Heat sink mylar??

[juice28]

I have a design that uses 6 TO47 trasistors mounted to a very large heat
sink. I was wondering if anyone knows of a supplier for some sort of
insulator tape? I see this stuff used on car audio amps all the time, but
can't seem to find anyone that has it.

I would rather not have to use 6 seperate insulators and 6 screw. I would
like to run a piece of tape down the heat sink and them use a solid piece of
steel to clamp all the transistors down at once.

Thanks,

Fred
arcadexpo@mchsi.com

 

[Jason D.]

On Mon, 15 Sep 2003 21:01:14 GMT, "juice28" <arcadexpo@mchsi.com>
wrote:

I have a design that uses 6 TO47 trasistors mounted to a very large heat
sink. I was wondering if anyone knows of a supplier for some sort of
insulator tape? I see this stuff used on car audio amps all the time, but
can't seem to find anyone that has it.

I would rather not have to use 6 seperate insulators and 6 screw. I would
like to run a piece of tape down the heat sink and them use a solid piece of
steel to clamp all the transistors down at once.

Thanks,

How is your clamping assembly is designed, we would like to see your
idea described.

My assumption:
Problem with this mono-clamp is middle transistors will not get
clamped that when two screws at either end of bar is bolted down,
whole assembly bow outwards. Still have to put 7 screws thru bar so
each transistor is clamped between screws for even pressure on all six
transistors. Use lockwashers and washers to keep screws locked and
maintain clamping pressure.

Mylar is flexible clear plastic usually used for helium balloons and
it's not a thermal pad. Mica is fragible and stiff, breaks &
scratches easily, grey rubbery pads in all shapes and different
thickness is best and take awhile to find electronics supplier that
has long tape for your specs. Individual grey pads is easier to find.
Buy them or collect them from junked electronics.

The junked big amps boxes has big heatsinks and clamping stuff all
there already so why not use that?

Cheers,

Wizard

 

[juice28]

Because we are making a run of 100 units its not feasable to take them out
of car amps. I aactually found a supplier for 40" x 23" .004" mica insulator
material. Price was right $13.00. Yes the clamp method is with multiple
screws. I was more concerned with sourcing a mylar material in quanity then
the clamping scheme.

Thanks,

Fred


"Jason D." <jpero@sympatico.ca> wrote in message
news:3f664372.5144368@news1.on.sympatico.ca...

On Mon, 15 Sep 2003 21:01:14 GMT, "juice28" <arcadexpo@mchsi.com
wrote:

I have a design that uses 6 TO47 trasistors mounted to a very large heat
sink. I was wondering if anyone knows of a supplier for some sort of
insulator tape? I see this stuff used on car audio amps all the time, but
can't seem to find anyone that has it.

I would rather not have to use 6 seperate insulators and 6 screw. I would
like to run a piece of tape down the heat sink and them use a solid piece
of
steel to clamp all the transistors down at once.

Thanks,

How is your clamping assembly is designed, we would like to see your
idea described.

My assumption:
Problem with this mono-clamp is middle transistors will not get
clamped that when two screws at either end of bar is bolted down,
whole assembly bow outwards. Still have to put 7 screws thru bar so
each transistor is clamped between screws for even pressure on all six
transistors. Use lockwashers and washers to keep screws locked and
maintain clamping pressure.

Mylar is flexible clear plastic usually used for helium balloons and
it's not a thermal pad. Mica is fragible and stiff, breaks &
scratches easily, grey rubbery pads in all shapes and different
thickness is best and take awhile to find electronics supplier that
has long tape for your specs. Individual grey pads is easier to find.
Buy them or collect them from junked electronics.

The junked big amps boxes has big heatsinks and clamping stuff all
there already so why not use that?

Cheers,

Wizard

 

[Jim Adney]

On Mon, 15 Sep 2003 23:58:31 GMT "juice28" <arcadexpo@mchsi.com>
wrote:

Because we are making a run of 100 units its not feasable to take them out
of car amps. I aactually found a supplier for 40" x 23" .004" mica insulator
material. Price was right $13.00. Yes the clamp method is with multiple
screws. I was more concerned with sourcing a mylar material in quanity then
the clamping scheme.

Mylar is a good electrical insulator, but it's not a good heat sink
insulator material. There are much better (better thermal
conductivity) materials out there.

Have you tried Googling "heat sink insulator"? That should point you
in the right direction to find the folks who make this stuff and can
sell it to you in sheets. Look for the grey silicone material. Sorry,
the maker's name escapes me.

-
-----------------------------------------------
Jim Adney jadney@vwtype3.org
Madison, WI 53711 USA
-----------------------------------------------

 

[James Sweet]

Digikey sells mica insulators, they're not very expensive.

"Jason D." <jpero@sympatico.ca> wrote in message
news:3f664372.5144368@news1.on.sympatico.ca...

On Mon, 15 Sep 2003 21:01:14 GMT, "juice28" <arcadexpo@mchsi.com
wrote:

I have a design that uses 6 TO47 trasistors mounted to a very large heat
sink. I was wondering if anyone knows of a supplier for some sort of
insulator tape? I see this stuff used on car audio amps all the time, but
can't seem to find anyone that has it.

I would rather not have to use 6 seperate insulators and 6 screw. I would
like to run a piece of tape down the heat sink and them use a solid piece
of
steel to clamp all the transistors down at once.

Thanks,

How is your clamping assembly is designed, we would like to see your
idea described.

My assumption:
Problem with this mono-clamp is middle transistors will not get
clamped that when two screws at either end of bar is bolted down,
whole assembly bow outwards. Still have to put 7 screws thru bar so
each transistor is clamped between screws for even pressure on all six
transistors. Use lockwashers and washers to keep screws locked and
maintain clamping pressure.

Mylar is flexible clear plastic usually used for helium balloons and
it's not a thermal pad. Mica is fragible and stiff, breaks &
scratches easily, grey rubbery pads in all shapes and different
thickness is best and take awhile to find electronics supplier that
has long tape for your specs. Individual grey pads is easier to find.
Buy them or collect them from junked electronics.

The junked big amps boxes has big heatsinks and clamping stuff all
there already so why not use that?

Cheers,

Wizard

 

[Asimov]

"juice28" bravely wrote to "All" (15 Sep 03 21:01:14)
--- on the heady topic of "Heat sink mylar??"

How about 2 layers of ordinary vinyl electrical tape? It should conduct
heat and stand up to at least as much heat as the transistors will work
up to. Unless it shrinks too much, then it could be bad. Don't take this
seriously, only half seriously, as I haven't done any tests but I've
seen it done at least once before.


ju> From: "juice28" <arcadexpo@mchsi.com>

ju> I have a design that uses 6 TO47 trasistors mounted to a very large
ju> heat sink. I was wondering if anyone knows of a supplier for some sort
ju> of insulator tape? I see this stuff used on car audio amps all the
ju> time, but can't seem to find anyone that has it.

ju> I would rather not have to use 6 seperate insulators and 6 screw. I
ju> would like to run a piece of tape down the heat sink and them use a
ju> solid piece of steel to clamp all the transistors down at once.

ju> Thanks,

ju> Fred
ju> arcadexpo@mchsi.com

.... You may be a tech if you're entertained by a 6-pack and sparking HV.

 

[legg]

On Mon, 15 Sep 2003 21:01:14 GMT, "juice28" <arcadexpo@mchsi.com>
wrote:

I have a design that uses 6 TO47 trasistors mounted to a very large heat
sink. I was wondering if anyone knows of a supplier for some sort of
insulator tape? I see this stuff used on car audio amps all the time, but
can't seem to find anyone that has it.

I would rather not have to use 6 seperate insulators and 6 screw. I would
like to run a piece of tape down the heat sink and them use a solid piece of
steel to clamp all the transistors down at once.

Thanks,

Fred
arcadexpo@mchsi.com

If this is only for low-voltage functional isolation, it works.
Adhesive backed mylar tape is available from most tape mfrs (3M, Tuck
etc) and is distributed widely (even Digikey).

Other tape materials for a higher temperature index (mylar is 130degC)
are available.

Plain mylar sheet and roll stock is available from most plastics
resellers in varying thicknesses; check the yellow pages for your
area.

Be advised that adhesive tape is generally .0025 thick, but only .001
of that is insulator, the rest is adhesive. Check the spec. When
fresh, the adhesive will flow under mounting pressure, which is ~good,
as it fill's in voids and uneven interfaces.

The adhesive dries out with age, which is bad, as this may re-create
voids that were previously filled.

Material specifically designed for this heatsink-mounting purpose is
available from Thermalloy, Chomerics, Keratherm and Bergquist. Typical
sheet sizes are 10x10inch for unprocessed stock.

If the isolation required is for safety purposes, refer to the
relevant safety standard re required thicknesses or acceptible
construction materials for this role.

RL