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Solution for clearing LED epoxy on emitter?

Steveggz

Oct 7, 2017
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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 frosted 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?
 

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Harald Kapp

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Even when you managed to remove the flux, most likely the plastic has been damaged.
You may try to use watch glass polish.
Or, as you suggested yourself, put on a coat of clear laquer. However, the LED may become hot during operation and the laquer may start to get tinted (yellowish or brownish) by the heat. Therefore I'd try polishing first.
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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I would probably ask Mr Cree what he recommends. Perhaps there is a type of flux or a method of soldering that is more compatible with the plastic.

Retrospectively... Polishing may work if it's a surface defect, but not if the flux has impregnated the lens.
 

Steveggz

Oct 7, 2017
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Yes, just found out some LED's come with frosted lenses to disperse the light differently. I just hope it won't reduce the light output. 104 Cree XT-E's 1 1/2 inched behind a remote phosphor plate. As long as the same amount of light outputs it shouldn't matter. Do you know if I will lose light output?

I tried the polishing unsuccessfully. Even at the lowest setting on my dremmel it ate down the lens to a flat one. The plastic coating on the emitters are pretty soft and make hard for polishing. I might test out some high temp lacquer just for fun.

Thanks for the watch glass polish suggestion I'll look into that first.
 

Hopup

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Use wet very fine type of sandpaper to sand it as smooth as possible and apply some kind of heat resistant coating on the led. Car headlight polishing kits might work for an example. You can sand the lens flat, it will result more dispersion but that should not matter in you application.
 

Steveggz

Oct 7, 2017
15
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Oct 7, 2017
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Use wet very fine type of sandpaper to sand it as smooth as possible and apply some kind of heat resistant coating on the led. Car headlight polishing kits might work for an example. You can sand the lens flat, it will result more dispersion but that should not matter in you application.

Nice! Will try.
 

(*steve*)

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If you're talking about those soft, jelly-like lenses, then you're not going to be able to fix them and I withdraw my suggestion about polishing them.

The cloudiness may change the radiation pattern, and possibly the colour. How much? It's hard to say. If it doesn't seem to affect the effectiveness of the LEDs in your application, if just leave them alone.
 
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