Manufacturing method for bonded structure, manufacturing method for laminated body, and bonding method

Abstract

A paste containing copper particles and an organic solvent is applied to a first object to be joined 11 to form a coating film 13a; a part of the organic solvent contained in the coating film 13a is removed; the second object to be joined 12 is pressed into the coating film 13a so that a part of the second object to be joined 12 is embedded in the coating film 13a to obtain a laminate 14 including the first object to be joined 11, the coating film 13a, and the second object to be joined 12 in that order; and the laminate 14 is heated. When the average thickness of the coating film 13a after the drying step and before the second object to be joined 12 is pressed into the coating film 13a is X, and the average distance from the upper surface 11b of the first object to be joined 11 to the lower surface 12b of the second object to be joined 12 in the state in which the laminate 14 is obtained is Y, a pressing ratio P defined as 100-(Y / Xx100) is 1.0 or more and 50 or less.

Description

[Technical field]

[0001] The present invention relates to a method for producing a bonded structure obtained by bonding two objects to be bonded, and also to a method for producing a laminate for obtaining the bonded structure and a method for bonding two objects to be bonded. [Background technology]

[0002] In recent years, semiconductor elements called power devices have come to be widely used as power conversion and control devices such as inverters. Power devices, unlike integrated circuits such as memory and microprocessors, 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 that is currently mainly used 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 particles with limited use of harmful chemical substances is used, and this is applied to an object by various coating means and then sintered. For example, Patent Document 1 describes a method in which a conductive paste containing metal particles is applied onto an electrode pattern, a semiconductor element is placed on top of it, and the conductive paste is heated while being pressurized by pressing down the semiconductor element, thereby forming a sintered layer of metal particles. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2016-127219 A Summary of the Invention

[0005] In the technique described in Patent Document 1, if a semiconductor element is placed on a coating layer of conductive paste and is transported in that state or is subjected to external vibration, the semiconductor element may shift from the correct bonding position, which may cause a problem in bonding between the semiconductor element and the electrode pattern. Therefore, the object of the present invention is to provide a method for manufacturing a bonded structure that can successfully bond objects to each other without causing the objects to shift position or fall off.

[0006] The present invention provides a method for producing a bonded structure in which a first bonded body and a second bonded body are bonded to each other via a bonding layer, comprising the steps of: applying a paste containing copper particles and an organic solvent to the first bonded body to form a coating film; a drying step for removing a part of the organic solvent contained in the coating film; a step of pressing the second object to be joined into the coating film so that a part of the second object to be joined is embedded in the coating film, thereby obtaining a laminate including the first object to be joined, the coating film, and the second object to be joined in this order; and heating the laminate. The average thickness of the coating film after the drying step and before the second bonded body is pressed into the coating film is defined as X (μm); When the average distance from the upper surface of the first bonded body to the lower surface of the second bonded body in the state where the laminate is obtained is Y (μm), The present invention provides a method for producing a joint structure in which a pressing ratio P defined as 100-(Y / X×100) is 1.0 or more and 50 or less.

[0007] The present invention also provides a method for manufacturing a laminate for bonding a first object to be bonded and a second object to be bonded, comprising the steps of: applying a paste containing copper particles and an organic solvent to the first bonded body to form a coating film; a drying step for removing a part of the organic solvent contained in the coating film; and pressing the second object to be joined into the coating film so that a part of the second object to be joined is embedded in the coating film, thereby obtaining a laminate including the first object to be joined, the coating film, and the second object to be joined in this order, The average thickness of the coating film after the drying step and before the second bonded body is pressed into the coating film is defined as X (μm); When the average distance from the upper surface of the first bonded body to the lower surface of the second bonded body in the state where the laminate is obtained is Y (μm), The present invention provides a method for producing a laminate in which a pressing ratio P defined by 100-(Y / X×100) is 1.0 or more and 50 or less.

[0008] The present invention further provides a method for joining a first object to be joined and a second object to be joined, comprising the steps of: applying a paste containing copper particles and an organic solvent to the first bonded body to form a coating film; a drying step for removing a part of the organic solvent contained in the coating film; a step of pressing the second object to be joined into the coating film so that a part of the second object to be joined is embedded in the coating film, thereby obtaining a laminate including the first object to be joined, the coating film, and the second object to be joined in this order; and heating the laminate. The average thickness of the coating film after the drying step and before the second bonded body is pressed into the coating film is defined as X (μm); When the average distance from the upper surface of the first bonded body to the lower surface of the second bonded body in the state where the laminate is obtained is Y (μm), The present invention provides a bonding method in which a pressing ratio P defined as 100-(Y / X×100) is 1.0 or more and 50 or less. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a process diagram showing one embodiment of the method for producing a bonded structure of the present invention (a process diagram up to the production of a laminate). [Diagram 2]FIG. 2 is an enlarged schematic view showing a main part of a laminate in which a second object to be joined is pressed into a dried coating film. [Diagram 3] 3(a) to 3(c) are schematic diagrams showing a method for measuring the values ​​of X and Y in order to calculate the value of the pressing ratio P defined as 100-(Y / Xx100). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The present invention will be described below based on its preferred embodiments. The present invention relates to a method for manufacturing a bonded structure in which two bonded bodies, i.e., a first bonded body and a second bonded body, are bonded via a bonding layer. This manufacturing method is roughly divided into the following steps. (1) A step of applying a paste containing copper particles and an organic solvent to a first object to be bonded to form a coating film. (2) A drying process to remove some of the organic solvent contained in the coating. (3) A step of pressing the second object to be joined into the coating film so that a portion of the second object to be joined is embedded in the coating film, thereby obtaining a laminate including the first object to be joined, the coating film, and the second object to be joined. (4) A step of heating the laminate. Each step will be described below with reference to FIG.

[0011] FIG. 1 is a process diagram showing one embodiment of a method for producing a bonded structure of the present invention. 1(a), a first object to be joined 11 is prepared, and a paste is applied onto one surface of the first object to be joined 11 to form a wet coating film 13a. The paste contains copper particles and an organic solvent. The method for applying the paste is not particularly limited, and the wet coating film 13a can be formed by, for example, a screen printing method, a gravure printing method, a dispense printing method, a reverse coating method, a doctor blade method, or the like.

[0012] From the viewpoint of ensuring sufficient bonding strength, the average thickness of the wet coating film 13a is preferably 18 μm or more, more preferably 20 μm or more, and even more preferably 25 μm or more. Furthermore, the average thickness of the wet coating film 13a is preferably 1000 μm or less, more preferably 800 μm or less, and even more preferably 500 μm or less, from the viewpoint of making the coating film easier to smooth and preventing cracking of the coating film after drying.

[0013] The average thickness of the wet coating film 13a can be calculated using, for example, a non-contact surface profiler that uses white light interference. For example, ZeGage Pro manufactured by AMETEK can be used as the non-contact surface profiler. In this case, ZYGO Mx version: 8.0.0 software is used, with a zoom lens of 1.0x and an objective lens of 1.4x. In the Basic Settings - Options tab of the MEASUREMENT tab of the software, select the scan length as Extended, enter a value that is 100 μm or more larger than the thickness of the wet coating film 13a to be measured, and select Bottom as the scan start position. The measurement field is set so that the first bonded body 11, which is the reference surface for the thickness, is partly included when the image of the wet coating film 13a to be measured is recognized. Specifically, the measurement field is set so that it extends 1 mm or more from the periphery of the wet coating film 13a. By setting the measurement field so that the first bonded body 11, which is the reference surface, is partly included, the rectangle R described later can be positioned within an appropriate range. After setting up, perform the measurement, and when it is complete, open the Level / Step item in the Investigation Tools in the ANALYSIS tab of the software and select Add Shapes (One Reference and One test Default rectangles). This will display a rectangle R for selecting the reference plane and a rectangle T for measuring the height from the reference plane. The rectangle R is arranged so that each side is 500 μm×500 μm or more in size at a position where the first bonded object 11 is present and so that the wet coating film 13a is not included. If any part other than the first bonded object 11 is included in the rectangle R, the reference will not be set correctly. Since the rectangle R is a reference for calculating the thickness of the measurement object, it must not include any part other than the first bonded object 11. Furthermore, by arranging the rectangle R so that it is 500 μm×500 μm or more in size, an average value that takes into account the surface roughness, etc. of the first bonded object 11 is used as the reference, so that the thickness of the wet coating film 13a can be calculated more accurately. Next, place rectangle T so that the vertical and horizontal sides of rectangle T are located 500 μm inward from the vertical and horizontal sides of the wet coating film 13a to be measured. After that, click Apply in the item labeled Level / Step, and a numerical value will be entered inside rectangle T. This numerical value is the average thickness of the wet coating film 13a.

[0014] The paste can be applied only to a position inside the periphery of one surface of the first object to be joined 11. Fig. 1(a) shows a state in which the paste is applied to a position inside the periphery 11a of one surface of the first object to be joined 11 to form one coating film (wet coating film 13a). From the viewpoint of ensuring reliable bonding between the first object to be joined 11 and the second object to be joined 12, it is preferable that the application area of ​​the paste is such that the wet coating film 13a formed by application extends beyond the periphery of the second object to be joined 12 described below.

[0015] Next, as shown in Fig. 1(b), the wet coating film 13a is dried to remove a part of the organic solvent contained in the wet coating film 13a to obtain a dry coating film 13b. By removing a part of the organic solvent from the wet coating film 13a, the shape retention of the dry coating film 13b is improved. From this viewpoint, in the drying step shown in Fig. 1(b), it is preferable to dry the wet coating film 13a so that the mass of the wet coating film 13a is reduced by 3.0 mass% or more, further 3.2 mass% or more, particularly 5.0 mass% or more, and particularly 7.0 mass% or more. On the other hand, if the organic solvent is removed excessively from the wet coating film 13a, the dry coating film 13b becomes hard, and the second object to be joined, which will be described later, may not be pressed successfully into the dry coating film 13b. From this viewpoint, in the drying step, it is preferable to dry the wet coating film 13a so that the mass of the wet coating film 13a is reduced by 30.0 mass % or less, particularly 28.0 mass % or less. The method for measuring the rate of mass loss of the wet coating film 13a will be explained in the examples below.

[0016] In the drying step shown in FIG. 1(b), from the viewpoint of successfully pressing the second object to be joined 12 into the dried coating film 13b, which will be described later, it is preferable to remove the organic solvent so that the average thickness X of the dried coating film 13b is 15 μm or more, more preferably 18 μm or more, and even more preferably 20 μm or more. On the other hand, from the viewpoint of facilitating obtaining a smooth coating film and preventing cracking of the coating film after drying, in the drying step, it is preferable to remove the organic solvent so that the average thickness X of the dried coating film 13b is 800 μm or less, more preferably the average thickness is 500 μm or less, and even more preferably the average thickness is 400 μm or less. The method for measuring the average thickness X of the dry coating film 13b will be described later.

[0017] In the drying step shown in Fig. 1(b), it is preferable to set the heating temperature of the wet coating film 13a within an appropriate range from the viewpoint of adjusting the amount of volatilization of the organic solvent contained in the wet coating film 13a to obtain an appropriate hardness of the dried coating film 13b. From this viewpoint, when the drying step is performed under atmospheric pressure, the heating temperature of the wet coating film 13a is preferably set to 20°C or higher and M°C or lower, more preferably 25°C or higher and [M-10]°C or lower, and even more preferably 30°C or higher and [M-20]°C or lower, where M(°C) is the boiling point of the organic solvent contained in the wet coating film 13a. When two or more organic solvents are contained in the wet coating film 13a, the boiling point of the organic solvent with the highest boiling point is defined as M.

[0018] In relation to the heating temperature, the heating time of the wet coating film 13a may be set under conditions that will result in a dry coating film 13b having a hardness that allows the second object to be joined 12, which will be described later, to be pressed into the dry coating film 13b smoothly. When the drying step is carried out under atmospheric pressure, it is preferable to carry out heating for about 1 minute or more and 120 minutes or less.

[0019] The formation of the dry coating film 13b by heating the wet coating film 13a can be carried out in an inert gas atmosphere or in the air. Alternatively, it may be carried out under reduced pressure. There is no particular limitation on the heating means. For example, the heating means may be blowing hot air, irradiating infrared rays, or heating in a heating furnace.

[0020] After the dry coating film 13b is formed, the second object to be joined 12 is 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 such that the dry coating film 13b extends from the periphery of the second object to be joined 12.

[0021] In this embodiment, prior to placing the second object to be joined 12 on the dry coating film 13b, it is not necessary to apply a fixing agent between the dry coating film 13b and the second object to be joined 12. As described later, in this embodiment, the second object to be joined 12 is pushed into the dry coating film 13b so that a part of the second object to be joined 12 is embedded in the dry coating film 13b, so there is no need to fix the dry coating film 13b and the second object to be joined 12 with a fixing agent. In this way, according to the manufacturing method of this embodiment, it is possible to omit the step of applying a fixing agent, thereby simplifying the manufacturing process and shortening the manufacturing time. Note that, although the above-mentioned fixing agent does not need to be used in the present invention, it is not prevented from using a fixing agent. Examples of 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 derivatives thereof, ketones, and carboxylic acids.

[0022] As described above, the dried coating film 13b has a part of the solvent remaining therein, and therefore has shape retention and deformability. Therefore, by applying pressure to the second object 12 placed on the dried coating film 13b, the dried coating film 13b is deformed, and the second object 12 is pressed into the dried coating film 13b so that a part of the second object 12 is embedded in the dried coating film 13b. This forms a laminate 14 consisting of the first object 11, the dried coating film 13b, and the second object 12 in this order. Note that the second object 12 may be pressed into the dried coating film 13b using, for example, a plate-shaped pressing jig 15 as shown in FIG. 1(d). Alternatively, the second object 12 may be directly pressed into the dried coating film 13b using a jig (not shown) used when placing the second object 12. Alternatively, an appropriate weight may be held by the jig used when placing the second object to be bonded 12, and the weight may be brought into contact with the second object to be bonded 12 and pressed into the dried coating film 13b.

[0023] 2 shows an enlarged view of the main part of the second object to be joined 12, which is pressed into the dry coating film 13b. As shown in the figure, when the second object to be joined 12 is pressed into the dry coating film 13b, the lower region in the thickness direction Z of the second object to be joined 12 is embedded in the dry coating film 13b, and the side surface 12a of the lower region is surrounded by the dry coating film 13b. As a result, the second object to be joined 12 is fixed by the dry coating film 13b. The fixation of the second object to be joined 12 by the dry coating film 13b is achieved by the engagement between the dry coating film 13b and the side surface 12a of the lower region of the second object to be joined 12. It is also achieved by the viscosity of the dry coating film 13b.

[0024] The present inventors have found that in order to reliably fix the second object to be joined 12 by the dried coating film 13b and subsequently join the first object to be joined 11 and the second object to be joined 12, it is necessary to satisfy the following predetermined relationship as a condition for pressing the second object to be joined 12. In detail, it is advantageous to press the second object to be joined 12 so that the value of the pressing ratio P defined by the following formula (1) is 1.0 or more, preferably 1.5 or more, more preferably 2.0 or more, and even more preferably 2.5 or more. On the other hand, 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 bonded structure obtained by sintering the laminate 14, it is desirable that the thickness of the dried coating film 13b located between the first object to be joined 11 and the second object to be joined 12 in the laminate 14 is not made thinner than necessary. From this viewpoint, the value of the pressing ratio P is 50 or less, preferably 30 or less, and more preferably 25 or less. P = 100 - (Y / X × 100) (1)

[0025] X (μm) in formula (1) is the average thickness of the dry coating film 13b after the drying step of the wet coating film 13a and before the second object to be bonded 12 is pressed into the dry coating film 13b. Y (μm) is the average distance from the upper surface 11b of the first object to be bonded 11 to the lower surface 12b of the second object to be bonded in a state in which the laminate 14 is obtained (see FIG. 2).

[0026] X and Y are measured as described below. After the drying process of the wet coating film 13a, the second bonded object 12 is mounted at the center of the dry coating film 13b at a low pressure of 0.004 MPa using a chip mounter as shown in FIG. 3(a). The time from when the second bonded object 12 contacts the dry coating film 13b until the pressure reaches 0.004 MPa is set to within 1 second, for example, and the pressure retention time after reaching 0.004 MPa is set to 0.4 seconds. Using the same method as for the wet coating film 13a, the average thickness A of the dry coating film 13b and the second bonded object 12 is calculated from the upper surface 11b of the first bonded object 11. Then, the average thickness A minus the average thickness B of the second bonded object 12 only (see FIG. 2) is set to the average thickness X (μm) of the dry coating film 13b. The average thickness B of the second bonded object 12 is measured in advance. The average thickness B of the second bonded object 12 can be calculated, for example, by placing the second bonded object 12 on a reference surface, which is a SiC substrate having an area 200% or more larger than that of the second bonded object 12 and a smooth surface (surface roughness of 0.03 μm or less according to JIS B 0601:1994), and then using a non-contact surface profiler in a manner similar to that of the wet coating film 13a. 3(b), a plate-shaped weight 20 having an area smaller than that of the second object to be bonded 12 is mounted on the second object to be bonded 12 by applying a pressure of 0.8 MPa using a chip mounter. The time from when the weight 20 comes into contact with the second object to be bonded 12 until the pressure applied thereto reaches 0.8 MPa is set to within 5 seconds from the time of contact, and the time from when the pressure reaches 0.8 MPa is set to 2 seconds. Next, as shown in FIG. 3(c), only the weight 20 is removed using suction tweezers to obtain the laminate 14. Then, the average distance D (see FIG. 2) from the upper surface 11b of the first bonded body 11 to the upper surface 12c of the second bonded body 12 in the laminate 14 is measured. The average distance D can be calculated using a method similar to the above-mentioned method for calculating the average thickness of the wet coating film 13a. Specifically, the rectangle T is arranged so that the vertical and horizontal sides of the rectangle T are located at the position where the second bonded body 12 is present and 500 μm inward from the vertical and horizontal sides of the second bonded body 12 to be measured, respectively, by performing calculations similar to the method for calculating the average thickness of the wet coating film 13a. Thus, the average distance D (see FIG. 2) from the upper surface 12c of the second bonded body 12 to the upper surface 11b of the first bonded body 11 is calculated. The average distance Y from the upper surface 11b of the first body to be bonded 11 to the lower surface 12b of the second body to be bonded is determined by subtracting the average thickness B of only the second body to be bonded 12 from the average distance D.

[0027] The value of the pressing rate P must be as described above. From the viewpoint of reliably fixing the second bonded object 12 by the dried coating film 13b and from the viewpoint of sufficiently increasing the bonding strength between the first bonded object 11 and the second bonded object 12, the value of the average distance Y itself in the formula (1), which defines the pressing rate P, is preferably 5 μm or more and 500 μm or less, and more preferably 10 μm or more and 300 μm or less.

[0028] The pressure when the second object to be joined 12 is pressed into the dry coating film 13b is preferably 0.004 MPa or more and 5 MPa or less, more preferably 0.01 MPa or more and 4.5 MPa or less, and even more preferably 0.05 MPa or more and 4 MPa or less, from the viewpoint of appropriately fixing the second object to be joined 12 by the dry coating film 13b and from the viewpoint of sufficiently increasing the joining strength between the first object to be joined 11 and the second object to be joined 12.

[0029] The maintenance time after the target pressure of the second bonded object 12 is reached is preferably 0.01 seconds or more, and more preferably 0.05 seconds or more, from the viewpoint of appropriately fixing the second bonded object 12 by the dried coating film 13b and of sufficiently increasing the bonding strength between the first bonded object 11 and the second bonded object 12 in the next heating step. Furthermore, the time for which the second bonded body 12 is maintained at the target pressure after the target pressure has been reached is not particularly limited as long as it does not significantly reduce productivity, and can be, for example, 7 seconds or less.

[0030] 2, the second object to be joined 12 is less likely to shift in position relative to the first object to be joined 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 process, for example, the heating process described below, it becomes possible to stably maintain the positional relationship between the first object to be joined 11 and the second object to be joined 12.

[0031] The laminate 14 in which the second object to be joined 12 is fixed by the dry coating film 13b is then subjected to a heating step. Since the heating step is performed at a location different from the step of obtaining the laminate described above, the laminate 14 is moved to a heating device. An external force such as vibration may be applied to the laminate 14 during the movement, but since the second object to be joined 12 is properly fixed to the dry coating film 13b by the step of obtaining the laminate described above, the positional deviation of the second object to be joined 12 is suppressed. Note that the heating device also serves as a device for placing the second object to be joined 12, and the laminate 14 may be heated in place without being moved.

[0032] In the heating step, heat is applied to the laminate 14 after the laminate 14 is pressed, or while the laminate 14 is being pressed or not pressed. The heating temperature is preferably 180° C. or higher and 350° C. or lower, more preferably 200° C. or higher and 300° C. or lower, from the viewpoints of reliably sintering the copper particles in the dried coating film 13b and reliably increasing the bonding strength between the first object to be bonded 11 and the second object to be bonded 12.

[0033] When the heating of the laminate 14 is carried out after pressurization or under pressure, from the viewpoint of properly fixing the second bonded body 12 by the dried coating film 13b, the pressure is preferably 0.1 MPa or more and 35 MPa or less, more preferably 1 MPa or more and 30 MPa or less, and even more preferably 2 MPa or more and 28 MPa or less. The atmosphere in the heating step may be, for example, air, an inert gas, or a reducing atmosphere.

[0034] By employing such a fixing method, a desired bonded structure (not shown) can be obtained, in which the first and second objects to be bonded are bonded via a bonding layer made of a sintered body of copper particles.

[0035] Next, the paste, the first object to be joined, and the second object to be joined that are used in the above-mentioned joining method by fixing will be described.

[0036] The paste used in the present invention contains copper particles and an organic solvent. The paste may further contain various regulators.

[0037] The shape of the copper particles contained in the paste is not particularly limited, and both spherical and non-spherical particles can be used. Copper particles are said to be spherical if their circularity coefficient is 0.85 or more. The circularity coefficient is calculated by taking a scanning electron microscope image of a copper particle, taking the area of ​​the two-dimensional projection image of the primary particle as S and the perimeter as L, and then calculating the circularity coefficient as 4πS / L. 2 It is calculated using the formula: The copper particles being non-spherical means that the circularity coefficient mentioned above is less than 0.85.

[0038] Specific examples of non-spherical shapes include flat, polyhedral such as hexahedron and octahedron, spindle shape, irregular shape, etc. Flat refers to a shape having a pair of plate faces forming the main faces of the particle and side faces perpendicular to these plate faces. The plate faces and the side faces may each independently be flat, curved, or uneven.

[0039] The copper particles may have two or more different shapes. In particular, it is preferable that the copper particles include flat copper particles and spherical copper particles from the viewpoint of obtaining a bonded structure with high bonding strength. In addition, the copper particles may have a plurality of copper particles having the same shape but different particle sizes, or copper particles having different shapes and particle sizes.

[0040] When the copper particles are spherical, the particle size is determined by the following method. More specifically, 50 or more copper particles that are clearly defined primary particles are selected using images observed by a scanning electron microscope at a magnification of 10,000 to 150,000 times, and the Heywood diameter of each particle is measured. Next, the volume of the particle is calculated from the obtained Heywood diameter when it is assumed that the particle is a perfect sphere, and the volume cumulative particle size at 50% of the cumulative volume is defined as the particle size of the copper particle.

[0041] The diameter of the copper particles is preferably more than 0.1 μm, more preferably 0.11 μm or more, and even more preferably 0.12 μm or more. On the other hand, the diameter of the copper particles is preferably 0.55 μm or less, and even more preferably 0.5 μm or less. When the diameter of the copper particles exceeds 0.1 μm, shrinkage cracks are less likely to occur when the dried coating film 13b is sintered to form a sintered body (bonding layer). On the other hand, when the diameter 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 made sufficient.

[0042] When the copper particles are flat, the particle size is determined by the following method. That is, a photograph of the copper particles with a clear outline is obtained using an observation image by a scanning electron microscope in the range of 500 times to 50,000 times, and the photographed image is image-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, and the long side of the circumscribing rectangle with the longest side is taken as the major axis. 50 or more particles are randomly selected, and the major axes are measured, and the arithmetic average value is calculated, which is taken as the particle size. For image analysis, for example, image analysis type particle size distribution software Mac-view manufactured by Mountec Co., Ltd. is used.

[0043] When the copper particles are flat, the particle size is preferably 0.3 μm to 50 μm, more preferably 0.5 μm to 40 μm, and even more preferably 1 μm to 20 μm. 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.

[0044] The content of copper particles in the paste is preferably 50% by mass or more and 95% by mass or less, 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 achieving sufficient bonding strength.

[0045] The copper particles may have a surface treatment agent attached to their surfaces. By attaching a surface treatment agent to the surfaces of the copper particles, excessive aggregation of the copper particles can be suppressed.

[0046] The organic solvent contained in the paste preferably has a boiling point M of 150°C or more and 300°C or less, particularly 160°C or more and 290°C or less, and particularly 170°C or more and 280°C or less. Specific examples include monoalcohols, polyhydric alcohols, polyhydric alcohol alkyl ethers, polyhydric alcohol aryl ethers, esters, nitrogen-containing heterocyclic compounds, amides, amines, and saturated hydrocarbons. These organic solvents can be used alone or in combination of two or more. By containing an organic solvent having a boiling point in the above temperature range in the paste, it becomes easier to adjust the amount of evaporation of the organic solvent contained in the wet coating film 13a, and it becomes easier to make the hardness of the dry coating film 13b appropriate. When the paste contains multiple types of organic solvents, it is preferable that at least one type of organic solvent has a boiling point within the above temperature range, and it is particularly preferable that all of the organic solvents have boiling points within the above range.

[0047] From the viewpoint of adjusting the amount of evaporation of the organic solvent contained in the wet coating film 13a and making the hardness of the dry coating film 13b appropriate, the content of the organic solvent in the paste is preferably 3.0 mass% or more and 30.0 mass% or less, more preferably 5.0 mass% or more and 29.0 mass% or less, and even more preferably 7.0 mass% or more and 28.0 mass% or less.

[0048] The paste may contain an appropriate regulator for adjusting various properties, such as a reducing agent, a viscosity regulator, or a surface tension regulator. 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, phosphites, hydrophosphites, phosphorous acid and its derivatives, etc. 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. The surface tension adjusting agent is preferably one that can adjust 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.

[0049] In order to improve the coating or printing properties of the paste, the viscosity of the paste is set to a value at a shear rate of 10 s -1 In this case, the viscosity is preferably from 10 Pa·s to 200 Pa·s, and more preferably from 15 Pa·s to 200 Pa·s. The viscosity of the paste can be measured using a rheometer MARS III manufactured by Thermo Scientific Corp. The conditions for measuring the viscosity of the 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

[0050] The first bonded body 11 and the second bonded body 12 are not particularly limited in type. In general, it is preferable that both the first bonded body 11 and the second bonded body 12 contain a metal on the bonding surface. For example, a member having a surface made of a 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.

[0051] When at least one of the first bonded object 11 and the second bonded object 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 a curved surface.

[0052] Specific examples of the first bonded object 11 and the second bonded object 12 each independently include, for example, a spacer or a heat sink made of the above-mentioned metals, a semiconductor element, and a substrate having at least one of the above-mentioned metals on its surface. As the substrate, 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. 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.

[0053] The first object to be bonded 11 is preferably a substrate, and the second object to be bonded 12 is preferably any one of a spacer, a heat sink, or a semiconductor element.

[0054] A dried paste containing metal fine particles and an organic solvent can also be used as at least one of the first bonded object 11 and the second bonded object 12. Specifically, a member having a surface made of metal can be used as the first bonded object 11, and a dried paste containing metal fine particles and an organic solvent can be used as the second bonded object 12. When a dried paste is used, it is preferable to coat the paste on a supporting base material made of a metal such as copper and dry it to obtain a dried paste.

[0055] The bonded structure obtained by this manufacturing method is suitable for use in devices that handle large currents, such as in-vehicle electronic circuits and electronic circuits equipped with power devices.

[0056] With respect to the above-described embodiments, the present invention further discloses the following manufacturing method for a bonded structure, manufacturing method for a laminate, and bonding method. [1] A method for manufacturing a bonded structure in which a first bonded body and a second bonded body are bonded to each other via a bonding layer, comprising the steps of: applying a paste containing copper particles and an organic solvent to the first bonded body to form a coating film; a drying step for removing a part of the organic solvent contained in the coating film; a step of pressing the second object to be joined into the coating film so that a part of the second object to be joined is embedded in the coating film, thereby obtaining a laminate including the first object to be joined, the coating film, and the second object to be joined in this order; and heating the laminate. The average thickness of the coating film after the drying step and before the second bonded body is pressed into the coating film is defined as X (μm); When the average distance from the upper surface of the first bonded body to the lower surface of the second bonded body in the state where the laminate is obtained is Y (μm), A method for manufacturing a bonded structure, in which a pressing ratio P defined as 100-(Y / X×100) is 1.0 or more and 50 or less.

[0057] [2] The method for producing a bonded structure according to [1], wherein an average thickness X of the coating film after the drying step is 15 μm or more. [3] The paste contains the organic solvent in an amount of 3.0% by mass or more and 30.0% by mass or less, The method according to [1] or [2], wherein in the drying step, the coating film is dried so that the mass of the coating film is reduced by 3.0 mass% or more and 30.0 mass% or less. [4] The boiling point M of the organic solvent is 150° C. or more and 300° C. or less, The method according to any one of [1] to [3], wherein the heating temperature in the drying step is 20°C or higher and M°C or lower. [5] The manufacturing method according to any one of [1] to [4], wherein in the step of obtaining the laminate, a pressure of 0.004 MPa or more and 5 MPa or less is applied to the second object to be joined, so that the second object to be joined is pressed into the coating film.

[0058] [6] A method for manufacturing a laminate for bonding a first object to be bonded and a second object to be bonded, comprising the steps of: applying a paste containing copper particles and an organic solvent to the first bonded body to form a coating film; a drying step for removing a part of the organic solvent contained in the coating film; and pressing the second object to be joined into the coating film so that a part of the second object to be joined is embedded in the coating film, thereby obtaining a laminate including the first object to be joined, the coating film, and the second object to be joined in this order, The average thickness of the coating film after the drying step and before the second bonded body is pressed into the coating film is defined as X (μm); When the average distance from the upper surface of the first bonded body to the lower surface of the second bonded body in the state where the laminate is obtained is Y (μm), A method for producing a laminate, in which a pressing ratio P defined as 100-(Y / X×100) is 1.0 or more and 50 or less.

[0059] [7] A method for joining a first object to be joined and a second object to be joined, comprising the steps of: applying a paste containing copper particles and an organic solvent to the first bonded body to form a coating film; a drying step for removing a part of the organic solvent contained in the coating film; a step of pressing the second object to be joined into the coating film so that a part of the second object to be joined is embedded in the coating film, thereby obtaining a laminate including the first object to be joined, the coating film, and the second object to be joined in this order; and heating the laminate. The average thickness of the coating film after the drying step and before the second bonded body is pressed into the coating film is defined as X (μm); When the average distance from the upper surface of the first bonded body to the lower surface of the second bonded body in the state where the laminate is obtained is Y (μm), A joining method in which the pressing ratio P defined as 100-(Y / X×100) is 1.0 or more and 50 or less. EXAMPLES

[0060] 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. In addition, unless otherwise specified, "%" means "% by mass".

[0061] [Examples 1 and 2 and Comparative Examples 1 and 2] (1) Preparation of paste The following components were used for the paste: Copper powder 1: Spherical copper particles with a particle size of 0.1 to 0.2 μm 53% Copper powder 2: 23% flat copper particles with a particle size of 4.5 μm Organic solvent 1: Hexylene glycol (boiling point 198°C) 18.9% Organic solvent 2: Diethylene glycol (boiling point 244.3°C) 2.4% Organic solvent 3: Polyethylene glycol 300 (boiling point 250°C) 0.76% Reducing agent: Bis(2-hydroxyethyl)iminotris(hydroxymethyl)methane 1.9%

[0062] (2) Applying the paste to the first object to be joined A copper substrate (20 mm×20 mm, thickness 2 mm) was used as the first bonded body. A paste was printed on the substrate using a metal mask (6 mm×6 mm, thickness 100 μm) to form a rectangular wet coating film. The wet coating film was dried in an air atmosphere at 40°C for the time shown in Table 1 below to remove the organic solvent, and a dry coating film was obtained. The percentage of mass loss of the coating film due to removal of the organic solvent is also shown in the same table. The thickness of the dry coating film is also shown in the same table.

[0063] The mass loss rate of the wet coating film was measured by the following method. The mass of the copper substrate was measured with an electronic balance, and the mass of the substrate including the wet coating film after the paste printing was measured with an electronic balance. The mass of the substrate including the wet coating film was subtracted from the mass of the substrate before printing to obtain the mass of the wet coating film obtained by printing. The substrate including the wet coating film was then dried for a predetermined time, and the mass of the substrate including the dried coating film was measured with an electronic balance. The mass of the substrate including the dried coating film was subtracted from the mass of the copper substrate alone to obtain the mass of the wet coating film reduced by drying. The mass of the wet coating film reduced by drying was divided by the mass of the wet coating film obtained by printing, and multiplied by 100 to calculate the mass reduction ratio (%) of the wet coating film.

[0064] (3) Placing the second object to be bonded on the dried coating Assuming that the second bonded object was a model component of a semiconductor power device, an Ag-plated SiC chip (5mm x 5mm) was prepared. The Ag-plated surface of this SiC chip was placed at the center of the dried coating film using a chip mounter at a pressure of 0.004MPa. The average thickness B of the second bonded object is shown in Table 1.

[0065] (4) Formation of the laminate The SiC chip was pressed into the dried coating film by applying the pressure shown in Table 1 for 2 seconds from the side opposite the Ag-plated side of the SiC chip, forming a laminate. The pressing rate P at this time was calculated using the method described above. The results are shown in Table 1. In Comparative Example 1, the mass loss rate of the wet coating was small at 3.1%, so the dry coating was easily deformed, and when pressure was applied, a part of the dry coating bulged up onto the second bonded body. The thicknesses were measured in this state, and the indentation ratio P was calculated.

[0066] (5) Firing of the laminate The laminate was transferred to a firing furnace, and the laminate was pressurized to 9 MPa in a nitrogen atmosphere, then heated to 280° C. and held for 5 minutes to fire the coating film to form a bonding layer, thereby obtaining a bonded structure.

[0067] [Rating 1] In the examples and comparative examples, the laminate obtained in "(4) Formation of laminate" was turned upside down for one second, and the presence or absence of displacement and falling off of the SiC chips was visually observed. The results are shown in Table 1.

[0068] [Evaluation 2] In the examples and comparative examples, in order to confirm the bonding strength of the bonded structures obtained in "(5) sintering of the laminated body", the shear strength was measured by the following method. The shear strength (MPa) was calculated by dividing the breaking pressure (N) by the base area of ​​the SiC chip (mm 2 ) The results are shown in Table 1. Note that for Comparative Example 2, the SiC chip fell during the evaluation of displacement and falling off of the SiC chip, so this evaluation was not performed and is indicated in Table 1 as "-". ·Measuring device name: Condor Sigma (manufactured by XYZTEC) Load cell: 200kgf Share tool: Width 6.0mm, thickness 2.0mm, shaft 1 / 4 inch (Model number: T0S663060) Shear speed: 50μm / s -Shear height: 0.02 mm (zero point is the top of the coating printed on a 6 mm square)

[0069] [Table 1]

[0070] As is clear from the results shown in Table 1, by adopting the method of the embodiment, the SiC chip does not shift or fall off. It is also found that sufficient bonding strength can be obtained. [Industrial Applicability]

[0071] According to the present invention, there is provided a method for manufacturing a bonded structure capable of bonding objects to each other with a bonding material without causing the objects to shift in position or fall off.

Claims

1. A method for manufacturing a bonded structure in which a first bonded body and a second bonded body made of a semiconductor element are bonded to each other via a bonding layer, comprising: a step of applying a paste containing 60% by mass or more and 95% by mass or less of copper particles including flat copper particles or spherical copper particles and 5% by mass or more and 30% by mass or less of an organic solvent having a boiling point of 170° C. or more and 280° C. or less to form a coating film on the first bonded body; a drying step for removing a part of the organic solvent contained in the coating film; a step of pressing the second object to be joined into the coating film at a pressure of 0.05 MPa or more and 4 MPa or less so that a part of the second object to be joined is embedded in the coating film, thereby obtaining a laminate including the first object to be joined, the coating film, and the second object to be joined in this order; and heating the laminate. The average thickness of the coating film after the drying step and before the second bonded body is pressed into the coating film is defined as X (μm); When the average distance from the upper surface of the first bonded body to the lower surface of the second bonded body in the state where the laminate is obtained is Y (μm), A method for producing a joint structure, wherein a pressing ratio P defined as 100-(Y / X×100) is 1.0 or more and 50 or less.

2. The method for producing a joint structure according to claim 1 , wherein an average thickness X of the coating film after the drying step is 15 μm or more.

3. The paste contains the organic solvent in an amount of 3.0% by mass or more and 30.0% by mass or less, The method according to claim 1 or 2, wherein in the drying step, the coating film is dried so that a mass of the coating film is reduced by 3.0 mass % or more and 30.0 mass % or less.

4. The boiling point M of the organic solvent is 150° C. or more and 300° C. or less, The method according to claim 1 or 2, wherein the heating temperature in the drying step is 20° C. or higher and M° C. or lower.

5. A method for manufacturing a laminate for bonding a first bonded object and a second bonded object including a semiconductor element, comprising: a step of applying a paste containing 60% by mass or more and 95% by mass or less of copper particles including flat copper particles or spherical copper particles and 5% by mass or more and 30% by mass or less of an organic solvent having a boiling point of 170° C. or more and 280° C. or less to form a coating film on the first bonded body; a drying step for removing a part of the organic solvent contained in the coating film; and pressing the second object to be joined into the coating film at a pressure of 0.05 MPa or more and 4 MPa or less so that a part of the second object to be joined is embedded in the coating film, thereby obtaining a laminate including the first object to be joined, the coating film, and the second object to be joined in this order, The average thickness of the coating film after the drying step and before the second bonded body is pressed into the coating film is defined as X (μm); When the average distance from the upper surface of the first bonded body to the lower surface of the second bonded body in the state where the laminate is obtained is Y (μm), A method for producing a laminate, wherein a pressing ratio P defined by 100-(Y / X×100) is 1.0 or more and 50 or less.

6. A method for bonding a first object to be bonded to a second object to be bonded which is a semiconductor element, comprising: a step of applying a paste containing 60% by mass or more and 95% by mass or less of copper particles including flat copper particles or spherical copper particles and 5% by mass or more and 30% by mass or less of an organic solvent having a boiling point of 170° C. or more and 280° C. or less to form a coating film on the first bonded body; a drying step for removing a part of the organic solvent contained in the coating film; a step of pressing the second object to be joined into the coating film at a pressure of 0.05 MPa or more and 4 MPa or less so that a part of the second object to be joined is embedded in the coating film, thereby obtaining a laminate including the first object to be joined, the coating film, and the second object to be joined in this order; and heating the laminate. The average thickness of the coating film after the drying step and before the second bonded body is pressed into the coating film is defined as X (μm); When the average distance from the upper surface of the first bonded body to the lower surface of the second bonded body in the state where the laminate is obtained is Y (μm), A pressing ratio P defined as 100-(Y / X×100) is 1.0 or more and 50 or less.

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