Effects of bump metallurgies, underfill material and its cure process on package warpage

Excessive warpage in flip-chip packages would raise concerns of process stability and reliability as well as customer acceptance concerns, making it critical to understand the thermal-mechanical mechanism of package warpage. In this paper, we report our comprehensive study focusing on the effects of the bump metallurgies, underfill material and its cure process on the package warpage. The warpage of the units with the Pb-free bump joints and its dependence on the underfill and its process were found significantly different from the units with other bump joints. The underline mechanism of package warpage formation is discussed.