Appeal No. 1997-2834
Application No. 08/190,729
A layer of palladium (Pd) [i.e., top metal
layer] may be formed over the nickel layer. . . The
palladium layer, however, will produce a galvanic
potential between the palladium layer and the copper
base, drawing copper ions to the surface. This
galvanic couple accelerates pore corrosion in the
palladium plated lead frame, which results in oxides
and sulfides and other reaction products of copper
appearing on the lead frame surface. The oxides and
sulfides and other corrosion products discolor the
surface of the lead frame and degrade its
solderability. [Specification, pp. 2-3.]
The appellant has solved the problem described above with an
isolation layer (e.g., a palladium/nickel alloy layer) between
the base metal layer and the intermediate layer
(specification, page 4).
The examiner admits that the appellant’s admitted prior
art does not teach how to solve the problem described above
(examiner’s answer, page 4). However, the examiner takes the
position that “[i]t would be obvious to one of ordinary skill
in the art that the known prior art concept of Levine would
solve the problem of ion migration and corrosion in the lead
frame construction disclosed as prior art by appellant because
the known mechanism causing degradation and the mechanism to
solve it are the same as Levine’s” (examiner’s answer, page
5). We disagree.
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