choosing a conformal coating and its applicator, then applying it (duh)

[broly]

hi

so mg chemicals has a few options

• acrylic (419) https://mgchemicals.com/products/conformal-coatings/acrylic-conformal-coatings/circuit-board-protective-coating/
• silicone (422b) https://mgchemicals.com/products/conformal-coatings/silicone-conformal-coatings/silicone-modified-conformal-coating/
• polyurethane (4223f) https://mgchemicals.com/products/conformal-coatings/polyurethane-conformal-coatings/urethane-conformal-coating/

according to their application guide: https://mgchemicals.com/downloads/application-guides/Application%20Guide-Conformal%20Coatings.pdf
 
the cure times for 419, 422b, and 4223f are 24, 48 and N/A hours at room temperature (or 25 degrees, so not room temperature. whatever)

i do not at this time have a temperature-controlled enclosure to keep the polyurethane coating, so i have to return it, or maybe not?

my questions for you guys are:

• which one should i buy?
• what applicator style should i get?
  
  • all 3 variants come in a 55mL bottle (25, 30ish, 40ish loserbux for acrylic, silicone, poly respectively), OR aerosol can
    
  • the 419x line comes as a (optionally coloured) pen (29 loserbux) and locally the 55mL bottle is sold out
• do the acrylic and silicone coating really need 24/48 hours to cure? do they dry before that? it's not a big deal, just wondering
  
  • if i just blast any of these using the hot air nozzle on my WPA2N, is that sufficient? does my willingness to do so change the recommendation?

at this time i am tempted to go with the acrylic pen in green, even though it doesn't have as much value. aesthetically it will probably look nicer, which i understand is irrelevant.

• the silicone coating seems appealing too, but the longer cure time is annoying.

in the store i thought the spray would be useless but i didn't realize solder removes the coatings, which now makes me think the spray is likely the best option since applying an iron to a coated contact will dissolve the coating?

• but the trouble is, again, no temperature controlled enclosure. so i don't know if the WPA2's hot air nozzle would be useful for aerosol application

and if i haven't implied it: i greatly value the concentrated expertise of forum members, whose answers to such particulars in decades past still echo through the chambers of SEO today (lol)

[JustMeHere]

Just get a spray can of the stuff. and spray on a few coats.  Use acrylic.  Put something like a paintable latex or a maybe even elmer's school glue over any surface you don't want to coat.  Then peel that off once the rest of everything cures.

[broly]

thanks for the tips.

these boards are rather small, so i'm wondering if the pen or brush 55mL bottle may be better for precision application.

do you have any experience with the pens? i am curious about the precision of the application.

and what about drying time? often drying time != curing time; i hope acrylic dries relatively fast so i don't have to wait the 24 (or 48 if i go silicone) for curing?

my next question would be: if i don't use mask, how hard is the coat to penetrate using solder with an iron?

have you used silicon coating? a rubbery finish seems cool in theory. i wonder if it's easier to penetrate when it comes to laziness for masking due to space constraints (i have way too much shit in a house that isn't mine, and i've run out of room for a workbench/desk. too much other shit.)

[JustMeHere]

I have experience with painting.  And a spray is the way to go.  Make a few quick passes past the board.  Let it dry for a bit.   Do it again from another angle.  And repeat once or twice more.  Then let it cure overnight.

If you've never spray painted, practice with spray paint on something first.  The trick is to start on one side of your target, make a full pass across, and then stop.  Start and Stop when not aiming at your target.  This gives you a good even coat.  And watch out for overspray.

You can inspect the spray coatings with a blacklight.

There is usually a "workable" time in the spec sheet, but overnight is good enough.  You can often speed up cure times.  RTFM on that.  Heat works sometimes; sometimes it is the wrong thing.
Test the spray on something to get these times.
When you do your work, you can spray a test subject so you can judge when the work is "workable"  --Beer cans work well for testing -- or a scrap board

[broly]

I have experience with painting.  And a spray is the way to go.  Make a few quick passes past the board.  Let it dry for a bit.   Do it again from another angle.  And repeat once or twice more.  Then let it cure overnight.

If you've never spray painted, practice with spray paint on something first.  The trick is to start on one side of your target, make a full pass across, and then stop.  Start and Stop when not aiming at your target.  This gives you a good even coat.  And watch out for overspray.

You can inspect the spray coatings with a blacklight.

There is usually a "workable" time in the spec sheet, but overnight is good enough.  You can often speed up cure times.  RTFM on that.  Heat works sometimes; sometimes it is the wrong thing.
Test the spray on something to get these times.
When you do your work, you can spray a test subject so you can judge when the work is "workable"  --Beer cans work well for testing -- or a scrap board

thanks

thoughts on silicone v acrylic? cure times markedly different (silicone being 2x per mg chemicals doc)?

what about board feel post cure?

and why no unreserved recommendation for silicone v acrylic, assuming cure time is irrelevant and technique is assumed to be 'competent'?

[JustMeHere]

I've used both.  Silicone isn't super tough and can be removed easily. Acrylic is basically plexiglass.  I will only use acrylic from here.

[Analog Kid]

Here's another choice for a board coating: epoxy.

Meaning liquid epoxy, not the thicker "glue". Like marine epoxy for coating fiberglass.

I had a project with a lot of somewhat fragile wiring I wanted to protect, done by point-to-point wiring on perfboard.
Ended up drenching it in liquid epoxy.

It stopped working for a while before it set, but was fine afterwards. (Epoxy is quite nonconductive).
And it's a really tough coating.

Not easily removable.