Chemtools PCT-7000Y Silicon Potting Compound - anyone familiar with?

[DTJ]

Has anyone personal experience with Chemtools PCT-7000Y Silicon Potting Compound?

I'm interested in how well it bonds to things, in particular the PCB & components and also to 304 stainless steel.
The data sheet does not mention its adhesive properties.


Data sheet: https://download.altronics.com.au/files/datasheets_H1620.pdf

I want to pour it down a 12mm ID x 100mm long metal tube to seal in a PCB (11.5mm x 80mm), the assembly will be immersed in water several meters deep.
It needs to be low viscosity (runny) so that the air bubbles all escape.

Thanks for any advice.

[Muttley Snickers]

I haven't used the Chemtools compound you mentioned but am aware of some other similar products which are distributed by G.V. Kinsman. One type of potting compound is shown in the video below but they have other stuff as well. Someone in the comments section also asked about a submerged connection.

www.gvk.com.au

[DTJ]

Thanks Muttley.

That stuff looks a little soft for my application but definitely interesting.

Lots of other useful items on that site, Cheers.

[IDEngineer]

It needs to be low viscosity (runny) so that the air bubbles all escape.

Many potting compound vendors point out that you can evacuate air bubbles by putting the freshly potted module into a vacuum chamber with a slight vacuum. Obviously this requires some extra equipment but it might be an option for what you're doing.

I can also tell you from personal experience that epoxies are far easier to keep bubble free than urethanes, which are also often used for potting. The latter are often preferred due to their softer cure (less risk of fracturing SMD's, particularly MLCC's) but our experience has taught us that epoxies yield better overall results in production. You can get epoxies with lower durometers if you look around, which helps offset the risk, and using a slower cure compound helps too. The one we use has a pot life of around 30 minutes and a full cure time of 24-48 hours at STP.

[DTJ]

It needs to be low viscosity (runny) so that the air bubbles all escape.

Many potting compound vendors point out that you can evacuate air bubbles by putting the freshly potted module into a vacuum chamber with a slight vacuum. Obviously this requires some extra equipment but it might be an option for what you're doing.

I can also tell you from personal experience that epoxies are far easier to keep bubble free than urethanes, which are also often used for potting. The latter are often preferred due to their softer cure (less risk of fracturing SMD's, particularly MLCC's) but our experience has taught us that epoxies yield better overall results in production. You can get epoxies with lower durometers if you look around, which helps offset the risk, and using a slower cure compound helps too. The one we use has a pot life of around 30 minutes and a full cure time of 24-48 hours at STP.

I've got the basics for degassing if  I need to.

I'm using a urethane now (70A shore) and I'm worried its a bit hard. I've used harder epoxy on other jobs and it worries me.

I found a better data sheet on the PCT-7000 on the chemtools website that clarifies the adhesion question. They promote it as an adhesive in that data sheet so it should do the job.

[IDEngineer]

I'm using a urethane now (70A shore) and I'm worried its a bit hard.

The two-part epoxy we've been using for 2-3 years is rated at Shore 70D. According to this chart:

https://www.minerelastomer.com/technical-data/tecspak-features/shore-shore-d-comparison/

...Shore 70D is about the same as Shore 100A, though the curve is flat in that region so precise comparisons are difficult.

That said, we've had very good luck with this Shore 70D material. You can just barely deform it with a sharp tool, so it's not "glass hard" and still has some mechanical compliance. We have lots of MLCC's on our stuff, and they're generally very susceptible to shear, so  I would say that 70D is acceptable for SMD boards.

Your Shore 70A material clocks in at about Shore ~20D on the above chart. Based on our experiences with 70D I wouldn't worry one bit about 70A.

[DTJ]

Thanks IDEngineer, that's good to hear.


I dug out a failed unit yesterday and found an 0805 ferrite had gone open circuit. It had no obvious cracks on it (under 40x microscope).

I don't know what to put this down to.
Was it potting stress? - probably not.
Soldering stress - they are hand reflowed with hot air.

Anyway I've grabbed some softer PCT-7000 and will try it today.

[wraper]

https://www.eevblog.com/forum/chat/its-silicon-not-silicone!/

[DTJ]

https://www.eevblog.com/forum/chat/its-silicon-not-silicone!/

Yeah but was it really worth a comment?