Residual stresses in plastic IC packages during surface mounting process preceded by moisture soaking test

Abstract

In the present study, moisture and temperature distributions and residual stresses in plastic encapsulated integrated circuit (IC) packages are evaluated in order to assess product reliability. Finite element analyses are utilized to calculate hygro-thermally induced deformations and stresses in plastic IC packages during the surface mounting process preceded by the moisture soaking test. Residual stresses developed in thin lead-on-chip (LOG) thin small outline packages (TSOP) during the reflow soldering process preceded by the 168 h 85/spl deg/C/85% RH moisture soaking test have been studied. Numerical results showed that substantially high positive stresses /spl sigma//sub z/ arose in the silicon chip and the leadframe while negative stresses were observed in the encapsulant below the chip when TSOP packages were exposed to the reflow soldering process. Such opposite stress development in the silicon chip and encapsulant below the chip may result in the delamination and popcorn crack. The results also showed that the magnitude of residual stresses in IC packages depended not only on the magnitude of loading but also on the loading history due to the hygro-thermo-viscoelastic behavior of plastic mold compound materials.