Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package – With contact or lead
Reexamination Certificate
2002-10-30
2004-09-07
Cao, Phat X. (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
With contact or lead
C257S693000
Reexamination Certificate
active
06787894
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to integrated circuit packaging. More particularly, the invention relates to interconnected and leadless packaging of semiconductor devices.
BACKGROUND OF THE INVENTION
Integrated circuits may be contained in a variety of different packages before they are integrated into portions of larger electronic systems. The packages are generally comprised of one or more semiconductor chips encapsulated in a packaging material. In the case of packages containing several chips, the chips are interconnected to permit the chips to cooperatively perform a variety of tasks. In addition to the interconnections between the chips within the package, other connections generally extend from the package to permit the integrated circuit to interact with other portions of a larger electronic system. The individual chips may be arranged in the package in a planar configuration with electrical interconnections extending between the chips, but increasingly, the individual chips are arranged in a vertical stack, with the interconnections extending between the chips comprising the stack. A stacked wafer-level package has numerous advantages over the planar arrangement, including reduced interconnection lengths, faster processing times, and substantial reductions in the size and weight of the package.
FIG. 1
is a partial cross sectional view showing a vertically stacked semiconductor package
10
according to the prior art. The package
10
generally includes a substrate
16
that supports a first semiconductor chip
14
, which is retained on the substrate
16
by an adhesive layer
18
. The adhesive layer
18
is generally comprised of an adhesive compound having a high dielectric strength to prevent electrical communication between the chip
14
and the substrate
16
. The chip
14
also generally includes one or more bond pads
15
that are electrically coupled to the circuits formed on the chip
14
, which form at least a portion of the signal input and/or signal output locations for the chip
14
. A second chip
12
is positioned on the chip
14
, and is similarly retained on the chip
14
by an adhesive layer
19
. The second chip
12
also includes one or more bond pads
11
that are coupled to the circuits formed on the chip
12
, and similarly form at least a portion of the signal input and/or signal output locations for the chip
12
. Electrical communication between the chip
12
and the chip
14
is obtained through one or more electrically conductive bonding wires
13
that couple the bond pad
11
on the chip
12
to the bond pad
15
on the chip
14
. The bonding wires
13
are generally comprised of gold or aluminum, and may be attached to the bond pads
11
and
15
by spot welding, soldering, or by various conductive adhesive compounds. The bonding wires
13
then generally proceed away from the package
10
to provide an electrical connection to other portions of a larger electronic system (not shown).
The prior art semiconductor package
10
shown in
FIG. 1
has numerous drawbacks, however. For example, the bonding wire
13
generally has a relatively long physical length in order to establish the required electrical interconnections between the bond pads
11
and
15
. The long physical length of bonding wire
13
may therefore lead to increased signal propagation delays between the chips
12
and
14
. Moreover, as the length of the bonding wire
13
increases, undesirable effects stemming from parasitic capacitance and/or inductance introduced by the bonding wire
13
also increase. Other shortcomings associated with the package
10
may include the reflection of at least part of the signal transmitted along the bonding wire
13
resulting from impedance discontinuities along the bonding wire
13
, or at the connection interface between the bonding wire
13
and the bond pads
11
and
15
. Still further, as the length of the bonding wire
13
increases, the bonding wire
13
becomes increasingly susceptible to electromagnetic interference since the bonding wire
13
may act as an antenna. Still other drawbacks are present in prior art package
10
. For instance, the size of the bond pads
11
and
15
formed on the chips
12
and
14
must generally be relatively large to accommodate the connections formed with the bonding wire
13
, which generally limits either the number of input and output locations, or the number of circuits that may be formed on the chips
12
and
14
. Moreover, since the bond pads
11
and
15
are generally comprised of gold, the relatively large bond pad areas require additional amounts of this material, which increases the cost of each unit.
Other prior art packaging methods mitigate some of the drawbacks associated with the use of bonding wire interconnections, as described above, but introduce still other drawbacks. For example, tape automated bonding (TAB) methods may be used to establish the interconnections between vertically stacked semiconductor chips. In TAB, metallic interconnection traces are formed on a multi-layer polymer tape (not shown). The polymer tape is positioned adjacent to the chips
12
and
14
with traces and bonding locations pre-formed on the tape that correspond to the bond pads
11
on the chip
12
, and the bond pads
15
on the chip
14
. The bonding locations on the tape are then attached to the bond pads
11
and
15
on the chips
12
and
14
using conventional joining techniques such as reflow soldering or conductive adhesives. Although TAB allows the bond pads
11
and
15
on the chips
12
and
14
to be spaced at closer intervals than is generally achievable using the foregoing bonding wire method, each chip must generally have its own tape that is individually patterned to conform to the bonding pad arrangements on the chips that are to be interconnected. Consequently, the time and cost associated with the design and fabrication of bonding tapes that are individually configured for each bonding requirement renders TAB methods suitable only to applications where large production quantities of semiconductor packages are anticipated.
The “flip-chip” method represents still another prior art semiconductor packaging method, which permits the bond pads on adjacent chips to be connected without the use of a discrete interconnecting elements, as employed in the foregoing bonding wire method, or in TAB. In the “flip chip” method, the contact pads of a chip are generally wetted with a reflowable material, such as a solder alloy. The chip is then brought into facial contact with an adjacent chip or substrate that has a corresponding set of bond pads. Reflowing the solder alloy in a furnace then electrically and mechanically joins the chips. Although the foregoing method eliminates many of the drawbacks associated with the wire bonding and TAB interconnection methods, other drawbacks are introduced. For example, the chips thus joined may exhibit significantly different rates of thermal expansion, which may lead to bonding failure between the chips. This shortcoming may be further exacerbated by the degradation of heat conduction through the chip stack that is due to an increase in the thermal resistance between the chips. Additionally, since the connections are formed between the chips, a visual inspection of the bond integrity is generally not possible.
Accordingly, there is a pronounced need for an interconnection apparatus and method for semiconductor packages comprised of vertical chip stacks that permits relatively short interconnecting lengths to extend between chip bonding pads that are patterned on the chips at relatively high densities, while avoiding the thermal incompatibility difficulties present in prior art methods, which is easily adaptable to small as well as larger production runs of semiconductor packages.
SUMMARY OF THE INVENTION
The present invention is directed to a leadless and interconnected semiconductor package. The package includes a first semiconductor chip with a second semiconductor chip positioned on the first chip to form a vertically stacked pa
Jeung Boon Suan
Poo Chia Yong
Waf Low Siu
Cao Phat X.
Micro)n Technology, Inc.
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