Corroded PCB from Rechargeable NiMH battery

Question

This NiMH battery began to leak battery acid onto the circuit board / PCB below it. Some of that acid ran down one of the wires connected to the battery and pooled up at the foot of the plug where it connects to the PCB.

Here's a closeup image of the black wire with battery acid gunk running down it onto the PCB below.

Here's what the PCB looked like after I sprayed some WD-40® Specialist® Electrical Contact Cleaner Spray and wiped with a Q-tip.

Is this exposed copper something I should worry about? Is there some means I can use to protect the copper?

For instance is it safe to dab some 100% silicone caulking on it or anything like that?

Answer 1

Is this exposed copper something I should worry about?

Maybe, in the presence of humidity the residual salts/acids that are on the copper and solder junctions could further corrode. The best way to corrode metal is with salts and water.

Is there some means I can use to protect the copper?

Yeah, go over everything with a soldering iron and protect all that copper with a layer of solder. Thats how regular PCB's are protected in the factory if you get a HASL surface finish (63% Tin 37% Lead) which is close to most solder compositions.

As an added benefit, if flux is used in the soldering operation, it will probably help clean some of the bad residues out of the corroded traces. Flux will also prevent solder bridges while soldering.

Don't burn the connector while soldering, either carefully unsolder, or in some cases the shroud can be 'slid' off while soldering and the installed after (be careful with that operation also if that's the route you go)

Answer 2

I did a little research into the silicone caulking application and contacted the customer support email for a tube of silicone caulking I happened to have on hand. Here's the exchange...

Here's my message...

--------------- Original Message ---------------

Comments: I was told that 100% Silicone caulking, in this case clear caulking, in inappropriate to seal electronic components because it releases acetic acid as it cures. Is this accurate? I have a tube of such caulking, with barcode 077027002843. Does this product release anything acidic as it cures? I read on the warning caption on the back of the tube "Methonol and ammonia are released during cure." Is there anything corrosive generated with caulking, especially if applied to copper?

And here's their response...

Good Afternoon,

Thank you for your inquiry.

We have both acetoxy (releases acetic acid) and Methoxy (releases methanol/ammonia) cure. Silicone 1 is the acetoxy cure and Silicone 2+ is the methoxy cure.

Since the Silicone 1 releases acetic acid during curing you would not want to use it on softer metals such as brass or copper. It can even cause corrosion on porous masonry substrates as well. Silicone 2+ is a "neutral' cure which makes it safe for those substrates where Silicone 1 is not.

The product you have is a Silicone 2+.

Thanks,

Here's an example of such a product page GE GE284 Silicone 2+ Kitchen and Bath Caulk 2.8 oz. Squeeze Clear by GE Momentive Performance Materials

Answer 3

There is a lot of white hazy looking film in your picture above the circled area so I would wonder if you really got this clean enough, but after you get it as clean as you can, a typical way to protect the area is to apply a coat or two of lacquer.

A popular consumer product containing lacquer is nail polish, and likewise, a popular product that can remove it if necessary later is nail polish remover (or straight acetone).

If you have no expectation you'd ever need to service this area at a later date and don't have lacquer (yet nail polish is cheap at the dollar store = $1) then if you happen to have any non-conductive (no metal in it which rules out JBWeld) epoxy, that would work too.

A soft setting silicone caulking is not the right choice, more suited to helping to hold components in place that are subject to vibration damage, like larger leaded capacitors or fine wire inductors.