epoxy compound for holding thermocouples  - Page 1
Forum section: electronics / projects

author: consumererik
author_rank: Newbie
timestamp: March 26, 2021, 09:18:36 pm
content: I'd like to find an epoxy or compound that I can use to attach thermocouple probes to power electronics components.Another nice feature, but maybe impractical, is finding a material that I could break free after my temperature testing is done. Basically, something rigid enough to hold stiff and unwieldy thermocouple probes during the test, but weak enough that I could break the probes free after. Can you think of anything like that? Perhaps I'm describing a silicon based epoxy? Or a silicon RTV?So far I've found:1. Supreme 3HTND-2GT from MasterBond2. 832TC from MG Chemicals3. Maybe even hot glue would work, especially if it was thermally conductive, but it melts about 80C (right?), and I want to measure 100CThis post is kinda related:https://www.eevblog.com/forum/beginners/black-goop-used-on-pcbs/

author: julian1
author_rank: Frequent Contributor
timestamp: March 26, 2021, 09:37:30 pm
content: Similar question here, with maybe some helpful answers.https://www.eevblog.com/forum/manufacture/glue-to-temporarily-attach-thermocouple-wire-to-fixtures/

author: ajb
author_rank: Super Contributor
timestamp: March 26, 2021, 10:17:56 pm
content: There's a thermally conductive electrical insulating epoxy from Kona as well that we've used, I don't have the info handy but it's available from McMaster-Carr in the us..But you may be able to get away with standard epoxy or even super glue, as long as the junction itself is in contact with the device the thermal resistance around the thermocouple probably won't affect the reading that much as long as you use a sparing amount. You can provide additional support to the thermocouple lead elsewhere on the board so the point of measurement doesn't have to be handle all of the mechanical load of the lead.

author: David Hess
author_rank: Super Contributor
timestamp: March 27, 2021, 01:36:19 am
content: I have used epoxy 907 for that sort of application but it would be tough to remove. I think a thick cyanoacrylate like you can get from a hobby shop with accelerator is the way to go; it can be released using a heat gun. The cyanoacrylate can be mixed with a metal oxide to improve thermal conductivity if necessary.

author: Mecanix
author_rank: Frequent Contributor
timestamp: March 27, 2021, 01:43:33 am
content: If you want 'accurate metrics' and be able to workout the TCE/TC/R math of the bounding in your application I'm afraid you'll need to go for a permanent and fairly solid 2-parts thermal epoxy. If accuracy isn't involved then I bet bubblegum or blue tack would work (tbc), no need for anything fancy I'd say.Not a huge fan of promoting cosmetics so I'll omit that, nonetheless we had excellent results with the 3M chems in the 2-parts epoxies (given it is a fresh batch).

author: wizard69
author_rank: Super Contributor
timestamp: March 27, 2021, 02:38:23 am
content: One option not mentioned yet is to consider a bolted on thermocouple if the device being probed has provision for it. These can be ring terminal type or even the more traditional bayonet type. You also have the option of ferruled mounting. All of these require a provision for the mount, but sometimes that is the best approach anyways.Other things to consider. Glass electrical tape designed for high temperature electrical connections. Here I'm talking: 3M™ Glass Cloth Electrical Tape 27, but you may also want to consider electrical friction tape. In the cases where i did this I was wrapping around round objects so adhesion to the surface was not critical. You also need to consider if you want direct contact or an isolated TC.Now here is the really bad part, measurement on the surface of an object will result in a huge error that obviously depends upon the exact circumstance. Making meaningful measurements may require insulating the TC on the exposed side.

author: penfold
author_rank: Frequent Contributor
timestamp: March 27, 2021, 03:12:58 am
content: For relatively low precision tests, superglue works pretty well, somewhat easy to remove, fast curing with an activator. It is what a test guy from UL used during some testing... not saying they're the gods of reliable test methods or anything, but I can't say I noticed any particular discrepancy between that approach and thermal epoxy, given the general uncertainty of a type-K thermocouple and all.I think one of the key points was that whilst it has a poorer thermal conductivity it has a lower thermal mass and better adherence to an unprepared surface - possibly something to do with the round shaped-ness of the thermocouple tip so it may not matter so much about thermal conductivity when the path of least resistance is always/should be in very close contact with the surface and its preferable for the excess adhesive to have minimal effect on the surface being measured or even provide a little insulation to the air-side of the thermocouple tip lowering the uncertainty due to air.

author: Miti
author_rank: Super Contributor
timestamp: March 27, 2021, 10:19:35 am
content: We use pink peelable solder mask at work. It turns black after a profile run but is easy to remove.

author: David Hess
author_rank: Super Contributor
timestamp: March 27, 2021, 09:10:30 pm
content: Another way I have done it in the past for very temporary installations is to dab the thermocouple in a bit of thermal paste, and then stick it in place with a piece of Kapton tape.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: April 01, 2021, 02:39:14 pm
content: Just sticking it with some thermal paste is a very simple and good temporary solution. Especially if you have a big contact surface. But you have to fix the wiring, preferably in two locations, so any bends in the long end do not propagate to the sensor itself.Silicone is a relative good heat conductor (compared to plastic) and I would use RTV over epoxy.If you want good accuracy, then also glue a part of the wiring (1 or two cm or so) to the heatsink, so the wiring of the thermocouple does not work as a heatsink and cool the thermocouple itself.

author: geggi1
author_rank: Frequent Contributor
timestamp: April 01, 2021, 04:07:04 pm
content: We use kapton tape at work. When building ATEX EX-D enclosures we had to log the temperature for all components inside until temperature stabilization.

author: jonpaul
author_rank: Super Contributor
timestamp: April 01, 2021, 04:32:06 pm
content: The TC firms have special ceramic loaded thick pastes for this use.We used all the methods mentioned in PSU testing -55..+85 C: Kapton tape, thermall paste, clamps.The epoxy and glue are not good at the high tempsJon