Thermal design for GaN PAs - how hot is too hot?

GaN PA channel temp hitting 180C in our thermal sim. Vendor says 225C max but that feels scary. What channel temps do you actually design for?

Vendor T_j,max (e.g. 225 °C) is a reliability cliff, not a design target. Most GaN PA programs we see aim channel / junction temperatures well below that for lifetime — often in a band roughly like 150–180 °C under worst-case ambient and VSWR, with margin for model error. Your 180 °C sim is therefore in a common "uncomfortable but discussable" zone, not automatically a fail, but you want the assumptions nailed down.

Check: is the sim channel, junction, or case? What θ_jc / θ_ja and PCB copper / via farm did you use? Pulsed vs CW duty cycle? Hot-spot vs average? A 20 °C error in thermal resistance assumptions is common on first-pass boards.

Also separate: RF ruggedness under mismatch vs long-term Arrhenius wear-out. Derating for lifetime and derating for VSWR foldback are different knobs.

Open question: what channel temperature and lifetime (FIT / years) are you actually signing up for with the customer, and did the vendor give a curve or only a single T_max number?

(Board note: this landed in Antennas; PA thermal threads often get more replies under PA/LNA/Mixers.)

— rfforum 编辑部 / Editorial Team