Electronics > Beginners
Heatsink Isolation
09d08:
I have two rather large bare aluminum heatsinks and want to use them to cool four IGBTs . Since the IGBTs are supposed to handle rectified mains and dissipate a high amount of power I need a way of attaching them to the heatsinks which provides electrical isolation as well as good thermal performance.
I thought of silicone pads so I attached a TO-247 BJT to one of the heatsinks using one just to test it but the side of the transistor with the markings reached around 50 degrees while dissipating around 12 watts. This didn't happen when I repeated everything with thermal paste instead of the pad. The IGBTs would probably get damaged after a while if I were to use pads so I need suggestions. I've thought of partially anodizing the heatsinks but I would like to avoid that if possible.
Thanks in advance
cur8xgo:
--- Quote from: 09d08 on June 28, 2019, 10:51:13 pm ---I have two rather large bare aluminum heatsinks and want to use them to cool four IGBTs . Since the IGBTs are supposed to handle rectified mains and dissipate a high amount of power I need a way of attaching them to the heatsinks which provides electrical isolation as well as good thermal performance.
I thought of silicone pads so I attached a TO-247 BJT to one of the heatsinks using one just to test it but the side of the transistor with the markings reached around 50 degrees while dissipating around 12 watts. This didn't happen when I repeated everything with thermal paste instead of the pad. The IGBTs would probably get damaged after a while if I were to use pads so I need suggestions. I've thought of partially anodizing the heatsinks but I would like to avoid that if possible.
Thanks in advance
--- End quote ---
just in case have you run the numbers on isolating thermal solutions to make sure that makes sense? Off hand I thought the performance hit of isolated thermal pads was not bad at all
wraper:
Silicone pads are very different, thermal conductivity may differ by an order of magnitude. In any case, mica (+ thermal paste) or ceramic insulator should provide better performance.
Ian.M:
Worst case: if you are really pushing the limits of what power the semiconductor package can handle, you may need a thick copper heat spreader directly under the semiconductor package to increase the area of mica (or other insulator) the heat is transferred through, to decrease its thermal resistance.
digsys:
I ran extensive tests ages ago for similar reasons. As others say, there is a HUGE difference between the types etc - These notes may be of help -
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