Ex parte Abbott

Board of Patent Appeals and Interferences

Sep 28, 2000

08190729 (B.P.A.I. Sep. 28, 2000)

The opinion in support of the decision being entered today was not written for
publication and is not binding precedent of the Board.
Paper No. 44
UNITED STATES PATENT AND TRADEMARK OFFICE
____________
BEFORE THE BOARD OF PATENT APPEALS
AND INTERFERENCES
____________
Ex parte DONALD C. ABBOTT
____________
Appeal No. 1997-2834
Application No. 08/190,729
____________
ON BRIEF
____________
Before KIMLIN, GARRIS, and DELMENDO, Administrative Patent
Judges.
DELMENDO, Administrative Patent Judge.
DECISION ON APPEAL
This is a decision on an appeal under 35 U.S.C. § 134
from the examiner’s final rejection of claims 51 through 59,
72 through 74, and 81 through 86 and refusal to allow claims
60 through 71, 75 through 80, and 87 through 94. These are
the only claims remaining in the application.
Appeal No. 1997-2834
Application No. 08/190,729
2
Claim 51 is illustrative of the claims on appeal and is
reproduced below:
51. A corrosion resistant lead frame for
electrically contacting an integrated circuit,
comprising:
a base metal layer having a first standard
reduction potential;
an isolation layer disposed upon said base metal
layer and having a second standard reduction
potential, said second standard reduction potential
being greater than said first standard reduction
potential;
an intermediate layer disposed upon said
isolation layer and having a third standard
reduction potential, said third standard reduction
potential being less than both said first and second
standard reduction potentials; and
a top metal layer disposed upon said
intermediate layer and having a standard reduction
potential substantially equal to said second
standard reduction potential.
The subject matter on appeal relates to a corrosion
resistant lead frame for an integrated circuit and a method
for fabricating such a lead frame (appeal brief, page 2). The
lead frame comprises the recited base metal, isolation,
intermediate, and top metal layers. According to the
appellant, the isolation layer is used to decouple the top
metal layer and the base metal layer by providing a standard
reduction potential that is substantially equal to the
standard reduction potential of the top metal layer (appeal
Appeal No. 1997-2834
Application No. 08/190,729
In the advisory action of February 6, 1995, the1
examiner withdrew the rejection of claims 60 through 71, 75
through 80, and 87 through 94 under the first paragraph of 35
U.S.C. § 112 as set forth on pages 2 and 3 of the final Office
action.
3
brief, page 3). This prevents the base metal ions, which are
typically soluble in the intermediate layer, from migrating
under the potential difference between the base metal layer
and the top metal layer to the surface of the top metal layer
to form corrosion products (id.).
As evidence of unpatentability, the examiner relies upon
the following prior art references:
Levine (Levine ‘958) 4,601,958 Jul. 22,
1986
Levine (Levine ‘796) 4,666,796 May 19,
1987
Levine (Levine ‘067) 4,835,067 May 30,
1989
In addition, the examiner relies upon the appellant’s
admission of the prior art, as described on pages 1 and 2 of
the present specification.
The sole ground of rejection presented for our review in
this appeal is as follows:1
Claims 51 through 94 stand rejected under 35 U.S.C. § 103
as unpatentable over the appellant’s admitted prior art in
Appeal No. 1997-2834
Application No. 08/190,729
4
view of Levine ‘958, Levine ‘796, or Levine ‘067 (examiner’s
answer, pages 4 and 5).
We have carefully reviewed the entire record, including
all of the arguments and evidence advanced by both the
examiner and the appellant in support of their respective
positions. This review leads us to conclude that the
examiner’s rejection is not well founded. Accordingly, we
reverse. The reasons for our determination follow.
The appellant explains the problem of a prior art lead
frame as follows:
. . . Typically, the base metal of the lead
frame is copper because of its high thermal
conductivity. . . In some instances, a nickel layer
[i.e., intermediate layer] on the order of 100
microinches is formed over the base metal to prevent
temperature driven diffusion of the copper to the
surface of the lead frame. Corrosion products
formed by copper diffusion, such as copper sulfides
and oxides, will degrade the solderability of the
lead frame and will reduce the shelf life of the
final product.
The nickel layer, however, contains pores
through which the corrosion products may migrate. A
nickel layer thickness of at least 400 microinches
would be needed to reasonably assure that no
continuous paths through the nickel layer would be
available for copper migration. Unfortunately, a
thickness of this magnitude will crack when the
leads are eventually bent to form the dual inline
package (DIP) or surface mount integrated circuit
(SMIC).
Appeal No. 1997-2834
Application No. 08/190,729
5
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.
Appeal No. 1997-2834
Application No. 08/190,729
6
As pointed out by the appellant, the problems to be
solved and/or the solutions to the problems in the Levine
patents are different from that of the present invention. We
do not find any teaching in the relied upon prior art to show
that a corrosion problem even existed in prior art lead
frames.
Specifically, Levine ‘067 is concerned with solving the
problem of corrosion in a sealing lid for semiconductor
packages in which the sealing lid comprises a metal substrate
(e.g., an iron alloy), a first layer of nickel, a first layer
of gold, a second layer of nickel, and a second layer of gold
(column 1, line 58 to column 2, line 6). Levine ‘067 solves
the problem of corrosion by forming a base layer of a metal
(e.g., gold) having an electromotive potential higher than the
metal substrate, an intermediate layer of a metal (e.g.,
nickel) having an electromotive potential substantially lower
than the electromotive potential of the base layer metal, and
a cover layer having a metal with an electromotive potential
which is high with respect to the base layer (column 2, lines
15-31). Although Levine ‘067 teaches that the intermediate
layer can have an electromotive potential “somewhat similar to
that of” the metal substrate (column 3, lines 41-46), there is
no teaching or suggestion in Levine ‘067 of an intermediate
Appeal No. 1997-2834
Application No. 08/190,729
7
layer having a standard reduction potential less than both the
isolation layer and the base metal layer as defined in the
appealed claims. Since Levine ‘067 is concerned with a
different problem relative to the claimed invention and thus a
different solution, we agree with the appellant that the
combined teachings of the admitted prior art and Levine ‘067
cannot render the subject matter of the appealed claims to be
unpatentable within the meaning of
35 U.S.C. § 103. In re Sponnoble, 405 F.2d 578, 585, 160 USPQ
237, 243 (CCPA 1969) (“[A] patentable invention may lie in the
discovery of the source of a problem even though the remedy
may be obvious once the source of the problem is identified.
This is part of the ‘subject matter as a whole’ which should
always be considered in determining the obviousness of an
invention under 35 U.S.C. 103.”).
Regarding Levine ‘796 and Levine ‘958, these prior art
references are concerned with solving the problem of corrosion
in sealing covers (or lids) comprising a base material (e.g.,
an iron alloy), a layer of nickel, and a layer of gold (column
1, line 15 to column 2, line 9 of Levine ‘796 and column 1,
line 9 to column 2, line 29 of Levine ‘958). However, the
solution proposed in these references is to use additional
nickel and gold layers 18 and 20 (figures 2 and 3, column 2,
Appeal No. 1997-2834
Application No. 08/190,729
8
lines 12-23, and column 4, line 65 to column 5, line 8 of
Levine ‘796 and figures 2 and 3, column 2, lines 33-43, and
column 5, lines 22-33 of Levine ‘958). Therefore, we cannot
agree with the examiner that the combined teachings of the
admitted prior art and Levine ‘796 or Levine ‘958 would have
led one of ordinary skill in the art to arrive at the subject
matter of the appealed claims, absent the benefit of the
appellant’s own disclosure.
The decision of the examiner is reversed.
REVERSED
EDWARD C. KIMLIN )
Administrative Patent Judge )
)
)
)
) BOARD OF PATENT
BRADLEY R. GARRIS ) APPEALS
Administrative Patent Judge ) AND
) INTERFERENCES
)
)
)
ROMULO H. DELMENDO )
Administrative Patent Judge )
Appeal No. 1997-2834
Application No. 08/190,729
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MARK E. COURTNEY
TEXAS INSTRUMENTS INC.
PATENT DEPARTMENT, M/S 219
P.O. BOX 655474
DALLAS, TX 75262
RHD/dal