Thanks for the inputs (Technetters in general)   Unfortunately immersion
gold does not work well with thermosonic gold ball bonding.  Aluminum
Ultrasonic bonding works great with immersion gold since it will "weld"
to the nickel.  Gold will not reliably "weld" to the nickel without
special surface preparation (i.e. plasma cleaning)  It sounds like we
need to use electrolytic.


Bill C.

-----Original Message-----
From: Dennis Fritz [mailto:[log in to unmask]]
Sent: Wednesday, August 22, 2001 10:20 AM
To: [log in to unmask]
Subject: Re: [TN] Ni/Au Plating Question


Bill,

As you are specifying electrolytic gold for the wire bonding, the design
MUST
be bussed together to deposit gold (or the nickel gold is plated before
the
copper circuit traces are formed).  In any case, if you can electroplate
the
gold, you can electroplate the nickel.  It is faster and cheaper to
electroplate the nickel (even though my company sells electroless
nickel).

You may have a bit of confusion between nickel gold for surface finish
and
nickel gold for tab connection or wire bonding.  The proposed 4552
standard
for nickel gold for surface finish is oriented toward soldering.  You
can
wire bond to electroless nickel/immersion gold, but you do not get the
thckness of gold you specify.

I suggest you electroplate the nickel if the gold is what you want, or
else
greatly reduce the gold thickness to make the electroless
nickel/immersion
gold process possible.

Denny Fritz
MacDermid, Inc.

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