Good point, Mike. There may have been something on the cell phone board that was not on my experimental board. I did however scrub the cell phone board twice with Radio Shack Electronics Cleaner and I think that there is still some effects left from the submersion. I only did the experiment since I thought that some were suggesting that there was some corrosive residue created by the material in the less than pure water, but they may in fact have been referring to residue materials of the type that you have suggested.
It sounds like you've been careful and thorough, but your board might benefit from additional scrubbings in some other solvents, since not everything is soluble in Radio Shack Electronics Cleaner.
In general, I clean things by starting with clean water, since it is the most universal solvent. If it is really dirty, I may start with soap and water and a toothbrush. Then I follow up with clean water, then distilled water, and finally alcohol, and I don't worry about the fact that it isn't 100% alcohol.
The purpose of the alcohol is to carry off as much of the water as possible, so that it can't dry in place and leave any residue. A side benefit is that the water that's in the alcohol will be extremely pure. Of course the residue will be minimized by the sequence of rinses above, but you can't always control what comes off the board.
If possible, use compressed air to blow the board off, thus minimizing remaining fluid which will leave a residue when it drys in place.
And finally, you probably can't do any of this if your board includes assemblies that water, etc, can get into but not easily back out. This includes things like switches, pots, and transformers.
And then, of course, you have to thoroughly dry the board.
I have a friend who tells of starting his cleaning process by running his boards thru the wash cycle of his kitchen dishwasher, with soap.
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----------------------------------------------- Jim Adney snipped-for-privacy@vwtype3.org Madison, WI 53711 USA
Bob Pease swears by this process. He writes (in "Troubleshooting Analog Circuits", a book I most strongly recommend) that when he's working on PC-board circuits which require low leakage currents, he'll run 'em through the dishwasher, standard cycle, using a normal load of Calgonite detergent. When the wash and rinse are complete, he takes them out, raps/shakes/blows off the rinse water, and stacks them in the dishstrainer to dry.
He says that this process results in lower board-leakage currents than the more traditional PC-board cleaning processes which use organic solvents.
I believe that the use of Calgonite is significant - I looked it up and found that it contains surfactants and calcium metasilicate, and is significantly alkaline, but it does not contain chlorine. Other powdered dish detergents (e.g. Cascade) do contain chlorine, and I suspect that they might corrode components on a circuit board.
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"Dan Dubosky" wrote in news:JJednSvfDsy0AvzVnZ2dnUVZ snipped-for-privacy@ptd.net:
It is likely that some SMT components or other components still have conductive residue between the part and the board.
I 'repaired' a laptop computer that had 'merlott' [wine] spilled in it. It was left powered on over the weekend.
The repair consisted of remove power sources disassembly Rinse with plenty of clean water rinse with alcohol scrubbing and scraping to remove visible conductive paths. rinse that area with water and alcohol. rebuilding a couple of conductors that had been eaten away completely drying. Many hours of sitting in the flow of warm, dry air from an air vent. The keyboard took a long time to dry. reassembly.
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bz 73 de N5BZ k
please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.
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There's a board that I repair commercially, that comes from an automatic drinks vending machine. Often, when I receive them, they are caked in ingredient residue that has been flying about inside the machine, which makes them pretty much impossible to work on, so the first thing they get is a wash. I just run the water until it's coming out of the sink tap (faucet for our U.S. colleagues ?) at its hottest, squirt a little ordinary washing up liquid on the board, flick some of the hot water on with a pan-scrubbing brush, and then work that up into a thick lather, scrubbing between the legs of the through-hole components. When it's had a good scrub, it gets run under that hot water stream, until all of the soap is off both sides. It then gets shaken, patted dry on a dish towel, before being stood vertically in front of an electric fan heater for about 5 minutes.
The result of all of this is a board that looks like it has just come out of the factory, and I have never had any future problems with any residues, and I've been doing it to this particular job for about 6 years now. As well as through-hole components, this board also has many s.m. components on it, including both I.C.s and passives. It does not, however, have any 'closed in' components such as coils, IF transformers etc, which as someone else suggested, would probably not take kindly to being flooded with water ...
I have cleaned stubborn high impedance loading by using mostly alcohol and the Weller air pencil set to a high flow and low temperature. The problems were under the components. I sometimes have to repeat many times before all the flux and residue is out. You have to move the air pencil around under components, going mostly in one direction. The old boss made me use alcohol.
By the way, the cell phone I worked with appears to be OK after much cleaning, cyclic baking, and a month delay.
Rosin flux doesn't dissolve completely in either water or alcohol, but I've found that by alternating rinses, I can eventually remove it. In cases like that, it might pay to invest in commercial flux remover, if only to get things started. I'd still finish up with water and then alcohol, however.
cyclic baking, and
In that case, there was probably something on the board that was just hard to get the water out of. The real test will be to see whether it continues to work in humid weather. That's when residue can resorb moisture and start causing problems again.
If there's no residue, then humid weather should not cause any problems.
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----------------------------------------------- Jim Adney snipped-for-privacy@vwtype3.org Madison, WI 53711 USA
Many thanks to all of you. The cell phone now appears to be back to normal. Yesterday, I purchased "denatured alcohol solvent" by a company called Sunnyside. It was in a well sealed can with a plastic top that had to be removed, and is said to contain denatured alcohol and less than 4% methanol. I don't know its purity, but when I stuck my finger in it and it got under my nail, it really burned.
I completely bathed the main circuit board in this solvent for about one minute while brushing around the main side of the board. I then let it completely dry for over 30 minutes, first in the sun and then under an incandescent light.
I charged the cell phone up last night, and this morning there is no significant discharge. The large SMT components have a sealant around their base but many of the smaller components do not have such a sealant. So moisture could easily have remained under them and within the many push button switches.
Today is a very humid day so it will be interesting to see how much discharge occurs.
The TEK field office in St. Paul used to clean 500 series gear amongst other things in a sort of dishwasher and also had the drying oven; was this equipment standardized amongst the field offices?
msg wrote in news:o_adnb5Kr65sTP7VnZ2dnUVZ snipped-for-privacy@posted.cpinternet:
Heh,I washed down a lot of 500 series tube scopes! It made a big difference,too.
well,everybody seems to have had different equipment for the task. I had to persuade the Orlando manager to ship the old wash/spray booth from the closed TEK-Indianapolis office,and their drying ovens were from different manufacturers.Some TEK field offices had NO wash/dry facilities. (moot point now;they're all closed.)
I had to take boards home to run through MY dishwasher. I didn't know of any TEK offices that had a auto dishwasher.
I have to side with Bob Pease. Over the years of reading his column in Electronic Design, and stuff in NSC's data books, he has had tons of experience with analog and is usually dead on. He was behind the now classic 'Floobydust' data book back in 1977. Back then everything was washed in a freon solvent tank but times have changed, no more freon tanks, Lead is being banned, etc. I never dismiss his stuff as rambling since he almost always puts in a nugget or two. Bill Baka
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