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Topic: PCB cleaning. (Read 11653 times) previous topic - next topic

OhMyCod

I occasionally make my own double sided PCBs using the photomask/UV/develop/etch/drill method.

After soldering the components on them I normally try to clean using Isopropyl alcohol and lint free free cloths. This looks ok to the naked eye, but as soon as I look under a magnifying glass I see lots of flux, flakes of solder and bits of lint free cloth that have snagged on the end of trimmed component leads.

Is there a better way of cleaning? if so what?

It has been suggested that I dunk the whole board in a ultrasonic cleaning tank full of Isopropyl alcohol, but I'm not sure if that's safe. I'm happy to do that for sealed components - resistors and regulators. But I'm concerned that things like electrolytic capacitors may 'leak' and that other components (like GPS units and LCD display) won't cope with total immersion.

Any ideas?

thanks

majenko

I immerse the board totally in isopropyl alcohol (where the board isn't too big) and leave it there for a few minutes.  Then I remove it and scrub it with a cheap tooth brush.

If the board has connectors with tape covers (like USB sockets, with the gold tape over the top) I only dunk it briefly so the tape doesn't come away.

Comes up a treat.

Oh, and if I am mixing hand soldering with reflow, and I need to do the hand soldering first (say to get a chip in the right position) I clean in between the two phases, as reflowing can burn the hand soldering flux.

cjdelphi

A little paint style brush / toothbrush and dab some isopropyl alchyhol  :D  to the tip and brush until shiney

pwillard

#3
Sep 25, 2013, 01:31 pm Last Edit: Sep 25, 2013, 05:06 pm by pwillard Reason: 1
You may get slightly quicker results if you use something like QD Electric Cleaner "spray" or a "made for electronics" product like MG Chemicals "Flux remover", but the only difference is that they have slightly stronger solvents.

Best results are still achieved with a an alcohol based solvent and a nice soft brush (as a opposed to a metal wire brush).  I use an industrial pig bristle brush designed for cleaning.  (Lasts longer than a discarded tooth brush)  As you noticed... a cloth is just not a good idea.

majenko

The best thing about a brush over a cloth is the bristles can get in between the pins of chips, and under the leads of through-hole components.

mirith

I've seen people just use some form of soap and a dishwasher before, but that was in a manufacturing setting and I do not know what soap they used.

I've been wondering this myself, as I sometimes have to solder large objects where I end up burning the no-clean flux in our solder, and my best efforts (I've resorted to IPA and a toothbrush) don't get it off.  Any suggestions?  Beyond "Don't burn it in the first place"?

JimboZA


I've seen people just use some form of soap and a dishwasher before, but that was in a manufacturing setting and I do not know what soap they used.


Years ago, Mark Minasi in his books about building and upgrading PCs, advocated chucking contaminated boards in the home dishwasher with whatever make of liquid was available. This stemmed from his experience with boards that had been mounted in marine buoys and were covered in saltiness. On the basis that they were stuffed already, he chucked them in the dishwasher. After that, they worked.....
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pwillard

#7
Sep 25, 2013, 03:41 pm Last Edit: Sep 25, 2013, 03:56 pm by pwillard Reason: 1
In the 70's and 80's the best cleaning method for removal of flux was CFC based (Freon).  When that was deemed unlawful to protect the ozone layer, the industry moved to water based cleaning.  (I once worked as a Wave Solder machine operator, so this is first hand.  early on,  we would buy 1,1,2-trichloro-1,2,2-trifluoroethane in 50 gallon drums for vapor "degreasing" as a flux removal step.)

So, aqueous based cleaning *is* one of the methods used in production line PCB manufacturing. Think of a big dishwasher with a conveyor belt. Special detergents were formulated but board designs and heat involved as well as parts that are installed can make the water based cleaning less desirable.

Alcohols and ketones are still the simplest "no heat"/no agitation cleaning methods.  Immersion is a good method if a lot of boards are being done... but it's not practical for "once off" boards.  Alchohol is the only sure thing for a "non-attacking" solvent.  Stronger solvents should always be analyzed before use.  (Ie; Acetone for example is a very nice solvent for a lot of things and you might have some lying around...   It will dissolve plastic connectors and remove ink... so lets avoid acetone)

Some of the best cleaning results can be achieved with some form of a HFE (HydroFlouroEther) which is a non ozone depleting replacement for CFC's and between 25khz to 38khz mechanical agitation. 


So yes, the advice about using an ultrasonic cleaning tank is not a bad recommendation... assuming that you have one.

Note: The QD Electronic Cleaner I mentioned is an HFE based solvent containing Ethanol, Hexane and 1,1 Diflouroethane (the HFE).  I believe that , due to the high vapor pressure of hexane (itself a good solvent) makes the QD (quick drying) behavior of the spray.


MarkT


A little paint style brush / toothbrush and dab some isopropyl alchyhol  :D  to the tip and brush until shiney


Definitely vote for toothbrush, needs to be quite stiff to shift rosin.  Rosin is rapidly precipitated out
of solution as it evaporates so an excess of solvent helps, overwise you just move the rosin about.
You have to dissolve the rosin out of the brush regularly too.
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OhMyCod

thanks for the suggestions - consensus seems to be that a brush is a good idea, but i'd still like to know if total immersion is or isn't a good idea.

Cheers

majenko

Total immersion is a good idea if it is practical.

I have a small air-tight tub that I use for small boards (< 7cm x 4cm).  If not practical, just a brush dipped in alcohol is good.

From an electronic PoV, immersion in alcohol is perfectly safe, but immersion in water based products will require thorough drying afterwards (in an oven, 80-100°C for a while)

polymorph

Yup, stiff brush. I don't like to completely immerse if there are open components like potentiometers that have grease or oil inside them. Capacitors are fine, if they leak, then they are bad anyway.

You can get trimpots and potentiometers that are sealed.
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SirNickity

The datasheets usually indicate if its safe to immerse that part.  If you have any question, just look up the parts you used.

On that note, I keep an organized folder on my NAS of datasheets for all the parts I've bought from Digikey (etc.)  Recommended practice.

JChristensen

I've been using ethanol, old tooth brushes, and compressed air or a hair dryer.

oric_dan

Oh lord, talk about an enormous P!TA. After years of soldering, I disagree with what everyone else here has said [LOL]. I "never" remove the rosin flux, just leave it on. The joints don't dissolve or corrode like some people seem to think.

If I do wish to have a clean board, for whatever reason, then I use "aqueous flux" solder, which  cleans off extremely easily with semi-hot distilled water and a toothbrush. Rinse with same after brushing. No real chemical mess, as compared with every method of trying to get rosin flux off, and the boards are spic and span clean.

Certain parts which are not well sealed, like electrolytics and switches or pots, I solder on after the above cleaning, usually using "no clean" flux solder, which leaves little residue. And I just leave that on without cleaning. So, there's the 1 vs 13 method.

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