Repairing corroded PCB

[ivan747]

Removing all of the components and cleaning the board properly.

I'm gonna try wiping 95% alcohol all over the bare board, then water all over the non metallic components and alcohol all over the metallic components. The reason I am not using water is because I don't want its minerals corroding this and I don't have access to distilled water for the moment.

[ivan747]

Having trouble desoldering the sockets. They do show some signs of corrosion:



I wonder what could be a good approach in this case.

[ivan747]

Just wiped the board with alcohol and it's looking amazing. The only problem is that the solder mask is indeed scraping off the copper traces:




I am thinking of lightly sanding the corrosion away, tin plating it and then, when the amp is assembled, apply some form of coating or enamel over it (ideally only over the top traces). Anything besides WD-40 and solder? I'm evaluating alternatives.


Edit:

Okay, I have found that there is lacquer specifically made for PCBs that is solderable and has appropriate dielectric properties. I just hope I find a liquid version, instead of a spray can, which is a nightmare to import by plane to my small country. I have not researched any brands yet.

[ivan747]

Perhaps unsurprisingly, the exposed corroded trace can't be soldered. I scrapped quite a bit of the trace and I still can't find "healthy" copper. I think I will coat the board to prevent any further damage, definitely.


Edit: well I found a "conformal coating pen". If that actually works for my application it would be ideal: it won't draw any attention at the postal service when it's inspected before being boarded on a plane, unlike aerosols. It doesn't weigh fifty million tons. Doesn't look like a hazardous material either.

590-422B-P
http://www.mouser.com/access/?pn=422B-P&sn=MG%20Chemicals&utm_source=mouseriphoneapp&utm_medium=app&utm_campaign=422B-P&utm_content=MG%20Chemicals

[ivan747]

Looking shiny




Hey, at least the copper trace still has great continuity (less than 0.1 ohm).


Edit: well, according to MG Chemicals, you can solder through the conformal coating that comes in their pen. Looks like this could be it. However, Mouser adds a ORM-D label that I wish they didn't. Gonna look for that pen somewhere else

[ivan747]

MG chemicals is starting to become my favorite chemicals company after Seachem in the aquarium hobby. Turns out they produce an "Overcoat pen" that comes in a variety of colors including, you guessed it, PCB green. It's acrylic conformal coating in different colors. Perfect to disguise the ugly corrosion that's occurring. My plan is to cover all the top traces with it, so that I "paint" them green. It can be applied to a board that has been cleaned by IPA, something I already have.

On amazon:
https://www.amazon.com/MG-Chemicals-Overcoat-Pen-Green/dp/B0111O7AJM/ref=sr_1_5?ie=UTF8&qid=1497751632&sr=8-5&keywords=conformal%2Bcoating%2Bpen&th=1

Product flyer:
http://www.mgchemicals.com/downloads/pdf/flyers/419D_P_Conformal_Coating_Overcoat_Pen.pdf

Datasheet:
http://www.mgchemicals.com/downloads/tds/tds-419d-p.pdf


A second alternative is to get a 55ml bottle of conformal coating (the kind that you can solder through) and just completely coat the board, but leaving the ugly traces there.

[james_s]

The traditional "WD-40" in a blue and yellow can is mostly kerosene. It's a water displacer and is marketed to do many things, none of which it does as well as a specialized product. It won't hurt a PCB, but it will make an oily mess, fortunately it's fairly easy to wash off. Those rust dissolving products do work well, I use one called Evaporust which works remarkably well, you just put the item in a pan or a ziplock freezer bag, pour some in and let it soak for a day or two. A soft brass bristled brush is also good for cleaning up this sort of thing. Once finished, shoot it with a coat of conformal coating or clear lacquer to prevent future corrosion. That board doesn't look too bad at all to me, it will clean up fine.

[ivan747]

The traditional "WD-40" in a blue and yellow can is mostly kerosene. It's a water displacer and is marketed to do many things, none of which it does as well as a specialized product. It won't hurt a PCB, but it will make an oily mess, fortunately it's fairly easy to wash off. Those rust dissolving products do work well, I use one called Evaporust which works remarkably well, you just put the item in a pan or a ziplock freezer bag, pour some in and let it soak for a day or two. A soft brass bristled brush is also good for cleaning up this sort of thing. Once finished, shoot it with a coat of conformal coating or clear lacquer to prevent future corrosion. That board doesn't look too bad at all to me, it will clean up fine.

Thank you. Looks like a nice product. I'll be looking for it and for the WD-40 "specialist rust remover" locally.

For preservation, I'm already looking into conformal coating and lacquer. I'm not sure what type to get still. Conformal coating is not available locally, so I have to import it.

Importing aerosols can be troublesome because air couriers just won't let you ship those. Also, large containers of chemical products will definitely call their attention.

 My only hope is liquid conformal coating, in a very small presentation. I've found several of those on Amazon, but I'm not sure how nice the finish will be on the PCB. After all, I'm brushing shinny stuff on a PCB. I think I will get a variant that can be removed with isopropyl alcohol, just in case it looks horrible.

I think I will display the board and the whole project. I will reassemble it as it was. The enclosure will be a "display box". It will consist of a wooden board that supports the kit, just like before, but this time larger. A small panel on the rear will give access to the power and audio connectors. An acrylic box will be placed on top of the wooden board to protect the whole project.
Something like this:



The acrylic box will be shaped in such a way that it accommodates the rear panel. This way I don't have to unplug anything when I want to put the acrylic box back on the project.

I managed to desolder the tube sockets. There is some corrosion in those. It has some blue or green deposit that looks like it could be some sort of salt. I wonder if it's copper with something else.

[Electro Detective]

WD40 on a cotton ear bud or Q tip? applied a couple of times will quickly fix that blue green crap/corrosion

It looks like similar gunk to corroded battery terminals in multimeters,

which many here at EEVblog love... to hate 

[james_s]

Surely some sort of aerosol lacquer is available locally? You could also use stuff out of a non-aerosol can in a small hobby airbrush or a cheap HVLP spray gun.

[ivan747]

Surely some sort of aerosol lacquer is available locally? You could also use stuff out of a non-aerosol can in a small hobby airbrush or a cheap HVLP spray gun.

I seriously doubt there is PCB-specific lacquer. If it is some other sort of lacquer then there is a very good chance that there's something out there. I just don't know what's safe to use.

[james_s]

Pretty much any clear lacquer or epoxy enamel ought to be fine, automotive clearcoat is durable stuff that should be available virtually anywhere. Test it on a scrap PCB if you are unsure.

[ivan747]

Pretty much any clear lacquer or epoxy enamel ought to be fine, automotive clearcoat is durable stuff that should be available virtually anywhere. Test it on a scrap PCB if you are unsure.

Okay, thanks. I will look into that. :-)

And yes, automotive clearcoat is widely available.

[Ian.M]

I'd be concerned about the valve sockets - it wouldn't take much corrosion to make a poor contact to the valve pins.  WD40 (spray oil) won't help - Copper chlorides and carbonates are not organic compounds, so all wetting them with WD40 will do is make them repel water and other water based chemicals that you need to use to clean them

Ideally replace them - otherwise try soaking in Coca-Cola (active ingredient Phosphoric acid). checking at least twice a day until you can see bright metal, then scrub with a tooth brush, clean out the pin holes with a wooden toothpick and rinse thoroughly several times finishing with boiling water to remoe all traces of the coke.   That will leave a raw copper or brass surface exposed wherever there was corrosion, so its probably a good idea to dip the cleaned sockets in silver plating solution (the type for metal plating by ion exchange, not chemical deposition on non-conductive surfaces), then wash thoroughly again,m dry and spritz the pin holes with contact cleaner lubricant before resoldering them to the cuircuit board.

[ivan747]

I'd be concerned about the valve sockets - it wouldn't take much corrosion to make a poor contact to the valve pins.  WD40 (spray oil) won't help - Copper chlorides and carbonates are not organic compounds, so all wetting them with WD40 will do is make them repel water and other water based chemicals that you need to use to clean them

Ideally replace them - otherwise try soaking in Coca-Cola (active ingredient Phosphoric acid). checking at least twice a day until you can see bright metal, then scrub with a tooth brush, clean out the pin holes with a wooden toothpick and rinse thoroughly several times finishing with boiling water to remoe all traces of the coke.   That will leave a raw copper or brass surface exposed wherever there was corrosion, so its probably a good idea to dip the cleaned sockets in silver plating solution (the type for metal plating by ion exchange, not chemical deposition on non-conductive surfaces), then wash thoroughly again,m dry and spritz the pin holes with contact cleaner lubricant before resoldering them to the cuircuit board.

Cool method, but I couldn't do the plating part... probably it's best to replace them, try some other method or leave them as is.

I think the corrosion doesn't reach the places where the tube pins make contact.


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[Electro Detective]

once the WD40 has done its magic on the contact pins,
you only need to work any crap off with a roughed up toothpick, fine mini file or very small threaded screw etc that fits in the valve socket pins

If the plating is gone, but the bare metal is clean, you might get away with it if the pin tensions are ok and dab some contact cleaner lubricant on.

You only want good metal to metal contact, so the valves do their thing without arcing and other nasties happening

This method described is STRICTLY for 'good enough'
...and to save money and a LOT of replacement work and bother you may not need.