Need a thermally conductive pad for switcher

[Product developer]

Anyone know of a good cost-effective compressible thermally conductive
pad that can be adhesively applied to a fixed surface of aluminum?

Application is a 60-watt switcher module that is docked onto a BMI
connector array and fastened with four screws to a large aluminum
plate. The switcher's driver MOSFET and output Schottky are tied to an
aluminum bracket that is tied to the switcher chassis bottom. It is
the switcher bottom plate that docks to the larger aluminum plate.
Since the driver and Schottky are electrically isolated the chassis to
chassis interface need not be. Therefore the thermally conductive pad
can be electrically conductive. Ideally the pad should be at least
..050" thick and compressible to adequately fill surface anomalies on
both surfaces.

Thank You for your help

 

[Tim Wescott]

Anyone know of a good cost-effective compressible thermally conductive
pad that can be adhesively applied to a fixed surface of aluminum?

Application is a 60-watt switcher module that is docked onto a BMI
connector array and fastened with four screws to a large aluminum
plate. The switcher's driver MOSFET and output Schottky are tied to an
aluminum bracket that is tied to the switcher chassis bottom. It is
the switcher bottom plate that docks to the larger aluminum plate.
Since the driver and Schottky are electrically isolated the chassis to
chassis interface need not be. Therefore the thermally conductive pad
can be electrically conductive. Ideally the pad should be at least
.050" thick and compressible to adequately fill surface anomalies on
both surfaces.

Thank You for your help

There's a thermally conductive epoxy out there that works quite well. I
can't remember the name, but you ought to be able to google for it. It
would have better conduction than your pad, and would allow metal-metal
contact in those areas where the parts can attain it.

 

[Ken Smith]

Anyone know of a good cost-effective compressible thermally conductive
pad that can be adhesively applied to a fixed surface of aluminum?

It depends a great deal on how you define "cost-effective". Bergquist
gap-pad does what you want but it does cost a bit.

 

[Tim Auton]

Anyone know of a good cost-effective compressible thermally conductive
pad that can be adhesively applied to a fixed surface of aluminum?

Application is a 60-watt switcher module

[snip]

You could look at the pads which are used on PC CPUs (most commonly
seen stuck to the bottom of your new CPU heatsink). They deal with
similar power loads. A few manufacturers who supply that market:

http://www.powerdevices.com/
http://www.bergquistcompany.com
http://www.chomerics.com/


Tim

 

[Product developer]

There's a thermally conductive epoxy out there that works quite well. I
can't remember the name, but you ought to be able to google for it. It
would have better conduction than your pad, and would allow metal-metal
contact in those areas where the parts can attain it.

Thanks Tim,

I should have disclosed that the docking module needs to be field
swappable requiring the pad to survive a few swaps over life of
product. The surface area of the module is 20 sq in.

 

[legg]

I should have disclosed that the docking module needs to be field
swappable requiring the pad to survive a few swaps over life of
product. The surface area of the module is 20 sq in.

You shouldn't get a large thermal drop across 20in^2 mating surfaces,
no matter how bad the contact, compared to total system impedance.

Normally non-isolated thermal interfaces that are this large don't
need enhancement unless the system is fluid cooled or the interface is
immediately adjacent to the main heat source.

RL

 

[Rich Grise]

I should have disclosed that the docking module needs to be field
swappable requiring the pad to survive a few swaps over life of
product. The surface area of the module is 20 sq in.

If it only gets swapped out a couple of times, what about just a
glob of ordinary thermal grease? You'd have to be sure there aren't
any voids, but that shouldn't be too hard. There are flexible heat
sink insulator pads, but I don't know what thickness they come in.
....<googles from memory>

Sil-Pad!

http://www.bergquistcompany.com/tm_sil_pad_list.cfm

Cheers!
Rich

 

[Product developer]

You shouldn't get a large thermal drop across 20in^2 mating surfaces,
no matter how bad the contact, compared to total system impedance.

Normally non-isolated thermal interfaces that are this large don't
need enhancement unless the system is fluid cooled or the interface is
immediately adjacent to the main heat source.

RL

My problem is dissimular aluminum surface integrity and heat transfer
efficiency. The module is a modified Hammond cast aluminum and the
second surface is .125" 6061 plate.

 

[Product developer]

Anyone know of a good cost-effective compressible thermally conductive
pad that can be adhesively applied to a fixed surface of aluminum?

Application is a 60-watt switcher module

[snip]

You could look at the pads which are used on PC CPUs (most commonly
seen stuck to the bottom of your new CPU heatsink). They deal with
similar power loads. A few manufacturers who supply that market:

http://www.powerdevices.com/
http://www.bergquistcompany.com
http://www.chomerics.com/


Tim

Thank you very much. In my research I missed the above sources and
will order samples tomorrow. Thanks again for your help gentlemen.

 

[legg]

My problem is dissimular aluminum surface integrity and heat transfer
efficiency. The module is a modified Hammond cast aluminum and the
second surface is .125" 6061 plate.

...and my maximum permissible thermal impedance across the junction
is...?

Dissimilar aluminium? You mean you are dealing with non-uniform
surfaces with irregular flatness that were not intended for this
purpose.

You have to know how irregular the surfaces are, or specify an
acceptible limit - to be included in the 'modification' of the
cast-aluminum part, as part of its finishing detail.

When two irregular al surfaces are bolted together, you can also get
orders of magnitude improvement in both electrical and thermal
impedance by using .003 tinned or silvered soft copper gasket material
in the interface. The aluminum should be chromate passivated.

There are limits to the irregularities that this, and bolt torque, can
overcome. Not everone's ideas of "docking modules" or "field
replaceable units" includes bolts.

If you are thinking pressure-fit only, then you may have to re-think
your thermal interface, to include dedicated functional heatsinking or
interface structures in the source part of the assy, unless you can
put up with a lot of grease in your fru.

Again, figure out the measurable thermal performance limits you are
aiming for.

RL

 

[Mike]

Did you try here http://www.thermagon.com/ yet?

 

[Product developer]

Did you try here http://www.thermagon.com/ yet?

Home run!

Exactly what I was looking for.

Thanks Ken!

 

[Product developer]

Did you try here http://www.thermagon.com/ yet?

Sorry Mike, I failed to look at the header. Thank You for your help.
This is the solution I was looking for.

Take Care,

Jack