What kind of glue is this? - Page 1
Forum section: electronics / projects

author: davorin
author_rank: Unknown
timestamp: February 27, 2025, 06:35:53 am
content: Good morningFor my SMT reflow oven project I would like to mount a NTC onto a heatsink like in the picture below.But what kind of glue is that which can handle high temperatures? Never used such thing in the past (o;

author: 5U4GB
author_rank: Super Contributor
timestamp: February 27, 2025, 12:18:15 pm
content: There's a whole bunch of automotive adhesives that can handle very high temperatures, but if it's been used on a heatsink then it's probably thermal adhesive, again available from many vendors, just search for that term.

author: benseno
author_rank: Regular Contributor
timestamp: March 04, 2025, 07:40:42 pm
content: Could be silicon based substance.

author: calzap
author_rank: Frequent Contributor
timestamp: March 04, 2025, 10:00:01 pm
content: I would also guess it’s silicone-based. But what is being glued in the picture? Looks like a cable glued to a heat sink, which seems strange.Mike

author: wraper
author_rank: Unknown
timestamp: March 04, 2025, 10:10:41 pm
content: Quote from: 5U4GB on February 27, 2025, 12:18:15 pmAnd most of them are of acetoxy curing silicone which is incompatible with electronics. You absolutely don't need thermal adhesive for this, as you don't transfer any significant power through it. Thermal conductivity of usual silicones is completely enough. I suggest using neutral silicone, preferably special stuff for electronics. Such as 70x (701-709) you can buy from China. Western stuff is expensive and does not come in small packaging. Or use usual neutral silicone from hardware store.

author: thm_w
author_rank: Super Contributor
timestamp: March 05, 2025, 12:58:34 am
content: Quote from: calzap on March 04, 2025, 10:00:01 pmAs OP says, its a NTC thermistor. Probably a bead on the end or a bead with some metal on one side to better conduct heat.https://www.iqsdirectory.com/articles/thermocouple/thermistors.htmlQuote from: wraper on March 04, 2025, 10:10:41 pmWould be fine in this case as its just going on a heatsink, but yes, neutral cure better to have around, should cure faster. GE silicone II or whatever:https://gesealants.com/products/advanced-silicone-2-kitchen-bath-sealant/2812565A smaller squeeze tube might be $8.

author: wraper
author_rank: Unknown
timestamp: March 05, 2025, 02:06:46 am
content: Here is example of what I mentionedhttps://www.aliexpress.com/item/1005001845373231.htmlThis stuff is great, better than what I bought from ACC silicones. I store it in moisture barrier bag with silica gel, so it can last for a few years easily with no observable degradation. 708 IMHO is the best for general use as it's very easy to squeeze but it does not flow away and keeps shape. It's like semi-liquid but does not flow by itself. 706 is more viscous but flows. 701 has low viscosity, 702-704 IIRC are a bit more viscous than 701.

author: coppercone2
author_rank: Super Contributor
timestamp: March 05, 2025, 02:12:50 am
content: It looks like some sort of electrical wire with a white glue like substance on it.Don't forget that if you had it with glue, you can drill a hole, tap a thread and screw on a small ring-mount thermal sensor to the heatsink, along with buying spares for easy replacement.The problem with glue is that if you really care about thermal response and accuracy, the glue adds uncertainty.Here is a look at a premium product that might be used in a assembly linehttps://www.electronics-cooling.com/2021/05/silicone-adhesive-features-high-thermal-conductivity-electrical-insulation/I never used a 'proper' thermal silicone glue, and if you just wanna use anything and wing it I would recommend quikchip silicone adhesive for electronicsAnd I think the chip-quik is actually usable from their small 14 gram tube, it stores OK AND its usable from the box.If you get a big tube of glue for bathtubs, for proper use on circuit cards IMO you have to also buy a box of plastic syringes and then fill one up and dispense from it, and it sometimes gets ugly filling them.I have however used thermal epoxy, from MG chemicals and a different large sized one used for potting electronics. The mg chemicals thermal adhesive (2 part) is brittle, and requires a oven cure, so its a bit of a ordeal to go through, and it might not be what you want.A silicone product like this IMO looks good, but I have NO IDEA about the performance. Perhaps someone should do a 'rubbery thermal adhesive showdown' on youtubehttps://www.ebay.com/itm/356567020278?chn=ps&var=625536816361&google_free_listing_action=view_item&gQT=1Its a counterpart of this product lol, notice the price difference of 140 vs 2 dollars. !https://www.hisco.com/Product/354964-34899I would hope you go for the hisco if you are making something for sale to other people...I also wonder about adding thermal conductive powder to normal silicone to make your own, the big problem is mixing (it needs to be like vacuum mixed, or rolled together, because you get a insane amount of air bubbles mixing gels. I think its pretty damn hard to degas silicone. Unless you start with a high flow one. I might try it, but I suspect all my flowy silicone is expired by now, with signs of animal activity.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: March 05, 2025, 04:12:49 am
content: Glue, especially silicone (drives me crazy when people call it silicon), make service way more difficult. I prefer a mechanical mount with a screw and maybe some thermal paste underneath to help conductivity.

author: jpanhalt
author_rank: Super Contributor
timestamp: March 05, 2025, 04:27:23 am
content: Is a peripheral fin of a heat sink supposed to get hot enough to melt hot melt glue? I doubt it. The TS gave no physical properties. Is it spongy, soft, semisoft (can you indent it with a fingernail), or hard? My optical durometer blew a fuse.It looks like hot melt (they come in different application temperature ranges). If it is semi-soft like hot melt, burn a tiny sliver, and I'll bet it smells like hot melt. So, maybe it's just hot melt?

author: coppercone2
author_rank: Super Contributor
timestamp: March 05, 2025, 04:30:59 am
content: Quote from: Conrad Hoffman on March 05, 2025, 04:12:49 amI believe you can also buy heatsinks that have a clip-in thermistor mount but nothing comes to mind, and you can buy heat sinks with thermal mounting point so you can design it in from the beginning