Sinterable conductive composition

Abstract

Provided herein is a sinterable conductive composition, more specifically, the conductive composition comprises sinterable silver particles dispersed in a binder resin, the binder resin not yet in a fully cured state when the composition is heated to a temperature at which the silver particles begin to sinter.

Description

[Technical field]

[0001] Provided herein is a sinterable conductive composition, more specifically, the conductive composition comprises sinterable silver particles dispersed in a binder resin, the binder resin not yet in a fully cured state when the composition is heated to a temperature at which the silver particles begin to sinter. [Background technology]

[0002] Brief description of the related art Sinterable compositions are known, see U.S. Patent Nos. 8,974,705; 10,000,670; 10,141,283; and 10,446,518; and U.S. Patent Application Publication Nos. 2016 / 0151864; 2017 / 0018325; and 2018 / 0056449.

[0003] Sinterable compositions are desirable for conductive adhesives and pastes because they tend to have improved electrical conductivity over similar adhesives and pastes filled with conductive particles. However, sinterable compositions often suffer from shortcomings in the development of certain physical properties and are considered inferior in some applications. To achieve higher electrical conductivity, higher filler loadings are usefully used. However, higher filler loadings result in brittleness and higher stresses, which are only two of the physical properties affected. Some end users have nevertheless accepted the tradeoff, finding such compromised physical properties acceptable for commercial applications in order to achieve higher electrical conductivity. In other cases, however, delamination during temperature cycling may occur, particularly when large dies are involved, making it less desirable.

[0004] It is therefore desirable in conductive adhesives and pastes to provide sinterable compositions that not only exhibit improved electrical conductivity, but also flexibility and strength. Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention provides this needed sinterable conductive composition. [Means for solving the problem]

[0006] More specifically, in this specification, about 2 to about 15 weight percent of a binder resin comprising a thermosetting resin (preferably one or more epoxy monomers, oligomers, or polymers, etc.); a silane adhesion promoter; and a hardener; about 65 to about 93 weight percent of a silver particle component having a particle size in the range of about 1 to about 7 μm, and optionally a second silver particle having a particle size in the range of about 0.3 to about 2 μm; about 1 to about 10 weight percent of one or more fillers having a particle size in the range of about 1 to about 20 μm, e.g., about 1 to about 10 μm, and selected from polymeric materials, inorganic materials, and combinations thereof; and Optionally, an organic diluent A composition for a sintering paste is provided comprising:

[0007] The composition, upon curing or sintering, has a modulus of at least 25 kg / mm2 at 260° C. for a 7×7 mm die. 2 and the composition exhibits a thermal conductivity of 70 W / mK.

[0008] Importantly, the composition is characterized in that the binder resin is not yet fully cured or fully dried when heated to a temperature at which the silver powder and silver flakes begin to sinter. That is, the curing or drying characteristics of the binder resin ensure that the binder resin is not in a cured state at the start of silver sintering. For example, the binder resin may not have begun to cure at the start of silver sintering, or the binder resin may be in a partially cured or partially dried state at the start of silver particle sintering.

[0009] According to a second aspect of the present invention, there is provided a method of using the composition of the present invention, the method comprising the steps of: i) providing a substrate; ii) providing a die; iii) depositing a composition of the present invention on at least one of a substrate or a die; and iv) heating the composition at a temperature of about 250° C. for a time sufficient to sinter the silver powder contained in the composition and to completely cure the composition. Includes. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Detailed Description As mentioned above, in this specification, about 2 to about 15 weight percent of a binder resin comprising a thermosetting resin (e.g., desirably one or more epoxy monomers, oligomers, or polymers, etc.); a silane adhesion promoter; and a hardener; about 65 to about 93 weight percent of a silver particle component having a particle size in the range of about 1 to about 7 μm, and optionally a second silver particle having a particle size in the range of about 0.3 to about 2 μm; about 1 to about 10 weight percent of one or more fillers having a particle size in the range of about 1 to about 20 μm, e.g., about 1 to about 5 μm, and selected from polymeric materials, inorganic materials, and combinations thereof; and Optionally, an organic diluent A composition for a sintering paste is provided comprising:

[0011] The composition, when cured or sintered, has a modulus of at least 25 kg / mm ​​at 260° C. for a 7×7 mm die. 2 and the composition exhibits a thermal conductivity of 70 W / mK.

[0012] Importantly, the composition is characterized in that the binder resin is not yet in a fully cured state when heated to a temperature at which the silver particles begin to sinter. That is, the curing properties of the binder resin ensure that the binder resin is not in a cured state at the start of silver sintering. For example, the binder resin may not have begun to cure at the start of silver particle sintering, or the binder resin may be in a partially cured or partially dried state at the start of silver particle sintering.

[0013] The binder resin typically includes a thermosetting resin selected from, for example, epoxy resins, oxetane resins, oxazoline resins, benzoxazines, resols, maleimides, cyanate esters, acrylate resins, methacrylate resins, maleates, fumarates, itaconates, vinyl esters, vinyl ethers, cyanoacrylates, styrene-based resins, and combinations thereof. Preferably, the thermosetting resin includes one or more of an epoxy resin and a (meth)acrylate resin. In particular, the thermosetting resin includes an epoxy resin.

[0014] Desirably, the binder resin should comprise a hydrogenated aromatic epoxy resin, a cycloaliphatic epoxy resin, or a mixture thereof. The binder resin should comprise an epoxy resin selected from the group consisting of 1,2-cyclohexanedicarboxylic acid diglycidyl ester, bis(4-hydroxycyclohexyl)methane diglycidyl ether, 4-methylhexahydrophthalic acid diglycidyl ester, 2,2-bis(4-hydroxycyclohexyl)propane diglycidyl ether, 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate, bis(3,4-epoxycyclohexylmethyl)adipate, and mixtures thereof.

[0015] The binder resin in one embodiment may include a hydrogenated aromatic epoxy resin, a cycloaliphatic epoxy resin, or a mixture thereof, and may further include an epoxy resin selected from urethane-modified epoxy resins; isocyanate-modified epoxy resins; epoxy ester resins; aromatic epoxy resins; and mixtures thereof to enhance certain properties and characteristics.

[0016] If applicable, some of these thermosetting resins may require a hardener or (reactive) curing agent to facilitate curing. The choice of hardener or curing agent is not particularly limited, except that it must contain suitable functional groups to react with functional groups on the thermosetting resin to affect crosslinking.

[0017] The epoxy resin may be a polymer, suitable examples of which include linear polymers having terminal epoxy groups, such as diglycidyl ethers of polyoxyalkylene glycols; polymeric backbone oxirane units, such as polybutadiene polyepoxides; and polymers having pendant epoxy groups, such as glycidyl methacrylate polymers or copolymers.

[0018] In one embodiment, the binder resin of the composition comprises an epoxy resin selected from cycloaliphatic epoxy resins; glycol modified cycloaliphatic epoxy resins; hydrogenated aromatic epoxy resins; epoxy phenol novolac and cresol novolac type epoxy resins; bisphenol A based epoxy resins; bisphenol F based epoxy resins; and mixtures thereof.

[0019] Here, the cycloaliphatic epoxy resin is a hydrocarbon compound containing at least one non-aryl hydrocarbon ring structure and containing one or more epoxy groups. The cycloaliphatic epoxy compound may contain an epoxy group condensed to the ring structure and / or an epoxy group present on the aliphatic substituent of the ring structure. In the present specification, the cycloaliphatic epoxy resin preferably has at least one epoxy group present on the aliphatic substituent of the ring. Suitable cycloaliphatic epoxy resins are also described in, among others, U.S. Patent Nos. 2,750,395; 2,890,194; 3,318,822; and 3,686,359, the disclosures of each of which are incorporated herein in their entirety.

[0020] The binder resin of the composition may include a hydrogenated aromatic epoxy resin, a cycloaliphatic epoxy resin, or a mixture thereof. Specifically, the binder resin may include an epoxy resin selected from 1,2-cyclohexanedicarboxylic acid diglycidyl ester; bis(4-hydroxycyclohexyl)methane diglycidyl ether; 4-methylhexahydrophthalic acid diglycidyl ester; 2,2-bis(4-hydroxycyclohexyl)propane diglycidyl ether; 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate; bis(3,4-epoxycyclohexylmethyl)adipate, and a mixture thereof. In particular, good results have been obtained when the cycloaliphatic epoxy resin includes 1,2-cyclohexanedicarboxylic acid diglycidyl ester; 2,2-bis(4-hydroxycyclohexyl)propane diglycidyl ether; or a mixture thereof.

[0021] In one embodiment of the die attach paste, the binder resin comprises a mixture of an epoxy resin and a flexible epoxy resin, the combination of which promotes reduced stress after curing, thereby improving the reliability of the cured product.

[0022] An example of the flexible epoxy resin is shown in formula (1) below. [ka] (wherein n is greater than 20, preferably 26).

[0023] Isocyanate-modified epoxy resins can have oxazolidine functionality, where the isocyanate reacts directly with the epoxy, or ureido functionality, where the isocyanate reacts with a secondary hydroxyl group present in the epoxy molecule. Commercially available examples of isocyanate- or urethane-modified epoxy resins useful herein include EPU-17T-6, EPU-78-11, and EPU-1761 available from Adeka Co.; DER 6508 available from Dow Chemical Co.; and AER 4152 available from Asahi Denka.

[0024] The thermosetting resin should be present in the binder resin in an amount of about 40 to about 60 weight percent.

[0025] In addition to the thermosetting resin, a silane adhesion promoter and a hardener are also included in the binder resin.

[0026] The silane adhesion promoter may be selected from gamma-glycidoxypropyltrimethoxysilane, gamma-methacryloxypropyltrimethoxysilane, and (3,4-epoxycyclohexyl)ethyltrimethoxysilane.

[0027] The silane adhesion promoter should be present in the binder resin in an amount of from about 1 to about 10 weight percent, such as from about 3 to about 5 weight percent.

[0028] The hardener may be selected from anhydrides such as dodecenylsuccinic anhydride, methylhexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, and nadic methyl anhydride.

[0029] The hardener should be present in the binder resin in an amount of from about 40 to about 60 weight percent, such as from about 45 to about 55 weight percent.

[0030] The thermosetting resin and hardener should be present in about a 1:1 equivalent ratio.

[0031] The binder resin itself should be present in an amount of from about 2 to about 15 weight percent, such as from about 3 to about 12 weight percent, and desirably from about 5 to about 10 weight percent.

[0032] The silver particle component may be a single type of silver or more than one type of silver. For example, the silver particles may be present in a range of about 65 weight percent to about 93 weight percent and referred to as silver powder. The silver powder may be pure silver powder, metal particles coated with silver on their surfaces, or a mixture thereof. The silver powder may be a commercially available product or may be prepared by methods known in the art, such as mechanical grinding, reduction, electrolysis, and gas phase processes.

[0033] When metal particles coated on the surface with silver are used as at least part of the silver powder, the core of the particle may be composed of copper, iron, zinc, titanium, cobalt, chromium, tin, manganese or nickel, or an alloy of two or more of said metals, and the silver coating should constitute at least 5% by weight, preferably at least 20% by weight, more preferably at least 40% by weight, based on the weight of the particle. Such a silver coating may be formed by electroless Ag-plating, electroplating or vapor deposition, as known in the art.

[0034] The silver powder present in the composition may be characterized by at least one of the following: i) a mass median diameter particle size (D50) of 0.3 to 8 μm, preferably 0.3 to 7.0 μm, more preferably 0.3 to 6.0 μm, and even more preferably 0.5 to 4.0 μm; ii) a mass median diameter (D50) of 1.2 μm to 8 μm, preferably 0.3 to 7.0 μm, more preferably 0.3 to 6.0 μm, and even more preferably 0.5 to 4.0 μm; 2 / g, preferably less than 1.0m 2 / g; and iii) a specific surface area of ​​3.5 to 8.0 g / cm 3 , preferably 4 to 6.5 g / cm 3 Tap density.

[0035] The silver powder will generally have a maximum particle diameter (D100) of less than 75 μm, such as less than 60 μm, less than 50 μm, less than 30 μm, or less than 25 μm. Alternatively, or in addition, the silver powder may have a D90 diameter of less than 20 μm, such as less than 15 μm (e.g., less than 10 μm).

[0036] D50 (mass median diameter), D90, and D100 particle sizes may be obtained using conventional light scattering techniques and equipment, such as a Hydro 2000 MU available from Malvern Instruments, Ltd. (Worcestershire, UK); or Sympatec Helos (Clausthal-Zellerfeld, Germany).

[0037] The "tap density" of the particles described herein is determined according to the International Organization for Standardization (ISO) standard ISO 3953. The principle of the specified method is to measure the tap density of a container (usually 25 cm 3 The tap density is determined by tapping a specific amount of powder in a graduated glass cylinder with a tapping device until the volume of the powder does not decrease any further. The mass of the powder is divided by its volume after the test to obtain its tap density.

[0038] "Specific surface area" refers to the surface area per unit mass of the particle. As known in the art, the specific surface area of ​​the particle may be measured using the Brunauer, Emmett, and Teller (BET) method, which includes flowing a gas over a sample, cooling the sample, and then measuring the volume of gas adsorbed on the surface of the sample at a specific pressure.

[0039] Commercially available silver powders suitable for use herein include FA-SAB-534, FA-SAB-573, FA-SAB-499, FA-SAB-195, FA-SAB-238, Ag-SAB-307, and Ag-SAB-136 available from Dowa; P554-19, P620-22, P698-1, P500-1, SA-31812, P883-3, SA0201, and GC73048 available from Metalor; SF134, SF120, and SF125 available from Ames-Goldsmith, and TC756, TC505, TC407, TC466, and TC465 available from Tokuriki.

[0040] Optionally, larger silver particles or silver powder can be blended with second, smaller silver particles to provide a bimodal silver system. For example, larger silver particles (approximately 5.7 g / cm 3 Tap density: approx. 0.6m 2 / g surface area; D50 of about 2.1 μm) and smaller silver particles (4.2 g / cm 3 Tap density of about 0.96m 2 / g surface area, with a D50 of approximately 1.2 μm.

[0041] When two types of silver particles are used, the larger silver particles, the silver powder, should be present in an amount of about 10 to about 90 weight percent, such as about 20 to about 80 weight percent, of the total silver powder. The second silver particle type should have a particle size in the range of about 0.3 to about 2 μm. When two types of silver particles are used, the second (or smaller) silver particles are smaller in size than the first (or larger) particle type.

[0042] The silver particle component should be present in the composition in an amount of about 65 to about 93 weight percent, such as about 75 to about 93 weight percent, and desirably about 85 to about 93 weight percent of the composition. Above about 93 weight percent, the cured or sintered composition achieves the desired thermal conductivity but becomes too brittle, causing excessive stress to the semiconductor package in which it is used. High stress on such semiconductor packages can lead to failure, for example, during temperature cycling.

[0043] Thus, by maintaining or reducing the amount of silver to about 93 weight percent or less and including fillers as described herein, the desired thermal conductivity is achieved without compromising the strength of the cured or sintered composition.

[0044] The filler may be selected from polymeric materials, inorganic materials, and combinations thereof. The polymeric material should not dissolve or swell in the liquid resins and solvents in the formulation. Also, the polymeric material should not melt during the curing process. The polymeric material may be a thermosetting or thermoplastic polymer, provided that it has a melting point higher than the curing temperature of the thermosetting resin of the binder resin.

[0045] Examples of polymeric materials include divinylbenzene polymer material available from Sekisui Chemical Co., Ltd., having a particle size of about 3.0 μm; 2 Examples of suitable polyimide include PTFE (commonly known as Teflon®) having a specific surface area in the range of 1 / g.

[0046] An example of an inorganic material is SE6050 available from Admatechs, which has an average particle size of about 1.7 to about 2.3 μm and a specific surface area of ​​about 1.7 to about 2.9 m. 2 / g of silica particles.

[0047] The filler should have a particle size in the range of about 1 to about 20 μm, for example about 1 to about 10 μm, which may vary depending on the nature and identity of the filler selected.

[0048] The filler should be used in an amount of from about 1 to about 15 weight percent, such as from about 1 to about 10 weight percent, and desirably from about 2 to about 7 weight percent.

[0049] The conductive composition may include a diluent in an amount of 0 to about 10 weight percent, such as 0 or 0.1 to about 8 weight percent, based on the total weight of the composition. In general, suitable diluents may be selected from alcohols, including high boiling alcohols; aromatic hydrocarbons; saturated hydrocarbons; chlorinated hydrocarbons; ethers, including glycol ethers; polyols; esters, including dibasic esters and acetates; kerosene; ketones; amides; heterocyclic aromatic compounds; and mixtures thereof.

[0050] The diluent should have a high boiling point so that it does not evaporate during processing of the composition, i.e., the boiling point of the diluent should be at least 115°C at one atmosphere pressure, and the melting point of the diluent should be less than 25°C. Examples of such diluents include dipropylene glycol, ethylene glycol, diethylene glycol, triethylene glycol, hexylene glycol, 1-methoxy-2-propanol, diacetone alcohol, 2-ethyl-1,3-hexanediol, tridecanol, 1,2-octanediol, butyl diglycol, alpha- or beta-terpineol, 2-(2-butoxyethoxy)ethyl acetate, 2,2,4-trimethyl-1,3-pentanediol diisobutyrate, 1,2-propylene carbonate, carbitol acetate, butyl carbitol acetate, butyl carbitol, ethyl carbitol acetate, 2-phenoxyethanol, hexylene glycol, dibutyl phthalate, dibasic ester (DBE), dibasic ester 9 (DBE-9), dibasic ester 7 (DBE-7), and mixtures thereof. Particularly desirable examples of such diluents include carbitol acetate; butyl carbitol acetate; dibasic ester (DBE); dibasic ester 9 (DBE-9); dibasic ester 7 (DBE-7); and mixtures thereof.

[0051] The conductive composition may further include additives and modifiers. These additives and modifiers serve many functions. For example, additives and modifiers may be used to stabilize the composition to improve shelf life or use time, and / or to control rheology, substrate adhesion, and appearance. The additives and modifiers may also help maintain a desired contact angle between the conductive composition and the substrate. Suitable additives and modifiers include thickeners; viscosity modifiers; rheology modifiers; wetting agents; leveling agents; adhesion promoters; and defoamers.

[0052] Additives and modifiers (such as rheology modifiers), when used, will typically be included in an amount of up to 10 weight percent, such as 0.01 to 5 weight percent (e.g., about 0.01 to about 1 weight percent), based on the total weight of the composition.

[0053] Suitable rheology modifiers include cellulosic materials such as carboxymethylcellulose (CMC), hydroxyethylcellulose (HEC), methylcellulose (Methocel or MC), methylhydroxyethylcellulose (MHEC), and methylhydroxypropylcellulose (MHPC); colloidal silica; metalloorganic gelling agents, for example, based on aluminates, titanates, or zirconates; natural gums, such as alginates, carrageen, guar, and / or xanthan gum; organoclays, such as attapulgite, bentonite, hectorite, montmorillonite; organic waxes, for example, castor oil derivatives (HCO waxes) and / or polyamide-based organic waxes; polysaccharide derivatives; and starch derivatives. A commercially available example of a suitable rheology modifier is Crayvallac® Super, available from Arkema Inc.

[0054] In a particularly desirable embodiment, the binder resin comprises: i) a hydrogenated aromatic epoxy resin and / or a cycloaliphatic epoxy resin as described herein; and ii) an additional epoxy resin selected from a urethane-modified epoxy resin, an isocyanate-modified epoxy resin, an epoxy ester resin, an aromatic epoxy resin, and mixtures thereof. For example, the binder may comprise: i) 40 to 100 weight percent, preferably 50 to 90 weight percent, of a cycloaliphatic resin and / or a hydrogenated aromatic epoxy resin, based on the total weight of the binder resin; and ii) 0 to 60 weight percent, preferably 10 to 50 weight percent, of an additional epoxy resin. A particular binder resin may, for example, have 55 to 65 weight percent of a cycloaliphatic resin and 35 to 45 weight percent of a modified urethane or isocyanate epoxy resin.

[0055] The conductive composition is formed by combining silver particles, binder resin, any necessary diluents or hardeners, and additives. The composition may be agitated during mixing of its components and / or subjected to a grinding process after formation to prevent or break up particle agglomerations. The selection of diluents and other liquid media, as well as particle loading, should aid in providing a composition with a viscosity suitable for application by dispensing, such as needle dispensing, jet dispensing, or by printing, such as with stencil printing, screen printing, and the like. One skilled in the art will be able to optimize the viscosity of the composition for a particular printing method.

[0056] After sintering and curing are complete, the sintered product may be cooled in the same atmosphere used for sintering, or in any other atmosphere deemed necessary to maintain the resin matrix. The sintering and cooling atmosphere should not have a significant adverse effect on the cured composite material.

[0057] The conductive compositions may be used as die attach pastes, especially in high power die attach applications where high thermal conductivity (or low thermal resistivity) and therefore good heat distribution is required. The paste serves to attach the semiconductor die to a suitable substrate, but also forms a metallurgical bond between the electrical terminals on the die and the corresponding electrical terminals on the substrate when the constituent silver particles sinter. These sinterable die attach pastes are stable in that they do not change or remelt during subsequent thermal processing, such as attachment of the device to a circuit board. Additionally, the compositions may be applied at the wafer level prior to singulation of the individual dies.

[0058] Typically, a droplet of the conductive composition is dispensed onto a substrate and the die placed on top, such that the composition is sandwiched between the substrate and the die, thereby forming a die / substrate package. The die is contacted with the composition with a sufficient degree of pressure and / or heat such that the composition spreads to completely cover the substrate beneath the die. The composition preferably also forms a fillet, i.e., a raised rim or ridge, around the periphery of the die. One skilled in the art can determine the appropriate amount of conductive composition, heat and pressure to apply such that the resulting die attach fillet is of the appropriate size.

[0059] When so disposed between the substrate and the die, the conductive composition needs to be heated for a time sufficient to both sinter the silver powder contained therein and to fully cure the composition. Typically, the die / substrate package is placed in an oven: the package may pass through several different temperature zones where the temperature is gradually increased, until the final zone, which is ideally at a temperature of 100°C to 250°C. The ramp rate (the rate at which the temperature of the package is increased) is selected to control both the evaporation of any volatiles in the conductive composition and the onset of sintering before the full cure of the binder resin therein. Furthermore, it is important that the rate of evaporation of the volatiles and the cure of the binder resin does not result in the formation of any voids in the final adhesive layer. Ramp rates of 30 to 60°C / min may be suitable. Independently, residence times of the package in the final zone of the oven of 15 to 90 minutes may be appropriate.

[0060] The viscosity of the conductive composition is, unless otherwise stated, i) for a 2 cm plate, a 500 micron gap, and 1.5 s -1 and 15s -1 or ii) a 2 cm plate, a 200 micron gap, and the shear rates shown below (10 s -1 and 100s -1 ), should be measured at 25 °C using a TA Instruments rheometer.

[0061] When the volume resistivity (VR) of a cured conductive composition is given herein, this parameter may be determined according to the following protocol: i) a sample of the composition was prepared with the composition on a glass plate at a wet thickness of about 40 μm and a sample length of more than 5.4 cm; ii) the sample was cured according to the requirements of the binder resin used; iii) after cooling the glass plate to room temperature, the sample thickness was measured using a Mitutoyo Gauge and the sample width was measured using a backlit microscope; iv) the resistance (R) was measured using a Keithley 4-point probe over a sample length of 5.4 cm; and v) the volume resistivity was calculated from the formula: VR = (sample width (cm) x sample thickness (cm) x resistance (ohms)) / sample length (cm). In the following examples, the volume resistivity (VR) is the average of three duplicate measurements, each made according to this protocol.

[0062] A "die" is a single semiconductor element disposed on a semiconductor wafer and typically separated from its adjacent dies by scribe lines. After the semiconductor wafer fabrication process is completed, the dies are typically separated into elements or units by a dicing process, such as sawing. EXAMPLES

[0063] Examples 1-4 To form the conductive compositions set forth in Table 1 below, the binder resin, silver component, filler and diluent were mixed together under suitable conditions and for a time sufficient to ensure proper mixing with little or no agglomeration of the silver and / or filler observed. The composition values ​​shown in Table 1 are weight percents based on the total weight of the composition. The compositions were then evaluated as indicated below.

[0064] [Table 1]

[0065] After curing, with no diluent present, the total silver weight percent for Samples 1-4 is 92, 89, 89, and 89.

[0066] [Table 2]

[0067] Referring to Tables 1 and 2, compared to the high silver loading (i.e., 92 wt%) of sample No. 1, each of samples No. 2 to No. 4 shows that, despite the low silver loading, the die shear strength at 260° C. for large dies (i.e., 5×5 mm and 7×7 mm) is equal to or higher, and the modulus at 25° C. and 250° C. is lower. This indicates that the filler particles have the effect of improving the adhesive strength of the sintered paste at low silver loading and low modulus observations.

[0068] Die Shear Strength (DSS): A sample of each composition was placed at a thickness of 50 microns between a 5×5 mm and 7×7 mm silver die, respectively, and a PPF (nickel-palladium-gold) lead frame. The temperature of each die substrate package was then ramped from 25° C. to 200° C. over approximately 2 hours, and then held at 200° C. for 60 minutes to cure the composition. Each sample was cooled to room temperature before being tested for die shear strength; each test was performed at least twice for each sample. The results were collated and averaged, and the die shear strength is shown in Table 2.

[0069] Thermal Conductivity: A sample of each composition was placed in a Teflon mold 25 mm wide and 0.7 mm deep (thickness). The temperature of the composition was then increased from 25° C. to 200° C. over about 2 hours, and then held at 200° C. for 60 minutes to cure the composition, thereby forming a thermally diffusive pellet. The thermal conductivity of the pellet was then determined by laser flash according to the test method specified in ASTM E 1461.

[0070] Examples 5-11 To form the conductive compositions set forth in Table 3 below, the binder resin, silver particle component, filler and diluent were mixed together under suitable conditions and for a time sufficient to ensure proper mixing with little or no agglomeration of the silver and / or filler observed. The composition values ​​shown in Table 3 are weight percents based on the total weight of the composition. The compositions were then evaluated as indicated below.

[0071] [Table 3]

[0072] Once the diluent had evaporated and the binder resin had hardened, the silver loadings (weight percent) for Samples Nos. 5-11 were 92, 91, 89, 88, 89, 87, and 87, respectively.

[0073] The performance of samples 5 to 11 is shown in Table 4 below.

[0074] [Table 4]

[0075] Referring to Tables 3 and 4, bimodal silver filled compositions are designated as Sample Nos. 5-8, and bimodal silver filled compositions containing filler particles are designated as Sample Nos. 9-11.

[0076] Each of samples Nos. 9-11 has a lower silver loading than samples Nos. 5-8, but for the larger dies (i.e., 5×5 mm and 7×7 mm), they exhibit similar or even higher die shear strength at 260° C. and lower modulus at temperatures of 25° C. and 250° C. Interestingly, samples Nos. 9-11 also exhibit significantly higher thermal conductivity. This demonstrates the effect of filler particles in improving the adhesive strength of the sinter paste in the observation of lower silver loading, lower modulus, and increased thermal conductivity.

[0077] Typically, at low silver loadings (e.g., below about 90 weight percent), sintering may not occur at all or may occur very poorly, however, at such lower silver loadings, it may be observed that the addition of filler particles improves the adhesive strength, reduces the modulus, and increases the thermal conductivity of the sintered paste at lower silver loadings.

Claims

1. a binder resin comprising a thermosetting resin; a silane adhesion promoter; and a curing agent in an amount of about 2 to about 15 weight percent; about 65 to about 93 weight percent of the silver particle component; about 1 to about 10 weight percent of one or more fillers having a particle size ranging from about 1 μm to about 20 μm and selected from the group consisting of polymeric materials, inorganic materials, and combinations thereof; and Optionally, an organic diluent A hardenable or sinterable composition comprising: The composition, upon curing or sintering, has a modulus of at least 25 kg / mm ​​for a 7×7 mm die at 260° C. ２ and has a shear strength of A curable or sinterable composition, wherein the composition exhibits a thermal conductivity of from 70 W / m.K to 88.8 W / m.K.

2. The conductive composition of claim 1 , wherein the silver particle component comprises silver particles having two different particle size ranges.

3. The silver particle component has a density of 1 to about 7 g / cm ３ and a silver powder having a tap density of 1 to about 7 g / cm ３ 13. The conductive composition of claim 1 comprising silver flakes having a tap density of

4. The conductive composition according to claim 1, wherein the silver particle component has a mass median diameter (D50) of 0.3 to 6.0 μm.

5. The specific surface area of ​​the silver particle component is 1.5 m ２ The conductive composition of claim 1 , wherein the composition has a viscosity of less than 1000 s / g.

6. The conductive composition of claim 1 , wherein the binder resin comprises a hydrogenated aromatic epoxy resin, a cycloaliphatic epoxy resin, or a mixture thereof.

7. 2. The conductive composition of claim 1, wherein the binder resin comprises an epoxy resin selected from the group consisting of 1,2-cyclohexanedicarboxylic acid diglycidyl ester; bis(4-hydroxycyclohexyl)methane diglycidyl ether; 4-methylhexahydrophthalic acid diglycidyl ester; 2,2-bis(4-hydroxycyclohexyl)propane diglycidyl ether; 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate; bis(3,4-epoxycyclohexylmethyl)adipate, and mixtures thereof.

8. 2. The conductive composition of claim 1, wherein the binder resin further comprises an epoxy resin selected from the group consisting of urethane-modified epoxy resins; isocyanate-modified epoxy resins; epoxy ester resins; aromatic epoxy resins; and mixtures thereof.