Flip-chip plastic ball grid array (FC-PBGA) packages are widely used in high performance components. However, its die back is normally under tensile stress at low temperatures. This paper presents a probabilistic mechanics approach to predict the die failure rate in the FC-PBGA qualification process. The methodology consists of three parts:

1. die strength test using four-point bending (4PB) method;
2. the radius of curvature (ROC) measurement of the assembled FC-PBGA at room temperature;
3. Finite element method (FEM) stress analysis.