Thermal Design and Analysis of a Flip-Chip GaN-on-SiC HEMT

Gallium nitride-on-silicon carbide high electron mobility transistors (GaN-on-SiC HEMTs) are widely used for high-power and high-frequency circuit applications. Their high power density leads to high heat flux and requires efficient thermal management. For wire-bond chips, the heat is usually directed downwards. However, packaging printed circuit boards (PCBs) typically have low thermal conductivities, which poses significant challenges in heat dissipation. In this study, we propose to integrate the chip via flip-chip and dissipate heat from its top. Wire-bond and flip-chip samples are fabricated, and the corresponding thermal simulation models are built and validated with the test data. Comparison among different samples shows that the thermal performance of the flip-chip sample is good and significantly better than that of the wire-bond sample with a common packaging PCB (FR4-based). Radio frequency (RF) tests are conducted using a vector network analyzer, and the results are in consistency with the thermal analysis. This study demonstrates the effectiveness of the proposed thermal design for GaN-on-SiC HEMT and can facilitate our next-step development of heterogeneous integration of multiple chips.