conformal coating best practices

[markxengineerin]

I have a few autopilot control computers on the bench, some broken already, some trying to avoid becoming broken. The issue with the Simrad AP22 is known to be the poor method of connecting the (silicon?) keypad cover to the case, which lets water through. I can't figure out a foolproof way to improve the interface, as there's not a lot of room for a new structure, and I don't trust a glue to stick to a flexible and flexing silicon rubber, special primer or not.

A backup idea would be to spray the whole board with this stuff
https://www.techspray.com/sr-silicon...rmal-coating-2, which if done well and enough times would make it waterproof, I think.

Is there a good reason why all marine circuit boards are not coated like this? I have had so many failures due to corrosion, might just start opening up brand new stuff and spraying this everywhere.



Once the board is "waterproof", is a drain a good idea? The water has to get out somehow or it will build up.

[Spot]

What kinds of switches are under the buttons of the panel?
If they are carbon pucks or shorting patches the conformal may render them permanently open.

Has Simrad been able to supply you info on the corroded component?

PS there are weathertight 'vents' for electronic panels that use a Goretex insert in a threaded plastic plug.

[goboatingnow]

Once you conformal coat you’ll not be fixing it again !!

[AndyEss]

Originally Posted by goboatingnow

Once you conformal coat you’ll not be fixing it again !!

you can scrape conformal coatings off, carefully clean, and solder on previously coated boards. Silicon based conformal coatings do present cleaning challenges

[Startracker]

Originally Posted by markxengineerin

I have a few autopilot control computers on the bench, some broken already, some trying to avoid becoming broken. The issue with the Simrad AP22 is known to be the poor method of connecting the (silicon?) keypad cover to the case, which lets water through. I can't figure out a foolproof way to improve the interface, as there's not a lot of room for a new structure, and I don't trust a glue to stick to a flexible and flexing silicon rubber, special primer or not.

A backup idea would be to spray the whole board with this stuff
https://www.techspray.com/sr-silicon...rmal-coating-2, which if done well and enough times would make it waterproof, I think.

Is there a good reason why all marine circuit boards are not coated like this? I have had so many failures due to corrosion, might just start opening up brand new stuff and spraying this everywhere.



Once the board is "waterproof", is a drain a good idea? The water has to get out somehow or it will build up.

The problem with conformal coatings is easiest to me to think of like painted aluminium. It delays the start of problems but once the problem is there...
The best practice but no longer serviceable after option is epoxy potting in my opinion.
I do coat exposed circuit boards however I use much lighter products.
https://www.google.com/url?sa=t&rct=...RMl9B9jHQ60vJY
Is great, it's a self healing coating designed for outboard legs, when scratched it will seal again. Merc teaches techs to fog engines/engine mounted control boards with it with good success.
Or Wurth's version of it. https://shop.wurth.ca/lubricants-gre...40-G/893.3300/

Or
https://shop.wurth.ca/electrical/ele...50-mL/890.104/

or https://skygeek.com/krylon-1307-batt...tor-spray.html

I aim for an easy to remove product, the merc/wurth ones clean up just fine with alcohol. Krylon is a bit harder but still easily cleanable.

I like them because none produce a layer that traps moisture, and they are all see through.

[team karst]

Epoxy potting is not without risk. Namely, unequal CTE pulling stuff apart. Car makers got burned on this many years ago. I'd be thinking acrylic CC. btw, potting is a bit different than CC.

Also, second vote for teflon breathable vents. For small stuff, you might have to package the fabric yourself, as opposed to OTS vents.

[markxengineerin]

There are the buttons

If they are carbon pucks or shorting patches the conformal may render them permanently open.

Great point- can you tell from the photo?

Has Simrad been able to supply you info on the corroded component?

I have not contacted Simrad about the problem.

[Spot]

Originally Posted by markxengineerin

There are the buttons


Great point- can you tell from the photo?

The ones I mentioned look more like this, where an element on the pad shorts the fingers on the circuit board:





I don't think you'd have a problem with those on yours just coating the PCB.

[markxengineerin]

Thanks everyone, I'm going to give it a try and will report back if anything bad happens.

[s/v Jedi]

Just mask those switches before spraying. Don’t forget to clean all the corrosion first.

[Spot]

Originally Posted by s/v Jedi

Just mask those switches before spraying. Don’t forget to clean all the corrosion first.

Good idea! Better five minutes up front than heartache down the road...

[mako]

OP wouldn’t it be better to figure out how to tightly seal the case, even if it is permanent? You can purge the interior with some nitrogen gas or even toss a small desiccant pack inside.

[OzeLouie]

We conformal coat air cooled condenser fins and coat PCB's etc with Elmptherm 005-008 spray and VA00 clear 400 (From 'Swift, Sydney)
But as s/v Jedi indicated, be careful.. If it gets into switches or relays etc it will be a problem otherwise a brilliant product at protecting PCB's and other potential corrodible parts.

Cheers OzeLouie

[goboatingnow]

Originally Posted by markxengineerin

There are the buttons


Great point- can you tell from the photo?


I have not contacted Simrad about the problem.

Yep cheap Chinese component. Dime a dozen.

[thomm225]

Originally Posted by AndyEss

you can scrape conformal coatings off, carefully clean, and solder on previously coated boards. Silicon based conformal coatings do present cleaning challenges

Yeah most everything we had to troubleshoot and repair back in the day (military hardware) was covered with that crap.

You can remove it, but it's a royal PITA. Even getting a good connection with your meter or O'scope through that stuff was a tough