Conductive paste for bonding

Abstract

A conductive paste for joining, comprising a metal powder and a solvent, wherein the metal powder comprises a first metal powder and a second metal powder, wherein the particle diameter (D50) of the first metal powder is 50 to 150 nm and the particle diameter (D50) of the second metal powder is 151 to 500 nm, and wherein the conductive paste further comprises 0.05 to 5 wt.% of a polymer, the wt.% being based on the total wt.% of the conductive paste.

Description

AREA OF INVENTION

[0001] The present invention relates to a conductive paste for bonding and a method for manufacturing an electronic device using the conductive paste. TECHNICAL BACKGROUND OF THE INVENTION

[0002] An electronic device often includes an electrical component such as a semiconductor chip, which is connected to an electrically conductive layer of a substrate using a conductive paste.

[0003] In this approach, the electrical component is physically and electrically connected to the electrically conductive layer by the following steps: applying a conductive paste to the electrically conductive layer, attaching the electrical component to the conductive paste, and then heating the conductive paste. It has been found that currently used manufacturing processes and pastes often do not provide sufficient contact between the attached electrical component and the substrate to achieve a satisfactory electrical device design.

[0004] JP 2016-069710 discloses a compound material for the manufacture of an electrical device. The compound material comprises silver nanoparticles with a particle diameter of 1 to 200 nm and octanediol.

[0005] EP 2805783 A1 discloses a binder containing silver nanoparticles coated with an organic substance having 6 or fewer carbon atoms and having a mean primary particle diameter of 10 to 30 nm as the main silver particles, silver nanoparticles coated with an organic substance having 6 or fewer carbon atoms and having a mean primary particle diameter of 100 to 200 nm as the secondary silver particles, two types of solvents with different boiling points and a dispersant.

[0006] JP2016-148089 A discloses silver powder produced by the reduction of silver carboxylate. The particle size distribution of the primary particles of the silver powder exhibits a first maximum in the range of 20 to 70 nm and a second maximum in the range of 200 to 500 nm.

[0007] US2012 / 0219787 A1 discloses a conductive metal paste composition comprising conductive metal particles, including first metal particles with a particle size of less than 100 nm and second metal particles with a particle size of more than 100 nm, as well as a surface coated with a cover material; a binder; and a solvent. US2015 / 0263192 A1 discloses an electrically conductive paste containing Ag nanoparticles and spherical Ag microparticles for the manufacture of electrodes. SUMMARY OF THE INVENTION

[0008] The present invention relates generally to the following: a conductive paste capable of satisfactorily bonding an electrical component to a substrate during a manufacturing process, and a method for manufacturing an electrical or electronic device using the conductive paste.

[0009] One aspect of the invention relates to the method claimed in claim 10 for manufacturing an electrical device. The method comprises the following steps: manufacturing a substrate comprising an electrically conductive layer; applying a conductive paste to the electrically conductive layer; wherein the conductive paste is a conductive bonding paste comprising a metal powder and a solvent, wherein the metal powder comprises a first metal powder and a second metal powder, wherein the particle diameter (D50) of the first metal powder is 50 to 150 nm and the particle diameter (D50) of the second metal powder is 151 to 500 nm, and wherein the conductive paste further comprises 0.05 to 5 wt.-% of a polymer, where the weight percent value is based on the total weight of the conductive paste; attaching an electrical component to the applied conductive paste; heating the conductive paste to bond the electrically conductive layer and the electrical component.

[0010] In one embodiment, the total content of the first metal powder and the second metal powder is 80 to 95 wt% and the solvent is 5 to 20 wt%, the wt% value being based on the total weight of the conductive paste.

[0011] In one embodiment, the first metal powder and the second metal powder are selected from the group consisting of: silver, copper, gold, palladium, platinum, rhodium, nickel, aluminium, an alloy thereof and a combination thereof.

[0012] In one embodiment, the mixing weight ratio of the first metal powder and the second metal powder (first metal powder: second metal powder) is 1:10 to 30:10.

[0013] According to the invention, the conductive paste further comprises 0.05 to 5 wt.% % of a polymer, wherein the wt.% value is based on the total weight of the conductive paste.

[0014] In one embodiment, the particle diameter of the second metal powder is at least 50 nm larger than the particle diameter of the first metal powder.

[0015] In one embodiment, the electrical component is a semiconductor chip. In another embodiment, the electronic component comprises a plating layer selected from the group consisting of nickel, gold, and alloys thereof.

[0016] In one embodiment, the method further comprises a step of drying at 40 to 150°C after applying the conductive paste to the electrically conductive layer and before attaching the electronic component to the applied conductive paste.

[0017] Another aspect of the invention relates to a conductive paste for bonding according to claim 1. The conductive paste comprises a metal powder and a solvent, wherein the metal powder comprises a first metal powder and a second metal powder, wherein the particle diameter (D50) of the first metal powder is 50 to 150 nm and the particle diameter (D50) of the second metal powder is 151 to 500 nm, and wherein the conductive paste further comprises 0.05 to 5 wt.% of a polymer, the wt.% being based on the total weight of the conductive paste.

[0018] The electronic component can be sufficiently connected to the substrate by means of the conductive paste for bonding and the method for manufacturing an electronic device using the conductive paste of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a schematic drawing showing an example of an electronic device in a cross-sectional view. DETAILED DESCRIPTION OF THE INVENTION

[0019] An electronic device comprises at least one substrate comprising an electrically conductive layer and an electrical component. The electrically conductive layer of the substrate and the electrical component are connected by the conductive paste. An embodiment of a method for manufacturing an electronic device 100 is described with reference to Fig. 1 explained.

[0020] The device is built on a substrate 101 comprising an electrically conductive layer 103. In various embodiments, the conductive layer 103 can comprise a metallic conductor or a semiconductor. In certain embodiments, the electrically conductive layer 103 can also be an electrical circuit, an electrode, or an electrical pad. In another embodiment, the electrically conductive layer 103 can be a layer of any suitable metal. In another embodiment, the metal layer can comprise copper, silver, gold, nickel, palladium, platinum, or alloys thereof. In yet another embodiment, the electrically conductive layer 103 can be a copper layer or a silver layer.

[0021] The conductive paste 105 is capable of connecting one metallic conductor to another, a metallic conductor to a semiconductor, or a semiconductor to another semiconductor. The conductive paste 105 is applied to the electrically conductive layer 103. In one embodiment, the applied conductive paste 105 can be 50 to 500 µm thick, in another embodiment 80 to 300 µm thick, and in yet another embodiment 100 to 200 µm thick. The conductive paste 105 is applied by any suitable deposition technique, including, but not limited to, screen printing. A mask (usually made of metal) can be used for screen printing in some embodiments.

[0022] The applied conductive paste 105 is optionally dried. The drying temperature can be 40 to 150°C in one embodiment, 50 to 120°C in another, and 60 to 100°C in yet another. The drying time is 10 to 150 minutes in one embodiment, 15 to 80 minutes in another, and 20 to 30 minutes in yet another.

[0023] The electrical component 107 is attached to the applied conductive paste 105. The electrical component 107 is not particularly restricted as long as it functions electrically. For example, the electrical component 107 can be selected from the group consisting of a semiconductor chip, an integrated circuit (IC) chip, a chip resistor, a chip capacitor, a chip inductor, a sensor chip, and a combination thereof. In another embodiment, the electrical component 107 can be a semiconductor chip. In another embodiment, the semiconductor chip can be a silicon (Si) chip or a silicon carbide (SiC) chip.

[0024] In some embodiments, the electrical component 107 comprises a metallization layer that may be arranged in contact with the adjacent layer of the applied conductive paste 105. The material of the metallization layer may be selected from the group consisting of copper, silver, gold, nickel, palladium, platinum, alloys thereof, and, in another embodiment, a mixture thereof. In another embodiment, the metallization layer comprises gold and / or nickel. In yet another embodiment, the metallization layer comprises a lamination of a gold layer and a nickel layer. In another embodiment, the metallization layer is provided by plating.

[0025] The layer of conductive paste 105 is heated to achieve the required bond. In various embodiments, the heating is carried out in a chip bonder set to a temperature between 150, 180, 200, or 220°C and 260, 290, 310, and 400°C for a heating time in the range of 0.1, 0.5, 3, or 8 minutes and 3, 5, 13, 15, 20, or 30 minutes. Alternatively, the heating step can be carried out in an oven or using another suitable heat source. Thermal damage to the electrical component 107 can be minimized or eliminated because the conductive paste 105 can be bonded at a relatively low temperature.

[0026] In various embodiments, the heating step is carried out in different atmospheres, such as a reduction atmosphere (e.g., a nitrogen atmosphere) or in air. 2

[0027] To improve the adhesion of the electrical component 107e to the conductive paste layer 105, pressure is applied to the electrical component 107e during heating in some embodiments. The pressure can range from 0.1, 1, 5, 7, 15, or 25 MPa to 15, 25, 36, 40, or 45 MPa. A hot-press forming machine or a chip bonder equipped with a pressure and heating mechanism for semiconductor bonding can be used. Alternatively, the electrical component 107e can be bonded without applying pressure.

[0028] The composition of conductive paste 105 is explained below. Conductive paste 105 comprises a metal powder and a solvent. metal powder

[0029] The metal powder comprises a first metal powder and a second metal powder. The particle diameter (D50) of the first metal powder is 50 to 150 nm, and the particle diameter (D50) of the second metal powder is 151 to 500 nm. The particle diameter (D50) is a volume-mean particle diameter (D50), measured by a dynamic light scattering method using a dynamic light scattering particle size analyzer (LB 550, Horiba Ltd.).

[0030] In various embodiments, the particle diameter (D50) of the first metal powder ranges from a lower limit of 50, 55, 65, 75, 85 or 95 nm to an upper limit of 70, 80, 90, 105, 110, 120, 130 or 150 nm.

[0031] The first metal powder is selected from the group consisting of: silver, copper, gold, palladium, platinum, rhodium, nickel, aluminum, an alloy thereof, and a combination thereof in one embodiment. The first metal powder is selected from the group consisting of: silver, copper, nickel, an alloy thereof, and a combination thereof in another embodiment. In yet another embodiment, the first metal powder is silver.

[0032] The shape of the first metal powder is flocculent, spherical, amorphous, or a mixture thereof in one embodiment. In another embodiment, the shape of the first metal powder is a mixture of flocculent and spherical. "Spherical powder" means a powder of particles having a ratio of the largest diameter of each particle to its smallest diameter of at most 2:1. In other embodiments, the ratio is at most 1.8:1, 1.5:1, or 1.3:1, depending on how the powder is produced.

[0033] The particle size of the metal powder used in the present composition can be specified by values ​​of D50. Unless otherwise stated, the term "particle diameter" here refers to a value of "D50", which is a mean particle size by volume that can be determined using a laser diffraction method performed with a Microtrac X-100 (Montgomeryville, PA) instrument.

[0034] In some embodiments, the first metal powder itself is a mixture of two types of metal powders with different particle sizes. The first metal powder comprises a first metal powder A and, in another embodiment, a first metal powder B. The particle diameter (D50) of first metal powder A is 50 to 80 nm, and the particle diameter (D50) of first metal powder B is 81 to 150 nm in another embodiment. The particle diameter (D50) of first metal powder A is 50 to 65 nm in another embodiment. The particle diameter (D50) of first metal powder B is 85 to 140 nm in another embodiment, 88 to 130 nm in another embodiment, 92 to 120 nm in another embodiment, and 95 to 110 nm in another embodiment.

[0035] The particle diameter of the first metal powder B is 10 to 100 nm larger than the particle diameter of the first metal powder A in one embodiment. The particle diameter of the first metal powder B is 20 to 80 nm larger than the particle diameter of the first metal powder A in another embodiment. The particle diameter of the first metal powder B is 30 to 60 nm larger than the particle diameter of the first metal powder A in yet another embodiment.

[0036] The mixing ratio of the first metal powder A and the first metal powder B (first metal powder A : first metal powder B) is 1:10 to 30:10 in one embodiment, 4:10 to 22:10 in another embodiment, 6:10 to 18:10 in another embodiment, 8:10 to 15:10 in another embodiment, 9:10 to 12:10 in another embodiment.

[0037] In one aspect, the present disclosure relates to an embodiment of the conductive paste, wherein the first metal powder is a mixture of the first metal powder A and the first metal powder B with different particle diameters, wherein the particle diameter (D50) of the first metal powder A is 10 to 80 nm and the particle diameter (D50) of the first metal powder B is 81 to 150 nm, and wherein the conductive paste further comprises 0.05 to 5 wt.% of a polymer, the wt. percent being based on the total weight of the conductive paste. The first metal powder is a mixture of the first metal powder A and the first metal powder B in one embodiment. The first metal powder is the first metal powder A in another embodiment. The first metal powder is the first metal powder B in yet another embodiment.

[0038] The particle diameter (D50) of the second metal powder is 160 to 350 nm, in another embodiment 175 to 290 nm, in another embodiment 182 to 250 nm.

[0039] The second metal powder is selected from the group consisting of: silver, copper, gold, palladium, platinum, rhodium, nickel, aluminum, an alloy thereof, and a combination thereof in one embodiment. The second metal powder is selected from the group consisting of: silver, copper, nickel, an alloy thereof, and a combination thereof in another embodiment. In yet another embodiment, the second metal powder is silver.

[0040] The second metal powder has a flocculent, spherical, amorphous, or a mixture thereof in one embodiment. In another embodiment, the second metal powder is a mixture of flocculent and spherical shapes.

[0041] The mixing ratio of the first metal powder and the second metal powder (first metal powder : second metal powder) is 1:10 to 30:10 in one embodiment, 3:10 to 25:10 in another embodiment, 4:10 to 23:10 in another embodiment, 5:10 to 21:10 in another embodiment, 7:10 to 17:10 in another embodiment, 8:10 to 14:10 in another embodiment, 9:10 to 12:10 in another embodiment.

[0042] The total amount of the first metal powder and the second metal powder in various embodiments ranges from a lower limit of 60 wt.%, 72 wt.%, 80 wt.% or 85 wt.%, to an upper limit of 93 wt.%, 95 wt.% or 97 wt.%, based on the total weight of the conductive paste 105.

[0043] The particle diameter of the second metal powder is 50 to 200 nm larger than the particle diameter of the first metal powder in one embodiment. In another embodiment, the particle diameter of the second metal powder is 80 to 150 nm larger than the particle diameter of the first metal powder. In yet another embodiment, the particle diameter of the second metal powder is 90 to 110 nm larger than the particle diameter of the first metal powder.

[0044] In one embodiment, the particle size distribution of the mixed powder of the first metal powder and the second metal powder could exhibit two peak values. In another embodiment, the particle size distribution of the first metal powder and the particle size distribution of the second metal powder could differ from each other. In yet another embodiment, the first metal powder and the second metal powder with different particle diameters could be different types of metal powder.

[0045] As experts know, virtually all particulate materials on the market are offered as an ensemble of individual particles with a range of sizes, so that "particle size" must be specified by parameters that statistically characterize the actual distribution. The D50 value, or mean particle size by volume, is commonly used to represent the approximate particle size. Unless otherwise stated, references herein to the "particle diameter" of an ensemble of particles are therefore to be understood as the D50 value of the ensemble. Other common statistically derived measures of particle size include D10 and D90, which indicate that 10 vol% and 90 vol% of the particles in the ensemble have a size smaller than D10 and D90, respectively.These values, taken either individually or in combination with the D50 values, can provide additional characterization of a particle distribution, which is particularly useful for distributions that are not symmetrical, multimodal, or complex. Values ​​such as D10 and D90 are commonly reported together with D50 by commercial particle size analyzers. The width of the particle distribution can typically be characterized by how much the D10 and / or D90 values ​​differ from D50; a large difference is usually associated with a wide distribution.

[0046] A particle size distribution taken from the mixed metal powder provided in the present disclosure can be multimodal, meaning that a graphical representation of the distribution exhibits more than one peak, corresponding to the differences in particle size distributions that characterize the various numerous powder sources. Each of the peaks corresponds to a particle size. For example, a metal powder produced by mixing two powders with different particle size distributions and different D50 values ​​typically shows a particle size distribution of the combined powders with two peaks that approximately correspond to the D50 values ​​of the two subpopulations. The heights of the different peaks depend on the relative amounts of the different powder sources in the mixture, the width of their distributions, and the difference between their D50 values.For some embodiments, several discrete peaks are evident in the overall powder size distribution, each peak corresponding approximately to a D50 value of one of the constituent powders used to prepare the mixture. In others, the multimodal distribution may manifest as one or more shoulders on a more intense peak. Known numerical methods can be used to determine the presence of multiple peaks in such multimodal distributions.

[0047] In one embodiment, the particle size distribution comprises a first mode corresponding to a particle size of 50 to 150 nm and a second mode corresponding to a particle size of 151 to 500 nm. The first and second modes correspond to particle sizes that differ by at least 50 nm in one embodiment. solvent

[0048] The metal powder is dispersed in a suitable solvent to form the conductive paste. The amount of solvent can be varied to adjust the viscosity so that the conductive paste 105 can be easily applied to the substrate 101 or the electrically conductive layer 103. All or most of the solvent evaporates from the conductive paste 105 during the drying or heating step.

[0049] The molecular weight of the solvent is 600 or less in one embodiment, 520 or less in another embodiment, 480 or less in another embodiment, and 400 or less in another embodiment. The molecular weight of the solvent is at least 10 in one embodiment, at least 100 in another embodiment, at least 150 in another embodiment, and at least 180 in another embodiment.

[0050] All or most of the solvent evaporates from the conductive paste 105 during the drying or heating step. The boiling point of the solvent is 100 to 450°C in one embodiment, 150 to 320°C in another embodiment, and 200 to 290°C in yet another embodiment. In one embodiment, the solvent is an organic solvent.

[0051] Suitable solvents include those selected from the group consisting of: ester alcohols, 1-phenoxy-2-propanol, terpineol, carbitol acetate, ethylene glycol, butyl carbitol, dibutyl carbitol, dibutyl acetate propylene glycol phenyl ether, ethylene glycol monobutyl ether, butyl carbitol acetate, 1,2-cyclohexanedicarboxylic acid diisononyl ester, and a mixture thereof in another embodiment. A preferred ester alcohol is the monoisobutyrate of 2,2,4-trimethyl-1,3-pentanediol, commercially available from Eastman Chemical (Kingsport, TN) under the trade name TEXANOL™.

[0052] In some embodiments, the conductive paste 105 has a viscosity between 10, 12 or 15 Pa·s and 50, 100 or 300 Pa·s when measured at a shear rate of 10 sec using a rheometer (HAAKE™ MARS™ III, -1 Thermo Fisher Scientific Inc.) with a titanium cone plate C20 / 1°.

[0053] In some embodiments, the solvent is present in an amount ranging from 5, 6.5, 7.8 or 8.8 parts by weight to 13, 15 or 20 parts by weight when the metal powder constitutes 100 parts by weight of the conductive paste. polymer

[0054] The conductive paste 105 comprises a polymer, optionally a solvent-soluble polymer with a molecular weight (Mw) of 1000 or more. In other embodiments, the molecular weight (Mw) of the polymer is between 1000, 5000, 10000, 18000, 25000, or 32000 and 200000, 350000, 4800000, 610000, 780000, or 900000. Unless otherwise specified, references to the molecular weight of the polymers in this application refer to the weight-average molecular weight (Mw) that can be measured using a high-performance liquid chromatography system such as an Alliance 2695 system (Nippon Waters Co., Ltd.) or the like.

[0055] In one embodiment, the polymer in the present composition is selected from the group consisting of: ethylcellulose, methylcellulose, hydroxypropylcellulose, polyvinyl butyral resin, phenoxy resin, polyester resin, epoxy resin, acrylic resin, polyimide resin, polyamide resin, polystyrene resin, butyral resin, polyvinyl alcohol resin, polyurethane resin, and a mixture thereof. In another embodiment, the polymer is ethylcellulose.

[0056] The glass transition temperature of the polymer is -30 to 250°C in one embodiment, 10 to 180°C in another embodiment, and 80 to 150°C in yet another embodiment.

[0057] In the invention, the conductive paste comprises 0.05 to 5 wt.% of a polymer. In some embodiments, the polymer is present in an amount ranging from 0.1, 0.5 or 1.5 wt.% to 3.1, 3.5 or 4 wt.% based on the total weight of the conductive paste 105. Additive

[0058] One or more additives, including but not limited to surfactants, dispersants, emulsifiers, stabilizers, plasticizers, or other known paste additives, may further be added to the conductive paste 105 to improve its functional properties, formulation, storage, and / or end-use characteristics. In one embodiment, the conductive paste 105 does not include a glass frit. Embodiments in which the conductive paste 105 does not include a curing agent or a crosslinking agent are also considered here.

[0059] Without being bound to a specific theory of the operation, it is assumed that the first metal powder promotes sintering and bonding between metals at low temperature in the conductive paste, while the second metal powder suppresses abrupt shrinkage in the conductive paste. As a result, an electronic device can be provided in which an electronic component is adequately bonded to a substrate. EXAMPLES

[0060] The present invention is illustrated by the following examples, without being limited thereto. Examples 1-2

[0061] Conductive pastes were produced by dispersing various silver powders in a mixture of an organic solvent and a polymer. Dispersion was achieved by mixing the components in a mixer, followed by processing in a three-roll mill. The solvent was TEXANOL ester alcohol.

[0062] Spherical silver powders with different particle diameters (D50) (60 nm, 100 nm, 200 nm, 300 nm) were prepared and incorporated into the pastes of Examples 1 to 2 and Comparison Examples 1 to 3, as shown in Table 1. The viscosity of each conductive paste was 25 to 30 Pa·s, measured at a shear rate of 10 sec⁻¹ using a rheometer (HAAKE™ MARS™ III, titanium cone plate: C20 / 1°, Thermo Fisher Scientific Inc.).

[0063] Next, a conductive paste layer was formed for each example by applying the conductive paste to a copper plate. A series of pressure-sensitive tapes (Scotch) ® Magic™ MP-18 transparent tape (3M Corporation) was applied to copper plates (15 mm wide, 30 mm long, 1 mm thick), maintaining a 15 mm gap between adjacent pieces. Conductive paste was applied over the tapes using a scraper to fill the spaces between them. The tapes were then removed, leaving the applied conductive paste in a pattern of squares measuring 10 mm wide, 10 mm long, and 150 µm thick. The conductive paste layer was oven-cured at 80°C for 60 minutes.

[0064] A SiC chip (3 mm wide, 3 mm long, 360 µm thick) was applied to the conductive paste layer. The SiC chip was bonded to the copper plate using a chip bonder (T-3002M, Tresky AG) under a heating condition of 10 MPa / 280°C / 1 minute.

[0065] A thermal cycling test was performed on the fused body of the copper plate and the resulting SiC chip. For each cycle, the fused body was first exposed to -55°C for 30 minutes and then to 175°C for 30 minutes, with a transition time of 30 seconds or less between temperatures. The cycling process was repeated 300 times.

[0066] Subsequently, an ultrasonic microscope (SAT, Fine SAT200III, Hitachi Power Solutions Co., Ltd.) was used to determine the bonding area for each sample, that is, the relative portion of the chip area that remained attached to the substrate after the thermal cycle test. Specifically, the bonding areas were evaluated from images generated by the intensity of reflection or transmission of the ultrasonic waves emitted by the SAT onto the bonded body on the SiC chip side. The results are shown in Table 1. The bonding area was 80% or greater for pastes where the metal powder consisted of a mixture of two silver powders, the first having a particle diameter of 100 nm and the second having a particle diameter of either 200 nm or 300 nm (Examples 1 and 2, respectively).A significantly smaller bonding area was observed for comparison examples 1 to 3, which were formulated either with single silver powders with a particle diameter of 200 nm or 100 nm (comparison examples 1 and 2, respectively) or with a mixture of silver particles with diameters of 100 nm and 60 nm. Each of comparison examples 1-3 exhibited a bonding area of ​​66% or less. Table 1 (weight parts) Comparison example 1 Comparison example 2 Comparison example 3 Example 1 Example 2 Ag powder (D50) (300 nm) 0 0 0 50 0 (200 nm) 100 0 0 0 50 (100 nm) 0 100 50 50 50 (60 nm) 0 0 50 0 0 solvent 10.5 10.5 10.5 10,5 10,5 polymer 0.4 0.4 0.4 0.4 0.4 Connection area (%) 65.5 64,1 45.0 82,7 94.5 Examples 3-5

[0067] The effect of the mixing ratio of the silver powder (first metal powder) with a particle diameter of 100 nm and the silver powder (second metal powder) with a particle diameter of 200 nm on the adhesive strength was investigated. Conductive pastes were prepared in the same manner as in Examples 1 and 2, except that the mixing ratio of the first silver metal powder (particle diameter of 100 nm) and the second silver metal powder (particle diameter of 200 nm) was varied, as shown in Table 2. The conductive paste was applied to the copper plate in the same manner as in Examples 1 and 2, except that copper chips were used instead of SiC chips. The chips were bonded using the same chip bonder and then subjected to the same thermal cycle test.

[0068] The bond strength between the copper chip and the copper plate for each sample was measured after the thermal cycle. The test was performed according to a standard chip shear test procedure (MIL STD-883) using a bond tester (4000 Plus, Nordson Advanced Technology Co., Ltd.). Bond strength was defined as the strength with which the copper chip was pulled away from the bond tester.

[0069] The results are shown in Table 2. The adhesion strength was 28 MPa or more for all tested mixture ratios. Table 2 (weight parts) Example 3 Example 4 Example 5 Ag powder (D50) (200 nm) 50 33 67 (100 nm) 50 67 33 solvent 10,5 10,5 10,5 polymer 0,4 0,4 0,4 Adhesive strength (MPa) 39,8 28,0 30,4 Examples 6-8

[0070] Next, the effect of changing the amount of metal powder in the paste composition was investigated. Conductive pastes were prepared in the same manner as in Examples 1 to 5, except that the total amount of metal powder relative to the solvent and polymer was varied, as shown in Table 3. For each example, the silver powder contained equal weights of silver particles with particle diameters (D50) of 100 nm and 200 nm.

[0071] Copper chips were re-bonded to a copper plate substrate using the same chip bonder as before, thermally cycled, and then tested to determine the bonding area using the SATU ultrasonic microscope in the same manner as in Examples 1 and 2. The bonding area was 77% or greater when the metal powder was 85.3 wt%, 86.6 wt%, and 87.8 wt% (Examples 6 to 8). Table 3 (wt.%) Example 6 Example 7 Example 8 Ag powder 85,3 86,6 87,8 solvent 13,7 12,6 11,5 polymer 1,0 0,8 0,7 Connection area (%) 77 87 95 * The Ag powder contained equal weight proportions of particles with D50 of 100 nm and 200 nm. Examples 9-10

[0072] A conductive paste was prepared in the same manner as in Example 2, except that the type of metal powder was changed, as shown in Table 4. The copper chip was bonded to the copper plate using the conductive paste, and the bond strength was measured. The bonding procedure was the same as in Example 3, except that the heating condition was 10 MPa / 250°C / 10 minutes. The bond strength measurement procedure was the same as in Example 3. The results are shown in Table 4. The bond strength was 56 MPa or greater when the mixing ratio of the 200 nm silver powder and the 60 nm silver powder was 68:32 (Example 9), and when the mixing ratio of the 200 nm silver powder, the 100 nm silver powder, and the 60 nm silver powder was 67:17:16 (Example 10). Table 4 (weight parts) Example 9 Example 10 Ag powder (D50) (200 nm) 68 67 (100 nm) 0 17 (60 nm) 32 16 solvent 14 13 polymer 0,4 0,4 Adhesive strength (MPa) 65,5 56,6

[0073] After the invention has been described in more detail, it is understood that this detail need not be strictly adhered to, but that further changes and modifications may be apparent to those skilled in the art, all of which fall within the scope of the invention as defined by the attached claims.

[0074] For example, experts will recognize that the choice of raw materials could unintentionally contain impurities that can be incorporated into the oxide composition or other paste components during processing.

[0075] These random impurities can be present in the range of hundreds to thousands of parts per million. Impurities commonly found in the industrial materials used here are known to experts.

[0076] Where a range of numerical values ​​is specified or defined herein, the range includes its endpoints and all individual integers and fractions within the range, and also includes each of the narrower ranges herein formed by all different possible combinations of these endpoints and internal integers and fractions to form subgroups of the larger group of values ​​within the specified range to the same extent as if each of these narrower ranges had been explicitly stated. Where a range of numerical values ​​herein is specified as greater than a stated value, the range is nevertheless finite and is bounded at its upper end by a value effective within the scope of the invention described herein. Where a range of numerical values ​​herein is specified as less than a stated value, the range is nevertheless bounded at its lower end by a non-zero value.It is not intended that the scope of the invention be limited to the specific values ​​specified when defining a range.

[0077] Unless expressly stated otherwise or indicated otherwise by the intended use, if an embodiment of the item is specified or described as comprising, including, containing, or consisting of certain features or elements, one or more features or elements in addition to those explicitly stated or described may be present in the embodiment. However, an alternative embodiment of the item may be specified or described as consisting essentially of certain features or elements, provided that such embodiment does not contain any features or elements that would substantially alter the operating principle or distinguishing characteristics of the embodiment.Another alternative embodiment of the subject matter may be specified or described as consisting substantially of certain features or elements, wherein in this embodiment or in inessential variations thereof only those features or elements that are specifically specified or described are present. Furthermore, the term "comprising" shall include examples contained in the expressions "essentially consisting of" and "consisting of". Likewise, the expression "consisting substantially of" shall include examples contained in the expressions "consisting of".

[0078] Unless expressly stated otherwise or contrary by the context of use, quantities, sizes, ranges, formulations, parameters and other quantities and features mentioned herein, especially when modified by the term "over", may be exact, but need not be exact, and may also be approximate and / or larger or smaller (as desired) than specified and reflect tolerances, conversion factors, rounding, measurement errors and the like, as well as the inclusion in a specified value of those values ​​outside of it which, within the scope of this invention, have a functional and / or operational equivalence to the specified value.

Claims

[1] Conductive paste for joining, comprising a metal powder and a solvent, wherein the metal powder comprises a first metal powder and a second metal powder, wherein the particle diameter (D50) of the first metal powder is 50 to 150 nm and the particle diameter (D50) of the second metal powder is 151 to 500 nm, and wherein the conductive paste further comprises 0.05 to 5 wt.% of a polymer, the wt.% being based on the total weight of the conductive paste. [2] Conductive paste according to claim 1, wherein the total content of the first metal powder and the second metal powder is 80 to 95 wt% and the solvent is 5 to 20 wt%, the wt% value being based on the total weight of the conductive paste. [3] Conductive paste according to claim 1, wherein the first metal powder and the second metal powder are selected from the group consisting of: silver, copper, gold, palladium, platinum, rhodium, nickel, aluminium, an alloy thereof and a combination thereof. [4] Conductive paste according to claim 1, wherein the mixing weight ratio of the first metal powder and the second metal powder (first metal powder: second metal powder) is 1:10 to 30:

10. [5] Conductive paste according to claim 1, wherein the particle diameter of the second metal powder is at least 50 nm larger than the particle diameter of the first metal powder. [6] Conductive paste according to claim 1, wherein the particle size distribution of the metal powder is multimodal. [7] Conductive paste for joining, comprising a metal powder and a solvent, wherein the particle size distribution of the metal powder is multimodal, the particle size distribution comprising a first mode corresponding to a particle size of 50 to 150 nm and a second mode corresponding to a particle size of 151 to 500 nm, and wherein the conductive paste further comprises 0.05 to 5 wt.% of a polymer, the wt.% being based on the total weight of the conductive paste. [8] Conductive paste according to claim 7, wherein the first mode and the second mode correspond to particle sizes that differ by at least 50 nm. [9] Conductive paste according to claim 7, wherein the total content of the first metal powder and the second metal powder is 80 to 95 wt.% and the solvent is 5 to 20 wt.% based on the total weight of the conductive paste. [10] Method for manufacturing an electronic device comprising the following steps: manufacturing a substrate comprising an electrically conductive layer; applying the conductive paste according to claim 1 to the electrically conductive layer; attaching an electrical component to the applied conductive paste; heating the conductive paste to bond the electrically conductive layer and the electrical component. [11] Method according to claim 10, wherein the electrical component is a semiconductor chip. [12] Method according to claim 10, wherein the electronic component comprises a plating layer selected from the group consisting of nickel, gold and alloys thereof. [13] Method according to claim 10, wherein the method further comprises the step of drying at 40 to 150°C after applying the conductive paste to the electrically conductive layer and before attaching the electronic component to the applied conductive paste. [14] Method for manufacturing an electronic device comprising the following steps: Producing a substrate that includes an electrically conductive layer; Applying the conductive paste according to claim 7 to the electrically conductive layer; Attaching an electrical component to the applied conductive paste; Heating the conductive paste to connect the electrically conductive layer and the electrical component.