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December 1999

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Subject:
From:
Ryan Grant <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 9 Dec 1999 14:33:54 -0700
Content-Type:
text/plain
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text/plain (78 lines)
Larry,

        You are absolutely correct.  However, in order for solder to make
contact with Ni, it must first dissolve the Pd.

        Several SMT solderability tests have used the technique of depositing
solder and measuring how far it spreads during reflow.  How far solder
will spread is a function of the surface energy interface of the liquid,
solid and gas, and the wetting angle.  By increasing the surface energy
of the solid, the liquid can more easily wet that surface.  Without
referencing a chart, I would guess that the energy interface of liquid
Tin is better for Gold than Palladium because Gold dissolves into Tin
faster.  Improving the solderability of Palladium by using flash gold
was suggested by Elizabeth Benedetto in her article in SMT Feb 99 titled
"Evaluation of Palladium Lead Plating".

        Dave Hillman did do solderability testing and wire bonding on Ni/Pd/Au
and found that surface finish has very good wire bondability. (Published
in SMI '96)  It is also corroborated by an NCMS consortium published in
SMI '96. And ITRI reported the same results in IPC expo 97.

        From the looks of the above stated articles, I guess I'm wrong about
the Au being used to improve solderability.  It sounds like the gold is
for wirebonding.

Ryan Grant

>-----Original Message-----
>From:  Larry Tawyea [SMTP:[log in to unmask]]
>Sent:  Thursday, December 09, 1999 11:16 AM
>To:    [log in to unmask]
>Subject:       Re: [TN] Ni/Pd/Au
>
>In a message dated 12/8/99 4:02:17 PM Central Standard Time,
>[log in to unmask] writes:
>
><<
>         The gold is an attempt to improve the solderability of the
>palladium. >>
>Ryan,
>
>Unless I am totally missing something from your response,  the issue is not
>how long the solder is in contact with the Au or Pd but how long is the NI in
>contact with the solder.  I'm not trying to take issue with your response,
>but I think the issue is what is the solderability of the Ni and how good of
>a solder joint have you made to the NI.
>
>Larry Tawyea
>
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