Effects of Constraints on Solder Joint Reliability of Electronic Packages

IC package modelling and simulation has been cornerstones in electronic package reliability for more than three decades. Although there is rich literature available on various modelling approaches and experimental data on package failure during thermal cycling tests, the understanding of system level effects such as bolt location on solder joint reliability is limited. For this analysis, thermal cycle tests on 256 pin 17mm × 17mm BGA and 2512 chip resistor were conducted at (1) -40oC to +125oC, and (2) +25oC to +125oC. Test results were compared with Finite Element Analysis (FEA) results. A total of ten samples of each package type were mounted onto a 1.6 mm thick printed circuit board (PCB) coupon. Four coupons were evaluated per condition with SAC305 solder. To understand the effects of constraints, the test coupons were bolted to an aluminum fixture. Three structural conditions were considered for the test, namely, (1) Free Warp, (2) Semi-Constrained, & (3) Fully Constrained. Moreover, four packages of each type were mirrored to better understand the solder joint reliability due to mirroring packages. All the packages were daisy chained and electrical resistance of the packages were monitored. A tenfold increase in resistance for five consecutive cycles was considered a complete failure. The cycles to failure were analyzed using a 2-parameter Weibull distribution for characteristic life.