An accurate assessment of interconnect fatigue life through power cycling

Abstract

A more realistic and accurate prediction of fatigue life in the second level solder interconnect was conducted through power cycling. Fatigue is the dominating failure mechanism of solder interconnects and enhancement of its life is one of the major concerns for package designers and users. Conventionally, fatigue life is obtained empirically through accelerated thermal cycling (ATC) with hundreds of parts. To reduce development time and cost, virtual qualification attempts are made using numerical simulation tools, such as finite element analysis. Modeling of life prediction has been conducted for ATC condition, which assumes uniform temperature throughout the assembly. In reality, an assembly is subjected to Power Cycling i.e. non-uniform temperature with chip as the only source of heat generation. This non-uniform temperature and different coefficient of thermal expansion (CTE) of each component makes the package deform differently than the case of uniform temperature. In this work, a proper power cycling (PC) analysis scheme was proposed and conducted to predict solder fatigue life for a flip chip plastic ball grid array (FC-PBGA) package. Numerical simulations were performed by combination of computational fluid dynamics (CFD) and finite element analyses (FEA). CFD analysis was used to extract transient heat transfer coefficients while subsequent thermal and structural FEA was performed with heat generation and heat transfer coefficient from CFD as thermal boundary condition. It was found that for organic packages Power Cycling was more severe condition and caused solder interconnects to fail earlier than ATC.