3D patternable thermal interface

Abstract

The three-dimensional shape of the thermal interface body may be customized to substantially fill irregular gaps along the heat dissipation path within the electronic package. The thermal interface body is fabricated by an additive deposition process, whereby continuous patterns of thermal interface material are coherently connected to other deposited patterns of thermal interface material.

Description

Technical Field

[0001] The present invention generally relates to thermal interfaces, and more specifically to a customizable thermal interface body for substantially filling the gap between an electronic component and a heat sink. The thermal interface body is formed by additive deposition to achieve a customizable shape.

Background Art

[0002] Thermally conductive materials are widely used, for example, as an interface between an electronic component that generates heat and a heat sink, and enable the transfer of excess thermal energy from the electronic component to the thermally coupled heat sink. Numerous designs and materials have been implemented for such thermal interfaces, and the highest performance is achieved when the gap between the thermal interface and each heat transfer surface is substantially avoided. Therefore, it is preferable that the thermal interface material conforms to the somewhat non-uniform heat transfer surfaces of each component.

[0003] Examples of suitable thermal interface materials include silicone polymers that form a matrix filled with thermally conductive particles such as aluminum oxide and boron nitride. This material typically has sufficient flexibility to conform to the irregularities of the interface surface, whether at room temperature or at high temperature. Silicone greases or waxes tend to have no shape stability, especially at high operating temperatures, and may bleed out from the interface position over time. To address this issue, some interface materials are packaged as films, sheets, tapes, or pads that require special attachment techniques and tools. In many cases, the form of such thermal interface materials exhibits a relatively high value of bulk modulus that hinders comprehensive conformity.

[0004] Some thermal interface materials are dispensed in a low-viscosity state and then cured to a high-viscosity state. While these form-in-place materials can overcome some of the challenges of other forms of thermal interface materials, they still have their own limitations. For example, conventional thermal interface materials have proven difficult to implement relatively thin bond lines, such as those less than 100 micrometers thick. A bond line in an assembly refers to a gap between thermal surfaces, where a thermal interface is desirable to mitigate the thermal barrier between surfaces. Three-dimensional pre-cured thermal interface structures, such as tapes, pads, and films, typically lack sufficient robustness and handling at thicknesses less than 100 micrometers. Conventionally, viscous gap fillers have been limited by the high assembly forces required for attachment to thin bond lines. Conventional grease-like materials have long-term reliability issues and do not exhibit acceptable mechanical modulus and dielectric strength for use as dielectric coatings in applications to thin bond lines.

[0005] Another challenge presented with thin bond lines is that surface irregularities have a relatively significant impact on the effectiveness of the thermal interface material. Surface irregularities and undulations, which may represent only a small portion of the overall heat pathways between heat surfaces in a large bond line system, can dramatically affect the expected thermal performance when applied to thin bond lines. Therefore, it would be desirable to customize the thermal interface material to an irregular shape that more closely interlocks with each heat surface along the heat dissipation pathway. Low distribution viscosity foam-in-place thermal interface materials allow the formulation to penetrate thin gaps before curing. Customizing the three-dimensional shape of thermal interface materials with foam-in-place compositions can optimize heat transfer performance. [Overview of the Initiative] [Means for solving the problem]

[0006] According to the present invention, the patternable thermal interface body may be constructed to more precisely match the gap shape between thermal surfaces, such as between an electronic component and a heat sink. The patternable thermal interface body may be constructed with various dispensing devices programmed to apply a fluid thermal interface material in an additional step.

[0007] A method for forming a thermal interface body comprises applying a first curable resin precursor to a surface in a first pattern of multiple separate volumes, the first curable resin precursor comprising silicone and exhibiting a first initial viscosity and a thermal conductivity of at least 0.2 W / m·K. The method further comprises applying at least one of the first curable resin precursor and a second material in a second pattern of separate volumes in contact with the first pattern. The second material may comprise 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 achieve a desired thermal conductivity, at least the first curable resin precursor may contain thermally conductive particles at a first loading concentration. In some embodiments, the second curable resin precursor may also contain thermally conductive particles at a second loading concentration. The first loading concentration of thermally conductive particles may differ from the second loading concentration. Each of the first and second curable resin precursors may contain thermally conductive particles having different particle size ranges. The maximum particle size may be at least 1.3 times the minimum particle size.

[0009] A 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 curing viscosity different from their respective initial viscosities. The curing viscosity may be substantially greater than their respective initial viscosities. At least the first curable resin precursor may contain a solvent, a reaction catalyst, and a reaction inhibitor effective in chemically interfering with the reaction catalyst, the reaction inhibitor exhibiting a lower vapor pressure than the solvent. In one example, the first curable resin precursor and the second curable resin precursor each contain a vinyl-containing silicone polymer and a hydride-containing silicone polymer. The first curable resin precursor may contain an excess of one of the vinyl-containing silicone polymer and the hydride-containing silicone polymer, and the second curable resin precursor may contain an excess of the other of the vinyl-containing silicone polymer and the hydride-containing silicone polymer.

[0010] A method for forming a thermal interface body may include distributing a first curable resin precursor on a surface in a first pattern of multiple individual volumes, and distributing the first curable resin precursor and at least one of the second material on the surface and at least one of the first pattern of individual volumes in a second pattern of multiple individual volumes. Following the distribution, 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 linked to a processor, specifying the dimensions of a first width, a second width, and a thickness of the gap as input parameters. The input parameters are supplied to the processor, and the dispenser, based on the input parameters, additionally applies a first layer of a first curable resin precursor to the 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 additionally applies a second layer of the first curable resin precursor or a second composition to contact the first layer. The first layer may comprise a first pattern of a plurality of individual volumes of the first curable resin precursor, and the second layer may comprise a second pattern of a plurality of individual volumes.

[0012] This method involves additionally constructing a thermal interface body from at least a first pattern and a second pattern to have dimensions of a first width, a second width, and a thickness, the thickness dimension may be non-uniform. In some embodiments, the thickness dimension may be less than 100 micrometers across the entire gap.

[0013] The second layer applied by this method may differ from the first layer in at least one of the following: thermal conductive particle load concentration, curing viscosity, initial pre-curing viscosity, average thermal conductive particle diameter, distribution of thermal conductive particle diameter, curing rate, and thickness.

[0014] The electronic package of the present invention includes electronic components, a heat sink, and a thermal interface body inserted between the electronic components and the heat sink and in thermal contact with them. The thermal interface body is formed from a plurality of deposited layers, each layer being deposited as an array of a plurality of separate volumes of curable resin precursors, which are subsequently cured. The thermal interface body exhibits a thermal conductivity of at least 0.2 W / m·K. In some embodiments, the first composition of the first layer is different from the second composition of the second layer of the thermal interface body. [Brief explanation of the drawing]

[0015] [Figure 1] Figure 1 is a schematic diagram of a system for forming a thermal interface body according to the present invention. [Figure 2] Figure 2 is an enlarged cross-sectional view of the thermal surface of an electronic component or heat sink. [Figure 3] Figure 3 is an enlarged cross-sectional view of the thermal interface body of the present invention, which has a shape that conforms to a hot surface. [Figure 4] Figure 4 is a cross-sectional view of the electronic package of the present invention. [Figure 5] Figure 5 shows an example of an accretionary deposition process. [Figure 6] Figure 6 shows an example of an accretionary deposition process. [Figure 7] Figure 7 shows an example of an accretionary deposition process. [Figure 8] Figure 8 shows an example of an accretionary deposition process. [Figure 9] Figure 8 shows an example of an accretionary deposition process. [Figure 10] Figure 10 shows an example of an accretionary deposition process. [Modes for carrying out the invention]

[0016] The objectives and advantages listed above, along with other objectives, features, and advances represented by the present invention, are hereby presented in relation to the detailed embodiments described with reference to the accompanying drawings. Other embodiments and aspects of the present invention are recognized to be within the scope of those skilled in the art.

[0017] FIG. 1 provides a schematic view of an additive deposition system 10, which includes a dispenser head 12 from which material is supplied from a reservoir 16 for deposition on a surface 14. Material 20 is dispensed from an opening 18 of the dispenser head 12. The controller 22 may include a processor 24 and a signal generator 26 and may be programmed to control the dispenser head 12 when dispensing one or more materials 20 in a predetermined pattern on the surface 14. The controller 22 may be programmed to create a three-dimensional thermal interface body through an additive deposition process, and one or more dispenser heads 12 may be controlled to cooperatively dispense one or more materials 20 respectively to additionally construct the three-dimensional thermal interface body. Thus, the dispenser head 12 may represent one or more of an array of individual dispenser heads forming part of the additive deposition system 10, and it should be understood that one or more of the dispenser head 12 and the surface 14 may be movable relative to each other to achieve deposition of the material 20 in a predetermined pattern supported by the surface 14.

[0018] The additive deposition system 10 may include one or more of various deposition devices capable of an additive deposition process. Examples of useful dispensers include nozzle printers, drop dispensers, line dispensers, metering spray heads, venturi printers, and the like.

[0019] The additive deposition system 10 may further include a curing system 30 for providing an input for curing the curable material 20. Examples of curing systems include heating means such as an oven or an infrared lamp, an ultraviolet radiation source such as an ultraviolet lamp, a source of chemical curing agent for application to the material 20, and / or other known means for curing the curable material 20. For the purposes of this specification, the term "curing" means a change in the properties of a resin by a chemical reaction including condensation or addition, with or without pressure.

[0020] The additive deposition system 10 may be adapted to distribute one or more materials 20 via one or more dispenser heads 12. In some embodiments, a single dispenser head 12 may be adapted to distribute multiple individual materials 20 simultaneously or sequentially. In other embodiments, the additive deposition system 10 may include multiple dispenser heads 12, which may be adapted to distribute single materials 20 simultaneously or sequentially, or multiple materials 20 simultaneously or sequentially.

[0021] The additive deposition system 10 may use one or more materials 20 in the additive deposition process to form the thermal interface body. The material 20 may be a thermoplastic or thermosetting polymer and may be selected from a variety of polymers such as silicone, fluorosilicone, acrylic, thermoplastic elastomer, epoxy, polyester, polyolefin, polyetheretherketone, polyamide, nylon, polyimide, polyurethane, and combinations thereof. Silicone resins such as polysiloxane / polyorganosiloxane have useful compatibility and other characteristic properties in the thermal interface body of the present invention. In some embodiments, the material 20 may be dispensed from the dispenser head 12 in a curable state, and the base polymer resin may be crosslinked or further crosslinked. Crosslinking activity may be initiated spontaneously or upon effective exposure to a curing agent. For the purposes of this specification, “curable resin precursor” includes a dispensable material that may undergo further polymerization, crosslinking, vulcanization, curing, drying, or other chemical or physical changes from its pre-dispensing state. Such materials may also be called form-in-place materials, which are placed on a thermal path surface and then the distributed material hardens. It is intended that a combination of form-in-place material and pre-cured material may be used in the present invention. In some embodiments, each of the material 20 contributes to the form-in-place composition and structure. It should be understood that the term “resin” as used herein is intended to include resins, oligomers, prepolymers, elastomers, and other polymers.

[0022] The thermal interface body of the present invention is preferably thermally conductive and exhibits a thermal conductivity of at least 0.2 W / m·K. Since the thermal conductivity of compatible polymers is relatively low, a thermally conductive filler may 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, and these factors may be affected by the particle size and distribution of the filler. The thermally conductive filler may include particles of a uniform particle size or particles having a distribution range of particle sizes. The thermally conductive particles may be electrically insulating in order to maintain the electrical resistance characteristics with respect to the thermal interface body. Examples of electrically insulating thermally conductive particles suitable for use in 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 body may preferably shield electromagnetic interference (EMI), and thus, conductive and thermally conductive particulate fillers may be used. Examples of conductive particulate fillers include metals such as aluminum copper, gold, nickel, silver, and combinations thereof. The shape of the thermally conductive filler particles is not particularly limited and may include a single thermally conductive filler or a combination of two or more thermally conductive fillers having at least one different characteristic such as particle shape, average particle size, particle size distribution, and filler type. The type of particles, particle size, particle size distribution, loading concentration, and blend may affect thermal transfer, EMI shielding, and viscosity characteristics.

[0023] For the benefit of certain chemical and / or physical properties, additional fillers and additives including plasticizers, pigments, surfactants, stabilizers, oxidants, flame retardants, and spacers may be included in the material 20.

[0024] The applicant has determined that the surface of the component to which the thermal interface body is applied may typically be somewhat non-planar and may exhibit peaks and valleys that deviate by more than 100 micrometers from the base plane. The standard material roughness of the surface may exhibit further deviations in the range of about 5 to 25 micrometers. Figure 2 shows a hypothetical magnified view of the surface 14 of, for example, an electronic component or heat sink. The first deviation dimension "a" is defined between the base plane 15 of the surface 14 and the primary peaks 40, and the second deviation dimension "b" is defined between the base plane 15 and the primary valleys 42 of the surface 14. Each of the first deviation dimension a and the second deviation dimension b may be up to 100 micrometers in some embodiments and may be larger in some cases. Furthermore, the roughness 44 on the surface 14 may include secondary peaks 46 and secondary valleys 48. The surface roughness 44 may represent deviations of more than 25 micrometers. To optimize heat transfer from surface 14 to the thermal interface body, it is desirable to apply a thermal interface body that conforms as closely as possible to surface 14, including accommodating any deviations. Figure 3 schematically shows a desirable thermal interface body 50 that closely conforms to surface 14. The added-on thermal interface body 50 may be formed into a three-dimensional shape that allows for improved conformity to the non-uniform surface 14.

[0025] Figure 4 shows an exemplary electronic package 80 comprising a heat-generating electronic component 60 having a first thermal surface 14a and a heat sink 70 having a second thermal surface 14b. A thermal interface body 50 is inserted between the first thermal surface 14a and the second thermal surface 14b and is in thermal contact with them. The thermal interface body 50 may have an irregular shape to best conform to the uneven and rough first thermal surface 14a and the second thermal surface 14b. The thermal interface body 50 may exhibit an irregular shape at the operating temperature of the electronic component 60, as well as at temperatures lower than such operating temperatures, including room temperature. In some embodiments, the thermal interface body 50 may be formed in place with an irregular shape that substantially fills the gap between the electronic component 60 and the heat sink 70. Such an irregular shape may be specially manufactured by the additive deposition process of the present invention.

[0026] The gap "G" between the electronic component 60 and the heat sink 70 may be defined by various methods of encapsulating three-dimensional optical surface profiling. Information from such measurements, such as width and thickness dimensions, may be provided to the controller 22 as input parameters. The controller 22 may be programmed to read the input parameters to generate control output instructions for driving the additive deposition system 10 in a manner that additionally constructs the thermal interface body 50 with the three-dimensional shape of the gap "G".

[0027] The three-dimensional shape of the thermal interface body may be customized by additionally applying thermal interface material to multiple application passes. The thermal interface material applied to any given pass of one or more dispenser heads 12 may be identical, similar, or dissimilar in physical and / or chemical properties. The thermal interface material distributed in each pass may preferably be combined with the thermal interface material distributed in another pass, so that the coherent thermal interface body 50 is ultimately constructed by the additive deposition process. Differences between the thermal interface materials applied in different passes of the additive deposition process include average thermal conductive particle size, distribution of thermal conductive particle size, thermal conductive particle load concentration, curing viscosity, pre-curing viscosity, curing rate, thickness, and composition of excess and limiting reactants. Other chemical and physical differences between thermal interface material deposits of a given thermal interface body 50 are also contemplated by the present invention.

[0028] The customizable structure of the thermal interface body 50 may also be controlled by distributing a specified amount in a predetermined pattern, such that at least a portion of a first pattern of multiple individual volumes of thermal interface material may be in contact with at least a portion of a second pattern of deposited thermal interface material, which may be identical, similar, or dissimilar to the thermal interface material deposited in the first pattern of individual volumes. In some embodiments, the deposited thermal interface material 20 may exhibit predetermined rheological parameters to best address the fluidity requirements when additionally constructing the thermal interface body 50. [Examples]

[0029] The following examples illustrate specific deposition techniques for constructing a thermal interface body with a customized shape. However, many other deposition techniques may be utilized within the scope of the present invention.

[0030] (Example 1) The first and second curable resin precursors may have different pre-curing viscosities to control the curing and flow patterns. A low-viscosity resin precursor can wet the surface 14, while a high-viscosity resin helps to hold the thermal interface material deposited before curing in place. Figure 5 illustrates a multi-pass deposition technique using a deposition pattern of volumes that wet the surface and integrate into an adhesive layer before applying the second curable resin precursor to contact the first pattern, using the first curable resin precursor applied to the surface in a first pattern of multiple individual volumes. In some embodiments, the second pass may be carried out by a second dispenser head, or alternatively, by distributing the cured material to contact the first curable resin precursor. Further 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.

[0031] (Example 2) The first curable resin precursor and the second curable resin precursor may be applied in multiple passes of one or more dispenser heads, and the first and second curable resin precursors exhibit at least different curing Young's moduli. Figure 6 shows an example of an additive deposition process in which the first material is distributed to a surface in a first pattern of multiple individual volumes, and then the second material is applied in a second pattern of individual volumes in contact with the first material. The first and second materials may be cured before or after deposition. The illustrated embodiment shows a curable resin precursor that is distributed in a curable state and cured after deposition. The first material may be cured by additive deposition before or after the second pass, with the second material in contact with the first material. In some embodiments, the first material exhibits a relatively low Young's moduli, the second material exhibits a relatively high Young's moduli, the first material forms a first compressible layer that can easily conform to the heat transfer surface, and the second layer forms a durable shell on top of the first layer.

[0032] (Example 3) The first and second materials are distributed in multiple individual volume patterns, and the first and second materials have different thermal conductivity particle size distributions. A material with a relatively large particle size distribution may be applied in the first pattern of individual volumes to better fill the primary valleys of the applicable surface. To satisfy the thermal conductivity requirements, the filler packing may be optimized.

[0033] (Example 4) Figure 7 shows the application of multiple thermal interface materials with different load concentrations of thermally conductive filler. In some embodiments, this method may involve applying the first curable resin precursor and the second curable resin precursor in separate patterns during the addition deposition process.

[0034] (Example 5) The first and second curable resin precursors may have various resin compositions with different physical properties such as adhesion, Young's modulus, and distribution viscosity. Figure 8 shows the first curable resin material deposited on a surface in a first pattern of multiple individual volumes, followed by the second curable resin precursor applied in a second pattern of individual volumes in contact with the first material. The first curable resin precursor may be cured before or after applying the second pattern and bringing it into contact with the first material. Similarly, the second curable resin precursor may be applied to come into contact with the first material before or after curing. The illustrated embodiment shows a method in which the first and second curable resin precursors are cured after applying the second pattern of individual volumes to come into contact with the first material.

[0035] (Example 6) The thermal interface material may be applied in a continuous pattern of multiple individual volumes using one or more dispenser heads, and the distribution parameters of each distribution path and / or within each distribution path may differ. Possible differences include differences in the dispenser head velocity, the volume distribution velocity through the dispenser head's distribution opening, and the material viscosity, which affect the deposition flow rate. Figure 9 shows an example of an additive deposition process using one or more dispenser heads with different velocities used in the additive deposition process.

[0036] (Example 7) Two dispenser heads may be used to distribute the thermally conductive material along planes that are substantially perpendicular to each other. Figure 10 shows the application of first and second patterns of multiple individual volumes along planes that are substantially perpendicular to each other.

[0037] It should be understood that various patterns may be used to suit specific applications. For example, the topography of a particular surface 14 may be studied through a known measurement process such as 3D optical scanning, and as a result, a suitable thermal interface body shape may be mapped. Forming the thermal interface body may require one or more passes of a dispenser head, including one or more layers of thermal interface material deposited to come into contact with one or more patterns of thermal interface material. It should be further understood that individual patterns or sets of patterns do not need to occupy similar areas, volumes, or shapes. Instead, a particular pattern of thermal interface material may be applied to a selected area of ​​the thermal interface body. It is also possible to cure only a portion of the applied thermal interface material pattern before or after applying another pattern of thermal interface material.

[0038] This invention is described herein in considerable detail to provide those skilled in the art with the information necessary to apply the novel principle and to construct and use embodiments of the invention as needed. However, it should be understood that various modifications can be achieved without departing from the scope of the invention itself. [Explanation of Symbols]

[0039] 10. Accretionary Sedimentation System 12 dispenser heads 14 Surface 14a 1st thermal surface 14b 2nd thermal surface 15 Base Plane 16 Reservoir 18 Opening 20 materials 22 controllers 24 processors 26 Signal Generator 30 Curing System 40 Primary mountain 42 Primary Valley 44. Surface roughness 46 Secondary Mountain 48 Secondary Valley 50 Thermal Interface Unit 60 Electronic Components 70 Heat sink 80 Electronic Packages G Gap a. First deviation dimension b. Second deviation dimension

Claims

1. applying a first material to a surface in a first pattern comprising a plurality of discrete volume applications, the first material comprising a first curable resin precursor, the first curable resin precursor comprising a silicone and exhibiting a first initial viscosity and a thermal conductivity of at least 0.2 W / m·K; and applying at least one of the first curable resin precursor and a second material in a second pattern comprised of separate volumetric deposits in contact with the first material, the second material exhibiting a second viscosity different from the first viscosity and a thermal conductivity of at least 0.2 W / mK; Including, 1. A method for forming a thermal interface body, wherein the first curable resin precursor comprises a first fill concentration of thermally conductive particles and the second material comprises a second fill concentration of thermally conductive particles, the first fill concentration being different from the second fill concentration.

2. 13. The method of claim 1, wherein the applying is performed by an additive manufacturing dispenser.

3. 10. The method of claim 1, wherein the first curable resin precursor comprises thermally conductive particles having a range of different particle sizes, the largest particle size being at least 1.3 times larger than the smallest particle size.

4. The method of claim 1 , comprising applying at least the first pattern or the second pattern in spaced apart independent patterns.

5. The method of claim 4 , wherein at least some of the independent patterns are integrated after application.

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

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

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

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

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

11. 2. The method of claim 1, wherein the first curable resin precursor comprises a solvent, a reaction catalyst, and a reaction inhibitor effective to chemically interfere 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. 12. The method of claim 11, wherein the first and second curable resin precursors comprise a vinyl-containing silicone polymer and a hydride-containing silicone polymer, respectively.

13. 13. The method of claim 12, wherein the first curable resin precursor comprises an excess of one of a vinyl-containing silicone polymer and a hydride-containing silicone polymer, and the second curable resin precursor comprises an excess of the other of a vinyl-containing silicone polymer and a hydride-containing silicone 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 prior to 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 a pluggable optical module.

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