Thermal interface materials and methods of application

Abstract

A thermal interface material delivered as a single-component precursor mixture that reacts to form a flexible, solid material. Thermally conductive particles are dispersed in a reactive polymer matrix, resulting in a composite material with high thermal conductivity. A reaction inhibitor is provided so that the one-component system is stable for storage and handling at room temperature and curable at elevated temperatures. The uncured precursor material is easily dispensed using conventional single-component automated pumping equipment and then cured in place.

Description

[Technical Field]

[0001] The present invention relates generally to thermal interface materials, and more particularly to mechanically conformable, thermally conductive materials that may be formed in place after dispensing from a container. [Background technology]

[0002] Thermally conductive materials are widely used, for example, as interfaces between heat-generating electronic components and heat sinks, allowing the transfer of excess thermal energy from the electronic component to the thermally coupled heat sink. Many designs and materials for such thermal interfaces have been implemented, with best performance achieved when air gaps between the thermal interface material and the respective heat transfer surfaces are substantially avoided, facilitating conductive heat transfer from the electronic component to the heat sink. Therefore, it is preferable for the thermal interface material to mechanically conform to the rough and uneven heat transfer surfaces of the respective components.

[0003] Examples of suitable thermal interface materials include silicone polymers that form a matrix filled with thermally conductive particles such as aluminum oxide, aluminum nitride, and boron nitride. Thermal interface materials are typically flexible enough to conform to the irregularities of the interface surface, whether at room and / or elevated temperatures. While useful in numerous applications, conventional interface formulations still have limitations in certain situations. For example, some applications are subject to wide temperature cycles and must withstand mechanical stress and strain throughout the applicable temperature range. Industrial and automotive electronics exposed to outdoor environments require long-term reliability over a temperature range including -400°C to 200°C. These conditions can cause conventional interface materials to flow, crack, or slide off the electronic package over a lifetime of thousands of hours, thereby reducing the performance of the electronic device.

[0004] Thermal interface materials commonly used in these applications are known as "gels" and are typically non-reactive (pre-cured) silicones with low crosslink density blended with ceramic fillers. These materials have good thermal conductivity but exhibit low flow rates due to their relatively high viscosity as fully cured silicones. They also suffer from long-term reliability issues due to a lack of strength, rigidity, and adhesion to substrates within electronic packages.

[0005] One attempted solution to the shortcomings of pre-cured silicone gels is a thermally conductive liquid adhesive that bonds to substrates within electronic packages. However, the use of adhesives prevents disassembly for rework during manufacturing. Furthermore, adhesives typically exhibit relatively high modulus or hardness values, which can transfer high levels of mechanical stress and strain to sensitive electrical components.

[0006] Some thermal interface materials are dispersed in a low-viscosity condition and then cured to a high-viscosity state. While these foam-in-place materials can overcome some of the challenges of other thermal interface material formats, they still have their own limitations. Foam-in-place materials traditionally involve a two-component curable liquid reactant formulation that is dispensed in contact with each other for "in-place" curing. Two-component solutions require complex and expensive material handling and dispensing equipment. Summary of the Invention [Problem to be solved by the invention]

[0007] It is therefore an object of the present invention to provide a foam-in-place material that is dispensable from single component dispensing systems currently used in electronics manufacturing. The dispensable material is preferably stable and remains dispensable from the single component dispensing system for extended periods of time.

[0008] Another object of the present invention is to provide a thermal interface material that is dispensable from a single component dispensing system and that exhibits improved long-life durability and functionality. [Means for solving the problem]

[0009] According to the present invention, mechanically compliant solid thermal interface materials may be formed in place on electronic packages and dispensed from single component form factor dispensing systems that are widely available, cost-effective, and easily implemented into automated manufacturing processes. The resulting thermal interface materials offer an enhanced blend of strength, adhesion, conformability, and durability compared to conventional products.

[0010] One embodiment of the present invention includes a precursor mixture for forming a thermally conductive material having a thermal conductivity of at least 0.5 W / m·K. The precursor mixture includes a first reactant composition including a silicone and a second reactant composition that reacts with the first reactant composition to form a siloxane. The precursor mixture further includes a reaction inhibitor effective to slow the rate of reaction between the first reactant composition and the second reactant composition at storage temperatures below 40°C. The initial viscosity of the mixture maintained at the storage temperature increases by less than 100% over 14 days.

[0011] The second reactant composition may react with the first reactant composition to form a polydimethylsiloxane, which may include terminal vinyl groups, pendant vinyl groups, terminal silicon hydrides, or pendant silicon hydrides. The precursor mixture may also include a reaction catalyst inhibited by a reaction inhibitor. Examples of thermally conductive particles dispersed in at least one of the first reactant composition and the second reactant composition include aluminum oxide, aluminum nitride, silicon oxide, zinc oxide, and boron nitride.

[0012] A package for dispensing a curable mixture to form a thermal conductor includes a container defining a chamber in fluid communication with an orifice, the curable mixture including a first reactant composition comprising a silicone, a second reactant composition that reacts with the first reactant composition to form a siloxane, a reaction catalyst, a reaction inhibitor, and thermally conductive particles dispersed in at least one of the first reactant composition and the second reactant composition. The reaction inhibitor is preferably effective to inhibit catalytic reactions between the first reactant composition and the second reactant composition at temperatures below 40°C, and the initial viscosity of the curable mixture maintained at a storage temperature below 40°C increases by less than 100% in 14 days. The curable mixture may be dispenseable through the orifice at a flow rate of 5 to 200 g / min under a pressure of 90 psi for at least 14 days after initial combination of the curable mixture with the chamber when maintained at a storage temperature below 40°C.

[0013] A method for applying a thermal interface material to a surface includes providing a curable mixture including a first reactant composition comprising a silicone, a second reactant composition that reacts with the first reactant composition to form a siloxane, a reaction catalyst, a reaction inhibitor, and thermally conductive particles dispersed in at least one of the first reactant composition and the second reactant composition. The reaction inhibitor is effective to interact with the reaction catalyst to slow the rate of reaction between the first reactant composition and the second reactant composition. The method further includes storing the curable mixture in a container for more than 24 hours and dispensing the curable mixture from the container through an orifice onto the surface. The surface may be part of a heat-generating electronic component.

[0014] Some embodiments of the present invention include a method for applying an interface material to a thermal gap between a heat-generating electronic component and a heat dissipation member. The method comprises applying an interface material to a thermal gap between a heat-generating electronic component and a heat dissipation member at 100° C. s-1The method includes providing a curable mixture having a viscosity of less than 500 Pa·s at room temperature, storing the curable mixture in a container for greater than 24 hours, dispensing the curable mixture from the container onto at least one surface of a heat-generating electronic component and a heat-dissipating member, and heating the curable mixture to a temperature greater than 40°C for a time sufficient to form a thermal interface material solely from the curable mixture. The thermal interface material exhibits a durometer hardness of at least Shore 00=5 and a thermal conductivity of at least 0.5 W / m·K. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic diagram of a precursor mixture being dispensed from a container onto a surface. [Figure 2] FIG. 2 is a cross-sectional view of an electronic package incorporating the thermally conductive interface material of the present invention. [Figure 3] FIG. 3 is a chart plotting the flow rate of the precursor mixture over time. [Figure 4] FIG. 4 is a chart plotting durometer hardness versus mass concentration of the polymeric components of the thermal interface material of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0016] The thermally conductive interface material of the present invention comprises a highly conformal silicone polymer filled with thermally conductive particles. Generally, the silicone may be an organosiloxane having the following structural formula:

[0017] [ka]

[0018] wherein "R1" represents hydrogen, a hydroxyl group, or a methyl group, and "X1" and "X2" represent integers ranging from 1 to 1,000 and do not have to be equal. The thermally conductive interface material may be prepared as the reaction product of an organosiloxane and a chain extender / crosslinker, such as a hydride-terminated polydimethylsiloxane having the following structural formula:

[0019] [ka]

[0020] In the formula, "R2" represents either hydrogen, a methyl group, or a hydroxyl group, and "Y" represents an integer having a value from 1 to 1,000.

[0021] Generally, the thermally conductive interface material is a curable composition formed from a precursor mixture of a first reactant composition containing a silicone, a second reactant composition that reacts with the first reactant composition to form a siloxane, and a reaction catalyst. Organosiloxanes useful in the first reactant composition may contain at least two aliphatically unsaturated organic groups, such as vinyl, allyl, butenyl, hexenyl, ethenyl, and propenyl. The unsaturated functional groups may be located at terminal or pendant positions.

[0022] Exemplary first reactant compositions of the curable mixtures of the present invention include polydiorganosiloxanes, such as various vinyl- or siloxy-terminated polydimethylsiloxanes (PDMS). Examples of commercially available PDMS materials include Nusil PLY-7500, 7905, 7924, and 7925 available from Avantor; Evonik VS100, 200, 500, 10000, 20000, and 65000 available from Evonik Industries AG; and Gelest DMS-V21, V22, V41, V42, and V43 available from Gelest. The first reactant composition may include, for example, one or more polymers differing in molecular weight, viscosity, and molecular architecture.

[0023] The second reactant composition reacted with the first reactant composition may include a crosslinker for the hydrosilylation reaction. The second reactant composition may include a dihydroxyaliphatic chain extender, such as a hydride-terminated polydimethylsiloxane. The silicon-bonded hydrogen atoms may be located at terminal, pendant, or both terminal and pendant positions. The second reactant composition may include one or more organohydrogenpolysiloxanes that may differ in at least one of molecular weight, viscosity, and molecular structure. Examples of commercially available methylhydrogenpolydimethylsiloxanes useful as the second reactant composition reacted with the first reactant composition include Nusil XL-173, 176, and 177 available from Avantor, Gelest HMS-071, 082, and 991 available from Gelest, and Andisil XL-1B and 1340 available from AB Specialty Silicones.

[0024] In some embodiments, the precursor mixture for forming the thermally conductive material includes a reaction catalyst, such as a catalyst effective in hydrosilylation-curable compositions. Suitable hydrosilylation catalysts are known in the art and commercially available. Hydrosilylation catalysts may include, for example, platinum, rhodium, palladium, osmium, and their complexes and organometallic compounds. Examples of commercially available catalysts include Nusil Catalyst from Avantor, Gelest SIP6030.3 from Gelest, Evonik Catalyst 512 from Evonik Industries AG, and Sigma-Aldrich 479519.

[0025] To enhance the thermal conductivity of the thermally conductive material, the composition of the present invention may include thermally conductive particles dispersed therein. The particles may be both thermally and electrically conductive. Alternatively, the particles may be thermally conductive and electrically insulating. Examples of thermally conductive particles include aluminum oxide, silicon oxide, aluminum trihydrate, zinc oxide, graphite, magnesium oxide, aluminum nitride, boron nitride, metal particles, and combinations thereof. It is contemplated that the thermally conductive particles may be of various shapes and sizes, and particle size distributions may be used to meet the parameters of any particular application. In some embodiments, the thermally conductive particles may have an average particle size of about 0.1 to 250 micrometers and may be present in the thermally conductive material at a weight concentration of about 20 to 95%.

[0026] The thermally conductive particles may be dispersed in at least one of the first reactant composition and the second reactant composition at a loading concentration of about 20-95 wt %. Desirably, sufficient thermally conductive particles are provided so that the thermally conductive material formed from the precursor mixture exhibits a thermal conductivity of at least 0.5 W / m·K.

[0027] A reaction inhibitor effective to inhibit the reaction between the first reactant composition and the second reactant composition is preferably provided in the precursor mixture of the present invention. One embodiment of the present invention allows the precursor mixture to be stored in a container as a single form-factor preparation that is stable at room temperature for at least 14 days. For purposes of this specification, a preparation or precursor mixture that is stable at room temperature is one in which the initial viscosity of the precursor mixture maintained at a storage temperature of less than 40°C increases by less than 100% over a 14-day period. This stability of the precursor mixture allows the mixture to be packaged in a container and stored for long periods of time before distribution. Long-term stability allows the manufacturing and packaging of the thermally conductive material to be carried out at a location and / or time that is different from the location and / or time of a system, such as an electronic package assembler.

[0028] In some embodiments, the reaction inhibitor may be effective in interacting with the reaction catalyst to slow the reaction rate between the first reactant composition and the second reactant composition. Generally, the reaction inhibitor may include one or more of maleate, acetylenic alcohol, and fumarate. Examples of reaction inhibitors include dimethyl maleate, diallyl maleate, bis(methoxy-2-propyl) maleate, dibutyl maleate, dimethyl maleate, diallyl maleate, bis(1-methoxy-2-propyl) maleate, dibutyl maleate, 1-ethynyl-cyclohexanol, 2-methyl-3-butyn-2-ol, 3,7,11-trimethyl-1-dodecyn-3-ol, 3,5-dimethyl -1-Hexyn-3-ol, 1-ethynyl-1-cyclopentanol, 3-methyl-1-dodecyn-3-ol, 4-ethyl-1-octyn-3-ol, 1,1-diphenyl-2-propyn-1-ol, 2,3,6,7-tetramethyl-4-octyn-3,6-diol, 3,6-diethyl-1-nonyn-3-ol, 3-methyl-1-pentadecin-3-ol, 2,5-dimethyl-3-hexyn-2,5 -diol, 2,7-dimethyl-3,5-octadiyne-2,7-diol, 3-methyl-1-pentyn-3-ol, 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 1,4-bis(1'-hydroxycyclohexyl)-1,3-butadiyne, 3,4-dimethyl-1-pentyne-3,4-diol, 1-(1-butynyl)cyclopentanol, 2,5-dimethyl-5-hexen-3-yn-2-ol ol, 5-dimethylamino-2-methyl-3-pentyl-2-ol, 3,6-dimethyl-6-hepten-4-yn-3-ol, 3-methyl-1-octyn-3-ol, 3,4,4-trimethyl-1-pentyn-3-ol, 3-isobutyl-5-methyl-1-hexyn-3-ol, 2,5,8-trimethyl-1-nonen-3-yn-5-ol, and 1-(1-propynyl)cyclohexanol.

[0029] It is contemplated that the compositions of the present invention may optionally include a variety of other ingredients, such as adhesion promoters, surfactants, stabilizers, fillers, and combinations thereof.

[0030] The precursor mixtures of the present invention are preferably stable at room temperature and react at elevated temperatures, such as above 40°C, to harden into a solid form-in-place interface. The rate of this reaction can be controlled by the concentration of reactive functional groups, catalysts, and reaction inhibitors. The rheology of the dispersion may be further controlled by the size, shape, and loading concentration of the thermally conductive particles dispersed therein.

[0031] FIG. 1 illustrates an exemplary application of the present invention in which a curable mixture 10 is contained within a container 12 having an orifice 14 through which the curable mixture may be dispensed. In the illustrated embodiment, the curable mixture 10 is dispensed onto a surface 22 of a component 20. As known in the art, one or both of the container 12 and the component 20 may be moved relative to one another along directional arrows 8 to apply the curable mixture 10 to the surface 22 as needed. The component 20 may be, for example, a heat-generating electronic component or a heat-dissipating component. FIG. 2 illustrates the curable mixture 10 disposed between a heat-generating electronic component 30 and a heat-dissipating component 40. The curable mixture 10 may be heated to above 40° C. for a time sufficient to form a thermal interface material from the curable mixture 10 alone. "In-situ" heating of the curable mixture may be accomplished by known heating means, such as a heat oven. [Example]

[0032] Table 1 below shows examples of precursor mixtures.

[0033] [Table 1]

[0034] The precursor mixture exhibits a controlled reaction rate, indicated by a small change in the material's viscosity at room temperature over a long working time of at least 14 days. Figure 3 plots the flow rate of the precursor mixture through a 2 mm orifice at 25°C and 90 psi pressure over time. This allows for automated processing with tight control over dispensing volume and pattern. The long working time also allows for flexibility in the handling, transportation, and assembly processes of electrical components.

[0035] The final cured thermal interface material exhibits a flexible, engineered hardness with good adhesion to common metal and plastic substrates found in electronic devices. Figure 4 illustrates how various hardness levels can be tailored and controlled through the reactivity and concentration of the first and second reactant compositions. The flexibility of the thermal interface material allows the material to flex and resist cracking when the device undergoes thermal cycling during operation. Table 2 below shows the physical property parameters of the precursor mixture and the hardness of the cured thermally conductive material.

[0036] [Table 2]

[0037] The present invention has been described in considerable detail herein in order to comply with the patent statutes and to provide those skilled in the art with the information necessary to apply the novel principles and to make and use embodiments of the invention as appropriate. However, it should be understood that various modifications can be made without departing from the scope of the invention itself. [Explanation of symbols]

[0038] 8-way arrow 10 Curable mixture 12 containers 14 Orifice 20 Components 22 Surface 30 Heat-generating electronic components 40 Heat dissipation material

Claims

1. A precursor mixture for forming a thermally conductive material having a thermal conductivity of at least 0.5 W / m·K, A first reaction composition comprising 5 to 15% by weight of an organosiloxane having at least two aliphatic unsaturated organic groups, Second reaction composition containing organohydrogenpolysiloxane: 1 to 5% by weight, Reaction catalyst less than 0.1% by weight, Less than 0.1% by weight of a reaction inhibitor selected from the group consisting of maleate esters and fumarate esters, and 50 to less than 94% by weight of thermally conductive particles dispersed in at least one of the first reactant composition and the second reactant composition, Includes, The total content of all components in the aforementioned precursor mixture is 100% by weight. The initial viscosity of the precursor mixture is 100 s at 25°C. －１ 50 to 500 Pa·s, or 1.0 s at 25°C －１ The pressure ranges from 100 to 3,500 Pa·s. A precursor mixture in which the initial viscosity of the precursor mixture, maintained at a storage temperature of 25°C, increases by less than 100% in 14 days.

2. The precursor mixture according to claim 1, wherein the reaction catalyst is selected from the group consisting of platinum, rhodium, palladium, osmium, and their complexes and organometallic compounds.

3. The precursor mixture according to claim 1, wherein the reaction inhibitor is dimethyl maleate.

4. The precursor mixture according to claim 1, which is thixotropic.

5. The precursor mixture according to claim 1, wherein the thermally conductive material is curable from the precursor mixture and exhibits a curing durometer between Shore 00=5 and Shore 00=90 at 25°C.

6. The precursor mixture according to claim 1, wherein the thermally conductive particles include one or more of aluminum oxide, aluminum nitride, silicon oxide, zinc oxide, and boron nitride.

7. A package for distributing a curable mixture to form a heat conductor, comprising a container defining an orifice and a chamber that has fluid contact with it, The curable mixture is placed inside the chamber, The curable mixture is A first reaction composition comprising 5 to 15% by weight of an organosiloxane having at least two aliphatic unsaturated organic groups, Second reaction composition containing organohydrogenpolysiloxane: 1 to 5% by weight, Reaction catalyst less than 0.1% by weight, Less than 0.1% by weight of a reaction inhibitor selected from the group consisting of maleate esters and fumarate esters, and The first reactant composition and the second reactant composition contain 50 to less than 94% by weight of thermally conductive particles dispersed in at least one of them. The total content of all components in the curable mixture is 100% by weight. The initial viscosity of the curable mixture is 100 s at 25°C. －１ 50 to 500 Pa·s, or 1.0 s at 25°C －１ The pressure ranges from 100 to 3,500 Pa·s. The initial viscosity of the curable mixture, maintained at a storage temperature of 25°C, increases by less than 100% in 14 days, according to the package.

8. The package according to claim 7, wherein the thermal conductor exhibits a thermal conductivity of at least 0.5 W / m·K.

9. The package according to claim 7, wherein the curable mixture is curable to a durometer hardness between Shore 00=5 and Shore 00=90.

10. The package according to claim 7, wherein the curable mixture can be initially combined in the chamber when it has been maintained at a storage temperature below 40°C, and then dispensed from an orifice at a flow rate of 5 to 200 g / min under a pressure of 90 Psi for at least 14 days.

11. The package according to claim 10, wherein the diameter of the orifice is 2 mm or less.

12. A method for applying a thermal interface material to a surface, (a) To provide a curable mixture containing the following, (i) 5 to 15% by weight of the first reaction composition comprising an organosiloxane having at least two aliphatic unsaturated organic groups, (ii) 1 to 5% by weight of the second reaction product composition containing organohydrogenpolysiloxane (iii) Reaction catalyst less than 0.1% by weight, (iv) Less than 0.1% by weight of a reaction inhibitor selected from the group consisting of maleate esters and fumarate esters, (v) 50 to less than 94% by weight of thermally conductive particles dispersed in at least one of the first reactant composition and the second reactant composition, The total content of all components in the curable mixture is 100% by weight. (b) storing the curable mixture in a container for more than 24 hours, (c) Distributing the curable mixture from the container through the orifice onto the surface, Methods that include...

13. The method according to claim 12, further comprising heating the curable mixture to over 40°C for a time sufficient to cure the curable mixture, following the distribution.

14. The method according to claim 12, wherein the thermal interface material exhibits a thermal conductivity of at least 0.5 W / m·K.

15. The method according to claim 12, wherein the surface is part of a heat-generating electronic component.

16. The method according to claim 15, comprising distributing the curable mixture between the surface and the heat dissipation member.

17. The method according to claim 12, wherein the diameter of the orifice is 2 mm or less.

18. A method for applying a thermal interface material to a surface in order to fill the thermal gap between a heat-generating electronic component and a heat-dissipating member, wherein the method is: (a) 100 s at 25°C －１ To provide a curable mixture having a viscosity of less than 500 Pa·s, The curable mixture is A first reaction composition comprising 5 to 15% by weight of an organosiloxane having at least two aliphatic unsaturated organic groups, Second reaction composition containing organohydrogenpolysiloxane: 1 to 5% by weight, Reaction catalyst less than 0.1% by weight, Less than 0.1% by weight of a reaction inhibitor selected from the group consisting of maleate esters and fumarate esters, and The first reactant composition and the second reactant composition contain 50 to less than 94% by weight of thermally conductive particles dispersed in at least one of them. The total content of all components in the curable mixture is 100% by weight. (b) Storing the curable mixture in a container for more than 24 hours. (c) Distributing the curable mixture from the container to at least one surface of the heat-generating electronic component and the heat dissipation member, (d) Heat the curable mixture to a temperature above 40°C for a sufficient time to form a thermal interface material from the curable mixture alone. Includes, The thermal interface material exhibits a durometer hardness of at least 5 Shore 00 and a thermal conductivity of at least 0.5 W / m·K.

19. The method according to claim 18, comprising storing the curable mixture in a container at a temperature below 40°C.

20. The method according to claim 18, further comprising sandwiching the thermal interface material between the heat-generating electronic component and the heat-dissipating member.

21. The method according to claim 20, wherein the thermal interface material is in physical contact with the heat-generating electronic component and the heat dissipation member, respectively.

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