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In this paper, a systematic underfill selection approach has been presented to characterize and identify favorable underfill encapsulants for 21 times 21 mm2 flip chip ball grid array (FCBGA) package with 150 mum interconnect pitch. A total of six evaluation factors of equal ranking weightage were considered in this underfill selection approach. Based on the approach adopted, we have selected the best underfill material suitable for 15 times 15 mm2 FCBGA packages. The target property ranges for underfill materials proposed by the IBM are further being refined. Now, a wider choice of underfill material was found to be applicable for 15 times 15 mm2 FCBGA packages. The new approach has helped to widen the selection criteria for underfill material used in 15 times 15 mm2 FCBGA packages. These findings will assist researchers in having a wider option in underfill selection for future FCBGA packages, which are more challenging.