Would covering a 555 timer and isolated gate driver circuit with silicone glue which hardens and is very electrically insulating cause ESD or other issues?

https://www.ebay.com/itm/133044149654

Measured this in its still liquid for with a DMM as open with probes ~2-3mm apart completely covered with it and it measures open when cured. But not sure if this can cause issues. The circuit will be enclosed in a junction box with a fan blowing air thru it.

This is the circuit to be covered.

 

hi 48,
I would not expect an ESD issue, but one point that should be considered is the possible self heating of any components due to the thermal insulation.
E

 

Repairability = 0.
I have not done it, just test. Should be ok.

 

You do need to use an electronic grade silicone which will not use acetic acid to cure. The acetic acid is damaging.

 

Is there a simple method to determine whether the linked silicone glue has acetic acid in it?

you can just smell it, normal silicone smells like vinegar.

 

Vinegar is acetic acid, so yes it contains acetic acid.

 

hi 48,
A quick check for acidity, could be a Litmus paper test.
E

 

ESD damage is caused by a charged item coming too close to sensitive electronics. Or in contact with a charged item. Silicone in liquid form is not going to be charged, so you're not generating any static with it. Cured silicone likewise is unlikely to cause problems. ESD is generated by separation of items. When atoms are stripped away, such as pulling tape off a tape roll generates static charges. Rubbing things together causes static. Applying silicone will not cause static damage, nor will it protect the circuitry from damage.

Electrostatic fields can pass through many items. Conductive materials such as a Velostat bag will direct the static around sensitive components. Metal containers protect. Anything that forms a Faraday Cage will protect. It also will block radio waves, so you don't want to put BlueTooth in a Faraday Cage or metal container. Not unless it has an external antenna.

The only two issues I see are heat and repairability. Even though you say heat won't be a problem, the 7805 IS going to make some heat. I don't know silicone to have better thermal conductivity than air, but if you say so and are confident - - - . As for repairability, pulling silicone off can be very damaging. Those would be my biggest concerns.

 

Why use silicone when there are things available to do the job? Things made especially for the job and available pretty easily on the web.

 

Is covering it necessary? What sort of environment will it be in? There are spray coatings called "Conformal Coating" and come in a variety. I couldn't tell you which would be best, only that they exist. I don't think they're all that much more expensive than a regular can of paint. Oh, and don't paint your board. Probably even worse an idea than silicone.

 

In the factory, when PCB's are CC'd (conformal coated) areas that should not be coated are masked off - same as you do when painting your car. Once the CC is dry you can pull the masking off the board and are left with coated and uncoated areas as per choice or design.

 

You coat as many times as you want to get the thickness you desire. Usually 1-2 coats is not very thick but sufficient.

 

What thickness does CC give? Can a board be coated for more thickness?

Conformal coating. The link covers thickness and as mentioned just apply more coatings. Additionally the stuff can be thinned down.

Ron

 

Earlier I said that they were probably comparable to standard spray paint cans. I was wrong. Very wrong. Depending on what you get you can spend $15 to $150 (US). Have a look on Amazon to get an idea.

 

Why not just put some tape over it? All kinds of neat tape now.

 

The roundness of the epoxy has to do with surface tension. Like a bead of water on a freshly waxed car.

 

Epoxy is more costly.

Who said anything about epoxy? And your the only one that can judge what you circuit board is worth, and how you want to protect it. Any silicone I've ever used from a hardware store doens't flow it has to be pushed into creavices (like around chip, resistors, etc) The conformal coating are made to flow around the components and are formulated to conduct heat away from the circuit. But like all things with you, your the expert, so why even come here and ask the question?

 

@shortbus Flowable RTV.

I don't know if this would be suitable on electronics though.

 

@shortbus Flowable RTV.

I don't know if this would be suitable on electronics though.

Nope!

If you read the description it contains acetic acid. Electronics and acetic acid do not get along.

 

Well, to Shortbus's comment about having to push RTV, I've used pourable types of RTV in the distant past.