This is like one of those puzzlers on Car Talk.  The answer to your
question is in the question.  A likely cause is the microetch.  The etch
rate of nickel is notoriously fast.  In the "proper" conditions it can
be so fast as to completely undercut the gold resulting in lift off.

> ----------
> From:         Brian L Guidi[SMTP:[log in to unmask]]
> Reply To:     TechNet E-Mail Forum.;Brian L Guidi
> Sent:         Friday, August 28, 1998 8:28 AM
> To:   [log in to unmask]
> Subject:      [TN] Direct Metalization Over Gold
>
> Hello again fellow 'Techies',
> We have an interesting scenario which has raised some questions. We
> have an
> application in which we are processing some panels through direct
> metalization, after they have been selectively gold plated. After
> removing
> the conductive colloid via micro-etch, we noticed significant
> Gold/Nickel
> adhesion problems. At sporadic  locations throughout the panels, the
> Ni/Au
> was completely peeling away. The Au to Ni adhesion appears intact.
> However,
> the Ni to Cu adhesion is were the problem appears to be. We are
> interpreting this as a cleanliness issue prior to plating. We find it
> difficult to believe that there is something in the direct
> metalization
> process that is attacking the Ni/Au and causing it to peel away from
> the
> Cu. Does anyone have any previous experience with this scenario? Does
> anyone know of any reason why the direct metalization process would
> attack
> the adhesion properties of the Ni to Cu?
>
> Thanks in advance...
>
> Brian Guidi
> Methods Engineer
> Teledyne Electronic Technologies
> Printed Circuit Technology Division
>
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