HK1139968A - Silicone adhesive composition and method for preparing the same - Google Patents

Description

Silicone adhesive composition and method for preparing the same

Cross Reference to Related Applications

This application claims priority to U.S. provisional patent application serial No. 60/783,738, filed on 30.3.2006, which is incorporated herein by reference in its entirety.

Technical Field

The present invention relates to silicone adhesive compositions, and more particularly to silicone thermal interface materials.

Background

Many electrical components generate heat during operation. As electronic devices become more dense and more highly integrated, heat flux increases exponentially. Devices also need to operate at lower temperatures for performance and reliability considerations. The temperature difference between the heat generating portion of the device and the ambient temperature is reduced, which reduces the thermodynamic driving force for heat removal. The increased heat flux and reduced thermodynamic driving force require increasingly complex thermal processing techniques to facilitate heat removal during operation.

Thermal management techniques typically involve the use of some form of heat dissipation element to transfer heat away from high temperature regions in the electrical system. A heat-dissipating component is a structural member formed of a high thermal conductivity material that is mechanically attached to a heat-generating component to aid in heat removal. Heat flows from the heat generating elements into the heat dissipating elements through the mechanical interfaces between the elements.

In a typical electronics package, the heat-dissipating element is mechanically connected to the heat-generating component during operation by placing the planar surface of the heat-dissipating element against the planar surface of the heat-generating component and securing the heat-dissipating element in place using an adhesive or fasteners. There may be an air gap between the surface of the heat-dissipating element and the surface of the heat-generating component, which reduces the ability to transfer heat through the interface between the surfaces. To address this problem, a layer of thermal interface material is placed between the heat transfer surfaces to reduce the thermal resistance between the surfaces. Thermal interface materials are typically filled polymeric systems, such as one-part curable silicone adhesives.

U.S. patent No.5,021,494 to Toya discloses a filled thermally conductive silicone composition. The composition was cured at 150 ℃ for 1 hour.

U.S. patent application publication No.2005/0049350 discloses a filled silicone thermal interface material composition. The composition was cured at 150 ℃ for 2 hours.

There is a need for silicone thermal interface materials with shorter cure times and lower cure temperatures, as well as high adhesion.

Summary of The Invention

In one embodiment, a thermal interface composition includes a blend of a polymer matrix and a thermally conductive filler comprising particles having a maximum particle diameter of no greater than about 25 microns, the polymer matrix comprising an organopolysiloxane having at least two silicon-bonded alkenyl groups per molecule, an organohydrogenpolysiloxane (organohydrogenpolysiloxane) having at least two silicon-bonded hydrogen atoms per molecule, and a hydrosilylation catalyst comprising a transition metal, wherein the transition metal is present in an amount of about 10 to about 20ppm based on the weight of the non-filler components and the molar ratio of silicon-bonded hydrogen atoms to silicon-bonded alkenyl groups is about 1 to about 2.

In one embodiment, a method of making a thermal interface composition includes blending a polymer matrix comprising an organopolysiloxane having at least two silicon-bonded alkenyl groups per molecule, an organohydrogenpolysiloxane having at least two silicon-bonded hydrogen atoms per molecule, and a hydrosilylation catalyst comprising a transition metal, and a thermally conductive filler comprising particles having a maximum particle diameter of no greater than about 25 microns, wherein the transition metal is present in an amount of from about 10 to about 20ppm based on the weight of non-filler components, and the molar ratio of silicon-bonded hydrogen atoms to silicon-bonded alkenyl groups is from about 1 to about 2.

In another embodiment, a one-part, thermally-curable composition includes a blend of a polymer matrix and a thermally-conductive filler comprising particles having a maximum particle diameter of no greater than about 25 microns, the polymer matrix comprising an organopolysiloxane having at least two silicon-bonded alkenyl groups per molecule, an organohydrogenpolysiloxane having at least two silicon-bonded hydrogen atoms per molecule, and a hydrosilylation catalyst comprising a transition metal, wherein the transition metal is present in an amount of from about 10 to about 20ppm based on the weight of the non-filler components and the molar ratio of the silicon-bonded hydrogen atoms to the silicon-bonded alkenyl groups is from about 1 to about 2.

In another embodiment, a method of making a two-part thermal interface composition comprises mixing part a and part B in a weight ratio of about 1: 1 to form a composition, wherein the composition comprises a polymer matrix comprising an organopolysiloxane having at least two silicon-bonded alkenyl groups per molecule, an organohydrogenpolysiloxane having at least two silicon-bonded hydrogen atoms per molecule, and a hydrosilylation catalyst comprising a transition metal, and a thermally conductive filler comprising particles having a maximum particle size of no greater than about 25 microns, wherein the transition metal is present in an amount of about 10 to about 20ppm based on the weight of the non-filler components, and the molar ratio of silicon-bonded hydrogen atoms to silicon-bonded alkenyl groups is about 1 to about 2.

Various embodiments provide thermal interface compositions having faster cure rates, lower cure temperatures, and good adhesion.

Brief Description of Drawings

FIG. 1 is a DMA comparison of the G' G "crossover temperature (crossover) for the formulation of example 1 for comparative example 2.

FIG. 2 is a graph comparing DMA cure times at 150 ℃.

FIG. 3 is a graph comparing DMA cure times at 80 ℃.

FIG. 4 is a graph showing bond strength as a function of cure temperature.

Detailed Description

The singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. The endpoints of all ranges reciting the same characteristic are independently combinable and inclusive of the recited endpoint. All references are incorporated herein by reference.

The modifier "about" used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., includes the tolerance ranges associated with measurement of the particular quantity).

"optional" or "optionally" means that the subsequently described circumstance or circumstance may or may not occur, or that the subsequently described material may or may not be present, and that the description includes instances where the circumstance or circumstance occurs or where the material is present, and instances where the circumstance or circumstance does not occur or the material is not present.

In one embodiment, a thermal interface composition includes a blend of a polymer matrix and a thermally conductive filler comprising particles having a maximum particle size of no greater than about 25 microns, the polymer matrix comprising an organopolysiloxane having at least two silicon-bonded alkenyl groups per molecule, an organohydrogenpolysiloxane having at least two silicon-bonded hydrogen atoms per molecule, and a hydrosilylation catalyst comprising a transition metal, wherein the transition metal is present in an amount of from about 10 to about 20ppm based on the weight of the non-filler components and the molar ratio of silicon-bonded hydrogen atoms to silicon-bonded alkenyl groups is from about 1 to about 2.

The polymer matrix comprises an organopolysiloxane having at least two silicon-bonded alkenyl groups per molecule, an organohydrogenpolysiloxane having at least two silicon-bonded hydrogen atoms per molecule, and a hydrosilylation catalyst. The organopolysiloxanes can be linear, branched, hyperbranched, dendritic or cyclic. In one embodiment, the organopolysiloxane is linear.

The organopolysiloxane has at least two alkenyl groups bonded to a silicon atom per molecule. Alkenyl groups attached to the silicon atom include, but are not limited to: vinyl, allyl, butenyl, pentenyl, hexenyl, and heptenyl. In one embodiment, the alkenyl group is vinyl.

In addition to alkenyl groups, the organopolysiloxanes may have further organic groups bonded to silicon atoms. Other organic groups include, but are not limited to: alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl and heptyl, aryl groups such as phenyl, tolyl, xylyl and naphthyl, aralkyl groups such as benzyl and phenethyl, and halogenated alkyl groups such as chloromethyl, 3-chloropropyl and 3, 3, 3-trifluoropropyl. In one embodiment, the organopolysiloxane comprises methyl groups.

The silicon-bonded alkenyl groups in the polyorganosiloxanes can be located at the ends of the molecular chain and elsewhere, for example, pendant to the molecular chain or along the backbone of the molecular chain. In one embodiment, at least one terminus of each molecule comprises an alkenyl group.

In one embodiment, the organopolysiloxane is a methylvinylpolysiloxane capped at both ends of the molecular chain with trimethylsiloxy groups (trimethylsiloxy groups) or dimethylvinylsiloxane groups, or a dimethylpolysiloxane capped at both ends of the molecular chain with dimethylvinylsiloxane groups.

The organopolysiloxane may include: comprising a compound having the formula R¹ ₃SiO_1/2Siloxane units of the formula R¹ ₂R²SiO_1/2Siloxane units of the formula R¹ ₂SiO_2/2Siloxane units of the formula_4/2A copolymer of siloxane units of (a); comprising a compound having the formula R¹ ₂R²SiO_1/2Siloxane units of the formula R¹ ₂SiO_2/2Siloxane units of the formula_4/2A copolymer of siloxane units of (a); comprises a compound ofR¹R²SiO_2/2Siloxane units of the formula R¹SiO_3/2And siloxane units of the formula R²SiO_3/2A copolymer of siloxane units of (a); or a mixture of two or more of these organopolysiloxanes. In the above formulae, R¹Is a monovalent hydrocarbon group other than an alkenyl group and may be an alkyl group such as a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group or a heptyl group, an aryl group such as a phenyl group, a tolyl group, a xylyl group or a naphthyl group, an aralkyl group such as a phenethyl group or a halogenated alkyl group such as a chloromethyl group, 3-chloropropyl group or 3, 3, 3-trifluoropropyl group. In the above formulae, R²Is an alkenyl group, such as vinyl, allyl, butenyl, pentenyl, hexenyl, or heptenyl.

In one embodiment, the organopolysiloxane may comprise: a copolymer of methylvinylsiloxane and dimethylsiloxane blocked at the two ends of the molecular chain by trimethylsiloxy groups; copolymers of methylvinylsiloxane, methylphenylsiloxane and dimethylsiloxane blocked at the two ends of the molecular chain by trimethylsiloxy groups; copolymers of methylvinylsiloxane and dimethylsiloxane capped with dimethylvinylsiloxane groups at both ends of the molecular chain; copolymers of methylvinylsiloxane, methylphenylsiloxane and dimethylsiloxane terminated by dimethylvinylsiloxane groups at the two ends of the molecular chain.

There is no limitation on the viscosity of the organopolysiloxane. In one embodiment, the organopolysiloxane has a viscosity of from about 10 to about 500,000 centipoise as measured in pure form (neat) at 25 ℃ using a Brookfield type viscometer. In another embodiment, the organopolysiloxane has a viscosity of about 50 to about 5,000 centipoise as measured in neat form at 25 ℃ using a Brookfield type viscometer.

The organohydrogenpolysiloxane acts as a crosslinker and has an average of at least two hydrogen atoms bonded to silicon atoms per molecule. The organohydrogenpolysiloxane may be linear, branched, hyperbranched, dendritic or cyclic. In one embodiment, the organohydrogenpolysiloxane is linear.

In addition to hydrogen atoms, the organohydrogenpolysiloxane may have other organic groups attached to silicon atoms. Other organic groups include, but are not limited to: alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl and heptyl, aryl groups such as phenyl, tolyl, xylyl and naphthyl, aralkyl groups such as phenethyl, or halogenated alkyl groups such as chloromethyl, 3-chloropropyl or 3, 3, 3-trifluoropropyl. In one embodiment, the organohydrogenpolysiloxane comprises methyl groups.

The hydrogen atoms in the organohydrogenpolysiloxane may be located at the ends of the molecular chain and at other positions, such as side chains of the molecular chain or along the main chain of the polymer chain. In one embodiment, the hydrogen atoms are disposed along the backbone of the polymer chain. In another embodiment, the hydrogen atoms are at the ends of the molecular chain. In another embodiment, the hydrogen atoms are disposed at the ends of the polymer chain and along the backbone of the polymer chain.

In one embodiment, the organohydrogenpolysiloxane is methylhydrogenpolysiloxane capped with trimethylsiloxy groups at both ends of the molecular chain, dimethylpolysiloxane capped with dimethylhydrogensiloxy groups at both ends of the molecular chain, dimethylpolysiloxane capped with methylhydrogensiloxy groups at both ends of the molecular chain, and methylphenylpolysiloxane capped with dimethylhydrogensiloxy groups at both ends of the molecular chain.

The organohydrogenpolysiloxane may include: comprising a compound having the formula R¹ ₃SiO_1/2Siloxane units of the formula R¹ ₂HSiO_1/2Siloxane units of the formula_4/2A copolymer of siloxane units of (a); comprising a compound having the formula R¹ ₂HSiO_1/2Siloxane units of the formula_4/2A copolymer of siloxane units of (a); comprising a compound having the formula R¹HSiO_2/2Siloxane units of the formula R¹SiO_3/2Siloxane units of the formula HSiO_3/2A copolymer of siloxane units of (a) comprisingHaving the formula R¹HSiO_2/2Siloxane units of the formula R¹ ₂SiO_2/2And siloxane units of the formula R¹ ₂HSiO_1/2Or a mixture of two or more of these copolymers. In the above formulae, R¹Is a monovalent hydrocarbon group other than an alkenyl group and is an alkyl group such as a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group or a heptyl group, an aryl group such as a phenyl group, a tolyl group, a xylyl group or a naphthyl group, an aralkyl group such as a benzyl group or a phenethyl group, or a halogenated alkyl group such as a chloromethyl group, a 3-chloropropyl group or a 3, 3, 3-trifluoropropyl group.

In one embodiment, the organohydrogenpolysiloxane may include: a copolymer of methylhydrogensiloxane and dimethylsiloxane terminated with trimethylsiloxy groups at both ends of the molecular chain, a copolymer of methylhydrogensiloxane, methylphenylsiloxane and dimethylsiloxane terminated with trimethylsiloxy groups at both ends of the molecular chain, a copolymer of methylhydrogensiloxane and dimethylsiloxane terminated with dimethylhydrogensiloxyalkyl groups at both ends of the molecular chain, and a copolymer of methylphenylsiloxane and dimethylsiloxane terminated with dimethylhydrogensiloxyalkyl groups at both ends of the molecular chain.

There is no limitation on the viscosity of the organohydrogenpolysiloxane. In one embodiment, the organohydrogenpolysiloxane has a viscosity of about 1 to about 500,000 centipoise as measured in neat form at 25 ℃ using a Brookfield type viscometer. In another embodiment, the organohydrogenpolysiloxane has a viscosity of about 5 to about 5,000 centipoise as measured in neat form at 25 ℃ using a Brookfield type viscometer.

The molar ratio of hydrogen atoms bonded to silicon atoms in the organohydrogenpolysiloxane to alkenyl groups in the organopolysiloxane is from about 1 to about 2. In another embodiment, the molar ratio is from about 1.3 to about 1.6. In another embodiment, the molar ratio is from about 1.4 to about 1.5.

The organohydrogenpolysiloxane may be about 0.1 to about 50 parts by weight per 100 parts by weight of organopolysiloxane. In another embodiment, the amount is from about 0.1 to about 10 parts by weight per 100 parts by weight of organopolysiloxane.

The hydrosilylation catalyst comprises a transition metal. In one embodiment, the transition metal is any compound comprising a group 8-10 transition metal, such as ruthenium, rhodium, platinum, and palladium. In one embodiment, the transition metal is platinum. The platinum may be in the form of a complex, such as fine platinum powder, platinum black, platinum adsorbed on a solid support such as alumina, silica or activated carbon, chloroplatinic acid, platinum tetrachloride, a platinum compound complexed with an olefin or an alkenylsiloxane such as divinyltetramethyldisiloxane or tetramethyltetravinylcyclotetrasiloxane (complex).

The transition metal is present in an amount of about 10 to about 20ppm by weight based on the total weight of the non-filler components. In another embodiment, the transition metal is present in an amount of about 12 to about 19ppm based on the total weight of the non-filler components. In another embodiment, the transition metal is present in an amount of about 14 to about 17ppm based on the total weight of the non-filler components.

In one embodiment, the polymer matrix may comprise an adhesion promoter. Adhesion promoters include alkoxy or aryloxy silanes, e.g., gamma-aminopropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, bis (trimethoxysilylpropyl) fumarate, or tetracyclosiloxanes modified with acryloxytrimethoxysilyl or methacryloxypropyltrimethoxysilyl functionality, oligosiloxanes comprising alkoxysilyl functionality, oligosiloxanes comprising aryloxysilyl functionality, polysiloxanes comprising alkoxysilyl functionality, polysiloxanes comprising aryloxysilyl functionality, cyclosiloxanes comprising alkoxysilyl and Si-H functionality, cyclosiloxanes comprising aryloxysilyl functionality, titanates, trialkoxyaluminums, trialkoxy-methacrylates, and combinations thereof, Tetraalkoxysilanes, and mixtures thereof.

The adhesion promoter may be added in an amount of 0 to about 30 parts by weight per 100 parts by weight of the organopolysiloxane. In one embodiment, the amount of adhesion promoter is from about 0.001 to about 15 parts by weight per 100 parts by weight of organopolysiloxane. In another embodiment, the amount of adhesion promoter is from about 0.1 to about 10 parts by weight per 100 parts by weight of organopolysiloxane.

In one embodiment, the polymer matrix may contain a catalytic inhibitor to modify the curing profile and increase shelf life. Catalytic inhibitors include phosphine or phosphite compounds, amine compounds, isocyanurates, alkynols, maleates, mixtures thereof, and any other compound known to those skilled in the art. In one embodiment, the inhibitor may be triallylisocyanurate, 2-methyl-3-butyn-2-ol, dimethyl-1-hexyn-3-ol, or mixtures thereof.

The inhibitor may be added in an amount of 0 to about 10 parts by weight per 100 parts by weight of organopolysiloxane. In one embodiment, the inhibitor is present in an amount of about 0.001 to about 10 parts by weight per 100 parts by weight of organopolysiloxane. In another embodiment, the inhibitor is present in an amount of about 0.01 to about 5 parts by weight per 100 parts by weight of organopolysiloxane.

Other additives may be added to the polymer matrix such as reactive organic diluents, non-reactive diluents, flame retardants, pigments, flow control agents, thixotropic agents for viscosity control and filler treating agents.

Reactive organic diluents may be added to reduce the viscosity of the composition. Examples of reactive diluents include dienes such as 1, 5-hexadiene, olefins such as n-octene, styrenic compounds, acrylate or methacrylate compounds, vinyl or alkyl containing compounds, and combinations thereof.

Non-reactive diluents may be added to reduce the viscosity of the formulation. Examples of non-reactive diluents include aliphatic hydrocarbons such as octane, toluene, ethyl acetate, butyl acetate, 1-methoxypropyl acetate, ethylene glycol, dimethyl ether, polydimethylsiloxane, and combinations thereof.

Examples of flame retardants include phosphoramides, triphenyl phosphate (TPP), Resorcinol Diphosphate (RDP), bisphenol-a-diphosphate (BPA-DP), organic phosphine oxides, halogenated epoxy resins (tetrabromobisphenol A), metal oxides, metal hydroxides, and combinations thereof.

Additives may be added to the polymer matrix in amounts of 0 to about 20 parts by weight per 100 parts by weight of organopolysiloxane. In another embodiment, the additives may be added in an amount of about 0.5 to about 10 parts by weight per 100 parts by weight of organopolysiloxane.

The thermally conductive filler may be reinforced or non-reinforced. Fillers may include particles of fumed silica, fused silica, finely divided quartz powder, amorphous silica, carbon black, carbon nanotubes, graphite, diamond, metals such as silver, gold, aluminum or copper, silicon carbide, aluminum hydrate, metal alloys containing the elements gallium, indium, tin, zinc or any combination thereof, ceramics such as boron nitride, boron carbide, titanium carbide, silicon carbide or aluminum nitride, metal oxides such as aluminum oxide, magnesium oxide, beryllium oxide, chromium oxide, zinc oxide, titanium dioxide or iron oxide, thermoplastics or thermosets that contain thermally conductive fillers and are processed into fiber or powder form, and combinations thereof. In one embodiment, the thermally conductive filler is alumina, boron nitride, or a combination of the two.

The thermally conductive filler may be micron-sized, submicron-sized, nano-sized, or a combination thereof. In one embodiment, the thermally conductive filler is spherical with an aspect ratio of about 1 or approximately spherical with an aspect ratio of about 1. The maximum particle size of the thermally conductive filler particles should not exceed 25 microns. For thermally conductive fillers having a platelet or fiber shape, the maximum particle size is measured at the minimum size of the filler. For example, for plate-like filler particles, the maximum particle size is the maximum thickness. In one embodiment, the maximum particle size is less than about 25 microns. In another embodiment, the maximum particle size is from about 0.01 to about 24 microns.

In one embodiment, the average particle size is from about 0.01 microns to about 15 microns. In another embodiment, the average particle size is from about 1 micron to about 10 microns.

In one embodiment, the thermally conductive filler is present at about 100 parts by weight per 100 parts by weight of organopolysiloxane. In another embodiment, the thermally conductive filler is present at about 300 to about 750 parts by weight per 100 parts by weight of organopolysiloxane.

In one embodiment, the thermally conductive filler is present in a range of from about 10 wt% to about 95 wt%, based on the weight of the total composition. In another embodiment, the thermally conductive filler is present in a range of from about 20 wt% to about 92 wt%, based on the weight of the total composition.

The thermally conductive filler may be treated before, during, or after mixing. The filler treatment is not limited to a single process step but may include several different stages throughout the manufacturing process. Filler treatment includes, but is not limited to, ball milling, jet milling, roll milling (using a 2-roll mill or a 3-roll mill), chemical or physical coating or covering by methods such as treating the filler with chemicals such as silazanes, silanols, silanes, or siloxane compounds or polymers containing alkoxy, hydroxyl, or Si-H groups and any other commonly used filler treating agents, and any other method commonly employed by those skilled in the art.

Other reinforcing fillers may be added to the composition. Examples of suitable reinforcing fillers include fumed silica, hydrophobic precipitated silica, finely divided quartz, diatomaceous earth, fused talc, glass fibers, graphite, carbon, and pigments. The additional filler may be added in an amount of 0 to about 30 parts by weight per 100 parts of polyorganosiloxane.

In one embodiment, a method of making a thermal interface composition includes blending a polymer matrix comprising an organopolysiloxane having at least two silicon-bonded alkenyl groups per molecule, an organohydrogenpolysiloxane having at least two silicon-bonded hydrogen atoms per molecule, and a hydrosilylation catalyst comprising a transition metal, and a thermally conductive filler comprising particles having a maximum particle diameter of no greater than about 25 microns, wherein the transition metal is present in an amount of from about 10 to about 20ppm based on the weight of the non-filler components, and the molar ratio of the silicon-bonded hydrogen atoms to the silicon-bonded alkenyl groups is from about 1 to about 2.

The final composition may be mixed manually or by standard mixing equipment such as kneaders, planetary mixers, twin screw extruders, two or three roll mills, and the like. The blending of the composition may be carried out by any apparatus used by those skilled in the art, in a batch, continuous or semi-continuous manner.

The composition may be cured at a temperature of less than about 150 ℃. In one embodiment, the composition is cured at a temperature of from about 20 ℃ to about 100 ℃. In another embodiment, the composition is cured at a temperature of about 50 ℃ to about 80 ℃. In another embodiment, the composition is cured at 80 ℃. The curing time is less than 1 hour at 80 ℃.

Curing is typically carried out at pressures of from about 1 atmosphere to about 5 tons pressure per square inch, including from about 1 atmosphere to about 100 pounds per square inch.

The composition has good adhesion to silicon and to metal substrates that are commonly used as heat sinks in electronic devices. The composition also has good adhesion to metal substrates treated with coatings commonly used in the manufacture of heat sinks in the electronics industry. These fins include, but are not limited to, aluminum and copper. Heat sink coatings include, but are not limited to, gold, chromate, and nickel. The thermal interface composition may be used in electronic devices such as computers, semiconductors, or any device where heat transfer between components is desired. Typically, these components are made of metals such as aluminum, copper, silicon, and the like. The composition may be applied anywhere where heat is generated and heat removal is desired. For example, the compositions may be used to remove heat from motors or engines, to act as an underfill material in flip-chip designs (flip-chip designs), to facilitate heat transfer from a silicon chip surface to a heat sink, as die attach in electronic devices, and for any other application where efficient heat removal is desired.

In one embodiment, the composition may be preformed into a sheet or film and cut into any desired shape. The composition can be advantageously used to form a thermal interface pad or film between electronic components. Alternatively, the composition may be pre-applied to the heat generating or dissipating components of the device. The compositions may also be applied as grease, gel and phase change material formulations.

The thermal interface material may be in the form of a one-part heat-curable composition, a two-part heat-curable composition, or a two-part room temperature-curable composition.

In another embodiment, a one-part, heat-curable composition includes a blend of a polymer matrix comprising an organopolysiloxane having at least two silicon-bonded alkenyl groups per molecule, an organohydrogenpolysiloxane having at least two silicon-bonded hydrogen atoms per molecule, and a hydrosilylation catalyst comprising a transition metal, and a thermally conductive filler comprising particles having a maximum particle diameter of no greater than about 25 microns, wherein the transition metal is present in an amount of from about 10 to about 20ppm based on the weight of the non-filler components, and the molar ratio of the silicon-bonded hydrogen atoms to the silicon-bonded alkenyl groups is from about 1 to about 2.

In another embodiment, the one-part, heat-curable composition can be formulated as a two-part system. In one embodiment, a method of making a two-part thermal interface composition comprises mixing part a and part B in a weight ratio of about 1: 1 to form a composition, wherein the composition comprises a polymer matrix comprising an organopolysiloxane having at least two silicon-bonded alkenyl groups per molecule, an organohydrogenpolysiloxane having at least two silicon-bonded hydrogen atoms per molecule, and a hydrosilylation catalyst comprising a transition metal, and a thermally conductive filler comprising particles having a maximum particle size of no greater than about 25 microns, wherein the transition metal is present in an amount of about 10 to about 20ppm based on the weight of the non-filler components, and the molar ratio of silicon-bonded hydrogen atoms to silicon-bonded alkenyl groups is about 1 to about 2.

In two-component compositions, formulations are prepared in two components, component a and component B, and stored until it is desired to combine the two components and produce a thermal interface material. These components can be stored at room temperature but must be kept separate from each other. Components a and B may comprise any component of the thermal interface material in any amount, except that the organohydrogenpolysiloxane must be contained entirely in one component and the hydrosilylation catalyst must be contained entirely in the other component. In one embodiment, both component a and component B comprise a filler and an organopolysiloxane. In another embodiment, both component a and component B comprise the same amounts of filler and organopolysiloxane.

In one embodiment, a two-part composition may be prepared that cures at room temperature when component a and component B are combined. In another embodiment, a two-part composition may be prepared that requires heat curing when combining part a and part B.

Components A and B may be blended by hand mixing or by mixing via standard mixing equipment such as kneaders, planetary mixers, twin screw extruders, static mixers, two or three roll mills, and the like. The blending of components a and B can be carried out by any apparatus used by those skilled in the art, in a batch, continuous or semi-continuous manner. In one embodiment, components A and B are mixed together in a weight ratio of about 1: 1.

In order that those skilled in the art will be better able to practice the invention, the following examples are given by way of illustration and not of limitation.

Examples

Example 1

Two separate thermally conductive fillers were used in the present formulation. The first filler was a Denka DAW-05 alumina filler having an average particle size of 5 μm and a maximum particle size of 24 μm, and the second filler was a Sumitomo AA-04 alumina filler having an average particle size of 0.4 to 0.6 μm and a maximum particle size of about 1 μm. The thermally conductive fillers (604.30 parts total (483.58 parts first filler and 120.72 parts second filler)) were mixed in a laboratory scale Ross mixer (1 quart capacity) at 140-. Then cooling the filler toFrom 35 to 45 ℃ C, atmospheric pressure is brought to 100 parts of vinyl-terminated polydimethylsiloxane liquid (350-450cSt, about 0.48% by weight of vinyl groups; SL6000-D1 from GE Silicones) and 0.71 part of pigment masterbatch (50% by weight of carbon black and 50% by weight of 10,000cSt vinyl-terminated polydimethylsiloxane liquid; M-8016 from GE Toshiba) and a part of the hydride liquid-1.04 part of hydride-functionalized polyorganosiloxane liquid (about 0.82% by weight of hydride; 88466 from GESilicones). The formulation was mixed at about 18rpm for 6 minutes to combine the liquid and the pigment. The temperature was then raised to 140 ℃ and 160 ℃ and the mixture was stirred at about 18rpm under a vacuum pressure of 25-30 inches Hg for an additional 1.5 hours. The formulation was cooled to about 30 ℃ and the following components were added: 0.413 parts of triallyl isocyanurate and 0.043 parts of dimethyl-1-hexyne-3-ol (61) And 0.094 parts of tetramethyltetravinylcyclotetrasiloxane complexed platinum catalyst (GESilicones, 88346, which is a vinyl-D4 solution of about 1.7 weight percent platinum (the catalyst loading results in a platinum content of 14.65ppm based on the non-filler components in the final formulation)). The components were combined by stirring at about 18rpm for 8 minutes. The final components were then added to the mixer: 3.14 parts of a first adhesion promoter (cyclosiloxane containing alkoxysilyl and Si-H functional groups, GE Toshiba, A501S), 2.08 parts of a second adhesion promoter (glycidoxypropyltrimethoxysilane) and the remaining amount of hydride liquid-2.10 parts of hydride-functionalized polyorganosiloxane liquid (about 0.82% by weight hydride). Vi molar ratio of formulation was 1.399. The components were combined by stirring at about 18rpm for 5 minutes. The final formulation was mixed at about 18rpm and under vacuum pressure of 25-30 inches Hg for an additional 3 minutes. The formulation was removed from the mixer and immediately filtered through a 100 mesh screen. The material was then placed under a vacuum of 25-30 inches Hg for 3-8 minutes to remove any residual entrapped air prior to testing.

Comparative example 2

Two separate thermally conductive fillers were used in the present formulation. First kind of fillerIs a Denka DAW-05 alumina filler having a5 μm average particle size and a 24 μm maximum particle size, and the second filler is a Sumitomo AA-04 alumina filler having an average particle size of 0.4 to 0.6 μm and a maximum particle size of about 1 μm. The thermally conductive fillers (604.30 parts total (483.58 parts first filler and 120.72 parts second filler)) were mixed in a laboratory scale Ross mixer (1 quart capacity) at 140-. The filler was then cooled to 35-45 ℃ to atmospheric pressure and 100 parts of vinyl terminated polydimethylsiloxane liquid (350-450cSt, about 0.48 wt% vinyl; S16000-D1 from GE Silicones) and 0.71 part of pigment masterbatch (50 wt% carbon black and 50 wt% 10,000cSt vinyl terminated polydimethylsiloxane liquid; M-8016 from GE Toshiba) and a portion of the hydride liquid-0.70 part of hydride functionalized polyorganosiloxane liquid (about 0.82 wt% hydride; 88466 from GESilicones) were added. The formulation was mixed at about 18rpm for 6 minutes to combine the liquid and the pigment. The temperature was then raised to 140 ℃ and 160 ℃ and the mixture was stirred at about 18rpm under a vacuum pressure of 25-30 inches Hg for an additional 1.5 hours. The formulation was cooled to about 30 ℃ and the following components were added: 0.54 part of triallyl isocyanurate and 0.06 part of dimethyl-1-hexyne-3-ol (61) And 0.04 parts of tetramethyltetravinylcyclotetrasiloxane complexed platinum catalyst (GE Silicones, 88346, which is a vinyl-D4 solution of about 1.7 weight percent platinum (this catalyst loading results in 5.85ppm by weight platinum content based on the non-filler component of the final formulation)). The components were combined by stirring at about 18rpm for 8 minutes. The final components were then added to the mixer: 3.14 parts of a first adhesion promoter (cyclosiloxane containing alkoxysilyl and Si-H functional groups, GE Toshiba, A501S), 2.08 parts of a second adhesion promoter (glycidoxypropyltrimethoxysilane) and the remaining amount of hydride liquid-1.42 parts of hydride-functionalized polyorganosiloxane liquid (about 0.82% by weight hydride). Vi molar ratio of the formulation was 0.947. The components were combined by stirring at about 18rpm for 5 minutes. The final formulation was applied at about 18rpm and under vacuum of 25-30 inches HgMix under pressure for an additional 3 minutes. The formulation was removed from the mixer and immediately filtered through a 100 mesh screen. The material was then placed under a vacuum of 25-30 inches Hg for 3 minutes to remove any residual entrapped air prior to testing.

Example 3

Dynamic Mechanical Analysis (DMA) was performed using a TA Instruments Ares-LS2 to compare the gel points of two samples (example 1 versus comparative example 2) having parallel plate geometry when the temperature was ramped from 25 ℃ to 150 ℃ at a rate of 2 ℃/min. See table 1 and fig. 1.

The storage (elastic) modulus G' is directly measured by the molecular weight in the polymer system. When curing begins, the molecular weight increases and the G' value increases. When comparing the G 'curves of example 1 and comparative example 2, it is shown that the increase in G' for the example 1 sample occurs at a much lower temperature than for the comparative example 2 sample. Starting at about 30 ℃, the slope of the G' line for the example 1 sample is positive. In contrast, the slope of the G' curve for the sample of comparative example 2 remained at 0 up to about 65 ℃. This difference highlights the fact that: the example 1 sample started its curing reaction at a much lower temperature than the comparative example 2 sample.

The intersection between the storage and loss moduli of a material is a property known as the "gel point". At this point, the material achieves a sufficient degree of crosslinking, described as an infinite network structure. This crossover point is considered the first cure point, but full cure requires the continuous application of heat to reach the plateau value of storage modulus. The test shows that the sample of example 1 has a lower gelation temperature than the sample of comparative example 2. In the case of the sample of example 1, the gelation temperature was 10 ℃ lower.

The plateau temperature is at the point where cure is deemed complete and the G' slope returns to 0. The data collected in this test shows that the example 1 material achieves a plateau (full cure) about 35 ℃ lower than the comparative example 2 sample.

TABLE 1 comparison of the transition temperatures of example 1 to comparative example 2

	Positive G' slope temperature (. degree. C.)	G' G "temperature at the crossing point (. degree. C.)	Plateau temperature (. degree. C.)
				Example 1	30	72	95
Comparative example 2	65	82	130

Example 4

This example tests the time required to achieve full cure as a function of different curing temperatures. The G 'G "cross-over point indicates the onset of cure, and complete cure is indicated by the plateau for storage modulus (G') in the DMA test. Table 2 below shows that the final G 'value (final G') at the end of isothermal holding is substantially the same as the maximum G 'value (maximum G') obtained throughout each run. The maximum G' value is used for calculation to determine the degree of cure.

Table 2 shows that the maximum G' value of the example 1 sample only decreased 8% when the cure temperature was reduced from 150 ℃ to 80 ℃. This equivalent decrease in cure temperature for the comparative example 2 sample resulted in a 26% decrease in the maximum G' value. Lower G' plateau values indicate a decrease in crosslink density. The greater the decrease in G', the greater the decrease in crosslink density and the less the material cures. The fact that the comparative example 2 sample showed more than three times less reduction than the example 1 sample when cured at 80 ℃ is another indication that the example 1 sample had much better cure than the comparative example 2 sample at low temperatures of 80 ℃.

TABLE 2 comparison of the maximum G' storage modulus of the samples of example 1 in comparative example 2

	Curing temperature C	Final G' dyn/cm2	Maximum G' dyn/cm2	% difference of maximum G' to final G%	% reduction of maximum G' at 80 ℃ to 150 ℃
Example 1	150	3458600	3558300	3
						Example 1	80	3254400	3285000	1	8
						Comparative example 2	150	3861500	3880000	0
Comparative example 2	80	2853100	2875400	1	26

In table 3, the elapsed time (in minutes) required for each sample to reach 90%, 95% and 99% of its maximum G' value for each temperature is recorded. The results show that the sample of example 1 reaches 99% of its maximum G' value after about 35 minutes at 80 ℃. As shown in table 2 and described above, the example 1 sample tested at 80 ℃ achieved a maximum G 'value that was only 8% less than the maximum G' of the example 1 sample tested at 150 ℃. In contrast, the sample of comparative example 2 took more than 4.5 hours (278 minutes) at 80 ℃ to reach 99% of its maximum G' value. This in turn illustrates that the cure time for the example 1 sample is reduced by about 87%. Also as noted above, the maximum G 'value of the sample of comparative example 2 cured at 80 ℃ was 26% less than the maximum G' value when cured at 150 ℃. This means that even after 4.5 hours at 80 ℃, the comparative example 2 sample achieved a much lower degree of cure than the example 1 sample achieved only within 35 minutes at this temperature.

TABLE 3 time comparison of the maximum G' values achieved for the samples of example 1 in comparative example 2

	Curing temperature C	Time (min) to reach 90% of maximum G' value (t-90)	Time (min) to reach 95% of maximum G' value (t-95)	Time (min) to reach 99% of maximum G' value (t-99)	Example 1% reduction in cure time for comparative example 2 formulation
Example 1	150	2.1	2.3	16.3	55
						Example 1	80	19.3	23.4	35.4	87
						Comparative example 2	150	3.2	13.7	36.8
Comparative example 2	80	128.9	183.5	278.0

FIGS. 2 and 3 show a comparison of the cured forms of the samples of example 1 and comparative example 2.

Example 5

The storage modulus of a material is measured when the material achieves an optimal level of crosslink density and produces sufficient bond strength for the second and equally important component of the adhesive material to "effectively" cure. The reaction mechanisms leading to crosslinking and bonding in the adhesive system may vary, but a sufficient degree of crosslinking and bonding is required if the material is to be considered "cured" to an effective degree.

Table 4 and fig. 4 illustrate the difference in adhesive strength between the samples of example 1 and comparative example 2. Test samples were prepared by: a small amount of material was dispensed onto a nickel-plated copper substrate, an 8mm x 8mm silicon coupon (coupon) was placed on top, pressed with 10psi force and cured at the specified time and temperature. The mode shear adhesion (die shear adhesion) was then tested using a Dage 4000 mode shear tester with a 100Kg load cell. The values reported for each sample are the average of 9 replicates. The samples were conditioned at room temperature for a minimum of 3 days. This delay between cure time and test time is used to ensure that stable physical properties are achieved prior to testing.

The results show that example 1 sample can achieve a cure of 344psi after only 15 minutes cure at 80 ℃. As shown in the DMA curve data above, at this point the material is not fully crosslinked; however, the bond strength has greatly exceeded the minimum acceptable value for typical applications. In contrast, the comparative example 2 sample did not achieve sufficient adhesion or crosslinking after 15 minutes at 80 ℃ when tested in the same manner. The example 1 sample achieved a mode shear adhesion value of over 700psi after only 15 minutes at 125 ℃. The high adhesion level was not achieved by the comparative example 2 sample even after 15 minutes of curing at a higher temperature of 150 ℃.

TABLE 4 comparison of the modal shear adhesion strengths of example 1 to comparative example 2 samples

	15min@80℃	15min@125℃	15min@150℃
				Example 1(psi) mean (standard deviation)	344(100)	739(97)	841(70)
Comparative example 2(psi) mean (standard deviation)	0.5(0.1)Not cured	262(39)	380(40)

Example 6

Additional formulations were prepared using the feed amounts listed in table 5. A base stock comprising a thermally conductive filler, a vinyl terminated polydimethylsiloxane liquid, a pigment masterbatch and a portion of hydride liquid (33% of the total required formulation) was prepared in a Ross type planetary mixer according to the procedure described in example 1. After the vacuum mixing step was heated for 1.5 hours as described in example 1, the matrix material was cooled to room temperature and removed from the Ross mixer. This base was used to prepare the formulation of example 6. These formulations were prepared by mixing the base with the remaining feed as listed in table 5. These mixes were performed on a small scale using a Hauschild high shear rate mixer.

The following general procedure describes the mixing process for all formulations of example 6.

A portion of the matrix material was added to the mixing cup along with the target amounts of triallyl isocyanurate and dimethyl-1-hexyn-3-ol. The formulation was mixed at 1800rpm for about 10 seconds. A target amount of tetramethyltetravinylcyclotetrasiloxane complexed platinum catalyst was added to the mixing cup and the formulation was mixed at 1800rpm for about 10 seconds. A target amount of a501S adhesion promoter and a target amount of glycidoxypropyltrimethoxysilane adhesion promoter with the balance of the hydride liquid were added to the mixing cup and the formulation was mixed at 1800rpm for about 10 seconds. The material was then placed under a vacuum of 25-30 inches Hg for 3-8 minutes to remove any residual entrapped air prior to testing.

TABLE 5

DAW-05 is an alumina filler having an average particle size of 5 μm and a maximum particle size of 24 μm.

AA-04 is an alumina filler having an average particle size of 0.4 to 0.6 μm and a maximum particle size of about 1 μm.

SL6000-D1 is a vinyl terminated polydimethylsiloxane liquid (350-450cSt, about 0.48 wt% vinyl).

M-8016 is a pigment masterbatch (50M% carbon black and 50 wt% of 10,000cSt vinyl terminated polydimethylsiloxane fluid).

88346 is a tetramethyltetravinylcyclotetrasiloxane complexed platinum catalyst (1.7 wt% platinum in vinyl-D4).

TAIC is triallyl isocyanurate.

61 is dimethyl-1-hexyn-3-ol.

A501S is a cyclosiloxane containing alkoxysilyl and Si-H functional groups.

GPS-M is glycidoxypropyltrimethoxysilane.

The samples were cured and subjected to a mode shear test as described in example 5. The cure time test was conducted at an isothermal holding temperature of 80 deg.C using an instrument similar to the Ares-LS2 described in example 3. The T-95 value is the time to complete 95% of the cure. The viscosity was also measured based on storage at 25 ℃ for 24 hours. The viscosity was measured at 25 ℃ in pure form at a shear rate of 10/s using a parallel plate rheometer.

While typical embodiments have been described for purposes of illustration, the foregoing descriptions should not be deemed to be a limitation on the scope herein. Accordingly, various modifications, adaptations, and alternatives may occur to one skilled in the art without departing from the spirit and scope herein.

Claims (31)

1. A thermal interface composition comprising a blend of a polymer matrix and a thermally conductive filler comprising particles having a maximum particle diameter of no greater than about 25 microns, the polymer matrix comprising an organopolysiloxane having at least two silicon-bonded alkenyl groups per molecule, an organohydrogenpolysiloxane having at least two silicon-bonded hydrogen atoms per molecule, and a hydrosilylation catalyst comprising a transition metal, wherein the transition metal catalyst is present in an amount of from about 10 to about 20ppm based on the weight of the non-filler components and the molar ratio of silicon-bonded hydrogen atoms to silicon-bonded alkenyl groups is from about 1 to about 2.

2. The composition of claim 1 wherein the organopolysiloxane is linear.

3. The composition of claim 1, wherein the alkenyl group is vinyl.

4. The composition of claim 3, wherein the alkenyl group is at a terminal end of the molecular chain.

5. The composition of claim 1 wherein the organopolysiloxane is a dimethylpolysiloxane capped at both molecular terminals with dimethylvinylsiloxane groups.

6. The composition of claim 1, wherein the organohydrogenpolysiloxane comprises methyl groups.

7. The composition of claim 1, wherein the hydrogen atoms are located along the backbone of the molecular chain and at the ends of the molecular chain.

8. The composition of claim 1 wherein the organohydrogenpolysiloxane is a copolymer of methylhydrogensiloxane and dimethylsiloxane that is end-capped at both ends of the molecular chain with dimethylhydrogensiloxyalkyl groups.

9. The composition of claim 1 wherein the molar ratio of hydrogen atoms bonded to silicon atoms in the organohydrogenpolysiloxane to alkenyl groups in the organopolysiloxane is from about 1.3 to about 1.6.

10. The composition of claim 9 wherein the molar ratio of hydrogen atoms bonded to silicon atoms in the organohydrogenpolysiloxane to alkenyl groups in the organopolysiloxane is from about 1.4 to about 1.5.

11. The composition of claim 1, wherein the transition metal is present in an amount of about 12 to about 19ppm based on the total weight of the non-filler components of the composition.

12. The composition of claim 11, wherein the transition metal is present in an amount of about 14 to about 17ppm based on the total weight of the non-filler components of the composition.

13. The composition of claim 1, further comprising an adhesion promoter.

14. The composition of claim 1, further comprising a catalytic inhibitor.

15. The composition of claim 1, wherein the thermally conductive filler is selected from the group consisting of: boron nitride, boron carbide, titanium carbide, silicon carbide, aluminum nitride, aluminum oxide, magnesium oxide, beryllium oxide, chromium oxide, zinc oxide, titanium dioxide, and iron oxide.

16. The composition of claim 1, wherein the thermally conductive filler has a maximum particle size of less than 25 microns.

17. The composition of claim 1, wherein the thermally conductive filler has an average particle size of about 0.01 microns to about 15 microns.

18. A method of making a thermal interface composition comprising blending a polymer matrix and a filler comprising particles having a maximum particle diameter of no greater than about 25 microns, the polymer matrix comprising an organopolysiloxane having at least two silicon-bonded alkenyl groups per molecule, an organohydrogenpolysiloxane having at least two silicon-bonded hydrogen atoms per molecule, and a hydrosilylation catalyst comprising a transition metal, wherein the transition metal is present in an amount of from about 10 to about 20ppm based on the weight of the non-filler components and the molar ratio of silicon-bonded hydrogen atoms to silicon-bonded alkenyl groups is from about 1 to about 2.

19. The method of claim 18, wherein the alkenyl group is vinyl.

20. The method of claim 18 wherein the organopolysiloxane is a dimethylpolysiloxane capped at both molecular terminals with dimethylvinylsiloxane groups.

21. The method of claim 18, wherein the organohydrogenpolysiloxane comprises a methyl group.

22. The method of claim 18 wherein the organohydrogenpolysiloxane is a copolymer of methylhydrogensiloxane and dimethylsiloxane that is end-capped at both ends of the molecular chain with dimethylhydrogensiloxyalkyl groups.

23. The method of claim 18 wherein the molar ratio of hydrogen atoms bonded to silicon atoms in the organohydrogenpolysiloxane to alkenyl groups in the organopolysiloxane is from about 1.3 to about 1.6.

24. The method of claim 23 wherein the molar ratio of hydrogen atoms bonded to silicon atoms in the organohydrogenpolysiloxane to alkenyl groups in the organopolysiloxane is from about 1.4 to about 1.5.

25. The method of claim 18, wherein the transition metal is present in an amount of from about 12 to about 19ppm based on the total weight of the non-filler components of the composition.

26. The method of claim 25, wherein the transition metal is present in an amount of from about 14 to about 17ppm based on the total weight of the non-filler components of the composition.

27. The method of claim 18, further comprising an adhesion promoter.

28. The method of claim 18, further comprising a catalytic inhibitor.

29. The method of claim 18, wherein the thermally conductive filler is selected from the group consisting of: boron nitride, boron carbide, titanium carbide, silicon carbide, aluminum nitride, aluminum oxide, magnesium oxide, beryllium oxide, chromium oxide, zinc oxide, titanium dioxide, and iron oxide.

30. A one-part, thermally-curable composition comprising a blend of a polymer matrix and a thermally-conductive filler comprising particles having a maximum particle diameter of no greater than about 25 microns, the polymer matrix comprising an organopolysiloxane having at least two silicon-bonded alkenyl groups per molecule, an organohydrogenpolysiloxane having at least two silicon-bonded hydrogen atoms per molecule, and a hydrosilylation catalyst comprising a transition metal, wherein the transition metal is present in an amount of from about 10 to about 20ppm by weight based on the weight of the non-filler components, and the molar ratio of silicon-bonded hydrogen atoms to silicon-bonded alkenyl groups is from about 1 to about 2.

31. A method of making a two-part thermal interface composition comprising mixing part a and part B in a 1: 1 weight ratio to form a composition, wherein the composition comprises a polymer matrix and a thermally conductive filler comprising particles having a maximum particle diameter of no greater than about 25 microns, the polymer matrix comprising an organopolysiloxane having at least two silicon-bonded alkenyl groups per molecule, an organohydrogenpolysiloxane having at least two silicon-bonded hydrogen atoms per molecule, and a hydrosilylation catalyst comprising a transition metal, wherein the transition metal is present in an amount of from about 10 to about 20ppm based on the weight of the non-filler components and the molar ratio of silicon-bonded hydrogen atoms to silicon-bonded alkenyl groups is from about 1 to about 2.