PCB Coating

[Christopher]

I've found myself milling a lot of PCBs recently, with bare copper. Once these are installed in fixtures, there is a high chance of the copper going gash (oxidizing) even after cleaning the flux with Solvent cleaner, just weeks after soldering. Tinning is a good fix, but takes a lot of time on ground planes.

I have brush conformal coated before which does work but takes a long time to cure and renders the brush useless after one use! The concoat is also a bit thick which makes future repairs quite hard.

I have found this on RS, what do you think?  Seems like it will work OK, 24 hrs drying time and quick application due to being an aerosol.  I haven't used it before so I will ask the experts!

Can you recommend this or something similar from RS/Farnells?

http://uk.rs-online.com/web/p/conformal-coatings/4090956/

[Monkeh]

Why not just use a generic cheap spray on lacquer?

[RiverTown]

I'm using Plastik 70 spray. Manufacturer is KONTAKT CHEMIE.
Works like a charm.

[Christopher]

So something like this will be fine then? I don't wanna go buying something cheap to just throw it out. It's only £5 and takes 20 minutes to be touch-dry so worth a shot then!


http://uk.rs-online.com/web/p/electronics-varnishes-lacquers/0569307/

[con-f-use]

I'm using Plastik 70 spray. Manufacturer is KONTAKT CHEMIE.
Works like a charm.

[Monkeh]

So something like this will be fine then? I don't wanna go buying something cheap to just throw it out. It's only £5 and takes 20 minutes to be touch-dry so worth a shot then!


http://uk.rs-online.com/web/p/electronics-varnishes-lacquers/0569307/

Yes. You can get even cheaper if you visit a sane DIY shop, a can that size of generic lacquer is about £2.50.

[tggzzz]

I've found myself milling a lot of PCBs recently, with bare copper. Once these are installed in fixtures, there is a high chance of the copper going gash (oxidizing) even after cleaning the flux with Solvent cleaner, just weeks after soldering.

I wonder how real a problem this actually is. Why? Because I'm currently "repurposing" a digital clock I scratch-built (literally) in 1974. It was the first digital most people had ever seen. Several really disliked it because they could see the seconds of their life ticking away!

The PCBs are cruder than you are likely to imagine, but they still work perfectly. So what conformal coating did I apply? Conformal coating - what's on earth's that? I had enough problems getting decent etch resist! From the look of the boards, it looks like I used nail varnish or similar, and hand-scraped away the varnish where I needed a gap.

But there's nothing wrong with the boards, even the 1000uF power supply electrolytic still works fine. Pah! Youngsters today! Don't know how easy they have it.

YMMV

[Christopher]

My mentor at work doesn't like the fact the boards can go gash and has suggested concoating. Something which will take a lot of time (which i don't have). So a quick spray has got to be better than no coating at all.

I agree for a home project why bother? But for something I want to work in a few years time and not have to repair it. Or the next guy in five years say "look at these green circuit boards. What a chump!"

DIY store is pretty much out of the question as it's a work thing. I'll stick a can on my next RS order as I have a metric bucket-load of PCBs to make up next week

[SeanB]

Grab a couple of cans, as you will find that those conformal coat cans have a very poor seal on the sprayer, and will leak the butane propellant out after you use it a few times. The problem is the rubber seal is attacked by the solvent in the laquer, and this is fine until you start using the can.

[nukie]

Attached is an excerpt from a Fluke service manual. My device is built in 1972. The Polyurethane coating is beautiful and glossy gold transparent. It's no high tech coating but the sealant should last 40 years if applied correctly as proven by the Fluke device that I have.

The price for the device in 1990 is RRP $11,950 I'm pretty sure Fluke have a lot of trust in this sealant.

Here's a link that discuss different types of conformal coating
http://www.paryleneengineering.com/pdf/conformal_coating_removal_techiques.pdf

You can buy small amount of UV cure soldermask, smear a very thin coat over your circuit and cure it with the right UV wavelength. It cures immediately and it is permanent and super hard.
http://www.taiyoamerica.com/index.php/products/products-pcbs/

[SeanB]

Parylene is a solder through coating ( if you keep well away from the fumes it makes) and is easy to reinstate afterwards with a brush. There are other 2 part conformal coats that are harder, but are not solder through. Some of those are so tough that even if you placed the board in an ultrasonic vapour phase cleaner for 5 minutes, which normally would mean the actual PCB itself delaminates to fibres, the coating would hold together.

[ampdoctor]

what's wrong with liquid tin? While it's not as good as actually tinning the board, it seems it might be more than adequate for the OP's needs.

As an aside, I had a thought the other day about using nail polish for areas where the creepage is marginal on home rolled prototypes. I do a lot of work with prototyping circuits with 400v+ rails so normally I'm stuck figuring out how to route them with clearances >=100mil, so the idea of getting it down inside the 50 mil range is appealing. Point being, in my info search I found that some nail polishes as well as lacquers can be conductive depending on the chemistry. So show caution before you spray down your board with an over the counter lacquer from your local hardware store.