SparkFun Forums

[dsmith16]

Hello, all!

I have a need to enclose the pins of an opto-interrupt sensor and a couple of resistors that will be soldered to the o-i's pins. I need to enclose them in a small plastic tube (1/2" OD, 3/8"ID). I know that some substances, like silicone caulking, would be bad for this purpose (due to substances being released during curing that are corrosive, e.g., acetic acid in the case of common silicone caulk).

Someone suggested to me to use "regular epoxy." Well, I'm not sure what that is, since there are so many types these days. I would also appreciate using something that can be purchased in either small or larger quantities, without great expense. UV and/or waterproof protection is *not* required. Some flexibility in the filler substance would be *nice* (i.e., no rigid), but is not a firm requirement.

I'd appreciate any suggestions that you may have! I don't want to put product out there that I'd have to do a bunch of repairs on later!

Many thanks,
Deb

[lyndon]

Master Bond (Bond. Master Bond) has a variety of epoxies suitable for potting electronics. Should be available from McMaster-Carr, Newark, and perhaps Digikey

[Dave Mueller]

Dow Corning 748 is a non-corrosive silicone sealant made for electronics. A 3 Oz tube is about $11 from McMaster-Carr.

[dsmith16]

Great! Thanks for the tips, Lyndon and Dave!

I appreciate your taking the time, and passing on the product suggestions.

Thanks and Cheerio,
Deb

[Dave Mueller]

Hot melt glue.

[MichaelN]

Regular hardware store silicone is OK, provided you DON'T use the stuff labelled as "acidic cure". If it smells like vinegar, don't use it!

[dsmith16]

Thanks for your additional suggestion, Dave. Hot melt glue is also dirt cheap. Just messy!

MichaelN, thanks for your suggestion to use non-"acidic cure" silicone. I did think of that myself, but wasn't sure if the other various curing compounds were non-corrosive or not (I've spent a fair amount of time standing in the aisles reading labels, and wondering). Do you happen to know of the names of ones that are fine for electronics? Unfortunately, I do not have a great memory (and so may be incorrect about this), but I don't remember any of the tubes being labelled as "acidic cure." I'll go look again!

Thanks again to you both!
Deb

[MichaelN]

Do you happen to know of the names of ones that are fine for electronics?

All of the brands will have both variants, and they should be labelled. Anyway, I'm in Australia and we probably have different brands here. Sometimes you can sniff the plunger end of the tube to determine if there's a vinegar smell.

When potting electronics, make sure you don't apply it too thick or it will take ages to cure. Apply multiple layers if needed.

[Duane Degn]

I've used Sugru and Polymoph to encase electronics. They both seem to work fine. You do need to make sure anything encased in Polymoph doesn't get very warm or the Polymorph will melt. Polymorph sticks to wire insulation really well so keep warm Polymorph away from any insulation you're not planning on encasing.

https://www.sparkfun.com/products/11228

https://www.sparkfun.com/products/10950

[RonnyM]

On the hot melt thread... You can get polyethylene (nylon) sticks from Ski repair shops. It needs a little higher temp, but works in a gluegun. Extremely waterproof, and wears very well. Available natural white color, and black. Also non reactive on skin for wearable devices.
For hotmelt, get the translucent sticks, not white, if you are potting an RF device. The white stuff is like a short at RF frequencies.

[MichaelN]

You can get polyethylene (nylon) sticks...

Nylon isn't polyethylene (it's a polyamide), and melts at a very high temp, so I assume those sticks are polyethylene. Good to know that such sticks are available though.

For hotmelt, get the translucent sticks, not white, if you are potting an RF device. The white stuff is like a short at RF frequencies.

really? That'd surprising, as I would have thought it would need to be conductive to achieve that.