Influence of the duration of elevated temperatures caused by laser micro welding on the thermal damage in printed circuit boards

Aging, growth of whisker, and thermal damage are the major issues when soldering electronic components. The authors present investigations to determine the influence of process times on the threshold temperature leading to thermal damage in epoxy-based printed circuit boards (PCBs). Experimentally verified numerical modeling was used to determine the temperature distribution at the interface of copper and the epoxy resin. The results show that the threshold temperature significantly increases with decreasing process times. With interaction times shorter than 5 ms, the threshold temperatures are found to be 900 K higher than the ones specified for longer heating times according to the data sheet for PCBs with FR4 epoxy resin.