Any experience with heat pump control board degradation in high humidity environments?

#12

Joined Nov 30, 2010
18,186
non conductive petroleum jelly as a moisture protective coating.
That reminds me...silicone (dielectric) spark plug grease.
It lasts longer than Vaseline (petrolatum, petroleum jelly) and it's actually made for use on electrical stuff!
Besides, if your connectors are greased, spray paint won't adhere to them.
Smart move!
 

Roderick Young

Joined Feb 22, 2015
408
I did a bit of forensic work on board corrosion at my previous job. As the others mentioned, a conformal coating can help. The best time to put that sort of thing on is at manufacturing, but having something is better than nothing. Note that the board will be harder to rework, if that is an issue.

What we found in our case was that the no-clean flux process left ionic contaminants (salts) on the board. A water wash process with not very clean water might do this, too. Normally, the trace amounts of salt would be harmless, but where there was condensing humidity, and electrical bias (that is, the board was powered on), there would be the start of salt bridges. We noted that the boards never failed except in certain countries like Vietnam and the Philippines. Never in a nordic country. And even in the humid countries, out equipment did not fail when stored outside before being put into service outside. The failures occurred when the equipment was kept in an air conditioned building, then for some reason moved through the outside environment where humidity could condense, then put into service elsewhere. Over the long term, trace contamination could have attracted moisture and caused corrosion, but the focus of the investigation was a quick failure, equipment dying in a matter of weeks. The particular device did not need to have a 10 year life, as it became obsolete with the natural advance of technology.

The solution in our case was to improve our process so that the boards were thoroughly washed. The conformal coating was never necessary. Note that we were a large company with an actual department dedicated to failure analysis and corporate quality, and had the ability to measure things like ionic contamination.

How relevant that case is to your situation is unclear. Two possible suggestions are that humidity is not really an issue unless it is condensing humidity (but your manufacturer says otherwise, so you take your chances), and the other is to make sure your boards are clean. Hopefully it's not also a marine environment? 2 miles or less from the ocean will have its own issues with salt spray.
 

Thread Starter

VERYBASIC

Joined May 12, 2016
8
I did a bit of forensic work on board corrosion at my previous job. As the others mentioned, a conformal coating can help. The best time to put that sort of thing on is at manufacturing, but having something is better than nothing. Note that the board will be harder to rework, if that is an issue.

What we found in our case was that the no-clean flux process left ionic contaminants (salts) on the board. A water wash process with not very clean water might do this, too. Normally, the trace amounts of salt would be harmless, but where there was condensing humidity, and electrical bias (that is, the board was powered on), there would be the start of salt bridges. We noted that the boards never failed except in certain countries like Vietnam and the Philippines. Never in a nordic country. And even in the humid countries, out equipment did not fail when stored outside before being put into service outside. The failures occurred when the equipment was kept in an air conditioned building, then for some reason moved through the outside environment where humidity could condense, then put into service elsewhere. Over the long term, trace contamination could have attracted moisture and caused corrosion, but the focus of the investigation was a quick failure, equipment dying in a matter of weeks. The particular device did not need to have a 10 year life, as it became obsolete with the natural advance of technology.

The solution in our case was to improve our process so that the boards were thoroughly washed. The conformal coating was never necessary. Note that we were a large company with an actual department dedicated to failure analysis and corporate quality, and had the ability to measure things like ionic contamination.

How relevant that case is to your situation is unclear. Two possible suggestions are that humidity is not really an issue unless it is condensing humidity (but your manufacturer says otherwise, so you take your chances), and the other is to make sure your boards are clean. Hopefully it's not also a marine environment? 2 miles or less from the ocean will have its own issues with salt spray.
THANK YOU FOR a great summary. I will review with my R+D engineer from the home office!
 
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