The flip-chip bump interconnection for millimeter-wave GaAs MMIC

The flip-chip bump interconnection structure has become popular for microwave and millimeter-wave package applications. The structure is expected to provide higher performance and a low cost packaging method. This paper presents the results of an evaluation of flip-chip assembled RF devices. A co-planar line type GaAs MMIC (monolithic microwave IC) was mounted on an Al₂O₃ substrate using the flip-chip bump interconnection method. The electrical performance (S-parameter) was measured and the reliability of the interconnection was tested. The DC characteristics of a 30 GHz band and a 60 GHz band LNA (low noise amplifier) were the same between before and after mounting and the RF performance of the assembled MMIC was the same as the bare chip without packaging; however, the influence of underfilling was confirmed. When epoxy resin was injected into the gap between the bare chip and the substrate, the frequency band of the MMIC shifted to the low side. The reliability of the bump interconnection was excellent. The interconnection resistance did not change in a temperature cycle (-55°C to +125°C, 1000 cycles) test