Components bonded to heatsink. - Page 1
Forum section: electronics / repair

author: BurningTantalum
author_rank: Frequent Contributor
timestamp: August 06, 2018, 07:58:41 am
content: I have a piece of equipment for repair. I need to remove two TO247 (large) IGBTs from an aluminium heatsink but they, along with a big bridge and a thermal cut-out, are stuck down with some kind of setting thermal compound. There are no screws or clips holding the components, and I cannot prise them off. I have tried a reasonable amount of heat from a hot-air tool but to no avail. Does anyone have any tips or tricks?Regards, BT

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 06, 2018, 08:58:19 am
content: Bigger hammer? Chisel?If they're epoxied down, that's about the end of that.I've seen that in a few PDP TVs before. Just as well buy the replacement module, or failing that (it's probably more expensive than the whole set), tell customer to cut their losses.Only other thing it could be, phase change compound; but that should soften at modest temperatures, and shouldn't be used without screws or clamps.Tim

author: BurningTantalum
author_rank: Frequent Contributor
timestamp: August 06, 2018, 12:32:16 pm
content: Thanks Tim. The 'customer' unfortunately, is me !It isn't viable to buy a new module so I guess I will try heating it up as hot as I dare and use a bigger hammer and a sharp ground chisel. I will remove the heatsink and clamp it in a vice. One of the IGBTs had died but the second one may be OK so I didn't want to risk shattering the package. I cannot remove the pins from the PCB without loosening the devices from the heatsink.I have a second unit with the same fault so it is worth a bash ! They are induction heaters for seized (frozen) fasteners.BT

author: Gregg
author_rank: Super Contributor
timestamp: August 06, 2018, 02:32:08 pm
content: If you can hold the aluminum base in a milling machine vise and mill the dead components away with a carbide mill cutter, it would leave a nice new flat for the replacements.A picture may help inspire unique solutions. Paint remover containing methylene chloride will eat away most organic based adhesives and a lot of other things you may not want to destroy.

author: Shock
author_rank: Super Contributor
timestamp: August 06, 2018, 06:20:25 pm
content: Try acetone to release it from the surface. If you can also chip a small piece off you can test what melts it.

author: Terry01
author_rank: Frequent Contributor
timestamp: August 06, 2018, 06:57:44 pm
content: Hand grenade? 💥If that doesn't work you could always try and hit it REALLY hard with a rubber chicken.....if those gont work i'm all out of ideas buddy.

author: Bashstreet
author_rank: Frequent Contributor
timestamp: August 06, 2018, 07:09:59 pm
content: Why not try freeze the epoxy they often get bridle when cold worth a try any case. (just use air-can upside down)

author: amyk
author_rank: Super Contributor
timestamp: August 06, 2018, 08:15:26 pm
content: Quote from: BurningTantalum topic=130355.msg1726055#msg1726055That means it's time to tryunreasonable heat or force.

author: Jwillis
author_rank: Super Contributor
timestamp: August 06, 2018, 11:51:01 pm
content: Hope this helps.Its a PDF on Reworking, Removing and “Decapsulating” Cured Epoxies.

author: BurningTantalum
author_rank: Frequent Contributor
timestamp: August 07, 2018, 08:23:32 am
content: And the winner is...Amyk !- LOTS of heat; as much as I dared whilst monitoring the packages with an IR thermometer, plus a sharpened scrap 'jewellers' screwdriver and toffee hammer.Thanks for all suggestions- serious and otherwise.The PDF from the epoxy company is interesting- I like the photos of the woodworkers chisels.I think I posted before about my attempts to dissolve slate-loaded epoxy potting, to allow a force balance amplifier to be copied (the manufacturer had long since gone).A sales rep claimed to sell chemicals that would dissolve anything known to mankind, so we dunked the amp in a tub of the Acme Epoxy Killer and left it over the weekend. Of course, on the Monday we found a tub full of grey sludge and pulled out a wavy mat of glass fibre and copper foil with bare semiconductor chips on leads. Doh, well it was 40 years ago..!BT

author: PKTKS
author_rank: Super Contributor
timestamp: August 09, 2018, 02:19:42 pm
content: Good to knowWould you mind to give us a clue about what the method of heating...Air gun ? ... Oven...And what temperature base ...Several videos and tips around frequently lack this setupwhich happens to make different results.ThanksPaul

author: BurningTantalum
author_rank: Frequent Contributor
timestamp: August 10, 2018, 09:37:28 am
content: Hi Paul,I used a heat gun with about a 4mm nozzle, just because that was the one fitted, and directed it onto the heatsink behind the big IGBT until the device reached an indicated temp of around 180C- then I rested it on a vice and with a pretty assistant, whacked it with a sharpened screwdriver and a hammer between the device and the alloy, et voila ! The second device came off the same but with no further heating, which was good as it was not blown.BT