Ceramic circuit board and manufacturing method therefor

Abstract

A ceramic circuit board according to an embodiment includes: a ceramic substrate having a first surface; and a first metal plate joined to the first surface via a first joining layer. In a cross section perpendicular to the first surface, the first metal plate satisfies the following conditions. The ratio Lb / Lt of the width Lb [mm] of a lower side to the width Lt [mm] of an upper side is 1.005-1.050. The ratio L1 / L2 of the maximum width L1 [mm] to the minimum width L2 [mm] in an intermediate part positioned between 0.4 and 0.6 times the thickness T of the metal plate from the lower side is 1.0-1.010. The ratio L1 / L2 of the maximum width L1 [mm] to the minimum width L2 [mm] in an intermediate part positioned between 0.4 and 0.6 times the thickness T of the metal plate from the lower side is 1.0-1.010. The ratio Lb / Lt is greater than the ratio L1 / L2}. The width Lb is greater than the minimum width L1.

Description

Ceramic circuit board and manufacturing method thereof

[0001] The embodiments described below generally relate to ceramic circuit boards and methods for manufacturing the same.

[0002] Ceramic substrates have excellent electrical insulation, heat resistance, and mechanical strength. Copper has excellent thermal and electrical conductivity. Ceramic circuit boards, in which a metal plate such as copper is bonded to a ceramic substrate, are widely used as circuit boards for power modules. The characteristics of ceramic circuit boards are important for achieving high output from power modules.

[0003] The main characteristics required for ceramic circuit boards are heat dissipation and durability in thermal cycle tests (TCT). Here, durability against thermal cycles is also referred to as TCT characteristics. The larger the current that flows through the semiconductor elements included in the power module, the more heat the semiconductor elements generate. By improving heat dissipation and TCT characteristics, it is possible to pass a larger current through the semiconductor elements, making it possible to accommodate semiconductor elements that generate more heat.

[0004] When the temperature of a ceramic circuit board changes, thermal stress occurs due to the difference in the thermal expansion coefficient between the ceramic board and the metal plate circuit. This thermal stress can cause the ceramic circuit board to warp, and the metal plate to peel or crack. These can lead to poor insulation withstand voltage. Therefore, ceramic circuit boards are required to have high thermal cycle durability so that they can withstand high-power usage environments.

[0005] One method for improving the heat dissipation of a ceramic circuit board is to increase the thickness of the metal plate, and one method for improving the thermal cycle durability is to bond the ceramic substrate and the metal plate via a bonding layer and provide a structure that contributes to alleviating thermal stress around the bonding layer and on the side of the metal plate.

[0006] For example, International Publication No. 2018 / 021472 (Patent Document 1) proposes providing a sloped (bottomed) shape on the side of a metal plate (copper plate). The side of the metal plate contacts the bonding layer at an angle of 40 to 84 degrees. International Publication No. 2015 / 019602 (Patent Document 2) proposes a ceramic circuit substrate in which the thickness of the metal plate (copper plate) is 1.0 mm or more and 7.0 mm or less, and the bonding layer has a predetermined amount of protrusion and creep-up.

[0007] Generally, thickening a metal plate improves the allowable current capacity and heat dissipation. However, it also increases stress during temperature changes, impairing thermal cycle durability. Furthermore, structures such as protruding and creeping-up portions of the bonding layer alone may not be sufficient to relieve stress. Furthermore, an etching process is required to create a skirt-shaped structure on the side of the metal plate, as in Patent Document 1. When using an etching process, it is difficult to use a thick metal plate due to reasons such as cost and environmental impact. Furthermore, in circuit boards with a large amount of creeping-up, as in Patent Document 2, the distance between circuit patterns must be set large. Increasing the distance between patterns reduces the number of circuits that can be provided on the ceramic substrate, resulting in a lower circuit density.

[0008] International Publication No. WO 2018 / 021472 International Publication No. WO 2015 / 019602

[0009] The problem to be solved by the present invention is to provide a circuit board having excellent heat dissipation properties and high thermal cycle reliability even when the metal plate is thick, and a method for manufacturing the same.

[0010] A ceramic circuit board according to an embodiment includes a ceramic substrate having a first surface, and a first metal plate bonded to the first surface via a first bonding layer. In any cross section perpendicular to the first surface, the first metal plate satisfies the following condition: width L of a lower side ｂ [mm] and top width L ｔ Ratio L to [mm] ｂ / L ｔ The maximum width L at the intermediate portion located between the lower side and a portion 0.4 to 0.6 times the thickness T of the metal plate is 1.005 or more and 1.050 or less.１ [mm] and minimum width L ２ Ratio L to [mm] １ / L ２ is 1.0 or more and 1.010 or less. ｂ / L ｔ is the ratio L １ / L ２ And the width L ｂ is the minimum width L １ longer than.

[0011] Figures 1(a) and 1(b) are cross-sectional schematic views showing an example of the configuration of a ceramic circuit board according to an embodiment. Figure 2 is a cross-sectional schematic view showing an example of the structure of the side shapes of a metal plate and a bonding layer. Figure 3 is a cross-sectional schematic view showing an example of the configuration of a ceramic circuit board according to an embodiment. Figure 4 is a cross-sectional schematic view showing an example of the configuration of a ceramic circuit board according to an embodiment. Figure 5 is a flowchart showing a method for manufacturing a ceramic circuit board according to an embodiment.

[0012] A ceramic circuit board according to an embodiment includes a ceramic substrate having a first surface, and a first metal plate bonded to the first surface via a first bonding layer. In any cross section perpendicular to the first surface, the first metal plate satisfies the following condition: width L of a lower side ｂ [mm] and top width L ｔ Ratio L to [mm] ｂ / L ｔ The maximum width L at the intermediate portion located between the lower side and a portion 0.4 to 0.6 times the thickness T of the metal plate is 1.005 or more and 1.050 or less. １ [mm] and minimum width L ２ Ratio L to [mm] １ / L ２ is 1.0 or more and 1.010 or less. ｂ / L ｔ is the ratio L １ / L ２ And the width L ｂ is the minimum width L １ longer than.

[0013] Hereinafter, a ceramic circuit board and a method for manufacturing the same according to an embodiment will be described with reference to the drawings. Figures 1(a) and 1(b) are cross-sectional schematic diagrams showing an example of the configuration of a ceramic circuit board according to an embodiment. Reference numeral 1 denotes a ceramic circuit board, reference numeral 2 denotes a ceramic substrate, reference numeral 3 denotes a metal plate, and reference numeral 4 denotes a bonding layer. Reference numeral T denotes a metal plate thickness, reference numeral L ｔ is the width of the upper edge of the metal plate, symbol L ｂ is the width of the bottom edge of the metal plate. １ is the maximum width at the middle of the metal plate. ２ is the minimum width at the intermediate portion. The intermediate portion is a portion of the metal plate 3 located between the lower edge and 0.4 to 0.6 times the thickness T of the metal plate.

[0014] The ceramic circuit substrate 1 shown in Figures 1(a) and 1(b) includes a ceramic substrate 2, a metal plate 3 (first metal plate), and a bonding layer 4. The ceramic substrate 2 has a first surface 2a and a second surface 2b opposite to the first surface 2a. The metal plate 3 is provided on the first surface 2a of the ceramic substrate 2. The bonding layer 4 bonds the ceramic substrate 2 and the metal plate 3. Figures 1(a) and 1(b) illustrate the ceramic circuit substrate 1 viewed from the same direction to indicate each reference symbol.

[0015] Here, the first surface 2 a of the ceramic substrate 2 is also referred to as the "front surface," and the second surface 2 b is also referred to as the "back surface." For example, the shape of the ceramic substrate 2 when viewed from the front surface is rectangular. The planar shape of the ceramic substrate 2 may be circular (including oval), triangular, L-shaped, U-shaped, etc.

[0016] The ceramic substrate 2 is, for example, a silicon nitride substrate, an aluminum nitride substrate, a silicon oxide substrate, a silicon carbide substrate, an aluminum oxide substrate, a zirconium oxide substrate, or an alumina-zirconia substrate. A silicon nitride substrate is preferred because of its excellent mechanical strength.

[0017] The silicon nitride substrate preferably has a thermal conductivity of 70 W / m·K or more and a three-point bending strength of 600 MPa or more. When the thermal conductivity and three-point bending strength are within the above ranges, a silicon nitride substrate having excellent heat dissipation properties and thermal cycle durability can be obtained.

[0018] The metal plate 3 is provided on at least one surface of the ceramic substrate 2. The metal plate 3 is mainly used as a circuit board or a heat sink, but may have other uses. The type of the metal plate 3 is not particularly limited. For example, a metal plate 3 made of copper or a copper alloy is preferred in terms of electrical conductivity and heat dissipation.

[0019] 2 is a cross-sectional view showing an example of the structure of the side surface of the metal plate and the bonding layer. In FIG. 2, reference numeral 5 denotes a first portion and reference numeral 6 denotes a second portion. Explanation of reference numerals common to FIG. 1 will be omitted.

[0020] Here, the direction perpendicular to the first surface 2a is defined as the Z direction, any direction parallel to the first surface 2a is defined as the X direction, and the direction perpendicular to the X and Z directions is defined as the Y direction.

[0021] As shown in FIG. 2 , the metal plate 3 includes a first portion 5. The first portion 5 is located at the bottom of the metal plate 3. The side surface of the first portion 5 is inclined with respect to the Z direction. In the first portion 5, the width of the metal plate 3 increases toward the bonding layer 4. The "width" is the length in one direction parallel to the first surface 2 a. The bottom surface of the first portion 5 is in contact with the bonding layer 4.

[0022] As shown in FIG. 2 , the metal plate 3 further includes a second portion 6. The second portion 6 is located on the first portion 5 and includes an upper portion and a middle portion of the metal plate 3. The inclination of the side surface of the second portion 6 with respect to the Z direction is smaller than the inclination of the side surface of the first portion 5 with respect to the Z direction. The inclination of the side surface of the second portion 6 with respect to the Z direction is within a range of 90°±5°. The side surface of the second portion 6 may be parallel to the Z direction.

[0023] The first portion 5 and the second portion 6 are parts of a single metal plate 3. In other words, the metal plate 3 is not formed by joining a metal plate corresponding to the first portion 5 and a metal plate corresponding to the second portion 6. For example, in the single metal plate 3, the portion that widens toward the joining layer 4 is the "first portion 5," and the portion whose side surface is approximately perpendicular to the joining surface is the "second portion 6." Note that the upper ends of the side surfaces may be subjected to light chamfering, R-chamfering, C-chamfering, or the like.

[0024] In FIG. 2 , the symbol r1 denotes the first region, the symbol r2 denotes the second region, and the symbol r3 denotes the third region. As shown in FIG. 2 , the bonding layer 4 includes a first region r1, a second region r2, and a third region r3. The first region r1 is provided between the ceramic substrate 2 and the metal plate 3 in the Z direction. The second region r2 is provided around the first region r1 along the first surface 2a. The second region r2 extends outside the metal plate 3. In other words, when viewed from the Z direction, the first region r1 overlaps with the metal plate 3, and the second region r2 does not overlap with the metal plate 3. The third region r3 is located above the second region r2 and is provided on the side surface of the metal plate 3. For example, the third region r3 is provided on the side surface of the first portion 5. The third region r3 may also be provided on the side surface of the second portion 6. The third region r3 may be in contact with the side surface of the metal plate 3.

[0025] In FIG. 2, the symbol W １ is the length of the second region r2 in the direction from the first region r1 to the second region r2. ２ is the length of the third region r3 in the Z direction. １ is called the "extension amount" and is denoted by the symbol W ２ is called the "rise amount."

[0026] In the ceramic circuit board according to the embodiment, the metal plate 3 has the following shape in any longitudinal cross section along the Z direction.

[0027] First, the width of the lower side L ｂ [mm] and top width L ｔ Ratio L to [mm] ｂ / L ｔ is 1.005 or more and 1.050 or less. The lower side is the side located at the bottom of the metal plate 3 in the longitudinal section. The width of the first portion 5 increases as it approaches the bonding layer 4. Therefore, in the metal plate 3, the lower side has the longest length in one direction parallel to the first surface 2a of the ceramic substrate 2. The width L of the lower side ｂ is the length of the widest part in the longitudinal section of the metal plate 3. ｂ is also the width of the portion in contact with the bonding layer 4.

[0028] The upper side is the side located at the top of the metal plate 3 in the vertical cross section. ｔ is the length of the narrowest part in the longitudinal section. ｂ and the width of the top edge L ｔ The lengths of the respective portions are measured in a direction parallel to the first surface 2 a of the ceramic substrate 2 in one longitudinal cross section.

[0029] Ratio L ｂ / L ｔ When the ratio L is in the range of 1.005 to 1.050, the width of the lower side of the metal plate 3 is longer than the width of the upper side. ｂ / L ｔ is preferably 1.010 or more and 1.050 or less.

[0030] Secondly, in the longitudinal section, the maximum width L １ [mm] and minimum width L ２ Ratio L to [mm] １ / L ２ is 1.0 or more and 1.010 or less. Here, the thickness of the metal plate 3 is T [mm]. The middle part is a part of the metal plate 3 located between the lower side and 0.4 to 0.6 times the thickness T. The maximum width L １ and minimum width L ２ is measured in a direction parallel to the first surface 2a in the longitudinal section. In the intermediate portion, the maximum length in the direction parallel to the first surface 2a is the maximum width L １ and the minimum length in the direction parallel to the first surface 2a is the minimum width L ２ The ratio L １ / L ２ is in the range of 1.0 or more and 1.010 or less, the maximum width L １ and minimum width L ２ This indicates that the difference between the ratio L and the ratio L is 1% or less at most. In other words, this indicates that the side surface of the metal plate 3 is substantially perpendicular to the Z direction in the intermediate portion, and the metal plate 3 includes the second portion 6. １ / L ２ is preferably 1.0 or more and 1.005 or less.

[0031] Third, in the longitudinal section, the ratio L ｂ / L ｔ is the ratio L１ / L ２ Ratio L is greater than ｂ / L ｔ is the ratio L １ / L ２ indicates that the difference in width between the top and bottom sides is greater than the difference in width at the middle.

[0032] Fourth, the width of the lower side L ｂ is the maximum width L of the middle part １ Larger than width L ｂ But the maximum width L １ , the ratio L is larger than the width of the metal plate 3 in the lower part than in the middle part. ｂ / L ｔ >Ratio L １ / L ２ and width L ｂ >Maximum width L １ indicates that the metal plate 3 includes the first portion 5.

[0033] Bottom width L ｂ , width of upper side L ｔ , maximum width L １ , and the minimum width L ２ The shape of the metal plate 3 satisfies the above conditions in any of the longitudinal cross sections of the ceramic circuit board 1.

[0034] Preferably, the metal plate 3 has the above-mentioned shape in a plurality of longitudinal cross sections. For example, the metal plate 3 has the above-mentioned shape in both one longitudinal cross section and another longitudinal cross section perpendicular to the one longitudinal cross section. Most preferably, the metal plate 3 has the above-mentioned shape in any longitudinal cross section passing through the center of the metal plate 3 in the X-Y plane. The "center" is, for example, the point at which the sum of the distances from each point on the outer edge is greatest when the metal plate 3 is viewed in a plane.

[0035] Thickness T of the metal plate 3, width L of the lower edge ｂ , width of upper side L ｔ , maximum width L １ , and the minimum width L ２For the measurement, an enlarged photograph of the longitudinal section observed with an optical microscope or a scanning electron microscope (SEM) is used. It is recommended to set the magnification at about 6 times.

[0036] The metal plate 3 may have the following shapes instead of the above shapes. The following shapes may be combined with the above shapes. First, in any longitudinal section, the maximum width L at the middle part of the metal plate 3 is １ and minimum width L ２ The value obtained by dividing the difference between the thickness T and the thickness L by 0.4 times is 0.05 or less (including 0). １ -L ２ ) / 0.4T≦0.05. Secondly, the width L of the lower side ｂ and the width of the top edge L ｔ Ratio L ｂ / L ｔ is in the range of 1.005 or more and 1.050 or less. １ -L ２ ) / 0.4T is 0.04 or less (including 0), and the ratio L ｂ / L ｔ is in the range of 1.010 or more and 1.050 or less. １ -L ２ ) / 0.2T<(L ｂ -L ｔ ) / T is more preferable. ｂ >L １ It is more preferable that:

[0037] The metal plate 3 may have the following shapes instead of the above shapes. The following shapes may be combined with the above shapes. First, in any longitudinal section, the maximum width L at the middle part of the metal plate 3 is １ and minimum width L ２ The difference between the thickness T and the thickness L is 0.05 or less (including 0), or １ and minimum width L ２ The difference between the L １ -L ２ ) / 0.4T ≦ 0.05, or L １ -L ２ ≦100 μm. (L １ -L ２) / 0.4T≦0.05 and L １ -L ２ ≦100 μm. Secondly, in the same vertical section, the width L of the lower side may be ｂ and the width of the top edge L ｔ Ratio L ｂ / L ｔ is in the range of 1.005 or more and 1.050 or less. １ -L ２ ) / 0.4T ≦ 0.04, and L １ -L ２ At least one of the following is satisfied: ｂ / L ｔ is in the range of 1.010 or more and 1.050 or less. １ -L ２ ) / 0.2T<(L ｂ -L ｔ ) / T. In addition, L ｂ >L １ It is preferable that:

[0038] (L １ -L ２ ) / 0.4T≦0.05 and L １ -L ２ ≦100 μm indicates that the metal plate 3 has a second portion 6 whose side surface is substantially parallel to the Z direction. １ -L ２ ) / 0.2T<(L ｂ -L ｔ ) / T similarly indicates that the metal plate 3 has a second portion 6 whose side surface is substantially parallel to the Z direction.

[0039] The thickness T of the metal plate 3 corresponds to the shortest distance between the lower and upper edges of the metal plate in a longitudinal cross section when the thickness of the ceramic substrate and the thickness of the bonding layer are constant. Typically, the thickness T roughly corresponds to the thickness of the metal plate 3 before bonding. Therefore, for simplicity, the thickness of the metal plate before bonding may be used as the thickness T.

[0040] When the metal plate 3 is joined, components of the joining layer 4 may diffuse into the metal plate 3. In this case, the distance in the Z direction from the tip to the upper edge of the first portion 5 of the metal plate 3 in the longitudinal cross section may be used as the thickness T. The "tip of the first portion 5" is the part of the joining portion between the metal plate 3 and the joining layer 4 that is closest to the ceramic substrate 2.

[0041] The thickness of the metal plate 3 may vary from part to part. The thickness T of the metal plate 3 may not be constant in any cross section. For example, the surface of the metal plate 3 may have recesses or protrusions. When recesses or protrusions are provided on the surface, the maximum thickness of a single metal plate 3 is defined as the thickness T. For example, when a recess with a depth of 1 mm is provided on a copper plate with a thickness of 2 mm, the thickness T is 2 mm. When a protrusion with a height of 0.5 mm is provided on a copper plate with a thickness of 2 mm, the thickness T is 2.5 mm.

[0042] Another metal plate may be joined to the surface of the metal plate 3 that has the first portion 5 and the second portion 6 and satisfies the above conditions. For example, another metal plate having an uneven structure may be joined to the surface of the metal plate 3. In this case, the distance between the upper and lower edges of the single metal plate 3 is used as the thickness T.

[0043] Width L ｂ , width L ｔ , maximum width L １ , and the minimum width L ２ satisfies the above-mentioned relationship, a partial structure may be provided on the side surface of the metal plate 3. For example, a structure other than the second portion 6 may be partially provided on the metal plate 3, and part of the side surface of the metal plate 3 may not be parallel to the Z direction.

[0044] For example, in any longitudinal cross section, when the side surface of the metal plate 3 can be approximated as a straight line, a curve, or a hyperbola as a whole, a concave or convex portion such as a depression, a slit, a protrusion, or a flange may be provided on the side surface above the intermediate portion or on the side surface of the first portion 5. Even in this case, in any longitudinal cross section, ｂ , width L ｔ , maximum width L １ , and the minimum width L ２ It is sufficient if the above relationship is satisfied.

[0045] As will be described later, by controlling the conditions in the process of thermally bonding the ceramic substrate and the metal plate, the metal plate 3 is bonded to include the first portion 5 while maintaining the shape of the second portion 6 .

[0046] The ceramic circuit board 1 according to the embodiment can alleviate thermal stress acting on the ceramic board during temperature changes by providing the metal plate 3 with the first portion 5. Specifically, providing the metal plate 3 with the first portion 5 can suppress stress concentration at the joint end of the metal plate 3.

[0047] The side surface of the first portion 5 is inclined with respect to the Z direction, and the width of the first portion 5 increases toward the bonding layer 4. In other words, at the outer periphery of the first portion 5, the thickness of the first portion 5 decreases toward the side. This inclined shape can reduce stress concentration.

[0048] Furthermore, providing the third region r3 on the side surface of the first portion 5 further improves the effect of alleviating stress concentration. Specifically, when the third region r3 is provided, the stress relaxation effect is enhanced when the metal plate has a thickness of 1.0 mm or more. Stress concentration occurs at the side edge of the first portion 5. At this time, if the metal plate is thick, the stress increases further due to thermal expansion of the side surface of the metal plate. By providing the third region r3, the stress generated at the side edge of the first portion 5 is dispersed not only to the first region r1 and the second region r2 but also to the third region r3. As a result, even when a thick metal plate is provided, stress due to thermal expansion of the side surface can be alleviated.

[0049] The reduction in thermal stress allows the use of a thicker metal plate 3. That is, according to the embodiment, the heat cycle resistance characteristics can be improved and the heat dissipation performance can also be improved. On the other hand, when the first portion 5 exceeds the above range (the width L ｂ is the width L ｔ If the thickness exceeds 1.050 times the thickness of the metal plate 3, it will be necessary to increase the size of the metal plate 3, as will be described later, which may result in a decrease in circuit density.

[0050] In addition, since the metal plate 3 has the second portion 6, it is possible to increase the volume of the metal plate 3 and improve heat dissipation while realizing the stress relief effect of the first portion 5. For example, according to the embodiment, the volume of the metal plate 3 can be increased compared to when the side surfaces of the metal plate 3 are uniformly inclined.

[0051] Furthermore, the embodiment is suitable for a method that does not use etching when processing the metal plate 3 into a circuit shape, which reduces restrictions on the thickness of the metal plate 3 that arise from the perspective of etching costs, environmental load, and the like.

[0052] Furthermore, according to the embodiment, the area of ​​the upper surface of the metal plate 3 can be increased, which increases the degree of freedom in circuit design regarding the mounting of semiconductor elements, etc. It is also possible to improve the accuracy of position detection using a CCD camera, etc.

[0053] Furthermore, by providing the second portion 6 on the metal plate 3, the distance between patterns on the ceramic circuit board 1 can be shortened. The "distance between patterns" refers to the shortest distance between the second regions r2 that extend beyond the side surfaces of multiple metal plates 3 when the side surfaces of the metal plates 3 face each other, or when the side surfaces of portions of a single metal plate 3 face each other. By shortening the distance between patterns on the ceramic circuit board 1, the circuit density can be increased. The distance between patterns on the ceramic circuit board 1 is preferably 0.4 mm or more. If the distance between patterns is less than 0.4 mm, current leakage between the patterns may occur.

[0054] For example, when a circuit shape is formed on a thick metal plate 3 by etching, the side surfaces of the metal plate 3 are inclined by the etching process. Considering variations due to the etching process, the thicker the metal plate 3, the greater the need to set the inter-pattern distance. Furthermore, if the metal plate 3 is thick and the side surfaces are inclined, the size of the metal plate 3 in the X-Y plane also increases in order to ensure the area necessary for mounting semiconductor elements on the upper surface of the metal plate 3. Therefore, using etching on a thick metal plate 3 results in a decrease in circuit density. According to the embodiment, the metal plate 3 includes a second portion 6 whose side surfaces are substantially parallel to the Z direction. In other words, in the ceramic circuit substrate 1 according to the embodiment, the circuit shape of the metal plate 3 is formed by a method other than etching, such as press processing or wire cutting. By forming a circuit shape on the metal plate 3 using these methods, variations in the inter-pattern distance can be reduced, allowing the inter-pattern distance to be set shorter. Furthermore, even when the metal plate 3 is thick, the increase in the size of the metal plate 3 in the X-Y plane can be suppressed, thereby increasing circuit density.

[0055] According to the embodiment, the distance between patterns on the ceramic circuit board 1 can be, for example, 10 mm or less. The distance between patterns on the ceramic circuit board 1 may be 7 mm or less, or may be 5 mm or less. Preferably, the distance between patterns on the ceramic circuit board 1 is 0.4 mm or more and 3 mm or less.

[0056] 3 and 4 are cross-sectional schematic views showing an example of the configuration of a ceramic circuit substrate according to an embodiment. In the ceramic circuit substrate 1, as shown in FIG. 3, a plurality of metal plates 3 may be provided on one surface of a ceramic substrate 2, each with a plurality of bonding layers 4 interposed therebetween. Typically, one metal plate 3 is bonded to the ceramic substrate 2 via one bonding layer 4. If necessary, a plurality of metal plates 3 may be bonded to the ceramic substrate 2 via one bonding layer 4, or one metal plate 3 may be bonded to the ceramic substrate 2 via a plurality of bonding layers 4 that are spaced apart from each other in the X-Y plane.

[0057] 4, the ceramic circuit board 1 may include a plurality of metal plates 3 (metal plates 3a and 3b). The metal plate 3a is bonded to the first surface 2a of the ceramic substrate 2 via a bonding layer 4a (first bonding layer). The metal plate 3b (second metal plate) is bonded to the second surface 2b of the ceramic substrate 2 via a bonding layer 4b (second bonding layer).

[0058] In the example shown in Fig. 4, two metal plates 3a are bonded to the first surface 2a, and one metal plate 3b is bonded to the second surface 2b. This example is not limiting, and three or more metal plates 3a may be bonded to the first surface 2a, or multiple metal plates 3b may be bonded to the second surface 2b, as necessary. In the example shown in Fig. 4, the metal plate 3b is used as a heat sink. A metal plate 3b used as a circuit may be bonded to the second surface 2b.

[0059] 3 and 4, the same components as those of the ceramic circuit board 1 shown in FIGS. 1 and 2 are described in the same manner as in the ceramic circuit board 1 shown in FIGS. 1 and 2.

[0060] The thickness T of the metal plate 3 is preferably 0.5 mm or more and 10 mm or less. If the thickness of the metal plate 3 is less than 0.5 mm, sufficient heat dissipation performance may not be obtained. If the thickness of the metal plate is greater than 10 mm, the amount of deformation due to thermal expansion may increase, and the heat cycle resistance characteristics may deteriorate. If the thickness of the metal plate 3 varies from part to part, it is preferable that the minimum thickness and maximum thickness of the metal plate 3 be within the range of 0.5 mm or more and 10 mm or less.

[0061] 4, when metal plates 3a and 3b are provided on the first surface 2a and the second surface 2b of the ceramic substrate 2, respectively, the thickness of metal plate 3a is preferably 0.5 mm to 10 mm, and the thickness of metal plate 3b is preferably 0.5 mm to 10 mm. More preferably, the thickness of metal plate 3a is 1.0 mm to 6.0 mm, and the thickness of metal plate 3b is 1.0 mm to 6.0 mm. When the thicknesses of metal plates 3a and 3b are within the above ranges, the heat cycle resistance characteristics are improved.

[0062] When a plurality of metal plates 3 are provided on the same plane, the thicknesses of the metal plates 3 may differ from each other. The difference in thickness is not particularly limited, but is preferably 3.0 mm or less. Width L ｂ , width L ｔ , maximum width L １ , and the minimum width L ２ By satisfying the above-mentioned relationship, it is possible to improve the heat cycle resistance characteristics even when there is a difference in thickness between the metal plates 3. In other words, if the difference in thickness between the metal plates 3 exceeds 3.0 mm, there is a possibility that the heat cycle resistance characteristics will be reduced.

[0063] As shown in FIG. 4 , when metal plates 3 are provided on both sides of a ceramic substrate 2, the ratio of the volume of the metal plate 3a to the volume of the metal plate 3b is not particularly limited, but may be 0.98 or more and 1.02 or less. The volume ratio is calculated using the sum of the volumes of one or more metal plates 3a provided on the first surface 2a and the sum of the volumes of one or more metal plates 3b provided on the second surface 2b. The volume ratio is calculated by dividing the total volume of one or more metal plates 3a by the total volume of one or more metal plates 3b. In other words, the volume ratio is calculated by dividing the total volume of the front metal plate 3 by the total volume of the back metal plate 3. A volume ratio within the range of 0.98 or more and 1.02 or less can reduce the difference between the stress generated when one or more metal plates 3a are thermally deformed and the stress generated when one or more metal plates 3b are thermally deformed. As a result, the thermal cycle resistance characteristics can be improved.

[0064] Even when the thickness of the metal plate 3 varies from part to part and the thickness T is not constant even in the longitudinal section, the heat cycle resistance characteristics can be improved by setting the volume ratio within the above range. Even when recesses or protrusions are provided on the surface of a single metal plate 3, or when another metal plate is joined to the surface of a single metal plate, the heat cycle resistance characteristics can be improved.

[0065] The bonding layer 4 bonds the ceramic substrate 2 and the metal plate 3. The metal plate 3 is, for example, a copper plate (including a copper alloy plate) or an aluminum plate (including an aluminum alloy plate). For example, a paste of an active metal brazing material containing Ti is applied to the ceramic substrate 2, and the metal plate 3 is placed on the active metal brazing material paste. The ceramic substrate 2 and the metal plate 3 are fixed together by heating them. At this time, the active metal brazing material paste melts and then solidifies, forming the bonding layer 4.

[0066] The active metal brazing material contains, for example, 0 mass % to 70 mass % of Ag, 15 mass % to 85 mass % of Cu, and Ti or TiH. ２ It is preferable that the active metal brazing material contains 1 mass % or more and 15 mass % or less of Ti and TiH. ２ When the active metal brazing material contains both Ag and Cu, the total content of these elements is preferably in the range of 1 mass % to 15 mass %. When the active metal brazing material contains both Ag and Cu, the Ag content is preferably 20 mass % to 60 mass % and the Cu content is preferably 15 mass % to 40 mass %. If necessary, the active metal brazing material may contain one or two elements selected from Sn and In in an amount of 1 mass % to 50 mass %. If necessary, the active metal brazing material may contain C in an amount of 0.1 mass % to 2 wt %.

[0067] Ag or Cu is a component that becomes the base material of the brazing material. Sn or In has the effect of lowering the melting point of the brazing material. C (carbon) has the effect of controlling the fluidity of the brazing material and the effect of controlling the structure of the joining layer by reacting with other components. Low-melting point metals such as Bi, Sb, or Ga may be used instead of Sn or In. When the composition of the active metal brazing material is within the above range, a first portion 5 is formed on the metal plate 3 when heat joining is performed under the conditions described below.

[0068] 2, the bonding layer 4 preferably includes a protruding portion (second region r2) that protrudes outside the metal plate 3. By including the second region r2 in the bonding layer 4, it is possible to improve the bonding strength and the heat cycle resistance characteristics.

[0069] The length of the second region r2 in the direction from the first region r1 to the second region r2 is defined as the protrusion amount W １ It is called the protrusion amount W １ The protrusion amount W is measured based on the point on the outer periphery of the bonding layer 4 that is farthest from the end of the first portion 5 of the metal plate 3. １ The protrusion amount W is preferably 0.1 mm or more and 2 mm or less. １ If the protrusion amount W is less than 0.1 mm, the stress relaxation during the TCT cycle tends to be insufficient. １ If the protrusion amount W exceeds 2 mm, it is difficult to obtain the effect of improving the joining strength. １ It is more preferable that the protrusion amount W is 0.2 mm or more and 0.7 mm or less. １ can be controlled by, for example, the composition of the active metal brazing material and the heat treatment conditions during joining.

[0070] 2, the bonding layer 4 preferably includes a third region r3 provided on the side surface of the metal plate 3. By including the third region r3 in the bonding layer 4, it is possible to improve the bonding strength and the heat cycle resistance characteristics.

[0071] The length of the third region r3 in the Z direction is defined as the lift amount W ２ The amount of increase W ２ The length of the bonding layer 4 in contact with the side surface of the metal plate 3 is measured in the thickness direction (Z direction) of the metal plate 3. ２ The amount of lift W is preferably, for example, 0.05 mm or more and 5 mm or less. ２ If the height W is less than 0.05 mm, the effect of stress relaxation tends to be insufficient. ２ If the rise amount W exceeds 5 mm, it is difficult to obtain the effect of improving the joining strength. ２ The upper limit of the lift amount W is the thickness T of the metal plate 3. ２ is controlled to a range not exceeding the thickness T of the metal plate.

[0072] The bonding layer 4 may include the second region r2 and the third region r3 in any longitudinal cross section. Preferably, the second region r2 and the third region r3 are provided over the entire outer periphery of the bonding layer 4. In this case, the amount of rise W２ For example, the amount of rise W at each point on the periphery of the bonding layer 4 is ２ When measuring the amount of rise W ２ Maximum value and increase amount W ２ The difference between the minimum value of the lift amount W and the lift amount W is preferably 0.1 mm or more. ２ can be controlled by, for example, the composition of the active metal brazing material and the heat treatment conditions during joining.

[0073] Next, a method for manufacturing the ceramic circuit board 1 according to the embodiment will be described. There are no particular limitations on the manufacturing method as long as the ceramic circuit board 1 satisfies the above configuration. Here, an example of an efficient method for manufacturing a circuit board will be described.

[0074] First, a ceramic substrate 2 is prepared. As described above, the ceramic substrate 2 is a silicon nitride substrate, an aluminum nitride substrate, a silicon oxide substrate, a silicon carbide substrate, an aluminum oxide substrate, a zirconium oxide substrate, an alumina-zirconia substrate, etc. When a silicon carbide substrate is used, an insulating film may be provided on the surface.

[0075] Next, a brazing material paste for forming the bonding layer is prepared. A metal powder or a metal compound powder is used as the brazing material. The brazing material is preferably, for example, an active metal brazing material. The active metal brazing material preferably contains titanium as the active metal. Titanium hydride (TiH ２ Here, titanium hydride powder is also included in the category of metal powder.

[0076] When the metal plate 3 is a copper plate, the active metal brazing material preferably contains one or both of Ag (silver) and Cu (copper), and Ti (titanium). The active metal brazing material preferably further contains one or both of Sn (tin) and In (indium). C (carbon) may be added to the active metal brazing material. The proportions of the active metal elements, Ag (silver), Cu (copper), Sn (tin), In (indium), and C (carbon) in the active metal brazing material are as described above. A metal powder in which the raw material elements are alloyed may also be added.

[0077] When the metal plate is an aluminum plate, the active metal brazing material preferably contains Al (aluminum) and Si (silicon). In this case, Si is the active metal. For example, the active metal brazing material contains 0.1 mass % to 20 mass % Si, with the remainder being aluminum.

[0078] The active metal brazing paste can be prepared by mixing the mixed powder of the metal powders with a binder and an organic solvent. The average particle size of each metal powder is preferably 1 μm or more and 7 μm or less.

[0079] Next, the active metal brazing paste is applied onto the first surface 2a of the ceramic substrate 2. The thickness of the coating layer (brazing material layer) of the active metal brazing paste is preferably 5 μm or more and 80 μm or less. The thickness of the coating layer refers to the thickness after the applied paste has dried. If the thickness of the coating layer is less than 5 μm, the bonding strength may be insufficient. In addition, it becomes difficult to form a brazing material diffusion region on the metal plate 3. If the thickness of the coating layer exceeds 80 μm, the thermal stress during the bonding process may increase, which may result in significant warping of the circuit board. Furthermore, it is difficult to improve properties such as bonding strength, and this may increase manufacturing costs. The thickness of the coating layer is more preferably 10 μm or more and 50 μm or less.

[0080] Here, a method for forming the brazing material layer has been described in which brazing material paste is applied to the ceramic substrate 2. Another method is to arrange a brazing material foil.

[0081] Next, a metal plate 3 is placed on the coating layer. As the metal plate 3, a circuit board processed to a desired size by press working, wire cutting, or the like may be used. By using press working, wire cutting, or the like, the shape of the metal plate 3 can be easily adjusted to include the second portion 6. The metal plate 3 may be processed in advance to prepare a metal plate 3 including the first portion 5 and the second portion 6. The metal plate 3 is, for example, a copper plate (including a copper alloy plate) or an aluminum plate (including an aluminum alloy plate).

[0082] Portions corresponding to the second region r2 and the third region r3 may be formed in advance in the coating layer so that the bonding layer 4 after thermal bonding includes the second region r2 and the third region r3. After the metal plate 3 is placed, brazing paste may be applied to the side surface of the metal plate 3 to form the portions corresponding to the second region r2 and the third region r3. Pressure may be applied to the coating layer when the metal plate 3 is placed. By being pressed by the metal plate 3, the coating layer spreads toward the periphery and a portion of the coating layer rises along the side surface of the metal plate 3.

[0083] In the manufacturing method of the ceramic circuit board 1 according to the embodiment, the metal plate 3 is arranged in a predetermined circuit shape. In other words, there is no need to impart the circuit shape by an etching process. Furthermore, forming the third region r3 in the bonding layer 4 means that the circuit shape is not imparted by an etching process. In other words, the ceramic circuit board 1 according to the embodiment is an etching-less product.

[0084] When a metal plate 3 (back metal plate) is provided on the second surface 2b of the ceramic substrate 2, or when multiple metal plates 3 are provided on the first surface 2a, these metal plates 3 are also arranged using the same process as described above.

[0085] Next, thermal bonding is performed. The bonding temperature is preferably 600°C or higher and 950°C or lower. The "bonding temperature" refers to the maximum temperature reached during heating, and the laminate including the ceramic substrate 2 and the metal plate 3 is maintained at the bonding temperature for a predetermined time. If the bonding temperature is lower than 600°C, sufficient bonding reliability may not be obtained. If the first portion 5 is not formed in advance on the metal plate 3, the first portion 5 may not be formed on the metal plate 3. If the bonding temperature is higher than 950°C, excessive residual stress may be generated, which may reduce the reliability of the product.

[0086] The melting point of copper is 1085°C, and the melting point of aluminum is 660°C. When copper plates are used, the bonding temperature is preferably 700°C or higher and 950°C or lower, and more preferably 750°C or higher and 930°C or lower. When aluminum plates are used, the bonding temperature is preferably 600°C or higher and 700°C or lower. When the melting point of the metal plates used is lower than 700°C, it is preferable to perform heat bonding at a bonding temperature lower than the melting point of the metal plates.

[0087] In the heat bonding, it is preferable to maintain the bonding temperature within the above range for 15 minutes or more in order to sufficiently melt the brazing material.

[0088] In the heat bonding process, a temperature holding process may be performed when raising the temperature from 200°C to the bonding temperature. The temperature holding process refers to holding the laminate at a temperature lower than the bonding temperature. The time for the temperature holding process is preferably 10 minutes or more and 4 hours or less. The holding temperature in the temperature holding process is preferably within the range of 400°C or more and 900°C or less. By providing a temperature holding process in the temperature raising process, the temperatures of the ceramic substrate 2, the brazing material layer, and the metal plate 3 can be made uniform. After the temperature holding process, the ceramic substrate 2, the brazing material layer, and the metal plate 3 are heated to the bonding temperature.

[0089] After the thermal bonding process, it is preferable to provide a temperature holding process when lowering the temperature from the bonding temperature to room temperature. During the temperature holding process during the temperature lowering process, the laminate is held at a temperature lower than the bonding temperature and 10°C to 150°C below the bonding temperature. The time for the temperature holding process is preferably 10 minutes to 4 hours. By providing a temperature holding process that satisfies these conditions in the temperature lowering process, the laminate can be uniformly heated to a temperature near the solidification point of the brazing material, thereby strengthening the bond. In other words, it is preferable to use a brazing material whose solidification point is 10 to 150°C lower than the bonding temperature. Furthermore, by uniforming the temperature within the laminate, it is possible to suppress variations in the amount of thermal deformation. By uniforming the temperature within the furnace, it is possible to improve the reliability of the bond.

[0090] In the thermal bonding process, the metal plate 3 expands slightly at the bonding temperature. The portion of the metal plate 3 in contact with the bonding layer 4 also expands. By providing a temperature holding process in the temperature drop process, the portion of the metal plate 3 in contact with the bonding layer 4 is bonded in an expanded state. Furthermore, in the temperature drop process, the upper side of the metal plate 3 contracts. This allows the first portion 5 to be formed in the metal plate 3.

[0091] From the above viewpoints, in order to form the first portion 5, it is preferable to provide the above-mentioned temperature holding step when lowering the temperature from the bonding temperature to room temperature. When the ceramic substrate 2 and the metal plate 3 are bonded using a continuous furnace as described below, it is preferable to perform cooling while blowing nitrogen gas onto the bonded body instead of providing the above-mentioned temperature holding step, since this achieves the same effect. By blowing nitrogen gas, cooling of the upper edge side of the metal plate 3 progresses. This allows the ceramic substrate 2 and the metal plate 3 to be bonded in a state in which the portion of the metal plate 3 in contact with the bonding layer is expanded. The temperature holding step in the temperature lowering step and cooling by blowing nitrogen gas may be combined.

[0092] The atmosphere during the heat bonding step is preferably a vacuum or a non-oxidizing atmosphere. The non-oxidizing atmosphere is a nitrogen atmosphere, an argon atmosphere, a hydrogen atmosphere, or the like. The pressure in the vacuum is preferably 0.3 kPa or less, and 10 －３ Pa or less is more preferable. Ti in the brazing filler metal may be oxidized or nitrided by oxygen or nitrogen in the atmosphere before reacting with the ceramic substrate 2. By performing the thermal bonding in a vacuum, it is possible to prevent Ti from being oxidized or nitrided before reacting with the ceramic substrate 2.

[0093] A nitrogen atmosphere refers to an atmosphere containing 90 vol% to 100 vol% nitrogen. If nitrogen is present in the atmosphere during the joining process, the Ti in the brazing filler metal may be nitrided by the nitrogen in the atmosphere before reacting with the ceramic substrate. However, if the Ti content in the brazing filler metal is 6 mass% or more, the Ti in the brazing filler metal can sufficiently react with the ceramic substrate 2 even in a nitrogen atmosphere.

[0094] When the ceramic substrate 2 and the metal plate 3 are bonded in a vacuum, a vacuum furnace is used. When the ceramic substrate 2 and the metal plate 3 are bonded in a nitrogen atmosphere, a continuous furnace may be used.

[0095] In the thermal bonding, a load may be applied to the laminate including the ceramic substrate 2, the active metal brazing material, and the metal plate 3. It is preferable to fix the laminate with a jig and apply a load of 0.5 kPa or more to the laminate. Applying a load of 0.5 kPa or more facilitates adhesion of the bonding interface. It also facilitates the formation of the first portion 5 in the metal plate 3. A member other than the jig may be used to apply the load, or the weight of the jig may be used as the load.

[0096] By performing the heat bonding under the above conditions, the first portion 5 is formed on the metal plate 3 while maintaining the shape of the second portion 6. This method also makes it possible to make the ceramic circuit board an etching-less product. Because etching is no longer necessary, costs and environmental impact can be reduced.

[0097] FIG. 5 is a flowchart showing a method for manufacturing a ceramic circuit board according to an embodiment. First, a ceramic substrate 2, an active metal brazing material paste, and a metal plate 3 are prepared (step St1). The metal plate 3 is preferably pre-processed into a circuit shape by pressing or wire cutting. The active metal brazing material paste is applied to the ceramic substrate 2 and dried (step St2). The metal plate 3 is placed on the dried coating layer (step St3). The laminate including the ceramic substrate 2, the active metal brazing material, and the metal plate 3 is heated to bond the ceramic substrate 2 and the metal plate 3 (step St4). A temperature holding step may be added during the temperature rise process up to the bonding temperature. After bonding, a temperature holding step is performed during the temperature drop (step St5). Through the above processes, the ceramic circuit substrate 1 according to an embodiment is manufactured.

[0098] A semiconductor device is manufactured by mounting a semiconductor element on the ceramic circuit substrate 1. Wire bonding, a lead frame, or the like may be mounted on the semiconductor device as needed. Furthermore, a resin mold may be applied as needed. Potting resin or the like is used for the resin mold.

[0099] EXAMPLES Specific examples and their evaluation results are described below. In the examples, a silicon nitride substrate having a thermal conductivity of 90 W / m·K, a three-point bending strength of 700 MPa, and dimensions of 30 mm long, 50 mm wide, and 0.3 mm thick was prepared as the ceramic substrate.

[0100] An active metal brazing paste was prepared and applied to the first and second surfaces of the ceramic substrate. The composition of the active metal brazing paste used is shown in Table 1. Table 1 lists the values ​​when the total of each metal component is 100 wt %.

[0101]

[0102] Next, a metal plate processed to the desired shape was prepared and placed on the coating layer of the active metal brazing paste. The type, thickness, and shape of the metal plate used are shown in Table 2. Table 3 shows the configuration of the ceramic substrate on which the metal plate was placed in each example. In Table 3, the metal plate placed on the first surface of the ceramic substrate is referred to as the "front metal plate," and the metal plate placed on the second surface is referred to as the "back metal plate." Each metal plate was processed to have a second portion. Mold press processing was suitable for this processing. Therefore, an etching process was not required, and no etching waste liquid was generated.

[0103]

[0104] Next, a brazing paste was applied to a ceramic substrate and dried to form a coating layer. A metal plate was placed on the coating layer to prepare a laminate. The laminate was fixed with a jig, and a load of 0.5 kPa or more was applied to the laminate in a vacuum (1 × 10 －３ Heat bonding was performed at a temperature of 400 to 900°C or less. Table 3 shows whether or not a temperature holding step was performed during the temperature rise process, the bonding temperature, the holding temperature during the temperature drop process, and the load for each example. In Comparative Example 1, no temperature holding step was performed during the temperature rise process or the temperature drop process. The temperature holding step during the temperature rise process was performed at a temperature lower than the bonding temperature within the range of 400 to 900°C.

[0105]

[0106] Ceramic circuit boards according to the examples and comparative examples were fabricated by the above steps. The distance between patterns on each of the ceramic circuit boards according to the examples and comparative examples was set to 0.4 mm or more and 3 mm or less.

[0107] In Examples 1, 3, 5 to 6, 8 to 12 and Comparative Example 1, the volume of the back metal plate [cm ３ ] to the volume of the surface metal plate [cm ３ ] is in the range of 0.98 or more and 1.02 or less. In Example 2, a back metal plate is not provided. In Examples 4, 7, Comparative Examples 2, and 3, the volume [cm ３ ] to the volume of the surface metal plate [cm ３ In all of the examples and comparative examples, the ratio of the maximum width L １ and minimum width L ２ The difference between the thickness of the metal plate and the thickness of the metal plate was 100 μm or less (including 0). １ -L ２ ) / 0.2T<(L ｂ -L ｔ ) / T was met.

[0108] For the ceramic circuit boards according to each example and each comparative example, four arbitrary vertical cross sections of the metal plate were prepared. Each vertical cross section was enlarged six times and photographed, and each dimension of the vertical cross section was measured from the photograph. The width L of the upper side of the metal plate was measured using the enlarged photograph. ｔ , the width of the lower edge of the metal plate L ｂ , the maximum width L at the middle part of the metal plate １ , the minimum width L at the middle of the metal plate ２ , the protrusion amount W in the bonding layer １ , the rise amount W in the bonding layer ２ The thickness T of the metal plate was the thickness of the metal plate before joining.

[0109] From the results obtained, the ratio L ｂ / L ｔ , ratio L １ / L ２ , (L １ -L ２ ) / 0.4T was calculated. ｂ / L ｔThe longitudinal section with the largest ratio L ｂ / L ｔ , ratio L １ / L ２ , (L １ -L ２ ) / 0.4T are shown in Table 4.

[0110] Also, the maximum L ｂ / L ｔ From the photograph of the vertical cross section obtained, the protrusion amount W of the bonding layer １ and the amount of rise W ２ The protrusion amount and the rise amount were measured at both ends of the metal plate in one longitudinal section, and the larger protrusion amount was defined as the protrusion amount W of the bonding layer. １ The larger amount of rise is the amount of rise W of the bonding layer. ２ In addition, the larger of the two measured lift amounts is called the "lift amount W ２ The maximum value of W ２ｍａｘ ” and a smaller rise amount is “rise amount W ２ The minimum value W ２ｍｉｎ " The amount of overhang W １ , the amount of rise W ２ , and the amount of lift W ２ The maximum value of W ２ｍａｘ and the minimum value W ２ｍｉｎ The differences are shown in Table 4.

[0111]

[0112] From Table 4, in the example, the ratio L ｂ / L ｔ is 1.005 or more and 1.050 or less, and the ratio L １ / L ２ is 1.0 or more and 1.010 or less, and the ratio L ｂ / L ｔ >Ratio L １ / L ２ , and width L ｂ >Maximum width L １ It can be seen that the four conditions are met. In Table 4, the ratio L ｂ / L ｔ The data shown is for the location where the value was the largest, but in the example, the four conditions were also satisfied at the other three locations.

[0113] In contrast, in the comparative example, the ratio L ｂ / L １ In the comparative example, the ratio L ｂ / L １ That is, in the comparative example, the first portion was not formed on the metal plate.

[0114] Next, the thermal cycle durability of the ceramic circuit boards according to each example and comparative example was evaluated by TCT. TCT is a test in which a test sample is placed in an environment that is successively changed from low to high temperatures to confirm resistance to temperature changes. In the TCT, the sample is held at -40°C for 30 minutes, then at room temperature for 10 minutes, then at 175°C for 30 minutes, and then at room temperature for 10 minutes. This constitutes one cycle, and 500, 1000, and 5000 cycles were performed. The area of ​​cracks occurring between the ceramic substrate and the metal plate was then determined using an ultrasonic flaw detector, and the integrity rate η of each ceramic circuit board was calculated according to the following formula (1), to evaluate the thermal cycle resistance of each silicon nitride circuit board.

[0115] (Formula 1) η=(1-Σd / D)×100(%)

[0116] In equation 1, "D" is the value when the perimeter of the joint of the circuit board is taken as 100%. When multiple copper plates are joined, it indicates the total perimeter of the joint. In other words, "D" is the total length of the copper plate edge path where a crack may occur. "Σd" is the sum of the lengths (d1, d2, ... dn) of each crack that occurred on the above path. A soundness rate η of 100% indicates that no cracks were observed. Examples where the soundness rate η was 100% were evaluated as "good", examples where the soundness rate η was less than 100% but 95% or more were evaluated as "passable", and examples where the soundness rate η was less than 95% were evaluated as "unsatisfactory", and the results are shown in Table 5.

[0117]

[0118] Table 5 shows that when the number of cycles is small, there is no significant difference in the integrity rate η between the Examples and Comparative Examples. However, at 5,000 cycles, cracks occurred in all Comparative Examples, and the integrity rate η fell below 95%. This is thought to be because the Examples have a first portion formed in the metal plate. By including the first portion in the metal plate, the thermal stress applied to the ceramic substrate during temperature changes can be alleviated compared to a metal plate that does not include the first portion. As a result, it is thought that the Examples have achieved better thermal cycle durability than the Comparative Examples.

[0119] More specifically, in Table 5, Examples 2, 4, and 7 showed a lower thermal cycle durability at 5,000 cycles than the other Examples. This is thought to be because Example 2 did not have a back metal plate. In Examples 4 and 7, the volume [cm3] of the back metal plate ３ ] to the volume of the surface metal plate [cm ３ ] is outside the range of 0.98 to 1.02. From these results, it is clear that it is preferable to bond metal plates to both sides of the ceramic substrate. In addition, the volume [cm ３ ] to the volume of the surface metal plate [cm ３ It can be seen that the ratio of [Ratio of R ... 1.02 to 1.98] is preferably within the range of 0.98 to 1.02.

[0120] In addition, position detection was performed on the ceramic circuit boards according to the examples using a CCD camera. In the position detection, the ceramic circuit board was photographed from the Z direction using the CCD camera to obtain an image. From the obtained image, the outer peripheral edge of the upper surface of the copper plate was detected. In all examples, the position of the detected outer peripheral edge was within a range of 0.1 mm from the actual outer peripheral edge of the upper surface of the copper plate, demonstrating good position detection accuracy. This is because the copper plate includes the second portion 6 in the ceramic circuit boards according to the examples. The more vertical the side surface of the upper copper plate is, the easier it is to detect the outer peripheral edge of the upper surface of the copper plate.

[0121] The present invention includes the following features: (Feature 1) A ceramic circuit board including a ceramic substrate having a first surface, and a first metal plate bonded to the first surface via a first bonding layer, wherein in any cross section perpendicular to the first surface, the first metal plate has a lower side width L ｂ [mm] and top width L ｔ Ratio L to [mm] ｂ / L ｔ a maximum width L at an intermediate portion located between the lower side and a portion 0.4 to 0.6 times the thickness T of the metal plate; １ [mm] and minimum width L ２ Ratio L to [mm] １ / L ２ is 1.0 or more and 1.010 or less, ratio L ｂ / L ｔ is the ratio L １ / L ２ and width L ｂ is the minimum width L １a ceramic circuit board that satisfies the condition that the thickness T of the one or more first metal plates is greater than or equal to 0.5 mm and the thickness T of the one or more first metal plates is greater than or equal to 10 mm; a ceramic circuit board that satisfies the condition that the thickness T of the one or more first metal plates is greater than or equal to 0.5 mm and the thickness T of the one or more first metal plates is greater than or equal to 10 mm; a ceramic circuit board that satisfies the condition that the thickness T of the one or more first metal plates is greater than or equal to 0.5 mm and the thickness T of the one or more second metal plates is greater than or equal to 10 mm; a ceramic circuit board that satisfies the condition that the thickness T of the one or more first metal plates is greater than or equal to 0.5 mm and the thickness T of the one or more second metal plates is greater than or equal to 10 mm; a ceramic circuit board that satisfies the condition that the thickness T of the one or more first metal plates is greater than or equal to 0.5 mm and the thickness T of the one or more second metal plates is greater than or equal to 10 mm; (Feature 5) The ceramic circuit board according to Feature 2 or 3, further comprising a second metal plate bonded to a second surface of the ceramic opposite to the first surface via a second bonding layer, wherein one or more second metal plates are bonded to the second surface, wherein the thickness T of each of the plurality of first metal plates is 0.5 mm or more and 10 mm or less, and wherein a ratio of a total volume of the plurality of first metal plates to a total volume of the one or more second metal plates is 0.98 or more and 1.02 or less. (Feature 6) The ceramic circuit board according to any one of Features 2 to 5, wherein a difference in thickness among the plurality of first metal plates is 0 mm or more and 3.0 mm or less, and wherein the thickness T of each of the plurality of first metal plates is 1.0 mm or more and 6.0 mm or less. (Feature 7) The ceramic circuit board according to any one of Features 1 to 6, wherein the first bonding layer includes: a first region provided between the first surface and the first metal plate; a second region provided along the first surface around the first region and extending outside the first metal plate; and a third region located on the second region and provided on a side surface of the metal plate.(Feature 8) The ceramic circuit board according to Feature 7, wherein a length of the second region in a direction from the first region toward the second region is 0.05 mm or more, and a length of the third region in a first direction perpendicular to the first surface is 0.1 mm or more. (Feature 9) The ceramic circuit board according to any one of Features 1 to 8, wherein the ceramic substrate is a silicon nitride substrate. (Feature 10) The ceramic circuit board according to any one of Features 1 to 9, wherein the first metal plate is a copper plate. (Feature 11) A method for manufacturing a ceramic circuit board, comprising forming a brazing material layer containing an active metal brazing material on a first surface of a ceramic substrate, placing a metal plate on the brazing material layer, and joining the ceramic substrate and the metal plate by heating, wherein the first metal plate of the manufactured ceramic circuit board has a lower side width L in any cross section perpendicular to the first surface. ｂ [mm] and top width L ｔ Ratio L to [mm] ｂ / L ｔ a maximum width L at an intermediate portion located between the lower side and a portion 0.4 to 0.6 times the thickness T of the metal plate; １ [mm] and minimum width L ２ Ratio L to [mm] １ / L ２ is 1.0 or more and 1.010 or less, ratio L ｂ / L ｔ is the ratio L １ / L ２ and width L ｂ is the minimum width L １ (Feature 12) The method for manufacturing a ceramic circuit substrate according to Feature 11, wherein the bonding temperature during the bonding is 700°C or higher and 950°C or lower, and the temperature of the ceramic circuit substrate is maintained at a temperature that is lower than the bonding temperature and that is 10°C or higher and 150°C or lower during cooling after the bonding. (Feature 13) The method for manufacturing a ceramic circuit substrate according to Feature 11 or Feature 12, wherein the thickness T of the metal plate is 0.5 mm or higher, and the ceramic substrate is a silicon nitride substrate.

[0122] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied 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 modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims.

[0123] REFERENCE SIGNS LIST 1... ceramic circuit board 2... ceramic substrate 2a... first surface 2b... second surface 3, 3a, 3b... metal plate 4, 4a, 4b... bonding layer 5... first portion 6... second portion T... thickness of metal plate L ｔ ...Width of the upper edge of the metal plate L ｂ …Width of the bottom edge of the metal plate L １ …Maximum width L at the middle of the metal plate ２ ...Minimum width at the middle of the metal plate r1...First region r2...Second region r3...Third region W １ ...Protrusion amount in the bonding layer W ２ …Amount of rise in the bonding layer

Claims

1. A ceramic circuit board comprising: a ceramic substrate having a first surface; and a first metal plate bonded to the first surface via a first bonding layer, wherein in any cross section perpendicular to the first surface, the first metal plate has a lower side width L ｂ [mm] and top width L ｔ Ratio L to [mm] ｂ / L ｔ The maximum width L at the intermediate portion located between the lower side and 0.4 to 0.6 times the thickness T of the metal plate is 1.005 or more and 1.050 or less. １ [mm] and minimum width L ２ Ratio L to [mm] １ / L ２ is 1.0 or more and 1.010 or less, ratio L ｂ / L ｔ is the ratio L １ / L ２ and width L ｂ is the minimum width L １ Ceramic circuit boards that meet the requirements of longer than .

2. The ceramic circuit board according to claim 1, wherein a plurality of said first metal plates are bonded to said first surface.

3. A ceramic circuit board as described in claim 1, wherein a plurality of said first metal plates are joined to said first surface, and the shortest distance between adjacent said first metal plates among said plurality of said first metal plates is 10 mm or less.

4. The ceramic circuit board according to claim 1, further comprising a second metal plate bonded via a second bonding layer to a second surface of the ceramic opposite to the first surface, wherein one or more of the first metal plates are bonded to the first surface and one or more of the second metal plates are bonded to the second surface, wherein the thickness T of each of the one or more first metal plates is 0.5 mm or more and 10 mm or less, and wherein the ratio of the total volume of the one or more first metal plates to the total volume of the one or more second metal plates is 0.98 or more and 1.02 or less.

5. A ceramic circuit board as described in claim 2 or 3, further comprising a second metal plate bonded via a second bonding layer to a second surface of the ceramic opposite to the first surface, one or more second metal plates being bonded to the second surface, the thickness T of each of the plurality of first metal plates being 0.5 mm or more and 10 mm or less, and a ratio of a total volume of the plurality of first metal plates to a total volume of the one or more second metal plates being 0.98 or more and 1.02 or less.

6. A ceramic circuit board as described in any one of claims 2 to 5, wherein the difference in thickness between the plurality of first metal plates is not less than 0 mm and not more than 3.0 mm, and the thickness T of each of the plurality of first metal plates is not less than 1.0 mm and not more than 6.0 mm.

7. A ceramic circuit board as described in any one of claims 1 to 6, wherein the first bonding layer includes: a first region provided between the first surface and the first metal plate; a second region provided around the first region along the first surface and extending outside the first metal plate; and a third region located on top of the second region and provided on a side surface of the metal plate.

8. A ceramic circuit board as described in claim 7, wherein the length of the second region in the direction from the first region to the second region is 0.05 mm or more, and the length of the third region in a first direction perpendicular to the first surface is 0.1 mm or more.

9. The ceramic circuit board according to any one of claims 1 to 8, wherein the ceramic board is a silicon nitride board.

10. The ceramic circuit board according to any one of claims 1 to 9, wherein the first metal plate is a copper plate.

11. A method for manufacturing a ceramic circuit board, comprising forming a brazing material layer containing an active metal brazing material on a first surface of a ceramic substrate, placing a metal plate on the brazing material layer, and bonding the ceramic substrate and the metal plate by heating, wherein the first metal plate of the manufactured ceramic circuit board has a lower side width L of 0.01 mm or less in any cross section perpendicular to the first surface. ｂ [mm] and top width L ｔ Ratio L to [mm] ｂ / L ｔ The maximum width L at the intermediate portion located between the lower side and 0.4 to 0.6 times the thickness T of the metal plate is 1.005 or more and 1.050 or less. １ [mm] and minimum width L ２ Ratio L to [mm] １ / L ２ is 1.0 or more and 1.010 or less, ratio L ｂ / L ｔ is the ratio L １ / L ２ and width L ｂ is the minimum width L １ A method for manufacturing a ceramic circuit board that satisfies the conditions of:

12. A method for manufacturing a ceramic circuit board as described in claim 11, wherein the bonding temperature in the bonding is 700°C or higher and 950°C or lower, and the temperature of the ceramic circuit board is maintained at a temperature lower than the bonding temperature and with a temperature difference from the bonding temperature of 10°C or higher and 150°C or lower during cooling after the bonding.

13. The method for producing a ceramic circuit board according to claim 11 or 12, wherein the thickness T of the metal plate is 0.5 mm or more, and the ceramic board is a silicon nitride board.

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