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January 2002

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Subject:
From:
Brian Ellis <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Sat, 19 Jan 2002 10:20:47 +0200
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Genny

The innocuousness or otherwise of markers is a subject that comes up
from time to time. The alcohols you mention are of no concern as they
evaporate completely. It is what is left behind that may be. This
consists of some form of polymer, dyes and pigments. As a rule, most
polymers are probably fairly benign unless they are hygroscopic (as can
happen). As for the pigments, I'd be rather wary of black markers,
because the pigment is almost surely carbon black (a form of very fine
soot formed by burning petroleum derived gases/vapours under controlled
conditions without admixture of oxygen). The same carbon black is also
used for making cheap and nasty resistors - need I say more? Pigments
derived from natural earths are usually harmless. Synthetic ones and
dyes may be less so, especially if they are not chemically or physically
stable. There is therefore a risk in using any marker and their use must
be qualified after practical lab trials - and never change the
manufacturer or type without requalification.

As for cleaning marker marks: again qualification is the only way of
finding out whether a process is safe. Remember that you may remove some
components of the ink yet leave others, which may be invisible but
electrically malign. Above all, remember that some markers will actually
penetrate the surface of some items, especially polymers, making it
impossible to clean away.

Conclusion: test and see, but be mistrustful.

Brian

Genny Gibbard wrote:
>
> Happy Friday! (tappity, tappity - doing the Friday dance)
> We have ceramic resonators with silver coating on several products.  We
> started handling those OEM boards with gloves during our test processes
> because the customer expressed concern with skin oil contamination.
> At times these components have been marked in house, for various reasons,
> with a standard sharpie marker.  In fact, at an early point in the
> production schedule, the CM we were using at the time was marking them on
> their own, because the resonators are so close in size they were having
> trouble telling them apart and getting them installed in the right locations
> (due to tight time requirements, we got a shipment of bulk parts that were
> being placed by hand).  The marks looked like they were marker applied and
> used a variety of dot and line patterns in various colours.  We have never
> noticed any harmful effect on their response, although build quantities were
> low.
> Now someone on our production floor is asking whether the ink may be a
> contamination that we should avoid.  We have easily cleaned this marker off
> of other surfaces with board wash.  They wanted to know if they should clean
> the components with board wash.  I think that if the marker is already on
> there and a contaminant, don't compound it by rubbing board wash on it.
> >From what I can tell, from the MSDS on the marker website, the ink is
> primarily propanol/butanol/alcohol based.  The board wash is alcohol based.
> Chemistry is my weak subject.  Is alcohol - related substances on silver
> coated components a concern?
>
> Genny Gibbard (mailto:[log in to unmask])
> Product Transition and Support
> Wavecom Electronics Inc.
> 202 Cardinal Crescent
> Saskatoon, SK, Canada
> ph:     (306) 955-7075 ext. 229
> fax:    (306)384-0086
>
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