Guenter,
It certainly takes time--and thermal energy--to allow gold/silver layers to
disperse more or less uniformly throughout the solder joint to prevent
embrittling concentrations. But you need to form intermetallics, otherwise
you have no metallurgical bond. Cu/Sn intermetallics form much more rapidly
than Ni/Sn intermetallics, because of the much higher dissolution rate of Cu
in Sn. However, the danger of inadequate wetting (no intermetallics) is much
greater for real product than the danger from excessive growth of the
intermetallic layer(s). 
 
Regarding the IEEE Compliant Lead Task Force, I responded to a similar
question from Dave Hillman with:
Your second question is certainly a good one. There is a situation that shows
how naive engineers can be. We had the catastrophic failures of the TI PLCC-J
solder joints at IBM-Austin scaring everybody stiff. Consequently, the
engineers from numerous competing companies formed the IEEE Compliant Lead
Task Group with Jack Balde chairing. The idea was that everybody would
contribute, we would test all submitted PLCCs, and evaluate and publish the
results. Participating companies were Apple, AMP, AT&T (Bell Labs multiple
locations), Burroughs, Bourns, DEC, Delco, Diacon, Fairchild, GTE,  Hitachi,
IBM, HP, IDC, Intel, ITT (US & England), Jade, Kyocera, Lockheed, LSI,
Motorola, NCR, NEC, NSC, Signetics, Sperry, TI, T&B, United Technologies.
There certainly was no lack of cooperation and most companies had at least
one active participant. 
We published preliminary results from Phase I and other developments that
occurred at different companies concurrently with the CLTF. You might my
references interesting, if you can find them that is because some were only
recorded on video tapes made during IEPS conferences:
1.	Engelmaier, W., "Test Method Considerations for SMT Solder Joint
Reliability," Proc. 4th Annual Int. Electronics Packaging Conf. (IEPS),
Baltimore, MD, October 1984, pp. 360-369; also in Brazing & Soldering, No. 9,
Autumn 1985, p. 40.
2.	Engelmaier, W., "Solder Joint Reliability and Testing Considerations for
Leaded Chip Carriers," Proc. Nepcon/West, Anaheim, CA, February, 1985, pp.
884-885; Presentation available on IEPS Videotape VR 001, Lead Compliance and
Solder Integrity of Surface Mount Leaded Packages.
3.	Engelmaier, W., "Interim Report on the Test Results of IEEE Compliant Lead
Test Program," IEPS Videotape VR 004, IEEE Compliant Lead Task Force Results
of Phase A, 1985.
4.	Engelmaier, W., "IEEE Compliant Lead Task Force--Phase I: Correlation and
Analysis of Solder Joint Fatigue Results Obtained at Different Cyclic
Frequencies and Temperatures," Proc. 5th Annual Int. Electronics Packaging
Conf. (IEPS), Orlando, FL, October 1985, p. 279; Presentation available on
IEPS Videotape VR 002, Second Interim Report of the IEEE Compliant Lead Task
Force.
5.	Kotlowitz, R. W., and W. Engelmaier, "Impact of Lead Compliance on the
Solder Attachment Reliability of Leaded Surface Mount Devices," Proc. 6th
Annual Int. Electronics Packaging Conf. (IEPS), San Diego, CA, November 1986,
p. 841.
6.	Engelmaier, W., "Surface Mount Attachment Reliability of Clip-Leaded
Ceramic Chip Carriers on FR-4 Circuit Boards," Proc. 7th Annual Int.
Electronics Packaging Conf. (IEPS), Boston, MA, November 1987, p. 104; also
in IEPS J., Vol. 9, No. 4, January 1988, p. 3; also in Proc. Nepcon/East,
Boston, MA, June 1988, p. 121.
7.	Engelmaier, W., "The Importance of Continuous Monitoring for SMT Solder
Joint Failures During Accelerated Fatigue Testing," IPC Spring Meet.,
Hollywood, FL, April 1988.
8.	Engelmaier, W., "IEEE Compliant Lead Task Force--A Progress Report," Proc.
8th Annual Int. Electronics Packaging Conf. (IEPS), Dallas, TX, November
1988, p. 891.
9. Engelmaier, W., "Surface Mount Solder Joint Reliability: Issues, Design,
Testing, Prediction" Workshop Notes, Engelmaier Associates, Inc., Mendham,
NJ, 1996.

You will not, however, find the results from Phase III which included the
fatigue test data for the components from all the participants that had
submitted components.  As is logical, the results were rank-ordered; that is
when the lawyers of the two (2) companies on the bottom of the rank-order
list got a hold of the data. Those two companies threatened to sue the IEEE
and all other participants if the data were made public. Well guess
what--they never saw the light of day. We could not even publish them without
the company names, because the package designs had been thoroughly evaluated
and the results together with all the design details published. The
references listed above certainly contain the pertinent findings from the
CLTF and the insights gained from this round robin--therefore, what is
generally applicable has not been lost.

Werner Engelmaier
Engelmaier Associates, Inc.
Electronic Packaging, Interconnection and Reliability Consulting
23 Gunther Street
Mendham, NJ  07945  USA
Phone & Fax: 201-543-2747
E-mail: [log in to unmask]  

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