Appeal No. 2004-0760
Application No. 10/010,392
Attention is directed to the main and reply briefs (Paper
Nos. 12 and 14) and the answer (Paper No. 13) for the respective
positions of the appellants and the examiner regarding the merits
of this rejection.
DISCUSSION
Maheshwari discloses a method of attaching silicon dies
(i.e., flip chips) onto flexible substrates in a manner which
minimizes warping and cracking of the dies. In a typical flip
chip attaching process, the die is fluxed and placed on the
substrate with bond pads on the die aligned with bond pads on the
substrate, solder is reflowed between the bond pads, the die is
underfilled with a thermoset material, and the underfill material
is fully cured (see column 1, lines 16 through 21). The warpage
problem stems from the so-called “bi-metallic strip” effect
caused by relatively large differences in the respective
coefficients of thermal expansion (CTE) of the die and the
thermoset underfill material. The following passage fairly
summarizes Maheshwari’s solution to this problem:
The “bi-metallic strip” effect . . . can be
compensated for by applying an opposing layer of
thermoset component adhered to a metal sheet or other
material with applicable CTE on the top of the die, as
illustrated in FIG. 2. This offsetting layer of
material causes the die to warp on the other side and
as a result the two self-opposing warpage effects will
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