Hi Grant,
There is no such thing as 'curing' for solder joints.
The grain structure of solder is inherently unstable and will with time and
temperature, or time, temperature and cyclic loading, coarsen. For instance,
a fine-grained solder joint will be coarse grained after about one year of
just storage. T-cycle testing of fine-grained solder joints will yield
fatigue lives about a factor of 2 longer than coarse-grained solder joints;
that is why one had better artificially 'age' the solder joints to create
coarse-grained solder joints prior to accelerated reliability testing (see
IPC-SM-785).
But none of this can even remotely be thought of as curing.
Depending on how rapidly you cool from reflow, you may have residual stresses
frozen into your assembies; however, these residual stresses will be stress
relieved by the creep of the solder within 24 hours at RT. Maybe that is what
your 'test guy' are referring to.

Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL  32174  USA
Phone: 904-437-8747, Fax: 904-437-8737
E-mail: [log in to unmask], Website: www.engelmaier.com

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