Hi Phil,

I can only comment on the last of your questions from a laboratory failure
analysis viewpoint.  We have one customer whose PCB assemblies exhibited the
"black pad" separations on a BGA component.  They thought that underfilling
the BGA would help hold the solder balls onto the board, but cross-sections
after the underfill process showed that the balls separated anyway. I don't
know if would happen with every type of underfill process, but it did not
seem to have a positve effect for this customer.

Wade McFaddin
Nextek Inc.

> -----Original Message-----
> From: phil bavaro [SMTP:[log in to unmask]]
> Sent: Friday, February 22, 2002 11:34 AM
> To:   [log in to unmask]
> Subject:      [TN] ENIG black pad issues
>
> We have used ENIG as our primary BGA board finish for many many, many
> boards built for cellular communications without issues regarding this
> problem.
>
> We have a major PWB fabricator telling us that they cannot control what
> appears to be a "black pad" problem and that we should be changing to
> Entek's OSP combined with a selective gold process for our standard
> finish.
>
> I cannot say that we have never had this problem before but usually it was
> more a case of unrinsed soldermask on a pad rather than corroded nickel
> plating beneath the gold finish.
>
> I did the cross sectioning myself and took some great pictures of the
> contaminated pad surfaces that were yielding when subjected to drop
> testing.
>
> I am convinced that ENIG is a solid finish but I know that it can be
> susceptible to nickel wetting problems.  I have three questions:
>
> 1)  What kind of frequency are the rest of you finding "black pad" to
> occur
> on ENIG boards?
> 2)  What finish do you use for high density BGA/CSP double sided boards
> that have surface contact (gold) plating requirements?
> 3)  Are any of you using underfill to hopefully negate the solder joint
> brittleness that the black pad surface inherently creates?
>
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