Semiconductor device manufacturing: process – Packaging or treatment of packaged semiconductor – Assembly of plural semiconductive substrates each possessing...
Reexamination Certificate
1999-07-06
2001-04-03
Picardat, Kevin M. (Department: 2822)
Semiconductor device manufacturing: process
Packaging or treatment of packaged semiconductor
Assembly of plural semiconductive substrates each possessing...
C438S109000, C438S118000
Reexamination Certificate
active
06210993
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to semiconductor packaging, and specifically to an improved high density semiconductor package containing multiple dice, and to a method for fabricating the package.
BACKGROUND OF THE INVENTION
Semiconductor packages can include multiple semiconductor dice in a stacked configuration. One type of package, known as a “connector”, has parallel spaced cavities wherein the dice are mounted. The package can be mounted to a supporting substrate, such as a printed circuit board, to form multi chip modules and other electronic assemblies. For example, memory modules can include multiple memory devices, such as DRAMs, housed in the same package.
With some packages, direct electrical connections can be made between the bond pads on the dice, and mating contacts on the supporting substrate. Alternately, the packages can include electrical members for contacting the dice and supporting substrate. One feature of most prior art semiconductor packages is that the electrical connections between the dice and packages, or between the dice and supporting substrates, are permanent connections. For example, the connections are typically bonded connections, such as reflowed solder, or a cured conductive adhesive material.
The permanent electrical connections make assembly and disassembly of the packages difficult. In particular, the permanent electrical connections permit the packages to be assembled and disassembled only by semiconductor and electronics manufacturers having specialized equipment. It would be advantageous for packages to be constructed to allow disassembly and re-assembly by other users of the packages, such as consumers. This would permit the dice in the packages to be removed and replaced as required. For example, packages used for computer memory modules could be upgraded by consumers using the latest memory devices to replace the original dice in the packages.
Another problem with conventional semiconductor packages is stress generated by thermal cycling. In particular, the coefficient of thermal expansion (CTE) for the dice is typically different than the CTE of the packages and supporting substrates. Accordingly, the dice can expand by a different amount, stressing the electrical connections. Solder electrical connections are particularly susceptible to cracking and separation. It would be advantageous to provide packages with non-bonded electrical connections. This would permit movement of the dice to absorb thermal stresses.
Another aspect of semiconductor packages is that dice are being manufactured with large numbers of bond pads (e.g., 50 or more) which provide increased input/output paths to the integrated circuits contained on the dice. This requires a large number of electrical connections and associated electrical paths to be made to the dice. Optimally, a semiconductor package is constructed to accommodate large numbers of device bond pads.
The present invention is directed to an improved semiconductor package which can be easily disassembled and re-assembled without special equipment. In addition, the package includes resilient non-bonded electrical connections, which facilitate disassembly and re-assembly, and which absorb thermal stresses. Still further, the package can accommodate dice having large numbers of bond pads.
SUMMARY OF THE INVENTION
In accordance with the present invention an improved semiconductor package, and a method for fabricating the package are provided. The package comprises multiple semiconductor dice contained in a housing and mounted to a substrate. The housing includes a separate cavity for each die, and a force applying member for biasing the dice against the substrate. In addition, the dice include polymer interconnects bonded to their faces, and configured to provide electrical connections with the substrate.
The polymer interconnects comprise lengths of polymer tape having patterns of conductors on one side, and microbump contacts on an opposing side. The microbump contacts can be bonded to the die bond pads, with the polymer tape and conductors wrapped around the sides of the dice to form edge contacts. This construction allows the dice to be mounted on their sides (i.e., edge mounted) with the edge contacts on the polymer tape in electrical contact with mating contacts on the substrate. In addition, the edge contacts on the polymer interconnects, and the mating contacts on the substrate can include a resilient compressible member.
In accordance with the method of fabrication, a lead frame containing multiple polymer interconnects is provided. Initially, the dice are flip chip mounted to the lead frame with the die bond pads bonded to microbumps on the lead frame. Each die is then separated from the lead frame, with the polymer interconnects attached to the faces of the dice. The polymer interconnects are longer than the dice to permit folding along edges of the dice, followed by attachment to sides of the die. Exposed portions of the conductors on the polymer interconnects form edge contacts for electrically engaging the mating contacts on the substrate. The conductors can also be cantilevered from the sides of the dice to provide spring contacts, or formed in a multi-level configuration to provide ground or voltage planes on the interconnects.
Following bonding of the polymer interconnects to the dice, each die can be placed within a cavity of the housing, and the force applying member can be attached to the housing. The force applying member includes a lid that clips to the housing, and a compressible member for biasing the dice against the mating contacts on the substrate. The package can be disassembled by detaching the lid and removing the dice. This permits the dice to be replaced by an end user of the package such as a consumer.
The assembled package can be used to construct electronic devices such as multi chip modules. For example, the semiconductor dice can be provided as memory devices, such that the package forms a memory module. In addition, the substrate of the package can be provided with an edge connector or other external contacts, such that the package can be surface mounted to a printed circuit board or other supporting substrate.
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Akram Salman
Brooks Mike
Cloud Eugene
Farnworth Warren M.
Wood Alan G.
Gratton Stephen A.
Micro)n Technology, Inc.
Picardat Kevin M.
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