JP2020059914A - Particles for joining material and production method thereof, joining paste and preparation method thereof, and production method of joined body - Google Patents

Abstract

To provide particles for a joining material that are excellent in oxidation resistance during storage and excellent in low-temperature sinterability during bonding, reduce gas components generated when a protective film is released, and enhance the joining strength upon joining.SOLUTION: The particles for a joining material are produced by forming an organic protective film on the surface of copper nanoparticles, have a BET specific surface area in a range of 3.5 m/g to 8 m/g and a BET diameter in a range of 80 nm to 200 nm, and include the organic protective film in a range of 0.5 to 2.0 mass% with respect to the particles for the joining material. When the particles for the joining material are analyzed using a time-of-flight secondary ion mass spectrometry (TOF-SIMS) method, the amounts of detected CHOions and CHOions are respectively in a range of 0.05 times to 0.2 times the amount of detected Cuions, and the amount of detected Cor higher ions is in a range of less than 0.005 times the amount of detected Cuions.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a bonding material particle, which is used as a raw material for a bonding paste at the time of assembling or mounting electronic components, and has an organic protective film formed on the surface of copper nanoparticles, and a method for producing the same. It also relates to a bonding paste containing the particles for bonding material and a method for preparing the same. Further, the present invention relates to a method for manufacturing a bonded body using this bonding paste.

  When assembling or mounting electronic components, a joining material is generally used when joining two or more components. As such a bonding material, a paste-shaped bonding material in which metal particles are dispersed in a solvent is known. When joining components using a joining material, the joining material is applied to the surface of one component, the other component is brought into contact with the application surface, and heating is performed in this state to perform joining.

  Raw metal particles used for such applications are generally required to have high thermal conductivity and high heat resistance. Therefore, metal particles such as gold and silver are often used, and among them, silver, which is cheaper than gold, is often used. However, when silver particles are used, there is a problem that migration is likely to occur in the formed joints and wiring portions.

  Regarding the suppression of migration, it is more effective to use a copper material than a silver material. In particular, copper nanoparticles sinter at a relatively lower temperature than bulk copper, and the resulting bonding layer is excellent in thermal conductivity and high heat resistance. Further, although the cost is lower than that of the silver material, there is a problem that the surface of the copper nanoparticles is easily oxidized due to the large specific surface area of the copper nanoparticles.

  As a method for preventing the oxidation of the copper nanoparticles, a method of coating the periphery of the copper nanoparticles with a silicone oil (see, for example, Patent Document 1 (Claim 1)) or malic acid during the production of fine copper powder , A method of suppressing oxidation by adding an additive such as citric acid or tartaric acid (see, for example, Patent Document 2 (Claims 1 and 3)) or a method of producing copper nanoparticles having citric acid on the particle surface. (For example, refer to Patent Document 3 (Claim 1).) In the method of Patent Document 3, the amount of citric acid is set to 15 wt% or more and 40 wt% or less with respect to the weight of copper.

JP, 2005-060779, A JP, 2007-258123, A Japanese Patent No. 5227828

  The copper nanoparticles coated with silicone oil disclosed in Patent Document 1 are very excellent in terms of oxidation resistance, but since the silicone oil that has not completely volatilized after the heat treatment remains in the bonding layer, baking is not performed. There is a problem in that the bonding strength and the thermal conductivity are greatly reduced due to poor binding.

  In the method disclosed in Patent Document 2, an additive that suppresses oxidation is added later to the produced copper powder and the copper powder is adsorbed by a ball mill or the like. However, it is difficult to completely prevent the oxidation of the copper nanoparticles because it is difficult to uniformly coat with this method.

  In the method disclosed in Patent Document 3, oxidation is suppressed by producing copper nanoparticles having citric acid on the surface. However, the amount of this citric acid is very large, 15 wt% or more and 40 wt% or less with respect to the mass of the copper, and the gas generated by desorption of the surface protective film at the time of forming the bonded body causes voids at the bonded portion such as the bonded film. There was a problem that became. From the above, copper for a bonding material that has a surface protective film to which oxidation resistance has been imparted, and that the protective film has an extremely small amount of gas components generated during desorption, and has excellent low-temperature sinterability Nanoparticles are needed.

  Further, in the method disclosed in Patent Document 3, copper nanoparticles are produced by mixing a first aqueous solution and a second aqueous solution, each of which is adjusted to have a pH range of 10 or more and less than pH 12. However, in a basic solution, copper ions become copper (II) hydroxide, and this copper (II) hydroxide is apt to precipitate, and there is a problem that the target particle yield decreases. From the above, there is a demand for a method for producing copper nanoparticles for a bonding material, which has a surface protective film provided with oxidation resistance and is excellent in low-temperature sinterability, in high yield.

  A first object of the present invention is that it has excellent resistance to oxidation during storage, excellent low-temperature sinterability during bonding, less gas components generated when the protective film is released, and enhanced bonding strength during bonding. It is to provide particles for a bonding material. A second object of the present invention is to provide a method for producing particles for a bonding material, which are excellent in oxidation resistance during storage, excellent in low temperature sinterability during bonding, and high in bonding strength during bonding, in a high yield. To do. A third object of the present invention is to provide a bonding paste containing such particles for bonding material and a method for preparing the same. A fourth object of the present invention is to provide a method for manufacturing a bonded body using such a bonding paste.

A first aspect of the present invention is a bonding material particle in which an organic protective film is formed on the surface of copper nanoparticles, wherein the bonding material particle has a BET specific surface area of 3.5 m ² / g or more and 8 m ² / g or less. The BET diameter converted from the specific surface area is 80 nm or more and 200 nm or less, and the organic protective film is 0.5% by mass or more and 2.0% by mass with respect to 100% by mass of the particles for bonding material. % Of C ₃ H when the particles for bonding material are analyzed by using time-of-flight secondary ion mass spectrometry (TOF-SIMS). The detection amount of each of ₃ O ₃ ⁻ ions and C ₃ H ₄ O ₂ ⁻ ions is in the range of 0.05 times to 0.2 times the detection amount of Cu ⁺ ions, and C ₅ or more. 0.005 detection of ions to the detection amount of Cu ⁺ ions A bonding material particles, characterized in that in the range below.

  A second aspect of the present invention is the invention based on the first aspect, wherein the organic protective film decomposes by 50% by mass or more when heated at a temperature of 300 ° C. for 30 minutes in an inert gas atmosphere, and decomposes. The particles for bonding material are carbon dioxide gas, nitrogen gas, vaporized gas of acetone, and water vapor.

  A third aspect of the present invention is a bonding paste containing a volatile solvent and the particles for bonding material of the first or second aspect.

  A fourth aspect of the present invention is to add a pH adjusting agent to an aqueous dispersion of copper citrate at room temperature to adjust the pH to pH 3 or more and less than pH 7, and to carry out the pH adjustment of the aqueous dispersion of copper citrate in an inert gas atmosphere. By adding and mixing a hydrazine compound to the liquid and heating the mixed liquid to a temperature of 60 ° C. or higher and 80 ° C. or lower in an inert gas atmosphere and holding it for 1.5 hours or more and 2.5 hours or less, the copper citrate is removed. This is a method of producing copper nanoparticles by reduction and producing particles for a bonding material in which an organic protective film is formed on the surfaces of the copper nanoparticles.

  A fifth aspect of the present invention is to form a bonding paste by mixing a volatile solvent with the particles for bonding material of the first or second aspect or the particles for bonding material produced by the method of the fourth aspect. This is the method of preparation.

  A sixth aspect of the present invention is to form a coating layer by applying the bonding paste of the third aspect or the bonding paste prepared by the method of the fifth aspect to the surface of the substrate or the electronic component, The step of superposing the substrate and the electronic component via the coating layer, and the superposed substrate and the electronic component, under a pressure of 30 MPa or less, under an inert atmosphere, 200 ℃ or more 300 ℃ or less And a step of forming a bonding layer by sintering the coating layer by heating the coating layer and bonding the substrate and the electronic component by the bonding layer.

The particles for bonding material according to the first aspect of the present invention are excellent in oxidation resistance during storage because the copper nanoparticles, which are the base particles, are coated on the organic protective film. Since the BET specific surface area of the particles for bonding material is in the range of 3.5 m ² / g or more and 8 m ² / g or less and the BET diameter converted from the specific surface area is in the range of 80 nm or more and 200 nm or less, The reaction area is large, and the reactivity due to heating at the time of bonding is high, which allows the particles for bonding material to be sintered at a relatively low temperature. In addition, the ratio of the organic protective film to 100% by mass of the particles for bonding material is 0.5% by mass or more and 2.0% by mass or less, which is significantly smaller than the ratio of 15% by mass or more and 40% by mass or less described in Patent Document 3. Therefore, the amount of gas that the organic protective film decomposes during firing is small, and the number of voids at the bonding site such as the bonding film due to the decomposed gas is reduced, and the bonding strength can be increased.

In addition, when the particles for bonding material are analyzed by time-of-flight secondary ion mass spectrometry (TOF-SIMS), the detected amounts of C ₃ H ₃ O ₃ ⁻ ions and C ₃ H ₄ O ₂ ⁻ ions are detected. However, since it is in the range of 0.05 times to 0.2 times the detected amount of Cu ⁺ ions, there is no excess or deficiency in the amount of the organic protective film in protecting the copper nanoparticles. Therefore, the organic protective film prevents the bonding material particles from aggregating without oxidizing the surface of the copper nanoparticles. Further, since the detected amount of C ₅ or more ions is in the range of less than 0.005 times the detected amount of Cu ⁺ ions, it is possible to raise the sintering temperature without impairing the sinterability of the bonding material particles. There is no.

  In the particles for bonding material according to the second aspect of the present invention, the organic protective film is decomposed by 50% by mass or more when heated at a temperature of 300 ° C. for 30 minutes in an inert gas atmosphere. There is little residue, and the above-mentioned bonding strength is not reduced. In addition, since the decomposition gas of the organic protective film is carbon dioxide gas, nitrogen gas, vaporized gas of acetone, and water vapor, the particles for bonding material are covered with the organic protective film which is easily desorbed at a relatively low temperature. There is a feature called.

  Since the bonding paste according to the third aspect of the present invention contains the bonding material particles and a volatile solvent, the paste can sinter the bonded body at a low temperature, and the bonding material in the bonding portion or the wiring portion. There is a feature that migration of components does not occur.

  In the method for producing particles for a bonding material according to the fourth aspect of the present invention, when a hydrazine compound that is a reducing agent is added to and mixed with an acidic liquid having a pH of 3 or more and less than pH 7, copper nanoparticles are generated in the liquid. The citric acid generated from rapidly coats the surface of the copper nanoparticles and suppresses the dissolution of the copper nanoparticles. As a result, when copper citrate is reduced, copper ions are unlikely to be copper (II) hydroxide and are unlikely to precipitate as copper (II) hydroxide, and target particles can be produced in high yield.

  In addition, since the manufactured copper nanoparticles, which are the base particles, are covered with the organic protective film, the oxidation resistance during storage is excellent. In addition, since the produced base particles are copper nanoparticles, the reaction area of the bonding material particles is large and the reactivity by heating during bonding is high, which allows the bonding material particles to be sintered at a relatively low temperature. You can

  Furthermore, the produced bonding material particles have a small amount of gas that decomposes the organic protective film during firing, and the number of voids in the bonding film due to the decomposed gas is reduced, so that the bonding strength can be increased.

  In the method for preparing a bonding paste according to the fifth aspect of the present invention, since the paste is manufactured by mixing the particles for bonding material and the volatile solvent, the manufactured paste sinters the bonded body at a low temperature. Therefore, there is a feature that migration of the bonding material component does not occur in the bonding portion and the wiring portion.

  In the method for manufacturing a bonded body according to the sixth aspect of the present invention, the bonding paste containing the particles for bonding material is used to apply an inert pressure while applying a pressure of 30 MPa or less to the substrate and the electronic component via the coating layer. In an atmosphere, heating is performed at a temperature of 200 ° C or higher and 300 ° C or lower. By this method, it is possible to manufacture a bonded body having high bonding strength with high productivity at a relatively low temperature of 200 ° C. or higher and 300 ° C. or lower without causing mechanical damage and thermal damage to the substrate and electronic components. it can.

It is the figure which represented typically the cross-section of the particle | grains for bonding materials of embodiment of this invention. FIG. 3 is a photograph of the aggregate of particles for bonding material of Example 1, taken with a microscope.

  Next, an embodiment for carrying out the present invention will be described based on the drawings.

[Particles for bonding material]
As shown in FIG. 1, in the particles 10 for a bonding material of this embodiment, the base particles 11 are made of copper nanoparticles, and the surfaces of the base particles 11 are covered with the organic protective film 12.

The BET specific surface area of the bonding material particles 10 is 3.5 m ² / g or more and 8 m ² / g or less, and the BET diameter converted from the specific surface area is 80 nm or more and 200 nm or less. A preferable BET specific surface area is in the range of 4.0 m ² / g or more and 8.0 m ² / g or less, and a preferable BET diameter is in the range of 80 nm or more and 170 nm or less. If the BET specific surface area is less than 3.5 m ² / g or the BET diameter exceeds 200 nm, the reaction area of the particles for bonding material is not large, and the reactivity due to heating during bonding is low, which results in firing at a relatively low temperature. I can't conclude. Further, if the BET specific surface area exceeds 8 m ² / g or the BET diameter is less than 80 nm, there is a problem that the viscosity increases with a predetermined composition when a paste is prepared. The shape of the particles for the bonding material is not limited to a spherical shape, and may be a needle shape or a flat plate shape. Since the melting point of the copper nanoparticles, which is the base powder, is 1085 ° C., the heat resistance of the bonding portion such as the bonding film after the bonding paste is applied and reflowed is excellent.

  The organic protective film 12 is a film derived from citric acid, which covers the surface of the copper nanoparticles that are the base particles 11 and prevents the oxidation of the copper nanoparticles during storage from the production to the bonding paste. Play a role. The organic protective film 12 is contained in an amount of 0.5% by mass or more and 2.0% by mass or less, preferably 0.8% by mass or more and 1.8% by mass or less, based on 100% by mass of the bonding material particles. When the coating amount or the content of the organic protective film 12 is less than 0.5% by mass, the organic protective film does not completely cover the copper nanoparticles, and part of the copper nanoparticles becomes an oxide, Sintering of particles for bonding material does not proceed during bonding. When the coating amount or content of the organic protective film 12 exceeds 2.0% by mass, a void is generated at a bonding site such as a bonding film due to a gas generated by desorption of the organic protective film during bonding, Bonding strength decreases.

  In the particles for bonding material according to the present embodiment, the organic protective film covers the copper nanoparticles of the base particles at a ratio of 0.5% by mass or more and 2.0% by mass or less, and therefore, the organic protective film does not contain nitrogen gas, argon gas or the like. When heated at a temperature of 300 ° C. for 30 minutes in an active gas atmosphere, the organic protective film decomposes by 50% by mass or more. Further, since it is an organic protective film derived from citric acid, carbon dioxide gas, nitrogen gas, vaporized gas of acetone and water vapor are generated during decomposition.

The particles 10 for bonding material have a C ₃ H ₃ O ₃ ⁻ ion and a C ₃ H ₄ O ₂ ⁻ ion, respectively, when analyzed using time-of-flight secondary ion mass spectrometry (TOF-SIMS). detecting the amount, in the range of not less than 0.2 times 0.05 times or more relative to the detected amount of Cu ⁺ ion, the detection amount of C ₅ or more ions to the detection amount of Cu ⁺ ions 0.005 It is in the range of less than double.

C ₃ H ₃ O ₃ ⁻ ions and C ₃ H ₄ O ₂ ⁻ ions for Cu ⁺ ions detected in time-of-flight secondary ion mass spectrometry, and ions of C ₅ or higher coat the surface of the copper nanoparticles. It originates from the organic protective film. Therefore, if the detected amount of each of C ₃ H ₃ O ₃ ⁻ ion and C ₃ H ₄ O ₂ ⁻ ion is less than 0.05 times the detected amount of Cu ⁺ ion, the surface of the copper nanoparticles is detected. When the amount of the organic protective film coating is too small, the surface of the copper nanoparticles becomes active and the copper nanoparticles are easily oxidized, and the copper nanoparticles are easily aggregated. The viscosity increases and the coatability decreases. On the other hand, when the detected amount of each of C ₃ H ₃ O ₃ ⁻ ions and C ₃ H ₄ O ₂ ⁻ ions exceeds 0.2 times the detected amount of Cu ⁺ ions, a gas void is formed when a bonded body is formed. Since (voids) are generated, the bonding strength is likely to decrease. Further, the amount of the organic protective film coating the surface of the copper nanoparticles becomes too large, and the sinterability of the bonding material particles decreases, so that the heating temperature for sintering the bonding material particles becomes high. There is a need. The oxidation resistance during storage of the bonding material particles further improved, and in order to further improve the low-temperature sintering properties at the time of bonding, C ₃ H ₃ O ₃ ^- ions and C ₃ H ₄ O ₂ ^- ions each detection amount is preferably in the range of not less than 0.16 times 0.08 times or more relative to the detected amount of Cu ⁺ ion, the detection amount of C ₅ or more ions within the detected amount of Cu ⁺ ions On the other hand, it is preferably in the range of less than 0.003 times. Further, when the detected amount of C ₅ or more ions with respect to Cu ⁺ ions detected in the time-of-flight secondary ion mass spectrometry is 0.005 times or more, the reduction reaction is insufficient and particles used for the bonding material. Not suitable as

[Method for producing particles for bonding material]
The particles for bonding material of the present embodiment is a copper citrate aqueous dispersion liquid in which a pH adjuster is added to an aqueous dispersion liquid of copper citrate to adjust the pH to 3 or more and less than pH 7, and the pH is adjusted under an inert gas atmosphere. In addition, 1.0 times equivalent or more and 1.2 times equivalent or less hydrazine compound capable of reducing copper ions is added and mixed as a reducing agent, and the mixed solution is heated to 60 ° C. or higher and 80 ° C. or lower under an inert gas atmosphere. By heating to a temperature and holding for 1.5 hours or more and 2.5 hours or less, the copper citrate is reduced to produce copper nanoparticles, and an organic protective film is formed on the surface of the copper nanoparticles. .

  For the aqueous dispersion of copper citrate, powdered copper citrate is added to pure water such as distilled water or ion-exchanged water so as to have a concentration of 25% by mass or more and 40% by mass or less, and stirring blades are used. It is prepared by stirring and uniformly dispersing. Examples of pH adjusters include triammonium citrate, ammonium hydrogen citrate, and citric acid. Of these, triammonium citrate is preferable because it is easy to adjust the pH mildly. The reason why the pH is adjusted by the pH adjuster to be pH 3 or more and less than pH 7 is that when the pH is less than 3, the elution of copper ions from copper citrate is slow, the reaction does not proceed quickly, and the target particles are difficult to obtain. Further, when the pH is 7 or more, when the copper citrate is reduced with a hydrazine compound, the eluted copper ions are likely to be copper (II) hydroxide and easily precipitated, and the particles for bonding material cannot be produced with a high yield. Further, the reducing power of hydrazine becomes strong and the reaction easily proceeds, so that it is difficult to obtain target particles. The preferred pH is 4 or more and 6 or less.

  Reduction of copper citrate with a hydrazine compound is carried out under an inert gas atmosphere. This is to prevent the oxidation of copper eluted in the liquid. Examples of the inert gas include nitrogen gas and argon gas. The hydrazine compound has advantages that, when reducing copper citrate under acidic conditions, no residue is generated after the reduction reaction, the safety is relatively high, and the handling is easy. Examples of the hydrazine compound include hydrazine monohydrate, anhydrous hydrazine, hydrazine hydrochloride and hydrazine sulfate. Of these, hydrazine monohydrate is preferable because it is desirable that there be no component such as sulfur or chlorine that can become impurities.

  Generally, the copper produced in an acidic liquid having a pH of less than 7 will dissolve. However, in the present embodiment, when a hydrazine compound that is a reducing agent is added to and mixed with an acidic liquid having a pH of less than 7 to generate copper nanoparticles in the liquid, a component derived from citrate ions generated from copper citrate is copper nanoparticles. It quickly coats the surface and suppresses the dissolution of copper nanoparticles. The acidic liquid having a pH of less than 7 is preferably kept at a temperature of 50 ° C. or higher and 70 ° C. or lower because the reduction reaction proceeds easily.

  Heating the mixed solution of the hydrazine compound mixed under an inert gas atmosphere to a temperature of 60 ° C. or higher and 80 ° C. or lower and holding it for 1.5 hours or more and 2.5 hours or less is to reduce copper citrate to form copper nanoparticles. This is because the organic protective film derived from copper citrate is formed and coated on the surface of the copper nanoparticles in the range of 0.5% by mass or more and 2.0% by mass or less. The heating and holding in an inert gas atmosphere is for preventing the oxidation of the copper nanoparticles. Copper citrate, which is a starting material, usually contains about 35% by mass of a copper component. A hydrazine compound that is a reducing agent is added to copper citrate containing a copper component of this degree, and the temperature is raised to the above temperature range and heated, and held for a predetermined time, whereby the reduction of copper citrate proceeds, copper The component becomes particles having a content of 98% by mass or more and 99.5% by mass or less. The amount of the components other than the copper component of the particles, which is 0.5% by mass or more and 2.0% by mass, becomes the organic protective film. When the heating temperature is less than 60 ° C. and the holding time is less than 1.5 hours, copper citrate is not completely reduced, and the copper component does not become particles of 98 mass% or more. Exceeds 2.0 mass%. As a result, as described above, due to the gas generated by the detachment of the organic protective film at the time of bonding, voids are generated at the bonding site such as the bonding film and the bonding strength is reduced. Further, when the heating temperature exceeds 80 ° C. and the holding time exceeds 2.5 hours, the copper component exceeds 99.5 mass% and the coating amount or the formation amount of the organic protective film becomes less than 0.5 mass%. As a result, as described above, the organic protective film does not completely cover the copper nanoparticles and a part of the copper nanoparticles becomes an oxide, so that the sintering of the bonding material particles proceeds at the time of bonding. do not do. A preferable heating temperature is 65 ° C. or higher and 75 ° C. or lower, and a preferable holding time is 2 hours or longer and 2.5 hours or shorter.

  Particles produced from a solution obtained by reducing copper citrate are separated from this solution under an inert gas atmosphere by using, for example, a centrifuge, solid-liquid separation, and dried by freeze-drying or vacuum drying. Then, the particles for bonding material, which are target particles, in which the organic protective film is formed on the surface of the above-mentioned copper nanoparticles are obtained. Since the surfaces of the copper nanoparticles are covered with the organic protective film, the particles for the bonding material can prevent the particles from being oxidized even if they are stored in the air until they are used as a bonding paste.

[Paste for bonding]
A bonding paste containing the bonding material particles and a volatile solvent will be described. Examples of the volatile solvent include alcohol solvents, glycol solvents, acetate solvents, hydrocarbon solvents and amine solvents. Specific examples of the alcohol solvent include α-terpineol and isopropyl alcohol. Specific examples of the glycol solvent include ethylene glycol, diethylene glycol and polyethylene glycol. A specific example of the acetate solvent is butyl tol carbitate acetate. Specific examples of the hydrocarbon solvent include decane, dodecane, and tetradecane. Specific examples of the amine solvent include hexylamine, octylamine and dodecylamine.

  The content of the bonding material particles in the bonding paste is preferably 50% by mass or more, and particularly preferably 70% by mass or more and 95% by mass or less, based on the total amount of the bonding paste. When the content of the bonding material particles is within the above range, the viscosity of the bonding paste does not become too low, and the bonding paste can be stably applied to the surface of the member. Further, by firing the bonding paste, a sintered body (bonding layer) having a high density and a small amount of voids can be obtained. Further, the bonding paste may further contain additives such as an antioxidant and a viscosity modifier. The content of these additives is preferably in the range of 1% by mass or more and 5% by mass or less based on 100% by mass of the bonding paste.

[Method for preparing bonding paste]
The bonding paste can be produced, for example, by kneading a mixture obtained by mixing the volatile solvent and the particles for bonding material using a kneading device. As a kneading device, a three roll mill can be mentioned.

[Method of manufacturing joined body]
The bonded body of the present embodiment, a step of applying a bonding paste described above to the surface of a substrate or an electronic component to form a coating layer, a step of superposing the substrate and the electronic component via the coating layer, The substrate and the electronic component thus laminated are heated at a temperature of 200 ° C. or more and 300 ° C. or less in an inert atmosphere while applying a pressure of 30 MPa or less to sinter the coating layer to form a bonding layer. It is manufactured through the steps of forming and joining the substrate and the electronic component by the joining layer.

  The substrate is not particularly limited, but for example, an oxygen-free copper plate, a copper molybdenum plate, a high heat dissipation insulating substrate (for example, DBC (Direct Copper Bond)), a semiconductor element mounting base material such as an LED (Light Emitting Diode) package Etc. Further, as the above-mentioned electronic parts, IGBT (Insulated Gate Bipolar Transistor), diode, Schottky barrier diode, MOS-FET (Metal Oxide Semiconductor Field Effect Transistor), thyristor, logic, sensor, analog integrated circuit, LED, semiconductor laser, transmission A semiconductor element such as a container is used. The coating method is not particularly limited, and examples thereof include spin coating method, metal mask method, spray coating method, dispenser coating method, knife coating method, slit coating method, inkjet coating method, screen printing method, offset printing method, die coating method. Etc.

  After forming the coating layer, the substrate and the electronic component are superposed on each other with the coating layer interposed therebetween. The thickness of the coating layer is preferably uniform. The superposed substrate and electronic component are heated at a temperature of 200 ° C. or higher and 300 ° C. or lower in an inert atmosphere while applying a pressure of 30 MPa or lower. If the applied pressure exceeds 30 MPa, there is a risk of mechanical damage to the substrate or electronic components. The applied pressure is preferably 5 MPa or more and 30 MPa or less. If the pressure is less than 5 MPa, the copper nanoparticles in the coating layer will be difficult to sinter, and the bonding layer may not be formed. In addition, as the atmosphere, an inert atmosphere such as nitrogen gas or argon gas is specified from the viewpoint that there is no risk of ignition due to fire and oxidation of the bonded body is prevented. If the heating temperature is less than 200 ° C., the copper nanoparticles in the coating layer will be difficult to sinter, and the bonding layer may not be formed. On the other hand, if the temperature exceeds 300 ° C, the substrate or the electronic component may be thermally damaged. A preferable heating temperature is 230 ° C. or higher and 300 ° C. or lower.

  By heating the substrate and the electronic component thus laminated together under pressure at a temperature of 200 ° C. or higher and 300 ° C. or lower in an inert atmosphere, the copper nanoparticles in the coating layer are sintered and The joined body according to the embodiment is manufactured.

  Next, examples of the present invention will be described in detail together with comparative examples.

<Example 1>
First, a commercially available copper citrate 2.5 hydrate (manufactured by Wako Pure Chemical Industries, Ltd.), which is a starting material, is placed in ion-exchanged water at room temperature and stirred using a stirring blade to obtain a copper citrate having a concentration of 30% by mass. An aqueous dispersion of was prepared. Next, an aqueous solution of ammonium citrate as a pH adjuster was added to this aqueous dispersion of copper citrate to adjust the pH of the above aqueous dispersion to 3. Next, the pH-adjusted liquid is brought to a temperature of 50 ° C., and under a nitrogen gas atmosphere, a 1.2 times equivalent amount of an aqueous solution of hydrazine monohydrate capable of reducing copper ions as a reducing agent in the pH-adjusted liquid (2 times (Dilution) was added all at once and mixed uniformly using a stirring blade. Further, in order to synthesize the target particles for bonding material, the mixed solution of the aqueous dispersion and the reducing agent was heated to the maximum temperature of 70 ° C. under a nitrogen gas atmosphere and kept at 70 ° C. for 2 hours. . Using a centrifuge, the particles generated in the liquid kept heated were subjected to solid-liquid separation and collected. The collected particles were dried by a reduced pressure drying method to produce the particles for bonding material of Example 1. FIG. 2 shows a micrograph of the aggregate of particles for bonding material of Example 1 taken at a magnification of 30,000. It can be seen from FIG. 2 that the aggregate of particles for the bonding material of Example 1 is composed of particles of about 100 nm. Table 1 below shows the production conditions of the particles for bonding material of Example 1 and Examples 2 to 11 described below and Comparative Examples 1 to 9.

<Examples 2 to 11, Comparative Examples 1 to 3 and Comparative Examples 6 to 9>
In Examples 2 to 8, reduction was performed by changing the pH of the aqueous dispersion of copper citrate shown in Example 1 as shown in Table 1 without changing the starting material and the reducing agent of Example 1. The redox potential E of the agent was changed to change or maintain the maximum temperature and the holding time when synthesizing the particles for the bonding material. Except for that, the particles for bonding materials of Examples 2 to 8, Comparative Examples 1 to 3 and Comparative Examples 6 to 9 were manufactured in the same manner as in Example 1. In Examples 9 to 11, anhydrous hydrazine was used as a reducing agent, the redox potential E of the reducing agent was -0.6 V, the maximum temperature during synthesis was 70 ° C, and the holding time was 2.0 hours. .

It is known that hydrazine-based reducing agents such as hydrazine monohydrate have different reactions in the acidic region and the alkaline region. Further, in Examples 2 to 11, Comparative Examples 1 to 3 and Comparative Examples 6 to 9, the reducing power was changed by changing the pH in the reaction liquid. Table 1 shows the redox potential E (V) under each condition.
(Acid range) N ₂ H ₅ ⁺ = N ₂ + 5H ⁺ + 4e ⁻
(Alkaline region) N ₂ H ₄ + 4OH ⁻ = N ₂ + 4H ₂ O + 4e ⁻
Redox potential E: -0.23 -0.975 pH

<Comparative example 4>
The reducing agent hydrazine monohydrate in Example 1 was changed to ammonium formate, and the redox potential E of this reducing agent was changed (E: 0.3 V). For the bonding material of Comparative Example 4, the pH value of the aqueous dispersion of copper citrate was changed without changing the maximum temperature during synthesis of Example 1 and its holding time, and otherwise the same as in Example 1. Particles were produced.

<Comparative Example 5>
The reducing agent hydrazine monohydrate of Example 1 was changed to formic acid, and the redox potential E of this reducing agent was changed (E: -0.2 V). The pH value of the aqueous dispersion of copper citrate of Example 1, the maximum temperature during synthesis, and the holding time thereof were not changed. Otherwise in the same manner as in Example 1, the particles for bonding material of Comparative Example 5 were produced.

<Comparison evaluation test and results>
The respective production yields of particles when the particles for bonding material were manufactured in Examples 1 to 11 and Comparative Examples 1 to 9 and 20 kinds of bonding materials obtained in Examples 1 to 11 and Comparative Examples 1 to 9 mother particle composition of use particles, the BET specific surface area and BET diameter, time-of-flight secondary ion mass spectrometry associated with organic protective layer C ₃ H with respect to the detection of (TOF-SIMS) on by Cu ⁺ ions ₃ O ₃ ^- The detected amounts of ions and C ₃ H ₄ O ₂ ⁻ ions, and the detected amounts of C ₅ or more ions were calculated or measured. The results are shown in Table 2 below.

  Further, the mass ratio of the organic protective film to the bonding material particles, the decomposition amount ratio of the organic protective film in a nitrogen atmosphere, and the gas component generated when the bonding material particles were fired were calculated or measured. The results are shown in Table 3 below. BET specific surface area, BET diameter, and characteristics of the organic protective film were not measured for particles (Comparative Example 1, Comparative Examples 4 to 6, and Comparative Example 9) whose production yield could not be calculated due to insufficient reduction.

(1) Production yield of particles The production yield of particles was determined as the production yield, which is the ratio of the amount of recovered powder after drying when the amount of copper contained in copper citrate is the theoretical amount.

(2) BET Specific Surface Area of Particles The specific surface area of particles was determined from the amount of N ₂ gas adsorbed to the cooled particles for bonding material using QUANTACHROME AUTOSORB-1 (manufactured by Kantachrome Instruments) as a measuring device.

(3) BET diameter of particles The BET diameter of particles is calculated on the assumption that all the areas are spheres after measuring the specific surface area (BET method), and the copper nanoparticles are true spheres. Shows the theoretical diameter of.

(4) Measurement by Time-of-Flight Secondary Ion Mass Spectrometry The detection of C ₃ H ₃ O ₃ ⁻ ion and C ₃ H ₄ O ₂ ⁻ ion with respect to Cu ⁺ ion, and ions of C ₅ or more are carried out by time-of-flight type ion detection. It measured as follows using the secondary ion mass spectrometry (TOF-SIMS). A sample for measurement was obtained by burying copper powder on the surface of the In foil. As the measuring device, nanoTOFII manufactured by ULVAC PHI was used. The measurement range was 100 μm square, the primary ion was Bi ₃ ⁺⁺ (30 kV), and the measurement time was 5 minutes to obtain a TOF-SIMS spectrum. From the resulting TOF-SIMS spectrum, Cu ⁺ ions, C ₃ H ₃ O ₃ ^- ions, C ₃ H ₄ O ₂ ^- ions, determined a detectable amount of C ₅ or more ions, C ₃ H ₃ O ₃ ^- ions the C ₃ H ₄ O ₂ ^- ions, a detectable amount of C ₅ or more ions, each divided by the detected amount of Cu ^{+ _{ions, Cu + C 3 H 3 O}} 3 on ion ^- ion and C ₃ H ₄ O The detected amounts of ₂ ^- ions and C ₅ or more ions were calculated.

(5) Mass ratio of the organic protective film in the particles for the bonding material The mass ratio of the organic protective film in the particles for the bonding material is determined by weighing out the particles for the bonding material and heating at 300 ° C. for 30 minutes in a nitrogen atmosphere, After cooling to room temperature, the mass of the metal particle aggregate was measured. It was calculated from the following formula.
Mass ratio of organic protective film in particles for bonding material (mass%) = (AB) / A × 100
However, A is the mass of the bonding material particles before heating, and B is the mass of the bonding material particles after heating.

(6) Decomposition rate of the organic protective film in a nitrogen atmosphere The decomposition rate of the organic protective film is the same as the method of calculating the mass ratio of the organic protective film. It was heated at the temperature of 30 minutes and the ratio of the decrease amount under the condition of 300 ° C. to the decrease amount under the condition of 500 ° C. was determined as the decomposition amount ratio.

(7) Gas component generated during firing of particles for bonding material The gas component generated during firing of particles for bonding material was identified by gas decomposition from room temperature to 300 ° C using pyrolysis gas chromatography.

(8) Manufacturing conditions of bonded body, bonding conditions and bonding strength 15 kinds of particles for bonding material obtained in Examples 1 to 11 and Comparative Examples 2, 3, 7, and 8 were treated with ethylene glycol (EG ) Was added to prepare a bonding paste. Specifically, a solvent and particles were placed in a polypropylene container at a ratio of 85% by mass of ethylene glycol and 15% by mass of particles for bonding material, and kneaded by a kneader (THINKY, Awatori Kentaro). Kneading: 1,000 rpm × 60 seconds and defoaming: 1,000 rpm × 60 seconds, preliminarily kneading, and using a triple roll (manufactured by EXACT, 80E), Gap width: 1st time: 50 μm, 2nd time : 10 μm, 3rd time: 5 μm, and kneaded in earnest. This prepared the bonding paste.

  The bonding paste was printed on an oxygen-free copper plate (0.8 mmt) using a metal mask plate (2.5 mm, 50 μmt) set in a metal mask printing machine, and a Si dummy element was mounted after 30 minutes of preliminary drying at room temperature. . The firing conditions were set to four levels of 200 ° C., 230 ° C., 250 ° C. and 300 ° C. under a nitrogen atmosphere using a pressure bonding device (RB-50 manufactured by Ayumi Kogyo Co., Ltd.). The joining load was set to 10 MPa when the joining temperature was 300 ° C., 20 MPa when the joining temperature was 230 ° C. and 250 ° C., and 30 MPa when the joining temperature was 200 ° C. The temperature rising rate was 30 ° C./minute, and the bonding holding time was set to 15 minutes when the bonding temperature was 230 ° C., 250 ° C. and 300 ° C., and 30 minutes when the bonding temperature was 200 ° C.

  A joined body was manufactured under the above joining conditions. The bonding strength of the obtained bonded body was evaluated using a bonding tester (Tensilon RTF-1310 manufactured by Orientec Co., Ltd.), and the bonded body having a strength of 15 MPa or more was evaluated as good. The results are shown in Tables 4 to 6 below.

  As is clear from Tables 1 to 3 and 6, in Comparative Example 1, since the reducing agent was added and mixed under strong acidity of pH 2, the synthetic solution was heated at 70 ° C. for 2 hours, but the reduction of copper citrate did not occur. This was not completed, resulting in a large mass ratio of the organic protective film, and the target particles could not be manufactured.

In Comparative Example 2, since the reducing agent was added and mixed under the alkaline condition of pH 8, copper ions became copper (II) hydroxide in the liquid, and the production yield of particles was not high at 90%. Further, grain growth occurs in the liquid, the BET specific surface area of the obtained bonding material particles is as small as 1.9 m ² / g, the BET diameter is as large as 353 nm, and the mass ratio of the organic protective film is 0.4 mass. % Was low. In the time-of-flight secondary ion mass spectrometry, the detected amounts of C ₃ H ₃ O ₃ ⁻ ions and C ₃ H ₄ O ₂ ⁻ ions were 0.21 times the detected amount of Cu ⁺ ions and 0. It was as large as .48 times. As a result, the low temperature sinterability was poor and the bonding strength was low at 4 MPa and 8 MPa.

In Comparative Example 3, since the reducing agent was added and mixed under an alkaline condition of pH 10, copper ions became copper (II) hydroxide in the liquid, and the production yield of particles was not high at 80%. Also, grain growth occurs in the liquid, the BET specific surface area of the obtained bonding material particles is as small as 1.8 m ² / g, the BET diameter is as large as 373 nm, and the mass ratio of the organic protective film is 0.3 mass. % Was low. In time-of-flight secondary ion mass spectrometry, the detected amounts of C ₃ H ₃ O ₃ ⁻ ions and C ₃ H ₄ O ₂ ⁻ ions are 0.30 times and 0 times the detected amount of Cu ⁺ ions. It was as large as 50 times. The detected amount of C ₅ or more ions was as large as 0.010 times the detected amount of Cu ⁺ ions. As a result, the low temperature sinterability was poor and the bonding strength was low at 4 MPa and 8 MPa.

  In Comparative Examples 4 and 5, since ammonium formate and formic acid were used as the reducing agents, the reduction of copper citrate did not proceed and the target particles could not be produced.

  In Comparative Example 6, since the synthetic solution was heated at 70 ° C. for only 1 hour, reduction of copper citrate was not completed, and target particles could not be produced.

In Comparative Example 7, since the synthetic liquid was heated at 70 ° C. for a long time of 3 hours, the reduction of copper citrate proceeded too much, and grain growth occurred in the liquid, and the BET specific surface area of the obtained bonding material particles was The BET diameter was as small as 2.5 m ² / g, the BET diameter was as large as 268 nm, and the mass ratio of the organic protective film was as low as 0.4 mass%. In the time-of-flight secondary ion mass spectrometry, the detected amount of C ₃ H ₃ O ₃ ⁻ ions was 0.04 times smaller than the detected amount of Cu ⁺ ions. As a result, the low-temperature sinterability was poor and the bonding strength was as low as 10 MPa.

In Comparative Example 8, since the synthetic solution was heated at a high temperature of 85 ° C. for 1.5 hours, the reduction of copper citrate proceeded too much, and grain growth occurred in the solution, so that the specific surface area of the obtained bonding material particles was It was as small as 2.9 m ² / g and had a large BET diameter of 231 nm. The time-of-flight secondary ion mass spectrometry, C ₃ H ₃ O ₃ ^- ions and C ₃ H ₄ O ₂ ^- each of the detected amount of ions, and 0.03 times the detected amount of Cu ⁺ ions 0. It was as small as 04 times. As a result, the low-temperature sinterability was poor and the bonding strength was as low as 12 MPa.

  In Comparative Example 9, since the synthetic liquid was heated at a low temperature of 55 ° C. for 2.5 hours, reduction of copper citrate was not completed and target particles could not be produced.

On the other hand, as is clear from Tables 1 to 6, in Examples 1 to 11, a reducing agent was added and mixed under acidic conditions of pH 3 or more and less than pH 7, and hydrazine monohydrate and anhydrous hydrazine were used as the reducing agent. Since the maximum temperature during heating of the synthetic solution was set to 60 ° C. or higher and 80 ° C. or lower and the holding time was set to 1.5 hours or more and 2.5 hours or less, the production yield of the bonding material particles was 90% or more and 97% or more. The BET specific surface area was as large as 3.5 m ² / g or more and 7.5 m ² / g or less. The BET diameter was as small as 89 nm or more and 192 nm. The mass ratio of the organic protective film was 0.5 mass% or more and 2.0 mass% or less, and the copper nanoparticles of the mother particles were completely covered. In time-of-flight secondary ion mass spectrometry, the detected amount of each of C ₃ H ₃ O ₃ ⁻ ion and C ₃ H ₄ O ₂ ⁻ ion is 0.05 times or more the detected amount of Cu ⁺ ion. In the range of 0.2 times or less, the detected amount of C ₅ or more ions was less than 0.005 times the detected amount of Cu ⁺ ions. In addition, the decomposition rate of the organic protective film was as high as 75% by mass or more and 88% by mass or less, and the residue of the organic protective film was small. The gas components generated during the firing of the particles for bonding material were N ₂ , H ₂ O, CO ₂ , and C ₃ H ₆ O. From these facts, good joining strength as a joined body of 15 MPa or more and 52 MPa or less in the joining temperature range of 200 ° C. or more and 300 ° C. or less was obtained.

  The particles for bonding material of the present invention can be used as lead-free bonding particles for fine pitch, and the bonding paste obtained by using these bonding particles as a raw material can be suitably used for mounting fine electronic components.

10 Particles for bonding material 11 Base powder (copper nanoparticles)
12 Organic protective film

Claims (6)

In the particles for bonding material in which the organic protective film is formed on the surface of the copper nanoparticles,
The particles for bonding material have a BET specific surface area of 3.5 m ² / g or more and 8 m ² / g or less, and a BET diameter converted from the specific surface area of 80 nm or more and 200 nm or less,
The organic protective film is included in the range of 0.5 mass% or more and 2.0 mass% or less with respect to 100 mass% of the particles for bonding material,
When the particles for bonding material were analyzed by time-of-flight secondary ion mass spectrometry (TOF-SIMS), the respective detected amounts of C ₃ H ₃ O ₃ ⁻ ions and C ₃ H ₄ O ₂ ⁻ ions were detected. However, the detection amount of Cu ⁺ ions is in the range of 0.05 times or more and 0.2 times or less, and the detection amount of C ₅ or more ions is less than 0.005 times the detection amount of Cu ⁺ ions. Particles for a bonding material, characterized in that   The organic protective film decomposes by 50% by mass or more when heated at a temperature of 300 ° C. for 30 minutes in an inert gas atmosphere, and the decomposed gas is carbon dioxide gas, nitrogen gas, vaporized gas of acetone, and water vapor. 1. The particle for bonding material according to 1.   A bonding paste containing a volatile solvent and the particles for bonding material according to claim 1 or 2.   A pH adjuster is added to an aqueous dispersion of copper citrate at room temperature to adjust the pH to pH 3 or more and less than pH 7, and an hydrazine compound is added to and mixed with the aqueous dispersion of copper citrate whose pH is adjusted under an inert gas atmosphere, By heating this mixed solution to a temperature of 60 ° C. or higher and 80 ° C. or lower in an inert gas atmosphere and holding it for 1.5 hours or more and 2.5 hours or less, the copper citrate is reduced to produce copper nanoparticles. , A method for producing particles for bonding material, in which an organic protective film is formed on the surface of the copper nanoparticles.   A method for preparing a bonding paste by mixing a volatile solvent with the particles for bonding material according to claim 1 or 2 or the particles for bonding material manufactured by the method according to claim 4.   A step of applying a bonding paste according to claim 3 or a bonding paste prepared by the method according to claim 5 on a surface of a substrate or an electronic component to form a coating layer, and the substrate through the coating layer. The step of stacking the electronic component and the coating layer by heating the stacked substrate and the electronic component at a temperature of 200 ° C. or more and 300 ° C. or less under an inert atmosphere while applying a pressure of 30 MPa or less. And a step of forming a bonding layer by sintering, and bonding the substrate and the electronic component by the bonding layer.