allisonportable at gmail.com
Tue Apr 25 09:01:49 CDT 2017
On 4/25/17 6:06 AM, Pete Turnbull via cctech wrote:
> On 25/04/2017 10:08, jim stephens via cctalk wrote:
>> On 4/25/2017 1:39 AM, Pete Turnbull via cctalk wrote:
>>> "Little residue" would be more accurate, and some of that residue
>>> will be water (look up "azeotrope") - plus you need a lot of
>>> alcohol for something the size of a PDP-8 backplane. Blow dry,
>>> even after an alcohol rinse.
> I should perhaps have mentioned that the idea is to flush the remaining
> water or alcohol out by blowing, not evaporate it like your hairdresser
> would :-) And you ought to use dry air, ideally - most compressors
> have water in their air.
>> In the process of cleaning optics indeed you need air and other
>> means to do that, you are right. But in this case I'm suggesting
>> the alcohol as a way to displace water out of internal parts. The
>> spotting or such is not much to worry about in the cleaning job on a
>> computer part.
> Except those spotty residues are usually hygroscopic, which can lead to
> corrosion later.
>> But in optics the process is much longer and elaborate, but still
>> needs the ventilation to be sure you don't have a problem with
> Sure. Outside of electronics, my experience is in a chemistry lab
> needing clean dry glassware. The process would go something like this:
> - preliminary clean with whatever is best, often water and a little
> detergent/surfactant, then drain most off
> - rinse with distilled water
> - rinse with ethanol to flush out remaining water, then drain
> - rinse with acetone to remove the alcohol/water residue
> - air dry
Considering your also trying to remove possible hazardous material and
leave a noncontaminating
surface its overkill to the max for a backplane.
> In photography, on the other hand, the final rinse would just be water
> - tap water if not too hard - with a tiny amount of a wetting agent
> (eg detergent) in it.
Again you are striving to neutralize the chemistry used.
> For a backplane or some PCBs I'd compromise, but closer to the
> photographic example than the chem lab. In fact I've done that with
> my PDP-8s, rinsing the backplanes then blowing out most of the residue.
Considering a fan(s) has been blowing dust and who knows what else at it
cleaning is good and any residue is nothing compared to the crud that
was formerly there.
In the pre-freon days the standard cleaner (when they did!) was a
modified dish washer.
The usual mod was reshape the racks to hold the boards and lower the
used for drying. A week rarely went by that someone had open it mid
cycle to see if
it was done.
>> We had a booboo in assembly that required cleaning and we no longer
>> had freon cleaner we wanted to use in that quantity, so we went with
>> the water / alcohol process. A switch had defective sticky seals on
>> it and they had all gotten waterlogged. Vendor claimed they would
>> survive water process wash and they were wrong. Paid us quite a bit
>> in credit for messing up a couple hundred boards before we caught
>> the problem.
Plastics and elastic materials require more care for compatibility.
Water is usually the safest but, none can remain.
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