Method for manufacturing joining sheet and method for manufacturing joined body

Abstract

To reduce the risk of breakage.SOLUTION: A method for producing a bonding sheet includes the steps of: alternately laminating a copper particle layer 10A which is a layer of a plurality of copper particles with a BET diameter of 300 nm or less and a member for lamination P to obtain a laminate 10 L; and pressurizing the laminate 10 L at 1 MPa or more and 30 MPa or less while heating at 150°C or more and 300°C or less, to sinter the copper particles, thereby producing a bonding sheet including a sintered body of copper.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a bonding sheet and a method for manufacturing a bonded body. [Background technology]

[0002] A bonding material is sometimes used to bond two or more components when assembling or mounting electronic components, etc. For example, Patent Document 1 describes a method for producing a bonding sheet by mixing copper particles with a solvent having a boiling point of 150°C or higher and pressing the mixture at room temperature. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-116463 Summary of the Invention [Problem to be solved by the invention]

[0004] Such bonding sheets are required to be able to suppress the risk of breakage.

[0005] The present invention has been made in view of the above, and has an object to provide a method for manufacturing a bonding sheet and a method for manufacturing a bonded body that can reduce the risk of breakage. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems and achieve the object, the manufacturing method of a joining sheet according to the present disclosure includes the steps of alternately stacking a copper particle layer, which is a layer of multiple copper particles having a BET diameter of 300 nm or less, and a lamination member to obtain a laminate, and heating the laminate at 150°C or more and 300°C or less while applying a pressure of 1 MPa or more and 30 MPa or less to sinter the copper particles, thereby manufacturing a joining sheet including a copper sintered body.

[0007] In the step of obtaining the laminate, it is preferable that two or more copper particle layers are laminated.

[0008] In the step of obtaining the laminate, the copper particle layer and the lamination members are preferably laminated in a frame-shaped mold.

[0009] In the step of producing the bonding sheet, it is preferable that the laminate is heated while being pressed for a holding time of 1 minute or more and 30 minutes or less.

[0010] In order to solve the above-mentioned problems and achieve the objectives, the manufacturing method of a bonded body according to the present disclosure includes the steps of placing a bonding sheet manufactured by the manufacturing method of a bonding sheet on a first member, placing a second member on the bonding sheet to obtain a laminate in which the bonding sheet is disposed 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. [Effects of the Invention]

[0011] According to the present invention, the risk of breakage can be reduced. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram of the bonding sheet according to this embodiment. [Figure 2] FIG. 2 is a flow chart illustrating the method for manufacturing the bonding sheet according to this embodiment. [Figure 3] FIG. 3 is a schematic diagram for explaining the lamination step. [Figure 4] FIG. 4 is a schematic diagram for explaining the heating step and the removal step. [Figure 5] FIG. 5 is a schematic partially enlarged view of the bonding sheet. [Figure 6] FIG. 6 is a schematic diagram for explaining a method for producing a bonded body. [Figure 7]FIG. 7 is a table showing the properties and evaluation results of the bonding sheets of the examples. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described in detail below with reference to the drawings. Note that the present invention is not limited to the following modes for carrying out the invention (hereinafter referred to as embodiments). Furthermore, the components in the following embodiments include those that can be easily imagined by a person skilled in the art, those that are substantially the same, and those that are within the so-called equivalent range. Furthermore, the components disclosed in the following embodiments can be combined as appropriate.

[0014] (Method of manufacturing the bonding sheet) FIG. 1 is a schematic diagram of a bonding sheet according to this embodiment, and FIG. 2 is a flowchart illustrating a manufacturing method of the bonding sheet according to this embodiment. In the manufacturing method according to this embodiment, a bonding sheet 10 is manufactured. The bonding sheet 10 is a sheet-like member for bonding members together. As shown in FIG. 1, the bonding sheet 10 is a sintered copper body, and has a structure in which a plurality of copper particles 12 are bonded by sintering. It is preferable that the bonding sheet 10 is one in which sintering further progresses when heated at 150°C to 300°C (150°C or higher and 300°C or lower). In other words, the bonding sheet 10 can be said to be a pre-sintered copper body. Here, "progression of sintering" refers to an increase in the packing ratio as the bonding between the copper particles 12 further progresses. Because the bonding sheet 10 is a pre-sintered body, it can maintain a high Young's modulus, suppress the risk of breakage, and appropriately bond members together by progressing the sintering. The characteristics of the bonding sheet 10 will be described later. The bonding sheet 10 may contain a pre-sintered copper body, and may also contain unsintered copper particles in part.

[0015] 2, in this manufacturing method, a preparation step S0, a lamination step S10, a heating step S20, and a removal step S30 are performed to manufacture the bonding sheet 10. Each step will be specifically described below.

[0016] (Preparation step) In the preparation step S0, copper particles 12A are prepared. The copper particles 12A here are copper particles that are the raw material of the joining sheet 10, and can also be said to be copper powder before pre-sintering. In other words, by pre-sintering the copper particles 12A, the joining sheet 10 in which the copper particles 12 are bonded by pre-sintering is manufactured. The copper particles before pre-sintering can be said to be the copper particles 12A, and the copper particles after pre-sintering can be said to be the copper particles 12.

[0017] The copper particles 12A have a BET diameter of 300 nm or less. By making the BET diameter of the copper particles 12A 300 nm or less, the surface area is increased, sintering proceeds appropriately, and damage to the bonding sheet 10 can be suppressed. The BET diameter is a particle diameter calculated from the BET specific surface area and 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.

[0018] The BET diameter of the copper particles 12A is preferably 50 nm or more and 300 nm or less, more preferably 80 nm or more and 200 nm or less, and particularly preferably 80 nm or more and 170 nm or less.

[0019] The BET specific surface area of ​​copper particles 12A is 2.0m 2 / g or more 8.0m 2 / g or less, and 2 / g or more 8.0m 2 / g or less, and more preferably 4.0m 2 / g or more 8.0m 2 / g or less. The shape of the copper particles 12A is not limited to a spherical shape, but may be a needle shape or a flat plate shape.

[0020] The surfaces of the copper particles 12A are preferably coated with an organic protective film, which is a film of an organic substance. By being coated with the organic protective film, oxidation of the copper particles 12A is suppressed, and a decrease in sinterability due to oxidation of the copper particles 12A is further reduced. Note that the organic protective film coating the copper particles 12A 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 12A is not a copper oxide film formed by the oxidation of copper.

[0021] The fact that the copper particles 12A are coated with an 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 this embodiment, the copper particles 12A are coated with an organic protective film. + C3H3O3 vs. detected ion amount - Ratio of detected ions (C3H3O3 - / Cu + It is preferable that the ratio is 0.001 or more. - / Cu + The ratio is more preferably in the range of 0.05 to 0.2. Note that the surface of copper particles 12A in this analysis does not refer to the surface of copper particles 12A after the organic protective film has been removed from copper particles 12A, but refers to the surface of copper particles 12A including the organic protective film that covers them (i.e., the surface of the organic protective film).

[0022] Copper particle 12A was analyzed by time-of-flight secondary ion mass spectrometry to identify C3H4O2 - Cu ions and ions of C5 or higher may be detected. + C3H4O2 vs. detected ion amount - Ratio of detected ions (C3H4O2 - / Cu + The ratio is preferably 0.001 or more. + The ratio of the amount of ions detected above C5 to the amount of ions detected (ions above C5 / Cu + It is preferable that the ratio is less than 0.005.

[0023] C3H3O3 detected in time-of-flight secondary ion mass spectrometry - Ions and C3H4O2 - The ions and C5 or higher ions originate from the organic protective film that covers the surface of the copper particles 12A. - / Cu + Ratio and C3H4O2 - / Cu + When each of these ratios is 0.001 or more, the surfaces of the copper particles 12A are less likely to be oxidized, and the copper particles 12A are less likely to aggregate. - / Cu + Ratio and C3H4O2 - / Cu + When the ratio is 0.2 or less, oxidation and aggregation of the copper particles 12A can be suppressed without excessively reducing the sinterability of the copper particles 12A, 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. - / Cu + Ratio and C3H4O2 - / Cu + The ratio is preferably in the range of 0.08 to 0.16. + If the ratio is 0.005 or more, the particle surface will have a large amount of organic protective film with a relatively high desorption temperature, resulting in insufficient sintering and making it difficult to obtain a strong bonding layer. + Preferably, the ratio is less than 0.003.

[0024] The organic protective film is preferably derived from citric acid. A method for producing copper particles 12A coated with a 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 to 2.0% by mass, more preferably 0.8% by mass to 1.8% by mass, and even more preferably 0.8% by mass to 1.5% by mass, relative to 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 12A to be uniformly coated with the organic protective film, thereby more reliably suppressing oxidation of the copper particles 12A. Furthermore, a coating amount of the organic protective film of 2.0% by mass or less prevents voids from being generated 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. The heating rate is 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) × 100 (wt%). Measurements can be performed three times using copper particles from the same lot, and the arithmetic mean value can be used as the amount of coating.

[0025] It is preferable that 50% by mass or more of the organic protective film of copper particles 12A decomposes when heated for 30 minutes at 300° C. in an inert gas atmosphere such as argon gas. The organic protective film derived from citric acid generates carbon dioxide gas, nitrogen gas, evaporated acetone gas, and water vapor upon decomposition.

[0026] 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 this aqueous dispersion to adjust the pH to 2.0 or higher and 7.5 or lower. 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 aqueous dispersion of copper citrate and mixed. The resulting mixture is heated to a temperature of 60 to 80°C in an inert gas atmosphere and maintained for 1.5 to 2.5 hours. This reduces the copper ions eluted from the copper citrate to produce copper particles 12A, and also forms an organic protective film derived from citric acid on the surface of the copper particles 12A.

[0027] The copper citrate aqueous dispersion can be prepared by adding powdered copper citrate to pure water, such as distilled water or ion-exchanged water, to a concentration of 25% by mass to 40% by mass, and stirring with a stirring blade to uniformly disperse the copper citrate. Examples of pH adjusters include triammonium citrate, ammonium hydrogen citrate, and citric acid. Among these, triammonium citrate is preferred because it is easy to adjust the pH to a mild level. The pH of the copper citrate aqueous dispersion is set to 2.0 or higher to increase the elution rate of copper ions eluted from the copper citrate, thereby facilitating the rapid production of copper particles and obtaining the desired fine copper particles 12A. The pH is set to 7.5 or lower to prevent the eluted copper ions from becoming copper(II) hydroxide, thereby increasing the yield of copper particles 12A. Setting the pH to 7.5 or lower also prevents the reducing power of the hydrazine compound from becoming excessively high, making it easier to obtain the desired copper particles 12A. The pH of the copper citrate aqueous dispersion is preferably adjusted to within the range of 4 or more and 6 or less.

[0028] The reduction of copper citrate with a hydrazine compound is carried out under an inert gas atmosphere to prevent oxidation of copper ions dissolved in the solution. Examples of inert gases include nitrogen gas and argon gas. When copper citrate is reduced under acidic conditions, hydrazine compounds have the advantages of not producing residue after the reduction reaction, 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 because they do not contain components that could become impurities, such as sulfur and chlorine.

[0029] 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 12A 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 12A, thereby suppressing dissolution of the copper particles 12A. 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.

[0030] 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 12A and to form an organic protective film on the surface of the generated copper particles 12A. The heating and maintaining in an inert gas atmosphere is intended to prevent oxidation of the generated copper particles 12A. Copper citrate, the starting material, typically contains approximately 35% by mass of copper. Adding a hydrazine compound, which serves as a reducing agent, to a copper citrate aqueous dispersion containing this amount of copper component is heated to the above temperature and maintained for the above time period, resulting in a balanced generation of copper particles 12A and the generation of an organic protective film on the surface of the copper particles 12A. This allows for the production of copper particles 12A with an organic protective film coverage of 0.5% to 2.0% by mass of copper particles (100% by mass). If the heating temperature is less than 60°C and the holding time is less than 1.5 hours, the copper citrate may not be completely reduced, the rate of production of copper particles 12A may become too slow, and the amount of organic protective film coating copper particles 12A may become excessive. If the heating temperature exceeds 80°C and the holding time exceeds 2.5 hours, the rate of production of copper particles 12A may become too fast, and the amount of organic protective film coating copper particles 12A 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.

[0031] The copper particles 12A produced in the mixed solution are subjected to solid-liquid separation from the mixed solution in an inert gas atmosphere, for example, using a centrifuge, and then dried by freeze-drying or vacuum drying, thereby obtaining copper particles 12A whose surfaces are coated with an organic protective film. Because the copper particles 12A have their surfaces 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.

[0032] (Layer step) 3 is a schematic diagram illustrating the lamination step. In the lamination step S10, copper particle layers 10A, which are layers of a plurality of copper particles 12A, and lamination members P are alternately laminated to obtain a laminate 10L. This will be specifically described below.

[0033] As shown in FIG. 3, in the stacking step S10, a frame-shaped mold T is prepared as shown in step S10A. The mold T includes a frame member T1 and a bottom member T2. The bottom member T2 is a plate-shaped member that serves as a base for stacking the laminate 10L. The frame member T1 is a frame-shaped member provided on the surface T2a of the bottom member T2. In other words, when the axial direction is defined as a direction that passes through the center of the bottom member T2 and is aligned with the stacking direction when viewing the bottom member T2 from the stacking direction, it can be said that the frame member T1 extends around the entire circumferential direction, surrounding the center of the bottom member T2. In the lamination step S10, the copper particle layer 10A and the lamination members P are laminated inside the frame member T1. That is, the mold T forms a space SP surrounded by the surface T2a of the bottom member T2 and the inner circumferential surface T1a of the frame member T1, and it can be said that the copper particle layer 10A and the lamination members P are laminated in the space SP to form the laminate 10L. In this embodiment, the frame member T1 has a shape that forms the sides of a rectangle when viewed from the stacking direction of the laminate 10L. However, this is not limited thereto, and the shape and size of the mold T (frame member T1 and bottom member T2) may be any shape and size. Furthermore, the mold T (frame member T1 and bottom member) is made of metal, for example, aluminum, but the material of the mold T may also be any material. However, it is preferable that the mold T is made of a material with a higher melting point than the copper particles 12A.

[0034] In the lamination step S10, as shown in step S10B, a plurality of copper particles 12A are filled into the space SP, and a copper particle layer 10A composed of the plurality of copper particles 12A is formed. Thereafter, as shown in step S10C, a lamination member P is placed on the copper particle layer 10A in the space SP, and the copper particle layer 10A and the lamination member P are laminated together. Thereafter, as shown in step S10D, further copper particles 12A are filled on the lamination member P placed on the copper particle layer 10A in the space SP, and the copper particle layer 10A is formed on the lamination member P. That is, the copper particle layers 10A and the lamination members P are alternately laminated in the space SP. In this way, by repeating the step of alternately laminating the copper particle layers 10A and the lamination members P in the space SP, a laminate 10L in which the copper particle layers 10A and the lamination members P are alternately laminated is formed as shown in step S10E.

[0035] The lamination member P is a member disposed between two copper particle layers 10A. The size and shape of the lamination member P may be any size and shape, but in this embodiment, it is a plate-shaped member. The lamination member P is made of metal, for example, aluminum, but the material may be any material. However, the lamination member P is preferably made of a material with a higher melting point than the copper particles 12A.

[0036] As described above, the copper particle layer 10A is a layer containing a plurality of copper particles 12A, and can be considered to be a layer in which the plurality of copper particles 12A are aggregated in an unsintered state. The copper particle layer 10A is laminated so as to be surrounded by the inner circumferential surface of the mold T and sandwiched between two lamination members P (or the lamination members P and the blocks BL described below). Therefore, the copper particle layer 10A can be considered to be compressed by the mold T and the lamination members P (or the blocks BL described below) to form a compact of the plurality of copper particles 12A. The Young's modulus of the compact-form copper particle layer 10A is preferably 5 GPa or less, more preferably 1 GPa to 4 GPa, and even more preferably 2 GPa to 3 GPa. Young's modulus can be measured using a Picodentor HM500 (manufactured by Fisher Instruments, analysis software WIN-HCU ver.7.0), which is a device that complies with the ISO 14577 standard for nanoindentation. Nanoindentation is a method for calculating hardness and Young's modulus from the load and indentation depth applied to a sample. In this embodiment, the Young's modulus of the copper particle layer 10A is determined by measuring the upper surface of the copper particle layer 10A five times at five randomly selected locations using the device and analysis software. The measurement conditions were a Vickers indenter terminal, an indentation depth of 2 μm, an indentation speed of 0.067 μm / sec, and a measurement temperature of 25°C. The copper particle layer 10A was placed on a 0.4 mm thick silicon wafer larger than the copper particle layer 10A. The Young's modulus values ​​hereafter may refer to values ​​measured using a similar method. For example, the Young's modulus of the bonding sheet 10 may also refer to a value measured using a similar method.

[0037] 3, the laminate 10L has a total of seven layers of copper particle layers 10A and lamination members P, but the number of layers is not limited to seven and may be any number. However, the laminate 10L preferably has at least two or more copper particle layers 10A laminated therein, and more preferably has two or more copper particle layers 10A and two or more lamination members P laminated therein. Furthermore, it is preferable that the copper particle layers 10A of each layer have the same amount of copper particles 12A, but this is not limiting and each layer may have a different amount of copper particles 12A. It is also preferable that the lamination members P of each layer have the same shape, size and material, but this is not limiting and at least one of the shape, size and material of the lamination members P of each layer may be different. In addition, in the explanation of FIG. 3, the copper particle layer 10A is formed first (as the first layer), and then ( In the example of FIG. 3, the lamination member P is placed as the seventh layer, but the lamination order is not limited to this and is arbitrary, and the lamination member P may be placed first and the copper particle layer 10A may be formed thereon. In addition, in the example of FIG. 3, the copper particle layer 10A is formed last (as the seventh layer in the example of FIG. 3), but this is not limited to this and the last layer (top layer) may be the lamination member P. In addition, in the description of Figure 3, the copper particle layer 10A and the lamination member P are laminated within the mold T, i.e., within the space SP, to form the laminate 10L. However, the copper particle layer 10A and the lamination member P may be laminated at any location, not limited to within the mold T.

[0038] (heating step) FIG. 4 is a schematic diagram illustrating the heating step and the removal step. In the heating step S20, the laminate 10L is heated to a predetermined temperature while being pressurized at a predetermined pressure (hot-pressed at a predetermined pressure and a predetermined temperature), thereby pre-sintering the copper particles 12A contained in the copper particle layer 10A and producing the bonding sheet 10. In other words, the pre-sintered body of the copper particle layer 10A can be said to be the bonding sheet 10. The predetermined pressure here is preferably 1 MPa to 30 MPa, more preferably 10 MPa to 30 MPa, more preferably 11 MPa to 25 MPa, and even more preferably 12 MPa to 20 MPa. The predetermined temperature here is preferably 150°C to 250°C, more preferably 160°C to 240°C, and even more preferably 170°C to 230°C. Furthermore, the holding time for holding the laminate 10L at a predetermined pressure and a 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 even more preferably 3 minutes or more and 20 minutes or less. By hot pressing the laminate 10L under such conditions, it is possible to appropriately manufacture the bonding sheet 10 that can suppress the risk of breakage.

[0039] In this embodiment, as shown in FIG. 4, the laminate 10L is placed in a mold T and then hot-pressed. Specifically, a block BL is placed on the laminate 10L, and the laminate 10L is sandwiched between the block BL and the bottom member T2 in the stacking direction. A load is then applied in a direction that brings the block BL and the bottom member T2 closer to each other, thereby applying a predetermined pressure to the laminate 10L and heating the laminate 10L to a predetermined temperature. The block BL may have any shape or size. The block BL is made of metal, such as aluminum, but may be made of any material. However, it is preferable that the block BL be made of a material with a higher melting point than the copper particles 12A. In the heating step S20, the laminate 10L is not limited to being hot-pressed while placed in the mold T; for example, the laminate 10L may be hot-pressed after being removed from the mold T.

[0040] (Removal step) After the heating step S20 is performed, the removing step S30 is performed. In the removing step S30, the bonding sheet 10, which is the temporarily sintered copper particle layer 10A, is removed from the mold T.

[0041] (Characteristics of the bonding sheet) By manufacturing the bonding sheet 10 by the manufacturing method described above, it is possible to manufacture the bonding sheet 10 containing a copper sintered body, and to reduce the risk of breakage of the bonding sheet 10. The characteristics of the bonding sheet 10 manufactured by this manufacturing method will be described in more detail below.

[0042] The bonding sheet 10 preferably has a filling rate of 50% to 70%, more preferably 52% to 68%, and even more preferably 55% to 65%. By having the filling rate within this range, the Young's modulus can be maintained high, and further sintering can be appropriately promoted, allowing the members to be appropriately bonded to each other. The packing ratio is the ratio of bulk density to true density (bulk density / true density). Here, true density refers to the density of the material (copper in this case) itself when it is assumed that there are no pores or cracks in the sintered body, i.e., the theoretical density. Furthermore, bulk density refers to the value obtained by dividing the weight of the bonding sheet 10 by the volume calculated from the external dimensions of the bonding sheet 10. The volume calculated from the external dimensions refers to the total volume of the bonding sheet 10, including the pores. The true density is, for example, the literature value of the density of copper (e.g., 8.96 g / cm 3 ) can be used. The bulk density can also be measured using a balance, a coordinate measuring machine, and a micrometer. For example, the area and thickness of the bonding sheet 10 are measured using the coordinate measuring machine and the micrometer, and the value obtained by multiplying the area and the thickness is taken as the volume calculated from the external dimensions. Then, the weight of the bonding sheet 10 is measured using a balance, and the value obtained by dividing the measured weight by the volume calculated from the external dimensions is taken as the bulk density. As will be described later, the bonding sheet 10 may have a copper sintered body impregnated with resin. In this case, the filling rate refers to the filling rate of the copper sintered body excluding the resin. Hereinafter, the characteristics of the bonding sheet 10 other than the filling rate are specified, but they may also refer to the characteristics of the copper sintered body excluding the resin.

[0043] 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. The arithmetic mean roughness Ra of the bonding sheet 10 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. The arithmetic mean roughness Ra of at least one of the surfaces 10a and 10b of the bonding sheet 10 may be within the above range. When the arithmetic mean roughness Ra (surface roughness) is within this range, further sintering can be appropriately progressed, and the members can be appropriately bonded to each other. The arithmetic mean roughness Ra can be measured in accordance with the provisions of JIS B 0601:2001.

[0044] 5 is a schematic partial enlarged view of the bonding sheet. The bonding sheet 10 has an average particle size, which is the average value of the particle size D of each copper particle 12, of preferably 100 nm to 350 nm, more preferably 150 nm to 300 nm, and even more preferably 200 nm to 250 nm. By having the average particle size within this range, the surface area of ​​the bonding sheet 10 can be kept large, allowing further sintering to proceed appropriately. In addition, since the copper particles 12 in the joining sheet 10 are bonded together by sintering, the average particle size of the copper particles 12 can be said to be the average value of the particle sizes of the copper particles 12 separated by the interfaces between the bonded copper particles 12 in the joining sheet 10. For example, the BET diameter calculated based on the BET specific surface area may be used as the average particle size of the copper particles 12. In this case, the amount of nitrogen gas adsorbed by the bonding sheet 10 was measured using a specific surface area measuring device (QUANTACHROME AUTOSORB-1, manufactured by Quantachrome Instruments), and the specific surface area of ​​the bonding sheet 10 was calculated by the BET method. The obtained specific surface area S (m 2 / g) and the density of copper particles ρ (g / cm 3 ) and the BET diameter may be calculated from the following formula, and this may be used as the average particle size of the copper particles 12. BET diameter (nm) = 6000 / (ρ(g / cm 3 )×S(m 2 / g))

[0045] The Young's modulus of the bonding sheet 10 is preferably 5 GPa or more and 25 GPa or less, more preferably 10 GPa or more and 25 GPa or less, even more preferably 11 GPa or more and 20 GPa or less, and even more preferably 12 GPa or more and 15 GPa or less. When the Young's modulus is in this range, the risk of breakage can be suppressed.

[0046] The bonding sheet 10 preferably has a thermal conductivity of 10 W / mK to 60 W / mK, more preferably 15 W / mK to 55 W / mK, and even more preferably 20 W / mK to 50 W / mK. When the thermal conductivity is within this range, the heat of the members to be bonded can be suitably transferred. Thermal conductivity can be calculated, for example, by converting resistivity. Specifically, the sheet resistance of a 10 mm x 10 mm bonding sheet at 25°C is measured using a Loresta (MCP-250T, manufactured by Mitsubishi Yuka Co., Ltd.) by the four-probe method, and the resistivity is calculated by multiplying it by the sheet film thickness. Thermal conductivity at 25°C is calculated by converting resistivity using the Wiedemann-Franz law.

[0047] 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 refers to the distance in the thickness direction Z between the point on the surface 10a that protrudes most from the surface 10a and the point on the surface 10b that protrudes most from the surface 10b. In addition, the projected area of ​​the bonding sheet 10 when projected in the direction Z is 10000 mm 2 It is preferable that it is less than 6400 mm 2 It is more preferable that it is less than 3600 mm 2 It is more preferable that: By using the bonding sheet 10 having a thickness W and a projected area within this range, members can be bonded appropriately.

[0048] The large area bonding index D1 is defined as the value (thickness W / filling rate) obtained by dividing the thickness W of the bonding sheet 10 by the filling rate (%) of the bonding sheet 10. 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 is in this range, the members can be appropriately bonded to each other while suppressing breakage.

[0049] The bonding sheet 10 may be a copper sintered body impregnated with a resin. That is, the bonding sheet 10 may have at least some of the internal pores filled with a resin. Examples of the resin include epoxy resin and silicone resin. By impregnating the bonding sheet 10 with a resin, it is possible to impart appropriate functions to the bonding sheet 10.

[0050] (Method of manufacturing a bonded body) Next, a method for manufacturing a bonded body 100 by bonding members together using the bonding sheet 10 will be described. FIG. 6 is a schematic diagram for explaining a method for manufacturing a bonded body. In this embodiment, the bonded body 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 body 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.

[0051] In this manufacturing method, as shown in step S100 in Fig. 6, the bonding sheet 10 is placed on the surface of the first member A. In the example in Fig. 6, the bonding sheet 10 is placed on the first member A so that the surface 10b of the bonding sheet 10 contacts the surface of the first member A.

[0052] Next, as shown in step S102, the solvent 20 is applied onto the surface 10a of the bonding sheet 10 (the surface on the side not in contact with the first component A). The solvent 20 acts as a binder for the copper particles 12. The solvent 20 is an organic solvent. Note that the addition of the solvent 20 is not essential.

[0053] The solvent 20 preferably has a boiling point of 150°C or higher, and preferably 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 of 100 to 1000, more preferably 200 to 800, and particularly preferably 200 to 600. The solvent is preferably a compound having a reducing group at its terminal. The reducing group is preferably a hydroxyl group. The solvent 20 preferably has a dielectric constant 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.).

[0054] As the solvent 20, for example, a diol compound or a triol compound can be used. 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.

[0055] The solvent 20 is preferably added in an amount of 0.5% to 10% by mass, more preferably 1% to 8% by mass, and even more preferably 2% to 5% by mass relative to the bonding sheet 10. When the amount of the solvent 20 added is within this range, it is possible to maintain appropriate bonding properties.

[0056] As shown in step S104, the solvent 20 penetrates into and fills the pores of the bonding sheet 10. In other words, the bonding sheet 10 is impregnated with the solvent 20.

[0057] Thereafter, as shown in step S106, the second member B is placed on the surface 10a of the bonding sheet 10 impregnated with the solvent 20. That is, the bonding sheet 10 impregnated with the solvent 20 is placed between the first member A and the second member B.

[0058] Thereafter, the laminate in which the bonding sheet 10 is disposed between the first member A and the second member B is heated to further promote sintering of the bonding sheet 10, thereby producing a bonded body 100 in which the first member A and the second member B are bonded together by a bonding layer (sintered bonding sheet 10). The heating temperature of the laminate may be, for example, in the range of 150°C to 300°C. The heating time of the laminate may be, for example, in the range of 10 minutes to 1 hour. The heating of the laminate is preferably carried out in an inert gas atmosphere while applying pressure to the laminate in the stacking direction. Nitrogen gas or argon gas can be used as the inert gas. The pressure applied to the laminate is preferably in the range of 0.5 MPa to 30 MPa.

[0059] (effect) As described above, the manufacturing method of the bonding sheet according to this embodiment includes the steps of alternately stacking copper particle layers 10A, each of which is a layer of a plurality of copper particles 12A having a BET diameter of 300 nm or less, and lamination members P to obtain a laminate 10L (lamination step S10), and heating the laminate 10L at 150°C to 300°C while applying a pressure of 1 MPa to 30 MPa to sinter the copper particles 12A, thereby producing a bonding sheet 10 containing a copper sintered body and having a Young's modulus of 5 GPa to 25 GPa (heating step S20). This manufacturing method can reduce the risk of damage to the bonding sheet 10. Specifically, hot pressing at the pressure and temperature used in this manufacturing method appropriately pre-sinters the copper particles 12A, increasing the Young's modulus of the bonding sheet 10 and reducing damage, while also allowing further sintering to proceed appropriately during bonding of the components, thereby enabling the components to be properly bonded. Furthermore, by stacking and hot pressing as in the present manufacturing method, uneven loads applied to the copper particle layers 10A can be suppressed, and breakage from areas subjected to low loads, for example, can be suppressed.

[0060] In the step of obtaining the laminate 10L, it is preferable to laminate two or more copper particle layers 10A. By laminating two or more copper particle layers 10A, it is possible to appropriately suppress unevenness in the load applied to each copper particle layer 10A, and thus to suitably suppress breakage.

[0061] In the step of obtaining the laminate 10L, the copper particle layer 10A and the lamination member P are preferably laminated in a frame-shaped mold T. By laminating the layers in the mold T, it is possible to appropriately suppress unevenness in the load applied to each copper particle layer 10A, and thus to suitably suppress breakage.

[0062] In the step of producing the bonding sheet 10, the laminate 10L is heated under pressure for a holding time of 1 minute to 30 minutes. By performing the hot pressing within this time range, the copper particles 12A can be appropriately pre-sintered, and breakage can be suitably suppressed.

[0063] The manufacturing method of 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.

[0064] (Example) Next, examples will be described. Fig. 7 is a table showing the properties and evaluation results of the bonding sheets of the respective examples.

[0065] 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 to the resulting aqueous dispersion as a pH adjuster to adjust the pH of the copper citrate dispersion to 5. The resulting aqueous dispersion was then heated to 50°C, and while maintaining that 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 added was 1.2 times the amount required to reduce all the 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.

[0066] 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 calculated by the BET method. The obtained specific surface area S (m 2 / g) and the density of copper particles ρ (g / cm3 ) and the BET diameter was calculated using the following formula. BET diameter (nm) = 6000 / (ρ(g / cm 3 )×S(m 2 / g))

[0067] (Creation of bonding sheets) An aluminum frame with outer dimensions of 50 mm square x 30 mm and inner dimensions of 30 mm square x 30 mm with a hole was prepared as a mold for filling the prepared copper particles. 1.5 g of copper particles was filled into this aluminum frame to form a copper particle layer. A 29 mm square x 29 mm lamination member was placed on the copper particle layer, and the copper particle layer and the lamination member were alternately laminated to form a laminate with a total of five copper particle layers and lamination members. In other words, the number of copper particle layers in Example 1 was three. A 30 mm square x 20 mm aluminum block was placed on the laminate, and the laminate was subjected to a hot press treatment in the atmosphere under conditions of an applied pressure of 30 MPa, a heating temperature of 150°C, and a holding time of heating and pressing for 15 minutes to produce a bonding sheet. A CYPT-50kN hot press machine (manufactured by Shinto Kogyo Co., Ltd.) was used. After the hot pressing, the sheet was cooled to room temperature, and the 30 mm square x 0.4 mm bonding sheet sandwiched between the aluminum block and lamination members was peeled off from the aluminum block to obtain the desired bonding sheet. In Fig. 7, the copper particle layers and lamination members alternately laminated are designated as "laminated." Also, Fig. 7 shows the number of laminated copper particle layers. Also, Fig. 7 shows the shape of the mold for filling the copper particles. Since a frame-shaped mold was used in Example 1, the mold shape is designated as "frame-shaped." Also, Fig. 7 shows the BET diameter of the copper particles, the heating temperature of the laminate, the pressure applied to the laminate, and the holding time for heating and pressurizing the laminate.

[0068] (Characteristics of the bonding sheet) The Young's modulus of the bonding sheet was measured using a Picodentor. The Young's modulus was measured using the method described in this embodiment. The filling rate of the bonding sheet was also measured. The filling rate was measured as follows: The volume calculated from the external dimensions of the bonding sheet was measured using a vernier caliper and a micrometer. Specifically, five points on each of the two horizontal sides of the bonding sheet were measured at random, and the product of the average values ​​was used as the area of ​​the bonding sheet. Furthermore, the thickness of the bonding sheet was measured at 10 points at random using a micrometer, and the average value was used as the thickness of the bonding sheet. The product of the area and the thickness was used as the volume calculated from the external dimensions of the bonding sheet. Next, the weight of the bonding sheet was measured. The weight of the bonding sheet was then divided by the volume calculated from the external dimensions of the bonding sheet 10 to calculate the bulk density. The volume calculated from the external dimensions refers to the total volume of the bonding sheet 10, including the pores. The true density was then calculated as 8.96 g / cm. 3 The ratio of the bulk density to the true density was calculated as the packing ratio. The thermal conductivity of the bonding sheet was also measured. Specifically, the sheet resistance at 25°C of a 10mm x 10mm bonding sheet was measured using a Loresta (MCP-250T, manufactured by Mitsubishi Yuka Co., Ltd.) by the four-probe method, and the specific resistance was calculated by multiplying it by the sheet thickness. The thermal conductivity at 25°C was then calculated by converting the specific resistance using the Wiedemann-Franz law. The measured values ​​of Young's modulus, packing ratio, and thermal conductivity are shown in Figure 7.

[0069] (Examples 2-4) In Example 2-4, a bonding sheet was produced in the same manner as in Example 1, except that at least one of the BET diameter of the copper particles, the heating temperature, and the pressure was changed as shown in Figure 7. The measured values ​​of Young's modulus, filling rate, and thermal conductivity are shown in Figure 7.

[0070] (Comparative Examples 1-5) In Comparative Example 1-5, a bonding sheet was produced in the same manner as in Example 1, except that at least one of the BET diameter of the copper particles, the heating temperature, and the pressure was changed as shown in Figure 7. The measured values ​​of Young's modulus, filling rate, and thermal conductivity are shown in Figure 7.

[0071] (evaluation) The strength of the bonding sheet of each example and the shear strength of the bonded body in which members were bonded together using the bonding sheet were evaluated.

[0072] (Evaluation of the strength of the bonding sheet) To evaluate the strength of the bonding sheet, a 30mm x 30mm bonding sheet was placed on a 50mm x 50mm x 1mm thick oxygen-free copper plate, and the height of the center of the top surface of the bonding sheet was set to 0mm. A 20mm diameter zirconia bead (Nikkato, YTZ-20) was then gently dropped from a height of 0mm. This operation of dropping one bead per sheet was repeated 10 times, and the bonding sheets were visually inspected. If 7 or more sheets were found to be free of cracks or chips, they were judged as passing (◯), and if 6 or fewer sheets were found, they were judged as failing (×).

[0073] (Evaluation of shear strength of joint) The bonding sheet of each example 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 oxygen-free copper substrate. Next, polyethylene glycol was applied as a solvent to the bonding sheet piece at 0.05 g per 0.95 g of sheet piece weight, and then 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 oxygen-free copper substrate and the 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 250 °C, to prepare a bonded body (Sample A) in which a 2.5 mm square oxygen-free copper substrate and an oxygen-free copper dummy element were bonded via a copper bonding layer.

[0074] The shear strength of the resulting bonded assembly (Sample A) was measured according to 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). The load (maximum shear load) at which the oxygen-free copper dummy element peeled off 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 maximum shear load obtained 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 assemblies were fabricated, and the shear strength of each was measured. The results are shown in Figure 7.

[0075] In the evaluation, a joining sheet having a strength rating of ◯ and a shear strength of 30 MPa or more was deemed to be pass. On the other hand, a joining sheet having a strength rating of ◯ and a shear strength of 30 MPa or more was deemed to be fail if at least one of these conditions was not met.

[0076] 7, the bonding sheet of the example manufactured by alternately laminating copper particle layers containing copper particles with a BET diameter of 300 nm or less and lamination members, and heating at 150°C to 300°C while applying pressure of 1 MPa to 30 MPa passed the evaluation of the strength of the bonded body and the shear strength of the bonded body, indicating that breakage can be appropriately suppressed. On the other hand, the bonding sheet of the comparative example, which did not satisfy at least one of the above manufacturing conditions, failed at least one of the evaluation of the strength and the shear strength of the bonded body, indicating that breakage cannot be appropriately suppressed.

[0077] (Void ratio of bonded body) In addition, as an optional evaluation, the void ratio of the bonded structure was evaluated. The bonding sheet was cut using a commercially available cutter knife to prepare bonding sheet pieces (10 mm square x 500 μm thick). The above bonding sheet piece (10 mm square x 500 μm thick) was placed on a 30 mm square x 1 mm thick oxygen-free copper substrate. Next, polyethylene glycol was applied as a solvent to the bonding sheet piece at 0.05 g per 0.95 g of sheet piece weight, and then an oxygen-free copper dummy element (10 mm square x 1 mm thick) was placed on the bonding sheet piece. In this way, a laminate was obtained in which the oxygen-free copper substrate and the oxygen-free copper dummy element were stacked 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 pressure of 5 MPa, and a temperature of 250°C, thereby producing a bonded body (Sample B) in which a 2.5 mm square oxygen-free copper substrate and an oxygen-free copper dummy element were bonded via a copper bonding layer.

[0078] The copper bonding layer of the resulting bonded body (Sample B) was measured for ultrasonic flaw detection 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 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

[0079] Seven bonded bodies were fabricated, and the void ratio was measured for each bonded body. The results are shown in Figure 7.

[0080] Although the embodiments of the present invention have been described above, the embodiments are not limited to the contents of these embodiments. Furthermore, the above-described components include those that can 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 called equivalents. Furthermore, the above-described components can be combined as appropriate. Furthermore, various omissions, substitutions, or modifications of the components can be made without departing from the spirit of the above-described embodiments. [Explanation of symbols]

[0081] 10. Bonding sheet 10A copper particle layer 10L laminate 12, 12A copper particles P Lamination material T type

Claims

1. A step of alternately laminating copper particle layers, which are layers of a plurality of copper particles having a BET diameter of 50 nm or more and 300 nm or less, and lamination members to obtain a laminate; A step of producing a bonding sheet including a copper sintered body by heating the laminate at 150 ° C. or more and 300 ° C. or less while applying a pressure of 1 MPa or more and 30 MPa or less to sinter the copper particles; Including, A method for manufacturing a bonding sheet.

2. The method for manufacturing a bonding sheet according to claim 1 , wherein in the step of obtaining the laminate, two or more copper particle layers are laminated.

3. The method for manufacturing a bonding sheet according to claim 1 or 2, wherein in the step of obtaining the laminate, the copper particle layer and the lamination members are laminated in a frame-shaped mold.

4. The method for manufacturing a joining sheet according to any one of claims 1 to 3, wherein in the step of manufacturing the joining sheet, the laminate is heated while being pressurized for a holding time of 1 minute or more and 30 minutes or less.

5. A step of placing a bonding sheet manufactured by the manufacturing method of a bonding sheet according to any one of claims 1 to 4 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.

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