Is Palladium really an acceptable choice for solder joints?

We have worked with Palladium as an underbump metallization for silicon
chips. After bump formation with SnPb solder we investigated the
reactions of the solder with Palladium in reliability tests. We observed
a very fast growth of various Pd-Sn intermetallics which were consuming
most of the tin in the solder. In addition the intermetallic phases
PdSn3 and PdSn4 growed perpendicular to the layer formed as large plates
into the solder. The measured growth rate of intermetallics was so large
that even the bump shape changes with time from ball to prolonged posts.
After a few hundred hours at 125°C no tin could be found in the solder
anymore. Pure lead remains between the intermetallic plates and on top
of the solder bump. Shear values decreased dramaticly by high
temperature storage. The same was found after longer time storage at
85°C as well. All this we published at 3rd 1999 IEMT/IMC Symposium on
„Microelectronics Packaging Innovation for the New Century“, April
21-23, 1999, Sonic-City – Omiya, Tokyo, Japan.

Because nearly all solders contain large quantities of tin we expect
these reactions of tin and Palladium in lead-free solders as well. Did
anyone investigate this already and could share these results?

Regards,

Hermann

--
Dr. Hermann Oppermann
Fraunhofer IZM
Gustav-Meyer-Allee 25
D-13355 Berlin, Germany
--------------------------------------------------
phone: +49-30-46403-163, -160
Fax:   +49-30-46403-161
email: [log in to unmask]
--------------------------------------------------
Dept. Chip Interconnection Technologies
Group Optoelectronics, HF and Sensor Integration
http://www.izm.fhg.de/
http://www.izm.fhg.de/avt/index.htm
http://www.izm.fhg.de/avt/opperm.htm
--------------------------------------------------

"Romm, Doug" schrieb:

>      For anyone interested, you can view the TI Lead-Free
>      Solutions Web Page at the following link:
>
>      http://www.ti.com/sc/leadfree
>
>      Of couse the contents of this page will be updated as new
>      information becomes available.
>      Regards,
>      Doug Romm
>

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