Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
1999-02-26
2001-04-03
Thompson, Gregory (Department: 2835)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C174S252000, C361S749000
Reexamination Certificate
active
06212076
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to a printed circuit board, and more particularly to an improved printed circuit board design which enhances heat dissipation from electronic components, such as a memory integrated circuit assembly, mounted on the printed circuit board.
BACKGROUND OF THE INVENTION
A memory component comprises a memory integrated circuit (IC) mounted on a chip carrier. The memory component may include a resin package with external leads for mounting the component to an external surface of a multilayer printed circuit board. Other electronic components such as capacitors can also be mounted on the external mounting surfaces. Multilayer printed circuit boards used for these purposes typically include insulating layers, wiring layers between the insulating layers, and wiring layers on the external surface of the multilayer printed circuit board. The external leads of each memory component are typically soldered to pads or other conductors printed on the external surface of the multilayer printed circuit board.
FIG. 1
illustrates a memory module
1
according to the prior art. Memory components
3
A,
3
B,
3
C each comprise an IC mounted on a chip carrier surface and molded in resin material (not shown). The memory components are mounted on an external mounting surface of a multilayer printed circuit board
4
. Each memory component has external metal leads
5
soldered to metal pads (not shown) on the external mounting surface
7
. A capacitor
2
is also mounted on the external mounting surface. A row of electrical contacts
6
is also shown on the edge of the multilayer printed circuit board to provide electrical contact to other printed circuit boards. U.S. Pat. No. 5,412,538, to Kikinis et al, entitled Space Saving Memory Module, issued on May 2, 1995 depicts a similar memory module as that shown in FIG.
1
.
In the memory module
1
described above, heat generation by the ICs increases as the operating speed of the ICs is increased. Total heat generation is also increased by an increased number of ICs, often stacked (in stacked memory modules), needed to increase memory density and performance. Each IC dissipates heat directly into the surrounding air and from the external leads
5
and the metal pads on the external mounting surface to the surrounding air.
The path from the metal pads to the surrounding air is not very effective because there is usually resist or solder mask covering the pads. Furthermore, the external surface of the multilayer printed circuit board is typically comprised of a resin material which has a low heat transfer coefficient. While the direct heat dissipation from the memory component to the surrounding air is more effective than through the printed circuit board, the total heat dissipation is often insufficient to maintain the ICs at the desired temperature especially where the memory components are stacked. Therefore optimal performance cannot be obtained.
Multilayer rigid/flexible printed circuit boards are also known in the field. Typically, a rigid/flexible printed circuit board includes a flexible printed circuit board portion which extends from the periphery of a rigid section or sections with the rigid sections being used for mounting mechanical hardware of electrical components. Circuit boards having these flexible portions offer numerous advantages over standard rigid printed circuit boards. They are easier to handle and can be used where limited space is required since they can be inserted in virtually any shape or space in a system and occupy less space in that system. Also, they offer the advantage of allowing the rigid section of the printed circuit board to be mounted or located in one area, where space is at a premium, allowing the flexible portion to be mounted in a remote area away from the area in which the rigid section is located.
OBJECTS OF THE INVENTION
A primary objective of the present invention is to provide a printed circuit board that significantly enhances heat dissipation from electronic components, such as memory components, mounted on the printed circuit board.
Another object of the present invention is to provide a rigid/flexible printed circuit board having a flexible portion that enhances heat dissipation from electronic components mounted on the rigid section of the printed circuit board.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention there is provided a printed circuit board comprising a substrate including a plurality of dielectric layers laminated together, a conductor on a surface of one of the dielectric layers, an electronic component mounted on the conductor, and a first thermally conductive layer between two of the dielectric layers. The printed circuit board further includes a thermally conductive aperture positioned within the substrate, connected to the conductor and thermally coupling the electronic component to the first thermally conductive layer, a second thermally conductive layer on a portion of the surface of the dielectric layer, spaced from the electronic component, and a plurality of thermally conductive apertures positioned within the substrate and thermally coupling the second thermally conductive layer to the first thermally conductive layer whereby the electronic component is thermally coupled to the second thermally conductive layer.
In accordance with another aspect of the present invention there is provided a printed circuit board comprising a first plurality of dielectric layers laminated together, a conductor on a surface of the first plurality of dielectric layers, an electronic component mounted on the conductor, a second plurality of dielectric layers laminated together, and a flexible web located between the first and second plurality of dielectric layers. The flexible web includes a first thermally conductive layer which is also sandwiched between two of the first plurality of dielectric layers and two of the second plurality of dielectric layers. A thermally conductive aperture positioned within the first plurality of dielectric layers, is connected to the conductor, and thermally couples the electronic component to the first thermally conductive layer. A second thermally conductive layer is included on a portion of a surface of the second plurality of dielectric layers and is spaced from the electronic component. A plurality of thermally conductive apertures is positioned within the second plurality of the dielectric layers and thermally couples the second thermally conductive layer to the first thermally conductive layer whereby the electronic component is thermally coupled to the second thermally conductive layer.
REFERENCES:
patent: 5195021 (1993-03-01), Ozmat et al.
patent: 5258887 (1993-11-01), Fortune
patent: 5297107 (1994-03-01), Metzger et al.
patent: 5412538 (1995-05-01), Kikinis et al.
patent: 5461201 (1995-10-01), Schonberger et al.
patent: 5563773 (1996-10-01), Katsumata
patent: 5621616 (1997-04-01), Owens et al.
patent: 5708566 (1998-01-01), Hunninghaus et al.
patent: 5978223 (1999-11-01), Hamilton et al.
patent: 5982630 (1999-11-01), Bhatia
patent: 363307768 (1988-12-01), None
MacQuarrie Stephen W.
Stutzman Randall J.
Zalesinski Jerzy M.
International Business Machines - Corporation
Samodovitz Arthur J.
Thompson Gregory
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