Amp 7 FET mounting question

[more10]

The nylon spacers are 9.6 mm thick. I guess these are for mounting the board.
The Silica Insulators are 1.9 mm thick.
The FETs are 5.0 mm thick.
Insulators and FETS are together 6.9 mm, 2.7 mm shorter than the spacers.

The nuts are 2.4 mm thick. Should a nut be used between the insulater and the FET to tighen the insulater firmly to the board? Or should I put a nut between the board and the insulator? I guess 0.3 mm is ok since the board is flexible, and the solderings also takes some space. If one should use the nuts for this purpose, there are 4 of them missing. Or are the spacers 2.7 mm too long?

The screws are 12.4 mm. The board is 1.7 mm. The washers are 0.7 mm. Washer + board + nut + fet + insulator = 1.7 + 0.7 + 2.4 + 5.0 + 1.9 = 11.7 mm. This leaves 0.7 mm for whatever the board is to be mounted on. Too less I guess.

[krilli]

Hmm!
I think you want direct contact between board and insulator, and insulator and FET, to get the heat out of the FET. If that makes sense, I think you design the rest around that - which would make the spacers-2.7-mm-too-long theory most likely correct. IMO.

[V-bro]

I placed the fets flat on the board myself to keep the wire lengths as short as possible and used this as the only mounting of the whole board. The fets are in a place where most weight is and the board is mounted steady enough on those four bolts for my purpose....

------X-max. can be several meters on any driver, too bad it can be done only once...------

[more10]

I rather like the idea of using insulators between the board and the fets. Not that I am going to use it for 1kW output now, but you never know.

But the insulators are too wide and long, they will sit on soldering points of the litz wire. I guess I will have to cut them in a mill. I also need to cut the spacers to 6.9 mm, with 0.001 mm accuracy. I guess I will be overdoing it :-)

And I will use the srews and the nuts for something else.