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Old 16th Sep 2019, 10:33 am   #21
kalee20
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Default Re: Spraying PCB boards with alcohol

I have found IPA to be sufficiently conductive to upset things. It is a useful cleaning agent, but you have to give it plenty of time to evaporate afterwards.

I use white spirit to remove greasy residues (or paraffin if very dirty - rinse with white spirit using a trigger spray bottle that we get lots of containing household cleaners).

After that, I use an IPA/water mixture.

One thing I have found with many organic solvents - they seem to provoke cracks in clear plastic such as meter covers etc. even though they don't dissolve the plastic.

I note Tektronix had a practice of thoroughly washing (with water) equipment returned for service (and then drying obviously) - even items with fans in! Personally I keep water and solvents away from toggle switches, motors, bearings (unless dismantling anyway) but they developed practices described here.
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Old 16th Sep 2019, 12:07 pm   #22
Welsh Anorak
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Default Re: Spraying PCB boards with alcohol

In an old (1967) issue of Practical Television, there was a feature on Tektronix 'scopes returned to the factory for repair. They took the valves out and washed them in water jets, followed by comprehensive drying. I assume it's the drying that's important.
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Old 17th Sep 2019, 12:28 am   #23
cjacek2000
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Default Re: Spraying PCB boards with alcohol

Incredibly informative replies. Thank you all very much. In my case, however, I think I'll just keep my OCD in check and leave it alone. Just keep repeating to myself "it's clean enough, leave it alone, it's clean enough, leave it alone, it's clean en.....".
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Old 17th Sep 2019, 1:55 am   #24
Bazz4CQJ
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Default Re: Spraying PCB boards with alcohol

Quote:
Originally Posted by kalee20 View Post
I have found IPA to be sufficiently conductive to upset things. It is a useful cleaning agent, but you have to give it plenty of time to evaporate afterwards.

One thing I have found with many organic solvents - they seem to provoke cracks in clear plastic such as meter covers etc. even though they don't dissolve the plastic.

described here.
Remember that IPA (and ethanol and methanol) is hygroscopic - absorbing water from the atmosphere at every opportunity; "pure IPA" is quite a rare substance.

As for cracking, any fluid, but particularly one with low surface tension, can promote crack growth; check out "Griffith Crack" theory. Professional glass-blowers wishing to cut a piece of thick glass rod will usually score it with a glass knife, then wet the score with spit before snapping it. Unfortunately, people will sometimes attribute cracking to a particular cleaning or lubricating agent, when the accident was ready to happen irrespective of the identity of liquid which came in to contact with the component.

B
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Old 17th Sep 2019, 3:07 am   #25
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Default Re: Spraying PCB boards with alcohol

In the spec sheets for all the components bought by HP under contract in the good old days was the clause "Must survive a dishwasher cycle with calgonite detergent"

Coming from a part of Yorkshire, I'd never heard of Calgonite. I wondered if it was something superman would be wary of.

We use IPA at work, it dissolves flux, but unless you use lots, it leaves a residue. One of the defluxing foam cleaners gets rid of the residue fairly quickly as it's softened from the IPA. Distilled water for the rinse.

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Old 17th Sep 2019, 5:51 am   #26
Argus25
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Default Re: Spraying PCB boards with alcohol

One thing I found with IPA, it is pretty well useless for cleaning off anything with ionic or salty compounds, the best example being leaked electrolyte from electrolytic capacitors.
I had a pcb with a green porous coating that was contaminated with electrolyte. The inter track leakage resembled testing an electrolytic capacitor on a meter; with an initial higher current (lower resistance) followed by a decay, reminiscent of a capacitor charging. IPA was useless in removing it. So I ran hot water over the board for 1/2 hr then washed it after that with de-ionized H20, and the leakage was cured as I had successfully leached the salts out of the surface.
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