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February 1999

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Subject:
From:
Lourdes Mertens <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 18 Feb 1999 05:55:31 -0800
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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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