Effect of Voids on the Thermal Fatigue Reliability of PBGA Solder Joints through Submodel Technology

Abstract

Voids in ball grid array (BGA) solder joints have been considered as a main problem in lead-free soldering process. Compared with tin-lead solder, worse wetting capability of lead-free solder aggravates the formation of voids. Along with the wide application of BGA packages and the transition of lead-free soldering, the effect of voids on the reliability of BGA solder joints has been concerned. In this paper, a 3D strip model of lead-free BGA mounted at PCB with coarser mesh is developed and analyzed under accelerated temperature cycling condition(-25 °C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">~</sub> 100 °C) firstly. According to the principle of strain failure, the critical solder joint is identified. Then, five kinds of voids are designed in critical solder joint and the submodels with refined meshes are established and analyzed respectively. The results show that the effect of voids on thermal fatigue reliability of solder joints has a double characteristic. When the void located at the initial maximum stress region, the accumulation of creep strain is aggraved, this kind of voids have negative effect on the thermal fatigue reliability of solder joints. In case of voids at the center of solder joints, even if the voids areas is 25% of solder joint section, the creep strain still is smaller than the solder joints without void. At last, in case of voids away from the initial maximum strain region, the effevt of void on the thermal fatigue reliability of solder joints is no obvious.