Re: restoring circuit boards

[mjmahon@aol.com (Michael J. Mahon)]

Mark Cummings wrote:

>> Anyway, that's a really cool web page!!! I posed the question on cleaning
>&
>> restoring logic boards awhile back on this newsgroup. Your procedure is
>> quite interesting, and it's almost exactly what I originally had in mind.
>> It's also different from the ones mentioned on the replies to my request.
>> Some of the other recommendations included dipping the logic board into a
>> cleaning solvent and using a vibration process, or even dipping the logic
>> board into soap & water, then let it drip-dry for a couple of days.
>
>dipping into a cleaning solvent like isopropyl alcohol (which I think is the
>same or similar to rubbing alcohol ?) is fine if you can find enough of it.
>you'd need about a litre though which is a bit of a waste and costly. using
>a brush and a dispenser you'd be using less than 50mL I guess.
>
>for professional cleaning the first step is to clean with a brush and
>isopropyl first to remove most of the built up flux, then submerge in
>isopropyl in an ultrasonic cleaner overnight. having a large ultrasonic
>cleaner that could fit a motherboard in is not normally that easy to get
>hold of for your average hobbyist, and the results are not that much better
>to an untrained eye.
>
>definately don't leave it drip dry, what happens is that the contaminants in
>the water will dry onto the contacts inside switches etc. possibly starting
>corrosion. also you will see watermarks all over the place. after blowing it
>dry you can see instant success and if it's not 100% you can have another go
>straight away. besides that you can re-assemble it straight away and switch
>it back on.

It is, of course, perferable to dry a board quickly, with compressed air or
an alcohol dip, but it is not _necessary_ to achieve good results.

The key to avoiding the contaminant problem is to triple-rinse the board
in _distilled_ water, removing as much excess water as possible between
rinses.  (Mild "centrifugal extraction" by swinging the board works pretty
well if done safely.)

The primary source of "contaminants" in washing is the stuff dissolved
from the board itself, to be re-deposited as the solvent evaporates.  This
problem is minimizes, regardless of solvent, by rinsing multiple times
(preferably with clean solvent each time) and removing as much of the
lingering solvent as possible after each rinse.

In the end, letting the board sit (warming helps) for many hours or days
is required to eliminate the last of the trapped solvent.

-michael

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