Thermal interface material and application method

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 generally relates to thermal interface materials, and more specifically to mechanically conformable thermal conductive materials that may be formed at a predetermined location after dispensing from a container.

Background Art

[0002] Thermal conductive materials are widely used, for example, as interfaces between heat-generating electronic components and heat sinks, enabling the transfer of excess thermal energy from the electronic components to the thermally coupled heat sink. Many designs and materials for such thermal interfaces have been implemented, and an air gap between the thermal interface material and each heat transfer surface is substantially avoided, achieving optimal performance when promoting conductive heat transfer from the electronic component to the heat sink. Therefore, the thermal interface material preferably mechanically conforms to the rough and non-flat heat transfer surfaces of each component.

[0003] Examples of conforming 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 typically have sufficient flexibility to conform to irregularities in the interface surface, whether at room temperature and / or high temperature. Conventional interface formulations are useful in numerous applications, but still have limitations in certain situations. For example, some applications are exposed to wide temperature cycles and need to withstand mechanical stresses and strains throughout the applicable temperature range. Industrial and automotive electronic devices exposed to outdoor environments require long-term reliability over a temperature range including -400°C to 200°C. These conditions cause conventional interface materials to flow out of the electronic package, crack, and slip off over a lifespan of thousands of hours, thereby resulting in a degradation of 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 crosslinking density blended with ceramic power fillers. While these materials have good thermal conductivity, they exhibit low flow rates due to their relatively high viscosity as fully cured silicones. They also have problems with long-term reliability due to a lack of strength, rigidity, and adhesion to substrates within electronic packages.

[0005] One solution attempted to address the shortcomings of pre-cured silicone gel is the use of a thermally conductive liquid adhesive to bond to the substrate within the electronic package. However, the use of adhesives prevents decomposition for rework during manufacturing. Furthermore, adhesives generally exhibit relatively high modulus or high hardness values, which can transmit high levels of mechanical stress and strain to delicate electrical components.

[0006] Some thermal interface materials are dispersed under low viscosity conditions and then cured to a high viscosity state. While these form-in-place materials can overcome some of the challenges of other thermal interface material types, they still have their own limitations. Form-in-place materials traditionally consist of two-component curable liquid reactant formulations that are dispensed in contact with each other for "in-situ" curing. Two-component solutions require complex and expensive material handling and dispensing equipment. [Overview of the project] [Problems that the invention aims to solve]

[0007] Therefore, an object of the present invention is to provide an in-place foam material that can be dispensed from a single-component dispensing system currently used in the manufacture of electronic devices. The dispenseable material is preferably stable and remains dispenseable from a single-component dispensing system over a long period of time.

[0008] Another object of the present invention is to provide a thermal interface material that can be dispensed from a single-component distribution system and exhibits improved lifespan and functionality. [Means for solving the problem]

[0009] The present invention allows for the formation of a mechanically adaptable solid thermal interface material at a predetermined location on an electronic package and its distribution from a single-component form-factor dispensing system. These dispensing systems are widely available, cost-effective, and easily implementable in automated manufacturing processes. The resulting thermal interface material provides a blend with enhanced strength, adhesion, fit, 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 containing 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 in slowing the reaction rate between the first reactant composition and the second reactant composition at a storage temperature of less than 40°C. The initial viscosity of the mixture, maintained at the storage temperature, increases by less than 100% in 14 days.

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

[0012] A package for distributing a curable mixture to form a thermal conductor includes a container defining an orifice and a chamber in fluid contact, the curable mixture comprising a first reactant composition containing silicone, a second reactant composition reacting with the first reactant composition to form a siloxane, a reaction catalyst, a reaction inhibitor, and thermal conductive particles dispersed in at least one of the first and second reactant compositions. The reaction inhibitor is preferably effective in inhibiting the catalytic reaction between the first and second reactant compositions 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. When maintained at a storage temperature below 40°C, the curable mixture may be distributable 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 the initial combination of the curable mixture into the chamber.

[0013] A method for applying a thermal interface material to a surface includes providing a curable mixture comprising a first reactant composition containing 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 and second reactant compositions. The reaction inhibitor is effective in interacting with the reaction catalyst to slow the reaction rate between the first and second reactant compositions. The method further includes storing the curable mixture in a container for more than 24 hours and distributing the curable mixture from the container to the surface through an orifice. 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-dissipating member. This method is performed at 25°C. s-1The method includes providing a curable mixture having a viscosity of less than 500 Pa·s, storing the curable mixture in a container for more than 24 hours, distributing the curable mixture from the container to at least one surface of a heat-generating electronic component and a heat-dissipating member, and heating the curable mixture to a temperature above 40°C for a sufficient time to form a thermal interface material from the curable mixture alone. 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 drawing]

[0015] [Figure 1] Figure 1 is a schematic diagram of the precursor mixture being distributed from the container onto the surface. [Figure 2] Figure 2 is a cross-sectional view of an electronic package incorporating the thermally conductive interface material of the present invention. [Figure 3] Figure 3 is a chart plotting the flow rate of the precursor mixture over time. [Figure 4] Figure 4 is a chart plotting the durometer hardness against the mass concentration of the polymer component of the thermal interface material of the present invention. [Modes for carrying out the invention]

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

[0017] [ka]

[0018] In the formula, "R1" represents hydrogen, a hydroxyl group, or a methyl group, and "X1" and "X2" represent integers in the range of 1 to 1,000, and they may not be equal. The thermally conductive interface material may be prepared as a reaction product of an organosiloxane and a chain extender / crosslinking agent such as a hydride-terminated polydimethylsiloxane having the following structural formula.

[0019] [Chemical formula]

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

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

[0022] Exemplary first reactant compositions of the curable mixture 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 one or more polymers having different molecular weights, viscosities, and molecular structures, for example.

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

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

[0025] To enhance the thermal conductivity of a thermally conductive material, the composition of the present invention may contain thermally conductive particles dispersed therein. The particles may be both thermally conductive and electrically conductive. Alternatively, the particles may be both 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. The thermally conductive particles may have various shapes and sizes, and it is thought that a particle size distribution may be used to suit 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 approximately 20-95% by weight. It is desirable that 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] Preferably, a reaction inhibitor effective in inhibiting the reaction between the first reactant composition and the second reactant composition is provided in the precursor mixture of the present invention. One aspect 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 the 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 below 40°C, increases by less than 100% over 14 days. This stability of the precursor mixture allows the mixture to be packaged in a container and stored for a long period before distribution. Long-term stability makes it possible to manufacture and package thermally conductive materials at a location and / or time 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 is one or more maleic acids. ester acetylene alcohol and fumaric acid ester It may contain the following. 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-ethinylcyclohexanol, 2-methyl-3-butyne-2-ol, 3,7,11-trimethyl-1-dodecine-3-ol, and 3,5-dimethyl -1-hexyn-3-ol, 1-ethynyl-1-cyclopentanol, 3-methyl-1-dodecine-3-ol, 4-ethyl-1-octin-3-ol, 1,1-diphenyl-2-propyne-1-ol, 2,3,6,7-tetramethyl-4-octin-3,6-diol, 3,6-diethyl-1-nonin-3-ol, 3-methyl-1-pentadecin-3-ol, 2,5-dimethyl-3-hexyn-2,5 -diol, 2,7-dimethyl-3,5-octadiin-2,7-diol, 3-methyl-1-pentin-3-ol, 2,4,7,9-tetramethyl-5-decine-4,7-diol, 1,4-bis(1'-hydroxycyclohexyl)-1,3-butadiine, 3,4-dimethyl-1-pentin-3,4-diol, 1-(1-butynyl)cyclopentanol, 2,5-dimethyl-5-hexen-3-in-2-ol Examples include 5-dimethylamino-2-methyl-3-pentyl-2-ol, 3,6-dimethyl-6-hepten-4-in-3-ol, 3-methyl-1-octin-3-ol, 3,4,4-trimethyl-1-pentin-3-ol, 3-isobutyl-5-methyl-1-hexyn-3-ol, 2,5,8-trimethyl-1-nonen-3-in-5-ol, and 1-(1-propynyl)cyclohexanol.

[0029] The compositions of the present invention may optionally include various other components such as adhesion promoters, surfactants, stabilizers, fillers, and combinations thereof.

[0030] The precursor mixture of the present invention is preferably stable at room temperature and reacts at high temperatures, such as above 40°C, to cure into a solid as a form-in-place interface. The rate of this reaction can be controlled by the concentrations of the reactive functional group, catalyst, and reaction inhibitor. The rheology of the dispersion may be further controlled by the size, shape, and loading concentration of the thermally conductive particles dispersed therein.

[0031] Figure 1 shows an exemplary application of the present invention in which the curable mixture 10 is contained in a container 12 having an orifice 14 into which the curable mixture may be distributed. In the illustrated embodiment, the curable mixture 10 is distributed onto the surface 22 of a member 20. As is known in the art, one or both of the container 12 and the member 20 may be moved relative to each other along the directional arrow 8 to apply the curable mixture 10 to the surface 22 as needed. The member 20 may be, for example, a heat-generating electronic component or a heat-dissipating member. Figure 2 shows the curable mixture 10 placed between a heat-generating electronic component 30 and a heat-dissipating member 40. The curable mixture 10 may be heated 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 carried out by known heating means such as a heat oven. [Examples]

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

[0033] [Table 1]

[0034] The precursor mixture exhibits a suppressed reaction rate, indicated by a small change in the viscosity of the material 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 over time under a pressure of 90 Psi at 25°C. This enables automated processing with tightly controlled dispensing volume and pattern. The long working time also provides flexibility in the handling, transportation, and assembly processes of the electrical components.

[0035] The final cured thermal interface material exhibits a flexible hardness, providing good adhesion to common metal and plastic substrates found in electronic devices. Figure 4 illustrates how to adjust and control various hardness levels by varying the reactivity and concentration of the first and second reactant compositions. The flexibility of the thermal interface material allows it to bend and withstand cracking as the device undergoes thermal cycling during operation. Table 2 shows the physical property parameters of the precursor mixture and the hardness of the cured thermal conductive material.

[0036] [Table 2]

[0037] This invention is described herein in considerable detail in accordance with patent law, to provide those skilled in the art with the information necessary to apply the novel principle and, as necessary, to construct and use embodiments of the invention. However, it should be understood that various modifications can be achieved 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 components

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 dissipation 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.

Images