Numerical-experimental analysis of combined bulk and interface fracture in a leadless package

In the 1960´s surface mounted technology was developed. This technology as an alternative for through-hole technology made it easier to place components on both sides of the board by soldering, decreased package sizes, simplified assembly and reduced costs. Furthermore, higher mechanical robustness was obtained. In this paper, a numerical-experimental study is performed to investigate the robustness of two surface mounted devices (SMDs) under EN 60068-2-21:1999 Test Ue1 `Robustness of Terminations and Integral Mounting Devices: Substrate Bending Test´ as described in [1]. The relevant failure modes, body cracks between the pads and delamination of the leadframe/plastic interface is identified by experiments. Numerical analysis is carried out to explain the occurring failure and to explain differences between the two SMDs under investigation. First, straight-forward stress analysis gives insight in the stress distribution of the plastic body. As this analysis cannot explain the occurring delamination cohesive zone modeling is used to investigate the delamination sensitivity of the leadframe/EMC interfaces. These results give insight in the failure mechanism but do not explain the differences between the two SMDs. Therefore, a third numerical analysis with combined bulk and interface fracture is performed. This analysis is capable to explain the failure mechanism and the differences between the two SMD packages. This work shows that for this specific example more advanced numerical analysis is needed to explain the actual failure behavior of semiconductor packages.