Method for manufacturing a bonded body, and method for manufacturing a circuit board

Abstract

To provide a method for manufacturing a bonded structure that is highly durable against heat cycles and can be produced with high productivity. [Solution] A method for manufacturing a bonded body, comprising heating a laminate comprising a ceramic substrate, a brazing material, and a metal plate in that order, wherein the laminate is heated and held at a holding temperature of 750 to 900°C for 10 minutes or more, and an annealing temperature T in the range of 550 to 700°C is obtained from the holding temperature at a first average cooling rate of 4 to 15°C / min. A A first cooling step to cool the above laminate down to T A The present invention provides a method for manufacturing a bonded body, comprising an annealing step of holding the laminated body within a range of ±10℃ for 5 minutes or more, wherein the heating step, the first cooling step, and the annealing step are performed in an inert gas atmosphere while transporting the laminated body using a continuous furnace.

Description

[Technical Field]

[0001] This disclosure relates to a method for manufacturing a bonded body and a method for manufacturing a circuit board. [Background technology]

[0002] In recent years, power modules for high-power control have been used in industrial equipment such as motors, and in products such as electric vehicles. Such power modules utilize circuit boards equipped with ceramic substrates to efficiently dissipate heat generated from semiconductor elements and suppress leakage current. Such circuit boards are usually required to have excellent resistance to thermal cycling. For example, Patent Document 1 describes obtaining a circuit board with excellent resistance to thermal cycling by joining a ceramic substrate and a metal plate using a batch-type electric furnace.

[0003] Batch-type furnaces require heating and temperature maintenance for each batch, limiting the number of joints that can be produced at one time. Therefore, manufacturing methods using continuous furnaces, which can heat the objects while transporting them, are being considered. Patent Document 2 proposes improving the yield of joints by using a continuous furnace. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. 2021 / 200866 [Patent Document 2] International Publication No. 2022 / 244769 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] This disclosure provides a method for manufacturing a bond that is highly durable against heat cycles and can be produced with high productivity. Furthermore, it provides a method for manufacturing a circuit board that is highly reliable and can be produced with high productivity by using such a bond. [Means for solving the problem]

[0006] One aspect of this disclosure provides a method for manufacturing the following jointed body.

[0007] [1] A method for manufacturing a bonded body, comprising heating a laminate comprising a ceramic substrate, a brazing material, and a metal plate in this order, A heating step of raising the temperature of the laminate and holding it at a holding temperature of 750 to 900°C for 10 minutes or more, Annealing temperature T is in the range of 550 to 700°C, achieved by a first mean cooling rate of 4 to 15°C / min from the aforementioned holding temperature. A A first cooling step to cool the laminate down to a certain temperature, T A The process includes an annealing step in which the laminate is held in a temperature range of ±10℃ for 5 minutes or more. A method for manufacturing a bonded body, wherein the heating step, the first cooling step, and the annealing step are performed in an inert gas atmosphere while the laminate is being transported using a continuous furnace.

[0008] The method for manufacturing the bonded body described in [1] above allows for the continuous heating of multiple laminates while transporting them using a continuous furnace, thus enabling the production of bonded bodies with high productivity. Furthermore, the annealing temperature T within a predetermined temperature range in the continuous furnace is also important. A Then the annealing process is performed, T ABy maintaining the temperature within a range of ±10℃, the residual stress at the joint caused by the difference in thermal expansion between the metal plate and the ceramic substrate can be sufficiently reduced by heating the laminate. Reducing residual stress suppresses the occurrence of cracks in the ceramic substrate. Therefore, a joint with excellent resistance to heat cycling can be obtained. Furthermore, by keeping the first mean cooling rate within a predetermined range, the residual stress at the joint can be further reduced while maintaining productivity, resulting in a joint with excellent resistance to heat cycling.

[0009] The method for manufacturing the joint described in [1] above may be any one of the following [2] to [5].

[0010] [2] The method for manufacturing a bonded body according to [1], wherein the holding temperature is 750°C or higher and less than 860°C. [3] A method for manufacturing a joint according to [1] or [2], wherein the first average cooling rate is 4 to 11°C / min. [4] A method for manufacturing a bonded body according to any one of [1] to [3], wherein the laminate is heated from 50°C to the holding temperature at an average heating rate of 30 to 50°C / min. [5] A method for manufacturing a bonded body according to any one of [1] to [4], comprising a second cooling step after the annealing step, in which the temperature is cooled to 50°C at a second mean cooling rate of 5 to 20°C / min.

[0011] The method for manufacturing the bond described in [2] above, by setting the holding temperature to 750°C or higher and less than 860°C, suppresses hardening of the metal plate due to grain growth of the metal, and makes it possible to obtain a bond with even better durability against heat cycles.

[0012] The method for manufacturing the joint described in [3] above, by setting the first mean cooling rate to 4 to 11°C / min, can suppress the thermal expansion of the metal plate and further reduce residual stress at the joint. As a result, a joint with even better durability against heat cycles can be obtained.

[0013] The manufacturing method of the joint body of [4] can manufacture a joint body with excellent durability against heat cycles with higher productivity by heating up to the holding temperature at an average heating rate of 30 to 50 °C / min.

[0014] The manufacturing method of the joint body of [5] can manufacture a joint body with excellent durability against heat cycles with higher productivity by cooling down to 50 °C at a second cooling rate of 5 to 20 °C / min after the annealing process.

[0015] One aspect of the present disclosure provides a method for manufacturing the following circuit board.

[0016] [6] A method for manufacturing a circuit board, comprising a step of removing a part of the metal plate in the joint body obtained by the manufacturing method according to any one of [1] to [5] above to obtain a circuit board having a conductor portion.

[0017] The manufacturing method of the circuit board of [6] uses the joint body obtained by the manufacturing method of the joint body. Therefore, a highly reliable circuit board with excellent durability against heat cycles can be manufactured with high productivity.

Effect of the Invention

[0018] The present disclosure can provide a manufacturing method of a joint body capable of manufacturing a joint body with excellent durability against heat cycles with high productivity. Further, by using such a joint body, a manufacturing method of a circuit board capable of manufacturing a highly reliable circuit board with high productivity can be provided.

Brief Description of the Drawings

[0019] [Figure 1] It is a cross-sectional view of the laminate cut along the lamination direction. [Figure 2] It is a perspective view showing an example of the joint body. [Figure 3] It is a cross-sectional view of the joint body of FIG. 2 cut along line III-III. [Figure 4] It is a plan view showing an example of the circuit board. [Modes for carrying out the invention]

[0020] Embodiments of the present disclosure are described below. However, the following embodiments are illustrative examples for illustrating the present disclosure and are not intended to limit the present disclosure to the following. In the description, the same reference numerals are used for elements that are the same or have the same function, and redundant explanations are omitted where necessary. Also, unless otherwise specified, positional relationships such as up, down, left, and right are based on the positional relationships based on the orientation of the reference numerals shown in the drawings. The dimensional ratios of each element are not limited to the ratios shown. The numerical ranges illustrated as "a~b" are numerical ranges that include a and b, with a lower limit being a and an upper limit being b. The present disclosure also includes the case in which the upper or lower limit of each numerical range is replaced with the numerical values ​​of any embodiment. When multiple materials are illustrated, one of them may be used alone, or multiple may be used in combination.

[0021] A method for manufacturing a bonded body according to one embodiment is a method for manufacturing a bonded body by heating a laminate comprising a ceramic substrate, a brazing material, and a metal plate in that order, and comprises a heating step, a first cooling step, and an annealing step. The heating step, the first cooling step, and the annealing step are performed in an inert gas atmosphere while transporting the laminate using a continuous furnace.

[0022] A continuous furnace is a furnace that heats a stack of materials to be heated while transporting it via a belt conveyor or the like. Examples of continuous furnaces include rotary kilns, screw conveyor furnaces, tunnel furnaces, pusher furnaces, tunnel-type pusher furnaces, belt furnaces, and roller hearth kilns. Because continuous furnaces can heat the stacks while transporting them, they can process a larger quantity at once than batch furnaces, resulting in superior productivity. Furthermore, since the stacks can be heated under an inert gas atmosphere, vacuuming the furnace is not required. Therefore, vacuuming the furnace is no longer essential, and the production time is shorter than with batch furnaces, resulting in superior productivity. Examples of inert gases introduced into a continuous furnace include nitrogen gas.

[0023] The continuous furnace does not need to be sealed. The pressure inside the continuous furnace may be atmospheric pressure, or it may be increased to a pressure above atmospheric pressure by introducing an inert gas. Furthermore, heating may be performed while pressurizing one or more laminates using a pressurizing jig. By using a pressurizing jig, ceramic substrates and metal plates can be joined with high uniformity. In addition, since multiple laminates can be processed at once, the productivity of the joined products can be further improved.

[0024] Figure 1 is a cross-sectional view of the laminate cut along the lamination direction. The laminate 100 is made by applying brazing material 30 to both main surfaces 10A and 10B of a ceramic substrate 10, and then layering a metal plate 20 on top of it. Figure 1 shows a pair of metal plates 20 layered on both main surfaces 10A and 10B, but is not limited to this. As a modification, the laminate 100 may be made by applying brazing material 30 to one main surface 10A (10B) of the ceramic substrate 10 and then layering a metal plate 20 on top. Examples of methods for applying the brazing material 30 include the roll coater method, the screen printing method, and the transfer method.

[0025] The material of the ceramic substrate 10 is not particularly limited. Examples of ceramics included in the ceramic substrate 10 include nitride-based ceramics such as silicon nitride and aluminum nitride, oxide-based ceramics such as aluminum oxide and zirconium oxide, carbide-based ceramics such as silicon carbide, and boride-based ceramics such as lanthanum boride. When joining metal plates using the active metal method, the material of the ceramic substrate 10 may be a non-oxide-based ceramic such as aluminum nitride and silicon nitride. Of these, the ceramic substrate 10 may be composed of silicon nitride from the viewpoint of mechanical strength and fracture toughness. The thickness of the ceramic substrate 10 may be, for example, 0.10 to 3.0 mm, 0.20 to 1.2 mm, or 0.25 to 1.0 mm.

[0026] The brazing material 30 may be composed of an Ag-Cu-Sn-based brazing material containing silver, copper, tin, and an active metal including at least one selected from the group consisting of titanium, zirconium, hafnium, and niobium. The brazing material 30 hardens upon heating and can join the ceramic substrate 10 and the metal plate 20. The silver content in the brazing material 30 may be 70-90% by mass or more, or 80-90% by mass or more. This can improve the bonding strength between the ceramic substrate 10 and the metal plate 20.

[0027] The copper content in the brazing material 30 may be 5 to 20% by mass, or 7 to 15% by mass. This further reduces the residual stress in the joint 40 after heating while improving the joint's properties. The tin content in the brazing material 30 may be 0.5 to 5% by mass, or 1 to 4% by mass. This further reduces the residual stress in the joint 40 after heating while improving the wettability of the brazing material 30.

[0028] The active metal content in the brazing material 30 may be 1 to 5 mass%, or 2 to 4 mass%. By setting the active metal content to 1 mass% or more, the bonding strength between the ceramic substrate 10 and the metal plate 20 can be improved. On the other hand, by setting the active metal content to 5 mass% or less, the formation of a brittle alloy layer at the bonding interface can be suppressed. The active metal may be included as a hydride, for example, titanium hydride (TiH2). The TiH2 content in the brazing material 30 may be 1 to 5 mass%, or 2 to 4 mass%. This makes it possible to sufficiently increase the bonding strength between the ceramic substrate 10 and the metal plate 20.

[0029] The metal plate 20 may be a copper plate from the viewpoint of improving conductivity and heat dissipation. The thickness of the metal plate 20 may be 0.10 to 1.5 mm or 0.20 to 1.2 mm. From the viewpoint of improving heat dissipation, the thickness of the metal plate 20 may be 0.30 mm or more or 0.40 mm or more. The metal plate 20 may have a plating film on its surface. From the viewpoint of improving weather resistance and solder wettability, the plating film may be a Ni plating film, a Ni alloy plating film, or a gold plating film. The Ni plating film may be an electroless Ni plating film.

[0030] The laminate 100 is heated in a continuous furnace under an inert gas atmosphere through a heating step, a first cooling step, and an annealing step. This makes it possible to obtain a bonded body 105 in which the ceramic substrate 10 and the metal plate 20 are bonded via a bonding layer 35, as shown in Figures 2 and 3.

[0031] Each process, such as the heating process, the first cooling process, and the annealing process, can be carried out in processing zones with multiple temperature gradients inside the continuous furnace. This allows the temperature of the laminate 100 to be adjusted within the continuous furnace. The time required for each process can be adjusted by the transport speed and transport distance of the laminate 100. The transport speed of the laminate 100 may be constant or may be changed during each process. The transport path of the continuous furnace may be straight or curved. The transport path may be flat or include slopes. To prevent the laminate 100 from shifting during transport, the transport path may be straight and flat.

[0032] In the heating process, the laminate 100 is heated and held at a holding temperature of 750 to 900°C for 10 minutes or more. By holding at a holding temperature of 750 to 900°C for 10 minutes or more, the laminate 100 can be sufficiently heated, and the bonding strength of the bonding layer 35 can be improved. From the viewpoint of suppressing the hardening of the metal plate 20 due to grain growth of the metal and further improving the durability of the bonding body 105 against heat cycles, the holding temperature may be 880°C or less, less than 860°C, or 850°C or less. Also, from the viewpoint of sufficiently heating the laminate 100 and improving the bonding strength of the bonding layer 35, the holding temperature may be 780°C or higher, or 800°C or higher. The holding temperature may be, for example, 750°C or more and less than 860°C, 780 to 880°C, 780°C or more and less than 860°C, or 780 to 850°C.

[0033] The holding time may be 12 minutes or more, or 14 minutes or more, from the viewpoint of sufficiently heating the laminate 100 to further improve the bonding strength of the bonding layer 35. Also, from the viewpoint of further improving the productivity of the bonded body 105, the holding time may be 30 minutes or less, 25 minutes or less, or 22 minutes or less. The holding time may be, for example, 10 to 30 minutes, 12 to 25 minutes, or 14 to 22 minutes.

[0034] In the heating process, the temperature fluctuation range may be maintained within ±10°C, ±7°C, or ±5°C relative to the holding temperature. This allows the laminate 100 to be heated with high uniformity, and the ceramic substrate 10 and the metal plate 20 to be joined with high uniformity.

[0035] The laminate 100 may be heated from 50°C to the holding temperature at an average heating rate of 30 to 50°C / min. If the average heating rate is 30°C / min or higher, the productivity of the bonded body 105 can be further improved. If the average heating rate is 50°C / min or lower, the occurrence of temperature differences within the laminate 100 can be suppressed. The average heating rate may be, for example, 35 to 45°C / min or 37 to 43°C / min.

[0036] In the first cooling process, the annealing temperature T within the range of 550 to 700 °C is cooled from the holding temperature at a first average cooling rate of 4 to 15 °C / min. A until reaching the annealing temperature T. A The annealing temperature T may be within the range of 550 to 650 °C, or 570 to 630 °C. From the perspective of further improving productivity, the first average cooling rate may be 4.5 °C / min or more. From the perspective of sufficiently reducing the residual stress at the joint 40 and further improving the durability of the joined body 105 against heat cycles, the first average cooling rate may be 13 °C / min or less, 12 °C / min or less, or 11 °C / min or less. Also, from the perspective of maintaining productivity and further improving the durability of the joined body 105 against heat cycles, the first average cooling rate may be, for example, 4 to 11 °C / min.

[0037] In the annealing process, the laminate is held for 5 minutes or more within the range of T A ±10 °C. By annealing at an annealing temperature T lower than such a holding temperature and with a small variation range, the residual stress at the joint 40 caused by the difference in thermal expansion between the ceramic substrate 10 and the metal plate 20 can be reduced. From the perspective of further reducing the residual stress at the joint 40, the annealing temperature T A may be maintained within the range of T A ±8 °C, or T A ±6 °C. A

[0038] After the annealing process, a second cooling process may be performed in which the temperature is cooled to 50 °C at a second average cooling rate of 5 to 20 °C / min. The second average cooling rate may be, for example, 6 to 15 °C / min, or 7 to 12 °C / min. By the second average cooling rate being within the above range, damage to the joined body 105 due to rapid cooling can be suppressed while maintaining productivity. The second cooling process may be performed directly in a continuous furnace, or may be transferred to another furnace such as a batch furnace for the operation.

[0039] A method for manufacturing a circuit board according to one embodiment includes the step of removing a portion of the metal plate 20 in the bonded body 105 obtained by the above-described manufacturing method to obtain a circuit board 200 having a conductive portion 25. This step may be performed, for example, by photolithography. Specifically, first, a photosensitive resist is printed on the main surface of the bonded body 105 (the main surface of the metal plate 20). Then, a resist pattern having a predetermined shape is formed using an exposure apparatus. The resist may be negative or positive. Uncured resist is removed, for example, by washing. After forming the resist pattern, the portion of the metal plate 20 not covered by the resist pattern is removed by etching. As a result, a portion of the main surface 10A and main surface 10B of the ceramic substrate 10 is exposed in that portion. After that, by removing the resist pattern, a circuit board 200 having a circuit pattern of conductive portion 25 on the main surface of the ceramic substrate 10 is obtained, as shown in Figure 4.

[0040] There are no particular restrictions on the etching solution; for example, ferric chloride solution, cupric chloride solution, sulfuric acid, and hydrogen peroxide solution can be used. If, after etching, the bonding layer 35 or the like remains on the main surfaces 10A and 10B of the ceramic substrate 10, the residue may be removed using a solution containing at least one selected from the group consisting of ammonium halide aqueous solution, an inorganic acid such as sulfuric acid and nitric acid, and hydrogen peroxide solution. The method for removing the resist pattern is not particularly limited; for example, it may be done by immersion in an alkaline aqueous solution.

[0041] The circuit board 200 obtained in this manner uses a bonding body 105, so the residual stress at the joint 40 between the ceramic substrate 10 and the conductor part 25 is sufficiently reduced. Therefore, the circuit board 200, like the bonding body 105, has excellent durability against heat cycles. Furthermore, since the bonding body 105 is obtained using a continuous furnace, the circuit board 200 using the bonding body 105 has excellent productivity. Because such a circuit board 200 has excellent durability against heat cycles, it may be used, for example, in power modules that handle high currents.

[0042] The crack rate of the circuit board 200 or bonded body 105 after the heat cycle test may be less than 1.3 area%, 1.2 area%, 1.0 area%, or 0.5 area. The heat cycle test referred to here is a test in which a series of steps of holding at -78°C for 5 minutes, 25°C for 5 minutes, 350°C for 5 minutes, and 25°C for 5 minutes constitutes one cycle, and this is performed 15 times. After the heat cycle test, the conductor part 25 or metal plate 20 and the bonding layer 35 are removed by etching, and the crack area in the ceramic substrate 10 is calculated using image analysis. The crack rate is the ratio of the crack area to the bonding area between the bonding layer 35 that bonded the conductor part 25 or metal plate 20 to the ceramic substrate 10 and the ceramic substrate 10.

[0043] Although embodiments have been described in this disclosure, this disclosure is not limited in any way to the embodiments described above. [Examples]

[0044] The contents of this disclosure will be described in more detail with reference to examples and comparative examples, but this disclosure is not limited to the following examples.

[0045] [Example 1] (Fabrication of the joint) A silicon nitride sintered body with dimensions of 40 mm × 35 mm × 0.3 mm (length × width × thickness) was prepared as a ceramic substrate. A brazing material was applied to both main surfaces of this silicon nitride sintered body. The composition of the brazing material was Ag:Cu:Sn:TiH2 = 85:9:3:3 by mass ratio. Subsequently, a copper plate with dimensions of 40 mm × 35 mm × 0.8 mm (length × width × thickness) was laminated to both main surfaces of the silicon nitride sintered body via the brazing material to obtain a laminate.

[0046] The fabricated laminate was introduced into a continuous furnace under a nitrogen gas atmosphere, and the heating process, first cooling process, annealing process, and second cooling process were carried out while the laminate was being transported. Each process was performed in multiple processing zones within the continuous furnace. The inlet temperature of the continuous furnace (temperature at which heating began) was 20°C.

[0047] In the heating process, the laminate was heated from 20°C to a holding temperature of 830°C at an average heating rate of 40°C / min, and held at 830°C for 20 minutes. Subsequently, in the first cooling process, the laminate was cooled from 830°C (holding temperature) to 600°C (annealing temperature: T) at a first average cooling rate of 7°C / min. A The temperature was reduced to ). In the annealing process, the annealing temperature T is shown in Table 1. A The laminate was held within a range of ±5°C for 20 minutes. Subsequently, in the second cooling step, the laminate was cooled from 600°C to room temperature at a second average cooling rate of 10°C / min. A bonded body was obtained in this manner.

[0048] (Circuit board fabrication) An etching resist was printed on predetermined locations on both main surfaces of the copper plate in the fabricated bonded body. After forming a resist pattern with a predetermined shape on the main surface of the copper plate using an exposure apparatus, etching was performed using a ferric chloride solution. Further etching was performed using a mixed solution of ammonium fluoride and hydrogen peroxide to remove areas where the resist pattern was not formed, thereby forming a conductive part of a predetermined shape bonded to the ceramic substrate via a bonding layer.

[0049] Next, after pretreatment by degreasing and chemical polishing, rust prevention treatment was performed using a benzotriazole compound. In this way, a circuit board having a circuit pattern on a ceramic substrate was obtained as shown in Figure 4.

[0050] (Evaluation of heat cycle characteristics) A heat cycle test was performed on the fabricated circuit board. Specifically, one cycle consisted of a series of steps: -78°C for 5 minutes, 25°C for 5 minutes, 350°C for 5 minutes, and then holding at 25°C for 5 minutes. This was repeated 15 times. After that, etching was performed using a ferric chloride solution, followed by etching with a mixed solution of ammonium fluoride and hydrogen peroxide to remove the conductor and bonding layers.

[0051] Using a scanner, images of the main surface of the ceramic substrate, with the conductor and bonding layer removed, were acquired at a resolution of 600 dpi x 600 dpi. The images were binarized using the image analysis software GIMP2 (threshold 140) to calculate the crack area in the ceramic substrate. The crack ratio was determined by dividing the calculated crack area by the bonding area between the bonding layer that joined the conductor and the ceramic substrate and the ceramic substrate itself. The results are shown in Table 1.

[0052] [Examples 2 to 9] A circuit board was fabricated using the same procedure as in Example 1, except for the heating conditions shown in Table 1, and its heat cycle characteristics were evaluated. The results of the crack rate measurement are shown in Table 1.

[0053] [Comparative Examples 1, 2] Circuit boards were fabricated using the same procedure as in Example 1, except for the heating conditions shown in Table 1, and the heat cycle characteristics were evaluated. Comparative Examples 1 and 2 did not undergo an annealing process, so the holding time in the annealing process was 0 minutes. The results of the crack rate measurement are shown in Table 1.

[0054] [Table 1]

[0055] As shown in Table 1, it was demonstrated that performing an annealing process during the fabrication of bonded components in a continuous furnace results in circuit boards with a low crack rate. Therefore, since continuous furnaces have higher productivity than batch furnaces, using a continuous furnace allows for the high-productivity manufacturing of highly reliable circuit boards with excellent resistance to heat cycles. [Industrial applicability]

[0056] This disclosure provides a method for manufacturing a bond that is highly durable against heat cycles and can be produced with high productivity. Furthermore, by using such a bond, it is possible to provide a method for manufacturing a circuit board that is highly reliable and can be produced with high productivity. [Explanation of Symbols]

[0057] 10...Ceramic substrate, 10A, 10B...Main surface, 20...Metal plate, 30...Brazing material, 35...Bonding layer, 40...Bond, 100...Laminate, 105...Bond, 25...Conductor part, 200...Circuit board.

Claims

1. A method for manufacturing a bonded body, comprising heating a laminate comprising a ceramic substrate, a brazing material, and a metal plate in this order, A heating step of raising the temperature of the laminate and holding it at a holding temperature of 750 to 900°C for 10 minutes or more, Annealing temperature T is in the range of 550 to 700°C, achieved by a first average cooling rate of 4 to 15°C / min from the aforementioned holding temperature. Ａ A first cooling step involves cooling the laminate down to a certain temperature, T Ａ The process includes an annealing step in which the laminate is held in a temperature range of ±10°C for 5 minutes or more. A method for manufacturing a bonded body, wherein the heating step, the first cooling step, and the annealing step are performed in an inert gas atmosphere while the laminate is being transported using a continuous furnace.

2. The method for manufacturing a bonded body according to claim 1, wherein the holding temperature is 750°C or higher and less than 860°C.

3. The method for manufacturing a bonded body according to claim 1 or 2, wherein the first average cooling rate is 4 to 11°C / min.

4. A method for manufacturing a bonded body according to claim 1 or 2, wherein the laminate is heated from 50°C to the holding temperature at an average heating rate of 30 to 50°C / min.

5. A method for manufacturing a bonded body according to claim 1 or 2, further comprising a second cooling step of cooling to 50°C at a second average cooling rate of 5 to 20°C / min after the annealing step.

6. A method for manufacturing a circuit board, comprising the step of removing a portion of the metal plate from a joint obtained by the manufacturing method described in claim 1 or 2 to obtain a circuit board having a conductive portion.

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