Has anyone done this? I need to get the mounting screw height down.

I guess I'll have to try it.

mandag den 19. juni 2023 kl. 17.50.16 UTC+2 skrev John Larkin:
> Has anyone done this? I need to get the mounting screw height down.
>
> I guess I'll have to try it.

how low do you need? https://www.mcmaster.com/products/low-profile-head-socket-cap-screws/alloy-steel-ultra-low-profile-socket-head-screws/

On Monday, June 19, 2023 at 11:50:16 AM UTC-4, John Larkin wrote:
> Has anyone done this? I need to get the mounting screw height down.
>
> I guess I'll have to try it.

Countersink it for a flat head. Head should end up flush with the package, can't beat that:

https://www.homedepot.com/b/Hardware-Fasteners-Screws-Machine-Screws/Flat-Head/N-5yc1vZc27iZ1z18t94

On Mon, 19 Jun 2023 08:57:14 -0700 (PDT), Lasse Langwadt Christensen
<langwadt@fonz.dk> wrote:

>mandag den 19. juni 2023 kl. 17.50.16 UTC+2 skrev John Larkin:
>> Has anyone done this? I need to get the mounting screw height down.
>>
>> I guess I'll have to try it.
>
>how low do you need? https://www.mcmaster.com/products/low-profile-head-socket-cap-screws/alloy-steel-ultra-low-profile-socket-head-screws/

The heights are good, the prices aren't!

A regular screw and a lockwasher cost me over 0.1", and I need less.
With locktite, I can eliminate the lockwasher.

A really thin custom AlN insulator will help a bit. Isolated TO-247s
are expensive and hard to get.

I could just epoxy the fets down, but that has downsides.

On Mon, 19 Jun 2023 08:57:14 -0700 (PDT), Lasse Langwadt Christensen
<langwadt@fonz.dk> wrote:

>mandag den 19. juni 2023 kl. 17.50.16 UTC+2 skrev John Larkin:
>> Has anyone done this? I need to get the mounting screw height down.
>>
>> I guess I'll have to try it.
>
>how low do you need? https://www.mcmaster.com/products/low-profile-head-socket-cap-screws/alloy-steel-ultra-low-profile-socket-head-screws/

You are really good at parts research. Please email me.

mandag den 19. juni 2023 kl. 18.13.01 UTC+2 skrev John Larkin:
> On Mon, 19 Jun 2023 08:57:14 -0700 (PDT), Lasse Langwadt Christensen
> <lang...@fonz.dk> wrote:
>
> >mandag den 19. juni 2023 kl. 17.50.16 UTC+2 skrev John Larkin:
> >> Has anyone done this? I need to get the mounting screw height down.
> >>
> >> I guess I'll have to try it.
> >
> >how low do you need? https://www.mcmaster.com/products/low-profile-head-socket-cap-screws/alloy-steel-ultra-low-profile-socket-head-screws/
> The heights are good, the prices aren't!

yeh, but now you konw they exist and they can surely be found much cheaper, I guess you want something like #4-40, but M3 seems to be more common

https://www.ebay.co.uk/itm/284167006281
https://ogsecure.co.uk/products/m3-ultra-thin-wafer-flat-head-low-profile-screws-bolt-allen-key-stainless-steel?variant=40403358318653

mandag den 19. juni 2023 kl. 18.13.01 UTC+2 skrev John Larkin:
> On Mon, 19 Jun 2023 08:57:14 -0700 (PDT), Lasse Langwadt Christensen
> <lang...@fonz.dk> wrote:
>
> >mandag den 19. juni 2023 kl. 17.50.16 UTC+2 skrev John Larkin:
> >> Has anyone done this? I need to get the mounting screw height down.
> >>
> >> I guess I'll have to try it.
> >
> >how low do you need? https://www.mcmaster.com/products/low-profile-head-socket-cap-screws/alloy-steel-ultra-low-profile-socket-head-screws/
> The heights are good, the prices aren't!
>
> A regular screw and a lockwasher cost me over 0.1", and I need less.
> With locktite, I can eliminate the lockwasher.
>
> A really thin custom AlN insulator will help a bit. Isolated TO-247s
> are expensive and hard to get.
>
> I could just epoxy the fets down, but that has downsides.

maybe something like this? https://www.digikey.dk/da/products/detail/aavid-thermal-division-of-boyd-corporation/MAX08NG/1625322

On Mon, 19 Jun 2023 10:32:14 -0700 (PDT), Lasse Langwadt Christensen
<langwadt@fonz.dk> wrote:

>mandag den 19. juni 2023 kl. 18.13.01 UTC+2 skrev John Larkin:
>> On Mon, 19 Jun 2023 08:57:14 -0700 (PDT), Lasse Langwadt Christensen
>> <lang...@fonz.dk> wrote:
>>
>> >mandag den 19. juni 2023 kl. 17.50.16 UTC+2 skrev John Larkin:
>> >> Has anyone done this? I need to get the mounting screw height down.
>> >>
>> >> I guess I'll have to try it.
>> >
>> >how low do you need? https://www.mcmaster.com/products/low-profile-head-socket-cap-screws/alloy-steel-ultra-low-profile-socket-head-screws/
>> The heights are good, the prices aren't!
>>
>> A regular screw and a lockwasher cost me over 0.1", and I need less.
>> With locktite, I can eliminate the lockwasher.
>>
>> A really thin custom AlN insulator will help a bit. Isolated TO-247s
>> are expensive and hard to get.
>>
>> I could just epoxy the fets down, but that has downsides.
>
>maybe something like this? https://www.digikey.dk/da/products/detail/aavid-thermal-division-of-boyd-corporation/MAX08NG/1625322

I've done that

https://www.dropbox.com/s/nmyb9pz0qpma2xa/Amp.jpg?dl=0

but it adds more height. I'll have boards in a card cage on 1.6"
centers, and I'm stacking a CPU cooler/fan thing with giant mosfets.
The screw heads could hit adjacent boards.

I could go to TO220s, which need less screw height.

On 2023-06-19 11:49, John Larkin wrote:
> Has anyone done this? I need to get the mounting screw height down.
>
> I guess I'll have to try it.
>

Be careful about overtorqueing it, because stretching the metal might
conceivably cause the die to crack or delaminate.

I'd definitely want to torture-test for that possibility.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

On Mon, 19 Jun 2023 09:04:46 -0700 (PDT), Fred Bloggs
<bloggs.fredbloggs.fred@gmail.com> wrote:

>On Monday, June 19, 2023 at 11:50:16?AM UTC-4, John Larkin wrote:
>> Has anyone done this? I need to get the mounting screw height down.
>>
>> I guess I'll have to try it.
>
>Countersink it for a flat head. Head should end up flush with the package, can't beat that:
>
>https://www.homedepot.com/b/Hardware-Fasteners-Screws-Machine-Screws/Flat-Head/N-5yc1vZc27iZ1z18t94

That's the idea, as long as it doesn't destroy the silicon.

We'd need carbide countersinks. That mosfet epoxy is hell on tools.

mandag den 19. juni 2023 kl. 20.11.58 UTC+2 skrev John Larkin:
> On Mon, 19 Jun 2023 09:04:46 -0700 (PDT), Fred Bloggs
> <bloggs.fred...@gmail.com> wrote:
> >On Monday, June 19, 2023 at 11:50:16?AM UTC-4, John Larkin wrote:
> >> Has anyone done this? I need to get the mounting screw height down.
> >>
> >> I guess I'll have to try it.
> >
> >Countersink it for a flat head. Head should end up flush with the package, can't beat that:
> >
> >https://www.homedepot.com/b/Hardware-Fasteners-Screws-Machine-Screws/Flat-Head/N-5yc1vZc27iZ1z18t94
> That's the idea, as long as it doesn't destroy the silicon.
>
> We'd need carbide countersinks. That mosfet epoxy is hell on tools.

might be better with a counter bore instead of a counter sink

On Mon, 19 Jun 2023 11:27:39 -0700 (PDT), Lasse Langwadt Christensen
<langwadt@fonz.dk> wrote:

>mandag den 19. juni 2023 kl. 20.11.58 UTC+2 skrev John Larkin:
>> On Mon, 19 Jun 2023 09:04:46 -0700 (PDT), Fred Bloggs
>> <bloggs.fred...@gmail.com> wrote:
>> >On Monday, June 19, 2023 at 11:50:16?AM UTC-4, John Larkin wrote:
>> >> Has anyone done this? I need to get the mounting screw height down.
>> >>
>> >> I guess I'll have to try it.
>> >
>> >Countersink it for a flat head. Head should end up flush with the package, can't beat that:
>> >
>> >https://www.homedepot.com/b/Hardware-Fasteners-Screws-Machine-Screws/Flat-Head/N-5yc1vZc27iZ1z18t94
>> That's the idea, as long as it doesn't destroy the silicon.
>>
>> We'd need carbide countersinks. That mosfet epoxy is hell on tools.
>
>might be better with a counter bore instead of a counter sink

Yes, we could drop in a lockwasher.

On Mon, 19 Jun 2023 08:49:52 -0700, John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote:

>Has anyone done this? I need to get the mounting screw height down.
>
>I guess I'll have to try it.

I'm working from home today and I have a hand drill and a very rusty
old countersink, a family heirloom.

https://www.dropbox.com/scl/fi/y5s1bsc2omn341rnxkicq/TO247_countersunk_4-40.jpg?dl=0&rlkey=cqenr4ev8iic5zgujqor8cns1

This looks OK. The 4-40 screw should apply plenty of force and it
centers the fet nicely. It would need locktite so thermal cycling
doesn't loosen it up.

On Mon, 19 Jun 2023 09:12:39 -0700, John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote:

>On Mon, 19 Jun 2023 08:57:14 -0700 (PDT), Lasse Langwadt Christensen
><langwadt@fonz.dk> wrote:
>
>>mandag den 19. juni 2023 kl. 17.50.16 UTC+2 skrev John Larkin:
>>> Has anyone done this? I need to get the mounting screw height down.
>>>
>>> I guess I'll have to try it.
>>
>>how low do you need? https://www.mcmaster.com/products/low-profile-head-socket-cap-screws/alloy-steel-ultra-low-profile-socket-head-screws/
>
>The heights are good, the prices aren't!
>
>A regular screw and a lockwasher cost me over 0.1", and I need less.
>With locktite, I can eliminate the lockwasher.
>
>A really thin custom AlN insulator will help a bit. Isolated TO-247s
>are expensive and hard to get.
>
>I could just epoxy the fets down, but that has downsides.

Stainless steel flat head hex socket screws with a 100-degree cone
total angle are common, originally developed for use in airplanes.

..<https://www.mcmaster.com/90729A166/>

Suitable 100-degree carbide countersinks are also available.

Joe Gwinn

On Tuesday, 20 June 2023 at 01:50:16 UTC+10, John Larkin wrote:
> Has anyone done this? I need to get the mounting screw height down.
>
> I guess I'll have to try it.

Rivets?

--
Cheers,
Chris.

On 6/19/23 18:57, Chris wrote:
> On Tuesday, 20 June 2023 at 01:50:16 UTC+10, John Larkin wrote:
>> Has anyone done this? I need to get the mounting screw height down.
>>
>> I guess I'll have to try it.
>
> Rivets?
>
> --
> Cheers,
> Chris.
A copper rivet could work, but there are issues with installing: the
nose of the rivet setting tool may want to mash something else nearby...

On Monday, June 19, 2023 at 8:50:16 AM UTC-7, John Larkin wrote:
> Has anyone done this? I need to get the mounting screw height down.
>
> I guess I'll have to try it.

The hole is 3.5mm, so an M3 flat head cap screw with a countersinked washer would
hold it down; here are 1.8mm thick offerings for M3 screws. Is 1.8mm too high?

<https://www.mcmaster.com/products/countersunk-washers/>

I'm not seeing any measure of the recess dimensions around the clear hole, though.
The screw would be capable of touching the tab, which might not work for you.

On 2023-06-19, John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote:
> Has anyone done this? I need to get the mounting screw height down.

Sounds risky, the wedge shape of the screw head will be working
against the glass-filled resin of the body. I don't think that stuff
is very strong in tension.

> I guess I'll have to try it.

--
Jasen.
🇺🇦 Слава Україні

On 2023-06-20, Chris <chris.863@live.com> wrote:
> On Tuesday, 20 June 2023 at 01:50:16 UTC+10, John Larkin wrote:
>> Has anyone done this? I need to get the mounting screw height down.
>>
>> I guess I'll have to try it.
>
> Rivets?

blind rivets tend to cause mechanical shock when the stem snaps
leading to early failures. Swage rivets - maybe that could work
if you can find a way to set them without damaging the MOSFET.

--
Jasen.
🇺🇦 Слава Україні

On Mon, 19 Jun 2023 18:57:31 -0700 (PDT), Chris <chris.863@live.com>
wrote:

>On Tuesday, 20 June 2023 at 01:50:16 UTC+10, John Larkin wrote:
>> Has anyone done this? I need to get the mounting screw height down.
>>
>> I guess I'll have to try it.
>
>Rivets?

Rework would be difficult, and a rivet adds height too.
The reason to not just epoxy the fets down would be the rework issue.
And the mess, although there are some instant-set thermally conductive
super-glue things.

On Mon, 19 Jun 2023 22:54:50 -0700 (PDT), whit3rd <whit3rd@gmail.com>
wrote:

>On Monday, June 19, 2023 at 8:50:16?AM UTC-7, John Larkin wrote:
>> Has anyone done this? I need to get the mounting screw height down.
>>
>> I guess I'll have to try it.
>
>The hole is 3.5mm, so an M3 flat head cap screw with a countersinked washer would
>hold it down; here are 1.8mm thick offerings for M3 screws. Is 1.8mm too high?
>
><https://www.mcmaster.com/products/countersunk-washers/>

That might work, depending on how deep I dare to countersink the
mosfet. The ideal height of the screw is zero.

>
>I'm not seeing any measure of the recess dimensions around the clear hole, though.
>The screw would be capable of touching the tab, which might not work for you.

TO247s have insulated holes, so that's not a problem. No metal shows
up on the one I countersunk.

I could use TO-220s, but they would need an insulating shoulder
washer, and they are not as good thermally, having a smaller metal
footprint than a TO247.

I'm trying to get maximum power dissipation with a bunch of mosfets on
a K199 copper CPU cooler. 200 watts would be nice.

On Tue, 20 Jun 2023 03:46:47 -0700, John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote:

>On Mon, 19 Jun 2023 18:57:31 -0700 (PDT), Chris <chris.863@live.com>
>wrote:
>
>>On Tuesday, 20 June 2023 at 01:50:16 UTC+10, John Larkin wrote:
>>> Has anyone done this? I need to get the mounting screw height down.
>>>
>>> I guess I'll have to try it.
>>
>>Rivets?
>
>Rework would be difficult, and a rivet adds height too.
>The reason to not just epoxy the fets down would be the rework issue.
>And the mess, although there are some instant-set thermally conductive
>super-glue things.

Aluminum solid rivets with a 100-degree cone angle are also available.
Set with an arbor press to avoid shock.

..<https://www.mcmaster.com/96685A149/>

Joe Gwinn

mandag den 19. juni 2023 kl. 20.09.37 UTC+2 skrev John Larkin:
> On Mon, 19 Jun 2023 10:32:14 -0700 (PDT), Lasse Langwadt Christensen
> <lang...@fonz.dk> wrote:
>
> >mandag den 19. juni 2023 kl. 18.13.01 UTC+2 skrev John Larkin:
> >> On Mon, 19 Jun 2023 08:57:14 -0700 (PDT), Lasse Langwadt Christensen
> >> <lang...@fonz.dk> wrote:
> >>
> >> >mandag den 19. juni 2023 kl. 17.50.16 UTC+2 skrev John Larkin:
> >> >> Has anyone done this? I need to get the mounting screw height down.
> >> >>
> >> >> I guess I'll have to try it.
> >> >
> >> >how low do you need? https://www.mcmaster.com/products/low-profile-head-socket-cap-screws/alloy-steel-ultra-low-profile-socket-head-screws/
> >> The heights are good, the prices aren't!
> >>
> >> A regular screw and a lockwasher cost me over 0.1", and I need less.
> >> With locktite, I can eliminate the lockwasher.
> >>
> >> A really thin custom AlN insulator will help a bit. Isolated TO-247s
> >> are expensive and hard to get.
> >>
> >> I could just epoxy the fets down, but that has downsides.
> >
> >maybe something like this? https://www.digikey.dk/da/products/detail/aavid-thermal-division-of-boyd-corporation/MAX08NG/1625322
> I've done that
>
> https://www.dropbox.com/s/nmyb9pz0qpma2xa/Amp.jpg?dl=0
>
> but it adds more height. I'll have boards in a card cage on 1.6"
> centers, and I'm stacking a CPU cooler/fan thing with giant mosfets.
> The screw heads could hit adjacent boards.

like this? https://www.dynatron.co/product-page/k199

can't just clamp the whole stack with the four screws already there?

mandag den 19. juni 2023 kl. 22.37.26 UTC+2 skrev John Larkin:
> On Mon, 19 Jun 2023 08:49:52 -0700, John Larkin
> <jla...@highlandSNIPMEtechnology.com> wrote:
>
> >Has anyone done this? I need to get the mounting screw height down.
> >
> >I guess I'll have to try it.
> I'm working from home today and I have a hand drill and a very rusty
> old countersink, a family heirloom.
>
> https://www.dropbox.com/scl/fi/y5s1bsc2omn341rnxkicq/TO247_countersunk_4-40.jpg?dl=0&rlkey=cqenr4ev8iic5zgujqor8cns1
>
> This looks OK. The 4-40 screw should apply plenty of force and it
> centers the fet nicely. It would need locktite so thermal cycling
> doesn't loosen it up.

I'd be worried about the wedge effect of the countersink

maybe xray or decap a transistor to see how much room there is for a counter bore, I think I've seem some manufacturers say that a washer must be used

On Tue, 20 Jun 2023 08:48:06 -0700 (PDT), Lasse Langwadt Christensen
<langwadt@fonz.dk> wrote:

>mandag den 19. juni 2023 kl. 20.09.37 UTC+2 skrev John Larkin:
>> On Mon, 19 Jun 2023 10:32:14 -0700 (PDT), Lasse Langwadt Christensen
>> <lang...@fonz.dk> wrote:
>>
>> >mandag den 19. juni 2023 kl. 18.13.01 UTC+2 skrev John Larkin:
>> >> On Mon, 19 Jun 2023 08:57:14 -0700 (PDT), Lasse Langwadt Christensen
>> >> <lang...@fonz.dk> wrote:
>> >>
>> >> >mandag den 19. juni 2023 kl. 17.50.16 UTC+2 skrev John Larkin:
>> >> >> Has anyone done this? I need to get the mounting screw height down.
>> >> >>
>> >> >> I guess I'll have to try it.
>> >> >
>> >> >how low do you need? https://www.mcmaster.com/products/low-profile-head-socket-cap-screws/alloy-steel-ultra-low-profile-socket-head-screws/
>> >> The heights are good, the prices aren't!
>> >>
>> >> A regular screw and a lockwasher cost me over 0.1", and I need less.
>> >> With locktite, I can eliminate the lockwasher.
>> >>
>> >> A really thin custom AlN insulator will help a bit. Isolated TO-247s
>> >> are expensive and hard to get.
>> >>
>> >> I could just epoxy the fets down, but that has downsides.
>> >
>> >maybe something like this? https://www.digikey.dk/da/products/detail/aavid-thermal-division-of-boyd-corporation/MAX08NG/1625322
>> I've done that
>>
>> https://www.dropbox.com/s/nmyb9pz0qpma2xa/Amp.jpg?dl=0
>>
>> but it adds more height. I'll have boards in a card cage on 1.6"
>> centers, and I'm stacking a CPU cooler/fan thing with giant mosfets.
>> The screw heads could hit adjacent boards.
>
>like this? https://www.dynatron.co/product-page/k199

Yes, I'll probably use K199. It measures about 0.25 K/W. It's miles
better than machining a heat sink and adding a separate fan. It's
copper, too, a great heat spreader.

>
>can't just clamp the whole stack with the four screws already there?
>
>

I plan to remove the spring thingies and bolt the cooler hard to the
PCB, with the fets on the bottom side. We tried squashing the fets
metal-side-up, between the cooler and the board, and I didn't like
that. Fet contact force would be iffy and nothing would be
inspectable. The thermal grease situation would be ikky.

With fets bolted on the bottom (with a big hole in the board) each fet
is accessable, including for temperature measurement and possible
rework.