Generally, underfill material is adopted for encapsulation of flip chip package. And, the role of the underfill materials has become important day by day due to variant requirements for higher reliability of flip chip package. Also lower warpage gives higher mount-ability of the flip chip package and the small changes in the warpage of the package during the thermal cycle mitigate the stress working at the bump/substrate interface and bump/chip interface. Therefore, controlling the warpage of the flip chip package becomes very important problem for enhancing the performance of the package, i.e., the higher mount-ability and longer interconnect life. In this study, the effect of physical properties of underfill materials and substrates on the warpage behavior and the interconnect reliability of the flip chip package is reported. It was found from the experiments that the selection of an underfill and a substrate gave the highest interconnect reliability for the bump bonds. In addition to control the warpage behavior of the package during assembly, by selecting the suitable underfill material and substrate, the flip chip package with lower warpage and higher interconnect reliability can be realized.