Hot Solder Dip and Minimizing Thermal Gradients

The semiconductor industry’s move to pure-tin finishes is creating a dilemma for the high-reliability community. Most military and aerospace companies forbid the use of pure-tin because of the risk of tin whiskers. To resolve this dilemma, hot solder dip is being implemented to convert components to alternative finishes. However, poorly designed solder dip temperature profiles can induce severe thermal gradients within components, which can cause acute and/or latent defects. This paper addresses the thermodynamic aspects of the solder dip process and provides solutions for minimizing these thermal gradients. The temperature distribution in a component was modeled using finite element analysis during three different solder dip processes. It was determined that differential temperatures were minimized when profiles with gradual preheat and gradual cool down were utilized. In addition, the model was verified by experimental results, which demonstrated a good correlation between simulated and actual measurements.