Yes, you are correct. But some variation may be present due to slight
difference in the chemicals involved and exposure time.

Alain Savard, B.Sc.
Chemical Process Analyst
CAE Electronics Ltd.
e-mail: [log in to unmask]

-----Original Message-----
From: Martin Christie
Subject: Re: [TN] gold immersion plating--An attempted explanation

From your explanation I would assume that this process is self limiting in
terms of the amount of the deposit i.e. where you get the 0.2 micron Gold
deposit from.

Am I correct in assuming this?

Martin Christie
>
>Metals in solution are too low in electrons, and thus have a positive
charge.
> Solid metals, in their shiney form, have the proper number of electrons.
>When a more "active" metal (meaning a metal that does not bind its
electrons
>tightly) is immersed into a solution of a metal that does bind its
electrons
>tightly, like Gold, the electrons shift from the substrate metal, (the
>substrate under Gold is almost always Nickel) to the metal in solution,
>causing the metal in solution to plate out spontaneously on to the
substrate
>metal....in other words, a Nickel coated PCB, when immersed into a solution
>of Gold, will cause the Gold to plate out spontaneously on to the Nickel,
and
>in the process some of the Nickel is dissolved and goes into solution.
>
>This continues until the substrate Nickel is covered, and no more Nickel is
>available for this chemical reaction, and you wind up with around 7-8
>microinches (0.2 micron) of Gold from this type of plating.
>
>Hope this helped...
>
>Rudy Sedlak
>RD Chemical Company

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