Thanks Dan, That was an interesting read I thoroughly plan to never have to do that anything that I or my customers own !
Bob ellison Bob Ellison On Aug 16, 2013, at 8:11 AM, Exeltech <exelt...@yahoo.com> wrote: > Bill, > > My short answer is .. if things work after all this .. I wouldn't recommend > doing anything to the circuit board after cleaning it. Instead, I'd take > steps to keep the mice from ever getting into the inverter again. > > > Long answer... > > Normally, circuit boards will have been coated with a conformal protective > material at the time of manufacture. For those who may not know what > "conformal coating" is, it's a clear polymer liquid (usually silicone based) > that's applied to circuit boards, typically as a spray (like spray paint). > When dry, it forms a very durable polymer layer that's highly protective > against moisture, dirt, and moisture. It's also very electrically resistant, > and is accepted by Underwriters Laboratories and other Nationally Recognized > Testing Labs as an insulating material. However, unless the circuit board is > literally dunked in the liquid conformal material (not done for a variety of > reasons), there are always going to be areas on the circuit board (under > components, or the back-side of integrated circuit pins away from our view) > that are not covered by the conformal coating. > > Even when conformal coating is well applied, urine can and will still sit on > top of the coating and form a conductive path to otherwise unprotected areas > of pins and leads. This is what I suspect happened here. Done properly, a > distilled water / alcohol bath combination will dissolve and remove these > unwanted conductive paths without harming the conformal coating. A concern I > still have in this: there may be components on the circuit board that would > be damaged or otherwise affected by the water and/or alcohol. Examples would > be transformers, switches, relays, etc.. > > Good quality conformal coating materials aren't affected by water or alcohol, > so this procedure is safe to use for cleaning purposes as long as none of the > electronic parts themselves would be affected. Parts that have very small > distances between their pins, such as microprocessors and similar, are the > components most subject to unwanted conductive paths. > > Another aspect of the circuit board to consider are where "through-hole" > parts are installed, such as relays or other components have leads that > penetrate through the circuit board. Such parts can be very difficult to > fully seal with conformal coating because the spray simply doesn't penetrate > shadowed or hidden locations. > > One still must be cautious in cleaning a circuit board, as it's possible the > water could penetrate the circuit board edges if it's not completely sealed, > and either liquid may affect parts on the circuit board itself. As > mentioned, this procedure is only if the need is dire .. and replacement > isn't an easy option. > > I'd also be concerned with static electricity issues. I'd wager few if > anyone in the Wrench kingdom has the necessary static abatement protections > in place. Static electricity can and does permanently damage components, and > you'll never know it happened - except the circuit no longer works. Doesn't > take carpet either. Did you know you can walk across a tile floor and build > up a static charge? (The voice of experience here!) > > > Bill .. to your question: > Where would you apply the conformal coating? > > First .. if it were me, and I were lucky enough to recover from a mouse-pee > episode, I'd not use Krylon for this purpose. EVER. In fact, I'd be > hesitant to use anything at all. Instead, I'd take steps t protect the > hole(s) where the mouse got in so this never happens again. If it's a vent, > use metal window screen cut to size, and attach the screen on the inside of > the enclosure with a quality silicone adhesive, making sure not to create any > electrical or other hazards in the process. (Note I said "silicone > adhesive", not "silicone caulk" or "silicone seal". There's a difference.) > Use fine-mesh screen. Anything larger wont' work. Mice are better than > Houdini at getting in and out of tight spaces. (I've seen a mouse flatten > its body and squeeze through a louvered vent with less than 3/8 inch spacing.) > > If you're still totally bent on trying to increase the protection on the > circuit board, use a genuine conformal material from a company such as MG > Chemicals, Tech Spray, or others. It will be certified to a UL Standard for > the purpose. Expect to pay $20-30 for a spray-paint sized can, and it won't > be available from any hardware store. Buy it from Mouser, Digi-Key, or > similar sources. Get the version with the UV "tattle-tale" built in. That > way, when you spray the board, you can take it outside in bright sunlight and > see where the spray exists - and more importantly - where it doesn't. The > tattle-tale shows up as a blue-ish or purple-ish color when viewed under > ultraviolet light. Before spraying, cover all connectors, connector pins, > and sockets. You *don't* want to insulate those. Following the > manufacturer's instructions, lightly and evenly coat one side of the board > with the conformal material, and let it dry completely. Then, check it in > sunlight or under a UV lamp for even-ness of the coating. More coating can > be applied if needed. Just like spray paint, two or more light coats are > better than one heavy coat. When one side is done, do the other side of the > circuit board. A word of caution: like spray paint, conformal coating must > be applied in a well ventilated area. The board must be absolutely clean and > dry. If it's not, you'll be sealing moisture and/or other contaminants into > the board -- the exact opposite of the goal you're trying to achieve. > > Keep in mind that doing this task properly may help seal the circuit board > and its components.. doing it improperly may cause more problems than you > cure. > > My recommendation: close the doors to future mousies .. and leave conformal > coating to the manufacturers. > > Hope this helps. > > > Dan > > > -------------------------------------------- > On Fri, 8/16/13, Bill Loesch <solar1onl...@charter.net> wrote: > > Subject: Re: [RE-wrenches] Mouse pee in the SW > To: "RE-wrenches" <re-wrenches@lists.re-wrenches.org> > Date: Friday, August 16, 2013, 2:38 AM > > > Dan, et al, > > Once the board has been cleaned sufficiently that the inverter is no longer > operating intermittently and your "hope" has been realized, when would you > apply a field conformal coating? Would you choose/recommend something better > than Krylon clear spray? > > Bill Loesch > Solar 1 - Saint Louis Solar > 314 631 1094 > > > _______________________________________________ > List sponsored by Home Power magazine > > List Address: RE-wrenches@lists.re-wrenches.org > > Change email address & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out participant bios: > www.members.re-wrenches.org > _______________________________________________ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
