Interfacial delamination and reliability design of exposed pad packages

Abstract

Interfacial delamination between molding compound (MC) and die pad interface is the most crucial failure mechanism of exposed pad package under reliability testing due to high interfacial stress and weak adhesion strength. A combined interfacial adhesion characterization, JEDEC Moisture Sensitivity Level 3 and 3X IR reflows qualification and testing, finite element analysis as well as finite element modeling-based DOE have been developed for interfacial delamination reliability in this paper. Firstly, button shear tests are conducted to measure interfacial adhesion strength between MC and die pad at room temperature 25°C, molding temperature 175°C and reflow temperature 260°C, respectively. Secondly, QFN packages with bare copper die pad are subjected to JEDEC-MSL Level 3 qualification and testing to study interfacial delamination reliability. Thirdly, finite element modeling is carried out to study the interfacial stresses at MC/die pad interface of QFN package at reflow temperature 260°C, failure criteria based on the failure factor F for exposed pad packages are established. Then, DOE analysis of a 5-parameter, 2-levels matrix based on finite element modeling is carried out to investigate the effect of package design and material property on interfacial delamination reliability. Lastly, reliability design guidelines for exposed pad package are brought forward to improve the interfacial reliability.