Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package – Insulating material
Reexamination Certificate
1998-04-01
2001-10-02
Chaudhuri, Olik (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
Insulating material
C257S712000, C257S717000, C257S720000, C361S704000, C361S709000, C361S711000, C174S252000
Reexamination Certificate
active
06297550
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor package and method of packaging a semiconductor die, e.g., an integrated circuit, and more particularly to a semiconductor package wherein an anodized aluminum heatspreader is used to serve the dual purpose of heat dissipation and a ground or voltage plane.
In the last few decades, the electronics industry has literally transformed the world. Electronic products are used by, or affect the daily lives of, a large segment of the world's population. For example, telephones, television, radios, Personal Computers (PCS), laptop PCS, palmtop PCS, PCS with built-in portable phones, cellular phones, wireless phones, pagers, modems, and video camcorders, are just a few of the electronic products that have been developed in recent years and which have been made smaller and more compact, while providing more and/or enhanced functions than ever before. The integrated circuit (IC) chip, and the more efficient packaging of the IC chip, have played a key role in the success of these products.
The IC chip, sometimes referred to as the IC “die”, contains embedded electronic circuitry that performs, at least in part, the electrical/electronic functions for the particular electronic device wherein the IC chip is used. The IC chip, however, is not an isolated island. It must communicate with other chips in a circuit through an Input/Output (I/O) system of electrical interconnections, or “interconnects”. Moreover, the IC chip and its embedded circuitry are delicate, and must therefore be protected in a package that can both carry and protect it. As a result, the major functions of the IC package are: (1) to provide a path for the electrical current that powers the circuits on the chip; (2) to distribute the signals on to and off of the chip; (3) to remove the heat generated by the circuit; and (4) to support and protect the chip from hostile environments.
Integrated circuits are typically housed within a package that is mounted to a printed circuit board (PCB) or printed wiring board (PWB). As part of an IC package wherein a high performance IC die is housed, a heatspreader may be used. A heatspreader typically comprises a planar thermally-conductive element, such as a sheet of metal, that is located so as to have good thermal contact with the IC die. Heat generated in the IC die by operation of the circuits embedded therein is thus conducted to the heatspreader, where it is dissipated, thereby helping maintain the junction temperatures of the semiconductor devices included within the circuits of the IC die at safe operating levels.
It is also possible to use a heatspreader as a power or ground plane. Should the heatspreader double as a power or ground plane, however, it must be bondable, i.e., it must be electrically connected to the power or ground bond pads on the chip (die). Such electrical connection could be done with wire bonds, or (in the case of Tape Automated Bonding (TAB)) with beam bonds.
Examples of semiconductor packages that incorporate heatspreaders include Plastic Ball Grid Array (PBGA) packages, Tape Ball Grid Array (TBGA) packages, Plastic Pin Grid Array (PPGA) packages, and Plastic Quad Flat Packs (PQFP). In such packages, when a heatspreader is used, it is typically made of copper, with nickel and gold plating. The plating is required to prevent the copper from discoloring. Also, if electrical connection is made to the heatspreader, i.e., if the heatspreader is also used as a voltage or ground plane, then the plating is required to provide a stable surface for bonding a wire or beam thereto.
Disadvantageously, using copper as a heatspreader adds significant weight to the semiconductor package. Moreover, plating of the copper heatspreader adds substantial expense and cost to the total semiconductor package. Additionally, when used as a power or ground plane, the entire gold- or nickel-plated heatspreader is conductive, and care must thus be exercised to prevent inadvertent electrical shorting to the heatspreader. As a practical matter, this typically limits the heatspreader's use to a ground plane (zero voltage) because a heatspreader that also represents a “live” power voltage (non-zero voltage) is not generally acceptable for most users.
It is thus apparent that improvements are needed in the types of heatspreaders used within a semiconductor package. In particular, it is apparent that improvements are needed to reduce the cost and expense of making a heatspreader, to reduce its weight, to facilitate making electrical connections therewith (i.e., bonding wires or beams thereto), and to more readily make the heatspreader usable as a voltage plane (not just a ground plane).
SUMMARY OF THE INVENTION
The present invention addresses the above and other needs by providing a semiconductor package, e.g., a PBGA, TBGA, PPGA, or PQFP package, wherein the heatspreader is fabricated from aluminum or aluminum alloys. For cosmetic and adhesion purposes, the aluminum heatspreader is anodized. Sections of the aluminum surface are ground off to expose non-anodized areas that serve as bond areas for making electrical connection. Gold wires, aluminum wires, gold plated beams, or other electrical conductors may then be bonded to the exposed bond areas (non-anodized areas), thereby effectively using the heatspreader as a power or ground plane within the semiconductor package in order to improve the electrical performance of the package.
In accordance with one aspect of the invention a semiconductor package is provided that includes: (a) a substrate; (b) a semiconductor die electrically connected to the substrate; and (c) a heatspreader thermally bonded to the semiconductor die, the heatspreader being made from anodized aluminum.
In accordance with another aspect of the invention, a bondable aluminum heatspreader is provided for use within a semiconductor package wherein a semiconductor die is housed. The semiconductor die is thermally bonded to and electrically connected to the heatspreader. The bondable aluminum heatspreader is made from a piece (e.g., a sheet) of aluminum or an aluminum alloy that has been anodized so as to form a protective, insulative, aluminum oxide coating thereon.
In accordance with yet another aspect of the invention, there is provided a method of making a semiconductor package having a bondable aluminum heatspreader therein. Such method includes the steps of: (a) forming a package substrate having electrical input/output (I/O) means therein; (b) forming a heatspreader from a piece of aluminum; (c) anodizing the aluminum heatspreader to form a coating of aluminum oxide thereon; (d) grinding away a small area of the aluminum oxide layer to expose the piece of aluminum thereunder, thereby creating a connection area on the exposed surface of the aluminum; (e) attaching the anodized aluminum heatspreader to the package substrate; (f) thermally bonding a non-active surface of a semiconductor die to the heatspreader, an active surface of the semiconductor die thereby facing away from the heatspreader, and wherein the active surface of the semiconductor die has a plurality of contact pads thereon through which electrical connection may be established with the semiconductor die; (g) electrically connecting at least one of the contact pads on the active surface of the semiconductor die to the connection area on the exposed surface of the aluminum heatspreader; and (h) electrically connecting others of the contact pads on the active surface of the semiconductor die to the I/O means included within the package substrate.
It is feature of the invention to reduce the cost and expense associated with making a heatspreader.
It is another feature of the invention to provide a heatspreader for use within a semiconductor package that is light weight and which can be colored to a desired color for cosmetic or other purposes, e.g., to improve its heat dissipation properties.
It is yet a further feature of the invention to provide an electrically-insulated heatspreader having bondable contact areas to whic
Alagaratnam Maniam
Chia Chok J.
Variot Patrick
Chambliss Alonzo
Chaudhuri Olik
LSI Logic Corporation
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