"Unglueing" crees to remove die-board

Joe2009 · May 22, 2009

Hi folks,

after years of just reading this very interesting forum, i signed up today...
One year ago i bought a "Min-T" triple cree-housing, which worked fine over time with plenty of light.
Unfortunately i gave it to a friend for testing and indeed, testing was just too much:
he was playing around with the optic and finally was cutting the glas lenses :shakehead!!!
Result:
1 emitter still having the glas lens on, 1 still working without lens and the last one "electrically dead", thinking the wire bond is damaged, underlaying gel is partially removed.
Since the crees are sitting in their recess glued with thermal epoxy, they are rather hard to remove in order to be replaced with new ones.

I´m thinking of treating them with IPA or acetone in order to get rid of the thermal glue, not knowing if it is creeping under the crees...

Is that a good idea or do you have other ideas or tricks?
Any idea would be highly beneficial!!!

Cheers,

Joe

chimo · May 22, 2009

Heat usually softens the thermal adhesive enough to allow it to be pried off.

Joe2009 · May 22, 2009

Hi Chimo,

thank you so much for that tip!
I was doing a cold/hot change and just a few seconds ago, i was able to remove leds without any problem.
All the glue is gone away!!!!

Thank you!!!

Cheers,

Joe

tx101 · May 22, 2009

how much heat/cold did you use ?
I might need to remove some bare emitters that have been epoxied.

Will this damage the emitter in anyway ?

Joe2009 · May 22, 2009

Hi tx101,

i had in the freezer at -20°C for one hour and then had it in the oven at 120°C (not measured, just setting) for about 15 min...
The Led itself did not get damaged, just needed some press/pull movement and soft lifting movement!
I also noticed that residual glue could be removed more easily from the surface than before, glue getting more like a gel...
The leds look fine, only need surface cleaning on the back with a sharp knife or razorblade. :grin2:

Hope that helps,

Joe

bshanahan14rulz · May 22, 2009

Friends don't let friends destructively test LEDs.....without photos.:thumbsdow

:popcorn:

rolling · May 22, 2009

Joe2009 said:
i had in the freezer at -20°C for one hour and then had it in the oven at 120°C (not measured, just setting) for about 15 min...

Am I wrong or should the Crees be toast?

jenskh · May 22, 2009

It should be no problem. When reflow soldering leds, the recommended max temperature is above 200 deg C.

rolling · May 22, 2009

Yes for seconds...

jenskh · May 22, 2009

Well, if you are using lead free solder, the recommended time above 217 deg C is 60- 150 seconds.

bshanahan14rulz · May 22, 2009

Wasn't the op trying to remove dead crees from the board? I don't think it matters how hot a dead cree gets ;-)

kramer5150 · May 22, 2009

I think it can vary greatly depending on the type of adhesive used. from my experience with drop in modules, the adhesive from DX definitely needs more than 120-F. I have found the DX thermal adhesive is so impervious to heat that the XR-E solder will re-flow before the thermal adhesive degrades.

recently I cooked one of my XR-E emitters in a 1.4A drop in, and I wanted to salvage the brass pill. I pulled, pried... could not get the 14mm XR-E slug to come off the brass pill. I don't have a heat gun, but I tried a hairdryer, which I am certain brought the temperature up to around ~140F (too hot to touch) ... no dice :ohgeez:

Finally I just said heck with it... lets nuke the thing. Heated my stove coils RED HOT

... dropped the brass pill onto the coils for a good 2-3 minutes, burned the sucker off. I have no idea what temperature the brass was at but it was hot enough to set off the smoke detector in my kitchen....LOL:thumbsup: My wife came home 3-4 hours later ans asked "whats that smell"?

dom · May 23, 2009

Hi Joe
Will you use thermal paste instead this
time?

Good job on getting the LED's out anyway

Push down hard with your thumb on the optic for undoing/doing up ,the bezel.

Cheers
Dom

Joe2009 · May 23, 2009

Hi Dom,

nice to hear from you again!
This time i still will go again with Artic silver, but the lamp stays only with me, for interested friends it´s like:
"only look with your eyes" :grin2:

!!!!

In fact, i was also playing a lot with changing optics, having a look at leds, lighting without secondary optic;
that could have happened to me also!

This time i will pay more attention, for sure!

Cheers,

Joe

dom · May 25, 2009

kramer5150 said:
I think it can vary greatly depending on the type of adhesive used. from my experience with drop in modules, the adhesive from DX definitely needs more than 120-F. I have found the DX thermal adhesive is so impervious to heat that the XR-E solder will re-flow before the thermal adhesive degrades.

recently I cooked one of my XR-E emitters in a 1.4A drop in, and I wanted to salvage the brass pill. I pulled, pried... could not get the 14mm XR-E slug to come off the brass pill. I don't have a heat gun, but I tried a hairdryer, which I am certain brought the temperature up to around ~140F (too hot to touch) ... no dice

Finally I just said heck with it... lets nuke the thing. Heated my stove coils RED HOT... dropped the brass pill onto the coils for a good 2-3 minutes, burned the sucker off. I have no idea what temperature the brass was at but it was hot enough to set off the smoke detector in my kitchen....LOL:thumbsup: My wife came home 3-4 hours later ans asked "whats that smell"?

Impressive sounding glue Kramer - perhaps freezing might work -then again,perhaps not! hehe

Hi Joe
I though you may have used Arctic Alumina -perhaps the Arctic Silver is easier to get off. Did it stay gummy after your heat treatment?

Cheers
Dom

Joe2009 · May 25, 2009

Hi Dom,

you´re right: the glue was gummy after heat treating...
On the backside of the led it was like a rubber coating you could peel off with a razorblade.

Is there a certain ranking on glueing force and thermal toughness between common thermal adhesives one could look up?

Cheers,

Joe

dom · May 26, 2009

Hey Joe
I did read something awhile ago but i don't think there was much of a conclusion as to what was the best stuff.

The main thing is,is to have as little substance between the LED base and sink as possible for the best thermal transfer.

Cheers
Dom

lolzertank · May 26, 2009

rolling said:
Am I wrong or should the Crees be toast?

I thought the Crees are rated 150 degrees C for maximum junction temperature. Even if the junction gets as hot as the package, it should still be okay.

Now if you were talking about bread imitations of Crees... then it would be toast? :crazy:

"Unglueing" crees to remove die-board

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