Waterproof sealant curing in a confined space

Thread Starter

ebeowulf17

Joined Aug 12, 2014
3,274
This may be in the wrong forum - please feel free to move it as needed.

My company is building handheld, wired display/button pad interfaces as part of our espresso machines. The interface includes a PCB with a 4x20 character LCD display, a 20 pin ribbon cable that goes out to the main machine, and an 8-pin ZIF connector which connects to an FPC sticker overlay with buttons on the outside of the enclosure.

The enclosure needs to be waterproof (or at least very, very water resistant) and was originally designed with the intention of having it sealed up with caulk (DAP Kwik Seal Plus.) This seemed to work ok initially, but we've now had a large number of failures, all of which occur only after the caulk is added. The assemblies will run for days prior to caulking, but fail within hours after caulking. I've narrowed the problem down to the ZIF connection.

I believe that the caulk is releasing water vapor and other chemicals as it cures, and that the moisture and/or chemical vapors are what's causing the ZIF failures. Because of the design of the enclosure, the sealant is trapped inside with the electronics, so any vapor/fumes can't escape.

I'm hoping to find a sealant that can cure reasonably well in a confined space (or perhaps even one that never cures, but seals well enough in a tacky state.) More importantly, it needs to be something that is not releasing water vapor or corrosive chemicals as it cures. Does anyone have advice on a product we could use to seal our enclosure up without the sealant itself causing problems for the electronics, despite being in a confined space with no airflow? It would be very difficult to incorporate a custom gasket, and we'd rather avoid going that route unless there's no other way.

The area that needs to be sealed is already a fairly snug fit - we only need to lay down a bead about 1mm wide and fractions of a mm thick in order to get sealed up. Any advice is greatly appreciated.

Thanks!
 

DickCappels

Joined Aug 21, 2008
6,535
If your sealant smells like vinegar, you have the wrong sealant. There exists at least silicone sealant that does not contain acetic acid. These are sold for use in aquariums.
 

mcgyvr

Joined Oct 15, 2009
5,394
Call momentive or dow and let their engineering support recommend a neutral cure rtv for your application instead of a acetoxy cure.
 

Thread Starter

ebeowulf17

Joined Aug 12, 2014
3,274
Thanks for all the insights! One of my co-workers is designing a custom gasket to get quotes on that. Maybe it'll be more reasonable than we've feared. In case it doesn't work out, I'm going to do some more research into the neutral cure RTVs, which so far sound like the best solution aside from custom gaskets.
 

mcgyvr

Joined Oct 15, 2009
5,394
"hey boss.. Shouldn't we be addressing the water ingress protection early on in this design"

"nah... we will just go to home depot and grab some bathroom caulk"
:D
 

RichardO

Joined May 4, 2013
2,271
Thanks for all the insights! One of my co-workers is designing a custom gasket to get quotes on that. Maybe it'll be more reasonable than we've feared. In case it doesn't work out, I'm going to do some more research into the neutral cure RTVs, which so far sound like the best solution aside from custom gaskets.
I would think a custom gasket would be easy to try by getting some rubber sheet Laser-cut. For higher production volumes, a rule die would be the way to go.
 
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