Brazing material, joint, ceramic circuit board, and method for manufacturing the joint

Abstract

According to one embodiment of the present invention, a brazing filler material for bonding a ceramic substrate and a metal plate to each other is characterized by having an endothermic peak within the range of from 550°C to 700°C in the temperature raising step in the DSC curve as determined by a differential scanning calorimeter (DSC). It is preferable that the brazing filler material contains Ag, Cu and Ti. In addition, it is preferable that the brazing filler material has two or more endothermic peaks within the range of from 550°C to 650°C in the temperature raising step.

Description

[Technical Field]

[0001] The embodiments described later relate to brazing material, a bonded body, a ceramic circuit board, and a method for manufacturing the bonded body. [Background technology]

[0002] Joints of ceramic substrates and copper plates are used as circuit boards for mounting semiconductor elements and the like. International Publication No. 2018 / 021472 (Patent Document 1) discloses a ceramic copper circuit board in which a ceramic substrate and a copper plate are joined. Patent Document 1 uses a brazing material containing Ag, Cu, Ti, etc. in the bonding layer. Furthermore, the TCT characteristics are improved by controlling the nanoindentation hardness of the bonding layer. Patent Document 1 controls the nanoindentation hardness by including AgTi crystals or TiC in the bonding layer. Patent Document 1 improves bonding strength and TCT characteristics by controlling the nanoindentation hardness. Patent Document 1 describes bonding at high temperatures of 780-850°C. High bonding temperatures increase the load on bonding equipment. Furthermore, high-temperature bonding imparts thermal stress to the ceramic substrate or copper plate. This thermal stress load causes distortion of the ceramic copper circuit board. For this reason, bonding at lower temperatures was desired. For example, International Publication No. 2018 / 199060 (Patent Document 2) discloses a ceramic copper circuit board bonded at a bonding temperature of 720 to 800°C. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. 2018 / 021472 [Patent Document 2] International Publication No. 2018 / 199060 [Patent Document 3] Patent No. 5720839 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] Patent Document 2 achieves a lower bonding temperature than Patent Document 1, thus mitigating thermal stress. However, because Patent Document 2 aims to diffuse Ag into the copper plate, the amount of Ag in the bonding brazing material was high. This resulted in a significant cost burden. For example, Japanese Patent No. 5720839 (Patent Document 3) discloses a CuSnTi brazing material. Bonding is possible at 650°C using a brazing material that does not contain Ag. However, because Patent Document 3 involves sputtering the Ti material, it was not suitable for large substrates. This invention addresses these problems and provides a brazing material that enables bonding at low temperatures. [Means for solving the problem]

[0005] The brazing material according to this embodiment is for joining a ceramic substrate and a metal plate. The brazing material is characterized in that, when the DSC curve is measured with a differential scanning calorimeter (DSC), it has an endothermic peak within the range of 550°C to 700°C during the heating process. [Brief explanation of the drawing]

[0006] [Figure 1] A schematic diagram illustrating the DSC curve. [Figure 2] A diagram illustrating the method for calculating peak height in a DSC curve. [Figure 3] A temperature program for measuring DSC graphs. [Figure 4] An example of a DSC curve (450°C or higher) for the heating process in Example 1. [Figure 5] An example of a DSC curve (above 450°C) for the cooling process in Example 1. [Figure 6] An example of a DSC curve (above 450°C) for the heating process in Comparative Example 1. [Figure 7] An example of a DSC curve (above 450°C) for the cooling process in Comparative Example 1. [Figure 8] An example of the DSC curve (above 450 °C) in the heating process of Example 2. [Figure 9] An example of the DSC curve (above 450 °C) in the cooling process of Example 2. [Figure 10] An example of the DSC curve (below 550 °C) in the heating process of Example 3. [Figure 11] An example of the DSC curve (below 550 °C) in the cooling process of Example 3. [Figure 12] An example of the DSC curve (below 550 °C) in the heating process of Example 4. [Figure 13] An example of the DSC curve (below 550 °C) in the cooling process of Example 4. [Figure 14] An example of the DSC curve (below 550 °C) in the heating process of Example 5. [Figure 15] An example of the DSC curve (below 550 °C) in the cooling process of Example 5. [Figure 16] A diagram showing an example of a joined body using the brazing material according to the embodiment. [Figure 17] A diagram showing an example of a ceramic circuit board using the brazing material according to the embodiment. [Figure 18] A diagram showing an example of a ceramic circuit board using the brazing material according to the embodiment. [Figure 19] A diagram showing an example of a ceramic circuit board using the brazing material according to the embodiment.

Mode for Carrying Out the Invention

[0007] In one embodiment, the brazing material for joining a ceramic substrate and a copper plate contains Ag, Cu, and Ti. When the DSC curve of this brazing material is measured with a differential scanning calorimeter (DSC), it is characterized by having an endothermic peak within the range of 550 °C or higher and 700 °C or lower in the heating process.

[0008] The brazing material in this embodiment is for joining a ceramic substrate and a metal plate. Examples of ceramic substrates include silicon nitride substrates, aluminum nitride substrates, aluminum oxide substrates, and argil substrates. An argil substrate is a substrate in which aluminum oxide and zirconium oxide are mixed. Examples of metal plates include copper plates and aluminum plates. The copper plate is not limited to a pure copper plate, but may also be a copper alloy plate. Examples of copper plates include those specified in JIS-H-3100. Among these, oxygen-free copper (copper purity of 99.96 wt% or higher) is preferred.

[0009] The brazing material should preferably be an activated metal brazing material. The activated metal is selected from Ti (titanium), Zr (zirconium), and Hf (hafnium). The joining method using activated metal brazing material is called the activated metal joining method. Among the activated metals, Ti is preferred. Ti is a more activated metal than Zr and Hf. Also, the cost of Ti is lower than that of Zr and Hf. The activated metal may be added to the brazing material not only as a pure metal but also as a compound. Examples of compounds include hydrides, oxides, and nitrides. A joining method using activated metal brazing material is called activated metal joining. Activated metal joining is a method of manufacturing a joined body by placing activated metal brazing material between a ceramic substrate and a metal plate and then heat-bonding them. Through heat bonding, the activated metal brazing material becomes the bonding layer. In other words, the activated metal brazing material corresponds to the brazing material before bonding. The bonding layer represents the state after bonding. In the activated metal bonding method, an activated metal reacts with the ceramic to form a reaction layer. When titanium (Ti) is used as the activated metal, the Ti reacts with the ceramic substrate to form a Ti reaction layer. When a nitride-based ceramic substrate is used, a Ti reaction layer mainly composed of titanium nitride (TiN) is formed. When an oxide-based ceramic substrate is used, a Ti reaction layer mainly composed of titanium oxide (TiO2) is formed. Nitride-based ceramic substrates refer to silicon nitride substrates and aluminum nitride substrates. Oxide-based ceramic substrates refer to aluminum oxide substrates and argyl substrates. In addition, a portion of the activated metal brazing layer may diffuse into the metal plate by heat bonding. The brazing material preferably contains one or more components selected from Ag (silver), Cu (copper), Sn (tin), In (indium), and C (carbon) as components other than the active metal. Ag or Cu is the base material component of the brazing material. Sn or In has the effect of lowering the melting point of the brazing material. C has the effect of controlling the fluidity of the brazing material and controlling the structure of the bonded layer 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. Both Sn and In may be used. Instead of Sn or In, low-melting-point metals such as Bi (bismuth), Sb (antimony), or Ga (gallium) may be used.

[0010] First, the brazing material is measured using a differential scanning calorimetry (DSC) to obtain a DSC curve. The differential scanning calorimetry measures the presence or absence of an endothermic or exothermic reaction when heat is applied to the sample. When an endothermic or exothermic reaction occurs, a peak appears on the DSC curve. A peak in the negative direction indicates an endothermic reaction. A peak in the positive direction indicates an exothermic reaction. An endothermic reaction indicates that the sample is melting, decomposing, etc. An exothermic reaction indicates that the constituent elements of the sample are reacting with each other to form a compound (including alloying) or solidify. The larger the peak, the greater the heat of reaction. Here, a peak in the negative direction is called an endothermic peak, and a peak in the positive direction is called an exothermic peak. The peak's highest point is called the peak top. The difference between the peak's maximum and minimum points is called the peak height.

[0011] Figure 1 is a schematic diagram illustrating a DSC curve. In Figure 1, the horizontal axis represents temperature (°C), and the vertical axis represents heat flux (mW / mg). In the example in Figure 1, a positive peak is observed at 300°C. This indicates that an exothermic reaction is occurring at 300°C. Furthermore, a negative peak is observed at 600°C. This indicates that an endothermic reaction is occurring at 600°C.

[0012] Figures 2(a) and 2(b) illustrate the method for calculating peak height in the DSC curve. Figure 2(a) illustrates a peak in the positive direction. Figure 2(b) illustrates a peak in the negative direction. As shown in Figures 2(a) and 2(b), a baseline extension line B1 is generated to the left of the peak (left side as viewed from the paper). Baseline extension line B1 is a horizontal line from the base of the peak on the left (the so-called peak start). A tangent line T1 is generated as the longest line along the left side of the peak. The intersection point X of baseline extension line B1 and tangent line T1 is generated. A baseline extension line B2 is generated to the right of the peak (right side as viewed from the paper). Baseline extension line B2 is a horizontal line from the base of the peak on the right (the so-called peak end). A tangent line T2 is generated as the longest line along the right side of the peak. The intersection point Y of baseline extension line B2 and tangent line T2 is generated. The intersection point M is generated of the XY line connecting intersection point X and intersection point Y, and the line drawn perpendicularly from the peak top P to the horizontal axis. The distance between the intersection point M and the peak top P is defined as the peak height H. Here, peaks with a peak height H of 0.01 mW / mg or higher are extracted as peaks during both heating and cooling.

[0013] For example, an endothermic peak is in the negative direction, so it rises, falls, and rises again. An endothermic peak follows a sequence of maximum → minimum → maximum. This minimum (the lowest point) is the peak top. Of the maximum points on the low-temperature and high-temperature sides of the minimum, the one with the larger value is defined as the ultimate maximum. The peak height is the difference between the ultimate maximum and the minimum. The exothermic peak is in the positive direction, so it decreases, increases, and decreases again. The exothermic peak follows a sequence of local minimum → local maximum → local minimum. This local maximum (the point where it rises the highest) is the peak top. Of the local minimums on the low-temperature and high-temperature sides of the local maximum, the one with the larger value is defined as the minimum minimum. The peak height is the value obtained by subtracting the minimum minimum from the local maximum. Note that the endpoint of an endothermic peak (a peak in the negative direction) may sometimes appear as an exothermic peak (a peak in the positive direction), but here it will be counted as an exothermic peak. Alternatively, you may draw baseline extensions and determine each peak.

[0014] Figure 3 shows the temperature program for measuring the DSC curve. In Figure 3, the horizontal axis represents time (minutes) and the vertical axis represents temperature (°C). The heating process raises the temperature from room temperature to 500°C at a heating rate of 5°C / min. Next, the heating process maintains the temperature at 500°C for 60 minutes. Then, the heating process raises the temperature to 845°C at a heating rate of 5°C / min. After that, the temperature of 845°C is maintained for 30 minutes. The cooling process lowers the temperature from 845°C to room temperature at a cooling rate of 5°C / min. Furthermore, a NETZSCH TGA-DSC simultaneous thermal analyzer STA449-F3-Jupiter or an instrument with equivalent performance can be used as the DSC. The measurement is performed by dropping an appropriate amount of brazing material into an alumina container and using an Ar (argon) flow. It is necessary to prevent the brazing material from reacting with the atmosphere by measuring in an Ar atmosphere. The Ar flow rate is set to 20 ml / min on the sample side and 200 ml / min on the cooling side. The amount to be dropped (mg) is measured using a balance. Using the above method, DSC curves are measured in the range of 100°C to 845°C. In other words, a DSC curve is a profile obtained using DSC that plots the change in heat flux with respect to temperature. The DSC indicated on the vertical axis of the DSC curve refers to the heat flux measured by DSC. Furthermore, it is preferable to measure the DSC curve of the brazing material before the joining process. When measuring the DSC curve from the state of the joined body, the measurement is performed using a sample from which the joining layer has been separated from the joined body. In a bonded structure, the bonding layer exists between the ceramic substrate and the metal plate. When preparing a sample from which the bonding layer has been separated from the bonded structure, care should be taken to ensure that the ceramic substrate and metal plate are not included. The Ti reaction layer present on the surface of the ceramic substrate may be included in the bonding layer. If cutting at the boundary between the ceramic substrate and the Ti reaction layer is difficult, a portion of the Ti reaction layer may be included in the sample. Furthermore, the activated metal brazing material is bonded to the metal plate while diffusing. When preparing a sample by separating the bonded layer from the bonded body, care must be taken to exclude the area that has diffused into the metal plate. In other words, only the bonded layer portion should be used as the measurement sample. For example, when copper plates are joined using an Ag-Cu-Ti activated metal brazing material, the brazing material diffuses into the copper plates. Because Cu is used as a component of the brazing material, it may become difficult to distinguish the boundary between the joined layer and the copper plate. Therefore, the boundary is defined as being within 20 μm from the Ti reaction layer toward the copper plate. Also, the sample to be cut out should be 1 g.

[0015] The brazing material according to this embodiment is characterized by having an endothermic peak within the range of 550°C to 700°C during the heating process. Figure 4 shows the DSC curve during the heating process of Example 1. In Figure 4, the horizontal axis represents temperature (°C), and the vertical axis represents heat flux (mW / mg). Heat flux is denoted as DSC. Figure 4 shows the range above 450°C within the DSC curve between 100°C and 845°C. In this embodiment, peaks with a peak height of 0.01 mW / mg or higher were counted as peaks. In Figure 4, endothermic peaks are detected at 498°C, 606°C, 671°C, and 713°C. Exothermic peaks are also detected at 581°C and 619°C. Although not shown in the figure, endothermic peaks are also detected at 172°C and 498°C, as shown in Table 3. Similarly, an exothermic peak is detected at 224°C. In Figure 4, two endothermic peaks are detected within the temperature range of 550°C to 700°C during the heating process. Endothermic reactions indicate that melting or decomposition of the brazing material is occurring. The occurrence of endothermic peaks within the 550°C to 700°C range indicates that melting of the brazing material is occurring in this temperature range. Melting of the brazing material indicates that a bonding reaction is taking place. Of the endothermic peaks in the 550-700°C range, at least one peak height is preferably 0.04 mW / mg or higher. Peak height indicates the magnitude of the reaction. Having a large endothermic peak enables bonding in this temperature range. For this reason, a peak height of 0.04 mW / mg or higher, and more preferably 0.07 mW / mg or higher, is preferred.

[0016] The brazing material preferably contains Ag (silver), Cu (copper), and Ti (titanium). Brazing materials containing Ag, Cu, and Ti are a type of active metal brazing material. Active metal brazing materials can firmly bond ceramic substrates and copper plates. Because the brazing material has an endothermic peak at 550-700°C during the heating process, the bonding temperature can be reduced to 800°C or lower. Furthermore, it is preferable that the brazing material has two or more endothermic peaks within the temperature range of 550°C to 650°C during the heating process. Even with only one endothermic peak, bonding is possible. Having two or more endothermic peaks indicates that the melting reaction is occurring in multiple stages. As melting occurs in multiple stages, the bonded layer changes and the reaction proceeds. In addition, it is preferable that at least one of the endothermic peaks between 550°C and 650°C has a peak height of 0.04 mW / mg or more.

[0017] Furthermore, when comparing the endothermic peak at 550-650°C during the heating process with the endothermic peak at 700°C or above, it is preferable that the endothermic peak at 550-650°C is larger. That is, the peak height of the endothermic peak at 550-650°C during the heating process is greater than the peak height of the endothermic peak at 700°C or above during the heating process. If there are two or more endothermic peaks within the 550-650°C range, the largest peak among them is used as the reference. Similarly, if there are two or more endothermic peaks above 700°C, the peak with the largest peak height among them is used as the reference. The peak with the largest peak height is called the maximum peak. A larger endothermic peak between 550 and 650°C indicates that no significant melting reaction is occurring above 700°C. Furthermore, when comparing the ratio of peak heights, a ratio of 2 or greater is preferable. The ratio is expressed as (peak height of the largest endothermic peak between 550 and 650°C) / (peak height of the largest endothermic peak above 700°C). A peak ratio of 2 or greater suggests that the main melting reaction is completed within the 550-650°C range. Additionally, a smaller peak height for the endothermic peak above 700°C is preferable. Most preferably, there is no endothermic peak above 700°C. A smaller endothermic peak above 700°C indicates that no melting reaction is occurring. In other words, a smaller endothermic peak above 700°C indicates that the melting reaction is almost complete below 700°C, and even more so between 550 and 650°C.

[0018] The brazing material preferably has an endothermic peak within the range of 450°C to 520°C during the heating process. Furthermore, it is preferable that the peak height of the endothermic peak within this range is 0.07 mW / mg or higher. When titanium is incorporated into the brazing material by adding TiH2 (titanium hydride), a decomposition reaction between Ti and H occurs within the range of 450-520°C. This decomposition reaction is the main endothermic reaction. The hydrogen produced after decomposition has the effect of removing oxygen from the brazing material or activating metal components. Note that if a substance other than a hydride, such as elemental Ti, is added, this endothermic peak may not be present. The brazing material preferably has either an endothermic peak or an exothermic peak, or both, within the range of 140°C to 300°C in the DSC curve of the heating process. Furthermore, the peak height of either the endothermic or exothermic peak within the range of 140°C to 300°C is preferably 0.04 mW / mg or higher. (Figure) 10 Figure 10 shows the DSC curve for the heating process in Example 3. Figure 10 shows the range below 550°C within the DSC curve between 100°C and 845°C. As shown in Table 3 later, there are endothermic peaks at 172°C and 220°C. In addition, exothermic peaks were detected at 217°C and 232°C. To generate an endothermic or exothermic peak within the 140°C to 300°C range of the heating process, it is preferable to include tin (Sn) in the brazing material. For example, when Sn is included in an Ag-Cu-Ti brazing material, an endothermic reaction occurs due to the melting of Sn, and an exothermic reaction occurs due to the formation of a SnAg compound or SnCu compound. By generating an endothermic or exothermic peak at a temperature lower than the endothermic reaction (melting reaction) of 550-650°C, the reaction can be accelerated in multiple stages. This allows for the relaxation of thermal stress. In particular, the presence of an exothermic peak is preferable. Furthermore, the height of the exothermic peak is preferably 0.04 mW / mg or higher. This indicates that the reaction to form the SnAg compound or SnCu compound has proceeded sufficiently. For this reason, the height of the exothermic peak is preferably 0.04 mW / mg or higher, and more preferably 0.05 mW / mg or higher.

[0019] In the DSC curve for the cooling process, it is preferable that the peak in the range of 140°C to 300°C is small. A small peak in the range of 140°C to 300°C in the cooling process indicates that the reaction forming the SnAg compound or SnCu compound is hardly occurring. In other words, it indicates that the reaction forming the SnAg compound or SnCu compound in the heating process is sufficiently promoted. Note that a small peak means that no peak is detected or the peak height is less than 0.04 mW / mg. It is most preferable that no peak is detected in the range of 140°C to 300°C in the DSC curve for the cooling process. Figure 11 shows the DSC curve for the cooling process of Example 3. Figure 11 shows the range of 550°C and below within the DSC curve of 100°C to 845°C. Furthermore, as shown in Table 3 later, no peak was detected in the range of 140°C to 300°C in the DSC curve for the cooling process of Example 3. Furthermore, it is preferable that the exothermic peak occurs between 400°C and 700°C during the cooling process. It is also preferable that the maximum exothermic peak during the cooling process is within the range of 500°C to 650°C. The exothermic peak during the cooling process is generated by the formation or solidification of the compound (alloy) in the bonding layer. The greatest thermal stress occurs when the molten brazing material solidifies. This is because, after the bonding interface is formed, materials with different thermal expansion coefficients are constrained, resulting in stress due to the difference in thermal expansion during cooling. If the maximum exothermic peak during the cooling process is below 500°C, the solidification temperature may be too low, potentially reducing the reliability of the bond. On the other hand, if it is above 650°C, the thermal stress may become excessively large. It is important that the maximum exothermic peak during the cooling process is within the range of 500-650°C. By completing the main solidification reaction by 500°C during the cooling process, thermal stress can be relieved. The bonded layer of the completed joint does not need to be a completely molten structure; it may be partially molten. A partially molten bonded layer will consist of a mixture of molten and unmolten tissue. The unmolten tissue is also called a separated tissue. Furthermore, it is preferable that the peak temperature at which the exothermic peak occurs in the cooling process (400°C to 700°C) is at least 10°C lower than the peak temperature at which the endothermic peak occurs in the heating process (400°C to 700°C). By lowering the peak temperature in the cooling process, the generation of thermal stress in the cooling process can be suppressed.

[0020] Furthermore, it is preferable that the brazing material has an exothermic peak in the DSC curve of the cooling process within the range of 450°C to 520°C. The exothermic peak is a positively oriented peak. The endothermic peak in the 450-520°C range of the heating process is mainly due to the decomposition reaction of TiH2. In contrast, the exothermic peak in the cooling process is due to the exothermic reaction for solidification of the bonding layer or formation of the Ti compound. Examples of Ti compounds include TiN (titanium nitride), AgTi, CuTi, and TiC. Ti is an active metal. The bonding is more stable when Ti exists as a Ti compound in the bonding layer than when Ti exists as elemental Ti.

[0021] Figure 5 shows the DSC curve for the cooling process in Example 1. Figure 5 shows the range above 450°C. In Figure 5, exothermic peaks are detected at 477°C, 602°C, 644°C, and 688°C. In the DSC curve for the cooling process, no peaks are detected in the range between 140°C and 300°C. This indicates that the formation of SnAg or SnCu is promoted during the heating process. In addition, the maximum exothermic peak is detected between 500°C and 650°C during the cooling process.

[0022] Furthermore, the brazing material composition preferably contains 0% to 75% by mass of Ag (silver), 15% to 85% by mass of Cu (copper), and 1% to 15% by mass of Ti (titanium) or TiH2 (titanium hydride). When both Ti and TiH2 are used, the total amount should be within the range of 1% to 15% by mass. When both Ag and Cu are used, it is preferable that Ag be 20 to 60% by mass and Cu be 15 to 40% by mass. The brazing material composition may, as necessary, contain one or both of Sn (tin) or In (indium) in an amount of 1% to 50% by mass. Furthermore, the content of Ti or TiH2 is preferably 1% to 15% by mass, and more preferably 1% to 6% by mass. A Ti content of 6% by mass or less makes it easier to generate two or more endothermic peaks within the 550-650°C range when combined with Sn or In. Additionally, C (carbon) may be included in an amount of 0.1% to 2% by mass as necessary. The composition ratio of the brazing material is calculated by considering the total value of the mixed raw materials as 100% by mass. For example, if it is composed of three materials, Ag, Cu, and Ti, then Ag + Cu + Ti = 100% by mass. If it is composed of four materials, Ag, Cu, TiH2, and In, then Ag + Cu + TiH2 + In = 100% by mass. If it is composed of five materials, Ag, Cu, Ti, Sn, and C, then Ag + Cu + Ti + Sn + C = 100% by mass.

[0023] The mass ratio of Ag / Cu in the brazing material composition is preferably 1.3 or less. The endothermic peak at 550-700°C during the heating process is a reaction that melts the brazing material components and generates a liquid phase. The mass ratio of Ag / Cu in typical activated metal brazing materials is 2.3 (=7 / 3). This ratio is for the formation of an AgCu eutectic. If the mass ratio of Ag / Cu is 2.3, an endothermic peak is not formed at 550-700°C. This is because the liquid phase formation temperature becomes too high. The mass ratio of Sn / Ag in the brazing material composition is preferably 0.25 or higher. Furthermore, the mass ratio of In / Ag is preferably 0.25 or higher. By maintaining this range, an exothermic peak can be formed in the 140-300°C heating step. The peak in the 140-300°C heating step indicates both an endothermic reaction where Sn melts and an exothermic reaction where SnAg or SnCu is formed. By increasing the amount of SnAg or SnCu formed, the liquid phase formation temperature can be raised to around 600°C. This allows for a larger endothermic peak in the 550-700°C range. The same results can be obtained by using a low-melting-point metal such as In instead of Sn. C (carbon) has the effect of lowering the solidification temperature of the bonding layer in the temperature reduction process. As a result, the generation temperature of the peak top of the exothermic peak at 400°C or higher and 700°C or lower in the temperature reduction process can be 10°C or more lower than the generation temperature of the peak top of the endothermic peak at 400°C or higher and 700°C or lower in the temperature increase process.

[0024] The average particle diameter D of the Ag powder that is the raw material of the brazing material 50 is preferably 3.0 μm or less, and more preferably 2.0 μm or less. The average particle diameter D of the Cu powder 50 is preferably 6.0 μm or less, and more preferably 4.0 μm or less. The average particle diameter D of the Ti powder or TiH2 powder 50 is preferably 6.0 μm or less, and more preferably 4.0 μm or less. The average particle diameter D of the Sn powder or In powder 50 is preferably 6.0 μm or less, and more preferably 4.0 μm or less. The average particle diameter D of the C powder 50 is preferably 6.0 μm or less, and more preferably 4.0 μm or less. The average particle diameter D of the Ag powder 50 <The average particle diameter D of the Cu powder 50 is preferably this. The average particle diameter D of the Ag powder 50 <The average particle diameter D of the Sn powder or In powder 50 is preferably this. The average particle diameter D of the Cu powder 50 <The average particle diameter D of the Sn powder or In powder 50 is preferably this. By reducing the particle diameter of the Ag powder, the contact ratio of the Ag powder with other powders can be increased. As a result, the endothermic peak at 550 to 700°C can be increased. Or, the endothermic peak or exothermic peak at 140 to 300°C can be increased.

[0025] The brazing material as described above is suitable for a bonded body obtained by bonding a ceramic substrate and a metal plate. Examples of ceramic substrates include silicon nitride substrates, aluminum nitride substrates, aluminum oxide substrates, and argyl substrates. The thickness of the ceramic substrate is preferably between 0.1 mm and 1 mm. If the substrate thickness is less than 0.1 mm, the strength may decrease. If it is thicker than 1 mm, the ceramic substrate may act as a thermal resistor, which may reduce the heat dissipation of the ceramic copper circuit board. The silicon nitride substrate preferably has a three-point bending strength of 600 MPa or more. Furthermore, the silicon nitride substrate preferably has a thermal conductivity of 80 W / m·K or more. Increasing the strength of the silicon nitride substrate allows for a reduction in substrate thickness. Therefore, the three-point bending strength of the silicon nitride substrate is preferably 600 MPa or more, and more preferably 700 MPa or more. The substrate thickness of the silicon nitride substrate can be reduced to 0.40 mm or less, and more preferably 0.30 mm or less. The three-point bending strength of an aluminum nitride substrate is approximately 300-450 MPa. On the other hand, the thermal conductivity of an aluminum nitride substrate is 160 W / m·K or higher. Due to the low strength of the aluminum nitride substrate, a substrate thickness of 0.60 mm or more is preferable. Aluminum oxide substrates have a three-point bending strength of around 300-450 MPa, but are inexpensive. Argil substrates have a high three-point bending strength of around 550 MPa, but their thermal conductivity is only about 30-50 W / m·K. Silicon nitride substrates are preferred as ceramic substrates. Because silicon nitride substrates have high strength, excellent reliability can be obtained even when thick copper plates are bonded to them.

[0026] Examples of metal plates include copper plates and aluminum plates. However, copper plates are preferable. Copper plates are preferable to have a thickness of 0.6 mm or more. The thermal conductivity of copper plates is approximately 400 W / m·K. Increasing the thickness of the copper plate improves the heat dissipation of the circuit board. Therefore, the thickness of the copper plate is preferably 0.6 mm or more, and even more preferably 0.8 mm or more. Furthermore, because silicon nitride substrates have high strength, excellent reliability can be obtained even when thick copper plates are bonded to them. In other words, a silicon nitride copper circuit board, in which a silicon nitride substrate with a substrate thickness of 0.40 mm or less and a three-point bending strength of 600 MPa or more is bonded to a copper plate with a thickness of 0.6 mm or more, is a preferred combination.

[0027] According to the manufacturing method of the joint according to the embodiment, the joining temperature can be 800°C or lower. Furthermore, joining can be performed at a temperature above the maximum peak temperature of the endothermic peak present in the 550-650°C range during the heating process of the brazing material. In other words, the joining temperature is above the maximum peak temperature of the endothermic peak present in the 550-650°C range during the heating process. The difference between the joining temperature and the maximum peak temperature is preferably 50°C to 100°C. As mentioned above, it is preferable that the brazing material has an endothermic peak in the 550-650°C range. For example, if the largest endothermic peak is 600°C, it is preferable to set the joining temperature within the range of 650-700°C. Even in this case, it is possible to join at a temperature higher than 700°C. On the other hand, the higher the joining temperature, the greater the thermal stress. Thermal stress is deformation associated not only with the reaction and solidification of the brazing material, but also with grain growth of the copper plate. By lowering the joining temperature, thermal stress can be reduced. By reducing thermal stress, warping of the joint between the ceramic substrate and the copper plate can be reduced. Furthermore, by adding a circuit shape to the metal plate of the bonded structure, it becomes a ceramic circuit board. Etching can be used to add the circuit shape.

[0028] Increasing the thickness of the copper plate increases the thermal stress caused by the copper plate. Also, increasing the size of the ceramic substrate allows for the production of multiple parts. Multiple parts production is a method of obtaining smaller parts by cutting a large joint. Methods for dividing the joint or the ceramic circuit board are also available. Scribing may be applied to facilitate division. According to the embodiment of the joint, even if the ceramic substrate size is increased to 200 mm or more in length and 200 mm or more in width, the warping of the joint can be reduced. Therefore, it is possible to achieve both an increase in the size of the ceramic substrate and an increase in the thickness of the copper plate. In particular, by making the strength of the silicon nitride substrate 600 MPa or more, the warping of the joint can be reduced even if the substrate thickness is made as thin as 0.40 mm or less. Furthermore, the copper plates to be joined may be pre-processed into a circuit shape, or they may be solid copper plates. Solid copper plates are etched after joining. Copper plates may be joined to both sides of the ceramic substrate. When copper plates are joined to both sides, one side may be used as a circuit and the other as a heat sink, or both may be used as circuits. Also, when copper plates are joined to both sides, it is preferable that the thickness of one of them is 0.6 mm or more.

[0029] (Examples) (Examples 1-6, Comparative Example 1) The brazing material compositions shown in Tables 1 and 2 were prepared. Table 1 shows the particle size of the raw material powders. TiH2 powder was used for the Ti component.

[0030] [Table 1]

[0031] [Table 2]

[0032] Brazing pastes were prepared by mixing the brazing components from the examples and comparative examples with a resin binder. For each brazing paste, a differential scanning calorimeter (DSC) curve was measured. The DSC measurement device used was a NETZSCH TGA-DSC simultaneous thermal analyzer STA449-F3-Jupiter. Measurements were performed in an Ar flow state with an appropriate amount of brazing material dropped into an alumina container. The Ar flow rates during measurement were set to 20 ml / min on the sample side and 200 ml / min on the cooling side. The temperature program was set to the conditions shown in Figure 3. DSC curves were measured in the range of 100°C to 845°C. Table 3 shows the detection temperatures for the endothermic and exothermic peaks during the heating and cooling processes.

[0033] [Table 3]

[0034] Figure 4 shows an example of the DSC curve (above 450°C) for the heating process of Example 1. Figure 5 shows an example of the DSC curve (above 450°C) for the cooling process of Example 1. Figure 6 shows an example of the DSC curve (above 450°C) for the heating process of Comparative Example 1. Figure 7 shows an example of the DSC curve (above 450°C) for the cooling process of Comparative Example 1. Figure 8 shows an example of the DSC curve (above 450°C) for the heating process of Example 2. Figure 9 shows an example of the DSC curve (above 450°C) for the cooling process of Example 2. Figure 10 shows an example of the DSC curve (below 550°C) for the heating process of Example 3. Figure 11 shows an example of the DSC curve (below 550°C) for the cooling process of Example 3. Figure 12 shows an example of the DSC curve (below 550°C) for the heating process of Example 4. Figure 13 shows an example of the DSC curve (below 550°C) for the cooling process of Example 4. Figure 14 shows an example of the DSC curve (below 550°C) for the heating process in Example 5. Figure 15 shows an example of the DSC curve (below 550°C) for the cooling process in Example 5. In Comparative Example 1 (Figure 6), no endothermic peak was detected in the 550-700°C range during the heating process. In contrast, an endothermic peak was detected in the 550-700°C range for the brazing material in the example. When comparing the endothermic peak in the 550-700°C range with the endothermic peak in the range above 700°C, the endothermic peak in the range above 700°C was smaller. This indicates that the melting reaction of the brazing material is accelerated in the 550-700°C range. Furthermore, in Comparative Example 1 (Figure 7), no exothermic peak was detected in the 500-650°C range. In Examples 2, 4, and 5, two or more endothermic peaks were detected within the range of 550 to 650°C. Of the two detected endothermic peaks, at least one peak height was 0.07 mW / mg or higher. Furthermore, in Examples 2, 4, and 5, no endothermic peaks were detected at temperatures above 700°C.

[0035] Next, the bonding process between the ceramic substrate and the copper plate was carried out using the brazing materials of the examples and comparative examples. As the ceramic substrate, silicon nitride substrate 1 was prepared with a thermal conductivity of 90 W / m·K, a three-point bending strength of 700 MPa, and a plate thickness of 0.32 mm. Also, silicon nitride substrate 2 was prepared with a thermal conductivity of 85 W / m·K, a three-point bending strength of 650 MPa, and a plate thickness of 0.25 mm. An aluminum nitride substrate was prepared with a thermal conductivity of 170 W / m·K, a three-point bending strength of 400 MPa, and a plate thickness of 0.635 mm. Oxygen-free copper was used as the copper plate. Copper plate 1 with a plate thickness of 0.6 mm, copper plate 2 with a plate thickness of 0.8 mm, and copper plate 3 with a plate thickness of 0.3 mm were prepared. The ceramic substrate measures 250 mm in length and 200 mm in width. Solid copper plates were bonded to both sides of the ceramic substrate. The amount of warping of the resulting bonded structure was measured. The bonding strength of the copper plates was also measured. The amount of warpage of the joint was measured on the longer side. The amount of warpage of the ceramic substrate was observed from the side of the joint. A straight line was drawn connecting the ends of the longer side of the ceramic substrate. The warpage was defined as the point furthest from this line on the surface of the ceramic substrate. Joints with a curvature of 0.1 mm or less on the longer side were marked as good products (〇), and those with a curvature exceeding 0.1 mm were marked as defective products (×). Furthermore, the bonding strength was measured by a peel test. Specifically, samples for the peel test were prepared using the bonding conditions of each example and comparative example. The samples consisted of a strip-shaped copper plate bonded to a ceramic substrate. In this process, one end of the copper plate was bonded so that it protruded from the ceramic substrate. The peel strength was measured by pulling the protruding copper plate vertically. Joints with a joint strength of 20 kN / m or higher were classified as the best product (◎), those with a joint strength of 15 kN / m or higher as good product (〇), and those with a joint strength of 14 kN / m or lower as defective product (×). Table 4 shows the results.

[0036] [Table 4]

[0037] In the examples, the amount of warping was reduced even when the bonding temperature was 800°C or lower. Furthermore, high bonding strength was achieved. It was found that bonding could be performed at lower temperatures by controlling the endothermic and exothermic peaks in the DSC curve of the brazing material. In contrast, while Comparative Example 1A showed high joint strength at a bonding temperature of 850°C, it exhibited significant warping. This was due to high thermal stress caused by bonding at high temperatures. Furthermore, lowering the bonding temperature, as in Comparative Example 1B, resulted in decreased joint strength.

[0038] As a reference example, a silicon nitride substrate with dimensions of 50 mm (length) x 50 mm (width) x 0.32 mm (thickness) was prepared. A copper plate with dimensions of 50 mm (length) x 50 mm (width) x 0.6 mm (thickness) was also prepared. The brazing materials of Example 1 and Comparative Example 1 were used, and the bonding temperature was set to 850°C for bonding. Good quality was obtained for both the amount of warping and the bonding strength. In other words, even with conventional brazing materials, warping can be reduced if the bonded body is small. On the other hand, when the bonded body was made larger, such as 200 mm x 200 mm or more, the warping became larger. By using the brazing materials of the examples, it is possible to reduce warping while maintaining bonding strength at a lower bonding temperature. For this reason, the brazing materials of the examples are excellent for mass production of bonded bodies.

[0039] (zygote) Figure 16 shows an example of a joint using the brazing material according to the embodiment. In Figure 16, 10 is a ceramic circuit board. 12 is a ceramic substrate. 13 is a front metal plate. 14 is a bonding layer. 15 is a back metal plate. The front metal plate 13 and the back metal plate 15 are each bonded to the ceramic substrate 12 via the bonding layer 14. The brazing material according to the embodiment is suitable for the joint shown in Figure 16. By using the brazing material according to the embodiment, for example, the reliability of the joint can be improved. Furthermore, if a circuit shape is applied to the front metal plate 13 or the back metal plate 15 of the joint, a ceramic circuit board 10 can be obtained. In addition, the length and width dimensions of the front metal plate 13 or the back metal plate 15 in the joint may be the same as those of the ceramic substrate 12. The circuit shape can be applied using an etching process or the like.

[0040] (Assembled ceramic circuit board) Figures 17 to 19 show an example of a ceramic circuit board using the brazing material according to the embodiment. In the ceramic circuit board 10a shown in Figure 17, two surface metal plates 13, processed into a circuit shape, are bonded to the ceramic substrate 12. The embodiment is not limited to this example, and three or more surface metal plates 13 may be bonded to the ceramic substrate 12. The ceramic substrate may have through holes. Preferably, the ceramic circuit board has a structure in which the front metal plate and the back metal plate are electrically connected through the through holes. Figure 18 shows an example of a ceramic circuit board having through holes. Figure 18 is a cross-sectional view of the portion where the through holes are provided. In Figure 18, 10a is a ceramic circuit board. 12 is a silicon nitride substrate. 13 is a front metal plate. 14 is a bonding layer. 18 is a back metal plate. 19 is a through hole. In Figure 18, the front metal plate 13 and the back metal plate 18 are electrically connected through the through holes 19. In Figure 18, multiple through holes 19 connect multiple front metal plates 13 and multiple back metal plates 18, respectively. The embodiment is not limited to this structure. In the ceramic circuit board 10a, through holes 19 may be provided only for a portion of the multiple front metal plates 13. Through holes 19 may be provided only for a portion of the multiple back metal plates 18. It is preferable that the inside of the through-hole 19 be filled with the same material as the bonding layer 14. The internal structure of the through-hole 19 is not particularly limited as long as it allows electrical conductivity between the front metal plate and the back metal plate. For this reason, a thin metal film may be provided only on the inner wall of the through-hole 19. On the other hand, filling it with the same material as the bonding layer 14 can improve the bonding strength. The silicon nitride circuit board according to this embodiment is suitable for semiconductor devices. In a semiconductor device, semiconductor elements are mounted on a metal plate of a ceramic circuit board via a bonding layer. Figure 19 shows an example of a semiconductor device. In Figure 19, 10a is a ceramic circuit board. 20 is a semiconductor device. 21 is a semiconductor element. 22 is a bonding layer. 23 is wire bonding. 24 is a metal terminal. In Figure 19, a semiconductor element 21 is bonded to a metal plate of a ceramic circuit board 10a via a bonding layer 22. Similarly, a metal terminal 24 is bonded via a bonding layer 22. Adjacent metal plates are electrically connected by wire bonding 23. In Figure 19, in addition to the semiconductor element 21, wire bonding 23 and metal terminal 24 are bonded. The semiconductor device according to this embodiment is not limited to this structure. For example, only one of the wire bonding 23 or the metal terminal 24 may be provided. Multiple semiconductor elements 21, wire bonding 23, and metal terminals 24 may be provided on the front metal plate 13. The semiconductor elements 21, wire bonding 23, and metal terminals 24 can be bonded to the back metal plate 18 as needed. Various shapes can be applied to the metal terminals 24, such as lead frame shape and convex shape. By using the brazing material according to this embodiment in the ceramic circuit board or semiconductor device described above, for example, the reliability of these devices can be improved.

[0041] 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 brazing material for joining a ceramic substrate and a copper plate, The aforementioned brazing material contains one or two of Ag, Cu, Ti or TiH₂, and one of Sn or In as raw materials, with the total of these raw materials being 100%, Ag being higher than 0% by mass and 75% by mass or less, Cu being 15% by mass or more and 85% by mass or less, and Ti or TiH₂ ２ It contains one or two of the above in a total amount of 1% to 15% by mass, and one of either Sn or In in a total amount of 1% to 50% by mass. The ratio of the mass of Ag to the mass of Cu is 1.3 or less. The mass ratio of Sn to Ag or the mass ratio of In to Ag is 0.25 or greater. Average particle size of Ag D ５０ The average particle size of Cu is D ５０ Smaller than the average particle size D of Sn or In. ５０ Smaller than, A brazing material characterized in that, when the DSC curve is measured with a differential scanning calorimeter (DSC), it has an endothermic peak in the range of 550°C to 700°C during the heating process, and has either an endothermic peak or an exothermic peak or both in the range of 140°C to 300°C during the heating process, and the endothermic peak at 550°C to 650°C during the heating process is larger than the endothermic peak at 700°C or higher during the heating process.

2. The brazing material according to claim 1, characterized in that it has two or more endothermic peaks within the range of 550°C to 650°C during the heating step.

3. The brazing material according to claim 1 or 2, characterized in that it has an endothermic peak within the range of 450°C to 520°C during the heating step.

4. Ag is 20% by mass or more and 60% by mass or less, Cu is 15% by mass or more and 40% by mass or less, and Ti or TiH ２ The brazing material according to any one of claims 1 to 3, characterized in that it contains one or two of the above in a total amount of 1% by mass or more and 1% by mass or more and 50% by mass or less of either Sn or In.

5. The brazing material according to any one of claims 1 to 4, further characterized in that it contains 0.1% by mass or more and 2% by mass or less of carbon.

6. The brazing material according to any one of claims 1 to 5, characterized in that the temperature at which the peak top of the exothermic peak at 400°C to 700°C occurs in the cooling process is 10°C or more lower than the temperature at which the peak top of the endothermic peak at 400°C to 700°C occurs in the heating process.

7. Ceramic substrate and A copper plate with a thickness of 0.3 mm or more, A brazing material according to any one of claims 1 to 6 for joining the ceramic substrate and the copper plate, A joint equipped with [something].

8. The aforementioned ceramic substrate is a silicon nitride substrate, The joint according to claim 7, characterized in that the thickness of the copper plate is 0.6 mm or more.

9. A ceramic circuit board characterized by using the bonded body described in either claim 7 or claim 8.

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