Thermal-mechanical stress and fatigue failure analysis of a PBGA

One of the main package reliability limitations of Plastic Ball Grid Array (PBGA) is the thermal fatigue failure of the packaging materials. This paper uses finite element modeling to analyze the thermal-mechanical stress and fatigue failure of Epoxy Molding Compound (EMC) in a PBGA induced in the thermal loading. The encapsulating EMC is modeled by using a process and temperature dependent viscoelastic equation. The solder joints are considered to be temperature dependent elastic-plastic and rate dependent creep behavior. Based on the simulation results, the process-induced residual stress and the thermal stress during thermal cycling are analyzed and investigated. The results show that the stress level in the EMC is not very high, but under thermal cycling condition, fatigue cracking may be initiated.