Lead Free Wave Soldering: Process Optimization for Simple to Highly Complex Boards

Today’s wave soldering processes solder electronic assemblies within the large eutectic tin lead processing window. The issues surrounding the conversion to lead free assembly are multiple and varied. Logistics, cost, material selection, and equipment choices/options are some of these challenges that require planning and organization. However, at the core of lead free assembly is soldering. The iNEMI lead free wave soldering team embarked on a multitiered project that focuses specifically on two aspects: identifying the impact of critical parameters on the development of a reliable, robust lead free wave soldering process as well as determining the process that achieves the optimized soldered joint. The critical aspects of the lead free wave soldering process can be broken down into several categories which include component reliability, board reliability, flux type and specifications, alloy and alloy composition, its melting behavior, wave equipment capacity and power requirements, profile attributes and flexibility. This collaborative effort has investigated process parameter and material impact on the soldering process and joint formation. Addressed in this lead free implementation study were inspection criteria, failure definition and measurement, followed by root cause analysis and ultimately optimized process confirmation. The result of this investigation was to lay the foundation for a broader effort to characterize the reliability of through-hole joints on a test vehicle specifically designed to test the norms and practices used in tin lead wave soldering and develop new standards for lead free wave soldering. Overall, this investigation looks to bring an understanding of how critical wave soldering parameters correlate and provide the reader with the information necessary to make educated decisions in selecting materials. This study will also provide insight into the process issues that one will encounter so that a rational implementation strategy for a reliable and robust lead free wave soldering process can be achieved.