PCB protective liquid

Pitrus

Member
2019-06-11 1:12 am
Italy
Hi all,
I would like some advice on which excellent spray product to use to protect the soldering side PCBs after having cleaned, degreased and removed the original protection applied by manufacturers on old pcb's.
I don't want to leave the pcb without any protection.
Thanks
 

Pitrus

Member
2019-06-11 1:12 am
Italy
Many thanks, in the past I had already noticed these products but I have not trusted to buy anything as I am not aware of the feedback; if they work well, if they dry quickly or remain sticky, if you can solder or desolder after application.
For this I was looking for some good protective product that has already been used by some forumers without problems.
 
I'm not aware of any consumer gear that was conformal coated. Most people can't get a PCB to the level of cleanliness required for coating. If it isn't clean, reliability may be reduced by coating, not improved. That said, I've coated PCBs with Krylon clear plastic spray. They used to sell it as an electronic coating, but it seems they no longer do. You can also get various different products from Humiseal.
 

MJB11

Member
2016-03-15 1:26 am
The Gold standard in conformal coatings is Miller Stephenson. The problem I have had using other type of coatings has been certain plastic parts being attacked by the solvent in some spray coatings and the coatings cracking and peeling. I have used both the acrylic and silicone versions of the miller Stephenson coatings in high voltage equipment used in damp areas for arc suppression with good results.
This is a link to their article on selecting a conformal coating: https://miller-stephenson.com/conformal-coatings/
I have alway purchased directly from Miller Stephenson, but you can also find it in distribution.
 
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I use varnish on my computer SMPS, as it keeps dust off the tracks...in the monsoon here, we have 70% of the annual rainfall in two weeks at times, and extended high humidity with dust means arcing, flash over etc.

I also have used it on PLC boards.

Varnish is safer and more environmentally friendly, also very cheap compared to spray.
And no clogged nozzles after long storage, or gas leaks.

If it is a low voltage circuit, less than say 60 Volts, even furniture varnish should be suitable.

I paid about 90 cents for a 200 ml. bottle of motor varnish, which is a very small quantity if used in motors.
Sprays are rather more expensive.
 

Pitrus

Member
2019-06-11 1:12 am
Italy
If it is a low voltage circuit, less than say 60 Volts, even furniture varnish should be suitable.
Sprays are rather more expensive.

Thanks but I have no cost problems but I don't want to use paints not suitable for PCBs with the risk that vapors or solvents damage the plastic parts or the components themselves ... I don't like looking for experiments on other owners' pcbs if I loved experiments I would not have asked here.


Do prepare the surface, remove dust, flux and so on before applying the coating of your choice.
And let it cure for a day in a well ventilated area before assembling it back.

surely.
 

Bas Horneman

diyAudio Moderator Emeritus
2002-04-03 12:03 am
The Netherlands

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Pitrus

Member
2019-06-11 1:12 am
Italy
Since you are in the EU.

I have used both of the following :
https://www.reichelt.de/ch/de/korro...ck-kontakt-255-p9514.html?&trstct=pos_2&nbc=1
https://www.reichelt.de/ch/de/korro...ck-kontakt-213-p9474.html?&trstct=pos_3&nbc=1

The Plastik-70 is faster drying and has better isolation properties. But it is more brittle.
I personally like the Urethan-71 better as it is somewhat more elastic. Important for coils and transformers, etc.
Urethane-71 has a long curing time at room temperature, and is best oven cured at 60°C or so.

In both cases, it is very important to have all residual flux etc completely cleaned off.
And the PCB assembly baked dry (at say 60°C for 15 minutes) before spraying.
If any mositure is trapped inside the coating, you will surely get oxidation where you have exposed copper.

For low voltage circuits, it is not so critical.
But for high voltage I always wish to have the PCB assembly coated.

And desoldering best done after scrapping off the coating to avoid carbonised residuals.


My experience,
Patrick
 
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Bas Horneman

diyAudio Moderator Emeritus
2002-04-03 12:03 am
The Netherlands
Well many thanks important question: does it allow normal desoldering and soldering after application without problems if there are components to be replaced after some time (weeks, months, years) or does the paint tend to boil, cloud over or other problems with the heat of the soldering?
Well what is normal. It's not pretty when you desolder and resolder. You'll just have to clean it up. I usually just desolder (only once or twice ever) without removing it first. Then just scrape/clean...en recoat. Never as pretty as when you don't have to disturb it.
 
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The 'Plastik' spray is PVC dissolved in a chloroform like solvent, that can affect some plastics.

So my choice of using varnish is based on that fact also, some sprays contain solvents which may affect plastics, and aged plastics are even more risky in their reaction to solvents.

The 'Plastik' spray sold here is about 5 USD for a 400 ml. or so spray can, not very expensive, but I use it only on brand new circuits, never on more than 5 year old circuits.

Any coating will get damaged by soldering heat, so must not be used on a 'project', where you may repeatedly modify the circuit till satisfied.

But for long term use, it is okay, and yes, repair will be needed once it is removed or damaged. But that is a small risk, in comparison to the value of the circuit being protected.
 
"PLASTIK 70 is a low viscosity, solvent drying acrylic based conformal coating"
https://www.farnell.com/datasheets/318249.pdf

Not PVC, sir. And no mention of chloroform in the safety sheet either.

And any electronic component has to survive a solvent cleaning process in volume production.
I never had any issues with those two with any plastic components on a PCB.
The PCB itself is of course epoxy based thermoset, and solvent resistant.
Same goes for the silk screen and solder resist.


Cheers,
Patrick
 
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