Method for manufacturing joined body

Abstract

This method for manufacturing a joined body comprises: a step for manufacturing a laminated body provided with a laminated structure of a metal plate, a brazing material layer, and a ceramic substrate; a step for attaching a jig to the laminated body and applying a load thereto; a step for manufacturing the joined body by heating and joining the laminated body inside a joining furnace while applying the load to the laminated body; a step for cooling the joined body while maintaining a state in which the load is applied to the joined body after the heating and joining has occurred; a step for taking the joined body out of the joining furnace before the temperature of the joined body falls to room temperature; a step for holding the joined body until the temperature of the joined body reaches room temperature while maintaining a state in which the load is applied to the joined body, which has been taken out of the joining furnace; and a step for removing the jig from the joined body after holding the joined body until the temperature thereof reaches room temperature.

Description

Method for producing joined body

[0001] Embodiments relate to a method for producing a joined body.

[0002] Ceramic circuit boards are used as circuit boards on which semiconductor elements are mounted. For example, a ceramic circuit board in which the difference in thickness between the front and back metal plates is 0.1 mm or more and 0.3 mm or less is known. In the above ceramic circuit board, the amount of warpage on the long side and the amount of warpage on the short side are controlled within a predetermined range. Further, there is known a joined body that uses an Ag-free active metal brazing material and has a warpage amount of 0.3 mm or less. As described above, ceramic circuit boards are required to have a reduced amount of warpage.

[0003] A joined body is produced by heating a laminate in which an active metal brazing material layer and a metal plate are laminated on a ceramic substrate. For example, an example in which heat bonding is performed while applying a pressing force is known.

[0004] Japanese Patent No. 6829204, International Publication No. WO 2022 / 024832, Japanese Patent No. 7363583

[0005] The above-mentioned examples of ceramic circuit boards are bonded in a batch furnace using an active metal bonding method. A batch furnace is also called a vacuum furnace. Since a batch furnace uses vacuum, the inside of the furnace is a closed space. After bonding in a batch furnace, the bonded body is taken out from the batch furnace after waiting until the temperature drops to room temperature.

[0006] In another example of the above-mentioned ceramic circuit board, a continuous furnace is used. In a continuous furnace, laminates are bonded while being conveyed by a belt conveyor. The interior of a continuous furnace is divided into a temperature rising zone, a heat bonding zone, and a cooling zone. In addition, in a continuous furnace, it is necessary to lengthen the cooling zone until the temperature drops to room temperature.

[0007] Conventionally, in both batch furnaces and continuous furnaces, the bonded body is taken out from the bonding furnace after waiting until the bonded body cools down to room temperature. Since the bonding temperature in the active metal bonding method is as high as about 800° C., it takes a long time for the bonded body to cool down to room temperature, resulting in poor production efficiency.

[0008] A problem to be solved by the embodiments of the present invention is to provide a method for producing a joined body that can improve production efficiency.

[0009] A method for manufacturing a bonded body according to an embodiment is a method for manufacturing a bonded body having a ceramic substrate and a metal plate joined via a bonding layer, comprising the steps of: manufacturing a laminate having a laminated structure of a metal plate, a brazing layer and a ceramic substrate; attaching a jig to the laminate and applying a load; manufacturing a bonded body by heating and bonding the laminate in a bonding furnace while the load is applied to the laminate; cooling the bonded body after heating and bonding while maintaining the state in which the load is applied to the bonded body; removing the bonded body from the bonding furnace before the temperature of the bonded body drops to room temperature; holding the bonded body after it has been removed from the bonding furnace while maintaining the state in which the load is applied to the bonded body until the temperature of the bonded body reaches room temperature; and removing the jig from the bonded body after holding the bonded body until it reaches room temperature.

[0010] This figure shows an example of a laminate according to an embodiment. This figure shows an example of the process of attaching a jig for applying a load to the laminate according to the embodiment. This figure shows another example of the process of attaching a jig for applying a load to the laminate according to the embodiment. This figure shows yet another example of the process of attaching a jig for applying a load to the laminate according to the embodiment. This figure shows an example of the method for manufacturing a joined body according to the embodiment. This figure shows an example of a joined body according to the embodiment.

[0011] The embodiments will be described below with reference to the drawings. In each embodiment, substantially identical components will be denoted by the same reference numerals, and their descriptions may be partially omitted. The drawings are schematic, and the relationship between the thickness of each part and its planar dimensions, the ratio of the thicknesses of each part, etc., may differ from those in reality.

[0012] A method for manufacturing a bonded body according to an embodiment is a method for manufacturing a bonded body having a ceramic substrate and a metal plate joined via a bonding layer, comprising the steps of: manufacturing a laminate having a laminated structure of a metal plate, a brazing layer and a ceramic substrate; attaching a jig to the laminate and applying a load; manufacturing a bonded body by heating and bonding the laminate in a bonding furnace while the load is applied to the laminate; cooling the bonded body after heating and bonding while maintaining the state in which the load is applied to the bonded body; removing the bonded body from the bonding furnace before the temperature of the bonded body drops to room temperature; holding the bonded body after it has been removed from the bonding furnace while maintaining the state in which the load is applied to the bonded body until the temperature of the bonded body reaches room temperature; and removing the jig from the bonded body after holding the bonded body until it reaches room temperature.

[0013] Figure 1 shows an example of a laminate according to the embodiment. Figures 2, 3, and 4 show an example of the process of attaching a jig for applying a load to the laminate according to the embodiment. Figure 5 shows an example of a method for manufacturing a joined body according to the embodiment. Figure 6 shows an example of a joined body according to the embodiment. Figures 1 to 6 show a laminate 1, a ceramic substrate 2, a brazing layer 3, a metal plate 4, a jig 5 (5-1 to 5-4), a continuous furnace 6, a belt conveyor 7, a heating zone 8, a heating and joining zone 9, a cooling zone 10, a joined body 11, and a joining layer 12.

[0014] The process involves manufacturing a laminate 1 comprising a laminated structure of a metal plate 4, a brazing material layer 3, and a ceramic substrate 2. In Figure 1, the brazing material layer 3 and the metal plate 4 are laminated on both sides of the ceramic substrate 2. The laminated structure before heat bonding is referred to as the laminate 1, and the laminated structure after heat bonding is referred to as the bonded body 11. Although Figure 1 shows an example in which the metal plate 4 is laminated on both sides of the ceramic substrate 2, the metal plate 4 may also be laminated on only one side of the ceramic substrate 2. Furthermore, there may be one or more metal plates 4 laminated on one side of the ceramic substrate 2.

[0015] Next, the process of attaching the jig 5 to the laminate 1 is carried out. In Figure 2, the jigs 5 are placed above and below the laminate 1. Jig 5-1 is placed below the laminate 1. Jig 5-2 is placed above the laminate 1. The jig 5 is heat resistant and does not react with the metal plate 4. A boron nitride plate can be used as the jig 5. Alternatively, the load applied by the jig 5 may be achieved by the weight of the jig 5 itself. A boron nitride plate has a specific gravity (density) of 1 g / cm³. ３ It can handle weights larger than the above. Furthermore, the jig 5 may be fixed with screws or other fastening methods not shown. Also, the jig 5 itself may be stacked, or additional weights may be placed on it. Therefore, the weights are also included in the jig 5. Examples of weights include tungsten alloy.

[0016] When processing multiple laminates 1, the multiple laminates 1 may be placed on the jig 5. Alternatively, the multiple laminates 1 may be placed on top of each other. When placing multiple laminates 1 on top of each other, the jig 5 may be placed between the laminates 1 as needed. Figure 3 shows an example in which the jig 5-2 is placed between multiple laminates 1 (1-1, 1-2). The jig 5-1, laminate 1-1, jig 5-2, laminate 1-2, and jig 5-3 have a structure in which they are stacked on top of each other.

[0017] Figure 4 shows an example of placing jig 5-4 on top of jig 5-2. For example, jig 5-2 may be a boron nitride plate, and jig 5-4 may be a weight (such as a tungsten alloy). The weight (jig 5-4) placed on top of jig 5-2 (boron nitride plate) should be able to withstand the heat bonding temperature described later.

[0018] The weight of the jig 5 is preferably 0.5 kg or more. If the weight is less than 0.5 kg, the load may be insufficient. There is no particular upper limit to the weight of the jig 5, but it is preferably 10 kg or less. As will be described later, if it is too heavy, it is not suitable for the conveying process of a continuous furnace. For this reason, the weight of the jig 5 is preferably in the range of 0.5 kg to 10 kg, and more preferably 0.7 kg to 3 kg.

[0019] The jig 5 is preferably larger than the length and width dimensions of the ceramic substrate 2 and the metal plate 4. Using a larger jig improves the effect of reducing the warping of the joined body 11. The jig 5 is preferably 3 mm or more larger than the length and width dimensions of the ceramic substrate 2 and the metal plate 4.

[0020] When multiple jigs 5 are placed on the laminate 1, the total weight of the jigs is considered the weight of jig 5. For example, in the laminate structure shown in Figure 3, the sum of jigs 5-2 and 5-3 is the weight of jig 5. Similarly, in the laminate structure shown in Figure 4, the sum of jigs 5-2 and 5-4 is the weight of jig 5. Even when the number of laminates is increased, the total weight of the jigs 5 placed on top of the bottom laminate 1 is considered the weight of jig 5.

[0021] The load applied to the laminate 1 is preferably within the range of 0.001 MPa to 5 MPa. If the load is less than 0.001 MPa, the load will be insufficient, and the effect of suppressing warping may not be obtained. Also, the jig 5 may shift during transport. If the load is greater than 5 MPa, the jig 5 may become too heavy, increasing the load on transporting it to the joining furnace. Furthermore, if too much load is applied to the laminate 1, the brazing material layer 3 may be crushed, causing unwanted overflow. For this reason, the load applied to the laminate 1 is preferably within the range of 0.001 MPa to 5 MPa, and more preferably within the range of 0.01 MPa to 2 MPa.

[0022] When multiple jigs 5 are stacked, the load is considered to be the load on the bottommost stack 1. For example, in Figure 3, the load is the sum of jig 5-2, stack 1-2, and jig 5-3 placed on the bottommost stack 1-1. Similarly, in Figure 4, the load is the sum of jig 5-2 and jig 5-4. In the same way, when the number of stacked structures is increased, the load is the sum of stack 1 and jig 5 placed on the bottommost stack 1 (1-1).

[0023] Next, a process is carried out to produce a joined body 11 by heating and joining the laminate 1 in a joining furnace while a load is applied to it. Examples of joining furnaces include continuous furnaces and vacuum furnaces. In a continuous furnace, the laminate 1 can be heated and joined while being transported by a belt conveyor. In a vacuum furnace, the laminate 1 can be placed in a sealed space under vacuum and then heated and joined. The vacuum level is 10 －３ Examples include Pa or less. Vacuum furnaces are sometimes called batch furnaces. When using activated metal brazing materials, as described later, the heat bonding temperature is in the range of 700°C to 950°C. Furthermore, the heat bonding time is preferably in the range of 30 minutes to 10 hours. Also, in the case of a vacuum furnace, since it is a sealed space, unless a special cooling process is performed, the rate of cooling from the bonding temperature to room temperature is about 5°C / minute. Because vacuum furnaces (batch furnaces) are sealed spaces, the rate of cooling is slow. To increase the rate of cooling in a vacuum furnace, a cooling process using a blower or the like is required.

[0024] Figure 5 is a schematic diagram of the joining process using a continuous furnace 6. The continuous furnace 6 can heat and join a laminate 1 placed on a belt conveyor 7 while it is being transported. A jig 5 is placed on the laminate 1.

[0025] The continuous furnace 6 is divided into a heating zone 8, a heat bonding zone 9, and a cooling zone 10. The heating zone 8 is the region where the temperature is raised from room temperature to the heat bonding temperature. The heat bonding zone 9 is the region where the temperature is maintained at the heat bonding temperature. When using the activated metal brazing material described later, the heat bonding temperature will be in the range of 700°C to 950°C. The cooling zone 10 is the region where the temperature is cooled from the heat bonding temperature to room temperature. Furthermore, a bonded body 11 can be manufactured by performing heat bonding. The lengths of the heating zone 8, the heat bonding zone 9, and the cooling zone 10 are arbitrary. Also, each may be divided into multiple zones.

[0026] The heating and holding time is preferably between 10 minutes and 100 minutes. If the heating and holding time is less than 10 minutes, there may not be enough time for the brazing material to melt and solidify. Conversely, if it exceeds 100 minutes, the brazing material may diffuse too much into the metal plate.

[0027] In the cooling zone 10, a process is carried out to cool the material from the bonding temperature to a predetermined temperature or room temperature. The cooling rate is preferably 20°C / min or more and 100°C / min or less. The heating zone 8 is a process of raising the temperature from room temperature to the bonding temperature. The heating rate is preferably 20°C / min or more and 100°C / min or less. In the case of a continuous furnace 6, the heating rate or cooling rate can be controlled by dividing the heating zone 8 and the cooling zone 10 into multiple zones.

[0028] By transporting the laminated body 1 with the jig 5 still in place through the continuous furnace 6, the laminated body 1 can be heat-bonded while a load is applied to it. In the case of a vacuum furnace, by placing the laminated body 1 with the jig 5 still in place in a sealed space, the laminated body 1 can be heat-bonded while a load is applied to it. In other words, heat-bonding the laminated body 1 while a load is applied means that a load is applied to the laminated body 1 in advance, rather than pressurizing it using the function of the bonding furnace.

[0029] Next, after the heat bonding process, the bonded body 11 is cooled while maintaining the load applied to it. This indicates that the jig 5 placed on the bonded body 11 remains in place even during the cooling process after heat bonding. In the case of a continuous furnace 6, the cooling process indicates passing through the cooling zone 10. In the case of a vacuum furnace, the cooling process indicates cooling from the heat bonding temperature to room temperature.

[0030] Next, the joint 11 is removed from the joining furnace before it cools to room temperature. By removing the joint 11 before it cools to room temperature, the time it takes for it to cool to room temperature can be shortened. This results in a shorter lead time. Room temperature refers to the temperature of the room. Room temperature is generally within the range of 10°C to 50°C. In other words, it is not necessary to strictly control the room temperature to 25°C.

[0031] Typically, a continuous furnace 6 has a cooling zone 10 that exists until the temperature drops to room temperature. The step of removing the joined body 11 from the joining furnace before it drops to room temperature means removing the joined body 11 midway through the cooling zone 10. Another method is to bring the cooling zone 10 to a predetermined temperature and then remove the joined body 11 from the furnace. In the case of a vacuum furnace, the step is to remove the joined body 11 from the sealed space before it drops to room temperature.

[0032] The step of removing the joined body 11 from the joining furnace before it cools to room temperature is preferably within the range of 100°C to 400°C. Removing it within this temperature range allows for a reduction in lead time. If the temperature at which the joined body 11 is removed from the joining furnace is below 100°C, it is close to room temperature, which may result in insufficient lead time reduction. Furthermore, if the temperature at which the joined body 11 is removed from the joining furnace exceeds 400°C, the joining layer 12 may not have hardened, potentially causing warping. In particular, if the joining layer 12 is an activated metal brazing material layer, temperatures exceeding 400°C may cause warping. For this reason, the step of removing the joined body 11 from the joining furnace before it cools to room temperature is preferably within the range of 100°C to 400°C and 200°C to 350°C. Furthermore, the step of removing the joined body 11 from the joining furnace before it cools to room temperature is preferably performed using a robot. Examples of robots include automated guided vehicles (AGVs) and robotic arms. Automated guided vehicles also include those equipped with forklifts. By using a robot, it is possible to safely remove the product even at high temperatures between 100°C and 400°C.

[0033] By removing the joined body 11 from the joining furnace, the cooling rate can be increased to 10°C / min or more, and even to 20°C / min or more. Furthermore, it can be increased to 120°C / min or more. This not only eliminates the time it takes for the joined body 11 to cool down to room temperature inside the joining furnace, but also speeds up the cooling of the joined body 11. The cooling rate may be adjusted using natural cooling or a cooling process using a blower. In addition, if the jig 5 is left attached, warping can be suppressed even when a cooling process using a blower is performed.

[0034] Next, a step of holding the bonded body 11 taken out of the bonding furnace to room temperature while maintaining the state where a load is applied to the bonded body 11 is performed. Maintaining the state where a load is applied to the bonded body 11 means that the jig 5 attached to the bonded body 11 is not removed and is kept as it is. Note that there is no problem even if the jig 5 is slightly displaced during conveyance.

[0035] Next, after cooling to room temperature, a step of removing the load-applying jig 5 from the bonded body 11 is performed. A guideline for room temperature is 25° C. The jig 5 may be removed once cooled to approximately 30° C.

[0036] With the above steps, warpage of the bonded body 11 can be suppressed, and the lead time of the manufacturing process can be shortened. Therefore, manufacturing efficiency can be improved.

[0037] The ceramic substrate 2 may be one type selected from a silicon nitride substrate, an aluminum nitride substrate, an aluminum oxide substrate, and a zirconium oxide substrate. These are distinguished according to the component that is contained in the largest amount. For example, when the largest component is silicon nitride, the substrate is a silicon nitride substrate. Furthermore, sialon (SiAlON) substrates are included in silicon nitride substrates.

[0038] The thermal conductivity of the silicon nitride substrate is 40 W / m·K or higher, and more preferably 80 W / m·K or higher. Furthermore, it is preferable that the three-point bending strength of the silicon nitride substrate is 600 MPa or higher, and more preferably 700 MPa or higher.

[0039] The thermal conductivity of the aluminum nitride substrate is 160 W / m·K or higher, and more preferably 200 W / m·K or higher. The three-point bending strength of the aluminum nitride substrate is approximately 300 to 450 MPa.

[0040] The three-point bending strength of the aluminum oxide substrate is approximately 300 to 450 MPa. The aluminum oxide substrate is inexpensive compared to other substrates. Furthermore, the thermal conductivity of the aluminum oxide substrate is approximately 20 to 30 W / m·K.

[0041] The three-point bending strength of the zirconium oxide substrate is as high as approximately 550 MPa, but the thermal conductivity is approximately 30 to 50 W / m·K.

[0042] As described above, the silicon nitride substrate has high strength. Therefore, the thickness of the silicon nitride substrate can be set to 0.2 mm or more and 0.5 mm or less. From this point of view, application to a silicon nitride substrate is preferable.

[0043] The length of at least one side of the ceramic substrate 2 is preferably 100 mm or more. A large-sized substrate having a side length of 100 mm or more enables multiple production. Multiple production refers to obtaining individual bonded bodies 11 (or individual ceramic circuit boards) by dividing a large bonded body (a bonded body using a large-sized substrate). The upper limit of the length of one side of the ceramic substrate 2 is not particularly limited, but is preferably 400 mm or less. If the length of one side exceeds 400 mm, it may become difficult to prepare a flat substrate. For this reason, the length of at least one side of the ceramic substrate 2 is preferably within a range of 100 mm or more and 400 mm or less, more preferably 150 mm or more and 300 mm or less.

[0044] The metal plate 4 is preferably one type or two or more types selected from a copper plate (including copper alloy plates) or an aluminum plate (including aluminum alloy plates).

[0045] The brazing filler metal layer 3 forms the bonding layer 12. The brazing filler metal layer 3 is preferably made of an active metal brazing filler metal. When the metal plate 4 is a copper plate (including copper alloy plates), it is preferable to use an active metal brazing filler metal containing Ag or Cu as a main component. Further, when the metal plate 4 is an aluminum plate (including aluminum alloy plates), it is preferable to use an active metal brazing filler metal containing Al as a main component.

[0046] The active metal brazing filler metal composition containing Ag or Cu as a main component contains 0 mass% or more and 60 mass% or less of Ag (silver), 15 mass% or more and 70 mass% or less of Cu (copper), and Ti (titanium) or TiH ２ (titanium hydride) in an amount of 1 mass% or more and 15 mass% or less. Further, Ti and TiH ２When both are used, the total amount should be within the range of 1% by mass or more and 15% by mass or less. Furthermore, when both Ag and Cu are used, it is preferable that Ag be within the range of 20% by mass or more and 60% by mass or less, and Cu be within the range of 15% by mass or more and 40% by mass or less. Additionally, if necessary, one or both of Sn (tin) or In (indium) may be included in an amount of 1% by mass or more and 50% by mass or less. Also, Ti or TiH ２ The content of is preferably within the range of 1% by mass to 15% by mass. In addition, if necessary, carbon (C) may be included in a range of 0.1% by mass to 2 wt%.

[0047] The ratio of the active metal brazing alloy composition is calculated by considering the total mass of the raw materials to be mixed as 100% by mass. For example, if it is composed of three types of metals, Ag, Cu, and Ti, then Ag + Cu + Ti = 100% by mass. Also, Ag, Cu, TiH ２ When composed of four types of In, Ag + Cu + TiH ２ +In = 100% by mass. Also, if it is composed of five types of elements: Ag, Cu, Ti, Sn, and C, then Ag + Cu + Ti + Sn + C = 100% by mass.

[0048] Ag or Cu are components that form the base material of the brazing material. Sn or In have the effect of lowering the melting point of the brazing material. C (carbon) have the effect of controlling the fluidity of the brazing material and controlling the structure of the bonding layer 12 by reacting with other components. For this reason, examples of brazing material components include Ag-Cu-Ti, Ag-Cu-Sn-Ti, Ag-Cu-Ti-C, Ag-Cu-Sn-Ti-C, Ag-Ti, Cu-Ti, Ag-Sn-Ti, Cu-Sn-Ti, Ag-Ti-C, Cu-Ti-C, Ag-Sn-Ti-C, and Cu-Sn-Ti-C. In may be used instead of Sn. In addition, both Sn and In may be used. Furthermore, the activated metal brazing material may contain 0.1% to 10% by mass of one or more elements selected from tungsten (W), molybdenum (Mo), and rhenium (Re). Tungsten, molybdenum, and rhenium can control the fluidity of the activated metal brazing material. Magnesium (Mg) may also be added to the activated metal brazing material. Activated metal brazing materials containing Ag, Cu, Sn, and Ti as essential components are called Ag-Cu-Sn-Ti type brazing materials. Activated metal brazing materials that do not contain Ag but contain Cu, Sn, and Ti as essential components are called Cu-Sn-Ti type brazing materials.

[0049] When the metal plate 4 is an aluminum plate, the active metal brazing material is preferably an Al-Si or Al-Mg type brazing material. The content of one or two of Si or Mg in the active metal brazing material is preferably in the range of 0.1% by mass or more and 20% by mass or less.

[0050] A binder is added to the activated metal brazing material to form an activated metal brazing paste, which is then applied in a coating process. The brazing layer 3 is formed by applying the activated metal brazing paste to either the ceramic substrate or the metal plate 4 to form a coating layer. When joining the metal plate 4 to both sides of the ceramic substrate 2, it is preferable to apply the activated metal brazing paste to the ceramic substrate 2.

[0051] The thickness of the metal plate 4 is preferably 0.2 mm or more. Increasing the thickness of the metal plate 4 can improve heat dissipation and increase electrical conductivity. For this reason, the thickness of the metal plate 4 is preferably 0.2 mm or more, and more preferably 0.6 mm or more. The thermal conductivity of copper is 398 W / m·K, and the thermal conductivity of aluminum is 237 W / m·K. Copper has a higher thermal conductivity than aluminum. For this reason, it is preferable to use a thicker copper plate.

[0052] When joining metal plates 4 to both sides of a ceramic substrate 2, the difference in thickness between the pair of metal plates 4 (front and back metal plates) joined to both sides may be 0.01 mm or more. For example, if you want to increase the current capacity to the semiconductor element provided on the front metal plate, it is effective to make the front metal plate thicker. On the other hand, by changing the thickness of the front and back metal plates 4, warping is more likely to occur. With the manufacturing method of the joined body according to the embodiment, warping can be suppressed even if there is a difference in thickness between the front and back metal plates. Warping can be suppressed even if the difference in thickness between the front and back metal plates is 0.01 mm or more, and even 0.05 mm or more. There is no particular upper limit to the difference in thickness between the front and back metal plates, but it is preferable that it be 0.3 mm or less. If the difference in thickness between the front and back metal plates exceeds 0.3 mm, there is a possibility that warping will increase. For this reason, the difference in thickness between the front and back metal plates is preferably within the range of 0.01 mm to 0.3 mm, and even more preferably within the range of 0.05 mm to 0.2 mm.

[0053] A laminate 1 is fabricated by placing an activated metal brazing layer 3 and a metal plate 4 on a ceramic substrate 2. The heating and joining step of the laminate 1 is preferably performed at a heating temperature within the range of 600°C to 950°C. Furthermore, a batch furnace, continuous furnace, hot press, etc., can be used for the heating and joining step.

[0054] A bonded body 11 can be obtained by performing a heat bonding process. An etching process is then performed on the obtained bonded body 11 to impart a circuit shape to the metal plate 4. The etching process may be performed to control the side shape of the metal plate 4 and the size of the bonded layer overhang.

[0055] If the bonded body 11 is a large bonded body (a ceramic substrate with at least one side length of 100 mm or more), multiple cuts may be performed. Multiple cuts are a process of dividing the material into individual pieces by applying a scribing process. Examples of scribing processes include laser scribing. Applying a scribing process after creating a circuit shape makes it easier to divide the material.

[0056] The manufacturing method for the bonded body according to this embodiment can reduce the warpage of the bonded body 11 to 1.2 mm or less. Furthermore, it can shorten the lead time by reducing the cooling process time by 3 hours or more, because the jig 5 that applies the load also acts as a heat sink. It is also suitable for manufacturing large bonded bodies. Therefore, it can improve the mass productivity of ceramic circuit boards.

[0057] (Examples 1-6, Comparative Examples 1-3) As ceramic substrates, silicon nitride substrates as shown in Table 1 were prepared.

[0058]

[0059] Next, copper plates with the thicknesses shown in Table 2 were prepared as metal plates. The copper plates used were 10 mm smaller in both length and width than the ceramic substrates. For example, the copper plate to be joined to SIN1 was 130 mm long x 90 mm wide. The copper plate to be joined to SIN2 was 110 mm long x 110 mm wide.

[0060]

[0061] Next, activated metal brazing materials were prepared. Activated metal brazing material 1 is an Ag-Cu-Sn-Ti type brazing material. Activated metal brazing material 2 is a Cu-Sn-Ti type brazing material that does not contain Ag.

[0062] A laminate was fabricated by applying activated metal brazing paste to both sides of a ceramic substrate and placing a metal plate on top. The laminate has a five-layer structure consisting of a metal plate, an activated metal brazing layer, a ceramic substrate, another activated metal brazing layer, and a metal plate. The thickness of the activated metal brazing layer was approximately 20 μm. The combinations of ceramic substrate, metal plate, and activated metal brazing are shown in Table 3.

[0063]

[0064] A load-applying jig was attached to each laminate. The laminates were grouped in sets of 20, and the load-applying jig was attached to each set. The load was set within the range of 0.001 to 5 MPa. A boron nitride plate was used as the load-applying jig. The boron nitride plate used was larger than the length and width dimensions of the ceramic substrate and metal plate. The boron nitride plate was positioned so that it did not protrude from the ceramic substrate and metal plate. In addition, weights were placed on top of the boron nitride plate as needed to adjust the load. The total weight of the boron nitride plate and weight was set within the range of 0.5 to 3 kg. When grouping 20 laminates together, a boron nitride plate was added to every 5 laminates.

[0065] Next, a heat bonding process was performed. For the heat bonding process, either a batch furnace or a continuous furnace was used as the bonding furnace. In the batch furnace, heat bonding was performed at 850°C in a vacuum. The cooling rate of the batch furnace was approximately 5°C / min. In the continuous furnace, heat bonding was performed at 900°C in a nitrogen atmosphere. The cooling rate of the continuous furnace was approximately 20-30°C / min.

[0066] In Examples 1 to 6, after the heat bonding process, the bonded body, with the load-applying jig still attached, was removed from the bonding furnace at a temperature between 100°C and 400°C. After the bonded body, with the load-applying jig still attached, was cooled to room temperature (approximately 25°C), the jig was removed from the bonded body. Table 4 shows the temperature at which the bonded body was removed from the bonding furnace (removal temperature).

[0067] In Comparative Examples 1 and 2, the joined bodies, with the load-applying jig still attached, were cooled to room temperature (approximately 25°C) in the joining furnace before being removed from the furnace. In Comparative Example 3, the joined bodies were removed from the furnace at a temperature of 200°C. Each of the joined bodies was manufactured using this process.

[0068]

[0069] In Examples 1 to 6, the cooling rate from the removal temperature to room temperature (25°C) was set to 10°C / min or more, and further to 130°C / min or more. In Examples 1 to 6, and Comparative Examples 1 and 2, the temperature at which the load-applying jig was removed from the joint (removal temperature) was set to room temperature. In Comparative Example 3, the load-applying jig was removed at a removal temperature of 100°C.

[0070] The amount of warpage of the bonded bodies obtained by the manufacturing methods of each example and comparative example was investigated. The amount of warpage was determined by examining the warpage in the long-side or short-side direction of the ceramic substrate of the bonded body. A three-dimensional shape measuring machine was used for the measurement. For the warpage in the long-side direction, a straight line was drawn from one end of the long side to the other end, and the distance between this line and the ceramic substrate was defined as the amount of warpage. Similarly, for the warpage in the short-side direction, a straight line was drawn from one end of the short side to the other end, and the distance between this line and the ceramic substrate was defined as the amount of warpage.

[0071] The amount of warping of 20 joints was examined, and the average and maximum values ​​were shown. The average value is the average of the warping in the long-side direction and the warping in the short-side direction of the 20 joints. The maximum value was the largest amount of warping in the long-side direction and the short-side direction of the 20 joints.

[0072] The time taken from heat bonding until the removal of the load-applying jig at room temperature was measured. The time taken using a batch furnace is shown as a ratio (time ratio) to the time taken in Comparative Example 1, which was set to 100. Similarly, the time taken using a continuous furnace is shown as a ratio (time ratio) to the time taken in Comparative Example 2, which was set to 100. The results are shown in Table 5.

[0073]

[0074] The amount of warpage in the example is comparable to that of Comparative Examples 1 and 2. This indicates that removing the material from the joining furnace between 100°C and 400°C during the cooling process does not affect the warpage. Furthermore, because the material can be removed between 100°C and 400°C, holding time in the joining furnace is unnecessary. It was also found that the cooling rate increases, resulting in a time reduction.

[0075] Furthermore, as in Comparative Example 3, the warping increased when the jig that applied the load was removed before the temperature of the bonded body reached room temperature. Examples 1 to 6 were able to reduce the amount of warping even when the length of one side of the ceramic substrate was large, such as 100 mm or more, and shorten the manufacturing time. The examples were able to shorten the lead time by more than 3 hours. They are also suitable for multi-cavity molding, further improving mass productivity.

[0076] Although several embodiments of the present invention have been illustrated above, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. Modifications of these embodiments are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. Furthermore, the embodiments described above can be implemented in combination with each other.

Claims

1. A method for manufacturing a bonded body having a ceramic substrate and a metal plate joined via a bonding layer, comprising: a step of manufacturing a laminate having a laminated structure of the metal plate, a brazing layer and the ceramic substrate; a step of attaching a jig to the laminate and applying a load; a step of manufacturing the bonded body by heating and bonding the laminate in a bonding furnace while the load is applied to the laminate; a step of cooling the bonded body after the heating and bonding while maintaining the state in which the load is applied to the bonded body; a step of removing the bonded body from the bonding furnace before the temperature of the bonded body drops to room temperature; a step of holding the bonded body, which has been removed from the bonding furnace, while maintaining the state in which the load is applied to the bonded body until the temperature of the bonded body reaches room temperature; and a step of removing the jig from the bonded body after holding the bonded body until it reaches room temperature.

2. The step of removing the joined body from the joining furnace is performed when the temperature of the joined body is 100°C or higher and 400°C or lower, the method for manufacturing a joined body according to claim 1.

3. The method for manufacturing a joint according to claim 1 or claim 2, wherein the load is 0.001 MPa or more and 5 MPa or less.

4. The method for manufacturing a joined body according to claim 1 or claim 2, wherein the load is applied by placing the jig weighing 0.5 kg or more on the laminated body.

5. The method for manufacturing a joined body according to claim 3, wherein the load is applied by placing the jig weighing 0.5 kg or more on the laminated body.

6. The method for manufacturing a joined body according to claim 1 or claim 2, wherein the joining furnace is a continuous furnace, and the step of cooling the joined body is a step of passing through the cooling zone of the continuous furnace.

7. The method for manufacturing a joined body according to claim 5, wherein the joining furnace is a continuous furnace, and the step of cooling the joined body is a step of passing through the cooling zone of the continuous furnace.

8. The method for manufacturing a joint according to claim 1 or claim 2, wherein the brazing layer is a coating layer of activated metal brazing paste.

9. The method for manufacturing a bonded body according to claim 7, wherein the brazing layer is a coating layer of activated metal brazing paste.

10. The method for manufacturing a joined body according to claim 1 or claim 2, wherein the thickness of the metal plate is 0.2 mm or more.

11. The method for manufacturing a joined body according to claim 9, wherein the thickness of the metal plate is 0.2 mm or more.

12. The method for manufacturing a bonded body according to claim 1 or claim 2, wherein the bonded body has a pair of metal plates bonded to both sides of the ceramic substrate, and the difference in thickness between the pair of metal plates is 0.01 mm or more.

13. The method for manufacturing a bonded body according to claim 11, wherein the bonded body has a pair of metal plates bonded to both sides of the ceramic substrate, and the difference in thickness between the pair of metal plates is 0.01 mm or more.

14. The method for manufacturing a bonded body according to claim 1 or claim 2, wherein the ceramic substrate is a silicon nitride substrate and the metal plate is a copper plate.

15. The method for manufacturing a bonded body according to claim 13, wherein the ceramic substrate is a silicon nitride substrate and the metal plate is a copper plate.

16. The method for manufacturing a bonded body according to claim 1 or claim 2, wherein the length of at least one side of the ceramic substrate is 100 mm or more.

17. The method for manufacturing a bonded body according to claim 13, wherein the length of at least one side of the ceramic substrate is 100 mm or more.

18. The method for manufacturing a bonded body according to claim 15, wherein the length of at least one side of the ceramic substrate is 100 mm or more.

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