Mosfet Mounting - Doos it need the Nylon Tophat Washer?

[bcmatt]

It looks like I had something die on another of my VVR Circuits. This time it's the simpler cathode biased VVR are on my Liverpool. I have the MOSFET mounted under the preamp board, and here I am 13 years later, replacing it. It is quite the endeavour trying to get it all screwed down with all the layers and already electrically wired in. It's surprisingly going alot better than expected... EXCEPT.... I just can't seem to get that little Nylon top-hat insulating washer in it's hole with the screw that I am mounting from outside the chassis through a heatsink. I have to prop the amp up on one end so that I can have a small screw driver holding that screw in. The Mosfet is actually on the screw on the inside of the chassis, but after about 40 attempts at getting that Nylon washer on the screw and settles into the hole on the MOSFET, I am starting to wonder how necessary that little pice of plastic is. It sure loves to fly all over the place and get lost in the amp, or somewhere across the room. I understand it is to prevent the screw and nut from touching the MOSFET, but is the black part of the MOSFET even conductive? Is it too risky to let the metal nut touch it?
I've already had to unsolder about a quarter of the preamp eyelet board to lift it enough to work underneath. I really don't want to have to remove it completely... I could get that nut in there fine with my plyers, but that little nylon washer is a real B*****.

[Ten Over]

I understand it is to prevent the screw and nut from touching the MOSFET, but is the black part of the MOSFET even conductive? Is it too risky to let the metal nut touch it?

Which MOSFET is it and what package number?

With the appropriate package, I just bolt them on without a shoulder washer.

[FUCHSAUDIO]

You may want to find some teflon insulators. The quartz wafers sometimes will arc through with 400 or 500 volts on the tab of the device.
You can also use a small amount of grease and stack two quartz insulators, but I'm always afraid of losing thermal coupling.

[bcmatt]

It's the
IRFPE50PBF
Would the package number be 908K SD ?

20220902_144927.jpg

This is it here:
https://canada.newark.com/vishay/irfpe5 ... derack-GLB

[bcmatt]

You may want to find some teflon insulators. The quartz wafers sometimes will arc through with 400 or 500 volts on the tab of the device.
You can also use a small amount of grease and stack two quartz insulators, but I'm always afraid of losing thermal coupling.

YOu mean for underneath the Mosfet? I had one of those clear Mica(?) ones on the last Mosfet. I got some Silicone ones this time. I also added some thermal grease between the Heatsink and the chassis (on the outside of the amp chassis-the mosfet is on the inside.

20220902_150353.jpg

[sluckey]

Put a dab of heat sink grease on the shoulder washer then put it in the hole of the MOSFET. Should stay in place.

[Ten Over]

Would the package number be 908K SD ?

The package number is TO-247AC. That package doesn't need a shoulder washer.

[bcmatt]

Put a dab of heat sink grease on the shoulder washer then put it in the hole of the MOSFET. Should stay in place.

Ooh! That's a neat idea!

[bcmatt]

Would the package number be 908K SD ?

The package number is TO-247AC. That package doesn't need a shoulder washer.

Sweet! Thanks!
For a minute I thought you just knew from looking at it and have every package number memorized... then I realized that it was in the datasheet.

[Ten Over]

Sweet! Thanks!
For a minute I thought you just knew from looking at it and have every package number memorized... then I realized that it was in the datasheet.

I recognized the package from the picture because I have IRFPF40 with the same package, but I didn't have the number memorized.