Effect of Aging on BGA Solder Strengths Thermal Cycles for Low Temp. Hybrid Assembly

This paper presents two key aspects of reliability of ball grid array (BGA) technologies: one aspect for high-reliability and the other one for commercial applications. For high reliability, it presents the effect of isothermal aging at BGA level to address burn-in requirement for die screening per Mil standard specification. Pull and shear behavior of BGAs with tin-lead and SAC305 solder balls were characterized for a number of components before and after two burn-in conditions (125℃ and 150℃ for 240 hr). The burn-in and fresh BGAs were assembled onto PCBs and then subject to thermal cycling (TC) between –40℃ and 125℃ to determine cycles-to-failures (CTFs) for comparison. Pull and shear strength test results of tin-lead and SAC305 solder balls were presented for CABGA208, CTBGA228, and CVBGA360 with 0.8, 0.8, and 0.5 mm pitches. CTFs in Weibull plots were presented for the SnPb CABGA208 for fresh and burn-in conditions. The commercial aspect covered low temperature solder ball and solder paste for assembling of BGAs and other components. We evaluated two types of low temperature BiSn alloys with Cu/Ni or Ag additives and melting temperatures between 139˚C solidus and 174˚C liquidus. The mixed hybrid configuration utilized SAC305 BGAs using the SnBiAg alloy solder paste. The low temperature assemblies were subjected to two TCs (–40℃/105℃ and 0℃/105℃). CTF results are present for CABGA208 with failure analysis by X-sectional evaluation.