Heat resistance of IC parts - Potting PCB's with hot glue - Page 1
Forum section: electronics / beginners

author: dinoboy
author_rank: Contributor
timestamp: May 06, 2012, 02:05:40 pm
content: Hello,i've unscrewed the PCB (called "driver") of a small flashlight (for 1xAAA battery), and the PCB has a nice sandwich design, similar to the following photo:Sometimes flashlight manufacturers protect the IC parts by potting it with material other than simple epoxy, see this here:My question is, how would you feel about filling in the sandwich withhot glue? Would the heat (=high temperature of the hot glue) destroy those IC parts or is it more or less safe to use hot glue as potting material?The purpose of potting is clear and simple: to enhance the impact resistance of the flashlight. If a flashlight is dropped onto hard ground, parts of the PCB are less likely to break (or soldering points) if the driver is potted, see for example HDS (search page for term < potted >).Please some opinions, thanks!!

author: metalphreak
author_rank: Frequent Contributor
timestamp: May 06, 2012, 04:00:15 pm
content: hot glue melts much below the temperature of solder, and all those surface mount parts are soldered by heating them up to temperatureShould be fine.

author: dinoboy
author_rank: Contributor
timestamp: May 06, 2012, 04:30:42 pm
content: sounds good to me!Thanks for the answer, i will go and fetch my hot glue pistol then .. heheTime to make a hot glue mess between the 2 PCB discs

author: TriodeTiger
author_rank: Regular Contributor
timestamp: May 07, 2012, 01:56:02 am
content: I haven't thought about hot glue before, consider silicone (adhesive) if it is a powerful light. It goes on cold, may take awhile to bond, but survive molten iron temperatures.Not sure if your LED's heatsink will ever reach the melting point of low temperature thermoplastic adhesive (~120 °C), much less the normal stuff (~193 °C), so just an option if it does in the future.

author: amyk
author_rank: Super Contributor
timestamp: May 07, 2012, 08:54:21 am
content: Thermal epoxy might be a better choice. Hot glue does not have very much thermal conductivity.

author: metalphreak
author_rank: Frequent Contributor
timestamp: May 07, 2012, 10:05:24 am
content: http://www.jaycar.com.au/productView.asp?ID=NM2016&SPECIAL=NEW&form=SPECIALYou can get the "proper" stuff from Jaycar in Australia. Just saw it while browsing this afternoonI'm sure you can get similar stuff elsewhere too.

author: dinoboy
author_rank: Contributor
timestamp: May 07, 2012, 06:12:22 pm
content: the head of the flashlight doesnt get too hot with this particular flashlight model. 1.5V nominal operating voltage and 0.600A (=600mA) current, so no skin-burningly high temperature in the PCB area is to be expected (Cree power LED). Thanks for the tips with adhesive silicone and thermal epoxy, none of which i have in my household afaik. True, thermal conductivity is a bit of importance (otherwise). When i get around a local hardware store i will look into these two substances, thanks!at home i do have a hot glue pistol and it would be the easiest/cheapest/fastest to work with what i have already, that's why i had asked hehe. i do understand that hot glue, because of its poor heat conductivity, is no good choice if heat transfer is important.metalphreak, i didnt know that such a thing actually existed!! If my experiments with hot glue fail (e.g. when the flashlight is in use and the driver heats up and IC parts die), i will consider potting the driver from then on more "seriously", i.e. with such professional compounds.Thanks all!! will report back when there are news (good or bad)

author: SeanB
author_rank: Super Contributor
timestamp: May 07, 2012, 06:26:28 pm
content: A cheap potting method is to use Pratley Steel, or Araldite steel 2 pack epoxy. Take some tape to enclose the sides and pour in the mixed epoxy before it cures ( 2 minutes - work fast once mixing starts) and it will do a good job of potting and will do fair heat transfer. nice thing is that after it is fully gelled, but before cured fully, you can trim the edges and the spills to size with a sharp knife. After 24 hours you need a file or a grinder.I use the 2 pack epoxy to stick devices to heatsinks.

author: codeboy2k
author_rank: Super Contributor
timestamp: May 07, 2012, 07:09:17 pm
content: I won't use hot glue around electronic parts anymore. I did try it one time. I was like you, I thought it would never get hot enough to melt to the glue.But it did, and the glue became all sticky/tacky/gooey again, and my parts didn't stay "glued" for very long.You'd be better to find something with a much higher melting point than hot glue, which is too near to the component temperatures of some active components (that can still run hot at 90C, and be fine. 90C will soften the glue and things will displace. Plus I think the fact that hot glue is not thermally conductive helps to increase the temperature under the components, like a crucible, and it can reach temperatures exceeding the glue melting point. With several active components under the glue, the temperature builds up and the glue eventually melts. This is what I think I experienced in my case.I only glue wires down now, and components that do not ever get hot.SeanB suggested a two part epoxy. That's probably a good choice. I'm going to consider using his suggestions too in the future.

author: SeanB
author_rank: Super Contributor
timestamp: May 07, 2012, 07:18:07 pm
content: I did some testing and found a thin film of epoxy on clean smooth flat surfaces is pretty much equivalent to using thermal compound. As a bonus you do not need mounting screws, and this method works well to add extra heatsinking to hot running plastic packaged DIL IC's. I started doing this with 286 processors to add an extra heatsink for those chips that were on a board where it ran hot, but there was no way to mount a heatsink on it. I was able to overclock them from 12 to 16MHz with no problems, without they would crash after a while.

author: dinoboy
author_rank: Contributor
timestamp: May 07, 2012, 09:00:19 pm
content: wow codeboy2k, you actually tried the hot glue method a while back? That's terrific, real life practice experience, and you shared the same idea. posting in this forum (my home is the flashlight forum) was a great idea by me then, thanks all for your helpful comments!yeah, my flashlights average ~30$ apiece, and i should be knowing what i do when trying to pot the electronics. for testing and practice purposes (and gaining spot-on experience with temperature build up in flashlight drivers with hot glue), i will apply hot glue only for some tests. from the flashlight forums i've been learning that potting drivers is desirable but only very few manufacturers and modders (D.I.Y.) actually do it. That's why not very much practical documentation is posted on forums. It is not common at all to see potted flashlight drivers!meanwhile i will get the suggested dedicated substances for the final application. places like kaidomain.com sell lots of D.I.Y. flashlight parts and drivers for cheap, so testing out both the hot glue and the other compounds doesnt harm my purse too much.hmm.. good idea.. epoxy on computer IC's (processor chips)!!