Abstract
FC-BGA packages that have been used for high performance servers and communication systems, are exposed to mechanical stress during several tests such as In-Circuit Test (ICT), after mounted on a printed circuit board (PCB). Because fast bending load acts on PCB during ICT, high stress is generated in the solder joints of FC-BGA. Therefore, it is important to clarify the solder joint strength under this fast bending condition in order to improve reliability of solder joints. In this paper, fast four-point bending tests of BGA packages mounted on test substrates were performed, in order to develop the evaluation method of BGA solder joint strength corresponding to the mechanical load. Effect of hold time after package mount, loading rate and land plating conditions for solder joints were investigated by the fast four-point bending tests. It was found that a crack propagates in the intermetallic layer of Ni/Sn, and a lot of "Kirkendall Void" was observed in this layer. Furthermore, it was also found that the strength of Pb free solder is higher than that of Sn-Pb eutectic solder.
