Microwave Module Thermal Considerations for Future Higher Powered MMICs in Phased Array Radars

Advances in RF power generation capability at the device level will soon force a change in phased array radar thermal management. The efficiency in converting electrical power into transmitted power is not increasing as rapidly which means that higher RF power generating devices also dissipate more heat. Removing this waste heat creates several thermal challenges including the topic of this paper, namely thermal issues at the die and package level. A comparison of the temperature differences between the junction and ambient shows that even at present heat dissipation levels, the temperature difference at the integrated circuit level is already a significant fraction of the total rise. Further increases in the device level heat dissipation will increase the temperature difference at the integrated circuit level to nearly unmanageable levels unless device-level design changes are made. Maintaining acceptable junction temperature levels will require lower device mounting surface temperatures or some thermally better method of die attachment and heat removal. Dividing the thermal management of a phased array radar into two portions (integrated circuit level and everything else) reveals that while thermal improvements at the system and packaging level are useful for near-future radar designs, thermal design and management at the device and package levels are crucial.