Ceramic circuit board, semiconductor device, and method for manufacturing ceramic circuit board

Abstract

A ceramic circuit board according to an embodiment has a configuration in which a ceramic substrate and a metal plate are bonded to each other with a bonding layer interposed therebetween. The bonding layer has a bonding layer protruding part in which the bonding layer protrudes from the back surface edges of the metal plate, and the metal plate has, on the side surface side of the metal plate, an inclined part that expands from the front surface toward the back surface of the metal plate. The ceramic circuit board has, on at least the front surface of the metal plate, a first metal layer and a second metal layer of which a main component is different from that of the first metal layer, wherein the first metal layer and the second metal layer are provided only in an effective region that is a portion of the front surface of the metal plate and lays 50 μm or more inward from the front surface edges of the metal plate. In the ceramic circuit board, it is preferable that the second metal layer is overlaid on the first metal layer.

Description

Ceramic circuit board, semiconductor device, and method for manufacturing ceramic circuit board

[0001] The embodiments described below relate to a ceramic circuit board, a semiconductor device, and a method for manufacturing a ceramic circuit board.

[0002] Ceramic circuit substrates are used as circuit boards for mounting semiconductor elements. In recent years, with the increasing performance of semiconductor elements, ceramic circuit substrates are required to have improved TCT (Temperature Cycle Test) characteristics (heat cycle resistance characteristics). For example, Japanese Patent No. 6789955 (Patent Document 1) discloses a ceramic circuit substrate in which a ceramic substrate and a metal plate are bonded via an active metal bonding layer. In Patent Document 1, the TCT characteristics are improved by controlling the size and hardness of the protruding portion of the bonding layer.

[0003] In order to improve the mountability of semiconductor elements, etc., a plating layer may be provided on a metal plate. For example, in Japanese Patent Laid-Open No. 5-243699 (Patent Document 2), a Ni plating layer is provided on a metal plate. In Patent Document 2, the provision of the Ni plating layer improves the bondability with solder.

[0004] In recent years, SiC has been increasingly adopted for power semiconductor chips. Compared to current Si power semiconductors, these SiC power semiconductors offer higher performance, including higher switching conversion efficiency. They are also capable of operating at high temperatures, and to take advantage of this characteristic, chip joints must be able to withstand high temperatures. The melting point of lead-free solder is around 220°C. The heat generated by GaN and SiC elements is expected to reach around 200°C. At temperatures approaching the melting point of lead-free solder, the reliability of the joint decreases. For this reason, Ag sinter bonding is being attempted. Ag sinter bonding is a method of bonding by heating a coating made of Ag nanoparticles. The bonding temperature is around 200-300°C, and a metallic bond is formed after bonding. Therefore, Ag's high melting point ensures high reliability even when the operating temperature of semiconductor elements rises.

[0005] Patent No. 6789955 JP 5-243699 JP 2015-53414

[0006] To improve the reliability of Ag sinter bonding, a plating layer is provided on the metal plate. For example, in JP 2015-53414 A (Patent Document 3), Au plating, Ag plating, and Pd plating are used. In order to improve the bondability with Ag sinter bonding, materials other than Ni plating are used.

[0007] In addition to semiconductor elements, various other items can be mounted on ceramic circuit boards, such as lead frames, metal terminals, wire bonding, and discrete elements. In some cases, it is more cost-effective to mount these items using ultrasonic bonding or solder bonding. However, conventional ceramic circuit boards have not been equipped with a plating layer suitable for these mounting methods.

[0008] The problem to be solved by the present invention is to provide a ceramic circuit board and a semiconductor device having, on at least the surface of a metal plate, a first metal layer and a second metal layer (having a different main component from the first metal layer) suitable for a mounting method.

[0009] In one embodiment, a ceramic circuit board is formed by bonding a ceramic substrate and a metal plate via a bonding layer. The bonding layer has a protruding portion where the bonding layer protrudes beyond the edge of the back surface of the metal plate, and the metal plate has a side surface with a sloped portion that widens from the front surface toward the back surface of the metal plate. The ceramic circuit board has a first metal layer and a second metal layer having a different main component from the first metal layer on at least the front surface of the metal plate, and the first metal layer and the second metal layer are present only in an effective region of the front surface of the metal plate that is at least 50 μm inward from the front surface edge.

[0010] 1 is a cross-sectional view showing a first example of a ceramic circuit board according to an embodiment; 2 is a cross-sectional view showing a second example of a ceramic circuit board according to an embodiment; 3 is a cross-sectional view showing a third example of a ceramic circuit board according to an embodiment; 4 is a cross-sectional view showing a fourth example of a ceramic circuit board according to an embodiment; 5 is a cross-sectional view showing an example of a side shape of a metal plate provided on a ceramic circuit board according to an embodiment; 6 is a top view showing an example of a semiconductor device according to an embodiment; 7 is a cross-sectional view showing an example of a manufacturing process of a ceramic circuit board according to an embodiment; Embodiment

[0011] In one embodiment, a ceramic circuit board in which a ceramic substrate and a metal plate are bonded via a bonding layer has a bonding layer protruding portion where the bonding layer protrudes from the back edge of the metal plate, a side of the metal plate has a sloping portion that widens from the front side toward the back side of the metal plate, at least the front surface of the metal plate has a first metal layer and a second metal layer that has a different main component from the first metal layer, and the first metal layer and the second metal layer are only present in an effective area of ​​the surface of the metal plate that is 50 μm or more inward from the surface edge of the metal plate.

[0012] 1 to 4 show an example of a ceramic circuit board according to an embodiment. FIGS. 1 to 4 are cross-sectional views taken along a plane perpendicular to the plane of a ceramic substrate 2. In the figures, reference numeral 1 denotes a ceramic circuit substrate, reference numeral 2 denotes a ceramic substrate, reference numeral 3 denotes a bonding layer (front bonding layer), reference numeral 4 denotes a metal plate (front metal plate), reference numeral 5 denotes a first metal layer, reference numeral 6 denotes a second metal layer, reference numeral 13 denotes a bonding layer (rear bonding layer), reference numeral 14 denotes a metal plate (rear metal plate), reference numeral 3A denotes a bonding layer protruding portion 3A of the bonding layer 3, and reference numeral 13A denotes a bonding layer protruding portion 13A of the bonding layer 13. Reference numeral d denotes the distance from the surface edge of the metal plate 4, 14 to the outer end of the first metal layer 5 or the second metal layer 6.

[0013] The ceramic circuit board 1 according to the embodiment is a ceramic circuit board in which a ceramic substrate 2 and a metal plate 4 are bonded via a bonding layer 3. Furthermore, as shown in FIG. 4 , metal plates 4, 14 may be bonded to both the front and back surfaces of the ceramic substrate 2 via bonding layers 3, 13, respectively. For convenience, the metal plate 4 may be referred to as the front metal plate, and the metal plate 14 may be referred to as the back metal plate. Furthermore, the number of metal plates 4, 14 bonded to one surface of the ceramic substrate 2 may be one or more. When the ceramic circuit board 1 has metal plates 4, 14 on both the front and back surfaces of the ceramic substrate 2, the configuration of the front surface can be applied to the configuration of the back surface of the ceramic substrate 2 as is, and therefore, hereinafter, redundant explanations of the back surface will be omitted unless otherwise noted.

[0014] The bonding layer 3 has a bonding layer protrusion 3A that protrudes from the rear edge of the metal plate 4. The rear edge of the metal plate 4 is the lower end of the side of the metal plate 4, and indicates the boundary where it contacts the bonding layer 3. The ceramic circuit board 1 is provided with a first metal layer 5 and a second metal layer 6, and the bonding layer 3 corresponding to the metal plate 4 has a bonding layer protrusion 3A. Furthermore, regardless of whether or not the metal layers 5 and 6 are present, it is preferable that all bonding layers 3 corresponding to the metal plates 4 have a bonding layer protrusion 3A. By having the bonding layer protrusion 3A in the ceramic circuit board 1, the TCT characteristics can be improved.

[0015] In addition, the side surfaces of the metal plate 4 have inclined portions 4S that widen from the front surface toward the back surface of the metal plate 4. The side surfaces of the metal plate 4 on which the first metal layer 5 and the second metal layer 6 are provided have inclined portions 4S. It is preferable that the side surfaces of all the metal plates 4 are inclined, regardless of whether the metal layers 5 and 6 are present. Figure 5 shows an example of the shape of the side surface of the metal plate 4. Figure 5 is a cross-sectional view of the metal plate 4 taken along a plane perpendicular to the plane of the ceramic substrate 2.

[0016] As shown in FIGS. 5A to 5D, it is preferable that the side surfaces of the metal plate 4, which are close to the back surface, i.e., at least the side surfaces from the back surface of the metal plate 4 to the center C of the thickness t of the metal plate 4, are inclined. That is, all of the side surfaces of the metal plate 4 may be inclined (as shown in FIGS. 5A to 5C), or the side surfaces of the metal plate 4, which are close to the front surface, for example, a non-inclined portion 4N (shown in FIG. 5D), which is not inclined from the center C of the thickness of the metal plate 4 to the front surface, may be present. By providing an inclined portion 4S at least from the back surface of the metal plate 4 to the center C of the thickness of the metal plate 4, the TCT characteristics can be improved. The inclined shape of the bonding layer protrusion 3A and the side surfaces of the metal plate 4 can be determined by measuring the appearance of the ceramic circuit substrate 1. The inclined shape of the bonding layer protrusion 3A and the side surfaces of the metal plate 4 may also be determined by observing any cross section of the ceramic circuit substrate 1, if necessary.

[0017] Returning to the explanation of Figures 1 to 4, one or more metal plates 4 are provided on the ceramic substrate 2. At least the surface of at least one of the metal plates 4 has a first metal layer 5 and a second metal layer 6 having a different main component from the first metal layer 5. The main component refers to the metal layer 5, 6 that contains the most of the metal layer in terms of mass ratio. The first metal layer 5 and the second metal layer 6 have different main components. By providing the metal layers 5, 6 having different main components, it is possible to provide metal layers according to the mounting method.

[0018] As shown in FIGS. 1 and 4 , a second metal layer 6 may be superimposed on a first metal layer 5 bonded to the surface of a metal plate 4. Alternatively, as shown in FIGS. 2 and 3 , both the first metal layer 5 and the second metal layer 6 may be provided in parallel on the surface of the metal plate 4. Each metal plate 4 may have one or more first or second metal layers 5 and 6. FIG. 1 illustrates an example in which one second metal layer 6 is superimposed on one first metal layer 5. FIG. 2 illustrates an example in which one first metal layer 5 and one second metal layer 6 are provided in parallel on the surface of the metal plate 4. FIG. 3 illustrates an example in which two first metal layers 5 and one second metal layer 6 are provided in parallel on the surface of the metal plate 4. Thus, it is important to provide a first metal layer 5 and a second metal layer 6 on the surface of each metal plate 4.

[0019] Therefore, a structure having a first metal layer 5 and a second metal layer 6 on the surface of the metal plate 4 refers to both a structure in which the second metal layer 6 is superimposed on the first metal layer 5, and a structure in which the first metal layer 5 and the second metal layer 6 are separately arranged in parallel. An arrangement in which the second metal layer 6 is superimposed on the first metal layer 5 is sometimes called a stacked structure. On the other hand, an arrangement in which the first metal layer 5 and the second metal layer 6 are separately arranged in parallel is sometimes called a coplanar structure.

[0020] 1 and 4 illustrate a laminated structure. 2 and 3 illustrate a coplanar structure. In the laminated structure, it is preferable that the second metal layer 6 does not protrude from the first metal layer 5. In other words, it is preferable that the planar dimensions (excluding thickness) of the second metal layer are both equal to or smaller than the planar dimensions of the first metal layer. In other words, it is preferable that the surface area of ​​the first metal layer 5 is equal to or larger than the rear surface area of ​​the second metal layer 6. Furthermore, one or more first metal layers 5 are provided on each metal plate 4, and the number of second metal layers 6 superimposed on each first metal layer 5 may be one or more.

[0021] On the other hand, in the coplanar structure, the area of ​​the front surface (or back surface) of the first metal layer 5 and the area of ​​the front surface (or back surface) of the second metal layer 6 are arbitrary. Furthermore, there may or may not be a gap between adjacent first metal layers 5 and second metal layers 6. Furthermore, the number of first metal layers 5 and second metal layers 6 on each metal plate 4 is arbitrary.

[0022] The ceramic circuit board 1 has the first metal layer 5 and the second metal layer 6 only in the effective region 4A of the surface of the metal plate 4, which is at least a distance d inward from the surface edge. The length d is preferably 50 μm. In other words, the ceramic circuit board 1 does not have the first metal layer 5 and the second metal layer 6 in the peripheral region 4B of the surface of the metal plate 4, which is excluding the effective region 4A. The surface edge of the metal plate 4 refers to the location where the surface (flat portion) of the metal plate 4 contacts the side surface of the metal plate 4. In other words, it refers to the highest point on the side surface of the metal plate 4. The presence of the first metal layer 5 and the second metal layer 6 in the effective region 4A indicates that no plating layer is provided in the peripheral region 4B. Furthermore, the metal layers 5 and 6 may be provided anywhere in the effective region 4A. That is, the metal layers 5 and 6 may be provided 200 μm inward from the surface edge of the metal plate 4 or 500 μm inward from the surface edge of the metal plate 4.

[0023] The surface edge of the metal plate 4 is the point where the thickness t of the metal plate 4 begins to thin. This is the starting point where the surface of the metal plate 4, which was horizontal (flat), begins to tilt when viewed from the side. The surface edge of the metal plate 4 can be measured using a three-dimensional shape measuring machine. Examples of three-dimensional shape measuring machines include the 3D One Shot manufactured by Keyence or an equivalent machine.

[0024] As described above, the side surface of the metal plate 4 is inclined to widen from the front surface toward the back surface of the metal plate 4. As shown in FIG. 5 , the front surface edge P1 of the metal plate 4 is determined. When the metal plate 4 is viewed from above, the distance from the front surface edge P1 to the back surface edge P2 of the metal plate 4 is the expansion width h of the metal plate 4. The expansion width h of the metal plate 4 is preferably equal to or less than half the thickness t of the metal plate 4, as shown in the following formula (1). When the expansion width h satisfies the following formula (1), the slope becomes relatively steep, making it easier to detect the front surface edge P1 of the metal plate 4. While the lower limit of the expansion width h is not particularly limited, it is preferably equal to or greater than 1 / 10 of the thickness t of the metal plate 4, as shown in the following formula (2). If the expansion width h of the metal plate 4 is less than 1 / 10 of the thickness t, the stress relaxation effect may be insufficient. h≦0.5t (1) 0.1t≦h≦0.5t (2)

[0025] The spreading width h of the metal plate 4 may be one spreading width when one parallel plane of the side surfaces of the ceramic substrate 2 is viewed from above, or may be a representative value (e.g., average value, maximum value, or minimum value) of m spreading widths when m (m is an integer of 2 or more) parallel planes of the side surfaces of the ceramic substrate 2 are viewed from above. The spreading width h of the metal plate 4 is measured, as necessary, on a cross section of the ceramic circuit board 1 (e.g., a cross section perpendicular to the plane of the ceramic substrate 2).

[0026] As described above, since the metal layers 5, 6 are not present in the peripheral region 4B, the metal layers 5, 6 are unlikely to peel off from the metal plate 4. As will be described later, the inclined side surfaces of the metal plate 4 are formed by etching, but if etching is performed on the side surfaces of the metal plate 4 after the metal layers 5, 6 are provided on the metal plate 4, the metal plate 4 below the ends of the metal layers 5, 6 may disappear, exposing the ends of the metal layers 5, 6. As a result, if the ends of the metal layers 5, 6 are exposed, the metal layers 5, 6 may be likely to peel off from the metal plate 4.

[0027] Since there are no metal layers 5, 6 in the peripheral region 4B, the metal plate 4 is exposed in the peripheral region 4B. This improves visibility and position detection by a CCD camera or image sensor. Metals with different main components have different color and light reflection characteristics than the metal plate (the metal plate on which the metal layer is provided). Therefore, if a plating layer with a different main component exists on the surface of the metal plate 4, position detection by a CCD camera or image sensor may be impaired.

[0028] It is preferable that the metal layers 5, 6 are not applied to the side surfaces of the metal plate 4 or the protruding portion 3A of the bonding layer. For example, if the metal layers 5, 6 are applied after the protruding portion 3A of the bonding layer is formed, the side surfaces of the metal plate 4 or the protruding portion 3A of the bonding layer may be affected by the metal layers 5, 6. This influence may result in the formation of pores in the protruding portion 3A of the bonding layer or the formation of reaction products with the metal layers 5, 6. This is because the process of applying the metal layers 5, 6 uses chemicals such as plating solutions. Such protruding portion 3A of the bonding layer may also degrade the TCT characteristics. Therefore, as described below, the metal layers 5, 6 are applied to the side surfaces of the solid metal plate 4 and the bonding layer 3, and then the metal layers 5, 6 are removed by etching to form the side surfaces of the metal plate 4 and the protruding portion 3A of the bonding layer.

[0029] Furthermore, the metal plate 4 is preferably a copper plate (including a copper alloy plate) or an aluminum plate (including an aluminum alloy plate). Furthermore, the copper plate is preferably an oxygen-free copper plate. As specified in JIS-H3100, oxygen-free copper has a copper purity of 99.96 wt% or more. The thermal conductivity of copper is approximately 400 W / m·K, and the thermal conductivity of aluminum is approximately 240 W / m·K. Copper has a higher thermal conductivity than aluminum, improving heat dissipation. Furthermore, the aluminum plate is 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.

[0030] Furthermore, the thickness t of the metal plate 4 is preferably 0.3 mm or more. A larger thickness t of the metal plate 4 can improve the current-carrying capacity and heat dissipation properties. The upper limit of the thickness t of the metal plate 4 is not particularly limited, but is preferably 3 mm or less. If the thickness t of the metal plate 4 is greater than 3 mm, it may be difficult to form an inclined portion on the side surface of the metal plate 4 by etching. For this reason, the thickness t of the metal plate 4 is preferably in the range of 0.3 mm or more and 3 mm or less, and more preferably 0.6 mm or more and 2 mm or less.

[0031] 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, and the thickness of the ceramic substrate 2 is preferably 0.2 mm to 3 mm.

[0032] The silicon nitride substrate serving as the ceramic substrate 2 preferably has a three-point bending strength of 600 MPa or more. It also preferably has a thermal conductivity of 80 W / m·K or more. By increasing the strength of the silicon nitride substrate, the substrate thickness can be reduced. Therefore, the silicon nitride substrate preferably has a three-point bending strength of 600 MPa or more, and more preferably 700 MPa or more. In the case of a silicon nitride substrate, the substrate thickness can be reduced to 2 mm or less, and even to 0.40 mm or less.

[0033] The aluminum nitride substrate serving as the ceramic substrate 2 has a three-point bending strength of approximately 300 to 450 MPa. On the other hand, the thermal conductivity of the aluminum nitride substrate is 160 W / m·K or more. Because the aluminum nitride substrate has low strength, the substrate thickness is preferably 0.60 mm or more.

[0034] An aluminum oxide substrate as the ceramic substrate 2 has a three-point bending strength of about 300 to 450 MPa but is inexpensive. An aluminium substrate has a high three-point bending strength of about 550 MPa but a thermal conductivity of about 30 to 50 W / m·K.

[0035] It is particularly preferable that the ceramic substrate 2 be a silicon nitride substrate. This is because a silicon nitride substrate has high strength and can withstand the thermal contraction of the molding resin. Furthermore, by using a silicon nitride substrate with a thermal conductivity of 80 W / m·K or more, heat dissipation can be improved.

[0036] The bonding layer 3 is preferably an active metal bonding layer. When the metal plate 4 is a copper plate, the bonding layer 3 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).

[0037] The composition of the active metal brazing material containing either 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 80 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.

[0038] If necessary, the active metal brazing material may contain one or both of Sn (tin) and In (indium) 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.

[0039] The composition ratio of the active metal brazing material 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 total weight of the active metal brazing material 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.

[0040] 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 joining layer by reacting with other components. For this reason, 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.

[0041] 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.

[0042] When the metal plate 4 is an aluminum plate, the bonding layer is preferably an active metal bonding layer containing Al as a main component. The active metal may be one or more selected from silicon (Si) and magnesium (Mg).

[0043] The active metal brazing filler metal containing Al as a main component is preferably an Al-Si or Al-Mg brazing filler metal, and the content of one or both of Si and Mg in the active metal brazing filler metal is preferably in the range of 0.1 mass % to 20 mass %.

[0044] The first metal layer 5 preferably contains one selected from Ni, Pd, Au, and Cu as a main component. The first metal layer 5 is preferably a plated layer. Ni plating also includes Ni-P plating. The first metal layer 5 may have a multilayer structure. Examples of the multilayer structure include NiP / Au, Ni-P / Pd / Au, and Ni / Au. Examples of the multilayer structure include those obtained by performing the respective plating processes. When the first metal layer 5 is a plated film, it may also be referred to as a first plated layer.

[0045] The second metal layer 6 preferably has a different main component from the first metal layer 5 and is primarily composed of one selected from Ag, Co, Ni, Pd, Au, and Cu. The second metal layer 6 is preferably a plated layer. Ni plating also includes Ni-P plating. Co plating also includes Co-P plating and Co-W-P plating. The second metal layer 6 may have a multilayer structure. Examples of multilayer structures include Ni-P / Ag, Ni-P / Au, Ni-P / Pd / Au, and Ni / Au. Examples of multilayer structures include those obtained by performing the respective plating processes. When the second metal layer 6 is a plated film, it is sometimes referred to as a second plated layer.

[0046] The first metal layer 5 is preferably used for solder bonding or ultrasonic bonding. The second metal layer 6 is preferably used for Ag sinter bonding or Cu sinter bonding. When the metal plate 4 is a copper plate, Cu sinter bonding may be performed by directly bonding to the copper plate surface without using a plating layer.

[0047] When the metal plate 4 is a copper plate and Ag sinter bonding is used, it is preferable that the first metal layer 5 is Ni-plated and the second metal layer 6 is Ag-plated. It is also preferable to overlay the second metal layer 6, an Ag-plated layer, on the first metal layer 5, a Ni-plated layer. Applying Ag plating directly to the copper plate surface can cause the copper plate surface to become rough and pits to form. Pits are particularly likely to form when the Ag-plated layer is applied by displacement plating. Electroless plating includes displacement plating and reduction plating. Displacement plating utilizes the difference in ionization tendencies of metals. Displacement plating is a relationship in which the metal on the plated surface is more likely to ionize than the metal being plated. When displacement Ag plating is performed on the copper plate surface, the ionization tendency is Cu > Ag, which facilitates the formation of Cu ions. This facilitates the formation of pits on the copper plate surface. Pits are small irregularities formed on the copper plate surface. For this reason, it is preferable to apply an Ag-plated layer (second plating layer) on a Ni-plated layer (first plating layer).

[0048] The thicknesses of the first metal layer 5 and the second metal layer 6 are not particularly limited, but are preferably within the following thickness ranges. The thickness of the first metal layer 5 is preferably within the range of 0.01 μm or more and 7 μm or less. The thickness of the second metal layer 6 is preferably within the range of 0.01 μm or more and 5 μm or less. As mentioned above, if Ag plating is directly provided on the surface of a copper plate as the metal plate 4, pits may be formed on the surface of the copper plate. By making the Ag plating layer thicker, the effect of pits on the surface of the copper plate can be mitigated.

[0049] If the thickness of the first metal layer 5 is less than 0.01 μm, the effect as a bonding layer may be insufficient. Furthermore, if the thickness of the first metal layer 5 exceeds 7 μm, not only will the effect not be further improved, but warping may also result in increased costs. Therefore, the thickness of the first metal layer 5 is preferably in the range of 0.01 μm to 7 μm, and more preferably in the range of 0.2 μm to 5 μm.

[0050] If the thickness of the second metal layer 6 is less than 0.01 μm, the effect as a bonding layer may be insufficient. Furthermore, if the thickness of the second metal layer 6 exceeds 5 μm, not only will the effect not be further improved, but warping may also result in increased costs. Therefore, the thickness of the second metal layer 6 is preferably in the range of 0.01 μm to 5 μm, and more preferably in the range of 0.2 μm to 3 μm.

[0051] The laminated structure is effective when a material that reacts with the metal plate 4 is selected for the second metal layer 6. For example, when an Ag-plated layer is provided as the second metal layer 6 on a copper plate serving as the metal plate 4, there is a possibility that Cu and Ag will react and form an alloy. This alloying may reduce the effectiveness of the Ag-plated layer. By providing a Ni-plated layer between the copper plate and the Ag-plated layer, it is possible to prevent the Ag-plated layer from reacting with the copper plate. For this reason, when the second metal layer 6 and the metal plate 4 react with each other, it is preferable to use a laminated structure.

[0052] On the other hand, a coplanar structure is effective when utilizing the characteristics of the first metal layer 5 and the second metal layer 6. For example, a coplanar structure will be described below in which a Ni-plated layer as the first metal layer 5 and an Ag-plated layer as the second metal layer 6 are provided on a copper plate as the metal plate 4. In terms of thermal conductivity, Cu has a thermal conductivity of 413 W / m·K, Ag has a thermal conductivity of 429 W / m·K, and Ni has a thermal conductivity of 90 W / m·K. The Ni-plated layer has poorer heat dissipation properties than a copper plate or an Ag-plated layer. In a laminated structure in which an Ag-plated layer is provided on a Ni-plated layer, the Ni-plated layer may reduce heat dissipation properties. Therefore, a coplanar structure is preferable to utilize the heat dissipation properties of the Ag-plated layer.

[0053] When a back metal plate 14 is provided, one or both of a first metal layer and a second metal layer may be provided on the surface of the back metal plate 14. For example, the back metal plate 14 may be used as a heat sink. The heat sink is bonded to a mounting board (housing) or a heat sink. In this case, if bonding is performed via lead-free solder, it is preferable to provide a first metal layer. Furthermore, when the back metal plate 14 ceramic is used as a circuit board 1, it is preferable to provide a first metal layer 5 and a second metal layer 6, as with the metal plate 4. As with the bonding layer 3, the back surface bonding layer 13 preferably has a bonding layer protrusion portion 13A (shown in FIG. 4) that protrudes from the back surface edge of the metal plate 14. Furthermore, it is preferable that the side surface of the back surface metal plate 4 also has a sloped portion 14S (shown in FIG. 4) that widens from the front surface toward the back surface of the metal plate.

[0054] The ceramic circuit substrate 1 described above is suitable for a semiconductor device in which a semiconductor element is mounted on at least one of the first metal layer 5 and the second metal layer 6. FIG. 6 shows an example of a semiconductor device. In the figure, reference numeral 5 denotes the first metal layer, reference numeral 6 denotes the second metal layer, reference numeral 7 denotes the semiconductor device, reference numeral 8 denotes the semiconductor element, and reference numeral 9 denotes a copper lead frame (hereinafter referred to as "copper lead"). The semiconductor device 7 comprises the ceramic circuit substrate 1, the semiconductor element 8, and the copper lead 9. The ceramic circuit substrate 1 is exemplified by a metal layer consisting of only the first metal layer 5 (right side) and a laminated structure consisting of the first metal layer 5 and the second metal layer 6 (left side).

[0055] The ceramic circuit board 1 according to the embodiment includes metal layers 5 and 6 having different main components, allowing for a mounting method appropriate for each metal layer. The semiconductor element 8 is bonded to the metal layers 5 and 6 by solder bonding, sinter bonding (e.g., Ag sinter bonding and Cu sinter bonding), or ultrasonic bonding. For example, if the first metal layer 5 is to be soldered or ultrasonic bonded, the first metal layer 5 preferably contains one selected from Ni, Pd, Au, and Cu as its main component. Furthermore, if the second metal layer 6 is to be Ag sinter bonding or Cu sinter bonding, the second metal layer 6 preferably contains one selected from Ag, Co, Ni, Pd, Au, and Cu as its main component.

[0056] Examples of solder joints include lead-free solder. Lead-free solder is solder that does not contain lead. The typical composition of lead-free solder is specified in JIS-Z-3282 (2017). JIS-Z-3282 corresponds to ISO 9453. Many lead-free solders are primarily composed of Sn (tin). Sn readily reacts with Cu. If the metal plate 4 is a copper plate, the lead-free solder may react excessively with the copper plate, adversely affecting the copper plate. For example, the semiconductor element 8 may be mounted at an angle. For this reason, it is preferable to perform solder jointing via the first metal layer 5. Solder joints are used to join semiconductor elements 8, copper leads 9, metal terminals, etc. When combined with sintering joints, which will be described later, solder joints are preferably used to join elements that do not generate heat themselves, such as copper leads 9 or metal terminals.

[0057] Ultrasonic bonding is a bonding technique that involves applying ultrasonic waves to rub bonding surfaces together using ultrasonic vibrations. Ultrasonic bonding is used in wire bonding and other processes. Wire bonding is a method of forming wiring using wires (or ribbons) made of Cu, Al, Au, or other materials. Ball bonding is a method of melting the tip of a wire to form a ball and then connecting the wire using heat, ultrasonic waves, or pressure. Wedge bonding is a method of directly bonding the wire using ultrasonic waves or pressure without melting the tip. It is preferable that the first metal layer 5 be made of a material that has good bonding properties with wire bonding. A metal film containing a metal selected from Ni, Pd, Au, and Cu as its main component can improve bonding properties with wire bonding. From this perspective, when the first metal layer 5 is used as the location for solder bonding or ultrasonic bonding, it is preferable that the first metal layer 5 be made of a metal selected from Ni, Pd, Au, and Cu as its main component. Wire bonding also does not generate heat by itself.

[0058] Sinter bonding is a bonding method that uses sintering by heating. The method using Ag particles is called Ag sinter bonding. The method using Cu particles is called Cu sinter bonding. The particles used in sinter bonding are fine particles of 10 μm or less. For example, nanoparticle sinter bonding uses particles with an average particle size of 3 nm to 100 nm. Furthermore, particles with various particle sizes can be used in sinter bonding. Furthermore, metal compound particles such as metal oxide particles can be used in addition to metal particles.

[0059] Ag sinter bonding or Cu sinter bonding can be performed at temperatures of approximately 180°C or higher and 340°C or lower. Once bonded by metal bonding, unlike solder layers, they do not remelt at approximately 300°C. This makes them suitable for mounting semiconductor elements with heat generation temperatures of 200°C or higher. For this reason, when performing Ag sinter bonding or Cu sinter bonding, it is preferable that the second metal layer 6 contains one selected from Ag, Co, Ni, Pd, Au, and Cu as its main component. In particular, when performing Ag sinter bonding, it is preferable that the second metal layer 6 be an Ag plated layer, and when performing Cu sinter bonding, it is preferable that the second metal layer 6 be a Cu plated layer.

[0060] The semiconductor device 7 according to the embodiment has metal layers with different main components provided to match the mounted components. This allows the mounted components to have high bonding strength. As a result, a highly reliable semiconductor device 7 can be provided.

[0061] Next, a method for manufacturing the ceramic circuit board 1 according to the embodiment will be described. The method for manufacturing the ceramic circuit board 1 according to the embodiment is not limited as long as it has the above-described configuration, but the method for obtaining the ceramic circuit board 1 with a good yield is as follows.

[0062] The manufacturing method of the ceramic circuit board 1 according to the embodiment is characterized by comprising the steps of forming a first metal layer 5 on the surface of the metal plate 4 (including the side surfaces, eliminating the need for a mask) of a bonded body in which a ceramic substrate 2 and a metal plate 4 are bonded via a bonding layer 3; forming a resist film on a portion of the first metal layer 5; providing a second metal layer 6 on the first metal layer portion 5A (shown in FIG. 7(C)) of the first metal layer 5 on which the resist film is not provided; and etching the first metal layer portion 5A, the metal plate 4, and the bonding layer 3.

[0063] Figure 7 shows an example of the configuration of a ceramic circuit substrate 1 in each manufacturing process. Figure 7 is a cross-sectional view taken along a plane perpendicular to the plane of the ceramic substrate 2. In the figure, reference numeral 2 denotes a ceramic substrate, reference numeral 3 denotes a bonding layer (front bonding layer), reference numeral 4 denotes a metal plate (front metal plate), reference numeral 5 denotes a first metal layer, reference numeral 6 denotes a second metal layer, reference numeral 13 denotes a bonding layer (rear bonding layer), reference numeral 14 denotes a metal plate (rear metal plate), reference numeral 10 denotes a resist film, and reference numeral 20 denotes a bonded body. Figure 7 shows an example of the laminated structure and coplanar structure described above, in which a first metal layer 5 and a second metal layer 6 are laminated on a metal plate 4 using a laminated structure.

[0064] 7 shows an example in which a large bonded body 20 is used to produce a large number of ceramic circuit boards 1. The large bonded body 20 used to produce a large number of ceramic circuit boards 1 is sometimes called a master substrate. The master substrate is the bonded body 20 before a circuit pattern is imparted to the metal plate 4.

[0065] 7(A) shows a bonded body 20 in which a ceramic substrate 2 and a metal plate 4 are bonded via a bonding layer 3. The bonded body 20 is formed by bonding the ceramic substrate 2 and the metal plate 4 via the bonding layer 3, and bonding the ceramic substrate 2 and the back metal plate 14 via a bonding layer 13. The materials of the ceramic substrate 2, the bonding layers 3 and 13, and the metal plates 4 and 14 are as described above. As shown in FIG. 7(A), a metal plate having approximately the same length and width dimensions as the ceramic substrate 2 is called a solid metal plate.

[0066] FIG. 7B shows a state in which a first metal layer 5 is provided on at least the surface (e.g., the peripheral surface including the surface and side surfaces of the metal plate 4) of the bonded body 20. In FIG. 7B, the first metal layer 5 is provided on the surface and side surfaces of the metal plate 4 so as to cover the exposed portions of the metal plate 4 and the bonding layer 3. With this method, it is not necessary to apply a material that will become the resist 10 to the metal plate 4 in advance. In other words, if a master substrate is used, the step of providing the first metal layer 5 can be performed before the etching step for imparting the circuit shape. Furthermore, by providing the first metal layer 5 on the side surfaces of the metal plate 4 as well, the step of providing a mask material can be eliminated. Note that, if necessary, resist may be applied in advance to areas where the first metal layer 5 is not desired.

[0067] The step of providing the first metal layer 5 may be a plating process. The plating process is preferably either electrolytic plating or electroless plating.

[0068] Electrolytic plating is a plating method that uses a solution containing ions of the metal to be plated and electrodes. Usually, the material to be plated is the anode and the product is the cathode, and when an electric current is passed through the material, the metal ions move from the anode to the cathode, depositing a plating on the surface of the product. On the other hand, electroless plating is a plating method in which the product to be plated is immersed in a solution containing ions of the metal to be plated, and a chemical reaction is used to plate the product. Electroless plating is sometimes called "chemical plating."

[0069] In the state of the master substrate before the circuit shape is imparted by the etching process, there is only one metal plate 4 bonded to one surface of the ceramic substrate 2. Therefore, only one power supply electrode is required for electrolytic plating. For example, in the case of a master substrate in which one metal plate 4, 14 is bonded to each of the front and back surfaces of the ceramic substrate 2, two power supply electrodes are required in total, one on each surface. In the case of a ceramic substrate in which multiple circuits (metal plates 4) are bonded to the surface of the ceramic substrate 2, power must be supplied to each circuit, which requires a complex power supply jig. For this reason, a method of providing the first metal layer 5 on the master substrate by electrolytic plating is preferred.

[0070] On the other hand, electroless plating does not require a power supply and is therefore easy to form a film in a complex shape. For example, electrolytic plating is effective when a plating film is provided on the bonded body 20 before a pattern shape is provided on the metal sheet 4. Electroless plating is also effective when a plating film is provided after a pattern shape is provided on the metal sheet 4. Other metal layer formation methods include sputtering.

[0071] 7(C) shows a state in which a resist film 10 has been formed on a portion of the first metal layer 5. The resist film 10 is provided in areas where the second metal layer 6 is not desired (including the aforementioned peripheral region 4B and areas to be removed in a later process). The resist film 10 is provided at least 50 μm inward from the upper end of the metal plate 4. By controlling the position where the resist film 10 is provided, it becomes easier to obtain a structure in which the first metal layer and the second metal layer are laminated only in the aforementioned effective region 4A. Furthermore, when the first metal layer 5 and the second metal layer 6 are plated films, the resist film 10 becomes a plated resist film.

[0072] FIG. 7(D) shows a state in which a second metal layer 6 is provided on a first metal layer portion 5A (shown in FIG. 7(C)) of the first metal layer 5 where no resist film 10 is provided. FIG. 7(D) illustrates a structure in which a second metal layer 6 is provided between metal resist films 10. The second metal layer 6 may be attached to the first metal layer 5 on the side surface of the metal plate 4. The second metal layer 6 may be formed by either electrolytic plating or electroless plating. Electrolytic plating can be used before a circuit shape is imparted to the metal plate 4. Using electrolytic plating has cost advantages.

[0073] 7(E) shows a process of processing the metal plate 4 provided with the first metal layer 5 and the second metal layer 6 to form an inclined portion 4S on the side of the metal plate 4 and a bonding layer protrusion portion 3A in the bonding layer 3. The metal plate 4 is preferably processed using an etching process. The first metal layer 5 (and the second metal layer 6) formed on the side of the metal plate 4 and the side of the metal plate 4 are removed by the etching process. The process of etching the side of the metal plate 4 results in a structure in which the first metal layer 5 and the second metal layer 6 are present only in the effective region 4A of the metal plate 4. In other words, the peripheral region 4B of the metal plate 4 does not have the first metal layer 5 and the second metal layer 6.

[0074] When the second metal layer 6 is not provided on the side surface of the metal plate 4, a process of etching the first metal layer 5, the metal plate 4, and the bonding layer 3 where the second metal layer 6 is not provided is performed. The back metal plate 14 is also etched and processed into a back copper plate 14 to form individual ceramic circuit boards 1. An inclined portion 14S is formed in the back metal plate 14, and a bonding layer protrusion portion 3A is formed in the bonding layer 3.

[0075] 7(F) shows the state after the resist film 10 has been removed. A process of dividing the substrate into individual ceramic circuit substrates 1 is then carried out (FIG. 7(F) shows two separate substrates, one on the left and one on the right). A method of dividing the substrate by laser scribing can be used. This process allows the production of a ceramic circuit substrate 1 having a second metal layer 6 on a first metal layer 5. It is also possible to produce a ceramic circuit substrate 1 having inclined portions 4S, 14S on the side surfaces of the metal plates 4, 14, and in which the first metal layer 5 or the second metal layer 6 is not formed on the protruding portions 3A, 13A of the bonding layer.

[0076] 7 shows an example in which a master substrate is used. If there are multiple metal plates 4, the same process is performed on each of them before providing the first metal layer 5. Furthermore, if necessary, the back metal plate 14 is also subjected to the etching process.

[0077] The above manufacturing method eliminates the need for a plating process after the etching process for forming the inclined portions 4S, 14S on the side surfaces of the metal plates 4, 14 or the etching process for forming the bonding layer protrusion portion 3A. The plating process uses a plating solution. If the bonding layer protrusion portion 3A is an active metal bonding layer, it is easily damaged by the plating solution. Bonding layers 3 containing Ag or Cu as the main component are particularly susceptible to damage. Damage can result in the formation of pores in the bonding layer protrusion portion 3A or a reduction in the length or thickness of the bonding layer protrusion portion 3A. Furthermore, Ag or Cu eluted from the bonding layer protrusion portion 3A can adhere to the ceramic circuit substrate 1, potentially causing migration. Therefore, the manufacturing method for the ceramic circuit substrate 1 according to the embodiment is suitable for those having the bonding layer protrusion portion 3A.

[0078] 2 and 3 , when the first metal layer 5 and the second metal layer 6 are provided on the surface of the metal plate 4, the second metal layer 6 is provided after the first metal layer 5 is provided. Alternatively, the first metal layer 5 may be provided after the second metal layer 6 is provided. For example, a resist film is applied to the metal plate 4 in areas where the first metal layer 5 is not to be provided, and then the first metal layer is formed on the metal plate 4. Next, the applied resist film is removed, and then a resist film is applied to the metal plate 4 in areas where the second metal layer is not to be formed, and then the second metal layer 6 is formed on the metal plate 4. In this process, the first metal layer 5 and the second metal layer 6 can be provided on the surface of the metal plate 4.

[0079] Examples (Examples) (Examples 1 to 4, Comparative Examples 1 to 3) In Examples 1 to 4, a bonded body 20 was prepared in which a ceramic substrate 2 and a metal plate 4, 14 were bonded via a bonding layer 3, 13, and in which a silicon nitride substrate and a copper plate were bonded via an active metal bonding layer containing Ti. The bonded bodies 20 in Examples 1 to 4 were prepared by bonding copper plates to both sides of a silicon nitride substrate serving as the ceramic substrate 2. The sizes of the bonded bodies 20 in Examples 1 to 4 are shown in Table 1. Among Examples 1 to 4, Examples 1, 3, and 4 were master substrates for multiple production, and Example 2 was a ceramic circuit substrate 1 obtained by dividing the substrates into individual substrates and then plating them. As shown in Table 1, bonded bodies in Comparative Examples 1 and 3, which were fabricated under the same conditions as the bonded body 20 in Example 1, and a bonded body in Comparative Example 2, which was fabricated under the same conditions as the bonded body 20 in Example 2, were prepared.

[0080]

[0081] Next, a first metal layer 5 and a second metal layer 6 were provided (laminated structure or coplanar structure) on the front copper plate serving as the metal plate 4 provided in the bonded bodies 20 of Examples 1 to 4. The side surfaces of the metal plate 4 were then etched to form inclined portions 4S on the side surfaces of the metal plate 4 and to form bonding layer protrusions 3A in the bonding layer 3. The relationship between the expansion width h of the metal plate 4 and the thickness t of the metal plate satisfies the above formula (2). The same applies to the bonded bodies of Comparative Examples 1 and 3. For the bonding layer of Comparative Example 2, the side surfaces of the metal plate were etched to form inclined portions on the side surfaces of the metal plate and bonding layer protrusions in the bonding layer, respectively, and then the first metal layer and the second metal layer were formed.

[0082] The first metal layer 5 and the second metal layer 6 provided in the bonded body 20 according to Examples 1 to 4, and the first metal layer and the second metal layer provided in the bonding layer according to Comparative Examples 1 to 3, were formed by plating. The first metal layer 5 and the second metal layer 6 according to Examples 1, 3, and 4 were bonded using electrolytic plating. The first metal layer 5 and the second metal layer 6 according to Example 2, and the first metal layer and the second metal layer according to Comparative Examples 1 to 3, were bonded using electroless plating. Comparative Examples 1 to 3 have a structure in which a plating film is also provided in the peripheral region 4B.

[0083] Also shown are the materials and thicknesses of the first metal layer 5 and the second metal layer 6 provided in the bonded bodies 20 according to Examples 1 to 4, and the presence or absence of the first metal layer 5 and the second metal layer 6 in the peripheral region 4B. Similarly, also shown are the materials and thicknesses of the first metal layer and the second metal layer provided in the bonding layers according to Comparative Examples 1 to 3, and the presence or absence of the first metal layer and the second metal layer in the region corresponding to the peripheral region 4B.

[0084]

[0085] In Examples 1, 3, and 4, the second metal layer 6 was provided, followed by etching and dividing (dividing the master substrate), and in Example 2, the second metal layer 6 was provided, thereby producing a ceramic circuit substrate 1 including a first metal layer 5 and a second metal layer 6. In Comparative Examples 1 and 2, the first metal layer and the second metal layer were provided, followed by etching and dividing, and in Comparative Example 3, the first metal layer was provided, followed by etching and dividing, thereby producing a ceramic circuit substrate including a metal layer. Next, tests were conducted to measure durability (for example, TCT characteristics) and migration resistance characteristics for the ceramic circuit substrates 1 according to Examples 1 to 4 and the ceramic circuit substrates according to Comparative Examples 1 to 3.

[0086] The TCT characteristics were measured by checking whether or not there were any defects after 3000 cycles of -40°C x 30 minutes → room temperature x 10 minutes → 170°C x 30 minutes → room temperature x 10 minutes.

[0087] The migration resistance was evaluated by applying a voltage at high temperature and humidity and measuring the occurrence rate of Ag or Cu migration marks. The measurement device used was an electrochemical migration evaluation system manufactured by Espec Corporation. Measurement electrodes were placed on the front and back copper plates of the ceramic circuit boards 1 according to Examples 1 to 4 and the ceramic circuit boards according to Comparative Examples 1 to 3, and the measurement electrodes were sealed with a one-component silicone potting resin to prepare measurement samples. A DC voltage equivalent to approximately 1000 V / mm was applied between the measurement electrodes for 1000 hours in an environment of a temperature of 85°C and a humidity of 85%, and the insulation resistance was observed. ７ Ω or less is considered defective (there is a problem), and 10７ The ceramic circuit boards 1 according to Examples 1 to 4 and the ceramic circuit boards according to Comparative Examples 1 to 3 were all 10 ７ It was confirmed that it exceeded Ω.

[0088] The TCT test and migration test were performed on 10 ceramic circuit boards 1 corresponding to each of Examples 1 to 4, and on 10 ceramic circuit boards corresponding to each of Comparative Examples 1 to 3. If even one of the 10 ceramic circuit boards 1 corresponding to each Example or the 10 ceramic circuit boards corresponding to each of Comparative Examples experienced a defect, the result was rated as "yes," and if no defect occurred, the result was rated as "no." The results are shown in Table 3.

[0089]

[0090] As can be seen from Table 3, in the ceramic circuit boards 1 according to Examples 1 to 4, regardless of the arrangement structure, no defects occurred after the TCT test or defects due to migration, and the durability and migration resistance characteristics were good.

[0091] In contrast, the ceramic circuit boards according to Comparative Examples 1 to 3 experienced both defects after the TCT test and defects due to migration. In Comparative Examples 1 to 3, plating was performed after the protruding portion of the bonding layer was formed. In Comparative Examples 1 to 3, the protruding portion of the bonding layer was damaged by the plating solution, and pores were observed in the protruding portion of the bonding layer. For this reason, it is believed that the deterioration of the TCT characteristics and migration occurred in Comparative Examples 1 to 3.

[0092] Next, copper leads 9 were mounted using lead-free solder on the first metal layer (first plating layer) 5 of the ceramic circuit board 1 according to Examples 1 to 4 (see the first metal layer 5 on the right side of FIG. 5). Furthermore, a semiconductor element 8 was mounted using Ag sinter bonding on the second metal layer (second plating layer) 6 provided on the first metal layer 5 (see the first metal layer 5 on the left side of FIG. 5). Through this process, a semiconductor device 7 was fabricated.

[0093] In fabricating the semiconductor devices 7 according to Examples 1 to 4, the positioning of the copper leads 9 and the semiconductor element 8 was measured. The positioning was measured using a CCD camera to detect the position. The occurrence of misalignment of the copper leads 9 or the semiconductor element 8 was examined. Semiconductor devices were similarly fabricated from the ceramic circuit substrates according to Comparative Examples 1 to 3, and the positioning of the copper leads 9 and the semiconductor element 8 was measured. The positioning test was conducted on 100 semiconductor devices 7 corresponding to each of Examples 1 to 4, and on 100 semiconductor devices corresponding to each of Comparative Examples 1 to 3. If even one of the 100 semiconductor devices 7 corresponding to each Example or 100 semiconductor devices corresponding to each Comparative Example experienced misalignment, the result was rated "present." If no misalignment occurred, the result was rated "absent." The results are shown in Table 4.

[0094]

[0095] As can be seen from Table 4, no positioning problems occurred in the semiconductor devices 7 according to Examples 1 to 4. In contrast, problems occurred in some cases in the semiconductor devices according to Comparative Examples 1 to 3. When the plating film was formed up to the top edge of the copper plate, visibility was reduced, resulting in misalignment. Furthermore, in the semiconductor device according to Comparative Example 3, Ag sinter-bonding could not be achieved successfully with only Ni plating of the first metal layer.

[0096] From the above, the ceramic circuit board 1 according to the example has good durability (for example, TCT characteristics) and migration resistance, and also has good positioning properties in the semiconductor device 7 manufactured from the ceramic circuit board 1. Furthermore, the use of the first metal layer 5 and the second metal layer 6 in the ceramic circuit board 1 allows the use of an appropriate mounting method.

[0097] 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. Modifications of these embodiments 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 in which a ceramic substrate and a metal plate are bonded via a bonding layer, wherein the bonding layer has a bonding layer protruding portion that protrudes beyond the back edge of the metal plate, the side of the metal plate has a sloping portion that widens from the front surface toward the back surface of the metal plate, at least the front surface of the metal plate has a first metal layer and a second metal layer that has a different main component from the first metal layer, and the first metal layer and the second metal layer are only present in an effective area of ​​the surface of the metal plate that is at least 50 μm inward from the front edge of the metal plate.

2. The ceramic circuit board according to claim 1, wherein the second metal layer is superimposed on the first metal layer.

3. A ceramic circuit board according to claim 1 or 2, characterized in that the first metal layer has one selected from Ni, Pd, Au, and Cu as its main component, and the second metal layer has one selected from Ag, Co, Ni, Pd, Au, and Cu as its main component.

4. A ceramic circuit board according to claim 1 or 2, characterized in that the metal plate is a copper plate, and the bonding layer is an active metal bonding layer containing either Ag or Cu as a main component.

5. The ceramic circuit board according to claim 3, wherein the metal plate is a copper plate, and the bonding layer is an active metal bonding layer containing either Ag or Cu as a main component.

6. The ceramic circuit board according to claim 1, wherein the width of the inclined portion of said metal plate is not more than half the thickness of said metal plate.

7. A semiconductor device comprising: the ceramic circuit board according to claim 1; and a semiconductor element mounted on at least one of the first metal layer and the second metal layer of the ceramic circuit board.

8. A semiconductor device comprising: the ceramic circuit board according to claim 5; and a semiconductor element mounted on at least one of the first metal layer and the second metal layer of the ceramic circuit board.

9. The semiconductor device according to claim 7, wherein the semiconductor element is bonded by any one of solder bonding, Ag sintered bonding layer, Cu sintered bonding, and ultrasonic bonding.

10. The semiconductor device according to claim 8, wherein the semiconductor element is bonded by any one of solder bonding, Ag sintered bonding layer, Cu sintered bonding, and ultrasonic bonding.

11. A method for manufacturing a ceramic circuit board, comprising the steps of: forming a first metal layer on the surface of a metal plate in a bonded assembly in which a ceramic substrate and a metal plate are bonded via a bonding layer; forming a resist film on a portion of the first metal layer; providing a second metal layer on a portion of the first metal layer on which the resist film is not formed; and etching the first metal layer portion, the metal plate, and the bonding layer.

12. The method for manufacturing a ceramic circuit board according to claim 11, wherein the step of providing the first metal layer and the step of providing the second metal layer are steps of providing plating.

13. A method for manufacturing a ceramic circuit board according to claim 11 or 12, characterized in that the first metal layer has one selected from Ni, Pd, Au, and Cu as its main component, and the second metal layer has one selected from Ag, Co, Ni, Pd, Au, and Cu as its main component.

14. A method for manufacturing a ceramic circuit board as described in claim 11 or claim 12, characterized in that the ceramic circuit board obtained by the etching process has a protruding portion of the bonding layer that protrudes from the back edge of the metal plate, and the side surface of the metal plate is inclined so as to widen toward the bonding layer.

15. A method for manufacturing a ceramic circuit board as described in claim 11 or claim 12, characterized in that the ceramic circuit board obtained by the etching process has the first metal layer only on an effective area of ​​the surface of the metal plate that is at least 50 μm inward from the edge of the surface of the metal plate.

16. A method for manufacturing a ceramic circuit board as described in claim 14, characterized in that the ceramic circuit board obtained by the etching process has the first metal layer only on an effective area of ​​the surface of the metal plate that is at least 50 μm inward from the edge of the surface of the metal plate.

17. A method for manufacturing a ceramic circuit board according to claim 11 or 12, characterized in that the metal plate is a copper plate, and the bonding layer is an active metal bonding layer containing either Ag or Cu as a main component.

18. The method for manufacturing a ceramic circuit board according to claim 16, wherein the metal plate is a copper plate, and the bonding layer is an active metal bonding layer containing either Ag or Cu as a main component.

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