Method for manufacturing joined body and method for joining bodies to be joined

Abstract

This method for manufacturing a bonded body manufactures a bonded body in which a first body (11) to be bonded and a second body (13) to be bonded are bonded with a bonding layer interposed therebetween. A paste containing copper particles and an organic solvent is applied to the first body (11) to be bonded to form a coating film (12X). The second body (13) to be bonded is placed on the coating film (12X) to form a laminate (15). The laminate (15) is heated and pressed to sinter the copper particles in the coating film (12X) and thereby form the bonding layer. The heating is gradual from the heating start temperature until the maximum temperature Tm is reached, while the pressing is gradual from the pressing start pressure until the maximum pressure Pm is reached, wherein the pressure at the time when the heating temperature reaches 200°C is 15 MPa or less.

Description

[Technical Field]

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

[0002] In recent years, semiconductor devices called power devices, such as IGBTs, have been widely used as power conversion and control devices for inverters, etc. In manufacturing such semiconductor devices, various proposals have been made to use metal paste as a means of joining semiconductor elements to circuit boards, etc.

[0003] For example, Patent Document 1 discloses a method for manufacturing a semiconductor device that has high reliability in the sintered bonded portion and can suppress damage to the semiconductor element due to pressure. This document discloses that sinterable metal particles that will become the sintered bonded portion are heated and pressurized at a predetermined timing. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-110149 Summary of the Invention

[0005] According to the above-mentioned technology, high pressure is applied to the semiconductor element when the sintering start temperature is reached, which causes a problem in that cracks occur in the corners of the end region 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 a plane. Therefore, an object of the present invention is to provide a method for manufacturing a bonded body that can suppress the occurrence of cracks in the fillet portion.

[0006] The present invention provides a method for producing a bonded body in which a first body to be bonded and a second body to be bonded are bonded via a bonding layer, the method comprising the steps of: a step of applying a paste containing copper particles and an organic solvent to the first body to be bonded to form a coating film; placing the second object to be joined on the coating film to form a laminate; a firing step of heating and pressurizing the laminate to sinter the copper particles in the coating film and form the bonding layer, In the firing step, heating is gradually increased from a heating start temperature until a maximum temperature Tm is reached, and pressurization is gradually increased from a pressurization start pressure until a maximum pressure Pm is reached, and the pressure when the heating temperature reaches 200°C is 15 MPa or less.

[0007] The present invention further provides a method for joining objects to be joined, in which a first object to be joined and a second object to be joined are joined via a joining layer, the method comprising: a step of applying a paste containing copper particles and an organic solvent to the first body to be bonded to form a coating film; placing the second object to be joined on the coating film to form a laminate; a firing step of heating and pressurizing the laminate to sinter the copper particles in the coating film and form the bonding layer, In the firing step, heating is gradually increased from a heating start temperature until a maximum temperature Tm is reached, and pressurization is gradually increased from a pressurization start pressure until a maximum pressure Pm is reached, and the pressure when the heating temperature reaches 200°C is 15 MPa or less. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram showing the first step of the method for producing a bonded body of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing the step subsequent to the step shown in FIG. [Figure 3] FIG. 3 is a schematic diagram showing a crack occurring in the fillet portion of the bonded body. DETAILED DESCRIPTION OF THE INVENTION

[0009] The method for producing the bonded body of the present invention and the method for producing the bonded body will be described below. Joining The method will be described based on its preferred embodiment. The bonded body produced by the method of the present invention has a structure in which a first bonded body and a second bonded body are bonded via a bonding layer. As will be described later, the bonding layer is composed of a sintered body obtained by firing a paste containing copper particles and an organic solvent.

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

[0011] When the first object to be joined is a member having a surface made of metal, the surface made of metal may be made of one kind of metal, or may be made of two or more kinds of metals. When made of two or more kinds of metals, the surface may be an alloy. In general, the surface made of metal is preferably flat, but in some cases it may be curved.

[0012] Specific examples of the first object to be bonded include spacers made of the above-mentioned metals, heat sinks, semiconductor elements, and substrates having at least one of the above-mentioned metals on their surfaces. The substrate may be, for example, an insulating substrate 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 object to be bonded, the semiconductor element may contain one or more elements such as Si, Ga, Ge, C, N, and As.

[0013] 1 and 2 show the bonded structure of the present invention. manufacturing1 is a process diagram illustrating a method for manufacturing a substrate 10. In this manufacturing method, first, as shown in FIG. 1, a paste containing copper particles is applied onto a first object to be bonded 11 to form a coating film 12X. The method for applying the paste is not particularly limited, and examples thereof include screen printing, gravure printing, dispense printing, reverse coating, and doctor blade printing.

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

[0015] The copper particles contained in the paste include both pure copper particles and copper-based alloy particles, and may be only pure copper particles, only copper-based alloy particles, or a mixture of pure copper particles and copper-based alloy particles. It is permissible for the paste to contain a small amount of metal particles other than copper particles, provided that the effects of the present invention are not impaired.

[0016] The shape of the copper particles contained in the paste is not particularly limited, and either spherical or non-spherical particles may be used. Here, the copper particles being spherical means that the circularity coefficient measured by the following method is 0.85 or more. The circularity coefficient is calculated as follows: A scanning electron microscope image of a primary copper particle is taken, and the circularity coefficient of the copper particle is calculated by taking the area of ​​the two-dimensional projection image of the copper particle as S and the perimeter as L, and then calculating the circularity coefficient of the copper particle as 4πS / L. 2 It is calculated using the formula:

[0017] On the other hand, the copper particles being non-spherical means that the 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. particle It is preferable that any one of the above is a flat copper particle, and more preferable that the copper particles contain a flat copper particle and a spherical copper particle as described below. In the present invention, flat refers to a shape having a pair of plate surfaces forming the main surfaces of the particle and side surfaces perpendicular to these plate surfaces, and the plate surfaces and side surfaces may each independently be flat, curved, or uneven.

[0018] When the copper particles are spherical, the particle size is determined by the following method. More than 50 clearly defined primary copper particles are selected from scanning electron microscope images of the copper particles taken at a magnification range of 10,000 to 150,000 times, and the Heywood diameter of each particle is measured. Next, the volume of the particles is calculated from the obtained Heywood diameter assuming that the particles are truly spherical, and the volume-cumulative particle size at 50% by volume of the cumulative volume is defined as D. SEM50 It shall be determined as follows.

[0019] Copper particle D SEM50 is preferably greater than 0.1 μm, more preferably 0.11 μm or more, and even more preferably 0.12 μm or more. SEM50 is preferably 0.55 μm or less, and more preferably 0.5 μm or less. SEM50 By setting the thickness to be 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 the bonding strength between the fillet portion of the bonding layer and the first bonded body 11 can be made sufficient. SEM50 By setting the particle size to 0.55 μm or less, the copper particles present in the coating film 12X can be sintered sufficiently.

[0020] When copper particles are non-spherical, the particle size is the volume cumulative particle size D at 50% cumulative volume measured by the laser diffraction / scattering particle size distribution measurement method. 50 For example, this can be done by the following method. That is, 0.1 g of a measurement sample is mixed with an aqueous dispersant solution and dispersed for 1 minute using an ultrasonic homogenizer (US-300T, manufactured by Nippon Seiki Seisakusho). Then, the particle size distribution is measured using a laser diffraction scattering particle size distribution measuring device, such as the MT3300 EXII manufactured by Microtrackbell, to determine the D. 50is calculated.

[0021] Copper particle D 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 even more preferably 1 μm or more and 20 μm or less. 50 When the copper paste is formed into a coating film and fired, a densely sintered bonding layer is easily obtained by setting the copper paste in this range, and high bonding strength between the objects to be bonded and improved electrical conductivity reliability can be achieved.

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

[0023] Especially paste, D SEM50 Spherical copper particles (cuprous particles) with a diameter of more than 0.1 μm and less than 0.55 μm, and D 50 By including non-spherical copper particles (cupric particles) having a size of 0.3 μm to 50 μm, cracking of the coating film due to excessive volume shrinkage of the coating film can be prevented, while the sinterability of the coating film is excellent. To further enhance this advantage, the proportion of the cuprous particles relative to the total mass of the cuprous particles and the cupric particles is preferably 20% by mass to 95% by mass, more preferably 25% by mass to 90% by mass, and even more preferably 30% by mass to 85% by mass. In particular, it is preferable that the cuprous particles are spherical and the cupric particles are flat, since this results in a denser sintered body.

[0024] The surfaces of the copper particles may be coated with an organic surface treatment agent. The organic surface treatment agent is an agent for inhibiting aggregation between copper particles. Agents suitable for use in the present invention for inhibiting aggregation between copper particles include, for example, various fatty acids, aliphatic amines, and complexing agents having affinity for copper. In particular, saturated or unsaturated fatty acids or aliphatic amines having 6 to 18 carbon atoms, particularly 10 to 18 carbon atoms, are preferred 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. Complexing agents having affinity for copper include, for example, amino acids such as glycine, and dimethylglyoxime. These fatty acids, aliphatic amines, and complexing agents may be used alone or in combination of two or more.

[0025] The content of copper particles 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 increasing the filling ability of the copper particles and maintaining sufficient bonding strength as a bonding layer.

[0026] The thickness of the coating film 12X is preferably 1 μm or more and 300 μm or less, and more preferably 5 μm or more and 250 μm or less, so that the bonding layer formed from the coating film can ensure sufficient bonding strength.

[0027] The organic solvent contained in the paste can be any conventionally known organic solvent without any particular limitation. Examples include monoalcohols, polyhydric alcohols, polyhydric alcohol alkyl ethers, polyhydric alcohol aryl ethers, aliphatic organic acids, esters, nitrogen-containing heterocyclic compounds, amides, amines, saturated hydrocarbons, etc. These organic solvents can be used alone 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 a viscosity that allows it to be formed into a coating film, but it is generally preferably 5% by mass or more and 50% by mass or less based on the paste.

[0029] The paste may contain an appropriate modifier for adjusting various properties, such as a reducing agent, a viscosity modifier, or a surface tension modifier.

[0030] The reducing agent is preferably one that promotes sintering of copper particles, and examples thereof include monoalcohols, polyhydric alcohols, amino alcohols, citric acid, oxalic acid, formic acid, ascorbic acid, aldehydes, hydrazine and its derivatives, hydroxylamine and its derivatives, dithiothreitol, phosphite, hydrophosphite, phosphorous acid and its derivatives, etc.

[0031] The viscosity adjuster is preferably one that can adjust the viscosity of the paste, preferably within the above-mentioned viscosity range, and examples thereof include ketones, esters, alcohols, glycols, hydrocarbons, and polymers.

[0032] The surface tension adjuster may be any agent capable of adjusting the surface tension of the coating film 12X, and examples thereof include polymers such as acrylic surfactants, silicone surfactants, alkyl polyoxyethylene ethers, and fatty acid glycerol esters, as well as alcohol-based, hydrocarbon-based, ester-based, and glycol-based monomers.

[0033] The viscosity of the paste can be measured using a rheometer MARS III manufactured by Thermo Scientific. From the viewpoint of improving the coatability or printability of the copper paste, the viscosity is measured at a shear rate of 10 s -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 dependency 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 bonded 11 can be the same as those of the second object to be bonded 13 described later. Alternatively, the dimensions of the coating film 12X may be such that the coating film 12X extends from the periphery of the second object to be bonded 13 when the second object to be bonded 13 is placed on the coating film 12X. In the latter case, the first object to be bonded 11 and the second object to be bonded 13 are reliably bonded by the bonding layer, which is preferable. In this case, a portion of the coating film 12X extending from the periphery of the second object to be bonded 13, i.e., a fillet portion, is formed.

[0035] Once the coating film 12X has been formed on the surface of the first object to be bonded 11, as shown in Fig. 2, the second object to be bonded 13 is placed on the coating film 12X 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 laminated in this order. As the second object to be bonded 13, the same material as the first object to be bonded 11 described above can be used without any particular restrictions. When the first object to be bonded 11 is, for example, a substrate, the second object to be bonded 13 is preferably, for example, any of a spacer, a heat sink, or a semiconductor element.

[0036] When the second object to be bonded 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 the coating film 12X is formed on the first object to be bonded 11, the organic solvent can be removed by drying the coating film 12X by leaving it to dry naturally or by heating for a predetermined time.

[0037] Next, as shown in Fig. 2, the laminate 15 is sandwiched between predetermined plate-like jigs 16, 16, and the laminate 15 is heated and pressed with the jigs 16, 16 to perform a firing process. As the heating progresses, the organic solvent is removed from the coating film 12X, and sintering of the copper particles in the coating film 12X begins. Note that any conventionally known pressing device using the plate-like jigs 16, 16 can be used without any particular limitation.

[0038] Heating and pressurization may be started simultaneously, or pressurization may be started after a predetermined time has elapsed since heating was started, or conversely, heating may be started after a predetermined time has elapsed since pressurization was started.

[0039] In the sintering process, by controlling the heating and pressure profile, a bonding layer made of a sintered body of copper particles can be successfully formed. In particular, when the bonding layer has a fillet portion, cracks at the fillet portion can be effectively prevented. Specifically, in the sintering process, heating is gradually increased from the heating start temperature to the maximum temperature Tm. In addition, pressure is gradually increased from the pressure start pressure to the maximum pressure Pm. In the present invention, the "cracks" occurring in the fillet portion do not refer to cracks 17 occurring only at the corners of the fillet portion 14, as shown in FIG. 3, but also include cracks 17 occurring near the center of the fillet portion 14 and cracks that are not continuous from the end of the second bonded body 13 to the outer periphery of the fillet portion 14 but are present inside the fillet portion, although not shown. In addition, as used herein, "gradually heating" means that heating is performed from the start of heating in the firing step until the maximum temperature Tm is reached without a period of temperature decrease over time. Therefore, it is acceptable for the heating temperature to remain constant during the firing step. For example, heating in the firing step may be performed so that the temperature increases linearly over time, exponentially, logarithmically, or stepwise, or may be performed to draw a temperature increase line that combines these. In this specification, "gradually increasing pressure" means that pressure is applied from the start of pressure application in the firing step until the maximum pressure Pm is reached, without a period of pressure decrease over time. Therefore, a period of constant pressure is permitted in the firing step. For example, pressure application in the firing step may be performed so that the pressure increases linearly over time, exponentially, logarithmically, or stepwise, or may be performed to draw a pressure increase line that is a combination of these.

[0040] In the firing process, the heating and pressure are gradually increased, and the heating and pressure conditions are controlled so that the pressure is 15 MPa or less when the heating temperature reaches 200°C. By controlling the heating and pressure profile in this way, it is possible to effectively prevent cracks from occurring in the fillet portion. The reason for this is as follows.

[0041] Gradually increasing the heating and pressure of the laminate 15 is advantageous in terms of improving the manufacturing efficiency of the target bonded body. With this condition, by controlling the heating and pressure 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 below the second bonded body 13 (hereinafter also referred to as "directly below the die") and the portion extending from the periphery of the second bonded body 13, i.e., the fillet portion, shrink to approximately the same extent. This suppresses the occurrence of cracks in the fillet portion 14. On the other hand, when sintering of the copper particles begins as the pressure increases, a difference in shrinkage occurs between the area directly below the die and the portion extending from the periphery of the second bonded body 13, i.e., the fillet portion 14, making it more likely for cracks to occur in the fillet portion 14, especially in the corners of the fillet portion 14.

[0042] To make the above advantages more pronounced, the pressure when the heating temperature reaches 200°C is preferably 15 MPa or less, more preferably 13 MPa or less, and the lower the pressure, the better from the viewpoint of suppressing cracking. Note that pressure application may also 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 sintering of copper particles is generally estimated to occur at around 250°C, and therefore, at 200°C, sintering of the copper particles has not yet begun, making it possible to control the shrinkage of the coating film 12X.

[0044] In the firing step, as long as the pressure is 15 MPa or less when the heating temperature reaches 200°C, the heating may be performed so that the pressure reaches the maximum pressure Pm after the heating reaches the maximum temperature Tm, or conversely, the heating may be performed so that the pressure reaches the maximum pressure Pm after the heating reaches the maximum temperature Tm. Alternatively, the heating and the pressure may be controlled so that the maximum temperature Tm and the maximum pressure Pm are reached simultaneously. Preferably, from the viewpoint of more effectively suppressing cracks in the fillet, the pressure reaches the maximum pressure Pm after the heating reaches the maximum temperature Tm.

[0045] As long as the heating in the firing step is gradual, the temperature may be increased linearly, exponentially, logarithmically, or stepwise over time, or may be increased in a temperature rise line that is a combination of these. The same applies to the application of pressure in the firing step.

[0046] In any of the above-mentioned heating modes, it is preferable from the viewpoint of efficient production of a bonded body that there is no constant temperature step 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 step of 10 seconds or more, particularly 5 seconds or more, from the pressurization start pressure to the maximum pressure Pm. Note that when the firing process has both a constant temperature step and a constant pressure step, the duration of the constant temperature step and the constant pressure step can be set independently, and there is no need to synchronize the two.

[0047] In terms of efficiently producing a bonded body, the time required for heating the laminate in the firing step to reach the maximum temperature Tm from the start of heating is preferably 1 second to 30 minutes, more preferably 1 second to 10 minutes, and even more preferably 1 second to 1 minute.

[0048] When pressing the laminate in the firing step, the pressure increase rate is preferably 0.2 MPa / s or more, and may be 1 MPa / s or more, from the viewpoint of making the shrinkage of the coating film 12X approximately the same immediately below the die and in the fillet portion. The pressure increase rate is preferably 20 MPa / s or less, more preferably 10 MPa / s or less, and even more preferably 5 MPa / s or less. To prevent the fillet from floating, the pressure increase 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 pressure rise rate calculation does not include the constant pressure phase. 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 above range.

[0049] The maximum heating temperature Tm in the firing step is preferably set to 200°C or higher and 350°C or lower, from the viewpoints of not only sufficiently sintering the copper particles but also preventing the bonded bodies from being damaged by heat. From this viewpoint, the maximum temperature Tm is preferably set to 210°C or higher and 330°C or lower, and more preferably 220°C or higher and 310°C or lower. From the same viewpoint as above, the maximum pressure Pm applied in the firing step is preferably set to 1 MPa or more and 40 MPa or less, particularly 5 MPa or more and 40 MPa or less, and particularly preferably 5 MPa or more and 30 MPa or less.

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

[0051] The firing step can be carried out in an inert atmosphere or an oxygen-containing atmosphere. Examples of inert atmospheres include a nitrogen gas atmosphere and a rare gas atmosphere such as argon or neon. From the viewpoint of economy, a nitrogen gas atmosphere is preferable. Examples of oxygen-containing atmospheres include air.

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

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

[0054] In relation to the above-described embodiments, the present invention further discloses the following methods for producing a bonded body and methods for bonding bodies to be bonded. [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, comprising: a step of applying a paste containing copper particles and an organic solvent to the first body to be bonded to form a coating film; placing the second object to be joined on the coating film to form a laminate; a firing step of heating and pressurizing the laminate to sinter the copper particles in the coating film and form the bonding layer, In the firing step, heating is gradually increased from a heating start temperature to a maximum temperature Tm, and pressurization is gradually increased from a pressurization start pressure to a maximum pressure Pm, and the pressure when the heating temperature reaches 200°C is 15 MPa or less. [2] The coating film is formed so that when the second object to be bonded is placed on the coating film, the coating film extends beyond the periphery of the second object to be bonded. paste The manufacturing method described in [1], wherein the [3] The manufacturing method according to [1] or [2], wherein in the firing step, the heating is performed so as to reach the maximum temperature Tm, and then the pressing is performed so as to reach the maximum pressure Pm. [4] The method according to any one of [1] to [3], wherein the method does not include a constant temperature step of 10 seconds or more from the heating start temperature to the maximum temperature Tm. [5] The manufacturing method according to any one of [1] to [4], wherein there is no constant pressure period of 10 seconds or more from the pressurization start pressure until the maximum pressure Pm is reached. [6] The method according to any one of [1] to [5], wherein the maximum temperature Tm is 200°C or higher and 350°C or lower. [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 to Pm MPa.

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

[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 such examples. Unless otherwise specified, "%" means "% by mass."

[0056] Example 1 (1) Preparation of paste Cuprous particles (spherical, D SEM50 =0.16μm) and copper(II) particles (flat, D 50 = 4.2 μm), hexylene glycol (organic solvent), polyethylene glycol (molecular weight 300, organic solvent), and bis(2-hydroxyethyl)iminotris(hydroxymethyl)methane (reducing agent) were mixed to prepare a paste. The total content of the copper(I) particles and copper(II) particles in the paste was 82%, the content of the organic solvent was 17.9%, and the content of the reducing agent was 0.1%. The mass ratio of the copper(I) particles to the copper(II) particles was copper(I) particles:copper(II) particles=7:3.

[0057] (2) Formation of coating film The 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 film, which was then dried in the air at 110°C for 20 minutes.

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

[0059] (4) Heating and pressurizing the laminate Heating and pressure were simultaneously initiated from an initial temperature of 40°C with no weight applied (excluding its own weight). It took 15 seconds to heat the laminate from 40°C to 300°C, with an average heating rate of 17.3°C / s and a pressure increase rate of 1.3MPa / s. The temperature and pressure were increased linearly over time. The atmosphere was nitrogen gas. The pressure was 8.7MPa when the temperature reached 200°C. The temperature increase was stopped when the temperature reached the maximum temperature (Tm) of 300°C, and was then maintained at 300°C. The pressure also reached the maximum pressure (Pm) of 20MPa when the temperature reached 300°C, and was then maintained at 20MPa. Ten minutes after reaching the maximum temperature (Tm) and maximum pressure (Pm), heating and pressure were stopped, and the laminate was allowed to cool naturally to obtain the desired bonded structure.

[0060] Comparative Example 1 In "(4) Heating and pressurizing of laminate" in Example 1, the time required to heat from 40°C to 300°C was 30 seconds, the temperature increase rate was 8.7°C / s on average, and the pressure increase rate was 1.3 MPa / s. When the pressure reached the maximum pressure Pm of 20 MPa, the pressure increase was stopped, and the maximum pressure Pm was maintained thereafter. At this point, the temperature increase continued. When the temperature reached 200°C, the pressure was 20 MPa. When the temperature reached the maximum temperature Tm of 300°C, the temperature increase was stopped, and 300°C was maintained thereafter. 10 minutes after the maximum temperature Tm was reached, heating and pressurization were stopped, and the laminate was allowed to cool naturally, to obtain the desired bonded body.

[0061] Comparative Example 2 In "(4) Heating and pressurizing of laminate" in Example 1, the time required to heat from 40°C to 300°C was 40 seconds, the temperature increase rate was 6.5°C / s on average, and the pressure increase rate was 1.3 MPa / s. When the pressure reached the maximum pressure Pm of 20 MPa, the pressure increase was stopped, and the maximum pressure Pm was maintained thereafter. At this point, the temperature increase continued. When the temperature reached 200°C, the pressure was 20 MPa. When the temperature reached the maximum temperature Tm of 300°C, the temperature increase was stopped, and 300°C was maintained thereafter. 10 minutes after the maximum temperature Tm was reached, heating and pressurization were stopped, and the laminate was allowed to cool naturally, to obtain the desired bonded body.

[0062] 〔evaluation〕 The appearance of the bonded bodies obtained in Examples and Comparative Examples was visually observed to evaluate the presence or absence of defects in the fillets. As a result, no defects, including cracks, were observed in the fillets of the bonded body obtained in Example 1. In contrast, cracks were observed in the corners of the fillets of the bonded bodies obtained in Comparative Examples 1 and 2. [Industrial Applicability]

[0063] According to the present invention, there is provided a method for producing a bonded body in which the occurrence of cracks in the fillet portion is suppressed.

Claims

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, comprising: a step of applying a paste containing copper particles and an organic solvent to the first body to be joined to form a coating film; a step of placing the second object to be joined on the coating film to form a laminate; a firing step of heating and pressurizing the laminate to sinter the copper particles in the coating film and form the bonding layer, In the firing step, heating is gradually increased from a heating start temperature until a maximum temperature Tm is reached, and pressurization is gradually increased from a pressurization start pressure until a maximum pressure Pm is reached, and the pressure when the heating temperature reaches 200°C is 15 MPa or less, and the pressurization reaches the maximum pressure Pm after heating reaches the maximum temperature Tm.

2. 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, comprising: a step of applying a paste containing copper particles and an organic solvent to the first body to be joined to form a coating film; a step of placing the second object to be joined on the coating film to form a laminate; 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 producing a bonded body, wherein in the firing step, heating is gradually increased from a heating start temperature until a maximum temperature Tm is reached, and pressurization is gradually increased from a pressurization start pressure until a maximum pressure Pm is reached, and the pressure when the heating temperature reaches 200°C is 15 MPa or less, and there is no constant pressure step of 10 seconds or more from the pressurization start pressure to the maximum pressure Pm.

3. 3. The manufacturing method according to claim 1, wherein the paste is applied so that the coating film extends beyond the periphery of the second object to be bonded when the second object to be bonded is placed on the coating film.

4. 3. The method according to claim 1, wherein the heating step from the heating start temperature to the maximum temperature Tm does not include a constant temperature step of 10 seconds or more.

5. 2. The method according to claim 1, wherein the pressure does not remain constant for 10 seconds or more from the initial pressure until the maximum pressure Pm is reached.

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

7. The method according to claim 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 claim 1 or 2, wherein the maximum pressure Pm is set to 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 in the range of (Pm-5) MPa or more and Pm MPa or less.

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

11. A method for joining objects to be joined, which joins a first object to be joined and a second object to be joined via a joining layer, comprising: a step of applying a paste containing copper particles and an organic solvent to the first body to be joined to form a coating film; a step of placing the second object to be joined on the coating film to form a laminate; 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 bodies to be joined, wherein in the firing step, heating is gradually increased from a heating start temperature until a maximum temperature Tm is reached, and pressurization is gradually increased from a pressurization start pressure until a maximum pressure Pm is reached, and the pressure when the heating temperature reaches 200°C is 15 MPa or less, and there is no constant pressure step of 10 seconds or more from the pressurization start pressure to the maximum pressure Pm.

12. A manufacturing method as described in claim 10, which does not have a constant pressure process of 10 seconds or more from the start of pressurization pressure to reaching the maximum pressure Pm.

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