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 [1-5]. 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. This 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 0 degrees C and 100 degrees C. 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.