WO2022185600A1

WO2022185600A1 - Conductive composition, conductive member, and method for producing same

Info

Publication number: WO2022185600A1
Application number: PCT/JP2021/038153
Authority: WO
Inventors: 良憲清水; 貴彦坂上; 圭穴井; 真一山内
Original assignee: 三井金属鉱業株式会社
Priority date: 2021-03-02
Filing date: 2021-10-15
Publication date: 2022-09-09
Also published as: JPWO2022185600A1

Abstract

This conductive composition includes: first copper particles composed of a copper element; second copper particles composed of a copper element as a main component, and a second element other than a copper element, an oxygen element, a carbon element, and a nitrogen element; and a dispersion medium. The copper element and the second element are present, in a state of at least one among an alloy and a mixture, in at least a portion of the second copper particles. An integral value of the ratio (P2/P1) of a detection intensity P2 of the second element to a detection intensity P1 of the copper element is 7 to 20, when the conductive composition is measured in a region down to a depth of 50 nm from an outermost surface by X-ray photoelectron spectroscopy.

Description

Conductive composition, conductive member and manufacturing method thereof

The present invention relates to a conductive composition, a conductive member, and a method for producing the same.

Devices using SiC and GaN are being developed as next-generation power devices. In particular, devices using SiC are expected to have excellent high-temperature operability and high-speed operability. On the other hand, since devices using SiC can operate at high temperatures, peripheral members such as die bonding materials may not have sufficient heat resistance and bonding reliability due to the heat generated within the device.

Patent Document 1 discloses a copper alloy powder containing alloy particles of copper and silver, in which the silver concentration on the surface of the particles is higher than the average silver concentration of the particles, for the purpose of reducing the resistance of the conductive circuit. The document also discloses that this copper alloy powder can be produced by an inert gas atomization method.

Further, in Patent Document 2, for the purpose of increasing the bonding strength, Cu nanoparticles made of Cu particles having a particle size of 1000 nm or less and having an average particle size of 50 nm to 1000 nm and fine particles having an average particle size of 1 nm to 50 nm A metal nanoparticle mixture consisting of CuNi alloy nanoparticles is disclosed.

JP-A-07-331360 JP 2015-141860 A

Both the particles of

Patent Documents

1 and 2 are not sufficient from the viewpoint of bonding reliability when used as a constituent material of a device, and further improvement is desired.

Therefore, an object of the present invention is to provide a conductive composition that can exhibit high bonding reliability with other members.

The present invention provides first copper particles made of a copper element,
a second copper particle containing a copper element as a main component and containing a second element other than copper, oxygen, carbon and nitrogen;
a dispersion medium,
The copper element and the second element are present in at least a part of the second copper particles in the state of one or more of alloys and mixtures,
The integrated value of the ratio of the detected intensity P2 of the second element to the detected intensity P1 of the copper element (P2/P1) is 7 or more and 20 or less when measured in a region from the outermost surface to a depth of 50 nm by X-ray photoelectron spectroscopy. It provides a conductive composition.

FIG. 1 is a schematic diagram showing an example of a DC plasma apparatus capable of suitably producing the cupric particles contained in the conductive composition of the present invention. 2 is an ultrasonic image of a bonded structure formed using the conductive composition of Example 1. FIG. 3 is an ultrasonic image of a joint structure formed using the conductive composition of Comparative Example 1. FIG.

The present invention will be described below based on its preferred embodiments. The conductive composition of the present invention contains two types of copper particles, first copper particles and second copper particles, and a dispersion medium.

The first copper particles are composed of the copper element and do not contain other elements other than the copper element except for inevitable impurities. That is, the first copper particles inevitably contain other elements other than the copper element, and the surface of the first copper particles is inevitably slightly oxidized, so that the oxygen element is inevitably Containment is allowed.
Usually, the content of elements other than the copper element in the first copper particles is 5% by mass or less. The content of these elements can be measured by, for example, ICP emission spectrometry or inert gas fusion/non-dispersive infrared absorption method.

The cupric particles mainly contain a copper element, and further contain a second element that is an element other than copper (Cu), oxygen (O), carbon (C) and nitrogen (N). In addition, the second copper particles inevitably contain an element other than the copper element and the second element, or the surface of the second copper particles is inevitably slightly oxidized, so that the oxygen element is inevitably included. is allowed.

The content of the copper element in the cupric particles is 50 mass % or more, preferably 60 mass % or more and 99 mass % or less, more preferably 80 mass % or more and 97 mass % or less. When the content of the copper element in the second copper particles is within such a range, high electrical conductivity and thermal conductivity derived from copper are exhibited, and electrical conductivity with improved bonding reliability with other members It becomes a composition. The copper element content can be measured, for example, by ICP emission spectrometry.

The content of the second element with respect to 100% by mass of the copper element in the second copper particles is preferably 1% by mass or more and 40% by mass or less, more preferably 3% by mass or more and 20% by mass or less. When the content of the second element is in such a range, the second copper particles exhibit excessive thermal expansion and heat caused by rapid temperature changes while exhibiting high electrical conductivity and thermal conductivity derived from copper. Since the function of relieving shrinkage is exhibited, the conductive composition has high heat resistance and high bonding reliability. The content of the second element can be measured, for example, by ICP emission spectrometry.

The second element that can be contained in the cupric particles includes, for example, one or more metal elements other than copper or metalloid elements. Specifically, the metal elements include gold (Au), silver (Ag), palladium (Pd), yttrium (Y), titanium (Ti), zirconium (Zr), niobium (Nb), tantalum (Ta), molybdenum ( Mo), tungsten (W), cobalt (Co), transition metal elements such as nickel (Ni), alkaline earth metal elements such as magnesium (Mg), and other metal elements such as aluminum (Al). . Moreover, silicon (Si) etc. are mentioned as a metalloid element.

The second element contained in the second copper particles preferably exists in at least a part of the particles in one or more states of an alloy and a mixture, depending on the type of element. The alloy includes at least one aspect of solid solution, eutectic, and intermetallic compound. A specific mode of existence of the copper element and the second element in the second copper particles is, for example, a solid solution in which the second element is dissolved in copper, or a single substance of copper or a copper compound and a single substance of the second element or a second element. One or more of aspects such as a mixture with a two-element compound are included. Examples of the second element compound include oxides, nitrides, and carbides.
Existence of the second element in such a manner alleviates excessive thermal expansion and contraction caused by temperature changes when the conductive composition is subjected to firing, resulting in excellent bonding reliability. The mode of existence of these elements can be measured, for example, by a method such as X-ray diffraction analysis. The second copper particles containing the second element in the manner described above can be suitably produced, for example, by the production method described below.

When a metal element is included as the second element contained in the cupric particles, the metal element may exist as a single substance, or may exist as a copper-based alloy as a solid solution. Intermetallic compounds can also be taken as one form of copper-based alloys. In addition to or instead of this, the metal element and semimetal element contained as the second element are present in the form of one or more oxides, nitrides or carbides, and in the second copper particles, It may be copper alone, a copper-containing alloy, or a mixture with a copper-containing compound.

Examples of the second element that can form an alloy with copper include one or more metal elements selected from Au, Ag, Pd, Ti, Mo, W, Co, Ni, and Al.

Examples of the second element capable of forming an oxide include metal elements such as Y, Ti, Zr, Nb, Mg, and Al, and metalloid elements such as Si, and at least one element. Specific examples of oxides of the second element include Y ₂ O ₃ , TiO ₂ , ZrO ₂ , Nb ₂ O ₅ , MgO, Al ₂ O ₃ and SiO ₂ .

Examples of the second element capable of forming carbides include metal elements such as Nb and Ta, and metalloid elements such as Si. Specific examples of carbides of the second element include NbC, TaC, SiC, and the like.

Examples of the second element capable of forming a nitride include one or more of metal elements such as Al and metalloid elements such as Si. Specific examples of the nitride of the _second element include AlN, _Si3N4 , and the like.

Among these, the second element is more preferably one or more of Ag, Co, and Zr from the viewpoint of further increasing the bonding strength and improving the reliability of bonding with the member to be bonded. More preferably, it is one or more elements of Co. In this case, the mode of existence of the copper element and the second element in the second copper particles may be an alloy with copper or a mixture of copper and the oxide of the second element. In particular, when the second element is Ag, good electrical conductivity and thermal conductivity are maintained, and the solid solubility of Ag in copper is good, so that heat resistance and bonding strength are likely to be higher. Therefore, it is possible to form a bonding layer with less crack generation even when an excessive temperature change occurs.

In the second copper particles, it is preferable that the abundance ratios of the copper element and the second element in the particles are different between the particle surface and the inside. Specifically, the region from the outermost surface of the conductive composition to a sputtering depth of 50 nm in terms of SiO ₂ is measured by X-ray photoelectron spectroscopic analysis. At this time, the integrated value of the ratio of the detection intensity P2 of the second element to the detection intensity P1 of the copper element (hereinafter also referred to as "P2/P1 ratio") is preferably 7 or more, more preferably 9 or more, It is more preferably 10 or more. Also, the integrated value of the P2/P1 ratio is preferably 20 or less, more preferably 16 or less.

The integral value of the P2/P1 ratio described above indicates that the relative abundance of the copper element increases continuously or stepwise when the conductive composition is observed from the surface toward the inside. . This means that the relative existence ratio of the copper element increases continuously or stepwise from the surface to the center of the second copper particles existing on the outermost surface of the conductive composition. The integrated value of the P2/P1 ratio tends to exceed 20 and increase as the copper element and the second element are uniformly present in the second copper particles. In the case of copper particles in which a shell layer containing a second element is clearly observed on the surface of a core particle made of copper, the integrated value of the P2/P1 ratio tends to be small.
Therefore, since the integrated value of the P2/P1 ratio is within the range described above, the second element is relatively abundant on the surface of the second copper particles, and the copper element is relatively present in the center of the second copper particles. This indicates that there are many Due to this, it is possible to alleviate excessive thermal expansion and contraction due to temperature changes when the conductive composition is subjected to firing while expressing high conductivity and thermal conductivity derived from copper. . As a result, when the conductive composition containing the second copper particles is used to join objects to be joined, the conductivity is sufficiently exhibited, the heat resistance is high, and structural destruction is less likely to occur. , the bonding reliability is further increased. The cupric particles having the integral value of the ratio described above can be suitably produced, for example, by the production method described below.

X-ray photoelectron spectroscopy can be performed, for example, by the following method. That is, the conductive composition is introduced into an X-ray photoelectron spectrometer (Ulvac-Phi, VersaProbe III) and measured under the following conditions, and the sputtering depth in terms of _SiO2 from the outermost surface of the conductive composition The P2/P1 ratio in each region down to 50 nm is obtained respectively.
After that, after converting the minimum value of the P2/P1 ratio to zero, the P2/P1 ratio at each sputtering depth when the measured value of the P2/P1 ratio at the outermost surface is converted to 1 is taken on the vertical axis, From the graph in which the sputtering depth (nm) is taken on the horizontal axis, the integral value of the P2 / P1 ratio from the outermost surface of the conductive composition (corresponding to a sputtering depth of 0 mm) to a sputtering depth of 50 nm is calculated. This is the integral value of the present invention.

<Measurement conditions for X-ray photoelectron spectroscopy>
AlKα1 ray (1486.8 eV) was used as the X-ray source, X-ray irradiation area: 200 μmφ, pass energy: 23.5 eV, angle between sample and detector: 15°, measured sputter depth: 50 nm (in terms of SiO ₂ ). , measurement interval: 0.1 eV, tube voltage: 15 kV, tube current: 2.67 mA, and scanning is performed 10 times for each element. For data analysis, "Multipack Ver6.1A" manufactured by ULVAC-PHI is used.

Various shapes such as spherical, scale-like (flake-like), dendrite-like (dendritic) and polyhedral-like shapes can be independently adopted for each shape of the first copper particles and the second copper particles.

The particle diameter of the cuprous particles contained in the conductive composition is preferably 30 nm or more and 600 nm or less, more preferably 80 nm or more and 400 nm or less, and still more preferably 100 nm or more and 200 nm or less when the shape is spherical. When the cuprous particles have such a particle diameter, high sinterability at low temperatures is achieved while exhibiting high dispersibility between particles.

That the particles are spherical means that the circularity coefficient measured by the following method is preferably 0.85 or more, more preferably 0.90 or more. The circularity coefficient is obtained by observing the particles by a method similar to the method for measuring the particle diameter described below, where S is the area of the two-dimensional projected image of the particle, and L is the peripheral length. is calculated from the formula “4πS/L ² ”. Let the arithmetic mean value of the circularity coefficient of each particle be the circularity coefficient mentioned above. If the two-dimensional projection image of the particle is a perfect circle, the circularity coefficient of the particle is 1.

In addition, the particle size of the cuprous particles contained in the conductive composition is preferably 0.5 μm or more and 50 μm or less, more preferably 1 μm or more and 30 μm or less when the shape is flake-like. When the first copper particles have such a particle diameter, when the conductive composition is fired, the main surfaces of the flake particles are likely to be oriented substantially parallel to the bonding surface, so after sintering volume shrinkage of the joined body can be suppressed, and the joint strength with other members can be improved.

The particle size of the cupric particles contained in the conductive composition is preferably 30 nm or more and 1000 nm or less, more preferably 50 nm or more and 500 nm or less, and still more preferably 60 nm or more and 400 nm or less. When the second copper particles have such a particle size, when mixed with the first copper particles, the second copper particles can be easily present in the gaps between the first copper particles, and high filling properties can be obtained. As a result, when the conductive composition is fired, the bonding strength with other members can be further increased.

The particle size of each copper particle in the conductive composition can be measured by the following method. First, a conductive composition is applied on a flat plate. Thereafter, an elemental analysis is performed with a field emission scanning electron microscope (SU7000, manufactured by Hitachi High-Tech Co., Ltd.), and the first copper particles and the second copper particles are individually identified based on whether or not the second element is contained. Targeting the first copper particles or second copper particles thus separated, 200 or more particles are randomly selected from a scanning electron microscope image of each particle at a magnification of 150,000 times, and the particle size (Heywood diameter) is obtained. to measure. Next, the particle size distribution based on the number standard is obtained from the obtained particle size of each particle. Then, the particle size of the median value of the particle size distribution based on the number standard is defined as the particle size in the present invention.

The crystallite size of the cuprous particles contained in the conductive composition is preferably 5 nm or more and 35 nm or less, more preferably 10 nm or more and 20 nm or less, and still more preferably 12 nm or more and 18 nm or less. When the cuprous particles have such a crystallite size, the sintering effect can be exhibited at a low temperature.

The crystallite size of the cupric particles contained in the conductive composition is preferably 40 nm or more, more preferably 42 nm or more and 300 nm or less, and still more preferably 42 nm or more and 250 nm or less. By having such a crystallite size of the second copper particles, it is possible to achieve both low-temperature sinterability and high filling properties, and as a result, when the conductive composition is fired, bonding with other members Strength can be further increased.
The crystallite size of the second copper particles is based on the crystallite size of the alloy of copper with the second element when the second element is a metallic element capable of forming an alloy with copper. Also, if the secondary element is present in a mixture with copper, it is based on the crystallite size of metallic copper.

In addition, it is preferable that the crystallite size of the second copper particles is larger than the crystallite size of the first copper particles. By containing each copper particle so as to have such a crystallite size relationship, the crystal structure derived from the second copper particle having a large crystallite size can reduce expansion and contraction due to a rapid temperature change. Therefore, the conductive layer obtained from the conductive composition can sufficiently maintain the bonding strength with the member, and the bonding reliability can be further improved. This effect is exhibited more remarkably by satisfying the above-mentioned P2/P1 ratio. Each copper particle that can easily achieve these relationships can be obtained, for example, by the manufacturing method described below.

The crystallite size can be calculated, for example, from the peak width (half width) of the X-ray diffraction peak in the crystal plane with the highest intensity within the measurement range, using the Scherrer formula shown below.

Scherrer's formula: D=Kλ/β cos θ
D: crystallite size (unit: nm)
K: Scherrer constant (0.94)
λ: X-ray wavelength (unit: 1.54056 Å (Kα1))
β: full width at half maximum (unit: rad)
θ: diffraction angle (unit: rad)

The crystallite size is measured by subjecting the conductive composition to X-ray diffraction measurement under the following conditions. Under the following conditions, the diffraction peaks of the first copper particles and the second copper particles appear at similar angles, respectively. A fitting is made to the copper particles, respectively.
For example, when metallic copper is to be measured, the scan axis is 2θ/θ, the scan range is 0 to 150 deg, the step width is 0.01 deg, the scan speed is 1 deg/min, and X-rays are CuKα1 rays. The scan rate is chosen such that the maximum peak of the scan range is over 10000 counts.
The crystallite size is calculated by WPPF using analysis software PDXL2 manufactured by Rigaku. As an X-ray diffraction measurement device, for example, SmartLab manufactured by Rigaku Corporation can be used.

The ratio of the first copper particles to the total mass of the first copper particles and the second copper particles in the conductive composition is preferably 20% by mass or more and 80% by mass or less, more preferably 40% by mass or more and 80% by mass or less, More preferably, it is 60% by mass or more and 80% by mass or less.
Similarly, the ratio of the second copper particles to the total mass of the first copper particles and the second copper particles is preferably 20% by mass or more and 80% by mass or less, more preferably 20% by mass or more and 60% by mass or less, still more preferably It is 20 mass % or more and 40 mass % or less.
By having such a blending ratio, it is possible to uniformly develop a high bonding strength. In particular, by making the content of the first copper particles higher than the content of the second copper particles, there is an advantage that low-temperature sinterability can be exhibited and high bonding strength can be obtained.

The conductive composition contains a dispersion medium. That is, the form of the conductive composition is, for example, conductive slurry, conductive ink, or conductive paste. The conductive composition may further contain a binder resin and a reducing agent, if necessary.

Dispersion media used in conductive compositions include, for example, water, alcohols, ketones, esters, ethers and hydrocarbons. Among them, at least one of alcohols such as terpineol and dihydroterpineol, polyhydric alcohols such as polyethylene glycol and hexylene glycol, and ethers such as ethyl carbitol and butyl carbitol is preferable.
At least one of acrylic resin, epoxy resin, polyester resin, polycarbonate resin, cellulose resin, and the like can be used as the binder resin used in the conductive composition.
Examples of reducing agents used in the conductive composition include bis(2-hydroxyethyl)iminotris(hydroxymethyl)methane, 2-amino-2-(hydroxymethyl)-1,3-propanediol, 1,3 - aminoalcohol compounds such as bis(tris(hydroxymethyl)methylamino)propane.

Next, a suitable method for producing a conductive composition will be described. In this production method, the first copper particles and the second copper particles are produced separately, and then the first copper particles, the second copper particles and the dispersion medium are mixed at the same time, or in any order A step of mixing the first copper particles, the second copper particles and the dispersion medium is included.

First, the first copper particles are produced. The first copper particles can be produced by a wet reduction method, for example, according to the method described in JP-A-2003-34802, JP-A-2015-168878 or JP-A-2017-179555.
Specifically, a liquid medium containing water and preferably a monohydric alcohol having from 1 to 5 carbon atoms is added with one such as copper chloride, copper acetate, copper hydroxide, copper sulfate, copper oxide or cuprous oxide. A reaction solution containing a valent or divalent copper source is prepared. This reaction solution and hydrazine are mixed so that the ratio is preferably 0.5 mol or more and 50 mol or less with respect to 1 mol of copper, and the copper ions derived from the copper source are reduced, and the particle size and crystallites are reduced. To obtain cuprous particles whose size is easily controlled. The obtained copper particles may be washed by a washing method such as a decantation method or a rotary filter method, if necessary.
The cuprous particles obtained by this method are a slurry containing the aggregates or a dry powder comprising the aggregates. In any form, since the first copper particles are typically exposed to the atmosphere, the surface of the first copper particles may inevitably be slightly oxidized. Note that commercially available cuprous particles may be used.

Separately from the first copper particles, the second copper particles are produced. The second copper particles can be produced by a wet method, an atomization method, an RF plasma method, a DC plasma method, or the like. It is preferable to use the DC plasma method from the viewpoint of easily obtaining particles capable of efficiently exhibiting high bonding reliability with other members. An embodiment of a method for producing second copper particles by a DC plasma method will be described below.

Specifically, the method for producing the second copper particles includes supplying a mother powder containing a copper element and a second element to a plasma flame generated in a chamber, gasifying the mother powder, and gasifying the gasified mother powder is cooled to produce cupric particles.

As the mother powder containing the copper element and the second element to be gasified, one kind of mother powder containing the copper element and the second element having the same elemental composition as the composition of the target second copper particles may be supplied. . Instead of this, as the mother powder containing the copper element and the second element, a mother powder made of copper and containing no other elements other than copper except for unavoidable impurities (hereinafter also referred to as copper mother powder); A mother powder containing two elements (hereinafter also referred to as a second mother powder) is mixed at a ratio such that the elemental composition of the desired cupric particles is the same and supplied. may

When using two types of mother powder, a copper mother powder and a second mother powder, as the mother powder, the second mother powder consists of the second element and does not contain other elements other than the second element except for inevitable impurities. The mother powder may be a single substance of the second element, or may be a mother powder made of an oxide, carbide or nitride of the second element.
In the following description, unless otherwise specified, the mother powder of each of the above embodiments will be generically referred to simply as "mother flour".

Fig. 1 shows a DC plasma apparatus suitable for use in this manufacturing method. As shown in the figure, the DC plasma apparatus 1 includes a powder supply device 2, a chamber 3, a DC plasma torch 4, a recovery pot 5, a powder supply nozzle 6, a gas supply device 7 and a pressure adjustment device 8. In this apparatus, the mother powder passes through the inside of the DC plasma torch 4 from the powder feeder 2 through the powder feed nozzle 6 . A plasma gas is supplied to the DC plasma torch 4 from a gas supply device 7 to generate a plasma flame. In addition, after the mother powder is gasified in the plasma flame generated by the DC plasma torch 4 and discharged into the chamber 3, the gasified mother powder is cooled to form a powder that is an aggregate of cupric particles. As a result, it is accumulated and collected in the collection pot 5 . The inside of the chamber 3 is controlled by a pressure regulator 8 so that a negative pressure is maintained relative to the powder supply nozzle 6, which facilitates the supply of the mother powder to the DC plasma torch 4, and the plasma It has a structure that stably generates frames. The apparatus shown in FIG. 1 is an example of a DC plasma apparatus, and production of the second copper particles is not limited to this apparatus.

From the viewpoint of supplying sufficient energy to the mother powder in the plasma flame to obtain cupric particles having the above-described suitable P2/P1 ratio, particle diameter, and crystallite size with high productivity, the plasma flame is It is preferable to create a laminar flow state in which the aspect ratio of the frame length to the frame width is 3 or more when viewed from the side with the widest width.

In order to make the plasma flame thicker and longer in a laminar flow state, it is advantageous to adjust the plasma power and the plasma gas flow rate. Specifically, the plasma output of the DC plasma apparatus is preferably 2 kW or more and 100 kW or less, more preferably 2 kW or more and 40 kW or less.
The gas flow rate of the plasma gas is preferably 0.1 L/min or more and 25 L/min or less, more preferably 0.5 L/min or more and 21 L/min or less.
As the plasma gas, a reducing gas such as hydrogen gas, an inert gas such as nitrogen gas and argon gas, or a mixed gas thereof can be used. When using a mixed gas, the gas flow rate is the total value of each gas flow rate.

When producing cupric particles using the DC plasma apparatus having the structure described above, the chamber 3 has a reducing gas atmosphere containing hydrogen gas or the like, or an inert gas atmosphere containing nitrogen gas, argon gas or the like. A gas atmosphere is preferred. By adopting such a configuration, while the grain growth of the second copper particles proceeds efficiently, the aggregation of the particles is suppressed, the aggregation of the particles is small, and the predetermined P2/P1 ratio is satisfied. 2 copper particles can be obtained with high productivity.

From the viewpoint of further shortening the time from gasification of mother powder to cooling and efficiently producing cupric particles, a cooling gas is supplied to the inside of the chamber 3 to cool each gasified mother powder. is preferred. The cooling gas can be supplied, for example, by a cooling gas supply unit (not shown) connected through the wall of the chamber 3 . As the cooling gas, for example, reducing gas such as hydrogen gas, inert gas such as nitrogen gas and argon gas, or mixed gas thereof can be used. The cooling gas has a temperature of, for example, 0° C. or higher and 30° C. or lower on the condition that the pressure inside the chamber 3 is negative, and is applied near the tip of the plasma flame inside the chamber 3 and in the plasma. 1 L/min or more and 400 L/min or less can be supplied to the circumference that does not interfere with the formation of the frame.

When producing the second copper particles using the DC plasma apparatus 1 shown in FIG. 1, as described above, the copper element and the second element It is sufficient to use a mother flour containing

From the viewpoint of achieving both improvement of the plasma injection efficiency of the mother powder and reduction of the manufacturing cost, the particle diameter of the mother powder is preferably 3 independently regardless of whether a plurality of types of mother powder are used. 0 μm or more and 50 μm or less, more preferably 5.0 μm or more and 30 μm or less. The particle size of the mother powder can be measured by the same method as the measurement of the particle size of each copper particle described above.

The shape of the mother powder is not particularly limited, and examples include dendritic, rod-like, scale-like, cubic, and spherical shapes. From the viewpoint of stabilizing the supply efficiency of the mother powder to the plasma torch, it is preferable to use spherical mother powder.

From the viewpoint of the production efficiency of the metal particles to be obtained, the supply amount of the mother powder is preferably 5 g/min or more and 200 g/min or less in terms of the total amount, regardless of whether a plurality of types of mother powder are used. More preferably, it is 5 g/min or more and 100 g/min or less.

When using two types of mother powders, the copper mother powder and the second mother powder, the supply ratio of these mother powders can be appropriately changed according to the target elemental composition of the second copper particles. Specifically, the mass ratio of the second mother powder to 100% by mass of the copper mother powder is preferably 0.1% by mass or more and 20% by mass or less, more preferably 0.1% by mass or more and 15% by mass or less. supply to

In addition, from the viewpoint of efficiently obtaining secondary copper particles that satisfy the above-described P2/P1 ratio and also satisfy the above-described particle diameter and crystallite size, the elemental copper and the elemental second element or compound have a boiling point of are preferably in a specific relationship. Specifically, it is advantageous to use a second element element or compound having a boiling point lower than that of elemental copper.
By using elements having such a temperature relationship, in the process of producing cupric particles, copper in the vaporized mother powder is first cooled, causing nucleation, agglomeration and condensation, resulting in a large amount of copper element. Existing microparticles are formed. In addition, the vaporized copper is cooled, and the second element simple substance or compound in the vaporized mother powder is similarly cooled, and the nuclei are formed in a state in which both the copper element and the second element are contained on the surface of the fine particles. It is formed. Furthermore, cooling of the secondary element inclusions in the mother powder causes nucleation, agglomeration and condensation to occur on the surface of the particles, forming a state in which the secondary element is present in greater abundance than the copper element. In this way, the second element is formed so that the abundance of the second element increases continuously or stepwise from the inside of the particle toward the surface, that is, the second element formed so as to satisfy a predetermined P2/P1 ratio. Copper particles can be obtained efficiently. Further, since nucleation of the cupric particles proceeds efficiently, large crystallites can be formed, and the crystallite size is relatively large.

In addition, from the viewpoint of efficiently obtaining cupric particles that satisfy both the above-described P2/P1 ratio and the above-described particle size and crystallite size, the second element may be selected to be easily stabilized with oxygen. good. By using an element that is easily stabilized with oxygen as the second element, the second element reacts and precipitates in a stable state with external oxygen in the process of producing cupric particles, so that it moves to the outside of the particles and concentrates. Since the copper element is precipitated in such a manner as to be a metal, the copper element can be kept as a metal, and the preferable physical properties such as the integral value of the P2/P1 ratio, the particle size, and the crystallite size can be easily obtained. Preferred examples of such a second element include Zr, Al, Co, and the like.

The cupric particles thus obtained are accumulated and recovered in the recovery pot 5 in the form of powder, which is an aggregate of the particles. The recovered cupric particles may be used as they are, or may be classified or pulverized to remove coarsely aggregated particles present as contamination. Classification and pulverization may be carried out by using an appropriate classifier or pulverizer to separate coarse powder and fine powder so that the target particle size is the center. Since the recovered cupric particles are typically exposed to the atmosphere, the surface of the cupric particles may inevitably be slightly oxidized. The cupric particles thus produced satisfy the above P2/P1 ratio and easily satisfy the above particle diameter and crystallite size.

In the production method using the DC plasma method, which is a suitable method for producing the second copper particles, the mother powder is evaporated and vaporized at a high temperature and then cooled. The inclination of the element abundance ratio tends to become larger toward this direction. As a result, it is possible to obtain, with high productivity, cupric particles that satisfy the above-described P2/P1 ratio and that can mitigate excessive thermal expansion and thermal contraction caused by rapid temperature changes. The resulting cupric particles have high dispersibility between particles, and the particles are easy to handle, and the formed coating film has good smoothness. Various mother powders used in the DC plasma method may be particles obtained by a wet method, an atomization method, or an RF plasma method.

The conductive composition of the present invention can be obtained by mixing the cuprous particles and the cupric particles obtained by the above method with a dispersion medium. As a method for mixing each copper particle and a dispersion medium, a method commonly used in this technical field can be adopted. In addition to this, if necessary, a binder resin and a reducing agent may be mixed.

The mixing ratio of the first copper particles and the second copper particles in the conductive composition can be mixed in the same range as the above-described mass ratio range.
In addition, the mixing ratio of the dispersion medium in the conductive composition can be appropriately changed according to the desired properties of the conductive composition. , preferably 10 parts by mass or more and 40 parts by mass or less.

The conductive composition obtained through the above steps forms a conductive film having a desired pattern by, for example, applying it to the surface of an object to be applied by a predetermined means to form a coating film. be able to. If necessary, the coating film may be pressurized and heated to form a conductive film.

The conductive composition of the present invention is suitably used as a conductive bonding material such as a die-bonding material for bonding electronic parts. In addition, it can also be used as a material for filling vias in a printed wiring board, or as an adhesive for surface-mounting an electronic device on a printed wiring board.

Examples of electronic parts as bonding objects include spacers and heat sinks made of various conductive metals such as gold, silver, or copper, metal wires, substrates having such metals on their surfaces, and semiconductor elements. Electronic components may be conductors or insulators.

An example of a method of using a conductive composition as a bonding material for bonding electronic components is described below. The method includes a step of interposing a conductive composition between two electronic components and sintering the conductive composition, and through the steps, a conductive member can be obtained.

First, a conductive composition is applied to the surface of the first electronic component to form a coating film. There is no particular limitation on the means for applying the bonding composition, and known application means can be used. The coating film to be formed may be formed over the entire surface of the first electronic component, or may be formed discontinuously on the surface of the first electronic component. From the viewpoint of developing a higher bonding strength, it is preferable that the coating film is formed over the entire region where the second electronic component, which will be described later, is to be arranged.

The thickness of the coating film to be formed is preferably set to 1 μm or more and 500 μm or less, more preferably 5 μm or more and 300 μm or less, immediately after coating, from the viewpoint of forming a joint structure having high joint strength stably. .

Next, the formed coating film is dried to obtain a dry coating film. In this step, at least part of the dispersion medium is removed from the coating film by drying to obtain a dry coating film in which the amount of the dispersion medium in the coating film is reduced. By removing the dispersion medium from the coating film, the shape retention of the dried coating film can be further enhanced. A dry coating film is one in which the ratio of the dispersion medium to the total weight of the film is 9% by weight or less. Since the content of each constituent material other than the dispersion medium is substantially the same in the coating film and the dried coating film obtained by drying the coating film, the proportion of the dispersion medium is, for example, the ratio of the coating film before and after drying. Mass change can be measured and calculated.

In order to dry and remove the dispersion medium, the dispersion medium may be volatilized by using a drying method such as natural drying, hot air drying, infrared irradiation, hot plate drying, etc., which utilizes the volatility of the dispersion medium. . The drying conditions can be appropriately changed according to the composition of the conductive composition to be used.

A second conductor is then laminated onto the dried coating. Specifically, after the dry coating film is obtained through the above-described steps, the second electronic component is laminated on the dry coating film, and the first electronic component and the second electronic component are interposed therebetween. A conductive member is obtained in which the dry coating film as the conductive composition is arranged adjacently.
The first electronic component and the second electronic component may be of the same type or of different types.

Finally, the conductive member is heat-treated with no pressure or under pressure to sinter the metal powder contained in the dried coating film, thereby forming a bonding portion between the first electronic component and the second electronic component. forming a formed junction structure;
The term "non-pressurized" means that no pressure is applied other than the pressure load caused by changes in the atmospheric pressure or the weight of the constituent members. "Pressure" refers to intentionally applying a pressure of 0.001 MPa or more to the members to be joined from the outside, and the pressure load due to changes in atmospheric pressure and the weight of the constituent members alone The purpose is to exclude

The atmosphere during sintering is preferably a reducing gas atmosphere such as hydrogen or formic acid, or an inert gas atmosphere such as nitrogen or argon. The sintering temperature is preferably less than 300°C, more preferably 150°C or more and less than 300°C, still more preferably 200°C or more and less than 300°C, still more preferably 230°C or more and less than 300°C.
The pressure applied during sintering is preferably 0.001 MPa or more, more preferably 0.001 MPa or more and 20 MPa or less, and still more preferably 0.01 MPa or more and 15 MPa or less.
The sintering time is preferably 20 minutes or less, more preferably 0.5 minutes or more and 20 minutes or less, and still more preferably 1 minute or more and 20 minutes or less, provided that the sintering temperature is within the above range.

The bonding portion formed through the above steps is formed by sintering the conductive composition, and the dispersion medium does not substantially exist due to volatilization or the like. Specifically, the joint site is a sintered body of copper particles that constitute the conductive composition, and has electrical conductivity.

A bonding structure having such a bonding site can be used in environments exposed to high temperatures, such as automotive electronic circuits and electronic circuits mounted with power devices, by taking advantage of its high bonding strength, thermal conductivity, and heat resistance. It is preferably used for

The present invention will be described in more detail below with reference to examples. However, the scope of the invention is not limited to such examples.

[Example 1]
(1) Production of first copper particles According to the method described in Example 1 of JP-A-2015-168878, a slurry in which spherical first copper particles made of copper and containing inevitable impurities are dispersed in water is prepared. Obtained. The particle diameter of the cuprous particles measured by the method described above was 150 nm, and the crystallite size was 13 nm.

(2) Generation of Second Copper Particles Using the DC plasma apparatus shown in FIG. 1, second copper particles were produced by the following method.
Atomized copper powder (particle size: 10 μm, spherical) was used as the copper mother powder. Atomized silver powder (particle size: 5 to 20 μm, spherical) was used as the second mother powder.

A mixed mother powder obtained by mixing both mother powders with a mass ratio of 10.7 mass % of the second mother powder to 100 mass % of the copper mother powder used was supplied to the apparatus 1 . The supply amount of the mixed mother powder was set to 15 g/min, and the mixed mother powder was supplied to the DC plasma torch 4 through the powder supply nozzle 6 . A mixed gas of nitrogen gas and argon gas was used as the plasma gas. The flow rate of nitrogen gas was set to 4.5 L/min, and the flow rate of argon gas was set to 15 L/min. Also, the plasma output was set to 30 kW. The flame aspect ratio of the generated plasma flame was 4, and it was confirmed that the plasma flame was in a laminar flow state. The pressure inside the chamber 3 was set to a negative pressure rather than the atmospheric pressure. In addition, nitrogen gas at 25° C. was supplied at a flow rate of 140 L/min as a cooling gas during production.

Next, 2-propanol was added to the particles generated using a DC plasma device so that the particle concentration was 30% by mass, and then Nanomizer mark II (wet crushing device, Yoshida Kikai Kogyo Co., Ltd. product name: NM2-2000AR ). The crushing conditions were 75 MPa and 10 passes. The slurry after pulverization was filtered through a filter (TCP-3) with an opening of 3 μm, the supernatant of the filtrate was removed, and the remaining solid content was dried at 40° C. with a vacuum dryer (manufactured by ADVANTEC). Thereafter, the particles were pulverized with a sieve having an opening of 150 μm to obtain the second copper particles in the present example.
The second copper particles of this example are copper particles comprising a copper element, Ag as a second element, and inevitable impurities. Also, the cupric particles were an alloy of copper and Ag. The content ratio of Ag element to 100% by mass of copper element in the second copper particles was 10.7% by mass. The particle diameter of the cupric particles measured by the method described above was 300 nm, the copper crystallite size was 45 nm, and the P2/P1 ratio was 14.5.

(3) Preparation of conductive composition Mix so that the content of the first copper particles in the total copper particles is 70% by mass and the content of the second copper particles is 30% by mass, and the first copper particles and the second copper particles are mixed. Using 0.1 parts by mass of a reducing agent (bis(2-hydroxyethyl)iminotris(hydroxymethyl)methane) with respect to a total of 100 parts by mass of copper particles, using a mixture of polyethylene glycol and hexylene glycol as a dispersion medium, It was prepared so that the total amount of copper particles was 80% by mass with respect to the total mass of the paste.

[Example 2]
In the production of the second copper particles, Co powder (particle size: 5 to 20 μm, spherical) is used as the second mother powder, and the mass ratio of the second mother powder to 100% by mass of the copper mother powder used is 4.8 mass. %, and the mixed mother powder obtained by mixing both mother powders was supplied to a DC plasma apparatus. A conductive composition was produced in the same manner as in Example 1 except for this. The second copper particles were an alloy of copper and Co. The Co element content relative to 100% by mass of copper element in the second copper particles was 4.8% by mass. The particle diameter of the cupric particles measured by the method described above was 320 nm, the copper crystallite size was 81.7 nm, and the P2/P1 ratio was 10.8.

[Example 3]
In the production of the second copper particles, ZrO ₂ powder (particle size: 5 to 20 μm, spherical) is used as the second mother powder, and the mass ratio of the second mother powder to 100% by mass of the copper mother powder used is 0.5. % by mass, and the mixed mother powder obtained by mixing both mother powders was supplied to a DC plasma apparatus. A conductive composition was produced in the same manner as in Example 1 except for this. The cupric particles _were a mixture of copper and ZrO2. The Zr element content in the second copper particles was 0.5% by mass with respect to 100% by mass of the copper element. The particle diameter of the cupric particles measured by the method described above was 320 nm, the copper crystallite size was 73 nm, and the P2/P1 ratio was 9.13.

[Comparative Example 1]
In the production of the second copper particles, P ₂ O ₅ powder (particle size: 5 to 20 μm, spherical) is used as the second mother powder, and the mass ratio of the second mother powder to 100% by mass of the copper mother powder used is 0. 05% by mass, and the mixed mother powder obtained by mixing both mother powders was supplied to a DC plasma apparatus. A conductive composition was produced in the same manner as in Example 1 except for this. The cupric particles were an alloy of copper and phosphorus. The phosphorus (P) element content relative to 100% by mass of copper element in the second copper particles was 0.05% by mass. The particle diameter of the cupric particles measured by the method described above was 310 nm, the copper crystallite size was 95 nm, and the P2/P1 ratio was 5.5.

[Example 4]
In the preparation of the conductive composition, in the same manner as in Example 1, except that the content of the first copper particles in the total copper particles was 50% by mass and the content of the second copper particles was mixed so that the content was 50% by mass. A conductive composition was prepared.

[Example 5]
In the preparation of the conductive composition, in the same manner as in Example 2, except that the content of the first copper particles in the total copper particles was 50% by mass and the content of the second copper particles was mixed so that the content was 50% by mass. A conductive composition was prepared.

[Example 6]
In the preparation of the conductive composition, in the same manner as in Example 3, except that the content of the first copper particles in the total copper particles was 50% by mass and the content of the second copper particles was mixed so that the content was 50% by mass. A conductive composition was prepared.

[Comparative Example 2]
In the preparation of the conductive composition, in the same manner as in Comparative Example 1, except that the content of the first copper particles in the total copper particles was 50% by mass and the content of the second copper particles was mixed so that the content was 50% by mass. A conductive composition was prepared.

[Example 7]
In the preparation of the conductive composition, in the same manner as in Example 1, except that the content of the first copper particles in the total copper particles was 30% by mass and the content of the second copper particles was 70% by mass. A conductive composition was prepared.

[Example 8]
In the preparation of the conductive composition, in the same manner as in Example 2, except that the content of the first copper particles in the total copper particles was 30% by mass and the content of the second copper particles was mixed so that the content was 70% by mass. A conductive composition was prepared.

[Example 9]
In the preparation of the conductive composition, in the same manner as in Example 3, except that the content of the first copper particles in the total copper particles was 30% by mass and the content of the second copper particles was mixed to 70% by mass. A conductive composition was prepared.

[Comparative Example 3]
In the preparation of the conductive composition, in the same manner as in Comparative Example 1, except that the content of the first copper particles in the total copper particles was 30% by mass and the content of the second copper particles was mixed to 70% by mass. A conductive composition was prepared.

[Example 10]
In the preparation of the conductive composition, the first copper particles in the total copper particles were flaky copper particles manufactured by Mitsui Kinzoku Mining Co., Ltd. (1200YF: the particle diameter of the first copper particles measured by the above method was 3 μm, the crystal A conductive composition was prepared in the same manner as in Example 4, except that the particle size was changed to 31.4 nm).

[Evaluation of bonding strength]
A copper plate (20 mm long x 20 mm wide x 2 mm thick) was used as the first electronic component, and the conductive compositions of Examples and Comparative Examples were applied to the center of the surface of the copper plate with a size of 5 mm long x 5 mm wide x 100 µm thick. A coating film was formed by printing. After that, the coating film was dried at 110° C. for 20 minutes to obtain a dry coating film.
Next, as a second electronic component, an alumina plate (5 mm long × 5 mm wide × 0.5 mm thick) whose surface is Ag-plated is placed on the dry coating film to form a laminate, and each electronic component is adjacent to the coating film. A conductive member was formed that was arranged in such a way as to
The conductive member is heated to 280° C. at a heating rate of 120° C./min under a nitrogen atmosphere under a pressure of 6 MPa, and sintered at 280° C. for 20 minutes to sinter the conductive composition. A joint structure was obtained in which a copper plate and an alumina plate were joined together while forming a solid joint portion.

[Evaluation of bonding reliability]
A thermal cycle test (TCT) is performed for 1000 cycles on the bonded structure, and the state of peeling from the sintered body at that time is checked using an ultrasonic flaw detector (manufactured by Hitachi Power Solutions, model number: FineSATIII) using a 75 MHz probe. was observed from the outer surface of the alumina plate by a reflection method at . In TCT, one cycle was (1) -40°C for 7 minutes and (2) +175°C for 7 minutes.
With the apparatus described above, a good bonding state is observed in a dark color (black), and a region where a crack or peeling occurs and the bonding state is poor is observed in a light color (white). Among them, the image data of Example 1 and Comparative Example 1 are shown in FIGS.
Also, from the obtained image data, the black area ratio (bonding ratio after 1000 cycles of TCT; %) in the observed area was calculated. A higher bonding rate indicates a higher bonding reliability even when excessive temperature changes occur. Table 1 shows the results.

As shown in Table 1, the joint structure after TCT of each example was observed to have a higher black area ratio than that of the comparative example. The bonding reliability was high.

According to the present invention, a conductive composition is provided that can exhibit high bonding reliability with other members.

Claims

First copper particles made of a copper element;
a second copper particle containing a copper element as a main component and containing a second element other than copper, oxygen, carbon and nitrogen;
a dispersion medium,
The copper element and the second element are present in at least a part of the second copper particles in the state of one or more of alloys and mixtures,
The integrated value of the ratio of the detected intensity P2 of the second element to the detected intensity P1 of the copper element (P2/P1) is 7 or more and 20 or less when measured in a region from the outermost surface to a depth of 50 nm by X-ray photoelectron spectroscopy. A conductive composition.
The conductive composition according to claim 1, wherein the second element is present in the state of oxide, nitride or carbide in at least part of the cupric particles.
The conductive composition according to claim 2, wherein the second element is at least one of silicon, zirconium, aluminum, magnesium, yttrium, titanium, niobium, and tantalum.
the second element is a metal,
2. The electrically conductive composition according to claim 1, wherein the copper element and the second element are present in the form of an alloy in at least a portion of the second copper particles.
The conductive composition according to claim 4, wherein the second element is at least one of gold, silver, palladium, cobalt, nickel, tungsten, aluminum, titanium and molybdenum.
The ratio of the first copper particles to the total mass of the first copper particles and the second copper particles is 20% by mass or more and 80% by mass or less, according to any one of claims 1 to 5 Conductive composition.
The particle diameter of the cuprous particles measured by scanning electron microscope observation is 30 nm or more and 600 nm or less,
7. The conductive composition according to any one of claims 1 to 6, wherein the cupric particles have a particle size of 30 nm or more and 1000 nm or less as measured by scanning electron microscopy.
The conductive composition according to any one of claims 1 to 7, wherein the crystallite size of the second copper particles is larger than the crystallite size of the first copper particles.
The conductive composition according to any one of claims 1 to 8, wherein the crystallite size of the cupric particles is 40 nm or more.
The conductive composition according to any one of claims 1 to 9, which is used for bonding electronic parts.
A conductive member in which a sintered body of the conductive composition according to any one of claims 1 to 10 is arranged adjacently between two electronic components.
Manufacture of a conductive member having a step of interposing the conductive composition according to any one of claims 1 to 10 between two electronic components and sintering the conductive composition Method.