Quote:
Originally Posted by drbobwoolery
Anodizing aluminum for insulation requires PURE aluminum. This is particularly true of thin layers with parts bolted to them. Alloys produce unpredictable coatings both softer and more conductive than desired. Go over those MOSFET tabs with a whetstone to chamfer the edges and corners. You are probably better off with through holes, insulating sleeves, machine bolts and nuts than tapping holes and expecting the anodizing to insulate the threads. Last go-round on anodizing for insulation was microvolt level EEG signals.
Talk to your anodizing shop BEfore fabricating the parts. ask me how I know
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Good tips for increasing the contact area for a FET.
And good points about the threads! I was assuming that only the flat surfaces would need insulating and that the MOSFETs would be larger-cased version, like TO-247 and TO-264, where the screw (or clamp) never touches anything electrically hot. I agree, counting on the anodizing to hold up to the extreme forces on localized parts of the threads is not a good idea.
Talking to whomever is plating your parts is a very good idea!
I've had very good luck with Type III coating of 6061-T6 alloy with spring-clamped down TO-264 MOSFETs...but YMMV. I spec'd 0.5mil penetration and 0.5mil surface. I only had a few microamps of leakage at over 100VDC applied between a sanded bare spot and an anodized spot on the heat sink.