WO2019188511A1

WO2019188511A1 - Copper paste, bonding method, and method for producing bonded body

Info

Publication number: WO2019188511A1
Application number: PCT/JP2019/011213
Authority: WO
Inventors: 治之中城; 孝之小川; 雅張
Original assignee: ハリマ化成株式会社
Priority date: 2018-03-29
Filing date: 2019-03-18
Publication date: 2019-10-03
Also published as: EP3778069A1; TWI798404B; JP7220310B2; JP2022046765A; EP3778069A4; JPWO2019188511A1; TW201942372A

Abstract

This copper paste comprises metal particles and a dispersion medium. The metal particles comprise type-1 particles and type-2 particles. The type-1 particles are copper particles having nanostructures on the surfaces thereof, and having an average particle diameter of 1-100 μm. The type-2 particles are copper particles having an average particle diameter of 0.05-5 μm. The average particle diameter of the type-1 particles is 2-550 times the average particle diameter of the type-2 particles. For example, a laminate, in which a copper paste(5) is provided between a first member(1) and a second member(2), is heated in a reducing atmosphere to sinter the copper paste, whereby the first member and the second member can be bonded without processing.

Description

Copper paste, bonding method, and manufacturing method of bonded body

The present invention relates to a copper paste, a bonding method using the same, and a method for manufacturing a bonded body.

Conventionally, high melting point lead solder has been widely used for joining metals, semiconductors, etc., but from the viewpoint of environmental regulations and the like, joining materials that do not contain lead are required. A method using metal nanoparticles such as silver is known as a material capable of low-temperature bonding. Nanoparticles are fused at a temperature lower than the melting point due to the nanosize effect, so that low-temperature pressureless bonding is possible. However, silver nanoparticles are expensive in material cost, and at present, sufficient bonding strength is not obtained.

Some studies using copper particles have been reported as cheaper bonding materials. In Patent Document 1, copper particles having a particle diameter of the order of μm are used as a bonding material, and the surfaces of the copper particles are oxidized by in-situ synthesis to form nanoparticles, and then heated in a reducing atmosphere. A joining method is disclosed. Patent Document 2 proposes a method of performing pressureless bonding using a copper paste containing coated nanoparticles and microparticles whose surface is coated with organic molecules to enhance dispersibility.

JP 2017-074598 A JP 2014-167145 A

In the methods of Patent Document 1 and Patent Document 2, the bonding strength is not sufficient. In view of this problem, an object of the present invention is to provide a copper paste capable of realizing high bonding strength even at low temperature bonding.

The copper paste of the present invention contains metal particles and a dispersion medium. The metal particles include first type particles and second type particles. The first type particles are copper particles having an average particle diameter of 1 to 100 μm and having a nanostructure on the surface. The second type particles are copper particles having an average particle diameter of 0.05 to 5 μm. The average particle diameter D1 of the first kind particles is preferably 2 to 550 times the average particle diameter D2 of the second kind particles.

The nanostructure of the first type particles is formed by, for example, a heated oxide of copper. Examples of the nanostructure include an uneven shape, a particle shape, and a fiber shape.

The laminated body provided with the above copper paste between the members to be joined is prepared, and the laminated body is heated in a reducing atmosphere, so that the copper paste is sintered and the members can be joined.

The copper paste of the present invention can be applied to low-temperature pressureless bonding. By using the copper paste of the present invention, high strength bonding can be realized.

2 is a scanning micrograph of copper particles. It is sectional drawing which shows the structural example of the laminated body used for a non-pressure joining. 3 is a scanning micrograph of a bonding layer cross section of Example 1 and Comparative Example 3. FIG.

[Copper paste]
The copper paste of the present invention contains metal particles and a dispersion medium. The metal particles include first type particles and second type particles. The average particle diameter D1 of the first kind particles is 1 to 100 μm, and the average particle diameter D2 of the second kind particles is 0.05 to 5 μm. The average particle diameter D1 of the first kind particles is larger than the average particle diameter D2 of the second kind particles. D1 is preferably 2 to 550 times D2. In the present specification, the average particle diameter is a volume-based cumulative median diameter (D ₅₀ ) determined from a particle diameter distribution measured by a laser diffraction scattering method.

The first type particles have a nanostructure on the surface. Since the first type particles having nanostructures are fused on the surfaces at the time of heat bonding and the second type particles having a small particle diameter are filled in the gaps, there are few voids in the bonding material, and high bonding strength can be realized.

<Metal particles>
(First type particles)
The first type particles are copper particles having a nanostructure on the surface and an average particle diameter of 1 to 100 μm. Examples of the nanostructure on the copper particle surface include nano-sized irregularities, nanoparticles, and nanofibers. For example, by subjecting copper particles having a particle diameter of 1 to 100 μm to heat oxidation, copper particles having a (sub-) oxide nanostructure on the surface can be obtained.

FIG. 1 (A) is a scanning microscope (SEM) photograph of wet copper powder (“1400YM” manufactured by Mitsui Mining & Smelting Co., Ltd., average particle diameter of 4.2 μm) that has not been heat-treated. The surface of the copper powder before heat treatment is smooth and no nanostructure is formed.

Fig. 1 (B1) shows SEM photographs of wet copper powder heated in the air for 10 minutes at 100 ° C, 10 minutes at 150 ° C, 10 minutes at 200 ° C, 10 minutes at 250 ° C, and 10 minutes at 300 ° C. It is. FIG. 1 (B2) and FIG. 1 (B3) are SEM photographs of wet copper powder that was subjected to heat treatment by changing the heating time at 300 ° C. to 30 minutes and 120 minutes, respectively. FIG. 1 (C1) shows 10 minutes at 100 ° C., 10 minutes at 150 ° C., 10 minutes at 200 ° C., 10 minutes at 250 ° C., 10 minutes at 300 ° C., 10 minutes at 350 ° C., and 400 ° C. It is a SEM photograph of the wet copper powder heated for 10 minutes sequentially. FIG. 1 (C2) and FIG. 1 (C3) are SEM photographs of wet copper powder that was subjected to heat treatment by changing the heating time at 400 ° C. to 30 minutes and 120 minutes, respectively.

In (B1), fine irregularities are formed on the particle surface, and in (B2) and (B3), the irregularities on the surface grow into particles as the heating time at 300 ° C. becomes longer. I understand. In (C1) heated at 400 ° C., finer irregularities are formed than in (B1), and fine fiber-like nanostructures are formed. In (C2) and (C3), it can be seen that the nanofibers grow as the heating time at 400 ° C. becomes longer.

Although the melting point of copper is 1085 ° C., nanostructures such as nanoscale irregularities, particles and fibers formed on the surface of the copper particles show a melting point drop due to the size effect, similar to the nanoparticles. Therefore, the first type particles having a nanostructure on the surface can be fused at a temperature lower than the melting point of copper (for example, about 300 ° C.) to form a metal bond. That is, the first type particles can be bonded at a low temperature while having a particle size on the order of μm. In addition, since the nanostructures are fixed on the surface of the first type particles, the problems of aggregation and uneven distribution seen in the metal nanoparticles are unlikely to occur.

As described above, nanostructures can be formed on the surface by heating copper particles having a particle diameter of the order of μm (hereinafter sometimes referred to as “micro copper particles”).

The shape of the micro copper particles used as the raw material for the first type particles is not particularly limited, and examples thereof include a spherical shape, a lump shape, a needle shape, and a flake shape. Among these, the shape of the micro copper particles is preferably spherical or flaky because nanostructures are easily formed on the surface and the volume of voids between the particles when the particles are fused can be reduced. “Spherical” includes not only a perfect sphere but also a substantially spherical shape having an aspect ratio of 3 or less. “Flake shape” includes plate shapes such as plate shapes and scale shapes.

The particle size of the micro copper particles is preferably 1 to 100 μm. Since the particle size of the copper particles hardly changes before and after the formation of the nanostructure by heating, the particle size of the micro copper particles is substantially equal to the particle size of the first type particles. From the viewpoint of enhancing the dispersibility and facilitating the formation of the nanostructure, the particle size of the micro copper particles is preferably 2 μm or more, more preferably 3 μm or more, further preferably 3.5 μm or more, and particularly preferably 4 μm or more. From the viewpoint of enhancing the fusion between particles and reducing voids during bonding, the particle size of the micro copper particles is preferably 60 μm or less, more preferably 50 μm or less, further preferably 40 μm or less, and particularly preferably 30 μm or less. . Commercially available copper powder may be used as it is as the micro copper particles.

By setting the particle size of the micro copper particles within the above range, the particle size of the first type particles can be set within the range of 1 to 100 μm. The particle size of the first type particles is preferably 2 to 60 μm, more preferably 3 to 50 μm, still more preferably 3.5 to 40 μm, and particularly preferably 4 to 30 μm.

The nano structure is formed on the surface by heating the micro copper particles in an oxidizing atmosphere. The oxidizing atmosphere is an oxygen concentration atmosphere in which copper can be oxidized, and may be in the air (oxygen concentration of about 21%). The heating temperature is preferably 200 to 500 ° C. What is necessary is just to determine a heating time suitably so that a nanostructure may be formed on the surface of a micro copper particle according to heating temperature etc., for example, is about 5 to 300 minutes.

The reason why nanostructures are formed on the surface of micro copper particles by heating is not clear, but it is presumed that the difference in thermal expansion coefficient between copper and copper oxide (or cuprous oxide) is related. When the micro copper particles are heated in an oxidizing atmosphere, the surfaces of the copper particles are oxidized to form an oxide film. When further heating is performed in this state, oxidation proceeds from the surface of the particle toward the inside, and (sub-) copper oxide on the particle surface and copper in the core portion of the particle both thermally expand as the temperature rises. Copper has a larger coefficient of thermal expansion than copper oxide, so as the temperature rises, the internal copper expands the grain boundaries of the oxide film on the surface, and copper precipitates on the surface layer along the expanded grain boundaries. It is thought that copper is oxidized by being exposed to an oxidizing atmosphere, and nanostructures such as nanoparticles and nanofibers are formed.

As shown in FIG. 1, the nanostructure on the surface of the micro copper particles tends to grow as the heating temperature becomes higher and the heating time becomes longer. Moreover, the tendency for a fiber-like nanostructure (nanofiber) to be formed with an increase in heating temperature is observed. When nanofibers are formed on the surface of the first type particles, the fusion property of the copper particles tends to be improved. In order to form a fiber-like nanostructure, the temperature increase rate is decreased (for example, 5 ° C./min or less), or the temperature is increased stepwise to 350 ° C. or higher, and the temperature is 350 ° C. or higher. It is preferable to perform heating for 10 minutes or more. By gradually raising the temperature, it is considered that the deposition rate of the metal from the inside of the particle to the surface layer is controlled, and the precipitate is likely to grow in a fiber shape.

When the surface of the micro copper particle has an uneven or particulate nanostructure, the particle diameter of the nanostructure is preferably 500 nm or less, and more preferably 200 nm or less. When nanofibers are formed on the surface of the micro copper particles, the fiber diameter is preferably 100 nm or less, and more preferably 50 nm or less. Although the length of a fiber is not specifically limited, For example, it is 10 micrometers or less, Preferably it is 5 micrometers or less. When the size of the nanostructure is in the above range, good bondability at a low temperature (for example, about 200 to 500 ° C.) can be ensured. The size of the nanostructure is measured based on the SEM image of the particle.

(Second kind particles)
The second type particles are copper particles having an average particle diameter of 0.05 to 5 μm. The second type particles may have a nanostructure on the surface or may not have a nanostructure. The second type particles have an action of filling the gaps between the particles when the first type particles are fused and reducing the volume of the voids. Therefore, particles having an average particle diameter smaller than that of the first type particles are used as the second type particles.

In order to effectively fill the gap between the fused first type particles, the ratio D1 / D2 of the average particle size D2 of the second type particles to the average particle size D1 of the first type particles is preferably 2 or more. 5 or more is more preferable, and 3 or more is more preferable. On the other hand, D1 / D2 is preferably 550 or less, more preferably 300 or less, even more preferably 100 or less, and particularly preferably 50 or less, from the viewpoint of reducing the ratio of grain boundaries at the time of joining to ensure joining strength.

From the viewpoints of ensuring dispersibility and suppressing aggregation, and reducing the grain boundary at the time of joining, the average particle size of the second kind particles is preferably 0.07 μm or more, more preferably 0.1 μm or more, and 0.2 μm. The above is more preferable.

It is preferable that the second type particles have fusibility in a temperature range of 400 ° C. or lower. When the second type particles do not have a nanostructure on the surface, the average particle diameter D2 is preferably 4 μm or less, more preferably 3 μm or less, and even more preferably 2 μm or less in order to lower the melting point due to the size effect. When the second type particles have a nanostructure on the surface like the first type particles, low temperature fusion can be realized by the nanostructure, so the average particle diameter D2 of the second type particles is 5 μm or less. And the range of D1 / D2 may be within the above range.

The shape of the second type particles is not particularly limited, and examples thereof include a spherical shape, a block shape, a needle shape, and a flake shape. Especially, since the volume of the space | gap between particle | grains at the time of particle | grains fuse | melting can be made small, the shape of a 2nd seed particle has a preferable spherical shape or flake shape. As described above, the second type particles may have nanostructures formed on the surface.

The shape of the second type particles may be the same as or different from the shape of the first type particles. For example, both the first type particles and the second type particles may be spherical, the second type particles and the second type particles may both be flaky, and the first type particles may be flaky. The particles may be spherical, the first type particles may be spherical, and the second type particles may be flaky.

As the second kind particles, commercially available copper powder having an average particle size of 0.05 to 5 μm may be used as it is. Moreover, what formed the nanostructure on the surface by heat oxidation of commercially available copper powder can also be used.

(Other metal particles)
The copper paste may contain metal particles other than the first type particles and the second type particles. Examples of the metal particles other than the copper particles include copper nanoparticles, nickel, silver, gold, palladium, platinum and the like. The average particle size of metal particles other than copper particles is preferably about 0.01 to 50 μm. The amount of metal particles other than copper particles is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and still more preferably 5 parts by mass or less with respect to 100 parts by mass of the total amount of metal particles. In other words, the content of copper particles (including copper particles having an oxide nanostructure on the surface) with respect to 100 parts by mass of the total amount of metal particles is preferably 80 parts by mass or more, more preferably 90 parts by mass or more, and 95 masses. Part or more is more preferable. When the amount of the copper particles is within the above range, it becomes easy to ensure the bonding strength.

(Content of first type particles and second type particles)
As described above, the second type particles have an action of filling the gaps between the fused first type particles. What is necessary is just to set content of the 1st type particle | grains and 2nd type particle | grains in a metal particle so that 2nd type particle | grains may have the said effect | action according to ratio D1 / D2 of both particle diameters.

The content of the first type particles is preferably 20 to 95 parts by mass, more preferably 30 to 90 parts by mass, further preferably 35 to 85 parts by mass, and 40 to 80 parts by mass with respect to 100 parts by mass of the total amount of metal particles. Is particularly preferred. When the content of the first type particles is within the above range, high bonding strength and connection reliability due to fusion of the first type particles can be realized when the copper paste for pressureless bonding is sintered.

The content of the second kind particles is preferably 5 to 80 parts by mass, more preferably 10 to 70 parts by mass, further preferably 15 to 65 parts by mass, and 20 to 60 parts by mass with respect to 100 parts by mass of the total amount of metal particles. Is particularly preferred. If the content of the second type particles is within the above range, when the copper paste for pressureless bonding is sintered, the second type particles are easily efficiently filled in the gaps between the fused first type particles. . Therefore, the porosity can be reduced and the bonding strength can be improved. Further, the nanostructure on the surface of the first type particle is fused with the second type particle, and the bonding area is increased. For this reason, the bonding strength tends to increase as compared with the case where only the first type particles are included.

In order to promote fusion between the first type particles and efficiently fill the gaps between the first type particles with the second type particles, the amount of the second type particles is the amount of the first type particles. 0.05 to 5 times is preferable, 0.1 to 2 times is more preferable, 0.2 to 1.5 times is more preferable, and 0.25 to 1.3 times is particularly preferable.

<Dispersion medium>
The copper paste contains a dispersion medium (solvent) for dispersing the metal particles. The dispersion medium is not particularly limited as long as it can disperse the metal particles and can volatilize during sintering of the paste, and various aqueous solvents and organic solvents can be used. The boiling point of the dispersion medium is preferably about 150 to 400 ° C. A plurality of solvents having different boiling points may be mixed and used as a dispersion medium.

Specific examples of the dispersion medium include chain hydrocarbons, aromatic hydrocarbons, alicyclic hydrocarbons, chain alcohols, aromatic alcohols, alicyclic alcohols, polyhydric alcohols such as glycol and triol, ethers, glycol ethers. , Amines, amides, aldehydes, ketones and the like.

Among these, glycol or glycol ether is preferably used as the dispersion medium because of excellent dispersibility of the copper particles. Examples of the glycol include alkylene glycols such as ethylene glycol and propylene glycol, and polyalkylene glycols such as polyethylene glycol and polypropylene glycol (mainly having a molecular weight of 1000 or less). Examples of glycol ethers include polyalkylene glycol alkyl ethers such as diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monoethyl ether, tripropylene glycol monobutyl ether, and ester derivatives thereof ( For example, diethylene glycol monobutyl ether acetate).

The amount of the dispersion medium is about 5 to 100 parts by mass, preferably about 7 to 70 parts by mass with respect to 100 parts by mass of the metal particles. If content of a dispersion medium is in the said range, a metal particle can be disperse | distributed appropriately and the viscosity of a copper paste can be adjusted to a suitable range.

<Additives>
The copper paste may contain various additives as necessary. Examples of the additive include an antioxidant, a surfactant, an antifoaming agent, and an ion trapping agent.

As will be described later, the copper paste of the present invention promotes fusion of copper particles by heating in a reducing atmosphere. For the purpose of promoting copper fusion, the copper paste may contain a reducing agent. Reducing agents include sulfide, thiosulfate, oxalic acid, formic acid, ascorbic acid, aldehyde, hydrazine and its derivatives, hydroxylamine and its derivatives, dithiothreitol, phosphite, hydrophosphite, phosphorous acid and its derivatives Lithium aluminum hydride, diisobutylaluminum hydride, sodium borohydride and the like.

Copper paste contains resin components such as polyester resin, polyurethane resin such as blocked isocyanate, epoxy resin, acrylic resin, polyacrylamide resin, polyether resin, melamine resin, terpene resin, etc. It may be. These resin components can act as a binder for the metal particles. In addition, since the copper paste of the present invention can fill the voids between the first type particles by the second type particles having a smaller particle diameter than the first type particles, even when the resin component is not included, High bondability can be realized. In particular, when high electrical conductivity is required for the joint, the copper paste preferably does not substantially contain a resin component. The resin content in the copper paste is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, still more preferably 3 parts by mass or less, and particularly preferably 1 part by mass or less with respect to 100 parts by mass of the metal particles.

<Preparation of copper paste>
A copper paste can be prepared by mixing the above metal particles and any additive and a dispersion medium. The entire amount of the metal particles may be dispersed in the dispersion medium at once, or the remainder may be added after a part of the metal particles is dispersed. Further, after dispersing the second type particles, the first type particles may be added, or the first type particle dispersion and the second type particle dispersion may be mixed.

A stirring process may be performed after mixing the components. Moreover, you may remove an aggregate by classification operation before and after mixing of each component.

For the agitation treatment, Ishikawa-type stirrer, Silverson stirrer, cavitation stirrer, rotation and revolution type (planetary type) stirrer, ultra-thin film high-speed rotary disperser, ultrasonic disperser, reika machine, twin-screw kneader, bead mill, ball mill, A stirring / kneading device such as a three-roll mill, a homogenizer, a planetary mixer, an ultra-high pressure disperser, a thin-layer shear disperser, a wet ultra-fine atomizer, or a supersonic jet mill may be used.

Classification operation can be performed using filtration, natural sedimentation, and centrifugation. Examples of the filter for filtration include a water comb, a metal mesh, a metal filter, and a nylon mesh.

[Joint using copper paste]
The copper paste can be used for applications such as a conductive paste for forming various wirings and conductive films, and a bonding material for bonding a plurality of members. In particular, the above copper paste can realize high bondability by sintering in a reducing atmosphere, and is suitably used as a pressureless bonding paste.

In pressureless bonding, a laminate in which a copper paste is disposed between the first member and the second member is prepared, and the copper paste and the second member are disposed in a direction in which the weight of the first member acts, or The laminate is heated in a reducing atmosphere with a pressure of 0.01 MPa or less applied. When the copper paste is sintered by heating in a reducing atmosphere, fusion between the metal particles proceeds and the first member and the second member are joined.

(Preparation of laminate)
FIG. 2 is a cross-sectional view illustrating a configuration example of the laminate 10 in which the copper paste 5 is disposed between the first member 1 and the second member 2. Such a laminate can be prepared by, for example, providing the copper paste 5 in a predetermined region of the second member 2 and placing the first member 1 thereon.

The first member 1 and the second member 2 are not particularly limited, and various metal materials, semiconductor materials, ceramic materials, or resin materials can be used. Specific examples of the second member include a semiconductor substrate such as a silicon substrate; a metal substrate such as a copper substrate; a lead frame; a ceramic substrate with a metal plate (for example, DBC); a substrate for mounting a semiconductor element such as an LED package; a copper ribbon; Examples include power supply members such as blocks and terminals, heat sinks, and water cooling plates. Specific examples of the first member include a diode, a rectifier, a thyristor, a MOS gate driver, a power switch, a power MOSFET, an IGBT, a Schottky diode, a fast recovery diode, a power module, a transmitter, an amplifier, a sensor, and an analog integrated circuit. , Semiconductor laser, LED module and the like. The first member and the second member are not limited to the above. Moreover, what was mentioned above as an example of a 1st member is good also as a 2nd member, and what was mentioned above as an example of a 2nd member is good also as a 1st member.

The first member 1 and the second member 2 may contain a metal on the surface in contact with the copper paste 5 (joining material). Examples of the metal include copper, nickel, silver, gold, palladium, platinum, lead, tin, cobalt, manganese, aluminum, beryllium, titanium, chromium, iron, molybdenum, and alloys thereof.

As a method of providing the copper paste 5 as the bonding material on the second member 2, screen printing, transfer printing, offset printing, relief printing, intaglio printing, gravure printing, stencil printing, soft lithography, jet printing, dispenser, comma coat Various coating methods such as slit coating, die coating, gravure coating, bar coating, play coating, spin coating, and electrodeposition coating may be employed.

The thickness of the copper paste 5 (the thickness after drying the dispersion medium, that is, the thickness of the bonding layer) is, for example, about 1 to 1000 μm. The thickness of the bonding layer can be 10 μm or more, 30 μm or more, 50 μm or more, 70 μm or more, or 100 μm or more. The coating thickness can be 700 μm or less, 500 μm or less, 400 μm or less, 300 μm or less, or 200 μm or less.

The pressure-free bonding copper paste provided on the second member may be appropriately dried for the purpose of suppressing flow during sintering and generation of voids. The gas atmosphere at the time of drying may be air, an oxygen-free atmosphere, or a reducing atmosphere. Drying may be carried out at normal temperature and normal pressure, or may be accelerated by heating or reduced pressure.

For the arrangement of the first member 1 on the paste 5 provided on the second member 2, a chip mounter, a flip chip bonder, or the like may be used, or it may be performed manually using various jigs.

(Sintering)
The copper paste is sintered by heating the laminate. By heating in a reducing atmosphere, the (sub-) copper oxide nanostructure formed on the surface of the first-type particles is reduced to form a copper nanostructure. Progression of fusion proceeds. In the case where the second type particles have an oxide film or (sub-) cupric oxide nanostructure on the surface, the second type particles are also reduced in surface under a reducing atmosphere to promote fusion.

As the reducing atmosphere, there can be mentioned the presence of reducing gas such as hydrogen and formic acid. The reducing atmosphere gas may be a mixed gas of a reducing gas such as hydrogen or formic acid and an inert gas such as nitrogen or a rare gas. When the paste contains a reducing agent, heating may be performed in an oxidation-inhibiting atmosphere instead of using a reducing gas. In this case, the reducing agent is volatilized by heating to form a reducing atmosphere. Examples of the oxidation-inhibiting atmosphere include an inert gas atmosphere such as nitrogen and a rare gas, and a vacuum.

The maximum temperature reached during heating is preferably 200 to 500 ° C., and preferably 230 to 450 from the viewpoint of promoting volatilization of the dispersion medium and fusion of the metal particles while suppressing thermal damage to the first member and the second member. ° C is more preferable, and 250 to 400 ° C is more preferable.

The holding time in the above temperature range is preferably 1 minute or more and more preferably 5 minutes or more from the viewpoint of sufficiently promoting the volatilization of the dispersion medium and the fusion of the metal particles. The upper limit of the heating holding time is not particularly limited, but is preferably 60 minutes or less from the viewpoint of yield, process efficiency, and the like.

The die shear strength of the joined body in which the first member and the second member are joined via a copper paste sintered body (joining material) is preferably 20 MPa or more, more preferably 23 MPa or more, and further preferably 25 MPa or more. By using the copper paste, high shear strength can be realized by pressureless bonding at a low temperature below the melting point of copper.

As a presumable factor capable of realizing such a high bonding strength, the first type particles having a relatively large particle diameter have a nanostructure on the surface, so that low temperature fusion is possible and the first particle having a relatively small particle diameter. Since the two-type particles constitute a microstructure in which the voids between the first-type particles enter, and the sintering between the particles proceeds, it is possible to form a dense bonding layer with few voids. . The porosity in the cross section of the bonding layer after sintering the copper paste is preferably 25% or less, more preferably 20% or less, and even more preferably 15% or less. The porosity can be calculated from an SEM observation image of the bonded cross section (see FIG. 3).

In addition to the small number of voids, the use of microparticles reduces the volume shrinkage during sintering and suppresses strain in the bonding layer, which is considered to contribute to the improvement of bonding strength. Further, since the second type particles have a particle diameter that can be fused at a low temperature and hardly agglomerate, the fusion between the nanostructure on the first type particle surface and the second type particles and It is considered that the fusion between the second type particles proceeds and the bonding strength further increases. Furthermore, since the ratio D1 / D2 of the average particle diameter D1 of the first type particles and the average particle diameter D2 of the second type particles is within a predetermined range, the ratio of the grain boundary in the bonding layer is small. It is thought that it contributes to the rise of.

The joining method of the present invention can be applied to the manufacture of various electronic components and semiconductor devices. That is, the joined body obtained by joining a plurality of parts by sintering the copper paste of the present invention can be an electronic part or a semiconductor device. The joined body of the present invention has a high die shear strength at the joint and is excellent in connection reliability. In addition, since the bonding material is mainly made of copper and the voids are low by filling the voids between the first type particles with the second type particles, high thermal conductivity and electrical conductivity can also be realized.

Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the following examples.

[Preparation of copper particles]
Commercial products of the following A to I copper powders were prepared.
A: “Tn-Cu100” manufactured by Taiyo Nippon Sanso (spherical copper powder having an average particle size of 0.1 μm)
B: “1050YP” (flaky copper powder with an average particle size of 0.9 μm) manufactured by Mitsui Mining & Smelting
C: “MAC03K” manufactured by Mitsui Mining & Smelting Co., Ltd. (spherical copper powder with an average particle size of 3.0 μm)
D: “MAC03KP” manufactured by Mitsui Mining & Smelting Co., Ltd. (flaked copper powder having an average particle size of 4.0 μm)
E: “1400YM” manufactured by Mitsui Mining & Smelting Co., Ltd. (spherical copper powder having an average particle size of 4.2 μm)
F: “1400YP” manufactured by Mitsui Mining & Smelting Co., Ltd. (flaky copper powder having an average particle size of 5.2 μm)
G: “MA-CF” manufactured by Mitsui Mining & Smelting Co., Ltd. (flaky copper powder with an average particle size of 21.1 μm)
H: “Cu6500” manufactured by CuLox (spherical copper powder having an average particle diameter of 50 μm)
I: “MACNS” manufactured by Mitsui Mining & Smelting Co., Ltd. (spherical copper powder with an average particle size of 64 μm)

[Preparation of copper particles with nanofiber structure on the surface]
While stirring the above particles E under the atmosphere, the temperature was raised to 100 ° C. for 10 minutes, 150 ° C. for 10 minutes, 200 ° C. for 10 minutes, 250 ° C. for 10 minutes, 300 ° C. for 10 minutes, 350 ° C. And heated at 400 ° C. for 30 minutes. When the particles R after heating were observed with an SEM, almost no agglomerates were observed, and as shown in FIG. 1 (C2), fiber-like nanostructures were formed on the surface.

Using the above particles C, D, F, G, H, and I, heating is performed under the same conditions as the production of the particle R, and the particles P, Q, S, T, and U having a fiber-like nanostructure on the surface , V were produced.

[Example 1]
50 parts by mass of particles R as first type particles, 50 parts by mass of particles B as second type particles, and 30 parts by mass of tripropylene glycol monomethyl ether (MFTG; boiling point 242.4 ° C.) as a dispersion medium were mixed. Using a stirrer (“Mazerustar KK-V300” manufactured by Kurabo Industries) under reduced pressure, the mixture was subjected to planetary stirring at a revolution speed of 1340 rpm and a rotation speed of 737 rpm for 2 minutes to obtain a copper paste for pressureless joining.

[Examples 2 to 9 and Comparative Examples 1 to 6]
The compounding amounts of the metal particles and the solvent were changed as shown in Table 1 (the compounding values in Table 1 are parts by mass). Other than that was carried out similarly to Example 1, and obtained the copper paste.

[Evaluation]
(Preparation of die shear strength test sample)
After applying 0.009 g of copper paste to the center of a 20 mm × 20 mm copper plate (thickness 1 mm), contacting a 1 mm thick and 5 × 5 mm size Cu chip, the Cu chip was loaded with a load of 10 g. Lightly pressed to form a laminate.

This laminate was placed in a furnace of a reduction bonding apparatus (“RB-100” manufactured by Ayumi Industry), heated from room temperature to 130 ° C. over 4 minutes, and then kept at 130 ° C. for 5 minutes for preliminary drying. . Then, it heated up in 10 minutes from 130 degreeC to 300 degreeC. For the samples of Examples 1 to 9, Comparative Examples 1 to 3, and Comparative Example 6, the temperature was raised from room temperature to 300 ° C. in an air atmosphere. About the sample of the comparative example 4 and the comparative example 5, it heated up from room temperature to 300 degreeC by nitrogen atmosphere. After raising the temperature to 300 ° C., formic acid vapor was introduced into the furnace to form a formic acid atmosphere, and heating was performed at 300 ° C. for 30 minutes. After replacing the inside of the furnace with nitrogen gas and cooling to 35 ° C. or lower, a sample was taken out.

(Measurement of die shear strength)
Using a universal bond tester (4000 series manufactured by Nordson Advanced Technology) equipped with a DS-100 load cell, the die shear strength of the above sample was measured under the conditions of a measurement speed of 1 mm / min and a measurement height of 200 μm. .

Table 1 shows the compositions of the copper pastes of Examples and Comparative Examples, the ratio D1 / D2 of the average particle diameter of the metal particles in the copper paste, and the die shear strength of the joined sample. In Table 1, the content of the first type particles having a relatively large particle diameter is underlined. About the sample of Example 1 and Comparative Example 3, the SEM observation of the cross section was performed and the porosity was computed from the SEM photograph of FIG. 3 (A) (B).

In Comparative Example 1 and Comparative Example 2 using only copper particles having no nanostructure, the die shear strength of the bonded sample was less than 20 MPa. In Comparative Example 3 using only the micro copper particles having the nanostructure on the surface, the shear strength was further reduced as compared with Comparative Examples 1 and 2. The porosity of the bonded cross section of Comparative Example 3 obtained from FIG. 3 (B) was 30.4%.

In Examples 1 to 9, the metal particles include copper particles (second type particles) having a particle diameter smaller than that of the first type particles in addition to the micro particles (first type particles) having a nanostructure on the surface. However, the die shear strength was increased to 20 MPa or more. The porosity of the bonding cross section of Example 1 obtained from FIG. 3A is 11.5%, and the gap between particles in the order of μm is filled with fine particles. It was confirmed that the porosity was reduced. From these results, by using micro copper particles having nanostructures formed on the surface by heat oxidation and copper particles having a relatively small particle size, the voids between the micro copper particles are particles having a relatively small particle size. It can be seen that the bonding strength between the metal particles is enhanced and the bonding strength is increased.

Examples 8 and 9 using micro copper particles having a nanostructure on the surface as the second kind particles having a relatively small particle diameter also showed high bonding strength as in the other examples. On the other hand, in Comparative Example 4 and Comparative Example 5, similar to Comparative Example 1 and Comparative Example 2, two types of copper particles having different particle diameters were used, but the die shear strength was further lowered as compared with Comparative Examples 1 to 3. It was. From these results, in the examples, the nanostructure formed on the surface of the copper particles has the effect of promoting the fusion of the microparticles, so that the bonding strength is increased, whereas the nanostructure has In Comparative Examples 4 and 5 using microparticles that were not used, it was considered that the bonding strength was reduced because the microparticles were not fused together.

In Comparative Example 6 using the particle V having a nanostructure on the surface and an average particle diameter of 64 μm and the particle A having an average particle diameter of 0.1 μm, the microparticles having a nanostructure on the surface, a small particle diameter Despite the combined use of copper particles, the bonding strength was insufficient. In Comparative Example 6, since the D1 / D2 of the particle diameters of the two types of particles is large and the ratio of the grain boundaries is high, it is considered that the bonding strength has decreased. From this result, it is understood that high bondability can be realized by setting the ratio D1 / D2 of the average particle diameter of the first type particles and the second type particles within a predetermined range.

Claims

First type particles, and metal particles including second type particles having an average particle size smaller than the first type particles, and a dispersion medium,
The first type particles are copper particles having an average particle diameter of 1 to 100 μm and having a nanostructure on the surface,
The second kind particles are copper particles having an average particle diameter of 0.05 to 5 μm,
A copper paste, wherein the average particle size of the first type particles is 2 to 550 times the average particle size of the second type particles.
The copper paste according to claim 1, wherein the nanostructure of the first type particles is formed of a heated oxide of copper.
The copper paste according to claim 1 or 2, wherein the first type particles have a fiber-like nanostructure on the particle surface.
The copper paste according to any one of claims 1 to 3, wherein the average particle size of the first type particles is 3 to 50 µm, and the average particle size of the second type particles is 0.1 to 5 µm.
The copper paste according to any one of claims 1 to 4, comprising 5 to 100 parts by mass of the dispersion medium with respect to 100 parts by mass of the metal particles.
A laminated body provided with the copper paste according to any one of claims 1 to 5 between the first member and the second member is prepared,
A joining method in which the laminate is heated in a reducing atmosphere to sinter the copper paste.
A laminated body provided with the copper paste according to any one of claims 1 to 5 between the first member and the second member is prepared,
A method for manufacturing a joined body, wherein the first member and the second member are joined by heating the laminated body in a reducing atmosphere to sinter the copper paste.