Patent Description:
The present disclosure relates to a method, apparatus, and assembly for thermally connecting two layers.

A thermal interface material (TIM) can be used to thermally connect two or more layers together. For example, TIMs are often used in CPU packages to thermally connect the CPU die to the integrated heat spreader (IHS) of the CPU package. There are various types of TIMs that may be used. However, current TIMs present challenges.

The present invention is directed to an integrated circuit assembly comprising a die, an upper layer, and a thermal interface material disposed in contact with the die layer and the upper layer. The thermally interface material comprises a polymer and liquid metal droplets dispersed throughout the polymer. A bondline distance formed between the die and the upper layer is no greater than <NUM> microns.

The present invention can provide both a low contact resistance at the material interfaces and a low thermal resistance through the material. The low contact resistance can be enabled by the application of the polymer in an uncured state so that the polymer and liquid metal droplets can conform to the surface of the layer to achieve a desired contact resistance. The low thermal resistance through the material can be enabled by liquid metal droplets, including the size and/or shape of the liquid metal droplets. Additionally, the methods described herein may not need as high a pressure to install as compared to methods due to application of the polymer in the uncured state. Further, curing the polymer can inhibit pump out of the liquid metal droplets. These and other benefits realizable from various embodiments of the present invention will be apparent from the description that follows.

<CIT> refers to thermally conductive connections, and more particularly to a matrix material mixed with a thermally conductive, randomly dispersed filler containing a liquid metal for making thermally connecting surfaces such as electronic components.

<CIT> refers to a thermal interface material comprising a base oil and fillers.

<CIT> refers to a heat conductive material of high thermal conductivity containing a metal or an alloy which is liquid at room temperature or a fine powder of a heat conductive material dispersed in an organic material which is liquid at room temperature.

<CIT> refers to a conductive composition comprising liquid metal, particulate filler, and resin. The liquid metal and particulate filler are present in a ratio of <NUM>:<NUM>-<NUM>:<NUM>.

The features and advantages of various examples of the present invention, and the manner of attaining them, will become more apparent, and the examples will be better understood by reference to the following description of examples taken in conjunction with the accompanying drawing, wherein:.

Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate certain examples, in one form, and such exemplifications are not to be construed as limiting the scope of the examples in any manner.

Certain exemplary aspects of the present invention will now be described to provide an overall understanding of the principles of the composition, function, manufacture, and use of the compositions and methods disclosed herein. An example or examples of these aspects are illustrated in the accompanying drawing. Those of ordinary skill in the art will understand that the compositions, articles, and methods specifically described herein and illustrated in the accompanying drawing are non-limiting exemplary aspects and that the scope of the various examples of the present invention is defined solely by the claims. The features illustrated or described in connection with one exemplary aspect may be combined with the features of other aspects. Such modifications and variations are intended to be included within the scope of the present invention.

Applying a material to a die of an integrated circuit such that the material is between the die and an integrated heat spreader (IHS) can require balancing the thermal resistance through the material and the contact resistance at the material interfaces. For example, a polymeric material may have a low contact resistance at the material interfaces but a high thermal resistance through the material. A solid metal may have a low thermal resistance through the material but a high contact resistance at the material interfaces. Additionally, some solid materials (polymeric or metal) may require a large pressure during installation to achieve a desired contact resistance. Thus, the present invention provides, in various embodiments, a thermal interface material (TIM), an assembly for thermally connecting two layers, and a circuit assembly that can provide both a low contact resistance at the material interfaces and a low thermal resistance through the material. Additionally, the TIM may not need as high a pressure to install as compared to other solid materials. For example, the TIM may require a pressure of less than or equal to <NUM> pounds per square inch to install (e.g., compress). The TIM according to the present disclosure can comprise a polymer with liquid metal droplets dispersed through the polymer.

As used in this specification, the terms "polymer" and "polymeric" means prepolymers, oligomers, and both homopolymers and copolymers. As used in this specification, "prepolymer" means a polymer precursor capable of further reactions or polymerization by a reactive group or reactive groups to form a higher molecular mass or cross-linked state.

The polymer can be a thermosetting polymer, a thermoplastic polymer, or a combination thereof. As used herein, the term "thermosetting" refers to polymers that "set" irreversibly upon curing or cross-linking, where the polymer chains of the polymeric components are joined together by covalent bonds, which is often induced, for example, by heat or radiation. In various examples, curing or a cross-linking reaction can be carried out under ambient conditions. Once cured or cross-linked, a thermosetting polymer may not melt upon the application of heat and can be insoluble in conventional solvents. As used herein, the term "thermoplastic" refers to polymers that include polymeric components in which the constituent polymer chains are not joined (e.g., crosslinked) by covalent bonds and thereby can undergo liquid flow upon heating and are soluble in conventional solvents. In certain embodiments, the polymer can be elastomeric (e.g., rubbery, soft, stretchy) or rigid (e.g., glassy). For example, the polymer can be elastomeric.

Thermosetting polymers may include a cross-linking agent that may comprise, for example, aminoplasts, polyisocyanates (including blocked isocyanates), polyepoxides, beta-hydroxyalkylamides, polyacids, anhydrides, organometallic acid-functional materials, polyamines, polyamides, or a combination thereof. A polymer may have functional groups that are reactive with the cross-linking agent.

The polymer in the TIMs described herein may be selected from any of a variety of polymers well known in the art. For example, the thermosetting polymer may comprise an acrylic polymer, a polyester polymer, a polyurethane polymer, a polyamide polymer, a polyether polymer, a polysiloxane polymer (e.g., poly(dimethylsiloxone)), a fluoropolymer, a polyisoprene polymer (e.g., rubber), a copolymer thereof (e.g., styrene ethylene butylene styrene), or a combination thereof. The functional groups on a thermosetting polymer may be selected from any of a variety of reactive functional groups, including, for example, a carboxylic acid group, an amine group, an epoxide group, a hydroxyl group, a thiol group, a carbamate group, an amide group, a urea group, an isocyanate groups (including a blocked isocyanate group), a mercaptan group, and a combination thereof.

The thermoplastic polymer can comprise propylene-ethylene co-polymer, styrenebutadiene-styrene, styrene ethylene butylene styrene, or a combination thereof. The polymer can comprise a melting point of at least <NUM> degrees Celsius, such as, for example, at least <NUM> degrees Celsius, at least <NUM> degrees Celsius, or at least <NUM> degrees Celsius.

The liquid metal for the TIM can comprise gallium, a gallium alloy, indium, an indium alloy, tin, a tin alloy, mercury, a mercury alloy, or a combination thereof. The liquid metal can be in the liquid phase at least at a temperature of at least -<NUM> degrees Celsius (e.g., in its bulk form, can comprise a melting point of less than -<NUM> degrees Celsius), such as, for example, at least -<NUM> degrees Celsius, at least -<NUM> degrees Celsius, at least <NUM> degrees Celsius, at least <NUM> degrees Celsius, at least <NUM> degrees Celsius, at least <NUM> degrees Celsius, at least <NUM> degrees Celsius, or at least <NUM> degrees Celsius. The liquid metal can be in the liquid phase at least at a temperature of no greater than <NUM> degrees Celsius (e.g., in its bulk form, can comprise a melting point of less than <NUM> degrees Celsius), such as, for example, no greater than <NUM> degrees Celsius, no greater than <NUM> degrees Celsius, no greater than <NUM> degrees Celsius, no greater than <NUM> degrees Celsius, no greater than <NUM> degrees Celsius, no greater than <NUM> degrees Celsius, or no greater than -<NUM> degrees Celsius. The liquid metal can be in the liquid phase at least at a temperature in a range of -<NUM> degrees Celsius to <NUM> degrees Celsius (e.g., in its bulk form, can comprise a melting point of less than a temperature in a range of -<NUM> degrees Celsius to <NUM> degrees Celsius), such as, for example, -<NUM> degrees Celsius to <NUM> degrees Celsius, -<NUM> degrees Celsius to <NUM> degrees Celsius, or -<NUM> degrees Celsius to <NUM> degrees Celsius The determination of whether the liquid phase is achieved at the respective temperature can be made at a pressure of <NUM> atmosphere absolute. In certain embodiments, the TIM can comprise Gallium Indium Tin (Galinstan) and a melting point of -<NUM> degrees Celsius.

The TIM can be created by forming an emulsion of the polymer and the liquid metal such that liquid metal droplets are substantially dispersed throughout the polymer. For example, the polymer and liquid metal droplets can be mixed together with a high shear mixer, a centrifugal mixer, by shaking in a container, a mortar and pestle, sonication, or a combination thereof. More details about exemplary ways to form the emulsion are described in (<NUM>) published <CIT>, entitled "Method of Synthesizing a Thermally Conductive and Stretchable Polymer Composite" and (<NUM>) published U. application <CIT>, entitled "Polymer Composite with Liquid Phase Metal Inclusions," both of which are assigned to Carnegie Mellon University and both which are incorporated herein by reference in their entirety. The composition and/or mixing techniques can be chosen such that the viscosity of the TIM emulsion in an uncured state is less than <NUM>,<NUM> cP (centipoise), such as, for example, less than <NUM>,<NUM> cP, less than <NUM>,<NUM> cP, less than <NUM>,<NUM> cP, less than <NUM>,<NUM> cP, less than <NUM>,<NUM> cP, less than <NUM>,<NUM> cP, less than <NUM>,<NUM> cP, less than <NUM>,<NUM> cP, less than <NUM>,<NUM> cP, or less than <NUM>,<NUM> cP. The viscosity of the TIM emulsion can be measured by a rotary viscometer or a cone and plate viscometer at room temperature. The viscosity measurement can be performed at a select frequency suitable to produce a static viscosity (e.g., since the material is a non-newtonian fluid).

The TIM can comprise at least <NUM>% liquid metal droplets by total volume of the TIM, such as, for example, at least <NUM>% liquid metal droplets, at least <NUM>% liquid metal droplets, at least <NUM>% liquid metal droplets, at least <NUM>% liquid metal droplets, at least <NUM>% liquid metal droplets, at least <NUM>% liquid metal droplets, or at least <NUM>% liquid metal droplets, all based on the total volume of the liquid metal droplets. The TIM can comprise no greater than <NUM>% liquid metal droplets by total volume of the TIM, such as, for example, no greater than <NUM>% liquid metal droplets, no greater than <NUM>% liquid metal droplets, no greater than <NUM>% liquid metal droplets, no greater than <NUM>% liquid metal droplets, no greater than <NUM>% liquid metal droplets, or no greater than <NUM>% liquid metal droplets, all based on the total volume of the TIM. The TIM can comprise a range of <NUM> % to <NUM>% liquid metal droplets by total volume of the TIM, such as, for example, <NUM>% to <NUM>% liquid metal droplets, <NUM>% to <NUM>% liquid metal droplets, <NUM>% to <NUM>% liquid metal droplets, or <NUM>% to <NUM>% liquid metal droplets, all based on the total volume of the TIM.

The composition and/or mixing techniques can be selected to achieve a desired average particle size of the liquid metal droplets in the TIM. The average particle size of the liquid metal droplets can be at least <NUM> micron, such as, for example, at least <NUM> microns, at least <NUM> microns, at least <NUM> microns, at least <NUM> microns, at least <NUM> microns, at least <NUM> microns, at least <NUM> microns, at least <NUM> microns, at least <NUM> microns, at least <NUM> microns, at least <NUM> microns, at least <NUM> microns, at least <NUM> microns, or at least <NUM> microns. The average particle size of the liquid metal droplets can be no greater than <NUM> micron, such as, for example, no greater than <NUM> microns, no greater than <NUM> microns, no greater than <NUM> microns, no greater than <NUM> microns, no greater than <NUM> microns, no greater than <NUM> microns, no greater than <NUM> microns, no greater than <NUM> microns, no greater than <NUM> microns, no greater than <NUM> microns, no greater than <NUM> microns, no greater than <NUM> microns, no greater than <NUM> microns, or no greater than <NUM> microns. For example, the average particle size of the liquid metal droplets can be in a range of <NUM> microns to <NUM> microns, such as, for example, <NUM> microns to <NUM> microns, <NUM> microns to <NUM> microns, <NUM> microns to <NUM> microns, or <NUM> microns to <NUM> microns.

As used herein, "average particle size" refers to the mean average size measured using microscopy (e.g., optical microscopy or electron microscopy). The size can be the diameter of spherical particles or the length along the largest dimension if ellipsoidal or otherwise irregularly shaped particle.

The polydispersity of the liquid metal droplets can be unimodal or multimodal (e.g., bimodal, trimodal). Utilizing a multimodal polydispersity can increase the packing density of the liquid metal droplets in the TIM. In certain embodiments where the polydispersity is unimodal, the polydispersity of the liquid metal droplets in the polymer can be in a range of <NUM> to <NUM>.

The TIM can be stored in a container <NUM> as illustrated in <FIG> prior to use. For example, the container can comprise walls <NUM> defining a cavity and the TIM emulsion <NUM> can be stored in the cavity. The TIM <NUM> can be in an uncured state in the container <NUM>. Storage of the TIM <NUM> in the container <NUM> can inhibit curing of the TIM <NUM>. The container <NUM> can be a pillow pack, a syringe, a beaker, a jar, a bottle, a drum, or a combination thereof. In various examples, the container <NUM> can be a ready to use dispensing device, such as, for example, a pillow pack or a syringe. In other examples, the TIM <NUM> may not be stored and can be used after creation of the emulsion without storage.

As used in this specification, the terms "cure" and "curing" refer to the chemical cross-linking of components in an emulsion or material applied over a substrate or the increase of viscosity of the components in the emulsion or material applied over the substrate. Accordingly, the terms "cure" and "curing" do not encompass solely physical drying of an emulsion or material through solvent or carrier evaporation. In this regard, the term "cured," as used in this specification in examples comprising a thermosetting polymer, refers to the condition of an emulsion or material in which a component of the emulsion or material has chemically reacted to form new covalent bonds in the emulsion or material (e.g., new covalent bonds formed between a binder resin and a curing agent). The term "cured", as used in this specification in examples comprising a thermoplastic polymer, refers to the condition of an emulsion or material in which the temperature of the thermoplastic polymer decreases below the melting point of the thermoplastic polymer such that the viscosity of the emulsion or material increases. In examples comprises both a thermosetting polymer and a thermoplastic polymer, the term "cured" refers to one of or both of the polymers curing as described herein.

Curing of a thermosetting polymer can be achieved by applying a temperature of at least - <NUM> degrees Celsius to the TIM <NUM>, such as, for example, at least <NUM> degrees Celsius, at least <NUM> degrees Celsius, at least <NUM> degrees Celsius, or at least <NUM> degrees Celsius. Curing can be achieved by applying a temperature of no greater than <NUM> degrees Celsius to the TIM <NUM>, such as, for example, no greater than <NUM> degrees Celsius, no greater than <NUM> degrees Celsius, no greater than <NUM> degrees Celsius, no greater than <NUM> degrees Celsius, or no greater than <NUM> degrees Celsius. Curing can be achieved by applying a temperature in a range of -<NUM> degrees Celsius to <NUM> degrees Celsius to the TIM <NUM>, such as, for example, <NUM> degrees Celsius to <NUM> degrees Celsius or <NUM> degrees Celsius to <NUM> degrees Celsius. For example, curing can comprise thermally baking the TIM. The temperature can be applied for a time period of greater than <NUM> minute, such as, for example, greater than <NUM> minutes, greater than <NUM> minutes, greater than <NUM> hour, or greater than <NUM> hours.

The TIM <NUM> can be dispensed from the container <NUM> and applied to a layer in an uncured state. Thereafter, the TIM <NUM> can be cured to form a cured TIM <NUM>. Curing the TIM <NUM> can comprise heating the TIM <NUM> (e.g., in examples with a thermosetting polymer), adding a catalyst to the TIM <NUM>, exposing the TIM <NUM> to air, cooling the TIM <NUM> (e.g., in examples with a thermoplastic polymer), applying pressure to the TIM <NUM>, or a combination thereof. Curing the TIM <NUM> can increase the viscosity of the TIM emulsion to greater than <NUM>,<NUM> cP, such as, for example, greater than <NUM>,<NUM> cP, greater than <NUM>,<NUM> cP, greater than <NUM>,<NUM> cP, greater than <NUM>,<NUM> cP, greater than <NUM>,<NUM> cP, greater than <NUM>,<NUM> cP, or greater than <NUM>,<NUM> cP. For example, the polymer in the TIM <NUM> can be cured. In various examples, the TIM <NUM> can be an adhesive. The polymer in the TIM <NUM> can be selected to reduce off-gasing of the TIM <NUM> during curing.

The TIM according to the present disclosure can be applied to a first layer such that the TIM is between two layers of an assembly including the first layer and a second layer. The first layer can be a heat-generating electronic component (e.g., integrated circuit) and the second layer can be an upper layer that can be thermally conductive. For example, the upper layer can be a heat spreader, a heat sink, or packaging. Thereafter, the assembly can be compressed thereby deforming the liquid metal droplets in the TIM and the TIM can be cured to form the assembly. Applying the TIM <NUM> in an uncured state can achieve a desired contact resistance and enable lower pressures to be used when compressing an assembly. The TIM can be applied to various layers and devices and it described below with reference to <FIG> with reference to a circuit assembly but is not limited to only a circuit assembly.

Referring to <FIG>, a TIM <NUM> can be applied to a die <NUM> of an integrated circuit <NUM> such that the TIM <NUM> can be between the die <NUM> and an upper layer <NUM> of a circuit assembly <NUM>. Applying the TIM <NUM> to the die <NUM> can comprise spray coating, spin coating, dip coating, roll coating, flow coating, film coating, brush coating, extrusion, dispensing, or a combination thereof. The TIM <NUM> can be applied in an uncured state such that the TIM is conformable to the surfaces of the die <NUM> and the upper layer <NUM> such that a desired level of surface contact therebetween can be achieved. In various examples, the TIM <NUM> can be applied directly to the die <NUM> and, thereafter, the upper layer <NUM> can be applied directly to the TIM <NUM>. In various other examples, the TIM <NUM> can be applied directly to the upper layer <NUM> and, thereafter, the die <NUM> can be applied directly to the TIM <NUM>. In various examples, after application of the TIM <NUM>, the TIM <NUM> can be in direct contact with the die <NUM> and the upper layer <NUM>. In certain embodiments, the application of the TIM <NUM> may be limited to the surfaces of the die <NUM> such that the TIM <NUM> can be efficiently used.

As used in this specification, particularly in connection with layers, films, or materials, the terms "on," "onto," "over," and variants thereof (e.g., "applied on," "formed on," "deposited on," "provided on," "located on," and the like) mean applied, formed, deposited, provided, or otherwise located over a surface of a substrate but not necessarily in contact with the surface of the substrate. For example, a TIM "applied on" a substrate does not preclude the presence of another layer or other layers of the same or different composition located between the applied TIM and the substrate. Likewise, a second layer "applied on" a first layer does not preclude the presence of another layer or other layers of the same or different composition located between the applied second layer and the applied TIM.

The circuit assembly <NUM> can be compressed. For example, referring to the detailed views in <FIG>, the die <NUM> and the upper layer <NUM> can be urged together such that a first distance, d<NUM>, can decrease to a second, bondline distance, dbl. The average particle size of the liquid metal droplets <NUM> in the TIM <NUM> prior to applying and/or a compressing process can be selected to be greater than a desired bondline distance, dbl, formed between the die <NUM> and the upper layer <NUM>. For example, the average particle size of the liquid metal droplets <NUM> prior to applying and/or a compressing process can be greater than the bondline distance, dbl, such as, for example, <NUM>% greater than the bondline distance, dbl, <NUM>% greater than the bondline distance, dbl, <NUM>% greater than the bondline distance, dbl, <NUM>% greater than the bondline distance, dbl, <NUM>% greater than the bondline distance, dbl, <NUM>% greater than the bondline distance, dbl, <NUM>% greater than the bondline distance, dbl, <NUM>% greater than the bondline distance, dbl, <NUM>% greater than the bondline distance, dbl, or <NUM>% greater than the bondline distance, dbl. The average particle size of the liquid metal droplets <NUM> prior to applying and/or a compressing process can be no more than <NUM>% greater than the bondline distance, dbl, such as, for example, no more than <NUM>% greater than the bondline distance, dbl, no more than <NUM>% greater than the bondline distance, dbl, no more than <NUM>% greater than the bondline distance, dbl, no more than <NUM>% greater than the bondline distance, dbl, no more than <NUM>% greater than the bondline distance, dbl, no more than <NUM>% greater than the bondline distance, dbl, no more than <NUM>% greater than the bondline distance, dbl, no more than <NUM>% greater than the bondline distance, dbl, or no more than <NUM>% greater than the bondline distance, dbl. The average particle size of the liquid metal droplets <NUM> prior to applying and/or a compressing process can be in a range of <NUM>% to <NUM>% greater than the bondline distance, dbl, such as, for example, <NUM>% to <NUM>% greater than the bondline distance, dbl, <NUM>% to <NUM>% greater than the bondline distance, dbl, <NUM>% to <NUM>% greater than the bondline distance, dbl, or <NUM>% to <NUM>% greater than the bondline distance, dbl.

Compressing the circuit assembly <NUM> can apply a force to the TIM <NUM> and can deform the liquid metal droplets <NUM> dispersed within the polymer <NUM> of the TIM <NUM>. Since the TIM <NUM> is in the uncured state, the polymer is still conformable and moveable such that the compressing force can deform the liquid metal droplets <NUM>. The liquid metal droplets <NUM> can be in the liquid phase during deformation such that a lower pressure is required for the compression and a desired deformation is achieved.

The liquid metal droplets <NUM> can be generally spherical as shown in <FIG> and thereafter can be generally ellipsoidal as shown in <FIG>. In various examples, the liquid metal droplets <NUM> prior to compressing can have a first average aspect ratio and after compressing the liquid metal droplets <NUM> can have a second average aspect ratio. The second average aspect ratio can be different that the first average aspect ratio. For example, the second average aspect ratio can be greater than the first average aspect ratio. The average aspect ratio can be a mean ratios of the width of the liquid metal droplets <NUM> to the height of the liquid metal droplets <NUM>. In various examples, the first aspect ratio can be <NUM> and the second aspect ratio can be greater than <NUM>. In certain embodiments, the first aspect ratio can be in a range of <NUM> to <NUM>. In certain embodiments, the second aspect ratio can be at least <NUM> greater than the first aspect ratio, such as, for example, at least <NUM> greater than the first aspect ratio, at least <NUM> greater than the first aspect ratio, or at least <NUM> greater than the first aspect ratio. The width of the liquid metal droplets <NUM> can be substantially aligned with the longitudinal plane of the TIM <NUM> in the circuit assembly <NUM> and the height of the liquid metal droplets <NUM> can be substantially aligned with the thickness of the TIM <NUM> (e.g., the distance, d<NUM>). The width of the liquid metal droplets <NUM> can increase upon compression of the circuit assembly <NUM>. For example, in certain embodiments, the radius of a spherical liquid metal droplets prior to compressing can be <NUM> (e.g., first aspect ratio of <NUM>) and after compression to a bondline thickness of <NUM>, the liquid metal drop can be deformed to an ellipsoidal shape with a <NUM> width (e.g., second aspect ratio of <NUM>).

In certain examples, the liquid metal droplets <NUM> can be aligned in a substantially monolayer as shown in <FIG> after compressing. The monolayer can be achieved by selecting the average particle size of the liquid metal droplets <NUM> and the bondline distance, dbl. Configuring the liquid metal droplets <NUM> in a monolayer can reduce the thermal resistance of the TIM <NUM>.

The TIM <NUM> can be cured thereby forming the circuit assembly <NUM>. Curing the TIM <NUM> can increase the viscosity of the polymer <NUM> and can harden the polymer <NUM>. For example, the polymer <NUM> can become a solid. In various examples, the polymer <NUM> after curing is elastomeric. Curing the polymer <NUM> can inhibit pump out of the liquid metal droplets <NUM> during thermal cycling of the circuit assembly <NUM> and can provide a mechanical bond between the die <NUM> and the upper layer <NUM>.

The assembly <NUM> can comprise a bondline distance, dbl, formed between the die <NUM> and the upper layer <NUM> in the cured assembly that is no greater than <NUM> microns, such as, for example, no greater than <NUM> microns, no greater than <NUM> microns, no greater than <NUM> microns, no greater than <NUM> microns, no greater than <NUM> microns, no greater than <NUM> microns, no greater than <NUM> microns, no greater than <NUM> microns, no greater than <NUM> microns, or no greater than <NUM> microns. The assembly <NUM> can comprise a bondline distance, dbl, formed between the die <NUM> and the upper layer <NUM> in the cured assembly that is at least <NUM> microns, such as, for example, at least <NUM> microns, at least <NUM> microns, at least <NUM> microns, at least <NUM> microns, at least <NUM> microns, at least <NUM> microns, at least <NUM> microns, at least <NUM> microns, at least <NUM> microns, or at least <NUM> microns. The assembly <NUM> can comprise a bondline distance, dbl, formed between the die <NUM> and the upper layer <NUM> in the cured assembly that is in a range of <NUM> microns to <NUM> microns, such as, for example, <NUM> microns to <NUM> microns, <NUM> microns to <NUM> microns, <NUM> microns to <NUM> microns, <NUM> microns to <NUM> microns, or <NUM> microns to <NUM> microns.

The curing can occur for a first time period and the compressing can occur for a second time period. The first time period can be after or at least partially overlap with the second time period. For example, the liquid metal droplets <NUM> may be deformed prior to substantial curing of the polymer <NUM> such that a lower compression pressure may be used to deform the liquid metal droplets <NUM>.

The average particle size and deformation of the liquid droplets <NUM> can improve the thermal resistance value of the TIM <NUM>. For example, the TIM <NUM> after curing can comprise a thermal resistance value of no greater than <NUM> (°K*mm<NUM>)/W, such as, for example, no greater than <NUM> (°K*mm<NUM>)/W, no greater than <NUM> (°K*mm<NUM>)/W, no greater than <NUM> (°K*mm<NUM>)/W, no greater than <NUM> (°K*mm<NUM>)/W, no greater than <NUM> (°K*mm<NUM>)/W, no greater than <NUM> (°K*mm<NUM>)/W, or no greater than <NUM>(°K*mm<NUM>)/W. The TIM <NUM> after curing can comprise a thermal resistance value of at least <NUM> (°K*mm<NUM>)/W, such as, for example, at least <NUM> (°K*mm<NUM>)/W, at least <NUM> (°K*mm<NUM>)/W, at least <NUM> (°K*mm<NUM>)/W, at least <NUM> (°K*mm<NUM>)/W, or at least <NUM> (°K*mm<NUM>)/W. The TIM <NUM> after curing can comprise a thermal resistance value in a range of <NUM> (°K*mm<NUM>)/W to <NUM> (°K*mm<NUM>)/W, such as, for example, <NUM> (°K*mm<NUM>)/W to <NUM> (°K*mm<NUM>)/W, <NUM> (°K*mm2)/W to <NUM> (°K*mm<NUM>)/W, <NUM> (°K*mm<NUM>)/W to <NUM> (°K*mm2)/W, <NUM> (°K*mm<NUM>)/W to <NUM> (°K*mm<NUM>)/W, or <NUM> (°K*mm<NUM>)/W to <NUM> (°K*mm<NUM>)/W. The thermal resistance value can be measured using a DynTIM-S instrument available from Siemens (Munich, Germany), a TIMA instrument from NanoTest (Germany), and/or a LongWin LW <NUM> (Taiwan).

The die <NUM> can comprise, for example, an integrated circuit, such as a processor or an ASIC, or a system-on-a-chip (SOC). The upper layer <NUM> can be an integrated heat spreader. The TIM <NUM> can be applied directly between the processor and the integrated heat spreader. For example, the TIM <NUM> can be a TIM1, a TIM <NUM>, or a combination thereof A TIM1 can be used to thermally connect a die and an integrated heat spreader in a lidded package. <NUM> can be used to thermally connect a die to a heat sink in a bare die package.

In various other examples, referring to <FIG>, a TIM <NUM> can be applied between the upper layer <NUM> (e.g., integrated heat spreader) and a different upper layer <NUM>. The upper layer <NUM> can comprise a heat sink. For example, the TIM <NUM> can be a TIM2.

In various other examples, the TIM according to the present disclosure can be used in a system on a package. For example, a single horizontal TIM layer can be in contact with multiple dies on one side (e.g., the integrated circuit can comprise multiple dies or multiple integrated circuits can be in contact with the same side of the TIM) and a upper layer or layers on a different side.

A eutectic alloy of Gallium, Indium, and Tin (Galinstan) (melting temperature, Tm = <NUM>) was dispersed into an elastomer using shear mixing to prepare an uncured TIM emulsion of liquid metal droplets comprising an average particle size of <NUM> microns. The Galinstan loading was <NUM>% by volume of the uncured TIM emulsion. The uncured TIM emulsion was applied on a heat generating device (e.g., die) and was compressed between the heat sink and the die in the uncured state until a desired bondline thickness (BLT) was achieved to form an uncured assembly. While compressing the uncured TIM between the heat sink and the die, the pressure used for the compression was measured at the respective bondline thickness and the results are shown in <FIG>. As illustrated, the pressure for compression was no greater than <NUM> pounds per square inch gauge (psig) during compression from a BLT of <NUM> microns to <NUM> microns which is applicable for various packaging equipment.

Since Galinstan remains in the liquid phase during compression, a far-field mechanical deformation can deform the liquid metal droplets in the uncured TIM emulsion which can enhance directional heat dissipation properties of the TIM. For example, the thermal conductivity of the uncured TIM emulsion can increase 50x in the direction of strain.

Additional uncured assemblies were prepared according to the method described above with BLTs ranging from <NUM> microns to <NUM> microns. The contact thermal resistance of the uncured assemblies were measured using Siemens T3Ster equipment and the results are shown in <FIG>. As illustrated in <FIG>, the contact thermal resistance surprisingly changes at <NUM> microns and approaches effectively zero contact resistance at a BLT fo <NUM> microns indicating an enhanced thermal interface in the uncured assembly when the BLT is no greater than the average particle size of the liquid metal droplets in the TIM emulsion. It is believe that the contact thermal resistance will change minimally, if at all, after curing the TIM emulsion. Additionally, it is believe other inventive assemblies according to the present disclosure can achieve an enhanced thermal interface when the BLT is no greater than the average particle size of liquid metal droplets in the TIM emulsion used in the respective inventive example.

The total thermal resistance, including the contact thermal resistance, through the uncured TIM emulsion in an uncured assembly comprising a BLT of <NUM> microns was measured to be <NUM>*mm<NUM>/W. It is believe other inventive assemblies according to the present disclosure can achieve an enhanced thermal resistance properties.

Those skilled in the art will recognize that the herein described compositions, articles, methods, and the discussion accompanying them are used as examples for the sake of conceptual clarity and that various configuration modifications are contemplated. Consequently, as used herein, the specific exemplars set forth and the accompanying discussion are intended to be representative of their more general classes. In general, use of any specific exemplar is intended to be representative of its class, and the non-inclusion of specific components (e.g., operations), devices, and objects should not be taken as limiting.

Claim 1:
An integrated circuit assembly comprising:
a die (<NUM>);
an upper layer (<NUM>); and
a thermal interface material (<NUM>) disposed in contact with the die (<NUM>) and the upper layer (<NUM>),
wherein the thermal interface material (<NUM>) comprises a polymer (<NUM>) and liquid metal droplets (<NUM>) dispersed throughout the polymer (<NUM>),
wherein a bondline distance formed between the die (<NUM>) and the upper layer (<NUM>) is no greater than <NUM> microns,
wherein the liquid metal droplets (<NUM>) are in a liquid phase at least at a temperature in a range of -<NUM> degrees Celsius to <NUM> degrees Celsius, and
the polymer (<NUM>) is elastomeric.