Hygrothermal Failures From Small Defects in Lead-Free Solder Reflowed Electronic Packages

Steam-driven delamination failure is a main failure mode in electronics packages during solder reflow. Steam pressures built up within interfaces in packages are sensitive functions of the reflow temperature. The switch to lead-free soldering will raise re-flow temperature by more than 20degC and double the equilibrium saturated steam pressure within defects in the package. The effects of saturated steam driven interfacial failure was analyzed using finite element in this study. Analyses revealed that packages which are thin and made using high thermal conductivity materials are at higher risk of failure than conventional packages made using standard materials. This suggests that electronics made with thick and inexpensive encapsulants are less prone to failure when switched to lead-free solder. Portable and mobile electronics which have low profiles and are made of high thermal conductive encapsulants are at higher risk when switched to lead-free solder reflow. Moreover, the study found that the critical temperature for failure is dependent on the defect size in the package. Reduction of initial defect size can reduce failures in high risk packages in lead-free solder reflow.