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Amonia Gas Corrosion on Electronics

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mfoss

mfoss

Electrical
Nov 23, 2009
3
We have a customer asking us about our ability to operate in an environment where ammonia gas is present. We don't have any experience in this type of enviroment and I'm hoping someone here may be able to give us some insight.

We make an industrial meter that has several electronics modules housed in a fiberglass enclosure. The enclosure has polyurethane and nexprene seals and is IP55 rated (water resistant and dust resistant but not gas resistant).

The customer says that typical ammonia concentrations are less than 5ppm but could be up to 30 - 40 ppm. I don't know how frequently or for how long we could see the elevated concentrations.

I've seen some mention that ammonia is corrosive to copper but don't know how this would relate to a typical electronic assembly. Any info would be appreciated.
 
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I don't have any information regarding diffusion of ammonia gas through PU or nexprene seals, but ammonia will DEFINITELY corrode the copper components and degrade the conductivity of the contacts, etc. You should contact your seal provider(s) to discuss this application in detail.
 
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Very low concentrations of ammonia vapor will definitely cause problems with copper and it's alloys apart from the corrosion mentioned in the previous post ammonia vapor will cause stress cracking.
In your case it is hard to predict the problem with corrosion as you have to have a few water molecules as ammonium hydroxide is the culprit. As far as the stress cracking is concerned I've seen highly stressed copper alloys stress crack without water.

I would say if your housing can keep the components above the local dew point you are probably OK.

For added protection you might consider a Vapor Phase Inhibitor for the enclosure. We used these a lot in a highly corrosive area for enclosed electronics.
 
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Ammonia gas will be corrosive to copper and copper alloys. The potential for the problem will be:
- amount of ammonina that gets inside the case
- the amount of water that gets inside the case
- the sensitivity of your equipment, ie, primarily large components, circuit boards with fine traces, etc
- temperature and temperature swings

If the enclosure is fairly well sealed, then VCI would be an excellent choice.
 
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Conformal coat the boards. Use gold or tin plated connectors. There is an ISA standard which categorises atmospheric pollution into (I think) four categories from harmless to very hostile. I'll see if I can find the standard number. There's also an IEC standard defining classes of atmospheric pollution, but the conditions the ISA consider very hostile to electronics barely register on the industrial scale. It might be useful to reference these standards when speaking to suppliers.


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