Compressible thermal interface materials

Provided is a compressible thermal interface material including a polymer, a thermally conductive filler, and a phase change material. A formulation for forming a compressible thermal interface material and an electronic component including a compressible thermal interface material are also provided.

FIELD OF THE INVENTION

The present disclosure relates generally to thermal interface materials, and more particularly to compressible thermal interface materials.

DESCRIPTION OF RELATED ART

Thermal interface materials are widely used to dissipate heat from electronic components, such as central processing units, video graphics arrays, servers, game consoles, smart phones, LED boards, and the like. Thermal interface materials are typically used to transfer excess heat from the electronic component to a heat spreader, such as a heat sink.

Thermal interface materials include thermal grease, grease-like materials, elastomer tapes, and phase change materials. Traditional thermal interface materials include components such as gap pads and thermal pads.

It is desirable for thermal interface materials to have excellent thermal performance and compressibility.

SUMMARY OF THE INVENTION

The present disclosure provides compressible thermal interface materials that are useful in transferring heat from heat generating electronic devices, such as computer chips, to heat dissipating structures, such as heat spreaders and heat sinks.

In one exemplary embodiment, a compressible thermal interface material is provided. The compressible TIM includes a polymer; a thermally conductive filler; and a phase change material. The phase change material includes a wax having a needle penetration value of at least 50 as determined by ASTM D1321. In one more particular embodiment, the compressible thermal interface material has a compressibility of at least 5% under a pressure of 40 psi. In another more particular embodiment, the compressible thermal interface material has a springback ratio of 50% or less. In still yet another more particular embodiment, the phase change material comprises a second wax, the second wax having a needle penetration value of less than 50 as determined by ASTM D1321. In another more particular embodiment, the phase change material comprises a wax selected from the group consisting of: a polyethylene wax, a copolymer of ethylene-vinyl acetate wax, and an oxidized polyethylene wax. In a more particular embodiment of any of the above embodiments, the thermally conductive filler comprises aluminum. In another more particular embodiment, the thermally conductive filler comprises 10 wt. % to 95 wt. % of the total weight of the compressible thermal interface material. In a more particular embodiment of any of the above embodiments, the polymer is selected from the group consisting of: ethylene-propylene rubbers (EPR), ethylene-propylene diene monomer rubbers (EPDM), polyethylene-butylene, and polyethylene-butylene-styrene, polybutadiene, hydrogenated polybutadiene mono-ol, hydrogenated polypropadiene mono-ol, hydrogenated polypentadiene mono-ol, polybutadiene diol, hydrogenated polypropadiene diol, and hydrogenated polypentadiene diol. In an even more particular embodiment, the polymer is hydrogenated polybutadiene. In a more particular embodiment of any of the above embodiments, the compressible TIM further includes a coupling agent, an antioxidant, and a crosslinking agent.

In a more particular embodiment of any of the above embodiments, the compressible TIM further includes a silicone gel.

In another more particular embodiment of any of the above embodiments, the compressible TIM includes a middle layer comprising the polymer, the thermally conductive filler, and the wax having a needle penetration value of at least 50 as determined by ASTM D132; a first surface layer including at least one phase change material and at least one thermally conductive filler; and a second surface layer including at least one phase change material and at least one thermally conductive filler. In a more particular embodiment, a weight percentage content of thermally conductive filler in the middle layer is less than or equal to the weight percentage content of thermally conductive filler in at least one of the first and second surface layers. In another more particular embodiment, the weight percentage of thermally conductive filler in each of the first and second surface layers is independently from about 70 wt. % to about 99 wt. %.

In another embodiment, a formulation for forming a compressible thermal interface material is provided. The formulation includes a solvent; a polymer; a thermally conductive filler; and a phase change material, wherein the phase change material includes a wax having a needle penetration value of at least 50 as determined by ASTM D1321. In a more particular embodiment, the formulation has a viscosity of 1,000 centipoise to 100,000,000 centipoise.

In another embodiment, an electronic component is provided. The electronic component includes a heat sink, an electronic chip, and a compressible thermal interface material positioned between the heat sink and electronic chip, the compressible thermal interface material including: a polymer, a thermally conductive filler, and a wax having a needle penetration value of at least 50 as determined by ASTM D1321. In a more particular embodiment, a first surface of the compressible thermal interface material is in contact with a surface of the electronic chip and a second surface of the compressible thermal interface material is in contact with the heat sink. In another more particular embodiment, the electronic component includes a heat spreader positioned between the heat sink and the electronic chip, wherein a first surface of the compressible thermal interface material is in contact with a surface of the electronic chip and a second surface of the compressible thermal interface material is in contact with the heat spreader. In still yet another more particular embodiment, the electronic component includes a heat spreader positioned between the heat sink and the electronic chip, wherein a first surface of the compressible thermal interface material is in contact with a surface of the heat spreader and a second surface of the compressible thermal interface material is in contact with the heat sink.

DETAILED DESCRIPTION

The present invention relates to thermal interface materials useful in transferring heat away from electronic components.

FIG. 1Aschematically illustrates an electronic chip34, a heat spreader36, and a heat sink32with a first thermal interface material (TIM)10A connecting the heat sink32and heat spreader36and a second thermal interface material10B connecting the heat spreader36and electronic chip34. One or both of thermal interface materials10A,10B may be a compressible thermal interface material, as described below.FIG. 1Billustrates the exemplary thermal interface material10as a thermal interface layer designated as a TIM1.5positioned between an electronic chip34and a heat sink32, such that a first surface of TIM10is in contact with a surface of electronic chip34and a second surface of TIM10is in contact with a surface of heat sink32.FIG. 1Cillustrates the exemplary thermal interface material10as a thermal interface material designated as a TIM2positioned between a heat spreader36and a heat sink32, such that a first surface of TIM10is in contact with a surface of heat spreader36and a second surface of TIM10is in contact with a surface of heat sink32.FIG. 1Dillustrates an exemplary thermal interface material10as a thermal interface material designated as a TIM1positioned between an electronic chip34and a heat spreader36such that a first surface of TIM10is in contact with a surface of electronic chip34and a second surface of TIM10is in contact with a surface of heat spreader36.

Although TIM10is illustrated as a single continuous layer inFIG. 1, in other embodiments, TIM10may be comprised of more than one layer (seeFIG. 2A), wherein each layer may be composed of the same or different materials.

In some exemplary embodiments, the TIM10further comprises a thermal sheet. In some exemplary embodiments, the TIM10further comprises an dielectric layer. In some exemplary embodiments, the TIM10further comprises a thermal foil.

In some exemplary embodiments, the thermal interface material10is used in a smartphone, a tablet computer, a laptop computer, a desktop computer, a gaming console, a server, a telecom base station, a wireless router or other component, a light emitting diode (LED), a power module, an autoelectronic device, or insulated-gate bipolar transistor (IGBT).

A. Compressible Thermal Interface Material

In one exemplary embodiment, the TIM10is a compressible thermal interface material. In some exemplary embodiments, compressible TIM10comprises one or more polymers, one or more phase change materials, one or more thermally conductive fillers, and, optionally, additives. In some exemplary embodiments, TIM10comprises one or more elastomers containing one or more thermally conductive fillers.

In some exemplary embodiments, the TIM10includes one or more thermally conductive fillers. Exemplary thermally conductive fillers include metals, alloys, nonmetals, metal oxides and ceramics, and combinations thereof. Exemplary metals include but are not limited to aluminum, copper, silver, zinc, nickel, tin, indium, and lead. Exemplary nonmetals include but are not limited to carbon, graphite, carbon nanotubes, carbon fibers, graphenes, and silicon nitride. Exemplary metal oxides and ceramics include but are not limited to alumina, aluminum nitride, boron nitride, zinc oxide, and tin oxide.

The TIM10may comprise the one or more thermally conductive fillers in an amount as little as 10 wt. %, 20 wt. %, 25 wt. %, 50 wt. %, as great as 75 wt. %, 80 wt. %, 85 wt. %, 90 wt. %, 95 wt. %, or within any range defined between any two of the foregoing values, based on the total weight of the TIM10.

In some exemplary embodiments, the TIM10includes one or more silicone gels. In some embodiments, the TIM10may comprise the one or more silicone gels in an amount as little as 0.1 wt. %, 0.5 wt. %, 1 wt. % 1.5 wt. %, 2 wt. %, as great as 5 wt. %, 10 wt. %, 15 wt. %, or within any range defined between any two of the foregoing values, based on the total weight of the central layer12.

c. Phase Change Material

In some exemplary embodiments, the TIM10comprises one or more phase change materials. A phase change material is a material having a melting point or melting point range at or below the operating temperature of a portion of an electronic device in which the TIM10is to be used. An exemplary phase change material is a wax. Other exemplary phase change materials include low melting alloys, such as Wood's metal, Field's metal, or a metal or alloy having a melting point between about 20° C. and 90° C.

In some embodiments, the phase change material has a phase change temperature as low as 20° C., 30° C., 40° C., 45° C. 50° C., as high as 60° C., 70° C., 80° C., 90° C., 100° C., 110° C., or within any range defined between any two of the foregoing values. In some more particular embodiments, the phase change material has a phase change temperature as low as 30° C., 40° C., 45° C. as high as 50° C., 60° C., 70° C., or within any range defined between any two of the foregoing values.

The hardness of a wax may be characterized by a needle penetration value, such as a needle penetration value determined in accordance with ASTM D1321 at 25° C., the disclosures of which are hereby incorporated by reference in their entirety.

In some exemplary embodiments, the TIM10comprises one or more waxes having an ASTM D1321 needle penetration value as low as 40, 50, 60, as high as 70, 80, 90, 100, or greater, or within any range defined by any two of the foregoing values. In some exemplary embodiments, the TIM10comprises one or more waxes having an ASTM D1321 needle penetration value of at least 50. In some exemplary embodiments, the TIM10comprises one or more waxes having an ASTM D1321 needle penetration value of at least 60. In some exemplary embodiments, the TIM10comprises one or more waxes having an ASTM D1321 needle penetration value of at least 70.

Exemplary waxes having an ASTM D1321 needle penetration value greater than 70 include AC-1702 (a polyethylene wax), AC-430 (a copolymer of ethylene-vinyl acetate wax), and AC-6702 (an oxidized polyethylene wax), each available from Honeywell International Inc.

In some exemplary embodiments, the central layer12comprises at least two waxes, wherein the first wax is harder than the second wax. In some exemplary embodiments, the weight ratio of the softer wax based on the total weight of the waxes is as little as 10%, 25%, 50%, as high as 75%, 95%, 99%, or within any range defined between any two of the foregoing values.

In some exemplary embodiments, the first wax has an ASTM D1321 needle penetration value of less than 70 and the second wax has an ASTM D1321 needle penetration value of at least 70 or greater. In some exemplary embodiments, at least one of the first wax and second wax includes a polyethylene wax blended with polytetrafluoroethylene. An exemplary polytetrafluoroethylene-polyethylene wax mixture is PEW-0602F wax available from Nanjing Tianshi New Material Technologies.

An exemplary wax having an ASTM D1321 needle penetration value less than 70 includes TAC wax, available from The International Group, Inc., and RT44HC, available from Hangzhou Ruhr Tech.

In some exemplary embodiments, the TIM10comprises one or more additives. Exemplary additives include antioxidants, crosslinkers, and coupling agents, including titanate coupling agents. In some exemplary embodiments, the TIM10may comprise the one or more additives in an amount as little as 0.1 wt. %, 0.5 wt. %, 1 wt. % as great as 1.5 wt. %, 2 wt. %, 5 wt. %, 10 wt. %, or within any range defined between any two of the foregoing values, based on the total weight of the central layer.

B. Multilayer Thermal Interface Material

In some embodiments, the TIM is a multilayer thermal interface material (“TIM”)10′. Referring first toFIG. 2A, an exemplary multilayer10′ is illustrated. MultilayerTIM10′ includes a central layer12, first surface layer14, and second surface layer16.

Although certain components are exemplified below as being a part of the central layer12, first surface layer14, and/or second surface layer16, in some embodiments, each component may be found in any of the central layer12, the first surface layer14, and the second surface layer16

1. Central Layer

As illustrated inFIG. 2A, central layer12is positioned between first surface layer14and second surface layer16. In some embodiments, central layer12is directly in contact with first surface layer14and second surface layer16. Although central layer12is illustrated as a single continuous layer inFIG. 2A, in other embodiments, central layer12′ may be comprised of more than one layer, wherein each layer may be composed of the same or different materials (seeFIG. 2B).

In some exemplary embodiments, the central layer12has a composition similar to that of the TIM10as described above. In some exemplary embodiments, the central layer12comprises one or more polymers, one or more phase change materials, one or more thermally conductive fillers, and, optionally, additives, as described above with respect to TIM10. In some exemplary embodiments, the central layer12comprises one or more elastomers containing one or more thermally conductive fillers. In some exemplary embodiments, the central layer12includes a compressible material. In some embodiments, when subjected to a pressure of 40 psi, the central layer12has a compressibility as little as at least 5%, at least 10%, at least 15%, at least 20%, at least 30%, and as high as at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, or within any range defined between any two of the foregoing values. In some exemplary embodiments, the central layer returns to its original thickness following release of the pressure. In other exemplary embodiments, the central layer does not return to its original thickness following release of the pressure.

Referring next toFIG. 2B, in some exemplary embodiments, the central layer12′ comprises a gap pad18, a phase change material20, and an electromagnetic interference shielding sheet22. Typical materials used for electromagnetic shielding include metal sheets, metal screens, metal foam, and a coating including nano- or sub-micron size metal particles, such as copper or nickel. In some exemplary embodiments, the central layer12further comprises a thermal sheet. In some exemplary embodiments, the central layer12further comprises an dielectric layer. In some exemplary embodiments, the central layer12further comprises a thermal foil.

In some exemplary embodiments, the central layer12includes one or more thermally conductive fillers. In some exemplary embodiments, the weight percentage of thermally conductive filler in the central layer12is less than or equal to the weight percentage of thermally conductive filler in either the first surface layer14or second surface layer16. In some exemplary embodiments, the central layer12has a thermal conductivity less than or equal to the thermal conductivity of both the first and second surface layers. The central layer12may comprise the one or more thermally conductive fillers in an amount as little as 10 wt. %, 20 wt. %, 25 wt. %, 50 wt. %, as great as 75 wt. %, 80 wt. %, 85 wt. %, 90 wt. %, 95 wt. %, or within any range defined between any two of the foregoing values, based on the total weight of the central layer12.

In some exemplary embodiments, the central layer12further comprises a polymer, such as an elastomer. In some exemplary embodiments, the central layer includes one or more silicone gels. In some embodiments, the central layer12may comprise the one or more silicone gels in an amount as little as 0.1 wt. %, 0.5 wt. %, 1 wt. % 1.5 wt. %, 2 wt. %, as great as 5 wt. %, 10 wt. %, 15 wt. %, or within any range defined between any two of the foregoing values, based on the total weight of the central layer12.

c. Phase Change Material

In some exemplary embodiments, the central layer12comprises one or more phase change materials. In some exemplary embodiments, the central layer12comprises one or more waxes having an ASTM D1321 needle penetration value as low as 40, 50, 60, as high as 70, 80, 90, 100, or greater, or within any range defined by any two of the foregoing values. In some exemplary embodiments, the central layer12comprises one or more waxes having an ASTM D1321 needle penetration value of at least 50. In some exemplary embodiments, the central layer12comprises one or more waxes having an ASTM D1321 needle penetration value of at least 60. In some exemplary embodiments, the central layer12comprises one or more waxes having an ASTM D1321 needle penetration value of at least 70.

In some exemplary embodiments, the central layer12comprises one or more additives. In some exemplary embodiments, the central layer12may comprise the one or more additives in an amount as little as 0.1 wt. %, 0.5 wt. %, 1 wt. % as great as 1.5 wt. %, 2 wt. %, 5 wt. %, 10 wt. %, or within any range defined between any two of the foregoing values, based on the total weight of the central layer

2. Surface Layers

In some exemplary embodiments, first surface layer14is comprised of the same material as second surface layer16. In other exemplary embodiments, first surface layer14is comprised of a different material than second surface layer16. Exemplary materials that may be useful as first surface layer14and/or second surface layer16are disclosed in the following patents and applications, the disclosures of which are hereby incorporated by reference in their entirety: U.S. Pat. No. 6,451,422; U.S. Pat. No. 6,605,238; U.S. Pat. No. 6,673,434; U.S. Pat. No. 7,867,609; U.S. Pat. No. 6,797,382; U.S. Pat. No. 6,908,669; U.S. Pat. No. 7,244,491; U.S. 2007/0051773; U.S. 2011/0308782; and U.S. 2011/0038124.

Exemplary materials from which the first surface layer14and/or second surface layer16may be formed include PCM, LTM, and/or PTM series materials available from Honeywell International Inc. One exemplary PCM material is PCM45F, which is a substantially incompressible material comprising a polymer, a phase change material, and a thermally conductive filler. Another exemplary PCM material is PCM45F-SP, which is a screen-printable version of PCM45F comprising a polymer, a phase change material, and a thermally conductive filler. One exemplary PTM material is PMT3180, which is a substantially incompressible material comprising a polymer, a phase change material, and a thermally conductive filler. Another exemplary material is TS27, which is a compressible thermal interface material comprising a polymer, a hard wax and a soft wax and a thermally conductive filler. Another exemplary material is TC5026, which is a thermal grease including a thermally conductive filler, available from Dow Corning, Midland Mich.

In some exemplary embodiments, each of the first and second surface layers14,16are hard or substantially incompressible. In some exemplary embodiments, each of the first and second surface layers14,16, has a compressibility less than that of the central layer12when subjected to a pressure of 40 psi. In some embodiments, when subjected to a pressure of 40 psi, each of the first and second surface layers14,16has a compressibility as little as 0%, 1%, 2%, as high 3%, 5%, or within any range defined between any two of the foregoing values. In some embodiments, when subjected to a pressure of 40 psi, each of the first and second surface layers14,16has a compressibility of 5% or less. In other exemplary embodiments, each of the each of the first and second surface layers14,16are compressible. In some embodiments, when subjected to a pressure of 40 psi, each of the first and second surface layers14,16has a compressibility as little as 5%, 10%, 20%, 25%, as great as 50%, 75%, 80%, or within any range defined between any two of the foregoing values.

In some exemplary embodiments, each of the first and second surface layer14,16has a Shore A hardness according to ASTM D2240, the disclosure of which is hereby incorporated by reference in its entirety, as little as 30, 40, 50, as high as 60, 70, 80, or greater, or within any range defined between any two of the foregoing values. In some exemplary embodiments, each of the first and second surface layers14,16is independently less than the thickness of the central layer12. In some exemplary embodiments, each of the first and second surface layers14,16has a thickness as little as 0.05 mm, 0.1 mm, 0.25 mm, 0.5 mm, as great as 1 mm, 2 mm, 5 mm, or within any range defined between any two of the foregoing values. In some exemplary embodiments, each of the first and second surface layers14,16has a thickness less than 5 mm, a thickness less than 1 mm, a thickness less than 0.5 mm, a thickness less than 0.25 mm, or a thickness less than 0.1 mm.

In some exemplary embodiments, each of the first and second surface layers14,16comprise one or more thermal conductive fillers, a polymer matrix, at least one wax, and optional additives.

In some embodiments, each surface layer14,16includes one or more thermally conductive fillers. Each surface layer14,16may independently comprise the one or more thermally conductive fillers in an amount as little as 70 wt. %, 75 wt. %, 80 wt. %, 85 wt. %, as great as 90 wt. %, 95 wt. %, 99 wt. %, or within any range defined between any two of the foregoing values, based on the total weight of each surface layer14,16. In a more particular embodiment, the weight percentage of thermally conductive filler in each of the first surface layer14and second surface layer16is independently from 85 wt. % to 99 wt. % based on the total weight of each surface layer14,16.

In some exemplary embodiments, each surface layer14,16further comprises a polymer. In some embodiments, the polymer is polyethylene-butylene mono-ol. Each surface layer14,16may independently comprise the one or more polymers in an amount as little as 0.1 wt. %, 0.5 wt. %, 1 wt. %, 5 wt. %, as great as 8 wt. %, 10 wt. %, 20 wt. %, or within any range defined between any two of the foregoing values, based on the total weight of each surface layer14,16.

c. Phase Change Material

In some embodiments, each surface layer14,16independently comprises one or more phase change materials, such as a wax. In some exemplary embodiments, each surface layer14,16may comprise the one or more phase change materials in an amount as little as 0.1 wt. %, 0.5 wt. %, 1 wt. % as great as 2 wt. %, 3 wt. %, 5 wt. %, 10 wt. %, or within any range defined between any two of the foregoing values, based on the total weight of the first surface layer14or second surface layer16. In some embodiments, each surface layer14,16, includes a total softener content of soft waxes and silicone gel having a needle penetration value no less than 70 in an amount as little as 0.1 wt. %, 0.5 wt. %, 1 wt. % as great as 2 wt. %, 3 wt. %, 5 wt. %, or within any range defined between any two of the foregoing values, based on the total weight of the first surface layer14or second surface layer16.

In some exemplary embodiments, the first surface layer14and second surface layer16independently comprise one or more additives. In some exemplary embodiments, the central layer12may comprise the one or more additives in an amount as little as 0.1 wt. %, 0.5 wt. %, 1 wt. % as great as 1.5 wt. %, 2 wt. %, 5 wt. %, 10 wt. %, or within any range defined between any two of the foregoing values, based on the total weight of the first surface layer14or second surface layer16.

B. Methods of Forming a Compressible Thermal Interface Material

In some embodiments, the TIM10is formed from a dispensable formulation including one or more polymers, one or more phase change materials, one or more thermally conductive fillers, one or more solvents, and, optionally, one or more additives. Dispensable materials are typically paste-based material. In a typical embodiment, the dispensable material has a viscosity such that, when a suitable pressure or force is applied to the material, a portion of the material is pushed out of a container through a relatively narrow hole (dispense head). In some exemplary embodiments, the TIM materials are filled in a syringe, and the filled TIM can be pushed out from the syringe head or needle on to the surface of a heat spreader, chip, and/or heatsink. In some embodiments, the TIM is dispersed on to the surface in a customized pattern under the desired pressure. Typical dispensable parameters may include, but not limited to press force, dispense head size, dispense speed, and average pattern thickness.

Exemplary solvents are described in U.S. Patent Application Publication 2007/0517733, the disclosure of which is hereby incorporated by reference herein in its entirety. Suitable solvents include pure solvents or mixtures of organic or inorganic solvents that are volatilized at a desired temperature, such as the critical temperature, or that can facilitate any of the above-mentioned design goals or needs, and that are compatible with the phase change materials, in that they will interact with the phase change materials to achieve the previously-mentioned goals. In some embodiments, the solvent, solvent mixture or combination thereof will solvate the phase change material such that it can be applied by printing techniques. In some exemplary embodiments, the solvent or mixture of two or more solvents are selected from the hydrocarbon family of solvents. Hydrocarbon solvents comprise carbon and hydrogen. A majority of hydrocarbon solvents are non-polar; however, there are a few hydrocarbon solvents that are considered polar.

Hydrocarbon solvents are generally classified into three classes: aliphatic, cyclic and aromatic. Aliphatic hydrocarbon solvents comprise both straight-chain compounds and compounds that are branched and possibly crosslinked, however, aliphatic hydrocarbon solvents are not typically considered cyclic. Cyclic hydrocarbon solvents are those solvents that comprise at least three carbon atoms oriented in a ring structure with properties similar to aliphatic hydrocarbon solvents. Aromatic hydrocarbon solvents are those solvents that comprise generally three or more unsaturated bonds with a single ring or multiple rings attached by a common bond and/or multiple rings fused together. In some exemplary embodiments, the solvent or mixture of two or more solvents are selected from solvents that are not considered part of the hydrocarbon solvent family of compounds, such as ketones, alcohols, esters, ethers and amines. In yet other contemplated embodiments, the solvent or solvent mixture may comprise a combination of any of the solvents mentioned herein.

In one exemplary embodiment, the solvent includes one or more solvents selected from: pentane, hexane, heptane, cyclohexane, paraffin oils, isoparaffinic fluids, benzene, toluene, xylene and mixtures or combinations thereof. Exemplary isoparafinnic fluids include Isopar H, Isopar L, and Isopar M, available from Exxon Mobile Chemical. In some exemplary embodiments, the formulation may comprise the one or more solvents in an amount as little as 0.1 wt. %, 0.5 wt. %, 1 wt. % as great as 5 wt. %, 10 wt. %, 20 wt. %, 25 wt. % or within any range defined between any two of the foregoing values, based on the total weight of the formulation.

In some exemplary embodiments, the formulation has a viscosity as little as 500 centipoise, 1,000 centipoise, 5,000 centipoise, 10,000 centipoise, centipoise, as great as 150,000 centipoise, 1,000,000 centipoise, 100,000,000 centipoise, or within any range defined between any two of the foregoing values, when tested at room temperature using a viscometer according to DIN 53018, the disclosures of which are hereby incorporated by reference in their entirety.

In some exemplary embodiments, a method of forming a TIM10is provided. In some exemplary embodiments, forming the TIM10includes processes such as baking and drying the TIM10.

In some exemplary embodiments, baking the TIM10include baking at a temperature as low as 25° C., 50° C., 75° C., 80° C., as high as 100° C., 125° C., 150° C., 170° C., or within any range defined between any two of the foregoing values. In some exemplary embodiments, the TIM10is baked for as little as 0.5 minutes, 1 minute, 30 minutes, 1 hour, 2 hours, as long as 8 hours, 12 hours, 24 hours, 36, hours, 48 hours, or within any range defined between any two of the foregoing values.

C. Thermal Interface Material Properties

In one exemplary embodiment, the TIM10is a compressible thermal interface material. Compressibility is measured by applying a predetermined pressure to a material and determining the change in the thickness of the material. Compressibility is typically reported as a percent of the original thickness.

In some exemplary embodiments, the TIM10is compressible while maintaining good thermal properties. In some exemplary embodiments, the use of a compressible TIM10allows an improved contact with the electronic components and heat dissipation components, such as electronic component30or heat sink32(seeFIGS. 1A-1D). In some exemplary embodiments, the use of a compressible TIM10provides a reduction in the thermal contact resistance by providing better contact between the surfaces of the electronic components and heat dissipation components, such as electronic component30or heat sink32(seeFIGS. 1A-1D). In some exemplary embodiments, the use of a compressible TIM10allows for a greater variation in the tolerance or flatness of electronic components and heat dissipation components, such as electronic component30or heat sink32(FIGS. 1A-1D). In some exemplary embodiments, the use of a compressible TIM10allows for excellent heat transfer performance, even following component distortion or warping due to elevated temperatures.

In an exemplary embodiment, compressibility is determined by positioning a 1.3 cm by 1.3 cm sample between two 1.3 cm by 1.3 cm copper plates. The original thickness of the sample is determined by subtracting the thickness of the copper plates from the original thickness of the copper-sample-copper composite. The copper-sample-copper composite is submitted to a predetermined pressure for two minutes. After two minutes, the thickness of the copper-sample-copper composite is again measured. The compressed thickness of the sample is determined by subtracting the thickness of the copper plates from the compressed thickness of the copper-sample-copper composite. Compressibility of the sample is calculated as the (original sample thickness−compressed sample thickness)/original sample thickness*100%.

In some embodiments, when subjected to a pressure of 40 psi, the TIM10has a compressibility as little as at least 5%, at least 10%, at least 15%, at least 20%, at least 30%, and as high as at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, or within any range defined between any two of the foregoing values. In some exemplary embodiments, the TIM returns to its original thickness following release of the pressure. In other exemplary embodiments, the TIM does not return to its original thickness following release of the pressure.

The degree to which the TIM10returns to its original thickness may be determined using a spring back ratio. In an exemplary embodiment, the spring back ratio is determined by applying a predetermined pressure, such as 2 psi, to a sample for a first predetermined period of time, such as ten minutes. Following the first predetermined period of time, the pressure is released, and the sample is allowed to rest for a second predetermined period of time, such as twenty minutes. The spring back ratio is determined by:
(sample thickness following second period−sample thickness following first period)/(original sample thickness−sample thickness following first period)*100%.

In some embodiments, a low spring back ratio is desired. In some embodiments, the TIM10has a spring back ratio of less than 50%, less than 40%, less than 30%, less than 25%, less than 20%, less than 10%, less than 5%, or 0, or within any range defined between any two of the foregoing values.

In some exemplary embodiments, the TIM10has a thermal impedance following conditioning at a temperature of 130° C. and a relative humidity of 85% for 96 hours that is no more than 20% greater, no more than 10% greater, no more than 5% greater, or no more than the thermal impedance of the TIM10prior to said conditioning.

In some exemplary embodiments, the Tim10has a thermal impedance following conditioning at a temperature of 150° C. for 200 hours that is no more than 20% greater, no more than 10% greater, no more than 5% greater, or no more than the thermal impedance of the TIM10prior to said conditioning.

EXAMPLES

A. Compressible Thermal Interface Materials

The Kraton L-1203 is hydrogenated polybutadiene polymer available from Kurary Co., Ltd. The TAC wax is available from The International Group, Inc. The AC-1702 is a polyethylene wax available from Honeywell International Inc. The PEW-0602F wax is a polytetrafluoroethylene-polyethylene wax mixture available from Nanjing Tianshi New Material Technologies. The LICA 38 is a coupling agent additive available from Kenrich Petrochemical. The TTS is a coupling agent additive available from Kenrich Petrochemical. The Irganox 1076 is an antioxidant additive available from BASF. The Cymel 1156 is a crosslinking agent additive available from CYTEC. The thermal conductive filler was aluminum particles having a diameter between about 0.1 microns and 50 microns.

The phase change material (AC 1702), polymer (Kraton L-1203), additives (Irganox 1076, Cymel 1156, and TTS), and thermal conductive filler (aluminum powder) were added to a reactor in the amounts listed in Table 1. The mixture was stirred under 100° C. until a uniform dispersion was formed.

Comparative example 1 was coated at 100° C. between two layers of polyethylene terephthalate (PET) film. The compressibility of comparative example 1 is presented inFIG. 3.

The polymer (Kraton L-1203), additives (Irganox 1076 and LICA 38), and thermal conductive filler (aluminum powder) were added to a reactor in the amounts listed in Table 1. The mixture was stirred under 150° C. until a uniform dispersion was formed.

Comparative example 2 was coated at 80° C. between two layers of polyethylene terephthalate (PET) film. The compressibility of comparative example 2 is presented inFIG. 4A. The thermal impedance of comparative example 2 is presented inFIG. 4B.

The thermal conductivity of comparative example 2 was determined to be 3.64 W/m-K.

Comparative example 2 was tested using a Highly Accelerated Stress Test (HAST test) in which the sample was conditioned at a temperature of 130° C. and a relative humidity of 85% for 96 hours in an environmental chamber supplied by ESPEC. The thermal impedance of the sample was determined before or after the sample conditioning. An increase of less than 20% in thermal impedance indicated a passing HAST result, while an increase of 20% or more indicated a failing HAST result.

Comparative example 2 was also tested using a baking test in which the sample was conditioned at a temperature of 150° C. for 200 hours in an environmental chamber supplied by ESPEC. The thermal impedance of the sample was determined before or after the sample conditioning. An increase of less than 20% in thermal impedance indicated a passing baking test result, while an increase of 20% or more indicated a failing baking test result.

Comparative example 2 passed the HAST test and failed the Baking test.

The phase change materials (TAC wax, PEW-0602F), polymer (Kraton L-1203), additives (Irganox 1076, and LICA 38), and thermal conductive filler (aluminum powder) were added to a reactor in the amounts listed in Table 1. The mixture was stirred under 150° C. until a uniform dispersion was formed.

Example 1 was coated at 80° C. between two layers of polyethylene terephthalate (PET) film. The compressibility of example 1 is presented inFIG. 5A. The thermal impedance of example 1 is presented inFIG. 5B.

The thermal conductivity of example 1 was determined to be 4.41 W/m-K. Example 1 passed the HAST test.

The phase change materials (TAC wax, AC 1702, PEW-0602F), polymer (Kraton L-1203), additives (Irganox 1076, Cymel 1156, LICA 38, and TTS), and thermal conductive filler (aluminum powder) were added to a reactor in the amounts listed in Table 1. The mixture was stirred under 100° C. until a uniform dispersion was formed.

Example 2 was coated at 100° C. between two layers of polyethylene terephthalate (PET) film. The compressibility of example 2 is presented inFIG. 6A. The thermal impedance of example 2 is presented inFIG. 6B.

The thermal conductivity of example 2 was determined to be 2.94 W/m-K. Example 2 failed the HAST test and Baking test.

The phase change materials (TAC wax, AC 1702, PEW-0602F), polymer (Kraton L-1203), additives (Irganox 1076, Cymel 1156, LICA 38, and TTS), and thermal conductive filler (aluminum powder) were added to a reactor in the amounts listed in Table 1. The mixture was stirred under 150° C. until a uniform dispersion was formed

Example 3 was coated at 100° C. between two layers of polyethylene terephthalate (PET) film. The compressibility of example 3 is presented inFIG. 7A. The thermal impedance of example 3 is presented inFIG. 7B.

The thermal conductivity of example 3 was determined to be 2.72 W/m-K. Example 2 passed the HAST test and failed the Baking test.

A sample of Example 2, of a GP3000S30 putty pad, available from Bergquist Company, Chanhassen, Minn., USA, and of a TFLEX360 gap pad, available from Laird Technologies, Laird PLC, London, England, United Kingdom, were each compressed at 2 psi. After 10 minutes, the compressibility was determined as a percentage of the originally thickness, and the strain was released. After 20 minutes, the spring back was determined as a percentage of the original height. The spring back ratio was determined by dividing the % spring back by the % compressibility. The results of the testing for Example 2 are shown inFIG. 8A, and for the Laird pad inFIG. 8B, and are summarized in Table 2 below.

PTM3180, 200 g bulk, available from Honeywell International Inc., was placed into a Ross mixture with an oil temperature of 100° C. for about 30 minutes. After the bulk PTM3180 melted completely, 3 g TSE3051 ST silicone gel, supplied by Momentive, was added to the mixer. The PTM3180 and silicone gel were mixed at 20 rpm for 30 minutes.

The compressibility and thermal impedance of the PTM 3180 containing the silicone gel material was compared with that of the PTM 3180. The results are presented in Table 3.

The compressibility of the composite including the gel was about 33% at 40 psi, compared to nearly 0% for the PTM3180 material. The thermal conductive and thermal impedance of the silicone gel composite were tested according to ASTMD5470 and thermal conductivity was found to be 3.16 W/mK, and the thermal impedance was found to be 0.089° C. cm2/W. As shown in Table 4, the silicone gel composite material also passed the HAST test.

C. Multilayer Thermal Interface Materials

1. Comparative Examples

The thermal impedance of a 1 mm thickness TFLEX 640 gap pad, available from Laird Technologies, Laird PLC, London, England, United Kingdom, and a 1.5 mm thickness TFLEX 380 gap pad, also available from Laird Technologies, was determined at 70° C. using a thermal impedance tester from Longwin 9091IR following ASTM D5470, the disclosures of which is hereby incorporated by reference in its entirety.

The thermal impedance of each pad is provided in Table 5.

The gap pad TFLEX 640 was selected as the matrix of the central layer TIM, and cut to a size of 25×25 mm. A 25×25 mm piece of PCM45F, available from Honeywell International Inc., Morristown N.J., was applied to each of the top and bottom sides of the TFLEX 640 pad. The thermal impedance of the multilayered TIM was determined using a thermal impedance tester following ASTM D5470.

The gap pad TFLEX 380 was selected as the matrix of the central layer TIM, and cut to a size of 25×25 mm. A 25×25 mm piece of PCM45F, available from Honeywell International Inc., Morristown N.J., was applied to each of the top and bottom sides of the TFLEX 380 pad. The thermal impedance of the multilayered TIM was determined using a thermal impedance tester following ASTM D5470.

The thermal impedance of each composite TIM is provided in Table 5.

The gap pad TFLEX 640 was selected as the matrix of the central layer TIM, and cut to a size of 25×25 mm. PCM45-SP, available from Honeywell International Inc., Morristown N.J., was printed on each of the top and bottom sides of the TFLEX 640 pad then baked at 80° C. for 30 minutes for solvent drying. The thermal impedance of the multilayered TIM was determined using a thermal impedance tester following ASTM D5470.

The thermal impedance of the composite TIM is provided in Table 5.

4. Thermal Grease Surface Layers

The gap pad TFLEX640 was selected as the matrix of the central layer TIM, and cut to a size of 25×25 mm. Thermal grease, TC5026, available from Dow Corning, Midland Mich., was printed on each of the top and bottom sides of the TFLEX 640 pad. The thermal impedance of the multilayered TIM was determined using a thermal impedance tester following ASTM D5470.

The thermal impedance of the composite TIM is provided in Table 5.

5. PTM3180 with Gel Surface Layers

The gap pad TFLEX 640 was selected as the matrix of the central layer TIM, and cut to a size of 25×25 mm. A 25×25 mm piece of PTM3180 with gel, available from Honeywell International Inc., Morristown N.J., was applied to each of the top and bottom sides of the TFLEX 640 pad. The thermal impedance of the multilayered TIM was determined using a thermal impedance tester following ASTM D5470.

The thermal impedance of the composite TIM is provided in Table 5.

The gap pad TFLEX 640 was selected as the matrix of the central layer TIM, and cut to a size of 25×25 mm. A 25×25 mm piece of PCM45F, available from Honeywell International Inc., Morristown N.J., was applied to one side of the TFLEX 640pad. A 25×25 mm piece of PTM3180, available from Honeywell International Inc., Morristown N.J., was applied to the opposite side of the TFLEX 640 pad. The thermal impedance of the multilayered TIM was determined using a thermal impedance tester following ASTM D5470.

The thermal impedance of the composite TIM is provided in Table 5.

The gap pad TFLEX 640 was selected as the matrix of the central layer TIM, and cut to a size of 25×25 mm. A 25×25 mm piece of TS27 a compressible thermal interface material comprising a polymer, a hard wax and a soft wax and a thermally conductive filler was applied to each of the top and bottom sides of the TFLEX 640 pad. The thermal impedance of the multilayered TIM was determined using a thermal impedance tester following ASTM D5470.

The thermal impedance of the composite TIM is provided in Table 5.