Water like potting epoxy or similar?


#1

I’m looking for an electrical potting compound, preferably transparent, that has a viscosity near that of water before it sets. I’ve tried a few options so far (see https://hackaday.io/project/8343-borgcube-rov/log/30360-epoxies) and while I like the QSil, it still sufficiently viscous that it doesn’t easily flow into all the places I’d like. Anyone have any experience with alternatives? I’ve had a quick look on the forum but didn’t see anything appropriate.

Thanks


#2

Can you handle some yellowing? Do you require cure at ambient temperatures? What is the smallest feature you are trying to encapsulate?

I formulate epoxies for a living.


#3

Why do you need such a low viscosity? Depending on what you want to use it for, what you may be looking for is called “penetrating epoxy”. It’s typically used in porous materials (such as wood) to penetrate micro fissures and to re-enforce it. WEST Systems offers a penetrating epoxy as well as others.


#4

Some yellowing would be fine. It would be poured into an acrylic container, so ambient temperature might be easier, but not absolutely necessary (so long as the acrylic can survive). Feature size - I’m pouring around 0603 components so that’s probably the smallest size involved. The issue I’ve had with current experiments if getting the air out. Even with a vacuum, because the container is mostly enclosed with very few openings, the air gets trapped - hoping lower viscosity will help with this issue.


#5

I have had quite a bit of success with heating epoxies or polyurethane potting compounds to lower their viscosity. But it does dramatically reduce the setting time if they cure by exothermic reaction. I wouldn’t recommend doing this with a compound that has a short setting time e.g. 90 sec or 5 min. A set time of 2 hours or more would work well. I heat the epoxy container(s) by placing them into a jug of warm water before mixing. I can also confirm that my IMU acrylic container has survived this process.


#6

Hi Tim,

When we do potting here at OpenROV, especially for things like our external light cubes where we don’t want any air bubbles, we do all of our potting in warmer environments- in our case the only enclosed room in our office- and leave the heater running. This causes the viscosity of the epoxy to lower, making it easier to work with, and also it cures better. We use optically clear epoxy for the light cubes, and it is in this manner that they cure optically clear. Otherwise there is sometimes some fogging in the final cure. If you haven’t, check out McMasterCarr for epoxies- they are where we get all of our epoxy from, huge selection with lots of parameters to specify.

Hope that helps.


#7

Tim,

I threw a couple things together this morning and I think I have something that would work. It flows well and stays liquid for at least an hour. It should cure at room temp but this may take a few days to complete. If you can heat it to 60 C (140 F) it will cure in about an hour. I can collect viscosity info for you if you would like and could probably even send you a couple pouches if you wanted to try it. If you want to stay with a commercial solution, I’m not offended. Let me know how you want to proceed.


#8

I’ve done quite a bit of potting/ encapsulating in developing dive computer prototypes and other underwater electronics. Are you encapsulating electronics, and are any of those small SMT parts? If so I would be cautious about anything that sets up very firmly, thermal expansion can break PCB bonds down the road. It may be best to use a very soft compound like Dow Sylgard if that’s the case. I have found Smooth-On to be a good source for small amounts of urethane and epoxy resins of various types.

I had some success potting parts under pressure to reduce bubbles, putting them in a common painter’s pressure pot after pouring the potting compound.

Since our prototypes need to fly as well as go underwater, are exposed to ambient pressure, and we were using soft potting to preserve PCB bonds, what I eventually came to was the realization that I would never get our parts sufficiently bubble free without doing it under vacuum, even with very low viscosity resins. Unfortunately this needs a really good vacuum to be effective, I was able to get a high vacuum used lab pump on EBay reasonably, and make a chamber out of stainless restaurant containers. That’s made the process a lot easier.


#9

I would love to try it! I did my prototype using QSil but will probably do another version shortly, so I’d love to give what you mixed a go. Thanks!


#10

I’ve been using QSil which is a nice flexible silicone sealant. However, because it’s thicker than I’d like it tends to leave air bubbles and, even with a vacuum, I’ve not been able to get them all out. Part of the problem is the part the QSil is being poured into has a narrow channel (wide enough just to run a few wires) with few ways for air to escape. I’m hoping less viscosity will help less bubbles get caught, but I think I also need to look at how I can improve the design to give the air more places to go.