Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package – Insulating material
Reexamination Certificate
2003-04-22
2004-06-01
Clark, Jasmine (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
Insulating material
C257S778000, C257S723000, C257S724000, C257S786000, C257S693000, C257S678000
Reexamination Certificate
active
06744131
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to packages for integrated circuits (ICs). More particularly, the invention relates to an IC package that includes a lid specialized for including external capacitors within the package, while providing the structural rigidity that is needed when flexible substrates are used.
BACKGROUND OF THE INVENTION
IC packages are available in many different forms and configurations. One popular configuration is the “flip chip” configuration, in which the IC die is mounted face-down in the package (i.e., with the active surface of the die towards the package pins). Thus, the pads on the active surface of the IC (e.g., power pads, ground pads, and/or input/output or I/O pads) can be brought into contact (e.g., through “solder bumps”) with lands disposed across the surface of the substrate. The lands are in turn coupled through vias (i.e., holes through the substrate filled with a conductive material) to package pins (e.g., balls or pins) on the bottom surface of the package.
Some IC packages include provision for capacitors mounted inside the package. Providing capacitors within the package has some strong advantages over the alternative approaches of including capacitors on the surface of the die, or mounting capacitors outside the package. Including capacitors on the surface of the die increases the surface area, and thus the cost, of the die. Further, changing the size of a capacitor included on the die requires making new masks and manufacturing new die, while capacitors implemented as separate units from the die are easily modified. On the other hand, mounting capacitors outside the package introduces noise into the circuits in the die and consumes valuable area on the PC board.
ICs are becoming more sensitive to noise as the typical operating voltages drop to levels closer to the threshold voltages of the IC transistors on the die. Therefore, it is desirable to reduce noise as much as possible. Further, the number of pads per area of die is also increasing, so today's ICs typically have a higher switching current than in the past. Hence, the capability of mounting capacitors within an IC package is becoming more and more desirable.
FIG. 1
shows a well known type of flip chip package that includes capacitors within the package. On a laminate substrate
101
are mounted the die
102
and the desired number of capacitors
104
,
105
. The exemplary package in
FIG. 1
includes two different types of capacitors (
104
and
105
), but any number of different types of capacitors can be included. The terminals of the capacitors are coupled to connection points (e.g., ground pads, power pads, and/or I/O pads, not shown) of the die
102
through metal traces (not shown) layered in the laminate substrate
101
. The terminals of the capacitors can also be coupled through the metal traces to the package pins on the bottom surface of the package. Over the surface of this structure is laid a metal lid
103
, which is typically in direct contact with the backside of the die
102
(the upper surface as shown in FIG.
1
). If any of capacitors
104
,
105
protrudes above the backside of the die
102
, a rectangular portion of the inside surface of the lid
103
is manufactured to protrude from the inner surface of the lid, to maintain contact with the backside of the die.
One type of IC package that was once commonly used is the ceramic dual in-line (CERDIP) package, in which the IC die is mounted with the active surface away from the package pins. In CERDIP packages, the ceramic substrate and ceramic lid are made relatively thick to provide structural strength. A flip chip package is generally thinner than a ceramic package, partially because a laminate substrate is used rather than a ceramic substrate, and partially because a metal lid is used rather than a ceramic lid. The metal lid also has another advantage when used with a laminate substrate; it provides the structural rigidity that the flexible laminate substrate lacks. Without this structural rigidity, applying mechanical or thermal stress to the package could cause damage to the connections between the substrate and the board to which it is mounted, or between the pads of the die and the lands in the substrate. Also, the metal lid prevents the laminate substrate from warping under heat, e.g., when the package is being mounted to the board. This warping could cause disconnects or poor connections between the substrate and the board.
FIG. 2
illustrates a laminate substrate that can be used, for example, with the IC package structure shown in FIG.
1
. Laminate substrate
201
includes an inner region
206
(indicated by a dotted line) and an outer region
207
. The inner region
206
includes lands
208
, and the outer region
207
includes lands
209
. Inner lands
208
come into contact with pads on the IC die (e.g., die
102
in FIG.
1
), while outer lands
209
are coupled to terminals of the capacitors (e.g., capacitors
104
and
105
of FIG.
1
). Traces
210
interconnect the inner lands with the outer lands. The traces are typically copper traces sandwiched within the laminate substrate. Only two traces are shown in
FIG. 2
, for clarity, but many more traces are typically present. When the die (not shown) is in place, the traces electrically couple the capacitors (not shown) to one or more desired pads of the die.
There are drawbacks to the IC package structure shown in FIG.
1
. For example, it is not possible to visually inspect capacitors after the lid has been applied. In fact, it can be difficult or impossible even to test the capacitors, as they are not readily accessible to test probes after the lid has been applied. Further, the capacitors cannot be reworked without removing the lid, which process can damage or detach the die and otherwise undamaged capacitors.
FIG. 3
shows another known IC package that addresses these drawbacks by eliminating the lid altogether.
FIG. 3
illustrates substrate
301
, die
302
, and capacitors
304
,
305
. However, no lid is shown or provided. When the package of
FIG. 3
is used, the capacitors can be mounted in the package, yet remain available for visual inspection, testing, and replacement, if necessary. However, clearly the die is left exposed. A lid provides mechanical protection for the die that is often desirable and even necessary in many applications. The lid also provides mechanical protection for the capacitors, e.g., during the testing sequence of the packaged device. Further, as previously described, the lid also provides structural rigidity (i.e., acts as a “stiffener”) for the package. Removing the lid can make the package significantly more susceptible to warping, which can affect the second level board assembly and reliability.
Therefore, it is desirable to provide an IC package that can include capacitors within the package, make the capacitors accessible after the lid is applied, and still supply all the necessary structural rigidity required by the use of a flexible substrate.
SUMMARY OF THE INVENTION
The invention provides an IC package that provides structural rigidity to a flexible substrate, but still allows access to mounted capacitors after package assembly. In a flip chip package, the IC die is mounted face down on a flexible laminate substrate. A metal lid is mounted above and in contact with the die. The metal lid includes openings over portions of an outer region of the substrate to accommodate the capacitors. However, portions of the metal lid extend to the corners of the substrate to provide structural rigidity to the flexible substrate. Some embodiments are directed to packages configured as described above, but in which an IC die has yet to be mounted.
According to a first embodiment, a packaged IC includes a flexible substrate, an IC die, and a structurally rigid lid. The flexible substrate includes an inner region, an outer region, inner lands disposed in the inner region, outer lands disposed in the outer region, and a plurality of traces each coupled between an inner land and an outer land. The IC d
Do Hoa Lap
Hoang Lan Hoang
Zhang Leilei
Cartier Lois D.
Clark Jasmine
Xilinx , Inc.
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