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Can Water Contamination Cause Failure?



Can Water Contamination Cause Failure?
We have an operational circuit board that was accidentally exposed to rainwater for a few hours. Is there a greater likelihood of failure?
Board Talk
Board Talk is presented by Phil Zarrow and Jim Hall of ITM Consulting.
Process Troubleshooting, Failure Analysis, Process Audits, Process Set-up
CEM Selection/Qualification, SMT Training/Seminars, Legal Disputes
Phil Zarrow
Phil Zarrow
With over 35 years experience in PCB assembly, Phil is one of the leading experts in SMT process failure analysis. He has vast experience in SMT equipment, materials and processes.
Jim Hall
Jim Hall
A Lean Six-Sigma Master Blackbelt, Jim has a wealth of knowledge in soldering, thermal technology, equipment and process basics. He is a pioneer in the science of reflow.

Transcript


Phil
Welcome to Board Talk with Jim Hall and Phil Zarrow of ITM Consulting, the Assembly Brothers Place and Pick coming to you today from the ITM Elegant Ballroom high atop Mount Rialto.

We're here to talk about electronic assembly, materials, equipment, components, practices and procedures and maybe some other things.

And what exactly are we talking about today, Jim? 

Jim
Well it comes from H.M. We have an operational circuit board that was accidentally exposed to rainwater for a few hours.   

The circuit board was subsequently dried and has now been operational for 14 months. Is there a greater likelihood of failure at this stage compared to other circuit boards?

I assume they mean other circuit boards that haven't been exposed to rain.  

Phil
I guess my first impression is that the key operative thing here is properly dried. We don't know the details, but we'll take H.M.'s word for it that it was an appropriate procedure and it seems to have been effective.   

Jim
I can't think of anything that could have failure mode resulting from water exposure that wouldn't have showed up in 14 months. Assuming there's some regular operation and this isn't an emergency device that sits on the shelf for most of its time.

The main thing is that it was dried and if it wasn't dried properly it would have failed pretty quickly I would suspect.   

The other thing would be contamination. Whatever is going to happen, dendrites or corrosion, it should have happened by now.

Let's be honest. Most circuit boards are perfectly able to be water washed. It's very common so there really aren't any problems with water and circuit boards as long as they're clean.   

But extended exposure, again, you have to dry them out so that when you first turn the things on you don't boil or expand that water too quickly and crack or delaminate something.

The 14 months to me is the indicator. If it hasn't failed by now, it's probably just as good as - maybe better.  Maybe the rain water dissolved off some bad stuff that had been there before and now it's actually cleaner and less susceptible to corrosive attack.  

Phil
Who knows, maybe HM was an area where they have de-ionized rainwater. You never know about these things.

Well hopefully we answered that question. That's our opinion and I suspect there might be some input on this in our comment section.  

You've been listening to Phil and Jim on Board Talk, the Assembly Brothers.

Whatever you do and however you decide to clean off your boards with saponified water or rain water, don't reflow and don't wave solder and don't hand solder like my brother.  

Jim
Don't solder like my brother.

Comments

Unsealed electromechanical components (e.g. relays, switches) are prone to latent failures due to water exposure. After 14 months it is unlikely, but still possible.
Gregg Stearns, Emerson
HM doesn't say whether the board was powered or not during exposure. If it was powered during the exposure to rain, all bets are off.

Also, they should check all component datasheets for warnings about washing. Some parts (switches and relays for instance) are not sealed and should not be washed.
Christopher Holmes, Greatbatch Medical
If the rain water PH value is between 6-8, it shouldn't be any issue. But if the PH value is beyond that range, than boards have been contaminated, the active ions will state on the boards despite the drying process. corrosion will show up slowly depends on the environment (humidity and temperature). It might take 2-3 years to see the evidence.

So if you don't know the PH value, the safe way is to wash the board with proper solution (DI water or IPA) and completely dry the board to avoid any contamination.
Tim Li, Vecture Inc
I work in engineering and have built many a prototype in my day. I prefer solder with a water soluble flux because it is so quick, easy and environmentally friendly. The only problem I have ever had is when I accidentally let the water penetrate some momentary switches and needless to say then there was some rework involved.
Linda Klein, Clear One
I have found the only time water has been a problem is when the board has a power source. As little as a cmos battery of 3 volt can cause vast amounts of damage.
Clinton Morris, Gaming Capital Group, USA

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