The rapid growth of high-frequency wireless communication demands high-performance packaging structures at low cost. A flip-chip interconnect is one of the most promising technologies owing to its low parasitic effect and high performance at high frequencies. In this study, the in-house fabricated In0.6Ga0.4As metamorphic high electron mobility transistor (mHEMT) device was flip-chip-assembled using a commercially available low-cost organic substrate. The packaged device with the optimal flip-chip structure exhibited almost similar DC and RF results to the bare die. An exopy-based underfill was applied to the improvement of reliability with almost no degradation of the electrical characteristics. Measurement results revealed that the proposed packaging structure maintained a low minimum noise figure of 3 dB with 6 dB associated gain at 62 GHz. Such a superior performance after flip-chip packaging demonstrates the feasibility of the proposed low-cost organic substrate for commercial highfrequency applications up to the W-band.