Charlie,
I would suggest taking X-sections of the darker toned pads.  You'll likely
find that there is no nickel on those pads.  An XRF reading would probably
show 1-2 microinches of nickel and X-section will probably verify that the
problem is there, not the gold.  There are debates as to what causes this;
poor cleaning prior to nickel, galvanic reaction, poor initiation of the
nickel bath, problems with the activator (catalyst), static charge, and
probably others.  I've seen the same problem using two different ENIG
chemical suppliers.  Both had their own explanations, but neither vendor
was able to make it go away for good.  The problem occurred on basically
the same pads on several panels, making a strong argument for static charge
and/or galvanic cell reaction.  A third supplier that I'm working with now
has (so far) been able to make the problem go away.

In any event, your problem is not the lack of luster of the gold
finish......... it's the absence of nickel.  Immersion gold deposits by ion
replacement with nickel ions.  There was enough nickel deposited to get the
gold to take but that's it.  Immersion gold is sacrificial and is there
only to protect the solderability of the nickel.  In the case of these
boards you may find that there's no nickel there to solder to.

Mark Mazzoli


At 08:52 PM 12/7/00 -0500, you wrote:
>Hello All:
>
>When applying immersion gold onto 4mil wide x 8mil long pads for wire
>bonding, the gold finish result left much to be desired. In a string of pads
>adjacent to each other, we find a shiny surface of gold next to a very dull
>gold finish. In some cases the color is brown.
>
>What would cause such an effect in the  same plane?
>Any input would be greatly appreciated.
>
>Charlie

---------------------------------------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
---------------------------------------------------------------------------------