I have an all-in-one AC/furnace sitting outside. The circuit board was replaced a very short time ago, about two months ago. It is already showing signs of degradation (rust on a diode lead). Is there any spray coating I can put on this to prevent further degradation, assuming it is still in operating condition?
This is a link to the type of unit I have
What will probably do the job is something called "conformal coating".
Here's one example:
Ideal for high temperature environments. Silicone Conformal Coating (422A) is a flexible finish product that provides a protective coating for printed circuit boards against moisture, corrosion, and thermal shock. It protects and insulates electrical and electronic components and assemblies, including generators, motors, transformers, relays, and solenoid coils. For spraying, liquid can be thinned using M.G. Thinner Cleaner. Thin up to one half part thinner to one part coating. Also available in a micro tip pen format. ==============
I'd remove the board, clean it by pouring some drug-store alcohol over it while scrubbing it with a soft brush, let it dry completely and then apply the coating.
If the board is relatively clean, then maybe just turn off power the the AC unit and spray the board with the coating without taking it out.
In any repair situation, it's important to fix the thing that's broke. Any product designed to sit outside MUST be capable of withstanding the environment. Unless you're near an ocean, your environment is likely way less corrosive than the design/test environment.
I'd call the vendor or the installer and see what they have to say about it. Then I'd look at how the board is configured and make sure the enclosure isn't missing a gasket, or bent, or has an open screw hole in it. Seal it up tight. Make sure it's dry inside when you're done.
Conformal coating seems attractive on the surface. Of course, it's gonna void the warranty and make the board very difficult to repair. It has thermal resistance, so any component depending on convection cooling will be compromised.
If you decide to clean it, be aware that some components may not like being drenched in alcohol and water.
Spraying the board in place may not be effective. You need to seal the back and the edges of the board.
If you decide to coat it, dry it as discussed above, then dry it again. Doesn't do a lot of good to keep out the water when the water's already under the coating.
Still think I'd seal the enclosure first.
Oil floats on water, not the other way around. It evaporates quickly, so it's not a good lube.
That being said, sometimes after I wash electronics with water, Then spray with wd40, and continue drying with heat.
Aside from usual conformal coatings, when clean and dry, might spray with Krylon crystal clear varnish coating. Then bake.
Greg
It's more like automotive enamel. Don't use lacquer, a poor barrier against moisture.
Greg
What electronics do you wash with water?
I've washed hundreds of circuit boards with a water based solution and rinsed with plain old hard well water. Usually but not always I use compressed air to blow the water off the board. Just so it's dry before being powered up it's fine. I even ran some through the dishwasher once just to prove my point. I did use baking soda instead of dishwasher detergent. All of them survived.
Much of the electronics in the world has been washed in water as part of the assembly process. There are components that can't stand it, so you gotta be careful. I wash circuit boards in Simple Green cleaner, then alcohol then water then do it again. Blow off the water with compressed air between washes, then repeat again. Some gunk is soluble in simple green, some in alcohol, you need both. Scrub with a toothbrush at every stage. Doesn't do much good to dissolve the stuff then let the solvent evaporate. Blowing off is critical to the process. Get all the liquid out from under parts. Space under a surface mount IC can be tiny. Dry it then dry it again then dry it some more. Works wonders on removing residue from leaky electrolytic capacitors.
Some people use the dishwasher. I don't because It's harder to mask components that can't be washed. General rules of thumb include:
1)don't get solvent into anything that changes properties under the influence. 2)don't get solvent into electromechanical stuff. 3)don't get solvent into anything that it can't easily get out of. It's really easy to let contaminated solvent seep into a switch, but it's very difficult to get it ALL out. Evaporation is not an option, cause the process deposits more gunk and leaves it behind.
Silicone conformal coatings are very COMMON in the electronics world, and SHOULD be standard equipment on all circuit boards in things like furnaces , washers, dries, etc. You can easily buy them from electronics supply houses and apply them yourself (spray cans), taking care to protect connectors etc. The only problem is it makes board repair somewhat difficult - but the majority of circuit boards on equipment today is pretty much non-repairable anyway.
And not worth squat as a circuit board protector. Might want to try LPS2 - but at best it is also only a temporaty protection - and it holds dirt etc.
Like I said before - silicone conformal coating - applied to a CLEAN board when new.
I looked at the info on these coatings. They need to be baked on after application.
That's what we do. Wash all boards with hot deionized water in a commercial board washer. I think the temp is around 140 degrees F. Looks like a very expensive dish washer. All water is recirculated through tanks to clean and deionize the water. We have a regular Sears dish washer for backup and that water goes down the drain.
After the washer tries to dry the boards, the excess water is blown off using deionized compressed air, being extra careful to clear all water from under components. After that, they are air dried for a while.
All components that can't be washed are hand added after washing. Flux from that operation is cleaned with IPA, isopropal alcohol. Sometimes a manufacturer fails to state on their component spec sheet that the unit can't be washed and then there is trouble, but most do tell you.
Paul
LOL!!!!! The panel covering it is held on with two screws and the cover has no gasket and is ventilated to the outside. It experiences the same atmospheric conditions as exist outside, like an open porch with open horizontal blind style windows. To seal it up also would seal up the air from the furnace burner.
Total reengineering and moving the board to a totally new location.
gregz wrote in news: snipped-for-privacy@news.eternal-september.or g:
it's mostly kerosene,dewaxed.(around 70%) Check the MSDS....carefully.
spray your circuit boards or electronics with WD-40 and heat,and you'll end up with a gummy PCB/unit that attracts dirt. you want to REMOVE oils,not add them. If you want to remove water,use >90% isopropyl alcohol,then air dry.
At Tektronix,I washed PCBs,blew them off with air,and then dried them in an oven at 140degF. I used to spray-wash entire instruments(oscilloscopes,signal generators,etc),just to get all the dirt,oil and grease off them. Even tobacco film.(yecch) then 3 days minimum in the drying oven. I even used a home auto dishwasher and Calgonite to clean/degrease high-Z voltmeter PCBs.
Krylon makes an electical coating this should not be confused with clear Krylon. Board should be cleaned before it is applied or you may trap in corrosive material. already on the board.. Plug in connectors should be masked off to keep the Krylon out of the connectors. Use a little electrical grease on the connectors. The grease can be obtained at local automotive parts store. They sell it in little packets for greaseing up turn signal and break light bulbs.
Jimmie
Sounds like you've got a very bad design, or have installed an "inside" box outside where it doesn't belong. What does the vendor/installer say about it?
Most circuit boards that dont have switches or variable resistors or variable caps can be cleaned in a dishwasher just fine.I have cleaned many boards in an ultrasonic cleaner using water.
Jimmie
Jimmie
There are also catalyzed or self curing coatings.Master bond has UV cure coatings.
MG's product will room temperature cure in 48 hours, or it can be heated to speed it up. Dow Corning makes Room Temperature Vulcanizing elastomeric and Elastoplastic as well as solventless heat cured products. Nordson also produces UV, Heat, and Air Dry products.
Mike, Rust on diode leads is quite surprising as even the high current diodes with steel wire leads have a solder coating (tinned leads). Perhaps the leads were damaged during assembly or testing and the coating was broken.
If you can turn the power off and get to the leads, I would suggest cleaning off the rust and retinning the leads with a soldering iron and rosin core solder.
I had our heat pump serviced last week and watched the young man as he did his work. The circuit board controller is like yours, outside on the heat pump and and under a metal cover that protects it from all but blowing snow. Quite a bit of dust, but no other problems. The board does have three 2 watt resistors that have discolored the board from their heat. They should have been placed further from the board material.
Such heat producing devices are one good reason not to conformal coat the circuit board. Or they need to be masked so coating material is kept away from the resistors.
My electronic assembly company is required to conformal coat several different circuit boards. In most cases we use urethane applied with a brush and carefully avoid the locations the customer wants to not be coated. Connectors, switches, sensors, test points, and mounting holes.
Other customers have specified the silicon based coating. Both coating material is rather expensive. Much of it is ONLY available in metal one gallon cans because bottles can't be shipped UPS. Urethane is available in spray cans, but most cans are plugged up and won't spray, even right from the distributor. Shelf life is almost zero. There is no return on conformal coating material.
Paul
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.