I had a friend who was an engineer for a small TV station. I visited him at work once, and despite the fact that he wouldn’t let me climb the 1,200′ antenna tower, I had a great time. I was working for a video production studio at the time, so there was a fair amount in common about our jobs. One of the regular chores we faced was cleaning the heads on tape machines. He had a 5-gallon pail of cleaning solution under his bench that he told me was Freon, which he swore by for head cleaning and general contact cleaning. He gave me some for my shop in a little jar.
I never knew for sure if that stuff was Freon, but it was the mid-80s, shortly before CFCs were banned, so it might have been. All I know is that I’ve never found its equal for cleaning electronics gear. With that in mind, I thought I’d look at contact cleaners that are in use today, what’s really going on when you clean contacts, and why contacts even need cleaning in the first place.
Oxidation is the Enemy
It may not seem like it, but we live at the bottom of an ocean of corrosive gas. Oxygen in the atmosphere is the culprit, and metals are the victims. Pure metals rapidly combine with oxygen to form metal oxides, which usually have different properties than the base metal. Sometimes this is handy, as when an aluminum screen door forms a layer of aluminum oxide that makes it essentially impervious to further corrosion. Other times, metal oxides cause problems. The copper and zinc oxides are nowhere near as conductive as either base metal, so electrical contacts made of brass can have problems if there’s too much oxidation on them.
Exposure to the atmosphere isn’t the only source of trouble for contacts. Arcing across contacts can cause corrosion and oxidation too. In general, direct current is harder on contacts than alternating current, because AC arcs tend to self-extinguish during zero-crossing. But either way, the heat produced by the arc oxidizes the contacts and can produce debris that interferes with conductivity.
A certain amount of contact oxidation is unavoidable, and a properly engineered circuit will take it into account. Wetting current is one way of dealing with oxidation. Wetting current is the minimum current needed to “punch through” the resistance of the oxide layer on contacts. If the wetting current is too low, contacts that appear to be physically connected might actually still be open electrically. Snubber capacitors can be used to remedy this.
There comes a time when contacts need cleaning, though, and that job mainly consists of removing oxidation. This would seem to call for a solvent a little stronger than the lab standard, isopropyl alcohol (IPA). Metal oxides are not especially soluble in alcohols, so it would seem that IPA is a poor choice for dealing with them. But not all contact contamination is in the form of oxides — greases, oils, and organics can foul contacts too — and not all oxides are in the form of tough films. Some oxidation flakes off the base metal naturally but still sticks to it via the other gummy debris. So IPA and similar volatile solvents, like my long-ago Freon, are a good first choice for flushing away some of the gunk. The volatility of these solvents is key, since it quickly evaporates and leaves little residue behind.
Not all contact cleaning jobs are that simple, though. Sometimes the metal oxide films need a little more persuasion to leave the scene, and in these cases contact cleaners with more complex formulations might be needed. The gold standard for tough jobs for quite a long time has been DeoxIt by CAIG Laboratories. DeoxIt claims to be a “contact rejuvenator” that contains all sorts of goodies. Exactly what’s in DeoxIt is a trade secret — the Safety Data Sheet lists only “Proprietary Trade Secret” ingredients other than the propellant and mineral spirits. There seems to be an urban legend that the secret sauce is oleic acid, but CAIG denies that in their FAQ page. Something slightly acidic like oleic acid would make sense, as it would react with the metal oxide films and expose bare metal. Whatever is in there, it seems to work well enough to inspire fierce brand loyalty.
As good as it is, DeoxIt is expensive stuff – $18 or more for a 5-oz spray can. If you don’t want to shell out that kind of money, you might start looking for alternatives. There are plenty of commercial alternatives on the market, and some folks even claim that a 5% solution of oleic acid in naptha is a suitable DIY substitute for DeoxIt. There are a number of head-to-head comparison videos out there that pit DeoxIt against cheaper rivals, like WD-40. It’s not really clear from these highly unscientific tests how these cleaners stack up, though. But for something best used sparingly, my tendency would be to just buy the original and call it a day.
Now it’s your turn – how do you clean contacts and controls? There seems to be a fair amount of voodoo when it comes to contact cleaners, and we’d like to hear about your experiences. Leave a comment below and let everyone know what your go-to method for fighting contact corrosion is.
[Featured images from WD-40]