JP7164313B2 - Nickel fine particle composition, bonded structure and bonding method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a nickel fine particle composition that can be used in the production of electronic parts, a bonding method and a bonding structure using the same.

2. Description of the Related Art In recent years, in efforts to save power, efforts have been made to improve power conversion efficiency in power converters such as inverters. Among them, practical use of SiC (silicon carbide) is being studied as a next-generation power device semiconductor material that can be expected to reduce power loss. However, while the operating temperature of current Si (silicon) power devices is about 125°C, SiC is expected to operate at 250°C or higher. A bonding material (hereinafter, also referred to as a "bonding material") for bonding two members (also referred to as a "bonding member") is required to have reliability during operation in a high temperature range of 250° C. or higher.

Conventionally, a solder material has been used as a joining material. Regarding this solder material, the RoHS Directive enforced in the EU in 2006 requires a lead-free solder material. not obtained.

Bonding materials using metal fine particles are being studied instead of solder materials. For example, in Patent Document 1, bonding strength of about 20 to 40 MPa is obtained by volatilizing a volatile component from a silver fine particle bonding material of submicron to several micrometer size at 200° C. and heating it at 300° C. or 350° C. there is

Also disclosed is a bonding material that uses lower-cost copper fine particles instead of silver fine particles. For example, in Patent Document 2, a bonding material containing copper nanoparticles with a particle size of 1 to 35 nm and copper particles with a particle size of 35 to 1000 nm is pressure-sintered in hydrogen at 400 ° C. for 5 minutes to achieve a high bonding strength of 40 MPa or more. Materials shown are proposed.

As described above, the development of metal fine particle bonding materials (also called “nano sintering bonding materials”) is progressing. However, there are problems such as coarsening of voids and embrittlement of the joint layer. On the other hand, although the copper fine particle system (copper sinter system) is low in cost, there is a problem that deterioration due to oxidation occurs, resulting in peeling, cracking, and the like.

Therefore, the present inventors have studied a nickel (Ni) microparticle-based bonding material that is low in cost, resistant to deterioration due to oxidation, and expected to have high reliability. For example, in Non-Patent Document 1, a bonding material using 90 nm Ni nanoparticles maintains a bonding strength of 10 MPa or more even after 1000 cycles in a thermal cycle test of -40 ° C to +250 ° C, and further cross-sectional observation It has been disclosed that no cracks are observed in the high reliability.

However, nickel has a thermal conductivity of 90.9 W/m K, which is lower than that of silver (420 W/m K) and copper (398 W/m K). Further improvement in heat dissipation, which is an important characteristic for

In addition, in practice, the joining material joins the members to be joined together and is responsible for heat conduction between them. There was a need to develop materials that could exhibit conductivity.

JP 2011-236494 A JP 2013-91835 A

Journal of Smart Process Society Vol. 4 No. 4 Pages 190-195

An object of the present invention is to provide a bonding material that achieves both high reliability and excellent thermal conductivity in a bonded state.

The present inventors have found that nickel fine particles with an average particle size of 30 to 200 nm that cause sintering between particles and volume shrinkage of the entire bonding layer are reduced, peeling between the members to be bonded is suppressed, and high thermal conductivity is achieved. The inventors have found that the above problems can be solved by a nickel fine particle composition containing filler particles that ensure the desired properties.

The nickel fine particle composition of the present invention comprises the following components A to B;
A) fine nickel particles having an average particle size in the range of 30 to 200 nm as measured by scanning electron microscopic observation of the cross section of the dried composition, and containing 50% or more of the nickel element in terms of atomic number concentration in the metal elements;
B) filler particles having the following conditions (i) to (iv):
(i) The average particle size calculated from cross-sectional observation with a scanning electron microscope of the dry composition is in the range of 0.5 to 100 μm;
(ii) is formed from a core portion and a coating portion that coats the surface of the core portion;
(iii) the total amount of metal elements in the core portion is 50% or more in atomic number concentration;
(iv) the coating contains at least one element selected from nickel, palladium, gold, and silver at an atomic concentration of 50% or more;
It is characterized by containing Here, the atomic number concentration in the metal element indicates the content of the target element when the total atomic number concentration of the metal and silicon is taken as 100%.

Further, in the nickel fine particle composition of the present invention, the core part of the component B contains at least one element selected from copper, silver, gold, platinum, aluminum, and silicon in an atomic number concentration of 50% or more of the metal elements. You can stay.

Further, in the nickel fine particle composition of the present invention, the core part of the component B may contain 50% or more of the copper element in terms of atomic number concentration in the metal elements. Further, the coating part of the component B may contain copper element within the range of 1 to 30% in terms of atomic number concentration in the metal elements.

Further, in the nickel fine particle composition of the present invention, the total amount of nickel elements contained in the composition and the weight ratio of the main elements in the core portion of the filler particles of the component B (nickel element: main element) is 5:95 ~ It may be 80:20. Here, the main element of the core portion means that three points at the central portion of arbitrary filler particles in the cross section of the dried composition are observed by energy dispersive X-ray analysis (EDX) attached to a transmission electron microscope, It refers to an element that is observed at an average atomic number concentration of 50% or more in the metal element.

Further, in the nickel fine particle composition of the present invention, the average thickness of the coated portion of component B may be in the range of 0.001 μm to 1 μm.

Further, in the nickel fine particle composition of the present invention, the weight ratio (solid content concentration) of the nickel fine particles of component A and the filler particles of component B is in the range of 70 to 96% by weight of the entire composition. It is characterized by

The nickel fine particle composition of the present invention may further contain an organic solvent having a boiling point within the range of 100 to 350° C., and the content of the organic solvent is 4 to 30% by weight based on the total composition. may be within the range. Furthermore, an organic binder may be contained within the range of 0.1 to 2.5% by weight with respect to the total amount of particles.

Further, the bonded structure of the present invention is characterized in that two members to be bonded are bonded by a bonding layer derived from filler particles having nickel fine particles and coating portions in the nickel fine particle composition.

In the bonding method of the present invention, the nickel fine particle composition is interposed between members to be joined and heated at a temperature within the range of 200 to 400° C. in a reducing gas atmosphere. A joining layer is formed between the members to join the members to be joined.

According to the nickel fine particle composition and the bonding method of the present invention, a bonding layer having excellent thermal conductivity is formed while maintaining low cost and high reliability, which are the features of nickel fine particle-based bonding materials. becomes possible. Therefore, for example, it can be suitably used as a bonding material for bonding a power semiconductor chip using SiC and a mounting substrate, which requires reliability during operation in a high temperature range of 250 ° C. or higher. It can also be used to manufacture other joint structures that require heat dissipation, such as joints between LEDs and electrodes.

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below.

<Nickel Fine Particle Composition>
The nickel fine particle composition of the present invention contains the following components A and B.
Component A) Fine nickel particles having an average particle size of 30 to 200 nm as measured by scanning electron microscopic observation of the cross section of the dried composition, and containing 50% or more of the nickel element in atomic number concentration in the metal elements. ,
Component B) Filler particles having an average particle diameter within the range of 0.5 to 100 μm calculated from cross-sectional observation of the dried composition with a scanning electron microscope, wherein the filler particles are formed from a core portion and a coating portion. The total amount of metal elements in the core portion is 50% or more in terms of atomic number concentration, and at least one element selected from nickel, palladium, gold, and silver is added to the surface of the core portion in terms of atomic number concentration in the metal elements. Filler particles, characterized in that a coating portion containing 50% or more is formed.
Form examples of component A and component B are described below.

(Component A: nickel microparticles)
Component A is fine particles containing 50% or more of a metal element including nickel in terms of atomic concentration, and has an average particle diameter within the range of 30 to 200 nm when observed with a scanning electron microscope. Here, the atomic number concentration can be measured by performing an energy dispersive X-ray analysis attached to a transmission electron microscope on a cross section of the dried composition. For example, when the present nickel fine particle composition is heated and sintered at a temperature of 300° C. to form a bonding layer, the average particle size of component A is preferably in the range of 30 to 100 nm. When sintering is performed by heating at a temperature of 0° C., the average particle size of component A is preferably in the range of 30 to 160 nm. If the average particle size of component A is less than 30 nm, component A tends to aggregate with each other, making uniform mixing with component B difficult. On the other hand, if the average particle size of component A exceeds 200 nm, the sintering between the nickel fine particles or between the nickel fine particles and the filler particles becomes insufficient, resulting in a decrease in reliability and thermal conductivity.

The average particle size of component A is measured by observing the cross section of the dried composition with a scanning electron microscope. The dried composition can be obtained, for example, by coating the composition on a glass substrate to a thickness of 100 μm or more and drying at 100° C. for 30 minutes. After embedding this dried body in epoxy resin, additional polishing and cross-section polisher treatment were performed to expose a cross section, and from a cross-sectional photograph of the cross-sectional sample obtained by a scanning electron microscope, 200 nickel fine particles were randomly selected. are extracted, the area of each is calculated, the particle diameter when converted to a true sphere (circle equivalent particle diameter) is calculated, and the average particle diameter is derived. Incidentally, how to distinguish the nickel fine particles in the cross-sectional observation can be confirmed from the information of the constituent elements obtained by performing the energy dispersive X-ray analysis attached to the transmission electron microscope for three points of the central portion of the particle.

In addition, component A contains 50% or more of the nickel element in terms of atomic number concentration in the metal elements. Within this range, the bonding layer formed using this material is less likely to deteriorate due to oxidation, so cracks in the bonding layer can be suppressed during long-term use, and deterioration in reliability and thermal conductivity can be avoided. The atomic number concentration in the metal element can be measured by subjecting the cross section of the dried composition to energy dispersive X-ray analysis attached to a transmission electron microscope. There are no restrictions on the method for producing component A, and various techniques such as a vapor phase method and a wet method can be used.

(Component B: Filler particles)
Component B is filler particles having an average particle diameter within the range of 0.5 to 100 μm calculated from cross-sectional observation of the dried composition with a scanning electron microscope, and the filler particles are formed from the core portion and the coating portion. It is formed. The total amount of metal elements in the core portion and the coating portion is 50% or more in atomic number concentration. Here, the atomic number concentration can be measured by performing an energy dispersive X-ray analysis attached to a transmission electron microscope on a cross section of the dried composition. The core portion is formed with a covering portion containing at least one of nickel, palladium, gold and silver in an atomic concentration of 50% or more of the metal elements.

Component B is present between the objects to be joined, and from the viewpoint of good heat conduction between the objects to be joined and from the viewpoint of suppressing volumetric shrinkage during the formation of the joining layer by heating, the dry composition is The average particle size calculated from cross-sectional observation with a scanning electron microscope is in the range of 0.5 to 100 μm, preferably 0.5 to 30 μm. If the average particle size of the component B is less than 0.5 μm, the volume shrinkage is large at the time of forming the bonding layer by heating, and the objects to be bonded are not sufficiently bonded to each other. lead to decline. On the other hand, if the average particle size of the component B exceeds 100 μm, problems such as poor applicability to the object to be bonded and difficulty in adjusting the thickness of the bonding layer occur.

The measurement of the average particle size of component B can be confirmed by observing the cross section of the dried composition with a scanning electron microscope. The particle size (equivalent circle particle size) is calculated from the dried composition in the same manner as for component A to derive the average particle size.

From the viewpoint of improving the thermal conductivity, it is preferable to use a metal having a higher thermal conductivity than nickel for the core portion of the component B. Here, the metal includes silicon. A material having a thermal conductivity of 100 W/m·K or more is more preferable in order to exhibit excellent thermal conductivity when the bonding layer is formed.

Components constituting the core portion of component B preferably include copper, silver, gold, platinum, aluminum, silicon, etc., which have a thermal conductivity of 100 W/m·K or more as a single substance. At least one of these elements is preferably contained in the core portion at an atomic concentration of 50% or more in the metal elements. Here, the atomic concentration in the metal element can be measured by subjecting a cross section of the dried composition to energy dispersive X-ray analysis attached to a transmission electron microscope. These may be contained alone or in combination of two or more. More preferably, from the viewpoint of achieving both high thermal conductivity and low cost, the core portion is preferably made of a material containing 50% or more of the copper element as the atomic concentration in the metal elements. Moreover, when the core portion is made of a material containing 50% or more of the copper element in atomic number concentration, the contained components other than the copper element are not limited. Preferred components other than copper are, for example, silver, gold, platinum, aluminum, and silicon each having a thermal conductivity of 100 W/m·K or more as an element. Various shapes such as a spherical shape, a polyhedral shape, a fibrous shape, a spike shape, and a flake shape can be used as the shape of the core portion.

The manufacturing method of the core part of component B is not limited, and a commercially available product may be used. For example, commercially available products such as copper powder manufactured by Fukuda Metal Foil & Powder Co., Ltd. (product name: Cu-HWQ) and copper powder manufactured by Furukawa Chemicals Co., Ltd. (product name: FMC-10C) can be preferably used.

In addition, the coating part of component B has the effect of promoting metal diffusion between the nickel fine particles, and by strengthening the adhesion between the core part and the nickel fine particles, as a result, it has the effect of improving reliability. . In addition, it promotes metal diffusion between the members to be joined and promotes adhesion between the core and the members to be joined. can be achieved, and high thermal conductivity can be realized not only in the bonding layer alone but also in the bonding structure. In addition, it has an effect of preventing oxidation of the core portion and contributes to an improvement in reliability. It should be noted that the main element forming the covering portion is preferably a metal element different from the main element forming the core portion. Here, the main elements of the core or coating are defined as three points in the central portion of the core of any filler particle in the cross section of the dried composition, or three points in the coating, and the energy dispersion attached to the transmission electron microscope It refers to an element that is observed at an average atomic number concentration of 50% or more in the metal element when observed by type X-ray analysis (EDX).

In the coated portion of component B, the content of at least one element selected from nickel, palladium, gold, and silver is 50% or more in terms of atomic number concentration in the metal elements. Below this concentration, the adhesion between the nickel microparticles and the filler particles and the adhesion between the member to be joined and the filler particles are deteriorated, so that the thermal conductivity and reliability of the joined structure are lowered. A preferable content of at least one element selected from nickel, palladium, gold, and silver is 60% or more in atomic number concentration. The elemental content of the coating portion is obtained by performing point analysis on three points of the coating portion by means of energy dispersive X-ray analysis attached to a transmission electron microscope and averaging the results. The boundary between the coating portion and the core is defined as the point where the component of the coating portion exhibits an atomic number concentration of 40% in line analysis by energy dispersive X-ray analysis attached to a transmission electron microscope.

A preferable element for forming the coating portion of component B is nickel or gold from the viewpoint of excellent interdiffusibility with nickel fine particles and higher reliability. Various shapes such as a spherical shape, a polyhedral shape, a fibrous shape, a spike shape, and a flake shape can be used for the outer shape of the covering portion.

Moreover, the covering portion may be an alloy with the main element constituting the core portion, provided that the content rate conditions are satisfied. For example, when the main element of the core portion is copper and the covering portion contains copper, the content of copper in the covering portion is preferably in the range of 1 to 30% in atomic number concentration. When the content of copper is 1% or more in atomic number concentration, the diffusion between the copper electrode of the member to be joined is promoted, peeling is suppressed, and the reliability is improved. If the copper content in the covering portion exceeds 30% in atomic number concentration, the oxidation resistance of the bonding layer decreases, leading to a decrease in reliability.

Also, the average thickness of the coated portion of component B is preferably in the range of 0.001 μm to 1 μm. When the average thickness of the coating is within this range, metal diffusion between the nickel fine particles and the coating and adhesion between the coating and the member to be joined occur sufficiently, resulting in high reliability and high heat resistance as a joint structure. Contributes to conductivity. The average thickness of the coated portion can be measured by cross-sectional observation of the dried composition containing component B with a transmission electron microscope.

In addition, the coating portion may not be formed on all the filler particles of the component B in the nickel fine particle composition, but it is formed on the core portion of 50% or more of the total filler particles in terms of quantity. preferably. The number of filler particles and core portions can be counted by cross-sectional observation of the dried composition with a scanning electron microscope. Furthermore, the covering portion does not necessarily have to cover the entire surface of the core portion, and the covering portion may be chipped, but the coverage is preferably 50% or more. Here, the coverage refers to the ratio of the peripheral length of the portion covered with the filler particles to the peripheral length of the core portion, and can be calculated from cross-sectional observation of the dried composition with a scanning electron microscope.

Various known techniques can be used to prepare Component B. For example, there is a method of forming a covering portion on the surface of the core portion (particle) by powder plating, sputtering, a liquid phase reduction method, or the like. When an alloy is formed in the covering portion, the metal concentration can be controlled by controlling the concentration of metal ions added in powder plating or the liquid phase reduction method, controlling the process time, and diffusing the metal with the core portion.

(weight ratio)
In the nickel fine particle composition, the weight ratio of the total amount of nickel elements contained in the composition to the main element of the core portion is preferably in the range of 5:95 to 80:20. By keeping the weight ratio of the total amount of nickel elements and the main elements of the core within this range, sufficient heat conduction paths can be formed in the bonding layer, contributing to improved thermal conductivity as a bonded structure. do. If the proportion of the nickel element is higher than the above range, volume shrinkage increases during the formation of the bonding layer, and reliability and thermal conductivity tend to decrease. Further, when the ratio of the main element in the core portion increases, the number of contact points between the nickel fine particles and the filler particles tends to decrease, resulting in a decrease in reliability and thermal conductivity.
Incidentally, the weight ratio is, for example, ICP emission spectroscopy (high frequency inductively coupled plasma emission spectroscopy, ICP-OES/ICP-AES) of the dried composition and/or energy dispersive X-ray attached to a scanning electron microscope It can be measured by cross-sectional observation of particles by analysis. In this method, for example, when nickel-coated filler particles are used, it is not possible to distinguish between nickel fine particles and a nickel-coated film, but the thermal conductivity of the bonded structure depends on the total amount of nickel elements in the composition and the amount of the core. Since it depends on the ratio of the amounts of the main elements, there is no problem in manifesting the action and effect.

The total content (solid concentration) of nickel fine particles and filler particles in the nickel fine particle composition is preferably in the range of 70 to 96% by weight, more preferably in the range of 85 to 95% by weight. If the content is less than 70% by weight, the thickness of the bonding layer may become thin. For example, it may be necessary to repeat coating several times, which may cause unevenness and may not provide sufficient bonding strength. . On the other hand, if the solid content concentration exceeds 96% by weight, the fluidity of the paste is lost, and usability tends to deteriorate, such as difficulty in application.

The nickel fine particle composition of the present embodiment can further contain an organic solvent having a boiling point within the range of 100 to 350° C. as an optional component. The boiling point of the solvent contained in the nickel fine particle composition is preferably within the range of 150 to 260° C. from the viewpoint of practical use. If the boiling point of the organic solvent used is less than 100°C, it tends to lack long-term stability. and the formation of intermetallic compounds. The nickel fine particle composition is preferably in the form of a paste by adding an organic solvent with a high boiling point and then concentrating the mixture.

As the solvent having a boiling point within the range of 100 to 350° C., for example, alcohol-based, aromatic-based, hydrocarbon-based, ester-based, ketone-based, and ether-based solvents can be used. Examples of alcohol solvents include 1-heptanol, 1-octanol, 2-octanol, 2-ethyl-1-hexanol, 1-nonanol, 3,5,5-trimethyl-1-hexanol, 1-decanol, 1- Aliphatic alcohols having 7 or more carbon atoms such as undecanol and isobornylcyclohexanol, ethylene glycol, diethylene glycol, propylene glycol, trimethylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butane Polyhydric alcohols such as diols, 1,6-hexanediol, 1,8-octanediol, tetramethylene glycol and methyltriglycol, terpineols such as α-terpineol, β-terpineol and γ-terpineol, and ethylene glycol mono Propyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, triethylene glycol monomethyl ether, triethylene glycol monobutyl ether, methylmethoxybutanol, diethylene glycol, dipropylene glycol, 2-phenoxyethanol, 1-phenoxy-2-propanol alcohols having an ether group such as Examples of hydrocarbon solvents include octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, and pentadecane.

The content of the organic solvent in the nickel fine particle composition of the present embodiment is preferably within the range of 4 to 30% by weight, preferably within the range of 5 to 15% by weight, relative to the entire composition. If the content of the organic solvent in the bonding material is less than 4% by weight, the fluidity tends to be low and usability as the bonding material is reduced. On the other hand, if the content of the organic solvent exceeds 30% by weight, for example, it becomes necessary to repeat coating several times, which causes unevenness, and there is a tendency that sufficient bonding strength cannot be obtained.

In addition, the nickel fine particle composition of the present invention may contain an organic binder as an optional component. The organic binder connects the nickel microparticles of component A and the filler particles of component B to form a wide-ranging network structure, thereby contributing to the formation of a massive bonding layer with high bonding strength.

As the organic binder, any binder that can be dissolved in an organic solvent can be used without particular limitation. Thermoplastic resins such as resins, acrylic resins, methacrylic resins, nylon resins, acetal resins, and polyvinyl acetal resins can be used. Among these, a polyvinyl acetal resin is preferable, and a polyvinyl acetal resin having an acetal group unit, an acetyl group unit, and a hydroxyl group unit in the molecule is more preferable.

Further, the organic binder preferably has a molecular weight of 30,000 or more, more preferably 100,000 or more, in order to suppress sedimentation of the components A and B and maintain a sufficiently dispersed state.

As the organic binder, commercially available products such as polyvinyl acetal resin (S-lec BH-A; trade name) manufactured by Sekisui Chemical Co., Ltd. can be preferably used.

The amount of the organic binder in the nickel fine particle composition is preferably in the range of 0.1 to 2.5% by weight, more preferably 0.3 to 1.5% by weight, based on the total amount of particles. % by weight, more preferably 0.5 to 1.2% by weight. Here, "total particle amount" means the total weight of component A and component B. If the amount of the organic binder blended exceeds the above range, the sintering between component A and component B tends to be insufficient.

In addition to the components described above, the nickel fine particle composition may contain optional components such as a thickening agent, a thixotropic agent, a leveling agent, and a surfactant.

(Preparation of nickel fine particle composition)
The nickel fine particle composition can be prepared by homogeneously mixing the nickel fine particles of component A, the filler particles of component B, and optional components. The mixing method is not particularly limited, and known mixing means such as a mixer can be used.

(Joining method)
In addition, the nickel fine particle composition is interposed as a bonding material between members to be bonded, and in a reducing gas atmosphere, for example, at a temperature within the range of 200 to 400°C, preferably within the range of 230 to 350°C. By heating, a bonding layer can be formed between the members to be joined, and the members to be joined can be joined together. Here, "under a reducing gas atmosphere" includes an atmosphere containing hydrogen gas and an atmosphere containing formic acid. Preferably, the atmosphere is an atmosphere containing hydrogen gas, which has good reduction efficiency.
In this bonding method (hereinafter referred to as "this bonding method"), in order to promote sintering between the A components or between the A component and the B component, the surfaces of the coated portions of the A component and the B component are exposed. is considered necessary. The heating temperature for volatilizing or decomposing the organic substances present on these surfaces and removing the passivation layer is preferably 200° C. or higher, more preferably 250° C. or higher. On the other hand, if the heating temperature exceeds 400° C., the periphery of the semiconductor device as the member to be joined may be damaged.

This bonding method includes, for example, a step of applying a paste-like bonding material to the surfaces to be bonded of one or both of a pair of members to be bonded (application step), bonding the surfaces to be bonded together, preferably at a temperature of 200 to 400 ° C. , more preferably 250 to 400°C, more preferably 250 to 350°C, to sinter the bonding material (firing step).

In the coating step, for example, methods such as spray coating, inkjet coating, and printing can be employed. The bonding material can be applied in an arbitrary shape such as pattern, island, mesh, grid, stripe, etc., depending on the purpose. In the coating step, it is preferable to apply the bonding material so that the coating film has a thickness of, for example, 50 to 200 μm. By applying the coating with such a thickness, defects in the joint portion can be reduced, so that an increase in electrical resistance and a decrease in joint strength can be prevented.

In addition, in the firing step, the members to be joined are joined under pressure or under no pressure. When it is carried out under pressure, the pressure is preferably 40 MPa or less. By manufacturing under 40 MPa or less or under no pressure, the firing process can be simplified.

Through the steps described above, it is possible to manufacture a bonded structure in which two members to be bonded are bonded by a bonding layer derived from filler particles having nickel fine particles and a coating portion in the nickel fine particle composition.

This bonding method can be used, for example, in the bonding of Si-based and SiC-based semiconductor materials and in the manufacturing process of electronic parts. Here, as electronic parts, mainly semiconductor devices, energy conversion module parts, etc. can be exemplified. When the electronic component is a semiconductor device, for example, between the back surface of the semiconductor element and the substrate, between the semiconductor electrode and the substrate electrode, between the semiconductor electrode and the semiconductor electrode, between the power device or power module and the heat dissipation member It can be applied to joining such as

When bonding electronic components, in order to increase bonding strength, a contact layer made of Au, Cu, Pd, Ni, Ag, Cr, Ti, or alloys thereof is provided on one or both of the surfaces to be bonded in advance. It is preferable to provide When the material of the surfaces to be joined is SiC, Si, or an oxide film on their surfaces, a contact layer made of Ti, TiW, TiN, Cr, Ni, Pd, V, or alloys thereof is used. It is preferable to provide

In the above bonding structure, nickel forms an oxide passivation film of nickel oxide on the metal surface in the air, which can suppress the progress of oxidation beyond a certain level. , the occurrence of cracks and bonding interface detachment can be suppressed, resulting in high bonding reliability. Reliability can be evaluated, for example, by bonding a Si die and a heat dissipation substrate using a nickel fine particle composition, conducting a thermal cycle test under atmospheric conditions, and evaluating the change in die shear strength.

The nickel fine particle composition of the present invention has the effect of forming a heat transfer path by the filler particles of the B component having high thermal conductivity dispersed in the bonding layer, and the nickel fine particles having oxidation resistance and the filler particles that suppress shrinkage of the bonding layer. The thermal conductivity of the entire bonding layer is improved due to the effect of suppressing cracks. In addition, since the filler particles have an effect of promoting adhesion with the member to be joined by the coated portion and an effect of suppressing interfacial peeling from the member to be joined by suppressing shrinkage of the joining layer, the filler particles can be obtained using the nickel fine particle composition of the present invention. The bonded structure does not generate heat insulation due to interfacial peeling and exhibits high thermal conductivity.

Therefore, the nickel fine particle composition of the present invention can achieve both high reliability and high thermal conductivity, and can be particularly suitably used for various uses in high temperature ranges. For example, it can be suitably used as a bonding material for bonding a power semiconductor chip using SiC and a mounting substrate, which require reliability during operation in a high temperature range of 250° C. or higher. In addition, it can be used for joining a semiconductor chip and a mounting substrate using Si, joining an LED and an electrode, and the like.

EXAMPLES Examples are given below to more specifically describe the features of the present invention. However, the present invention is not restricted by the examples. In the following examples, unless otherwise specified, various measurements and evaluations are as follows.

[Preparation of nickel fine particle slurry]
A nickel fine particle slurry was prepared according to the following procedure. Tables 1 and 2 show the amounts of reagents used, heat treatment times, and the like.

[Synthesis Example 1]
To 182 parts by weight (910 g) of oleylamine was added 18.5 parts by weight (92.5 g) of nickel formate dihydrate and the nickel salt was dissolved by heating at 120° C. for 10 minutes under nitrogen gas flow. , to obtain a complexing reaction solution 1 (the above is the complexing reaction step). 121 parts by weight (605 g) of oleylamine was added to this complexing reaction liquid 1, and the mixture was heated at 180° C. for 10 minutes using microwaves to obtain nickel fine particle slurry 1 (the above is the heat treatment step).

[Preparation of slurry]
100 parts by weight of the resulting nickel fine particle slurry 1 was taken, 20 parts by weight of octanoic acid was added thereto, stirred for 15 minutes, and then washed with toluene to obtain nickel slurry 1 (solid concentration: 65.0% by weight). prepared (above, nickel slurry preparation step).
The amounts of reagents and process conditions, and the solids concentration of Nickel Slurry 1 are shown in Tables 1 and 2.

[Synthesis Examples 2 to 4]
Complexing reaction liquids 2 to 4, nickel fine particle slurries 2 to 4, and nickel slurry were prepared in the same manner as in Synthesis Example 1, except that the parts by weight of each raw material, the reaction temperature, and the reaction time were as shown in Tables 1 and 2. 2-4 were obtained. The amounts of reagents and process conditions, as well as the solids concentrations of nickel slurries 2-4 are shown in Tables 1 and 2.

[Preparation of nickel paste]
A nickel paste was prepared according to the following procedure. Tables 3 and 5 show the names and amounts of reagents used.

[Example 1]
A copper particle (FMC-10C manufactured by Furukawa Chemicals Co., Ltd.) serving as a core portion was coated with nickel by a reduction method to prepare filler particles having a copper particle core portion and a nickel coating portion.
Next, 100 parts by weight of nickel slurry 1, 160 parts by weight of filler particles, 16.0 parts by weight of hexyl carbitol as a solvent, and 1 part of polyvinyl acetal resin (S-Lec BH-A; manufactured by Sekisui Chemical Co., Ltd.) as a binder resin. .23 parts by weight of each were weighed and mixed, and concentrated at 60° C. and 100 hPa to obtain 245 parts by weight of nickel paste 1 (solid concentration: 93% by weight).

[Examples 2 to 28, Comparative Examples 1 to 4]
A nickel paste was obtained in the same manner as in Example 1, except that the composition of the raw material used and the type of the covering portion of the filler particles were as shown in Tables 3 and 5. In the nickel paste of Comparative Example 1, nickel particles having no coating portion were used as the filler particles, and in the nickel pastes of Comparative Examples 2 and 3, copper particles having no coating portion were used as the filler particles. As Comparative Example 4, general-purpose lead-free solder (tin-silver-copper) was used.

[Preparation of sample for thermal conductivity measurement]
Using a stainless steel mask (mask width; 10.0 mm × length; 10.0 mm × thickness; 0.3 mm), nickel paste is applied to a copper substrate (10 mm × 10 mm × 1 mmt) to form a coating film. and sandwiched between copper substrates (10 mm×10 mm×1 mmt). This was fired under a nitrogen gas flow mixed with 3% by volume of hydrogen. The obtained sintered body was used as a sample for thermal conductivity measurement.

[Evaluation of thermal conductivity]
Thermal conductivity was evaluated by measuring the thermal conductivity of the joint structure by the laser flash method using the sample for thermal conductivity measurement. A case of 5 times or more and less than 2 times was evaluated as ◯, and a case of less than 1.5 times was evaluated as X.

[Preparation of bonded sample]
The sample was applied to the substrate using a stainless steel mask (mask width: 2.0 mm x length: 2.0 mm x thickness: 0.1 mm). The substrate is a Ni-plated copper-laminated silicon nitride substrate (15 mm × 15 mm × 0.9 mmt) for reliability evaluation 1, and a copper-laminated silicon nitride substrate (15 mm × 15 mm × 0.9 mmt) for reliability evaluation 2. was used. After preheating the substrate on which the coating film was formed, a silicon die (width: 2.0 mm × length: 2.0 mm × thickness: 0.40 mm) was mounted, and 3% by volume of hydrogen was mixed. Firing was performed under nitrogen gas flow. The silicon die was formed by sputtering an Au film on the bonding surface of a Si substrate (thickness: 0.40 mm).

[Cold-heat cycle test]
Using the bonded sample prepared in the previous section, a -40°C/200°C thermal cycle test was performed for 1,000 cycles in the air. The holding time at each temperature was 30 minutes.

[Reliability evaluation]
[Die shear strength measurement]
The evaluation of the bonded sample after the thermal cycle test was performed by measuring the die shear strength of the test piece. A bonding strength tester (manufactured by Daisy Japan Co., Ltd., trade name: Bond Tester 4000) was used as an apparatus. A bond tester tool was pressed from the side of the die at a height of 50 μm from the substrate at a tool speed of 100 μm/sec, and the load at which the bond was sheared was defined as the shear strength (die shear strength). A shear strength of 20 MPa or more was evaluated as ⊚, a shear strength of 10 MPa or more and less than 20 MPa was evaluated as ◯, and a shear strength of less than 10 MPa was evaluated as x.

Tables 3, 4, 5 and 6 show the raw materials used, the average particle size and composition, the properties of the filler particles, the evaluation results of thermal conductivity, and the evaluation results of reliability.

In each example, by using a nickel paste containing highly thermally conductive filler particles, Comparative Example 1 using nickel particles as filler particles and Comparative Example using copper particles having no coating portion as filler particles 2 and Comparative Example 3, and the nickel paste of Comparative Example 3, and Comparative Example 4 using a general-purpose lead-free solder, it was confirmed that the thermal conductivity of the joint structure was improved. Moreover, the reliability of each example was substantially the same as that of Comparative Example 1, and it was confirmed that the examples could be suitably used as a bonding material.

Although the embodiments of the present invention have been described in detail for purposes of illustration, the present invention is not limited to the above embodiments.

Claims (7)

A nickel fine particle composition containing a component A and a component B,
Component A is nickel microparticles having an average particle size within the range of 30 to 200 nm as measured by scanning electron microscopic observation of the cross section of the dried composition, and containing 91% or more of the nickel element in atomic number concentration . can be,
Component B is a filler particle that satisfies the following conditions (i) to (iv):
(i) an average particle size of 0.5 to 100 μm as measured by scanning electron microscopic observation of a cross section of the dry composition;
(ii) formed from a core portion and a covering portion covering the core portion;
(iii) the core portion has a higher thermal conductivity than nickel and contains one or more metal elements selected from copper, silver, gold, platinum, aluminum, and silicon;
(iv) The coating portion contains at least one element selected from nickel, palladium, gold, and silver, or an alloy of these elements and the element constituting the core portion at an atomic concentration of 90% or more ;
and
The total amount of nickel elements contained in the composition and the weight ratio of the main elements in the core portion of the filler particles of component B (nickel element: main element) is 5:95 to 80:20 [here, the core part is the main element, when observing the energy dispersive X-ray analysis (EDX) attached to a transmission electron microscope for three points in the center of the core of any filler particle in the cross section of the dried composition, metal Means an element that is observed at an average atomic number concentration of 50% or more in the element],
A nickel fine particle composition, wherein the average thickness of the coated portion of component B is in the range of 0.001 μm to 1 μm. 2. The nickel fine particle composition according to claim 1, wherein the coating part of the component B contains the copper element within the range of 1 to 30% in terms of atomic concentration of the metal elements. The nickel according to claim 1 or 2, wherein the weight ratio of the nickel fine particles of component A and the filler particles of component B is in the range of 70 to 96% by weight with respect to the entire composition. fine particle composition. 4. The nickel microparticles according to claim 3, which contain an organic solvent having a boiling point in the range of 100 to 350° C., and the content of the organic solvent is in the range of 4 to 30% by weight with respect to the entire composition. Composition. 5. The nickel fine particle composition according to claim 3, further comprising an organic binder in the range of 0.1 to 2.5% by weight with respect to the total amount of particles. Two members to be joined are joined by a joining layer derived from filler particles having nickel fine particles and a coating portion in the nickel fine particle composition according to any one of claims 3 to 5. junction structure. The nickel fine particle composition according to any one of claims 3 to 5 is interposed between members to be joined and heated at a temperature within the range of 200°C to 400°C in a reducing gas atmosphere. A joining method, wherein a joining layer is formed between members to be joined, and the members to be joined are joined to each other.