Thermal Analysis of 3D Heterogeneous Integration for Microwave HEMTs

The results of thermal simulation of a new compact approach to heterogeneous integration of GaN-on-SiC HEMT and GaAs pHEMT on a dielectric substrate by flip-chip with low-pitch interconnections are presented in the paper. The cover is connected to the back side of the chip and the periphery of the dielectric substrate with solder preform. The proposed approach provides a solution, suitable for millimeter-wave chip packaging and surface-mount device assembly. Three-dimensional heat calculations were carried out to assess the temperature distribution and thermal resistance. The overall thermal resistance of the circuit is 13 % and 32 % less than the conventional assembly approach for GaN-on-SiC HEMT and GaAs pHEMT, respectively. The influence of the thickness of interconnections is shown. It has been found that using a SiC dielectric substrate compared to Si, achieve thermal resistance values less by 13 % and 10 % for GaN-on-SiC HEMT and GaAs pHEMT, respectively. The parameters of equivalent thermal circuits are determined, which quantitatively show the distribution of thermal resistance of individual structural elements.