Joining sheet and method for manufacturing joined body

Abstract

To provide a bonding sheet that improves bonding strength between members in the assembly or implementation of electronic components, and a method for producing a bonded body.SOLUTION: A bonding sheet 10 is made of copper and has a Young's modulus of 15 GPa or less and a filling factor of 45% or more. Preferably, the Young's modulus is 1 GPa or more and 10 GPa or less and the filling factor is 45% or more and 60% or less. In other embodiments, the bonding sheet has a coefficient of thermal conductivity of 1 W / mK or more and 20 W / mK or less, includes a sintered body of copper, or includes a solvent that acts as a binder to copper particles and has a boiling point of 150°C or higher.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to 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 bonding sheet formed by mixing copper particles and a solvent with 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 a bonding sheet is required to improve the bonding strength between members.

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

[0006] In order to solve the above-mentioned problems and achieve the object, the bonding sheet according to the present disclosure is made of copper, has a Young's modulus of 15 GPa or less, and a filling rate of 45% or more.

[0007] The bonding sheet preferably has a Young's modulus of 1 GPa or more and 10 GPa or less.

[0008] The bonding sheet preferably has a filling rate of 45% or more and 60% or less.

[0009] The bonding sheet preferably has a thermal conductivity of 1 W / mK or more and 20 W / mK or less.

[0010] The bonding sheet preferably contains a copper sintered body.

[0011] The bonding sheet preferably contains copper particles and a solvent having a boiling point of 150° C. or higher.

[0012] In order to solve the above-mentioned problems and achieve the objectives, the manufacturing method of the bonded body according to the present disclosure includes the steps of placing the bonding sheet on a first member, placing a second member on the bonding sheet to obtain a laminate in which the bonding sheet is placed between the first member and the second member, and heating the laminate to manufacture a bonded body in which the first member and the second member are bonded. [Effects of the Invention]

[0013] According to the present invention, the bonding strength between members can be improved. [Brief explanation of the drawings]

[0014] [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 schematic view of the bonding sheet according to the second embodiment. [Figure 6] FIG. 6 is a flow chart illustrating a method for manufacturing the bonding sheet according to the second embodiment. [Figure 7] FIG. 7 is a schematic diagram for explaining the method for producing the bonded body. [Figure 8] FIG. 8 is a table showing the properties and evaluation results of the bonding sheets of the examples. DETAILED DESCRIPTION OF THE INVENTION

[0015] 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.

[0016] (First embodiment) (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. The bonding sheet 10 is made of copper. In this embodiment, the bonding sheet 10 is a copper sintered body, and as shown in FIG. 1, it 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 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 includes a sintered body, the components can be appropriately bonded together by advancing the sintering. Note that the bonding sheet 10 of the first embodiment may include a copper sintered body, and may also include some unsintered copper particles.

[0017] The bonding sheet 10 has a filling rate of 45% or more, preferably 45% to 60%, more preferably 45% to 55%, and even more preferably 45% to 50%. By having the filling rate within this range, the surface area can be increased and sintering can proceed appropriately, allowing members to be bonded appropriately. 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.

[0018] 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.

[0019] 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 200 nm, more preferably 120 nm to 180 nm, and even more preferably 140 nm to 160 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 the bonding sheet 10, the copper particles 12 are bonded together by sintering, so 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 that are separated by the interfaces between the bonded copper particles 12 in the bonding 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 adsorption on 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))

[0020] The Young's modulus of the joining sheet 10 is 15 GPa or less, preferably 1 GPa to 15 GPa, more preferably 1 GPa to 10 GPa, and even more preferably 1 GPa to 8 GPa. When the Young's modulus is in this range, the sheet can deform appropriately to follow the members during joining, and the members can be joined appropriately. 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.

[0021] The bonding sheet 10 preferably has a thermal conductivity of 10 W / mK to 20 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.

[0022] 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.

[0023] 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 2.0 or more and 8.3 or less, and more preferably 2.2 or more and 5.0 or less. When the large area bonding index D1 is in this range, members can be bonded appropriately to each other.

[0024] 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.

[0025] (Method of manufacturing the bonding sheet) FIG. 3 is a flow chart illustrating the method for manufacturing the bonding sheet according to this embodiment.

[0026] (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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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 covering organic protective film (i.e., the surface of the organic protective film).

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] (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.

[0043] (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 1 MPa to 30 MPa, more preferably 1 MPa to 20 MPa, and even more preferably 1 MPa to 10 MPa. The predetermined temperature here is preferably 40°C to 250°C, more preferably 40°C to 200°C, and even more preferably 40°C to 150°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 15 minutes. By pre-sintering the copper particles 12A under such conditions, it is possible to appropriately manufacture the bonding sheet 10 which is appropriately deformed during bonding and can be bonded appropriately.

[0044] 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.

[0045] (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.

[0046] 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.

[0047] Next, as shown in step S22, 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.

[0048] 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.).

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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 pressurizing the laminate in the stacking direction. Nitrogen gas or argon gas can be used as the inert gas. The pressurizing pressure of the laminate is preferably in the range of 0.5 MPa to 30 MPa.

[0054] (effect) As described above, the bonding sheet 10 according to this embodiment is made of copper, has a Young's modulus of 15 GPa or less, and a packing ratio of 45% or more. The bonding sheet 10 according to this embodiment has such a relatively small Young's modulus that it can deform appropriately to follow the members during bonding, and the packing ratio within this range increases the surface area to allow sintering to proceed appropriately, so that the members can be bonded appropriately.

[0055] The Young's modulus of the bonding sheet 10 is preferably 1 GPa or more and 10 GPa or less. When the Young's modulus is in this range, members can be bonded together more appropriately.

[0056] The bonding sheet 10 preferably has a filling rate of 45% or more and 60% or less. When the filling rate is in this range, members can be bonded together more appropriately.

[0057] The bonding sheet 10 preferably has a thermal conductivity of 10 W / mK or more and 20 W / mK or less. When the thermal conductivity is in this range, the heat transfer properties of the bonded body 100 can be appropriately ensured.

[0058] The bonding sheet 10 preferably contains a copper sintered body. By containing a copper sintered body, the bonding sheet 10 can appropriately bond members together.

[0059] 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.

[0060] (Second embodiment) Next, a second embodiment will be described. The joining sheet 10A according to the second embodiment differs from the first embodiment in that it does not contain a copper sintered body. That is, the joining sheet according to the present disclosure may be one in which the copper particles 12A are sintered or one in which the copper particles 12A are not sintered. Explanations of parts of the second embodiment that are common to the first embodiment will be omitted.

[0061] Fig. 5 is a schematic diagram of a joining sheet according to the second embodiment. The joining sheet 10A according to the second embodiment is made of copper like the first embodiment, but is not a sintered copper body. As shown in Fig. 5, the joining sheet 10A contains copper particles 12A and a solvent 20. That is, the joining sheet 10A contains copper particles 12A in an unsintered (pre-sintered) state.

[0062] The characteristics of the copper particles 12A contained in the joining sheet 10A are similar to those of the copper particles 12A that are the raw material before pre-sintering of the joining sheet 10 of the first embodiment, and therefore a description thereof will be omitted.

[0063] The properties of the solvent 20 contained in the bonding sheet 10A are similar to those of the solvent 20 used in bonding the members A and B with the bonding sheet 10 in the first embodiment, and therefore a description thereof will be omitted.

[0064] The content ratio of the copper particles 12A to the solvent 20 in the bonding sheet 10A is preferably 99:1 to 90:10 (=copper particles:solvent) by mass. That is, the bonding sheet 10A preferably has a copper particle 12A content in the range of 90% by mass to 99% by mass and a solvent 20 content in the range of 1% by mass to 10% by mass. The content ratio of the copper particles 12A to the solvent 20 is more preferably 99:1 to 92:8 by mass, and even more preferably 98:2 to 95:5 by mass.

[0065] The bonding sheet 10A may have the same properties as the bonding sheet 10 of the first embodiment except that it does not contain a sintered body. That is, for example, the filling rate, Young's modulus, thermal conductivity, thickness W, projected area, and large area bonding index D1 of the bonding sheet 10A may be in the same range as those of the bonding sheet 10 of the first embodiment. Furthermore, the measuring methods for these properties may also be the same as those of the first embodiment.

[0066] (Method of manufacturing the bonding sheet) Fig. 6 is a flowchart illustrating a method for producing a bonding sheet according to a second embodiment. As shown in Fig. 6, in this production method, copper particles 12A and a solvent 20 are prepared (step S30), and the prepared copper particles 12A and solvent 20 are mixed (step S32). In the step of mixing copper particles 12A and solvent 20, copper particles 12A and solvent 20 may be mixed so that the content ratio of copper particles 12A to solvent 20 is preferably 99:1 to 90:10 (=copper particles:solvent), more preferably 99:1 to 92:8, and even more preferably 98:2 to 95:5 by mass. Copper particles 12A and solvent 20 may be mixed by any method, and for example, a rotation-revolution mixer or a planetary mixer may be used.

[0067] Next, the bonding sheet 10A is formed using the mixture of copper particles 12A and solvent 20 (step S34). In this step, the mixture of copper particles 12A and solvent 20 is pressed at a predetermined pressure for a predetermined time at room temperature to form a sheet, thereby producing the bonding sheet 10A. The room temperature may refer to room temperature, but is not limited thereto, and may be a temperature at which sintering of the copper particles 12A does not proceed (for example, 100°C or less). The predetermined pressure here is preferably 1 MPa to 30 MPa, more preferably 5 MPa to 25 MPa, and even more preferably 10 MPa to 20 MPa. The predetermined time (the time held at the predetermined pressure) here is preferably 1 minute to 30 minutes, more preferably 2 minutes to 25 minutes, and even more preferably 3 minutes to 20 minutes. By molding the bonding sheet 10A under these conditions, a bonding sheet 10 that can be properly deformed during bonding can be manufactured. The mixture can be molded into a sheet by a rolling method using a pressure roller or a pressing method using a mold. For example, the mixture can be molded into a sheet and then cut into a predetermined shape to produce the bonding sheet 10A.

[0068] The bonding sheet 10A is not limited to be manufactured by the above method, and any method for manufacturing the bonding sheet 10A may be used.

[0069] (Method of manufacturing a bonded body) Next, a method for manufacturing a bonded body 100A by bonding members together using the bonding sheet 10A will be described. Fig. 7 is a schematic diagram for explaining the method for manufacturing a bonded body. In this embodiment, the bonded body 100A is manufactured by bonding a first member A and a second member B using the bonding sheet 10A as a bonding layer.

[0070] The bonded body 100A can be produced by placing a bonding sheet 10A between a first member A and a second member B to obtain a laminate, and then heating the obtained laminate to sinter the copper particles 12A of the bonding sheet 10A to form a bonding layer. The heating temperature of the laminate is, for example, in the range of 150°C to 300°C. The heating time of the laminate is, for example, in the range of 10 minutes to 1 hour. The laminate is preferably heated in an inert gas atmosphere while being pressurized in the stacking direction of the laminate. Nitrogen gas or argon gas can be used as the inert gas. The pressurizing pressure of the laminate is preferably in the range of 0.5 MPa to 30 MPa.

[0071] As described above, the bonding sheet 10A according to the second embodiment contains copper particles 12A and a solvent 20 having a boiling point of 150° C. The bonding sheet 10A according to the second embodiment is a molded body of copper particles 12A and a solvent 20 that have not been pre-sintered, and has a Young's modulus of 15 GPa or less and a filling rate of 45% or more, so that it can deform appropriately to follow the members during bonding, and the surface area can be increased to allow sintering to proceed appropriately, thereby enabling the members to be bonded appropriately.

[0072] (Example) Next, examples will be described. Fig. 8 is a table showing the properties and evaluation results of the bonding sheets of the respective examples.

[0073] 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.

[0074] 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 / cm 3 ) and the BET diameter was calculated using the following formula. BET diameter (nm) = 6000 / (ρ(g / cm 3 )×S(m 2 / g))

[0075] (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 was prepared as a mold for filling the prepared copper particles. 1.5 g of copper particles was filled into this aluminum frame and evenly distributed using a 30 mm square x 20 mm aluminum block. PEG (polyethylene glycol) was added as a solvent, and the mixture was hot-pressed in air at 20 MPa and 40°C for 15 minutes to produce a bonding sheet. 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 30 mm square x 0.4 mm bonding sheet sandwiched between the aluminum blocks was peeled off from the aluminum block to obtain the desired bonding sheet.

[0076] (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 8. In Fig. 8, 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". In addition, Fig. 8 shows the type of solvent added to the bonding sheet. As shown in Fig. 8, the bonding sheet of Example 1 does not contain a sintered body, but contains copper particles and PEG as a solvent with a boiling point of 150°C or higher.

[0077] (Examples 2-8) In Examples 2-8, bonding sheets were produced in the same manner as in Example 1, except that at least one of the heating temperature, applied pressure, and pressure time was changed as shown in FIG. 8. Measured values ​​of Young's modulus, filling rate, and thermal conductivity, whether or not the bonding sheet contains a sintered body, and the solvent added to the bonding sheet are shown in FIG. 8. Note that Examples 1 and 2 are bonding sheets that do not contain a sintered body but contain copper particles and a solvent with a boiling point of 150°C or higher, as in the second embodiment, and Examples 3-8 are bonding sheets that contain a sintered body as in the first embodiment, and the bonding sheets of Examples 3-8 do not contain a solvent with a boiling point of 150°C or higher.

[0078] (Comparative Example 1-2) In Comparative Example 1-2, a bonding sheet was produced in the same manner as in Example 1, except that at least one of the heating temperature, applied pressure, and pressure time was changed as shown in Figure 8. The measured values ​​of Young's modulus, filling rate, and thermal conductivity, whether or not the sheet contains a sintered body, and the solvent added to the bonding sheet are shown in Figure 8.

[0079] (evaluation) A bonded structure was produced by bonding members together using the bonding sheet of each example, and the shear strength of the bonded structure was evaluated. Each 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 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 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, to produce 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.

[0080] 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 8.

[0081] In this evaluation, a shear strength of 40 MPa or more was rated as ◯ (pass), and a shear strength of less than 40 MPa was rated as × (fail). As shown in Figure 8, when the bonding sheets of the examples, which have a Young's modulus of 15 GPa or less and a filling rate of 45% or more, were used, the shear strength of the bonded body was high, and it was found that the bonding strength could be improved. On the other hand, when the bonding sheets of the comparative examples, which do not satisfy at least one of the Young's modulus of 15 GPa or less and the filling rate of 45% or more, were used, the shear strength of the bonded body was low, and it was found that the bonding strength could not be improved.

[0082] (optional evaluation) As an optional evaluation, the density of the bonding layer in a bonded structure produced using a bonding sheet was measured. 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 a 10 mm square x 1 mm thick oxygen-free copper dummy element was placed on it. 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.

[0083] 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

[0084] Seven bonded bodies were fabricated, and the void ratio was measured for each bonded body. The results are shown in Figure 8.

[0085] 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]

[0086] 10, 10A Bonding Sheet 12, 12A copper particles 20 Solvent

Claims

1. A copper pre-sintered body, wherein the average particle size of copper particles is 100 nm or more and 200 nm or less, the Young's modulus is 15 GPa or less, and the filling rate is 45% or more. Joining sheet.

2. The joining sheet according to claim 1, wherein the Young's modulus is 1 GPa or more and 10 GPa or less.

3. The bonding sheet according to claim 1 or 2, wherein the filling rate is 45% or more and 60% or less.

4. The bonding sheet according to any one of claims 1 to 3, wherein the thermal conductivity is 1 W / mK or more and 20 W / mK or less.

5. The bonding sheet according to any one of claims 1 to 4, comprising a copper sintered body.

6. The bonding sheet according to claim 1 , comprising copper particles and a solvent having a boiling point of 150° C. or higher.

7. A step of placing the bonding sheet according to any one of claims 1 to 6 on a first member; applying an organic solvent to a surface of the bonding sheet; 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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