Evaluation of Fatigue Strength for Solder Joints on NSMD Pads in Electronic Packages

Abstract

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 fracture 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 that this difference in behavior causes the life span of NSMD joints to be longer than that of SMD. In addition, we found that the relationship between the strain and life in NSMD joints is different from that in SMD, but the life of a package with NSMD pads can be predicted by relating the strain in the solder bumps, analyzed using a finite element method, to life span data from mechanical tests.