Investigation of Moisture Sensitivity Related Failure Mechanism of Quad Flat No-Lead (QFN) Packages

Abstract

Interfacial delamination is a long existing problem in the moisture preconditioning process and reflow. The failure is caused by the competition between interfacial strength and hygrothermal stress. Many simulations based on the finite element model have been applied to study the failure mechanism of this phenomenon. However, the difficulty in obtaining material properties of mini-size packages, the lack of experiment investigation of interfacial adhesion and the less-understood moisture analysis will always bring many challenges to simulations. To avoid the above issues, dummy QFN packages were fabricated as the test vehicle for the investigation of the moisture related failure. The major advantage of using dummy packages is that all material properties could be traced and all geometric parameters could be determined without ambiguities. With everything under control, failure modes could be generated within expectation. This would provide a good experiment comparison for future finite element analysis. In this study, several experiment procedures were implemented to establish the relationship between material selection and moisture sensitivity level (MSL) test performance. They were package fabrication, mechanical tests for interfacial adhesion, C-SAM and cross-section inspections. Based on the experimental results, features of the moisture related failure mechanism are presented in this paper.