Method for deposition of thermal interface materials and circuit assemblies formed therefrom

Abstract

A method for depositing a thermal interface material and an integrated circuit assembly formed therefrom is provided. The method includes depositing a constraint proximate a first layer of the circuit assembly. The method includes depositing the thermal interface material at a first layer thickness between the first layer of the circuit assembly and a second layer of the circuit assembly. The thermal interface material includes an emulsion of liquid metal droplets and 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 droplets. The diffusion of the thermal interface material across the surface of the first layer is limited by the constraint.

Description

[Technical Field]

[0001] <Priority Claim> This application claims priority to U.S. Provisional Patent Application No. 63 / 452,136, filed March 14, 2023, having the same names and inventors as set forth above, which is incorporated herein by reference in its entirety.

[0002] The present disclosure relates to methods for depositing thermal interface materials and integrated circuit assemblies formed therefrom. [Background technology]

[0003] 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 CPU package's integrated heat spreader (IHS) to a heat sink. There are various types of deposition methods that can be used to deposit TIMs. However, current TIM application methods present challenges. Summary of the Invention

[0004] In one general aspect, the present disclosure is directed to a method that includes depositing a constraint proximate a first layer of a circuit assembly. In various examples, the constraint includes a foam, which may be deformable in response to compression. The method includes depositing a thermal interface material at a first layer thickness between the first layer of the circuit assembly and a second layer of the circuit assembly. The thermal interface material includes an emulsion of liquid metal droplets and 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 droplets. Diffusion of the thermal interface material across a surface of the first layer is limited by the constraint.

[0005] The present invention can provide both low contact resistance at the material interface and low thermal resistance through the TIM. Low contact resistance and low thermal resistance through the TIM can be made possible by constraints that can hold the thermal interface material in a desired position during compression at various speeds. In addition, the methods described herein can achieve a desired distribution of liquid metal droplets on the circuit assembly, a desired uniformity of liquid metal droplets within the TIM, and / or a desired shape of liquid metal droplets within the TIM, thereby improving the effective thermal conductivity of the TIM. These and other advantages realizable from various embodiments of the present invention will be apparent from the description below. [Brief explanation of the drawings]

[0006] The features and advantages of various embodiments of the present invention, as well as the manner in which they are achieved, will become more apparent and the embodiments will be better understood by reference to the following description of exemplary embodiments taken in conjunction with the accompanying drawings.

[0007] [Figure 1] FIG. 2 is a cross-sectional perspective view of a circuit assembly according to the present disclosure after deposition of a thermal interface material.

[0008] [Figure 2] 2 is a cross-sectional side view of an integrated circuit formed by compressing the circuit assembly of FIG. 1;

[0009] [Figure 3] 3 is a top view of the integrated circuit of FIG. 2 with the second layer hidden from view.

[0010] Corresponding reference characters indicate corresponding parts throughout the several views. The examples described herein illustrate certain particular embodiments in one form, and such examples should not be construed as limiting the scope of the embodiments in any way. DETAILED DESCRIPTION OF THE INVENTION

[0011] Certain exemplary embodiments of the present invention are described herein to provide a general understanding of the principles and methods of the compositions, functions, manufacture, and use of the compositions disclosed herein. One or more examples of these embodiments are illustrated in the accompanying drawings. Those skilled in the art will understand that the compositions, articles, and methods specifically described herein and illustrated in the accompanying drawings are non-limiting exemplary embodiments, and that the scope of various examples of the present invention is defined only by the claims. Features illustrated or described in connection with one exemplary embodiment may be combined with features of other embodiments. Such modifications and variations are intended to be within the scope of the present invention.

[0012] Applying a thermal interface material (TIM) to a circuit assembly, such as one between an integrated heat spreader (IHS) and a heat sink, can require balancing the thermal resistance through the TIM with the contact resistance at the material interface. For example, a polymeric material may have low contact resistance at the material interface but high thermal resistance through the material. A solid metal may have low thermal resistance through the material but high contact resistance at the material interface. In addition, some solid materials (polymer or metal) may require significant pressure during installation to achieve the desired contact resistance. Furthermore, when utilizing a TIM with liquid metal droplets, the inventors have found that there are challenges in achieving the desired distribution of the liquid metal droplets on the circuit assembly, the desired shape of the liquid metal droplets on the circuit assembly, and uniformity of the liquid metal within the TIM, which can affect the effective thermal conductivity through the TIM.

[0013] For example, the inventors have observed that compressing a circuit assembly including a TIM at a certain compression rate can lead to non-uniformity of the TIM and / or undesirable coverage of surfaces within the circuit assembly. Therefore, in various examples, the inventors provide a method that includes depositing a constraint proximate a first layer of the circuit assembly. The method includes depositing a thermal interface material at a first layer thickness between the first layer of the circuit assembly and a second layer of the circuit assembly. The thermal interface material includes an emulsion of liquid metal droplets and 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 droplets. The diffusion of the thermal interface material across the surface of the first layer is limited by the constraint. Limiting the diffusion of the TIM can improve the uniformity of the TIM and / or improve the coverage of surfaces within the circuit assembly. Limiting the diffusion of the TIM can enable a wider range of compression speeds to be used in the circuit assembly.

[0014] As used herein, particularly in reference to layers, films, or materials, the terms "on," "onto," "over," and variations thereof (e.g., "applied on," "formed on," "deposited on," "provided on," "located on," etc.) mean applied to, formed on, deposited on, provided on, or otherwise located on 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 exclude the presence of another or other layer of the same or different composition located between the applied TIM and the substrate. Similarly, a second layer "deposited on" a first layer does not exclude the presence of another or other layer of the same or different composition located between the deposited second layer and the deposited TIM.

[0015] As used herein, the terms "polymer" and "polymeric" refer to prepolymers, oligomers, and both homopolymers and copolymers. As used herein, "prepolymer" refers to a polymer precursor capable of further reaction or polymerization through a reactive group or groups to form higher molecular weight or crosslinked states.

[0016] The polymer may be at least one of a polymer binder, a thermosetting 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 bonded together by covalent bonds, which are often induced, for example, by heat or radiation. In various examples, the curing or crosslinking reaction may be carried out under ambient conditions. Once cured or crosslinked, a thermosetting polymer may not flow upon application of heat, may irreversibly increase in viscosity, and / or may be insoluble in conventional solvents. As used herein, the term "thermoplastic" refers to a polymer comprising polymer components whose constituent polymer chains are not bonded (e.g., crosslinked) by covalent bonds, thereby capable of undergoing liquid flow upon heating and being soluble in conventional solvents. In certain embodiments, the polymer may be elastomeric (e.g., rubbery, soft, stretchy) or rigid (e.g., glassy). For example, the polymer may be an elastomer.

[0017] The thermosetting polymer may include at least one of a crosslinking agent, which may include, for example, aminoplasts, polyisocyanates (including blocked isocyanates), polyepoxides, beta-hydroxyalkylamides, polyacids, anhydrides, organometallic acid-functional materials, polyamines, polyvinyls, hydrogenated polysilicones, polyalcohols, polyacid chlorides, polyhalides, and polyamides. The polymer may have functional groups that react with the crosslinking agent.

[0018] The polymer in the TIM described herein can be selected from any of a variety of polymers known in the art. For example, the thermosetting 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., rubber), and a copolymer thereof (e.g., styrene-ethylene-butylene-styrene). The functional group on the thermosetting polymer can be selected from any of a variety of reactive functional groups, including at least one of 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 group (including a blocked isocyanate group), a vinyl group, a silicon hydride group, an acid chloride group, an acrylate group, a halide group, and a mercaptan group.

[0019] 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 include a melting point of at least 100 degrees Celsius, such as at least 120 degrees Celsius, at least 150 degrees Celsius, or at least 200 degrees Celsius.

[0020] The polymeric binder may be a polyether binder.

[0021] Liquid metal droplets for the TIM can include at least one of gallium, gallium alloy, indium, indium alloy, tin, tin alloy, mercury, and mercury alloy. The liquid metal droplets can include a melting point of 30 degrees Celsius or less, such as 25 degrees Celsius or less, 20 degrees Celsius or less, 15 degrees Celsius or less, 10 degrees Celsius or less, 5 degrees Celsius or less, 0 degrees Celsius or less, or -10 degrees Celsius or less. The liquid metal droplets 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 droplets can include 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 melting point determination can be performed at a pressure of 1 atmosphere absolute. In one particular embodiment, the TIM can include gallium indium tin (Galinstan) and a melting point of -19 degrees Celsius.

[0022] The TIM can be made by forming an emulsion of a polymer and liquid metal droplets such that the liquid metal droplets are dispersed substantially throughout the polymer. For example, the polymer and bulk liquid metal can be mixed together in at least one of a high shear mixer, a centrifugal mixer, by shaking in a container, with a mortar and pestle, or by sonication. More details regarding exemplary methods for forming emulsions and liquid metal droplets can be found in (1) published PCT application WO / 2019 / 136252, entitled "Method of Synthesizing a Thermally Conductive and Stretchable Polymer Composite," (2) published U.S. application Ser. No. 2017 / 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 application Ser. No. 2017 / 0218167, entitled "A method, apparatus, and assembly for thermally connecting layers with thermal interface materials comprising rigid particles." 2022 / 204689, all of which are incorporated herein by reference in their entireties.

[0023] The composition and / or mixing technique can be selected to provide a viscosity of less than 850,000 cP (centipoise), e.g., less than 750,000 cP, less than 500,000 cP, less than 250,000 cP, less than 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, etc. For example, the composition and / or mixing technique can be selected to provide a viscosity of the TIM of at least 1,000 cP, e.g., at least 2,000 cP, at least 5,000 cP, or at least 10,000 cP, etc. The composition and / or mixing technique can be selected so that the viscosity of the TIM is within the range of 1,000 cP to 850,000 cP, such as 2,000 cP to 750,000 cP, or 2,000 cP to 500,000 cP. The viscosity of the TIM emulsion can be measured with a parallel plate (40 mm) rheometer at 25 degrees Celsius, a frequency of 10 radians per second, and 5% strain. Selecting a viscosity can require a balance between installation pressure, which can increase with higher viscosities, and the TIM's ability to resist undesirable rapid spreading during application and pump-out during operation.

[0024] The TIM can comprise at least 1% liquid metal droplets by total volume of the TIM, for example, at least 5% liquid metal droplets, at least 10% liquid metal droplets, at least 20% liquid metal droplets, at least 30% liquid metal droplets, at least 40% liquid metal droplets, at least 50% liquid metal droplets, at least 60% liquid metal droplets, at least 70% liquid metal droplets, at least 80% liquid metal droplets, or at least 90% liquid metal droplets, all based on the total volume of the liquid metal droplets. The TIM can comprise 95% or less liquid metal droplets by total volume of the TIM, e.g., 93% or less liquid metal droplets, 90% or less liquid metal droplets, 80% or less liquid metal droplets, 70% or less liquid metal droplets, 60% or less liquid metal droplets, 50% or less liquid metal droplets, 40% or less liquid metal droplets, 30% or less liquid metal droplets, 20% or less liquid metal droplets, or 10% or less liquid metal droplets, all based on the total volume of the TIM. The TIM can comprise liquid metal droplets in a range of 1% to 95% by total volume of the TIM, e.g., 5% to 93% liquid metal droplets, 50% to 93% liquid metal droplets, 60% to 93% liquid metal droplets, or 70% to 93% liquid metal droplets, all based on the total volume of the TIM. The amount of liquid metal droplets can be selected to balance the desired elasticity and effective thermal conductivity of the TIM.

[0025] The composition and / or mixing technique may be adjusted to achieve the desired D of the liquid metal droplets in the TIM before compression. 50 and / or D. 90 The D of the liquid metal droplet can be selected to achieve 50 can be at least 1 micron before compression, e.g., at least 5 microns, at least 10 microns, at least 15 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 150 microns, all before compression. 50can be 200 microns or less, for example, 150 microns or less, 120 microns or less, 100 microns or less, 90 microns or less, 80 microns or less, 70 microns or less, 60 microns or less, 50 microns or less, 40 microns or less, 35 microns or less, 30 microns or less, 20 microns or less, 10 microns or less, or 5 microns or less, all before compression. For example, D of the liquid metal droplet 50 can be in the range of 1 micron to 200 microns, e.g., 5 microns to 150 microns, 15 microns to 150 microns, 35 microns to 150 microns, 35 microns to 70 microns, or 5 microns to 100 microns, all measured before compression. In various embodiments, the composition and / or mixing technique can be adjusted to, for example, 50 D of rigid particles in the TIM, if present, at least 1% greater, at least 2% greater, at least 5% greater, at least 10% greater, or at least 20% greater than 50 may be selected to achieve an average particle size of the liquid metal droplets greater than

[0026] As used herein, D 50 The D can be measured using microscopy (e.g., optical or electron microscopy). Size can be the diameter of a spherical particle, or the length along the largest dimension in the case of an ellipsoidal or other irregularly shaped particle. As used herein, the "D" of a particle X " represents the diameter at which X% of the particle volume has a smaller diameter.

[0027] D of liquid metal droplets 90 may be at least 1 micron, e.g., at least 5 microns, at least 10 microns, at least 15 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 150 microns, all before compression. 90can be 300 microns or less, e.g., 200 microns or less, 150 microns or less, 120 microns or less, 100 microns or less, 90 microns or less, 80 microns or less, 70 microns or less, or 50 microns or less, all before compression. For example, the D of the liquid metal droplet 90 may be in the range of 1 micron to 300 microns, such as 10 microns to 200 microns, 15 microns to 150 microns, 35 microns to 150 microns, 35 microns to 120 microns, or 50 microns to 100 microns, all measured before compression.

[0028] The TIM can optionally include other components, such as 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 be resistant to deformation and / or corrosion caused by liquid metal droplets. For example, the rigid particles can include a Young's modulus of at least 100 MPa (megapascals), such as 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 (gigapascals), or at least 2 GPa. Young's modulus can be measured according to ASTM E111-17. The TIM can include 0.1% to 30% rigid particles by total volume of the TIM, such as ranges of 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.

[0029] D of rigid particles in TIM 50can be selected to achieve a desired bond line thickness in the assembly. The average particle size of the rigid particles can be at least 1 micron, e.g., 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, etc. The D of the rigid particles 50 can be 150 microns or less, e.g., 125 microns or less, 120 microns or less, 100 microns or less, 90 microns or less, 80 microns or less, 70 microns or less, 60 microns or less, 50 microns or less, 40 microns or less, 35 microns or less, 30 microns or less, 20 microns or less, 10 microns or less, or 5 microns or less. For example, the D of the rigid particles 50 can be in the range of 1 micron to 150 microns, such as 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.

[0030] The TIM can be applied to various layers and devices and is described below with reference to FIGS. 1-3 with reference to a circuit assembly, but is not limited to circuit assemblies and can be applied to other assemblies. Referring to FIG. 1 , a method according to the present disclosure includes depositing a constraint 114 proximate a first layer 106 of a circuit assembly 102. The constraint 114 is used to inhibit movement of the TIM and maintain the TIM on desired areas of the first layer 106 and / or second layer 108 of the circuit assembly. For example, the constraint 116 can define a cavity 118 suitable for receiving the TIM and / or a layer, such as the first layer 106.

[0031] The constraint can include foam. The first layer 106 can be disposed on the third layer 116 of the circuit assembly 102. In various examples, the constraint 114 can be deposited on the third layer 116 and contact the first layer 106. The positioning of the constraint 114 can prevent the TIM from diffusing from the first layer 106 and contacting the third layer 116. The constraint can confine the TIM to only the contact surface within the cavity 118.

[0032] The method includes depositing a TIM 104 according to the present disclosure between a first layer 106 of a circuit assembly 102 and a second layer 108 of the circuit assembly 102 at a first layer thickness t1. The first layer thickness t1 may be selected to improve the effective thermal conductivity of the TIM 104 and / or the uniformity of the TIM 104.

[0033] As illustrated, the TIM 104 includes an emulsion of liquid metal droplets 112 and a polymer 110. The first layer thickness t1 is the D 90 of the liquid metal droplet 112 before compressing the circuit assembly 102 by at least 1.1 times 90 The first layer thickness t1 can be 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 thickness of the liquid metal droplet 112. 90 of the liquid metal droplet 112 before compressing the circuit assembly 102. 90 The first layer thickness t1 can be, for example, 500 times or less, 250 times or less, 150 times or less, 100 times or less, 50 times or less, 15 times or less, 10 times or less, 6 times or less, or 5 times or less. 90 of the liquid metal droplet 112 before compressing the circuit assembly 102. 90The first layer thickness t1 can be, for example, in the range of 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 of the liquid metal droplet 112 before compression. 90 , thereby achieving a desired distribution of liquid metal droplets on the circuit assembly 102 and uniformity of the liquid metal droplets 112 within the TIM 104, thereby improving the effective thermal conductivity of the TIM 104.

[0034] The first layer thickness t1 can be adjusted based on the wetting properties of the TIM 104. For example, a TIM having a high contact angle with the first layer 106 and / or second layer 108 may have poor wetting properties and may require an increased first layer thickness t1 compared to a TIM having a low contact angle with the first layer 106 and / or second layer 108 that has better wetting properties.

[0035] The first layer thickness t1 can be at least 200 microns, e.g., at least 300 microns, at least 400 microns, at least 500 microns, or at least 600 microns, etc. The first layer thickness t1 can be 2,000 microns or less, e.g., 1,500 microns or less, 1,000 microns or less, 750 microns or less, 600 microns or less, or 500 microns or less, etc. The first layer thickness t1 can be in the range of 200 microns to 2,000 microns, e.g., 200 microns to 1,000 microns, 200 microns to 750 microns, or 300 microns to 600 microns, etc.

[0036] The constrained portion 114 has a constrained portion thickness t 1 that is equal to or greater than the first layer thickness t 1 of the TIM 104. c may include:

[0037] Depositing the TIM 104 can include at least one of dispensing, extrusion (e.g., through a nozzle, such as a round nozzle, a fan nozzle, or other nozzle shape), application with an implement (e.g., a brush, a spatula), stencil printing, 3D printing, and screen printing. The TIM 104 can be conformably deposited so 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 to the first layer 106, and then the second layer 108 can be applied directly to the TIM 104. In various other examples, the TIM 104 can be applied directly to the second layer 108, and then the first layer 106 can be applied directly to 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, after deposition of the TIM 104 and compression of the circuit assembly 102, the TIM 104 may be in direct contact with the first layer 106 and the second layer 108. In certain examples, application of the TIM 104 may be limited to the surface of the first layer 106 so that the TIM 104 can be used efficiently.

[0038] The TIM can be dispensed from a container and applied to a conformable layer. The TIM can be stored in the container prior to use. The TIM 104 can be conformable in the container. The container can include at least one of a pillow pack, a syringe, a beaker, a jar, a bottle, and a drum. In various examples, the container can be a ready-to-use dispensing device, such as a pillow pack or a syringe. In certain examples, the TIM 104 may not be stored and can be used after the emulsion is created without storage.

[0039] The TIM 104 can be applied to at least 1% of the surface area of ​​the exposed side 106a of the first layer 106, or to the entire surface area of ​​the exposed side 106a of the first layer 106, such as at least 2%, at least 5%, at least 10%, at least 20%, at least 30%, at least 40%, or at least 50%, etc., of the surface area of ​​the exposed side 106a of the first layer 106, before compressing the circuit assembly 102. For example, the TIM 104 can be applied to between 1% and 100% of the surface area of ​​the exposed side 106a of the first layer 106, or to the entire surface area of ​​the exposed side 106a of the first layer 106, such as between 2% and 100%, between 5% and 90%, or between 5% and 80%, etc., of the surface area of ​​the exposed side 106a of the first layer 106, before compressing the circuit assembly 102.

[0040] The first layer 106 and the second layer 108 may individually be at least one of a battery, a heat-generating component (e.g., an integrated circuit such as a processor, ASIC, and / or system-on-chip (SOC)), a heat sink (e.g., fins, a fan, liquid cooling), an integrated heat spreader, and packaging. For example, the first layer 106 may be a heat-generating electronic component, and the second layer 108 may be a heat sink and / or an integrated heat spreader. The third layer 116 may be a support layer for the first layer 106. For example, the third layer 116 may be a circuit board.

[0041] After deposition of the TIM 104, the method includes compressing the circuit assembly 102 to reduce the first layer thickness t1 to a second layer thickness t2, thereby deforming the liquid metal droplet 112 and forming the integrated circuit 202. For example, with reference to the detailed views of FIGS. 1-2 , the first layer 106 and the second layer 108 can be biased 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 to the first layer 106 and the second layer 108 (e.g., by compressing the third layer 116 and / or other layers in contact with the first layer 106 or the second layer 108), such as 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.

[0042] The constraint 114 can limit the diffusion of the TIM across the exposed surface 106a of the first layer 106 and / or limit the diffusion of the TIM on the second layer 108. For example, the constraint 114 can prevent the TIM from contacting the other side of the first layer 106, other portions of the second layer 108, and / or the third layer 116. The constraint 114 can be deformable in response to a compressive force, such as compression of the circuit assembly 102. The deformability of the constraint 114 can be determined by the constraint thickness t c can be reduced to a second layer thickness t2.

[0043] In various examples, the relative liquid metal surface area coverage between the TIM 104 and the first and second layers 106, 108 can increase with compression. For example, the relative liquid metal surface area coverage after compression can be in a range of 1% to 100%, e.g., 1% to 5%, 5% to 10%, 10% to 30%, 30% to 50%, etc., or can increase until the liquid metal surface area coverage reaches 100%. As used herein, "relative liquid metal surface area coverage" is 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 surface area coverage can be measured using cross-sectioning followed by optical imaging using a ZEISS Axio Zoom.V16 or confocal scanning acoustic microscopy using a Hitachi FineSAT III for CSAM.

[0044] The second layer thickness t2 can be a bond line thickness, and the second layer thickness t2 can be 300 microns or less, e.g., 200 microns or less, 150 microns or less, 145 microns or less, 140 microns or less, 125 microns or less, 100 microns or less, 80 microns or less, 70 microns or less, 50 microns or less, 40 microns or less, 35 microns or less, or 30 microns or less, etc. The second layer thickness t2 can be at least 1 micron, e.g., 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, etc. The second layer thickness t2 can be in the range of 1 micron to 200 microns, such as 15 microns to 200 microns, 15 microns to 150 microns, 30 to 150 microns, 50 microns to 120 microns, 75 microns to 125 microns, or 15 microns to 100 microns.

[0045] The TIM may cover at least 90% of the surface area of ​​the exposed side 106a of the first layer 106 after the circuit assembly is compressed, such as at least 95% of the surface area of ​​the exposed side 106a.

[0046] Compressing the circuit assembly 102 can apply a force to the TIM 104, deforming the liquid metal droplets 112 dispersed within the polymer 110 of the TIM 104 and / or deforming the constraints 114. Because the polymer 110 remains conformable and mobile, the compressive force can deform the liquid metal droplets 112. The liquid metal droplets 112 can be in a liquid phase during deformation, such that less pressure is required for compression and the desired deformation is achieved. For example, the liquid metal droplets 112 can be approximately spherical, as shown in FIG. 1, and then approximately ellipsoidal, as shown in FIG. 2. In various examples, the liquid metal droplets 112 before compression can have a first average aspect ratio, and after compression, the liquid metal droplets 112 can have a second average aspect ratio. The second average aspect ratio can be different from 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 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 can be 1 and the second aspect ratio can be greater than 1. In certain embodiments, the first aspect ratio can be in the range of 1 to 1.5. In certain embodiments, the second aspect ratio can be at least 0.5 greater than the first aspect ratio, such as at least 1 greater than the first aspect ratio, at least 2 greater than the first aspect ratio, or at least 5 greater than the first aspect ratio. In certain embodiments, the second aspect ratio can be at least 2 after compressing the circuit assembly 102, such as at least 3 or at least 4 after compressing the circuit assembly 102.

[0047] The width (e.g., longest dimension) of the liquid metal droplet 112 may 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 may be substantially aligned with the thickness (e.g., distance, d1) of the TIM 104. The width of the liquid metal droplet 112 may increase upon compression of the circuit assembly 102. For example, in one particular example, the diameter of the liquid metal droplet before compression may be 200 μm (having a first aspect ratio of 1), and after compression to a bondline thickness of 100 μm, the liquid metal droplet may deform into an elliptical shape having a 400 μm width (e.g., a second aspect ratio of 4).

[0048] In certain instances, the liquid metal droplets 112 may be aligned in a substantially monolayer after compression, as shown in FIG. 50 and / or D. 90 This can be achieved by selecting a second thickness t2 and depositing a first layer thickness t1. Configuring the liquid metal droplets 112 in a single layer can reduce the thermal resistance of the TIM 104.

[0049] 3, the constraint 114 can surround the TIM 104 after compression, and the TIM 104 can contact the constraint 114. After compression, the TIM 104 can be bound by the first layer 106, the second layer 108, and the constraint 114.

[0050] Liquid metal droplet 112 D 50 and / or D. 90 The deformation of the liquid metal droplets 112, as well as the deposition method of the liquid metal droplets 112, can improve the thermal resistance of the TIM 104. For example, the TIM 104 has a thermal resistance of at least 5°K*mm. 2 ) / W, e.g., 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 has a thermal resistance of 30(°K*mm 2 ) / W or less, for example, 20(°K*mm 2 ) / W or less, 15(°K*mm 2 ) / W or less, 10(°K*mm 2 ) / W or less, 9(°K*mm 2 ) / W or less, 8(°K*mm 2 ) / W or less, 7(°K*mm 2 ) / W or less, or 5(°K*mm 2 The TIM 104 may have a thermal resistance of 0.5 (°K*mm) / W or less. 2 ) / W~30(°K*mm 2 ) / W, e.g., 0.5(°K*mm 2 ) / W~20(°K*mm 2 ) / W, 0.5(°K*mm 2 ) / W~15(°K*mm 2 ) / W, 1(°K*mm 2 ) / W~10(°K*mm 2 ) / W, 2(°K*mm 2 ) / W~10(°K*mm 2 ) / W, or 2(°K*mm 2 ) / W~8(°K*mm 2 ) / W, etc. Thermal resistance values ​​can be measured using a TIMA 5 device manufactured by NanoTest (Germany).

[0051] Liquid metal droplet 112 D 50 and / or D. 90The deformation of the liquid metal droplets 112, as well as the deposition method of the liquid 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 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 from 5 W / m*K to 50 W / m*K, such as from 10 W / m*K to 40 W / m*K, or from 10 W / m*K to 30 W / m*K. As used herein, effective thermal conductivity is the thickness of the TIM divided by the thermal resistance of the TIM.

[0052] The TIM 104 may or may not be cured, depending on the application. For example, the TIM 104 may be cured to a solid, or the TIM may be a paste. Curing the TIM 104 may increase the viscosity of the polymer 110, making the polymer 110 harder. For example, the polymer 110 may become a solid. In various examples, the cured polymer 110 is an elastomer. Curing the polymer 110 may inhibit pumping from the liquid metal droplets 112 during thermal cycling of the circuit assembly 102, provide a mechanical bond between the first layer 106 and the second layer 108, and / or maintain the second layer thickness t2.

[0053] Curing the TIM 104 can include at least one of heating the TIM 104 (e.g., in examples with a thermosetting polymer), adding a catalyst to the TIM 104, exposing the TIM 104 to air, cooling the TIM 104 (e.g., in examples with a thermoplastic polymer), 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 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.

[0054] As used herein, the terms "cure" and "hardening" refer to the chemical cross-linking of components in an emulsion or material applied to a substrate or an increase in viscosity of the components in an emulsion or material applied to a substrate. Thus, the terms "cure" and "hardening" do not solely encompass the physical drying of an emulsion or material through solvent or carrier evaporation. In this regard, when used herein in examples involving thermosetting polymers, the term "hardened" refers to the state of an emulsion or material in which the components of the emulsion or material have chemically reacted to form new covalent bonds within the emulsion or material (e.g., new covalent bonds formed between the binder resin and the hardener). When used herein in examples involving thermoplastic polymers, the term "hardened" refers to the state of an emulsion or material in which the temperature of the thermoplastic polymer has decreased below the melting point of the thermoplastic polymer, thereby increasing the viscosity of the emulsion or material. In examples involving both thermosetting and thermoplastic polymers, the term "hardened" refers to one or both of the polymers hardening as described herein.

[0055] In various other examples, a TIM according to the present disclosure can be used in a system on a package, for example, a single horizontal TIM layer can contact multiple dies on one side (e.g., an integrated circuit can include multiple dies, or multiple integrated circuits can contact the same side of the TIM) and can contact a top layer or layers on different sides.

[0056] Those skilled in the art will recognize that the compositions, articles, methods, and accompanying discussion described herein are used as examples for conceptual clarity, and that various configuration modifications are contemplated. Consequently, as used herein, the specific examples described and accompanying discussion are intended to be representative of their more general classes. In general, the use of any specific example is intended to represent that class, and the absence of specific components (e.g., acts), devices, and objects should not be considered limiting.

[0057] With respect to the appended claims, those skilled in the art will understand that the operations recited therein may generally be performed in any order. Also, while various operational flows are presented in a sequence, it should be understood that various operations may be performed in orders other than those illustrated, or may be performed simultaneously. Examples of such alternative orderings may include overlapping, interleaving, interrupting, reordering, incremental, preparing, complementary, simultaneous, reverse, or other variable orderings, unless the context dictates otherwise. Furthermore, terms such as "responsive to," "related to," or other past-tense adjectives are generally not intended to exclude such variations, unless the context dictates otherwise.

[0058] While various examples have been described herein, many modifications, variations, substitutions, changes, and equivalents to those examples may be implemented and will occur to those skilled in the art. Also, where materials are disclosed for a particular component, other materials may be used. It is therefore to be understood that the foregoing description and the appended claims are intended to cover all such modifications and variations as fall within the scope of the disclosed embodiments. The following claims are intended to cover all such modifications and variations.

[0059] Various aspects of the invention according to this disclosure include, but are not limited to, the aspects listed in the numbered clauses below.

[0060] Clause 1. A method, comprising: depositing a constraint proximate a first layer of a circuit assembly; depositing a thermal interface material at a first layer thickness between the first layer of the circuit assembly and a second layer of the circuit assembly, the thermal interface material comprising 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 constraint.

[0061] Clause 2. The method of clause 1, wherein the restraint comprises foam.

[0062] Clause 3. The method of clause 1 or 2, wherein the foam is deformable in response to compression.

[0063] Clause 4. The method of any one of clauses 1 to 3, wherein the first layer is on a third layer of the circuit assembly and the restraint is deposited on the third layer and in contact with the first layer.

[0064] Clause 5. The method of any one of clauses 1-4, wherein after compressing the circuit assembly, the restraint is in contact with the first layer and the second layer.

[0065] Clause 6. The first layer thickness is D of the liquid metal droplet in the thermal interface material before compressing the circuit assembly. 90 6. The method of any one of clauses 1 to 5, wherein the concentration is at least 1.1 times higher than that of the control.

[0066] Clause 7. The method of any one of clauses 1 to 6, wherein the first layer thickness is at least 200 microns.

[0067] Clause 8. The method of any one of clauses 1 to 7, wherein the second layer thickness is 300 microns or less.

[0068] Clause 9. D of liquid metal droplet before compressing the circuit assembly 50 9. The method of any one of clauses 1 to 8, wherein is in the range of 1 micron to 200 microns.

[0069] Clause 10. The method of any one of clauses 1-9, wherein the thermal interface material covers at least 90% of the surface area of ​​the exposed side of the first layer after compressing the circuit assembly.

[0070] Clause 11. The method of any one of clauses 1-10, wherein depositing the thermal interface material comprises at least one of dispensing, extrusion, applying with an instrument, stencil printing, 3D printing, and screen printing.

[0071] Clause 12. The method of any one of clauses 1-11, wherein compressing the circuit assembly includes applying a first pressure of at least 1 psi to the first layer and the second layer.

[0072] Clause 13. The method of any one of clauses 1-12, wherein the first layer and the second layer each comprise at least one of a battery, a heat-generating component, a heat sink, an integrated heat spreader, and packaging.

[0073] Clause 14. The method of any one of clauses 1 to 13, wherein the first layer comprises a heat-generating component and the second layer comprises a heat sink.

[0074] Clause 15. The method of any one of clauses 1-14, wherein the liquid metal droplets comprise at least one of gallium, gallium alloy, indium, indium alloy, tin, tin alloy, mercury, and mercury alloy.

[0075] Clause 16. The method of any one of clauses 1 to 15, wherein the liquid metal droplets have a melting point of 30 degrees Celsius or less.

[0076] Clause 17. The method of any one of clauses 1-16, wherein the thermal interface material after compression comprises an effective thermal conductivity value of at least 5 W / m*K.

[0077] Clause 18. The method of any one of clauses 1 to 17, wherein the polymer comprises a thermosetting polymer.

[0078] Clause 19. The method of any one of clauses 1 to 18, wherein the polymer comprises a thermoplastic polymer.

[0079] Clause 20. The method of any one of clauses 1 to 19, wherein the emulsion, prior to compression, has a viscosity in the range of 1,000 cP to 850,000 cP, measured at 25 degrees Celsius.

[0080] Clause 21. The method of any one of clauses 1 to 20, wherein the liquid metal droplet comprises an aspect ratio of at least 2 after compressing the circuit assembly.

[0081] Clause 22. The method of any one of clauses 1-21, further comprising curing the thermal interface material after compressing, thereby increasing the viscosity of the thermal interface material to maintain the second layer thickness.

[0082] Clause 23. An integrated circuit formed by the method of any one of clauses 1 to 22.

[0083] As used herein, "at least one of" a list of elements means one of the elements or any combination of two or more of the listed elements. By way of example, "at least one of A, B, and C" means A only, B only, C only, A and B, A and C, B and C, or A, B, and C.

[0084] Various features and characteristics are described herein to provide an understanding of the composition, structure, manufacture, function, and / or operation of the invention, including the disclosed compositions, coatings, and methods. It should be understood that the various features and characteristics of the invention described herein may be combined in any suitable manner, regardless of whether such features and characteristics are expressly described in combination herein. The inventors and applicants expressly intend that such combinations of features and characteristics be included within the scope of the inventions described herein. Thus, the claims may be amended to recite any features and characteristics explicitly or inherently described or otherwise explicitly or inherently supported by the specification, in any combination. Furthermore, applicants reserve the right to amend the claims to affirmatively reject features and characteristics that may exist in the prior art, even if those features and characteristics are not explicitly described herein. Accordingly, any such amendments will not add new matter to the specification or claims, but will comply with the requirements of written description, sufficiency of description, and added matter.

[0085] Any numerical range recited herein describes all subranges of the same numerical precision (i.e., having the same number of specified digits) contained within the recited range. For example, a recited range of "1.0 to 10.0" describes all subranges from the recited minimum value of 1.0 to the recited maximum value of 10.0 (including their upper and lower limits), such as "2.4 to 7.6," even if a range of "2.4 to 7.6" is not explicitly recited within the text of this specification. Accordingly, applicants reserve the right to amend this specification, including the claims, to explicitly recite any subrange of the same numerical precision contained within a range explicitly recited herein. All such ranges are inherently described herein, and therefore any amendment to explicitly recite any such subrange will comply with the requirements of written description, sufficiency of description, and added matter.

[0086] Additionally, unless expressly specified otherwise or required otherwise by context, all numerical parameters set forth herein (such as those representing values, ranges, amounts, percentages, etc.) can be read as if preceded by the word "about," even if the word "about" does not explicitly appear before the numerical value. In addition, numerical parameters set forth herein should be construed in light of the number of reported significant digits, numerical precision, and the application of ordinary rounding techniques. It should also be understood that the numerical parameters set forth herein necessarily reflect the inherent variability characteristic of the underlying measurement techniques used to determine the numerical value of the parameters.

[0087] Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values ​​set forth in the specific examples are reported as precisely as possible. However, any numerical value inherently contains certain errors necessarily resulting from the standard variation found in their respective testing measurements.

[0088] References throughout this specification to "various examples," "some examples," "one example," "an example," or the like mean that a particular feature, structure, or characteristic described in connection with the example is included in the example. Thus, the appearances of phrases such as "various examples," "some examples," "in one example," or "in an example" in various locations throughout this specification do not necessarily all refer to the same example. Furthermore, particular features, structures, or characteristics may be combined in any suitable manner in one or more examples. Thus, a particular feature, structure, or characteristic illustrated or described in connection with one example may be combined, in whole or in part, with a feature, structure, or characteristic of another example or other examples, without limitation. Such modifications and variations are intended to be included within the scope of the present embodiments.

[0089] Any patent, publication, or other document identified herein is incorporated herein by reference in its entirety, unless otherwise indicated, to the extent that the incorporated material does not conflict with existing descriptions, definitions, descriptions, illustrations, or other disclosure material expressly set forth herein. Accordingly, to the extent necessary, the explicit disclosure set forth herein supersedes any conflicting material incorporated by reference. Any material, or portion thereof, incorporated herein by reference that conflicts with an existing definition, description, or other disclosure material set forth herein is incorporated only to the extent that a conflict arises between the incorporated material and the existing disclosure material. Applicant reserves the right to amend this specification to explicitly recite any subject matter or portion thereof incorporated by reference. Amendments to this specification to add such incorporated subject matter will comply with the requirements of written description, sufficiency of description, and the added subject matter.

[0090] Although particular examples of the present invention have been described above for purposes of illustration, it will be apparent to those skilled in the art that many variations in the details of the invention can be made without departing from the invention as defined in the appended claims.

[0091] While this disclosure provides descriptions of various specific embodiments for the purpose of illustrating various aspects of the disclosure and / or its potential applications, it should be understood that variations and modifications will occur to those skilled in the art. Accordingly, the invention or inventions described herein should be understood to be at least as broad as they are claimed, and not more narrowly defined by the specific illustrative embodiments provided herein.

[0092] It is to be understood that the invention described herein is not limited to the examples summarized in the Summary or Detailed Description. Various other aspects are described and illustrated herein.

Claims

1. 1. A method comprising: depositing a constraint proximate to a first layer of the circuit assembly; depositing a thermal interface material at a first layer thickness between a first layer of a circuit assembly and a second layer of the circuit assembly, the thermal interface material comprising an emulsion of liquid metal droplets and a polymer; 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 constraint.

2. The method of claim 1 , wherein the restraint comprises foam.

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

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

5. The method of claim 1 , wherein the constraint contacts the first layer and the second layer after compressing the circuit assembly.

6. The first layer thickness is a thickness of the liquid metal droplet in the thermal interface material prior to compressing the circuit assembly. ９０ 2. The method of claim 1, wherein the solubility of the hydroxyl group is at least 1.1 times greater than the solubility of the hydroxyl group.

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 300 microns or less.

9. D of the liquid metal droplet before compressing the circuit assembly ５０ 10. The method of claim 1, wherein is 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 the surface area of ​​the 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 a tool, stencil printing, 3D printing, and screen printing.

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

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

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 droplets comprise at least one of gallium, gallium alloys, indium, indium alloys, tin, tin alloys, mercury, and mercury alloys.

16. The method of claim 1 , wherein the liquid metal droplets comprise a melting point of 30 degrees Celsius or less.

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

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

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

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

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

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

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

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