Ceramic circuit board

Abstract

According to an embodiment of the present invention, a ceramic circuit board has a plurality of metal plates bonded to at least one surface of a ceramic substrate. The ceramic circuit board has a portion satisfying T≥P, where T is the thickness of each metal plate of the plurality of metal plates and P is the shortest distance between adjacent metal plates among the plurality of metal plates. Side surfaces facing each other between adjacent metal plates among side surfaces of the plurality of metal plates have at least a first inclined portion and a second inclined portion, which have different inclination angles, in this order from the ceramic substrate, and the protrusion width of upper ends of the adjacent metal plates is ±40 μm or less. In addition, the upper ends of the adjacent metal plates preferably have a radius of curvature of 15 μm or less.

Description

Ceramic Circuit Board

[0001] The embodiments described below generally relate to ceramic circuit boards.

[0002] In recent years, as industrial equipment has become more sophisticated, the power modules mounted on them have become increasingly powerful. This has led to an increase in the power output of semiconductor elements. The guaranteed operating temperature for semiconductor elements is 125°C to 150°C, but this may rise to 175°C or higher in the future. Ceramic circuit boards are used as circuit boards on which semiconductor elements are mounted. Examples of ceramic substrates include silicon nitride substrates, aluminum nitride substrates, and aluminum oxide substrates.

[0003] For example, Japanese Patent No. 6789955 (Patent Document 1) discloses a ceramic circuit board in which a ceramic substrate and a metal plate are bonded via a bonding layer. In the ceramic circuit board described in Patent Document 1, the size and hardness of the protruding portion of the bonding layer are controlled. Furthermore, Japanese Patent No. 7332588 (Patent Document 2) discloses a ceramic circuit board in which the width of the inclined portion is 0.1 to 0.5 times the thickness of the metal plate. In Patent Documents 1 and 2, this provides a ceramic circuit board with excellent characteristics in a temperature cycling test (TCT).

[0004] An etching process is used to control the size of the protruding portion of the bonding layer and the slope of the side surface of the metal plate. For example, an etching process is shown in Japanese Patent No. 7278215 (Patent Document 3). In Patent Document 3, the protruding portion of the bonding layer and the metal plate are etched by combining the etching process of the bonding layer containing Ag and Cu, the etching process of the titanium nitride layer, and chemical polishing.

[0005] Patent Document 4 describes a metal-ceramic circuit board in which a recess is formed in the lower portion of the metal circuit board, carved out so as to curve inward on the side surface of the circuit pattern, and the distance between the upper ends of the linear portions of the opposing side surfaces of adjacent circuit patterns is greater than the distance between the lower ends of the linear portions. ＢThe metal-ceramic circuit board has a ratio of the thickness T of the circuit pattern to the thickness T of the circuit pattern of 0.3 or more, more preferably 0.8 or more, 1 or more, and most preferably 2 or more.

[0006] Patent No. 6789955 Patent No. 7332588 Patent No. 7278215 Patent No. 6566586

[0007] There is a demand for miniaturization of semiconductor modules. Miniaturization of modules also requires miniaturization of ceramic circuit boards. Reducing the spacing between metal plates is an effective way to achieve miniaturization while maintaining the mounting area for semiconductor elements, etc. However, when attempting to impart a predetermined inclined structure to the side of a metal plate to improve TCT characteristics, it has been difficult to reduce the spacing between the metal plates. While conventional etching processes are effective in imparting an inclined structure to the side of a metal plate, they are not suitable for reducing the spacing between metal plates.

[0008] The problem to be solved by the present invention is to provide a ceramic circuit board in which the intervals between the metal plates are narrowed.

[0009] In one embodiment, a ceramic circuit board having multiple metal plates bonded to at least one surface of a ceramic substrate has a location where T≧P, where T is the thickness of each of the multiple metal plates and P is the shortest distance between adjacent metal plates among the multiple metal plates, and the side of the multiple metal plates that faces the adjacent metal plate has at least a first inclined portion and a second inclined portion with different inclination angles, in that order from the ceramic substrate side, and the protrusion width of the upper ends of adjacent metal plates is ±40 μm or less.

[0010] FIG. 1 is a side cross-sectional view showing an example of a ceramic circuit board according to an embodiment. FIG. 1 is a side cross-sectional view showing another example of a ceramic circuit board according to an embodiment. FIG. 2 is a side cross-sectional view showing an example of an inclined portion of a front metal plate in a ceramic circuit board according to an embodiment. FIG. 3 is a side cross-sectional view showing an example of a contact point of an inclined portion of a front metal plate in a ceramic circuit board according to an embodiment. FIG. 4 is a side cross-sectional view for explaining a protrusion width of a front metal plate in a ceramic circuit board according to an embodiment. FIG. 5 is a side cross-sectional view showing another example of an inclined portion of a front metal plate in a ceramic circuit board according to an embodiment. FIG. 6 is a side cross-sectional view showing an example of a front metal plate having a stepped portion in a ceramic circuit board according to an embodiment. FIG. 7 is a sectional view showing a bonded body and the like for explaining an example of an etching step in a manufacturing method of a ceramic circuit board according to an embodiment. FIG. 8 is a side cross-sectional view showing another example of a front metal plate in a ceramic circuit board according to an embodiment. Embodiment

[0011] A ceramic circuit board according to an embodiment has a plurality of metal plates bonded to at least one surface of a ceramic substrate, and is characterized in that, when T is the thickness of each of the plurality of metal plates and P is the shortest distance between adjacent metal plates among the plurality of metal plates, the board has a portion where T≧P, and the side of the plurality of metal plates that faces the adjacent metal plate has at least a first inclined portion and a second inclined portion that have different inclination angles from the ceramic substrate side, and the protrusion width 9 of the upper end portions of the adjacent metal plates is ±40 μm or less.

[0012] 1 to 4 show side cross-sectional views (X-Z cross-sections) of an example of a ceramic circuit board according to an embodiment. In the drawings, reference numeral 1 denotes a ceramic circuit board, reference numeral 2 denotes a ceramic substrate, reference numeral 3 denotes a front metal plate among the metal plates, reference numerals 31 and 32 denote front metal plates among the front metal plate 3, reference numeral 4 denotes a rear metal plate among the metal plates, reference numeral 5 denotes a bonding layer, reference numeral 6 denotes a first inclined portion, reference numeral 7 denotes a second inclined portion, reference numeral 8 denotes an upper end portion of the front metal plate 3, reference numeral 9 denotes a protrusion width of the upper end portion 8, reference numeral 10 denotes a contact line of the inclined portions (in the side cross-sectional view, inclined portion contact points), reference numeral 11 denotes a difference in height between the inclined portion contact points 10, reference numeral T denotes a thickness of the front metal plate 3, reference numeral P denotes the shortest distance between adjacent front metal plates 3, reference numeral θ1 denotes an inclination angle of the first inclined portion 6, reference numeral θ2 denotes an inclination angle of the second inclined portion 7, and reference numeral D denotes a combined width of the inclined portions 6 and 7. 1 to 9, the plane of the ceramic substrate 2 is defined as the X-axis and Y-axis, and the direction perpendicular to the X-axis and Y-axis is defined as the Z-axis (thickness direction).

[0013] For convenience, the metal plate to which a circuit pattern is imparted is referred to as the front metal plate 3, and the metal plate used as a heat sink is referred to as the back metal plate 4. In the ceramic circuit board 1 according to the embodiment, a circuit pattern may also be imparted to the back metal plate 4. Furthermore, although two front metal plates 3 are arranged in one direction (X-axis direction) in FIGS. 1 to 4 and 8, three or more front metal plates 3 may be arranged in one direction. The same applies when a circuit pattern is imparted to the back metal plate 4. Furthermore, although FIGS. 1 to 4 illustrate an example in which the ceramic substrate 2 and the metal plates 3 and 4 are joined via a joining layer 5, the ceramic substrate 2 and at least one of the metal plates 3 and 4 may be joined without a joining layer 5.

[0014] The ceramic circuit board 1 according to the embodiment has multiple front metal plates 31, 32 bonded to at least one surface of a ceramic substrate 2 (front metal plate 3 in FIGS. 1 to 4 ). The front metal plates 3 are arranged in a one-to-multiple, multiple-to-one, or multiple-to-multiple configuration in the X-axis and Y-axis directions. When the thickness of the front metal plate 3 is T and the shortest distance between adjacent front metal plates 31, 32 is P, there is a location where T≧P. In FIG. 1 , the shortest distance P between adjacent front metal plates 31, 32 refers to the distance between the ends of the front metal plate 3 that contact the bonding layer 5 (or the ceramic substrate 2). The shortest distance P is not limited to the lower end of the metal plate as shown in FIG. 1 , but may also be the upper end 8 or other location. The shortest distance P between adjacent front metal plates 31, 32 is sometimes simply referred to as the shortest distance P.

[0015] The locations where T≧P indicate locations where the shortest distance P between adjacent front metal plates 31, 32 is the same or is smaller than the thickness T of the front metal plates 31, 32. By having a location where the shortest distance P is smaller than the metal plate thickness T, the bonding area of ​​the front metal plate 3 can be secured. Furthermore, it is possible to reduce the size of the ceramic circuit board 1 compared to when the bonding area of ​​the front metal plate 3 is the same. Furthermore, when the size of the ceramic substrate 2 is the same, the bonding area of ​​the front metal plate 3 can be increased.

[0016] The thickness T of the front metal plate 3 is the thickness of a single metal plate. When multiple front metal plates are stacked, the thickness T is the thickness of the front metal plate 3 bonded to the ceramic substrate 2 or the bonding layer 4. The side of the front metal plate 31 facing the adjacent front metal plate 32 has at least a first inclined portion 6 and a second inclined portion 7, which have different inclination angles, in that order from the ceramic substrate 2 side. The side surfaces of the adjacent front metal plates 31, 32 have a first inclined portion 6 and a second inclined portion 7. The first inclined portion 6 and the second inclined portion 7 need only differ in inclination angle by 1° or more. In the plane of FIGS. 1 to 9, the side of the front metal plate 31 facing the adjacent front metal plate 32 is the right side of the front metal plate 31. In the plane of FIGS. 1 to 4 and 8, the side of the front metal plate 32 facing the adjacent front metal plate 31 is the left side of the front metal plate 32.

[0017] The tangent line (contact point in the side cross section) between the first inclined portion 6 and the second inclined portion 7 is the inclined portion contact point 10. The inclined portion closer to the ceramic substrate 2 (or the bonding layer 5) is the first inclined portion 6. The inclined portion closer to the upper end portion 8 of the front metal plate 3 is the second inclined portion 7. The first inclined portion 6 and the second inclined portion 7 have a substantially linear shape when viewed in side cross section. At least one of the first inclined portion 6 and the second inclined portion 7 may have an R-shape when viewed in side cross section. The first inclined portion 6 and the second inclined portion 7 may be an inclined portion that combines a substantially linear shape and an R-shape when viewed in side cross section.

[0018] The protrusion width 9 of the upper end portions 8 (shown in FIG. 3 ) of adjacent front metal plates 31, 32 is ±40 μm or less. The protrusion width 9 of the upper end portions 8 of the front metal plates 31, 32 is the sum of the length (−40 μm) by which the upper end portions 8 protrude from the line in the Z-axis direction passing through the inclined portion contact point 10 of the front metal plate 31 and the length (+40 μm) by which the upper end portions 8 are recessed from the line in the Z-axis direction passing through the inclined portion contact point 10. In other words, |protrusion width|≦40. As shown in FIG. 5( a), if the upper end portions 8 extend beyond the line in the Z-axis direction passing through the inclined portion contact point 10 toward the adjacent front metal plate (positive direction of the X-axis), the protrusion width 9 is a negative value. As shown in FIG. 5( b), if the upper end portions 8 extend beyond the line in the Z-axis direction passing through the inclined portion contact point 10 toward the opposite side of the adjacent front metal plate (negative direction of the X-axis), the protrusion width 9 is a positive value. 5 shows only the inclined portion on the right side for convenience, but the same consideration can be given with the Z-axis line as the reference when the inclined portion is on the left side. Also, when the upper end 8 is on the Z-axis line passing through the inclined portion contact point 10 of the front metal plate 31, the protrusion width 9 of the front metal plate 31 is 0 (zero).

[0019] The protrusion width 9 of the upper end portion 8 is a value that depends on the angle θ2. Therefore, a protrusion width 9 of ±40 μm or less indicates that the angle θ2 is close to 90°. This allows the width between the upper end portions 8 of adjacent front metal plates 31, 32 to be wide, even if T≧P, thereby suppressing discharge and maintaining insulation. For this reason, the protrusion width 9 is preferably ±40 μm or less, and even more preferably ±20 μm or less. Furthermore, it is preferable that the protrusion width 9 does not extend beyond the lower end of the front metal plate 3 in the X-axis direction. This is because if the protrusion width 9 extends along the X-axis beyond the lower end of the front metal plate 3, the gap between the upper end portion 8 of the front metal plate 31 and the upper end portion 8 of the front metal plate 32 will be narrowed, potentially reducing insulation.

[0020] The shortest distance P, the presence or absence of the inclined portions 6, 7, and the protrusion width 9 of the upper end portions 8 of the front metal plates 31, 32 are observed in a cross-sectional SEM photograph of the ceramic circuit board 1. A cross section perpendicular to the thickness direction of the adjacent front metal plates 31, 32 is observed. The SEM photograph used is a magnification of 50 times.

[0021] The upper end portions 8 of adjacent front metal plates 31, 32 preferably have a shape with a radius of curvature of 15 μm or less. Having a radius of curvature of 15 μm or less means that the upper end portions 8 of the front metal plates 31, 32 are almost completely curved, allowing for a wider flat surface on the surface of the front metal plates 31, 32. A wider flat surface allows for a larger mounting area for semiconductor devices and the like. Therefore, the upper end portions 8 of adjacent front metal plates 31, 32 preferably have a radius of curvature of 15 μm or less, and even 7 μm or less. The radius of curvature is measured using the aforementioned SEM photograph (50x magnification). The angles θ1 and θ2, the protrusion width 9, the radius of curvature, and the like may be calculated using imaging software. For example, ImageJ can be used as imaging software.

[0022] It is preferable that the angle θ1 of the first inclined portion 6 and the angle θ2 of the second inclined portion 7 satisfy the following formula (1). The angle θ1 shown in Fig. 3 is the angle between the bottom surface of the front metal plate 31 and the first inclined portion 6. The angle θ2 is the angle between the upper side (surface) of the front metal plate 31 and the second inclined portion 7. Note that the front metal plate 32 is not shown in Fig. 3. θ1 < θ2 (1) It is also preferable that the angle of the first inclined portion 6 is in the range of 20° to 75°, and the angle of the second inclined portion 7 is in the range of 80° to 110°.

[0023] The first inclined portion 6 is an inclined portion starting from the lower end of the side surface of the front metal plate 3 that is in contact with the ceramic substrate 2 or the bonding layer 5. The second inclined portion 7 is an inclined portion starting from the upper end 8 of the front metal plate 3. When the angle θ1 of the first inclined portion 6 and the angle θ2 of the second inclined portion 7 satisfy the above formula (1), the thermal stress relaxation effect at the lower end of the side surface of the metal plate is improved.

[0024] The angle θ1 of the first inclined portion 6 is preferably within a range of 20° to 75°. The angle θ1 of the first inclined portion 6 is sometimes simply referred to as the angle θ1. By setting the angle θ1 to 20° to 75°, it is possible to achieve both a stress relaxation effect and a reduction in the combined width D of the inclined portions 6 and 7. For this reason, the angle θ1 is preferably within a range of 20° to 75°, and more preferably within a range of 30° to 60°.

[0025] The angle θ2 of the second inclined portion 7 is preferably within a range of 80° to 110°. The angle θ2 of the second inclined portion 7 is sometimes simply referred to as the angle θ2. By setting the angle θ2 within a range of 80° to 110°, it becomes easier to control the protrusion width 9 to ±40 μm or less. It also becomes easier to control the radius of curvature of the upper end portion 8 of the front metal plate 3 to 15 μm or less. For this reason, the angle θ2 is preferably within a range of 80° to 110°, and more preferably within a range of 85° to 100°.

[0026] The angles θ1 and θ2 are measured using the SEM photograph (50x magnification) described above. A straight line is drawn at the location of the first inclined portion 6 and the second inclined portion 7, and the respective angles are determined. In this case, even if there are small irregularities (e.g., irregularities of 5 μm or less) on the surfaces of the first inclined portion 6 and the second inclined portion 7, they are treated as straight lines.

[0027] Even when the inclined portions 6 and 7 have an R-shape, a straight line is drawn at the location of the first inclined portion 6 and the second inclined portion 7 using an SEM photograph (50x magnification) to determine the respective angles.

[0028] It is preferable that the ratio D / T of the combined width D of the inclined portions 6 and 7 of the front metal plate 3 to the thickness T of the front metal plate 3 satisfies the following formula (2): D / T≦0.5 (2)

[0029] The combined width D of the inclined portions 6 and 7 of the front metal plate 3 is sometimes simply referred to as width D. Width D is the distance from the intersection of a line in the X-axis direction passing through the top end 8 of the front metal plate 31 and a line in the Z-axis direction passing through the edge of the bottom end of the front metal plate 31 to the top end 8 of the front metal plate 31. A ratio D / T of 0.5 or less indicates that width D is 1 / 2 or less of the thickness T of the front metal plate 3. While the lower limit of the ratio D / T is not limited, it is preferable that the ratio D / T be 0.1 or greater. If the ratio D / T is less than 0.1, the small width D may make it difficult to provide the first inclined portion 6 and the second inclined portion 7. Therefore, even if width D is reduced to 0.1 or greater and 0.5 or less relative to the thickness T of the front metal plate 3, the number of locations satisfying T≧P can be increased. Width D is measured using the SEM photograph (50x magnification) described above.

[0030] It is preferable that the thickness T of the front metal plate 3 satisfy the following formula (3): T≧0.5 mm (3) Increasing the thickness of the front metal plate 3 can improve heat dissipation and current-carrying capacity. For this reason, the thickness T of the front metal plate 3 is preferably 0.5 mm or more, and more preferably 0.8 mm or more. Because the front metal plate 3 has the first inclined portion 6 and the second inclined portion 7 with different inclination angles, a portion where T≧P can be achieved can be created even if the front metal plate 3 is thick. The upper limit of the thickness T of the front metal plate 3 is not particularly limited, but is preferably 5 mm or less. For this reason, the thickness T of the front metal plate 3 is preferably within a range of 0.5 mm to 5 mm, and more preferably 0.8 mm to 3 mm.

[0031] When the point of contact between the first inclined portion 6 and the second inclined portion 7 is defined as the inclined portion contact point 10, the height difference between the inclined portion contact points 10 between adjacent front metal plates 31, 32 is preferably within a range of 100 μm. The height difference between the inclined portion contact points 10 between adjacent front metal plates 31, 32 is sometimes simply referred to as the height difference between the inclined portion contact points 10. The inclined portion contact point 10, which is the point of contact between the first inclined portion 6 and the second inclined portion 7, is observed in the SEM photograph (50x magnification) described above. A line is drawn in the X-axis direction from the inclined portion contact point 10 on the front metal plate 31 to the inclined portion contact point 10 on the opposing front metal plate 32. The height difference between the line in the X-axis direction related to the front metal plate 31 and the line in the X-axis direction related to the front metal plate 32 is defined as the height difference 11 of the inclined portion contact points 10. For example, the difference in height (thickness direction of the front metal plate 3) between a line in the X-axis direction passing through the inclined portion contact point 10 of the front metal plate 31 and a line in the X-axis direction passing through the inclined portion contact point 10 of the front metal plate 32 is measured.

[0032] When the height difference 11 of the inclined portion contact points 10 is 100 μm or less, this indicates that the side shapes of the adjacent front metal plates 31, 32 are similar. This makes it possible to improve the TCT characteristics even if there are locations where T≧P. The similarity of the side shapes of the adjacent front metal plates 31, 32 makes it possible to homogenize the effects of thermal expansion. For this reason, it is preferable that the height difference 11 of the inclined portion contact points 10 be 100 μm or less, and more preferably within the range of 0 μm to 50 μm.

[0033] The inclined portions 6 and 7 may each have an R-shape as shown in Fig. 9. In this case, it is preferable that the inclined portion contact point 10 is a point where the radius of curvature of the first inclined portion 6 and the second inclined portion 7 differ by 50 µm or more. It is preferable that the radius of curvature of the first inclined portion 6 and the radius of curvature of the second inclined portion 7 satisfy the following formula (4): radius of curvature of first inclined portion 6 ≥ radius of curvature of second inclined portion 7 (4)

[0034] The radius of curvature of the first inclined portion 6 is preferably in the range of 600 μm to 850 μm, and the radius of curvature of the second inclined portion 7 is preferably in the range of 350 μm to 550 μm. Note that the front metal plate 32 is not shown in FIG. 9 .

[0035] When the radius of curvature of the first inclined portion 6 is large within the range of 600 μm or more and 850 μm or less, the first inclined portion 6 has a gentler slope than the second inclined portion 7. Therefore, the angle θ1 of the first inclined portion 6 can also be made small. On the other hand, when the radius of curvature of the second inclined portion 7 is large within the range of 350 μm or more and 550 μm or less, the slope becomes steep (close to vertical), and the angle θ2 of the second inclined portion 7 becomes large.

[0036] Therefore, by satisfying the above formula (4), the above formula (1) is satisfied as described above, and it is possible to improve the thermal stress relaxation effect at the lower end of the side surface of the front metal plate 3. The method for measuring the radius of curvature was to use an SEM photograph (50x magnification) to draw circles along the slopes of the R parts of the first inclined portion 6 and the second inclined portion 7, and the difference in the radii of the circles was taken as the radius of curvature.

[0037] The number of inclined portions on the side surface of the front metal plate 3 is not limited to two, and may be three or more. Figure 6 illustrates a front metal plate 31 having three inclined portions. In the figure, reference numeral 31 denotes the front metal plate, reference numeral 6 denotes a first inclined portion, reference numeral 7 denotes a second inclined portion, and reference numeral 12 denotes a third inclined portion. When there are three inclined portions, there are two inclined portion contact points 10: the contact point between the first inclined portion 6 and the third inclined portion 12, and the contact point between the second inclined portion 7 and the third inclined portion 12. Even when there are multiple inclined portion contact points 10, it is preferable that the height difference 11 between the inclined portion contact points 10 is 100 μm or less. The angle of the third inclined portion 12 is indicated by θ3. The angle θ3 is the angle formed between the line in the X-axis direction passing through the tangent point 10 between the first inclined portion 6 and the third inclined portion 12 and the tangent point with the third inclined portion 12, and is greater than angle θ1 and smaller than angle θ2.

[0038] Although not shown, when a fourth inclined portion is provided on the front metal plate 3, the fourth inclined portion is provided on the second inclined portion 7 side of the third inclined portion 12. The inclination angle of the fourth inclined portion is the angle formed between the tangent point of the fourth inclined portion and a line in the X-axis direction passing through the tangent point of the third inclined portion 12 and the fourth inclined portion. As the number of inclined portions becomes n, the angle of the inclined portion is represented by θn.

[0039] Among the multiple front metal plates 3, at least one front metal plate 3 may have a step portion on its surface. Figure 7 shows an example of a front metal plate 31 having a step portion. In the figure, reference numeral 31 denotes the front metal plate, reference numeral 6 denotes the first inclined portion, reference numeral 7 denotes the second inclined portion, reference numeral 8 denotes the upper end of the front metal plate 31, reference numeral 13 denotes the step portion (protrusion), and reference numeral T denotes the thickness of the front metal plate 31. The step portion 13 is integrated with the front metal plate 31. The step portion 13 is not formed by joining a separate metal plate to the front metal plate 31. Providing the step portion 13 can improve the heat dissipation and current-carrying capacity of that portion. Furthermore, the thickness T of the front metal plate 31 having the step portion 13 is the thickness up to the upper end 8 of the front metal plate 31, which is the starting point of the second inclined portion 7. The side of the step portion 13 itself may or may not have an inclined portion.

[0040] The range of 50% to 100% of the shortest distance P between adjacent front metal plates 31, 32 may be such that T>P is satisfied. The total length in the Y-axis direction of the side surfaces of the front metal plates 31, 32 adjacent in the X-axis direction that face each other is taken as 100%, and this shows the proportion of the length in the Y-axis direction of the side surfaces that satisfy T>P. This means that the following formula (5) is satisfied: 50%≦(length of side surface that satisfies T>P / total length of side surface facing adjacent surface)×100≦100% ... (5)

[0041] The length of the side surface that satisfies T > P refers to the length of the side surface that satisfies T > P among the lengths in the Y-axis direction of the side surface of the front metal plate 31 that faces the adjacent front metal plate 32 in the X-axis direction when viewed from above the ceramic substrate 2. The length of the side surface facing the adjacent surface refers to the length in the Y-axis direction of the side surface of the front metal plate 31 that faces the adjacent front metal plate 32. Note that the side surface of the front metal plate 31 that faces the adjacent front metal plate 32 is not necessarily straight when viewed from above, and may be bent. In such cases, the length in the Y-axis direction of the side surface of the front metal plate 31 that faces the adjacent front metal plate 32 includes the length of the bent portion. The same applies to the case where the front metal plate 31 faces the adjacent front metal plate in the Y-axis direction as to the case where the front metal plate faces the adjacent front metal plate in the X-axis direction. By increasing the number of side surfaces for which the shortest distance P between adjacent front metal plates 31, 32 satisfies T > P in relation to the thickness T of the front metal plate 3, the ceramic circuit substrate 1 can be made smaller.

[0042] When viewing the X-Z cross section of the ceramic substrate 2 in an SEM image (50x magnification), the distance between adjacent front metal plates 31, 32, i.e., the inter-pattern distance S, varies depending on the position in the thickness direction. The proportion of the inter-pattern distance S that satisfies S<T with respect to the thickness of the front metal plate 3 may be 25% or more and 100% or less. In other words, the proportion of areas where the inter-pattern distance S is wider than the thickness T of the metal plate may be within the range of 30% or more and 100% or less. By setting the proportion that satisfies S<T to 25% or more and 100% or less, the heat dissipation properties of the front metal plate 3 can be improved. This makes it possible to achieve a miniaturization of the ceramic circuit substrate 1.

[0043] It is preferable that the ratio Mm / Mc of the area Mc of one surface of the ceramic substrate 2 to the total area Mm of the front metal plate 3 bonded to that surface satisfies the following formula (6): Mm / Mc≧0.8 (6) Mm is the total area of ​​the bonding surfaces of the front metal plate 3 bonded to one surface of the ceramic substrate 2. An Mm / Mc ratio of 0.8 or more indicates that the bonding area of ​​the front metal plate 3 is 80% or more. This means that even if the bonding area of ​​the front metal plate 3 is set to 80% or more, a location that satisfies T≧P can be created. Because a location that satisfies T≧P can be created while increasing the bonding area of ​​the front metal plate 3, the ceramic circuit substrate 1 can be made smaller than conventional ceramic circuit substrates to which metal plates of the same size or area are bonded.

[0044] The ceramic substrate 2 and the front metal plate 3 are bonded via a bonding layer 5, and the bonding layer 5 preferably has a protruding portion that protrudes from the end of the front metal plate 3. By having the bonding layer 5 protrude from the end of the front metal plate 3 (the lower end of the metal plate), the thermal stress relaxation effect is enhanced. The protruding length of the protruding portion of the bonding layer is preferably within the range of 10 μm to 150 μm. If the protruding length is less than 10 μm, the stress relaxation effect may be insufficient. If the protruding length exceeds 150 μm, poor conductivity with the adjacent metal plate may occur.

[0045] Of the side surfaces of the front metal plate 3 of the ceramic substrate 2, the side surface that does not face the adjacent front metal plate may or may not have multiple inclined portions with different inclination angles. What is effective is to control the inclination of the side surface that faces the adjacent front metal plate. In addition, the inclined portions according to the embodiment may be provided on both sides of the front metal plate 3 and the back metal plate 4.

[0046] The ceramic substrate 2 is preferably one selected from the group consisting of a silicon nitride substrate, an aluminum nitride substrate, an aluminum oxide substrate, and a zirconium oxide substrate.

[0047] The thermal conductivity of silicon nitride substrates is 50 W / m·K or more, and even 80 W / m·K or more. Furthermore, the three-point bending strength of silicon nitride substrates is 600 MPa or more, and even 700 MPa or more. The thermal conductivity of aluminum nitride substrates is 150 W / m·K or more, and even 200 W / m·K or more. The three-point bending strength of aluminum nitride substrates is approximately 300 to 450 MPa. The three-point bending strength of aluminum oxide substrates is approximately 300 to 450 MPa, but aluminum oxide substrates are less expensive than other substrates. Furthermore, the thermal conductivity of aluminum oxide substrates is approximately 20 to 30 W / m·K. The three-point bending strength of zirconium oxide substrates is high, approximately 550 MPa, but the thermal conductivity is approximately 30 to 50 W / m·K.

[0048] The thickness of the ceramic substrate 2 is preferably in the range of 0.2 mm to 3 mm, and more preferably 0.2 mm to 1 mm. If the thickness of the ceramic substrate is less than 0.2 mm, the strength may be insufficient. If the thickness of the ceramic substrate exceeds 3 mm, the ceramic substrate may become a thermal resistor and the heat dissipation performance may be reduced. Furthermore, since silicon nitride substrates have high strength, the thickness can be set to the range of 0.2 mm to 1.0 mm, and even 0.2 mm to 0.5 mm. From the viewpoint of thinning the substrate, it is preferable to use a silicon nitride substrate.

[0049] The metal plates 3 and 4 are preferably copper plates (including copper alloy plates) or aluminum plates (including aluminum alloy plates). Furthermore, the copper plates are preferably oxygen-free copper plates. Oxygen-free copper has a copper purity of 99.96 wt% or higher, as specified in JIS-H-3100. The thermal conductivity of copper is approximately 400 W / m·K, while the thermal conductivity of aluminum is approximately 240 W / m·K. Because copper has a higher thermal conductivity than aluminum, it improves heat dissipation. Furthermore, the aluminum plates are preferably pure aluminum. Pure aluminum is specified in JIS-H-4000. JIS-H-4000 corresponds to ISO 6361. JIS-H-3100 corresponds to ISO 197 and other standards. For this reason, it is preferable that the ceramic substrate 2 be a silicon nitride substrate with a thickness of 1.0 mm or less, and the metal plates 3 and 4 be copper plates with a thickness of 0.5 mm or more.

[0050] The bonding layer 5 is preferably an active metal bonding layer. When the metal plates 3 and 4 are copper plates, the bonding layer 5 is preferably an active metal bonding layer containing either Ag or Cu as a main component. The active metal may be one or more selected from titanium (Ti), zirconium (Zr), hafnium (Hf), and niobium (Nb).

[0051] The composition of the active metal brazing material containing Ag or Cu as the main component is 0 mass % or more and 60 mass % or less of Ag (silver), 15 mass % or more and 70 mass % or less of Cu (copper), Ti (titanium) or TiH ２ It is preferable that the titanium hydride is contained in an amount of 1 mass % or more and 15 mass % or less. ２ When both Ag and Cu are used, the total content is preferably in the range of 1% by mass to 15% by mass. When both Ag and Cu are used, the Ag content is preferably in the range of 20% by mass to 60% by mass and the Cu content is preferably in the range of 15% by mass to 40% by mass.

[0052] If necessary, one or both of Sn (tin) and In (indium) may be contained in an amount of 1 mass % to 50 mass %. ２The content of is preferably in the range of 1% by mass to 15% by mass. If necessary, C (carbon) may be contained in an amount of 0.1% by mass to 2% by mass.

[0053] The ratio of the active metal brazing material composition is calculated by taking the total of the mixed raw materials as 100% by mass. For example, when the active metal brazing material is composed of three elements, Ag, Cu, and Ti, the ratio is Ag + Cu + Ti = 100% by mass. ２ , and In, Ag + Cu + TiH ２ In addition, when the alloy is composed of five elements, Ag, Cu, Ti, Sn, and C, the total weight of the alloy is Ag+Cu+Ti+Sn+C=100% by mass.

[0054] Ag or Cu is a component that serves as 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 controlling the structure of the bonding layer 5 by reacting with other components. Therefore, examples of components of the brazing material include Ag-Cu-Ti, Ag-Cu-Sn-Ti, Ag-Cu-Ti-C, Ag-Cu-Sn-Ti-C, Ag-Ti, Cu-Ti, Ag-Sn-Ti, Cu-Sn-Ti, Ag-Ti-C, Cu-Ti-C, Ag-Sn-Ti-C, and Cu-Sn-Ti-C. In addition, In may be used instead of Sn. Furthermore, both Sn and In may be used.

[0055] The active metal brazing filler metal may contain 0.1 mass % to 10 mass % of one or more elements selected from tungsten (W), molybdenum (Mo), and rhenium (Re). Tungsten, molybdenum, and rhenium can control the fluidity of the active metal brazing filler metal. Magnesium (Mg) may also be added to the active metal brazing filler metal.

[0056] When the metal plates 3 and 4 are aluminum plates, the bonding layer 5 is preferably an active metal bonding layer primarily composed of Al. The active metal may be one or more selected from silicon (Si) and magnesium (Mg). The active metal brazing material primarily composed of Al is preferably an Al-Si or Al-Mg brazing material. The content of one or both of Si and Mg in the active metal brazing material is preferably within the range of 0.1% by mass to 20% by mass. The active metal brazing material is made into a paste to prepare an active metal brazing material paste. The active metal brazing material paste is applied to the ceramic substrate 2, and the metal plates are placed on top of it. When bonding the metal plates 3 and 4 to both sides, the active metal brazing material paste is applied to both sides, and the metal plates 3 and 4 are then placed.

[0057] Thereafter, the ceramic substrate 2 and the metal plates 3, 4 are heated and bonded at a temperature in the range of 600°C to 960°C, thereby obtaining a bonded body. The bonded body is subjected to an etching process, thereby producing the ceramic circuit board 1 according to the embodiment. Also, a direct bonding method may be used instead of the active metal bonding method.

[0058] Next, a method for manufacturing the ceramic circuit board 1 according to the embodiment will be described. The manufacturing method for the ceramic circuit board 1 according to the embodiment is not limited as long as it has the above-described configuration. However, the following method can be used to obtain a high yield. Hereinafter, a manufacturing method in which an etching process is performed on a bonded body obtained by the active metal bonding method will be exemplified. FIG. 8 shows an example of the manufacturing process. In the figure, reference numeral 3 denotes a metal plate, reference numeral 13 denotes a bonded body, and reference numeral 14 denotes a resist. FIG. 8 is a side cross-sectional (X-Z cross-sectional) view illustrating a bonded body, etc., for explaining the process of forming inclined portions 6 and 7 between adjacent front metal plates 31 and 32. Although FIG. 8 shows two adjacent metal plates, this number can be increased as needed.

[0059] 8(a) shows the process of applying resist 14 to the joined body. This shows the process of applying resist 14 to the front metal plate 3 of the joined body. The resist 14 is an etching resist. The resist 14 is provided at the location where it is desired to provide a circuit pattern on the front metal plate 3. Furthermore, in locations where it is desired to satisfy T≧P, the resists 14 are arranged so that the gap W between them is within the range of 0.2 to 0.6 times the shortest distance P. Note that in locations where it is not necessary to satisfy T≧P, the gap between the resists 14 is arbitrary. The resist 14 may be applied to both sides of the front metal plate 3 and the back metal plate 4.

[0060] FIG. 8(b) shows a process of etching the gaps between the resists 14. FIG. 8(b) shows a process of etching a portion of the thickness T of the front metal plate 3. A method of etching a portion of the thickness of the front metal plate 3, but not all of it, is called half-etching. The depth of each half-etching is preferably within a range of 0.2 to 0.7 times the thickness T of the front metal plate 3. The depth of the first half-etching serves to form the second inclined portion 7 of the front metal plate 3. Furthermore, by making the gaps between the resists 14 within a range of 0.2 to 0.6 times the shortest distance P between adjacent front metal plates after manufacturing, the shortest distance P between the front metal plates formed by the first half-etching can be T≧P. This allows the final shape to satisfy T≧P, or even T>P.

[0061] For example, when the metal plates 3 and 4 are copper plates, the etching solution may be an etching solution containing copper chloride or ferric chloride.

[0062] 8(c) shows a second etching step performed on the bonded body that has been subjected to the first half-etching. Fig. 8 illustrates a step of etching the front metal plate 3 twice to expose the bonding layer 5. In the manufacturing method according to the embodiment, the number of times the front metal plate 3 is etched is not limited to two, i.e., the number of inclined portions is not limited to two, and etching may be performed three or more times. Fig. 8(c) shows a step of etching until the bonding layer 5 is exposed.

[0063] For example, if two inclined portions are formed in two etching steps to expose the bonding layer 5, the first inclined portion 6 is formed in the second etching step. Alternatively, if three inclined portions are formed in three etching steps to expose the bonding layer 5, the third inclined portion 12 (shown in FIG. 6 ) is formed in the second etching step, and the first inclined portion 6 is formed in the third etching step. In other words, the number of inclined portions formed is equal to the number of etching steps. While the upper limit of the number of etching steps is not particularly limited, five or less is preferable. Increasing the number of etching steps may result in a loss of further benefits and may actually increase costs. Although the description assumes that one etching step is performed per inclined portion, this is not limited to this case. Multiple etching steps per inclined portion may also be performed.

[0064] By changing the etching conditions for the first and second etchings, the angle θ1 of the first inclined portion 6 and the angle θ2 of the second inclined portion 7 can be made different. Examples of etching conditions include the etching time, the etching solution (the concentration and components of the etchant), and the presence or absence of ultrasonic waves. For example, when the same etching solution is used, by making the second etching time shorter than the first etching time, the angle θ1 of the first inclined portion 6 and the angle θ2 of the second inclined portion 7 can satisfy the above formula (1).

[0065] FIG. 8(d) shows the step of etching the bonding layer 5. When the bonding layer 5 is an active metal bonding layer, the etching method described in Patent Document 3 can be used. For example, when a silicon nitride substrate serving as the ceramic substrate 2 and a copper plate serving as the front metal plate 3 are bonded using a Ti-containing active metal brazing material, a titanium nitride layer is formed on the surface of the silicon nitride substrate. Because the titanium nitride layer is conductive, removing it by etching can prevent poor electrical connection between adjacent copper plates. The etching step of the bonding layer 5 also serves to control the size of the protruding portion of the bonding layer. If necessary, the side surface of the front metal plate 3 may also be etched. By etching the side surface of the front metal plate 3, the size of the protruding portion of the bonding layer of the front metal plates 31 and 32 can be more precisely controlled.

[0066] At least one of a chemical polishing step and a water washing step may be provided between multiple etching steps. When providing a front metal plate 31 having a step 13 as shown in Fig. 7, a method may be used in which a front metal plate 3 having a step 13 is previously bonded. Alternatively, the bonded front metal plate 3 may be subjected to etching or cutting to form the step 13.

[0067] The ceramic circuit board 1 according to the embodiment can be manufactured by the steps described above with reference to FIG.

[0068] (Examples) (Examples 1 to 6, Comparative Examples 1 and 2) A silicon nitride substrate with a thermal conductivity of 90 W / m·K and a three-point bending strength of 650 MPa was prepared as the ceramic substrate 2. An active metal brazing material containing Ti was used as the brazing material. Copper plates (front copper plate and back copper plate) with a thickness of 0.5 mm or more were used as the metal plates 3 and 4. Bonded bodies 1 to 4 were prepared in which copper plates were bonded to both sides of a silicon nitride substrate via an active metal bonding layer. Of bonded bodies 1 to 4, bonded body 4 had a step portion 13 provided on the front copper plate. The size of the bonded body is as shown in Table 1.

[0069]

[0070] Next, an etching process was performed on the bonded bodies 1 to 4. In the etching process of the examples, half-etching of the front copper plate was repeated two to four times to expose the bonding layer 5. Thereafter, the bonding layer 5 was etched. Each half-etching performed multiple times means a process (batch type) from immersion in an etching solution to removal from the etching solution. In addition, between the previous half-etching and the subsequent half-etching, the bonding layer 5 was washed with water. In the comparative example, the front copper plate was etched once to expose the bonding layer. In Example 5, half-etching was performed four times to form two inclined portions. In addition, the gaps between the resists are as shown in Table 2.

[0071]

[0072] Furthermore, a ceramic circuit substrate was fabricated by an etching process. The following were measured for the resulting ceramic circuit substrate: the shortest distance P between adjacent metal plates, the protrusion width 9, the radius of curvature of the upper end of the front metal plate, the angle θ1 of the first inclined portion, the angle θ2 of the second inclined portion, the angle θ3 of the third inclined portion, the difference in height between the inclined portion contact points, the combined width D of the multiple inclined portions formed on the front copper plate / the metal plate thickness T, the percentage of cases where the shortest distance P between adjacent metal plates is T>P, and the size of the protrusion portion of the bonding layer. The ratio Mm / Mc, where Mc is the area of ​​one surface of the ceramic substrate and Mm is the total area of ​​the metal plates bonded to that surface, was also determined. The results are shown in Tables 3 and 4. The protrusion width in Table 3 has a lower limit of 0 (zero) when the protrusion width value is positive, and an upper limit of 0 (zero) when the protrusion width value is negative.

[0073]

[0074]

[0075] As can be seen from Tables 3 and 4, in the examples, ceramic circuit boards were produced in which the side surfaces satisfying T>P accounted for 50% or more of the entire side surfaces. Furthermore, in examples 1, 2, 3, and 6, in which half etching was performed twice, a first inclined portion 6 and a second inclined portion 7 were formed. Furthermore, in example 4, in which half etching was performed three times, a first inclined portion 6, a second inclined portion 7, and a third inclined portion 12 were formed. In example 5, in which half etching was performed four times, a first inclined portion 6 and a second inclined portion 7 were formed.

[0076] In addition, Comparative Example 1 does not have any portion where T>P. This is because the bonding layer was exposed by a single etching. In Comparative Example 1, the shortest distance P was large, so Mm / Mc could not be made 0.8 or more. In Comparative Example 2, although T>P was satisfied, the first inclined portion and the second inclined portion with different angles were not provided.

[0077] Examples 3 and 4 and Comparative Examples 1 and 2 use the bonded body 3. In Examples 3 and 4, the number of locations where T>P is increased, which makes it possible to increase the bonding area of ​​the copper plates 3 and 4 to the ceramic substrate 2. In other words, this shows that if the bonding area of ​​the copper plates 3 and 4 is the same, it is possible to reduce the size of the ceramic circuit substrate 1.

[0078] In Example 6, the first inclined portion 6 and the second inclined portion 7 have an R-shape (see FIG. 9 ). The radius of curvature of the first inclined portion 6 in Example 6 was 450 μm, while the radius of curvature of the second inclined portion 7 was 700 μm. Therefore, Example 6 satisfies the above formula (4).

[0079] Next, TCT was performed on the ceramic circuit substrates of the examples and comparative examples. TCT was performed 3,000 times, with one cycle consisting of -40°C x 30 minutes → room temperature x 10 minutes → 170°C x 30 minutes → room temperature x 10 minutes. After TCT, the ceramic circuit substrates were observed for defects. The results are shown in Table 5.

[0080]

[0081] As can be seen from Table 5, the TCT characteristics of the examples were good. This shows that durability is good even when the region where T>P is increased. Comparative Example 1 had good TCT characteristics because T<P. Furthermore, the TCT characteristics of Comparative Example 2 deteriorated. This is because Comparative Example 2 does not have a first inclined portion and a second inclined portion with different inclination angles. Therefore, it can be seen that the examples can improve the TCT characteristics by increasing the region where T≧P and even T>P.

[0082] Although several embodiments of the present invention have been described above, these embodiments are presented by way of example only 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, modifications, etc. 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, as well as within the scope of the invention and its equivalents as set forth in the claims. Furthermore, the above-described embodiments can be implemented in combination with each other.

Claims

1. A ceramic circuit board having a plurality of metal plates bonded to at least one surface of a ceramic substrate, wherein when the thickness of each of the plurality of metal plates is T and the shortest distance between adjacent metal plates among the plurality of metal plates is P, the ceramic circuit board has a portion where T≧P, and the side of the plurality of metal plates that faces the adjacent metal plate has at least a first inclined portion and a second inclined portion with different inclination angles, in that order from the ceramic substrate side, and the protrusion width of the upper end of the adjacent metal plates is ±40 μm or less.

2. The ceramic circuit board according to claim 1, wherein the upper ends of the adjacent metal plates have a radius of curvature of 15 μm or less.

3. A ceramic circuit board according to claim 1 or 2, wherein the angle of the first inclined portion is within the range of 20° to 75°, and the angle of the second inclined portion is within the range of 80° to 110°.

4. A ceramic circuit board according to any one of claims 1 to 3, wherein the ratio D / T of the combined width D of the first inclined portion and the second inclined portion to the thickness T of each of the metal plates is 0.5 or less.

5. A ceramic circuit board according to any one of claims 1 to 4, wherein the thickness T of each of the metal plates is 0.5 mm or more.

6. A ceramic circuit board according to any one of claims 1 to 5, wherein when the tangent line between the first inclined portion and the second inclined portion is defined as the inclined portion contact line, the difference in height of the inclined portion contact line between the adjacent metal plates is within a range of 100 μm.

7. A ceramic circuit board according to any one of claims 1 to 6, wherein the ratio of the length of the side surface where the adjacent metal plates face each other in the Y-axis direction that satisfies T>P is within the range of 50% or more and 100% or less.

8. A ceramic circuit board according to any one of claims 1 to 7, wherein the ratio Mm / Mc of the area Mc of the surface to which the plurality of metal plates are bonded to the total area Mm of the metal plates bonded to said surface is 0.8 or more.

9. A ceramic circuit board according to any one of claims 1 to 8, wherein the ceramic substrate and the plurality of metal plates are bonded via a bonding layer, and the bonding layer has a protruding portion that protrudes from the end of the metal plate.

10. A ceramic circuit board according to any one of claims 1 to 9, wherein the ceramic substrate is a silicon nitride substrate having a thickness of 1.0 mm or less, and the metal plate is a copper plate having a thickness of 0.5 mm or more.

11. A ceramic circuit board according to any one of claims 1 to 10, wherein at least one of the plurality of metal plates has a stepped portion on its surface.

12. A ceramic circuit board according to any one of claims 1 to 11, wherein the protrusion width of the upper end portions of the adjacent metal plates is ±20 μm or less.

13. A ceramic circuit board according to any one of claims 1 to 12, wherein the first inclined portion and the second inclined portion are R-shaped inclined portions, and the point where the radius of curvature of the R-shaped inclined portions differs by 50 μm or more is the inclined portion contact point between the first inclined portion and the second inclined portion.

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