Non-VOC Silicone RTV Sealant for LED Application

billz19834

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Forgive me if I am overlooking something but I am struggling to find a non-VOC silicone RTV sealant I can use in close quarters to LEDs. CREE has a tech note that references some dow corning numbers, but I couldn't find anything commercially available based on the numbers provided by CREE. Your help is much appreciated.
 

SemiMan

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You will likely need to buy from Kraydon or similar ... and they are not remotely cheap.
 

brickbat

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Most of the RTV silicone sealants I've seen have no VOCs. They're solventless.

The problem with many RTV silicone sealants is the water-vapor cure based chemistry. In some of these sealants, acetic acid is formed during the cure reaction, making them pretty unfriendly to nearby electronics.

There are 1-part RTV silicone sealants that are non-acetic acid based, such as Dow Corning 737 or 738, which are 'Neutral Cure', ie no acetic acid is formed during curing. Its available on eBay, Amazon, and probably lots of other places. Watch the expiration date - if it gets too old, it might not cure.
 
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brickbat

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It's Dow Corning, not Dow. 3145 is neutral cure, and OK for electronics. 732 is not!

Momentive RTV102 is acetic-acid cure - not suitable.
 
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Steve K

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for what it's worth, I've used GE280, purchased at a hardware store for a few bucks, to mount optics to Cree XRE LEDs (and some others) for home projects. I give it plenty of time to outgas before sealing up the housing (also with GE280). I've done this on bike lights, which have been in use for 8 or 9 years without issues.

I wouldn't recommend it for a production environment, but judicious use for home projects may be acceptable.

OTOH, how does the price for Dow Corning 3145 compare nowadays? The last time I looked for electronics grade RTV, it was rather pricey.
 

mercrazy

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if you're totally sealing the LED lens, you better do long term testing. i was told several products could be used for sealing that actually caused the LED lens to become cloudy after 72 hours or more. several products can be used if lens can breathe.
 
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