Conformal Coating for Hi-Z parts

[Seeker]

Im looking for a recommendation for conformal coating, specifically for high impedance sections of microphones...  I live in Fl and have occasional problems, a quick cleaning solves it, but it always happens at awkward times.  Anyone know what the red gunk you find on many commercial mics is? 

 

[Gene Pink]

  Anyone know what the red gunk you find on many commercial mics is?

Probably glyptal.

Not the real deal, but I use this product:

http://www.mgchemicals.com/products/insulating-coatings/red-insulating-varnish-4228

It comes with a small brush attached to the cap, or at least it did, the last time I got some. Note the 3KV per mil insulation spec.

Radio Shack used to carry something similar, but I imagine the nearest thing you'll find there these days, is a red cell phone.

Gene

 

[joaquins]

  That looks good to prevent arcs but I don't know about leakage , that is what he's asking for.

  How high impedance do you have that you need the coating? Bare board leakage problems or prevention for long term reliability?

  I'm thinking in a way to do soft potting but I haven't find the solution yet, I'm probably going to try with silicon but I need a non acetic one to start, which is not the one you buy on anywhere, that would be bad for your traces. I read somewhere that car body sealant could work.

JS

 

[RuudNL]

It seems this one is especially well suited for hi-Z parts in microphones:

MG Chemicals 419C Acrylic Lacquer Conformal Coating

 

[Seeker]

Thanks  Gene, I dont know much about coatings, so my first thought was use what the pros do... maybe thats Glyptal 1201? 
EDIT: Actually after a little more looking I'm thinking maybe not....

I saw another product by MG chemicals

http://www.mgchemicals.com/products/conformal-coatings/acrylic-conformal-coating-419c

they also make a silicon based product

http://www.mgchemicals.com/products/conformal-coatings/silicone-conformal-coating-422b

And yes leakage is my primary concern.  I make most of the very high impedance connections on my mics in the air, or with teflon standoffs, the mics are nice and quiet...  But in Fl its hard to avoid the humidity, esp when on location.  So in answer to your question Joaquins, Its long term stability, not solving a problem in mic construction.

Thanks guys!

 

[Seeker]

You beat me to it RuudNL.... the 419c looks good

 

[AusTex64]

I would be terrified to use a conformal coating on a mic with 1G resistors. My concern is spraying it on, powering up the mic and hearing noise. What then? How would you get it off?

 

[gyraf]

Check the mic for dirt-noise before coating?

Jakob E.

 

[zephyrmic]

And make doubly sure that there is no overspray anywhere near the capsule!! That could be a capsule killer!
zephyrmic

 

[RuudNL]

Don't use spraycans! Apply it with a small brush!

 

[AusTex64]

Check the mic for dirt-noise before coating?

Jakob E.

Well yeah, but what if something sneaks in? Or the humidity in the air decides to condense around the high Z components since it's trapped under the coating? Just seems people have been using condensers in high humidity environments for a long time (it's also quite humid here in Austin and Houston) successfully. We regularly have days here of 80%+ relative humidity and I've never had a problem.

Curious - is the OP using the mics indoors or outdoors? Indoors the air will be dried considerably by A/C and heating.

 

[Andy Peters]

Check the mic for dirt-noise before coating?

Jakob E.

Well yeah, but what if something sneaks in? Or the humidity in the air decides to condense around the high Z components since it's trapped under the coating?

Do the coating in a clean room, or at least in a well-air-conditioned environment under a laminar-flood vent hood.

 

[Seeker]

specifically I have some hand build pencil mics that occasionally need a cleaning.... However, conformal coating is pretty common on many commercial mics... I've removed it to solder components but never bothered replacing it, until now.

Recently I recorded in a building with high ceilings where the AC had been off until the day I set up, it was reasonably sticky... The mics were left setup overnight & when I came back apparently my room mics (the pencil mics) picked up some noise.  A quick cleaning fixed it....

So I'm figuring a good cleaning, testing, and then a coating will stop the issue...