JP7797874B2 - Joining sheet and method for manufacturing joined body - Google Patents

Description

The present invention relates to a bonding sheet and a method for manufacturing a bonded structure.

When assembling or mounting electronic components, a bonding material may be used to bond two or more components. For example, Patent Document 1 describes a bonding sheet formed by mixing copper particles with a solvent with a boiling point of 150°C or higher and pressing the mixture at room temperature.

Japanese Patent Application Laid-Open No. 2021-116463

Such bonding sheets are required to properly bond Ni.

The present invention was made in consideration of the above, and aims to provide a bonding sheet that can properly bond Ni, and a method for manufacturing a bonded body.

In order to solve the above-mentioned problems and achieve the objectives, the bonding sheet according to the present disclosure comprises copper particles and at least one additive selected from the group consisting of carboxylic acid, carboxylate, amine, and amine salt, wherein the content ratio of the additive to the copper particles is 1:95 to 5:95 by mass, the BET diameter of the copper particles is 500 nm or less, and the additive is at least one of carboxylic acid, carboxylate, amine, and amine salt having 2 to 8 carbon atoms.

The additive is preferably at least one of citric acid, ethylhexanoic acid, and ethylhexylamine.

It is preferable that the solution further contains a polyhydric alcohol solvent.

It is preferable that the solvent is polyethylene glycol.

It is preferable that the content ratio of the solvent to the copper particles is 1:95 to 5:95 by mass.

In order to solve the above-mentioned problems and achieve the objectives, the method for manufacturing a bonded body according to the present disclosure includes the steps of placing the bonding sheet on a first member, placing a second member on the bonding sheet to obtain a laminate in which the bonding sheet is placed between the first member and the second member, and heating the laminate to manufacture a bonded body in which the first member and the second member are bonded.

According to the present invention, Ni can be properly joined.

FIG. 1 is a schematic diagram of a bonding sheet according to this embodiment. FIG. 2 is a flowchart illustrating the method for manufacturing the bonding sheet according to this embodiment. FIG. 3 is a schematic diagram for explaining the method for manufacturing the bonded body. FIG. 4 is a table showing the properties and evaluation results of the bonding sheets of the examples.

The present invention will now be described in detail with reference to the drawings. The present invention is not limited to the following modes for carrying out the invention (hereinafter referred to as "embodiments"). The components in the following embodiments include those that would be easily conceivable to a person skilled in the art, those that are substantially the same, and those that are within the scope of what is known as equivalents. Furthermore, the components disclosed in the following embodiments can be combined as appropriate.

Figure 1 is a schematic diagram of a bonding sheet according to this embodiment. As shown in Figure 1, the bonding sheet 10 according to this embodiment contains copper particles 12, a solvent 20, and an additive 30.

(Copper particles)
The copper particles 12 have a BET diameter of 500 nm or less, preferably 50 nm to 300 nm. The BET diameter is calculated from the BET specific surface area and true density of the copper particles, assuming that the copper particles 12 are spherical or cubic, as determined by the BET method. Specifically, the BET diameter can be determined by the method described in the Examples below.

When the BET diameter of the copper particles 12 is 500 nm or less, the reaction area is increased, improving sinterability and allowing for proper bonding. If the BET diameter of the copper particles 12 is 50 nm or more, it is difficult to form strong agglomerates. This allows the surface of the copper particles 12 after pre-sintering to be uniformly coated with the solvent 20 described below. On the other hand, if the BET diameter of the copper particles 12 is 300 nm or less, the reaction area is large and sinterability upon heating is increased, allowing for the formation of a strong bonding layer. The BET diameter of the copper particles 12 is preferably in the range of 80 nm to 200 nm, and particularly preferably in the range of 80 nm to 170 nm.

The BET specific surface area of the copper particles 12 is preferably in the range of 2.0 m ² /g to 8.0 m ² /g, more preferably in the range of 3.5 m ² /g to 8.0 m ² /g, and particularly preferably in the range of 4.0 m ² /g to 8.0 m ² /g. The shape of the copper particles 12 is not limited to spherical, but may be acicular or flat plate-like.

The surfaces of the copper particles 12 are preferably coated with an organic protective film, which is a film of an organic substance. By being coated with an organic protective film, oxidation of the copper particles 12 is suppressed, making it even less likely that a decrease in sinterability due to oxidation of the copper particles 12 will occur. Note that the organic protective film coating the copper particles 12 is not formed by the solvent 20, and can be said to be not derived from the solvent 20. It can also be said that the organic protective film coating the copper particles 12 is not a copper oxide film formed by the oxidation of copper.

The fact that copper particles 12 are coated with an organic protective film can be confirmed by analyzing the surface of copper particles 12 using time-of-flight secondary ion mass spectrometry (TOF-SIMS). Therefore, in this embodiment, copper particles 12 preferably have a ratio of the amount of C 3 H 3 O ₃ ^- ions to the amount of Cu ⁺ ions detected by surface analysis using time-of-flight secondary ion mass spectrometry (C ₃ H ₃ O ₃ ^- /Cu ⁺ ratio) of 0.001 or more. It is more preferable that the C ₃ H _{3 O 3} ^- /Cu ⁺ ratio is in the range of 0.05 or more and 0.2 or less. Note that the "surface of copper particles 12 _" in this analysis does not refer to the surface of copper particles 12 after the organic protective film has been removed from the copper particles 12, but refers to the surface of copper particles 12 including the organic protective film coating them (i.e., the surface of the organic protective film).

The copper particles 12 may _be subjected to surface analysis using time-of ^- flight secondary ion mass spectrometry to detect _C3H4O2- ions and _C5 or larger ions. The ratio of the detected amount of _C3H4O2- ions to the detected amount of Cu ⁺ ions ( _{C3H4O2- / Cu} ^{+ ratio} ) is preferably 0.001 ^or greater. Furthermore, the ratio of the detected amount of _{C5 or} larger ions to the detected amount of Cu ⁺ ions ( _{C5 or} larger ions/ _Cu ⁺ ratio) is preferably less than 0.005.

_{The C3H3O3-} ions ^, _C3H4O2- ions _, and _{C5 or} larger ions detected by time-of-flight secondary ion mass spectrometry originate from ^the organic protective film coating the surface of the copper particles 12. Therefore _, when _{the C3H3O3-} ^/ _Cu ⁺ ratio and _{the C3H4O2-} /Cu+ ratio are each 0.001 or more, the surfaces of the copper particles 12 are less likely to oxidize _and the copper particles 12 are less likely to aggregate. Furthermore, when _the ^{C3H3O3- /} Cu ⁺ ratio and _{the C3H4O2-} /Cu ⁺ ratio are _0.2 ^or less, oxidation and aggregation ^of the copper particles 12 can be suppressed without excessively reducing the sinterability of the copper particles 12, and further _, the generation of decomposition gas of _the organic protective film during heating can be suppressed, thereby forming a bonding layer with fewer voids. To further improve the oxidation resistance of copper particles 12 during storage and the sinterability at low temperatures, the _C3H3O3- ^/ _Cu ⁺ ratio and the _C3H4O2- /Cu ⁺ ratio are preferably in the range of 0.08 to _0.16 . Furthermore, if _{the C5 or} larger ^ion /Cu ⁺ ratio is 0.005 or larger, a large amount of organic protective film with a relatively high desorption temperature is present on the particle surface, resulting in insufficient sinterability and a difficult to obtain strong bonding layer. The _C5 or larger ion/Cu ⁺ ratio is preferably less than 0.003.

The organic protective film is preferably derived from citric acid. A method for producing copper particles 12 coated with a citric acid-derived organic protective film is described below. The coating amount of the organic protective film on the copper particles 12 is preferably in the range of 0.5% to 2.0% by mass, more preferably 0.8% to 1.8% by mass, and even more preferably 0.8% to 1.5% by mass, based on 100% by mass of the copper particles. A coating amount of the organic protective film of 0.5% by mass or more allows the copper particles 12 to be uniformly coated with the organic protective film, thereby more reliably suppressing oxidation of the copper particles 12. Furthermore, a coating amount of the organic protective film of 2.0% by mass or less prevents the generation of voids in the sintered body (bonding layer) of the copper particles due to gas generated by decomposition of the organic protective film upon heating. The coating amount of the organic protective film can be measured using a commercially available device. For example, the coating amount can be measured using a differential thermobalance TG8120-SL (manufactured by RIGAKU Corporation). In this case, for example, copper particles from which moisture has been removed by freeze-drying are used as the sample. Measurements are made in nitrogen (G2 grade) gas to prevent oxidation of the copper particles, and the temperature is raised at a rate of 10°C/min. The weight loss rate when heated from 250°C to 300°C can be defined as the amount of organic protective film coating. In other words, coating amount = (sample weight after measurement) / (sample weight before measurement) x 100 (wt%). Measurements can be made three times using copper particles from the same lot, and the arithmetic mean value can be used as the amount of coating.

When the copper particles 12 are heated at 300°C for 30 minutes in an inert gas atmosphere such as argon gas, it is preferable that at least 50% by mass of the organic protective film decomposes. The citric acid-derived organic protective film generates carbon dioxide gas, nitrogen gas, acetone vapor, and water vapor upon decomposition.

Copper particles 12 coated with a citric acid-derived organic protective film can be produced, for example, as follows. First, an aqueous dispersion of copper citrate is prepared, and a pH adjuster is added to this copper citrate aqueous dispersion to adjust the pH to 2.0 or more and 7.5 or less. Next, in an inert gas atmosphere, 1.0 to 1.2 equivalents of a hydrazine compound capable of reducing copper ions are added as a reducing agent to this pH-adjusted copper citrate aqueous dispersion and mixed. The resulting mixture is heated to a temperature of 60°C to 80°C in an inert gas atmosphere and held for 1.5 to 2.5 hours. This reduces the copper ions eluted from the copper citrate to produce copper particles 12, and also forms an organic protective film derived from citric acid on the surface of the copper particles 12.

An aqueous dispersion of copper citrate can be prepared by adding powdered copper citrate to pure water, such as distilled water or ion-exchanged water, to a concentration of 25% to 40% by weight, and stirring with a stirring blade to uniformly disperse the mixture. Examples of pH adjusters include triammonium citrate, ammonium hydrogen citrate, and citric acid. Among these, triammonium citrate is preferred because it facilitates mild pH adjustment. The pH of the aqueous dispersion of copper citrate is set to 2.0 or higher to accelerate the elution rate of copper ions eluted from the copper citrate, thereby facilitating the rapid production of copper particles and achieving the desired fine copper particles 12. The pH is set to 7.5 or lower to prevent the eluted copper ions from converting to copper(II) hydroxide, thereby increasing the yield of copper particles 12. A pH of 7.5 or lower prevents the reducing power of the hydrazine compound from becoming excessively high, making it easier to obtain the desired copper particles 12. The pH of the copper citrate aqueous dispersion is preferably adjusted to a range of 4 to 6.

The reduction of copper citrate with a hydrazine compound is carried out in an inert gas atmosphere to prevent oxidation of copper ions dissolved in the liquid. Examples of inert gases include nitrogen gas and argon gas. Hydrazine compounds have the advantages of not leaving any residue after the reduction reaction when reducing copper citrate under acidic conditions, being relatively safe, and being easy to handle. Examples of such hydrazine compounds include hydrazine monohydrate, hydrazine anhydrous, hydrazine hydrochloride, and hydrazine sulfate. Among these hydrazine compounds, hydrazine monohydrate and hydrazine anhydrous are preferred, as they do not contain components that could become impurities, such as sulfur and chlorine.

Generally, copper produced in an acidic solution with a pH of less than 7 dissolves. However, in this embodiment, a hydrazine compound, which serves as a reducing agent, is added to and mixed with an acidic solution with a pH of less than 7, and copper particles 12 are produced in the resulting mixture. As a result, components derived from citric acid produced from copper citrate quickly coat the surfaces of the copper particles 12, thereby suppressing dissolution of the copper particles 12. After adjusting the pH, the aqueous dispersion of copper citrate is preferably kept at a temperature of 50°C or higher and 70°C or lower to facilitate the reduction reaction.

The mixed solution containing the hydrazine compound is heated to a temperature of 60°C to 80°C in an inert gas atmosphere and maintained for 1.5 to 2.5 hours to generate copper particles 12 and to form an organic protective film on the surface of the generated copper particles 12. Maintaining the heated solution in an inert gas atmosphere is intended to prevent oxidation of the generated copper particles 12. The starting material, copper citrate, typically contains approximately 35% by weight of copper. Adding a hydrazine compound reducing agent to a copper citrate aqueous dispersion containing this amount of copper, heating it to the above temperature, and maintaining it for the above time ensures a balanced generation of copper particles 12 and the formation of an organic protective film on the surface of the copper particles 12. This allows for the production of copper particles 12 to be obtained, with the organic protective film covering the copper particles 12 in a range of 0.5% to 2.0% by weight based on 100% by weight of copper particles. If the heating temperature is below 60°C and the holding time is less than 1.5 hours, the copper citrate may not be completely reduced, the rate at which copper particles 12 are produced may become too slow, and the amount of organic protective film coating the copper particles 12 may become excessive. If the heating temperature exceeds 80°C and the holding time exceeds 2.5 hours, the rate at which copper particles 12 are produced may become too fast, and the amount of organic protective film coating the copper particles 12 may become too small. The preferred heating temperature is 65°C or higher and 75°C or lower, and the preferred holding time is 2 hours or higher and 2.5 hours or lower.

The copper particles 12 produced in the mixed solution are separated from the mixed solution in an inert gas atmosphere using, for example, a centrifuge, and then dried using freeze-drying or vacuum drying to obtain copper particles 12 whose surfaces are coated with an organic protective film. Because the surfaces of these copper particles 12 are coated with an organic protective film, they are resistant to oxidation even when stored in the air until they are used as the bonding sheet 10.

(solvent)
The solvent 20 acts as a binder for the copper particles 12. The solvent 20 may be any solvent, but is preferably an organic solvent, and more preferably a polyhydric alcohol.

The boiling point of solvent 20 is preferably 150°C or higher, and preferably 200°C or lower. The boiling point of solvent 20 is more preferably 150°C or higher and 300°C or lower, and even more preferably 200°C or higher and 250°C or lower. Furthermore, solvent 20 preferably has a molecular weight in the range of 100 to 1000, more preferably 200 to 800, and particularly preferably 200 to 600. Furthermore, the solvent is preferably a compound having a reducing group at its terminal. The reducing group is preferably a hydroxyl group. Furthermore, solvent 20 preferably has a dielectric constant in the range of 4 to 80, more preferably 10 to 45, and even more preferably 20 to 40. The dielectric constant may be measured using a liquid dielectric constant meter (Model 871, manufactured by Nippon Luft Co., Ltd.).

For example, diol compounds and triol compounds can be used as the solvent 20. Examples of diol compounds include ethylene glycol, diethylene glycol, and polyethylene glycol. Examples of triol compounds include glycerin, butanetriol, and polyoxypropylenetriol. These organic solvents and polymer solvents may be used alone or in combination of two or more.

Note that the solvent 20 is not an essential component and does not need to be included in the bonding sheet 10.

(Additives)
The additive 30 is at least one of a carboxylic acid, a carboxylate, an amine, or an amine salt. The additive 30 is at least one of a carboxylic acid, a carboxylate, an amine, or an amine salt having 2 to 8 carbon atoms. That is, the additive 30 can be said to include at least one of a carboxylic acid having 2 to 8 carbon atoms, a carboxylate having 2 to 8 carbon atoms, an amine having 2 to 8 carbon atoms, and an amine salt having 2 to 8 carbon atoms. The number of carbon atoms here refers to the number of C atoms in the chemical formula of the additive. Furthermore, the additive 30 is more preferably at least one of citric acid, ethylhexanoic acid, and ethylhexylamine. Using such a material as the additive 30 allows for appropriate bonding of Ni.

(Characteristics of the bonding sheet)
In the bonding sheet 10, the content ratio of the solvent 20 to the copper particles 12 is preferably 1:95 to 5:95 by mass (=solvent:copper particles), more preferably 1.5:95 to 4.5:95, and even more preferably 2:95 to 4:95. For example, a content ratio of the solvent 20 to the copper particles 12 of 1:95 to 5:95 by mass means that the content of the solvent 20 is in the range of 90% by mass to 95% by mass and the content of the copper particles 12 is in the range of 1% by mass to 5% by mass, and the same applies to other content ratios.
In the bonding sheet 10, the content ratio of the additive 30 to the copper particles 12 is preferably 1:95 to 5:95 (=additive:copper particles) by mass, more preferably 1.5:95 to 4.5:95, and even more preferably 2:95 to 4:95.
In the bonding sheet 10, the content ratio of the additive 30 to the solvent 20 is preferably 1:5 to 3:3 (=additive:solvent) by mass, more preferably 1.5:4.5 to 3:3, and even more preferably 2:4 to 3:3.

The bonding sheet 10 preferably has a density of 50% to 90%. The density is the proportion of the space occupied by copper particles 2 in the bonding sheet 1. A density of 50% or more enhances adhesion between the copper particles 2, making it easier to form a dense bonding layer with fewer voids. Furthermore, a density of 90% or less allows the surfaces of the copper particles 2 to be covered with the solvent 3, making oxidation of the copper particles 2 less likely to occur and further suppressing the deterioration of sinterability due to oxidation of the copper particles. The density is more preferably 55% to 75%, and even more preferably 60% to 70%. The density of the bonding sheet 1 can be calculated by observing a cross section of the bonding sheet 1 with a scanning electron microscope (SEM), binarizing the resulting SEM image, and separating it into the copper particle 2 portion and the space containing the solvent 3. Specifically, it can be calculated using the method described in the examples below.

There are no particular restrictions on the shape or size of the bonding sheet 10. The bonding sheet 10 may be, for example, a circular sheet with a diameter of 1 mm to 50 mm, or a rectangular sheet with one side measuring 1 mm to 50 mm. There are no particular restrictions on the thickness of the bonding sheet 10, but it is preferably in the range of 50 μm to 1000 μm.

(Method for manufacturing bonding sheet)
2 is a flowchart illustrating a method for manufacturing a bonding sheet according to this embodiment. As shown in FIG. 2, in this manufacturing method, copper particles 12, a solvent 20, and an additive 30 are prepared (step S10), and the prepared copper particles 12, solvent 20, and additive 30 are mixed (step S12). In this step, the copper particles 12, solvent 20, and additive 30 may be mixed so that the content ratio of the copper particles 12, solvent 20, and additive 30 falls within the range specified above. The copper particles 12, solvent 20, and additive 30 may be mixed by any method, but for example, a rotation-revolution mixer or a planetary mixer may be used.

Next, the bonding sheet 10 is formed using a mixture of copper particles 12, solvent 20, and additive 30 (step S14). In this process, the mixture of copper particles 12, solvent 20, and additive 30 is pressed at room temperature under a predetermined pressure for a predetermined time to form a sheet, thereby obtaining the bonding sheet 10. Room temperature may refer to room temperature, but is not limited thereto, and may be a temperature at which sintering of the copper particles 12 does not proceed (for example, 100°C or less). The predetermined pressure here is preferably 1 MPa or more and 30 MPa or less, more preferably 1 MPa or more and 20 MPa or less, and even more preferably 1 MPa or more and 10 MPa or less. The predetermined temperature here is preferably 40°C or more and 250°C or less, more preferably 40°C or more and 200°C or less, and even more preferably 40°C or more and 150°C or less. The predetermined time (the time for maintaining the predetermined pressure and temperature) is preferably 1 minute or more and 30 minutes or less, more preferably 2 minutes or more and 25 minutes or less, and even more preferably 3 minutes or more and 15 minutes or less.
By molding the bonding sheet 10 under these conditions, the bonding sheet 10 can be appropriately manufactured. The method for molding the mixture into a sheet may be a rolling method using a pressure roller or a pressing method using a mold. For example, the bonding sheet 10 may be obtained by molding the mixture into a sheet and cutting the resulting molded product into a predetermined shape.

Note that the bonding sheet 10 is not limited to being manufactured by the above method, and any method for manufacturing the bonding sheet 10 may be used.

(Method for manufacturing a bonded body)
Next, a method for manufacturing a bonded structure 100 by bonding members together using the bonding sheet 10 will be described. FIG. 3 is a schematic diagram for explaining a method for manufacturing a bonded structure. In this embodiment, the bonded structure 100 is manufactured by bonding a first member A and a second member B using the bonding sheet 10 as a bonding layer. The first member A and the second member B may be any members. For example, one of the first member A and the second base member B may be a substrate, and the other may be an electronic component. That is, a semiconductor module in which a substrate and an electronic component are bonded by a bonding layer may be manufactured as the bonded structure 100. The substrate is not particularly limited, but examples thereof include an oxygen-free copper plate, a copper-molybdenum plate, a high-heat-dissipation insulating substrate (e.g., DCB (Direct Copper Bond)), and a substrate for mounting a semiconductor element such as an LED (Light Emitting Diode) package. Examples of electronic components include semiconductor elements such as IGBTs (Insulated Gate Bipolar Transistors), diodes, Schottky barrier diodes, MOS-FETs (Metal Oxide Semiconductor Field Effect Transistors), thyristors, logic, sensors, analog integrated circuits, LEDs, semiconductor lasers, and oscillators.
In the following description, a first member A and a second member B are joined using one joining sheet 10, but this is not limited to this. A first member A and a second member B may be joined using multiple joining sheets 10 to form a joined body 100, or three or more members may be joined using one or multiple joining sheets 10 to form a joined body 100.

Moreover, in this embodiment, at least one of the first member A and the second member B has Ni on its surface. "Having Ni on its surface" means that the entire member may be Ni, or that only the surface may be coated with Ni. Furthermore, Ni here refers to the elemental metal Ni.

The bonded body 100 can be produced by placing a bonding sheet 10 between a first member A and a second member B to obtain a laminate, and then heating the resulting laminate to sinter the copper particles 12 of the bonding sheet 10 to form a bonding layer. The heating temperature for the laminate is, for example, in the range of 150°C to 300°C. The heating time for the laminate is, for example, in the range of 10 minutes to 1 hour. The laminate is preferably heated in an inert gas atmosphere while being pressurized in the stacking direction. Nitrogen gas or argon gas can be used as the inert gas. The pressurization pressure for the laminate is preferably in the range of 0.5 MPa to 30 MPa.

(effect)
As described above, the bonding sheet 10 according to this embodiment includes copper particles 12 and at least one additive 30 selected from the group consisting of a carboxylic acid, a carboxylate, an amine, and an amine salt. The additive 30 to copper particles 12 content ratio is 1:95 to 5:95 by mass. The copper particles 12 have a BET diameter of 500 nm or less. The additive 30 is at least one of a carboxylic acid, a carboxylate, an amine, and an amine salt having 2 to 8 carbon atoms. The bonding sheet 10 according to this embodiment can properly bond Ni by including the additive 30 having 2 to 8 carbon atoms within this range. Furthermore, by using copper particles 12 with a diameter of 500 nm or less, the surface area is increased, improving sinterability and allowing Ni to be properly bonded.

The additive 30 is preferably at least one of citric acid, ethylhexanoic acid, and ethylhexylamine. Using such an additive 30 allows for more appropriate bonding of Ni.

The bonding sheet 10 preferably further contains a polyhydric alcohol solvent 20. Using the solvent 20 allows sintering to proceed properly, allowing for more appropriate bonding of the Ni.

The solvent 20 is preferably polyethylene glycol. Using polyethylene glycol (PEG) as the solvent 20 allows the sintering to proceed properly, resulting in better bonding of the Ni.

The content ratio of the solvent 20 to the copper particles 12 is preferably 1:95 to 5:95 by mass. By including this amount of solvent 20, sintering can proceed properly, allowing the Ni to be bonded more appropriately.

The manufacturing method for the bonded structure 100 according to this embodiment includes the steps of placing the bonding sheet 10 on a first member A, placing a second member B on the bonding sheet 10 to obtain a laminate in which the bonding sheet is placed between the first member and the second member, and heating the laminate to manufacture the bonded structure 100 in which the first member A and the second member B are bonded. According to this manufacturing method, the bonded structure 100 can be manufactured appropriately by using the bonding sheet 10.

(Example)
Next, examples will be described. Fig. 4 is a table showing the properties and evaluation results of the bonding sheets of the respective examples.

Example 1
(Preparation of copper particles)
In Example 1, copper citrate 2.5 hydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and ion-exchanged water were stirred and mixed using a stirring blade to prepare an aqueous dispersion of copper citrate with a concentration of 30% by mass. Next, an aqueous solution of ammonium citrate was added as a pH adjuster to the resulting aqueous dispersion, adjusting the pH of the copper citrate dispersion to 5. The resulting aqueous dispersion of copper citrate was then heated to 50°C, and while maintaining the temperature, an aqueous solution of hydrazine monohydrate (diluted 2-fold) was added all at once as a copper ion reducing agent under a nitrogen gas atmosphere, followed by stirring and mixing using a stirring blade. The amount of hydrazine monohydrate aqueous solution added was 1.2 times the amount required to reduce all copper ions. The resulting mixture was heated to 70°C under a nitrogen gas atmosphere and maintained at that temperature for 2 hours to produce copper particles. The produced copper particles were collected using a centrifuge. The collected copper particles were dried by a reduced pressure drying method to prepare copper particles.

A specific surface area measuring device (Quantachrome Instruments, QUANTACHROME AUTOSORB-1) was used. After removing the adsorbed gas in advance at a degassing temperature of 50°C for 60 minutes, the amount of nitrogen gas adsorbed by the copper particles was measured, and the specific surface area of the copper particles was determined by the BET method. Using the obtained specific surface area S (m ² /g) and the density ρ (g/cm ³ ) of the copper particles, the BET diameter was calculated according to the following formula.
BET diameter (nm) = 6000/(ρ (g/cm ³ ) x S (m ² /g))

(Production of bonding sheet)
Copper particles were mixed with polyethylene glycol (average molecular weight 200) as a solvent and citric acid as an additive. Figure 4 shows the BET diameter of the copper particles, the type of solvent, the type of additive, and the number of carbon atoms in the additive (number of carbon atoms in the additive). Figure 4 also shows the mixing ratio of the copper particles, solvent, and additive, i.e., the mass ratio of the copper particles, solvent, and additive (copper particles:solvent:additive).
Next, the obtained mixture was rolled using a powder rolling mill (2RM-63K, manufactured by Ohno Roll Co., Ltd.) with a pressure roller at a gap width of 500 μm to obtain a bonding sheet having a thickness of 500 μm. The density of the obtained bonding sheet was measured by the following method.

(Density of bonding sheet)
After sealing the bonding sheet with epoxy resin, the bonding sheet was cut horizontally relative to the thickness direction of the bonding sheet. The cut surface of the bonding sheet was subjected to mechanical polishing and cross-polishing to expose the cross section of the bonding sheet. Next, the cut surface of the bonding sheet was observed at 50,000x magnification using a scanning electron microscope (SEM). The obtained SEM image was binarized using image processing software (ImageJ, manufactured by the National Institutes of Health, USA) to separate the particle portion and the void portion, and the density was calculated using the following formula.
Density (%)=(total area of particle parts/(total area of particle parts+total area of pore parts))×100

The density was measured from 10 randomly taken SEM images. The value shown in Figure 4 is the average density calculated from the 10 SEM images.

(Production of zygotes)
The bonding sheet was cut using a commercially available cutter knife to prepare a bonding sheet piece (2.5 mm square x 500 μm thick). The above bonding sheet piece (2.5 mm square x 500 μm thick) was placed on a 30 mm square x 1 mm thick nickel-plated oxygen-free copper substrate. Next, a 2.5 mm square x 1 mm thick oxygen-free copper dummy element was placed on the bonding sheet piece. In this way, a laminate was obtained in which the nickel-plated oxygen-free copper substrate and the 2.5 mm square oxygen-free copper dummy element were laminated via the bonding sheet piece. The obtained laminate was held for 15 minutes using a die bonder (HTB-MM, manufactured by Alpha Design Co., Ltd.) under conditions of a nitrogen gas atmosphere, a pressurized pressure of 5 MPa, and a temperature of 300 ° C., to produce a bonded body (Sample A) in which the nickel-plated oxygen-free copper substrate and the 2.5 mm square oxygen-free copper dummy element were bonded via a copper bonding layer.

(Example 2-7)
In Examples 2-7, a bonded body was obtained in the same manner as in Example 1, except that at least one of the type of additive, the compounding ratio of the additive and the solvent, and the type of copper particles was changed as shown in FIG.

(Comparative Examples 1-4)
In Comparative Example 1-4, a bonded body was obtained in the same manner as in Example 1, except that at least one of the type of additive, the compounding ratio of the additive and the solvent, and the type of copper particles was changed as shown in FIG.

(evaluation)
The bonded bodies of each example were evaluated, and the evaluation was carried out by evaluating the shear strength of the bonded bodies.

The shear strength of the bonded structures was evaluated using a method in accordance with JIS Z 3198-7 (Lead-Free Solder Test Methods - Part 7: Shear Test Method for Solder Joints of Chip Components). Specifically, a load was applied to an oxygen-free copper dummy element using a tool from a bond tester (Nordson DAGE, SERIES 4000), and the load (maximum shear load) at which the oxygen-free copper dummy element peeled from the copper bonding layer was measured. The tool movement speed was 50 μm/sec, and the gap between the tip of the tool and the oxygen-free copper substrate was 50 μm. The obtained maximum shear load was converted to Newtons and divided by the area of the copper bonding layer (2.5 mm × 2.5 mm) to obtain the shear strength (unit: MPa). Seven bonded structures were fabricated, and the shear strength of each was measured. The results are shown in Figure 4.

In the evaluation, a joint with a shear strength of 30 MPa or more was considered pass, and a shear strength of less than 30 MPa was considered fail.

As shown in Figure 4, in examples using bonding sheets in which at least one additive selected from carboxylic acids, carboxylates, amines, and amine salts with a carbon number of 2 to 8 was added to copper particles with a BET diameter of 500 nm or less, with the additive to copper particles content ratio being 1:95 to 5:95 by mass, the shear strength was 30 MPa or more, indicating that Ni could be properly bonded. On the other hand, in comparative examples that did not satisfy at least one of the following conditions: using a BET diameter of 500 nm or less, using at least one additive selected from carboxylic acids, carboxylates, amines, and amine salts with a carbon number of 2 to 8, and keeping the additive to copper particle content ratio within the above range, the shear strength was unsatisfactory, indicating that Ni could not be properly bonded.

(option evaluation)
As an optional evaluation, the void ratio of the bonded body was also evaluated.

(Void ratio of bonded body)
The copper bonding layer of the resulting bonded body (Sample B) was measured for an ultrasonic flaw detection image using an ultrasonic flaw detector (FINE-SAT, manufactured by Hitachi High-Technologies Corporation). The obtained ultrasonic flaw detection image was binarized using image processing software (ImageJ, manufactured by the National Institutes of Health, USA) to separate the image into voids (cavities) and the bonded body (copper particle sintered body), and the void fraction was calculated using the following formula.
Void rate (%) = (total area of voids / area of copper bonding layer (10 mm x 10 mm)) x 100

Seven bonded bodies were produced, and the void ratio was measured for each bonded body. The results are shown in Figure 4.

Although the embodiments of the present invention have been described above, the embodiments are not limited to the content of these embodiments. Furthermore, the components described above include those that would be easily imagined by a person skilled in the art, those that are substantially the same, and those that are within the scope of what is known as equivalents. Furthermore, the components described above can be combined as appropriate. Furthermore, various omissions, substitutions, or modifications of the components can be made without departing from the spirit of the embodiments described above.

10 Bonding sheet 12 Copper particles 20 Solvent 30 Additive

Claims (6)

copper particles and at least one additive selected from the group consisting of a carboxylic acid, a carboxylic acid salt, an amine, and an amine salt;
The content ratio of the additive to the copper particles is 1:95 to 5:95 by mass,
The BET diameter of the copper particles is 50 nm or more and 500 nm or less,
the additive is at least one of a carboxylic acid, a carboxylic acid salt, an amine, and an amine salt, each having from 2 to 8 carbon atoms;
The copper particles are unsintered and have surfaces coated with an organic protective film, which is an organic film.
Joining sheet. The bonding sheet according to claim 1, wherein the additive is at least one of citric acid, ethylhexanoic acid, and ethylhexylamine. The bonding sheet according to claim 1 or claim 2, further comprising a solvent for a polyhydric alcohol. The bonding sheet according to claim 3, wherein the solvent is polyethylene glycol. The bonding sheet according to claim 3 or 4, wherein the content ratio of the solvent to the copper particles is 1:95 to 5:95 by mass. A step of placing the bonding sheet according to any one of claims 1 to 5 on a first member;
A step of arranging a second member on the bonding sheet to obtain a laminate in which the bonding sheet is arranged between a first member and a second member;
a step of manufacturing a bonded body in which the first member and the second member are bonded by heating the laminate;
Including,
A method for manufacturing a bonded body.