WO2021195576A1

WO2021195576A1 - Thin thermal conductive composite adhesives and methods for making the same

Info

Publication number: WO2021195576A1
Application number: PCT/US2021/024502
Authority: WO
Inventors: Kaoru Ueno; Seyyed Yahya MOUSAVI; Guang Pan; Nitin Mehra
Original assignee: Nitto Denko Corporation
Priority date: 2020-03-27
Filing date: 2021-03-26
Publication date: 2021-09-30
Also published as: TW202144517A

Abstract

The present disclosure relates to thin thermal conductive composite adhesives comprising a porous thermally conductive metal sheet, which are highly thermally conductive, and methods for preparing the same.

Description

THIN THERMAL CONDUCTIVE COMPOSITE ADHESIVES AND METHODS FOR

MAKING THE SAME

Inventors: Kaoru Ueno, Seyyed Yahya Mousavi, Guang Pan, Nitin Mehra

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 63/001,174, filed March 27, 2020, which is incorporated by reference herein in its entirety.

FIELD

The present disclosure related to composites for preparing a bonding material with good thermal conductivity for use in the semiconductor industry.

BACKGROUND

Adhesive materials which are thermally conductive and electrically insulative are widely used in the manufacture of electronic components and systems, including the attachment of heat sinks, die attach adhesives, and encapsulation of electronic components, etc. Composites comprising a polymer matrix plus fillers are commonly used as thermally conductive adhesives. Since the polymer matrixes themselves do not have high thermal conductivity, large concentrations of thermally conductive fillers, such as ceramics, carbon, and metals, are widely used. To reach high thermal conductivity, e.g. > 5 Wm^K ¹, large amounts of fillers, e.g. > 60 vol%, are required.

Conventional methods for creating thermally conductive adhesive materials involve mixing fillers within a polymer matrix or polymer solution to form a filler/polymer slurry. The fillers are usually some thermally and electrically conducting material. The filler/polymer slurries are then coated or cast onto a substrate to fabricate thin films or coatings. Dispersity of the fillers within the polymer matrix and viscosity of the slurries are important factors in the fabrication of thin uniform coatings. As the thermal conductivity requirements of present and future electronic devices increase, conventional methods present increased costs and other challenges as the loading of fillers within the polymer matrices increases.

Furthermore, it is well known that thermal interfaces between filler and the matrix polymerare one of the bottlenecks of thermal conduction in the adhesive composites, due to the phonon spectral mismatching between the fillers and the matrix polymer. Methods attempting to improve the thermal conductivity of the adhesive composites, by modifying the surface of the fillers to match the phonon spectra with the polymer matrixes, have resulted in a limited effect the thermal conductivity of adhesive composite.

Thus, there is a need for improved thermally conductive composite adhesives.

SUMMARY

The present disclosure provides improved thermally conductive composite adhesives, and methods for their preparation.

Some embodiments include a thin thermally conductive composite comprising: a first substrate, a second substrate, and a porous thermally conductive metal sheet having a first surface and an opposing second surface, wherein the porous thermally conductive metal sheet has a plurality of defined conduits extending completely through the porous thermally conductive metal sheet from the first surface to the opposing second surface, wherein the conduits contain a thermoset resin, the thermoset resin adheres the porous thermally conductive metal sheet to the first substrate, and the thermoset resin adheres the porous thermally conductive metal sheet to the second substrate.

Some embodiments include a first substrate, a second substrate, and a porous thermally conductive metal sheet positioned between the first substrate and the second substrate. In some embodiments, the first substrate is coated with a thermoset resin. In other embodiments, the second substrate is coated with a thermoset resin. In some examples, the porous thermally conductive metal sheet is in contact with the thermoset resin of the first coated substrate. In other examples, the porous thermally conductive metal sheet is in contact with the thermoset resin of the second coated substrate. In some embodiments, the porous thermally conductive metal sheet is in contact with the thermoset resin of the first coated substrate and the second coated substrate. In other embodiments, the porous thermally conductive metal sheet is directly coated on the second substrate and in contact with the thermoset resin of the first coated substrate. In some examples, the porous thermally conductive metal sheet comprises aluminum. In some embodiments, the porous thermally conductive metal sheet comprises copper. In some embodiments, the porous thermally conductive metal sheet is etched to define the plural conduits which extend from the first surface of the metal sheet to the second opposite surface. In some embodiments, the first substrate comprises a PET substrate. In other embodiments, the second substrate comprises a PET substrate. In some embodiments, the second substrate comprises a PET substrate, wherein the PET substrate is coated with a porous thermally conductive copper metal sheet. In some embodiments, the second substrate comprises a copper foil, wherein the copper foil is coated with a porous thermally conductive copper metal sheet. Some embodiments include a porous thermally conductive copper metal sheet comprising a mixture of copper particles and a dispersing agent coated onto the second substrate, wherein the coated mixture is sintered at about 100 °C to about 140 °C. In some embodiments, the thermoset resin comprises an epoxy resin. In some examples, the thermoset resin is disposed within and through the defined conduits of the thermally conductive metal sheet by heating at about 50 °C to 70 °C. In some embodiments, the thermally conductive composite have defined conduits that comprise at least 5% of the thermally conductive metal sheet. In some examples, the thermally conductive composite adhesive further comprises a backing layer, wherein the backing layer is disposed on the adhesive surface of the thermally conductive adhesive.

Some embodiments include a method for making a thermally conductive composite comprising a first substrate, a second substrate and a porous thermally conductive metal sheet. The method may comprise disposing a thermoset resin upon the surface of the first substrate and/or the second substrate. The method may comprise conjoining a porous thermally conductive metal sheet with an epoxy coated first substrate and an optionally epoxy coated second substrate, wherein the porous thermally conductive metal sheet is positioned between the coated first substrate and the optionally coated second substrate. The method may also comprise heating conjoined layers at a temperature high enough to allow the thermoset resin to migrate through the conduits of the thermally conductive metal sheet, thus adhering the conjoined layers, but low enough in order not to cure the thermoset resin. In other embodiments, the second substrate may comprise a copper foil or a PET substrate coated with a porous thermally conductive copper metal sheet. In other embodiments, the method of providing a porous thermally conductive metal sheet of copper may include dispersing copper particles within a dispersing agent, coating the copper particles onto a substrate and then sintering the coatings at about 100 °C to about 140 °C. In some embodiments, a porous thermally conductive copper sheet may be coated on a substrate, wherein the substrate may comprise a copper foil or PET film. In some embodiments, the defined conduits may comprise at least 5% of the thermally conductive metal sheet. In some embodiments, the thermally conductive adhesive may further comprise a backing layer. The backing layer may be disposed on an adhesive surface of the thermally conductive adhesive. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram depicting the structure of an embodiment described herein.

FIG. 2 is a diagram depicting the structure of an embodiment described herein.

DETAILED DESCRIPTION

The present disclosure describes thermally conductive composite adhesives and methods for makingthe same. The thermally conductive composites of the present disclosure comprise a porous thermally conductive metal sheet having a first surface and a second opposing (or opposite) surface. In some embodiments, the porous thermally conductive metal sheet is disposed between two substrates. In some embodiments, one of the substrates comprises a thermoset resin layer which is in contact with the first surface of the porous thermally conductive metal sheet. In other embodiments, the first substrate and the second substrate comprise a thermoset resin layer in contact with the first surface and the second surface, respectively, of the porous thermally conductive metal sheet. Other embodiments and methods for preparing the thermally conductive composite adhesives are described in more detail below. The thermally conductive composites described herein comprise a first substrate, a second substrate, and a porous thermally conductive metal sheet positioned between and in contact with the first substrate and the second substrate. The porous thermally conductive metal sheets described herein have a plurality of defined conduits extending completely through the conductive metal sheet from a first surface to a second opposing surface. The term "conduits," as used herein, is equivalent to the terms passageways or channels. In some embodiments, the first substate is coated with a thermoset resin. In other embodiments, the first surface of the porous thermally conductive metal sheet is in contact with the thermoset resin coating of the first substrate. In some embodiments, the second substate is coated with a thermoset resin. In other embodiments, the second surface of the porous thermally conductive metal sheet is in contact with the thermoset resin coating of the second substrate. In other examples, the second surface of the porous thermally conductive metal sheet is in direct contact with the second substrate. In some embodiments, the layers comprising the substrates, the thermoset resin, and the porous thermally conductive metal sheets, may be heated at a temperature sufficient to allow the thermoset resin to migrate through the conduits of the thermally conductive metal sheets, thereby adhering the conjoined plural layers.

The method for preparing a porous thermally conductive metal sheet is not particularly limited. In some embodiments, the porous thermally conductive metal sheet may comprise aluminum. In other embodiments, the porous thermally conductive metal sheet may comprise copper. The method of synthesizing the porous thermally conductive metal sheets of the present disclosure is not particularly limited, as long as the plurality of conduits extend through the metal sheet from a first surface to a second opposite surface and provide in order to provide conductive contact with both surfaces with the thermally conductive metal sheet. Some methods for producing the plurality of conduits include etching or sintering of the metal sheet. The number of conduits through the thermally conductive metal sheet is not limited, as long as the conduits comprise at least 5% of the thermally conductive metal sheet. In some embodiments, the conduits which extend from the first surface of the metal sheet to the second opposite surface may be created by etching the metal sheet for a sufficient amount of time to create the conduits. The amount of time may vary depending on the metal and thickness of the metal sheet, and one skilled in the art would be able to determine the etching time required to produce a plurality of conduits through a particular metal sheet.

In some embodiments, the porous thermally conductive metal sheets may comprise aluminum. In some embodiments, the porous thermally conductive aluminum sheet comprises aluminum foil. Any suitable method may be used to make porous aluminum foil. In the present disclosure, the aluminum foil may be chemically etched to produce porous aluminum foil. Prior to chemical etching, the aluminum foil may be pretreated. In some embodiments, the aluminum foil is pretreated by annealing the aluminum foil at 550 °C for 2 to 3 hours, immersing in 1 M NaOH solution for 3 minutes at room temperature, rinsing with water and drying. In some embodiments, the pretreated aluminum foil may be chemically etched by immersion into a room temperature solution comprising 1-3 M HCI, 1-3 M HNO3 and 0-0.5 M AICI3 for 3-40 minutes, rinsing with water and then drying. In other embodiments, the aluminum foil, which is not pretreated, may be chemically etched by immersion into a room temperature solution comprised of 1-3 M HCI, 1-3 M HNO3 and 0-0.5 M AICI3 for 3-40 minutes, rinsing with water and then drying. The length of time for chemical etching of the aluminum foil is not limited, but only has to produce conduits comprising at least 5% of the thermally conductive aluminum foil sheets. It is believed that annealing the aluminum foil prior to etching enlarges the grain size of the aluminum, resulting in a smoother surface after etching, resulting in a better adhesion.

In some embodiments, the porous thermally conductive metal sheets may comprise copper. In some embodiments, the porous thermally conductive copper sheets may comprise dispersing copper particles within a dispersing agent and coating the dispersed copper particles onto a substrate, followed by sintering. In some embodiments, the copper particles may comprise copper formate tetrahydrate. In some examples, the copper particles may comprise elemental copper. In some cases, the copper particles comprise copper formate tetrahydrate and elemental copper. In some embodiments, the dispersing agent is amino 2- propanol. The substrate may be a cooper foil or polyethylene terephthalate (PET). The term "sintered" or sintering" as used herein refers to a process in which copper powder particles are bonded together on a substrate by heating to form a contiguous copper surface or sheet of copper. Once the copper particles are coated onto a substrate, they may be sintered between about 100 °C to about 140 °C for a time sufficient to produce conduits comprising at least 5% of the thermally conductive copper sheets.

In some embodiments, the porous thermally conductive copper sheet may be prepared through sintering of a Cu ink/Cu powder composite slurry. Copper ink may be prepared by mixing copper formate tetrahydrate with amino-2-propanol. Elemental copper powder may be added to the resulting copper ink mixture to make a Cu ink/Cu powder slurry. The slurry may be coated onto a substrate. In some embodiments, the substrate is PET. In some embodiments, the substrate is copper foil. The Cu ink/Cu powder coatings may then be sintered at 100 °C to 140 °C in N2 or vacuum. The thickness of the porous thermally conductive copper sheets afforded after sintering may be between 10 pm to 30 pm. The thermally porous thermally conductive metal sheet may have any suitable thickness, such as about 1 pm to 30 pm, about 1-2 pm, about 2-3 pm, about 3-4 pm, about 4- 5 pm, about 5-6 pm, about 6-7 pm, about 7-8 pm, about 8-9 pm, about 9-10 pm, about 10- 15 pm, about 15-20 pm, about 20-25 pm, about 25-30 pm, about 10 pm, about 30 pm, or about any value in a range bounded by any of these values.

The thermoset resin may be any thermoset resin which may be partially cured (or B- staged). Thermoset resins that meet this requirement include, but are not limited to, epoxies, phenolics, novalacs (both phenolic and cersolic), polyesters, polyimides, polyurethanes, and polyureas, etc. The thermoset resin not particularly limited, as long as its viscosity is low, and the resin is flowable at about 50 °C to about 70 °C. The thermoset resin used in the present disclosure may be a cross linkable thermoset resin. In some embodiments, the thermoset resin may comprise an epoxy resin. In some examples, the epoxy resin may be composed of a single epoxy resin, or any combination of two or more epoxy resins. The epoxy resin may be any organic or inorganic resin with epoxy functionality. Commercial sources of epoxy resins may include, for example, EPON 164 (Hexion), EPON 1031 (Hexion), D.E.N. 424 (Olin), EN 425 (Olin), DEN 426 (Olin), DEN 43-EK85 (Olin), DEN 438-A85 (Olin), EP-49-23 (Adeka), Ep-4085 (Adeka), or EPALLOY 8280 (CVC Thermoset Specialties). In some embodiments, the epoxy resin is EPON 164.

In some embodiments, the thermoset resin, such as an epoxy resin, may comprise about 30 wt% to about 60 wt%, about 30-45 wt%, 40-55 wt%, about 45-50 wt % about 45-46 wt%, about 46-47 wt%, about 47-48 wt%, about 48-49 wt%, about 40-50 wt%, about 50-51 wt%, about 51-52 wt%, about 52-53 wt%, about 53-54 wt%, about 54-55 wt%, about 55-60 wt%, or about 52.3 wt% of the total weight of the thermally conductive composite, or about any value in a range bounded by the above values. In some embodiments, the thermoset resin comprises an epoxy resin. In some examples, the thermoset resin further comprises a diluent. In other embodiments, the thermoset resin further comprises a curing agent. In some embodiments, the thermoset resin further comprises a cross-linking catalyst. Some embodiments include an epoxy resin, a diluent, a curing agent, a cross-linking catalyst, or any combination of these elements. In some embodiments, the thermoset resin may further comprise a diluent. The diluent may be mixed with the thermoset resin. The diluent may comprise a reactive or non reactive diluent. The diluent may decrease the viscosity of the thermally conductive composite, resulting in an increase of flowability and processability of the composite. The diluent may be but is not limited to diglycidyl ether of polyether polyols such as DER 732 and DER 736, diglycidyl ether, resorcinol diglycidyl ether, 1,4-butanediol diglycidyl ether, butadiene dioxide, vinyl cyclohexane dioxide, butyl glycidyl ether, 2-ethylhexyl glycidyl ether, phenyl glycidyl ether, o-cresyl glycidyl ether, Dibutyl phthalate, nonyl phenol, furfuryl alcohol, 2513HP (glycidyl ether, Cardolite),or ERL 0510 (tryglycidyl-p-aminophenol, Union Carrbide) or DEF 732 (diepoxy resin, Plyscience). In some embodiments, the diluent may be a low viscosity epoxy resin such as, for example, bisphenol F diglycidyl ether, trimethylolpropane triglycidiyl ether, or glycerol polyglycidyl ether. In some embodiments, the diluent may be DRE 732.

The amount of diluent used in the thermally conductive composite may be between about 5 wt% and about 20 wt%, about 5-10 wt%, about 10-15 wt%, about 15-20 wt%, or about 10 wt%, about 11 wt%, about 12 wt%, about 13 wt%, about 14 wt%, about 15 wt%, about 16 wt%, about 17 wt%, about 18 wt%, about 19 wt%, about 20 wt%, about 15.7 wt% of the total weight of the thermally conductive composite, or any about any range bound by any of these values.

The thermoset resin of the thermally conductive composite may further comprise any suitable curing agent. The curing agent may enable the thermoset resin to thermally cure. The thermal curing agent may enable the thermally conductive composite to cross-link, thereby fully curing the composite to form a thermoset polymer adhesive. In some embodiments, the curing agent may be MEHC 7851 (Meiwa Plastic Industries, LTD).

The thermally conductive composite may comprise any suitable amount of curing agent. In some embodiments, the curing agent may comprise about 10 to 40 wt%, about 10- 15 wt%, about 15-20 wt%, about 20-25 wt%, about 25-30 wt%, about 30-35 wt%, about 35- 40 wt%, about 31 wt%, about 32 wt%, about 33 wt%, about 34 w%, about 35 wt%, about 30.3 wt% or about any wt% of the thermally conductive composite, or any percentage in a range bounded by any of the above values. When coated on the first substrate and/or the second substrate, the thermoset resin (such as an epoxy coating) may have any suitable thickness, such as about 0.1-100 pm, about 0.1-1 pm, about 1-10 pm, about 10-20 pm, about 20-30 pm, about 30-40 pm, about 40-50 pm, about 4-10 pm, about 4-6 pm, about 6-10 pm, about 8-10 pm, about 4.8 pm or about 5 pm, about 9 pm, or about 10 pm. In some embodiments, the thermoset resin may have a volume that is about 10-200%, about 10-30%, about 30-50%, about 50-80%, about 80-110%, about 110-150%, or about 150-200% of the volume of the porous thermally conductive metal sheet, wherein the volume of the porous thermally conductive metal sheet includes the total volume of the metal and the pores of the sheet. The thermoset resin of the thermally conductive composite may further comprise a catalyst for cross-linking the thermoset resin. The catalyst (also described as an accelerator) contemplated for use in the thermally conductive composite includes phenols, or other agents known to those skilled in the art. Any suitable catalyst capable of cross-linking the thermosetting resin may be selected. In some embodiments, phenols are used as a catalyst. In some embodiments, the catalyst may comprise triphenylphosphine (TTP).

The amount of the catalyst may comprise about 0.5 to 5 wt%, about 0.5-1 wt%, about 1-2 wt%, about 2-3 wt%, about 3-4 wt%, about 4-5 wt%, or about 1 wt%, about 1.5 wt%, about 2 wt%, about 2.5 wt%, about about 3 wt%, about 3.5 wt%, about 4 wt%, about 4.5 wt%, about 5 wt%, or about 1.7 wt% of the thermally conductive composite, or about any value in a range bounded by any of these values.

In some embodiments, the thermally conductive composite may have a thermal conductivity that is about 0.1 Wm ^_1K ¹ or higher, or about 5 Wm ^_1K ¹ or higher, such as about 0.1-1 Wm ^_1K ^_1, about 1-2 Wm ^_1K ^_1, about 2-3 Wm ^_1K ^_1, about 3-4 Wm ^_1K ^_1, about 4-5 Wm ^_1K ^_1, about 5-6 Wm ^_1K ^_1, about 6-10 Wm ^_1K ^_1, about 10-20 Wm ^_1K ^_1, or about 20 Wm ^_1K ¹ or higher, as determined by the equation: l [Wm ^_1K ^_1] = a [mm²s ^_1] x p [gem ³] x C_p [J K ^_1g ^_1] where a is thermal diffusivity determined with a flash analyzer, p is specific density determined from sample weight using a micro balance and dimensions, and C_p is specific heat capacitance determined by differential scanning calorimetry. In some embodiments, the thermally conductive composite comprises a thermoset resin disposed upon a substrate. The substrate may be a release liner. Any suitable release liner may be used. In some embodiments, the release liner may comprise non-woven material, woven material, or woven substrates. Examples of woven substrates include, but are not limited to, carbon fiber, metal oxide, minerals, ceramics, or other synthetic man-made fibers. Examples of non-woven fibers include, but are not limited to, cellulose, rayon, cloth polyamide fluoride (PVDF), polyethylene (PE), polyethylene terephthalate (PET), polyether ketone (PEEK), and/or mixtures thereof. In some embodiments, the thermoset resin is disposed upon polyethylene terephthalate.

The method of making a thermally conductive composite may comprise conjoiningthe porous thermally conductive metal sheet with a first substrate coated with a thermoset resin and a second substrate coated with a thermoset resin, wherein the porous thermally conductive metal sheet is positioned between the thermoset resin layers of the two coated substrates. In some embodiments, the thermally conductive metal sheet may comprise a porous aluminum foil. The aluminum metal sheet may be porous aluminum foil between 10 pm to 30 pm thick. In other embodiments, the thermally conductive metal sheet may comprise a porous copper foil. The copper metal sheet may be porous copper foil between 4 pm to 30 pm thick.

A depiction of the thermally conductive composite is shown in FIG. 1. A first thermoset coated substrate, such as coated substrate 13a, comprises the first substrate, such as substrate 10a, coated with a thermoset layer, such as layer 11a. A second thermoset coated substrate, such as coated substrate 13b, comprises the second substrate, such as substrate 10b, coated with a thermoset layer, such as layer lib. A porous thermally conductive metal sheet having a first surface and a second opposing surface, such as layer 12, comprising a porous aluminum foil or a porous copper foil may have its first surface placed in contact with layer 11a of the coated substrate 13a, and its second surface in contact with layer lib of the coated substrate 13b. The thermoset coatings 11a and lib may be in physical contact with the opposing surfaces of the porous thermally conductive metal sheet.

Another depiction of the thermally conductive composite is shown in FIG. 2. A first substrate, such as substrate 20, is coated with a thermoset layer, such as layer 21. A porous thermally conductive metal sheet having a first surface and a second opposing surface, such as layer 22, comprising a porous aluminum foil, or a porous copper foil, or a thermally conductive copper sheet, may have its first surface placed in contact with layer 21 of the first substrate 20, and its second opposing surface in contact with a second substrate, such as second substrate 23. The thermoset coating of layer 21 and the second substrate 23 may be in physical contact with the opposing surfaces of the porous thermally conductive metal sheet, such as layer 22.

The method of making the thermally conductive composite comprises heating the conjoined plural layers, as described above and also in FIGs. 1 and 2, at a sufficient temperature to allow the thermoset resin to migrate through the conduits of the porous thermally conductive metal sheets, thereby adhering the conjoined plural layers together. In some embodiments, the method of heating the conjoined plural layers may comprise placing the conjoined plural layers into a vacuum disposition chamber. The thermoset resin is then vacuum disposed at a temperature between 50 °C to 70 °C to allow the resin to flow through the conduits of the thermally conductive metal sheet. Vacuum disposition at between 50 °C to 70 °C allows flow of the thermoset resin, and is too low of a temperature for the thermoset resin to fully cure.

In some embodiments, a thermally conductive composite adhesive may further comprise a backing layer. The backing layer may be disposed upon an adhesive surface of the thermally conductive composite adhesive. The backing layer is not particularly limited. Some examples of backing layers include, but are not limited to, non-woven material, woven material, or woven substrates. Examples of woven substrates include, but are not limited to, carbon fiber, metal oxides, minerals, ceramics, or other synthetic man-made fibers. Examples of non-woven fibers include, but are not limited to, cellulose, rayon, cloth polyamide fluoride (PVDF), polyethylene (PE), polyethylene terephthalate (PET), polyether ketone (PEEK), and/or mixtures thereof. In some embodiments, the thermoset resin is disposed upon polyethylene terephthalate.

Use of the term "may" or "may be" should be construed as shorthand for "is" or "is not" or, alternatively, "does" or "does not" or "will" or "will not," etc. For example, the statement "a thermally conductive composite adhesive may further comprise a backing layer" should be interpreted as, for example, "In some embodiments , a thermally conductive composite adhesive further comprises a backing layer," or "In some embodiments, a thermally conductive composite adhesive does not further comprise a backing layer."

Unless otherwise indicated, all numbers expressing quantities of ingredients, properties, such as, molecular weight, reaction conditions, and so forth used in the specification and embodiments are to be understood as being modified in all instances by the term "about." Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and attached embodiments are approximations that may vary depending upon the desired properties sought to be obtained. At the very least, and not as an attempt to limit the application of the doctrine of equivalents. To the scope of the embodiments, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

For the processes and/or methods disclosed, the functions performed in the processes and methods may be implemented in differing order, as may be indicated by context. Furthermore, the outlined steps and operations are only provided as examples and some of the steps and operations may be optional, combined into fewer steps and operations, or expanded into additional steps and operations.

This disclosure may sometimes illustrate different components contained within, or connected with, different other components. Such depicted architectures are merely examples, and many other architectures may be implemented which achieve the same or similar functionality.

The terms used in this disclosure and in the appended embodiments, (e.g., bodies of the appended embodiments) are generally intended as "open" terms (e.g., the term "including" should be interpreted as "including, but not limited to," the term "having" should be interpreted as "having at least," the term "includes" should be interpreted as "includes, but not limited to," etc.). In addition, if a specific number of elements is introduced, this may be interpreted to mean at least the recited number, as may be indicated by context (e.g., the bare recitation of "two recitations," without other modifiers, means at least two recitations of two or more recitations). As used in this disclosure, any disjunctive word and/or phrase presenting two or more alternative terms should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phase "A or B": will be understood to include the possibilities of "A" or "B" or "A and B."

The terms "a," "an," "the" and similar referents used in the context of describing the present disclosure (especially in the context of the following embodiments) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The use of any and all examples, or representative language (e.g., "such as") provided herein is intended merely to better illuminate the present disclosure and does not pose a limitation on the scope of any embodiments. No language in the specification should be construed as indicating any non-embodied element essential to the practice of the present disclosure.

Groupings of alternative elements or embodiments disclosed herein are not to be construed as limitations. Each group member may be referred to and embodied individually or in any combination with other members of the group or other elements found herein. It is anticipated that one or more members of a group may be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is deemed to contain the group as modified thus fulfilling the written description of all Markush groups used in the appended embodiments.

Certain embodiments are described herein, including the best mode known to the inventors for carrying out the present disclosure. Of course, variations on these described embodiments, will become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventor expects skilled artisans to employ such variations as appropriate, and the inventors intend for the present disclosure to be practiced otherwise than specifically described herein. Accordingly, the embodiments include all modifications and equivalents of the subject matter recited in the embodiments as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is contemplated unless otherwise indicated herein or otherwise clearly contradicted by context. In closing, it is to be understood that the embodiments disclosed herein are illustrative of the principles of the embodiments. Other modifications that may be employed are within the scope of the embodiments. Thus, by way of example, but not of limitation, alternative embodiments may be utilized in accordance with the teachings herein. Accordingly, the embodiments are not limited to the embodiments precisely as shown and described.

EMBODIMENTS

Embodiment 1. A method for making a thermally conductive composite comprising the steps of: a. Providing a porous thermally conductive metal sheet, said sheet having a plurality of defined passageways/conduits extending completely through the conductive metal sheet from a first surface to a second opposite surface and providing conductive contact with both surfaces with the thermally conductive metal sheet; b. Disposing a thermoset resin upon the surface of a substrate; c. Conjoining the porous thermally conductive metal sheet with at least one thermoset resin coated substrate and a second substrate, wherein the porous thermally conductive metal sheet is intermediate the at least one epoxy coated substrates and the second substrate; and d. Heating the conjoined plural layers of step C at a sufficient temperature to allow the thermoset resin to migrate through the conduits of the thermally conductive metal sheets adhering the conjoined plural layers.

Embodiment 2. The method of embodiment 1, wherein the second substrate is copper foil or PET substrate coated with porous thermally conductive copper metal sheet.

Embodiment s. The method of embodiment 1, wherein the second substrate is a thermoset resin coated substrate.

Embodiment 4. The method of embodiment 1, wherein the thermoset resin comprises an epoxy resin.

Embodiment 5. The method of embodiment 1, wherein the thermoset resin is vacuum disposed within and through the defined conduits of the thermally conductive sheet.

Embodiment 6. The method of embodiment 1, wherein the defined conduits comprise at least 5% of the thermally conductive metal sheet.

Embodiment 7. The method embodiment 1, wherein the porous thermally conductive metal sheet comprises aluminum. Embodiment s. The method of embodiment 1, wherein the porous thermally conductive metal sheet comprises copper.

Embodiment 9. The method of embodiment 1, wherein providing a porous thermally conductive metal sheet includes etching said metal sheet a sufficient amount of time to define the plural conduits which extend from the first surface of the metal sheet to the second opposite surface.

Embodiment 10. The method of embodiment 1, wherein providing a porous thermally conductive metal sheet of copper includes dispersing copper particles within a dispersing agent, coating the copper particles onto a substrate and then sintering the coatings at about 100 °C to about 140 °C.

Embodiment 11. The method of embodiment 10, wherein the substrate comprises a copper foil or PET film.

Embodiment 12. A thermally conductive adhesive comprising; a. A thermally conductive metal sheet defining a plurality of conduits therethrough; and b. A thermosetting adhesive material disposed within said defined plural conduits.

Embodiment 13. The thermally conductive adhesive of embodiment 12, further comprising a backing layer, said backing layer disposed on an adhesive surface of the thermally conductive adhesive.

EXAMPLES

Example 1: Preparation of Porous Metal Sheets Example 1.1: Porous Aluminum Foil

Pretreatment: Aluminum foil (either 22 miti or 12.7 miti thick) were cut into 2.5-inch-wide by 4.5-inch-long pieces. Some of the cut pieces of aluminum foil were subjected to annealing at 550 °C for 2 to 3 hours in a box furnace (Thermolyne benchtop muffle furnace, ThermoFisher Scientific, Waltham, MA, USA) under air. Some of the cut pieces of aluminum foil were immersed in a 1M NaOH aqueous solution, at room temperature, for 3 minutes, rinsed with water and dried. Some of the cut pieces of aluminum foil were directly etched without any pretreatment.

Chemical etching: After the cut aluminum foil pieces were pretreated, they were chemical etched. The pretreated aluminum foil was immersed in a mixture of 1-3 M HCI, 1-3 M HNO3 and 0-0.5 M AICI₃ in water in a 500 mL beaker at room temperature for 5-40 minutes. After etching, the aluminum foil pieces were rinsed with water thoroughly, and then dried.

Example 1.2: Porous Copper Coating: Porous copper coatings were fabricated through sintering of Cu ink/Cu powder composite slurry. Copper ink was prepared by mixing copper formate tetrahydrate (CXCU045, Gellest) with amino-2-propanol (93%, 110248,

MilliporeSigma) at a molar ratio of 1:1. Thus, 2.49 mL of amino-2-propanol was added to 6.77 g of copper formate tetrahydrate in a 20 mL vial. The mixture was stirred for 2-3 hours until forming a uniform liquid slurry (Cu ink). Then, the desired amount of Cu powder (Spherical, APS 10 pm, 42689, Alfa Aesar or APS 3.45 pm, 42455 Alfa Aesar, 0.3 pM Skyspring) was added to the above Cu ink at a molar ratio of Cu²⁺:Cu from 1:2 to 1:12 and ethanol (1 mL per 1 g of Cu ink) for adjusting viscosity, to make Cu ink/Cu powder slurry. Mixing media (Zr02 beads with a diameter of 3-6 mm) was added if necessary. The slurry was mixed for 2 hours to 2 days on a roller bar mixer. The slurry was coated onto a substrate comprised of either 9 pm Cu foil, PET film, primarized PET film, or PET film with release liner with a film applicator (Multiple Clearance Square Applicator, AP-B5363, Paul N. Gardner Company, Inc. Pompano Beach, FL, USA) at different gaps (0.5-3 mils). The Cu ink/Cu powder coatings were then sintered at 100 °C to 140 °C in N2 flow (0.5-1 L/min) or in vacuum. The thickness of porous Cu after sintering was between 4 pm to 30 pm.

Example 2: Preparation of Epoxy Coating: In a 100 mL jar, EPON 164 (Hexion, 7.7 g) was added to MEHC 7851 (Meiwa Plastic Industries, LTD, 10.5 g), then DER 732 (Polysciences, Inc., 4.8 g) and finally MEK (23 g) were added. The mixture was stirred using a magnetic stirrer for 30 min at room temperature to fully dissolve all of the ingredients into MEK. A 10 wt% solution of triphenylphosphine (TPP) in MEK was added to the mixture as the catalyst at the amount of 1 pph based on solids and the mixing was continued for 15 minutes.

The epoxy resin solution was coated onto the release liner coated polyester film (Hostaphan 3ACK, Mitsubishi Polyester Film, Inc., Greer, SC 29652 USA) using an applicator with the gap size of 0.2, 0.5, 1.0, and 1.5 mils . The coated films were left at room temperature overnight to slowly evaporate the solvent without making any void. They were then put into an oven at 55 ^°C for 90 min for complete evaporation of the solvent.

Example 3: Preparation of Epoxy-filler Coating. The coatings of a filler into epoxy resin with the filler content of 5, 10, 15. 20, 25, or 30 vol% into epoxy resin matrix was produced with the following procedure. The calculated amount of filler which is Cu or Ag with the diameter of 20 nm, 50 nm, 100 nm, 0.5 pm, 1 pm, or 1.5 pm were weight and put into a jar. The calculated amount of the epoxy resin prepared based on the method mentioned in Example 2 was added to the jar. The calculated amount of MEK was added to adjust the total solid content of the slurry to 40-60 vol% based on the required thickness of the final coating. The slurry was mixed using a stirrer at highest intensity for 2 h. Then, the slurry was sonicated with a probe ultrasonicator (Fisherbrand, Model FB120) for 2 h at the pulse intensity of 80%. During ultrasonication, the jar was cooled in an ice bath. Then, the mixture was mixed using a magnetic stirrer at highest intensity overnight. Just before making the coating, 10 wt% solution of triphenylphosphine (TPP) in MEK was added to the mixture as the catalyst at the amount of 1 pph based on solid weight of TPP and epoxy resin. The mixing continued for 15 minutes

The epoxy resin-filler slurry was coated onto the release liner coated polyester film (Hostaphan 3ACK, Mitsubishi Polyester Film, Inc., Greer, SC 29652 USA) using an applicator with the gap size of 0.2, 0.5, 1.0, or 1.5 mils. The coated films were left at room temperature overnight to slowly evaporate the solvent without making any void. They were then put into an oven at 55 ^°C for 90 min for complete evaporation of the solvent.

Example 4: Fabrication of Porous Thermally Conductive Composite: Example 4.1: Fabrication of Porous Aluminum Composite: Porous etched aluminum foil was sandwiched between epoxy coated substrates and was vacuum laminated at 55 ^°C and then pressed at 101 kPa for 5 minutes using a vacuum laminator (model LM-50x50-S produced by NPC incorporated, Tokyo, Japan). The epoxy formulation from example 2 becomes fluid at > 55 ^°C and the epoxy may fill the conduits within the porous aluminum foil. The laminated samples were cut in two pieces. One was cured into a hot press

(Mitsubishi NV 30-cs, Tokyo, Japan) at 53 MPa and 120 ^°C overnight, the another was cured in an oven with no external pressure at 120 ^°C overnight. After the samples were cooled down to room temperature, the polyester films were peeled off. Thermal diffusivity, specific density, and heat capacity were measured to determine their thermal conductivity. Example 4.2 Fabrication of Porous Aluminum Composite with filler: Porous etched aluminum foil was sandwiched between Ag/epoxy or Cu/epoxy coated substrates and was vacuum laminated at 55 - 80 ^°C and 101 kPa for 10 - 30 minutes using a vacuum laminator (model LM-50x50-S produced by NPC incorporated, Tokyo, Japan). The epoxy formulation from example 2 becomes fluid at >55 ^°C and the epoxy can fill the conduits within the porous aluminum foil.

The laminated samples were cut in two pieces. One was cured into a hot press (Mitsubishi NV 30-cs, Tokyo, Japan) at 53 MPa and 120 ^°C overnight, the another was cured in an oven with no external pressure at 120 ^°C overnight. After the samples were cooled down to room temperature, the polyester films were peeled off. Thermal diffusivity, specific density, and heat capacity were measured to determine their thermal conductivity.

Example 4.3 Porous Aluminum Composite between Si wafer: Using the obtained porous aluminum composites, Si/porous aluminum composite/Si was fabricated. After peeling off the PET substrate with release liner from porous aluminum composite, diced Si wafer (1 cm x 1 cm, about 400 pm thick) was placed on the porous aluminum composite, and then Si wafer was adhered by using vacuum lamination at 80 °C for 30 minutes at 101 kPa. After cooling down, another side PET was peeled off, another Si wafer was placed on the other side and adhered by using the same vacuum lamination conditions. The obtained Si/porous aluminum composite/Si was cured at 150 C for 1 hour in the convection oven (Yamato). Example 4.4: Fabrication of Porous Copper Composite: Porous copper coated copper foils were vacuum laminated with epoxy coated substrates at 55 ^°C and 101 kPa for 5 min using a vacuum laminator (model LM-50x50-S produced by NPC incorporated, Tokyo, Japan). The epoxy formulation from example 2 becomes fluid at > 55 ^°C the epoxy may fill the conduits within the porous copper coated copper foils. The laminated samples were cut in two pieces. One was cured into a hot press

(Mitsubishi NV 30-cs, Tokyo, Japan) at 53 MPa and 120 ^°C overnight, the another was cured in an oven with no external pressure at 120 ^°C overnight. After the samples were cooled down to room temperature, the polyester films were peeled off. Thermal diffusivity, specific density, and heat capacity were measured to determine their thermal conductivity. Example 4.5 Fabrication of Porous Copper Composite between PET with release liner by single lamination process: Porous copper coated PET with release liner was vacuum laminated with Cu/epoxy coated PET with release liner at 80 °C and 101 kPa for 30 min using vacuum laminator (model LM-50x50-S produced by NPC incorporated, Tokyo, Japan). The epoxy formulation from example 2 becomes fluid at >55 ^°C and the epoxy can fill the conduits within the porous copper coated copper foils.

Example 4.6 Fabrication of Porous Copper Composite between PET with release liner by double lamination process: Porous copper coated PET with release liner was vacuum laminated with Cu/epoxy coated PET with release liner at 80 °C and 101 kPa for 30 min using vacuum laminator (model LM-50x50-S produced by NPC incorporated, Tokyo, Japan). The epoxy formulation from example 2 becomes fluid at >55 ^°C and the epoxy can fill the conduits within the porous copper coated copper foils. Then, PET on Cu/epoxy coating side was peeled off, and another porous Cu coating was laminated.

Example 5: Thermal conductivity measurements Example 5.1: Measurement of thermal conductivity (l) of the composites: The thermal conductivity was determined by the following equation: l [Wm ^_1K ^_1] = a [mm²s ^_1] x p [gem ³] x C_p [JK^g ¹] where a, p and C_p are thermal diffusivity, specific density and specific heat capacitance, respectively. Thermal diffusivity was determined with a flash analyzer (LFA-467, Netzsch), specific density was determined from sample weight using a micro balance and dimensions (thickness and area), and Cp was determined by a differential scanning calorimetry (Q2000, TA instrument). For thermal diffusivity measurement, sample configuration of porous metal/epoxy composites on Cu foil was always used. The measured thermal conductivity is summarized below in Table 1. Example 5.2: Measurement of thermal diffusivity (a) of the composites in Si/composite/Si structure: Thermal diffusivity of the composite was determined by Temperature Wave Analysis (ai-Phase, Japan). The contribution of Si wafer was subtracted using the thermal diffusivity of Si separately measured by temperature wave analysis. Density and heat capacity was calculated from the known composition, and thermal conductivity was determined from the above equation in Example 5.1.

Table 1:

Claims

1. A thermally conductive composite comprising: a first substrate, a second substrate, and a porous thermally conductive metal sheet having a first surface and an opposing second surface, wherein the porous thermally conductive metal sheet has a plurality of defined conduits extending completely through the porous thermally conductive metal sheet from the first surface to the opposing second surface, wherein the conduits contain a thermoset resin, the thermoset resin adheres the porous thermally conductive metal sheet to the first substrate, and the thermoset resin adheres the porous thermally conductive metal sheet to the second substrate.

2. The thermally conductive composite of claim 1, wherein: a first side of the first substrate is coated with the thermoset resin; a first side of the second substrate is optionally coated with a thermoset resin; the first surface of the porous thermally conductive metal sheet is placed in contact with the thermoset resin of the first substrate; the second surface of the porous thermally conductive metal sheet is placed in contact with the first side of the second substrate; and wherein the first side of the first substrate, the second side of the second substrate, and the porous thermally conductive metal sheet are conjoined by heating at a sufficient temperature to allow the thermoset resin to migrate through the plurality of defined conduits of the thermally conductive metal sheet.

3. The method of claim 1, wherein the second substrate is a thermoset resin coated substrate, wherein the porous thermally conductive metal sheet is positioned between and in contact with the thermoset resin of the first substrate and the thermoset resin of the second substrate.

4. The thermally conductive composite claim 1, 2, or 3, wherein the porous thermally conductive metal sheet comprises aluminum.

5. The thermally conductive composite claim 1, 2, or 3, wherein the porous thermally conductive metal sheet comprises copper.

6. The thermally conductive composite of claim 1, 2, 3, 4, or 5, wherein a porous thermally conductive metal sheet is etched to form the plurality of defined conduits which extend from the first surface of the metal sheet to the second opposite surface.

7. The thermally conductive composite of claim 1, 2, 3, 4, 5, or 6, wherein the first substrate comprises a PET substrate.

8. The thermally conductive composite of claim 1, 2, or 3, wherein the second substrate comprises a PET substrate, wherein the PET substrate is coated with a porous thermally conductive copper metal sheet.

9. The thermally conductive composite of claim 1, 2, or 3, wherein the second substrate comprises a copper foil, wherein the copper foil is coated with a porous thermally conductive copper metal sheet.

10. The thermally conductive composite of claim 8 or 9, wherein the porous thermally conductive copper metal sheet comprises a mixture of copper particles and a dispersing agent coated onto the second substrate, wherein the coated mixture is sintered at about 100 °C to about 140 °C.

11. The thermally conductive composite of claim 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10, wherein the thermoset resin comprises an epoxy resin.

12. The thermally conductive composite of claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or 11, wherein the thermoset resin is disposed within and through the defined conduits of the thermally conductive metal sheet by heating the thermoset resin about 50 °C to 70 °C.

13. The thermally conductive composite of claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12, wherein the defined conduits comprise at least 5% of the thermally conductive metal sheet.

14. The thermally conductive adhesive of claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, or 13, further comprising a backing layer, wherein the backing layer is disposed on an adhesive surface of the thermally conductive adhesive.

15. A method for preparing a thermally conductive composite, comprising: coating a first substrate with a thermoset resin; placing a porous thermally conductive metal sheet having a first surface and an opposing second surface in contact with the thermoset resin of the first substrate, wherein the porous thermally conductive metal sheet has a plurality of defined conduits extending completely through the thermally conductive metal sheet from the first surface to the opposing second surface; placing a second substrate in contact with the porous thermally conductive metal sheet; and conjoining the first substrate, the second substrate, and the porous thermally conductive metal sheet by heating at a sufficient temperature to allow the thermoset resin to migrate through the conduits of the thermally conductive metal sheet.