Hi Lee,
"However a fast cool down will result in the solder joint having a smaller 
grain
size. This should improve the solder joint’s fatigue resistance. I've
heard of stories where folks would "quench" with cold air the hardware
right after soldering but I never personally seen it in the shops I
supported or tried it."
That is a really bad idea. In accelerated thermal cycling, and ONLY in ACT, 
will fine-grained solder structure result in an increase in creep-fatigue life 
by roughly a factor of 2. The grain structure of solder will coarsen with 
temperature and time following an Arrhenius relationship with an activation energy 
of abour 0.52 eV, and after a year in the field--or on the shelf, you will be 
unable to tell whether the initial grain structure was fine or coarse. Thus, 
industry documents like IPC-9701 and IPC-SM-785 recommend accelerated aging of 
test assemblies prior to ACT to start with a solder joint grain structure 
equivalent to about a one-year-old solder joint. This is done to make the test 
results more representative of product reliability.

Regards,
Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL 32174 USA
Phone: 386-437-8747, Fax: 386-437-8737, Cell: 386-316-5904
E-mail: [log in to unmask], Website: www.engelmaier.com


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