JP2023098497A - Method for manufacturing joined body - Google Patents

Abstract

To appropriately carry out joining while simplifying a joining process.SOLUTION: A method for manufacturing a joined body includes the steps of: disposing a joining sheet 10 including a copper sintered body on a first member A; adding a solvent 20 to the joining sheet 10; obtaining a laminate in which the joining sheet 10 with the solvent 20 added thereto is disposed between the first member A and a second member B by disposing the second member B on the joining sheet 10; and manufacturing a joined body 100 with the first member A and the second member B joined to each other by heating the laminate at a heating temperature of 200°C or above.SELECTED DRAWING: Figure 4

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a joined body.

2. Description of the Related Art A bonding material is sometimes used to bond two or more components when assembling or mounting electronic components. For example, Patent Literature 1 describes that a joined body is produced by joining members together using a joining sheet formed by mixing copper particles and a solvent.

JP 2021-116463 A

When joining members together using a joining sheet, it is desired to join them appropriately while simplifying the joining process.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for manufacturing a bonded body that can be properly bonded while simplifying the bonding process.

In order to solve the above-described problems and achieve the object, a method for manufacturing a joined body according to the present disclosure includes the steps of placing a joining sheet containing a sintered body of copper on a first member; By adding a solvent to the sheet and placing the second member on the bonding sheet, the bonding sheet added with the solvent is formed between the first member and the second member. obtaining an arranged laminate; and heating the laminate at a heating temperature of 200° C. or higher to manufacture a joined body in which the first member and the second member are joined. include.

In the step of manufacturing the bonded body, it is preferable to heat the laminate at the heating temperature while applying pressure to the laminate at 1 MPa or more and 30 MPa or less.

It is preferable to use the bonding sheet having a filling rate of 50% or more.

It is preferable to use the joining sheet having a Young's modulus of 1 GPa or more.

It is preferable to use the joining sheet having a Young's modulus of 10 GPa or more.

It is preferable to use the bonding sheet having a thermal conductivity of 10 W/mK or more and 50 W/mK or less.

In the step of adding the solvent, it is preferable to use a polyhydric alcohol as the solvent.

It is preferable to further include the step of adding at least one of carboxylic acid, carboxylate, amine, and amine salt to the joining sheet.

ADVANTAGE OF THE INVENTION According to this invention, it can join appropriately, simplifying a joining process.

FIG. 1 is a schematic diagram of a bonding sheet according to this embodiment. FIG. 2 is a schematic partially enlarged view of the joining sheet. FIG. 3 is a flow chart illustrating a method for manufacturing a joining sheet according to this embodiment. FIG. 4 is a schematic diagram for explaining the manufacturing method of the joined body. FIG. 5 is a table showing manufacturing conditions and evaluation results for each example.

Hereinafter, the present invention will be described in detail with reference to the drawings. It should be noted that the present invention is not limited by the following modes for carrying out the invention (hereinafter referred to as embodiments). In addition, components in the following embodiments include those that can be easily assumed by those skilled in the art, those that are substantially the same, and those that fall within a so-called equivalent range. Furthermore, the constituent elements disclosed in the following embodiments can be combined as appropriate.

(First embodiment)
In the method for manufacturing a joined body according to the present embodiment, the joining sheet 10 is used to join the first member and the second member, thereby joining the first member and the second member together. manufacture the body. First, the joining sheet 10 will be described.

(bonding sheet)
FIG. 1 is a schematic diagram of a bonding sheet according to this embodiment. The joining sheet 10 according to this embodiment is a sheet-shaped member for joining members together. As shown in FIG. 1, the joining sheet 10 is a sintered body of copper, and has a structure in which a plurality of copper particles 12 are bonded by sintering. It is preferable that the joining sheet 10 is further sintered when heated at 150° C. to 300° C. (150° C. to 300° C.). Here, the progress of sintering indicates that the bonding between the copper particles 12 progresses further, thereby increasing the filling rate. Since the joining sheet 10 contains a sintered body, it is possible to maintain a high Young's modulus, suppress the possibility of breakage, and proceed with sintering to appropriately join the members. Note that the joining sheet 10 may contain a sintered body of copper, and may partially contain copper particles that have not been sintered.

The bonding sheet 10 preferably has a filling rate of 50% or more, more preferably 50% or more and 70% or less, even more preferably 52% or more and 68% or less, and 55% or more and 65% or less. is more preferable. When the filling rate falls within this range, further sintering can proceed appropriately, and the members can be appropriately joined together.
The filling rate is the ratio of bulk density to true density (bulk density/true density). Here, the true density refers to the density of the material itself (copper in this case), ie, the theoretical density, assuming that there are no pores, cracks, or the like in the sintered body. The bulk density refers to a value obtained by dividing the weight of the bonding sheet 10 by the volume determined from the external dimensions of the bonding sheet 10 . The volume determined from the external dimensions refers to the total volume including the pores of the joining sheet 10 .
For the true density, for example, the literature value of copper density (eg, 8.96 g/cm ³ ) can be used. Also, the bulk density can be measured using a balance, a three-dimensional measuring machine, and a micrometer. For example, the area and thickness of the bonding sheet 10 are measured using a three-dimensional measuring machine and a micrometer, and the value obtained by multiplying the area and thickness is taken as the volume obtained from the external dimensions. Then, the weight of the bonding sheet 10 is measured with a balance, and the value obtained by dividing the measured weight by the volume determined from the external dimensions is defined as the bulk density.
As will be described later, the bonding sheet 10 may be a sintered body of copper impregnated with a resin. The filling rate in this case refers to the filling rate of the copper sintered body excluding the resin. Although the properties of the joining sheet 10 other than the filling rate are defined in the following description, they may also refer to the properties of the sintered body of copper excluding the resin.

The bonding sheet 10 has a surface 10a which is a main surface on one side and a surface 10b which is a main surface on the other side.
is preferably 1 μm or more and 40 μm or less, more preferably 1 μm or more and 35 μm or less, and even more preferably 1 μm or more and 30 μm or less. At least one of the surface 10a and the surface 10b of the bonding sheet 10 may have an arithmetic mean roughness Ra within the above range. When the arithmetic mean roughness Ra (surface roughness) falls within this range, further sintering can proceed appropriately, and members can be properly joined together.
The arithmetic mean roughness Ra can be measured according to JIS B 0601:2001.

FIG. 2 is a schematic partially enlarged view of the joining sheet. In the bonding sheet 10, the average particle diameter, which is the average value of the particle diameters D of the copper particles 12, is preferably 100 nm or more and 350 nm or less, more preferably 150 nm or more and 300 nm or less, and 200 nm or more and 250 nm or less. is more preferable. By keeping the average particle size within this range, the surface area of the joining sheet 10 can be kept large, and further sintering can proceed appropriately.
In the bonding sheet 10, the copper particles 12 are bonded to each other by sintering, so the average particle size of the copper particles 12 means that the bonding sheet 10 is separated from the bonded copper particles 12 at the interface, It can be said that it is the average value of the particle size of each of the separated copper particles 12 .
For example, the BET diameter calculated based on the BET specific surface area may be used as the average particle diameter of the copper particles 12 . In this case, a specific surface area measuring device (QUANTACHROME AUTOSORB-1 manufactured by Quantachrome Instruments) is used to measure the amount of nitrogen gas adsorbed by the bonding sheet 10, and the specific surface area of the bonding sheet 10 is determined by the BET method. rice field. Using the obtained specific surface area S (m ² /g) and the density ρ (g/cm ³ ) of the copper particles, the BET diameter is calculated from the following formula, and the average particle diameter of the copper particles 12 is obtained. may be
BET diameter (nm) = 6000/(ρ (g/cm ³ ) x S (m ² /g))

The joining sheet 10 preferably has a Young's modulus of 1 GPa or more, more preferably 10 GPa or more, still more preferably 10 GPa or more and 30 GPa or less, even more preferably 11 GPa or more and 20 GPa or less, and 12 GPa. It is more preferable to be 15 GPa or less. When the Young's modulus falls within this range, the bonding sheet 10 can be prevented from being damaged and the handling property can be improved, so that the bonding process can be simplified and the members can be bonded with high shear strength.
The Young's modulus can be measured using a Picodenter HM500 (manufactured by Fisher Instruments, analysis software WIN-HCU ver.7.0), which is an apparatus conforming to ISO14577, which is the standard for the nanoindentation method. The nanoindentation method is a method of calculating hardness and Young's modulus from the load applied to the sample and the indentation depth.
In the present embodiment, the upper surface of the bonding sheet 10 is measured five times at random using the apparatus and analysis software, and the indentation Young's modulus obtained is measured five times. Young's modulus. The measurement conditions were as follows: the terminal was a Vickers indenter; the indentation depth was 2 μm; the indentation speed was 0.067 μm/sec; the measurement temperature was 25° C.; It was measured while placed on a thick silicon wafer. Young's modulus hereinafter may refer to a value measured by a similar method.

The bonding sheet 10 preferably has a thermal conductivity of 10 W/mK or more and 60 W/mK or less, more preferably 15 W/mK or more and 55 W/mK or less, and 20 W/mK or more and 50 W/mK or less. is more preferred. When the thermal conductivity falls within this range, the heat of the members to be joined can be suitably transferred.
Thermal conductivity can be obtained by converting from specific resistance, for example. Specifically, the sheet resistance of a bonding sheet molded to 10 mm × 10 mm at 25 ° C. is measured by the four-probe method using Loresta (MCP-250T, manufactured by Mitsubishi Yuka Co., Ltd.), and further multiplied by the sheet thickness. Calculate the resistivity. The thermal conductivity at 25° C. is obtained by converting the specific resistance using the Wiedemann-Franz law.

The thickness W of the bonding sheet 10 is preferably 0.1 mm or more and 1 mm or less, more preferably 0.2 mm or more and 0.7 mm or less, and even more preferably 0.3 mm or more and 0.5 mm or less. . As shown in FIG. 1, the thickness W is the direction Z, which is the thickness direction, between the portion of the surface 10a that protrudes the most from the surface 10a and the portion of the surface 10b that protrudes the most from the surface 10b. refers to the distance in
The projected area of the bonding sheet 10 when projected in the direction Z is preferably 10000 mm ² or less, more preferably 6400 mm ² or less, and even more preferably 3600 mm ² or less.
By using the joining sheet 10 having the thickness W and the projected area within this range, the members can be joined appropriately.

A value obtained by dividing the thickness W of the bonding sheet 10 by the filling rate (%) of the bonding sheet 10 (thickness W/filling rate) is defined as a large area bonding index D1. In this case, the large area bonding index D1 is preferably 1.50 or more and 10.0 or less, and more preferably 4.0 or more and 8.0 or less.
When the large-area bonding index D1 falls within this range, the members can be appropriately bonded together while suppressing breakage.

The joining sheet 10 may be a sintered body of copper impregnated with a resin. That is, the bonding sheet 10 may have resin filled at least partially inside the pores. Examples of resins used here include epoxy resins and silicone resins. By impregnating the resin, the bonding sheet 10 can be provided with appropriate functions.

(Manufacturing method of joining sheet)
FIG. 3 is a flow chart illustrating a method for manufacturing a joining sheet according to this embodiment.

(Preparation of copper particles)
As shown in FIG. 3, in this manufacturing method, copper particles 12A are first prepared (step S10). The copper particles 12A here are particles of copper as a raw material of the joining sheet 10, and can also be said to be copper powder before preliminary sintering. That is, by pre-sintering the copper particles 12A, the bonding sheet 10 in which the copper particles 12 are bonded by pre-sintering is manufactured. It can be said that the copper particles before pre-sintering are copper particles 12A, and the copper particles after pre-sintering are copper particles 12A.

The copper particles 12A preferably have a BET diameter of 50 nm or more and 300 nm or less. The BET diameter is a particle diameter calculated from the BET specific surface area and the true density of the copper particles obtained by the BET method, assuming that the copper particles 12A are true spheres or cubes. Specifically, it can be determined by the method described in the examples below.

When the BET diameter of the copper particles 12A is 50 nm or more, it is difficult to form firm aggregates. Therefore, the surfaces of the copper particles 12 after pre-sintering can be uniformly coated with the solvent 20 described below. On the other hand, when the BET diameter of the copper particles 12A is 300 nm or less, the reaction area is large and the sinterability by heating is high, so that a strong bonding layer can be formed. The BET diameter of the copper particles 12A is preferably in the range of 80 nm or more and 200 nm or less, and particularly preferably in the range of 80 nm or more and 170 nm or less.

The BET specific surface area of the copper particles 12A is preferably in the range of 2.0 m ² /g or more and 8.0 m ² /g or less, and is in the range of 3.5 m ² /g or more and 8.0 m ² /g or less. more preferably 4.0 m ² /g or more and 8.0 m ² /g or less is particularly preferable. Moreover, the shape of the copper particles 12A is not limited to a spherical shape, and may be a needle shape or a flat plate shape.

The surface of the copper particles 12A is preferably covered with an organic protective film, which is an organic film. By being coated with the organic protective film, the oxidation of the copper particles 12A is suppressed, and the deterioration of the sinterability due to the oxidation of the copper particles 12A is even less likely to occur. It can be said that the organic protective film covering the copper particles 12A is not formed by the solvent 20 and is not derived from the solvent 20 . Moreover, it can be said that the organic protective film covering the copper particles 12A is not a copper oxide film formed by oxidation of copper.

The fact that the copper particles 12A are coated with the organic protective film can be confirmed by analyzing the surfaces of the copper particles 12A using time-of-flight secondary ion mass spectrometry (TOF-SIMS). Therefore, in the present embodiment, the copper particles 12A are C ₃ H ₃ O ₃ ⁻ ions relative to the detected amount of Cu ⁺ ions detected by analyzing the surface using time-of-flight secondary ion mass spectrometry. (C ₃ H ₃ O ₃ ⁻ /Cu ⁺ ratio) is preferably 0.001 or more. More preferably, the C ₃ H ₃ O ₃ ⁻ /Cu ⁺ ratio is in the range of 0.05 or more and 0.2 or less. In addition, the surface of the copper particles 12A in this analysis is not the surface of the copper particles 12A when the organic protective film is removed from the copper particles 12A, but the surface of the copper particles 12A containing the covering organic protective film (i.e. surface of the organic protective film).

By analyzing the surface of the copper particles 12A using time-of-flight secondary ion mass spectrometry, C ₃ H ₄ O ₂ ^- ions and C ₅ or higher ions may be detected. The ratio of the detected amount of C ₃ H ₄ O ₂ ⁻ ions to the detected amount of Cu ⁺ ions (C ₃ H ₄ O ₂ ⁻ /Cu ⁺ ratio) is preferably 0.001 or more. Further, the ratio of the detected amount of C5 _or higher ions to the detected amount of Cu ⁺ ions (C5 _or higher ions/Cu ⁺ ratio) is preferably less than 0.005.

The C ₃ H ₃ O ₃ ^- ions, C ₃ H ₄ O ₂ ^- ions, and C ₅ or higher ions detected in the time-of-flight secondary ion mass spectrometry are the organic protective ions covering the surfaces of the copper particles 12A. derived from the membrane. Therefore, when each of the C ₃ H ₃ O ₃ ⁻ /Cu ⁺ ratio and the C ₃ H ₄ O ₂ ⁻ /Cu ⁺ ratio is 0.001 or more, the surfaces of the copper particles 12A are difficult to oxidize and the copper particles 12A becomes difficult to aggregate. Further, when the C ₃ H ₃ O ₃ ⁻ /Cu ⁺ ratio and the C ₃ H ₄ O ₂ ⁻ /Cu ⁺ ratio are 0.2 or less, the copper particles 12A can be sintered without excessively decreasing the sinterability of the copper particles 12A. Oxidation and agglomeration of 12A can be suppressed, and generation of decomposition gas from the organic protective film during heating can be suppressed, so that a bonding layer with few voids can be formed. In order to further improve the oxidation resistance during storage of the copper particles 12A and to further improve the sinterability at low temperatures, the C ₃ H ₃ O ₃ ⁻ /Cu ⁺ ratio and the C ₃ H ₄ O ₂ ^{The −} /Cu ⁺ ratio is preferably in the range of 0.08 to 0.16. In addition, when the C ₅ or higher ion/Cu ⁺ ratio is 0.005 times or higher, a large amount of organic protective film having a relatively high desorption temperature exists on the particle surface, and as a result, sufficient sinterability cannot be expressed. Therefore, it is difficult to obtain a strong bonding layer. Preferably, the _C5 and above ions/Cu ⁺ ratio is less than 0.003.

The organic protective film is preferably derived from citric acid. A method for manufacturing the copper particles 12A coated with the citric acid-derived organic protective film will be described later. The coating amount of the organic protective film on the copper particles 12A is preferably in the range of 0.5% by mass or more and 2.0% by mass or less with respect to 100% by mass of the copper particles, and 0.8% by mass or more and 1.8% by mass. It is more preferably in the range of 0.8% by mass or more and 1.5% by mass or less. When the coating amount of the organic protective film is 0.5% by mass or more, the copper particles 12A can be uniformly coated with the organic protective film, and oxidation of the copper particles 12A can be suppressed more reliably. In addition, since the coating amount of the organic protective film is 2.0% by mass or less, the generation of voids in the sintered body (bonding layer) of the copper particles due to the gas generated by the decomposition of the organic protective film due to heating is prevented. can be suppressed. 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 type differential thermal balance TG8120-SL (manufactured by RIGAKU). In this case, for example, copper particles from which moisture has been removed by freeze-drying are used as the sample. In order to suppress oxidation of copper particles, measurement was performed in nitrogen (G2 grade) gas, and the temperature increase rate was 10 ° C./min. can be defined as That is, the coating amount=(sample weight after measurement)/(sample weight before measurement)×100 (wt %). The measurement may be performed three times for each copper particle of the same lot, and the arithmetic average value may be taken as the coating amount.

When the copper particles 12A are heated at a temperature of 300° C. for 30 minutes in an inert gas atmosphere such as argon gas, 50% by mass or more of the organic protective film is preferably decomposed. The organic protective film derived from citric acid generates carbon dioxide gas, nitrogen gas, evaporative gas of acetone and water vapor when decomposed.

The copper particles 12A coated with an organic protective film derived from citric acid can be produced, for example, as follows. First, an aqueous dispersion of copper citrate is prepared, and a pH adjuster is added to the aqueous dispersion of copper citrate 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 was added as a reducing agent to the pH-adjusted copper citrate aqueous dispersion. to mix. The resulting mixed solution is heated to a temperature of 60° C. or higher and 80° C. or lower in an inert gas atmosphere and held for 1.5 hours or longer and 2.5 hours or shorter. As a result, copper ions eluted from copper citrate are reduced to form copper particles 12A, and an organic protective film derived from citric acid is formed on the surfaces of the copper particles 12A.

An aqueous dispersion of copper citrate is prepared by adding powdered copper citrate to pure water such as distilled water or ion-exchanged water so that the concentration is 25% by mass or more and 40% by mass or less, and using a stirring blade. It can be prepared by stirring and dispersing uniformly. Examples of pH adjusters include triammonium citrate, ammonium hydrogen citrate, and citric acid. Of these, triammonium citrate is preferred because it facilitates mild pH adjustment. The reason why the pH of the copper citrate aqueous dispersion is 2.0 or more is that the elution rate of copper ions eluted from the copper citrate is increased, the generation of copper particles is rapidly progressed, and the target fine copper is obtained. This is so that the particles 12A can be obtained. The reason why the pH is set to 7.5 or less is to suppress eluted copper ions from becoming copper (II) hydroxide, thereby increasing the yield of the copper particles 12A. Moreover, by setting the pH to 7.5 or less, it is possible to prevent the reducing power of the hydrazine compound from becoming excessively high, making it easier to obtain the target copper particles 12A. The pH of the copper citrate aqueous dispersion is preferably adjusted within the range of 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 oxidation of copper ions dissolved in the liquid. Examples of inert gases include nitrogen gas and argon gas. A hydrazine compound has advantages such as not producing a residue after a reduction reaction when copper citrate is reduced in an acidic environment, relatively high safety, and easy handling. The hydrazine compound includes hydrazine monohydrate, anhydrous hydrazine, hydrazine hydrochloride, hydrazine sulfate, and the like. Among these hydrazine compounds, preferred are hydrazine monohydrate and anhydrous hydrazine, which do not contain impurities such as sulfur and chlorine.

In general, copper generated in an acid solution with a pH of less than 7 dissolves. However, in the present embodiment, a hydrazine compound, which is a reducing agent, is added to and mixed with an acidic liquid having a pH of less than 7, and the copper particles 12A are generated in the obtained mixed liquid. Therefore, the citric acid-derived component generated from the copper citrate quickly coats the surfaces of the copper particles 12A, thereby suppressing the dissolution of the copper particles 12A. The aqueous dispersion of copper citrate after adjusting the pH is preferably kept at a temperature of 50° C. or higher and 70° C. or lower to facilitate the progress of the reduction reaction.

Heating the mixed liquid in which the hydrazine compound is mixed in an inert gas atmosphere to a temperature of 60° C. or more and 80° C. or less and holding it for 1.5 hours or more and 2.5 hours or less is to generate the copper particles 12A and to generate This is for forming and covering the surfaces of the copper particles 12A with an organic protective film. The reason for heating and holding in the inert gas atmosphere is to prevent the generated copper particles 12A from being oxidized. Copper citrate, which is a starting material, usually contains about 35% by mass of a copper component. A hydrazine compound, which is a reducing agent, is added to a copper citrate aqueous dispersion containing such a copper component, heated to the above temperature, and held for the above time to generate copper particles 12A, Since the formation of the organic protective film on the surface of the copper particles 12A proceeds in a well-balanced manner, the coating amount of the organic protective film is in the range of 0.5% by mass or more and 2.0% by mass or less with respect to 100% by mass of the copper particles. It is possible to obtain the copper particles 12A inside. When the heating temperature is less than 60° C. and the holding time is less than 1.5 hours, the copper citrate is not completely reduced, and the generation rate of the copper particles 12A becomes too slow, resulting in the formation of the organic protective film covering the copper particles 12A. The amount may be excessive. If the heating temperature exceeds 80° C. and the holding time exceeds 2.5 hours, the generation rate of the copper particles 12A becomes too fast, and the amount of the organic protective film covering the copper particles 12A may become too small. . A preferred heating temperature is 65° C. or higher and 75° C. or lower, and a preferred holding time is 2 hours or longer and 2.5 hours or shorter.

The copper particles 12A generated in the mixed liquid are solid-liquid separated from the mixed liquid in an inert gas atmosphere, for example, using a centrifuge, and dried by a freeze-drying method or a reduced-pressure drying method. A copper particle 12A coated with an organic protective film is obtained. Since the surfaces of the copper particles 12A are covered with an organic protective film, the copper particles 12A are not easily oxidized even if they are stored in the atmosphere until they are used as the bonding sheet 10 .

(Filling of copper particles into a mold)
Next, as shown in FIG. 3, the mold is filled with prepared copper particles 12A (step S12). The shape and material of the mold to be filled with the copper particles 12A may be arbitrary.

(Temporary sintering of copper particles)
Next, the copper particles 12A filled in the mold are pressurized at a predetermined temperature to pre-sinter the copper particles 12A, thereby producing the bonding sheet 10 (step S14). In this step, the copper particles 12A filled in the mold are held at a predetermined temperature for a predetermined period of time while being pressurized with a predetermined pressure, thereby pre-sintering the copper particles 12A to generate the bonding sheet 10. The predetermined pressure here is preferably 10 MPa or more and 30 MPa or less, more preferably 11 MPa or more and 25 MPa or less, and even more preferably 12 MPa or more and 20 MPa or less. The predetermined temperature here is preferably 150° C. or higher and 250° C. or lower, more preferably 160° C. or higher and 240° C. or lower, and even more preferably 170° C. or higher and 230° C. or lower. Here, the predetermined time (the time for holding at the predetermined pressure and the predetermined temperature) is preferably 1 minute or more and 30 minutes or less, more preferably 2 minutes or more and 25 minutes or less, and 3 minutes or more and 20 minutes or less. It is even more preferable to have
By pre-sintering the copper particles 12A under such conditions, the bonding sheet 10 capable of simplifying the bonding process can be appropriately manufactured.

In addition, the bonding sheet 10 is not limited to being manufactured by the above method, and the manufacturing method of the bonding sheet 10 may be arbitrary.

(Manufacturing method of joined body)
Next, a method for manufacturing the joined body 100 by joining members together using the joining sheet 10 will be described. FIG. 4 is a schematic diagram for explaining the manufacturing method of the joined body. In this embodiment, the joined body 100 is manufactured by joining the first member A and the second member B using the joining sheet 10 as a joining layer. Although the first member A and the second member B may be arbitrary, for example, one of the first member A and the second base material B may be a substrate and the other an electronic component. you can That is, a semiconductor module in which a substrate and an electronic component are bonded with a bonding layer may be manufactured as the bonded body 100 . The substrate is not particularly limited, but for example, an oxygen-free copper plate, a copper molybdenum plate, a high heat dissipation insulating substrate (e.g., DCB (Direct Copper Bond)), a substrate for mounting a semiconductor element such as an LED (Light Emitting Diode) package, etc. are mentioned. Electronic components include, for example, 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, Examples include semiconductor devices such as oscillators.
In the following description, one joining sheet 10 joins the first member A and the second member B. The joined body 100 may be formed by joining the member B of the above, or the joined body 100 may be formed by joining three or more members with one or a plurality of joining sheets 10 .

In this manufacturing method, the joining sheet 10 is arranged on the surface of the first member A, as shown in step S20 of FIG. In the example of FIG. 4, the joining sheet 10 is arranged on the first member A so that the surface 10b of the joining sheet 10 is in contact with the surface of the first member A. In the example of FIG.

Next, the solvent 20 is added to the bonding sheet 10 as shown in step S22. In the example of this embodiment, the solvent 20 is added to the bonding sheet 10 placed on the first member A. More specifically, the surface 10a of the bonding sheet 10 (the side not in contact with the first member A) A solvent 20 is added (applied) onto (surface of ). However, the timing of adding the solvent 20 is not limited thereto. For example, the solvent 20 may be added to the bonding sheet 10 in advance, and the bonding sheet 10 added with the solvent 20 may be placed on the first member A. Further, for example, the solvent 20 may be added to the bonding sheet 10 after the bonding sheet 10 is arranged between the first member A and the second member B. Further, the position where the solvent 20 is added is not limited to the surface 10a and may be arbitrary.

Solvent 20 acts as a binder for copper particles 12 . Solvent 20 can be any, but is preferably an organic solvent, more preferably a polyhydric alcohol.

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

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

The solvent 20 is preferably added in a mass ratio of 0.5% to 10%, preferably 1% to 8%, and 2% to 5% by mass relative to the bonding sheet 10. more preferably. By setting the amount of the solvent 20 to be added within this range, the bondability can be appropriately maintained.

As shown in step S24, the solvent 20 penetrates into the pores of the bonding sheet 10 and fills the pores. That is, it can be said that the bonding sheet 10 is impregnated with the solvent 20 .

After that, as shown in step S26, the second member B is arranged on the surface 10a of the bonding sheet 10 impregnated with the solvent 20. As shown in FIG. That is, the bonding sheet 10 impregnated with the solvent 20 is placed between the first member A and the second member B. As shown in FIG. Hereinafter, a state in which the bonding sheet 10 to which the solvent 20 is added (impregnated) is arranged between the first member A and the second member B is referred to as a laminate.

After that, by heating the laminate, the sintering of the bonding sheet 10 is further advanced, and the first member A and the second member B are bonded by the bonding layer (sintered bonding sheet 10). A combined assembly 100 is produced. The heating temperature of the laminate is 200° C. or higher, preferably 200° C. or higher and 300° C. or lower, and more preferably 250° C. or higher and 300° C. or lower. By setting the heating temperature within this range, the joining sheet 10 can be sintered appropriately, and the joined body 100 can be produced appropriately.
The heating time for the laminate is preferably 1 minute or more and 60 minutes or less, more preferably 3 minutes or more and 45 minutes or less, and even more preferably 5 minutes or more and 30 minutes or less. By setting the heating time within this range, the sintering of the joining sheet 10 can be appropriately advanced, and the joined body 100 can be produced appropriately.
Moreover, it is preferable to heat the laminate while pressurizing the laminate in the lamination direction of the laminate in an inert gas atmosphere. Nitrogen gas, argon gas, or the like can be used as the inert gas, for example. The applied pressure of the laminate is preferably 0.5 MPa or more, more preferably 1 MPa or more and 30 MPa or less, still more preferably 3 MPa or more and 25 MPa or less, and even more preferably 5 MPa or more and 20 MPa or less. , 10 MPa or more and 15 MPa or less.

(effect)
As described above, the method for manufacturing a joined body according to the present embodiment includes the steps of placing the joining sheet 10 containing a sintered body of copper on the first member A, and applying the solvent 20 to the joining sheet 10. By adding and placing the second member B on the bonding sheet 10, the bonding sheet 10 to which the solvent 20 is added is disposed between the first member A and the second member B. and heating the laminate at a heating temperature of 150° C. or higher to manufacture a joined body in which the first member A and the second member B are joined.

In this manufacturing method, a bonding sheet 10 containing a sintered body of copper is placed between the first member A and the second member B, and the bonding step (heating) is performed. Therefore, the handling of the joining sheet 10 in the joining process can be improved, and the joining process can be simplified. Moreover, by adding the solvent 20 to the joining sheet 10 and heating the joining sheet 10 at 200° C. or higher, the sintering of the joining sheet 10 is appropriately advanced, and the members can be appropriately joined together. In addition, since the bonding sheet 10 containing a sintered body of copper is used, the solvent 20 can be added during the bonding process. It is possible to reduce the trouble of transportation and storage.

In the step of manufacturing the joined body, it is preferable to heat the laminated body at a heating temperature while applying pressure to the laminated body at 1 MPa or more and 30 MPa or less. By hot-pressing the laminate in this manner, the members can be appropriately joined together.

In this manufacturing method, it is preferable to use a bonding sheet 10 having a filling rate of 50% or more. Thereby, sintering can be appropriately advanced and the members can be appropriately joined together.

In this manufacturing method, it is preferable to use a joining sheet 10 having a Young's modulus of 1 GPa or more. This makes it possible to suppress breakage of the joining sheet 10 and improve the handleability more appropriately, thereby simplifying the joining process.

In this manufacturing method, it is preferable to use a joining sheet 10 having a Young's modulus of 10 GPa or more. This makes it possible to suppress breakage of the joining sheet 10 and improve the handleability more appropriately, thereby simplifying the joining process.

In this manufacturing method, it is preferable to use a bonding sheet 10 having a surface arithmetic mean roughness Ra of 1 μm or more and 40 μm or less. Thereby, sintering can be appropriately advanced and the members can be appropriately joined together.

In this manufacturing method, it is preferable to use a bonding sheet 10 having a thermal conductivity of 10 W/mK or more and 50 W/mK or less. Thereby, heat can be appropriately transferred between the members.

A polyhydric alcohol is preferably used as the solvent 20 in the solvent adding step. By using polyhydric alcohol, the members can be properly joined together.

(Second embodiment)
Next, a second embodiment will be described. The second embodiment differs from the first embodiment in that a carboxylic acid additive is added to the bonding sheet 10 in the manufacturing process of the bonded body 100 . In the second embodiment, descriptions of parts having the same configuration as in the first embodiment are omitted.

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

In the second embodiment, an additive is added to the bonding sheet 10 in addition to the solvent 20 in step S22.

At least one of carboxylic acids, carboxylates, amines, and amine salts is used as the additive. As the additive, it is preferable to use at least one of carboxylic acids, carboxylic acid salts, amines and amine salts having 2 to 8 carbon atoms. The number of carbons here refers to the number of Cs in the chemical formula of the additive. At least one of citric acid, ethylhexanoic acid, and ethylhexylamine is more preferably used as the additive. By using such a material as an additive, the first member A and the second member B can be properly formed even when the surface of at least one of the first member A and the second member B contains Ni. can be joined to

The additive is preferably added in a mass ratio of 0.1% or more and 10% or less, preferably 0.5% or more and 7% or less, and 1% or more and 5% with respect to the bonding sheet 10. It is more preferable to add the following. Ni can be appropriately joined by the addition amount of the additive falling within this range.
Further, the additive is preferably added in a mass ratio of 20% or more, preferably 40% or more, and more preferably 60% or more with respect to the solvent 20 . Ni can be appropriately joined by the addition amount of the additive falling within this range.

In addition, in the example of this embodiment, the solvent 20 and the additive are added to the bonding sheet 10 at the same timing. In this case, for example, the solvent 20 and the additive may be mixed and the mixture may be added to the bonding sheet 10 . However, it is not limited thereto, and the solvent 20 and the additive may be individually added to the bonding sheet 10 at the same timing. Moreover, the order of addition of the additive and the solvent 20 may be arbitrary.
Furthermore, the timing of adding the additive may be arbitrary. For example, the solvent 20 and the additive are added to the bonding sheet 10 first, and the bonding sheet 10 to which the solvent 20 and the additive are added is added. , may be placed on the first member A. Further, for example, after the bonding sheet 10 is arranged between the first member A and the second member B, the solvent 20 and the additive may be added to the bonding sheet 10 . Moreover, the position where the additive is added is not limited to the surface 10a and may be arbitrary.

In the second embodiment, as shown in step S26, the second member B is arranged on the surface 10a of the bonding sheet 10 impregnated with the solvent 20 and the additive. That is, the bonding sheet 10 impregnated with the solvent 20 and the additive is placed between the first member A and the second member B. As shown in FIG. Hereinafter, a state in which the bonding sheet 10 to which the solvent 20 and the additive are added (impregnated) is arranged between the first member A and the second member B is referred to as a laminate.

After that, by heating the laminate, the sintering of the bonding sheet 10 is further advanced, and the first member A and the second member B are bonded by the bonding layer (sintered bonding sheet 10). A combined assembly 100 is produced.

As described above, the second embodiment further includes a step of adding at least one of carboxylic acid, carboxylate, amine, and amine salt (additive) to the joining sheet 10 . By adding at least one of a carboxylic acid, a carboxylate, an amine, and an amine salt to the joining sheet 10, Ni can be appropriately joined, and the joined body 100 containing Ni can be produced appropriately. However, the second embodiment is not limited to the application of joining Ni. In other words, the surfaces of the first member A and the second member B in the second embodiment may not contain Ni.

(Example)
Next, examples will be described. FIG. 5 is a table showing manufacturing conditions and evaluation results for each example.

(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 obtain citric acid having a concentration of 30% by mass. An aqueous dispersion of copper was prepared. Next, an ammonium citrate aqueous solution as a pH adjuster was added to the obtained aqueous copper citrate dispersion to adjust the pH of the aqueous copper citrate dispersion to 5. Next, the resulting copper citrate aqueous dispersion was heated to 50° C., and while maintaining that temperature, an aqueous hydrazine monohydrate solution (diluted twice as a reducing agent for copper ions) was placed under a nitrogen gas atmosphere. ) was added all at once, and stirred and mixed using a stirring blade. The amount of the hydrazine monohydrate aqueous solution added was 1.2 equivalents of the amount required to reduce the total amount of copper ions. The resulting mixed solution was heated to 70° C. in a nitrogen gas atmosphere and held at that temperature for 2 hours to generate copper particles. The produced copper particles were recovered using a centrifuge. The collected copper particles were dried by a vacuum drying method to produce copper particles.

A specific surface area measuring device (QUANTACHROME AUTOSORB-1 manufactured by Quantachrome Instruments) was used. After removing the adsorbed gas in advance at a degassing temperature of 50° C. for a degassing time of 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 from the following formula.
BET diameter (nm) = 6000/(ρ (g/cm ³ ) x S (m ² /g))

(Generation of joining sheet)
As a mold to be filled with the prepared copper particles, an aluminum frame having an outer dimension of 50 mm x 30 mm and an inner dimension of 30 mm x 30 mm was prepared. This aluminum frame is filled with 1.5 g of copper particles, smoothed uniformly with an aluminum block of 30 mm square × 20 mm, and hot pressed for 15 minutes in the atmosphere under the conditions of an applied pressure of 30 MPa and a heating temperature of 150 ° C. It was processed to produce a joining sheet comprising a sintered body of copper. CYPT-50kN (manufactured by Shinto Kogyo Co., Ltd.) was used as a hot press device. After the hot press treatment, it was cooled to room temperature, and the bonding sheet of 30 mm square×0.4 mm sandwiched between the aluminum blocks was peeled off from the aluminum blocks to obtain the desired bonding sheet.

(Characteristics of joining sheet)
In FIG. 5, the bonding sheet in which at least a part of the copper particles was sintered, that is, the bonding sheet containing the sintered body of copper was designated as the sintered body "◯". In FIG. 5, a bonding sheet in which not all copper particles were sintered, that is, a bonding sheet containing no copper sintered body was designated as a sintered body "x". As shown in FIG. 5, the joining sheet of Example 1 includes a sintered body in which at least a portion of copper particles is sintered.
Also, the Young's modulus of the bonding sheet was measured using a picodenter. The Young's modulus was measured by the method described in this embodiment.
Also, the filling rate of the joining sheet was measured. The fill factor was measured as follows. The volume determined from the external dimensions of the bonding sheet was measured with a vernier caliper and a micrometer. Specifically, two sides of the bonding sheet in the horizontal direction were measured at five points each at random, and the product of each average value was defined as the area of the bonding sheet. Further, the thickness of the bonding sheet was measured at random with a micrometer at 10 points, and the average value was taken as the thickness of the bonding sheet. The product of the area and the thickness was taken as the volume of the joining sheet. Next, the weight of the bonding sheet was measured. Then, the bulk density was calculated by dividing the weight of the bonding sheet by the volume determined from the external dimensions of the bonding sheet 10 . The volume determined from the external dimensions refers to the total volume including the pores of the joining sheet 10 . Assuming that the true density was 8.96 g/cm ³ , the ratio of the bulk density to the true density was calculated as the filling rate.
Also, the thermal conductivity of the bonding sheet was measured. Specifically, the sheet resistance at 25° C. of a bonding sheet molded into a size of 10 mm×10 mm was measured by the four-probe method using a Loresta (MCP-250T, manufactured by Mitsubishi Yuka Co., Ltd.), and the sheet film thickness was multiplied. Then the resistivity was calculated. Then, the thermal conductivity at 25° C. was obtained by converting the specific resistance using the Wiedemann-Franz law.
The measured values of Young's modulus, filling factor and thermal conductivity are shown in FIG.

(Generation of zygotes)
The bonding sheet was cut using a commercially available cutter knife to prepare a bonding sheet piece (2.5 mm square×500 μm thick). The bonding sheet piece (2.5 mm square×500 μm thickness) was placed on a 30 mm square×1 mm thick oxygen-free copper substrate. Next, polyethylene glycol as a solvent was applied to the bonding sheet piece so as to be 0.05 g per sheet piece weight of 0.95 g and impregnated, and then an oxygen-free copper dummy element of 2.5 mm square × 1 mm thickness. was placed. Thus, a laminate was obtained in which the oxygen-free copper substrate and the oxygen-free copper dummy element were laminated via the joining sheet piece. Using a die bonder (manufactured by Alpha Design Co., Ltd., HTB-MM), the obtained laminate was held for 15 minutes under the conditions of a pressure of 5 MPa and a temperature of 300 ° C. in a nitrogen gas atmosphere to obtain a 2.5 mm square. A joined body (Sample A) in which the oxygen-free copper substrate and the oxygen-free copper dummy element were joined through the copper joining layer was produced.

(Example 2-11)
In Example 2-11, the method was the same as in Example 1, except that at least one of the bonding sheet manufacturing conditions, heating temperature, applied pressure, pressurization time, and type of solvent was changed as shown in FIG. generated a zygote.

(Comparative Example 1-3)
Comparative Example 1-3 was the same as Example 1 except that at least one of the manufacturing conditions of the bonding sheet, the heating temperature, the applied pressure, the pressurization time, and the presence or absence of solvent addition was changed as shown in FIG. A zygote was produced by the method. In Comparative Example 1, the heating temperature during the production of the bonding sheet is as low as 40° C., so the bonding sheet of Comparative Example 1 does not contain a sintered body. In Comparative Example 2, no solvent was added to the bonding sheet. In Comparative Example 3, the heating temperature of the laminate is 100°C.

(evaluation)
Each example conjugate was evaluated. For the evaluation, the easiness of the bonding process (configuration for heating the laminate) and the shear strength of the bonded body were evaluated.

As the easiness of the joining process, the strength of the joining sheet of each example was evaluated. A bonding sheet of 30 mm x 30 mm is placed on an oxygen-free copper plate of 50 mm x 50 mm x 1 mm thick. company, YTZ-20) was gently dropped. After repeating the operation of dropping once per sheet 10 times, the bonding sheets were visually observed, and if 7 or more sheets were found to have no cracks or chips, they were evaluated as passing (○), and 6 sheets or less. The case was set as failed (x). The results are shown in FIG.

In the evaluation of the shear strength of the bonded body, the shear strength was measured by a method conforming to JIS Z 3198-7 (Lead-free solder test method-Part 7: Chip component solder joint shear test method). Specifically, a load was applied to the oxygen-free copper dummy element using a bond tester (SERIES 4000 manufactured by Nordson DAGE), and the load (maximum shear load) when the oxygen-free copper dummy element was peeled off from the copper bonding layer. was measured. The moving speed of the tool was set to 50 μm/sec, and the gap between the tip of the tool and the oxygen-free copper substrate was set to 50 μm. The shear strength (unit: MPa) was obtained by converting the obtained maximum shear load into Newton and dividing it by the area of the copper bonding layer (2.5 mm×2.5 mm). Seven joined bodies were produced, and the shear strength of each joined body was measured. The results are shown in FIG.

In the evaluation, when the easiness of the bonding process was evaluated as ◯ and the shear strength of the bonded body was 30 MPa or more, it was determined as acceptable. On the other hand, when at least one of the evaluation of the easiness of the bonding process being ◯ and the shear strength of the bonded body being 30 MPa or more being not satisfied, it was determined as disqualified.

As shown in FIG. 5, in an example in which a solvent was added to a joining sheet containing a sintered copper body and the heating temperature was set to 200° C. or higher during the production of the joined body, the easiness of the joining process was improved. It can be seen that the evaluation is pass, the joining process can be easily performed, and the shear strength is 30 MPa or more, and it can be joined appropriately. On the other hand, in the comparative example, the evaluation of the easiness of the joining process or the shear strength failed, and it can be seen that the simplification of the joining process and the joinability cannot be achieved at the same time. That is, Comparative Example 1, which does not use a bonding sheet containing a sintered copper body, cannot simplify the bonding process. , it can be seen that they cannot be properly spliced.

(optional evaluation)
Also, as an option evaluation, the void fraction of the joined body was evaluated.

(Void fraction of bonded body)
An ultrasonic flaw detection image of the copper bonding layer portion of the obtained bonded body (sample B) was measured using an ultrasonic flaw detector (FINE-SAT, manufactured by Hitachi High-Technologies Corporation). The obtained ultrasonic flaw detection image is binarized using image processing software (ImageJ manufactured by the National Institutes of Health, USA), divided into voids (cavities) and joined bodies (copper particle sintered bodies), and the following equation The void fraction was calculated from
Void ratio (%) = (total area of void portions/area of copper bonding layer (10 mm x 10 mm)) x 100

Seven joined bodies were produced, and the void fraction was measured for each joined body. The results are shown in FIG.

Although the embodiment of the present invention has been described above, the embodiment is not limited by the contents of this embodiment. In addition, the components described above include those that can be easily assumed by those skilled in the art, those that are substantially the same, and those within the so-called equivalent range. Furthermore, the components described above can be combined as appropriate. Furthermore, various omissions, replacements, or modifications of components can be made without departing from the gist of the above-described embodiments.

10 joining sheet 12, 12A copper particles 20 solvent

Claims (8)

placing a bonding sheet containing a sintered body of copper on the first member;
adding a solvent to the bonding sheet;
obtaining a laminate in which the bonding sheet to which the solvent is added is disposed between the first member and the second member by arranging the second member on the bonding sheet; ,
a step of manufacturing a joined body in which the first member and the second member are joined by heating the laminate at a heating temperature of 200° C. or higher;
including,
A method for producing a conjugate. 2. The method of manufacturing a joined body according to claim 1, wherein in the step of producing said joined body, said laminated body is heated at said heating temperature while being pressurized at 1 MPa or more and 30 MPa or less. 3. The method for producing a joined body according to claim 1, wherein the joining sheet having a filling rate of 50% or more is used. 4. The method for producing a joined body according to claim 1, wherein the joining sheet having a Young's modulus of 1 GPa or more is used. 5. The method for producing a joined body according to claim 4, wherein the joining sheet having a Young's modulus of 10 GPa or more is used. 6. The method for producing a joined body according to claim 1, wherein the joining sheet having a thermal conductivity of 10 W/mK or more and 60 W/mK or less is used. 7. The method of manufacturing a joined body according to claim 1, wherein in the step of adding the solvent, a polyhydric alcohol is used as the solvent. 8. The method for producing a joined body according to any one of claims 1 to 7, further comprising the step of adding at least one of carboxylic acid, carboxylate, amine, and amine salt to said joining sheet. .

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