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 oozing out of a joint material and generation of solder stains on the surface of a copper member by flow, and is excellent in joint reliability.SOLUTION: A method for manufacturing a copper / ceramic assembly in which a copper member composed of copper or a copper alloy and a ceramic member are joined to each other includes a joint material arrangement step of arranging a joint material between the copper member and the 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 contains Ag powder and active metal powder, and the Ag powder has low oxygen Ag powder having oxygen concentration of lower than 0.3 mass%, and high oxygen Ag powder having oxygen concentration of 0.3 mass% or more.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 and 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 surface of the copper member, resulting in solder stains. The occurrence of solder stains may have a negative impact on 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 surface of copper members 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 good, which makes it easier for the bonding material to seep out and cause solder stains on the copper plate surface, but it is possible to suppress a decrease in the bonding rate after thermal cycling.

[0010] The present invention has been made based on the above-mentioned findings. A method for producing a copper / ceramic bonded body of the present invention is a method for producing a copper / ceramic bonded body obtained by bonding a copper member made of copper or a copper alloy to a ceramic member, the method comprising the steps of: providing a bonding material between the copper member and the ceramic member; stacking the copper member and the ceramic member with the bonding material interposed therebetween; and bonding the laminated copper member and the ceramic member, which have been stacked with the bonding material interposed therebetween, by heat treatment in a vacuum atmosphere while applying pressure to the copper member and the ceramic member, the laminated copper member and the ceramic member being bonded together, the bonding material comprising Ag powder and an active metal powder, the Ag powder including low-oxygen Ag powder having an oxygen concentration of less than 0.3 mass% and high-oxygen Ag powder having an oxygen concentration of 0.3 mass% or more.

[0011] According to this method for producing a copper / ceramic bonded body, the bonding material contains Ag powder and active metal powder, and the Ag powder includes low-oxygen Ag powder with an oxygen concentration of less than 0.3 mass% and high-oxygen Ag powder with an oxygen concentration of 0.3 mass% or more. The high-oxygen Ag powder causes the active metal in the bonding material to react with oxygen to generate compounds, which reduce the fluidity of the liquid phase and suppress the occurrence of solder stains on the surfaces of the copper members due to the fluidity of the bonding material. Furthermore, the inclusion of low-oxygen Ag powder prevents excessive generation of compounds between the active metal and oxygen, thereby suppressing a decrease in the bonding rate after thermal cycling. Although the detailed mechanism has not yet been clarified, it is thought that the coexistence of Ag powder with a high oxygen concentration creates spots of low fluidity, which effectively suppress the fluidity of the Ag powder with a low oxygen concentration.

[0012] In the method for producing a copper / ceramic bonded body of the present invention, it is preferable that a weight ratio A / B of a content A of the low-oxygen Ag powder to a content B of the high-oxygen Ag powder in the bonding material is in the range of 0.2 or more and 2.0 or less. In this case, the weight ratio A / B of the content A of the low-oxygen Ag powder to the content B of the high-oxygen Ag powder in the joining material is set to 0.2 or more, so that the content of the low-oxygen Ag powder is secured, the excessive generation of compounds of active metal and oxygen can be further suppressed, and the decrease in the joining rate after thermal cycle loading can be further suppressed. On the other hand, since the weight ratio A / B of the content A of the low-oxygen Ag powder to the content B of the high-oxygen Ag powder in the bonding material is set to 2.0 or less, the content of the high-oxygen Ag powder is secured, the fluidity of the liquid phase can be reliably reduced, and the occurrence of solder stains on the surface of the copper member due to the seepage and flow 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 is bonded to a ceramic substrate, and includes the following steps: 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 in the laminating direction; 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 to them in the laminating direction; the bonding material contains Ag powder and active metal powder, and the Ag powder includes low-oxygen Ag powder having an oxygen concentration of less than 0.3 mass% and high-oxygen Ag powder having an oxygen concentration of 0.3 mass% or more.

[0014] According to this method for manufacturing an insulated circuit board, the bonding material contains Ag powder and active metal powder, and the Ag powder includes low-oxygen Ag powder with an oxygen concentration of less than 0.3 mass% and high-oxygen Ag powder with an oxygen concentration of 0.3 mass% or more. The high-oxygen Ag powder causes the active metal in the bonding material to react with oxygen to generate compounds, which reduces the fluidity of the liquid phase and prevents solder stains on the surfaces of the copper members due to the flow of the bonding material. Furthermore, the inclusion of low-oxygen Ag powder prevents excessive generation of compounds between the active metal and oxygen, thereby preventing a decrease in the bonding rate after thermal cycling.

[0015] In the method for producing an insulating circuit board of the present invention, it is preferable that the weight ratio A / B of the content A of the low-oxygen Ag powder to the content B of the high-oxygen Ag powder in the bonding material is within the range of 0.2 or more and 2.0 or less. In this case, the weight ratio A / B of the content A of the low-oxygen Ag powder to the content B of the high-oxygen Ag powder in the joining material is set to 0.2 or more, so that the content of the low-oxygen Ag powder is secured, the excessive generation of compounds of active metal and oxygen can be further suppressed, and the decrease in the joining rate after thermal cycle loading can be further suppressed. On the other hand, since the weight ratio A / B of the content A of the low-oxygen Ag powder to the content B of the high-oxygen Ag powder in the bonding material is set to 2.0 or less, the content of the high-oxygen Ag powder is secured, the fluidity of the liquid phase can be reliably reduced, and the occurrence of solder stains on the surface of the copper member 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 surface of copper members due to the seepage and flow of 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. 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. This circuit layer 12 has a circuit pattern formed by joining the above-mentioned copper plates 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 3.0 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) First, as shown in FIG. 4, bonding materials 25 are disposed 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, respectively. In this embodiment, an Ag-Ti paste containing Ag powder and active metal powder (Ti in this embodiment) is printed as a bonding material 25 between the copper plate 22 that becomes the circuit layer 12 and the ceramic substrate 11, and between the copper plate 23 that becomes the metal layer 13 and the ceramic substrate 11. 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 be added.

[0030] The active metal powder may be one or more powders selected from the group consisting of Ti, Zr, Nb, and Hf. Hydrides of these elements may also be used. The average particle size of the active metal powder is preferably in the range of 1 μm to 20 μm.

[0031] In this embodiment, the Ag powder contained in the bonding material 25 includes low-oxygen Ag powder with an oxygen concentration of less than 0.3 mass % and high-oxygen Ag powder with an oxygen concentration of 0.3 mass % or more. The average particle size of the low-oxygen Ag powder and the high-oxygen Ag powder is preferably in the range of 0.5 μm to 20 μm.

[0032] 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.

[0033] On the other hand, low-oxygen Ag powder can be produced by, for example, 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, the lower limit of the oxygen concentration in the low-oxygen Ag powder is not particularly limited. 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.

[0034] In this embodiment, the weight ratio A / B of the content A of the low-oxygen Ag powder to the content B of the high-oxygen Ag powder in the bonding material 25 is preferably in the range of 0.2 to 2.0. Here, by setting the weight ratio A / B of the content A of the low-oxygen Ag powder to the content B of the high-oxygen Ag powder to be 0.2 or more, it is possible to suppress the excessive generation of active metal compounds. On the other hand, by setting the weight ratio A / B of the content A of low-oxygen Ag powder to the content B of high-oxygen Ag powder to 2.0 or less, active metal compounds can be sufficiently generated and the fluidity of the liquid phase can be reliably reduced.

[0035] The lower limit of the weight ratio A / B of the content A of the low-oxygen Ag powder to the content B of the high-oxygen Ag powder in the bonding material 25 is more preferably 0.25 or more, and even more preferably 0.3 or more. On the other hand, the upper limit of the weight ratio A / B of the content A of the low-oxygen Ag powder to the content B of the high-oxygen Ag powder in the bonding material 25 is more preferably 1.25 or less, and even more preferably 1.0 or less.

[0036] (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.

[0037] (Joining process S03) Next, the copper plate 22, bonding material 25, ceramic substrate 11, bonding material 25, and copper plate 23 are loaded into a vacuum heating furnace and heated while being pressurized in the stacking direction (pressure of 0.01 MPa to 3.5 MPa) to melt the bonding material 25. If necessary, the bonding material may be dried and desolvated. Then, the molten bonding material 25 is 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 heating time is set to a range of 1 minute to 60 minutes.

[0038] 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 bonding material 25 contains high-oxygen Ag powder, the active metal (Ti) contained in the bonding material 25 reacts with oxygen to generate Ti compounds, which reduces the fluidity of the liquid phase. This makes it possible to prevent the bonding material from seeping out. Furthermore, since the bonding material 25 contains low-oxygen Ag powder, excessive generation of Ti compounds can be suppressed, and a decrease in the bonding rate after thermal cycle loading can be suppressed.

[0039] 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.

[0040] (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.

[0041] (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.

[0042] According to the manufacturing method of the insulated circuit board (copper / ceramic bonded body) of this embodiment configured as described above, bonding material 25 disposed between copper sheets 22, 23 and ceramic substrate 11 contains Ag powder and active metal powder (Ti powder). The Ag powder includes low-oxygen Ag powder having an oxygen concentration of less than 0.3 mass% and high-oxygen Ag powder having an oxygen concentration of 0.3 mass% or more. The high-oxygen Ag powder causes the active metal (Ti) and oxygen (O) in bonding material 25 to react with each other to generate a compound. This reduces the fluidity of the liquid phase generated during the temperature rise process in bonding step S03, thereby preventing the bonding material from seeping out and flowing, resulting in solder staining on the surfaces of copper sheets 22, 23. Furthermore, the inclusion of low-oxygen Ag powder prevents excessive generation of compounds of the active metal (Ti) and oxygen (O), thereby preventing a decrease in the bonding rate after thermal cycling.

[0043] In addition, in this embodiment, when the weight ratio A / B of the content A of low-oxygen Ag powder to the content B of high-oxygen Ag powder in the joining material 25 is set to 0.2 or more, the content of low-oxygen Ag powder is secured, the excessive generation of compounds of active metal (Ti) and oxygen (O) can be further suppressed, and the decrease in the joining rate after thermal cycle loading can be further suppressed. On the other hand, since the weight ratio A / B of the content A of low-oxygen Ag powder to the content B of high-oxygen Ag powder in the joining material 25 is set to 2.0 or less, the content of high-oxygen Ag powder is secured, the fluidity of the liquid phase generated during the temperature rise process in the joining step S03 can be reliably reduced, and the bleeding of the joining material can be further suppressed.

[0044] 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.

[0045] 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]

[0046] A confirmation experiment conducted to confirm the effectiveness of the present invention will be described.

[0047] First, a ceramic substrate (40 mm×40 mm, thickness shown in Table 1) and a copper plate (38 mm×38 mm, thickness shown in Table 1) were prepared. The bonding materials shown in Table 1 were prepared. The low-oxygen Ag powder was produced by gas atomization using Ar gas, and the high-oxygen Ag powder was produced by wet reduction. The above-mentioned bonding material was then applied to the surface of the ceramic substrate to a thickness of 10 μm, and a copper plate was laminated thereon via the bonding material, and the ceramic substrate and the copper plate were bonded together under the conditions shown in Table 2. In this example, a paste consisting of 85 mass % of powder component, 1.5% of acrylic resin, and 13.5% of α-terpineol was used as the bonding material.

[0048] The obtained insulating circuit board (copper / ceramic bonded body) was evaluated as follows for the bond rate at the initial stage of bonding, the bond rate after thermal cycle loading, and solder staining.

[0049] (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. (Bonding rate) = {(total area of ​​circuit layer) - (peeling area)} / (total area of ​​circuit layer) x 100

[0050] (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.

[0051] (Evaluation of wax stains) The width of the wax stain was measured as follows. The circuit layer surface was visually observed from above, and the area where the brazing filler metal had spread due to its flow was considered to be a brazing stain. The distance from the edge of the 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 of the conditions listed, and the average value was calculated. If the width was 300 μm or less, it was rated as "A," if it was more than 300 μm and less than 500 μm, it was rated as "B," and if it was more than 500 μm, it was rated as "C."

[0052] [Table 1]

[0053] [Table 2]

[0054] In Comparative Example 1, which did not contain low-oxygen Ag powder with an oxygen concentration of less than 0.3 mass%, but contained only high-oxygen Ag powder with an oxygen concentration of 0.3 mass% or more, the bonding rate after the thermal cycle was low at 93.4%, which is presumably due to the excessive generation of compounds of active metal and oxygen. In Comparative Example 2, high-oxygen Ag powder with an oxygen concentration of 0.3 mass% or more was not contained, and only low-oxygen Ag powder with an oxygen concentration of less than 0.3 mass% was contained, and the evaluation of brazing stains was "C." This is presumably because compounds between active metal and oxygen were not sufficiently generated, resulting in high fluidity of the joining material.

[0055] In contrast, in Inventive Example 1-9, which contained low-oxygen Ag powder with an oxygen concentration of less than 0.3 mass% and high-oxygen Ag powder with an oxygen concentration of 0.3 mass% or more, the solder stain evaluation was "A" or "B," and the bonding rate after the thermal cycle was 94.5% or more. This is presumably because compounds of active metal and oxygen were properly generated. In addition, in Examples 1-7 and 1-9 of the present invention, in which the weight ratio A / B of the content A of the low-oxygen Ag powder to the content B of the high-oxygen Ag powder was 0.2 or more, the bonding rate after the thermal cycle was 97.5% or more. In addition, in Inventive Example 1-8 in which the weight ratio A / B of the content A of low-oxygen Ag powder to the content B of high-oxygen Ag powder was 2.0 or less, the evaluation of solder staining was "A".

[0056] 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 surface of the copper member 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]

[0057] 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 contains Ag powder and an active metal powder, and the Ag powder includes low-oxygen Ag powder having an oxygen concentration of less than 0.3 mass% and high-oxygen Ag powder having an oxygen concentration of 0.3 mass% or more.

2. 2. The method for producing a copper / ceramic joined body according to claim 1, wherein a weight ratio A / B of a content A of the low-oxygen Ag powder to a content B of the high-oxygen Ag powder in the joining material is in the range of 0.2 to 2.

0.

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, the bonding material contains Ag powder and activated metal powder, and the Ag powder has low-oxygen Ag powder having an oxygen concentration of less than 0.3 mass% and high-oxygen Ag powder having an oxygen concentration of 0.3 mass% or more.

4. 4. The method for manufacturing an insulating circuit board according to claim 3, wherein a weight ratio A / B of a content A of the low-oxygen Ag powder to a content B of the high-oxygen Ag powder in the bonding material is within a range of 0.2 to 2.0.

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