Unusual Thermal Paste

[2X]

Hi,
I removed the below heatsink and it had an unusual thermal paste where was very sticky and very hardly could dissolve with Isopropyl Alcohol. I used zippo (Lighter Fluid) to dissolved and remove it. Can you recognise from the color what kind of thermal paste is? I believe is a kind o thermal paste that don’t need to replaced (like the thermal pastes that used on PC CPUs for instance) until the heatsink is removed. This paste I beleive I have seen it again in Isolated DC/DC Converters.

Random picture of an Isolated DC/DC Converter
https://ae01.alicdn.com/kf/He3c76c1c55ce445a8c6416fb8a5cf2924.jpg_640x640Q90.jpg_.webp

[coromonadalix]

you can find thermal pads with variable thickness,  they start at 0.5mm and up

[2X]

Hi,
finally I found the below "phase change material". If anyone has experience about the performance of the thermal relief of this material, please tell me.

https://www.digikey.com/en/products/filter/thermal/pads-sheets/218?s=N4IgjCBcpgHAzFUBjKAzAhgGwM4FMAaEAeygG0R5YA2AFjEQF0iAHAFyhAGU2AnASwB2AcxABfImACcsKUhCpImXIRLkQABhCMJIALS15i5fiKlIFAKwb4UuUWqWwl2CAdPLAdjchHz%2B%2BBgYNQaEEQATJ7wnpY%2B9J70PtGwYIZEyc4%2BYBq0ttQ%2BkdH56Z4p3iWw4eFJpcHaunrV0ApQfACuquYUcjpiYkA

[T3sl4co1l]

Pictured is not phase change. If it were, you wouldn't be able to pry it off, at least not without heating.

Thermal paste never needs to be replaced, in and of itself.  Only if separation has occurred (flowed out of joint, oil sweating, dry filler compound), or the joint is opened and the paste must be redistributed (or added) to maintain an excess to squish out on reassembly.

Tim

[2X]

The heatsink I removed it by heating it with a hot air gun... I couldn't remove it cold as long as I tried.

[wraper]

Paste on the picture looks like golden Chinese shit like this https://www.aliexpress.com/item/1005006831807705.html I don't know any reputable manufacturer making that.

[T3sl4co1l]

The heatsink I removed it by heating it with a hot air gun... I couldn't remove it cold as long as I tried.

Well that would be important information then!

[BlownUpCapacitor]

Copper-infused thermal paste?

Also, almost any fluid can be used as a thermal paste to help transfer heat, including toothpaste. Just some will have better performance than others.

[tooki]

Maybe it’s not a thermal paste at all, but a thermal adhesive.

[nctnico]

Thermal paste never needs to be replaced, in and of itself.  Only if separation has occurred (flowed out of joint, oil sweating, dry filler compound), or the joint is opened and the paste must be redistributed (or added) to maintain an excess to squish out on reassembly.

Thermal paste needs to be replaced always when taking something apart. And there shouldn't be an excess at all. Only a thin film should be applied. Just enough to fill the gaps due to surface roughness. In 99.9% of the cases, thermal paste is applied wrong. You can get much more consistent quality by using thermal pads (silicone rubber, graphite, etc).

[2X]

Maybe it’s not a thermal paste at all, but a thermal adhesive.

Thanks for the reply.
I have used thermal adhesive pads but I didn't knew that exists thermal adhesives. I will search to find a good brand and I will give a try (until now I have found from brands Henkel and MGChemicals).

https://mgchemicals.com/category/adhesives/thermally-conductive-adhesives/

https://next.henkel-adhesives.com/us/en/applications/thermal-management-materials/thermally-conductive-adhesives.html


The below thermal adhesive pad I have used for square heatisinks that attached directly on the package of the mosfets (attached image).
https://www.digikey.gr/en/products/detail/t-global-technology/GT10D-150-150-0-25-2A/17628371

[2X]

Thermal paste never needs to be replaced, in and of itself.  Only if separation has occurred (flowed out of joint, oil sweating, dry filler compound), or the joint is opened and the paste must be redistributed (or added) to maintain an excess to squish out on reassembly.

Thermal paste needs to be replaced always when taking something apart. And there shouldn't be an excess at all. Only a thin film should be applied. Just enough to fill the gaps due to surface roughness. In 99.9% of the cases, thermal paste is applied wrong. You can get much more consistent quality by using thermal pads (silicone rubber, graphite, etc).

One thermal pad that i have find with a good performance is the P.N.: COH-4065LVC-200-10-1NT

[wraper]

Thermal paste never needs to be replaced, in and of itself.  Only if separation has occurred (flowed out of joint, oil sweating, dry filler compound), or the joint is opened and the paste must be redistributed (or added) to maintain an excess to squish out on reassembly.

Thermal paste needs to be replaced always when taking something apart. And there shouldn't be an excess at all. Only a thin film should be applied. Just enough to fill the gaps due to surface roughness. In 99.9% of the cases, thermal paste is applied wrong. You can get much more consistent quality by using thermal pads (silicone rubber, graphite, etc).

It's nearly impossible to apply it in just enough layer even if it is a highly repeatable factory process. There always is some flatness variation in usual mass produced parts. It's completely OK some excessive paste gets squeezed out. There is no penalty for it as long as mounting force is sufficient. It's better to apply some extra paste than taking chance some gaps may not be filled. Also if you apply it as a thin film, voids are almost guaranteed as during assembly air will be trapped with no path to escape.

[T3sl4co1l]

Thermal paste never needs to be replaced, in and of itself.  Only if separation has occurred (flowed out of joint, oil sweating, dry filler compound), or the joint is opened and the paste must be redistributed (or added) to maintain an excess to squish out on reassembly.

Thermal paste needs to be replaced always when taking something apart. And there shouldn't be an excess at all. Only a thin film should be applied. Just enough to fill the gaps due to surface roughness. In 99.9% of the cases, thermal paste is applied wrong. You can get much more consistent quality by using thermal pads (silicone rubber, graphite, etc).

Thank you for repeating part of what I said

Roughness though, how would you measure that?  It sounds noisy, statistical. How do you know when you've put on a thick enough film to fill the gap?

Short of intensive surface characterization, the easiest way by far is to put on a modest excess, and let it squidge out of the joint.

Simple game-theory calculus applies: is it better to have too little paste and expect voids and significantly increased resistance? Or too much and eliminate voids but have a modestly increased thermal resistance as a consequence?

It also depends on adequate clamping pressure, to actually move the paste (or enough movement to help it along, twist and slide and push etc.).  Or where paste doesn't manage to squeeze out, how well the design tolerates increased thermal resistance there (by using a more conductive paste, or more conservative derating).

On that note, I've seen some horrendously thick pastes; the PC "enthusiast" space especially revels in their hi-K materials, putty more than paste.  Especially easy to misapply those, and end up with a worse joint despite the higher K.

The next best science, is knowing where to apply excess, and how much.  A typical plan is to use a halftone density approach, with less near the mounting pads (e.g. bolted modules), more in the unsupported center span; or inversely for parts made with a somewhat rounded surface (intended to flatten out under clamping pressure).

Here's an example of both:
https://www.infineon.com/dgdl/Infineon-AN2006_02_Application_of_screen_print_templates-ApplicationNotes-v01_10-EN.pdf?fileId=db3a304412b407950112b40ed3f71297
they don't say how repeatable the surface is (or what or why the surface is like that in the first place), unfortunately, but they do show *a* characterization, and corresponding paste pattern.  The resulting fill looks quite even indeed.

Tim

[artag]

On a related subject, I want to measure temperature at a number of points over a chassis to determine whether I've created a problem by fitting quiet fans. This is often done by using a bunch of thermocouples and a multiplexer, but I'm aiming to use a string of DS18B20 'one-wire' sensors.

I want a way to fix these TO-92 packages to various heatsinks without gobs of thermal paste or thermal epoxy. I'm thinking maybe use thin thermal pads and some sort of spring clip.

Does anyone have better suggestions ?

[perieanuo]

Pictured is not phase change. If it were, you wouldn't be able to pry it off, at least not without heating.

Thermal paste never needs to be replaced, in and of itself.  Only if separation has occurred (flowed out of joint, oil sweating, dry filler compound), or the joint is opened and the paste must be redistributed (or added) to maintain an excess to squish out on reassembly.

Tim

all do respect, don't agree, i saw multiple laptops where the thermal paste un the uP was dried and ineffective, thermal shutdown occurring when using sw like prime for pushing mcu to max, after "changing" the paste with a good one all was fine.
there are low cost thermal paste that just dries (the compund element), you left with some scrapped dried metal stuff

[Haenk]

all do respect, don't agree, i saw multiple laptops where the thermal paste un the uP was dried and ineffective, thermal shutdown occurring when using sw like prime for pushing mcu to max, after "changing" the paste with a good one all was fine.
there are low cost thermal paste that just dries (the compund element), you left with some scrapped dried metal stuff

I agree with your disagreement. Ever so often I stumbled upon white thermal paste, which hardened and became crusty. Probably some cheap stuff and not silicone based. Then again I had decades old computers with thermal paste looking "like new" that could easily be re-used.

[T3sl4co1l]

I would call that "separation" then -- though if the oil fraction just up and left (evaporation? polymerization?) it wouldn't be my first choice of word!

There's also the case where grease was used inappropriately with Sil-Pad or the like, and ends up congealed, but I'd say that's a separate issue.

Tim

[coppice]

Thermal paste never needs to be replaced, in and of itself.  Only if separation has occurred (flowed out of joint, oil sweating, dry filler compound), or the joint is opened and the paste must be redistributed (or added) to maintain an excess to squish out on reassembly.

Some pastes say they need to be replaced at intervals. In most uses they still seem fine after years of operation, when you finally remove the heatsink for some reason. Other times the same brand of paste has clearly "dried out" in some sense, turned to a powder, and seems unlikely to have been doing a good job of filling the empty voids in our existence.

[T3sl4co1l]

Other times the same brand of paste has clearly "dried out" in some sense, turned to a powder, and seems unlikely to have been doing a good job of filling the empty voids in our existence.

That's when you realize you left the cap off the bottle of whiskey.

Tim

[BlownUpCapacitor]

https://www.coollaboratory.com/product/coollaboratory-liquid-copper/

Perhaps this. Going off my previous reply about copper-infused thermal paste.