A full consideration of PCB design, component choice and manufacturing steps is essential for efficient and optimal selective soldering of through-hole components.