Three-dimensionally patternable thermal interface

Abstract

This invention relates to a three-dimensional geometric thermal interface body that can be customized to substantially fill irregular gaps along heat dissipation paths in an electronic package. The thermal interface system is manufactured via an addition deposition process, wherein a continuous pattern of thermal interface material is coherently connected to other deposited patterns of thermal interface material.

Description

[Technical Field]

[0001] Generally, the present invention relates to thermal interfaces, and more specifically to customizable thermal interface bodies for substantially filling the gap between electronic components and heat sinks. The thermal interface system is formed via addition deposition to achieve customizable geometry. [Previous Technology]

[0002] Heat transfer materials are widely used as interfaces, for example, between heat-generating electronic components and heat sinks, to allow excess heat energy to be transferred from the electronic components to the thermally coupled heat sink. Several designs and materials have been implemented for such heat interfaces, in which maximum efficiency is achieved while substantially avoiding gaps between the heat interface and the individual heat transfer surfaces. Thus, heat interface materials are better adapted to the slightly uneven heat transfer surfaces of the individual components.

[0003] Examples of conformable thermal interface materials include polysiloxane polymers forming a matrix filled with thermally conductive particles (such as alumina and boron nitride). Whether at room temperature or high temperatures, the material is generally flexible enough to conform to the irregularities of the interface surface. Polysiloxane greases or waxes, especially at higher operating temperatures, tend to be shape-instantaneous and therefore prone to seepage from the interface over time. To address this challenge, some thermal interface materials are encapsulated as films, sheets, tapes, or gaskets requiring specialized installation techniques and tools. Typically, these types of thermal interface materials exhibit relatively high bulk modulus values ​​that suppress overall conformability.

[0004] Some thermal interface materials are dispensed under low viscosity conditions and subsequently cured to a high viscosity state. These form-in-place materials overcome some of the challenges of other thermal interface material types, but still have their own limitations. For example, in conventional thermal interface materials, it has been proven difficult to obtain relatively thin bond lines, such as less than 100 micrometers. Bond lines in assemblies refer to the gaps between hot surfaces into which the thermal interface is ideally mounted to reduce the thermal barrier between surfaces. Three-dimensional pre-cured thermal interface structures (such as tapes, gaskets, and films) typically lack sufficient robustness and maneuverability when the thickness is less than 100 micrometers. Conventionally, viscous gap fillers are limited by the high assembly forces required to mount them into thin bond lines. Traditional grease-based materials have long-term reliability issues and do not exhibit acceptable mechanical modulus and dielectric strength for use as dielectric coatings in thin bond line applications.

[0005] Another challenge in thin bond lines is that the profile of the thermal surfaces has a relatively significant impact on the effectiveness of the thermal interface material. Surface irregularities and profiles, which may otherwise represent a small portion of the total thermal path between thermal surfaces in a large bond line system, can alternatively have a significant impact on the expected thermal performance in thin bond line applications. Therefore, it is desirable to customize the thermal interface material into an irregular geometry to achieve a tighter fit with individual thermal surfaces along the heat dissipation path. In-situ formed thermal interface materials with low partition viscosity allow the formulation to penetrate into the thin gaps before curing. Customizing the three-dimensional geometry of the thermal interface material with in-situ formed compositions can optimize heat transfer performance. [Summary of the Invention]

[0006] With the aid of the present invention, patternable thermal interface bodies can be constructed to more closely match the gap geometry between thermal surfaces (such as between electronic components and heat sinks). Patternable thermal interface bodies can be constructed using a dispensing device programmed to apply flowable thermal interface material during an additive process.

[0007] A method for forming a thermal interface material includes applying a first curable resin precursor to a surface in a first pattern of a plurality of discrete volumes, wherein the first curable resin precursor comprises polysiloxane and exhibits a first initial viscosity and a thermal conductivity of at least 0.2 W / m*K. The method further includes applying at least one of the first curable resin precursor and a second material in a second pattern of discrete volumes to contact the first pattern. The second material may include a second curable resin precursor exhibiting a second initial viscosity different from the first initial viscosity and a thermal conductivity of at least 0.2 W / m*K.

[0008] To obtain the desired thermal conductivity, at least the first curable resin precursor may include thermally conductive particles at a first loading concentration. In some embodiments, the second curable resin precursor may also include thermally conductive particles and a second loading concentration. The first loading concentration of the thermally conductive particles may be different from the second loading concentration. Each of the first curable resin precursor and the second curable resin precursor may include thermally conductive particles with different particle size ranges. The maximum particle size may be at least 1.3 times the minimum particle size.

[0009] The method for forming a thermal interface body may further include curing one or more of the first curable resin precursor and the second curable resin precursor to a cured viscosity different from their respective initial viscosities. The cured viscosity may be substantially greater than the respective initial viscosities. At least the first curable resin precursor may include a solvent, a reaction catalyst, and a reaction inhibitor that effectively chemically interferes with the reaction catalyst, wherein the reaction inhibitor exhibits a lower vapor pressure than the solvent. In one example, the first curable resin precursor and the second curable resin precursor each comprise a vinyl-containing polysiloxane polymer and a hydrogenated polysiloxane polymer. The first curable resin precursor may include an excess of one of the vinyl-containing polysiloxane polymer and the hydrogenated polysiloxane polymer, and the second curable resin precursor includes an excess of the other of the vinyl-containing polysiloxane polymer and the hydrogenated polysiloxane polymer.

[0010] A method for forming a thermal interface body may include dispensing a first curable resin precursor onto a surface in a first pattern of a plurality of discrete volumes, and dispensing at least one of the first curable resin precursor and a second material onto the surface and at least one of the first pattern of discrete volumes in a second pattern of a plurality of discrete volumes. After dispensing, the method includes curing the first curable resin precursor to adjust its viscosity. The thermal interface body may exhibit a thermal conductivity of at least 0.2 W / m*K.

[0011] A method for filling a gap between an electronic component and a heat sink includes providing a dispenser communicatively connected to a processor and defining a first width, a second width, and a thickness dimension of the gap as input parameters. The input parameters are supplied to the processor such that, based on the input parameters, the dispenser additively applies a first layer of a first curable resin precursor to a surface associated with at least one of the electronic component and the heat sink. The first layer preferably exhibits a thermal conductivity of at least 0.2 W / m*K. The dispenser then additively applies a second layer of the first curable resin precursor or a second composition in contact with the first layer. The first layer may include a first pattern of a plurality of discrete volumes of the first curable resin precursor, and the second layer may include a second pattern of a plurality of discrete volumes.

[0012] The method includes additively constructing a thermal interface body from at least the first pattern and the second pattern to have a first width, a second width, and a thickness dimension, wherein the thickness dimension may be non-uniform. In some embodiments, the thickness dimension may be less than 100 micrometers throughout the gap.

[0013] The second layer applied by this method differs from the first layer in that at least one of the following is present: thermally conductive particle load concentration, curing viscosity, initial pre-cured viscosity, average thermally conductive particle size, distribution of thermally conductive particle size, curing rate, and thickness.

[0014] The electronic package of the present invention includes an electronic component, a heat sink, and a thermal interface material inserted between and in thermal contact with the electronic component and the heat sink. The thermal interface system is formed by a plurality of deposition layers, wherein each layer is deposited in an array of a plurality of discrete volumes of a curable resin precursor and subsequently cured. The thermal interface material exhibits a thermal conductivity of at least 0.2 W / m*K. In some embodiments, a first composition of a first layer of the thermal interface material is different from a second composition of a second layer.

Implementation Method

[0025] The objectives and advantages listed above, as well as other objectives, features, and developments represented by the invention, will now be presented in the form of detailed embodiments described with reference to the accompanying drawings. Other embodiments and variations of the invention are to be recognized as being within the grasp of those skilled in the art.

[0026] Figure 1 provides a schematic illustration of an addition deposition system 10 with a dispenser head 12, which supplies material for deposition from a reservoir 16 onto a surface 14. Material 20 is dispensed from an orifice 18 of the dispenser head 12. A controller 22, which may include a processor 24 and a signal generator 26, may be programmed to control the dispenser head 12 to dispense one or more materials 20 onto the surface 14 in a predetermined pattern. The controller 22 may be programmed to generate a three-dimensional thermal interface via an addition deposition process, wherein one or more dispenser heads 12 may be controlled to each dispense one or more materials 20 in a coordinated manner to additively construct the three-dimensional thermal interface. Therefore, it should be understood that the dispenser head 12 may represent one or more of an array of different dispenser heads forming part of an addition deposition system 10, in which one or more of the dispenser head 12 and surface 14 may move relative to each other to achieve the deposition of material 20 in a predetermined pattern supported by the surface 14.

[0027] The addition deposition system 10 may include one or more of a variety of deposition devices capable of performing addition deposition processes. Examples of suitable dispensers include nozzle printers, droplet dispensers, line dispensers, metering spray heads, Venturi printers, and the like.

[0028] The addition deposition system 10 may further include a curing member 30 for providing input for curing the curable material 20. Examples of curing members include heating members, such as ovens or infrared lamps; ultraviolet radiation sources, such as ultraviolet lamps; sources of chemical curing agents for application to the material 20; and / or other known members for curing the curable material 20. For purposes herein, the term "curing" means altering the properties of a resin by means of a chemical reaction (including by condensation or addition) with or without pressure.

[0029] The addition deposition system 10 may be adapted to dispense one or more materials 20 via one or more dispenser heads 12. In some embodiments, a single dispenser head 12 may be adapted to dispense a plurality of different materials 20 simultaneously or sequentially. In other embodiments, the addition deposition system 10 may include a plurality of dispenser heads 12, which may be adapted to dispense a single material 20 simultaneously or sequentially, or dispense a plurality of materials 20 simultaneously or sequentially.

[0030] The addition deposition system 10 may employ one or more materials 20 to form a thermal interface in the addition deposition process. The material 20 may be a thermoplastic or thermosetting polymer, selected from a variety of polymers such as polysiloxane, fluoropolysiloxane, acrylic resin, thermoplastic elastomer, epoxy resin, polyester, polyolefin, polyetheretherketone, polyamide, nylon, polyimide, polyurethane, and combinations thereof. Polysiloxane resins such as polysiloxane / polyorganosiloxane have conformability characteristics and other properties suitable for the thermal interface of the present invention. In some embodiments, the material 20 may be dispensed from the dispenser head 12 under curable conditions in which the matrix polymer resin may be crosslinked or further crosslinked. Crosslinking activity may be initiated spontaneously or upon effective exposure to a curing agent. For purposes herein, "curable resin precursor" includes dispensable materials that may undergo further polymerization, crosslinking, vulcanization, curing, drying, or other chemical or physical changes prior to dispensing, depending on their conditions. Such materials may be referred to as in-situ formed materials, wherein the dispensed material cures after being placed on a surface of a thermal path. The present invention may employ a combination of in-situ formed materials and pre-cured materials. In some embodiments, each of the materials 20 facilitates the in-situ formation of compositions and structures. It should be understood that the term "resin" as used herein is intended to include resins, oligomers, prepolymers, elastomers, and other polymers.

[0031] The thermal interface material of the present invention is preferably thermally conductive, exhibiting a thermal conductivity of at least 0.2 W / m*K. Because the thermal conductivity of the adaptable polymer is relatively low, thermally conductive fillers can be added to the polymer matrix. The thermal conductivity of the filled thermal interface material depends on various factors, including the thermal conductivity of the filler and the loading concentration of the filler in the polymer matrix, which may be affected by the filler particle size and distribution. The thermally conductive filler may include particles of uniform particle size or with a particle size distribution range. The thermally conductive particles may be electrically insulating to maintain the resistive properties of the thermal interface material. Examples of electrically insulating and thermally conductive particles suitable for the present invention include boron nitride, aluminum oxide, aluminum nitride, magnesium oxide, zinc oxide, silicon carbide, beryllium oxide, aluminum trihydrate, and combinations thereof. In some embodiments, the thermal interface material may preferably shield electromagnetic interference (EMI), and therefore conductive and thermally conductive particle fillers may be used. Examples of conductive particle fillers include metals such as aluminum, copper, gold, nickel, silver, and combinations thereof. The shape of the thermally conductive filler particles is not specifically limited and may include a single thermally conductive filler or a combination of two or more thermally conductive fillers that differ in at least one characteristic, such as particle shape, average particle size, particle size distribution, and filler type. Particle type, size, size distribution, loading concentration, and admixtures can affect heat transfer, EMI shielding, and viscosity characteristics.

[0032] For specific chemical and / or physical property benefits, material 20 may include additional fillers and additives, including plasticizers, pigments, surfactants, stabilizers, oxidants, flame retardants and spacers.

[0033] The applicant has determined that the component surface to which the thermal interface material is applied can typically be slightly uneven, exhibiting peaks and valleys that can deviate from a reference plane by 100 micrometers or more. The standard material roughness of the surface may have further deviations in the range of approximately 5-25 micrometers. Figure 2 shows a hypothetical magnified view of surface 14, such as that of an electronic component or heat sink. A first deviation dimension "a" is defined between the reference plane 15 of surface 14 and the main peak 40, while a second deviation dimension "b" is defined between the reference plane 15 of surface 14 and the main valley 42. In some embodiments, each of the first deviation dimension and the second deviation dimensions a, b can be up to 100 micrometers, and even larger in some cases. Additionally, the roughness 44 of surface 14 may include secondary peaks and valleys 46, 48. Surface roughness 44 can represent a deviation of up to 25 micrometers or more. To optimize heat transfer from surface 14 to the thermal interface material, it is desirable to apply a thermal interface material that conforms as closely as possible to surface 14, including by conforming to its deviations. Figure 3 schematically illustrates the desired thermal interface 50 that closely conforms to surface 14. The thermal interface 50 of the present invention can be additively constructed into a three-dimensional geometry that allows for enhanced conformability to uneven surface 14.

[0034] Figure 4 illustrates an example electronic package 80 having a heat-generating electronic component 60 with a first hot surface 14a and a heat sink 70 with a second hot surface 14b. A thermal interface body 50 is inserted between and in thermal contact with the first and second hot surfaces 14a, 14b. The thermal interface body 50 may have an irregular geometry to best conform to the wavy and rough first and second hot surfaces 14a, 14b. The thermal interface body 50 may exhibit an irregular geometry at the operating temperature of the electronic component 60 and at temperatures below such operating temperatures (including at room temperature). In some embodiments, the thermal interface body 50 may be formed in situ with an irregular geometry that substantially fills the gap between the electronic component 60 and the heat sink 70. Such an irregular geometry may be specifically manufactured via the addition deposition process of the present invention.

[0035] The gap "G" between the electronic component 60 and the heat sink 70 can be defined by various methods, including three-dimensional optical surface analysis. Information from such measurements (such as width and thickness dimensions) can be provided as input parameters to the controller 22. The controller 22 can be programmed to interpret the input parameters for generating control output commands that drive the addition deposition system 10 by additively constructing the thermal interface body 50 in the three-dimensional shape of the gap "G".

[0036] The three-dimensional geometry of the thermal interface body 50 can be customized by additively applying thermal interface materials in multiple application passes. The thermal interface materials applied in any given pass of one or more dispenser heads 12 may be the same, similar, or different in terms of physical and / or chemical properties. The thermal interface materials dispensed in each pass are preferably bonded to the thermal interface materials dispensed in another pass, so that a coherent thermal interface body 50 can ultimately be constructed via an addition deposition process. Differences between the thermal interface materials applied in different passes of the addition deposition process include average thermal conductivity particle size, thermal conductivity particle size distribution, thermal conductivity particle load concentration, cured viscosity, pre-cured viscosity, curing rate, thickness, and excess and limited reactant composition. The present invention also covers other chemical and physical differences between thermal interface material deposits of a given thermal interface body 50.

[0037] The customizable construction of the thermal interface material 50 can also be controlled by allocating specified volumes with a predetermined pattern, wherein at least a portion of a first pattern of a plurality of discrete volumes of thermal interface material can contact at least a portion of a second pattern of deposited thermal interface material, the deposited thermal interface material being the same as, similar to, or different from the thermal interface material deposited in the first pattern of the discrete volumes. In some embodiments, the deposited thermal interface material 20 can exhibit predetermined three rheological parameters to optimally meet flow requirements when additively constructing the thermal interface material 50. Example

[0038] The following examples illustrate a specific addition deposition method for constructing custom geometric thermal interface bodies. However, it is considered that many other addition deposition methods can be used within the scope of this invention.

[0039] Example 1: The first and second curable resin precursors may have different pre-cured viscosities to control the curing and flow patterns. The lower viscosity resin precursor can wet the surface 14, while the higher viscosity resin helps to hold the deposited thermal interface material in situ before curing. Figure 5 illustrates a multi-pass deposition method in which the first curable resin precursor is applied to the surface in a first pattern of a plurality of discrete volumes, wherein the pattern of the deposited discrete volumes wets the surface to coalesce into a viscous layer before the second curable resin precursor is applied to contact the first pattern. In some embodiments, the second pass may be performed by a second dispenser head and alternatively dispenses the curing material to contact the first curable resin precursor. Alternatively, at least a portion of the first curable resin precursor may be cured before the second pass in which the second material is applied.

[0040] Example 2: A first curable resin precursor and a second curable resin precursor may be applied in multiple passes of one or more dispenser heads, wherein the first curable resin precursor and the second curable resin precursor exhibit at least different curing Young's modulus values. Figure 6 illustrates an example addition deposition process in which a first material is dispensed onto a surface in a first pattern of multiple discrete volumes, followed by the application of a second material in a second pattern of discrete volumes to contact the first material. The first and second materials may be cured before or after deposition. The illustrated embodiment depicts a curable resin precursor dispensed under curable conditions and cured after deposition. The first material may be additively deposited with the second material to cure before or after a second pass in contact with the first material. In some embodiments, the first material exhibits a relatively low Young's modulus, while the second material exhibits a relatively high Young's modulus, wherein the first material forms a first compressible layer that readily adapts to a heat transfer surface, and the second layer forms a durable shell over the first layer.

[0041] Example 3: A first material and a second material are respectively patterned in a plurality of discrete volumes, wherein the first material and the second material include different thermally conductive particle size distributions. The relatively larger particle size distribution material can be applied to the first pattern of the discrete volumes to better fill the main valleys of the applicable surface. Filler encapsulation optimization can be performed to meet thermal conductivity requirements.

[0042] Example 4 Figure 7 illustrates the application of various thermal interface materials with different thermally conductive filler loading concentrations. In some embodiments, this method may include a first curable resin precursor and a second curable resin precursor applied in different patterns during an addition deposition process.

[0043] Example 5 For different physical properties such as adhesion, Young's modulus, and distribution viscosity, the first curable resin precursor and the second curable resin precursor may have different resin compositions. Figure 8 illustrates a first curable resin material deposited on a surface in a first pattern of multiple discrete volumes, followed by the application of a second curable resin precursor in a second pattern of discrete volumes to contact the first material. The first curable resin precursor may be cured before or after the application of the second pattern to contact the first material. Similarly, the second curable resin precursor may be applied before or after curing to contact the first material. The illustrated embodiment demonstrates a method in which the first curable resin precursor and the second curable resin precursor are cured after the application of the second pattern of discrete volumes to contact the first material.

[0044] Example 6: Thermal interface materials can be applied using one or more distributor heads in a continuous pattern of multiple discrete volumes, wherein the distribution parameters used for each distribution pass and / or during each distribution pass can be different. Possible variations include distributor head speed, volume distribution rate through the distribution orifice of the distributor head, and different material viscosities affecting the deposition flow rate. Figure 9 illustrates an example addition deposition process using different speeds of one or more distributor heads employed in an addition deposition process.

[0045] Example 7 Two dispenser heads can be used to dispense thermally conductive material along planes that are substantially perpendicular to each other. Figure 10 shows a first pattern and a second pattern for applying a plurality of discrete volumes along planes that are substantially perpendicular to each other.

[0046] It should be understood that various patterns can be used to meet specific applications. For example, the configuration of a particular surface 14 can be studied via known metrological processes such as three-dimensional optical scanning, allowing for the mapping of appropriate thermal interface body geometry. The formation of the thermal interface body may require one or more passes of a dispenser head, including additively depositing one or more layers of thermal interface material to contact one or more patterns of the thermal interface material. It should be further understood that different patterns or sets of patterns do not need to occupy similar areas, volumes, or geometries. Instead, certain patterns of the thermal interface material may be applied to selected areas of the thermal interface body. It is also possible to cure only a portion of the applied pattern of the thermal interface material before or after applying another pattern of the thermal interface material.

[0047] The present invention has been described in considerable detail herein to provide those skilled in the art with information necessary for applying novel principles and for constructing and using embodiments of the invention as needed. However, it should be understood that various modifications may be made without departing from the scope of the invention itself. [Simplified Explanation of the Diagram]

[0015] Figure 1 is a schematic illustration of a system for forming a thermal interface body according to the present invention.

[0016] Figure 2 is an enlarged cross-sectional view of the hot surface of an electronic component or heat sink.

[0017] Figure 3 is an enlarged cross-sectional view of the thermal interface body of the present invention having a geometry that conforms to the thermal surface.

[0018] Figure 4 is a cross-sectional view of the electronic package of the present invention.

[0019] Figure 5 illustrates an example addition deposition process.

[0020] Figure 6 illustrates an example addition deposition process.

[0021] Figure 7 illustrates an example addition deposition process.

[0022] Figure 8 shows an example addition deposition process.

[0023] Figure 9 shows an example addition deposition process.

[0024] Figure 10 illustrates an example addition deposition process.

Claims

1. A method for forming a thermal interface body, the method comprising: applying a first material comprising a first curable resin precursor onto a surface in a first pattern of a plurality of discrete volumes, wherein the first curable resin precursor comprises polysiloxane and exhibits a first initial viscosity and a thermal conductivity of at least 0.2 W / m*K; and prior to curing the first curable resin precursor, applying at least one of the first curable resin precursor and a second material in a second pattern of discrete volumes to contact the first material, wherein the second material exhibits a second initial viscosity different from the first initial viscosity and a thermal conductivity of at least 0.2 W / m*K, wherein the application is performed by an additively patternable dispenser.

2. The method of claim 1, wherein the first curable resin precursor comprises thermally conductive particles at a first load concentration, and the second material comprises thermally conductive particles at a second load concentration, wherein the first load concentration is different from the second load concentration.

3. The method of claim 2, wherein the first curable resin precursor comprises thermally conductive particles with different particle size ranges, wherein the maximum particle size is at least 1.3 times the minimum particle size.

4. The method of claim 1, comprising applying at least the first pattern or the second pattern to spaced discrete volumes.

5. The method of claim 4, wherein at least some of the discrete volumes are merged together after application.

6. The method of claim 1, wherein the second material comprises polysiloxane.

7. The method of claim 1, comprising curing the first curable resin precursor to a cured viscosity substantially greater than the first initial viscosity.

8. The method of claim 7, wherein the first initial viscosity is less than 200,000 cP.

9. The method of claim 8, comprising curing the second material to a second cured viscosity modulus substantially greater than the second initial viscosity.

10. The method of claim 9, wherein the second initial viscosity is less than 200,000 cP.

11. The method of claim 1, wherein the first curable resin precursor comprises a solvent, a reaction catalyst, and a reaction inhibitor that effectively chemically interferes with the reaction catalyst, the reaction inhibitor having a lower vapor pressure than the solvent, and the second material comprises a second curable resin precursor.

12. The method of claim 11, wherein the first curable resin precursor and the second curable resin precursor each comprise a vinyl-containing polysiloxane polymer and a hydrogenated polysiloxane polymer.

13. The method of claim 12, wherein the first curable resin precursor comprises an excess of one of the vinyl-containing polysiloxane polymer and the hydrogenated polysiloxane polymer, and the second curable resin precursor comprises an excess of the other of the vinyl-containing polysiloxane polymer and the hydrogenated polysiloxane polymer.

14. The method of claim 11, comprising removing at least 80% of the solvent in the first curable resin precursor of the first pattern before printing the second pattern.

15. The method of claim 1, wherein the surface is a heat dissipation surface of an electronic component.

16. The method of claim 15, wherein the electronic component is an insertable optical module.

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