Strength Evaluation of Plastic Packages During Solder Reflow Process Using Stress Intensity Factors of V-Notch

A crack initiated from a V-notch corner in the molding resin, such as a corner of die pad, is one of the main causes of the failure in plastic packages. The stress intensity factors of the asymptotic solution of a corner of jointed dissimilar materials are utilized for the evaluation of a solder reflow crack in a quad flat package (QFP). First, we estimate the critical vapor pressure, which causes a crack from a corner in the molding resin, using the critical stress intensity factor of a V-notch corner. This critical factor was measured by V-notched three-point bending tests and the displacement extrapolation method along with the three dimensional (3-D) finite element method (FEM). Moisture concentration in the QFP after absorption is analyzed, and vapor pressure caused by the solder reflow process is estimated. The critical moisture absorption time, which results in crack occurrence during the solder reflow process, can be predicted using this evaluation technique. Furthermore, we perform infrared solder reflow tests of the QFP for verifying the present failure evaluation technique.