Compositions and Composite Materials

Abstract

A composition comprising an oxygen scavenger solvent, a co-solvent, and a plurality of silver particles suspended in a mixture of the oxygen scavenger solvent and the co-solvent, wherein the oxygen scavenger solvent comprises one or more compounds of the formula C n O m H 2n+2-p (OH) p , where n, m, and p are integers, provided that 1 ≦ (n + m) / p ≦ 8, and the mixture of the oxygen scavenger solvent and the co-solvent contains hydroxyl groups at a concentration in the range of 2M to 20M. A method of forming the composition is also provided. A method of forming a composition material and a device comprising the composite material are also provided.

Description

Technical Field

[0001] Cross - References to Related Applications This application claims priority to Singapore Application No. 10202205139Y, filed on May 17, 2022 with the Intellectual Property Office of Singapore, the content of which is incorporated herein by reference. The present invention generally relates to a composition comprising an oxygen scavenger solvent, a co - solvent, and a plurality of silver particles suspended in a mixture of the oxygen scavenger solvent and the co - solvent. The present invention also relates to a method of forming the composition. The present invention further relates to a method of forming a composite material from the composition and a device comprising the composite material.

Background Art

[0002] High - performance electrical and thermal conductive materials are required as thermal interface, die attach, electrical interconnect, and electrode materials to meet the challenges of next - generation devices, especially the high - power and high - speed electronics associated with 5G. Thermal interface materials provide thermal contact between a semiconductor chip and its heat sink, while die attach materials bond the chip to its substrate or package, often also providing electrical and / or thermal contact. Electrical interconnect and electrode materials are used for contacts, busbars, antennas, and wiring in components such as solar cells, switches, capacitors, sensors, and other parts of printed electronics.

[0003] Conventionally, powder - based silver (Ag) sintered materials offer high performance including high - temperature resistance, with a high electrical conductivity (6.2x10 5Since a high electrical conductivity (5.9×10 Silver sintered pastes have advantages and have been widely deployed, yet several common challenges still remain. Silver powder, mainly used in the form of flakes, generally requires the application of high pressure (above 5 MPa) and sintering temperatures far exceeding 250°C for extended periods to reach electrical conductivities greater than 1.0×10 5 S / cm and thermal conductivities greater than 75 W / mK. Conventionally referred to as "low temperature sintering", the required temperatures and times are not desirable for future thermal management and electrical interconnection technologies.

[0004] Furthermore, sintering requires the formation of local silver bridges between adjacent silver microparticles in the powder at temperatures considerably lower than its melting point. This process is not fully understood, except to the extent that it depends on the decomposition or reduction of native Ag2O on the surface of the silver microparticles to silver. The Ellingham diagram shows that Ag2O is thermodynamically unstable, especially for the decomposition of silver above 147°C, but has a high activation energy. The deoxidation reaction of Ag2O proceeds at a significant rate only when the temperature exceeds 300°C in air or nitrogen. However, this reaction occurs at a much lower temperature, below 200°C, in a reducing atmosphere of carbon monoxide, hydrogen, or ethylene. However, such a reducing atmosphere poses its own challenges and may not be desirable for the manufacture of electrical materials. Furthermore, a pure sintered silver thin film generally adheres well to layers of silver, gold, platinum, and palladium, as well as substrates metallized with these layers, but does not adhere to other layers such as semiconductors, oxides, and plastics without special pretreatment. Since the total thermal resistance is the sum of the bulk resistance through the thermal interface material and the contact resistance at each of the two interfaces, the above becomes a problem specific to thermal interface materials. To minimize the thermal resistance, it is necessary not only that the thermal conductivity of the interface material is high, but also that the thermal conductance at both sides of the interface is good. This generally requires good adhesion to both the surface of the die and the surface of the substrate or heat sink.

[0005] To improve adhesion, another conventional sintering material in the formulation contains a thermosetting resin such as acrylate, epoxy, polyimide, polyurethane, or polysiloxane, resulting in a polymer matrix. The resin may be pre-polymerized or may be polymerizable as a reactive one-pot formulation or two-pot formulation. This conventional material is known in the art as an electrically conductive adhesive (ECA), but still has limitations in electrical conductivity and thermal conductivity. In particular, the above conventional materials generally achieve good adhesion (lap shear strength better than 3 MPa) to a number of surfaces, but even after sintering at 200 °C or higher, they each have a bulk electrical conductivity and thermal conductivity lower than 7×10 4 less than S / cm and less than 50 W / mK, respectively, at the expense of even lower values. Furthermore, several major classes of silver sintering pastes are also conventionally known, each having its own advantages and limitations. For example, μm silver paste is produced by ball milling and thus is based on silver flakes in the μm size range of 0.2 to 20 μm coated with a grinding aid such as oleic acid or stearic acid. For good performance, the above silver paste usually requires a sintering temperature of 200 °C or higher, typically 250 to 300 °C, and a sintering pressure of 0.5 MPa or higher, usually 2 to 5 MPa. These conventional materials have the longest development history and are proven to be reliable on record.

[0006] Numerous improvements to the paste formulation for reducing the sintering temperature and improving adhesion have been conventionally known. When Ag(I) compounds such as oxides, formates, and carbonates, which have a low decomposition temperature, decompose to silver and form cross-links between the filler powders below their normal sintering temperature, the above compounds and oxidizing agents can be added to lower the required sintering temperature. Oxidizing agents such as organic peroxides and inorganic peroxides can also be added to promote the oxidative decomposition and volatilization of the organic coatings on the silver powder. This also helps to lower the sintering temperature, but it poses a risk to the reliability of the substrate and die. Acidic fluxes and reducing agents can be added to remove the oxide layer on the metallized surface such as copper, thereby promoting adhesion to the sintered silver. Nevertheless, this paste usually still has an electrical conductivity of less than 1.0×10 5 less than S / cm and a thermal conductivity of less than 75 W / mK when sintered at a temperature of 200 °C or lower and a pressure of 2 MPa or lower in an inert atmosphere. To achieve a higher conductivity, pressure sintering at a temperature of about 230 to 250 °C and a pressure exceeding 3 MPa is required.

[0007] Silver nano-paste is also conventionally known and is usually based on nano-sized silver crystals suspended in a polymer binder. The Ag filler is produced by chemically reducing an Ag(I) salt in the presence of a capping ligand or capping agent such as methyl octylamine, dodecylamine, hexadecylamine, myristyl alcohol, 1-dodecanol, 1-decanol, stearic acid, oleic acid, palmitic acid or dodecanethiol. A capping ligand or capping agent is required to stabilize the silver nanocrystals. When the required volume fraction of the capping agent is high (usually more than 65% by volume of the total solids), sintering is usually delayed until above 250 °C. Polymer binders include poly(diallyldimethylammonium chloride), polyvinylpyrrolidone, polyacrylic acid, polystyrene sulfonate, polyvinyl alcohol, polyvinyl butyral and ethyl cellulose. In the case of silver nanoparticles with short ligands coated with a small amount of sub-monolayer, the sintering temperature required to reach an electrical conductivity of 1.0×10 5 S / cm could be reduced to 150 °C without applying pressure. This demonstrates that it is not surface melting, as previously thought, but shell volatilization that determines the sintering temperature of the nanocrystals, and thus the sintering temperature can be controlled by the choice of ligand. Nevertheless, silver nano-paste requires the chemical synthesis of silver nano, which is much more costly and time-consuming than the production of silver powder by ball milling. Furthermore, the environmental and health impacts of nanomaterials are still under discussion.

[0008] Hybrid silver pastes are also known in the art. These pastes, together with μm-sized and nano-sized silver particles, provide a higher packing density. Typically, bimodal formulations have a diameter ratio of about 3:x (x ≤ 1) and a corresponding mass ratio of about 2:1. Trimodal formulations have a diameter ratio of about 10:3:x, and the total mass ratio of the larger fraction to the smaller fraction is also about 2:1. Hybrid silver pastes can achieve higher packing density and shear strength than μm Ag or nano Ag alone. However, to achieve the desired characteristics, the sintering temperature of the hybrid silver paste must be higher than 300 °C and the sintering pressure must be higher than 2 MPa. Accordingly, there is a need for compositions and composite materials that address one or more of the above disadvantages. SUMMARY OF THE INVENTION

[0009] In one aspect, a composition comprising a deoxidizer solvent and a co-solvent, and a plurality of silver particles suspended in a mixture of the deoxidizer solvent and the co-solvent, The deoxidizer solvent comprises one or more compounds of the formula C n O m H 2n+2-p (OH) p wherein n, m, and p are integers, provided that 1 ≤ (n + m) / p ≤ 8, The mixture of the deoxidizer solvent and the co-solvent comprises hydroxyl groups at a concentration in the range of 2M to 20M, and a composition is provided. In another aspect, a method of forming a composition is provided, comprising the step of dispersing a plurality of silver particles in a deoxidizer solvent, or in a mixture of a deoxidizer solvent and a co-solvent, in the presence of the co-solvent. In another aspect, a method of forming a composite material is provided, comprising the step of sintering the composition described herein on a substrate.

[0010] Advantageously, the present composition does not require air or oxygen to "burn off" excess organic matter during the sintering process. Thus, the present composition is compatible with the interconnects of Cu and Al that may be present in the die. This is because any organic polymer used is present only in small amounts on the surface of the silver particles. Even more advantageously, the sintering of the present composition does not require a cumbersome reducing atmosphere. This is because the deoxidizer solvent and co-solvent supply the chemicals necessary for the reduction of silver oxide. Even more advantageously, the sintering of the present composition does not require high pressure. Thus, the method does not require an expensive pressure conversion device. This improves the reliability of the die or substrate attached to the composite material. This advantage is derived from the more efficient sintering achieved by the present method. In one example, the sintering temperature is less than 200 °C. Advantageously, the present composition can have native silver oxide with an increased degree of decomposition or reduction, in which case the sintering temperature is less than 200 °C. In another aspect, a device is provided that includes a composite material formed by the method described herein.

[0011] Definitions The following words and terms used herein shall have the indicated meanings: The term "substantially" does not exclude "completely"; for example, a composition that "substantially does not contain" Y may completely not contain Y. If necessary, the term "substantially" may be omitted from the definition of the present invention. Unless otherwise specified, the terms "comprising" and "comprise" and their grammatical variations are intended to represent an "open" or "inclusive" phraseology such that they include the recited elements, but also permit the inclusion of additional unrecited elements. The term "about", as used herein, generally means either the specified value or the larger of + / −10% of one unit of the last digit of the specified value.

[0012] Throughout this disclosure, certain embodiments may be disclosed in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the disclosed range. Accordingly, a description of a range should be considered to have specifically disclosed all the possible sub-ranges within that range, as well as the individual numerical values within that range. For example, a description of a range such as 1 to 6 should be considered to have specifically disclosed sub-ranges such as 1 to 3, 1 to 4, 1 to 5, 2 to 4, 2 to 6, 3 to 6, as well as the individual numbers within that range, such as 1, 2, 3, 4, 5, and 6. This applies regardless of the width of the range. Certain embodiments may also be described herein in broad and general terms. Narrower species and quasi-inclusive groupings that fall within the scope of the comprehensive disclosure also each form part of this disclosure. This includes comprehensive descriptions of embodiments with conditions or negative limitations that exclude some subject matter from the genus, regardless of whether the deleted material is specifically listed herein.

DETAILED DESCRIPTION OF THE INVENTION

[0013] Exemplary and non-limiting embodiments of the composition are disclosed hereinafter. The composition includes an oxygen scavenger solvent and a co-solvent, and a plurality of silver particles suspended in a mixture of the oxygen scavenger solvent and the co-solvent. The oxygen scavenger solvent includes one or more compounds of the formula C n O m H 2n+2-p (OH) p wherein n, m, and p are integers, provided that 1 ≤ (n + m) / p ≤ 8. The mixture of the oxygen scavenger solvent and the co-solvent contains hydroxyl groups at a concentration in the range of 2M to 20M. Advantageously, from the composition, by sintering at a temperature of 200°C or lower, at least about 1.0×10 5A composite material having an electrical conductivity of S / cm and a thermal conductivity of at least about 75 W / mK can be produced. The deoxidizer solvent and the co-solvent can have a total mass percentage in the range of about 6% to about 30%, about 12% to about 25% or about 18% to about 25% based on the total mass of the composition. The deoxidizer solvent and the co-solvent can have a volume ratio in the range of about 1:1.0 to about 1:10 or about 1:1.0 to about 1:5.

[0014] Advantageously, when the deoxidizer solvent is present in a diluted form, it can avoid the formation of gas bubbles during the sintering of the present composition. The plurality of silver particles can have an average diameter in the range of about 0.2 μm to about 20 μm, about 5 μm to about 20 μm, about 10 μm to about 20 μm, about 15 μm to about 20 μm, about 0.2 μm to about 15 μm, about 0.2 μm to about 10 μm or about 0.2 μm to about 5 μm. When measured by particle size analysis (e.g., laser light scattering method), the plurality of silver particles can have a size distribution (i.e., the spread of the 16% to 84% of the cumulative distribution by mass) in the range of about ±10% (i.e., narrow distribution) to about ±70% (i.e., wide distribution), ±20% to about ±70%, about ±50% to about ±70%, about ±10% to about ±50% or about ±10% to about ±20%. The size distribution can be a unimodal distribution, a bimodal distribution or a multimodal distribution. When the size distribution is a bimodal distribution, this size distribution can have a size ratio in the range of about 10:3 to about 10:0.3, about 10:1.0 to about 10:0.3 or about 10:3 to about 10:1.0. When the size distribution is a multimodal distribution, this size distribution can have a size ratio of about 10:3:1.0.

[0015] Advantageously, the plurality of silver particles includes both smaller particles and larger particles, in which case the smaller particles can fill the voids between the larger particles, so that due to the above size distribution, the plurality of silver particles is particularly suitable for the composition of the present invention. The plurality of silver particles may be in the form of flakes, granules, spheroids, or a combination thereof. The plurality of silver particles may be in the form of flakes. Advantageously, the flake form can provide a lower final porosity, better conductivity, and adhesion properties to the composite material made from the present composition compared to other forms. When the plurality of silver particles is in the form of flakes, the plurality of silver particles may have a specific surface area (i.e., the exposed surface area per unit mass) in the range of about 0.6 m 2 / g to about 2.5 m 2 / g, about 1 m 2 / g to about 2.5 m 2 / g, about 2 m 2 / g to about 2.5 m 2 / g, about 0.6 m 2 / g to about 2 m 2 / g or about 0.6 m 2 / g to about 1.0 m 2 / g. The specific surface area can be measured as the BET surface area by gas adsorption. Thus, the specific surface area can depend on how the plurality of silver particles is prepared (e.g., by a milling process).

[0016] When the plurality of silver particles is in the form of spheroids and has an average diameter of about 2 μm, the plurality of silver particles can have a specific surface area of about 0.3 m 2 / g. The plurality of silver particles can increase in rigidity as the specific surface area decreases. When the plurality of silver particles is measured by a tapped volume meter, it can have a tapped density (i.e., the ratio between the total mass of the plurality of silver particles and the total volume occupied by the plurality of silver particles after tapping the plurality of silver particles until a constant volume is reached) of at least about 2.5 g / cm 3 or at least about 3.5 g / cm 3 . The plurality of silver particles can include particles of silver element, particles of silver alloy, silver-coated particles, silver oxide particles, or combinations thereof. The silver-coated particles may be copper particles coated with silver.

[0017] The composition may further contain a silver additive. Non-limiting examples of the silver additive include silicon dioxide coated with silver, silicon carbide coated with silver, boron nitride coated with silver, ceramic oxide coated with silver, glass coated with silver, silver oxide, or combinations thereof. Advantageously, the presence of the silver additive can bring a higher mechanical strength to the composite material made from the composition.

[0018] As described above, (n + m) / p represents the hydroxyl number. A deoxidizer solvent having a lower hydroxyl number (for example, about 1 to about 2) has a high concentration of hydroxyl groups, and thus, this deoxidizer solvent can be used in a small amount (by mass) to achieve a deoxidizing effect. However, such a deoxidizer solvent also tends to cause an active reaction that generates gas bubbles during deoxidation, which is not desirable because the gas bubbles spread to the composite material during sintering. The composite material made from the composition may have a lower conductivity and mechanical strength due to the generation of gas bubbles, and therefore, it is necessary to dilute the deoxidizer solvent. When the deoxidizer solvent has a large number of hydroxyl numbers (for example, about 5 to about 8), a large amount (by mass) of the deoxidizer solvent is required to achieve the deoxidizing effect, and the deoxidation can proceed more slowly and smoothly. Advantageously, it is convenient and cost-effective to adjust the deoxidizer solvent to control the deoxidation of the composition if necessary.

[0019] The deoxidizer solvent can have a boiling point in the range of about 190°C to about 350°C, about 250°C to about 350°C, about 300°C to about 350°C, about 190°C to about 300°C, or about 190°C to about 250°C. Advantageously, when the deoxidizer solvent has the above boiling point, the deoxidizer solvent has a sufficiently low vapor pressure to remain substantially with the composition during deoxidation of the composition. In particular, deoxidation of the present composition occurs at a deoxidation temperature, which is the lowest temperature at which a plurality of silver particles can be reduced at a significant reduction rate. The deoxidation temperature can be estimated by a number of methods, such as reacting bulk silver oxide powder with a putative deoxidizer solvent under a low heating rate (e.g., 2 °C per minute). Even more advantageously, since the deoxidizer solvent is in liquid form, it can be completely removed by drying (e.g., annealing for a longer time, annealing at a higher temperature, annealing under vacuum conditions, or a combination of the above), leaving no residues that would cause undesirable corrosion or other defects in the composite material made from the present composition. Thus, the deoxidizer solvent works better than a solid-state deoxidizer or reducing agent that is not easily removed by a drying process.

[0020] Before reaching the deoxidation temperature, if the deoxidizer solvent is substantially lost (e.g., by evaporation), the deoxidizer solvent is not effective. As noted above, the boiling point of the deoxidizer solvent serves as a surrogate for its vapor pressure at lower temperatures. The inventors have found that certain deoxidizer solvents have a significant evaporation rate (e.g., on the order of about 2 microns per minute) at a temperature about 100 °C lower than their boiling point. That is, with respect to interconnect applications, if the rate of evaporation is not appropriately attenuated for the desired printed or dispensed pattern of the composition, the deposited composition is exposed and not covered by another component, so the boiling point of the deoxidizer solvent may be at least about 100 °C or about 150 °C higher than the deoxidation temperature. Alternatively, in the case of thermal interfaces, die attach, and other bonding applications, the deoxidizer solvent can only evaporate along the edge (e.g., die), and the evaporation rate seems to depend on the size of the die. That is, the boiling point of the deoxidizer solvent may be even lower for these applications, for example, about 50 °C higher than the deoxidation temperature. When the composition is pre-dried, the pre-drying can be carried out at a temperature at least about 100 °C or about 150 °C lower than the boiling point of the deoxidizer solvent.

[0021] The deoxidizer solvent can be present in an amount calculated from the stoichiometry of the reaction. According to the following formula, the theoretical specific amount (N) of hydroxyl groups required per unit mass of a plurality of silver particles can be derived from the specific surface area (S) of the plurality of silver particles, the thickness (d) of the plurality of silver particles, the density (ρ) of the plurality of silver particles, the formula weight (M) of the plurality of silver particles, and the stoichiometric number (ξ) of the plurality of silver particles: N = S×d×ρ / (M×ξ) The plurality of silver particles have a thickness (d) of 2×10 -9 m, a density (ρ) of 7.14×10 6 g / m 3 , a formula weight (M) of 231.7 g / mol, and can have a stoichiometric number (ξ) of 1 assuming that each hydroxyl group acts as a 2-electron reducing agent (i.e., 1 formula unit of Ag2O is reduced to Ag). In reality, primary hydroxyl groups can act as 4-electron reducing agents with a stoichiometric number (ξ) of 2. Therefore, when the plurality of silver particles are silver flakes having a specific surface area (S) in the range of about 0.6 m 2 / g to about 2.5 m 2 / g, the theoretical specific amount (N) of hydroxyl groups calculated from the above formula is about 35 μmol / g to about 150 μmol / g. The inventors have found that the theoretical specific amount (N) of hydroxyl groups is sufficient to complete deoxidation. Alternatively, the deoxidizer solvent may be present in an amount up to 4 times the theoretical amount to offset the decrease (e.g., evaporation) of the deoxidizer solvent when treating the composition.

[0022] Non-limiting examples of the deoxidizer solvent include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, isomers of propanediol, isomers of butanediol, isomers of pentanediol, isomers of hexanediol, isomers of heptanediol, isomers of octanediol, glycerol, pentaerythritol, dipentaerythritol, 2-(2-methoxyethoxy)ethanol, 2-(2-ethoxyethoxy)ethanol, and combinations thereof. Surprisingly, the above deoxidizer solvent becomes a powerful deoxidizer for bulk silver oxide powder Ag2O at low temperatures (e.g., about 130 °C). Thus, the deoxidizer solvent can advantageously promote the sintering of the present composition as a deoxidizer. Even more advantageously, when present in a diluted form, the deoxidizer solvent can avoid the formation of gas bubbles during the sintering of the present composition and limit the activity of the deoxidation reaction.

[0023] The deoxidizer solvent and the co-solvent are miscible with each other and form a homogeneous mixture when combined. The co-solvent can have a boiling point in the range of about 60 °C to about 350 °C, about 100 °C to about 350 °C, about 200 °C to about 350 °C, about 300 °C to about 350 °C, about 60 °C to about 300 °C, about 60 °C to about 200 °C, or about 60 °C to about 100 °C. Advantageously, the co-solvent can determine the rheology of the present composition in combination with a plurality of silver particles and the deoxidizer solvent. The co-solvent can further improve the sintering characteristics of the present composition. The co-solvent can further improve the shelf life, pot life, and working time of the present composition. The co-solvent can have one or more of the following functions: (i) The low-boiling co-solvent can improve the rheology of the present composition as a diluent or carrier solvent, resulting in the desired concentration of a plurality of silver particles. (ii) The high-boiling cosolvent can improve the metal filling rate in the composite material made from this composition by diluting the deoxidizer solvent to an optimal concentration for a smooth deoxidation reaction. (iii) The high-boiling cosolvent can improve the joints formed between multiple silver particles. The cosolvent can also improve the joints formed between the composite material made from this composition and other surfaces. In this function, the cosolvent acts as a sintering aid, wetting agent, or co-deoxidizer solvent at the deoxidation temperature set by the deoxidizer solvent, thereby improving the conductivity and cohesive / adhesive strength of the composite material made from this composition.

[0024] When the cosolvent acts as a carrier solvent intended to be evaporated and removed during the pre-drying treatment of the deoxidizer solvent, the boiling point of the cosolvent may be at least about 40 °C or 80 °C lower than the boiling point of the deoxidizer solvent. Advantageously, the lower boiling point of the cosolvent may improve the density of the composition during the pre-drying treatment before sintering of the composition. The improvement in density results in better performance for thermal interface and die attach applications, as well as the formation of laminates from this composition onto the surface of a plastic carrier film. The deoxidizer solvent, cosolvent, or a mixture thereof can contain hydroxyl groups at a concentration in the range of about 2M to about 20M, about 2M to about 14M, about 4M to about 14M, or about 6M to 14M. Both the deoxidizer solvent and the cosolvent can contribute to the total hydroxyl group concentration as long as the final concentration of the hydroxyl groups falls within the above range. At the above concentrations, the composition can advantageously be sintered smoothly. This concentration can reduce the formation of gas bubbles and thus reduce the expansion of the composite material made from this composition. Further or alternatively, when the co-solvent acts as a co-deoxidizing agent solvent, the co-solvent may contain polar groups such as alkenyl groups, aromatic groups, carbonyl groups, ether groups, etc. Advantageously, the polar groups can, in particular, contribute to transporting Ag(I) ions and / or silver atoms from the local site where silver is dissolved to the local site where it is deposited at the above-mentioned joints (e.g., the neck region or the bridge region). Further, the co-solvent can induce the formation of a silver mirror from the Ag2O powder to the glass surface without substantially reducing the Ag2O powder at a moderate temperature (e.g., about 130 °C). Thus, the co-solvent can act as a co-deoxidizing agent solvent by facilitating the transport of metal atoms or ions throughout the co-solvent, thereby enhancing the sintering of the present composition. Since the co-solvent can act as a co-deoxidizing agent solvent, the co-solvent can continue to exist at the deoxidation temperature. Thus, in this case, the co-solvent may have a boiling point similar to or higher than that of the above-mentioned deoxidizing agent solvent. For this purpose, again, the co-solvent can act as a wetting solvent for the deoxidizing agent solvent.

[0025] Non-limiting examples of the co-solvent include xylene isomers, mesitylene, tetralin, terpinene, limonene, linalool, α-terpineol, geraniol, citronellol, diglyme, 1,2-dibutoxyethane, diethylene glycol butyl methyl ether, triethylene glycol dimethyl ether, diethylene glycol butyl ether, tripropylene glycol methyl ether, triethylene glycol ethyl ether, triethylene glycol butyl methyl ether, triethylene glycol butyl ether, propylene glycol methyl ether, sulfolane, 2-(2-butoxyethoxy)ethanol, phenoxyethanol, 2-(benzyloxy)ethanol, di(propylene glycol) methyl ether, 2-butoxyethyl acetate, ethylene glycol diacetate, propylene glycol methyl ether acetate, di(propylene glycol) methyl ether acetate, 2-(2-ethoxyethoxy)ethyl acetate, ethylene glycol monobutyl ether acetate, 2-ethoxyethyl acetate, ethylene glycol monoethyl ether acetate, 2-butoxyethyl acetate, ethanolamine, diethanolamine, texanol(trademark) ester alcohol, diethyl adipate, dimethyl succinate, methyl benzoate, N-methylpyrrolidone, γ-butyrolactone, diethyl carbonate, propylene carbonate, safrole, anethole, cyclohexanone, cyclohexanol, carvone, ethyl sorbate, pseudoionone, farnesene, 2,6-dimethyl-2,4,6-octatriene, o-cresol, methyl salicylate, and combinations thereof.

[0026] The co-solvent and the deoxidizer solvent may be selected such that a composition having a viscosity in the range of about 500 cP to about 500,000 cP, about 5,000 cP to about 50,000 cP, about 50,000 cP to 500,000 cP, or about 500 cP to about 5,000 cP is obtained so as to have a desirable rheology. The viscosity can be measured at about 5 revolutions per minute. The co-solvent and the deoxidizer solvent may be selected such that a composition having a thixotropic index in the range of about 3 to about 8, about 5 to about 8, or about 3 to about 5 is obtained so as to have a desirable rheology. The thixotropic index can be measured at a speed of about 0.5 to about 5 revolutions per minute.

[0027] The composition may further comprise a modifier polymer. Polymers are commonly used as binders to fill the voids between metal particles and to improve the adhesion between metal particles and the substrate. A typical polymer is a macromolecule having a molecular weight greater than about 1 kDa and more than 10 repeating units that are joined together. Polymers are typically included in the composition at a volume ratio in the range of about 20:100 to about 50:100 with respect to the metal particles. However, typical polymers severely hinder the sintering of metal particles and limit the electrical and thermal conductivities of the sintered metal particles. Unexpectedly, a particular class of polymers may be advantageously used as modifier polymers that form a molecularly thin coating on the surface of multiple silver particles. The coating can have a thickness in the range of about 3.5 nm to about 9 nm, about 5.5 nm to about 9 nm, about 7 nm to about 9 nm, about 3.5 nm to about 7 nm, or about 3.5 nm to about 5.5 nm. The modifier polymer can have one or more of the following functions: (i) The modifier polymer can improve the rheology and dispersibility of the composition by preventing the aggregation of multiple silver particles. (ii) The modifier polymer can improve the adhesion between multiple silver particles and a non-metallized surface (e.g., the surface of a semiconductor, oxide, or plastic substrate). (iii) The modifier polymer can improve the sintering of the composition as a sintering aid by reducing the sintering temperature required to sinter the composition and improving the conductivity of the composite material made from the composition.

[0028] The modifier polymer can include a hydrogen-bonding group, a polar group, an acidic group, a basic group, other polar groups, or a combination thereof. The modifier polymer can include ethylene glycol ether (-CH2CH2O-), acetal (-OCRR’O-), amine (-R”NH2, -R”N(H)R’’’-, -R”N(R)R’’’-), pendant amide (-C(=O)NH-, -C(=O)N(R)-), urea (-NH(C=O)NH-), hydroxyl (-OH), carboxylic acid (-COOH), carboxylate (-COO - M + ), sulfonic acid (-SO3H), sulfonate (-SO3 - M + ), phosphonic acid (-PO3H2), phosphonate (-PO3H - M + ), alkene (-C(R)=C(R’)-), aromatic group, or a combination thereof, where R, R’, R” and R’’’ are independently H or an organic moiety. R and R’ can be methyl or ethyl. R” and E’’’ can be C1-C6 alkylene or C6-C10 arylene (e.g., phenylene or naphthylene).

[0029] The hydrogen-bonding group, polar group, acidic group, basic group, and other polar groups can independently be present on the main chain, block chain, side chain, or graft chain of the modifier polymer. The modifier polymer can bind to the surface of Ag / Ag2O or the non-metallized surface described above. The modifier polymer contains ethylene glycol ether (-CH2CH2O-), acetal (-OCR’R”O-), amine (-R”NH2, -R”N(H)R’’’-, -R”N(R’)R’’’-), pendant amide (-C(=O)NH-, -C(=O)N(R)-), urea (-NH(C=O)NH-), hydroxyl (-OH), alkene (-C(R)=C(R’)-), aromatic group, or a combination thereof, where R, R’, and R” are independently H or an organic moiety. The modifier polymer facilitates the transport of metal atoms or ions on the surface of a plurality of metal particles, thereby accelerating the formation of junctions (e.g., bridge contacts and neck regions) between adjacent silver particles and the coarsening of the neck regions. The modifier polymer can be thermally stable when a device made from the composition is used. The modifier polymer can be thermally stable up to at least about 300 °C as determined by thermogravimetric analysis.

[0030] Non-limiting examples of modifier polymers include poly(ethylene oxide), polyethyleneimine (both ethoxylated and non-ethoxylated), polyaniline, polypyrrole, poly(3,4-ethylenedioxythiophene), poly(lysine), poly(arginine), poly(histidine), poly(acrylic acid), poly(methacrylic acid), poly(aspartic acid), poly(glutamic acid), polyacrylamide, poly(vinylpyrrolidone), poly(acrylamide-2-methyl-1-propanesulfonic acid), poly(vinylsulfonic acid), poly(styrenesulfonic acid), poly(vinylphosphonic acid), poly(dopamine), dextran, carboxymethylcellulose, alginate, poly(serine), poly(2-hydroxyethyl methacrylate), poly(vinyl alcohol) (40 - 97% hydrolyzed), poly(vinyl butyral) and poly(hydroxystyrene), and, where applicable, their salts; doped conductive polymers (including poly(ethylenedioxythiophene):poly(styrenesulfonic acid), poly(thiophene-3-[2-(2-methoxyethoxy)ethoxy]-2,5-diyl) and poly(triarylaminium-alt-fluorene) and their derivatives).

[0031] Since the modifier polymer is not used as a typical polymer such as a binder, the modifier polymer can be present in a smaller amount in the composition compared to typical polymers. For example, the modifier polymer can be in a specific amount (P) per unit mass of a plurality of silver particles, derived from the specific surface area (S) of the plurality of silver particles, the apparent thickness (d) of the modifier polymer, and the density (ρ) of the modifier polymer, according to the following formula: P = S × d × ρ The modifier polymer can be present in a specific amount (P) per unit mass of a plurality of silver particles, derived from the specific surface area (S) of the plurality of silver particles, the apparent thickness (d) of the modifier polymer, and the density (ρ) of the modifier polymer. The modifier polymer can have a density (ρ) of about 1.1×10 6 g / m 3 The modifier polymer can have a density (ρ) of about 1.1×10 -9 m to about 9×10 -9 m, about 6×10 -9 m to about 9×10 -9m or about 3.5×10 -9 m to about 6×10 -9 m can have an apparent thickness (d) in the range.

[0032] Thus, when a plurality of silver particles are silver flakes having a specific surface area (S) of about 1.6 m 2 / g, the modifier polymer and the plurality of silver particles can have a mass ratio in the range of about 0.6:100 to about 1.6:100, about 1.1:100 to about 1.6:100 or about 0.6:100 to about 1.1:100. The above mass ratio can correspond to a volume ratio between the modifier polymer and the plurality of silver particles in the range of about 6:100 to about 15:100, about 10:100 to about 15:100 or about 6:100 to about 10:100. Advantageously, the above mass ratio and volume ratio are significantly lower than the mass ratio and volume ratio of the above typical polymers. When a plurality of silver particles are present in a mass percentage in the range of about 65% by mass to about 94% by mass based on the total mass of the composition, and have a specific surface area in the range of about 1.0 m 2 / g to about 2.2 m 2 / g, the modifier polymer can be present in a mass percentage in the range of about 0.3% by mass to about 1.9% by mass based on the total mass of the composition (or about 0.4% by mass to about 2% by mass based on the total mass of the plurality of silver particles). When the plurality of silver particles are silver-coated particles (for example, silver-coated copper particles), the modifier polymer can be present in a similar mass percentage since the silver-coated particles can have a density similar to the density of silver.

[0033] The composition may further contain a reducing metal. The reducing metal can include aluminum, magnesium, chromium, manganese or a combination thereof. The reducing metal may be present in a mass percentage of up to about 2.0% by mass or about 1.0% by mass based on the total mass of the composition. The reducing metal can have an average diameter similar to the average diameter of the plurality of silver particles. Advantageously, the reducing metal reacts with the deoxidizer solvent and / or water at the sintering temperature to reduce the native oxides on the surfaces of the silver particles and silver additives, and other metal oxides on the die or substrate surface, thereby generating initial hydrogen at a low and safe concentration. The hydrogen may be released and can reduce residual silver oxide and other metal oxides on the surface of the substrate or die. Exemplary and non-limiting embodiments of a method of forming a composition are disclosed hereinafter. The method includes dispersing a plurality of silver particles in a deoxidizer solvent, or in a mixture of a deoxidizer solvent and a co-solvent, in the presence of the co-solvent.

[0034] The plurality of silver particles, the deoxidizer solvent, and the co-solvent can be as described herein. The method can further include treating the plurality of silver particles with a modifier polymer. When the modifier polymer is substantially soluble in the deoxidizer solvent and / or the co-solvent, the treating step may be performed after the dispersing step. The treating step can include dissolving the modifier polymer in the composition and mixing the composition. Thus, the method can be as follows: a) dispersing a plurality of silver particles in a deoxidizer solvent in the presence of a co-solvent to form a dispersion, b) dissolving a modifier polymer in the dispersion, and c) mixing the dispersion to form a composition and can include.

[0035] The mixing step (c) may be performed by shear mixing or ultrasonic irradiation. In the mixing step, the modifier polymer may spontaneously replace the protective molecular monolayer or other processing aids on the surfaces of the plurality of silver particles. This exchange may occur further when the composition formed by the method is sintered. Alternatively, if the modifier polymer is not substantially soluble in the deoxidizer solvent and / or cosolvent, the treatment step may be carried out before the dispersion step. The treatment step may include dissolving and mixing the modifier polymer and the plurality of silver particles in an exchange solvent, and subsequently separating the plurality of silver particles. Thus, the method may include the following: a) dissolving a plurality of silver particles and a modifier polymer in an exchange solvent to form a dispersion b) mixing the dispersion c) separating the plurality of silver particles from the dispersion, and d) dispersing the plurality of silver particles in a deoxidizer solvent in the presence of a cosolvent to form a composition can be included.

[0036] In the dissolution step (a), the exchange solvent may have good solubility for the protective molecular monolayer or other processing aids on the surface of the plurality of silver particles. The exchange solvent may have a relatively low solubility for the modifier polymer. To determine whether the dissolution step is successfully carried out, the dispersion in step (a) can be characterized by surface analysis techniques such as X-ray photoelectron spectroscopy. The mixing step (b) may be carried out by shear mixing or ultrasonic irradiation. The mixing step (b) may be carried out at a temperature in the range of about 20°C to about 100°C, about 60°C to about 100°C, or about 20°C to about 60°C. In the mixing step (b), the modifier polymer may spontaneously replace the protective molecular monolayer or other processing aids on the surface of the plurality of silver particles. The separation step (c) may be carried out by filtration or centrifugation. The separation step (c) may further include rinsing the plurality of silver particles with a rinsing solvent to remove excess modifier polymer that does not bind to the plurality of silver particles during the mixing step. The rinsing solvent can have a low boiling point so that this solvent can be easily removed. The rinsing solvent may be ethanol, isopropanol, or a combination thereof. The separation step (c) may further include a step of drying the plurality of silver particles. The exchange solvent and the rinsing solvent (if present) can be removed from the plurality of silver particles by drying. Thereafter, the plurality of silver particles can be used in the dispersion step (d) to form a composition.

[0037] When the plurality of silver particles have a specific surface area in the range of about 1.0 m 2 / g to about 2.2 m 2 / g, after the treatment step, the plurality of silver particles can include silver particles with a mass percentage in the range of about 98% by mass to about 99.6% by mass and a modifier polymer with a mass percentage in the range of about 0.4% by mass to about 2% by mass, based on the total mass of the plurality of silver particles. The composition described herein may be formed by the method described herein. Exemplary and non-limiting embodiments of a method for forming a composite material are disclosed hereinafter. The method includes a step of sintering the composition described herein on a substrate.

[0038] Advantageously, the present composition does not require air or oxygen to "burn out" excess organics during the sintering process. Thus, the present composition is compatible with the interconnects of Cu and Al that may be present in the die. This is because any organic polymer used is present only in small amounts on the surface of the silver particles. Even more advantageously, the sintering of the present composition does not require a cumbersome reducing atmosphere. This is because the deoxidizing agent solvent and the co-solvent supply the chemical agents necessary for the reduction of silver oxide. Even more advantageously, the sintering of the present composition does not require high pressure. Thus, the method does not require an expensive pressure conversion device. This improves the reliability of the die or substrate attached to the composite material. This advantage is derived from the more efficient sintering achieved by the present method.

[0039] The sintering process may be carried out at a temperature of about 200 °C or lower. The sintering process may be carried out at a temperature in the range of about 140 °C to about 180 °C or about 150 °C to about 180 °C. The temperature may be set and / or monitored by a digital hot plate or an oven. Advantageously, the composition can have native silver oxide with an increased degree of decomposition or reduction, in which case the sintering temperature is less than 200 °C. The sintering process may be carried out in an inert atmosphere. The sintering process may be carried out in nitrogen. Advantageously, the sintering process can convert the composition into a high-density and substantially fused agglomerated metal powder that does not contain microscopic voids or a polymer phase. The method may further include a step of pre-drying the composition before the sintering process. The method may further include a step of bringing the composition into contact with a second substrate or component before the sintering process.

[0040] The contacting step may be carried out by depositing the composition on the surface of the second substrate or component. The deposition of the composition can be carried out using various printing techniques and coating techniques such as needle dispersion, blade coating, stencil printing, screen printing, gravure printing, or flexographic printing. When the composition is deposited simultaneously on the substrate and the surface of the second substrate or component, the method may be as follows: a) depositing the composition described herein on the substrate and the surface of the second substrate or component, and b) sintering the composition can be included. Alternatively, the composition may be deposited sequentially on one or more substrate surfaces. Accordingly, the method may be as follows: a) depositing the composition described herein on the substrate surface b) pre-drying the composition to form a laminate c) bringing the laminate into contact with a second substrate or component, and d) sintering the laminate can be included.

[0041] The substrate may be a plastic thin film. The pre-drying step (b) may be performed at a temperature lower than the temperature of the sintering step (d). The pre-drying step (if present) may be performed before the contacting step (if present). The second substrate or component may be a device, a wafer, or a die. Advantageously, the pre-drying step (b) can shorten the processing time of the second substrate or component, achieve good control of the lamination thickness, and enable greater processing flexibility. In the contacting step (c), the second substrate or component can be selected from the group consisting of electronic components and thermal components. Therefore, after the sintering step, the present composite material can bond the substrate and the second substrate or component. The present composite material can be regarded as a device together with the substrate and the second substrate or component. Therefore, the present method can be regarded as a method for fabricating a device for connecting vertical electronic components or thermal components. In this device, the present composite material may be sandwiched between a first electronic component and a second electronic component or thermal component.

[0042] Alternatively or additionally, the present method can be regarded as a method for fabricating a device for connecting lateral electronic components or thermal components, or for connecting different regions of electronic components or thermal components. In this device, the present composite material may be formed in a lateral pattern that joins electronic components or thermal components, or different regions, or electronic components or thermal components. Advantageously, the present composite material can be used as an electrically conductive material and a thermally conductive material, such as a thermal interface, a die attach, an electrical interconnect, or an electrode material. When used as a thermal interface material, the composite material can provide thermal contact between the semiconductor chip and the heat sink. When this composite material is used as a die attach material, it can bond a chip to a substrate or package, thereby also providing electrical contact and / or thermal contact.

[0043] When the composite material is used as a thermal interface material or a die attach material, it can be fabricated to have a thickness in the range of about 10 μm to about 500 μm, about 50 μm to about 500 μm, about 200 μm to about 500 μm, about 10 μm to about 200 μm, about 10 μm to about 50 μm, or about 50 μm to about 200 μm. When this composite material is used as an electrical interconnect material or an electrode material, it can be utilized for contacts, bus bars, antennas, and wirings such as those in solar cells, switches, capacitors, sensors, and other components of printed electronics. This composite material can be fabricated to a thickness in the range of about 100 nm to about 10 μm, about 1.0 μm to about 10 μm, or about 100 nm to about 1 μm. When this composite material is deposited on the surface of a device or substrate, the composite material can be fabricated to have a width in the range of about 10 μm to about 1.0 mm, about 100 μm to about 1.0 mm, or about 10 μm to about 100 μm. The composite material can have a length in the range of about 10 μm to about 10 m, about 100 cm to about 10 m, about 1.0 m to about 10 m, about 10 cm to about 1.0 m, or about 10 cm to about 100 cm.

[0044] When this composite material is deposited on a heat generating device or an associated substrate, it can be fabricated to have a length in the range of about 10 mm to about 1.0 cm, about 100 mm to about 1.0 cm, or about 10 mm to about 100 mm. The composite material can be fabricated to have a width in the range of about 10 mm to about 1.0 cm, about 100 mm to about 1.0 cm, or about 10 mm to about 100 mm. This composite material may be used in the absence of a substrate. Thus, the method may further include a step of removing the substrate. Exemplary and non-limiting embodiments of the composite material are disclosed hereinafter. This composite material can be prepared by the method described in this specification. Therefore, this composite material can include high-density and substantially fused agglomerated metal powders that do not contain microscopic voids or polymer phases. This composite material may be used to transport electric current and / or heat flow to connected electronic components. Advantageously, this composite material can have an electrical conductivity of at least about 1.0×10 5 S / cm and a thermal conductivity of at least about 75 W / mK.

[0045] Exemplary and non-limiting embodiments of the device are disclosed hereinafter. This device can be prepared by the method described in this specification. Therefore, the device may include a composite material formed by the method described in this specification. This device may be an electronic device. The accompanying drawings illustrate the disclosed embodiments and serve to explain the principles of the disclosed embodiments. However, it should be understood that the drawings are designed for illustrative purposes only and not as a definition of the limitations of the present invention.

Brief Description of the Drawings

[0046]

Figure 1A

Figure 1B

Figure 1C

Figure 1D

Figure 1E

Figure 1F

Examples

[0047] Non-limiting examples of the present invention are further described in more detail by reference to specific examples, which should not be construed as in any way limiting the scope of the present invention. The actual performance depends on the properties of the particles, the details of the formulation, the processing, and the application method. In some cases, tapping operations and centrifugation are used to improve the metal filling rate. (Example 1) Preparation of a paste containing silver flakes and a modifier polymer The following examples show pastes containing silver flakes and a modifier polymer, which were formulated by first dissolving the modifier polymer in a solvent system and then mixing it with the metal powder. The silver flakes and spheres used herein are available from commercial suppliers such as Heraeus, Hitachi, Henkel, Inframat Advanced Materials, ACS Material, Fukuda Metal Foil & Powder, Hongwu Material Tech, Tanaka Precious Metals, Johnson Matthey, DuPont, Technic, Doduco, Yamamoto Precious Metal, Mitsui Kinzoku, Ningbo Jingxin, Changgui Metal Powder, and American Elements.

[0048] Example 1a To a mixture of diglyme (purchased from Sigma-Aldrich (Singapore)), glycerol (purchased from Sigma-Aldrich (Singapore)), and ethylene glycol (purchased from Sigma-Aldrich (Singapore)) (6.0:0.5:1.5 v / v), 0.22 mL of poly(hydroxystyrene) (purchased from Sigma-Aldrich (Singapore)) dissolved at a polymer concentration of 54 mg / mL was added. Using a vortex mixer and a bath-type ultrasonic device, 1.0 g of silver flakes (manufacturer's specifications: flake size = 3 - 5 μm; tap density = 2.8 - 3.8 g / cm 3 ; and specific surface area = 0.6 - 1.3 m 2 / g) were mixed, and a paste containing 81.7 wt% silver, 1.0 wt% polymer, and the remainder as solvent was obtained. This formulation corresponded to 29 vol% silver with respect to the total volume of the formulation. This formulation was applied by the doctor blade method to a wet thickness of 250 μm and an area of 8 × 8 mm 2 on a native SiO2 / Si substrate. The paste was pre-dried in air at 60 °C for 20 minutes, attached to glass coated with a fluoropolymer (purchased from Sigma-Aldrich (Singapore)), and then heated in nitrogen at a heating rate of 7.5 °C per minute to 160 °C and held isothermally for 30 minutes.

[0049] Figure 1A is an SEM of the cross-section of the bulk portion of a 130-μm-thick metal composite of silver flakes (having an average size of about 3 - 5 μm) containing 1.0 wt% poly(hydroxystyrene), as described in Example 1a. This metal composite was formulated with diglyme, glycerol, and ethylene glycol in a volume ratio of 6.0:0.5:1.5 and sintered at atmospheric pressure in nitrogen at 160 °C for 30 minutes. Figure 1B is an SEM of the cross-section at the interface between the metal composite shown in Figure 1A and native SiO2 / Si.

[0050] Example 1b A mixture of α-terpineol (purchased from Sigma-Aldrich (Singapore)) and triethylene glycol (purchased from Sigma-Aldrich (Singapore)) (7:1 v / v) was added to 0.22 mL of 40% hydrolyzed poly(vinyl alcohol) (purchased from Mitsubishi Chemical Corporation (Japan)) dissolved at a polymer concentration of 41 mg / mL. Using a vortex mixer and a bath-type ultrasonic device, 1.0 g of silver flakes (manufacturer's specifications: flake size = 5 - 8 μm; tap density = 2.2 - 2.8 g / cm 3 ; specific surface area, 0.6 - 1.2 m 2 / g) was mixed to obtain a paste containing 81.9 wt% silver, 0.7 wt% polymer, and the remainder as solvent. This formulation corresponded to 29 vol% silver based on the total volume of the formulation. This formulation was applied by the doctor blade method to a wet thickness of 250 μm and an area of 8 × 8 mm 2 on a native SiO2 / Si substrate. The paste was partially surrounded by a cover glass and then heated to 200 °C at a single heating rate of 3 °C per minute in nitrogen and held isothermally for 30 minutes.

[0051] Example 1c A mixture of diglyme, glycerol, and ethylene glycol (6.0:0.5:1.5 v / v) was added to 0.22 mL of 40% hydrolyzed poly(vinyl alcohol) dissolved at a polymer concentration of 41 mg / mL. Using a vortex mixer and a bath-type ultrasonic device, 1.0 g of silver flakes (manufacturer's specifications: flake size = 5 - 8 μm; tap density = 2.2 - 2.8 g / cm 3 ; specific surface area = 0.6 - 1.2 m 2 / g) was mixed to obtain a paste containing 81.9 wt% silver, 0.7 wt% polymer, and the remainder as solvent. This formulation corresponded to 29 vol% silver based on the total volume of the formulation. This formulation was applied by the doctor blade method to a wet thickness of 250 μm and an area of 8 × 8 mm 2It was applied to the area of

[0052] Figure 1C is a SEM of the bulk portion of a 120-μm thick metal composite of silver flakes (average size of about 5 - 8 μm) containing 0.7 mass% of 40% hydrolyzed poly(vinyl alcohol), compounded with diglyme, glycerol and ethylene glycol (6.0:0.5:1.5 v / v) and sintered at 160 °C for 30 minutes under normal pressure in nitrogen, as described in Example 1c. Figure 1D is a SEM of the cross-section at the interface between the metal composite shown in Figure 1C and native SiO2 / Si.

[0053] Example 1d To a mixture of propylene glycol methyl ether acetate (purchased from Sigma-Aldrich (Singapore)), diethylene glycol (purchased from Sigma-Aldrich (Singapore)) and tetralin (purchased from Sigma-Aldrich (Singapore)) (5:2:1 v / v), 0.22 mL of 40% hydrolyzed poly(vinyl alcohol) dissolved at a polymer concentration of 41 mg / mL was added and mixed with 1.0 g of silver flakes (manufacturer's specifications: flake size = 8 - 12 μm; tap density = 3.5 - 4.2 g / cm 3 ; specific surface area, 0.6 - 1.0 m 2 / g) using a vortex mixer and a bath-type ultrasonic device to obtain a paste containing 81.9 mass% silver, 0.7 mass% polymer, and the remainder as solvent. This formulation corresponded to 29 volume% silver with respect to the total volume of the formulation. This formulation was applied by the doctor blade method to a wet thickness of 250 μm and an area of 8 × 8 mm 2 on a native SiO2 / Si substrate. This paste was pre-dried in air at 60 °C for 20 minutes, a fluoropolymer-coated glass was attached, and then heated to 160 °C at a heating rate of 7.5 °C per minute in nitrogen and held isothermally for 30 minutes.

[0054] Figure 1E is a SEM of the bulk portion of a 110-μm-thick metal composite of silver flakes (average size 8 - 12 μm) containing 0.7 wt% of 40% hydrolyzed poly(vinyl alcohol), compounded with propylene glycol methyl ether acetate, diethylene glycol, and tetralin (5:2:1 v / v) as described in Example 1d and sintered at 160 °C for 30 minutes at atmospheric pressure in nitrogen. Figure 1F is a SEM of the cross-section at the interface between the metal composite shown in Figure 1E and native SiO2 / Si. Figures 1A - 1F show that the tested metal composites contain high-density and substantially fused aggregates of silver powder, without microscopic voids or polymer phases, regardless of the size of the silver flakes, and have no visible polymer "binder". Micrographs at the SiO2 / Si interface reveal that the silver flakes are equiangular and most densely packed with respect to that interface. In some cases, sub-μm-thick silver thin films appeared to be deposited on SiO2. This explains the unexpectedly favorable adhesion to the substrate.

[0055] Example 1e To a mixture of diglyme, glycerol, and ethylene glycol (6.0:0.5:1.5 v / v), 0.22 mL of poly(hydroxystyrene) dissolved at a polymer concentration of 54 mg / mL was mixed with 1.0 g of silver flakes (manufacturer's specifications: flake size = 8 - 12 μm; tap density = 3.5 - 4.2 g / cm 3 ; specific surface area = 0.6 - 1.0 m 2 / g) using a vortex mixer and a bath-type ultrasonic device, resulting in a paste containing 81.7 wt% silver, 1.0 wt% polymer, and the remainder as solvent. This formulation corresponded to 29 vol% silver with respect to the total volume of the formulation. This formulation was applied by the doctor blade method to a wet thickness of 250 μm and 8 × 8 mm on a native SiO2 / Si substrate. 2It was applied to the area. This paste was pre-dried in air at 60 °C for 20 minutes, a fluoropolymer-coated glass was attached, and then it was heated to 160 °C at a heating rate of 7.5 °C per minute in nitrogen and held isothermally for 15 minutes.

[0056] Example 1f To a mixture of α-terpineol and triethylene glycol (7:1 v / v), 0.22 mL of poly(ethyleneimine) (purchased from Sigma-Aldrich (Singapore)) dissolved at a polymer concentration of 27 mg / mL was added in a vortex mixer and a bath-type ultrasonic device to 1.0 g of silver flakes (manufacturer's specifications: flake size = 8 - 10 μm; tap density = 2.8 - 3.8 g / cm 3 ; specific surface area = 0.7 - 1.3 m 2 / g), and a paste containing 82.1 mass% silver, 0.5 mass% polymer, and the balance as solvent was obtained. This formulation corresponded to 29 volume% silver with respect to the total volume of the formulation. This formulation was applied by the doctor blade method to a wet thickness of 250 μm and an area of 8×8 mm 2 on a native SiO2 / Si substrate. This paste was partially surrounded by a cover glass and then heated to 200 °C at a single heating rate of 3 °C per minute in nitrogen and held isothermally for 30 minutes.

[0057] Example 1g To a mixture of α-terpineol and triethylene glycol (7:1 v / v), 0.22 mL of 40% hydrolyzed poly(vinyl alcohol) dissolved at a polymer concentration of 41 mg / mL was added in a vortex mixer and a bath-type ultrasonic device to 1.0 g of silver flakes (manufacturer's specifications: flake size = 8 - 10 μm; tap density = 2.8 - 3.8 g / cm 3 ; specific surface area = 0.7 - 1.3 m 2When mixed with / g), a paste containing 81.9% by mass of silver, 0.7% by mass of polymer, and the balance being solvent was obtained. This formulation corresponded to 29% by volume of silver based on the total volume of the formulation. This formulation was applied by the doctor blade method to a wet thickness of 250 μm and an area of 8 × 8 mm on a native SiO2 / Si substrate 2 and covered with a cover glass. Next, it was heated to 200 °C at a single heating rate of 3 °C per minute in nitrogen and held isothermally for 30 minutes.

[0058] Example 1h To a mixture of diglyme, glycerol and ethylene glycol (6.0:0.5:1.5 v / v), 0.22 mL of 40% hydrolyzed poly(vinyl alcohol) dissolved at a polymer concentration of 41 mg / mL was added in a vortex mixer and a bath-type ultrasonic device to 1.0 g of silver flakes (manufacturer's specifications: flake size = 8 - 10 μm; tap density = 2.8 - 3.8 g / cm 3 ; specific surface area = 0.7 - 1.3 m 2 / g). When mixed, a paste containing 81.9% by mass of silver, 0.7% by mass of polymer, and the balance being solvent was obtained. This formulation corresponded to 29% by volume of silver based on the total volume of the formulation. This formulation was applied by the doctor blade method to a wet thickness of 250 μm and an area of 8 × 8 mm on a native SiO2 / Si substrate 2 and covered with a cover glass. Next, it was heated to 200 °C at a single heating rate of 3 °C per minute in nitrogen and held isothermally for 30 minutes.

[0059] Example 1i To a mixture of diglyme, glycerol and ethylene glycol (6.0:0.5:1.5 v / v), 0.22 mL of poly(vinyl butyral) (purchased from Sigma-Aldrich (Singapore)) dissolved at a polymer concentration of 41 mg / mL was added in a vortex mixer and a bath-type ultrasonic device to 1.0 g of silver flakes (manufacturer's specifications: flake size = 5 - 8 μm; tap density = 2.2 - 2.8 g / cm 3; Specific surface area = 0.6 to 1.2 m 2 When mixed with / g), a paste containing 81.9% by mass of silver, 0.7% by mass of polymer, and the balance as solvent was obtained. This formulation corresponded to 29% by volume of silver with respect to the total volume of the formulation. This formulation was applied by the doctor blade method to a wet thickness of 250 μm and an area of 8 × 8 mm on a native SiO2 / Si substrate 2 . This paste was pre-dried in air at 60 °C for 20 minutes, a fluoropolymer-coated glass was attached, and then heated in nitrogen at a heating rate of 7.5 °C per minute to 160 °C and held isothermally for 30 minutes

[0060] (Example 2) Preparation of a paste containing silver spheroids and a modifier polymer The following examples show pastes containing silver spheroids and a modifier polymer, which were formulated by first dissolving the modifier polymer in a solvent system and then mixing it with the metal powder Example 2a To a mixture of α-terpineol and glycerol (7.5:0.5 v / v), 0.21 mL of poly(ethyleneimine) dissolved at a polymer concentration of 68 mg / mL was added in a vortex mixer and a bath-type ultrasonic device to 1.2 g of silver spheroids (manufacturer's specification: diameter = 6 μm; tap density = 4.0 g / cm 3 ) When mixed, a paste containing 84.7% by mass of silver, 1.0% by mass of polymer, and the balance as solvent was obtained. This formulation corresponded to 34% by volume of silver with respect to the total volume of the formulation. This formulation was applied by the doctor blade method to a wet thickness of 250 μm and an area of 8 × 8 mm on a native SiO2 / Si substrate 2 . This paste was partially surrounded by a cover glass and then heated in nitrogen at a single heating rate of 3 °C per minute to 200 °C and held isothermally for 30 minutes

[0061] Example 2b To a mixture of α-terpineol and glycerol (7:1 v / v), 0.11 mL of poly(ethyleneimine) dissolved at a polymer concentration of 126 mg / mL was added, and 1.2 g of silver spheroids (manufacturer's specifications: diameter = 6 μm; tap density = 4.0 g / cm 3 ) were mixed in a vortex mixer and a bath-type ultrasonic device to obtain a paste containing 90.7% by mass of silver, 1.1% by mass of polymer, and the solvent as the remainder. This formulation corresponded to 47% by volume of silver with respect to the total volume of the formulation. This formulation was applied by the doctor blade method to a wet thickness of 250 μm and an area of 8 × 8 mm 2 on a native SiO2 / Si substrate. The paste was partially surrounded by a cover glass and then heated to 200 °C at a single heating rate of 3 °C per minute in nitrogen and held isothermally for 30 minutes.

[0062] (Example 3) Preparation of a Paste Using Modified Polymer-Coated Silver Flakes The following examples show the preparation of silver flakes coated with a modifier polymer and a paste formulated by mixing the modified polymer-coated silver flakes in a solvent system. Example 3a To ethylene glycol, 1.2 mL of poly(vinylpyrrolidone) (purchased from Sigma-Aldrich (Singapore)) dissolved at a polymer concentration of 60 mg / mL was added, and 3.0 g of silver flakes (manufacturer's specifications: flake size = 5 - 8 μm; tap density = 2.2 - 2.8 g / cm 3 ; specific surface area = 0.6 - 1.2 m 2It was mixed with ( / g) and allowed to stand overnight. 12 mL of ethylene glycol was added, and the silver flakes were separated by centrifugation. The flakes were rinsed with 12 mL of Millipore® water, separated by centrifugation, further rinsed with 12 mL of isopropanol (purchased from Sigma-Aldrich (Singapore)), separated by centrifugation, and finally dried under vacuum. When 0.22 mL of a mixture of diglyme, glycerol, and ethylene glycol (6.0:0.5:1.5 v / v) was mixed with 1.0 g of polymer-coated silver flakes in a vortex mixer and a bath-type ultrasonic device, a paste containing 82.6% by mass of silver and the remainder as solvent was obtained. This formulation corresponded to 30% by volume of silver based on the total volume of the formulation. This formulation was applied by the doctor blade method to a wet thickness of 250 μm and an area of 8 × 8 mm on a native SiO2 / Si substrate. 2 This paste was pre-dried in air at 60 °C for 20 minutes, a fluoropolymer-coated glass was attached, and then heated to 160 °C at a heating rate of 7.5 °C per minute in nitrogen and held isothermally for 30 minutes.

[0063] Example 3b To ethylene glycol, 1.2 mL of poly(2-hydroxyethyl methacrylate) (purchased from Sigma-Aldrich (Singapore)) dissolved at a polymer concentration of 60 mg / mL was added in a vortex mixer and a bath-type ultrasonic device to 3.0 g of silver flakes (manufacturer's specifications: flake size = 5 - 8 μm; tap density = 2.2 - 2.8 g / cm 3 ; specific surface area = 0.6 - 1.2 m 2It was mixed with ( / g) and allowed to stand overnight. 12 mL of ethylene glycol was added, and the silver flakes were separated by centrifugation. The flakes were rinsed with 12 mL of Millipore® water, separated by centrifugation, further rinsed with 12 mL of isopropanol, separated by centrifugation, and finally dried under vacuum. When 0.22 mL of a mixture of diglyme, glycerol, and ethylene glycol (6.0:0.5:1.5 v / v) was mixed with 1.0 g of polymer-coated silver flakes using a vortex mixer and a bath-type ultrasonic device, a paste containing 82.6% by mass of silver and the solvent as the remainder was obtained. This formulation corresponded to 30% by volume of silver with respect to the total volume of the formulation. This formulation was applied by the doctor blade method to a wet thickness of 250 μm and an area of 8 × 8 mm on a native SiO2 / Si substrate. 2 This paste was pre-dried in air at 60 °C for 20 minutes, a fluoropolymer-coated glass was attached, and then heated to 160 °C at a heating rate of 7.5 °C per minute in nitrogen and held isothermally for 30 minutes.

[0064] Example 3c To ethylene glycol, 1.2 mL of 80% hydrolyzed poly(vinyl alcohol) (purchased from Mitsubishi Chemical Corporation (Japan)) dissolved at a polymer concentration of 60 mg / mL was added, and 3.0 g of silver flakes (manufacturer's specifications: flake size = 5 - 8 μm; tap density = 2.2 - 2.8 g / cm 3 ; specific surface area = 0.6 - 1.2 m 2It was mixed with ( / g) and allowed to stand overnight. 12 mL of ethylene glycol was added, and the silver flakes were separated by centrifugation. The flakes were rinsed with 12 mL of Millipore® water, separated by centrifugation, further rinsed with 12 mL of isopropanol, separated by centrifugation, and finally dried under vacuum. When 0.22 mL of a mixture of propylene glycol methyl ether acetate (purchased from Sigma - Aldrich (Singapore)), diethylene glycol and tetralin (5:2:1 v / v) was mixed with 1.0 g of polymer - coated silver flakes in a vortex mixer and a bath - type ultrasonic device, a paste containing 82.6 mass% silver and the solvent as the remainder was obtained. This formulation corresponded to 30 volume% silver with respect to the total volume of the formulation. This formulation was applied by the doctor - blade method to a wet thickness of 250 μm and an area of 8×8 mm 2 on a native SiO2 / Si substrate. The paste was pre - dried in air at 60 °C for 20 minutes, a fluoropolymer - coated glass was attached, and then heated in nitrogen at a heating rate of 7.5 °C per minute to 160 °C and held isothermally for 30 minutes.

[0065] (Example 4) Preparation of a paste using modifier - polymer - coated silver flakes in diglyme The following example is a paste formulated by mixing modifier - polymer - coated silver flakes in diglyme. Example 4a When 0.22 mL of diglyme was mixed with 1.0 g of poly(2 - hydroxyethyl methacrylate) - coated silver flakes (described in Example 3b) in a vortex mixer and a bath - type ultrasonic device, a paste containing 82.6 mass% silver and the solvent as the remainder was obtained. This formulation corresponded to 30 volume% silver with respect to the total volume of the formulation. This formulation was applied by the doctor - blade method to a wet thickness of 250 μm and an area of 8×8 mm 2It was applied to the area. This paste was pre-dried in air at 60 °C for 20 minutes, then poured into 0.02 mL of a mixture of geraniol and diethylene glycol in a volume ratio of 1:1, a fluoropolymer-coated glass was attached, and then heated to 160 °C at a heating rate of 7.5 °C per minute in nitrogen and held isothermally for 30 minutes.

[0066] (Example 5) Preparation of a paste without a modifier polymer The following examples are pastes formulated by mixing silver flakes into a solvent system. These examples are each useful as a thermal interface material or die attach material for metallized surfaces, such as directly bonded copper or contact parts. Example 5a 0.22 mL of a mixture of α-terpineol and triethylene glycol (7:1 v / v) was mixed with 1.0 g of silver flakes (manufacturer's specifications: flake size = 5 - 8 μm; tap density = 2.2 - 2.8 g / cm 3 ; specific surface area = 0.6 - 1.2 m 2 / g) in a vortex mixer and a bath-type ultrasonic device to obtain a paste containing 82.6% by mass of silver and the remainder as solvent. This formulation corresponded to 30% by volume of silver based on the total volume of the formulation. This formulation was applied by the doctor blade method to a wet thickness of 250 μm and an area of 8 × 8 mm 2 on a native SiO2 / Si substrate. This paste was pre-dried in air at 100 °C for 20 minutes, a fluoropolymer-coated glass was attached, and then heated to 200 °C at a heating rate of 7.5 °C per minute in nitrogen and held isothermally for 30 minutes.

[0067] Example 5b 0.33 mL of a mixture of propylene glycol methyl ether acetate, geraniol (purchased from Sigma-Aldrich (Singapore)) and diethylene glycol (2:4:4 v / v) was mixed with 1.0 g of silver flakes (manufacturer's specifications: flake size = 5 - 8 μm; tap density = 2.2 - 2.8 g / cm 3; Specific surface area = 0.6 - 1.2 m 2 When mixed with it, a paste containing 75.4% by mass of silver and the balance as a solvent was obtained. This formulation corresponded to 23% by volume of silver based on the total volume of the formulation. This formulation was dispensed onto the surface of a native SiO2 / Si substrate. A fluoropolymer-coated glass was attached to this paste, and then it was heated from 60 °C to 160 °C at a heating rate of 3 °C per minute in nitrogen and held isothermally for 30 minutes.

[0068] Example 5c 0.33 mL of a mixture of propylene glycol methyl ether acetate, α-terpineol and diethylene glycol (2:4:4 v / v) was mixed with 1.0 g of silver flakes (manufacturer's specification: flake size = 5 - 8 μm; tap density = 2.2 - 2.8 g / cm 3 ; Specific surface area = 0.6 - 1.2 m 2 When mixed with it, a paste containing 75.4% by mass of silver and the balance as a solvent was obtained. This formulation corresponded to 23% by volume of silver based on the total volume of the formulation. This formulation was dispensed onto the surface of a native SiO2 / Si substrate. A fluoropolymer-coated glass was attached to this paste, and then it was heated from 60 °C to 160 °C at a heating rate of 3 °C per minute in nitrogen and held isothermally for 30 minutes.

[0069] Example 5d 0.33 mL of a mixture of propylene glycol methyl ether acetate, α-terpineol and diethylene glycol (2:4:4 v / v) was mixed with 1.0 g of silver flakes (manufacturer's specification: flake size = 5 - 8 μm; tap density = 2.2 - 2.8 g / cm 3 ; Specific surface area = 0.6 - 1.2 m 2When mixed with 0.05 g of silver oxide (purchased from Sigma-Aldrich (Singapore)), a paste containing 71.8 wt% silver, 3.8 wt% silver oxide (purchased from Sigma-Aldrich (Singapore)), and the balance as solvent was obtained. This formulation corresponded to 23 vol% silver based on the total volume of the formulation. This formulation was dispensed onto the surface of a native SiO2 / Si substrate. A fluoropolymer-coated glass was attached to this paste, and then it was heated from 60 °C to 160 °C at a heating rate of 3 °C per minute in nitrogen and held isothermally for 30 minutes.

[0070] Example 5e 0.51 mL of a mixture of propylene glycol methyl ether acetate, α-terpineol, and diethylene glycol (2:4:4 v / v) was vortexed and sonicated in a bath-type ultrasonic device with 1.0 g of silver flakes (manufacturer's specifications: flake size = 5 - 8 μm; tap density = 2.2 - 2.8 g / cm 3 ; specific surface area = 0.6 - 1.2 m 2 / g) and 0.15 g of silver oxide, a paste containing 60.2 wt% silver, 9.0 wt% silver oxide, and the balance as solvent was obtained. This formulation corresponded to 16 vol% silver based on the total volume of the formulation. This formulation was dispensed onto the surface of a native SiO2 / Si substrate. A fluoropolymer-coated glass was attached to this paste, and then it was heated from 60 °C to 160 °C at a heating rate of 3 °C per minute in nitrogen and held isothermally for 30 minutes.

[0071] Example 5f 0.28 mL of a mixture of propylene glycol methyl ether acetate, α-terpineol, and diethylene glycol (3:5:2 v / v) was vortexed and sonicated in a bath-type ultrasonic device with 1.0 g of silver flakes (manufacturer's specifications: flake size = 5 - 8 μm; tap density = 2.2 - 2.8 g / cm 3 ; specific surface area = 0.6 - 1.2 m 2When mixed with / g), a paste containing 76.5% by mass of silver and the remainder as a solvent was obtained. This formulation corresponded to 26% by volume of silver with respect to the total volume of the formulation. This formulation was applied by the doctor blade method to a wet thickness of 250 μm and an area of 8 × 8 mm on a native SiO2 / Si substrate. 2 The paste was pre-dried in air at 60 °C for 20 minutes, a fluoropolymer-coated glass was attached, and then heated in nitrogen at a heating rate of 3 °C per minute to 160 °C and held isothermally for 30 minutes.

[0072] Summary of the Example The exemplary formulations according to the present application described above illustrate the diversity of high-performance paste formulations that can be realized to encompass a wide range of applications. Without further optimization, the dc electrical conductivity of the thin films derived from these formulations was already better than 1.0×10 5 S / cm in nitrogen and below 200 °C, and in many cases, after sintering at a temperature of 160 °C, and the corresponding thermal conductivity was better than 75 W / mK. In many cases, the dc electrical conductivity of the thin films was better than 1.2x10 5 S / cm, and the corresponding thermal conductivity was better than 90 W / mK. In some cases, the dc electrical conductivity of the thin films was better than 1.4x10 5 S / cm, and the corresponding thermal conductivity was better than 105 W / mK.

[0073] The lap shear strength against untreated smooth native SiO2 was usually better than 1 MPa. In some cases, the lap shear strength was better than 2 MPa. In a typical test protocol, the silver paste was formulated as shown above and applied by the doctor blade to a wet thickness of 250 μm and an area of 8 × 8 mm on the surface of a Si wafer containing native oxide. 2The area was covered. A typical drying and sintering temperature-time profile was applied without optimization and without applying any pressure to the paste film. Usually, a pre-drying step was carried out at 60 °C for 20 minutes in air, and a fluoropolymer-coated glass was attached to simulate the attachment of the second component (however, it is removable for measuring the conductivity), and then it was heated to 160 °C at a heating rate of 7.5 °C per minute in nitrogen and held isothermally for 15 minutes. In some experiments, a single heating rate of 3 °C per minute up to 200 °C with a 30-minute isothermal hold was used. The coated paste was partially surrounded by a cover glass to slow down the solvent evaporation.

[0074] Both flake and spheroid silver powders were tested. Even in the case of spheroid silver powder, the effectiveness and usability of this paste are demonstrated by the fact that high conductivity can be obtained by atmospheric pressure sintering at 200 °C or lower in an inert atmosphere. However, the sintered spheroid silver thin film had no adhesion to native SiO2. Heating was carried out on a digital hot plate that was first calibrated with a melting point standard. The dc electrical conductivity was measured by the four-probe method and corrected for the thickness and size of the thin film. A high-precision microvoltmeter was used to measure the microvolt voltage. The thickness of the thin film was measured by a profilometer or a micrometer gauge. The thermal conductivity was estimated by the Wiedemann-Franz law, which treats that the ratio of thermal conductivity to electrical conductivity is constant since free electrons realize both thermal transport and electrical transport in metals. The double shear strength was measured with a self-made device with double-sided tape attached to the bottom surface of the Si die and the upper surface of the metal thin film after sintering. This was sufficient to demonstrate that there was appropriate adhesion strength even on a demanding substrate such as native SiO2, although reliable measurement was limited to 2 MPa due to poor adhesion of the attachment tape. The formulation sintered well on the surfaces of silver, gold, platinum, and palladium. In summary, the above examples are 1.0×10 5It had an electrical conductivity better than S / cm. The corresponding thermal conductivity was estimated to be better than 75 W / mK based on the Wiedemann-Franz law for silver powder composites. The adhesion strength of the above flake formulation to the native SiO2 / Si surface was usually higher than 1 MPa. For comparison, in the absence of a modifier polymer and a co-deoxidizer solvent, the adhesion strength was less than 0.1 MPa.

[0075] (Comparative Example 1) PELCO® Conductive Silver Paint PELCO® Conductive Silver Paint (manufactured by Ted Pella Inc, product number 16062) was used as received and applied by the doctor blade method to a wet thickness of 250 μm and an area of 8×8 mm on the native SiO2 / Si substrate surface. 2 This paste was pre-dried in air at 60 °C for 20 minutes, a fluoropolymer-coated glass was attached, and then heated to 160 °C at a heating rate of 7.5 °C per minute in nitrogen and held isothermally for 30 minutes. This comparative example had an electrical conductivity of 2×10 4 S / cm.

[0076] (Comparative Example 2) Silver Flakes in Ethylene Glycol Ethylene glycol is a commonly used solvent in the art. When 0.22 mL of ethylene glycol was mixed with 1.0 g of silver flakes (manufacturer's specifications: flake size = 5 - 8 μm; tap density = 2.2 - 2.8 g / cm3; specific surface area = 0.6 - 1.2 m 2 / g) in a vortex mixer and a bath-type ultrasonic device, a paste containing 82.6% by mass of silver and the remainder as the solvent was obtained. This formulation corresponded to 30% by volume of silver based on the total volume of the formulation. This formulation was applied by the doctor blade method to a wet thickness of 250 μm and an area of 8×8 mm on the native SiO2 / Si substrate. 2 This paste was pre-dried in air at 90 °C for 15 minutes, a fluoropolymer-coated glass was attached, and then heated to 160 °C at a heating rate of 7.5 °C per minute in nitrogen and held isothermally for 30 minutes. This comparative example had an electrical conductivity of 2×104 had an electrical conductivity of S / cm.

[0077] (Comparative Example 3) Silver flakes in α-terpineol 0.22 mL of α-terpineol was mixed with 1.0 g of silver flakes (manufacturer's specifications: flake size = 5 - 8 μm; tap density = 2.2 - 2.8 g / cm 3 ; specific surface area = 0.6 - 1.2 m 2 / g) in a vortex mixer and a bath-type ultrasonic device, and a paste containing 82.6% by mass of silver and the remainder as the solvent was obtained. This formulation corresponded to 30% by volume of silver with respect to the total volume of the formulation. This formulation was applied by the doctor blade method to a wet thickness of 250 μm and an area of 8 × 8 mm on a native SiO2 / Si substrate. 2 This paste was pre-dried in air at 100 °C for 15 minutes, a fluoropolymer-coated glass was attached, and then heated to 200 °C at a heating rate of 7.5 °C per minute in nitrogen and held isothermally for 30 minutes. This comparative example had an electrical conductivity of 8 × 10 4 S / cm.

[0078] (Comparative Example 4) Silver flakes and poly(hydroxystyrene) in α-terpineol 0.22 mL of 40% hydrolyzed poly(vinyl alcohol) dissolved in α-terpineol was mixed with 1.0 g of silver flakes (manufacturer's specifications: flake size = 5 - 8 μm; tap density = 2.2 - 2.8 g / cm 3 ; specific surface area = 0.6 - 1.2 m 2 / g) in a vortex mixer and a bath-type ultrasonic device, and a paste containing 81.9% by mass of silver, 0.7% by mass of polymer, and the remainder as the solvent was obtained. This formulation corresponded to 29% by volume of silver with respect to the total volume of the formulation. This formulation was applied by the doctor blade method to a wet thickness of 250 μm and an area of 8 × 8 mm on a native SiO2 / Si substrate. 2was applied to the area. This paste was pre-dried in air at 100 °C for 15 minutes, a fluoropolymer-coated glass was attached, and then heated to 200 °C at a heating rate of 7.5 °C per minute in nitrogen and held isothermally for 30 minutes. This comparative example had an electrical conductivity of 8×10 4 S / cm.

[0079] (Comparative Example 5) Silver flakes and poly(vinylpyrrolidone) in propylene glycol methyl ether acetate To ethylene glycol, 1.2 mL of poly(vinylpyrrolidone) dissolved at a polymer concentration of 60 mg / mL was mixed with 3.0 g of silver flakes (manufacturer's specifications: flake size = 5 - 8 μm; tap density = 2.2 - 2.8 g / cm 3 ; specific surface area = 0.6 - 1.2 m 2 / g) in a vortex mixer and a bath-type ultrasonic device and allowed to stand overnight. 12 mL of ethylene glycol was added, and the silver flakes were separated by centrifugation. The flakes were rinsed with 12 mL of Millipore® water, separated by centrifugation, further rinsed with 12 mL of isopropanol, separated by centrifugation, and finally vacuum-dried. When 0.22 mL of propylene glycol methyl ether acetate was mixed with 1.0 g of the pre-exchanged silver flakes in a vortex mixer and a bath-type ultrasonic device, a paste containing 82.6% by mass of silver and the solvent as the remainder was obtained. This formulation corresponded to 30% by volume of silver with respect to the total volume of the formulation. This formulation was applied by the doctor blade method to a wet thickness of 250 μm and an area of 8×8 mm 2 on a native SiO2 / Si substrate. This paste was pre-dried in air at 60 °C for 20 minutes, a fluoropolymer-coated glass was attached, and then heated to 160 °C at a heating rate of 7.5 °C per minute in nitrogen and held isothermally for 30 minutes. This comparative example did not sinter.

[0080] (Comparative Example 6) Silver flakes and poly(2-hydroxyethyl methacrylate) in diglyme To 1.2 mL of poly(2-hydroxyethyl methacrylate) dissolved in ethylene glycol at a polymer concentration of 60 mg / mL, 3.0 g of silver flakes (manufacturer's specification: flake size = 5 - 8 μm; tap density = 2.2 - 2.8 g / cm 3 ; specific surface area, 0.6 - 1.2 m 2 / g) were added and mixed using a vortex mixer and a bath-type ultrasonic device, and left standing overnight. 12 mL of ethylene glycol was added, and the silver flakes were separated by centrifugation. The flakes were rinsed with 12 mL of Millipore® water, separated by centrifugation, further rinsed with 12 mL of isopropanol, separated by centrifugation, and finally dried in vacuo. When 0.22 mL of diglyme was mixed with 1.0 g of the pre-exchanged silver flakes using a vortex mixer and a bath-type ultrasonic device, a paste containing 82.6 mass% silver and the solvent as the remainder was obtained. This formulation corresponded to 30 volume% silver with respect to the total volume of the formulation. This formulation was applied by the doctor blade method to a wet thickness of 250 μm and an area of 8 × 8 mm 2 on a native SiO2 / Si substrate. This paste was pre-dried in air at 60 °C for 20 minutes, a fluoropolymer-coated glass was attached, and then heated to 160 °C at a heating rate of 7.5 °C per minute in nitrogen and held isothermally for 30 minutes. This comparative example did not sinter.

Industrial Applicability

[0081] The compositions and composite materials of the present disclosure can be used in various applications such as electrically conductive materials and thermally conductive materials, thermal interfaces, die attach, electrical interconnections, and electrode materials.

[0082] After a cursory reading of the foregoing disclosure, it will be apparent to those skilled in the art that various other modifications and adaptations of the present invention can be made without departing from the spirit and scope of the invention, and all such modifications and adaptations are intended to be within the scope of the appended claims.

Claims

**Claim 1** A composition comprising an oxygen scavenger solvent, a co-solvent, and a plurality of silver particles suspended in a mixture of the oxygen scavenger solvent and the co-solvent, The deoxidizing agent solvent contains one or more compounds of the formula C n O m H 2n+2-p (OH) p wherein n, m and p are integers, provided that 1 ≦ (n + m) / p ≦ 8 wherein the mixture of the oxygen scavenger solvent and the co-solvent contains a hydroxyl group at a concentration in the range of 2M to 20M. **Claim 2** The composition according to claim 1, wherein the oxygen scavenger solvent and the co-solvent have a total mass percentage in the range of 6% by mass to 30% by mass based on the total mass of the composition. **Claim 3** The composition according to claim 1 or 2, wherein the plurality of silver particles are in the form of flakes, granules, spheroids, or a combination thereof. **Claim 4** The composition according to any one of claims 1 to 3, wherein the plurality of silver particles include particles of silver element, particles of silver alloy, silver-coated particles, silver oxide particles, or a combination thereof. **Claim 5** The composition according to any one of claims 1 to 4, wherein the oxygen scavenger solvent has a boiling point in the range of 190°C to 350°C. **Claim 6** The composition according to any one of claims 1 to 5, wherein the oxygen scavenger solvent is selected from the group consisting of ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, isomers of propanediol, isomers of butanediol, isomers of pentanediol, isomers of hexanediol, isomers of heptanediol, isomers of octanediol, glycerol, pentaerythritol, dipentaerythritol, 2-(2-methoxyethoxy)ethanol, 2-(2-ethoxyethoxy)ethanol, and combinations thereof. **Claim 7** The composition according to any one of claims 1 to 6, wherein the co-solvent has a boiling point in the range of 60°C to 350°C. **Claim 8** The composition according to any one of claims 1 to 7, wherein the co-solvent contains one or more polar groups selected from an alkenyl group, an aromatic group, a carbonyl group, or an ether group. **Claim 9** The composition according to any one of claims 1 to 8, wherein the co-solvent is selected from the group consisting of xylene isomers, mesitylene, tetralin, terpinene, limonene, linalool, α-terpineol, geraniol, citronellol, diglyme, 1,2-dibutoxyethane, diethylene glycol butyl methyl ether, triethylene glycol dimethyl ether, diethylene glycol butyl ether, tripropylene glycol methyl ether, triethylene glycol ethyl ether, triethylene glycol butyl methyl ether, triethylene glycol butyl ether, propylene glycol methyl ether, sulfolane, 2-(2-butoxyethoxy)ethanol, phenoxyethanol, 2-(benzyloxy)ethanol, di(propylene glycol) methyl ether, 2-butoxyethyl acetate, ethylene glycol diacetate, propylene glycol methyl ether acetate, di(propylene glycol) methyl ether acetate, 2-(2-ethoxyethoxy)ethyl acetate, ethylene glycol monobutyl ether acetate, 2-ethoxyethyl acetate, ethylene glycol monoethyl ether acetate, 2-butoxyethyl acetate, ethanolamine, diethanolamine, texanol (trademark) ester alcohol, diethyl adipate, dimethyl succinate, methyl benzoate, N-methylpyrrolidone, γ-butyrolactone, diethyl carbonate, propylene carbonate, safrole, anethole, cyclohexanone, cyclohexanol, carvone, ethyl sorbate, pseudoisoinone, farnesene, 2,6-dimethyl-2,4,6-octatriene, o-cresol, methyl salicylate, and combinations thereof.

10. The composition according to any one of claims 1 to 9, further comprising a modifier polymer.

11. The composition according to any one of claims 1 to 10, further comprising a reducing metal.

12. A method for forming a composition, comprising the step of dispersing a plurality of silver particles in a deoxidizer solvent, in the presence of a co-solvent, or in a mixture of a deoxidizer solvent and a co-solvent.

13. A method for forming a composite material, comprising the step of sintering the composition according to any one of claims 1 to 11 on a substrate.

14. The method according to claim 13, wherein the sintering step is carried out at a temperature in the range of 140°C to 200°C.

15. The method according to claim 13 or 14, wherein the sintering step is carried out in an inert atmosphere.

16. The method according to any one of claims 13 to 15, further comprising a step of pre-drying the composition before the sintering step.

17. The method according to any one of claims 13 to 16, further comprising a step of bringing the composition into contact with a second substrate or component before the sintering step.

18. The method according to claim 17, wherein one or more substrates are selected from the group consisting of electrical components and thermal components.

19. A device comprising a composite material formed by the method according to any one of claims 13 to 18.

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