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Old 03-03-2010, 08:23 PM   #3053 (permalink)
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Originally Posted by ElectricZX2 View Post
Hard anodizing the heat spreader seems like a great idea for electrical isolation. The only thing I would worry about would be the degradation of thermal conductivity. I get what you're saying about the layer being very thin Camlight, but it might be nice to have some numbers. Type III anodizing is used in industry to provide a thermal barrier in addition to an electrical barrier in some applications (which makes sense since thermal and electrical conductivity are generally directly correlated in metals). For example, part of the reason pistons in ICE engines are hard anodized is to reduce the thermal conductivity of the piston and therefore mitigate thermal expansion allowing for tighter tolerances....
With the heat sinks used in my 400W electronic loads, using four TO-264 MOSFETs, the sink-to-ambient thermal resistance (of my heat sink and fan combo) was increased approximately 0.04C/W over the bare aluminum number. This is at least 10x better than any other material that can be used.

Don't underestimate the power of being thin.
Type III anodizing, while being a VERY efficient insulator (electrically and thermally) is so thin when applied to a heat sink that it really doesn't matter. Yea, if you increase the thickness you can probably block a blowtorch, but when thin, it allows enough heat to flow vs. its dielectric strength (ability to electricall insulate) that there's just about no other material that can match it. Certainly not any thermal pad, mica, kapton tape, etc. They might be able to if they were 1/2 mil thick...but they're not.

Do you know how thick the Type III lining was for those ICE piston? I suspect it's more for reduced friction and wear-resistance than heat-flow blocking...unless a very thick layer was applied.
John M.
CamLight Systems

Last edited by CamLight; 03-03-2010 at 08:33 PM..
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