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May 10, 2018

Circuit Board Exposed to Rain

We have an operational circuit board that was accidentally exposed to rain water 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?

H. M.

Experts Comments

The most likelihood of failure at this stage would probably occur in unsealed components that would be susceptible to failure or at least a decrease in their mean-time-between-failure (MTBF) when exposed to water (a buzzer, relay or transformer, for example).

These are typically parts or components that are manually or hand-assembled to the printed circuit board after aqueous cleaning has been performed for specifically this reason.

Once water gets into them (especially rainwater which itself is unpure and contains contaminants from the atmosphere), it is very possible that corrosion or oxidation can occur which can affect the MTBF of the assembly.

Even beyond that, once the rainwater is dried off, it might be possible that residual conductive contaminents are still left on the board (and possibly inside unsealed components or underneath other components) even if it seems to appear clean.

Based on all of this, I would suggest that there would be a greater likelihood of failure of the circuit board at this stage compared to other circuit boards that have not been exposed to rainwater, especially if unsealed components are present.

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David Bonito
Sales & Marketing Manager
Technical Manufacturing Corp.
David has been active in all areas of the contract electronics manufacturing industry for over fifteen years. He is currently in charge of all Sales and Marketing related activities for Technical Manufacturing Corporation.

The short answer is maybe.

It really depends on the specifics of the rain exposure. During manufacturing, circuit boards are often immersed in liquid. If dried thoroughly, we usually recommend about 1 hour at 300F after the exposure to moisture, I would not expect there to be any long term effect to the board.

However, if the board were allowed to only air dry after the exposure, then I could see there being a potential for long term reliability problems. One of the possible issues would be the laminate material absorbing moisture which over time has the ability to cause delamination (separation) of the material.

I would be willing to bet that after 14 months of operation that the potential is not highly likely. If there was any exposed copper (not covered with solder or other surface finish) on the product during the exposure to moisture, there could be a potential for long term reliability issues due to corrosion of the copper feature that was directly exposed to moisture and not dried completely.

14 months is a pretty good time frame that if there are no issues currently that there are not likely going to be any that surface.

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Matt Stevenson
Director of Marketing
Sunstone Circuits
Matt Stevenson has over 20 years experience in the PCB industry. Serving in roles as a Chemical Lab Technician, Process Engineer, Quality Engineer, Quality Manager, and Marketing Manager. He has proven himself to be an invaluable resource.

That really depends on a two factors:

  1. What was the quality of the rain water? A difficult one to answer but if it was rain water in a polluted city environment it will be very different from clean rain water and may contain sulphur etc.
  2. Is the board clean or no clean? The flux residues on a no clean board may have been affected by the water.

Just because of the unknowns I would say that it is possibly more likely to fail.

If this unit is safety critical I would suggest cleaning the board with a product designed for cleaning circuit boards.

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Chris Palin
European Manager
HumiSeal
Chris Palin is currently managing European sales and support for HumiSeal Conformal Coatings. His expertise is in test & reliability, solder technology, power die attach and conformal coating.

I would say that your board is susceptible to early failure. Even thought the board was dried after exposure there is still potential contamination which could result in latent failure.

If the board was protected with a conformal coating the rain should not hurt the board meaning you will see normal life out of the board.

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Steve Cook
Director of Product Technology
Techspray
Steve Cook is the Director of Product Technology at Techspray, a division of Illinois Tool Works (ITW) and a leading manufacturer of chemical products for the electronics industry.

One would have to ask first what the board is used for and how important its function is. The problem is that anything that makes one board different from any others can affect the way it works and can affect reliability.

So you can assume that if it has survived 14 months the chances are good that it is OK but there are no guarantees. A sudden change in humidity or temperature could cause something odd to happen.

If the rain was in a particularly industrial area, then there is a risk that there may have been some acidity which could leave you with some long term corrosion or reliability issues.

If this is something that may potentially happen again, then perhaps conformal coating to protect it in the future may be an option. There is a good overview video on different methods of PCB Protection that might be worth watching http://www.youtube.com/watch?v=LEsIHhpzKyc.

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Richard Boyle
Global Product Champion
Henkel Electronics
Richard Boyle is a Global Product Champion at Henkel Electronics. He has over 25 years experience in the electronics assembly industry and is responsible for the global technical service of all of Henkel's solder materials.
It really comes down to if power was applied when it was exposed to the rain water. Since most circuit assemblies are designed to be cleaned in water, water alone will not cause a serious problem. This would not be the case if power is applied because water in contact with metals with a voltage applied will immediately initiate electrochemical reactions freeing metal ions into the water.

Similar reactions without voltage applied proceed very slowly (days to years depending on the metals and environment. If these assemblies were rain upon with voltage applied to the circuit, I would be worried about early failure much more than if no voltage were applied.
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Steve Stach
President
Austin American Technology
Founder and President of AAT. Steve holds numerous patents and has authored numerous research papers and articles in cleaning and soldering. Steve is a founding member of the Central Texas Electronics Association and is a past Director of IMAPS. Steve is active on several IPC cleaning committees.
Reader Comment
We have faced the same problem in no clean processed assemblies. Normally after dried out of rain water the white patches are formed and aesthetically looking bad.
Prakash M, Silvan Innovation labs, India
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