Methods for depositing thermal interface materials and circuit assemblies formed therefrom

Abstract

Methods of depositing thermal interface materials and integrated circuit components formed therefrom are provided. The method includes depositing a stop structure on a first layer proximate to the circuit component. The method includes depositing a thermal interface material at a first layer thickness between a first layer of the circuit component and a second layer of the circuit component. The thermal interface material includes liquid metal droplets and an emulsion of a polymer. The method includes compressing the circuit assembly to reduce the first layer thickness to the second layer thickness, thereby deforming the liquid metal droplet. Diffusion of the thermal interface material across the surface of the first layer is limited by the limiting structure.

Description

[0001] CLAIM OF PRIORITY

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 452,136, filed March 14, 2023, which has the same name and inventors as the present application, the entire contents of which are hereby incorporated by reference. TECHNICAL FIELD

[0003] The present invention relates to methods of depositing thermal interface materials and integrated circuit assemblies formed thereby. BACKGROUND

[0004] Thermal interface materials (TIMs) can be used to thermally connect two or more layers together. For example, TIMs are often used in CPU packages to thermally connect the integrated heat spreader (HIS) of the CPU package to a heatsink. Various types of methods of depositing TIMs can be used. However, there are challenges with current methods of applying TIMs. SUMMARY

[0005] In one general aspect, the present invention relates to a method comprising depositing a constraint proximate to a first layer of a circuit assembly. In various examples, the constraint comprises a foam, and the foam is deformable in response to compression. The method comprises depositing a thermal interface material between the first layer of the circuit assembly and a second layer of the circuit assembly at a first layer thickness. The thermal interface material comprises droplets of liquid metal and an emulsion of a polymer. The method comprises compressing the circuit assembly to reduce the first layer thickness to a second layer thickness, thereby deforming the droplets of liquid metal. Diffusion of the thermal interface material across a surface of the first layer is limited by the constraint.

[0006] The present invention can provide low contact resistance at the material interface and low thermal resistance through the TIM. The low contact resistance and low thermal resistance through the TIM can be achieved by a constraint that can hold the thermal interface material in a desired location during compression at various speeds. Additionally, the methods described herein can achieve a desired distribution of droplets of liquid metal on the circuit assembly, a desired uniformity of the droplets of liquid metal within the TIM, and / or a desired shape of the droplets of liquid metal within the TIM, thereby enhancing the effective thermal conductivity of the TIM. These and other benefits realized from the various embodiments of the present invention will be apparent from the description that follows, taken in connection with the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0007] The features and advantages of the various embodiments of the present invention will become more apparent from the detailed description in connection with the accompanying drawings upon

[0008] Figure 1 is a cross-sectional perspective view of a circuit assembly according to the present application after deposition of a thermal interface material;

[0009] Figure 2 is a cross-sectional side view of an integrated circuit formed by compressing Figure 1 a circuit assembly of

[0010] Figure 3 is a top view of an integrated circuit of Figure 2 wherein the second layer is hidden in the view.

[0011] In the several views, like reference numerals designate like components throughout the several views. Examples described herein illustrate certain embodiments and such examples should not be construed as limiting the scope of embodiments. DETAILED DESCRIPTION

[0012] Certain illustrative aspects of the disclosure will now be described in providing a full and enabling disclosure of the composition and methods disclosed herein. One or more embodiments of these aspects are illustrated in the accompanying drawings. Those of ordinary skill in the art will understand that the compositions, articles, and methods specifically described herein are merely illustrative and that the scope of the disclosure is limited solely by the claims. Features shown or described with respect to one example aspect can be combined with features of other aspects. Such modifications and variations are intended to fall within the scope of the present disclosure.

[0013] Applying a thermal interface material (TIM) to a circuit assembly to position the TIM between an integrated heat spreader (IHS) and a heat sink can require balancing the thermal resistance through the TIM and the contact resistance at the material interface. For example, a polymeric material can have a low contact resistance at the material interface, but have a high thermal resistance through the material. A solid metal can have a low thermal resistance through the material, but have a high contact resistance at the material interface. Further, some solid materials (polymeric or metallic) can require a large pressure during installation to achieve a desired contact resistance. Further, when utilizing a TIM having liquid metal droplets, the inventors have determined that there are challenges in achieving a desired distribution of the liquid metal droplets on the circuit assembly, a desired shape of the liquid metal droplets on the circuit assembly, and uniformity of the liquid metal within the TIM, which impacts the effective thermal conductivity through the TIM.

[0014] For example, the inventors observed that when compressing a circuit assembly including a TIM, certain compression rates can result in non-uniformity of the TIM and / or undesirable coverage of surfaces in the circuit assembly. Accordingly, in various embodiments, the inventors provide a method that includes depositing a containment structure proximate a first layer of a circuit assembly. The method includes depositing a thermal interface material between the first layer of the circuit assembly and a second layer of the circuit assembly at a first layer thickness. The thermal interface material includes a liquid metal droplet and an emulsion of a polymer. The method includes compressing the circuit assembly to reduce the first layer thickness to a second layer thickness, thereby deforming the liquid metal droplet. The spreading of the thermal interface material across a surface of the first layer is limited by the containment structure. Limiting the spreading of the TIM can enhance the uniformity of the TIM and / or enhance coverage of surfaces in the circuit assembly. By limiting the spreading of the TIM, a wider range of compression rates can be used in the circuit assembly.

[0015] As used in this specification, particularly with respect to a layer, film or material, the terms "on," "over," "above," and variations thereof (e.g., "applied over," "formed over," "deposited over," "provided over," "located over," etc.) refer to being applied, formed, deposited, provided or located above the surface of a substrate, but not necessarily in contact with the surface of the substrate. For example, a TIM "deposited on" a substrate does not preclude the presence of another layer or layers of the same or different composition between the deposited TIM and the substrate. Likewise, a second layer "deposited on" a first layer does not preclude the presence of another layer or layers of the same or different composition between the deposited second layer and the deposited TIM.

[0016] The terms "polymer" and "polymeric" as used in this specification refer to prepolymers, oligomers, as well as homopolymers and copolymers. "Prepolymer" as used in this specification refers to a polymer precursor that is capable of further reaction or polymerization through one or more reactive groups to form a higher molecular weight or crosslinked state.

[0017] The polymer can be at least one of a polymeric adhesive, a thermoset polymer, and a thermoplastic polymer. As used herein, the term "thermoset" refers to a polymer that irreversibly "sets" upon curing or crosslinking, where the polymer chains of the polymer components are linked together by covalent bonds, which are typically induced by, for example, heat or radiation. In various examples, the curing or crosslinking reaction can be carried out at ambient conditions. Once cured or crosslinked, the thermoset polymer can not flow upon heating, can otherwise irreversibly increase in viscosity, and / or can not be soluble in conventional solvents. As used herein, the term "thermoplastic" refers to a polymer comprising polymer components where the component polymer chains are not linked (e.g., crosslinked) by covalent bonds, such that upon heating, the polymer can undergo liquid flow and be soluble in conventional solvents. In certain embodiments, the polymer can be elastomeric (e.g., rubbery, soft, elastic) or rigid (e.g., glassy). For example, the polymer can be an elastomer.

[0018] The thermoset polymer can include at least one of a crosslinking agent, which can include, for example, an aminoplast, a polyisocyanate (including blocked isocyanates), a polyepoxide, a beta-hydroxyalkylamide, a polyacid, an anhydride, an organometallic acid functional material, a polyamine, a polyvinyl compound, a polysilicon hydride, a polyol, a polyacyl chloride, a polyhalide, and a polyamide. The polymer can have functional groups that react with the crosslinking agent.

[0019] The polymer in the TIM described herein can be selected from any of a variety of polymers known in the art. For example, the thermoset polymer can include at least one of an acrylic polymer, a polyester polymer, a polyurethane polymer, a polybutadiene, a polyamide polymer, a polyether polymer, a polysiloxane polymer (e.g., poly(dimethylsiloxane)), a fluoropolymer, a polyisoprene polymer (e.g., a rubber), and copolymers thereof (e.g., styrene ethylene butylene styrene). The functional groups on the thermoset polymer can be selected from any of a variety of reactive functional groups, including, for example, carboxylic acid groups, amine groups, epoxy groups, hydroxyl groups, thiol groups, carbamate groups, amide groups, urea groups, isocyanate groups (including blocked isocyanate groups), vinyl groups, silicon hydride groups, acyl chloride groups, acrylate groups, halogen groups, and thiol groups.

[0020] The thermoplastic polymer can include at least one of a propylene-ethylene copolymer, a styrene-butadiene-styrene, and a styrene-ethylene-butylene-styrene. The polymer can have a melting point of at least 100 degrees Celsius, for example, at least 120 degrees Celsius, at least 150 degrees Celsius, or at least 200 degrees Celsius.

[0021] The polymeric adhesive can be a polyether adhesive.

[0022] The liquid metal droplet for the TIM can include at least one of gallium, a gallium alloy, indium, an indium alloy, tin, a tin alloy, mercury, and a mercury alloy. The liquid metal droplet can have a melting point of no greater than 30 degrees Celsius, such as no greater than 25 degrees Celsius, no greater than 20 degrees Celsius, no greater than 15 degrees Celsius, no greater than 10 degrees Celsius, no greater than 5 degrees Celsius, no greater than 0 degrees Celsius, or no greater than -10 degrees Celsius. The liquid metal droplet can include a melting point of at least -40 degrees Celsius, such as at least -20 degrees Celsius, at least -19 degrees Celsius, at least -10 degrees Celsius, at least 0 degrees Celsius, at least 5 degrees Celsius, at least 10 degrees Celsius, at least 15 degrees Celsius, at least 20 degrees Celsius, or at least 25 degrees Celsius. The liquid metal droplet can have a melting point in a range of -40 degrees Celsius to 30 degrees Celsius, such as -20 degrees Celsius to 30 degrees Celsius, -19 degrees Celsius to 30 degrees Celsius, or -19 degrees Celsius to 25 degrees Celsius. The determination of the melting point can be made at a pressure of 1 absolute atmosphere. In certain embodiments, the TIM can include gallium indium tin (Galinstan) and have a melting point of -19 degrees Celsius.

[0023] The TIM can be produced by forming an emulsion of polymer and liquid metal droplets such that the liquid metal droplets are substantially dispersed throughout the polymer. For example, the polymer and bulk liquid metal can be mixed together with at least one of a high shear mixer, a centrifugal mixer, by shaking in a container, a mortar and pestle, and ultrasonic treatment. More details about exemplary methods of forming emulsions and liquid metal droplets are described in (1) published PCT WO / 2019 / 136252, entitled “Method of Synthesizing a Thermally Conductive and Stretchable Polymer Composite,” (2) published U.S. Application US2017 / 0218167, entitled “Polymer Composite with Liquid Phase Metal Inclusions,” (3) U.S. Patent No. 10,777,483, entitled “Method, apparatus, and assembly for thermally connecting layers,” (4) U.S. Provisional Patent No. 63 / 268,134, entitled “Thermal interface material, an integrated circuit assembly, and a method for thermally connecting layers,” and (5) published PCT WO 2022 / 204689, entitled “A method, apparatus, and assembly for thermally connecting layers with thermal interface materials comprising rigid particles,” all of which are incorporated herein by reference in their entirety.

[0024] The components and / or mixing techniques can be selected such that the viscosity is less than 850,000 cP (centipoise), such as less than 750,000 cP, less than 500,000 cP, less than 250,000 cP, 200,000 cP, less than 150,000 cP, less than 100,000 cP, less than 50,000 cP, less than 15,000 cP, less than 14,000 cP, less than 13,000 cP, less than 12,000 cP, less than 11,000 cP, or less than 10,000 cP. For example, the components and / or mixing techniques can be selected such that the viscosity of the TIM is at least 1,000 cP, such as at least 2,000 cP, at least 5,000 cP, or at least 10,000 cP. The components and / or mixing techniques can be selected such that the viscosity of the TIM is in a range from 1,000 cP to 850,000 cP, such as from 2,000 cP to 750,000 cP, or from 2,000 cP to 500,000 cP. The viscosity of the TIM emulsion can be measured by a parallel plate (40 mm) rheometer at 25 degrees Celsius, a frequency of 10 radians per second, and a strain of 5%. Selecting the viscosity can require balancing the installation pressure, which can increase with high viscosity and the ability to resist rapid spreading during application of the TIM and pumping out during operation, and the desired effective thermal conductivity.

[0025] The TIM can include at least 1% of the liquid metal droplets by total volume of the TIM, such as at least 5% of the liquid metal droplets, at least 10% of the liquid metal droplets, at least 20% of the liquid metal droplets, at least 30% of the liquid metal droplets, at least 40% of the liquid metal droplets, at least 50% of the liquid metal droplets, at least 60% of the liquid metal droplets, at least 70% of the liquid metal droplets, at least 80% of the liquid metal droplets, or at least 90% of the liquid metal droplets, all based on the total volume of the liquid metal droplets. The TIM can include no more than 95% of the liquid metal droplets by total volume of the TIM, such as no more than 93% of the liquid metal droplets, no more than 90% of the liquid metal droplets, no more than 80% of the liquid metal droplets, no more than 70% of the liquid metal droplets, no more than 60% of the liquid metal droplets, no more than 50% of the liquid metal droplets, no more than 40% of the liquid metal droplets, no more than 30% of the liquid metal droplets, no more than 20% of the liquid metal droplets, or no more than 10% of the liquid metal droplets, all based on the total volume of the TIM. The TIM can include the liquid metal droplets in a range from 1% to 95% of the total volume of the TIM, such as, for example, 5% to 93% of the liquid metal droplets, 50% to 93% of the liquid metal droplets, 60% to 93% of the liquid metal droplets, or 70% to 93% of the liquid metal droplets, all based on the total volume of the TIM. The amount of liquid metal droplets can be selected while balancing the desired elasticity and the desired effective thermal conductivity of the TIM.

[0026] Component and / or mixing techniques can be selected to obtain the desired D of liquid metal droplets in the TIM prior to compression. 50 and / or D 90 D of liquid metal droplets 50 Before compression, it can be at least 1 micrometer, such as, for example, at least 5 micrometers, at least 10 micrometers, at least 15 micrometers, at least 20 micrometers, at least 30 micrometers, at least 35 micrometers, at least 40 micrometers, at least 50 micrometers, at least 60 micrometers, at least 70 micrometers, at least 80 micrometers, at least 90 micrometers, at least 100 micrometers, at least 120 micrometers, or at least 150 micrometers, all before compression. The D of the liquid metal droplet 50 It can be no larger than 200 micrometers, such as, for example, no larger than 150 micrometers, no larger than 120 micrometers, no larger than 100 micrometers, no larger than 90 micrometers, no larger than 80 micrometers, no larger than 70 micrometers, no larger than 60 micrometers, no larger than 50 micrometers, no larger than 40 micrometers, no larger than 35 micrometers, no larger than 30 micrometers, no larger than 20 micrometers, no larger than 10 micrometers, or no larger than 5 micrometers, all before compression. For example, the D of a liquid metal droplet. 50 The range can be from 1 micrometer to 200 micrometers, for example, 5 micrometers to 150 micrometers, 15 to 150 micrometers, 35 micrometers to 150 micrometers, 35 micrometers to 70 micrometers, or 5 micrometers to 100 micrometers, all of which are measured prior to compression. In various embodiments, component and / or mixing techniques can be selected to achieve D greater than that of rigid particles in the TIM (if present). 50 The average particle size of liquid metal droplets, such as, for example, greater than the D-size of rigid particles. 50 At least 1%, at least 2%, at least 5%, at least 10%, or at least 20%.

[0027] As used in this article, D 50 The size can be measured using a microscope (e.g., an optical microscope or an electron microscope). The size can be the diameter of a spherical particle, or, if the particle is elliptical or otherwise irregularly shaped, its length along its longest dimension. As used herein, the particle's "D"... X "" refers to the diameter when X% of the particle volume has a smaller diameter.

[0028] D of liquid metal droplets 90 It can be at least 1 micrometer, such as at least 5 micrometers, at least 10 micrometers, at least 15 micrometers, at least 20 micrometers, at least 30 micrometers, at least 35 micrometers, at least 40 micrometers, at least 50 micrometers, at least 60 micrometers, at least 70 micrometers, at least 80 micrometers, at least 90 micrometers, at least 100 micrometers, at least 120 micrometers, or at least 150 micrometers, all before compression. The D of the liquid metal droplet. 90may be no greater than 300 microns, such as, for example, no greater than 200 microns, no greater than 150 microns, no greater than 120 microns, no greater than 100 microns, no greater than 90 microns, no greater than 80 microns, no greater than 70 microns, or no greater than 50 microns, all prior to compression. For example, the D 90 may be in the range of 1 micron to 300 microns, such as, for example, 10 microns to 200 microns, 15 to 150 microns, 35 microns to 150 microns, 35 microns to 120 microns, or 50 microns to 100 microns, all measured prior to compression.

[0029] The TIM can optionally include other components, such as, for example, rigid particles, catalysts, and coupling agents. The rigid particles can include at least one of iron, iron alloys (e.g., steel), vanadium, vanadium alloys, niobium, niobium alloys, titanium, titanium alloys, copper, copper alloys (e.g., bronze), rigid polymers, glass, and ceramics. The rigid particles can resist deformation and / or resist corrosion by the liquid metal droplets. For example, the rigid particles can have a Young’s modulus of at least 100 MPa (megaPascal), such as, for example, at least 110 MPa, at least 150 MPa, at least 200 MPa, at least 250 MPa, at least 500 MPa, at least 750 MPa, at least 1 GPa (gigaPascal), or at least 2 GPa. The Young’s modulus can be measured according to ASTM E111-17. The TIM can include rigid particles in the range of 0.1% to 30% of the total volume of the TIM, such as, for example, 0.1% to 10% rigid particles, 0.1% to 5% rigid particles, 1% to 10% rigid particles, or 1% to 5% rigid particles, all based on the total volume of the TIM.

[0030] The D 50 to achieve a desired bondline thickness in the assembly. The average particle size of the rigid particles can be at least 1 micron, such as, for example, at least 5 microns, at least 10 microns, at least 20 microns, at least 30 microns, at least 35 microns, at least 40 microns, at least 50 microns, at least 60 microns, at least 70 microns, at least 80 microns, at least 90 microns, at least 100 microns, at least 120 microns, or at least 125 microns. The D 50 may be no greater than 150 microns, such as, for example, no greater than 125 microns, no greater than 120 microns, no greater than 100 microns, no greater than 90 microns, no greater than 80 microns, no greater than 70 microns, no greater than 60 microns, no greater than 50 microns, no greater than 40 microns, no greater than 35 microns, no greater than 30 microns, no greater than 20 microns, no greater than 10 microns, or no greater than 5 microns. For example, the D 50The TIM can be in a range of 1 micron to 150 microns, such as, for example, 15 to 150 microns, 5 microns to 125 microns, 35 microns to 125 microns, 35 microns to 70 microns, or 50 microns to 70 microns.

[0031] The TIM can be applied to various layers and devices, which will be described below with reference to Figures 1 to 3 circuit assembly, but the present application is not limited to circuit assemblies and can be applied to other devices as well. Referring to Figure 1 The method according to the present application includes depositing a containment structure 114 proximate to the first layer 106 of the circuit assembly 102. The containment structure 114 can be used to inhibit movement of the TIM and to keep the TIM on a desired area of the first layer 106 and / or the second layer 108 of the circuit assembly. For example, the containment structure 116 can define a cavity 118 adapted to receive the TIM and / or the layer (e.g., the first layer 106).

[0032] The containment structure can include a foam. The first layer 106 can be disposed on a third layer 116 of the circuit assembly 102. In various examples, the containment structure 114 can be deposited on the third layer 116 and in contact with the first layer 106. The disposition of the containment structure 114 can prevent the TIM from diffusing from the first layer 106 and contacting the third layer 116. The containment structure can limit the TIM to only contacting surfaces within the cavity 118.

[0033] The method includes depositing the TIM 104 according to the present application between the first layer 106 of the circuit assembly 102 and the second layer 108 of the circuit assembly 102 at a first layer thickness tl. The first layer thickness tl can be selected to enhance the effective thermal conductivity of the TIM 104 and / or the uniformity of the TIM 104.

[0034] As shown, the TIM 104 includes a liquid metal droplet 112 and an emulsion of a polymer 110. The first layer thickness tl can be at least 1.1 times, such as, for example, at least 2.5 times, at least 3 times, at least 4 times, at least 5 times, at least 6 times, at least 10 times, at least 20 times, at least 50 times, or at least 100 times, the D 90 of the liquid metal droplet 112 prior to compression of the liquid metal droplet 112 by the circuit assembly 102. The first layer thickness tl can be no more than 1000 times, such as, for example, no more than 500 times, no more than 250 times, no more than 150 times, no more than 100 times, no more than 50 times, no more than 15 times, no more than 10 times, no more than 6 times, or no more than 5 times, the D 90 of the liquid metal droplet 112 prior to compression of the liquid metal droplet 112 by the circuit assembly 102. The first layer thickness tl can be no more than 1000 times, such as, for example, no more than 500 times, no more than 250 times, no more than 150 times, no more than 100 times, no more than 50 times, no more than 15 times, no more than 10 times, no more than 6 times, or no more than 5 times, the D 90 of the liquid metal droplet 112 prior to compression of the liquid metal droplet 112 by the circuit assembly 102. The first layer thickness tl can be no more than 1000 times, such as, for example, no more than 500 times, no more than 250 times, no more than 150 times, no more than 100 times, no more than 50 times, no more than 15 times, no more than 10 times, no more than 6 times, or no more than 5 times, the D 90 of the liquid metal droplet 112 prior to compression of the liquid metal droplet 112 by the circuit assembly 102. The first layer thickness tl can be no more than 1000 times, such as, for example, no more than 500 times, no more than 250 times, no more than 150 times, no more than 100 times, no more than 50 times, no more than 15 times, no more than 10 times, no more than 6 times, or no more than 5 times, the D90 1.1 to 1000 times, such as, for example, 2 to 500 times, 2 to 150 times, 2 to 100 times, 2 to 50 times, 2 to 10 times, 3 to 10 times, or 3 to 6 times, the D 90 of the liquid metal droplet 112 prior to compression by the circuit component 102. Because the first layer thickness t1 can be at least 1.1 times the D 90 of the liquid metal droplet 112 prior to compression, a desired distribution of liquid metal droplets on the circuit component 102 and uniformity of the liquid metal droplets 112 within the TIM 104 can be achieved, thereby enhancing the effective thermal conductivity of the TIM 104.

[0035] The first layer thickness t1 can be adjusted according to the wetting properties of the TIM 104. For example, a TIM having a high contact angle with the first layer 106 and / or the second layer 108 can have poor wetting properties compared to a TIM having a low contact angle with the first layer 106 and / or the second layer 108 with better wetting properties, and can require an increased first layer thickness t1.

[0036] The first layer thickness t1 can be at least 200 microns, such as, for example, at least 300 microns, at least 400 microns, at least 500 microns, or at least 600 microns. The first layer thickness t1 can be no greater than 2,000 microns, such as, for example, no greater than 1,500 microns, no greater than 1,000 microns, no greater than 750 microns, no greater than 600 microns, or no greater than 500 microns. The first layer thickness t1 can be in a range of 200 microns to 2,000 microns, such as, for example, 200 microns to 1,000 microns, 200 microns to 750 microns, or 300 microns to 600 microns.

[0037] The stop structure 114 can include a stop structure thickness t c that is the same as or greater than the first layer thickness t1 of the TIM 104.

[0038] Depositing the TIM 104 can include at least one of dispensing, extruding (e.g., through a nozzle such as a circular nozzle, a fan nozzle, or other nozzle shape), applying with an implement (e.g., a brush, a spatula), stencil printing, 3D printing, and screen printing. The TIM 104 can be deposited in a conformable state such that the TIM 104 can conform to the surfaces of the first layer 106 and the second layer 108 to achieve a desired level of surface contact therebetween. In various examples, the TIM 104 can be applied directly onto the first layer 106, and then the second layer 108 can be applied directly onto the TIM 104. In various other examples, the TIM 104 can be applied directly onto the second layer 108, and then the first layer 106 can be applied directly onto the TIM 104. In certain examples, the TIM 104 can be applied to both the first layer 106 and the second layer 108, and then the first layer 106 and the second layer 108 can be applied together. In various examples, the TIM 104 can be in direct contact with the first layer 106 and the second layer 108 after the TIM 104 is deposited and the circuit assembly 102 is compressed. In certain examples, the application of the TIM 104 can be limited to the surface of the first layer 106 such that the TIM 104 can be used efficiently.

[0039] The TIM can be dispensed from a container and applied to the layer in a conformable state. The TIM can be stored in the container prior to use. The TIM 104 can be in a conformable state in the container. The container can include at least one of a pillow pack container, a syringe, a beaker, a jar, a bottle, and a bucket. In various embodiments, the container can be an off-the-shelf dispensing device, such as a pillow pack container or a syringe. In certain examples, the TIM 104 can not be stored and can be used without storage after the emulsion is created.

[0040] The TIM 104 can be applied to at least 1% of the surface area of the exposed side 106a of the first layer 106 prior to the compression of the circuit assembly 102, such as, for example, at least 2%, at least 5%, at least 10%, at least 20%, at least 30%, at least 40%, or at least 50%, all percentages relative to the surface area of the exposed side 106a of the first layer 106. For example, the TIM 104 can be applied to a range of 1% to 100% of the surface area of the exposed side 106a of the first layer 106 prior to the compression of the circuit assembly 102, such as, for example, 2% to 100%, 5% to 90%, or 5% to 80%, all percentages relative to the surface area of the exposed side 106a of the first layer 106.

[0041] The first layer 106 and the second layer 108 individually can be at least one of a battery, a heat-generating component (e.g., an integrated circuit such as a processor, an ASIC, and / or a system on a chip (SOC)), a heat sink (e.g., a heat spreader, a fan, a liquid cooling device), an integrated heat spreader, and a package. For example, the first layer 106 can be a heat-generating electronic component, and the second layer 108 can be a heat sink and / or an integrated heat spreader. The third layer 116 can be a support layer for the first layer 106. For example, the third layer 116 can be a circuit board.

[0042] After depositing the TIM 104, the method includes compressing the circuit assembly 102 to reduce the first layer thickness ti to a second layer thickness t2, thereby deforming and forming the integrated circuit 202 from the liquid metal droplet 112. For example, referring to the detail view in FIG. 2B, the first layer 106 and the second layer 108 can be pressed together, and the first layer 106 can contact the third layer 116. For example, compressing the circuit assembly 102 can include applying a pressure of at least 1 psi (e.g., by compressing the third layer 116 and / or other layers in contact with the first layer 106 or the second layer 108) to the first layer 106 and the second layer 108, such as, for example, at least 5 psi, at least 10 psi, at least 15 psi, or at least 20 psi. In various examples, the pressure can be in a range of 1 psi to 50 psi, such as 10 psi to 30 psi. Figures 1-2

[0043] The containment structure 114 can limit the spread of the TIM across the exposed surface 106a of the first layer 106 and / or limit the spread of the TIM across the second layer 108. For example, the containment structure 114 can prevent the TIM from contacting other sides of the first layer 106, other portions of the second layer 108, and / or the third layer 116. The containment structure 114 can deform in response to a compression force, such as compression of the circuit assembly 102. The deformability of the containment structure 114 can be such that the containment structure thickness t c The second layer thickness t2 can be reduced in response to compression of the circuit assembly 102.

[0044] ​In various examples, the relative liquid metal surface area coverage between the TIM 104 and the first and second layers 106, 108 can be increased by compression. For example, the relative liquid metal surface area coverage after compression can be in the range of 1% to 100%, such as, for example, 1% to 5%, 5% to 10%, 10% to 30%, 30% to 50%, or increased up to a liquid metal surface area coverage of 100%. As used herein, “relative liquid metal area coverage” refers to the surface area covered by liquid metal normalized by the total contact surface area between the TIM 104 and the first and second layers 106, 108. The relative liquid metal area coverage can be measured using the following method: prepare a cross-section, then optical imaging using a ZEISS Axio Zoom.V16, or confocal scanning acoustic microscopy using a Hitachi FineSAT III for CSAM.

[0045] The second layer thickness t2may be the bondwire thickness, and the second layer thickness t2may be no greater than 300 microns, such as, for example, no greater than 200 microns, no greater than 150 microns, no greater than 145 microns, no greater than 140 microns, no greater than 125 microns, no greater than 100 microns, no greater than 80 microns, no greater than 70 microns, no greater than 50 microns, no greater than 40 microns, no greater than 35 microns, or no greater than 30 microns. The second layer thickness t2may be at least 1 micron, such as, for example, at least 15 microns, at least 30 microns, at least 35 microns, at least 40 microns, at least 50 microns, at least 70 microns, at least 75 microns, at least 80 microns, at least 100 microns, at least 120 microns, at least 140 microns, or at least 145 microns. The second layer thickness t2may be in the range of 1 micron to 200 microns, such as, for example, 15 microns to 200 microns, 15 microns to 150 microns, 30 microns to 150 microns, 50 microns to 120 microns, 75 microns to 125 microns, or 15 microns to 100 microns.

[0046] After compressing the circuit assembly, the TIM can cover at least 90% of the surface area of the exposed side 106a of the first layer 106, such as, for example, at least 95% of the surface area of the exposed side 106a.

[0047] The compressed circuit assembly 102 can apply a force to the TIM 104 and can deform the liquid metal droplets 112 dispersed within the polymer 110 of the TIM 104 and / or deform the standoff structures 114. Because the polymer 110 and / or the standoff structures are still conformable and movable, the compression force can deform the liquid metal droplets 112. The liquid metal droplets 112 can be in a liquid phase during deformation, such that the compression requires a lower pressure to achieve the desired deformation. For example, the liquid metal droplets 112 can be as described in U.S. Patent No. 10, 1 12, 1 1 1, which is incorporated by reference in its entirety. Figure 1The shape shown is roughly spherical, and then it can be as follows: Figure 2 The liquid metal droplet 112 is generally elliptical in shape. In various examples, before compression, the liquid metal droplet 112 may have a first average aspect ratio, and after compression, the liquid metal droplet 112 may have a second average aspect ratio. The second average aspect ratio may differ from the first average aspect ratio. For example, the second average aspect ratio may be greater than the first average aspect ratio. The average aspect ratio may be the average ratio of the width of the liquid metal droplet 112 to the height of the liquid metal droplet 112. In various examples, the first aspect ratio may be 1, and the second aspect ratio may be greater than 1. In some examples, the first aspect ratio may be in the range of 1 to 1.5. In some examples, the second aspect ratio may be at least 0.5 larger than the first aspect ratio, such as, for example, at least 1 larger than the first aspect ratio, at least 2 larger than the first aspect ratio, or at least 5 larger than the first aspect ratio. In some examples, after compression of the circuit assembly 102, the second aspect ratio may be at least 2, such as, for example, after compression of the circuit assembly 102, the second aspect ratio may be at least 3 or at least 4.

[0048] The width (e.g., longest dimension) of the liquid metal droplet 112 can be substantially aligned with the longitudinal plane of the TIM 104 in the circuit assembly 102, and the height of the liquid metal droplet 112 can be substantially aligned with the thickness (e.g., distance d1) of the TIM 104. The width of the liquid metal droplet 112 can increase when the circuit assembly 102 is compressed. For example, in some examples, before compression, the diameter of the liquid metal droplet can be 200 μm (first aspect ratio 1), and after compression to a bonded line thickness of 100 μm, the liquid metal droplet can be deformed into an elliptical shape with a width of 400 μm (e.g., second aspect ratio 4).

[0049] In some examples, after compression, the liquid metal droplets 112 can be arranged essentially in a single layer, such as Figure 2 As shown. The D of the liquid metal droplet 112 can be selected. 50 and / or D 90 A second thickness t2 is deposited with the first layer thickness t1 to achieve a monolayer. Configuring the liquid metal droplet 112 as a monolayer can reduce the thermal resistance of TIM 104.

[0050] refer to Figure 3 After compression, the limiting structure 114 can surround the TIM 104, and the TIM 104 can contact the limiting structure 114. After compression, the TIM 104 can be bounded by the first layer 106, the second layer 108, and the limiting structure 114.

[0051] D of liquid metal droplet 112 50 and / or D 90deformation of the liquid metal droplets 112, and the deposition method of the liquid metal droplets 112 can improve the thermal resistance value of the TIM 104. For example, the TIM 104 can include a thermal resistance value of at least 5 (°K*mm 2 ) / W, such as, for example, at least 1 (°K*mm 2 ) / W, at least 2 (°K*mm 2 ) / W, at least 3 (°K*mm 2 ) / W, at least 5 (°K*mm 2 ) / W, or at least 10 (°K*mm 2 ) / W. The TIM 104 can include a thermal resistance value of not greater than 30 (°K*mm 2 ) / W, such as, for example, not greater than 20 (°K*mm 2 ) / W, not greater than 15 (°K*mm 2 ) / W, not greater than 10 (°K*mm 2 ) / W, not greater than 9 (°K*mm 2 ) / W, not greater than 8 (°K*mm 2 ) / W, not greater than 7 (°K*mm 2 ) / W, or not greater than 5 (°K*mm 2 ) / W. The TIM 104 can include a thermal resistance value in a range of 0.5 (°K*mm 2 ) / W to 30 (°K*mm 2 ) / W, such as, for example, 0.5 (°K*mm 2 ) / W to 20 (°K*mm 2 ) / W, 0.5 ((°K*mm 2 ) / W to 15 (°K*mm 2 ) / W, 1 (°K*mm 2 ) / W to 10 (°K*mm 2 ) / W, 2 (°K*mm 2 ) / W to 10 (°K*mm 2 ) / W, or 2 (°K*mm 2 ) / W to 8 (°K*mm 2 ) / W. The thermal resistance value can be measured using a TIMA5 instrument from Nano test (Germany).

[0052] The D 50 and / or D 90The deformation of the liquid metal droplets 112 and the deposition method of the metal droplets 112 can improve the thermal conductivity value of the TIM 104. For example, the TIM 104 can include an effective thermal conductivity value of at least 5 W / m*K, such as, for example, at least 10 W / m*K, at least 12 W / m*K, at least 15 W / m*K, at least 17 W / m*K, or at least 20 W / m*K. The TIM can include an effective thermal conductivity value in a range of 5 W / m*K to 50 W / m*K, such as, for example, 10 W / m*K to 40 W / m*K or 10 W / m*K to 30 W / m*K. As used herein, the effective thermal conductivity is the thickness of the TIM divided by the thermal resistance of the TIM.

[0053] The TIM 104 can or can not be cured depending on the application. For example, the TIM 104 can be cured to a solid, or the TIM can be a paste. Curing the TIM 104 can increase the viscosity of the polymer 110 and can harden the polymer 110. For example, the polymer 110 can become a solid. In various examples, the polymer 110 after curing is an elastomer. Curing the polymer 110 can inhibit the pump out of the liquid metal droplets 112 during thermal cycling of the circuit assembly 102, can provide mechanical bonding between the first layer 106 and the second layer 108, and / or can maintain the second layer thickness t2.

[0054] Curing the TIM 104 can include at least one of heating the TIM 104 (e.g., in examples with thermoset polymers), adding a catalyst to the TIM 104, exposing the TIM 104 to air, cooling the TIM 104 (e.g., in examples with thermoplastic polymers), applying electromagnetic radiation (e.g., photopolymerization), and applying pressure to the TIM 104. Curing the TIM 104 can increase the viscosity of the TIM emulsion to greater than 15,000 cP, such as, for example, greater than 20,000 cP, greater than 30,000 cP, greater than 50,000 cP, greater than 100,000 cP, greater than 150,000 cP, greater than 200,000 cP, greater than 250,000 cP, greater than 500,000 cP, greater than 750,000 cP, or greater than 850,000 cP. For example, the polymer in the TIM 104 can be cured. In various examples, the TIM 104 can be an adhesive. The polymer in the TIM 104 can be selected to reduce outgassing of the TIM 104 during curing.

[0055] As used in the present specification, the terms "cure" and "curing" refer to chemical cross-linking of components in an emulsion or material applied to a substrate, or an increase in viscosity of components in an emulsion or material applied to a substrate. Thus, the terms "cure" and "curing" include not only physical drying of an emulsion or material by evaporation of solvent or carrier. In this regard, as used in the present specification in examples including thermoset polymers, the term "cure" refers to a state of an emulsion or material in which components of the emulsion or material have chemically reacted to form new covalent bonds in the emulsion or material (e.g., new covalent bonds are formed between an adhesive resin and a curing agent). As used in the present specification in examples including thermoplastic polymers, the term "cure" refers to a state of an emulsion or material in which the temperature of the thermoplastic polymer is reduced below the melting point of the thermoplastic polymer such that the viscosity of the emulsion or material is increased. In examples including both thermoset polymers and thermoplastic polymers, the term "cure" refers to one or both of the polymer cures as described herein.

[0056] In various other examples, TIMs according to the present disclosure can be used in systems on package. For example, a single horizontal TIM layer can be in contact with multiple dies on one side (e.g., an integrated circuit can include multiple dies or multiple integrated circuits can be in contact with the same side of the TIM), and in contact with one or more overlying layers on different sides.

[0057] Those skilled in the art will recognize that the compositions, articles, methods, and discussions accompanying them, described herein are used as examples only and that various modifications to the configurations can be considered. Thus, as used herein, the particular examples set forth and the accompanying discussions are intended to be representative of their more general classes. In general, the use of any particular sample is intended to be representative of its class and the particular components (e.g., operations), devices and objects that should not be construed to limit the application.

[0058] With respect to the appended claims, those skilled in the art will appreciate that the operations therein typically can be carried out in any order. Additionally, although various operations can be presented herein in a sequential order, those skilled in the art will appreciate that various operations can in fact be handled in parallel, or in an interleaved fashion, or as recombinations of parallel or interleaved processes, unless otherwise specifically stated at some depth of detail. Also, while the various operations of example methods can be presented herein as sequential processes, those skilled in the art will appreciate that the various operations can in fact be handled in parallel, or in an interleaved fashion, or as recombinations of parallel or interleaved processes, unless otherwise specifically stated at some depth of detail. Additionally, depending on the context, unless otherwise clear from the context, the use of certain terminology can be taken to include the meaning well known to one of ordinary skill in the art to the context.

[0059] While various examples have been described herein, many modifications, variations, alternatives, combinations, and equivalents of these examples can be implemented and will occur to those skilled in the art. Additionally, where materials are disclosed herein for certain components, other materials are contemplated. Accordingly, the foregoing description and drawings are by way of example only, and are not intended to be limiting. The following claims are intended to cover all such modifications and variations as falling within the scope of the disclosed examples.

[0060] Various aspects of the application in accordance with the present disclosure include, but are not limited to, the aspects listed in the numbered clauses below.

[0061] Clause 1. A method comprising: depositing a containment structure proximate a first layer of a circuit assembly; depositing a thermal interface material between the first layer of the circuit assembly and a second layer of the circuit assembly at a first layer thickness, wherein the thermal interface material comprises an emulsion of liquid metal droplets and a polymer; and compressing the circuit assembly to reduce the first layer thickness to a second layer thickness, thereby deforming the liquid metal droplets, wherein diffusion of the thermal interface material across a surface of the first layer is limited by the containment structure.

[0062] Clause 2. The method of clause 1, wherein the containment structure comprises a foam.

[0063] Clause 3. The method of any of clauses 1-2, wherein the foam is deformable in response to the compressing.

[0064] Clause 4. The method of any of clauses 1-3, wherein the first layer is over a third layer of the circuit assembly, and the containment structure is deposited on the third layer and in contact with the first layer.

[0065] Clause 5. The method of any of clauses 1-4, wherein the containment structure is in contact with the first layer and the second layer after compressing the circuit assembly.

[0066] Clause 6. The method of any of clauses 1-5, wherein the first layer thickness is at least 1.1 times a D 90 of the liquid metal droplets in the thermal interface material prior to compressing the circuit assembly.

[0067] Clause 7. The method of any of clauses 1-6, wherein the first layer thickness is at least 200 microns.

[0068] Clause 8. The method of any of clauses 1-7, wherein the second layer thickness is no greater than 300 microns.

[0069] Clause 9. The method of any of clauses 1-8, wherein the liquid metal droplet has a D 50 in a range of 1 micrometer to 200 micrometers.

[0070] Clause 10. The method of any of clauses 1-9, wherein the thermal interface material covers at least 90% of a surface area of the exposed side of the first layer after compressing the circuit assembly.

[0071] Clause 11. The method of any of clauses 1-10, wherein depositing the thermal interface material comprises at least one of dispensing, extruding, applying with an applicator, stencil printing, 3D printing, and screen printing.

[0072] Clause 12. The method of any of clauses 1-11, wherein compressing the circuit assembly comprises applying a first pressure of at least 1 psi to the first layer and the second layer.

[0073] Clause 13. The method of any of clauses 1-12, wherein the first layer and the second layer individually comprise at least one of a battery, a heat-generating component, a heat sink, an integrated heat spreader, and a package.

[0074] Clause 14. The method of any of clauses 1-13, wherein the first layer comprises a heat- generating component and the second layer comprises a heat sink.

[0075] Clause 15. The method of any of clauses 1-14, wherein the liquid metal droplet comprises at least one of gallium, a gallium alloy, indium, an indium alloy, tin, a tin alloy, mercury, and a mercury alloy.

[0076] Clause 16. The method of any of clauses 1-15, wherein the liquid metal droplet comprises a melting point of no greater than 30 degrees Celsius.

[0077] Clause 17. The method of any of clauses 1-16, wherein the thermal interface material comprises an effective thermal conductivity value of at least 5 W / m*K after compression.

[0078] Clause 18. The method of any of clauses 1-17, wherein the polymer comprises a thermoset polymer.

[0079] Clause 19. The method of any of clauses 1-18, wherein the polymer comprises a thermoplastic polymer.

[0080] Clause 20. The method of any of clauses 1-19, wherein the emulsion has a viscosity of 1,000 cP to 850,000 cP measured at 25 degrees Celsius prior to compression.

[0081] Clause 21. The method of any of clauses 1-20, wherein the liquid metal droplet comprises an aspect ratio of at least 2 after compressing the circuit component.

[0082] Clause 22. The method of any of clauses 1-21, further comprising solidifying the thermal interface material after compressing, thereby increasing a viscosity of the thermal interface material to maintain the second layer thickness.

[0083] Clause 23. An integrated circuit formed by the method of any of clauses 1-22.

[0084] As used herein, “at least one of’ a list of elements means any combination of one or more of the elements in the list. For example, “at least one of A, B, and C” means only A; only B; only C; A and B; A and C; B and C; or A, B, and C.

[0085] Various features and characteristics described in this specification were presented to provide an understanding of the composition, structure, production, function, and / or operation of the present application, which includes the disclosed compositions, coatings, and methods. It should be understood that the various features and characteristics of the present application described in this specification can be combined in any suitable manner without regard to whether such features and characteristics are expressly described in combination in this specification. The inventors and applicants expressly intend such combinations, and the full scope of the application is expressly intended to encompass any such combinations. Accordingly, claims can be modified to recite any such features and characteristics in any combination, either expressly or inherently supported by the specification. Moreover, the applicants reserve the right to amend the claims to expressly recite features and characteristics that can be present in the art but not expressly described in the specification. Accordingly, any such amendments will not add new matter to the specification or claims and will comply with the written description, support, and added matter requirements.

[0086] Any numerical range described in this specification shall be understood to include each and every value within the range, including the end points and sub-ranges of the range. For example, a range of 1.0 to 10.0 should be read to include the end points 1.0 and 10.0, as well as sub-ranges such as 2.4 to 7.6, 3.5 to 5.5, and 7.8 to 8.2, etc. All such sub-ranges are intended to be inherently described. The specification and claims should not be read to require only the end points of the ranges or the exact numerical values used in the specification. All ranges include sub-ranges.

[0087] Also, unless explicitly stated otherwise or the context clearly requires otherwise, all numerical parameters in the specification including for example, expressed values, ranges, amounts, percentages, etc., can be understood as being prefaced by the word "about" even if the term does not expressly appear. Also, any numerical parameter described in the specification can be expressly combined with any other numerical parameter recited in the specification, even if the combination of numerical parameters is not expressly stated in the specification. Further, the numerical parameters described in the specification will be understood to include any and all sub-ranges of the numerical parameters expressly stated in the specification. Also, the numerical parameters described in the specification will be understood to include any and all sub-ranges of the numerical parameters expressly stated in the specification.

[0088] Notwithstanding that the numerical ranges and parameters setting forth the broadest scope of the application are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

[0089] References in the specification to "various examples," "some examples," "one example," "an example," etc., mean that a particular feature, structure, or characteristic described in connection with the example is included in at least one example. Thus, appearances of the phrases "in various examples," "in some examples," "in one example," "in an example," etc., in the specification do not necessarily all refer to the same example. Furthermore, the particular features, structures, or characteristics can be combined in any suitable manner in one or more examples. Thus, the particular features, structures, or characteristics illustrated or described in connection with one example can be combined, in whole or in part, with the features, structures, or characteristics of another without limitation. Such modifications and variations are intended to be included within the scope of the embodiments.

[0090] Any patent, publication, or other document identified in this specification is incorporated herein by reference in its entirety, unless otherwise indicated, to the extent that the incorporated material is not inconsistent with the express teachings of the specification. In case of inconsistencies, the present specification, including the definitions, will prevail. Thus, nothing in this specification is to be construed as a disclaimer of the explicit disclosure made explicitly herein. To the extent that any meaning or definition of a term in this document conflicts with that of a term of the same name used in another document, including any document incorporated by reference, the meaning or definition found within this document controls. The applicant(s) reserve the right to amend this specification to expressly recite any subject matter that is incorporated by reference or otherwise deemed or claimed to be part of the present application.

[0091] While, for purposes of illustration, the specific examples of the application have been described above, it will be apparent to those skilled in the art that a wide variety of modi fications can be made in the details of the present application without departing from the spirit thereof as defined by the appended claims.

[0092] While this disclosure has provided a description of various specific aspects, used to illustrate various aspects of the present disclosure and / or potential applications thereof, it will be appreciated that various changes and modifications will occur to those skilled in the art. Therefore, the present application described herein is to be understood as being at least as broad as they are required to be by the scope of the claims, and not by the narrower scope defined by the specific illustrative aspects provided herein.

[0093] It should be understood that the applications described in this specification are not limited to the examples summarized in the or the detailed description. Various other aspects are described and illustrated herein.

Claims

1. A method comprising: depositing a containment structure proximate a first layer of a circuit assembly; depositing a thermal interface material between the first layer of the circuit assembly and a second layer of the circuit assembly at a first layer thickness, wherein the thermal interface material comprises a liquid metal droplet and an emulsion of a polymer; and compressing the circuit assembly to reduce the first layer thickness to a second layer thickness, thereby deforming the liquid metal droplet, wherein diffusion of the thermal interface material across a surface of the first layer is limited by the containment structure.

2. The method of claim 1, wherein the containment structure comprises a foam.

3. The method of claim 1, wherein the foam is deformable in response to the compression.

4. The method of claim 1, wherein the first layer is over a third layer of the circuit assembly, and the containment structure is deposited on the third layer and in contact with the first layer.

5. The method of claim 1, wherein the containment structure is in contact with the first layer and the second layer after compressing the circuit assembly.

6. The method of claim 1, wherein the first layer thickness is at least 1.1 times a D of the liquid metal droplets in the thermal interface material prior to compressing the circuit assembly. 90 1.

7. The method of claim 1, wherein the first layer thickness is at least 200 microns.

8. The method of claim 1, wherein the second layer thickness is no greater than 300 microns.

9. The method of claim 1, wherein the liquid metal droplet has a D 50 In the range of 1 micron to 200 microns.

10. The method of claim 1, wherein the thermal interface material covers at least 90% of a surface area of an exposed side of the first layer after compressing the circuit assembly.

11. The method of claim 1, wherein the depositing the thermal interface material comprises at least one of dispensing, extruding, applying with an applicator, stencil printing, 3D printing, and screen printing.

12. The method of claim 1, wherein compressing the circuit assembly comprises applying a first pressure of at least 1 psi to the first layer and the second layer.

13. The method of claim 1, wherein the first layer and the second layer individually comprise at least one of a battery, a heat-generating component, a heat sink, an integrated heat spreader, and a package.

14. The method of claim 1, wherein the first layer comprises a heat-generating component and the second layer comprises a heat sink.

15. The method of claim 1, wherein the liquid metal droplet comprises at least one of gallium, a gallium alloy, indium, an indium alloy, tin, a tin alloy, mercury, and a mercury alloy.

16. The method of claim 1, wherein the liquid metal droplet comprises a melting point of no greater than 30 degrees Celsius.

17. The method of claim 1, wherein the thermal interface material comprises an effective thermal conductivity value of at least 5 W / m*K after compression.

18. The method of claim 1, wherein the polymer comprises a thermoset polymer.

19. The method of claim 1, wherein the polymer comprises a thermoplastic polymer.

20. The method of claim 1, wherein the emulsion comprises a viscosity in a range of 1,000 cP to 850,000 cP measured at 25 degrees Celsius before compression.

21. The method of claim 1, wherein after compressing the circuit component, the liquid metal droplet comprises an aspect ratio of at least 2.

22. The method of claim 1, further comprising solidifying the thermal interface material after compression, thereby increasing a viscosity of the thermal interface material to maintain the second layer thickness.

23. An integrated circuit formed by the method of claim 1.

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