Solution for clearing LED epoxy on emitter?

[steveggz]

While soldering Cree XT-E surface mount LEDs I managed to get rosin flux on the epoxy/plastic coating of the emitter (see attached pictures). Has anyone successfully managed to clear up that coating? I've tried everything from 91% alcohol and scrubbing to acetone and even polishing it with a dremmel and buffing wheel. I tried all this on a spare Cree LED to see if it would work and nothing worked.

Is there anything I can do or is that plastic epoxy coating damaged for good?

As soon as the alcohol or liquids I use to clean it evaporate the coating becomes frosted and unclear. Is there anything I can put over it like a coat of lacquer to keep it clear. Or epoxy?

[ivaylo]

Nah, plastic can be polished... Unless you overheated it or something. How many RPM do you run your Dremel at? I assume you are aware of products like these https://www.amazon.com/gp/product/B002UD0GGS

[Gyro]

Your best action would have been to check the manufacturer's website for cleaning methods before you started, specifically the soldering and handling instructions:  http://www.cree.com/led-components/media/documents/XLamp_XT_SH.pdf

Recommended Cleaning solutions
Cree has found the following chemicals to be safe to use with XT Family LeDs.
• Water
• Isopropyl alcohol (IPA)

Chemicals Tested as Harmful
In general, subject to the specifics in Cree’s Chemical Compatibility Application Note, Cree has found certain chemicals to be harmful to
XT Family LeDs. Cree recommends not using these chemicals anywhere in an LeD system containing XLamp XT Family LeDs. The fumes
from even small amounts of the chemicals may damage the LeDs.
• Chemicals that might outgas aromatic hydrocarbons (e.g., toluene, benzene, xylene)
• Methyl acetate or ethyl acetate (i.e., nail polish remover)
• Cyanoacrylates (i.e., “Superglue”)
• Glycol ethers (including Radio Shack ® Precision electronics Cleaner - dipropylene glycol monomethyl ether)
• Formaldehyde or butadiene (including Ashland ® PLIOBOND ® adhesive)

It sounds as if you didn't use sufficient passes of the IPA (hopefully it was IPA) to completely remove the flux residue, if there was any left then, yes it would have gone cloudy again as it dried. I think the Acetone will have softened the plastic and permanently crazed the surface. I doubt if Dremmels feature anywhere in the proper handling procedures  - best case, you will change the lens profile, it would be advisable to short each one to avoid static damage too.

I'd say, at this point, you'd be best off replacing them.

[steveggz]

I tried Meguiars ultra cut compound. I used the lowest setting on my Dremmel but it basically shaved down the led coating to a flat one. I think the plastic coasting is too soft to polish

Thanks Gyro, I actually used both of their recommended cleaning solutions with no luck. I only tried the more harmful ones in a attempt to salvage them but they also didn't work. It seems the rosin flux either baked on the lens or chemically changed the surface of the emitter coating.

[jmelson]

I've tried everything from 91% alcohol and scrubbing to acetone and even polishing it with a dremmel and buffing wheel.

I suspect the acetone has partially melted the plastic.  It will take some buffing with polishing compound to remove all the frosted surface.  This will change the shape of the dome, so the light pattern will be altered.  If that is not a problem, then go at it.

Acetone is really hard on most plastics.

Jon

[rdl]

Assuming the plastic was crystal clear originally, a thin coat of clear acrylic such as Krylon, or even clear nail polish will mostly fix it. Why does it need to be clear (just curious)?

[Habropoda]

The lens is not plastic epoxy; it is silicone.  It is slightly rubbery.  It is unlikely that polishing will help.

Exactly which rosin flux are you using?  Try a long soak in IPA; a couple of hours or even a full day.

[rdl]

Ah, well if it's silicone you can probably forget about using any kind of clear paint on it - most likely nothing will stick to it.