In the spirit of continuing to make minor hardware changes that don't seem too hard, I opened up my sBitx DE today. First I removed the big heatsink on the back of the case and removed the mica washers the electrically (and thermally?) insulate the finals from the heatsink. In their place I inserted Al Nitride insulators that I heard about in the group here. The Al Nitride washers are .6 mm thin, but still about twice as thick as the original mica.

The bar providing some clamping pressure to hold the FETs against the heat sink had three screws in it. I thought it seemed unlikely I get tighten them all down equally with the clamping bar wanting to bow, so I shortened it leaving only a single screw between the two FETs. I believe it provides plenty of pressure. I did use a bit of thermal paste from a computer fan installation, both on the new washers and the clamping bar.

No temperature graphs or measurements but here's a picture of the clamping bar, with the Al Nitride washers barely visible.

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Mike - kb2ml

Hi Mike,

My Al Nitride insulators should be here tomorrow and I will do the same thing starting with my DE then the V2, it's got to be better right? I'm thinking I'm going to to try to attach that little buck converter to the heat sink also, ( probably use thermal glue), it gets mighty hot. Thanks for the picture.

Joel
N6ALT

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Thanks, guys, my insulators arrived, but I managed to leave the thermal paste two states away.… more arriving Wednesday. ?

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Where does one find?Al Nitride washers?

I'm thinking of using Artic Silver that was used on computer CPU to fan heat syncs.

I got mine from here,

Joel
N6ALT

On Thu, Aug 3, 2023 at 02:20 AM, kc5kwz wrote:

I'm thinking of using Artic Silver that was used on computer CPU to fan heat syncs.

Before you go with Arctic Silver, it may be good to review the information for the product.
Some silver bearing thermal compounds are electrically conductive.

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I haven’t put an ohmmeter on it but a simple solution is to wipe off the excess off edges of the aluminum nitride insulator, so that the heat sink compound isnt bridging across that much. ?A qtip would work. ? Ordinary silicone type “grease” can seal the edges to reduce any excess of water if that’s a concern. ?