Manufacturing method for a joined body and method for joining bodies to be joined.

Abstract

To provide a method for manufacturing a joint that can suppress the occurrence of cracks in the fillet portion. [Solution] A bonded body is manufactured by joining a first body to be joined 11 and a second body to be joined 13 via a bonding layer. A paste containing copper particles and an organic solvent is applied to the first body to be joined 11 to form a coating film 12X. The second body to be joined 13 is placed on the coating film 12X to form a laminate 15. The laminate 15 is heated and pressurized to sinter the copper particles in the coating film 12X and form a bonding layer. Heating is gradually increased from the heating start temperature to the maximum temperature Tm, and pressurization is gradually increased from the pressurization start pressure to the maximum pressure Pm, and the pressure when the heating temperature reaches 200°C is kept at 15 MPa or less.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a joined body and a method for joining two bodies. [Background technology]

[0002] In recent years, semiconductor devices known as power devices, such as IGBTs, have been widely used as power conversion and control devices, including inverters. Various methods have been proposed for using metal paste to bond semiconductor elements to circuit boards and other components during the manufacturing of such semiconductor devices.

[0003] For example, Patent Document 1 discloses a method for manufacturing a semiconductor device that offers high reliability of the sintered joint and suppresses damage to the semiconductor element due to pressurization. The same document discloses heating and pressurizing the sinterable metal particles that will form the sintered joint at predetermined timings. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2018-110149 [Overview of the Initiative]

[0005] According to the technology described above, a high pressure is applied to the semiconductor element when the sintering start temperature is reached, which presents a problem in that cracks occur at the corners and other parts of the sintered joint where the semiconductor element is not placed (hereinafter also referred to as the "fillet portion") when the sintered joint is viewed in plan. Therefore, the object of the present invention is to provide a method for manufacturing a joint that can suppress the occurrence of cracks in the fillet portion.

[0006] The present invention relates to a method for manufacturing a bonded body in which a first bonded body and a second bonded body are joined via a bonding layer, A step of applying a paste containing copper particles and an organic solvent to the first object to be bonded to form a coating film, A step of placing the second object to be bonded on the coating film to form a laminate, The process includes a firing step of heating and pressurizing the laminate to sinter the copper particles in the coating film and form the bonding layer, The present invention provides a method for manufacturing a bonded body, wherein the firing process involves gradually increasing the heating from the heating start temperature to the maximum temperature Tm, gradually increasing the pressurization from the pressurization start pressure to the maximum pressure Pm, and maintaining a pressure of 15 MPa or less when the heating temperature reaches 200°C.

[0007] Furthermore, the present invention relates to a method for joining two objects to be joined, wherein a first object to be joined and a second object to be joined are joined via a bonding layer. A step of applying a paste containing copper particles and an organic solvent to the first object to be bonded to form a coating film, A step of placing the second object to be bonded on the coating film to form a laminate, The process includes a firing step of heating and pressurizing the laminate to sinter the copper particles in the coating film and form the bonding layer, The present invention provides a method for joining objects to be joined, wherein the firing process involves gradually increasing the heating from the heating start temperature to the maximum temperature Tm, gradually increasing the pressurization from the pressurization start pressure to the maximum pressure Pm, and keeping the pressure at which the heating temperature reaches 200°C 15 MPa or less. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic diagram showing the first step in the manufacturing method of the joint according to the present invention. [Figure 2] Figure 2 is a schematic diagram showing the next step in the process shown in Figure 1. [Figure 3] Figure 3 is a schematic diagram showing a crack that occurred in the fillet portion of the joint. [Modes for carrying out the invention]

[0009] The method for manufacturing a joined body and a method for joining bodies of the present invention will be described below based on preferred embodiments. The joined body manufactured by the method of the present invention has a structure in which a first body to be joined and a second body to be joined are joined via a joining layer. As will be described later, the joining layer is composed of a sintered body obtained by firing a paste containing copper particles and an organic solvent.

[0010] There are no particular restrictions on the type of the first object to be joined. Generally, it is preferable that the first object to be joined contains metal on its joining surface. For example, a member having a metal surface can be used as the first object to be joined. In this specification, "metal" refers to metal itself that does not form compounds with other elements, or an alloy of two or more metals. Examples of such metals include copper, silver, gold, aluminum, palladium, nickel, or alloys consisting of two or more of these.

[0011] If the first object to be joined is a member having a surface made of metal, the metal surface may be made of one type of metal or two or more types of metal. If it is made of two or more types of metal, the surface may be an alloy. Generally, the metal surface is preferably flat, but it may be curved in some cases.

[0012] Specific examples of the first object to be joined include, for example, spacers, heat sinks, semiconductor elements made of the above-mentioned metals, and substrates having at least one of the above-mentioned metals on their surface. Examples of substrates include insulating substrates having a metal layer such as copper on the surface of a ceramic or aluminum nitride plate. When a semiconductor element is used as the bonded material, the semiconductor element may contain one or more elements such as Si, Ga, Ge, C, N, and As.

[0013] Figures 1 and 2 are process diagrams for explaining the method for manufacturing the bonded body of the present invention. In this manufacturing method, first, as shown in Figure 1, a paste containing copper particles is applied onto the first adherend 11 to form a coating film 12X. The method for applying the paste is not particularly limited, and examples thereof include a screen printing method, a gravure printing method, a dispensing printing method, a reverse coating method, and a doctor blade method.

[0014] The paste used in the present invention contains copper particles and an organic solvent described later, and further appropriately contains an adjuster described later as needed.

[0015] The copper particles contained in the paste include both pure copper particles and copper-based alloy particles. The copper particles contained in the paste may be only pure copper particles, only copper-based alloy particles, or a mixture of pure copper particles and copper-based alloy particles. As long as the effects of the present invention are not impaired, it is allowed that the paste contains a small amount of metal particles other than copper particles.

[0016] The shape of the copper particles contained in the paste is not particularly limited, and either spherical or non-spherical particles can be used. Here, when the copper particles are spherical, it means that the circularity coefficient measured by the following method is 0.85 or more. The circularity coefficient is calculated by the following method. That is, a scanning electron microscope image of the primary particle copper particles is taken, and when the area of the two-dimensional projection image of the copper particles is S and the perimeter is L, the circularity coefficient of the copper particles is 4πS / L , is calculated from the formula of.

[0017] On the other hand, when the copper particles are non-spherical, it means that the above-mentioned circularity coefficient is less than 0.85. Specific examples of non-spherical shapes include flat shapes, polyhedral shapes such as hexahedrons and octahedrons, spindle shapes, irregular shapes, etc. In the present invention, it is preferable that any of two or more types of copper particles is flat copper particles, and it is more preferable to contain flat copper particles and spherical copper particles as described later. In this invention, "flattened" refers to a shape having a pair of plate-like surfaces that form the main surface of the particle, and sides perpendicular to these plate-like surfaces, and the plate-like surfaces and sides can each be independently flat, curved, or uneven.

[0018] The particle size of copper particles when they are spherical shall be determined by the following method. Specifically, the Heywood diameter of each of the 50 or more primary copper particles with clear outlines selected from scanning electron microscope images of copper particles taken at a magnification range of 10,000x to 150,000x shall be measured. Next, the volume assuming that the particles are perfectly spherical shall be calculated from the obtained Heywood diameters, and the cumulative particle size at 50% of the cumulative volume shall be D SEM50 It shall be determined by [the relevant law].

[0019] D of copper particles SEM50 It is preferable that it is greater than 0.1 μm, more preferably 0.11 μm or more, and even more preferably 0.12 μm or more. On the other hand, D SEM50 It is preferable that the particle size is 0.55 μm or less, and more preferably 0.5 μm or less. SEM50 By setting the thickness to more than 0.1 μm, shrinkage cracks are less likely to occur when the coating film 12X formed by applying the paste is fired to form a bonding layer, and sufficient bonding strength can be achieved between the fillet portion of the bonding layer and the first object to be bonded 11. On the other hand, D SEM50 By setting the thickness to 0.55 μm or less, sufficient sintering of copper particles present in the coating film 12X can be achieved.

[0020] When copper particles are non-spherical, their particle size is determined by the volume cumulative particle size D at 50% cumulative volume, as measured by laser diffraction scattering particle size distribution analysis. 50 The determination shall be made by the following method. For example, it can be done by the following method: Mix 0.1 g of the sample to be measured with an aqueous solution of dispersant and disperse it for 1 minute using an ultrasonic homogenizer (US-300T, manufactured by Nippon Seiki Seisakusho). Then, measure the particle size distribution using a laser diffraction scattering particle size distribution analyzer, for example, the MT3300 EXII manufactured by Microtrac Bell, and D 50is calculated.

[0021] The D of the copper particles 50 is preferably 0.3 μm or more and 50 μm or less, more preferably 0.5 μm or more and 40 μm or less, and still more preferably 1 μm or more and 20 μm or less. When the D 50 is within such a range, when the copper paste is formed into a coating film and fired, it becomes easy to obtain a densely sintered joint layer, and high joint strength between the joined bodies and improvement in electrical conductivity reliability can be realized.

[0022] The copper particles can be produced by various methods known in the art. For example, copper powder can be produced by a wet reduction method, an atomization method, an electrolysis method, etc. Which method to adopt can be appropriately selected according to the particle size, shape, etc. of the copper particles. The paste may be composed of only copper particles of one of these shapes, or may be composed of a combination of two or more shapes of copper particles. Further, a mixture of copper particles having a predetermined average particle size and copper particles having a different average particle size from this may be used.

[0023] Particularly, when the paste SEM50 contains spherical copper particles (first copper particles) with D 50 exceeding 0.1 μm and 0.55 μm or less and non-spherical copper particles (second copper particles) with D

[0024] Copper particles may have an organic surface treatment agent applied to their surface. The organic surface treatment agent is an agent for suppressing aggregation between copper particles. Suitable agents for suppressing aggregation between copper particles in the present invention include, for example, various fatty acids, aliphatic amines, and complexing agents having an affinity for copper. In particular, it is preferable to use saturated or unsaturated fatty acids or aliphatic amines having 6 to 18 carbon atoms, especially 10 to 18 carbon atoms, from the viewpoint of improving oxidation resistance. Specific examples of such fatty acids or aliphatic amines include benzoic acid, pentanoic acid, hexanoic acid, octanoic acid, nonanoic acid, decanoic acid, lauric acid, palmitic acid, oleic acid, stearic acid, pentylamine, hexylamine, octylamine, decylamine, laurylamine, oleylamine, and stearylamine. Examples of complexing agents having an affinity for copper include amino acids such as glycine, and dimethylglyoxime. These fatty acids, aliphatic amines, and complexing agents can each be used individually or in combination of two or more.

[0025] The copper particle content in the paste is preferably 50% by mass or more, and more preferably 60% by mass or more and 95% by mass or less, from the viewpoint of improving the packing of copper particles and maintaining sufficient bonding strength as a bonding layer.

[0026] The thickness of the coating film 12X is preferably 1 μm to 300 μm, and more preferably 5 μm to 250 μm, in order to ensure that the bonding layer formed from the coating film has sufficient bonding strength.

[0027] The organic solvents used in the paste can be conventionally known ones without any particular limitations. Examples include monoalcohols, polyhydric alcohols, polyhydric alcohol alkyl ethers, polyhydric alcohol aryl ethers, aliphatic organic acids, esters, nitrogen-containing heterocyclic compounds, amides, amines, and saturated hydrocarbons. These organic solvents can be used individually or in combination of two or more.

[0028] The amount of organic solvent in the paste is not particularly limited as long as the paste has sufficient viscosity to form a coating film, but generally it is preferable that it is between 5% by mass and 50% by mass relative to the paste.

[0029] The paste may contain modifiers as appropriate to adjust various properties. Examples of modifiers include reducing agents, viscosity modifiers, and surface tension modifiers.

[0030] Suitable reducing agents include those that promote the sintering of copper particles, such as monoalcohols, polyhydric alcohols, aminoalcohols, citric acid, oxalic acid, formic acid, ascorbic acid, aldehydes, hydrazines and their derivatives, hydroxylamines and their derivatives, dithiothreitol, phosphites, hydrophosphites, phosphorous acid and its derivatives, and the like.

[0031] Viscosity modifiers are preferably those that can adjust the viscosity of the paste to be within the above viscosity range, and examples include ketones, esters, alcohols, glycols, hydrocarbons, and polymers.

[0032] Any surface tension modifier that can adjust the surface tension of the coating film 12X is acceptable, and examples include polymers such as acrylic surfactants, silicone surfactants, alkyl polyoxyethylene ethers, and fatty acid glycerol esters, as well as monomers such as alcohols, hydrocarbons, esters, and glycols.

[0033] The viscosity of the paste can be measured using a Thermo Scientific MARS III rheometer. From the viewpoint of improving the applicability or printability of the copper paste, a shear rate of 10s is used. -1 The viscosity value at this time is preferably 10 Pa·s or more and 200 Pa·s or less, and more preferably 15 Pa·s or more and 200 Pa·s or less. The conditions for measuring the viscosity of the copper paste are as follows. Measurement mode: Shear rate dependence measurement Sensor: Parallel type (Φ20mm) Measurement temperature: 25℃ Gap: 0.300mm Shear rate: 0.05~120.01s -1 Measurement time: 2 minutes

[0034] The dimensions and shape of the coating film 12X formed on the first object to be joined 11 can be the same as the dimensions and shape of the second object to be joined 13, which will be described later. Alternatively, the dimensions may be such that when the second object to be joined 13 is placed on the coating film 12X, the coating film 12X extends from the periphery of the second object to be joined 13. In the latter case, the first object to be joined 11 and the second object to be joined 13 are reliably joined by the bonding layer, which is preferable. In this case, a portion of the coating film 12X that extends from the periphery of the second object to be joined 13, i.e., a fillet portion, is formed.

[0035] Once the coating film 12X is formed on the surface of the first object to be bonded 11, the second object to be bonded 13 is placed on the coating film 12X, as shown in Figure 2, to form a laminate 15 in which the first object to be bonded 11, the coating film 12X, and the second object to be bonded 13 are stacked in this order. The second object to be bonded 13 can be the same as the first object to be bonded 11 described above, without any particular limitations. If the first object to be bonded 11 is, for example, a substrate, then the second object to be bonded 13 is preferably, for example, a spacer, a heat sink, or a semiconductor element.

[0036] When the second workpiece 13 is placed on the coating film 12X, the concentration of the organic solvent contained in the coating film 12X may be substantially the same as, or lower than, the concentration of the organic solvent contained in the paste. In the latter case, after forming the coating film 12X on the first workpiece 11, the coating film 12X can be dried and the organic solvent removed by natural drying by leaving it for a predetermined time or by heat drying.

[0037] Next, as shown in Figure 2, the laminate 15 is clamped between predetermined plate-shaped jigs 16, 16, and a firing process is performed in which the laminate 15 is heated and pressurized by the jigs 16, 16. As heating progresses, the organic solvent is removed from the coating film 12X, and the sintering of copper particles in the coating film 12X begins. Conventional pressurizing devices using the plate-shaped jigs 16, 16 can be used without any particular limitations.

[0038] Heating and pressurizing may be started simultaneously, or pressurizing may be started after a predetermined time has elapsed since the start of heating, or conversely, heating may be started after a predetermined time has elapsed since the start of pressurizing.

[0039] In the firing process, a bonding layer consisting of a sintered body of copper particles can be successfully formed by controlling the heating and pressurizing profiles. In particular, when the bonding layer has a fillet, the occurrence of cracks in the fillet can be effectively suppressed. Specifically, in the firing process, heating is gradually increased from the heating start temperature to the maximum temperature Tm. In addition, pressurizing is gradually increased from the pressurizing start pressure to the maximum pressure Pm. In this invention, the term "crack" occurring in the fillet portion refers not only to cracks 17 that occur only at the corners of the fillet portion 14, as shown in Figure 3, but also to cracks 17 that occur near the center of the fillet portion 14, and, although not shown, cracks that are not continuous from the end of the second joined body 13 to the outer circumference of the fillet portion 14, but are inherent in the fillet portion. Furthermore, in this specification, "gradually increasing heating" means that heating is carried out in such a way that there is no period of cooling over time from the start of heating in the firing process until the maximum temperature Tm is reached. Therefore, it is permissible for the heating temperature to remain constant for a period of time in the firing process. For example, heating in the firing process may be carried out so that the temperature rises linearly over time, exponentially, logarithmically, in steps, or in a combination of these to create a temperature rise curve. Furthermore, in this specification, "gradually increasing pressure" means that the pressure is increased in such a way that there is no period of decreasing pressure over time from the start of pressurization in the firing process until the maximum pressure Pm is reached. Therefore, it is permissible for the pressure to remain constant for a period of time during the firing process. For example, the pressurization in the firing process may be carried out so that the pressure increases linearly over time, exponentially, logarithmically, in steps, or in a combination of these to create a pressure rise curve.

[0040] In the firing process, heating and pressurizing are gradually increased, and the heating and pressurizing conditions are controlled so that the pressure is 15 MPa or less when the heating temperature reaches 200°C. By controlling the heating and pressurizing profile in this way, the occurrence of cracks in the fillet can be effectively suppressed. The reason for this is as follows.

[0041] Gradually increasing the heating and pressurizing of the laminate 15 is advantageous in terms of improving the manufacturing efficiency of the target bond. Under this condition, by controlling the heating and pressurizing conditions so that the pressure is 15 MPa or less when the heating temperature reaches 200°C, the portion of the coating film 12X located directly beneath the second body to be bonded 13 (hereinafter also referred to as the "die-sub-dead portion") and the portion extending from the periphery of the second body to be bonded 13, i.e., the fillet portion, shrink to roughly the same extent. This suppresses the occurrence of cracks in the fillet portion 14. In contrast, when sintering of copper particles begins under increasing pressure, a difference in shrinkage occurs between the area directly below the die and the portion extending from the periphery of the second body to be joined 13, i.e., the fillet portion 14. This makes the fillet portion 14, especially the corners of the fillet portion 14, more prone to crack formation.

[0042] From the viewpoint of making the above advantages even more pronounced, it is preferable to set the pressure when the heating temperature reaches 200°C to 15 MPa or less, more preferably 13 MPa or less, and the lower the pressure, the better from the viewpoint of suppressing crack formation. Note that pressurization may be started after the heating temperature reaches 200°C.

[0043] The reason for controlling the pressure based on a temperature of 200°C is that copper particles are generally estimated to sinter at around 250°C. At 200°C, the sintering of copper particles has not yet begun, and therefore the shrinkage of the coating 12X can be controlled.

[0044] In the firing process, if the pressure is 15 MPa or less when the heating temperature reaches 200°C, the heating may be set to reach the maximum pressure Pm after the heating reaches the maximum temperature Tm, or conversely, the heating may be set to reach the maximum temperature Tm after the pressurization reaches the maximum pressure Pm. Alternatively, heating and pressurization may be controlled to reach the maximum temperature Tm and maximum pressure Pm simultaneously. Preferably, from the viewpoint of more effectively suppressing the occurrence of cracks in the fillet, the heating is set to reach the maximum temperature Tm before the pressurization reaches the maximum pressure Pm.

[0045] As long as the heating in the firing process is gradually increasing, the temperature may rise linearly over time, exponentially, logarithmically, in steps, or in a combination of these to create a temperature rise curve. The same applies to the pressurization in the firing process.

[0046] In any of the heating methods described above, it is preferable from the viewpoint of efficient joint production that there is no constant temperature process of 10 seconds or more, particularly 5 seconds or more, from the heating start temperature to the maximum temperature Tm. For the same reason, it is preferable that there is no constant pressure process of 10 seconds or more, particularly 5 seconds or more, from the pressurization start pressure to the maximum pressure Pm. If the firing process includes both a constant temperature process and a constant pressure process, the duration of the constant temperature process and the duration of the constant pressure process can be set independently, and it is not necessary to synchronize them.

[0047] In the firing process, from the viewpoint of efficiently manufacturing the bonded body, it is preferable that the time required from the start of heating until the temperature reaches the maximum temperature Tm is between 1 second and 30 minutes, preferably between 1 second and 10 minutes, and more preferably between 1 second and 1 minute.

[0048] In the pressurization of the laminate during the firing process, from the viewpoint of making the shrinkage of the coating film 12X approximately the same in the area directly below the die and in the fillet area, it is preferable that the pressurization rate be 0.2 MPa / s or higher, and may be 1 MPa / s or higher. Furthermore, the pressure boosting speed is preferably 20 MPa / s or less, more preferably 10 MPa / s or less, and even more preferably 5 MPa / s or less. From the viewpoint of preventing floating in the fillet portion, the pressurization rate is preferably 0.2 MPa / s or more and 10 MPa / s or less, and more preferably 0.2 MPa / s or more and 5 MPa / s or less. The constant-pressure process is not included in the calculation of the boosting rate. If the rate of pressure increase until the maximum pressure Pm is reached is not constant, it is sufficient that the rate of pressure increase falls within the aforementioned range.

[0049] Setting the maximum heating temperature Tm in the firing process to 200°C to 350°C is preferable not only for sufficiently sintering the copper particles but also for preventing the joined material from being damaged by heat. From this viewpoint, the maximum temperature Tm is preferably 210°C to 330°C, and more preferably 220°C to 310°C. From the same viewpoint as described above, it is preferable to set the maximum pressurization pressure Pm in the firing process to 1 MPa or more and 40 MPa or less, and in particular to set it to 5 MPa or more and 40 MPa or less, and especially to set it to 5 MPa or more and 30 MPa or less.

[0050] Once the heating reaches the maximum temperature Tm, the temperature Tm may be maintained thereafter, or it may be lowered below Tm. In either case, once the maximum temperature Tm is reached, it is preferable to keep the heating temperature constant within the temperature range of (Tm-30)°C to Tm°C from the viewpoint of sufficiently sintering the copper particles. Regarding pressurization, once the pressurization reaches the maximum pressure Pm, it may be maintained at that pressure Pm or reduced below Pm. In either case, once the maximum pressure Pm is reached, it is preferable to maintain a constant heating temperature within the temperature range of (Pm-5)MPa to PmMPa from the viewpoint of sufficiently sintering the copper particles.

[0051] The firing process can utilize, for example, an inert atmosphere or an oxygen-containing atmosphere. Examples of inert atmospheres include a nitrogen gas atmosphere and a noble gas atmosphere such as argon or neon. From an economic standpoint, it is preferable to use a nitrogen gas atmosphere. An example of an oxygen-containing atmosphere can be used, such as an atmospheric atmosphere.

[0052] By subjecting the laminate 15 to a firing process, a sintered body, which is a bonding layer, is formed from the coating film 12X in the laminate 15, and the first to be bonded 11 and the second to be bonded 13 are bonded with high bonding strength. Furthermore, even if a fillet portion exists in the bonding layer, the occurrence of cracks in the fillet portion is effectively suppressed, so the bonded body is highly reliable. Therefore, the bonded body obtained by this manufacturing method is suitable for use in devices that handle high currents, such as automotive electronic circuits and electronic circuits on which power devices are mounted.

[0053] Although the present invention has been described above based on its preferred embodiments, the present invention is not limited to the above embodiments.

[0054] With respect to the embodiments described above, the present invention further discloses the following methods for manufacturing a joined body and joining bodies to be joined. [1] A method for manufacturing a bonded body in which a first body to be bonded and a second body to be bonded are bonded via a bonding layer, A step of applying a paste containing copper particles and an organic solvent to the first object to be bonded to form a coating film, A step of placing the second object to be bonded on the coating film to form a laminate, The process includes a firing step of heating and pressurizing the laminate to sinter the copper particles in the coating film and form the bonding layer, A method for manufacturing a bonded body, wherein in the firing process, heating is gradually increased from the heating start temperature to the maximum temperature Tm, pressurization is gradually increased from the pressurization start pressure to the maximum pressure Pm, and the pressure when the heating temperature reaches 200°C is 15 MPa or less. [2] The manufacturing method according to [1], wherein when the second object to be joined is placed on the coating film, the paste is applied such that the coating film extends from the periphery of the second object to be joined. [3] The manufacturing method according to [1] or [2], wherein in the firing step, the heating reaches the maximum temperature Tm, and then the pressurization reaches the maximum pressure Pm. [4] A manufacturing method according to any one of [1] to [3], wherein there is no constant temperature process of 10 seconds or more from the heating start temperature to the maximum temperature Tm. [5] A manufacturing method according to any one of [1] to [4], wherein there is no constant pressure process of 10 seconds or more from the pressurization start pressure to the maximum pressure Pm. [6] The manufacturing method according to any one of [1] to [5], wherein the maximum temperature Tm is 200°C or more and 350°C or less. [7] The manufacturing method according to [6], wherein once the maximum temperature Tm is reached, the heating temperature is kept constant in the range of (Tm-30)°C or higher and Tm°C or lower. [8] The manufacturing method according to any one of [1] to [7], wherein the maximum pressure Pm is 1 MPa or more and 40 MPa or less. [9] The manufacturing method according to [8], wherein once the maximum pressure Pm is reached, the pressure is kept constant in the range of (Pm-5)MPa or more and PmMPa.

[10] A method for joining two objects to be joined, comprising joining a first object to be joined and a second object to be joined via a bonding layer, A step of applying a paste containing copper particles and an organic solvent to the first object to be bonded to form a coating film, A step of placing the second object to be bonded on the coating film to form a laminate, The process includes a firing step of heating and pressurizing the laminate to sinter the copper particles in the coating film and form the bonding layer, A method for joining objects to be joined, wherein in the firing process, heating is gradually increased from the heating start temperature to the maximum temperature Tm, pressurization is gradually increased from the pressurization start pressure to the maximum pressure Pm, and the pressure when the heating temperature reaches 200°C is 15 MPa or less. [Examples]

[0055] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to these examples. Unless otherwise specified, "%" means "mass%".

[0056] [Example 1] (1) Preparation of paste Cuprous particles (spherical, D SEM50 =0.16μm) and second copper particles (flattened, D 50 A paste was prepared by mixing (4.2 μm) hexylene glycol (organic solvent), polyethylene glycol (molecular weight 300, organic solvent), and bis(2-hydroxyethyl)iminotris(hydroxymethyl)methane (reducing agent). The total content of primary and secondary copper particles in the paste was 82%, the content of organic solvent was 17.9%, and the content of reducing agent was 0.1%. The mass ratio of primary to secondary copper particles was primary:secondary copper = 7:3.

[0057] (2) Formation of coating film A paste was printed onto a copper substrate using a metal mask measuring 6.0 mm in length, 6.0 mm in width, and 200 μm in thickness to form a rectangular coating. The coating was dried in an air atmosphere at 110°C for 20 minutes.

[0058] (3) Formation of the laminate Assuming a model component for a semiconductor power device, an alumina chip plated with silver (Ag) was prepared (5 mm long, 5 mm wide, 0.5 mm thick). The Ag-plated surface of this alumina chip was placed on a dried coating, and a load of 0.8 MPa was applied for 2 seconds to form a laminate consisting of the first substrate, the coating, and the second substrate in that order.

[0059] (4) Heating and pressurizing of the laminate Heating and pressurization were started simultaneously from an initial temperature of 40°C and an unloaded state (excluding its own weight) of the laminate. The time required to rise from 40°C to 300°C was 15 seconds, with an average heating rate of 17.3°C / s and a pressurization rate of 1.3 MPa / s. Heating and pressurization were carried out linearly with respect to the passage of time. The atmosphere was a nitrogen gas atmosphere. The pressure was 8.7 MPa when the temperature reached 200°C. Heating was stopped when the temperature reached the maximum temperature Tm of 300°C, and the temperature was maintained at 300°C thereafter. When the temperature reached 300°C, the pressure also reached the maximum pressure Pm of 20 MPa, and the pressure was maintained at 20 MPa thereafter. Heating and pressurization were stopped 10 minutes after reaching the maximum temperature Tm and maximum pressure Pm, and the desired bonded body was obtained by natural cooling.

[0060] [Comparative Example 1] In Example 1, under "(4) Heating and Pressurizing the Laminate," the time required to raise the temperature from 40°C to 300°C was 30 seconds, the average heating rate was 8.7°C / s, and the pressurizing rate was 1.3 MPa / s. Pressurization was stopped when the pressure reached the maximum pressure Pm of 20 MPa, and the maximum pressure Pm was maintained thereafter. Heating continued at this point. The pressure when the temperature reached 200°C was 20 MPa. Heating was stopped when the temperature reached the maximum temperature Tm of 300°C, and the temperature was maintained thereafter. Heating and pressurization were stopped 10 minutes after reaching the maximum temperature Tm, and the desired bonded body was obtained by natural cooling.

[0061] [Comparative Example 2] In Example 1, under "(4) Heating and Pressurizing the Laminate," the time required to raise the temperature from 40°C to 300°C was 40 seconds, the average heating rate was 6.5°C / s, and the pressurizing rate was 1.3 MPa / s. Pressurization was stopped when the pressure reached the maximum pressure Pm of 20 MPa, and the maximum pressure Pm was maintained thereafter. Heating continued at this point. The pressure when the temperature reached 200°C was 20 MPa. Heating was stopped when the temperature reached the maximum temperature Tm of 300°C, and the temperature was maintained thereafter. Heating and pressurization were stopped 10 minutes after reaching the maximum temperature Tm, and the desired bonded body was obtained by natural cooling.

[0062] 〔evaluation〕 The appearance of the joints obtained in the examples and comparative examples was visually inspected to evaluate whether defects occurred in the fillet portions. As a result, no defects, including cracks, were observed in the fillet portions of the joint obtained in Example 1. In contrast, cracks were observed at the corners of the fillet portions of the joints obtained in Comparative Examples 1 and 2. [Industrial applicability]

[0063] The present invention provides a method for manufacturing a joint in which the occurrence of cracks in the fillet portion is suppressed.

Claims

1. A method for manufacturing a joined body in which a first joined body and a second joined body are joined via a bonding layer, A step of applying a paste containing copper particles and an organic solvent to the first object to be bonded to form a coating film, A step of placing the second object to be bonded on the coating film to form a laminate, The process includes a firing step of heating and pressurizing the laminate to sinter the copper particles in the coating film and form the bonding layer, A method for manufacturing a bonded body, wherein in the firing process, heating is gradually increased from the heating start temperature until the maximum temperature Tm is reached, and pressurization is gradually increased from the pressurization start pressure until the maximum pressure Pm is reached, and the pressure when the heating temperature reaches 200°C is 15 MPa or less.

2. The manufacturing method according to claim 1, wherein when the second object to be joined is placed on the coating film, the paste is applied such that the coating film extends from the periphery of the second object to be joined.

3. The manufacturing method according to claim 1 or 2, wherein in the firing step, the pressurization reaches the maximum pressure Pm after the heating reaches the maximum temperature Tm.

4. The manufacturing method according to claim 1 or 2, wherein there is no constant temperature process of 10 seconds or more from the heating start temperature to the maximum temperature Tm.

5. The manufacturing method according to claim 1 or 2, wherein there is no constant pressure process of 10 seconds or more from the pressurization start pressure to the maximum pressure Pm.

6. The manufacturing method according to claim 1 or 2, wherein the maximum temperature Tm is 200°C or more and 350°C or less.

7. The manufacturing method according to claim 6, wherein once the maximum temperature Tm is reached, the heating temperature is kept constant within the range of (Tm-30)°C or higher and Tm°C or lower.

8. The manufacturing method according to claim 1 or 2, wherein the maximum pressure Pm is 1 MPa or more and 40 MPa or less.

9. The manufacturing method according to claim 8, wherein once the maximum pressure Pm is reached, the pressure is kept constant within the range of (Pm-5) MPa or more and Pm MPa or less.

10. A method for joining two objects to be joined, comprising joining a first object to be joined and a second object to be joined via a joining layer, A step of applying a paste containing copper particles and an organic solvent to the first object to be bonded to form a coating film, A step of placing the second object to be bonded on the coating film to form a laminate, The process includes a firing step of heating and pressurizing the laminate to sinter the copper particles in the coating film and form the bonding layer, A method for joining objects to be joined, wherein in the firing process, heating is gradually increased from the heating start temperature to the maximum temperature Tm, pressurization is gradually increased from the pressurization start pressure to the maximum pressure Pm, and the pressure when the heating temperature reaches 200°C is 15 MPa or less.

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