Method for manufacturing joint structure, method for manufacturing laminate, and joint method

Abstract

A paste containing copper particles and an organic solvent is applied to a first member (11) to form a coating layer (13a); the organic solvent is partially removed from the coating layer (13a); pressing a second member (12) into the coating layer (13a) to partially embed the second member (12) in the coating layer (13a) to form a stack having the first member (11), the coating layer (13a), and the second member (12) in that order, and heating the stack (14). A press-in ratio P, defined as 100 - (Y / X × 100), is 1.0 to 50, wherein X is an average thickness of the coating layer (13a) in a state after the drying step and before pressing the second member (12) into the coating layer (13a); and Y represents an average distance from the upper surface (11b) of the first member (11) to the lower surface (12b) of the second member (12) in the state after forming the stack (14).

Description

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

[0001] The present invention relates to a method for manufacturing a bonded structure formed by bonding two objects to be bonded, and also to a method for manufacturing a laminate for obtaining the bonded structure and a method for bonding two 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, which limits the use of harmful chemicals, is used, and this paste is applied to an object by various coating means and then fired. For example, Patent Document 1 describes a method in which a conductive paste containing metal fine particles is applied to an electrode pattern, a semiconductor element is placed on top of it, and the semiconductor element is pressed down to apply pressure to the conductive paste while heating, thereby forming a sintered layer of metal fine particles.

[0004] JP 2016-127219 A

[0005] In the technology 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 vibrations, the semiconductor element may shift from the appropriate bonding position, which may cause problems in bonding between the semiconductor element and the electrode pattern. Therefore, an 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 or fall off.

[0006] The present invention provides 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 paste containing copper particles and an organic solvent to the first object to be bonded to form a coating film; drying the paste to remove a portion of the organic solvent contained in the coating film; pressing the second object to be bonded into the coating film so that a portion of the second object to be bonded is embedded in the coating film, thereby obtaining a laminate including the first object to be bonded, the coating film, and the second object to be bonded in that order; and heating the laminate, wherein, when the average thickness of the coating film after the drying step but before the second object to be bonded is pressed into the coating film is X (μm), and the average distance from the upper surface of the first object to be bonded to the lower surface of the second object to be bonded in the laminated state is Y (μm), a pressing ratio P defined by 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, the method comprising the steps of: applying a paste containing copper particles and an organic solvent to the first object to be bonded to form a coating film; a drying step of removing part of the organic solvent contained in the coating film; and a step of pressing the second object to be bonded into the coating film so that part of the second object to be bonded is embedded in the coating film, thereby obtaining a laminate including the first object to be bonded, the coating film, and the second object to be bonded in this order, wherein: when the average thickness of the coating film after the drying step but before the second object to be bonded is pressed into the coating film is X (μm), and the average distance from the upper surface of the first object to be bonded to the lower surface of the second object to be bonded in the obtained laminate is Y (μm), a pressing ratio P defined by 100 - (Y / X × 100) is 1.0 or more and 50 or less.

[0008] The present invention also provides a method for joining a first object to be joined and a second object to be joined, the method comprising the steps of: applying a paste containing copper particles and an organic solvent to the first object to be joined to form a coating film; a drying step of removing a portion of the organic solvent contained in the coating film; 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 in that order; and heating the laminate, wherein, after the drying step and before the second object to be joined is pressed into the coating film, an average thickness of the coating film is X (μm), and an average distance from the upper surface of the first object to be joined to the lower surface of the second object to be joined in the laminated state is Y (μm), a pressing ratio P defined by 100 - (Y / X × 100) is 1.0 or more and 50 or less.

[0009] 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). Fig. 2 is a schematic diagram showing an enlarged view of a main part of a laminate in which a second bonded body is pressed into a dried coating film. Figs. 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 / X x 100).

[0010] The present invention will be described below based on preferred embodiments. The present invention relates to a method for manufacturing 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 paste containing copper particles and an organic solvent to the first object to be bonded to form a coating film; (2) a drying step of removing a portion of the organic solvent contained in the coating film; (3) a step of pressing the second object to be bonded into the coating film so that a portion of the second object to be bonded is embedded in the coating film, thereby obtaining a laminate including the first object to be bonded, the coating film, and the second object to be bonded; and (4) a step of heating the laminate. Each step will be described below with reference to FIG. 1.

[0011] 1A and 1B are process diagrams showing one embodiment of a method for manufacturing a bonded structure of the present invention. First, as shown in FIG. 1A, a first object to be bonded 11 is prepared, and a paste is applied to one surface of the first object to be bonded 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. For example, the wet coating film 13a can be formed by screen printing, gravure printing, dispense printing, reverse coating, doctor blade, or the like.

[0012] 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 from the viewpoint of ensuring sufficient bonding strength, and is preferably 1000 μm or less, more preferably 800 μm or less, and even more preferably 500 μm or less from the viewpoint of facilitating smoothing of the coating film 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 utilizes white light interference. Examples of such a non-contact surface profiler include the ZeGage Pro manufactured by AMETEK. In this case, ZYGO Mx version 8.0.0 software is used, with a 1.0x zoom lens and a 1.4x objective lens. In the Basic Settings - Options tab of the software's MEASUREMENT tab, the scan length is selected as Extended, a value 100 μm or more greater than the thickness of the wet coating film 13a to be measured is entered, and the scan start position is selected as Bottom. The measurement field is set so that the first bonded body 11, which serves as the reference surface for the thickness, is partially 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 of view so that it partially includes the first bonded object 11, which serves as the reference surface, the rectangle R, described below, can be positioned within an appropriate range. After setting the field of view, the measurement is performed. After the measurement is completed, open the Level / Step item in the Investigation Tools section of the ANALYSIS tab in the software, and select Add Shapes (One Reference and One test Default rectangles). This displays the rectangle R for selecting the reference surface and the rectangle T for measuring the height from the reference surface. The rectangle R is positioned at the position where the first bonded object 11 is located, with each side measuring 500 μm × 500 μm or more, so as not to include the wet coating film 13 a. If the rectangle R includes any part other than the first bonded object 11, the reference will not be correctly determined. Since the rectangle R is a reference for calculating the thickness of the object to be measured, it must not include any part other than the first object to be bonded 11. Furthermore, by arranging the rectangle R to have a size of 500 μm × 500 μm or more, an average value that takes into account the surface roughness, etc. of the first object to be bonded 11 can be used as the reference, allowing for more accurate calculation of the thickness of the wet coating film 13a. Next, a rectangle T is arranged so that the vertical and horizontal sides of the rectangle T are located 500 μm inward from the vertical and horizontal sides of the wet coating film 13a to be measured.Thereafter, when Apply is clicked in the item labeled Level / Step, a numerical value is entered inside a rectangle T. This numerical value is set as 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 reliable joining of the first object to be joined 11 and the second object to be joined 12, it is preferable that the area to which the paste is applied 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 portion of the organic solvent contained in the wet coating film 13a, thereby obtaining a dried coating film 13b. Removing a portion of the organic solvent from the wet coating film 13a enhances the shape retention of the dried coating film 13b. From this perspective, 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% by mass or more, preferably 3.2% by mass or more, particularly 5.0% by mass or more, and particularly 7.0% by mass or more. On the other hand, if the organic solvent is removed excessively from the wet coating film 13a, the dried coating film 13b becomes hard, which may make it difficult to successfully press the second bonded object into the dried coating film 13b, as described below. From this perspective, 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% by mass or less, particularly 28.0% by 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] 1(b), from the viewpoint of successfully pressing the second object to be joined 12 described later into the dried coating film 13b, 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 easily obtaining a smooth coating film and preventing cracks in the coating film after drying, it is preferable to remove the organic solvent in the drying step so that the average thickness X of the dried coating film 13b is 800 μm or less, more preferably 500 μm or less, and even more preferably 400 μm or less. A method for measuring the average thickness X of the dried coating film 13b will be described later.

[0017] 1(b), the heating temperature of the wet coating film 13a is preferably set within an appropriate range from the viewpoint of adjusting the amount of evaporation of the organic solvent contained in the wet coating film 13a and thereby achieving an appropriate hardness for 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 will allow the second object to be joined 12, which will be described later, to be pressed into the dry coating film 13b successfully. When the drying step is carried out under atmospheric pressure, it is preferable to carry out heating for approximately 1 minute to 120 minutes.

[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, or 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, or heating in a heating furnace can be used.

[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 so 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 below, in this embodiment, the second object to be joined 12 is pressed into the dry coating film 13b so that a portion of the second object to be joined 12 is embedded in the dry coating film 13b. Therefore, it is not necessary to fix the dry coating film 13b and the second object to be joined 12 with a fixing agent. As described above, 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 is not required in the present invention, it is not prohibited to use 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 their derivatives, ketones, and carboxylic acids.

[0022] As described above, the dried coating film 13b retains some of the solvent, and therefore has shape retention and deformability. Therefore, by applying pressure to the second object to be joined 12 placed on the dried coating film 13b, the dried coating film 13b deforms, and the second object to be joined 12 is pressed into the dried coating film 13b so that a portion of the second object to be joined 12 is embedded in the dried coating film 13b. This forms a laminate 14 that is composed of the first object to be joined 11, the dried coating film 13b, and the second object to be joined 12 in this order. Note that the second object to be joined 12 may be pressed using, for example, a plate-shaped pressing jig 15 as shown in FIG. 1(d). Alternatively, the second object to be joined 12 may be directly pressed into the dry coating film 13b using the jig (not shown) used when placing the second object to be joined 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 is an enlarged view of a main portion of the second object to be joined 12, showing the state in which the second object to be joined 12 has been 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, a 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 fit between the dry coating film 13b and the side surface 12a of the lower region of the second object to be joined 12. This fixation 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. Specifically, 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 joined 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 unnecessarily thin. From this viewpoint, the value of the pressing ratio P is 50 or less, preferably 30 or less, and even more preferably 25 or less. P=100-(Y / X×100) (1)

[0025] In formula (1), X (μm) 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 joined 12 is pressed into the dry coating film 13b, and Y (μm) is 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 after the laminate 14 is obtained (see FIG. 2).

[0026] X and Y are measured by the method 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 using a chip mounter at a low pressure of 0.004 MPa, 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, for example, within 1 second, and the pressure is maintained for 0.4 seconds after reaching 0.004 MPa. 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. The average thickness X (μm) of the dry coating film 13b is then calculated by subtracting the average thickness B of the second bonded object 12 alone (see FIG. 2) from the average thickness A. 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 using a non-contact surface profiler in the same manner as for the wet coating film 13a. For example, the second bonded object 12 is placed on a reference surface, which is a SiC substrate with 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). Then, as shown in FIG. 3(b), a plate-shaped mass 20 with an area smaller than that of the second bonded object 12 is mounted on the second bonded object 12 using a chip mounter with a pressure of 0.8 MPa. The time from when the mass 20 contacts the second bonded object 12 until the applied pressure reaches 0.8 MPa is set to within 5 seconds, and the time after reaching 0.8 MPa is set to 2 seconds. Next, as shown in FIG. 3(c), the mass 20 alone is removed using suction tweezers to obtain the laminate 14. Then, an average distance D (see FIG. 2) from the upper surface 11b of the first object to be bonded 11 to the upper surface 12c of the second object to be bonded 12 in the laminate 14 is measured. The average distance D can be calculated using a method similar to the method for calculating the average thickness of the wet coating film 13a described above.Specifically, the average distance D (see FIG. 2 ) from the upper surface 12 c of the second object to be bonded 12 to the upper surface 11 b of the first object to be bonded 11 is calculated in the same manner as the calculation of the average thickness of the wet coating film 13 a, except that the rectangle T is positioned so that its vertical and horizontal sides are located at a position where the second object to be bonded 12 is present and 500 μm inward from the vertical and horizontal sides of the second object to be bonded 12 to be measured. The average distance Y from the upper surface 11 b of the first object to be bonded 11 to the lower surface 12 b of the second object to be bonded is calculated by subtracting the average thickness B of the second object to be bonded 12 only from the average distance D.

[0027] The value of the pressing rate P needs to be as described above, and the value of the average distance Y in formula (1), which is the definition formula of 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, from the viewpoint of reliably fixing the second bonded object 12 by the dried coating film 13 b and from the viewpoint of sufficiently increasing the bonding strength between the first bonded object 11 and the second bonded object 12.

[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 time for which the pressure is maintained after the target pressure of the second objects to be bonded 12 is reached is preferably 0.01 seconds or more, and more preferably 0.05 seconds or more, from the viewpoint of properly fixing the second objects to be bonded 12 by the dried coating film 13b and of sufficiently increasing the bonding strength between the first objects to be bonded 11 and the second objects to be bonded 12 in the heating step that is the next step. The time for which the pressure is maintained after the target pressure of the second objects to be bonded 12 is 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, when the second object to be bonded 12 is 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 heating 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.

[0031] The laminate 14 in which the second objects to be joined 12 are 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. While an external force such as vibration may be applied to the laminate 14 during the movement, the second objects to be joined 12 are properly fixed to the dry coating film 13b by the step of obtaining the laminate described above, displacement of the second objects to be joined 12 is suppressed. Note that the heating device described above may also serve as a device on which the second objects to be joined 12 are placed, 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 pressurizing the laminate 14, or while the laminate 14 is being pressed or not being 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 13 b and reliably increasing the bonding strength between the first body to be joined 11 and the second body to be joined 12.

[0033] When the heating of the laminate 14 is performed after pressurization or under pressure, 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, from the viewpoint of appropriately fixing the second object to be bonded 12 by the dried coating film 13b. The atmosphere in the heating step can be, for example, air atmosphere, inert gas atmosphere, or reducing atmosphere.

[0034] By employing such a fixing method, a desired bonded structure (not shown) can be obtained, in which the first and second bonded bodies are bonded together 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 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 adjusting agents.

[0037] The shape of the copper particles contained in the paste is not particularly limited, and both spherical and non-spherical ones can be used. Copper particles are considered spherical when 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, where S is the area of ​​the two-dimensional projection image of the primary particle, and L is the perimeter, and the formula is 4πS / L. ２ The copper particles being non-spherical means that the circularity coefficient is less than 0.85.

[0038] 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 perpendicular to these plate surfaces. The plate surfaces and side surfaces may each independently be flat, curved, or irregular.

[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. Furthermore, 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. 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.

[0041] The particle size of the copper particles is preferably greater than 0.1 μm, more preferably 0.11 μm or more, and even more preferably 0.12 μm or more. On the other hand, 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.

[0042] 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.

[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. By having the particle size 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 higher and 300°C or lower, particularly 160°C or higher and 290°C or lower, and particularly 170°C or higher and 280°C or lower. 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 incorporating an organic solvent having a boiling point within the above temperature range into the paste, it becomes easier to adjust the amount of evaporation of the organic solvent contained in the wet coating film 13a, making it easier to achieve an appropriate hardness for the dried coating film 13b. When the paste contains multiple types of organic solvents, it is preferable that at least one organic solvent has a boiling point within the above temperature range, and it is particularly preferable that all 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 modifier for adjusting various properties. Examples of modifiers include reducing agents, viscosity modifiers, and surface tension modifiers. Reducing agents that promote sintering of copper particles are preferred, such as 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, and the like. Viscosity modifiers that adjust the viscosity of the paste, preferably within the above-mentioned viscosity range, are preferred, such as ketones, esters, alcohols, glycols, hydrocarbons, and polymers. Surface tension modifiers that adjust the surface tension of the wet coating film 13a are preferred, such as 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 －１ In this case, the viscosity is preferably 10 Pa·s or more and 200 Pa·s or less, and more preferably 15 Pa·s or more and 200 Pa·s or less. The viscosity of the paste can be measured using a rheometer MARS III manufactured by Thermo Scientific. The measurement conditions for the viscosity of the paste are as follows: Measurement mode: Shear rate dependency measurement Sensor: Parallel type (Φ20 mm) Measurement temperature: 25°C Gap: 0.300 mm Shear rate: 0.05 to 120.01 s －１ Measurement time: 2 minutes

[0050] 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.

[0051] 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.

[0052] Specific examples of the first bonded body 11 and the second bonded body 12 include, independently of one another, spacers or heat sinks made of the above-mentioned metals, semiconductor elements, and substrates having at least one of the above-mentioned metals on their surfaces. Examples of the substrate include an insulating substrate having a metal layer such as copper on the surface of a ceramic or aluminum nitride plate. When semiconductor elements are used as the first bonded body 11 and / or the second bonded body 12, the semiconductor elements contain 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 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 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 paste containing metal fine particles and an organic solvent can be used as the second body to be bonded 12. When a dried paste is used, it is preferable to coat the paste on a support base 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 electronic circuits for automobiles and electronic circuits equipped with power devices.

[0056] In relation to the above-described embodiments, the present invention further discloses the following manufacturing method of a bonded structure, manufacturing method of a laminate, and bonding method. [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: a step of applying a paste containing copper particles and an organic solvent to the first object to be bonded to form a coating film; a drying step of removing a portion of the organic solvent contained in the coating film; a step of pressing the second object to be bonded into the coating film so that a portion of the second object to be bonded is embedded in the coating film, thereby obtaining a stacked body including the first object to be bonded, the coating film, and the second object to be bonded in that order; and a step of heating the stacked body, wherein, after the drying step and before the second object to be bonded is pressed into the coating film, an average thickness of the coating film after the drying step but before the second object to be bonded is pressed into the coating film is X (μm), and an average distance from the upper surface of the first object to be bonded to the lower surface of the second object to be bonded in the stacked body is Y (μm), a pressing ratio P defined by 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 the average thickness X of the coating film after the drying step is 15 μm or more. [3] The method for producing a bonded structure according to [1] or [2], wherein the paste contains 3.0 mass % or more and 30.0 mass % or less of the organic solvent, and wherein, in the drying step, the coating film is dried so that the mass of the coating film decreases by 3.0 mass % or more and 30.0 mass % or less. [4] The method for producing a bonded structure according to any one of [1] to [3], wherein the boiling point M of the organic solvent is 150° C. or more and 300° C. or less, and the heating temperature in the drying step is 20° C. or more and M° C. or less. [5] The method for producing a bonded structure 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 bonded body to press the second bonded body 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: a step of applying a paste containing copper particles and an organic solvent to the first object to be bonded to form a coating film; a drying step of removing a portion of the organic solvent contained in the coating film; and a step of pressing the second object to be bonded into the coating film so that a portion of the second object to be bonded is embedded in the coating film, thereby obtaining a laminate including the first object to be bonded, the coating film, and the second object to be bonded in this order, wherein, after the drying step and before the second object to be bonded is pressed into the coating film, an average thickness of the coating film after the drying step but before the second object to be bonded is pressed into the coating film is X (μm), and an average distance from the upper surface of the first object to be bonded to the lower surface of the second object to be bonded after the laminate is obtained is Y (μm), a pressing ratio P defined by 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: a step of applying a paste containing copper particles and an organic solvent to the first object to be joined to form a coating film; a drying step of removing a portion 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 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 in this order; and a step of heating the laminate, wherein, after the drying step and before the second object to be joined is pressed into the coating film, an average thickness of the coating film after the drying step but before the second object to be joined is pressed into the coating film is X (μm), and an average distance from the upper surface of the first object to be joined to the lower surface of the second object to be joined after the laminate is obtained is Y (μm), a pressing ratio P defined by 100 - (Y / X × 100) is 1.0 or more and 50 or less.

[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. Furthermore, unless otherwise specified, "%" means "% by mass."

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

[0062] (2) Application of the paste to the first object to be bonded A copper substrate (20 mm × 20 mm, thickness 2 mm) was used as the first object to be bonded. The paste was printed on this 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 the air at 40°C for the time shown in Table 1 below to remove the organic solvent, thereby obtaining a dry coating film. 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 using the following method. The mass of the copper substrate was measured using an electronic balance, and then the mass of the substrate including the wet coating film after paste printing 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 dried coating film from the mass of the copper substrate alone. 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.

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

[0065] (4) Formation of a 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 surface of the SiC chip, thereby forming a laminate. The value of the pressing rate P at this time was calculated using the method described above. The results are shown in Table 1. For Comparative Example 1, the mass loss rate of the wet coating film was small at 3.1%, so the dried coating film was easily deformed, and when pressure was applied, part of the dried coating film bulged up onto the second bonded body. The thicknesses of each material were measured in this state, and the pressing rate P was calculated.

[0066] (5) Firing of Laminate The laminate was moved to a firing furnace, and the laminate was pressurized to 9 MPa in a nitrogen atmosphere, and 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] [Evaluation 1] In the examples and comparative examples, the stacks obtained in "(4) Formation of stack" were 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, the shear strength was measured by the following method to confirm the bonding strength of the bonded structures obtained in "(5) Firing of the laminated body." 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. 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 as "-" in Table 1. - 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 is the top of the 6 mm square printed coating film)

[0069]

[0070] As is clear from the results shown in Table 1, when the method of the example is adopted, the SiC chip does not shift in position or fall off, and sufficient bonding strength is obtained.

[0071] According to the present invention, there is provided a method for manufacturing a bonded structure that can bond objects to each other with a bonding material without causing displacement or detachment of the objects to be bonded.

Claims

1. A method for producing 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 paste containing copper particles and an organic solvent to the first object to be bonded to form a coating film; drying the paste to remove a portion of the organic solvent contained in the coating film; pressing the second object to be bonded into the coating film so that a portion of the second object to be bonded is embedded in the coating film to obtain a laminate comprising the first object to be bonded, the coating film, and the second object to be bonded in that order; and heating the laminate, wherein: after the drying step, an average thickness of the coating film before the second object to be bonded is pressed into the coating film is X (μm); and when an average distance from an upper surface of the first object to be bonded to a lower surface of the second object to be bonded in the laminate is Y (μm), a pressing ratio P defined by 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 the average thickness X of the coating film after the drying step is 15 μm or more.

3. The manufacturing method described in claim 1 or 2, wherein the paste contains 3.0 mass % or more and 30.0 mass % or less of the organic solvent, and 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 method according to claim 1 or 2, wherein the boiling point M of the organic solvent is 150° C. or higher and 300° C. or lower, and the heating temperature in the drying step is 20° C. or higher and M° C. or lower.

5. A manufacturing method according to claim 1 or 2, 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, thereby pressing the second object to be joined into the coating film.

6. A method for manufacturing a laminate for bonding a first object to be bonded and a second object to be bonded, comprising: a step of applying a paste containing copper particles and an organic solvent to the first object to be bonded to form a coating film; a drying step of removing a portion of the organic solvent contained in the coating film; and a step of pressing the second object to be bonded into the coating film so that a portion of the second object to be bonded is embedded in the coating film to obtain a laminate including the first object to be bonded, the coating film, and the second object to be bonded in that order, wherein: after the drying step, an average thickness of the coating film before the second object to be bonded is pressed into the coating film is X (μm); and after the laminate is obtained, an average distance from the upper surface of the first object to be bonded to the lower surface of the second object to be bonded is Y (μm), a pressing ratio P defined as 100-(Y / X×100) is 1.0 or more and 50 or less.

7. A method for bonding a first object to be bonded and a second object to be bonded, comprising: a step of applying a paste containing copper particles and an organic solvent to the first object to be bonded to form a coating film; a drying step of removing a portion of the organic solvent contained in the coating film; a step of pressing the second object to be bonded into the coating film so that a portion of the second object to be bonded is embedded in the coating film to obtain a laminate including the first object to be bonded, the coating film, and the second object to be bonded in that order; and a step of heating the laminate, wherein, after the drying step, an average thickness of the coating film before the second object to be bonded is pressed into the coating film is X (μm), and an average distance from the upper surface of the first object to be bonded to the lower surface of the second object to be bonded in the state in which 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.