The copper surface has a given plating potential. If features are connected
together, the TOTAL surface drives the plating potential. Hence, smaller
surfaces have lower plating potential and are harder to plate. A floating
feature, not connected to any plane, is harder to plate. When one feature does
not plate, others connected to it do not plate. This phenomenon is sometimes
called the galvanic effect. Other variants of this phenomenon are also
encountered when using electroless processes.


Jacques Coderre
e-mail:[log in to unmask]


---------------------- Forwarded by Jacques A Coderre/Bromont/IBM on 10/16/97
09:49 AM ---------------------------


[log in to unmask] on 10/15/97 04:14:55 PM
Please respond to [log in to unmask] @ internet

To: [log in to unmask] @ internet
cc:
Subject: [TECHNET] Exposed copper pads/Immersion NiAu

PWB manufacturers:
Has anyone seen the phenomonen of exposed copper SMT pads after
immersion NiAu. To further complicate this issue, any pad (via or SMT)
that is tied to this pad in a net also does not get plated. This condition
does not occur on every panel within the rack. One panel will have it,
while the adjacent panel does not.
Are we looking at a static charge on the panel that keeps certain nets
from plating?
Any ideas on what's causing this would be appreciated.

Thank you
Ron Hayashi

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