eblc1388 said:
Bad bad bad advice. Never heard anyone done that.
Don't ever rely on the anodized coating as the insulation. Nine times out of ten the insulation breakdown if sufficient pressure is applied to the fastening hardware.
My original comment was written late, and I was too brief. Let me clarify what I meant, which was to emphasize that the surface of anodized aluminum is non-conductive, and that property can be used to advantage. In fact, I got the idea for mounting mosfets in my application from examining some commercial power supplies used in laboratory equipment. Obviously, one needs to be careful about applying excessive pressure at point contacts and edges.
My application was a high-current, 12V supply. The mosfets were attached directly to 0.025 inch copper sheet, which in turn was bonded to the anodized heatsink with Loctite 383 adhesive. No additional insulation was used, except in areas where high pressure or point was anticipated. That adhesive is sold as a thermally conductive, electrically non-conductive, one-part material. It relies on surface activation to cure.
I have attached some photographs of the power module portion of the controller. On the left side of the assembly, where the 0.25 inch diameter screws are for connection to the cables, I used a small piece of mica under the copper and beneath the terminal block. It looks a bit like a shadow in the photos. The remainder of the copper is attached directly to the heatsink with adhesive. No other screws were used, except for those that were used to stabilize the conductors next to the terminal block.
This supply was not fully enclosed. It was simply attached by the four standoffs seen in the pictures to the winch it was used to control. It has been used for about 8 years on weekends outdoors and shows tarnish and corrosion from that service. The solder joints are really not as bad as they appear, but I would caution people who haven't tried it that soldering to heavy copper sheet requires a much larger iron than one would use for most other electronic work. John