Board Level Thermal Cycle Reliability of BGA for a New Type of Pad Structure with OSP Surface Finish

In tins paper, the effect of a new type of pad structure in which the copper pad is half etched with OSP surface finish on board level thermal cycle reliability of BGA is evaluated comparing conventional flat pad with ENIG surface finish. The test data is presented, including resulting Weibull analyses indicating characteristic life. The solder joint with flat pad Ni/Au surface finish has a little longer lifetime than that with dent pad OSP surface finish. A three dimensional finite element analysis is also applied and confirmed the experimental result. Two failure mechanisms for dent pad structure were observed, which decrease the thermal fatigue lifetime of the solder joints.