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May 2000

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Subject:
From:
Jonathan A Noquil <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 1 Jun 2000 07:42:29 +0800
Content-Type:
text/plain
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text/plain (88 lines)
Agree with George Black Nickel result form uncontrolled bath chemistry. My
experience
before, was that thick nickel have deposited on tank sidewalls (unpassivated)
thereby Nickel metal content
in the solution become not balance and deposit become black as you check the
concentration of the solution
it was no longer balance. So check out your tank passivation and dragging in of
Di water onto your bath too.

hope this helps






George Milad <[log in to unmask]> on 06/01/2000 03:24:11 AM

Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond to
      [log in to unmask]

To:   [log in to unmask]
cc:    (bcc: Jonathan A Noquil/Cebu/Fairchild)
Subject:  Re: [TN] Black nickel barrier problem w/immersion Ni/Ag




The Black Nickel issue is a very low level defect (ppm), with big
ramifications when it is encountered.  In absence of a good understanding of
how this occurs, it has become a  "Catch all" for any solderability issues
associated with ENIG.  Many defects that may have other explanations go un
investigated once they are labeled "Black Nickel".

The immersion gold step is a controlled corrosion reaction.   Occasionally
this could go out of control and may create a  "Black Ni" pad, under the
immergent Au.  This gold will have a tendency to peel if tape tested,
depending on the degree of severity of the corrosion. The underlying  Ni is
compromised and may not wet.

Some of the ways that this can occur are:
Uneven Ni deposit:
    An uneven Cu surface (pitted, corroded etc)
    Solder mask residues on the incoming Cu surface
    Cu/tin intermetallics as above
    Uneven catalyzation.  Catalyst bath operated out of control.
    Ni bath chemistry out of the specified operating range

Gold bath too aggressive:
    Excessive dwell time in the Au bath
    High Temperature (outside the control limits)
    Au bath chemistry out of specified range.

Most board shops today are fully aware of this condition and are making sure
that their ENIG processes are running within the specified vendor
recommendations.
George Milad
Shipley

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