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May 1998

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Subject:
From:
Bill Davis <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 27 May 1998 07:57:13 -0700
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Nicolas-

A lot of the exposed copper fears date back to military usage, when the exposed Cu was subjected to a wide variety of environs. Today, as a matter of practice, we have exposed copper on IC leads, especially when they are plated as opposed to dipped. I would ask myself, what would happen in extreme usage of the application-that is, if you're building boards for use in a PC desktop, the interior is not generally exposed to airborne acids or extremes in temperatures. Alternatively, if your application is for use in waste water treatment plants where all kinds of airborne contaminants exist, then one may be rightly concerned.

As a matter of pragmatic thinking, we, as an industry, need to get used to exposed copper. The IC industry is quickly moving to copper interconnects on their products, and only hermetic packages can guarantee no exposed copper...

Regards,
Bill

> -----Original Message-----
> From: Michael Carano [SMTP:[log in to unmask]]
> Sent: Tuesday, May 26, 1998 9:12 PM
> To:   [log in to unmask]
> Subject:      Re: [TN] HASL alternative.Exposed copper
>
> SteveZeva wrote:
> >
> > Hi Nicolas!
> >
> >      As far as the exposed copper that results from an OSP process, there
> > isn't an issue as far as I know. Yes the copper will oxidize, but from the
> > little bit I know about metallurgy, it's my understanding is that the copper
> > will be coated with a layer of oxidation, and then it slows down dramatically.
> > For a illustration of that just think about some of the copper water lines in
> > old houses, the copper telephone lines exposed to the elements for years and
> > years...that shows that it takes quite a while for copper to deteriorate.
> >
> >      Somebody correct me if I'm wrong about this, but the exposed copper
> > problems that are defects usually have something to do with the exposed copper
> > being an indicator of some other problem, not the fact that the copper itself
> > is exposed. Oxidation of the copper is normally only a problem when trying to
> > solder to it...
> >
> > C-ya,
> >
> > -Steve Gregory-
> >
> > ################################################################
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> > ################################################################Hi Nicolas,
> I have come across this question of the exposed copper with respect to
> OSP's. While solder paste spreading will vary from paste to paste and OSP
> to OSP, no one has ever(to my knowledge) determined that the exposed
> copper caused a long term reliability problem. Maybe Jack Crawford at
> the IPC can help with this one.
>
> Best regards,
>
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> ################################################################
>

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