Evaluation of Fatigue Strength for Solder Joints on NSMD Pads in Electronic Packages(<Special Issue>Thermal and Mechanical Reliability of Electronic Device and Mechanical Engineering)

We developed a method for evaluating the life of solder joints for an electronic package with non-solder-mask-defined (NSMD) solder pads. Generally, the thermal-cycling life of a package with NSMD pads is longer than that of a package with solder-mask-defined (SMD) pads, which are usually used in packages. However, the fractural mechanism of joints on NSMD pads has not been sufficiently investigated. Therefore, we conducted mechanical fatigue tests on the joints of NSMD pads. We found that the crack propagation behavior in NSMD joints is different from that in SMD, and found that the difference of that behavior causes the life span of NSMD joints to be longer than that of SMD. In addition, we found that the life of a package with NSMD pads can be predicted from the strain in the solder bumps that is analyzed by using a finite element method, which compares the relationships between the strain and life span in the mechanical test data, although the relationship between the strain and life in NSMD joints is different from that in SMD.