Thermal interface materials

Details Thermal interface materials Thermal interface materials

2002-01-14

2004-01-06

Kiliman, Leszek (Department: 1713)

Stock material or miscellaneous articles

Web or sheet containing structurally defined element or...

Including a second component containing structurally defined...

C428S325000, C428S328000, C428S330000, C428S492000, C442S336000, C442S367000, C442S374000, C442S375000, C106S270000, C106S272000, C106S638000, C106S640000, C106S641000, C106S660000, C252S500000, C252S512000, C252S514000, C252S519300, C252S519310, C252S519330, C252S520200

Reexamination Certificate

active

06673434

ABSTRACT:

FIELD OF THE INVENTION
The field of the invention is interface materials in electronic component and layered materials applications.
BACKGROUND OF THE INVENTION
Electronic components are used in ever increasing numbers of consumer and commercial electronic products. Examples of some of these consumer and commercial products are televisions, personal computers, internet servers, cell phones, pagers, palm-type organizers, portable radios, car stereos, or remote controls. As the demand for these consumer and commercial electronics increases, there is also a demand for those same products to become smaller, more functional, and more portable for consumers and businesses.
As a result of the size decrease in these products, the components that comprise the products must also become smaller. Examples of some of those components that need to be reduced in size or scaled down are printed circuit or wiring boards, resistors, wiring, keyboards, touch pads, and chip packaging.
Components, therefore, are being broken down and investigated to determine if there are better building materials and methods that will allow them to be scaled down to accommodate the demands for smaller electronic components. In layered components, one goal appears to be decreasing the number of the layers while at the same time increasing the functionality and durability of the remaining layers. This task can be difficult, however, given that several of the layers and components of the layers should generally be present in order to operate the device.
Also, as electronic devices become smaller and operate at higher speeds, energy emitted in the form of heat increases dramatically. A popular practice in the industry is to use thermal grease, or grease-like materials, alone or on a carrier in such devices to transfer the excess heat dissipated across physical interfaces. Most common types of thermal interface materials are thermal greases, phase change materials, and elastomer tapes. Thermal greases or phase change materials have lower thermal resistance than elastomer tape because of the ability to be spread in very thin layers and provide intimate contact between adjacent surfaces. Typical thermal impedance values range between 0.6-1.6° C. cm
2
/w. However, a serious drawback of thermal grease is that thermal performance deteriorates significantly after thermal cycling, such as from 65° C. to 150° C., or after power cycling when used in VLSI chips. It has also been found that the performance of these materials deteriorates when large deviations from surface planarity causes gaps to form between the mating surfaces in the electronic devices or when large gaps between mating surfaces are present for other reasons, such as manufacturing tolerances, etc. When the heat transferability of these materials breaks down, the performance of the electronic device in which they are used is adversely affected.
Thus, there is a continuing need to: a) design and produce thermal interface materials and layered materials that meet customer specifications while minimizing the size of the device and number of layers; and b) develop reliable methods of producing desired thermal interface materials and layered materials and components comprising contemplated thermal interface and layered materials.
SUMMARY OF THE INVENTION
A contemplated crosslinkable thermal interface material is produced by combining at least one rubber compound, at least one amine resin and at least one thermally conductive filler. This contemplated interface material takes on the form of a liquid or “soft gel”. The gel state is brought about through a crosslinking reaction between the at least one rubber compound composition and the at least one amine resin composition. More specifically, the amine resin is incorporated into the rubber composition to crosslink the primary hydroxyl groups on the rubber compounds thus forming the soft gel phase. Therefore, it is contemplated that at least some of the rubber compounds will comprise at least one terminal hydroxyl group.
Amine or amine-based resins are added or incorporated into the rubber composition or mixture of rubber compounds primarily to facilitate a crosslinking reaction between the amine resin and the primary or terminal hydroxyl groups on at least one of the rubber compounds. The crosslinking reaction between the amine resin and the rubber compounds leads to a “soft gel” phase to the mixture, instead of a liquid state.
Once the foundation composition that comprises at least one rubber compound, at least one amine resin, and at least one thermally conductive filler has been prepared, the composition must be compared to the needs of the electronic component, vendor, or electronic product to determine whether a phase change material is needed to change some of the physical properties of the composition.
Phase change materials are useful in thermal interface material applications because they store and release heat as they oscillate between solid and liquid form. A phase change material gives off heat as it changes to a solid state, and as it returns to a liquid, it absorbs heat. The phase change temperature is the melting temperature at which the heat absorption and rejection takes place.
A method for forming the crosslinkable thermal interface materials disclosed herein comprises a) providing at least one saturated rubber compound, b) providing at least one amine resin, c) crosslinking the at least one saturated rubber compound and the at least one amine resin to form a crosslinked rubber-resin mixture, d) adding at least one thermally conductive filler to the crosslinked rubber-resin mixture, and e) adding a wetting agent to the crosslinked rubber-resin mixture. This method can also further comprise adding at least one phase change material to the crosslinked rubber-resin mixture.
The contemplated thermal interface material can be provided as a dispensable liquid paste to be applied by dispensing methods and then cured as desired. It can also be provided as a highly compliant, cured, elastomer film or sheet for pre-application on interface surfaces, such as heat sinks. It can further be provided and produced as a soft gel or liquid that can be applied to surfaces by any suitable dispensing method. Even further, the material can be provided as a tape that can be applied directly to interface surfaces or electronic components.
Applications of the contemplated thermal interface materials described herein comprise incorporating the materials into a layered material, an electronic component or a finished electronic product.
Various objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the invention.


REFERENCES:
patent: 5194480 (1993-03-01), Block et al.
patent: 5989459 (1999-11-01), Nguyen et al.
patent: 6238596 (2001-05-01), Nguyen et al.
patent: 6451422 (2002-09-01), Nguyen et al.
M. Eaton “Differential Phase Change Thermal Interface Materials” pp. 1-9, May 1998.*
PCT International Search Report dated May 28, 2003.
Manford Eaton, entitled “Differential Phase Change Thermal Interface Materials” dated May 1998, pp. 1-9.

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