Thermal Paste on Cold Side of Peltier Freezing and not transferring "Heat", what gives?

Question

I am running a peltier element, and on the cold side an aluminum heat sink to effectively spread out the cool surface to the maximum possible surface area.

I just bought this new thermal paste: Coolermaster Nano, and whenever it touches the cold side of the peltier (less than 10 Fahrenheit) it freezes into a rock, while thermal paste such as Arctic MX-4 does not.

I had a hunch that this freezing affect was causing problem as temperatures using the Coolermaster Nano thermal paste were far far higher than the Arctic MX-4 (16 Fahrenheit vs 0). So, I ended up removing all thermal paste and saw that even with no thermal paste between cold side and heat sink, the temperature was lower than with using Coolermaster Nano, at 10 Fahrenheit.

I was wondering if someone could explain this to me: are some thermal pastes not designed or suited for low temperatures? Is there something I should look out for when purchasing a thermal paste (carbon based?)

Answer 1

Yes, of course. A thermal paste intended for CPUs is rarely used below 25C. You need to read their datasheet or search for cryogenic thermal compounds.

It is probably cheaper to select some of the consumer grade ones through their datasheet and test the best for your application. Arctic Silver 5, for example, claims to be stable down to -50C.

Answer 2

Part of your problem is the expansion and contraction of aluminum, which can be a lot per linear yard/meter. I also had to find a bonding compound to bind an aluminum (5052) bracket to a stainless steel enclosure. Every epoxy and glue I tried failed within 48 hours of heating and freezing twice.

Aluminum contracts a lot when frozen. The solution was to use RTV type compounds, specifically RTV type 262, which had no ammonia to corrode the metals or electronics.

It is only a suggestion that you consider 'rubbery' type compounds that do not freeze per se, but instead shrink with the metal, so it maintains a grip. For Arctic Silver 5 to work, you may need a more rigid metal, but hard steels can be brittle under extreme cold. Copper is an alternative, with Beryllium copper an expensive alternative, but still cheaper than SS.

Answer 3

I curiously just ran into a thermal compound designed specially for Peltier applications. It is called "TP-1", it got an operational temperature from -40C to 200C. This range of temperatures makes me think that the compound is good for the cold and the hot side. Here's the link to the website: https://tetech.com/product/tp-1/. I'll order one of these for some testing and I'll leave an update in case anyone is still interested.