Effects of Element Partition on the Fatigue Life Predictions of Lead-Free Solder Joints

On the complicated manufacturing processes of the high- density packages, the reliability of solder bumped IC chip on substrate and/or PCB has been confirmed by many researchers through thermal cycling tests, mechanical tests and computational modeling. In this study, the high-density package. 256-pin plastic ball grid array (PBGA) on printed circuit board (PCB) subjected to temperature cycling with the effects of element spacing ratio on the thermal- fatigue life of lead-free (95.5Sn-3.9Ag-0.6Cu) solder joints are investigated by using the validated finite-element analyses. Tins research studies the determination of thermal- fatigue life, creep responses and creep strain energy density per cycle with the various spacing ratio (-1, -5. -10, and -15) of the meshed lead-free solder joint for a range of cycling temperatures. Temperature loads are applied to the models that represent the cycling environment of chamber. After starting at room temperature, the model is subject of 5 cycles consisting of 10-minute ramps and 10- minute holds at each of 10 degC and 100 degC. Five cycles are executed in order to confirm the stabilization of the creep responses. For all the cases, the lead-free solder is assumed to obey the Garofalo- Arrhenius creep constitutive law.