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Ultr-Sonic Cleaning of PC Boards


Bob VandenBoom
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Bob VandenBoom

Just wondering if anybody has used an ultra-sonic wash on their assembled boards. I don't see any components except the transformer that would worry me. I was looking to wash the board prior to attaching the transformer. I want to clean them and use a light coat of conformal coating to help guard against moisture in the event that water does happen to get inside the enclosure.

Thoughts? Comments? Anybody conformal coating?

Thanks,

Bob




edit: spelling

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My wife and I work at an electronics manufacturing facility. Ultra sonic cleaning often breaks the die bond wires in IC’s that connect the die to the pins of the IC package. This can happen even if the IC’s are in the fully encapsulated plastic packages. This also affects transistor type devices.

The best bet would be to keep the board cleaned as you go using alcohol and a brush. We use the metal handled acid brushes and trim the bristles down to ¼ to ½”. If the board has already sat with flux on it you could try soaking it in alcohol and scrubbing.

Maybe LOR can provide info on specific parts on their board that can be damaged by ultra sonic cleaning (or soaking in alcohol).

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Bob VandenBoom

I am a bit leary of ultra sonic cleaning as well. That's why I asked. I usually use your method of a little alcohol, but I have 12 boards and was looking for an easy, quick way out. I can strip the flux of with some board cleaner, but the residue left from that is not that pretty either. I thought a minute in the ultra sonic bath would clean it up. I figured a minute might not be long enough for the harmonics to damage the wire bonds. I'll have to check and see if the cleaner in a variable frequency cleaner.

Thanks

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I saw alcohol mentioned.. WORD to the wise be careful with this. Most store bought rubbing alcohol is 70% or less alcohol. The rest is WATER! Yep you can scrub your boards nice and clean, then month later you will start to see oxidation, or parts will just start failing for no reason.

You can use alcohol from the Brand stores, but make sure it is no less than 90%, otherwise it is too much water.

I use an aerosol flux remover.. such as

http://www.hmcelectronics.com/cgi-bin/scripts/product/8591-0031

I have FRY's electronics just a few miles from my house, so I pick up a can here and there stuff works great...

... Most cases the aerosol pressure will wash flux right off. But I also scrub with an old faithful tootbrush.

BUT if you are using "clean solder" such as what Dan ships with his kits, then you should have very little or no residues on the boards.

a little bit on coating boards: Delco used to coat their Radio boards with some CRAP we used to call "scmegma", that took a special stripper to get off. You could not repair ANYTHING on those boards till this was stripped off. IT made finding bad solder joints a Beeeootttcchhh...( we used to use a pencil eraser and tap on the boards till the FM came back on, Then heat all the joint is that area. Yea I know a REALLY technical way of doing it)

From years of repairing radio's, I suggest not coating the boards in case you have to make a board level repair. Weird stuff on Circuit boards tend to do weird thing when trying to solder. Plus you will be cleaning again just to make the repair.

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Bob VandenBoom

mnkyboy wrote:

I saw alcohol mentioned.. WORD to the wise be careful with this. Most store bought rubbing alcohol is 70% or less alcohol. The rest is WATER! Yep you can scrub your boards nice and clean, then month later you will start to see oxidation, or parts will just start failing for no reason.


This is why a conformal coating would be benificial. Any ionic contamination, or oxidation between components or leads would be neutralized by the conformal coating. Yes, rework is an issue, but once you have all the cords connected, board mounted in the box, and box closed up, any repair is an issue.

Aerosol flux remover is great stuff, but you should clean the board with distilled water or a pure alcohol or acetone to remove the residue. Some flux removers do more harm in the long term if not cleaned properly. With the solder that comes with the kits, it's best to let the residue be. If you choose to clean it, just make sure you get all the residue from the flux and clleaners off the board.

The component pitches and mounting methods of the Light-O-Rama kits do not lend themselves to failure. If you are reading this and wonderig if there is a problem, rest assured there is not. We sometimes get a bit involed in our conversations and get carried away at times. I'll call this the Tim Taylor effect - things are great the way they are, but just one more tweak and it will be perfect.

Happy Building.
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  • 8 months later...

I use an ultrasonic cleaner at work to clean all of the circuit boards I work with. However, I use Branson's EC cleaning solution. This requires the solution to be between 130 and 160 degrees F. Optimum temp is 140 F which I check with one of those fancy 'laser' thermometers. This also requires a 10 minute degassing prior to use. Then I toss the boards in the cleaner and let it bzzz for no more than 5 minutes. A complete rinse with deionized water and a quick dry overnight in the rack, and we're ready to roll!!

So, it can be done, if done right. The problem is the cost. You'll need a ultrasonic cleaner with a heater, not cheap. You'll need the right cleaning solution, not cheap. This is way overkill for anything done at home, including LOR boards.

The breakdown of the bond wires are normally caused by letting the boards bzzz for more time than it should.

I use silcone conformal coating on all the boards I work on. I'm kind of partial to Miller-Stephenson conformal coating, as rework is not an issue because they have 'solder-through' coating. Troubleshooting isn't an issue either as all my probes are of the 'pin' type. Makes for some interesting wounds on me too! However, again, Miller-Stephenson products are a tad on the expensive side. I do believe the last time I bought a case of conformal spray it was 29 bucks for each 14oz can. This stuff is mil spec'd, so of course it's expensive.

I also just noticed this is an old thread.. Well, that's my two cents anyways...

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