There exists a phosphorous problem. Beyond that, it is inadvisable to
solder to any nickel surface - that is: No solder termination area
should be bare nickel. It should be coated or plated over with a metal,
or other surface finish, not allowing its normally very rapid oxidation.

More often now, people are talking about the deleterious affects
phosphorous, and some other components in the electroless coating
process, have on solderability, solder joint acceptance, and long term
reliability. There have been many discussions on this forum and in
others as the SMTNet.

Under electroless gold, phosphorous goes to the solder termination area
surface and forms intermetallics in amounts causing the problems
mentioned. This is according to some SMD suppliers and others
investigating this phenomonon.

Earl Moon

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