Hi Martin,
To my knowledge there are no direct studies on the reliability differences of
Cu-Ni-Sn/Pb solder bonds vs. Cu-Sn/Pb solder bonds. Given good wetting (where
'wetting' means both the spreading of the solder on the surface and a good
metallurgical bond with the formation of intermetallic compounds (IMCs))
there should be no reliability differences, because in good solder joints the
interfaces are not directly involved in fatigue failures. There are however,
differences in the pull strength of these solder joints (see Engelmaier, W.,
and B. Fuentes, "Alloy 42: A Material to be Avoided for Surface Mount Solder
Component Leads and Lead Frames," Proc. Surface Mount International Conf.,
San Jose, CA, August-September 1994, pp. 644-655; also in Proc. Int.
Electronics Packaging Conf. (IEPS), Atlanta, September 1994, pp. 503-516;
also in Proc. 19th Ann. Electronics Manufacturing Sem., Naval Air Warfare
Center, China Lake, CA, February 1995, pp. 5-20; also in Proc. NEPCON West
'95, Anaheim, CA, February-March 1995, pp. 385-395; also in Soldering &
Surface Mount Technology, No. 21, October 1995, pp. 20-25); the pull strength
to Ni-based surfaces is lower. That however, has no reliability consequences
because even the lower pull strength is much more than is needed for the
loading conditions experienced even under abusive manufacturing, handling and
shipping conditions.
It needs to be said however, that it is more difficult to form properly
'wetted' metallurgical bonds to Ni-based surfaces than Cu-based surfaces
because the dissolution rate of Ni into Sn is much lower than that of Cu.
Therefore, you need more heat at reflow. I recommend a 10 to 15 C higher peak
reflow temperature for Ni-based soldering surfaces; alternatively you could
spend more time at a lower peak temperature, but that is not practical in
most cases unless you use vapor phase reflow.
Werner Engelmaier
Engelmaier Associates, Inc.
Electronic Packaging, Interconnection and Reliability Consulting
23 Gunther Street
Mendham, NJ 07945 USA
Phone & Fax: 973-543-2747
E-mail: [log in to unmask]
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