Production method for joint structure and joining method for joined bodies

Abstract

A production method according to the present invention comprises: a step in which a wet coating film (13a) is formed by coating a first joined body (11) with a joining composition containing a copper powder and an organic substance that is a liquid at 25°C; a step in which a dry coating film (13b) is obtained by removing the organic substance from the wet coating film (13a); a step in which a second joined body (12) is temporarily fixed to the dry coating film (13b) by applying pressure and a layered body in which the first joined body (11), the dry coating film (13b), and the second joined body (12) are layered in this order is obtained; and a step in which the layered body is heated under pressure and the joined bodies (11), (12) are joined. The organic substance contains a first organic substance. At least one type of the first organic substance has a boiling point of 230°C or more and less than 300°C and a viscosity of 100 mPa·s or more under conditions in which the temperature is 25°C and the shear rate is 10 s-1.

Description

Manufacturing method of joined structure and joining method of joined objects

[0001] The present invention relates to a method for manufacturing a bonded structure formed by bonding two objects to be bonded, and a method for bonding objects to be bonded.

[0002] In recent years, semiconductor elements known as power devices have come into widespread use as power conversion and control devices, such as inverters. Unlike integrated circuits such as memory and microprocessors, power devices are designed to control high currents, and therefore generate a great deal of heat during operation. Therefore, the solder used to mount power devices must be heat-resistant. However, the lead-free solder currently in use has the disadvantage of being less heat-resistant than regular lead-containing solder.

[0003] Therefore, instead of using solder, various techniques have been proposed in which a paste containing metal fine particles with limited use of harmful chemicals is used, and this is applied to an object by various coating means and then fired. For example, Patent Document 1 proposes a method of manufacturing a power module by applying a sinterable metal bonding material made by dispersing silver nanoparticles in an organic solvent to an insulating substrate, drying the bonding material, and then placing and temporarily fixing a power semiconductor element on the insulating substrate, and then sintering the bonding material.

[0004] Japanese Patent Application Laid-Open No. 2019-186457

[0005] In the technology described in Patent Document 1, depending on the drying conditions, temporary fixing conditions, sintering conditions, etc., the bonding material may protrude outward from the periphery of the power semiconductor element, which may result in insufficient bonding strength or displacement of the power semiconductor element. Therefore, an object of the present invention is to provide a manufacturing method for a bonded structure that can successfully bond objects to each other without causing displacement or detachment of the objects to be bonded.

[0006] The present invention provides a method for manufacturing a bonded structure 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: applying a bonding composition containing copper powder and an organic substance that is liquid at 25°C to the first body to form a wet coating film; removing the organic substance from the wet coating film to obtain a dry coating film; temporarily fixing the second body to the dry coating film by applying pressure to obtain a laminate in which the first body to be bonded, the dry coating film, and the second body to be bonded are laminated in this order; and heating the laminate under pressure to sinter the copper powder in the dry coating film, and bonding the first body to be bonded and the second body to be bonded by the bonding layer formed by sintering, wherein the organic substance includes a first organic substance, and the first organic substance has a boiling point of 230°C or higher but lower than 300°C and is sintered at 25°C, a shear rate of 10 s －１ The present invention provides a method for manufacturing a bonded structure in which the viscosity under the above conditions is 100 mPa·s or more.

[0007] The present invention also provides a method for bonding a first body to be bonded and a second body to be bonded via a bonding layer, the method comprising the steps of: applying a bonding composition containing copper powder and an organic substance that is liquid at 25°C to the first body to be bonded to form a wet coating film; removing the organic substance from the wet coating film to obtain a dry coating film; temporarily fixing the second body to the dry coating film by applying pressure to obtain a laminate in which the first body to be bonded, the dry coating film, and the second body to be bonded are laminated in this order; and applying pressure and heat to the laminate to sinter the copper powder in the dry coating film, and bonding the first body to be bonded and the second body to be bonded by the bonding layer formed by sintering, wherein the organic substance includes a first organic substance, and the first organic substance has a boiling point of 230°C or higher but lower than 300°C and is sintered at 25°C and a shear rate of 10 s －１ The viscosity under the above conditions is 100 mPa·s or more.

[0008] Fig. 1 is a process diagram showing one embodiment of the method for manufacturing a bonded structure of the present invention (a process diagram up to the production of a laminate), and Fig. 2 is a plan view showing a part of the outer edge of a dried coating film before and after placing a second bonded body.

[0009] The present invention will be described below based on preferred embodiments. The present invention relates to a method for producing a bonded structure in which two objects to be bonded, i.e., a first object to be bonded and a second object to be bonded, are bonded via a bonding layer. This manufacturing method can be broadly divided into the following steps: (1) a step of applying a bonding composition containing copper powder and an organic substance that is liquid at 25°C (hereinafter also referred to as a "liquid organic substance") to the first object to be bonded to form a wet coating film (wet coating film forming step); (2) a step of removing the liquid organic substance from the wet coating to obtain a dry coating film (dry coating film forming step); (3) a step of temporarily fixing the second object to the dry coating film by applying pressure to obtain a laminate in which the first object to be bonded, the dry coating film, and the second object to be bonded are stacked in this order (laminate forming step); and (4) a step of heating the laminate under pressure to sinter the copper powder in the dry coating film and bonding the first object to the second object to be bonded by the bonding layer formed by the sintering (bonding step). Each step will be described below with reference to FIG. 1 . FIG. 1 is a process diagram showing one embodiment of the method for manufacturing a bonded structure of the present invention.

[0010] (1) Wet Coating Film Formation Step First, as shown in FIG. 1( a), a first object to be bonded 11 is prepared, and a bonding composition is applied to one surface 11 a of the first object to be bonded 11 to form a wet coating film 13 a. The bonding composition contains copper powder and a liquid organic substance. The method for applying the bonding composition is not particularly limited. For example, the wet coating film 13 a can be formed by screen printing, gravure printing, dispense printing, reverse coating, doctor blade, or the like.

[0011] The average thickness of the wet coating film 13a is preferably 20 μm or more, more preferably 30 μm or more, and even more preferably 35 μm or more, from the viewpoint of ensuring sufficient bonding strength, and is preferably 500 μm or less, more preferably 450 μm or less, and even more preferably 400 μm or less, from the viewpoint of facilitating smoothing of the coating film and preventing cracking of the coating film after drying.

[0012] The application area of ​​the bonding composition may be such that the wet coating film 13a formed by application extends beyond the periphery of the second object to be bonded 12 described below, or the two may have the same area, or the wet coating film 13a formed by application may have an area smaller than the periphery of the second object to be bonded 12 described below. In the embodiment shown in Fig. 1, the application area of ​​the bonding composition is such that the wet coating film 13a formed by application extends beyond the periphery of the second object to be bonded 12. By using such an application area, the first object to be bonded 11 and the second object to be bonded 12 can be bonded more reliably.

[0013] (2) Dry Coating Film Formation Step Next, as shown in Fig. 1(b), the liquid organic substance is removed from the wet coating film 13a to obtain a dry coating film 13b. By removing the liquid organic substance from the wet coating film 13a, the shape retention of the dry coating film 13b is improved.

[0014] 1(b), from the viewpoint of successfully temporarily fixing the second object to be joined 12 to the dried coating film 13b (described later), it is preferable to remove the liquid organic substance so that the average thickness of the dried coating film 13b is 20 μm or more, more preferably 25 μm or more, and even more preferably 30 μm or more. On the other hand, from the viewpoint of easily obtaining a smooth coating film and preventing cracks in the coating film after drying, it is preferable to remove the liquid organic substance in the drying step so that the average thickness of the dried coating film 13b is 400 μm or less, more preferably 350 μm or less, and even more preferably 300 μm or less.

[0015] If an excessive amount of liquid organic matter remains in the dried coating film 13b, the dried coating film 13b may become soft, reducing the strength of the temporary fixation of the second object to be joined 12 to the dried coating film 13b and the bond strength between the first object to be joined 11 and the second object to be joined 12 after sintering. Furthermore, when the first object to be joined 11 and the second object to be joined 12 are joined, the dried coating film 13b may protrude outside the first object to be joined 11 and the second object to be joined 12 in a plan view. To effectively suppress these problems, in the step shown in FIG. 1(b), it is preferable to sufficiently increase the amount of volatilization of the liquid organic matter contained in the wet coating film 13a to reduce the amount of liquid organic matter remaining in the dried coating film 13b. In this step, it is preferable to remove the liquid organic matter from the wet coating film 13a to such an extent that the dried coating film 13b does not have fluidity. The fluidity of the dried coating film 13b is determined as follows. For example, when the dried coating film 13b has a rectangular or approximately rectangular shape of x [mm] × y [mm] (x and y are numbers satisfying x≧y) in a plan view, a second object to be bonded 12 having a size of 5x / 6 [mm] × 5y / 6 [mm] in a plan view is placed on the dried coating film 13b at 25°C. If an excessive amount of liquid organic matter remains in the dried coating film 13b and the dried coating film 13b has fluidity, placing the second object to be bonded 12 under the above conditions will cause the dried coating film 13b to deform and shift from its original position (the position before the second object to be bonded 12 was placed). Therefore, if the dried coating film 13b is shifted by x / 5 [mm] or more from its original position after placing the second object to be bonded 12, it is determined that the dried coating film 13b has fluidity, and if it is shifted by less than x / 5 [mm], it is determined that the dried coating film 13b has no fluidity. The deviation of the dried coating film 13b after the second object to be bonded 12 is placed is defined as follows. That is, as shown in Fig. 2, the outer edge of the dried coating film 13b before the second object to be bonded 12 is placed is defined as C1, and the normal to C1 at an arbitrary point P on C1 is defined as L. The intersection of the normal L and the outer edge C2 of the dried coating film 13b after the second object to be bonded 12 is defined as Q. However, if there are multiple intersections between the normal L and the outer edge C2, the intersection that is the shortest distance from point P is defined as Q. Then, point P on C1 is selected so that the distance PQ between point P and point Q is maximized, and the distance PQ is defined as the deviation of the dried coating film 13b.

[0016] However, from the viewpoint of increasing the temporary fixing strength of the second object to be joined 12 to the dried coating film 13b, and from the viewpoint of increasing the bonding strength between the first object to be joined 11 and the second object to be joined 12 in the desired bonded structure, it is preferable that a small amount of liquid organic matter remains in the dried coating film 13b.

[0017] 1(b), from the viewpoint of sufficiently removing the liquid organic matter contained in the wet coating film 13a, the wet coating film 13a is preferably dried so that its mass is reduced by 15% by mass or more, more preferably 16% by mass or more, even more preferably 17% by mass or more, and particularly preferably 18% by mass or more. On the other hand, from the viewpoint of increasing the temporary fixing strength of the second object to be joined 12 to the dried coating film 13b and increasing the bonding strength between the first object to be joined 11 and the second object to be joined 12 in the intended bonded structure, the wet coating film is preferably dried so that its mass is reduced by 30% by mass or less, more preferably 29% by mass or less, even more preferably 28% by mass or less, thereby removing the liquid organic matter from the wet coating film 13a. A method for measuring the rate of mass reduction of the wet coating film 13a will be described in the Examples below.

[0018] From the viewpoint of increasing the temporary fixing strength of the second object to be joined 12 to the dry coating film 13b and increasing the bonding strength between the first object to be joined 11 and the second object to be joined 12 after sintering, the liquid organic substance is preferably removed from the wet coating film 13a so that the content of the liquid organic substance in the dry coating film 13b is 25 parts by mass or less, more preferably 24 parts by mass or less, and even more preferably 23 parts by mass or less, when the content of the liquid organic substance in the wet coating film 13a is taken as 100 parts by mass. Furthermore, as described above, it is preferable that a trace amount of liquid organic substance remains in the dry coating film 13b. Therefore, the liquid organic substance is preferably removed from the wet coating film 13a so that the content of the liquid organic substance in the dry coating film 13b is 5 parts by mass or more, more preferably 6 parts by mass or more, and even more preferably 7 parts by mass or more, when the content of the liquid organic substance in the wet coating film 13a is taken as 100 parts by mass.

[0019] From the viewpoint of sufficiently reducing the amount of liquid organic matter remaining in the dried coating film 13b, in this step, the wet coating film 13a is preferably heated to 100°C or higher, more preferably to 105°C or higher, and even more preferably to 110°C or higher. Furthermore, from the viewpoint of keeping the amount of liquid organic matter remaining in the dried coating film 13b within the above-mentioned range, in this step, the wet coating film 13a is preferably heated to 200°C or lower, more preferably to 190°C or lower, even more preferably to 180°C or lower, and particularly preferably to 160°C or lower. From the same viewpoint, when the drying step is carried out under atmospheric pressure, the heating time of the wet coating film 13a is preferably 10 minutes or longer, more preferably 15 minutes or longer, even more preferably 20 minutes or longer, and preferably 60 minutes or shorter, more preferably 50 minutes or shorter, and even more preferably 40 minutes or shorter.

[0020] The formation of the dry coating film 13b by heating the wet coating film 13a can be carried out in an inert gas atmosphere such as nitrogen gas or argon gas, or in the air. Heating may be carried out under reduced pressure. There are no particular limitations on the heating means. For example, heating means such as blowing hot air, irradiating with infrared rays, and heating in a heating furnace can be used.

[0021] (3) Laminate Formation Step Once the dry coating film 13b has been formed, the second object to be joined 12 is then placed on the dry coating film 13b as shown in Fig. 1(c). The second object to be joined 12 is preferably placed on the dry coating film 13b so that the dry coating film 13b extends from the periphery of the second object to be joined 12. However, the second object to be joined 12 may be placed so that the periphery of the second object to be joined 12 coincides with the periphery of the dry coating film 13b, or the second object to be joined 12 may be placed so that the second object to be joined 12 extends from the periphery of the dry coating film 13b.

[0022] In this embodiment, a temporary fixing agent may or may not be applied between the dry coating film 13b and the second object to be bonded 12 prior to placing the second object to be bonded 12 on the dry coating film 13b. As described below, the bonding composition used to manufacture the dry coating film 13b contains a small amount of a high-viscosity first organic substance, so the second object to be bonded 12 can be temporarily fixed to the dry coating film 13b without using a temporary fixing agent. As described above, the manufacturing method of this embodiment makes it possible to omit the step of applying a temporary fixing agent, thereby simplifying the manufacturing process and shortening the manufacturing time. Note that although the present invention does not require the use of a temporary fixing agent, it is not precluded from using one. Examples of temporary fixing agents include monoalcohols, polyhydric alcohols, polyhydric alcohol alkyl ethers, polyhydric alcohol aryl ethers, esters, heterocyclic compounds, amides, amines, saturated hydrocarbons, cyclic terpene alcohols and their derivatives, ketones, and carboxylic acids.

[0023] At least a portion of the highly viscous first organic substance (described in detail below) contained in the bonding composition remains in the dried coating film 13b. Therefore, by applying pressure to the second object to be bonded 12 placed on the dried coating film 13b (i.e., by pressing the second object to be bonded 12 into the dried coating film 13b), the second object to be bonded 12 can be temporarily fixed to the dried coating film 13b. This results in a laminate 14 that is composed, in order, of the first object to be bonded 11, the dried coating film 13b, and the second object to be bonded 12. The second object to be bonded 12 can be directly pressed into the dried coating film 13b using a jig (not shown) used when placing the second object to be bonded 12. In this specification, "temporary fixation" refers to a state in which the first bonded object 11 and the second bonded object 12 are temporarily fixed together, and the fixed state changes when a large external force is applied, but the fixed state does not change when a small external force is applied (for example, when a stack of the first bonded object 11 and the second bonded object 12 is placed so that the bonding surfaces of both bonded objects 11 and 12 are facing vertically, a force that would cause either the first bonded object 11 or the second bonded object 12 to fall under its own weight).

[0024] The pressure when the second object to be joined 12 is pressed into the dry coating film 13b is preferably 0.1 MPa or more, more preferably 0.2 MPa or more, and even more preferably 0.3 MPa or more, from the viewpoint of appropriately temporarily fixing the second object to be joined 12 by the dry coating film 13b and from the viewpoint of sufficiently increasing the bonding strength between the first object to be joined 11 and the second object to be joined 12 in the subsequent bonding step. Moreover, the pressure when the second object to be joined 12 is pressed into the dry coating film 13b is preferably 5 MPa or less, more preferably 4.5 MPa or less, and even more preferably 4.0 MPa or less.

[0025] The time for which the pressure is maintained after the target pressure is reached is preferably 0.01 seconds or more, and more preferably 0.1 seconds or more, from the viewpoint of appropriately temporarily fixing the second object to be bonded 12 by the dried coating film 13b and from the viewpoint of sufficiently increasing the bonding strength between the first object to be bonded 11 and the second object to be bonded 12 in the subsequent bonding step. Furthermore, the time for which the pressure is maintained after the target pressure is reached is not particularly limited as long as it does not significantly reduce productivity, and can be, for example, 5 seconds or less.

[0026] During the temporary fixation, the second object to be joined 12 and / or the dried coating film 13b may be at room temperature or may be heated. From the viewpoint of appropriately temporarily fixing the second object to be joined 12 by the dried coating film 13b, it is preferable to heat the second object to be joined 12 and / or the dried coating film 13b when pressing the second object to be joined 12 into the dried coating film 13b. In other words, it is preferable to temporarily fix the second object to be joined 12 to the dried coating film 13b by applying pressure and heat. Specifically, the heating temperature of the second object to be joined 12 is preferably 15°C or higher, more preferably 18°C ​​or higher, even more preferably 20°C or higher, and preferably 300°C or lower, more preferably 270°C or lower, and even more preferably 250°C or lower. The heating temperature of the dried coating film 13b is preferably 15°C or higher, more preferably 18°C ​​or higher, even more preferably 20°C or higher, and preferably 230°C or lower, more preferably 220°C or lower, and even more preferably 210°C or lower. By setting the heating temperature within the above range, it is possible to appropriately temporarily fix the second object to be bonded 12 while suppressing an excessive decrease in the amount of liquid organic matter remaining in the dried coating film 13b.

[0027] When the second objects to be joined 12 are temporarily fixed by applying pressure while heating the second objects to be joined 12 and / or the dry coating film 13b, it is not necessary to sinter the copper powder in the wet coating film 13a by this heating and pressurizing treatment. This is because, as described below, the dry coating film 13b contains a trace amount of a high-viscosity first organic substance (described in detail below), which allows the temporary fixing strength of the second objects to be joined 12 to be sufficiently increased without sintering the copper powder. By performing the laminate formation process under conditions that do not sinter the copper powder in the wet coating film 13a, the sintering of the copper powder can be sufficiently promoted in the subsequent joining process, thereby further improving the bonding strength and bonding reliability of the resulting joined structure. Conditions that do not sinter the copper powder include, for example, heating the second objects to be joined 12 and the dry coating film 13b to a temperature of 250°C or less and a heating time of less than 50 seconds.

[0028] When the second object to be bonded 12 is temporarily fixed, the position of the second object to be bonded 12 is less likely to shift relative to the first object to be bonded 11 even if an external force is applied to the laminate 14. Therefore, when the laminate 14 is transported to a firing furnace for the next step, for example, the bonding step described below, it becomes possible to stably maintain the positional relationship between the first object to be bonded 11 and the second object to be bonded 12.

[0029] (4) Bonding Process The laminate 14, in which the second object to be bonded 12 is temporarily fixed by the dry coating film 13b, is then subjected to the bonding process. In the bonding process, the laminate 14 is heated under pressure to sinter the copper powder in the dry coating film 13b, and the first object to be bonded 11 and the second object to be bonded 12 are bonded by the bonding layer formed by the sintering. Since the bonding process is performed in a different location from the laminate formation process described above, the laminate 14 is moved to a heating device. While external forces such as vibrations may be applied to the laminate 14 during the transfer, the second object to be bonded 12 is appropriately temporarily fixed to the dry coating film 13b by the laminate formation process described above, so that displacement and detachment of the second object to be bonded 12 are suppressed. Note that if the heating device also serves as a device on which the second object to be bonded 12 is placed, the laminate 14 may be heated in situ without being moved.

[0030] The heating temperature in the bonding step is preferably 180° C. or higher, more preferably 200° C. or higher, and preferably 450° C. or lower, and more preferably 400° C. or lower, from the viewpoint of reliably sintering the copper particles in the dried coating film 13b and reliably increasing the bonding strength between the first body to be bonded 11 and the second body to be bonded 12. From the same viewpoint, the heating time in the bonding step is preferably 1 minute or higher, more preferably 2 minutes or higher, and preferably 30 minutes or lower, and more preferably 25 minutes or lower.

[0031] From the viewpoint of appropriately fixing the second object to be bonded 12 by the dried coating film 13b, the pressure applied in the bonding step is preferably 1 MPa or more, more preferably 2 MPa or more, even more preferably 3 MPa, and preferably 35 MPa or less, even more preferably 32 MPa or less, even more preferably 30 MPa or less. The atmosphere used in the bonding step may be, for example, air, an inert gas, or a reducing atmosphere. Of these, it is preferable to use an inert gas or a reducing atmosphere.

[0032] In the joining step, it is preferable to sinter the copper powder so that the bond strength between the first body to be joined 11 and the second body to be joined 12 is 32 MPa or more by appropriately selecting sintering conditions such as temperature, time, and pressure when sintering the copper powder. Moreover, the bond strength between the first body to be joined 11 and the second body to be joined 12 is more preferably 35 MPa or more, and even more preferably 40 MPa or more. A method for measuring the bond strength between the first body to be joined 11 and the second body to be joined 12 will be described in the examples below.

[0033] In the bonded structure obtained by the sintering process, the bonding layer bonding the first bonded body 11 and the second bonded body 12 preferably has a low void fraction. Specifically, the void fraction of the bonding layer is preferably 30% or less, more preferably 20% or less, and even more preferably 15% or less. The void fraction of the bonding layer is the ratio of the volume of voids (space not occupied by the constituent material of the bonding layer) in the bonding layer to the apparent volume of the bonding layer. For convenience, in measuring the void fraction, instead of the volume ratio, the occupied area ratio of voids on one surface of the bonding layer may be calculated and regarded as the void fraction. The void fraction of the bonding layer can be measured, for example, as follows. First, using a 50 MHz frequency probe in an ultrasonic imaging device (Hitachi High-Technologies FineSAT FS300 III), the bonding interface between the second bonded body and the sintered copper powder compact is analyzed by reflection at a horizontal pitch of 30 μm, and an ultrasonic flaw detection (SAT) image is obtained. When observing the peeling state of the bonding layer, the gain value is set to 25 to 35 dB, and then the delay and width of the S gate are adjusted so that the S gate peak position is on the surface of the first bonded body. The delay of the F gate is adjusted to specify the observation range of the bonding layer, and the width is set to an appropriate peak width. The Z-axis coordinate of the probe is adjusted to maximize the amplitude of the observed peak, and observation is performed. The contrast of the observed image is adjusted using the automatic function. The bonded region of the second bonded body in the obtained SAT image is binarized using image processing software (Image J), ​​and the percentage of the black area (bonding rate; %) within the observed area is calculated. That is, after launching Image-J, select Analyze-Set measurement and check Area, Area fraction, and Limit to Threshold. Then, select File-Open to open the image data for which the joining rate is to be calculated, and then specify the range (A) of the second object to be joined in the image. Next, select Edit-Copy to system to copy the specified range (A), and then select File-New-System clipboard to paste the image of the specified range (A).Then, to clarify the bonded portion, Image-Type-8bit is selected, the image is converted, and then Image-Adjust-Threshold is selected to adjust the image threshold to 100. Then, a black area (B) existing within the area (A) of the second bonded object mounting portion in the adjusted image is specified. The black area (B) is a range where the threshold is 100 or less, and can be considered as the bonded portion of the second bonded object. The bonding rate (%) is calculated by dividing the area of ​​(B) by the area of ​​(A) × 100. The void rate (%) can be calculated by subtracting the bonding rate (%) from the area of ​​(B).

[0034] It is more preferable that any two of the temperature, pressure, and time when sintering the copper powder in the bonding step are higher or longer than any two of the temperature, pressure, and time when temporarily fixing the second bonded object 12 to the dry coating film 13b in the laminate-forming step. It is further preferable that all of the temperature, pressure, and time when sintering the copper powder in the bonding step are higher and longer than the temperature, pressure, and time when temporarily fixing the second bonded object 12 to the dry coating film 13b in the laminate-forming step. By carrying out the laminate-forming step and the bonding step under such conditions, the thermal energy required during temporary fixing can be reduced, and good bonding strength can be obtained during heat-and-pressure bonding.

[0035] By employing such a fixing method, a desired bonded structure (not shown) can be obtained, in which the first bonded body 11 and the second bonded body 12 are bonded via a bonding layer made of a sintered body of copper particles.

[0036] Next, the bonding composition, the first body to be bonded 11, and the second body to be bonded 12 used in the bonding method by temporary fixing described above will be described.

[0037] The bonding composition used in the present invention contains copper powder and a liquid organic substance as described above. The bonding composition may further contain various adjusting agents.

[0038] The shape of the copper particles constituting the copper powder contained in the bonding composition is not particularly limited, and both spherical and non-spherical ones can be used. Copper particles being spherical means that they have a circularity coefficient of 0.85 or more. The circularity coefficient is calculated by taking a scanning electron microscope image of the copper particles, and where S is the area of ​​the two-dimensional projection image of the primary particle and L is the perimeter, and the ratio is 4πS / L. ２ The copper particles being non-spherical means that the circularity coefficient is less than 0.85.

[0039] Specific examples of non-spherical shapes include flat shapes, polyhedral shapes such as hexahedrons and octahedrons, spindle shapes, irregular shapes, etc. Flat shapes refer to shapes having a pair of plate surfaces forming the main surfaces of the particle and side surfaces intersecting these plate surfaces. The plate surfaces and side surfaces may each independently be flat, curved, or irregular.

[0040] The copper powder may contain copper particles having two or more different shapes. In particular, it is preferable that the copper powder contains flat copper particles and spherical copper particles from the viewpoint of obtaining a bonded structure with high bonding strength. Furthermore, the copper powder may contain copper particles having the same shape but different particle sizes, or copper particles having different shapes and particle sizes.

[0041] When the copper particles are spherical, the particle size is determined by the following method. Specifically, 50 or more clearly defined primary copper particles are selected using a scanning electron microscope at a magnification of 10,000 to 150,000 times, and the Heywood diameter of each particle is measured. The volume of the particles is then calculated from the Heywood diameter, assuming that the particles are truly spherical. The volume-cumulative particle size at 50% by volume of the calculated volume is defined as the particle size of the copper particles.

[0042] When the copper particles constituting the copper powder are spherical, their particle size is preferably greater than 0.10 μm, more preferably 0.11 μm or more, and even more preferably 0.12 μm or more. On the other hand, the particle size of the copper particles is preferably 0.55 μm or less, and even more preferably 0.5 μm or less. When the particle size of the copper particles exceeds 0.1 μm, shrinkage cracks are less likely to occur when the dried coating film 13b is fired to form a sintered body (bonding layer). On the other hand, when the particle size of the copper particles is set to 0.55 μm or less, the sintering of the copper particles present in the dried coating film 13b can be sufficient.

[0043] When the copper particles are flat, the particle size is determined by the following method. That is, images of the copper particles with clear outlines are obtained using a scanning electron microscope at a magnification of 500x to 50,000x, and the images are then analyzed. Specifically, while rotating the flat copper particles 360 degrees in a direction horizontal to the plate surface, a virtual circumscribing rectangle is considered in each two-dimensional projection image. The long side of the circumscribing rectangle with the longest side is taken as the major axis. At least 50 particles are randomly selected, and the major axes are measured, and the arithmetic average value is calculated and used as the particle size. For image analysis, for example, Mac-view, an image analysis particle size distribution software manufactured by Mountec Co., Ltd., is used.

[0044] When the copper particles are flat, the particle size is preferably 0.3 μm or more, more preferably 0.5 μm or more, even more preferably 1 μm or more, and preferably 50 μm or less, more preferably 40 μm or less, even more preferably 20 μm or less. When the particle size is within this range, when combined with spherical copper particles, cracking of the sintered body due to excessive volumetric shrinkage of the dried coating film 13b is prevented, and the dried coating film 13b has excellent sinterability.

[0045] The content of copper powder in the bonding composition is preferably 50% by mass or more, more preferably 60% by mass or more, and preferably 95% by mass or less, more preferably 90% by mass or less, from the viewpoint of increasing the filling ability of the copper powder and achieving sufficient bonding strength.

[0046] The copper particles may be surface-treated or not. By using surface-treated copper particles, excessive aggregation of the copper particles can be suppressed.

[0047] The bonding composition contains a liquid organic substance. The content of the liquid organic substance in the bonding composition is preferably 10% by mass or more, more preferably 11% by mass or more, even more preferably 12% by mass or more, and preferably 30% by mass or less, more preferably 29% by mass or less, and even more preferably 28% by mass or less. When the bonding composition contains 10% by mass or more of the liquid organic substance, it is possible to achieve both good dispersibility and printability. Furthermore, when the bonding composition contains 30% by mass or less of the liquid organic substance, the bonding strength of the bonded body obtained after the bonding step can be further increased.

[0048] The liquid organic substance contained in the bonding composition has a boiling point of 230°C or more and less than 300°C, and is heated at 25°C and a shear rate of 10 s －１ The bonding composition includes an organic substance (hereinafter also referred to as "first organic substance") having a viscosity of 100 mPa·s or more under the above conditions. Since the first organic substance has the boiling point and viscosity described above, it can remain stably in trace amounts even after the dry coating film forming step, and as a result, it becomes possible to temporarily fix the second object to be bonded 12 to the dry coating film 13b. From this viewpoint, the boiling point of the first organic substance is preferably 230°C or more, and more preferably 235°C or more. Furthermore, from the viewpoint of improving the reliability of the bonding composition after bonding, it is preferably 290°C or less, and more preferably 280°C or less.

[0049] From the viewpoint of successfully temporarily fixing the second object to be bonded 12 to the dried coating film 13b, the temperature is set to 25°C, the shear rate is set to 10 s －１ The viscosity of the first organic substance under the conditions is 100 mPa·s or more, preferably 110 mPa·s or more, more preferably 120 mPa·s or more, and particularly preferably 140 mPa·s or more. In addition, from the viewpoint of ease of handling when preparing a paste, the viscosity of the first organic substance under the conditions is 25°C, a shear rate of 10 s －１The viscosity of the first organic material under these conditions is preferably 5000 mPa·s or less, more preferably 4000 mPa·s or less, even more preferably 3000 mPa·s or less, even more preferably 2000 mPa·s or less, even more preferably 1000 mPa·s or less, and particularly preferably 500 mPa·s or less. The viscosity of the first organic material can be measured using a rheometer (for example, a MARS III rheometer manufactured by Thermo Scientific). The measurement conditions for the viscosity of the first organic material are as follows: Measurement mode: shear rate dependency measurement Sensor: parallel type (Φ60 mm) Measurement temperature: 25°C Gap: 0.300 mm Shear rate: 0.05 to 120.01 s －１ Measurement time: 2 minutes

[0050] From the viewpoint of promoting sintering of the copper powder in the bonding step, the first organic substance is preferably a compound having a plurality of hydroxyl groups.

[0051] Examples of the first organic substance include 2-ethyl-1,3-hexanediol (hereinafter also referred to as "octylene glycol"), 3-methyl-1,5-pentanediol, 2,4-diethyl-1,5-pentanediol, and 1,5-pentanediol.

[0052] The bonding composition may contain an organic material other than the first organic material (hereinafter also referred to as a "second organic material"). There is no limitation on the type of the second organic material. The second organic material may have a boiling point of less than 230°C or equal to or greater than 300°C, or may have a melting point of 230°C or greater but less than 300°C. The second organic material may be heated at 25°C and a shear rate of 10 s －１ The viscosity under the above condition may be less than 100 mPa·s or may be 100 mPa·s or more.

[0053] From the viewpoint of appropriately temporarily fixing the second object to be bonded 12 by the dried coating film 13b and from the viewpoint of sufficiently increasing the bonding strength between the first object to be bonded 11 and the second object to be bonded 12 in the bonding step, the content of the first organic substance in the bonding composition is preferably 10% by mass or more, more preferably 11% by mass or more, even more preferably 12% by mass or more, and preferably 30% by mass or less, more preferably 29% by mass or less, and even more preferably 28% by mass or less. From the same viewpoint, the bonding composition preferably contains 15 parts by mass or more of the first organic substance per 100 parts by mass of the copper powder, more preferably 16 parts by mass or more, and even more preferably 17 parts by mass or more. Furthermore, the bonding composition preferably contains 45 parts by mass or less of the first organic substance per 100 parts by mass of the copper powder, more preferably 40 parts by mass or less, and even more preferably 35 parts by mass or less. From the viewpoint of the printability, dispersibility, and temporary fixability of the bonding composition, the content of the second organic substance in the bonding composition is preferably 2 mass% or more, more preferably 3 mass% or more, even more preferably 4 mass% or more, and preferably 20 mass% or less, more preferably 18 mass% or less, even more preferably 17 mass% or less.

[0054] From the viewpoint of improving the coatability or printability of the bonding composition and of successfully performing temporary fixing, the content of the organic substance in the bonding composition is preferably 9% by mass or more, more preferably 10% by mass or more, and even more preferably 11% by mass or more. Also, the content of the organic substance in the bonding composition is preferably 35% by mass or less, more preferably 33% by mass or less, and even more preferably 30% by mass or less.

[0055] From the viewpoint of promoting sintering of copper powder in the bonding process, the bonding composition preferably contains at least one substance having reducing properties. The reducing substance may be a first organic substance, a second organic substance, or an inorganic substance. Examples of reducing substances include monoalcohols, aminoalcohols, polyhydric 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. Among these, the bonding composition preferably contains an aminoalcohol and / or a polyhydric alcohol as the reducing substance. From the viewpoint of increasing its reducing power, the aminoalcohol contained in the bonding composition preferably has two or more hydroxyl groups, more preferably three or more, even more preferably four or more, and particularly preferably five or more. From the viewpoint of sufficiently promoting sintering of copper powder in the bonding step and from the viewpoint of ensuring a sufficient content of components other than amino alcohol, when the bonding composition contains an amino alcohol, the content of the amino alcohol in the bonding composition is preferably 0.0001% by mass or more, more preferably 0.0002% by mass or more, and even more preferably 0.0003% by mass or more. Furthermore, the content of the amino alcohol in the bonding composition is preferably 5% by mass or less, more preferably 4% by mass or less, and even more preferably 3.5% by mass or less.

[0056] Examples of polyhydric alcohols contained in the bonding composition include glycerin, 1,2,6-hexanetriol, polytetramethylene glycol, polypropylene glycol, and polyethylene glycol. From the viewpoint of promoting sintering of the copper powder in the bonding step, polyhydric alcohols contained in the bonding composition preferably have a number-average molecular weight of 20 or more, more preferably a number-average molecular weight of 50 or more, even more preferably a number-average molecular weight of 100 or more, and preferably a number-average molecular weight of 10,000 or less, more preferably a number-average molecular weight of 5,000 or less, and even more preferably a number-average molecular weight of 4,000 or less. When the bonding composition contains a polyhydric alcohol, from the viewpoint of sufficiently promoting sintering of the copper powder in the bonding step and ensuring a sufficient content of components other than the polyhydric alcohol, the content of the polyhydric alcohol in the bonding composition is preferably 0.1% by mass or more, more preferably 0.15% by mass or more, even more preferably 0.2% by mass or more, and preferably 10% by mass or less, more preferably 9% by mass or less, and even more preferably 8% by mass or less.

[0057] From the viewpoint of more reliably temporarily fixing the second object to be joined 12 to the dried coating film 13b and promoting sintering of the copper powder in the joining process, the joining composition preferably contains a first organic substance and one or more substances that have reducing properties and are different from the first organic substance, more preferably contains the first organic substance and an amino alcohol or polyethylene glycol, even more preferably contains the first organic substance and polyethylene glycol, and particularly preferably contains the first organic substance, polyethylene glycol, and an amino alcohol.

[0058] The bonding composition may contain components other than those described above. Examples of such components include a viscosity modifier and a surface tension modifier. Viscosity modifiers are suitable for adjusting the viscosity of the bonding composition, preferably within the viscosity range described below, and examples thereof include ketones, esters, alcohols, glycols, hydrocarbons, and polymers. Surface tension modifiers are suitable for adjusting the surface tension of the wet coating film 13a, and examples thereof include acrylic surfactants, silicone surfactants, polymers such as alkyl polyoxyethylene ethers and fatty acid glycerol esters, and monomers such as alcohols, hydrocarbons, esters, and glycols.

[0059] In order to improve the coating or printing properties of the bonding composition, the viscosity of the bonding composition is －１ Under these conditions, the viscosity is preferably 5 Pa s or more, more preferably 7 Pa s or more, and preferably 100 Pa s or less, more preferably 80 Pa s or less. The viscosity of the bonding composition can be measured by the same method as the method for measuring the viscosity of the first organic material described above.

[0060] There are no particular limitations on the type of the first bonded body 11 and the second bonded body 12. In general, it is preferable that both the first bonded body 11 and the second bonded body 12 contain a metal on their bonding target surfaces. For example, a member having a surface made of metal can be used as at least one of the first bonded body 11 and the second bonded body 12. 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, or nickel, or an alloy made of a combination of two or more of these metals.

[0061] When at least one of the first bonded body 11 and the second bonded body 12 is a member having a surface made of metal, it is generally preferable that the surface made of metal is flat, but in some cases it may be curved.

[0062] Specific examples of the first bonded body 11 and the second bonded body 12 each independently include, for example, a spacer or heat sink made of the above-mentioned metal, a semiconductor element, and a substrate having at least one of the above-mentioned metals on its surface. For example, an insulating substrate having a metal layer such as copper on the surface of a ceramic or aluminum nitride plate can be used as the substrate. When a semiconductor element is used as the first bonded body 11 and / or the second bonded body 12, the semiconductor element contains one or more elements such as Si, Ga, Ge, C, N, and As.

[0063] The first object to be bonded 11 is preferably a substrate, and the second object to be bonded 12 is preferably a spacer, a heat sink, or a semiconductor element.

[0064] A dried body of a bonding composition containing metal fine particles and an organic substance can also be used as at least one of the first body to be bonded 11 and the second body to be bonded 12. Specifically, a member having a surface made of metal can be used as the first body to be bonded 11, and a dried body of a bonding composition containing metal fine particles and an organic substance can be used as the second body to be bonded 12. When a dried body of a bonding composition is used, it is preferable to coat the bonding composition on a supporting substrate made of a metal such as copper and dry it to obtain a dried body.

[0065] The bonded structure obtained by this manufacturing method is suitable for use in devices that handle large currents, such as electronic circuits for automobiles and electronic circuits equipped with power devices.

[0066] Although the manufacturing method of the present invention has been described above based on its preferred embodiment, the present invention is not limited to the above embodiment. For example, when the wet coating film contains an organic substance that is solid at 25° C., in addition to the liquid organic substance, some or all of the organic substance that is solid at 25° C. may be removed from the wet coating film in the dry coating film formation step.

[0067] The above-described embodiments of the present invention include the following technical ideas: [1] A method for manufacturing a bonded structure 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: applying a bonding composition containing copper powder and an organic substance that is liquid at 25°C to the first body to form a wet coating film; removing the organic substance from the wet coating film to obtain a dry coating film; temporarily fixing the second body to the dry coating film by applying pressure to obtain a laminate in which the first body to be bonded, the dry coating film, and the second body to be bonded are laminated in this order; and heating the laminate under pressure to sinter the copper powder in the dry coating film, and bonding the first body to the second body to be bonded by the bonding layer formed by sintering, wherein the organic substance includes a first organic substance, and the first organic substance has a boiling point of 230°C or higher but lower than 300°C and is heated at 25°C, a shear rate of 10 s －１[2] The manufacturing method of [1], wherein any two of the temperature, pressure, and time when the copper powder is sintered are higher or longer than any two of the temperature, pressure, and time when the second bonded body is temporarily fixed to the dry coating film. [3] The manufacturing method of [1] or [2], wherein the organic matter is removed from the wet coating film to obtain the dry coating film having no flowability. [4] The manufacturing method of [3], wherein the organic matter is removed from the wet coating film so that the mass of the wet coating film is reduced by 15% by mass or more and 30% by mass or less. [5] The manufacturing method of any one of [1] to [4], wherein the organic matter is removed from the wet coating film so that the content of the organic matter in the dry coating film is 25 parts by mass or less when the content of the organic matter in the wet coating film is 100 parts by mass. [6] The manufacturing method according to any one of [1] to [5], wherein the wet coating film is heated at 100°C or higher and 200°C or lower for 10 minutes or longer in an air atmosphere or an inert gas atmosphere, and the organic substance is removed to obtain the dried coating film. [7] The manufacturing method according to any one of [1] to [6], wherein the bonding composition contains at least one substance having reducing properties. [8] The manufacturing method according to [7], wherein at least one of the substances is an aminoalcohol compound. [9] The manufacturing method according to any one of [1] to [8], wherein the bonding composition contains 15 parts by mass or higher and 45 parts by mass or lower of the first organic substance per 100 parts by mass of the copper powder.

[10] The manufacturing method according to any one of [1] to [9], wherein the second object to be bonded is temporarily fixed to the dried coating film by applying pressure and heat.

[11] The manufacturing method according to any one of [1] to

[10] , wherein at least one of the first organic substances is a compound having multiple hydroxyl groups.

[12] The manufacturing method according to any one of [1] to

[11] , wherein the second bonded body is temporarily fixed to the dry coating film under conditions where the copper powder in the wet coating film is not sintered, to obtain the laminate.

[13] The manufacturing method according to any one of [1] to

[12] , wherein the copper powder is sintered so that the bonding strength between the first bonded body and the second bonded body in the bonded structure is 30 MPa or more.

[14] A method for bonding a first object to be bonded and a second object to be bonded via a bonding layer, the method comprising the steps of: applying a bonding composition containing copper powder and an organic substance that is liquid at 25°C to the first object to be bonded to form a wet coating film; removing the organic substance from the wet coating to obtain a dry coating film; temporarily fixing the second object to the dry coating film by applying pressure to obtain a laminate in which the first object to be bonded, the dry coating film, and the second object to be bonded are stacked in this order; and pressurizing and heating the laminate to sinter the copper powder in the dry coating film, and bonding the first object to be bonded and the second object to be bonded by the bonding layer formed by sintering, wherein the organic substance includes a first organic substance, and the first organic substance has a boiling point of 230°C or higher and lower than 300°C, and is heated at 25°C and a shear rate of 10 s. －１ The viscosity under the conditions of (a) to (c) is 100 mPa·s or more.

[0068] 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."

[0069] Examples 1 to 4 and Comparative Examples 1 and 2 (1) Preparation of Bonding Compositions Bonding compositions were prepared by mixing copper powder consisting of spherical copper particles with a particle size of 0.1 to 0.2 μm and flat copper particles with a particle size of 4.5 μm with an organic substance in the mass ratios shown in Table 2. PEG-300 refers to polyethylene glycol with a number-average molecular weight of 300, and Bis-tris refers to bis(2-hydroxyethyl)iminotris(hydroxymethyl)methane (an amino alcohol having five hydroxyl groups). Both PEG-300 and Bis-tris have reducing properties. Table 1 shows the boiling points of organic substances that are liquid at 25°C and their boiling points at 25°C and a shear rate of 10 s among the organic substances used in each Example and Comparative Example. －１ The viscosity under the conditions shown in Table 1 is unknown. As is clear from Table 1, octylene glycol and 3-methyl-1,5-pentanediol correspond to the first organic substance, and hexylene glycol, diethylene glycol, and PEG-300 correspond to the second organic substance. The Bis-tris used in each example and comparative example is solid at 25°C.

[0070] (2) Application of the Bonding Composition to the First Bonded Body A substrate (20 mm × 20 mm, 2 mm thick) composed of copper and ceramic laminated in the thickness direction was used as the first bonded body. The bonding composition was printed on the copper side of this substrate using a metal mask (6 mm × 6 mm, 100 μm thick) to form a rectangular wet coating film. The wet coating film was dried at 120°C for 30 minutes under the atmosphere shown in Table 2 to remove the liquid organic substance, yielding a dried coating film. Table 2 also shows the mass loss of the wet coating film due to the removal of the liquid organic substance. The same table also shows the content of the liquid organic substance in the dried film, assuming that the content of the liquid organic substance in the wet coating film was 100 parts by mass. The content of the liquid organic substance in the dried film was calculated assuming that no components other than the liquid organic substance were removed from the wet coating film when the liquid organic substance was removed from the wet coating film to form the dried coating film. In all of the Examples and Comparative Examples, the dried coating film lacked fluidity.

[0071] The mass loss rate of the wet coating film was measured using the following method. The mass of the substrate formed by laminating copper and ceramic was measured using an electronic balance, and then the mass of the substrate including the wet coating film after printing with the bonding composition was measured using the electronic balance. The mass of the wet coating film obtained by printing was determined by subtracting the mass of the substrate before printing from the mass of the substrate including the wet coating film. The substrate including the wet coating film was then dried for a predetermined period of time, and the mass of the substrate including the dried coating film was measured using the electronic balance. The mass of the wet coating film reduced by drying was determined by subtracting the mass of the substrate including the dry coating film from the mass of the substrate including the wet coating film. The mass loss rate (%) of the wet coating film was calculated by dividing the mass of the wet coating film reduced by drying by the mass of the wet coating film obtained by printing and multiplying the result by 100.

[0072] (3) Placing the second bonded object on the dried coating film Assuming a model component of a semiconductor power device as the second bonded object, an Ag-plated SiC chip (5 mm × 5 mm × 1.92 mm, weight: 0.016 g) was prepared. The Ag-plated surface of the SiC chip was placed on the center of the dried coating film using a chip mounter.

[0073] (4) Formation of a laminate After heating the SiC chip to 170°C, a pressure of 2.4 MPa was applied for 0.4 seconds from the side opposite the Ag-plated surface of the SiC chip to press the SiC chip into the dried coating film, temporarily fixing the SiC chip to form a laminate.

[0074] (5) Firing of Laminate The laminate was moved to a firing furnace, and the laminate was pressurized to 25 MPa under a nitrogen atmosphere, and then heated to 300°C and held for 5 minutes to fire the coating film into a bonding layer, thereby obtaining a bonded structure.

[0075] [Evaluation 1] In the examples and comparative examples, the stacks obtained in "(4) Formation of stack" were turned upside down for one second, and visually observed for the presence or absence of the SiC chips falling off. The results are shown in Table 2.

[0076] [Evaluation 2] In Examples 1 and 2, where no SiC chip detachment was observed in "Evaluation 1," the shear strength was measured by the following method to confirm the bonding strength of the bonded structure obtained in "(5) Firing of the laminate." The shear strength is a value defined as "breaking load / bottom area of ​​the SiC chip." The results are shown in Table 2. In Table 2, "-" indicates not measured. - Name of measuring device: Condor Sigma (manufactured by XYZTEC Corporation) - Load cell: 200 kgf - Shear tool: Width 6.0 mm, thickness 2.0 mm, shaft 1 / 4 inch (model number: T0S663060) - Shear speed: 50 μm / s - Shear height: 0.02 mm (the zero point was set at the top of the 6 mm square printed coating film).

[0077]

[0078]

[0079] As is clear from Table 2, in Examples 1 to 4, in which octylene glycol or 3-methyl-1,5-pentanediol having a suitable viscosity was used, the first and second objects to be joined could be successfully joined together without causing the second object to fall off, even though no temporary fixing agent was used. Furthermore, the joining strength of the joined structures produced in these Examples was sufficiently high.

[0080] According to the present invention, there are provided a manufacturing method and a joining method for a joined structure that are capable of joining objects to be joined together with a joining material without causing displacement or detachment of the objects to be joined.

Claims

1. A method for manufacturing a bonded structure in which a first object to be bonded and a second object to be bonded are bonded via a bonding layer, the method comprising the steps of: applying a bonding composition containing copper powder and an organic substance that is liquid at 25°C to the first object to form a wet coating film; removing the organic substance from the wet coating film to obtain a dry coating film; temporarily fixing the second object to the dry coating film by applying pressure to obtain a laminate in which the first object to be bonded, the dry coating film, and the second object to be bonded are laminated in this order; and heating the laminate under pressure to sinter the copper powder in the dry coating film, and bonding the first object to be bonded and the second object to be bonded by the bonding layer formed by sintering, wherein the organic substance includes a first organic substance, and the first organic substance has a boiling point of 230°C or higher but lower than 300°C and is sintered at 25°C and a shear rate of 10 s －１ The viscosity under the above conditions is 100 mPa·s or more.

2. The manufacturing method described in claim 1, wherein any two of the temperature, pressure, and time when sintering the copper powder are higher or longer than any two of the temperature, pressure, and time when temporarily fixing the second bonded body to the dried coating film.

3. The manufacturing method according to claim 1 or 2, wherein the organic matter is removed from the wet coating film to obtain the dry coating film having no fluidity.

4. The manufacturing method according to claim 3, wherein the organic matter is removed from the wet coating film so that the mass of the wet coating film is reduced by 15% by mass or more and 30% by mass or less.

5. A manufacturing method according to claim 1 or 2, wherein the organic matter is removed from the wet coating film so that the content of the organic matter in the dry coating film is 25 parts by mass or less when the content of the organic matter in the wet coating film is 100 parts by mass.

6. The manufacturing method according to claim 1 or 2, wherein the wet coating film is heated in an air atmosphere or an inert gas atmosphere at 100°C or higher and 200°C or lower for 10 minutes or longer, and the organic matter is removed to obtain the dry coating film.

7. The manufacturing method according to claim 1 or 2, wherein the bonding composition contains at least one substance having reducing properties.

8. The method of claim 7, wherein at least one of the substances is an amino alcohol compound.

9. The manufacturing method according to claim 1 or 2, wherein the bonding composition contains 15 parts by mass or more and 45 parts by mass or less of the first organic substance per 100 parts by mass of the copper powder.

10. A manufacturing method according to claim 1 or 2, wherein the second object to be joined is temporarily fixed to the dried coating film by applying pressure and heat.

11. The manufacturing method according to claim 1 or 2, wherein the first organic substance is a compound having multiple hydroxyl groups.

12. The manufacturing method according to claim 1 or 2, wherein the laminate is obtained by temporarily fixing the second object to be joined to the dry coating film under conditions that do not cause the copper powder in the wet coating film to sinter.

13. The manufacturing method according to claim 1 or 2, wherein the copper powder is sintered so that the bonding strength between the first and second members to be bonded in the bonded structure is 30 MPa or more.

14. A method for bonding a first object to be bonded and a second object to be bonded via a bonding layer, comprising the steps of: applying a bonding composition containing copper powder and an organic substance that is liquid at 25°C to the first object to be bonded to form a wet coating film; removing the organic substance from the wet coating to obtain a dry coating film; temporarily fixing the second object to the dry coating film by applying pressure to obtain a laminate in which the first object to be bonded, the dry coating film, and the second object to be bonded are laminated in this order; and applying pressure and heat to the laminate to sinter the copper powder in the dry coating film, and bonding the first object to be bonded and the second object to be bonded by the bonding layer formed by sintering, wherein the organic substance includes a first organic substance, and the first organic substance has a boiling point of 230°C or higher but lower than 300°C and is sintered at 25°C and a shear rate of 10 s －１ The viscosity under the conditions of (a) to (c) is 100 mPa·s or more.

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