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Thermal INSULATOR Pad to Reduce Housing Temperature? (Desperate!)
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TimNJ:
Hi all,

I've hit a point of desperation at work. I inherited a project from my boss (who left) and I'm running out of steam and tensions are getting high. We are designing a power supply for one of our medical customers. There is a housing "touch temperature" requirement in IEC60601 that we have to meet. Basically, cannot have hot-spots on user accessible points that might cause burns/injury.

We have been maxed out on efficiency (for this topology) for months now. We have a few hot-spots on the enclosure that are just a degree or two too hot.

The drawing below shows the basic mechanical construction of the power supply. Very ordinary. PCB assembly with 90degree heatsink inside of a plastic housing.



Our issue is on the top of the housing. There is a small gap, maybe 1 or 2mm, between the top heatsink and the plastic housing. We've tried filling that with thermal RTV among other things. But now, at my wits end, I'm wondering if perhaps a thermal insulator on the hotspot could get us the reduction in temperature we need.

Does anyone have any experience with these kind of materials?

https://www.srpco.com/insulators/thermal-insulators-isolators/

Does anyone have  manufacturer, series, or part number of a product they like?

Any other suggestions on how to make this work?

Thanks a lot.
Tim
edpalmer42:
Random thoughts:

- Go to Home Depot or Lowes and see what ideas you can come up with.  I'm not suggesting you buy something there, although you could, just look for ideas.
- Does the case have to be sealed?  Maybe ventilation would help.
- If the heatsink in that spot is too hot, what would happen if you drilled out that spot?  Would the hot spot spread out to other parts of the heatsink and so, reduce the peak temperature?
- Similar to above, could you make the heatsink thicker so it would spread the heat better.

Ed
Gyro:
Likewise, if you have that much of a hotspot on an Aluminium heatsink inside a closed space, then it's probably not thick enough.

As for thermally insulating foam, you need something that trap sufficient air in cells without being conductive enough to offset the benefit. Not easy in a thin section. You need something as close to aerogel (obviously not practical) as possible. It probably needs to be flame retardant too.

On balance, I think to will be better using some of the space to thicken up the Aluminium and spread the heat more evenly.


P.S. Any chance of changing the heatsink from Aluminium to more thermally conductive copper instead? (I've seen it done in premium quality laptop PSUs).
SilverSolder:
My "gut feeling" is that adding insulation will only raise the internal temperature and make matters worse...

A band of copper foil on the inside of the plastic box to help spread the heat?  Or an aluminum plate glued to the inside of the box, same idea?
Mr. Scram:

--- Quote from: SilverSolder on August 15, 2019, 07:02:50 pm ---My "gut feeling" is that adding insulation will only raise the internal temperature and make matters worse...

A band of copper foil on the inside of the plastic box to help spread the heat?  Or an aluminum plate glued to the inside of the box, same idea?

--- End quote ---
It's all about evening out what's there. A very thick aluminium casing will be very uniformly warm. Isolating parts may reduce hotspots even if average temperature rises.
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