Hi Denny! There ya go baiting us poor metallurgists again before we have
had time to get that first Diet Coke of the day! I think that the "degree
of brittleness" is more of a measure of the use environment the solder
joint experiences - all IMCs are brittle. The interaction of IMCs within
the solder joint structure The Sn/Cu IMCs and the Sn/Ni IMCs are very
different creatures which with the increased use of ENIG by the industry
has lots of folks conducting data gathering investigations. The Sn/Cu IMCs
and the Sn/Ni IMCs both have hexagonal crystal structures but their
constructions are different. The Sn/Cu IMCs have better wetting properties
than the Sn/Ni IMCs due to differences in diffusion kinetics. The Sn/Cu
IMCs form in two phases - Cu6Sn5 and Cu3Sn, and the Sn/Ni IMCs form Ni3Sn
in solder joints. There are two references which contain lots of
information on the Sn/Cu and Sn/Ni IMCs if you really want to do some
reading: Solder Mechanics: A State of the Art Assessment, ISBN
#0-87339-166-7 and Soldering Handbook, 3rd Edition, AWS, ISBN #
0-87171-618-6.  Also the Journal of Electronic Materials has had quite a
number of papers in the last few issues on Sn/Ni IMCs. Have fun!

And Denny - I am working on your SERA report!

Dave Hillman
Rockwell Collins
[log in to unmask]




                      Dennis Fritz
                      <[log in to unmask]>        To:       [log in to unmask]
                      Sent by: TechNet         cc:
                      <[log in to unmask]>        Subject:  Re: [TN]


                      02/18/2003 08:09
                      PM
                      Please respond to
                      "TechNet E-Mail
                      Forum."; Please
                      respond to
                      DDFRITZ






Just wondering if any of you metallurgists have a comment about copper tin
intermetallics vs. nickel tin.  We have heard the NiSn IMC is indeed
more brittle than the CuSn IMC's.  This is the contention of one particular
industry group.

Denny Fritz
MacDermid, Inc.

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