Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
1998-02-27
2001-01-16
Young, Lee (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C029S832000, C174S08800C, C174S09400S, C174S255000, C361S795000
Reexamination Certificate
active
06173489
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an integrated circuit package.
2. Description of Related Art
Integrated circuits are typically assembled into a package that is mounted to a printed circuit board. In some packages the integrated circuits are wire bonded to internal bond fingers of the package. The bond fingers are routed to external contacts that are soldered to the printed circuit board. The wire bonding process creates a process step that increases the cost of producing the package. Additionally, the bond wires may create an undesirable inductance within the package.
FIG. 1
shows an integrated circuit package commonly referred to as a “flip chip” package. Flip chip packages allow an integrated circuit
1
to be directly mounted to a substrate
2
without using bond wires. The flip chip substrate
2
is typically constructed as a printed circuit board which contains internal routing layers that couple a plurality of bond pads to external contacts of the substrate
2
. The integrated circuit
1
has a plurality of solder bumps
3
that are reflowed to mount the die
1
to the bond pads of the substrate
2
.
The integrated circuit
1
typically has a coefficient of thermal expansion that is different than the thermal coefficient of the substrate. As shown in
FIG. 2
, when the package is thermally cycled the integrated circuit die
1
expands at a different rate than the substrate
2
. The differential expansion creates mechanical strain and stresses on the solder bumps
3
. When thermally cycled the thermally induced stress may crack the solder bumps
3
and render the package inoperative. It has been found that the solder bumps of a flip chip package may fail at unacceptably high rates when the package is thermally cycled. It would be desirable to have a flip chip package that provides stress relief for the solder bumps to increase the life of the package.
SUMMARY OF THE INVENTION
The present invention is a flip chip integrated circuit package which provides stress relief for the solder bumps of the package. The package includes an integrated circuit that is mounted to a substrate. The integrated circuit is attached to a plurality of bond pads of the substrate by a number of corresponding solder bumps. The substrate has a first layer that is attached to a second layer. An area that is located between the layers and adjacent to the bond pads is left unattached so that a portion of the first layer can move relative to the remaining portion of the substrate. The unattached area allows the integrated circuit to “float” and expand at a different rate than the substrate when the package is thermally cycled.
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Mahajan Ravi
McMahon John F.
Blakely , Sokoloff, Taylor & Zafman LLP
Intel Corporation
Smith Sean
Young Lee
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