Your experience with thermal compounds silver/ceramic vs generic white - Page 1
Forum section: electronics / projects

author: Miyuki
author_rank: Frequent Contributor
timestamp: June 27, 2021, 04:31:45 pm
content: Hi folksI want to ask if you have experience with some fancy thermal compoundsIn cases when I don't need insulation, like have ISOPLUS 247 package or on an external ceramic insulator when I want to cool huge powers like 100-200WWith "common" grease, the table value of the thermal resistance case to heatsink is about 0.25 K/WI know on a bare die to heatsink it can make a huge difference with better compound

author: bobbydazzler
author_rank: Regular Contributor
timestamp: June 27, 2021, 09:54:28 pm
content: What about thermal compound designed for desktop cpus? It handles 100's of watts fine(maybe it doesn't age as well?).

author: Whales
author_rank: Super Contributor
timestamp: June 27, 2021, 10:56:44 pm
content: I have discovered that my cheap greases dry out after a year or so. If you want your product to last: might be worth seeing if thermal greases have datasheets specifying lifetime.Random notes:* If you can mechanically lap the two surfaces well enough: thermal grease becomes optional or worse of an option than direct contact.* There are super-thin thermal sheet like products available ("graphene" or something?) that could be worth considering.

author: sandalcandal
author_rank: Unknown
timestamp: June 27, 2021, 11:20:16 pm
content: Towards desktop CPUs and "pc enthusiasts", the highest performance (non-cryogenic temperature) compound used there was "liquid metal" thermal compounds ("Our special mixture of metals like tin, gallium and indium") which people used to good effect de-capping their CPUs and doing direct-die cooling. Advertised at 75 W/mkhttps://www.pccasegear.com/products/35854/thermal-grizzly-conductonaut-thermal-compound-1gThese systems did >200W dissipation in a very small package/die. The relevance of such modifications in the pc enthusiast space has decreased with Intel's apparent improvement of their die-to-case TIM improvements using iridium based solder and doing die thinning.Longevity from short term tests (1 year) looked okhttps://www.gamersnexus.net/guides/3359-liquid-metal-aging-one-year-test-how-often-to-replace-liquid-metalNot sure about industrial applications with >20yr life expectancies.Gallium based so NOT compatible with aluminium based heatsinks.Available in small consumer grade packages as above but I presume there are industrial suppliers.A quick search for Gallium TIM turned up thishttps://www.tomo-e.co.jp/upload/cProductsJA/25QU109-cProductsJA_content-001.pdf83 W/m*kSome of the more standard phase change TIM and greases I've been looking at are less than a 10th of thatPhase change TIM 7.5 W/m*khttps://www.laird.com/products/gap-fillers-thermal-interface-materials/phase-change/tpcm-7000Thermal grease 3.5 W/m*khttps://www.laird.com/products/gap-fillers-thermal-interface-materials/thermal-grease/tgrease-2500Edit: Good set of test results on high performance greases for consumer CPU coolinghttps://www.guru3d.com/articles_pages/guru3d_thermal_paste_roundup_round2_2021,10.html

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: June 27, 2021, 11:23:51 pm
content: If the interface is good, meaning the parts are smooth and flat, and if you don't use too much grease, the thermal conductivity of the grease doesn't matter much. It's all about getting the gap as small as possible. Do the math- it's interesting! ALL greases are pretty terrible compared to metals, even the fancy ones. IMO, you still need a trace of the stuff, unless you can get things gauge block flat. A name brand thermal grease/paste like Dow 340 or Aavid/Thermalloy will do the trick. Aavid Ultrastick is also something to investigate. It's a phase change compound that basically liquifies when it gets warm, giving the thinnest possible interface. Outperforms grease.

author: sandalcandal
author_rank: Unknown
timestamp: June 27, 2021, 11:25:49 pm
content: Quote from: Whales on June 27, 2021, 10:56:44 pmTest of carbon based thermal pad in consumer CPU applicationThere are also different carbon film products that are more heat spreaders rather than a TIM e.g. Panasonic Pyrolitic Graphite Sheets (there were some others that made similar products)Insanely high thermal conductivities (>1000W/m*k) but anisotropically only in the plane of the sheet, thermal conductivitythroughthe sheet is pretty average.

author: nctnico
author_rank: Super Contributor
timestamp: June 27, 2021, 11:29:45 pm
content: I'd use a pad. That will give a repeatable performance. I'm usually using the praphite / carbon type pads for CPUs but these are available for various package types.

author: bobbydazzler
author_rank: Regular Contributor
timestamp: July 01, 2021, 03:41:48 am
content: Quote from: sandalcandal on June 27, 2021, 11:20:16 pmUsing a copper heatsink and soldering the part to the heatsink would be best. Strange I never see that unless you count soldering a part like a dpak to a pcb with lots of copper.

author: mazurov
author_rank: Frequent Contributor
timestamp: July 01, 2021, 05:35:43 pm
content: Quote from: sandalcandal on June 27, 2021, 11:20:16 pmThe trade name for this (or very similar) compound is "Galinstan". $8-ish for a small syringe, lasts a long time, works very well on copper or nickel surfaces. In EU, modern household "mercury" body temp thermometers are filled with the same compound since it is less toxic than mercury.

author: Miyuki
author_rank: Frequent Contributor
timestamp: July 02, 2021, 06:04:08 pm
content: Quote from: bobbydazzler on July 01, 2021, 03:41:48 amHeating a huge heatsink to solder temperature will be a tough job and heatsink fins are better aluminum, so must be some dual-material job or something

author: james_s
author_rank: Super Contributor
timestamp: July 02, 2021, 06:15:57 pm
content: Something to watch out for is that some thermal compounds are conductive. I once made the mistake of using some Arctic Silver I had laying around on a TO-3 transistor with a mica wafer. A bit of the compound oozed into the gap around the transistor lead and burned.I don't think it matters if the compound dries out so long as the device is not disturbed. It is in liquid form so you can spread it on in the first place and it will fill the microscopic voids, once that has happened it shouldn't really matter if it dries out.