Hi Christina,
You do not describe what your problem is.
Solder becomes 'brittle' only when it is contaminated with too high a level
of Au or Ag. At smaller quantities, these metals serve to strengthen tin/lead
solder, but in quantity, the brittle and weak AuSn and AgSn intermetallic
compounds dominate physical behavior. Solder also will behave in a
'crystalline' manner at cold temperatures. When subject to creep-fatigue,
solder will develop microcracks along grain boundaries relatively early in
life; these microcracks may give the appearance of 'brittleness' upon
mechanical loading to failure.
I do not know what you mean by 'heat cycle'.
Boards should not be exceeding their Tg during any testing. When you say
'stress testing', what is the purpose of this testing?

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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