Speaking of that, Werner, do you remember me? I was the program engineer at Honeywell for the A-12 Flight control system in St. Louis Park, MN. You came in in 1986 to help me find out why we had excellent wetting characteristics of IC leads on a Cu-In-Cu assembly, but the solder joints were fracturing. The problem was that we were soldering to gold over nickel, and the nickel was heavily oxidized under the gold. This was a classic case of solder appearing to wet over the pad properly, but a good IMF never really formed, thus causing the "well-wetted" solder joints to fracture in the saddle during thermal cycling.
Hi Richard,
Good to hear from you.
Sure do--and have had a problem with the unfortunate choice of the word "wetting" ever since. For solder joints, 'wetting' does not mean 'wetting' in the hand-washing sense, but includes the dissolution of the base metal into the Sn of the solder, the formation of intermetallic layer(s), and the formation of a sound metallurgical bond. The choice of the word "wetting" for this process has led to a lot of problems over the years.
Werner Engelmaier

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