Manufacturing method of the bonded body

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]

[0001] The present invention relates to a method for producing a bonded body. [Background technology]

[0002] A bonding material may be used to bond two or more components when assembling or mounting electronic components, etc. For example, Patent Document 1 describes a method for manufacturing a bonded body by bonding components together using a bonding sheet formed by mixing copper particles and a solvent. [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] When joining members together using a joining sheet, it is required to simplify the joining process while still achieving proper joining.

[0005] The present invention has been made in view of the above, and an object of the present invention is to provide a method for manufacturing a bonded body that can perform appropriate bonding while simplifying the bonding step. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems and achieve the object, the manufacturing method of the bonded body according to the present disclosure includes the steps of placing a bonding sheet containing a copper sintered body on a first member, adding a solvent to the bonding sheet, and placing a second member on the bonding sheet to obtain a laminate in which the bonding sheet with the solvent added is placed between the first member and the second member, and heating the laminate at a heating temperature of 200°C or higher to manufacture a bonded body in which the first member and the second member are bonded.

[0007] In the step of producing the bonded body, the laminate is preferably heated at the heating temperature while being pressurized at a pressure of 1 MPa or more and 30 MPa or less.

[0008] It is preferable to use the bonding sheet having a filling rate of 50% or more.

[0009] It is preferable to use the bonding sheet having a Young's modulus of 1 GPa or more.

[0010] It is preferable to use the bonding sheet having a Young's modulus of 10 GPa or more.

[0011] It is preferable to use the bonding sheet having a thermal conductivity of 10 W / mK or more and 50 W / mK or less.

[0012] In the step of adding a solvent, it is preferable to use a polyhydric alcohol as the solvent.

[0013] It is preferable that the method further comprises a step of adding at least one of carboxylic acid, carboxylic acid salt, amine, and amine salt to the bonding sheet. [Effects of the Invention]

[0014] According to the present invention, it is possible to simplify the joining process and achieve appropriate joining. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic diagram of the bonding sheet according to this embodiment. [Figure 2] FIG. 2 is a schematic partially enlarged view of the bonding sheet. [Figure 3] FIG. 3 is a flow chart illustrating the method for manufacturing the bonding sheet according to this embodiment. [Figure 4] FIG. 4 is a schematic diagram for explaining a method for producing a bonded body. [Figure 5] FIG. 5 is a table showing the manufacturing conditions and evaluation results for each example. DETAILED DESCRIPTION OF THE INVENTION

[0016] 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.

[0017] (First embodiment) The method for manufacturing a bonded body according to this embodiment manufactures a bonded body in which a first member and a second member are bonded together by using a bonding sheet 10. First, the bonding sheet 10 will be described.

[0018] (bonding sheet) FIG. 1 is a schematic diagram of a bonding sheet according to this embodiment. The bonding sheet 10 according to this embodiment is a sheet-like member for bonding components together. As shown in FIG. 1, the bonding sheet 10 is a copper sintered body, and has a structure in which a plurality of copper particles 12 are bonded by sintering. The bonding sheet 10 preferably undergoes further sintering when heated at 150°C to 300°C (150°C or higher and 300°C or lower). Here, "progression of sintering" refers to an increase in the packing ratio as the bonding between the copper particles 12 progresses further. Since the bonding sheet 10 contains a sintered body, it is possible to maintain a high Young's modulus, suppress the risk of breakage, and appropriately bond components together by promoting sintering. Note that the bonding sheet 10 may contain any material as long as it contains a copper sintered body, and may also contain unsintered copper particles in part.

[0019] The joining sheet 10 preferably has a filling rate of 50% or more, more preferably 50% to 70%, even more preferably 52% to 68%, and even more preferably 55% to 65%. When the filling rate is within this range, further sintering can be properly progressed, and the members can be properly joined together. 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.

[0020] 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.

[0021] 2 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))

[0022] The Young's modulus of the bonding sheet 10 is preferably 1 GPa or more, more preferably 10 GPa or more, even more preferably 10 GPa to 30 GPa, even more preferably 11 GPa to 20 GPa, and even more preferably 12 GPa to 15 GPa. Having a Young's modulus within this range reduces the risk of breakage of the bonding sheet 10 and improves handleability, making it possible to simplify the bonding process and bond members with high shear strength. 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 bonding sheet 10 is measured five times at five randomly selected locations on the upper surface of the bonding sheet 10 using the device and analysis software, and the average value of the indentation Young's modulus obtained is taken as the Young's modulus of the bonding sheet 10. 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, and the measurement was performed with the bonding sheet 10 placed on a 0.4 mm thick silicon wafer that was larger than the bonding sheet 10. The Young's modulus hereinafter may also refer to values ​​measured using the same method.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] (Method of manufacturing the bonding sheet) FIG. 3 is a flow chart illustrating the method for manufacturing the bonding sheet according to this embodiment.

[0028] (Preparation of copper particles) 3, in this manufacturing method, first, copper particles 12A are prepared (step S10). 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.

[0029] 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 true density of the copper particles, which are determined by the BET method, assuming that the copper particles 12A are true spheres or cubes. Specifically, the BET diameter can be determined by the method described in the Examples below.

[0030] If the BET diameter of the copper particles 12A is 50 nm or more, it is difficult to form strong 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, if the BET diameter of the copper particles 12A is 300 nm or less, the reaction area is large and the sintering property 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 to 200 nm, and particularly preferably in the range of 80 nm to 170 nm.

[0031] 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.

[0032] 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.

[0033] 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).

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] (Filling copper particles into a mold) Next, the prepared copper particles 12A are filled into a mold (step S12), as shown in Fig. 3. The shape and material of the mold into which the copper particles 12A are filled may be arbitrary.

[0045] (Pre-sintering of copper particles) Next, the copper particles 12A packed in the mold are pressurized at a predetermined temperature to pre-sinter the copper particles 12A, thereby producing a joining sheet 10 (step S14). In this step, the copper particles 12A packed in the mold are pressurized at a predetermined pressure and held at a predetermined temperature for a predetermined time, thereby pre-sintering the copper particles 12A and producing a joining sheet 10. The predetermined pressure here is 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. The predetermined time here (the time held at the predetermined pressure and temperature) is preferably 1 minute to 30 minutes, more preferably 2 minutes to 25 minutes, and even more preferably 3 minutes to 20 minutes. By pre-sintering the copper particles 12A under such conditions, the bonding sheet 10 capable of simplifying the bonding step can be appropriately manufactured.

[0046] The bonding sheet 10 is not limited to be manufactured by the above method, and the bonding sheet 10 may be manufactured by any method.

[0047] (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. 4 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. In the following description, a first member A and a second member B are joined using one joining sheet 10, but this is not limited to this. A first member A and a second member B may be joined using multiple joining sheets 10 to form a joined body 100, or three or more members may be joined using one or multiple joining sheets 10 to form a joined body 100.

[0048] In this manufacturing method, as shown in step S20 in Fig. 4, the bonding sheet 10 is placed on the surface of the first member A. In the example in Fig. 4, 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.

[0049] Next, as shown in step S22, the solvent 20 is added to the bonding sheet 10. In this embodiment, the solvent 20 is added to the bonding sheet 10 placed on the first member A. More specifically, the solvent 20 is added (applied) to the surface 10a (the surface not in contact with the first member A) of the bonding sheet 10. 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 first, and the bonding sheet 10 with the solvent 20 added thereto may be placed on the first member A. Also, for example, the bonding sheet 10 may be placed between the first member A and the second member B, and then the solvent 20 may be added to the bonding sheet 10. Furthermore, the position where the solvent 20 is added is not limited to the surface 10a, and may be any position.

[0050] The solvent 20 acts as a binder for the copper particles 12. The solvent 20 may be any solvent, but is preferably an organic solvent, and more preferably a polyhydric alcohol.

[0051] 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.).

[0052] 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.

[0053] 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.

[0054] As shown in step S24, 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.

[0055] Thereafter, as shown in step S26, 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. Hereinafter, the state in which the bonding sheet 10 to which the solvent 20 has been added (impregnated) is placed between the first member A and the second member B will be referred to as a laminate.

[0056] Thereafter, the laminate is heated to further promote sintering of the bonding sheet 10, and a bonded body 100 is produced in which the first member A and the second member B are bonded by a bonding layer (sintered bonding sheet 10). 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, sintering of the bonding sheet 10 can be promoted appropriately, and the bonded body 100 can be properly manufactured. The heating time for the laminate is preferably 1 minute to 60 minutes, more preferably 3 minutes to 45 minutes, and even more preferably 5 minutes to 30 minutes. By setting the heating time within this range, the sintering of the bonding sheet 10 can be properly progressed, and the bonded body 100 can be properly produced. The laminate is preferably heated in an inert gas atmosphere while being pressurized in the stacking direction. Examples of the inert gas that can be used include nitrogen gas and argon gas. The pressure applied to the laminate is preferably 0.5 MPa or more, more preferably 1 MPa to 30 MPa, even more preferably 3 MPa to 25 MPa, even more preferably 5 MPa to 20 MPa, and even more preferably 10 MPa to 15 MPa.

[0057] (effect) As described above, the manufacturing method of the bonded body according to this embodiment includes the steps of placing a bonding sheet 10 containing a copper sintered body on a first member A, adding a solvent 20 to the bonding sheet 10, and placing a second member B on the bonding sheet 10 to obtain a laminate in which the bonding sheet 10 to which the solvent 20 has been added is placed 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 bonded body in which the first member A and the second member B are bonded.

[0058] In this manufacturing method, a bonding sheet 10 containing a copper sintered body is placed between a first member A and a second member B, and the bonding process (heating) is performed. This improves the handleability of the bonding sheet 10 in the bonding process, simplifying the bonding process. Furthermore, by adding a solvent 20 to the bonding sheet 10 and heating it at 200°C or higher, the sintering of the bonding sheet 10 can be properly advanced, allowing the members to be properly bonded together. Furthermore, since the bonding sheet 10 containing a copper sintered body is used, the solvent 20 can be added during the bonding process. This eliminates the need to pre-add the solvent 20 to, for example, commercially available bonding sheets 10, and reduces the effort required for transportation and storage.

[0059] In the step of producing the bonded body, it is preferable to heat the laminate at a heating temperature while applying a pressure of 1 MPa to 30 MPa. By hot-pressing the laminate in this manner, the members can be appropriately bonded to each other.

[0060] In this manufacturing method, it is preferable to use a bonding sheet 10 with a filling rate of 50% or more, which allows sintering to proceed appropriately and allows members to be bonded appropriately.

[0061] In this manufacturing method, it is preferable to use a bonding sheet 10 having a Young's modulus of 1 GPa or more. This makes it possible to suppress breakage of the bonding sheet 10 and more suitably improve the handling properties, thereby simplifying the bonding process.

[0062] In this manufacturing method, it is preferable to use a bonding sheet 10 having a Young's modulus of 10 GPa or more. This makes it possible to suppress breakage of the bonding sheet 10 and more suitably improve the handling properties, thereby simplifying the bonding process.

[0063] In this manufacturing method, it is preferable to use a joining sheet 10 having an arithmetic mean roughness Ra of the surface of 1 μm or more and 40 μm or less, which allows sintering to proceed appropriately and allows members to be joined appropriately.

[0064] 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, which allows for appropriate heat transfer between the members.

[0065] In the step of adding a solvent, it is preferable to use a polyhydric alcohol as the solvent 20. By using a polyhydric alcohol, the members can be bonded together appropriately.

[0066] (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, a description of the parts that are common to the first embodiment will be omitted.

[0067] In the second embodiment, at least one of the first member A and the second member B has Ni on the surface. "Having Ni on the surface" may mean that the entire member is made of Ni, or that only the surface is coated with Ni. Here, Ni refers to the elemental metal Ni.

[0068] In the second embodiment, in step S22, an additive is added to the bonding sheet 10 in addition to the solvent 20.

[0069] As the additive, at least one of carboxylic acid, carboxylate, amine, or amine salt is used. Furthermore, as the additive, at least one of carboxylic acid, carboxylate, amine, or amine salt having 2 to 8 carbon atoms is preferably used. Here, the number of carbon atoms refers to the number of C's in the chemical formula of the additive. Furthermore, as the additive, at least one of citric acid, ethylhexanoic acid, and ethylhexylamine is more preferably used. By using such a material as the additive, the first member A and the second member B can be appropriately bonded together even when Ni is contained on the surface of at least one of the first member A and the second member B.

[0070] The additive is preferably added in an amount of 0.1% to 10% by mass, more preferably 0.5% to 7% by mass, and even more preferably 1% to 5% by mass, relative to the bonding sheet 10. When the amount of additive added is within this range, Ni can be bonded appropriately. The additive is preferably added in a mass ratio of 20% or more, more preferably 40% or more, and even more preferably 60% or more, relative to the solvent 20. When the amount of additive added is within this range, Ni can be bonded appropriately.

[0071] In this embodiment, the solvent 20 and the additive are added to the bonding sheet 10 at the same time. 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, this is not limiting, and the solvent 20 and the additive may be added separately to the bonding sheet 10 at the same time. The order of adding the additive and the solvent 20 may be arbitrary. Furthermore, the timing of adding the additive may be arbitrary, and for example, the solvent 20 and the additive may be added to the bonding sheet 10 first, and then the bonding sheet 10 to which the solvent 20 and the additive have been added may be placed on the first member A. Also, for example, the bonding sheet 10 may be placed between the first member A and the second member B, and then the solvent 20 and the additive may be added to the bonding sheet 10. Furthermore, the position to which the additive is added is not limited to the surface 10a, and may be arbitrary.

[0072] In the second embodiment, as shown in step S26, the second member B is placed 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. Hereinafter, the bonding sheet 10 impregnated with the solvent 20 and the additive is placed between the first member A and the second member B, and this state is referred to as a laminate.

[0073] Thereafter, the laminate 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 by a bonding layer (sintered bonding sheet 10).

[0074] 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 bonding sheet 10. By adding at least one of carboxylic acid, carboxylate, amine, and amine salt to the bonding sheet 10, Ni can be appropriately bonded, and the bonded body 100 containing Ni can be appropriately manufactured. However, the second embodiment is not limited to applications for bonding Ni; in other words, the first member A and the second member B in the second embodiment do not have to contain Ni on their surfaces.

[0075] (Example) Next, examples will be described. Figure 5 is a table showing the manufacturing conditions and evaluation results of each example.

[0076] 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.

[0077] 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 (m2 / g) and the density of copper particles ρ (g / cm 3 ) and the BET diameter was calculated using the following formula. BET diameter (nm) = 6000 / (ρ(g / cm 3 )×S(m 2 / g))

[0078] (Creation of bonding sheets) An aluminum frame with outer dimensions of 50mm square x 30mm and inner dimensions of 30mm square x 30mm was prepared as a mold for filling the prepared copper particles. 1.5g of copper particles was filled into this aluminum frame, and the particles were evenly distributed using a 30mm square x 20mm aluminum block. The mixture was then hot-pressed in air at an applied pressure of 30MPa and a heating temperature of 150°C for 15 minutes to produce a bonding sheet containing a sintered copper body. A CYPT-50kN hot-press machine (manufactured by Shinto Kogyo Co., Ltd.) was used. After hot-pressing, the mixture was cooled to room temperature, and the 30mm square x 0.4mm bonding sheet sandwiched between the aluminum blocks was peeled off from the aluminum block to obtain the desired bonding sheet.

[0079] (Characteristics of the bonding sheet) In Fig. 5, the bonding sheet in which at least a part of the copper particles is sintered, that is, the bonding sheet containing the copper sintered body, is designated as a sintered body "◯". In Fig. 5, the bonding sheet in which all the copper particles are not sintered, that is, the bonding sheet not containing the copper sintered body, is designated as a sintered body "X". As shown in Fig. 5, the bonding sheet of Example 1 contains a sintered body in which at least a part of the copper particles is sintered. The Young's modulus of the bonding sheet was measured using a Picodentor by the method described in the present 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 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, and the value was calculated as 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 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 5.

[0080] (Zygote formation) The bonding sheet was cut using a commercially available cutter knife to prepare a bonding sheet piece (2.5 mm square x 500 μm thick). The above bonding sheet piece (2.5 mm square x 500 μm thick) was placed on a 30 mm square x 1 mm thick 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 300°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.

[0081] (Example 2-11) In Example 2-11, a bonded body was produced in the same manner as in Example 1, except that at least one of the manufacturing conditions of the bonding sheet, the heating temperature, the applied pressure, the pressing time, and the type of solvent was changed as shown in FIG.

[0082] (Comparative Examples 1-3) In Comparative Examples 1-3, bonded bodies were produced in the same manner as in Example 1, except that at least one of the manufacturing conditions of the bonding sheet, heating temperature, applied pressure, pressing time, and whether or not a solvent was added was changed as shown in Figure 5. In Comparative Example 1, the heating temperature during manufacturing of the bonding sheet was low at 40°C, so the bonding sheet of Comparative Example 1 did 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 was 100°C.

[0083] (evaluation) The bonded bodies of each example were evaluated, focusing on the ease of the bonding process (the configuration of heating the laminate) and the shear strength of the bonded bodies.

[0084] The ease of the bonding process was evaluated by evaluating the strength of each bonding sheet. A 30mm x 30mm bonding sheet was placed on a 50mm x 50mm x 1mm oxygen-free copper plate. The center of the bonding sheet's top surface was set at 0mm height, and 20mm diameter zirconia beads (Nikkato, YTZ-20) were gently dropped from a height of 30mm. This process was repeated 10 times, with one drop per sheet. The bonding sheets were then visually inspected. Seven or more sheets without cracks or chips were evaluated as passing (◯), and six or fewer sheets were evaluated as failing (×). The results are shown in Figure 5.

[0085] The shear strength of the joints was evaluated using a method conforming 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 joints were fabricated, and the shear strength of each joint was measured. The results are shown in Figure 5.

[0086] In the evaluation, a product was deemed to pass if the ease of the joining process was rated as good and the shear strength of the joined body was 30 MPa or more. On the other hand, a product was deemed to fail if at least one of the following conditions was not met: the ease of the joining process was rated as good and the shear strength of the joined body was 30 MPa or more.

[0087] As shown in Figure 5, in the example in which a solvent was added to a bonding sheet containing a copper sintered body and the heating temperature during production of the bonded body was 200°C or higher, the evaluation of ease of the bonding process passed, the bonding process could be easily performed, and the shear strength was 30 MPa or higher, indicating that proper bonding was achieved. On the other hand, in the comparative examples, the evaluation of ease of the bonding process or the shear strength failed, indicating that simplification of the bonding process and bondability could not be achieved at the same time. That is, it can be seen that Comparative Example 1, which does not use a bonding sheet containing a copper sintered body, cannot simplify the bonding process, and Comparative Example 2, which does not add a solvent, and Comparative Example 3, in which the heating temperature of the laminate is low, do not allow proper bonding.

[0088] (optional evaluation) As an optional evaluation, the void ratio of the bonded body was also evaluated.

[0089] (Void ratio of bonded body) 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

[0090] Seven bonded bodies were fabricated, and the void ratio was measured for each bonded body. The results are shown in Figure 5.

[0091] 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]

[0092] 10. Bonding sheet 12, 12A copper particles 20 Solvent

Claims

1. Placing a bonding sheet containing a copper sintered body and having a Young's modulus of 1 GPa or more on the first member; adding a solvent to the bonding sheet; A step of arranging a second member on the bonding sheet to obtain a laminate in which the bonding sheet to which the solvent has been added 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 at a heating temperature of 200° C. or more and 400° C. or less; Including, A method for manufacturing a bonded body.

2. The method for producing a bonded body according to claim 1 , wherein in the step of producing the bonded body, the laminate is heated at the heating temperature while being pressurized at a pressure of 1 MPa or more and 30 MPa or less.

3. The method for manufacturing a bonded body according to claim 1 or 2, wherein the bonding sheet has a filling rate of 50% or more.

4. The method for manufacturing a bonded body according to claim 1 , wherein the bonding sheet has a Young's modulus of 10 GPa or more.

5. The method for manufacturing a bonded body according to claim 1 , wherein the bonding sheet has a thermal conductivity of 10 W / mK or more and 60 W / mK or less.

6. 6. The method for manufacturing a bonded body according to claim 1, wherein in the step of adding a solvent, a polyhydric alcohol is used as the solvent.

7. The method for producing a bonded body according to claim 1 , further comprising the step of adding at least one of a carboxylic acid, a carboxylate, an amine, and an amine salt to the bonding sheet.

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