Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package – With provision for cooling the housing or its contents
Reexamination Certificate
1999-08-31
2002-07-23
Abraham, Fetsum (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
With provision for cooling the housing or its contents
Reexamination Certificate
active
06424033
ABSTRACT:
BACKGROUND OF THE INVENTION
1. The Field of the Invention
The present invention relates to the packaging of microelectronic devices. More particularly, the present invention relates to heat management for packaged microelectronic devices. Specifically, the present invention relates to the placement of a thermal grease heat transfer medium within an integrated circuit (IC) chip package for heat transfer away from the microchip. The grease acts as a heat sink to assist in the management of heat that is generated by an IC chip in the IC chip package.
2. The Relevant Technology
Miniaturization is the process of crowding an increasing number of microelectronic circuits onto a single chip. Additionally, miniaturization involves the reduction of the overall chip package size so as to achieve smaller and more compact devices such as hand-held computers, personal data assistants (PDA), portable telecommunication devices, and the like. Ideally, the chip package size would be no larger than the chip itself. Miniaturization has the counter-productive effect upon chip packaging of an increased heat load upon a smaller chip package. Heat management is therefore an important aspect of producing a reliable microelectronic device. A heat sink for a chip package allows for enhanced performance of the microelectronics.
In the packaging of microelectronic devices, protection of the microelectronic device and its connections to the outside world is critical during packaging and field use. A prior art solution to packaging of microelectronic devices was to cover the integrated circuit chip with a plastic or ceramic material after a manner that both the highly sensitive active surface of the chip as well as the electrical connections were protected. Plastic packaging such as an epoxy material is useful to protect the active surface as well as the electrical connections. Plastic packaging has the disadvantage of being a poor conductor of heat compared to ceramic packaging. Where a plastic material is used, its effect as a poor heat conductor often leads to additional measures that must be taken to extract generated heat from the chip package to allow proper functioning of the microelectronic device. Ceramic packaging has an advantage of a higher thermal conductivity compared to plastic, but it is often costly and bulky, as well as potentially brittle. Where the chip package receives a physical blow, the ceramic package may shatter.
What is needed in the art is a means of transferring heat away from a microelectronic device that overcomes the heat management problems of the prior art.
SUMMARY OF THE INVENTION
The present invention relates to an integrated circuit chip package having an IC chip with an active surface, where the active surface has extending therefrom an electrical connector in electrical communication with IC chip. The IC chip is mounted upon a substrate such as a printed circuit board (PCB). A grease is in contact with the active surface of the IC chip and a container is disposed upon the substrate. The grease is enclosed within the container and the substrate.
The present invention relates to the use of the grease as a protective substance to protect both the active surface of the IC chip and simultaneously as a heat transfer medium to transfer heat away from the IC chip. The present invention also relates to a method of heat transfer away from an IC chip using grease, a substrate upon which the IC chip is mounted, and a container.
In one embodiment of the present invention, an IC chip is configured as a board on chip (BOC) package and a thermal grease is disposed upon the exposed active surface of the chip as well as over the electrical connectors such as bond wires or solder balls if present. A protective shell covers the thermal grease to prevent disturbance of the grease during both assembly thereof and during field use. Alternatively, a dam structure may be disposed upon the board and the protective shell to hold the protective shell in place. Additionally, at least one vent hole may be disposed in the protective shell to allow for thermal expansion and contraction of the grease. The BOC configuration lends itself to a stacked BOC package where multiple occurrences of BOC may be enclosed within a single protective shell.
In another embodiment of the present invention, a chip on board (COB) chip package is configured with the grease disposed upon the active surface of the IC chip where the grease also covers the bond wires. The protective shell is disposed upon the grease and is secured against the substrate on the same surface onto which the IC chip is disposed. In a variation of this embodiment, the protective shell is configured to make direct contact with the active surface of the IC chip.
Another embodiment of the present invention includes an IC chip mounted directly upon a heat sink. A substrate is also mounted directly upon the heat sink, and grease covers both the active surface of the IC chip and the bond wires. Additionally, a protective shell is mounted upon the substrate, where the grease is enclosed by the protective shell and the substrate.
Another embodiment of the present invention comprises a flip chip configuration wherein the grease is disposed both upon the active surface of the flip chip and upon the balls of a flip chip ball array that provides electrical connections to the flip chip. A dam structure may be disposed upon both the flip chip substrate and the flip chip itself to assist in containing the grease. In a variation of the foregoing involving a flip chip upon a flexible substrate, a protective shell is disposed upon the flex substrate and grease substantially encompasses the entire flip chip as well as the flip chip ball array. In a still further variation, the protective shell is in direct contact with the inactive surface of the flip chip. Thereby, the protective shell simultaneously acts as a die attach and heat sink, and the flex substrate with the protective shell provide an enclosure for the grease.
Another embodiment of the present invention includes flip chip on die (FCOD) wherein the flip chip is disposed against a COB die. In a first configuration of this embodiment, the flip chip ball array is in contact with a grease and the bond wires from the die are enclosed in a second protective material that is typically a thermoplastic or thermoset resin.
An alternative embodiment of the FCOD configuration provides for grease to be in contact with both the flip chip ball array and the bond wires from the die. A protective shell is disposed upon the substrate supporting the die such that the protective shell and the substrate enclose therein both the flip chip and the die.
Another alternative embodiment of the FCOD configuration provides for a two-piece protective shell that may allow the inactive surface of the flip chip to be exposed. This alternative embodiment provides for the flip chip ball array and the bond wire to be encompassed by grease while allowing the inactive surface to radiate heat away from the flip chip.
These and other features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.
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Chiu, et al., Thermal Modeling of Greases—Types Interface Materials in PPGA Applications, IEEE, Thirtheen IEE Semi-Therm Syposium, 57-63.*
Hunadi, Ron, Ph.D. and Wells, Rich,Higs Thermal Conductivity Greases: Beneficial for use in CSPs and fl
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Abraham Fetsum
Andujar Leonardo
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