W. Engelmaier:

Is there any way to visually inspect for Au or Ag intermetallics in solder
joints?  i.e. can you see them in a cross section?  Or is there a better
method of analysis?

 Thanks, Sheila Smith, Tracor Aerospace


At 08:05 AM 10/16/97 -0400, you wrote:
>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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