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Circuit Sealant question

maverick96

Sep 19, 2022
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Hello all. Quick question. Is there a difference between Rutland 76R and 76A? I was looking at buying this one but wanted to make sure it’s safe for a circuit board. Thanks in advance!
 

hevans1944

Hop - AC8NS
Jun 21, 2012
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They are both room-temperature vulcanizing (RTV) rubber sealants that use acetic acid and oxygen in the air to perform the chemical conversion from a liquid-in-the-tube to a solid filler for high temperature caulking applications. The 76R has a 600F temperature rating and is red in color. The 76A has a 500F temperature rating and is black in color. More information at this Google link.

I would not use either one as a protective, conformal coating for circuit boards because the acetic acid that is released during the "cure" process will attack the circuit traces while the product "cures" into a rubbery solid. There are other conformal coatings that are better used to "seal" circuit boards.
 

ivak245

Jun 11, 2021
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Neutral cure silicon (like the ones used in aquariums) is OK for potting up electronics. Takes a little longer to go off when it is thick. There are resin potting mixes available for encapsulating boards, it flows better around and under components.
 

hevans1944

Hop - AC8NS
Jun 21, 2012
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When the only tool you have is a hammer, everything looks like a nail. If it's sticky and can be squeezed from a tube to harden in air into a rubbery-like substance, why not try it?

Conformal coatings for PCBs were invented to increase survivability of the circuits they encapsulated, while still allowing component-level replacement and repair. In the previous century we used clear Krylon spray to protect the PCBs we made. This is pretty much the same acrylic spray "paint" that is still in use today to protect artwork that hangs on your wall. So, use whatever you want, and find out what works for you, be it "neutral cure" aquarium sealant or some other RTV sealant. But I would suggest using the stuff that was made for PCB conformal protective coatings first.

Potting is a different story. This is often done more to hide the circuitry that is underneath the potting, rather than as protection from the environment, but potting also has a functional use as a means to hold mounting hardware and connecting sockets.

Thank you so much for explaining this to me! I will take a look at the options you gave as well. Out of curiosity would something like this work? I heard silicone sealant used in aquariums is good?

I have no idea whether what works for fish aquariums also works for electronics. There are many things that do "cross pollinate" well, but you have to find out by "trial and error". If I have "invested" a lot of time and effort to make a circuit board, I am not eager to find out if I made an error in covering it with a liberal coating of any RTV silicone rubber, neutral or not, made for aquariums or internal combustion engine... unless such usage is specifically recommended by the manufacturer. This is sort of like trusting "leakproof" dry cells to not leak and damage your expensive LED "tactical" flashlight. I do use them, but I take them out from time to time to check for leaks and corrosion and replace them when necessary.
 

maverick96

Sep 19, 2022
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Sep 19, 2022
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Awesome. Thank you all for explaining this and being understanding for a noob! I appreciate your help!
 
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