One thing to look at would be the possibility of copper being complexed with
the amines from the resist stripping solution. While each metal has a
specific deposition potential as an uncomplexed entity, these potentials can
be altered if that metal becomes chelated with amines, EDTA, etc.
> -----Original Message-----
> From: Lourdes Mertens [SMTP:[log in to unmask]]
> Sent: Thursday, February 18, 1999 7:56 AM
> To: [log in to unmask]
> Subject: Re: [TN] Immersion Gold contaminated with Copper
>
> How would you explain copper stains on electrolytic gold ( hard or soft)
> after it's been immersed in an amine based resist stripper at 140 F for
> about 15 minutes. The panels are copper, solder plated and selectively
> gold plated before resist strip.
>
> Lourdes Mertens
> >>> "<Rudy Sedlak>" <[log in to unmask]> 02/17 8:51 PM >>>
> In a message dated 2/17/99 4:14:33 PM Pacific Standard Time,
> [log in to unmask] writes:
>
> <<
> enough time) When I dropped a nickel/Iron component into the bath it
> immediately plated with the copper.
>
> Perhaps one of the
> plating gurus can explain the likelihood of electroless copper plating
> onto
> gold. >>
>
> You are confusing electroless and immersion plating.
>
> When you plate electroless, something in the bath, called a reducing agent
> causes the metal to plate out, this can be Formaldehyde, or Sodium
> Hypophophite, or many others.
>
> When you immersion plate, the substrate dissolves, and this causes the
> metal
> in solution to plate. One of the classic examples is putting a nail
> (iron)
> into an acidic Copper salt (like Copper Sulfate) solution. This is what
> happened when you did your experiment. The fact that there was Nickle in
> the
> Iron was incidental to what happened.
>
> It is difficult to explain clearly, but there are rules about what metal
> can
> immersion plate on to another, and roughly speaking, in order for a metal
> to
> immersion plate on to another metal, the metal in solution must be more
> "noble", or less readily oxidized, than the substrate. This is why Gold
> can
> immersion plate on to Copper, but Copper cannot immersion plate on to
> Gold....
>
> I'm tired, I am gonna stop now...
>
> Rudy Sedlak
> RD Chemical Company
>
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