Semiconductor device manufacturing: process – Packaging or treatment of packaged semiconductor – Metallic housing or support
Reexamination Certificate
1999-10-29
2001-12-04
Picardat, Kevin M. (Department: 2822)
Semiconductor device manufacturing: process
Packaging or treatment of packaged semiconductor
Metallic housing or support
C438S111000, C438S112000, C438S124000
Reexamination Certificate
active
06326242
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to semiconductor packaging. More particularly, this invention relates to improved semiconductor packages with heat sinks, and to improved methods for fabricating semiconductor packages with heat sinks.
BACKGROUND OF THE INVENTION
With advances in semiconductor manufacture, the density of integrated circuits on semiconductor dice has increased. The higher circuit density increases the power consumption of the dice, and also the heat generated by the dice. In order to dissipate heat, semiconductor packages are sometimes constructed with heat sinks for dissipating heat. One type of heat sink comprises a metal plate bonded to a face or backside of a semiconductor package. The plate can be surface mounted on the package or embedded in an encapsulant material of the package.
In the fabrication of electronic assemblies, it is sometimes necessary to attach the heat sink of a semiconductor package to a substrate, such as printed circuit board (PCB), or a multi chip module substrate. Electrical connections may also be required between the heat sink and the substrate. For example, some heat sinks require a path to ground. Typically, these electrical connections comprise solder joints bonded to the heat sink, and to corresponding contacts on the substrate. In addition to providing electrical paths, the solder joints provide thermally conductive paths between the heat sink and substrate, for dissipating heat by conduction to the substrate.
One problem with solder joints is that stresses can develop in the solder material due to differences in thermal expansion between the heat sink and substrate. Typically the heat sinks are formed of metals, such as copper, having relatively high coefficients of thermal expansion (CTE). On the other hand, the substrates are typically formed of materials, such as glass filled resins or ceramics, having a different coefficient of thermal expansion.
These stresses can cause cracks which weaken the solder joints. In some situations the joints can loosen and fail. In addition, the cracks can increase the electrical resistivity of the joints, and decrease the thermal conductivity through the joint. In view of the foregoing, improved semiconductor packages with heat sinks, and improved methods for fabricating semiconductor packages and electronic assemblies with heat sinks are required.
SUMMARY OF THE INVENTION
In accordance with the present invention, a semiconductor package, a method for fabricating the package, and electronic assemblies employing the package are provided. The package, simply stated, comprises a semiconductor die in thermal communication with a heat sink. In an illustrative embodiment the package includes an encapsulant, such as molded plastic, and the heat sink is attached to a surface of the encapsulant in thermal communication with the die.
The heat sink includes one or more pad structures on an exterior portion thereof, adapted to provide thermal paths from the heat sink to the substrate. The pad structures also provide an increased surface area, and a topography for forming bonded connections with the substrate. The bonded connections can comprise a metal such as solder, or alternately a thermally conductive polymer. In addition to providing thermal paths, the bonded connections can also provide an electrical function such as a path to ground.
Two main embodiments for the pad structures are provided. In a first embodiment, the pad structures include one, or more, openings formed in the heat sink to a selected depth and in a selected pattern. Representative patterns for the openings include U-shapes, L-shapes, multiple squares or rectangles, donut shapes and squares with solid center portions. The openings can extend completely through the heat sink, or to a selected depth less than a thickness of the heat sink. In addition, the pad structures can be covered with a bonding layer, such as a solder wettable layer or a thermally conductive polymer, to facilitate formation of the bonded connections. In a second embodiment, the pad structures comprises raised members, such as one or more studs, dimples or protrusions, formed in the heat sink, and adapted to provide bonding sites for the bonded connections.
The method for fabricating the semiconductor package includes forming multiple heat sinks on a frame similar to a semiconductor leadframe. In addition, the pad structures can be formed on the heat sinks by etching or stamping the openings in a selected pattern, or by stamping the raised members in a desired configuration. The heat sinks and frame can then be attached to encapsulated semiconductor dice contained on a leadframe. Singulation of the heat sink frame, and package leadframe, forms multiple semiconductor packages.
The semiconductor packages can be used to construct electronic assemblies, such as circuit board assemblies and multi chip modules, by mounting the packages to substrates for the assemblies. During mounting of the semiconductor packages to the substrates, the bonded connections can be formed between the pad structures on the heat sinks, and corresponding contacts on the substrates. Additional bonded connections can also be formed between package leads and other contacts on the substrates.
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Brooks Mike
Moden Walter L.
Gratton Stephen A.
Micro)n Technology, Inc.
Picardat Kevin M.
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