Appeal No. 1997-2834
Application No. 08/190,729
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).
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