John Waite wrote:
>
> Hi Scott,
>     Hmmmmmmmmmm..  Interesting scenario.  I need to ask a couple of obvious questions first.
>     Is the copper equal on both sides BEFORE You run the boards through the the soldering
> process?
>     Does the top side contain heavy shield as opposed to the bottom side?  If so, then you have a
> low current density area that is not plating both sides equally.
>     If not, Then the plating anode placement is out of whack.
> This is a tough question to answer without a lot more detail.  If you Email me, I can Talk some
> more detail.  JOHN WAITE
>
> Scott M. Severson wrote:
>
> > Hi All,
> >
> > Another question for who can ever answer it.
> >
> > What factors affect the dissolution of plated copper into solder during the
> > soldering process?  Lets ignore the soldering parameters (temperature,
> > composition, wave/pot turbulence....) and focus on the copper plating.
> >
> > We have PCBs that are seeing a 50% reduction in plated copper thickness
> > during a standard IPC TM-650 thermal stress.  We've cross-sectioned enough
> > thermal stressed boards to know that this isn't normal.   Another question.
> >  We are consistently seeing the reduction on the top side of the board (the
> > side that doesn't come in direct contact with the molten solder), why the
> > top side and not the solder side?
> >
> > The boards are 14 layer with 4 2oz copper power/ground planes.
> >
> > Thanks
> >
> > Scott Severson
> > Benchmark Electronics Inc.
> >
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> ################################################################When you say that the copper is dissolving, is it possible that you are
seeing smear of the solder over the copper and thus seeing the appearance
of copper loss? Generally, a small amount of copper will form with tin in
terms of the copper-tin intermetallic, but only a small amount.

good luck

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