Crack monitoring and life modeling technique towards high thermal cyclic and mechanical reliability of fcBGA solder joint

High reliability at the board level is challenging for a large flip chip ball-grid-array (fcBGA) where large die and stiff substrate are used. For those BGA solder joints, the difficulty is to achieve high reliability in both thermal cycling and mechanical dynamic tests. This paper presents experimental work on an fcBGA with a die size of 25×15mm, a body size of 40×40mm and over 1700 ball count. The reliability tests include thermal cycling from -40C to 85C up to 7,500 cycles, mechanical drop at 1500G and 9-point cyclic bending test run to failure. To develop a good reliability model, the integrity of both the solder joint and substrate copper traces are monitored using in-situ resistance measurement in combination with frequent cross-sectioning and dye-and-pry (DnP) to understand the progression of cracking in the solder joints. Using Finite Element Analysis (FEA), the solder joint failure mechanism was verified and a new failure mode in mechanical reliability testing has been confirmed.