Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
2003-05-07
2004-08-10
Chervinsky, Boris (Department: 2835)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C361S717000, C361S718000, C361S719000, C257S706000, C257S712000
Reexamination Certificate
active
06775140
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to methods and apparatus for the fabrication of integrated circuit devices, and more particularly to improved flip chip heat spreader structures and packages having better performance and lower fabrication costs.
BACKGROUND ART
In the electronics industry, a continuing objective is to further and further reduce the size of electronic devices with a simultaneous increase in performance and speed. Cellular telephones, personal data devices, notebook computers, camcorders, and digital cameras are but a few of the consumer products that require and benefit from this ongoing miniaturization of their sophisticated electronics.
Integrated circuit packages for such complex electronic systems typically have a large number of interconnected integrated circuit chips. The integrated circuit chips are usually made from a semiconductor material such as silicon or gallium arsenide. Photolithographic techniques are used to form the various semiconductor devices in multiple layers on the integrated circuit chips. After manufacture, the integrated circuit chips are typically incorporated into packages that may contain one or several such chips. These chip packages or modules are then typically mounted on printed circuit wiring boards.
In conventional multi-chip modules, a number of semiconductor devices are packed in close proximity within a single package. This eliminates individual packages for each of the semiconductor devices, improves electrical performance, and reduces the overall board space occupied by the devices.
Due to the increase in the packing density, however, the power density (heat output) of the multi-chip module is typically higher than when separately packaged. This requires more elaborate thermal design and thermal management structures to keep the device temperatures within acceptable ranges.
In conventional multi-chip modules, the devices are connected to a substrate, and electrical connections among the devices are accomplished within the substrate. One of the technologies used to connect the devices to the substrate is called “flip chip” or face down bonding, and employs the well-known controlled collapse chip connection (or “C4”) bonding technology. With this technology, solder bumps are first formed at the chip terminals. Subsequently, the semiconductor devices are flipped over onto the substrate and the solder bumps are melted to make connection to corresponding terminal pads on the substrate.
Heat management through this structure can be critical. The internal thermal resistance and the thermal performance of the flip chip interconnect technology are determined by a series of heat flow paths. The heat flows first from the semiconductor devices to the body of the semiconductor module or package into which it has been incorporated. The heat then flows to the package surface, and eventually to a heat sink attached to the package surface.
Typically, the top of the package body includes such a heat sink for large-scale heat dissipation. Underneath the surface of the package body is a cavity in which the semiconductor substrate and its associated devices are installed. To enhance the cooling performance, a heat spreader plate is adapted to engage the non-active side of the semiconductor chip or die. A layer of thermal grease or the like is spread between the chip and the heat spreader plate. The heat spreader plate then acts as a heat conductor to improve heat transfer.
Unfortunately, there are drawbacks associated with the use of known heat spreaders for flip chip packages. Among these drawbacks are heat spreader manufacturing costs, complicated assembly processes, and concerns about package reliability. These drawbacks can be understood, for example, by considering common prior art two-piece and single-piece structures.
One such heat spreader structure is a two-piece configuration having a stiffener with a hollow core that surrounds the flip chip, and a metal lid cover that is on top of the stiffener and the flip chip. Normally, the stiffener is thicker than the metal lid. Two different metal forming processes are therefore required to fabricate the two different pieces of the heat spreader from two different raw metal sheets of two different thicknesses.
In another prior art heat spreader structure, a hollow cavity and a lid are formed as a single piece. To form the cavity therein for the chip, a thick metal piece needs to be used, and a substantial amount of material needs to be removed to form the chip cavity. Thus, costly metal forming processes, like milling or casting, have to be employed to fabricate this type of heat spreader.
Additionally, either of the above prior art heat spreader types makes the flip chip packages undesirably bulky.
Consequently, there still remains a need for improved, more economical, more efficient, and more readily manufactured and assembled heat spreaders, heat spreader packages, and fabrication methods for use with flip chip semiconductor devices.
Solutions to these problems have been long sought but prior developments have not taught or suggested any solutions and, thus, solutions to these problems have long eluded those skilled in the art.
DISCLOSURE OF THE INVENTION
The present invention provides a method for fabricating a semiconductor device heat spreader from a unitary piece of metallic material. The metallic material is stamped to form a unitary heat spreader having an upper heat dissipation region, a lower substrate contact region, and supports connecting the upper heat dissipation region and the lower substrate contact region. A recess is formed within the supports and the upper and lower regions for receiving a semiconductor device. This provides improved heat spreader structures, methods, and packages for flip chip semiconductor devices using conventional manufacturing methods.
Certain embodiments of the invention have other advantages in addition to or in place of those mentioned above. The advantages will become apparent to those skilled in the art from a reading of the following detailed description when taken with reference to the accompanying drawings.
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Alvarez Sheila Marie L.
Ararao Virgil Cotoco
Chow Seng Guan
Emigh Roger
Shim Il Kwon
Chervinsky Boris
Ishimaru Mikio
ST Assembly Test Services Ltd.
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