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April 1999

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Subject:
From:
Paul Wilson <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 1 Apr 1999 11:11:08 -0500
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Phil,

I have read the mentioned paper.
Indeed one can simulate the effect with +1V charge application during IG.
 Is this a normal occurrence?

On page S18-5-6 the mechanism of black band formation is given as depletion
of surface nickel with "no gold, being deposited during the defect
corrosion process."    It is then stated on page S-18-5-8  that "while this
hypercorrosion is taking place a thicker than normal layer of IG is also
plating on top."

Perhaps this is a typo, but one might suggest that there are other
mechanisms of nickel starvation that lead to black band including thermal
characteristics at reflow.

Does anyone have information as to black pad formation versus type of
solder paste and reflow temperature?  Do different cycles give different
defect rates or is 63/37 the only used paste?

Perhaps the root cause is nickel starvation in the bath or during assembly,
but the side effect is the black pad?

Speculating some more,
Paul

-----Original Message-----
From:   Phillip E Hinton [SMTP:[log in to unmask]]
Sent:   Wednesday, March 31, 1999 1:32 PM
To:     [log in to unmask]
Subject:        [TN] Black Ni/Au pads

All interested in black-pad phenomena

The root cause and explanation of the the black pad condition is well
explained in Nick Buinno's (Hadco) paper published in the IPC Printed
Circuit
EXPO Paper No.
S-18-5.  Get a copy from IPC if you did not attend.

Phil Hinton



.

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