Benny,

        Th Pd is there to bond onto!!!

        Pd is "pretty common" in Au bonding (note the flying commas!)  and
     is used as the reliability for these is thought to be pretty damn
     good, this due to Pd being fully miscible in Au, so there are no
     intermetallics to worry about. As the layer is far harder than Au,
     capillary life is shorter and you'll need to play with power etc, some
     have found that a shorter capillary is needed although Ive never seen
     the need myself.

        There are some concerns about the system in that if you give it
     enough heat and time, all the Pd can be leached into the Au and leave
     you with a 2nd foot lift.  (this only really happens if the Pd is
     incredibly thin instead of just stupidly thin, OK results with 3-5 u
     in Pd!)  The other thing to watch for is that the Pd-Sn intermetalics
     form during soldering if its too thick, so keep it thin.

        If you have to bond them,  watch the temperature on the plate as Pd
     oxidises and goes green at high temps.

                Good Luck

     Roger Massey
     Metallurgist and wire bonder
     Motorola AIEG
     UK



______________________________ Reply Separator _________________________________
Subject: [TN] Palladium underplate for Cu-Ni-Au system
Author:  "TechNet E-Mail Forum." <[log in to unmask]> at #email
Date:    29/01/99 15:13


Hi technetters,

Does anybody know the purpose of a palladium layer between the Ni and Au for
wire bonding PCB? Recently, I've got a request to bond gold wire
(thermosonic) on PI flex which is plated with electroless Ni and immersion
Au. On one sample, the gold thickness is reduced and compensated by a
electroless palladium layer above Ni; while the other just is the normal
electroless Ni and immersion Au. The phosphorus contect is around 6-8%.

I would appreciate if anyone can advise me on the palladium function, cost
implication (cheaper by reducing the gold?), and bondability of this kind of
metalization.

Regards, Benny.
ASM Assembly Automation
Email :[log in to unmask]

################################################################
TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
################################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text
in the body:
To subscribe:   SUBSCRIBE TechNet <your full name>
To unsubscribe:   SIGNOFF TechNet
################################################################
Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for
additional information.
For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700
ext.312
################################################################

################################################################
TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
################################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body:
To subscribe:   SUBSCRIBE TechNet <your full name>
To unsubscribe:   SIGNOFF TechNet 
################################################################
Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information.
For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312
################################################################