Method for manufacturing copper / ceramic assembly, and method for manufacturing insulated circuit board

Abstract

To provide a method for manufacturing a copper / ceramic assembly capable of manufacturing a copper / ceramic assembly which can suppress generation of solder stains on the surface of a copper plate, can suppress hardening of a joint layer, and is excellent in joint reliability.SOLUTION: A method for manufacturing a copper / ceramic assembly includes a joint material arrangement step of arranging a joint material between a copper member and a ceramic member, a lamination step of laminating the copper member and the ceramic member through the joint material, and a joint step of heating the copper member and the ceramic member laminated through the joint material under vacuum atmosphere, in a state in which the members are pressurized in a lamination direction, and joining the members, wherein the joint material arrangement step arranges a first joint material containing low oxygen Ag powder having oxygen concentration of less than 0.3 mass% and active metal powder, between the copper member and the ceramic member, and arranges a second joint material containing high oxygen Ag powder having oxygen concentration of 0.3 mass% or more and active metal powder, so as to surround the periphery of the first joint material.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a copper / ceramic bonded body formed by bonding a copper member made of copper or a copper alloy to a ceramic member, and a method for producing an insulated circuit board formed by bonding a copper or copper alloy plate to a ceramic substrate. [Background technology]

[0002] In power modules, LED modules, and thermoelectric modules, a power semiconductor element, an LED element, and a thermoelectric element are bonded to an insulating circuit board having a circuit layer made of a conductive material formed on one side of an insulating layer. For example, power semiconductor elements for controlling large amounts of power, which are used to control wind power generation, electric vehicles, hybrid vehicles, etc., generate a large amount of heat during operation, and therefore, as a substrate for mounting these elements, an insulated circuit board has been widely used, which includes a ceramic substrate and a circuit layer formed by bonding a metal plate with excellent conductivity to one surface of the ceramic substrate. Note that an insulated circuit board in which a metal layer is formed by bonding a metal plate to the other surface of the ceramic substrate is also provided.

[0003] For example, Patent Document 1 proposes a ceramic circuit board in which the first and second metal plates constituting the circuit layer and metal layer are copper plates, and the copper plates are directly bonded to a ceramic substrate by the DBC method. In this DBC method, a eutectic reaction between copper and copper oxide is utilized to generate a liquid phase at the interface between the copper plate and the ceramic substrate, thereby bonding the copper plate and the ceramic substrate.

[0004] Furthermore, Patent Documents 2 and 3 propose a power module substrate in which a circuit layer and a metal layer are formed by bonding copper plates to one surface and the other surface of a ceramic substrate. In Patent Document 2, a ceramic substrate and a copper plate are joined together using an Ag-Cu-Ti brazing filler metal. In Patent Document 3, a ceramic substrate and a copper plate are joined together using an Ag—Ti brazing filler metal. In Patent Documents 2 and 3, a brazing filler metal containing Ti, an active metal, is used, which improves the wettability of the molten brazing filler metal with the ceramic substrate, resulting in good bonding between the ceramic substrate and the copper plate. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 01-251781 [Patent Document 2] Patent No. 3211856 [Patent Document 3] Patent No. 5757359 Summary of the Invention [Problem to be solved by the invention]

[0006] When joining a copper plate to a ceramic substrate using an Ag-Cu-Ti or Ag-Ti brazing filler metal, the liquid phase bonding material may seep out from the bonding interface. For example, when joining copper pieces punched into a specific shape and arranged in a circuit pattern, the fluidity of the exuded bonding material may cause it to wet and spread to the copper plate surface, resulting in solder stains. The occurrence of solder stains may adversely affect plating and the mounting of semiconductor elements.

[0007] Furthermore, when a copper plate and a ceramic substrate are joined using an Ag-Cu-Ti based brazing filler metal or an Ag-Ti based brazing filler metal, if a large amount of Ti compounds is present in the joining layer, cracks may occur in the ceramic substrate or the ceramic substrate and the copper plate may peel off when subjected to a thermal cycle, which could make it impossible to ensure joining reliability.

[0008] The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a method for manufacturing a copper / ceramic bonded body, which can suppress the occurrence of solder stains on the copper plate surface due to the seepage and flow of bonding material, and which can produce a copper / ceramic bonded body with excellent bonding reliability, and a method for manufacturing an insulated circuit board. [Means for solving the problem]

[0009] In order to solve these problems and achieve the above object, the present inventors have conducted extensive research and have come to the following findings. When the oxygen concentration of the Ag powder contained in the joining material is high, the active metal (Ti) in the joining material reacts with oxygen to form compounds, which reduces the fluidity of the liquid phase, inhibits the joining material from seeping out, and inhibits solder staining on the copper plate surface. However, the formed compounds reduce the joining rate after thermal cycling. On the other hand, when the oxygen concentration of the Ag powder contained in the bonding material is low, the fluidity of the liquid phase is high, which makes it easier for the bonding material to seep out and solder stains to occur on the copper plate surface, but this can prevent a decrease in the bonding rate after thermal cycling. In Ag-Cu-Ti and Ag-Ti brazing filler metals, a liquid phase is generated when the Cu-Ag eutectic melts. However, if the oxygen concentration of the Cu powder or Ag powder is high, the melting points of the powders decrease slightly, so the temperature at which the Cu-Ag liquid phase is generated may remain the same or may decrease slightly.

[0010] The present invention has been made based on the above-mentioned findings. A method for producing a copper / ceramic joined body of the present invention is a method for producing a copper / ceramic joined body obtained by joining a copper member made of copper or a copper alloy and a ceramic member, the method comprising: a bonding material providing step of providing a bonding material between the copper member and the ceramic member, a stacking step of stacking the copper member and the ceramic member with the bonding material interposed therebetween, and a joining step of heat-treating the stacked copper member and the ceramic member with the bonding material interposed therebetween in a vacuum atmosphere while applying pressure in the stacking direction, wherein the bonding material providing step includes preparing, as the bonding materials, a first bonding material containing low-oxygen Ag powder and active metal powder having an oxygen concentration of less than 0.3 mass%, and a second bonding material containing high-oxygen Ag powder and active metal powder having an oxygen concentration of 0.3 mass% or more, and disposing the first bonding material between the copper member and the ceramic member, and the second bonding material so as to surround the first bonding material.

[0011] According to this method for manufacturing a copper / ceramic bonded body, the bonding material disposing step includes providing a first bonding material containing low-oxygen Ag powder and active metal powder, and a second bonding material containing high-oxygen Ag powder and active metal powder, and the first bonding material is disposed between the copper member and the ceramic member, and the second bonding material is disposed so as to surround the first bonding material. Therefore, the liquid phase of the second bonding material containing the high-oxygen Ag powder generates a large amount of active metal compounds, reducing fluidity, thereby preventing solder stains on the copper sheet surface due to fluidity of the bonding material. Furthermore, the liquid phase of the first bonding material containing the low-oxygen Ag powder reduces the generation of active metal compounds, thereby preventing a decrease in bonding rate after thermal cycling.

[0012] Here, in the manufacturing method of the copper / ceramic bonded body of the present invention, in the bonding material disposing step, it is preferable that the ratio A / B of the disposing width A of the first bonding material to the disposing width B of the second bonding material is in the range of 2 or more and 12 or less, and the disposing width B of the second bonding material is 1 mm or more. In this case, in the bonding material disposing step, the ratio A / B of the width A of the first bonding material to the width B of the second bonding material is set to 2 or more, so that the amount of the first bonding material containing low-oxygen Ag powder to be disposed is ensured, the excessive generation of compounds of active metal and oxygen can be further suppressed, and the decrease in the bonding rate after thermal cycle loading can be further suppressed. On the other hand, the ratio A / B of the width A of the first bonding material to the width B of the second bonding material is set to 12 or less, and the arrangement width B of the second bonding material is set to 1 mm or more, so that the arrangement amount of the second bonding material containing high-oxygen Ag powder is ensured, the fluidity of the liquid phase can be reliably reduced, and the occurrence of solder stains on the copper plate surface due to the seepage of the bonding material can be further suppressed.

[0013] The method for manufacturing an insulated circuit board of the present invention is a method for manufacturing an insulated circuit board in which a copper plate made of copper or a copper alloy and a ceramic substrate are bonded together, and includes a bonding material disposing step of disposing a bonding material between the copper plate and the ceramic substrate, a laminating step of stacking the copper plate and the ceramic substrate with the bonding material interposed between them, and a bonding step of heat-treating the copper plate and the ceramic substrate, which have been stacked with the bonding material interposed between them, in a vacuum atmosphere while applying pressure in the laminating direction. In the bonding material disposing step, a first bonding material containing low-oxygen Ag powder and active metal powder having an oxygen concentration of less than 0.3 mass%, and a second bonding material containing high-oxygen Ag powder and active metal powder having an oxygen concentration of 0.3 mass% or more are prepared as the bonding materials, and the first bonding material is disposed between the copper plate and the ceramic substrate, and the second bonding material is disposed so as to surround the first bonding material.

[0014] In this method for manufacturing an insulated circuit board, the bonding material disposing step includes providing a first bonding material containing low-oxygen Ag powder and active metal powder, and a second bonding material containing high-oxygen Ag powder and active metal powder, and disposing the first bonding material between the copper member and the ceramic member and the second bonding material surrounding the first bonding material. The liquid phase of the second bonding material containing the high-oxygen Ag powder generates a large amount of active metal compounds, reducing fluidity and preventing solder stains on the copper plate surface due to bleeding of the bonding material. Furthermore, the liquid phase of the first bonding material containing the low-oxygen Ag powder reduces the generation of active metal compounds, preventing a decrease in bonding rate after thermal cycling.

[0015] Here, in the method for manufacturing an insulating circuit board of the present invention, in the bonding material disposing step, it is preferable that the ratio A / B of the disposing width A of the first bonding material to the disposing width B of the second bonding material is within the range of 2 to 12, and the disposing width B of the second bonding material is 1 mm or more. In this case, in the bonding material disposing step, the ratio A / B of the width A of the first bonding material to the width B of the second bonding material is set to 2 or more, so that the amount of the first bonding material containing low-oxygen Ag powder to be disposed is ensured, the excessive generation of compounds of active metal and oxygen can be further suppressed, and the decrease in the bonding rate after thermal cycle loading can be further suppressed. On the other hand, the ratio A / B of the width A of the first bonding material to the width B of the second bonding material is set to 12 or less, and the arrangement width B of the second bonding material is set to 1 mm or more, so that the arrangement amount of the second bonding material containing high-oxygen Ag powder is ensured, the fluidity of the liquid phase can be reliably reduced, and the occurrence of solder stains on the copper plate surface due to the seepage and flow of the bonding material can be further suppressed. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide a method for manufacturing a copper / ceramic bonded body that can suppress the occurrence of solder stains on the copper plate surface due to the seepage and flow of the bonding material and that can produce a copper / ceramic bonded body with excellent bonding reliability, and a method for manufacturing an insulated circuit board. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a schematic explanatory diagram of a power module using an insulating circuit board (copper / ceramic bonded body) according to an embodiment of the present invention. [Figure 2] FIG. 2 is an enlarged explanatory view of an insulating circuit board (copper / ceramic bonded body) according to an embodiment of the present invention. [Figure 3] FIG. 1 is a flow diagram showing a method for producing an insulating circuit board (copper / ceramic bonded body) according to an embodiment of the present invention. [Figure 4] 1A to 1C are explanatory diagrams showing a method for producing an insulating circuit board (copper / ceramic bonded body) according to an embodiment of the present invention. [Figure 5] FIG. 2 is an explanatory diagram of a bonding material providing step in the method for producing an insulated circuit board (copper / ceramic bonded body) according to an embodiment of the present invention. [Figure 6] FIG. 2 is an explanatory diagram of a bonding material providing step in the method for producing an insulated circuit board (copper / ceramic bonded body) according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the following embodiments are specifically described to provide a better understanding of the gist of the invention, and do not limit the present invention unless otherwise specified. Furthermore, the drawings used in the following description may show essential parts enlarged for convenience in order to make the features of the present invention easier to understand, and the dimensional proportions of each component may not necessarily be the same as those in reality.

[0019] The copper / ceramic bonded body of this embodiment is an insulating circuit board 10 formed by bonding a ceramic substrate 11 as a ceramic member made of ceramic to a copper plate 22 (circuit layer 12) and a copper plate 23 (metal layer 13) as copper members made of copper or a copper alloy. Fig. 1 shows a power module 1 including the insulating circuit board 10 of this embodiment.

[0020] This power module 1 includes an insulating circuit board 10 on which a circuit layer 12 and a metal layer 13 are arranged, a semiconductor element 3 joined to one surface (the upper surface in FIG. 1) of the circuit layer 12 via a solder layer 2, and a heat sink 31 arranged on the other side (the lower side in FIG. 1) of the metal layer 13.

[0021] The semiconductor element 3 is made of a semiconductor material such as Si, etc. The semiconductor element 3 and the circuit layer 12 are joined via the solder layer 2. The solder layer 2 is made of, for example, an Sn--Ag based, Sn--In based, or Sn--Ag--Cu based solder material.

[0022] The heat sink 31 is used to dissipate heat on the insulating circuit board 10 side. The heat sink 31 is made of aluminum or an aluminum alloy with good thermal conductivity, and in this embodiment, it is made of A6063 alloy. The thickness of the heat sink 31 is set within the range of 3 mm to 10 mm. The heat sink 31 and the metal layer 13 of the insulating circuit board 10 are bonded together by solid-state diffusion bonding.

[0023] As shown in Figures 1 and 2, the insulating circuit board 10 in this embodiment includes a ceramic substrate 11, a circuit layer 12 disposed on one surface (the upper surface in Figure 1) of the ceramic substrate 11, and a metal layer 13 disposed on the other surface (the lower surface in Figure 1) of the ceramic substrate 11.

[0024] The ceramic substrate 11 prevents electrical connection between the circuit layer 12 and the metal layer 13 and is made of ceramics with excellent insulating properties. Aluminum nitride, silicon nitride, alumina, etc. can be used as the ceramic substrate 11. In this embodiment, the ceramic substrate 11 is made of silicon nitride. The thickness of the ceramic substrate 11 is set within a range of 0.2 mm to 1.5 mm, and in this embodiment, it is set to 0.32 mm.

[0025] As shown in Fig. 4, the circuit layer 12 is formed by bonding a copper plate 22 (copper member) made of copper or a copper alloy to one surface of the ceramic substrate 11. As the copper or copper alloy, oxygen-free copper, tough pitch copper, or the like can be used. In this embodiment, the copper plate 22 constituting the circuit layer 12 is punched out from a rolled sheet of oxygen-free copper. A circuit pattern is formed on this circuit layer 12 by bonding the above-mentioned copper plate 22 in a pattern, and one surface (the upper surface in FIG. 1) serves as a mounting surface on which the semiconductor element 3 is mounted. The thickness of the circuit layer 12 is set within a range of 0.1 mm to 3.0 mm, and is set to 0.8 mm in this embodiment.

[0026] As shown in FIG. 4, the metal layer 13 is formed by joining a copper plate 23 made of copper or a copper alloy to the other surface (the lower surface in FIG. 4) of the ceramic substrate 11. In this embodiment, the metal layer 13 is formed by bonding a copper plate 23 made of a rolled sheet of oxygen-free copper to the ceramic substrate 11. The thickness of the copper plate 23 that will become the metal layer 13 is set within the range of 0.1 mm to 2.0 mm, and in this embodiment, it is set to 0.8 mm.

[0027] As shown in FIG. 2, a bonding layer 15 is formed at the bonding interface between the circuit layer 12 and the ceramic substrate 11 and between the metal layer 13 and the ceramic substrate 11. The bonding layer 15 is formed by melting and solidifying a bonding material 25, which will be described later.

[0028] A method for manufacturing the insulating circuit board 10 of this embodiment will be described below with reference to FIGS.

[0029] (Joint material placement process S01) 4, an Ag-Ti paste containing Ag powder and active metal powder (Ti in this embodiment) is printed between the copper plate 22 that will become the circuit layer 12 and the ceramic substrate 11, and between the copper plate 23 that will become the metal layer 13 and the ceramic substrate 11, to serve as the bonding material 25. As the solvent for the paste, a general solvent such as α-terpineol can be used, and a resin such as a cellulose resin or an acrylic resin may also be added.

[0030] At this time, as the bonding material 25, a first bonding material 25A containing low-oxygen Ag powder with an oxygen concentration of less than 0.3 mass% and active metal powder, and a second bonding material 25B containing high-oxygen Ag powder with an oxygen concentration of 0.3 mass% or more and active metal powder are prepared. Then, as shown in FIG. 5, a first bonding material 25A is disposed between the copper plates 22, 23 and the ceramic substrate 11, and a second bonding material 25B is disposed so as to surround the periphery of the first bonding material 25A.

[0031] High-oxygen Ag powder can be produced, for example, by a wet reduction method. Specifically, Ag powder can be obtained by adding a reducing agent to a silver nitrate solution and reducing and precipitating silver. During this process, organic matter is incorporated into the Ag powder, increasing the oxygen concentration. The amount of organic matter incorporated into the Ag powder can be adjusted by the amount of reducing agent added, making it possible to control the oxygen concentration. Here, the lower limit of the oxygen concentration in the oxygen-rich Ag powder is preferably 0.4 mass% or more, more preferably 0.5 mass% or more, and even more preferably 0.6 mass% or more. On the other hand, the upper limit of the oxygen concentration in the oxygen-rich Ag powder is preferably 1.5 mass% or less, more preferably 1.2 mass% or less, and even more preferably 1.0 mass% or less. The average particle size of the oxygen-rich Ag powder is preferably in the range of 0.5 μm to 20 μm.

[0032] Low-oxygen Ag powder can be produced, for example, by gas atomization. Specifically, Ag powder can be produced by melting silver and blowing it out of a nozzle using an inert gas. The use of an inert gas prevents oxygen from being mixed into the Ag powder, making it possible to obtain Ag powder with a low oxygen concentration. Here, there is no particular lower limit for the oxygen concentration in the low-oxygen Ag powder. On the other hand, the upper limit of the oxygen concentration in the low-oxygen Ag powder is preferably 0.25 mass% or less, more preferably 0.2 mass% or less, and even more preferably 0.1 mass% or less. The average particle size of the low-oxygen Ag powder is preferably in the range of 0.5 μm to 20 μm.

[0033] The active metal powder contained in the first bonding material 25A and the second bonding material 25B may be one or more powders selected from the group consisting of Ti, Zr, Nb, and Hf. Alternatively, hydrides of these metals may also be used. The average particle size of the active metal powder is preferably in the range of 1 μm to 20 μm.

[0034] Here, in this embodiment, as shown in Figures 6(a) and 6(b), in the bonding material disposition process S01, it is preferable that the ratio A / B of the disposition width A of the first bonding material 25A to the disposition width B of the second bonding material 25B is in the range of 2 or more and 12 or less, and that the disposition width B of the second bonding material 25B is 1 mm or more. As shown in FIG. 6(b), the outer peripheral edge of the second bonding material 25B may protrude outward from the copper plates 22 and 23 to be bonded, but the protrusion amount L is preferably set to 200 μm or less.

[0035] Here, by setting the ratio A / B of the arrangement width A of the first bonding material containing low-oxygen Ag powder to the arrangement width B of the second bonding material 25B containing high-oxygen Ag powder to 2 or more, it is possible to suppress excessive generation of active metal compounds. On the other hand, by setting the ratio A / B of the arrangement width A of the first bonding material containing low-oxygen Ag powder to the arrangement width B of the second bonding material 25B containing high-oxygen Ag powder to 12 or less and setting the arrangement width B of the second bonding material 25B to 1 mm or more, it is possible to sufficiently generate active metal compounds and reliably reduce the fluidity of the liquid phase.

[0036] The lower limit of the ratio A / B of the arrangement width A of the first bonding material containing low-oxygen Ag powder to the arrangement width B of the second bonding material 25B containing high-oxygen Ag powder is more preferably 3 or more, and even more preferably 4 or more. On the other hand, the upper limit of the ratio A / B of the arrangement width A of the first bonding material containing low-oxygen Ag powder to the arrangement width B of the second bonding material 25B containing high-oxygen Ag powder is more preferably 10 or less. Furthermore, the arrangement width B of the second bonding material 25B is preferably set in accordance with the width of the copper plates 22, 23 to be bonded, and is preferably 1.5 mm or more, and more preferably 2 mm or more.

[0037] (Lamination process S02) Next, a copper plate 22 is laminated on one surface (the upper surface in FIG. 4) of the ceramic substrate 11 with a bonding material 25 interposed therebetween. Furthermore, a copper plate 23 is laminated on the other surface (the lower surface in FIG. 4) of the ceramic substrate 11 with a bonding material 25 interposed therebetween.

[0038] (Joining process S03) Next, the copper plate 22, the bonding material 25, the ceramic substrate 11, the bonding material 25, and the copper plate 23 are loaded into a vacuum heating furnace and heated while being pressurized in the stacking direction (pressure of 0.01 MPa or more and 3.5 MPa or less) to melt the bonding material 25. If necessary, the bonding material may be dried and degreased. The molten bonding material 25 is then solidified to form a bonding layer 15, bonding the copper plate 22 to the ceramic substrate 11 and the ceramic substrate 11 to the copper plate 23. In this embodiment, the pressure inside the vacuum heating furnace is 10 -6 Pa or more 10 -3 The pressure is set to a range of 790°C to 850°C, and the holding time at the heating temperature is set to a range of 1 minute to 60 minutes.

[0039] In this bonding step S03, a liquid phase is generated at the interface between the copper plates 22, 23 and the ceramic substrate 11. However, since the second bonding material having high-oxygen Ag powder is disposed so as to surround the periphery of the first bonding material having low-oxygen Ag powder, in the liquid phase formed around the bonding surface, the active metal (Ti) and oxygen (O) contained in the bonding material 25 react with each other to generate Ti compounds, and the fluidity of the liquid phase decreases. This makes it possible to suppress the bleeding of the bonding material. Moreover, since the first bonding material 25A containing low-oxygen Ag powder is disposed, excessive generation of Ti compounds can be suppressed, and a decrease in the bonding rate after thermal cycle loading can be suppressed.

[0040] In this manner, the copper plate 22, the ceramic substrate 11, and the copper plate 23 are joined together to produce the insulating circuit board 10 of this embodiment.

[0041] (Heat sink bonding process S04) Next, a heat sink 31 is laminated on the other side of the metal layer 13 of the insulating circuit board 10, and the heat sink laminate formed by laminating the insulating circuit board 10 and the heat sink 31 is loaded into a vacuum heating furnace while being pressurized in the lamination direction using a pressure device, and is maintained at a heating temperature below the eutectic temperature of aluminum and copper, thereby solid-state diffusion bonding the metal layer 13 and the heat sink 31.

[0042] (Semiconductor element bonding process S05) Next, the semiconductor element 3 is joined to one surface of the circuit layer 12 of the insulating circuit board 10 by soldering. Through the above steps, the power module 1 shown in FIG. 1 is manufactured.

[0043] In the manufacturing method of the insulated circuit board (copper / ceramic bonded body) of this embodiment configured as described above, in bonding material disposing step S01, first bonding material 25A containing low-oxygen Ag powder and active metal powder having an oxygen concentration of less than 0.3 mass% and second bonding material 25B containing high-oxygen Ag powder and active metal powder having an oxygen concentration of 0.3 mass% or more are prepared as bonding materials 25. First bonding material 25A is disposed between copper plates 22, 23 and ceramic substrate 11, and second bonding material 25B is disposed so as to surround first bonding material 25A. Therefore, the liquid phase of second bonding material 25B containing high-oxygen Ag powder generates a large amount of active metal compounds, reducing fluidity and suppressing solder staining on the surfaces of copper plates 22, 23 due to bleeding of the bonding material. Furthermore, the liquid phase of first bonding material 25A containing low-oxygen Ag powder suppresses generation of active metal compounds, thereby suppressing a decrease in the bonding rate after thermal cycling.

[0044] In the present embodiment, when the ratio A / B of the arrangement width A of the first joining material 25A to the arrangement width B of the second joining material 25B in the joining material arrangement step S01 is set to 2 or more, the amount of the first joining material 25A containing low-oxygen Ag powder to be arranged is ensured, the excessive generation of compounds of active metal (Ti) and oxygen (O) can be further suppressed, and the decrease in the joining rate after the thermal cycle load can be further suppressed. On the other hand, when the ratio A / B of the arrangement width A of the first joining material 25A to the arrangement width B of the second joining material 25B in the joining material arrangement step S01 is set to 12 or less and the arrangement width B of the second joining material 25B is set to 1 mm or more, the amount of the second joining material 25B containing high-oxygen Ag powder to be arranged is ensured, the fluidity of the liquid phase can be reliably reduced, and the occurrence of bleeding of the joining material can be further suppressed.

[0045] Although the embodiment of the present invention has been described above, the present invention is not limited to this and can be modified as appropriate within the scope of the technical idea of ​​the invention. For example, in this embodiment, the circuit layer and the metal layer are both described as being made of copper or a copper alloy, but this is not limited to this and any structure in which a ceramic substrate and a copper plate are joined together may be used.

[0046] In addition, in the present embodiment, a power module is described as being configured by mounting power semiconductor elements on the circuit layer of an insulating circuit board, but this is not limiting. For example, an LED module may be configured by mounting LED elements on an insulating circuit board, or a thermoelectric module may be configured by mounting thermoelectric elements on the circuit layer of an insulating circuit board. [Example]

[0047] A confirmation experiment conducted to confirm the effectiveness of the present invention will be described.

[0048] First, we prepared a ceramic substrate (40 mm × 40 mm, material and thickness are listed in Table 1) and a copper plate (38 mm × 38 mm, material and thickness are listed in Table 1) shown in Table 1. OFC stands for oxygen-free copper, and TPC stands for tough pitch copper. Additionally, first and second bonding materials containing Ag powder with the oxygen concentrations shown in Table 1 were prepared. The Ag powder with an oxygen concentration of less than 0.3 mass% (low-oxygen Ag powder) was produced by a gas atomization method using Ar gas. The Ag powder with an oxygen concentration of 0.3 mass% or more (high-oxygen Ag powder) was produced by a wet reduction method. In this example, the first and second bonding materials were composed of a paste containing 85 mass% of powder component, 1.5 mass% of acrylic resin, and 13.5 mass% of α-terpineol.

[0049] Next, a first bonding material was applied to the surface of the ceramic substrate, and a second bonding material was applied to surround the first bonding material, as shown in Table 2. The thickness of the applied material was 10 μm. Then, a copper plate was laminated with the bonding materials (first bonding material and second bonding material) interposed therebetween. At this time, in a cross section along the stacking direction, the arrangement width A of the first bonding material and the arrangement width B of the second bonding material were adjusted as shown in Table 2. The arrangement widths B of the second bonding materials arranged on both ends of the first bonding material were made uniform.

[0050] Then, the ceramic substrate and the copper plate laminated with the bonding material interposed therebetween were pressurized and heated under the conditions shown in Table 2 to bond the ceramic substrate and the copper plate.

[0051] The obtained insulating circuit board (copper / ceramic bonded body) was evaluated for the initial bonding rate, the bonding rate after thermal cycling, and the exudation of the bonding material as follows. The evaluation results are shown in Table 2.

[0052] (Initial joining rate) The bonding rate between the copper plate (circuit layer) and the ceramic substrate was evaluated. Specifically, in an insulated circuit board, the bonding rate at the interface between the circuit layer and the ceramic substrate was evaluated using an ultrasonic flaw detector (FineSAT200 manufactured by Hitachi Power Solutions Co., Ltd.) and calculated using the following formula. Since peeling is indicated by a white area within the bond in an image obtained by binarizing the ultrasonic flaw detector image, the area of ​​this white area was taken as the peeling area. (Joining rate)={(Circuit layer area)-(Non-bonding area)} / (Circuit layer area)×100

[0053] (bonding rate after thermal cycle test) Using a thermal shock tester TSB-51 manufactured by Espec Corp., the power module substrate with heat sink was subjected to 1000 thermal cycles of -45°C x 10 minutes ←→ 125°C x 10 minutes in a liquid phase (Fluorinert). The bonding rate after the thermal cycle test was evaluated using the method described above.

[0054] (Evaluation of wax stains) The width of the wax stain was measured as follows. The copper circuit layer surface was visually observed from above, and the area where the brazing filler metal had spread was considered to be a brazing stain. The distance from the edge of the copper circuit layer to the tip of the brazing stain was measured for each side. The point with the greatest distance was taken as the width of the brazing stain, and measurements were taken for five bonded pieces under each condition and the average was calculated. A width of 300 μm or less was rated "A," a width of more than 300 μm but not more than 600 μm was rated "B," and a width of more than 600 μm was rated "C."

[0055] [Table 1]

[0056] [Table 2]

[0057] In Comparative Example 1, the first bonding material containing Ag powder with an oxygen concentration of 0.90 mass% was applied, and the second bonding material containing Ag powder with an oxygen concentration of 0.03 mass% was applied so as to surround the periphery of the first bonding material, and the evaluation of the brazing stain was "C." It is presumed that this is because the fluidity of the liquid phase of the bonding material applied to the periphery did not decrease. In Comparative Example 2, only the first bonding material containing Ag powder with an oxygen concentration of 0.03 mass% was used, and the evaluation of brazing stains was "C." This is presumably because the fluidity of the liquid phase of the applied bonding material did not decrease. In Comparative Example 3, only the first bonding material containing Ag powder with an oxygen concentration of 0.90 mass% was used, and the bonding rate after the thermal cycle was low at 94%. This is presumably because an excessive amount of compounds of active metal and oxygen was generated.

[0058] In contrast, in Inventive Example 1-4, a first bonding material containing Ag powder with an oxygen concentration of less than 0.3 mass% (low-oxygen Ag powder) was applied, and a second bonding material containing Ag powder with an oxygen concentration of 0.3 mass% or more (high-oxygen Ag powder) was applied so as to surround the periphery of the first bonding material, and the evaluation of solder stains was "A" or "B." In addition, the bonding rate after the cooling and heating cycle was 98% or more.

[0059] As a result of the above confirmatory experiments, it was confirmed that the present invention can provide a method for manufacturing a copper / ceramic bonded body and a method for manufacturing an insulated circuit board, which can suppress the occurrence of solder stains on the copper plate surface due to the seepage and flow of the bonding material and can produce a copper / ceramic bonded body with excellent bonding reliability. [Explanation of symbols]

[0060] 10 Insulated circuit board (copper / ceramic bonded body) 11 Ceramic substrate (ceramic component) 12 Circuit layer (copper material) 13 Metal layer (copper material)

Claims

1. A method for producing a copper / ceramic bonded body in which a copper member made of copper or a copper alloy and a ceramic member are bonded, comprising: a bonding material disposing step of disposing a bonding material between the copper member and the ceramic member; a lamination step of laminating the copper member and the ceramic member via the bonding material; a joining step of joining the copper member and the ceramic member stacked via the joining material by heat treatment in a vacuum atmosphere while applying pressure to the copper member and the ceramic member in the stacking direction, the bonding material disposing step includes preparing a first bonding material containing low-oxygen Ag powder having an oxygen concentration of less than 0.3 mass% and active metal powder, and a second bonding material containing high-oxygen Ag powder having an oxygen concentration of 0.3 mass% or more and active metal powder, and disposing the first bonding material between the copper member and the ceramic member and disposing the second bonding material so as to surround the periphery of the first bonding material.

2. 2. The method for manufacturing a copper / ceramic joined body according to claim 1, wherein in the bonding material disposing step, a ratio A / B of a width A of the first bonding material to a width B of the second bonding material is set in a range of 2 to 12, and the width B of the second bonding material is set to 1 mm or more.

3. A method for manufacturing an insulating circuit board in which a copper plate made of copper or a copper alloy and a ceramic substrate are bonded, comprising: a bonding material disposing step of disposing a bonding material between the copper plate and the ceramic substrate; a lamination step of laminating the copper plate and the ceramic substrate via the bonding material; a bonding step of bonding the copper plate and the ceramic substrate stacked via the bonding material by heat treatment in a vacuum atmosphere while applying pressure to the copper plate and the ceramic substrate in a stacking direction, In the bonding material disposing step, a first bonding material containing low-oxygen Ag powder having an oxygen concentration of less than 0.3 mass% and active metal powder, and a second bonding material containing high-oxygen Ag powder having an oxygen concentration of 0.3 mass% or more and active metal powder are prepared as the bonding materials, and the first bonding material is disposed between the copper plate and the ceramic substrate, and the second bonding material is disposed so as to surround the periphery of the first bonding material.

4. 4. The method for manufacturing an insulated circuit board according to claim 3, wherein in the bonding material disposing step, a ratio A / B of a width A of the first bonding material to a width B of the second bonding material is set within a range of 2 to 12, and the width B of the second bonding material is set to 1 mm or more.

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