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  • Moisture and Electronics

    In a recent thread the subject was..how to control surface rust of machine shop equipment, a problem seen more so in areas where there is high humidity/dewpoint. With the more and more use of programmed electronics to control and govern that machine, what measures are employed to counter moisture..the possibility of a short or corrosion of the components?

  • #2
    Originally posted by D35
    In a recent thread the subject was..how to control surface rust of machine shop equipment, a problem seen more so in areas where there is high humidity/dewpoint. With the more and more use of programmed electronics to control and govern that machine, what measures are employed to counter moisture..the possibility of a short or corrosion of the components?
    Conformal coatings on printed wiring boards is derigueur for all MIL. SPEC stuff.
    ...lew...

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    • #3
      Almost two decades ago when I started in the IT field just out of school, I got called in on Christmas eve to work on the computer used by our 24-7 dispatchers. It started exhibiting erratic problems. At that time, they allowed them to smoke since they had to spend the entire day in a room in front of a computer.

      The problem ended up being that the system board on that computer was located in a bottom panel of that case (an AT&T computer). I found that small space *packed* with cigarette ash that had been "breathed" in by the fan on the PC. Nothing was over temp....but cigarette ash in a humid environment becomes a bit like steel wool. I vaccuumed it out and returned it and it worked without any further problems.

      In short, keep the dust out of it. If it absorbs moisture, it becomes at least moderately conductive.

      Paul
      Paul Carpenter
      Mapleton, IL

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      • #4
        I have actually performed a test that indicates the nature of the issues.

        Put a piece of electronic equipment (an amplifier, which my then employer made, and which I had designed), in the freezer, let it cool for several hours, then took it out and immediately turned it on. This was a test of what happens when the customer leaves it out in the truck in Hibbing MN in January, then brings it into the bar (pub) for use with the band, and immediately turns it on.

        Predictably, it was quite erratic, made noises, the temperature controlled fan went fast, slow, and everything in between. Partly from cold electronics, which were not specified for well below zero C. Partly from condensation, in fact most likely it was nearly ALL the effect of condensation.

        The only ways around that are conformal coating, and/ or sealing the case.

        We simply suggested not turning it on until it had warmed up to near room temp. Without the fan pulling 50 CFM through it, condensation would not be much of an issue, since the airflow was ducted and casual drafts would not tend to blow through.

        Normally, the heat of operation will drive off moisture. If the case is sealed, and the inside is dry, it will stay that way for quite a while. And most condensation will be on the case, and not on the boards.

        Of course if the case is open, and the boards not coated, anything can and will happen if a condensing atmosphere exists.

        Most equipment is specified for "non-condensing" for a reason. Equipment for condensing atmospheres has electronics normally sealed in a case and/or coated.
        Last edited by J Tiers; 01-18-2008, 10:07 PM.
        1601

        Keep eye on ball.
        Hashim Khan

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        • #5
          Years ago I repaired electronic organs. Humidity could be a problem, so some owners purchased heaters - 15 to 25 Watts or so to put in the bottom of the organ cabinet. Kept humidity from condensing.
          Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
          ~Practitioner of the Electromechanical Arts~

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          • #6
            In our quest to shut down the use of VOCs for cleaning and remove lead from our electronics, there is lots of room for trouble with modern electronics.

            Much of the cleaning of electronic assemblies after soldering is now done via aqueous processes. The fluxes are basically organic acids which are washed away, almost by a soap-removal like process. When it is not done properly, ionic and other contaminants are left behind. When moisture is present, leakage currents and even small voltages are generated on assemblies. If the boards are not conformally coated, higher voltages can lead to the growth of dendritic bridges which can even cause short circuits in some cases.

            Thanks to the lead free processes coming into vogue thanks to world/global dictates, the formation of tin whiskers, hardly even understood by the experts, can also lead to circuit failures and tiny short circuits.

            Can offer much comfort except to buy good brands, preferably with a track record in the industry if you can.

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            • #7
              Humidity can have bad effects on electronics. But it frequently is not immediate. One of the worst cases I saw was a microwave transmitter that had been exposed to the sea air via an open window for 10 to 15 years in the Miami area. The transistors (it was a 50s or 60s design) had leads that were steel wire that had been plated with brass or gold for better solderability but the plating had worn away and the salt spray had just about completely eaten away the steel itself. They broke off the circuit board with a light touch. We had to replace all of them. Resistors and capacitors with copper leads were fine.

              I believe the moisture is not the main problem. However, it can attract other substances that are in the air and when the traces on the board and the components are coated with whatever, then corosion can and will set in. In a shop I would worry a lot more about chips and metal dust from grinding and other abrasive operations. The moisture can help these substances to stick and accumulate. It also can disolve chemicals that can set up galvanatic action.
              Paul A.

              Make it fit.
              You can't win and there is a penalty for trying!

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              • #8
                I had a few 'interesting' breakdowns to troubleshoot that involved a glue of some kind used to hold wires in place, keep nuts from loosening, etc, in electroinic gear. Turned out that circuit board traces were corroding under these glue spots. Maybe that type of glue was hygroscopic (absorbed water), or maybe it's own solvents were retained long enough for voltages in the equipment to slowly react with it and eat the copper. Once I realized what was going on, I could predict where a trouble spot might be, and many times I found where a trouble spot was developing but hadn't yet caused a problem.

                One day I opened a piece of gear, and it was full of these glued spots and multi-layered pc boards. Ok, close that one up and call it not worth fixing. That was almost as bad as opening up an amp and having cockroaches scrambling out. I saw a lot of corrosion in those days in africa. None of the pc boards had any coatings, and a lot of the gear smelled like urine. Some of the people I ran into could have used some kind of conformal coating themselves.

                But there it is. Keep the moisture off the traces and parts with a non-hygroscopic coating like epoxy, and keep connectors clean and dry.
                I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                • #9
                  The heads on our video cameas at work didn't like it at all. The condensation would pull the oxide off the video tape in extreme situations. What's extreme situation? Working in Buffalo New York in February and being asked to shoot a college swimming meet. We had to throw our coat over the camera on the floor for maybe an hour. Our Chief Photographer got the wise idea of using a electric heat gun from the janitor to warm up the lens and cracked the front element on a $5,000 lens. The rest of us normally used hair dryers on gentle heat. The homes of a lot of poor people are frequently kept in the 80's so doing interviews with folks in poor neighborhoods was also a real problem. Fornutately the "humidity" indicators on the cameras worked well to keep us from damaging the gear.
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                  It is true, there is nothing free about freedom, don't be so quick to give it away.

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                  • #10
                    Originally posted by darryl
                    Keep the moisture off the traces and parts with a non-hygroscopic coating like epoxy, and keep connectors clean and dry.
                    Do watch that the different coefficients of expansion of the epoxy & other parts, and the curing shrinkage, don't cause trouble. I've seen epoxy "potting" pull SMD parts right off the pcb.

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                    • #11
                      Typically most electronic devices are designed for a max humidity of 90%

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