Abstract: This paper develops 3-D shape predicting model of BGA through minimal energy principle, analyses stress distributing characteristic of different shape solder joint under thermal cycle.Based on analysis result, assembly technology is optimized of three kind of BGA with different lead center distance.Validated by environment screen testing, technical dising reliability is examined.The result indicates that, solder joint inner fatigue failure phenomenon is consistent with theory prediction under thermal stress, finite element analysis is an effective in solder joint reliability research.