Repairing a Battery Acid Damaged Circuit Board
By, William Stephens
(clicking any picture in this article will bring up an enlarged version)
The procedures outlined in this article are very dangerous for the clumsy and inept among us. If you think this applies to you then read but don't do, you might kill yourself.
Anyone reconditioning old video games will come across battery damaged circuit boards where the ni-cad rechargeable or plain old alkaline or household batteries have reached the end of their life and finally leaked battery electrolyte all through the components and circuit board.
Most often, eletrolyte leak is noticed 5 or 10 years after the leak ocurred. Pinball machines and arcade video games most often just get stored away in a warehouse or storage locker once problems of this nature happen. It is rare that this problem is caught while taking place and the best case course is to manage the aftermath rather than the actual ocurrence. If you catch this while it's happening, you can clean up by neutralizing acid with alkali or alkali with acid. A good alkali would be baking soda paste and a good acid would be vinegar. If you read a bit further you will see what kind of battery spills what kind of electrolyte (acid or alkali).
The Chemical Analysis
Popular myth has you using a baking soda type of paste to neutralize the battery electrolyte ooze. While this may be a reasonable recommendation for plain old household non-rechargeable batteries, which have a slightly acidic electrolyte containing zinc or ammonium chloride, this is not what is used in videogames and pinball machines. Batteries used for holding "high score" are usually nickel-cadmium rechargeables or the unchargeable alkaline battery. These batteries have a strong alkali electrolyte containing sodium or potassium hydroxide. The baking soda trick will do nothing to neutralize these chemicals.
The one key thing about these chemicals both acidic or alkali is that they react with circuit board metals (aluminum, tin and copper) only in the presence of mositure. If these chemicals have already dried out to crystallized or powdered residue, they no longer are reacting with the metals and your circuit board is no longer being eaten up.
What is left are deposits of oxides of pwb metals mixed with crystallized electrolyte. This residue is anywhere from white to dark gray or green and even blue. This residue is strongly bonded to the traces and leads where they came in contact with the electrolyte. Alkali electrolyte is especially fond of tin plating and will readily "wick" under the solder mask coating on the circuit board.
Lastly, this residue is unfortunately an excellent thermal insulator making unsoldering leads next to impossible. The only thing you can do is remove this residue before you can unsolder and replace damaged components... there are two schools of thought on this.
School #1: Blast It!
A good way is to employ a sand blasting technique to remove this material, you could use an airbrush type of sand blaster like a Paasche AEC ACER or the more powerful LAC#3. Add in a compressor, hose, regulator and water trap and use a 200-250 grit blasting medium. This will remove any bad stuff quite easily although, your pocketbook will feel a lot lighter after you go out and buy all these contraptions. This method does not care what kind of residue it removes and works equally well on both.
School #2: Dissolve It!
A chemical approach to the problem may not be as exciting as blasting but it is completely effective and cheap! The big question here is what to use. Basically what you want to do is dissolve rock, be it acidic or alkali rock. Industry does this all the time refining metals and they use great amounts of strong mineral acids. There are a lot to choose from: hydrochloric, sulfuric, nitric, phosphoric, chromic all of which will do the job and all of which are extremely caustic and dangerous.
What we need for our purposes is a diluted acid strong enough to dissolve rock but not so strong as to dissolve the circuit board and possibly your hands. It needs to be weak enough to not need extensive "neutralizing" or hopefully no neutralization at all.
If you look around the home you will see this type of property associated with many cleaners. One excellent choice is simple liquid toilet bowl cleaner. You can tell by catchwords on the label like "Removes Rust and Mineral Stains" and by the active ingredients, in this case, hydrogen chloride at 9.50%.
Hydrogen chloride produces hydrochloric acid when in the presence of moisture and this is what removes those stubborn mineral stains that form in toilets, sinks, faucets and other plumbing in the home. It's not so strong as to dissolve your toilet, but it does remove mineral deposits on the porcelain or metal surfaces without damage to the parent material. A simple wash with water removes the hydrogen chloride thus neutralizing any residue.
At this concentration you just don't dab this stuff on, wait and wipe because this would take all day. Cleaning a stained toilet bowl can requre the cleaner to sit on the stain for 1/2 to 1 hour for complete effectiveness. What would make this work better would be to insert a ferrous cathode in the mix like a small flat bladed screwdriver or scraping tool. This would get the ions flowing and accelerate the rock destruction.
Place a dab of cleaner at the effected pin and scrub or lightly scrape the residue with your cathode of choice. In a few moments you will notice the cleaner getting gray and cloudy, this is dissolved residue. Keep scrub/scrape-ing the pad and lead for a minute or two, by this time the acid will be spent being dilluted with all this dissolved rock. Wipe off the area with a paper towel and repeat if necessary. You may wash off the board after cleaning with running water or simply wipe it off good and that's it. All the acid or alkali is pretty much neutralized by this process.
Using the screwdriver or scraping tool as the cathode in this chemical mix actually creates a micro scale electroplating environment where the sacrificial anode is the circuit board metal/residue and the electrolyte would be the toilet bowl cleaner. The tool will eventually get copper plated because of this chemical reaction and the residue will get sacrificed or dissolved.
Clear the decks!
I just so happen to have a real world worst case example to show the chemical approach to repairing this kind of damage. I have a 1979 Midway Omega Race vector game in the shop with a near perfect cabinet having several electronic problems. These are that the monitor will not operate, the game kind of works and the game board is severly battery electrolyte damaged. The electrolyte damage is so severe as to have eaten through numerous component leads and actually dissolved areas of copper in the circuitboard.
I access the damage visually and then proceed to remove and discard any components that have come in contact with electrolyte, these all need replacing. You can try to salvage IC's or passive components but this is a mistake because once electrolyte has begun to creep up their leads the leads themselves are irreprable and will become a future problem that will be difficult to diagnose. What you really need to do is "Clear the Deck" removing any effected components. This lets you manicure and detail the pad lands and through holes and makes fixing missing copper areas and traces easy.