Temperature Cycling Reliability Of Plastic Packages Ball Grid Array Study

Zhang Liji (Material Physics and Chemistry) Directed by Professor Xie XiaomingThis paper is intended to solve problems for those who are designing, using PBGAs. Failure mechanism, as well as cycles to failure of two groups of PBGA samples ( with / without underfill) for thermal cycling conditions in the range of -40 ~125 , were presented. The experiment shows that solder ball in the samples without underfill cracked after 500 times cycle, no crack was found in the underfilled samples even after 2700 cycles. However, the die attach layer delaminated after 500 cycles and PCB cracked in the underfilled samples after long time cycling. C-SAM is employed to investigate the delamination in the underfilled samples. Highly concentrated stress-strain induced by the CTE mismatch between the BGA component and the PCB board, coarsened grain and two kinds of intermetallic compounds (NiSn / NiSns) which formed during reflow and thermal cycle and their impact on the reliability of solder joints are discussed in this paper. The initiation of the crack and its propagation are also presented in this paper. By means of dye penetrant test, the author reveals the distribution of microcrack in the solder ball array. In addition, this paper includes results of simulation, which further verified its conclusions.