Hi Jens,
While everything that has been said in the responses to your query, I don not
believe that your problem and its cause was addressed. When one solders to a
HASLed copper surface, one solders in effect to solder, since the wetting to
the Cu and the formation of the Cu/Sn intermetallic compound layers has
already been accomplished during the HASL process—and soldering to solder is
about the easiest. When soldering to Au-plated nickel, the Au facilitates the
liquid solder the cover the whole Ni area, than additional heat (plus time) is
needed to disolve some of the Ni into Sn to bring about the formation of Ni/Sn
IMCs and wetting to the Ni-base metal. Nickel is nowhere as easily disolved in
Sn as are Au, Ag, and Cu, and certainly not solder.
Therefore, assuming that the Au-overplated Ni-surface is solderable, it is
certainly possible that such a surface appears to have solderability problems
when previously HASLed surfaces soldered fine. The remedy is a combination of
better preheat, slower conveyor speed, and/or higher solder wave temperature.

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]


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