Ceramic circuit board and semiconductor device using same

Abstract

The present invention pertains to a ceramic circuit board that can improve reliability thereof. A ceramic circuit board according to an embodiment of the present invention includes a ceramic substrate and at least one metal member. The ceramic substrate has compressive stress applied thereto. The at least one metal member has tensile stress applied thereto. When the compressive stress Sc at an outer circumferential portion of the ceramic substrate and the tensile stress Sm in the vicinity of the outer circumferential portion of the at least one metal member are measured, the absolute value |Sm / Sc| of the ratio of the tensile stress Sm to the compressive stress Sc is in a range of more than 1.0 to not more than 1.8.

Description

Ceramic Circuit Board and Semiconductor Device Using the Same 【0001】 An embodiment generally relates to a ceramic circuit board and a semiconductor device using the same. 【0002】 The ceramic circuit board is used in a semiconductor device on which a semiconductor element such as a power element is mounted. The ceramic substrate and the metal member are joined via a joining layer. A silver (Ag) brazing material containing an active metal such as titanium (Ti) is used for the joining layer. Thereby, the joining strength and heat cycle characteristics are improved. 【0003】 Along with the improvement of reliability, the ceramic circuit board is used in applications such as an inverter. The inverter is included in, for example, automobiles (including electric vehicles), electric railway vehicles, solar power generation facilities, industrial machines, and the like. In a semiconductor device such as a power module, a semiconductor element is mounted on a metal member. For the conduction of the semiconductor element, wire bonding or a metal terminal may be joined to the metal member. In the manufacture of a semiconductor device, a semiconductor element, wire bonding, a metal terminal, and the like are joined to a metal member. 【0004】 As the miniaturization, weight reduction, and high-density mounting of the power module progress, the metal member has become thicker for the purpose of reducing the thermal resistance and inductance. A ceramic circuit board including a thick metal member is described in International Publication No. 2018-180965 (Patent Document 1). Patent Document 1 improves the assemblability of a ceramic copper circuit board by optimizing the number of grain boundaries on the surface of a copper circuit board. According to the ceramic copper circuit board of Patent Document 1, the joining property and alignment accuracy of a semiconductor element are improved. 【0005】 International Publication No. 2018-180965 【0006】On the other hand, in addition to the bonding or alignment accuracy mentioned above, problems arising from the increased thickness of metal components have become apparent. For example, when forming metal components on a ceramic substrate, if the residual stress of the metal component is not properly controlled, the reliability of the ceramic circuit board may decrease. In particular, if the tensile stress of the metal component is too high, the ceramic substrate may become prone to breakage. If the tensile stress of the metal component is too low, the bonding strength may be insufficient. Furthermore, the tensile stress of the metal component may cause waviness on the surface of the metal component. If the surface waviness of the metal component is large, it may adversely affect the uniformity of the thickness or flatness of the metal component and the bonding strength between the ceramic substrate and the metal component. This may reduce the performance or reliability of the electronic device. 【0007】 In recent years, power semiconductor modules have become smaller, lighter, and have higher density mounting. Consequently, there is a need to increase the thickness of metal components to reduce their thermal resistance and inductance. Furthermore, to increase mounting density, there is a need for finer patterning of metal components. As the junction temperature (Tj) of power semiconductor chips rises, there is also a need to improve the reliability of ceramic circuit boards. This embodiment addresses these problems and relates to a ceramic circuit board that can improve reliability. 【0008】 The ceramic circuit board according to this embodiment includes a ceramic substrate and one or more metal members. The ceramic substrate is subjected to compressive stress. The one or more metal members are subjected to tensile stress. When the compressive stress Sc at the outer periphery of the ceramic substrate and the tensile stress Sm near the outer periphery of the one or more metal members are measured, the absolute value of the ratio of the tensile stress Sm to the compressive stress Sc |Sm / Sc| is greater than 1.0 and within the range of 1.8 or less. 【0009】A side view showing an example of a ceramic circuit board according to the embodiment. A top view showing an example of a ceramic circuit board according to the embodiment. An enlarged view of part A of the ceramic circuit board according to the embodiment shown in Figure 2. An enlarged view of part B of the ceramic circuit board according to the embodiment shown in Figure 2. An enlarged view of part C of the ceramic circuit board according to the embodiment shown in Figure 2. A bottom view showing an example of a ceramic circuit board according to the embodiment. A top view showing another example of a ceramic circuit board according to the embodiment. A side view showing an example of a semiconductor device according to the embodiment. 【0010】 The ceramic circuit board according to this embodiment includes a ceramic substrate and one or more metal members. The ceramic substrate is subjected to compressive stress. The one or more metal members are subjected to tensile stress. When the compressive stress Sc at the outer periphery of the ceramic substrate and the tensile stress Sm near the outer periphery of the one or more metal members are measured, the absolute value of the ratio of the tensile stress Sm to the compressive stress Sc |Sm / Sc| is greater than 1.0 and within the range of 1.8 or less. 【0011】 Figure 1 is a side view showing an example of a ceramic circuit board. In Figure 1, 1 is a ceramic circuit board. 2 is a ceramic substrate. 3 is a metal member (front metal plate). 4 is a bonding layer containing brazing material (first bonding layer). 5 is a metal member (back metal plate). The ceramic substrate 2 has a front surface 2a (first surface) and a back surface 2b (second surface). The metal member 3 is bonded to the front surface 2a of the ceramic substrate 2 via the first bonding layer 4. The metal member 5 is bonded to the back surface 2b of the ceramic substrate 2 via another first bonding layer 4. 【0012】 In the example shown in Figure 1, multiple metal members 3 are each bonded to the front surface 2a via multiple first bonding layers 4. Each metal member 3 is a metal circuit patterned into a circuit shape. In addition, in the example shown in Figure 1, one metal member (back metal plate) 5 is bonded to the back surface 2b. The metal member 5 (back metal plate) functions as a heat sink. The metal member 5 is provided as needed. 【0013】The embodiments are not limited to those shown in the figures. One metal member 3 or three or more metal members 3 may be joined to the front surface 2a. Multiple metal members 5 patterned in a circuit shape may be joined to the back surface 2b. Hereafter, when metal members 3 and metal members 5 are not specifically distinguished, at least one of them will be referred to as a "metal member". 【0014】 In the ceramic circuit board 1 according to this embodiment, compressive stress is applied to the ceramic substrate 2. Tensile stress is applied to one or more metal members provided on at least one surface of the ceramic substrate 2. Compressive stress is the stress generated in an object when an external force is applied in a direction that compresses the object. Tensile stress is the opposite of compressive stress. Tensile stress is the stress generated in an object when an external force is a tensile force. Compressive stress is indicated by a negative value. Tensile stress is indicated by a positive value. 【0015】 In a ceramic circuit board 1, when the compressive stress Sc at the outer periphery of the ceramic substrate 2 and the tensile stress Sm near the outer periphery of one or more metal members are measured, the absolute value of the ratio of tensile stress Sm to compressive stress Sc |Sm / Sc| is greater than 1.0 and within the range of 1.8 or less. According to this stress relationship, the Thermal Cycle Test (TCT) characteristics of the ceramic circuit board 1 can be improved. 【0016】 Here, "peripheral area" refers to the portion of the ceramic substrate 2's surface that follows its outer edge. The peripheral area is located around the region on the ceramic substrate 2's surface where one or more metal members are provided. Regions located between metal members are not included in the peripheral area. 【0017】As described later, the ceramic circuit board 1 is manufactured by bonding metal members 3 and 5 to a ceramic substrate 2. When the compressive stress of the ceramic substrate 2 is controlled, the occurrence of defects can be suppressed when the metal members repeatedly expand and contract in the TCT. A defect is the occurrence of cracks or other defects in the ceramic substrate 2 or the first bonding layer 4. When the metal members expand, tensile stress is generated in the metal members. When the metal members contract, the tensile stress is canceled out and compressive stress is generated in the metal members. Cracks are particularly likely to occur when the metal members expand, that is, when the tensile stress becomes large. By applying a predetermined compressive stress to the surface of the ceramic substrate 2 in advance, the effect of increased tensile stress due to the expansion of the metal members can be mitigated. 【0018】 In the ceramic circuit board 1 according to this embodiment, compressive stress Sc is applied to the ceramic substrate 2 such that the absolute value of the ratio of tensile stress Sm to compressive stress Sc |Sm / Sc| does not exceed 1.8. By keeping the ratio |Sm / Sc| below 1.8, the effect of increased tensile stress during expansion of the metal member can be sufficiently mitigated. As a result, even if the metal member repeatedly expands and contracts, defects are less likely to occur in the ceramic substrate 2 or the first bonding layer 4. On the other hand, if the absolute value of the ratio |Sm / Sc| is 1.0 or less, the compressive stress of the ceramic substrate 2 is excessively large relative to the tensile stress Sm. Due to the synergistic effect with the compressive stress when the metal member contracts, cracks may occur in the ceramic substrate 2 or the first bonding layer 4. For this reason, it is preferable that the ratio |Sm / Sc| is greater than 1.0 and within the range of 1.8 or less. More preferably, the ratio |Sm / Sc| is within the range of 1.1 to 1.7, and even more preferably within the range of 1.2 to 1.6. 【0019】 The metals used in metal components include, for example, copper, copper alloys, aluminum, or aluminum alloys. Copper and copper alloys have high electrical conductivity and are excellent as electrical circuit materials. Furthermore, copper and copper alloys have high thermal conductivity and are excellent for heat dissipation of the semiconductor elements they are mounted on. 【0020】This section describes the method for measuring residual stress. Residual stress is measured using a single-incidence method with an X-ray residual stress analyzer. The X-ray residual stress analyzer used is the μ-X360s manufactured by PulseTech Industries Co., Ltd., or a device with equivalent performance. If the metal component is copper or a copper alloy, the measurement conditions are set to a vanadium target (V-Kα) and an incident angle of 35°. If the metal component is aluminum or an aluminum alloy, the measurement conditions are set to a chromium target (Cr-Kα) and an incident angle of 35°. The temperature of the object to be measured is set to room temperature (25°C). The X-ray target and diffraction peak are selected according to the material of the ceramic substrate. For selection, refer to the method recommended by the Ceramics Subcommittee within the X-ray Materials Strength Division of the Japan Society for Materials Science. 【0021】 Next, the measurement points for residual stress will be explained. Figure 2 is a top view showing an example of a ceramic circuit board according to an embodiment. In Figure 2, the top surface of the ceramic substrate 2 is rectangular. Rectangular metal members 3 are arranged at four locations on the top surface of the ceramic substrate 2. In both the long and short sides of the ceramic substrate 2, the pullback from the end face of the ceramic substrate 2 and the pullback between the metal members 3 are equal. "Pullback" refers to the distance between the end face of the ceramic substrate 2 and the end face of the metal member in a plan view, or the distance between the end faces of the metal members. 【0022】Residual stress is measured in at least two directions. The two directions are the longitudinal direction and the short direction of the ceramic substrate 2. The "longitudinal direction" is the direction along any side of the ceramic substrate 2 in which the dimensions of the ceramic substrate 2 are maximized. The "short direction" is the direction perpendicular to the longitudinal direction. If there are multiple longitudinal directions for the ceramic substrate 2, one of them may be randomly selected. If the ceramic substrate 2 is circular, one direction passing through the center of the ceramic substrate 2 is set as the longitudinal direction, and the direction perpendicular to it is set as the short direction. If the ceramic substrate 2 is polygonal, residual stress is measured in the diagonal directions in addition to the two directions mentioned above. If the ceramic substrate 2 is a polygon with five or more sides, it is possible to draw multiple diagonals from one corner to another. In this case, residual stress is measured in the direction along each diagonal. 【0023】 When measuring residual stress, a virtual line for measurement is set on the ceramic circuit board 1. The virtual line is set along at least two of the directions mentioned above. The virtual line is drawn so as to pass through at least one metal member. Furthermore, the virtual line is drawn so as to maximize the total dimensions of the metal members along that line. The residual stress is measured along the virtual line. 【0024】 If multiple metal members are provided on a ceramic substrate 2, and there are multiple combinations of one or more metal members through which a virtual line passes in one direction, a virtual line is drawn for each combination, and the residual stress is measured. However, if the shape, thickness, and size of each metal member are the same, and each combination of one or more metal members is arranged symmetrically on the ceramic substrate 2, the residual stress may be measured for only one combination, and the measurement for the other combinations may be omitted. The method for measuring residual stress will be explained below with reference to specific examples. 【0025】For example, as shown in Figure 2, a dashed line X1-X1 is drawn parallel to the long side direction (longitudinal direction) of the ceramic substrate 2. In the example shown in Figure 2, two metal members 3 (metal members 3a to 3d) are provided in the vertical and horizontal directions, respectively. The dashed line X1-X1 crosses the multiple metal members 3a and 3b that are aligned in the long side direction. The metal members 3a and 3b are rectangular in shape, and their long side directions are parallel to the long side direction of the ceramic substrate 2. Therefore, no matter how the dashed line X1-X1 is drawn passing through the metal members 3a and 3b, the sum of the dimensions of metal member 3a and metal member 3b on the dashed line X1-X1 will be constant and maximum. In this case, it is preferable that the dashed line X1-X1 is drawn so as to cross the center of the short side direction of each metal member 3. The fact that the dashed line X1-X1 crosses the central part of the metal members 3 means that, in a direction perpendicular to the dashed line X1-X1, the dashed line X1-X1 is located at an equidistant distance from the end face of each metal member 3. 【0026】 Figure 3 is an enlarged view of part A of the ceramic circuit board according to the embodiment shown in Figure 2. As shown in Figure 3, a measurement point 21 is set on the dashed line X1-X1, midway between the edge of the front surface 2a of the ceramic substrate 2 and the edge of the metal member 3a (the boundary between the ceramic substrate 2 and the metal member 3a). The distance 2a1 from the edge of the front surface 2a to the measurement point 21 is equal to the distance 2a2 from the measurement point 21 to the edge of the metal member 3a. Furthermore, a measurement point 31 is set on the metal member 3a on the dashed line X1-X1. The distance 3a1 from the edge of the metal member 3a to the measurement point 31 is equal to the distances 2a1 and 2a2. As a result, measurement points are set on the ceramic substrate 2 and the metal member 3a, respectively, in the outer periphery 2o1 and its vicinity. The outer periphery 2o1 is located on one end side in the long-side direction of the ceramic substrate 2. 【0027】As shown in Figure 2, measurement points are also set on the outer periphery 2o2 located on the other end of the ceramic substrate 2 in the long-side direction along the dashed line X1-X1. Specifically, on the outer periphery 2o2, measurement point 22 is set midway between the end of the front surface 2a and the end of the metal member 3b along the dashed line X1-X1. Measurement point 32 is set on the metal member 3b along the dashed line X1-X1. The distance from the end of the front surface 2a to measurement point 22, the distance from measurement point 22 to the end of the metal member 3b, and the distance from the end of the metal member 3b to measurement point 32 are equal to each other. 【0028】 Through the above steps, two measurement points are set on the ceramic substrate 2 along the dashed line X1-X1, and two measurement points are set on one or more metal members 3. Once the measurement points are set, the residual stress of the ceramic substrate 2 is measured between measurement point 21 and measurement point 22. The residual stress of one or more metal members 3 is measured between measurement point 31 and measurement point 32. These residual stress measurement results are recorded as the residual stress in the longitudinal direction (X1-X1 direction) of the ceramic circuit board 1. 【0029】 In the example shown in Figure 2, metal members 3a to 3d have the same shape, thickness, and size. Furthermore, the arrangement of metal members 3c and 3d is symmetrical to the arrangement of metal members 3a and 3b with respect to a line segment passing through the center of the short side of the ceramic substrate 2. For this reason, if residual stress is measured along the dashed line X1-X1 passing through metal members 3a and 3b, the measurement of residual stress along the dashed line X1-X1 passing through metal members 3c and 3d may be omitted. If the shapes, thicknesses, and sizes of metal members 3a to 3d differ from each other, residual stress is also measured for different sets of metal members 3. For example, if the thickness of metal member 3a and metal member 3c differ, after measuring the residual stress along the dashed line X1-X1 described above, another dashed line X1-X1 is drawn passing through metal members 3c and 3d. The residual stress of the ceramic substrate 2 and the residual stress of one or more metal members 3 are measured along this other dashed line X1-X1. 【0030】Next, as shown in Figure 2, a dashed line Y1-Y1 is drawn parallel to the short side direction (short edge direction) of the ceramic substrate 2. The dashed line Y1-Y1 crosses multiple metal members 3a and 3c that are arranged in the short side direction. In the example shown in Figure 2, no matter how the dashed line Y1-Y1 is drawn passing through the metal members 3a and 3c, the sum of the dimensions of metal member 3a and metal member 3c on the dashed line Y1-Y1 is constant and maximum. In this case, it is preferable that the dashed line Y1-Y1 is drawn so as to cross the center of each metal member 3 in the long side direction. The fact that the dashed line Y1-Y1 crosses the center of those metal members 3 means that, in a direction perpendicular to the dashed line Y1-Y1, the dashed line Y1-Y1 is located at an equidistant distance from the end face of each metal member 3. 【0031】 Figure 4 is an enlarged view of part B of the ceramic circuit board according to the embodiment shown in Figure 2. As shown in Figure 4, a measurement point 23 is set midway between the edge of the front surface 2a of the ceramic substrate 2 and the edge of the metal member 3a (the boundary between the ceramic substrate 2 and the metal member 3a) on the dashed line Y1-Y1. The distance 2a5 from the edge of the front surface 2a to the measurement point 23 is equal to the distance 2a6 from the measurement point 23 to the edge of the metal member 3a. Furthermore, a measurement point 33 is set on the metal member 3a on the dashed line Y1-Y1. The distance 3a5 from the edge of the metal member 3a to the measurement point 33 is equal to distances 2a5 and 2a6. As a result, measurement points are set on the ceramic substrate 2 and the metal member 3a, respectively, in the outer periphery 2o3 and its vicinity. The outer periphery 2o3 is located on one end side in the short-side direction of the ceramic substrate 2. 【0032】 As shown in Figure 2, measurement points are also set on the outer periphery 2o4 located on the other end of the short side of the ceramic substrate 2 along the dashed line Y1-Y1. Specifically, on the outer periphery 2o4, measurement point 24 is set midway between the end of the front surface 2a and the end of the metal member 3c along the dashed line Y1-Y1. Measurement point 34 is set on the metal member 3c along the dashed line Y1-Y1. The distance from the end of the front surface 2a to measurement point 24, the distance from measurement point 24 to the end of the metal member 3c, and the distance from the end of the metal member 3c to measurement point 34 are equal to each other. 【0033】Through the above steps, two measurement points are set on the ceramic substrate 2 along the dashed line Y1-Y1, and two measurement points are set on one or more metal members 3. The residual stress of the ceramic substrate 2 is measured between measurement point 23 and measurement point 24. The residual stress of one or more metal members 3 is measured between measurement point 33 and measurement point 34. The results of these residual stress measurements are recorded as the residual stress in the short direction (Y1-Y1 direction) of the ceramic circuit board 1. 【0034】 If the shapes, thicknesses, and sizes of the metal members 3a to 3d differ from each other, the residual stress is measured for each set of different metal members 3. For example, if the thickness of metal member 3a and metal member 3d differ, after measuring the residual stress along the dashed line Y1-Y1 described above, another dashed line Y1-Y1 is drawn passing through metal members 3b and 3d. The residual stress of the ceramic substrate 2 and the residual stress of one or more metal members 3 are measured along this other dashed line Y1-Y1. 【0035】 Next, as shown in Figure 2, a dashed line Z1-Z1 is drawn parallel to the diagonal direction of the ceramic substrate 2. The dashed line Z1-Z1 crosses a plurality of metal members 3b and 3c that are arranged diagonally. Figure 5 is an enlarged view of part C of the ceramic circuit board according to the embodiment shown in Figure 2. As shown in Figure 5, a measurement point 25 is set on the dashed line Z1-Z1 midway between the edge of the front surface 2a of the ceramic substrate 2 and the edge of the metal member 3c (the boundary between the ceramic substrate 2 and the metal member 3c). The distance 2a9 from the edge of the front surface 2a to the measurement point 25 is equal to the distance 2a10 from the measurement point 25 to the edge of the metal member 3c. Furthermore, a measurement point 35 is set on the metal member 3c on the dashed line Z1-Z1. The distance 3a9 from the edge of the metal member 3c to the measurement point 35 is equal to the distances 2a9 and 2a10. As a result, measurement points are set on the ceramic substrate 2 and the metal member 3c, respectively, at the corner between the outer peripheral portions 2o1 and 2o3 and in their vicinity. 【0036】As shown in Figure 2, a measurement point is also set on the opposite corner of the ceramic substrate 2 along the dashed line Z1-Z1. Specifically, at the corner between the outer periphery 2o2 and 2o3, a measurement point 26 is set midway between the end of the front surface 2a and the end of the metal member 3b along the dashed line Z1-Z1. A measurement point 36 is set on the metal member 3b along the dashed line Z1-Z1. The distance from the end of the front surface 2a to measurement point 26, the distance from measurement point 26 to the end of the metal member 3b, and the distance from the end of the metal member 3b to measurement point 36 are equal to each other. 【0037】 Through the above steps, two measurement points are set on the ceramic substrate 2 along the dashed line Z1-Z1, and two measurement points are set on one or more metal members 3. The residual stress of the ceramic substrate 2 is measured between measurement point 25 and measurement point 26. The residual stress of one or more metal members 3 is measured between measurement point 35 and measurement point 36. The results of these residual stress measurements are recorded as the residual stress in the diagonal direction (Z1-Z1 direction) of the ceramic circuit board 1. 【0038】 If the shapes, thicknesses, and sizes of the metal members 3a to 3d differ from each other, the residual stress is measured for each set of different metal members 3. For example, if the thickness of metal member 3a and metal member 3c differ, after measuring the residual stress along the dashed line Z1-Z1 described above, another dashed line Z1-Z1 is drawn passing through metal members 3a and 3d. The residual stress of the ceramic substrate 2 and the residual stress of one or more metal members 3 are measured along this other dashed line Z1-Z1. 【0039】 Figure 6 is a bottom view showing an example of a ceramic circuit board according to an embodiment. In Figure 6, 5 is a metal member (back metal plate). On the back surface 2b of the ceramic substrate 2, the residual stress of the ceramic substrate 2 and the residual stress of one or more metal members 5 are measured, similar to the examples shown in Figures 2 to 5. 【0040】Specifically, as shown in Figure 6, a dashed line X2-X2 is drawn parallel to the long side direction of the ceramic substrate 2. Preferably, the dashed line X2-X2 is drawn so as to cross the center of the short side direction of the metal member 5. The fact that the dashed line X2-X2 crosses the center of the short side direction means that, in a direction perpendicular to the dashed line X2-X2, the dashed line X2-X2 is located equidistant from the end face of the metal member 5. As shown in Figure 6, a measurement point 210 is set on the dashed line X2-X2 midway between the end of the back surface 2b and the end of the metal member 5 (the boundary between the ceramic substrate 2 and the metal member 5). The distance from the end of the back surface 2b to the measurement point 210 is equal to the distance from the measurement point 210 to the end of the metal member 5. Furthermore, a measurement point 51 is set on the metal member 5 on the dashed line X2-X2. The distance from the end of the metal member 5 to the measurement point 51 is equal to the distance from the measurement point 210 to the end of the metal member 5. 【0041】 A measurement point is also set on the other end of the ceramic substrate 2 in the direction of the long side, along the dashed line X2-X2. On the outer periphery of the other end, a measurement point 211 is set midway between the end of the back surface 2b and the end of the metal member 5, along the dashed line X2-X2. A measurement point 52 is set on the metal member 5 along the dashed line X2-X2. The distance from the end of the back surface 2b to measurement point 211, the distance from measurement point 211 to the end of the metal member 5, and the distance from the end of the metal member 5 to measurement point 52 are equal to each other. The residual stress of the ceramic substrate 2 is measured between measurement point 210 on the outer periphery 2o11 and measurement point 211 on the outer periphery 2o12. The residual stress of one or more metal members 5 is measured between measurement point 51 near the outer periphery 2o11 and measurement point 52 near the outer periphery 2o12. 【0042】As shown in FIG. 6, a broken line Y2 - Y2 parallel to the short side direction of the ceramic substrate 2 is drawn. The broken line Y2 - Y2 is preferably drawn so as to cross the central portion of the metal member 5 in the long side direction. That the broken line Y2 - Y2 crosses the central portion in the long side direction means that, in the direction perpendicular to the broken line Y2 - Y2, the broken line Y2 - Y2 is located at an equal distance from the end face of the metal member 5. As shown in FIG. 6, on the broken line Y2 - Y2, a measurement point 212 is set at the middle between the end of the back surface 2b and the end of the metal member 5. The distance from the end of the back surface 2b to the measurement point 212 is equal to the distance from the measurement point 212 to the end of the metal member 5. Further, on the broken line Y2 - Y2, a measurement point 53 is set on the metal member 5. The distance from the end of the metal member 5 to the measurement point 53 is equal to the distance from the measurement point 212 to the end of the metal member 5. 【0043】 On the other end side in the short side direction of the ceramic substrate 2 on the broken line Y2 - Y2, measurement points are also set. On the broken line Y2 - Y2 at the middle between the end of the back surface 2b and the end of the metal member 5 in the outer peripheral portion on the other end side, a measurement point 213 is set. On the broken line Y2 - Y2, a measurement point 54 is set on the metal member 5. The distance from the end of the back surface 2b to the measurement point 213, the distance from the measurement point 213 to the end of the metal member 5, and the distance from the end of the metal member 5 to the measurement point 54 are equal to each other. The residual stress of the ceramic substrate 2 is measured between the measurement point 212 in the outer peripheral portion 2o13 and the measurement point 213 in the outer peripheral portion 2o14. The residual stress of one or more metal members 5 is measured between the measurement point 53 near the outer peripheral portion 2o13 and the measurement point 54 near the outer peripheral portion 2o14. 【0044】 As shown in FIG. 6, a broken line Z2 - Z2 parallel to the diagonal direction of the ceramic substrate 2 is drawn. On the broken line Z2 - Z2, a measurement point 214 is set at the middle between the end of the back surface 2b and the end of the metal member 5. The measurement point 214 is located at the corner between the outer peripheral portion 2o11 and the outer peripheral portion 2o14. The distance from the end of the back surface 2b to the measurement point 214 is equal to the distance from the measurement point 214 to the end of the metal member 5. Further, on the broken line Z2 - Z2, a measurement point 55 is set on the metal member 5. The distance from the end of the metal member 5 to the measurement point 55 is equal to the distance from the measurement point 214 to the end of the metal member 5. 【0045】On the dashed line Z2-Z2, measurement points are also set at the corner of the ceramic substrate 2 on the opposite side. At the corner on the opposite side, a measurement point 215 is set at the middle between the end of the back surface 2b and the end of the metal member 5 on the dashed line Z2-Z2. The measurement point 215 is located at the corner between the outer peripheral portion 2o12 and the outer peripheral portion 2o13. On the dashed line Z2-Z2, a measurement point 56 is set on the metal member 5. The distance from the end of the back surface 2b to the measurement point 215, the distance from the measurement point 215 to the end of the metal member 5, and the distance from the end of the metal member 5 to the measurement point 56 are equal to each other. The residual stress of the ceramic substrate 2 is measured between the measurement point 214 and the measurement point 215. The residual stress of one or more metal members 5 is measured between the measurement point 55 and the measurement point 56. 【0046】 By the above method, the residual stress of the ceramic substrate 2 and the residual stress of the metal member 3 in three directions are measured for the front surface 2a of the ceramic substrate 2. For the back surface 2b, the residual stress of the ceramic substrate 2 and the residual stress of the metal member 5 in three directions are measured. For each measurement result in each direction, the absolute value |Sm / Sc| of the ratio of the tensile stress Sm of the metal member to the compressive stress Sc of the ceramic substrate 2 is calculated. From the calculated plurality of ratios |Sm / Sc|, the maximum ratio |Sm / Sc| is extracted. The extracted ratio |Sm / Sc| is used as the measurement result of the ratio |Sm / Sc| in the ceramic circuit board 1. In the embodiment, the obtained ratio |Sm / Sc| is in the range greater than 1.0 and less than or equal to 1.8. 【0047】 In the ceramic circuit board 1, the ratio |Sm / Sc| in any direction may be outside the above range. That is, some of the ratios |Sm / Sc| other than the maximum ratio |Sm / Sc| may be less than or equal to 1.0. As described above, when the metal member expands, cracks are likely to occur. By controlling the maximum ratio |Sm / Sc| within the range greater than 1.0 and less than or equal to 1.8, the occurrence of cracks during thermal cycling can be effectively suppressed. 【0048】 More preferably, the ratio |Sm / Sc| in any direction is controlled within the range greater than 1.0 and less than or equal to 1.8. Thereby, the occurrence of cracks during thermal cycling can be further suppressed. 【0049】 In this embodiment, the absolute value of the ratio of residual stress in the ceramic substrate 2 to the residual stress in the metal member, measured at the outer periphery, is controlled to be within a predetermined range. The absolute value of the ratio of residual stress measured at locations other than the outer periphery may fall outside this range. This is because the largest residual stress occurs at the outer periphery of the ceramic circuit board 1, and this residual stress has the greatest influence on defects such as cracks. 【0050】 Figure 7 is a top view showing another example of a ceramic circuit board according to the embodiment. In the example shown in Figure 7, the shape of the ceramic circuit board is hexagonal, not rectangular. 【0051】 First, as shown in Figure 7, dashed lines Xn1-Xn1, Xn2-Xn2, and Xn3-Xn3 are drawn along the longitudinal direction of the ceramic substrate 2, passing through the metal members 3a to 3c, respectively, and the residual stress of the ceramic substrate 2 and metal members 3 is measured along each dashed line. Next, dashed lines Yn-Yn are drawn along the short direction of the ceramic substrate 2, passing through the metal members 3a to 3c, and the residual stress of the ceramic substrate 2 and metal members 3 is measured along these dashed lines. Finally, dashed lines Zn1-Zn1, Zn2-Zn2, and Zn3-Zn3 are drawn along the diagonal direction of the ceramic substrate 2, passing through one or more metal members 3, and the residual stress of the ceramic substrate 2 and metal members 3 is measured along these dashed lines. Note that dashed line Zn3-Zn3 passes only through the respective ends of metal members 3b and 3c, and measurement points for metal members 3 cannot be set on dashed line Zn3-Zn3. Therefore, the measurement of residual stress along the dashed line Zn3-Zn3 is omitted. In the example shown in Figure 7, a diagonal line is drawn from the lower left corner of the ceramic substrate 2 in the drawing. A diagonal line is also drawn from another corner of the ceramic substrate 2, and the residual stress in that diagonal direction is measured. 【0052】 For each measurement result in each direction, the absolute value |Sm / Sc| of the ratio of the tensile stress Sm of the metal member to the compressive stress Sc of the ceramic substrate 2 is calculated. From the multiple calculated ratios |Sm / Sc|, the largest ratio |Sm / Sc| is extracted. The extracted ratio |Sm / Sc| is used as the measurement result of the ratio |Sm / Sc| in the ceramic circuit board 1. 【0053】 The ceramic substrate 2 is preferably one of the following: an aluminum oxide substrate, an aluminum nitride substrate, and a silicon nitride substrate. In addition, the ceramic substrate 2 may be an argil substrate. Argil is a sintered body consisting of 20 to 80 wt% aluminum oxide with the remainder being zirconium oxide. 【0054】 The three-point bending strength of aluminum nitride substrates or aluminum oxide substrates is approximately 300 to 450 MPa. The three-point bending strength of algil substrates is also around 550 MPa. The three-point bending strength of silicon nitride substrates can be increased to 600 MPa or more, and can even be increased to 700 MPa or more. The thermal conductivity of silicon nitride substrates can be increased to 50 W / (m·K) or more, and can even be increased to 80 W / (m·K) or more. In particular, in recent years, there are silicon nitride substrates that possess both high strength and high thermal conductivity. The thickness of the silicon nitride substrate is preferably 0.7 mm or less, and more preferably 0.32 mm or less. Because silicon nitride substrates have high strength, they can be made thinner, which can further improve heat dissipation. There is no particular lower limit set for the thickness, but it is preferably 0.1 mm or more. This is to ensure the electrical insulation of the silicon nitride substrate. Here, thickness refers to the dimension in the direction connecting the ceramic substrate 2 and the metal member 3. The ceramic circuit board according to this embodiment may comprise one ceramic substrate or two or more ceramic substrates. For example, multiple ceramic substrates and multiple metal members may be alternately laminated in the thickness direction. 【0055】If the ceramic substrate is a silicon nitride substrate, the residual stress is measured using a vanadium target (V-Kα) at ​​an incident angle of 30°. For silicon nitride substrates, the compressive stress is measured using the (411) diffraction peak. If the ceramic substrate is an aluminum oxide substrate, the residual stress is measured using an iron target (Fe-Kα) at ​​an incident angle of 30°. For aluminum oxide substrates, the compressive stress is measured using the (2.1.10) diffraction peak. If the ceramic substrate is an aluminum nitride substrate, the residual stress is measured using a chromium target (Cr-Kα) at ​​an incident angle of 30°. For aluminum nitride substrates, the compressive stress is measured using the (112) diffraction peak. The X-ray target and diffraction peak are selected according to the material of the ceramic substrate. The selection should refer to the method recommended by the Ceramics Subcommittee within the X-ray Material Strength Division Committee of the Japan Society for Materials Science. For example, this method is described in "JSMS-1-00 Standard Ceramics Method for X-ray Stress Measurement" published by the Japan Society for Materials Science. 【0056】 The ceramic circuit board according to this embodiment includes a ceramic substrate and a metal member. The tensile stress of the metal member is preferably in the range of 60 MPa to 250 MPa. 【0057】 If the tensile stress of the metal member is greater than 250 MPa, even if compressive stress is applied to the ceramic substrate 2, it may not be possible to sufficiently mitigate the increase in tensile stress due to the expansion of the metal member. If the tensile stress of the metal member is less than 60 MPa, cracks may occur due to the synergistic effect with the compressive stress when the metal member shrinks. For this reason, the tensile stress of the metal member is preferably in the range of 70 MPa to 200 MPa, and more preferably in the range of 80 MPa to 150 MPa. 【0058】 In this specification, a high compressive stress means that the numerical value has a larger absolute value on the negative side. A low compressive stress means that the numerical value has a smaller absolute value on the negative side. For example, between a compressive stress of -60 MPa and a compressive stress of -250 MPa, the compressive stress of -250 MPa is higher. 【0059】 The ceramic circuit board according to this embodiment includes a ceramic substrate and a metal member. The compressive stress of the ceramic substrate is preferably in the range of -250 MPa to -60 MPa. 【0060】 If the compressive stress of the ceramic substrate is less than -60 MPa, it may not effectively alleviate the tensile stress caused by the expansion of the metal component. If the compressive stress of the ceramic substrate is greater than -250 MPa, cracks may occur due to a synergistic effect with the decrease in tensile stress when the metal component shrinks. For this reason, the compressive stress of the ceramic substrate is preferably in the range of -200 MPa to -70 MPa, and more preferably in the range of -150 MPa to -80 MPa. 【0061】 Furthermore, the maximum height Sz of the metal member is preferably 120 μm or less. The maximum height Sz is the distance between the highest point (highest convex part) and the lowest point (lowest concave part) in the thickness direction of the surface. The maximum height Sz is defined in ISO 25178. The maximum height Sz is measured by a method in accordance with ISO 25178. A Keyence VR-5000 series one-shot 3D shape measuring machine or an equivalent device is used as the measuring device. The measurement range is set to 3 mm vertically x 3 mm horizontally. When measuring a 3 mm x 3 mm area near where the tensile stress of the metal member was measured, it is preferable that the maximum height Sz is 120 μm or less. 【0062】When the maximum height Sz is 120 μm or less, it is easier to control the tensile stress of the metal member within a predetermined range. As described later, adjustments to the bonding speed are made to control the compressive stress of the ceramic substrate 2 and the tensile stress of the metal member. When controlling residual stress by the bonding speed, it is effective to control the maximum height Sz so that it is within a predetermined range. The larger the maximum height Sz, the greater the variation in the thickness of the ceramic substrate 2. Residual stress increases in areas with greater thickness. If the maximum height Sz exceeds 120 μm, the tensile stress of the metal member increases locally, making it easier for defects such as cracks to occur. There is no particular lower limit to the maximum height Sz, but it is preferably 10 μm or more. If the maximum height Sz is less than 10 μm, the tensile stress of the metal member becomes too small, and the compressive stress during shrinkage of the metal member may increase. Furthermore, by controlling the maximum height Sz within a predetermined range, the bonding properties of the semiconductor element to the metal member can be improved. Therefore, the maximum height Sz is preferably 120 μm or less, and more preferably within the range of 10 μm to 120 μm. 【0063】 Preferably, the ceramic substrate 2 and the metal member 3 are joined via a first bonding layer 4. If a metal member (back metal plate) 5 is provided, preferably the metal member 5 is joined to the ceramic substrate 2 via the first bonding layer 4. 【0064】The first bonding layer 4 preferably contains at least two elements selected from the group consisting of Ag, Cu, Ti, Sn, In, Zr, Al, Si, C, and Mg. As an example, the first bonding layer 4 contains Ag (silver) and Ti (titanium). The first bonding layer 4 containing Ag and Ti is formed using an activated metal brazing material. Ti is the activated metal. In addition to Ti, the activated metal may also be Zr (zirconium). The activated metal brazing material is, for example, a mixture of Ti, Ag, and Cu (copper). For example, the Ti content is 0.1 to 10 wt%, the Cu content is 10 to 60 wt%, and the remainder is Ag. If necessary, one or more elements selected from the group consisting of In (indium), Sn (tin), Al (aluminum), Si (silicon), C (carbon), and Mg (magnesium) may be added in an amount of 1 to 15 wt%. The activated metal brazing method involves applying an activated metal brazing paste to the surface of a ceramic substrate and placing a copper plate on top. This laminate is then heated to 700-900°C to bond the components. This activated metal bonding method can achieve a bonding strength of 16 kN / m or more between the ceramic substrate and the metal component. 【0065】The heating rate is controlled by adjusting the thickness and size of each component, such as the ceramic substrate and metal component, or by adjusting the amount of material added to the temperature profile during heat bonding. Typically, the temperature is raised from room temperature to the bonding temperature at a rate of 5 to 10°C / minute. After maintaining the bonding temperature for 5 to 60 minutes, the temperature is lowered (cooled) back to room temperature. Normally, to reduce energy costs, natural cooling is used instead of forced cooling. However, in order to impart the compressive and tensile stresses described above to the ceramic substrate 2 and the metal component, it is preferable to make the cooling rate greater than or equal to the heating rate. That is, the ratio Rc / Rh of the cooling rate to the heating rate Rh is preferably in the range of 1.0 ≤ Rc / Rh ≤ 2.0. If Rc / Rh is less than 1.0, sufficient tensile and compressive stresses cannot be imparted to the ceramic substrate 2 and the metal component. When the Rc / Rh ratio exceeds 2.0, the tensile stress on the metal component increases, but rapid cooling can cause the ceramic substrate to crack due to the difference in thermal expansion between the metal component and the ceramic substrate. For this reason, the Rc / Rh ratio is preferably between 1.0 and 2.0, and more preferably between 1.2 and 1.8. 【0066】 A thin metal film may be provided on the surface of a metal component, with one of the following elements selected from the group consisting of Ni (nickel), Ag (silver), and Au (gold) as the main component. These thin metal films are, for example, plating films or sputtered films. By providing a thin metal film, properties such as corrosion resistance and solder wettability can be improved. 【0067】The ceramic circuit board 1 according to this embodiment is suitable for semiconductor devices in which semiconductor elements are mounted on metal members via bonding layers. Figure 8 is a side view showing an example of a semiconductor device. In Figure 8, 1 is a ceramic circuit board. 6 is a semiconductor device. 7 is a semiconductor element. 8 is a bonding layer (second bonding layer). 9 is wire bonding. 10 is a metal terminal. In the example shown in Figure 8, a semiconductor element 7 is bonded to one metal member 3 of the ceramic circuit board 1 via a second bonding layer 8. A metal terminal 10 is bonded to another metal member 3 via another second bonding layer 8. The semiconductor elements and metal terminals 10 of adjacent metal members 3 are electrically connected by wire bonding 9. The semiconductor device 6 according to this embodiment is not limited to this structure. For example, only one of the wire bonding 9 and the metal terminal 10 may be provided. Multiple semiconductor elements 7, wire bonding 9, or metal terminals 10 may be provided on a single metal member 3. A semiconductor element 7, wire bonding 9, or metal terminal 10 may be joined to the metal member 5 as needed. Various shapes can be applied to the metal terminal 10, such as a lead frame shape or a convex shape. 【0068】 Solder, brazing material, etc., are used in the second bonding layer 8 that joins the semiconductor element 7 or metal terminal 10. Lead-free solder is preferable. Solder refers to a bonding material with a melting point of 450°C or lower. Brazing material refers to a bonding material with a melting point exceeding 450°C. Bonding material with a melting point of 500°C or higher is called high-temperature brazing material. High-temperature brazing material, for example, mainly consists of silver (Ag). 【0069】In recent years, while semiconductor elements 7 have become smaller, the amount of heat generated from the chip has increased. Therefore, improved heat dissipation is required for the ceramic circuit board 1 on which the semiconductor elements 7 are mounted. In addition, multiple semiconductor elements 7 may be mounted on the ceramic circuit board 1 in order to improve the performance of the semiconductor device 6 (semiconductor module). If any of the semiconductor elements 7 exceeds its intrinsic temperature, its resistance changes to a negative temperature coefficient. Consequently, thermal runaway occurs, in which power flows concentratedly through that semiconductor element 7, and the semiconductor device 6 is instantly destroyed. For this reason, improving the reliability of the bonding of the ceramic circuit board 1 on which the semiconductor elements 7 are mounted is extremely effective. 【0070】 The semiconductor device 6 according to this embodiment can be used as a PCU, IGBT, or IPM module. These modules are used in inverters. Inverters are used in automobiles (including electric vehicles), railway vehicles, industrial machinery, and equipment such as air conditioners. Regarding automobiles, the adoption of electric vehicles is progressing. The more reliable the semiconductor device, the greater the safety of the automobile. The same applies to railway vehicles, industrial equipment, etc. 【0071】 Next, a method for manufacturing a ceramic circuit board according to the embodiment will be described. The manufacturing method of the ceramic circuit board is not particularly limited as long as it has the above-described configuration. Here, an example of a manufacturing method for obtaining a ceramic circuit board with good yield will be described. 【0072】 First, prepare a ceramic substrate and a metal plate. The metal plate is preferably made of copper or a copper alloy. The thickness of the metal plate is 0.5 mm or more. The ceramic substrate is preferably one selected from aluminum oxide substrates, aluminum nitride substrates, and silicon nitride substrates. In particular, considering the heat dissipation of the entire ceramic circuit board, the ceramic substrate is preferably a silicon nitride substrate with a thermal conductivity of 50 W / (m·K) or more and a three-point bending strength of 600 MPa or more. 【0073】When a metal component provided on the surface of a ceramic substrate and a metal plate provided on the back surface are to be electrically connected by through holes, a ceramic substrate having through holes is prepared. When providing through holes in a ceramic substrate, the through holes may be formed in advance at the molding stage. Alternatively, the through holes may be formed in the ceramic substrate (ceramic sintered body). The through holes are formed by methods such as laser processing and cutting. Cutting is, for example, drilling with a drill. 【0074】 The ceramic substrate and the metal plate are preferably joined by an activated metal bonding method. In the activated metal bonding method, an activated metal brazing material is used, which is a mixture of an activated metal such as Ti and Ag. The activated metal brazing material is, for example, a mixture of Ti, Ag, and Cu. In the activated metal brazing material, the Ti content is preferably 0.1 to 10 wt%, the Cu content is preferably 10 to 60 wt%, and the remainder is Ag. If necessary, one or more selected from the group consisting of In, Sn, Al, Si, C, and Mg may be added in a range of 1 to 15 wt%. The raw materials are mixed to form a paste of the activated metal brazing material. In the paste, the brazing material components and organic matter are mixed. It is preferable that the brazing material components are uniformly mixed in the paste. This is because if the brazing material components are not distributed uniformly, the brazing will not be stable and it will cause a bonding failure. 【0075】 The prepared activated metal brazing paste is applied to both sides of a ceramic substrate and dried. A metal plate is placed on top of the dried paste. The ceramic substrate with the metal plate is heated to 700-900°C to bond the materials. The heating process is carried out in a vacuum or a non-oxidizing atmosphere as necessary. When heat bonding is performed in a vacuum, the pressure is 1 × 10⁻⁶. －２ It is preferable that the pressure be Pa or less. Non-oxidizing atmospheres include, for example, nitrogen and argon atmospheres. By using a vacuum or non-oxidizing atmosphere, oxidation of the first bonding layer can be suppressed. This improves the bonding strength. It is also preferable to perform a degreasing step of the activated metal brazing paste during the heat bonding process. 【0076】In the heat bonding process, the bonding temperature is maintained within the range of 700 to 900°C. The rate of cooling from the bonding temperature back to room temperature is greater (faster) than the rate of heating from room temperature (temperature before placing in the furnace) back to the bonding temperature. For example, if the room temperature is 25°C and the bonding temperature is 825°C, setting the heating rate to 8.0°C / min will reach the bonding temperature in 100 minutes. Setting the cooling rate to 10.0°C / min will reach room temperature in 80 minutes. 【0077】 The copper plates to be joined may be pre-processed into a pattern shape, or they may be solid copper plates. If a solid plate is used, etching is performed after joining to create the pattern shape. This process allows for the manufacture of a ceramic circuit board. Next, a process of joining semiconductor elements to the ceramic circuit board is carried out. A second bonding layer is provided at the location where the semiconductor elements are to be joined. The second bonding layer preferably contains solder or brazing material. A second bonding layer of metal members is provided, and the semiconductor elements are placed on top of it. If necessary, metal terminals are joined via the second bonding layer of metal members. Wire bonding may be provided if necessary. The required number of semiconductor elements, metal terminals, and wire bonding are provided. 【0078】 (Examples 1-10, Comparative Examples 1-8) Silicon nitride substrates, aluminum nitride (AlN) substrates, and aluminum oxide (alumina) substrates were prepared as ceramic substrates. The thermal conductivity of the silicon nitride substrate was 90 W / (m·K), and the three-point bending strength was 650 MPa. The thermal conductivity of the aluminum nitride substrate was 170 W / (m·K), and the three-point bending strength was 300 MPa. The thermal conductivity of the aluminum oxide substrate was 20 W / (m·K), and the three-point bending strength was 350 MPa. The size of the ceramic substrate was 50 mm in length and 100 mm in width. A copper plate measuring 50 mm in length and 100 mm in width was prepared as a metal plate for the metal component. The thicknesses of the silicon nitride substrate, aluminum nitride substrate, alumina substrate, and copper plate are shown in Table 1. 【0079】Next, the ceramic substrate and the copper plate were joined using the activated metal bonding method. The activated metal brazing material used in the activated metal bonding method contained 2 wt% Ti, 10 wt% Sn, 30 wt% Cu, and the remainder being Ag. The materials to be used were mixed, and an activated metal brazing paste was prepared by mixing organic components. The activated metal brazing paste was applied to both sides of the ceramic substrate and dried. The copper plate was placed on both sides of the ceramic substrate after the paste had dried, and the heat bonding process was performed. The bonding temperature was set to 790 to 850°C. The heating rate to the bonding temperature and the cooling rate from the bonding temperature were set as shown in Table 1. The bonding time was set to 5 to 20 minutes, and the bonding was performed in a vacuum (1 × 10⁻⁶). －２ A ceramic substrate and a copper plate were bonded at a pressure of Pa or less. The front copper plate (front copper plate) was etched and processed into a circuit shape. As a result, the copper plate was processed into four circuit-shaped copper components as shown in Figure 2. The distance from the edge of the ceramic substrate to the copper component (pullback) was set to 5 mm, and the distance between copper components was set to 5 mm. The back copper component (back copper plate) was etched so that the pullback was 5 mm, as shown in Figure 6. 【0080】 【0081】 Next, the residual stress of the obtained ceramic circuit boards was measured. The residual stress was measured using a single-incidence method with an X-ray residual stress measuring device. The μ-X360s manufactured by PulseTech Industries Co., Ltd. was used as the X-ray residual stress measuring device. For copper components, the residual stress was measured using a vanadium target (V-Kα). For silicon nitride substrates, aluminum oxide substrates, and aluminum nitride substrates, the residual stress was measured using a vanadium target (V-Kα), an iron target (Fe-Kα), and a chromium target (Cr-Kα), respectively. In all measurements, the incident angle was set to 35°. For the front surface, the residual stress was measured in the three directions shown in Figure 2, and for the back surface, the residual stress was measured in the three directions shown in Figure 6. In both the example and the comparative example, the |Sm / Sc| in the Z2-Z2 direction on the back surface showed the largest value. The measurement results of the residual stress in the Z2-Z2 direction are shown in Table 2. 【0082】Furthermore, the maximum height Sz of the metal components in the obtained ceramic circuit board 1 was measured. A Keyence VR-5000 one-shot 3D shape measuring machine was used as the measuring device. For measuring the maximum height Sz, two measurement areas of 3 mm vertical x 3 mm horizontal were set near the two measurement points on the virtual line where the largest |Sm / Sc| was measured, including the measurement points. The maximum height Sz was measured in each measurement area, and the average of these measurement results was taken as the maximum height Sz of the metal components in the ceramic circuit board 1. 【0083】 Next, the reliability of the ceramic circuit boards according to the examples and comparative examples was evaluated. Reliability was assessed by evaluating the TCT characteristics after bonding of the semiconductor elements. For each example and comparative example, 100 samples were prepared under the same conditions, and their TCT characteristics were evaluated. 【0084】 Specifically, semiconductor elements were bonded to two copper components on the front surface of the ceramic circuit board using lead-free solder. Metal terminals were then bonded to two other copper components on the front surface. Wire bonding was then applied to establish electrical conductivity between the semiconductor elements and the metal terminals. This completed the fabrication of the semiconductor device. 【0085】 A temperature cycle test (TCT) was performed on semiconductor devices to investigate the incidence of conductivity failures. In the TCT, one cycle consisted of -40°C for 30 minutes → room temperature for 10 minutes → 150°C for 30 minutes → room temperature for 10 minutes. After 300 cycles, the area of ​​delamination due to cracks was calculated using ultrasonic testing (SAT). The percentage of undelaminated area η was then evaluated. The percentage of undelaminated area η was defined as η = 100% when no cracks occurred during the TCT, and η = 0% when cracks occurred across the entire bonding area of ​​the ceramic circuit board during the TCT. In this case, a value of η of 90% or higher was considered acceptable, and the failure rate was calculated accordingly. The measurement results are shown in Table 2. 【0086】 【0087】As can be seen from Table 2, in the examples, the absolute value of the ratio of the tensile stress Sm of the metal member to the compressive stress Sc of the ceramic substrate, |Sm / Sc|, was within a favorable range. In Comparative Examples 1 to 5, the ratio |Sm / Sc| was smaller than in the examples. In the examples, the cooling rate was greater than the heating rate, which is thought to have caused the absolute value of the compressive stress of the ceramic substrate to be greater than the absolute value of the tensile stress of the metal member. In Comparative Examples 6 to 8, the ratio |Sm / Sc| was larger than in the examples. In these comparative examples, the cooling rate was excessively greater than the heating rate, resulting in a smaller compressive stress in the ceramic substrate and a larger tensile stress in the metal member compared to the examples. 【0088】 Furthermore, in the examples, the maximum height Sz of the metal member was within a favorable range. In the examples, the absolute value of the ratio of the tensile stress Sm of the metal member to the compressive stress Sc of the ceramic substrate, |Sm / Sc|, is large. It is thought that by applying compressive stress to the ceramic substrate, the tensile stress associated with thermal expansion during joining was relieved, resulting in the maximum height Sz being within a favorable range. On the other hand, in the comparative example, the maximum height Sz was larger than in the examples. It is thought that the stress associated with thermal expansion during joining was not relieved, and this effect was reflected in the maximum height of the metal member surface. 【0089】 In the example, the TCT failure rate was sufficiently low. This is thought to be because, in the example, compressive stress was applied to the ceramic substrate and controlled so that the ratio |Sm / Sc| was within a predetermined range, thereby mitigating the tensile stress associated with the thermal cycle during TCT. On the other hand, in the comparative example, the TCT failure rate was high. This is thought to be because sufficient compressive stress was not applied to the ceramic substrate, and the tensile stress associated with the thermal cycle during TCT was not sufficiently mitigated. 【0090】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. These embodiments and their variations 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. 【0091】 1...Ceramic circuit board 2...Ceramic substrate 3, 3a-3d...Metal component (front metal plate) 4...First bonding layer 5...Metal component (back metal plate) 6...Semiconductor device 7...Semiconductor element 8...Second bonding layer 9...Wire bonding 10...Metal terminal

Claims

Ceramic substrate and The ceramic substrate comprises one or more metal members provided on the ceramic substrate, When compressive stress is applied to the ceramic substrate, Tensile stress is applied to one or more of the aforementioned metal members. A ceramic circuit board in which, when the compressive stress Sc at the outer periphery of the ceramic substrate and the tensile stress Sm near the outer periphery of one or more metal members are measured, the absolute value of the ratio of the tensile stress Sm to the compressive stress Sc |Sm / Sc| is greater than 1.0 and within the range of 1.8 or less. 　 The ceramic circuit board according to claim 1, wherein the tensile stress of the metal member is in the range of 60 MPa to 250 MPa. 　 The ceramic circuit board according to claim 1 or 2, wherein the compressive stress of the ceramic substrate is in the range of -60 MPa to -250 MPa. 　 The ceramic circuit board according to any one of claims 1 to 3, wherein the maximum height Sz of the metal member is 120 μm or less. 　 The ceramic circuit board according to any one of claims 1 to 4, wherein the metal member is made of copper or a copper alloy. 　 The ceramic circuit board according to any one of claims 1 to 5, wherein the ceramic substrate is made of alumina, aluminum nitride, or silicon nitride. 　 The ceramic circuit board according to any one of claims 1 to 6, wherein the thickness of the ceramic substrate is 0.7 mm or less. 　 The device further comprises a first bonding layer provided between the ceramic substrate and the metal member, The ceramic circuit substrate according to any one of claims 1 to 7, wherein the first bonding layer comprises at least two selected from the group consisting of Ag, Cu, Ti, Sn, In, Zr, Al, Si, C, and Mg. 　 A ceramic circuit board according to any one of claims 1 to 8, A semiconductor device comprising a semiconductor element mounted on the metal member of the ceramic circuit board via a second bonding layer.

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