Potential failure sites in a flip-chip package with and without underfill

In this study, the effect of underfill on the level of stress concentration s is investigated and possible failure sites are identified by using a glob al/local finite element approach. The global elements capture the exact sin gular behavior of the stresses near the geometric and material discontinuit ies. Application of the strain energy density criterion indicates the possi ble failure sites and how they shift due to the presence of underfill.