Ceramic circuit board and method for manufacturing same

Abstract

A ceramic circuit board according to an embodiment of the present invention comprises a ceramic substrate and a metal circuit. The metal circuit is bonded to a first surface of the ceramic substrate via an active metal brazing material layer. The thickness of the metal circuit is 1 mm or more. The metal circuit has a through hole penetrating the metal circuit along a first direction perpendicular to the first surface. A section of the first surface overlaps the through hole in the first direction. The active metal brazing material layer is provided on the aforementioned section of the first surface.

Description

Ceramic circuit board and manufacturing method thereof

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

[0002] Ceramic circuit substrates are used in semiconductor devices equipped with semiconductor elements such as power elements. The ceramic substrate and metal circuit section are bonded to each other via a bonding layer using a brazing material or the like. This improves bonding strength and heat cycle characteristics. As reliability improves, ceramic circuit substrates are used in automobiles (including electric vehicles), electric railway vehicles, solar power generation facilities, inverters for industrial machinery, and the like. In semiconductor devices such as power modules, semiconductor elements are mounted on the circuit section. Wire bonding or metal terminals may also be bonded to the circuit section for electrical continuity of the semiconductor elements. In the manufacture of semiconductor devices, semiconductor elements, wire bonding, metal terminals, etc. are bonded to the circuit section.

[0003] With the advent of power semiconductors such as SiC and GaN, there are now more cases where larger amounts of electricity are conducted to metal circuits than before. Thin wire bonding does not provide sufficient electrical capacity. Therefore, metal lead frames are used to electrically connect the metal circuit to external devices. Furthermore, when a large current flows through the metal circuit, heat is generated in the semiconductor element. To improve heat dissipation, metal circuits tend to be thicker and ceramic substrates tend to be thinner. Furthermore, as power modules become smaller, lighter, and more densely packed, ceramic substrates tend to become thinner and metal circuits tend to become thicker.

[0004] Ceramic circuit boards may include a metal lead frame. A ceramic circuit board including a metal lead frame may be configured as part of a semiconductor device. In this case, the ceramic circuit board can transmit and receive electrical signals to and from an external device via the metal lead frame. In some cases, pin-shaped metal lead frames are used instead of flat, plate-shaped metal lead frames. Patent Document 1 discloses a method of forming holes in a metal member and bonding a pin-shaped lead frame into the holes. According to Patent Document 1, a backing plate with vias is bonded to a sapphire detection diaphragm by bonding pads, thereby forming electrical leads.

[0005] Although not for the purpose of joining pin-shaped lead frames, ceramic circuit boards with holes formed in metal circuits have also been disclosed (Patent Documents 2 and 3). According to Patent Document 2, through-holes are formed by etching at the same time as the circuit section and heat dissipation section are formed. According to Patent Document 3, a copper plate with through-holes formed by punching is joined to a ceramic substrate by the DBC method.

[0006] JP-T-2006-529027 A JP-A-2013-175525 A JP-A-63-239964 A

[0007] In conventional metal circuit ceramic substrates, pattern circuits are formed by etching. For example, a brazing filler metal containing an active metal is printed on the ceramic substrate. A metal plate is placed on top of the brazing filler metal. The ceramic substrate and metal plate are heated to create a metal-bonded plate. A resist is then applied to the metal-bonded plate. The metal plate is etched using the resist as a mask to form a pattern on the metal plate.

[0008] When metal pins are provided on a ceramic circuit board, holes are formed in the metal circuit. A ceramic circuit board equipped with metal pins is manufactured by inserting the metal pins into the holes and fixing them. In this case, a method of forming holes for fixing the metal pins by etching is considered. However, if the thickness of the metal circuit exceeds 1 mm, it may be difficult to form holes that penetrate the metal circuit by etching. For this reason, in the past, holes that do not completely penetrate the metal circuit were formed, and the metal pins were bonded inside these holes. However, if the holes are shallow, the bonding area between the metal circuit and the metal pins is small, and the metal pins may not be sufficiently fixed.

[0009] The embodiments are intended to solve such problems, and have an object to provide a ceramic circuit board that enables improvement in the bonding strength between the metal circuit and the metal pin.

[0010] A ceramic circuit board according to an embodiment includes a ceramic substrate and a metal circuit. The metal circuit is joined to a first surface of the ceramic substrate via an active metal brazing material layer. The metal circuit has a thickness of 1 mm or more. The metal circuit has a through hole penetrating the metal circuit along a first direction perpendicular to the first surface. A portion of the first surface overlaps with the through hole in the first direction. The active metal brazing material layer is provided on the portion of the first surface.

[0011] 1. Side view showing an example of a ceramic circuit board according to an embodiment 2. Top view showing an example of a ceramic circuit board according to an embodiment 3. Cross-sectional view showing an enlarged metal pin bonded portion according to an embodiment 4. Cross-sectional view showing another example of a ceramic circuit board according to an embodiment 5. Plan view showing another example of a ceramic circuit board according to an embodiment 6. Flowchart showing an example of a manufacturing method of a ceramic circuit board according to an embodiment 7. Flowchart showing another example of a manufacturing method of a ceramic circuit board according to an embodiment 8. Cross-sectional view showing an enlarged metal pin bonded portion according to an embodiment 9. Cross-sectional view showing an enlarged metal pin bonded portion according to an embodiment 10. Cross-sectional view showing an enlarged metal pin bonded portion according to an embodiment 11. Cross-sectional view showing an enlarged metal pin bonded portion according to an embodiment 12. Cross-sectional view showing an enlarged metal pin bonded portion according to an embodiment

[0012] A ceramic circuit board according to an embodiment includes a ceramic substrate and a metal circuit. The metal circuit is joined to a first surface of the ceramic substrate via an active metal brazing material layer. The metal circuit has a thickness of 1 mm or more. The metal circuit has a through hole penetrating the metal circuit along a first direction perpendicular to the first surface. A portion of the first surface overlaps with the through hole in the first direction. The active metal brazing material layer is provided on the portion of the first surface.

[0013] 1 is a side view showing an example of a ceramic circuit board according to an embodiment, in which 1 is a ceramic circuit board, 2 is a ceramic substrate, 3 is a metal circuit, 4 is an active metal brazing material layer, and 5 is a metal heat sink.

[0014] The ceramic substrate 2 has an upper surface 2a (front surface, first surface) and a lower surface 2b (rear surface, second surface). The upper surface 2a and the lower surface 2b are substantially parallel. A metal circuit 3 is bonded to the upper surface 2a via an active metal brazing material layer 4. A metal heat sink 5 is bonded to the lower surface 2b via the active metal brazing material layer 4. The metal circuit 3 has a through hole 6 indicated by a dotted line. The through hole 6 penetrates the metal circuit 3 in a first direction d1 perpendicular to the upper surface 2a and the lower surface 2b. Here, the direction from the ceramic substrate 2 toward the metal circuit 3 is referred to as "up," and the direction from the ceramic substrate 2 toward the metal heat sink 5 is referred to as "down." These directions are based on the positional relationship between the ceramic substrate 2, the metal circuit 3, and the metal heat sink 5, and are unrelated to the direction of gravity.

[0015] In the example of FIG. 1 , multiple metal circuits 3 are bonded to the upper surface 2 a via multiple active metal brazing material layers 4. One metal heat sink 5 is bonded to the lower surface 2 b via one active metal brazing material layer 4. The structure of the ceramic circuit board 1 according to the embodiment is not limited to the example shown. For example, one metal circuit 3 or three or more metal circuits 3 may be bonded to the upper surface 2 a. The through holes 6 may be formed in each metal circuit 3, or may be formed in only some of the multiple metal circuits 3. Two or more through holes 6 may be formed in one metal circuit 3. Two or more metal heat sinks 5 may be bonded to the lower surface 2 b via two or more active metal brazing material layers 4. The metal heat sink 5 may have a circuit shape and be used as the metal circuit. In this case, the through holes 6 may be formed in the metal heat sink 5.

[0016] The ceramic substrate 2 is preferably one of a silicon nitride substrate, an aluminum nitride substrate, or an aluminum oxide substrate. An example of an aluminum oxide substrate is an Argil substrate. Argil is a sintered body composed of 20 to 80 wt % aluminum oxide and the remainder zirconium oxide. The three-point bending strength of an aluminum nitride substrate or an aluminum oxide substrate is approximately 300 to 450 MPa. The strength of an Argil substrate is also around 550 MPa. The three-point bending strength of a silicon nitride substrate is 600 MPa or more, and can be increased to 700 MPa or more. The thermal conductivity of a silicon nitride substrate is 50 W / m·K or more, and can be increased to 80 W / m·K or more. In recent years, silicon nitride substrates have emerged that combine both high strength and high thermal conductivity.

[0017] The thickness of the ceramic substrate 2 is preferably 0.7 mm or less. By making the ceramic substrate 2 thinner, the heat dissipation properties of the ceramic circuit board 1 are improved. "Thickness" refers to the dimension in the first direction d1. The ceramic substrate 2 may be a single plate or may have a three-dimensional structure (e.g., a multi-layer structure). There is no particular lower limit for the thickness, but it is preferably 0.1 mm or more. This is to ensure the electrical insulation of the ceramic substrate 2.

[0018] Silicon nitride substrates have high strength. Therefore, silicon nitride substrates can be made thin while maintaining the necessary strength. As a result, heat dissipation can be improved. For this reason, the ceramic substrate 2 is preferably a silicon nitride substrate. The thickness of the ceramic substrate 2 is preferably 0.635 mm or less, and more preferably 0.3 mm or less.

[0019] 2 is a plan view showing an example of a ceramic circuit board according to an embodiment. As shown in FIG. 2, a portion of the upper surface 2a overlaps with the through hole 6 in the first direction d1. In the ceramic circuit board 1, the active metal brazing material layer 4 is also provided on the portion of the upper surface 2a. For example, when the ceramic circuit board 1 is viewed from above, the active metal brazing material layer 4 can be seen at the bottom of the through hole 6.

[0020] FIG. 3 is an enlarged cross-sectional view showing the vicinity of the through hole. FIG. 3 corresponds to the A-A cross-sectional view of FIG. 2. As shown in FIG. 3, the through hole 6 includes a first end 6a located on the upper surface 3a of the metal circuit 3 and a second end 6b facing the active metal brazing material layer 4. The ratio (D2 / D1) of the dimension D2 of the second end 6b in the second direction d2 to the dimension D1 of the first end 6a in the second direction d2 is preferably greater than 1.00 and not greater than 1.10. The second direction d2 is perpendicular to the first direction d1. For example, the dimension of the through hole 6 in the second direction d2 gradually decreases with increasing distance from the ceramic substrate 2.

[0021] A metal pin can be inserted into the through hole 6. The inserted metal pin is bonded to the ceramic substrate 2 and the metal circuit 3. When the dimension D1 is larger than the dimension D2, the gap between the side surface of the through hole 6 and the metal pin at the second end 6b is larger than the gap between the side surface of the through hole 6 and the metal pin at the first end 6a. By increasing the gap at the second end 6b, the brazing material can easily enter the gap between the side surface of the through hole 6 and the metal pin. The volume of the brazing material disposed in the gap between the side surface of the through hole 6 and the metal pin can be increased, thereby increasing the bonding strength of the metal pin. Furthermore, the dimension D2 is preferably 1.10 times or less than the dimension D1 and is not too large compared to the dimension D1. By making the dimension D2 1.10 times or less than the dimension D1, the gap between the side surface of the through hole 6 and the metal pin can be reduced, making it easier to fix the metal pin. Furthermore, tilting of the metal pin with respect to the first direction d1 can be suppressed.

[0022] The dimensions D1 and D2 are measured in the following procedure. First, the ceramic circuit substrate 1 is cut approximately perpendicular to the upper surface 3a of the metal circuit 3. The cross section is photographed using an optical microscope or a scanning electron microscope (SEM). The obtained photograph is enlarged. The dimension near the upper surface 3a of the metal circuit 3 is measured as dimension D1. The dimension near the lower surface 3b of the metal circuit 3 is measured as dimension D2. The lower surface 3b is also the bonding surface with the active metal brazing material layer 4. The location for measuring dimension D1 is selected within a range from the upper surface 3a to within 5% of the thickness of the metal circuit 3. The location for measuring dimension D2 is selected within a range from the lower surface 3b to within 5% of the thickness of the metal circuit 3. In this case, the distance in the first direction d1 between the upper surface 3a and the measurement point of dimension D1 is set to be the same as the distance in the first direction d1 between the lower surface 3b and the measurement point of dimension D2.

[0023] The direction in which the dimensions D1 and D2 are measured can be selected arbitrarily as long as it is perpendicular to the first direction d1. For example, if the through hole 6 has an elliptical shape in a plan view, the ceramic circuit substrate 1 is cut in a direction passing through the center of the through hole 6 and parallel to the minor axis direction. If the through hole 6 has a polygonal shape in a plan view, the ceramic circuit substrate 1 is cut in a direction passing through the center of the through hole 6 and in which the dimension of the through hole 6 is shortest. For example, if the through hole 6 has a rectangular shape in a plan view, the ceramic circuit substrate 1 is cut in a direction passing through the center of the through hole 6 and parallel to the minor axis direction. The dimensions D1 and D2 are measured on the cut surface.

[0024] The metal circuit 3 can be formed by the following methods. In the first method, a metal circuit 3 with through holes 6 formed in advance is bonded to the ceramic substrate 2. In the second method, a metal plate is prepared in which a plurality of metal circuits 3 are integrated by bridges. Through holes 6 are formed in this metal plate, and the metal plate is bonded to the ceramic substrate 2. After bonding, the bridges are removed. To form the through holes, press work, electric discharge machining, or machining using a drill or the like can be used. At this time, it is preferable to adjust the ratio of dimension D2 to dimension D1 (D2 / D1) by cutting the second end 6b side.

[0025] In contrast, when forming the through hole 6 by etching the metal plate, dissolution of the metal plate proceeds along the crystal grain boundaries of the metal plate. Dissolution by etching proceeds not only in the thickness direction (first direction d1) but also in a planar direction parallel to the thickness direction. When etching a thick metal circuit 3, etching proceeds in the planar direction, causing side etching. Due to the side etching, the side surface of the through hole 6 is inclined with respect to the first direction d1. In other words, the dimension D1 becomes excessively large relative to the dimension D2. For this reason, from the viewpoint of controlling the ratio (D2 / D1), forming the through hole 6 using etching is not preferable.

[0026] When the ceramic circuit substrate 1 is used for applications such as a power module, a semiconductor element or the like is joined to the metal circuit 3. To reduce thermal resistance and inductance, the thickness of the metal circuit 3 is preferably 1.0 mm or more, more preferably 2.0 mm or more, and most preferably 3.0 mm or more.

[0027] The metal heat sink 5 is used as a heat dissipation member or is bonded to other components. To reduce thermal resistance, the thickness of the metal heat sink 5 is preferably 1.0 mm or more. The thickness of the metal heat sink 5 is more preferably 2.0 mm or more, and most preferably 3.0 mm or more. There are no particular limitations on the upper limit of the thickness of the metal circuit 3 or the metal heat sink 5, but both are preferably 10 mm or less. If the thickness of the metal circuit 3 or the metal heat sink 5 exceeds 10 mm, stress may concentrate at the bonding interface, potentially causing cracks in the ceramic substrate 2. This may make it difficult to make the ceramic substrate 2 thinner.

[0028] Fig. 4 is a cross-sectional view showing another example of a ceramic circuit board according to an embodiment. Fig. 5 is a plan view showing another example of a ceramic circuit board according to an embodiment. Fig. 4 corresponds to the B-B cross-sectional view of Fig. 5. In Fig. 4, 7 is a ceramic circuit board, and 8 is a metal pin. In the ceramic circuit board 7 shown in Figs. 4 and 5, the metal pin 8 is inserted into the through hole 6 of the metal circuit 3. The metal pin 8 is joined to the ceramic substrate 2 via the active metal brazing material layer 4.

[0029] The metal circuit 3, the metal heat sink 5, and the metal pins 8 preferably contain copper or a copper alloy. Copper and copper alloys have high electrical conductivity and are excellent materials for electrical circuits. Copper and copper alloys also have high thermal conductivity and can improve the heat dissipation of the mounted semiconductor element.

[0030] The shape of the metal pin 8 is, for example, a cylinder or a rectangular prism. When the metal pin 8 is a cylinder, the cross-sectional shape of the metal pin 8 perpendicular to the first direction d1 is a circle or an ellipse. When the metal pin 8 is a rectangular prism, the cross-sectional shape of the metal pin 8 perpendicular to the first direction d1 is a polygon. As described above, the shape of the through hole 6 in a plan view is circular, elliptical, or polygonal. The shape of the through hole 6 and the shape of the metal pin 8 in a plan view may be different. However, to facilitate insertion of the metal pin 8 into the through hole 6, it is preferable that the clearance between the through hole 6 and the metal pin 8 be uniform around the outer periphery of the metal pin 8. To increase the uniformity of the clearance, it is preferable that the shape of the insertion portion of the metal pin 8 be substantially the same as the shape of the through hole 6. For example, if the through hole 6 is circular in a plan view, it is preferable that the cross-sectional shape of the insertion portion of the metal pin 8 be circular.

[0031] The size of the metal pin 8 can be designed as appropriate as long as the metal pin 8 can be inserted into the through hole 6. The larger the ratio of the size of the metal pin 8 to the size of the through hole 6, the smaller the gap between the side surface of the through hole 6 and the metal pin 8. As a result, the bonding strength of the metal pin 8 can be improved. On the other hand, if the gap is small, it may be difficult to insert the metal pin 8. For example, the dimension of the inserted portion of the metal pin 8 in the second direction d2 is designed to be 0.7 to 0.98 times the dimension D1. The dimension of the inserted portion is preferably 0.75 to 0.97 times the dimension D1, more preferably 0.8 to 0.96 times the dimension D1, and most preferably 0.85 to 0.95 times the dimension D1.

[0032] The metal circuit 3 and the metal heat sink 5 are preferably joined to the ceramic substrate 2 via an active metal brazing layer 4. The active metal brazing layer 4 preferably contains at least one active metal selected from the group consisting of titanium (Ti), zirconium (Zr), hafnium (Hf), and niobium (Nb), and at least one active metal selected from the group consisting of silver (Ag), copper (Cu), tin (Sn), indium (In), zinc (Zr), aluminum (Al), silicon (Si), carbon (C), and magnesium (Mg).

[0033] When the metal circuit 3 and the metal heat sink 5 contain copper or a copper alloy, it is preferable to provide an active metal brazing material layer 4 containing copper and titanium between the ceramic substrate 2 and the metal circuit 3, and between the ceramic substrate 2 and the metal heat sink 5, respectively. The active metal brazing material layer 4 containing copper and titanium is formed by using an active metal brazing material containing copper and titanium for bonding. A mixture of titanium, copper, and silver may also be used as the active metal brazing material. For example, the titanium content is 0.1 to 10 wt %, the copper content is 10 to 60 wt %, and the remainder is silver. If necessary, 1 to 15 wt % of one or more elements selected from the group consisting of indium, tin, aluminum, silicon, carbon, and magnesium may be added.

[0034] In the active metal bonding method using an active metal brazing material, first, an active metal brazing material paste is applied to the upper surface 2a and lower surface 2b of the ceramic substrate 2. The metal circuit 3 and the metal heat sink 5 are placed on the active metal brazing material paste. The ceramic substrate 2, the metal circuit 3, and the metal heat sink 5 are heated to 600 to 900°C, thereby bonding the metal circuit 3 and the metal heat sink 5 to the ceramic substrate 2. According to the active metal bonding method, the bonding strength between the ceramic substrate 2 and the metal circuit 3 and the bonding strength between the ceramic substrate 2 and the metal heat sink 5 can be 50 MPa or more.

[0035] A metal thin film containing one selected from the group consisting of nickel (Ni), silver, and gold (Au) as its main component may be provided on the surface of the metal circuit 3. "Main component" refers to a component contained in an amount of 50% or more. The metal thin film is formed by plating or sputtering, for example. By providing a metal thin film, corrosion resistance, solder wettability, and the like can be improved.

[0036] In recent years, while semiconductor elements have become increasingly smaller, the amount of heat generated by them has increased. Therefore, improving heat dissipation has become important for ceramic circuit boards 1 on which semiconductor elements are mounted. Furthermore, to improve the performance of semiconductor devices (semiconductor modules), multiple semiconductor elements can be mounted on a single ceramic circuit board 1. When the temperature of a semiconductor element rises and exceeds its intrinsic temperature, the temperature parameter of the resistor becomes negative. As a result, thermal runaway occurs, causing current to flow intensively through the semiconductor element. Thermal runaway can instantly destroy the semiconductor device. When multiple semiconductor elements are mounted, it is necessary to prevent thermal runaway from occurring in each of the semiconductor elements. Therefore, improving the reliability of the bond between the semiconductor element and the metal circuit is extremely effective.

[0037] A semiconductor device using the ceramic circuit substrate 7 according to the embodiment can be used in PCU, IGBT, and IPM modules. PCU, IGBT, and IPM modules are used in inverters. Inverters are used in automobiles (including electric vehicles), electric railcars, industrial machinery, air conditioners, and the like. With regard to automobiles, electric vehicles are becoming increasingly popular. The more reliable the semiconductor device, the more safety the automobile can be improved. The same is true for electric railcars, industrial equipment, and the like.

[0038] According to the embodiment, the metal circuit 3 has a through hole 6, and the active metal brazing material layer 4 is also provided on the upper surface 2a of the ceramic substrate 2 in a portion overlapping with the through hole 6. The metal pin 8 inserted into the through hole 6 can be joined to the ceramic substrate 2 by the active metal brazing material. Therefore, the metal pin 8 can be firmly joined to the ceramic substrate 2.

[0039] For example, as a reference example, it is possible to join the metal pin 8 and the ceramic substrate 2 by a direct bonding method (DBC method) that does not use a brazing material. However, when using the DBC method, only the end face of the metal pin 8 is joined to the ceramic substrate 2, and therefore sufficient strength cannot be obtained. Depending on the joining position of the metal pin 8, the metal pin 8 may not come into contact with the side surface of the through hole, and the metal pin 8 may not be electrically connected to the metal circuit 3.

[0040] A method for manufacturing the ceramic circuit board according to the embodiment will now be described. The method for manufacturing the ceramic circuit board is not particularly limited as long as it has the above-described configuration. Here, an example of a method for obtaining the ceramic circuit board 7 with a high yield will be described.

[0041] 6 is a flowchart illustrating an example of a method for manufacturing a ceramic circuit board according to an embodiment. As shown in FIG. 6, a manufacturing method M1 according to an embodiment mainly includes printing and drying an active metal brazing material (step S11), arranging a metal circuit (step S12), arranging a metal heat sink (step S13), joining the metal circuit and the metal heat sink (step S14), inserting a metal pin (step S15), and joining the metal pin (step S16).

[0042] First, a ceramic substrate and a metal plate are prepared. The ceramic substrate is preferably one selected from an aluminum oxide substrate, an aluminum nitride substrate, and a silicon nitride substrate. In particular, considering the heat dissipation properties of the entire circuit board, the ceramic substrate is preferably a silicon nitride substrate having a thermal conductivity of 50 W / m·K or more and a three-point bending strength of 600 MPa or more. When the metal plate provided on the upper surface of the ceramic substrate is electrically connected to the metal plate provided on the lower surface via through holes, a ceramic substrate having through holes is prepared. When providing through holes in the ceramic substrate, the through holes may be provided in advance at the molded body stage. Alternatively, the through holes may be formed in the ceramic substrate (ceramic sintered body). The through holes are formed by laser processing, cutting processing, etc. Cutting processing is, for example, drilling using a drill or the like.

[0043] The material of the metal plate is preferably one selected from copper and copper alloys. The thickness of the metal plate is 1 mm or more. When etching is not used, it is preferable to use a metal plate processed into the shape of a metal circuit. When etching is used to form a metal circuit, it is preferable to use a metal plate with the same thickness as the metal circuit to be formed. The through holes in the metal circuit (metal plate) are formed by laser processing, cutting processing, etc. Cutting processing is, for example, drilling using a drill or the like.

[0044] The copper or copper alloy plate is preferably joined to the ceramic substrate by an active metal joining method. In the active metal joining method, an active metal brazing material containing a mixture of an active metal and copper is used. The active metal is preferably titanium. The active metal brazing material may be a mixture of titanium and copper, or a mixture of titanium, silver, and copper. For example, the active metal brazing material contains 0.1 to 10 wt % titanium, 10 to 60 wt % copper, and the remainder silver. If necessary, 1 to 15 wt % of one or more elements selected from the group consisting of indium, tin, aluminum, silicon, carbon, and magnesium may be added. The active metal brazing material components are mixed with an organic substance to form a paste. In the paste, the active metal brazing material components are preferably mixed uniformly. Non-uniform distribution of the active metal brazing material components results in unstable brazing, which can lead to poor joining.

[0045] In step S11, the active metal brazing paste is printed on the prepared ceramic substrate and dried. This produces a printed body on which the active metal brazing paste is printed. As shown in Figures 1 and 2, the active metal brazing paste is preferably printed over an area larger than the metal circuit. At this time, the active metal brazing paste is also printed on the upper surface 2a in the portion that is to overlap the through hole in the first direction d1.

[0046] In step S12, a metal circuit is placed on the upper surface of the ceramic substrate via an active metal brazing paste. In step S13, a metal heat sink is placed on the lower surface of the ceramic substrate via an active metal brazing paste. By placing the metal circuit and the metal heat sink, a laminate is produced. If a metal circuit is also placed on the lower surface, the metal circuit is placed instead of the metal heat sink.

[0047] In step S14, the laminate is heated to bond the metal circuit and the metal heat sink to the ceramic substrate. This produces a bonded assembly. When the metal circuit and the metal heat sink contain copper or a copper alloy, the laminate is heated at 700 to 900°C. The heating step is carried out in a vacuum or a non-oxidizing atmosphere as required. When carried out in a vacuum, the pressure is 1 x 10 －２ The pressure is preferably not more than 100 Pa. The non-oxidizing atmosphere is a nitrogen atmosphere, an argon atmosphere, or the like. By heating the laminate in a vacuum or a non-oxidizing atmosphere, oxidation of the bonding layer can be suppressed, thereby improving the bonding strength.

[0048] When the circuit is formed by etching, the metal plates are placed in step S12. After step S14, the joined metal plates are etched to form the circuit shape.

[0049] The above steps result in a ceramic circuit substrate that does not include metal pins. In this ceramic circuit substrate, the metal circuit has through holes that penetrate the metal circuit along the first direction d1. A portion of the upper surface of the ceramic substrate overlaps with the through holes in the first direction d1. An active metal brazing material layer is provided on the portion of the upper surface.

[0050] The method for manufacturing a ceramic circuit board according to the embodiment may include a step of joining a metal pin, as shown in FIG. 6 . In step S15, a metal pin is inserted into a through hole in the metal circuit. The tip of the inserted metal pin comes into contact with the active brazing metal material. The diameter of the metal pin is determined according to the shape of the through hole formed in the metal circuit. The metal pin has, for example, a slender columnar shape. If the clearance between the metal pin and the through hole is small, assembly is difficult. However, a brazing material layer is easily formed between the metal pin and the through hole, resulting in increased joint strength. If the clearance between the metal pin and the through hole is large, assembly is easy. However, a brazing material layer is less likely to form between the metal pin and the through hole, resulting in reduced joint strength.

[0051] In step S16, the bonded body and the metal pin are heated to bond the inserted metal pin to the ceramic substrate. If the metal pin contains copper or a copper alloy, the bonded body and the metal pin are heated to 700 to 900°C. The metal pin is bonded to the ceramic substrate, and the ceramic circuit board shown in Figures 4 and 5 is manufactured.

[0052] Fig. 7 is a flowchart showing another example of a method for manufacturing a ceramic circuit board according to an embodiment. Instead of the method shown in Fig. 6, a manufacturing method M2 shown in Fig. 7 may be performed. The manufacturing method M2 shown in Fig. 7 mainly includes printing and drying an active metal brazing material (step S21), arranging a metal circuit and metal pins (step S22), arranging a metal heat sink (step S23), and bonding (step S24).

[0053] First, a ceramic substrate and a metal plate are prepared, as in manufacturing method M1. In step S21, an active metal brazing paste is printed on the ceramic substrate and dried.

[0054] In step S22, a metal circuit and metal pins are placed on the upper surface of the ceramic substrate via an active metal brazing paste. In manufacturing method M1, the metal pins are placed after the metal circuits are joined. In contrast, in manufacturing method M2, the metal pins are placed before the metal circuits are joined. The metal circuit and metal pins may be placed at the same time. After the metal circuits are placed, the metal pins may be inserted into the through holes of the metal circuit and placed therein. In step S23, a metal heat sink is placed on the lower surface of the ceramic substrate via an active metal brazing paste. Steps S22 and S23 produce a laminate including metal pins.

[0055] In step S24, the laminate is heated to bond the metal circuit, the metal pins, and the metal heat sink to the ceramic substrate, thereby producing the ceramic circuit substrate shown in FIGS.

[0056] When etching a metal plate to form a metal circuit, manufacturing method M1 is preferable to manufacturing method M2. This is because the presence of metal pins during etching makes it difficult to etch the metal plate. Furthermore, manufacturing method M1 allows the metal circuit and metal pins to be individually aligned and positioned. Therefore, manufacturing method M1 improves the positional accuracy of the metal pins relative to the metal circuit compared to manufacturing method M2. On the other hand, manufacturing method M2 includes fewer steps than manufacturing method M1. For example, manufacturing method M2 requires only one heating step for bonding. Therefore, manufacturing method M2 can reduce costs compared to manufacturing method M1.

[0057] When manufacturing method M1 is performed, in step S14, the active metal brazing paste is melted by heating. The active metal brazing paste is then solidified by cooling to form an active metal brazing layer. A metal pin is placed on the active metal brazing layer. The melted and solidified active metal brazing layer is less soluble than the active metal brazing paste before melting. This may result in a decrease in the bonding strength between the ceramic substrate and the metal pin. To increase the bonding strength, methods include increasing the bonding temperature and adding a brazing material (e.g., silver brazing) to the bonding location of the metal pin. In manufacturing method M1, the bonding temperature in step S16 may be higher than the bonding temperature in step S14 to improve the bonding strength between the ceramic substrate and the metal pin. For example, the bonding temperature in step S16 is set to be 10° C. to 30° C. higher than the bonding temperature in step S14.

[0058] Increasing the joining temperature of the metal pin melts more of the active metal brazing material layer, contributing to the joining of the ceramic substrate and the metal pin. In the method of adding silver brazing material, for example, BAg-8 (72% silver, 28% copper) foil as specified in JIS Z 3261 can be used. The foil is placed at the bottom of the through-hole after the metal circuit and ceramic substrate are joined. The metal pin is placed on the ceramic substrate via the active metal brazing material layer and foil. By heating in this state, the foil melts in addition to the active metal brazing material layer. The metal pin is joined to the ceramic substrate by the active metal brazing material and foil. Hereinafter, the brazing material added to the active metal brazing material layer is also referred to as "supplementary brazing material."

[0059] 8 is an enlarged cross-sectional view showing an example of portion C in FIG. 4. In FIG. 8, 9 is a brazing filler metal layer. In the example shown in FIG. 8, the brazing filler metal layer 9 is part of the active metal brazing filler metal layer 4. When the metal pin 8 is joined, the active metal brazing filler metal melts. Part of the active metal brazing filler metal penetrates into the gap between the side surface of the through hole 6 and the metal pin 8. As a result, a brazing filler metal layer 9 is formed between the side surface of the through hole 6 and the metal pin 8 in a direction perpendicular to the first direction d1. The brazing filler metal layer 9 joins the metal pin 8 to the metal circuit 3. This improves the joining strength of the metal pin 8.

[0060] 9 is an enlarged cross-sectional view showing another example of portion C in FIG. 4 . In the example shown in FIG. 9 , the brazing material layer 9 is formed of a filler brazing material. By using the filler brazing material, the bonding area between the metal circuit 3 and the metal pin 8 is larger than in the example shown in FIG. 8 . Therefore, the bonding strength between the metal circuit 3 and the metal pin 8 can be further increased. For example, when BAg-8 foil is used as the filler brazing material, the mass percentage of silver in the brazing material layer 9 is greater than the mass percentage of silver in the active metal brazing material layer 4. The mass percentage of the active metal in the brazing material layer 9 is smaller than the mass percentage of the active metal in the active metal brazing material layer 4.

[0061] Fig. 10 is an enlarged cross-sectional view showing an example of portion D in Fig. 8. In Fig. 10, 8a is the tip of the metal pin 8. The position of the tip 8a in the first direction d1 is preferably approximately the same as the position of the lower surface 3b of the metal circuit 3 in the first direction d1. During joining, the active metal brazing material or the filler brazing material wets and spreads between the side surface of the through hole 6 and the metal pin 8. This joins the metal circuit 3 and the metal pin 8.

[0062] Capillary action occurs in the active metal brazing material or the filler brazing material. As a result, a portion of the brazing material layer 9 is lowered, as shown in FIG. 10 . As a specific example, one side of the brazing material layer 9 contacts the metal circuit 3. The other side of the brazing material layer 9 contacts the metal pin 8. The center of the brazing material layer 9 is located between the two side portions of the brazing material layer 9. The upper end of the center of the brazing material layer 9 is located lower than the upper ends of the two side portions of the brazing material layer 9.

[0063] The distance in the first direction d1 from the lower surface 3b of the metal circuit 3 to the upper end of the central portion of the brazing filler metal layer 9 is defined as the height H. The height H is preferably greater than 0 mm and equal to or less than the dimension of the through hole 6 in the first direction d1. That is, the upper end of the brazing filler metal layer 9 is preferably located between the lower and upper ends of the through hole 6. The dimension of the through hole 6 in the first direction d1 is, in other words, the thickness of the metal circuit 3 in the first direction d1. If the heating temperature during joining is low, the active metal brazing filler metal does not sufficiently wet and spread within the through hole 6. If the heating temperature during joining is low and no filler brazing filler metal is used, the brazing filler metal layer 9 is not formed between the side surface of the through hole 6 and the metal pin 8, and sufficient joint strength is not obtained. If the height H is greater than 0 mm and the brazing filler metal layer 9 is formed between the side surface of the through hole 6 and the metal pin 8, the joint strength between the metal circuit 3 and the metal pin 8 can be improved. The height H is preferably equal to or greater than 6% of the thickness of the metal circuit 3. The height H is more preferably 10% or more of the thickness, and most preferably 20% or more. The greater the height H, the more the bonding strength can be improved. From the viewpoint of bonding strength, the height H is preferably 100%. On the other hand, if the height H exceeds the dimension of the through hole 6, the active metal brazing material or the filler brazing material will wet and spread over the upper surface 3a of the metal circuit 3. This will hinder bonding of the semiconductor element in a subsequent process. Considering variations in the height H, the height H may be 95% or less of the thickness of the metal circuit 3, 90% or less of the thickness, or 85% or less of the thickness.

[0064] 11 is an enlarged cross-sectional view showing another example of portion D in FIG. 8. The ratio of dimension D2 to dimension D1 (D2 / D1) affects height H. FIG. 11 shows an example in which dimension D1 is smaller than dimension D2. That is, the ratio of D2 to D1 (D2 / D1) is greater than 1.00.

[0065] During joining, the active metal brazing material or the filler brazing material wets and spreads over the side surfaces of the through hole 6 and the metal pin 8. When the ratio (D2 / D1) is greater than 1.00, the gap between the side surface of the through hole 6 and the metal pin 8 narrows upward. That is, the gap becomes more easily filled with the active metal brazing material or the filler brazing material as it goes upward. The height H tends to increase, and the metal circuit 3 and the metal pin 8 can be joined more firmly.

[0066] FIG. 12 is an enlarged cross-sectional view showing a portion of a ceramic circuit board according to a reference example. FIG. 12 illustrates an example in which dimension D1 is larger than dimension D2. That is, the ratio of D2 to D1 (D2 / D1) is less than 1.00. In the example shown in FIG. 12 , the gap between the side surface of the through hole 6 and the metal pin 8 widens upward. When the brazing filler metal spreads between the side surface of the through hole 6 and the metal pin 8, the gap is less likely to be filled with the brazing filler metal. For example, as shown in FIG. 12 , the brazing filler metal may spread over the side surfaces of the through hole 6 and the metal pin 8, but the gap may not be filled. The portion of the brazing filler metal that spreads over the side surfaces of the through hole 6 and the metal pin 8 does not contribute much to the bond strength between the metal circuit 3 and the metal pin 8. That is, the height H has a greater effect on the bond strength. In the example shown in FIG. 12 , the brazing filler metal spreads over the side surfaces of the through hole 6 and the metal pin 8, but the height H is small. Therefore, if the ratio (D2 / D1) is less than 1.00, the bonding strength between the metal circuit 3 and the metal pin 8 is likely to decrease.

[0067] Therefore, it is preferable that the ratio of the dimension D2 to the dimension D1 (D2 / D1) is greater than 1.00. If D2 / D1 is greater than 1.00, the height H that contributes to the joining can be increased as shown in FIG.

[0068] On the other hand, if D2 / D1 is greater than 1.10, the gap between the side surface of the through hole 6 and the metal pin 8 at the second end 6b becomes larger. A larger amount of brazing material is required to fill the gap. As a result, the height H is more likely to decrease. Therefore, the ratio (D2 / D1) is preferably greater than 1.00 and not greater than 1.10. The ratio (D2 / D1) is more preferably 1.01 or greater and 1.09 or less, and even more preferably 1.02 or greater and 1.08 or less.

[0069] FIG. 13 is an enlarged cross-sectional view showing another example of a ceramic circuit board according to an embodiment. The gap between the side surface of the through hole 6 and the metal pin 8 may be adjusted by the ratio (D2 / D1) as shown in FIG. 11 . Alternatively, as shown in FIG. 13 , the gap between the side surface of the through hole 6 and the metal pin 8 may be adjusted by the shape of the metal pin 8. In FIG. 13 , the dimension of the metal pin 8 in the second direction d2 decreases downward. For example, the dimension of the metal pin 8 in the second direction d2 at the second end 6b is smaller than the dimension of the metal pin 8 in the second direction d2 at the first end 6a. Therefore, the gap between the side surface of the through hole 6 and the metal pin 8 at the first end 6a is smaller than the gap between the side surface of the through hole 6 and the metal pin 8 at the second end 6b.

[0070] 7 , as described above, the metal circuit 3 and the metal pin 8 are simultaneously bonded. If the clearance between the through hole 6 and the metal pin 8 is appropriate, the brazing filler metal will easily spread between the side surface of the through hole 6 and the metal pin 8 during bonding. Therefore, even if a filler brazing filler metal is not used, the bonding strength of the metal pin 8 can be increased.

[0071] The ceramic circuit board 7 according to the embodiment can be used in a power module or the like. Semiconductor elements or the like are bonded to the metal pins 8 of the ceramic circuit board 7. When semiconductor elements are bonded, a bonding layer is provided at the bonding location on the upper surface of the metal circuit 3. The bonding layer preferably contains solder, brazing material, or a conductive adhesive. A required number of semiconductor elements are provided on the bonding layer. An insulating resin may be provided around the semiconductor elements.

[0072] (Examples 1 to 7, Comparative Examples 1 to 7, Reference Example 1) In each of Examples 1 to 7, Comparative Examples 1 to 7, and Reference Example 1, a silicon nitride substrate was prepared as the ceramic substrate. The thickness of the silicon nitride substrate is as shown in Table 1. The thermal conductivity of the silicon nitride substrate is 90 W / m·K, and the three-point bending strength is 650 MP. The size of the ceramic substrate is 30 mm long x 55 mm wide.

[0073] Copper plates with the thicknesses shown in Table 1 were prepared as metal plates. In all examples except Comparative Example 4, a 17 mm × 17 mm copper plate was prepared as the metal circuit. A 17 mm × 44 mm copper plate was prepared as the metal heat sink. Two metal circuits and one metal heat sink were prepared for one silicon nitride substrate. In Comparative Example 4, copper plates with dimensions of 30 mm × 55 mm were prepared as the metal circuits and metal heat sink. One metal circuit and one metal heat sink were prepared for one silicon nitride substrate. In all examples except Comparative Example 4, one through hole was formed by machining in each of the prepared metal circuits. The diameter of the through hole was approximately 1 mm. In Comparative Example 4, no through holes were formed in any of the copper plates. Cylindrical copper members with a diameter of 1 mm (tolerance ±10%) were prepared as metal pins.

[0074] Next, a brazing filler paste was prepared for brazing the ceramic substrate and the metal plate. An active metal brazing filler was used for the joining. The active metal brazing filler contained 2 wt% titanium, 10 wt% tin, and 30 wt% copper, with the remainder being silver. The brazing filler paste was prepared by mixing organic components with the powders of these raw materials. The brazing filler paste was printed and dried on both sides of the ceramic substrate. In Comparative Examples 1 to 3, the brazing filler paste was not printed on the areas facing the through holes after assembly; in the other examples, the brazing filler paste was also printed on the areas facing the through holes after assembly. In Table 1, these conditions are listed in the "Through Hole Printing" column.

[0075] A metal plate was placed on the dried brazing paste to prepare a laminate. In some cases, a metal pin was placed at the same time as the metal plate. －２The laminate was heated at a bonding temperature of 830°C or higher (or 1000 Pa or less) for 10 minutes to perform bonding. In some examples, a filler solder material was used during bonding. In Table 1, these conditions are listed in the "Pin Bonding Method" column. In Table 1, examples in which a metal pin was placed and bonded after the metal plate was bonded are listed as "Post-Bonding." Examples in which a metal plate and a metal pin were simultaneously bonded to a ceramic substrate are listed as "Simultaneous Bonding." Examples in which 0.01 g of silver solder (BAg-8) foil was further used as a filler solder material under the "Post-Bonding" condition are listed as "Braze Material Bonding." The filler solder material was placed at the bottom of the through hole before the metal pin was placed. In Comparative Example 4, a through hole was formed by etching after the metal plate was bonded to the ceramic substrate. A metal pin was inserted into the formed through hole and bonded.

[0076] In Table 1, the temperature at which the metal plates were joined is listed in the "Joining Temperature" column, and the temperature at which the metal pin was joined is listed in the "Pin Joining Temperature" column. Under the "simultaneous joining" condition, the metal plates and the metal pins are joined simultaneously, so the joining temperatures of the metal plates and the metal pins are the same value. In Reference Example 1, the metal pins were joined at a pin joining temperature of 780°C.

[0077]

[0078] After joining the metal pin, the ceramic circuit board was cut so that it passed through the center of the through hole. The cross section was observed, and the dimensions D1 and D2 were measured. The ratio (D2 / D1) was calculated. In addition, the height H of the center of the brazing material within the through hole was measured. The results are shown in Table 2.

[0079] In addition, the pull strength was measured as the bonding strength of the metal pin. In measuring the pull strength, the ceramic circuit board was fixed to a jig, and the tip of the metal pin was pulled in a direction perpendicular to the surface of the ceramic board at a speed of 50 mm / min. The strength was measured when the metal pin peeled off from the ceramic circuit board. The results of the bonding strength measurement are also shown in Table 2. In Reference Example 1, the metal pin was not bonded, and the bonding strength could not be measured. This is because the temperature when bonding the metal pin was lower than the melting temperature of the active metal brazing material.

[0080]

[0081] In the cross sections of the ceramic circuit boards according to Examples 1 to 7, the height H exceeded 0 mm in all cases. In Examples 1 to 7, the brazing filler paste was printed even in the area facing the through hole. Therefore, it is believed that the brazing filler paste melted when the metal pin was joined, and the molten brazing filler paste rose into the gap between the side of the through hole and the metal pin. In particular, in Example 5, which used a filler filler, the height H reached 92% of the thickness of the copper plate. On the other hand, in Comparative Examples 1 to 3, the brazing filler paste was not printed in the area facing the through hole. In the cross sections of the ceramic circuit boards according to Comparative Examples 1 and 2, it was observed that the active metal brazing filler did not rise inside the through hole, and only a portion of the tip of the metal pin was joined to the ceramic substrate. In the cross section of the ceramic circuit board according to Comparative Example 3, as shown in FIG. 14, the brazing filler layer rose inside the through hole, but the active metal brazing filler was not observed in most of the joint between the tip of the metal pin and the surface of the ceramic substrate.

[0082] Furthermore, in the ceramic circuit boards according to Examples 1 to 7, the ratio of dimension D2 to dimension D1 (D2 / D1) was within a preferred range. Furthermore, in Examples 1 to 7, the height H was within a preferred range. In Examples 1 to 7, a high bonding strength of 30 N or more was obtained. This was because the tip of the metal pin was well bonded to the ceramic substrate via the active metal brazing material. Furthermore, because the ratio (D2 / D1) was within a preferred range, the metal pin was well bonded to the metal plate. In particular, in Example 3, the bonding strength exceeded 40 N, and in Example 5, the bonding strength exceeded 90 N.

[0083] On the other hand, in Comparative Examples 1 to 7, the bonding strength was below 20 N. In Comparative Examples 1, 2, and 4 to 7, the height H was 5% or less of the thickness of the metal plate. In Comparative Examples 4 to 7, the ratio (D2 / D1) was outside the preferred range. As a result, a sufficient height H was not obtained, and the bonding strength between the metal plate and the metal pin was reduced. In Comparative Examples 1 to 3, only a portion of the tip of the metal pin was bonded to the ceramic substrate via the active metal brazing material, resulting in reduced bonding strength. In particular, in Comparative Examples 1 and 2, the bonding strength was below 5 N. This is because no brazing paste was printed on the area facing the through hole, and no filler brazing material was used.

[0084] Embodiments of the present invention include the following features. (Feature 1) A ceramic circuit board comprising: a ceramic substrate; and a metal circuit joined to a first surface of the ceramic substrate via an active metal brazing layer, wherein the metal circuit has a thickness of 1 mm or more, the metal circuit has a through hole penetrating the metal circuit along a first direction perpendicular to the first surface, a portion of the first surface overlaps the through hole in the first direction, and the active metal brazing layer is provided on the portion of the first surface. (Feature 2) The through hole includes a first end portion located on an upper surface of the metal circuit and a second end portion facing the active metal brazing layer, and wherein a ratio (D2 / D1) of a dimension (D2) of the second end portion in the second direction parallel to the first surface to a dimension (D1) of the first end portion in the second direction is greater than 1.00 and is 1.10 or less. (Feature 3) The ceramic circuit board according to any one of Features 1 or 2, further comprising a metal pin joined to the portion of the first surface via the active metal brazing layer. (Feature 4) The ceramic circuit board according to Feature 3, further comprising a brazing layer provided between a side surface of the through hole and the metal pin, wherein an upper end of the brazing layer is located between a lower end and an upper end of the through hole. (Feature 5) The ceramic circuit board according to any one of Features 1 to 4, wherein the ceramic substrate is one of an aluminum oxide substrate, an aluminum nitride substrate, and a silicon nitride substrate. (Feature 6) The ceramic circuit board according to Feature 5, wherein the thickness of the ceramic substrate is 0.7 mm or less. (Feature 7) The ceramic circuit board according to Feature 5 or 6, wherein the metal circuit is made of one of copper or a copper alloy. (Feature 8) The ceramic circuit board according to any one of Features 5 to 7, wherein the active metal brazing layer includes at least one selected from the group consisting of titanium, zirconium, hafnium, and niobium, and at least one selected from the group consisting of silver, copper, tin, indium, zinc, aluminum, silicon, carbon, and magnesium.(Feature 9) A method for manufacturing a ceramic circuit board, comprising: printing and drying an active metal brazing material on each of a first surface and a second surface of a ceramic substrate; arranging a metal circuit having a through hole on the first surface via the active metal brazing material; arranging a metal heat sink on the second surface via the active metal brazing material; bonding the metal circuit and the metal heat sink to the ceramic substrate; inserting metal pins into the through holes of the joined metal circuits; and bonding the metal pins to the ceramic substrate. (Feature 10) A method for manufacturing a ceramic circuit board, comprising printing and drying an active metal brazing material on each of a first surface and a second surface of a ceramic substrate; arranging a metal circuit having a through hole and the metal pins inserted in the through holes on the first surface via the active metal brazing material; arranging a metal heat sink on the second surface via the active metal brazing material; and bonding the metal circuit, the metal pins, and the metal heat sink to the ceramic substrate. (Feature 11) The method for manufacturing a ceramic circuit substrate according to Feature 9 or 10, wherein the through hole includes a first end located on a surface of the metal circuit and a second end facing an active metal brazing material layer, and a ratio (D2 / D1) of a dimension (D2) of the second end in a second direction parallel to the first surface to a dimension (D1) of the first end in the second direction is greater than 1.00 and is not greater than 1.10.

[0085] 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.

[0086] REFERENCE SIGNS LIST 1...Ceramic circuit board 2...Ceramic substrate, 2a...Upper surface of ceramic substrate, 2b...Lower surface of ceramic substrate 3...Metal circuit, 3a...Upper surface of metal circuit, 3b...Lower surface of metal circuit 4...Active metal brazing material layer 5...Metal heat sink 6...Through hole 6a...First end, 6b...Second end 7...Ceramic circuit board to which metal pin is bonded 8...Metal pin, 8a...Tip of metal pin 9...Brazing material layer

Claims

1. Ceramic substrate and The ceramic substrate comprises a metal circuit bonded to its first surface via an activated metal brazing layer, The thickness of the aforementioned metal circuit is 1 mm or more. The metal circuit has through holes that penetrate the metal circuit along a first direction perpendicular to the first surface, A portion of the first surface overlaps with the through hole in the first direction, In a ceramic circuit board in which the active metal brazing material layer is provided on a portion of the first surface, The aforementioned through hole is The first end located on the upper surface of the metal circuit, The second end facing the activated metal brazing layer, Includes, A ceramic circuit board in which the ratio (D2 / D1) of the dimension of the second end (D2) in the second direction to the dimension of the first end (D1) in the second direction parallel to the first surface is greater than 1.00 and less than or equal to 1.

10.

2. Ceramic substrate and The ceramic substrate comprises a metal circuit bonded to its first surface via an activated metal brazing layer, The thickness of the aforementioned metal circuit is 1 mm or more. The metal circuit has through holes that penetrate the metal circuit along a first direction perpendicular to the first surface, A portion of the first surface overlaps with the through hole in the first direction, The active metal brazing material layer is provided on a portion of the first surface, The activated metal brazing layer has a solid phase temperature of 830°C or less, and is a ceramic circuit board.

3. The ceramic circuit board according to claim 1 or 2, further comprising a metal pin joined to a portion of the first surface via the activated metal brazing layer.

4. The ceramic circuit board according to claim 3, wherein the activated metal brazing layer has an interface that contacts the metal pin.

5. A brazing material layer is provided between the side surface of the through hole and the metal pin, The brazing layer has at least a portion containing an activated metal brazing material, The upper end of the brazing layer is located between the lower and upper ends of the through hole. The ceramic circuit board according to claim 3.

6. The ceramic circuit board according to claim 5, wherein the height of the brazing layer is 6% or more of the thickness of the metal circuit.

7. The ceramic circuit board according to claim 1, wherein the dimension of the insertion portion of the metal pin in the second direction is 0.7 times or more the dimension of the first end of the through hole in the second direction.

8. The ceramic circuit board according to claim 1 or 2, wherein the ceramic substrate is one of an aluminum oxide substrate, an aluminum nitride substrate, or a silicon nitride substrate.

9. The ceramic circuit board according to claim 8, wherein the thickness of the ceramic substrate is 0.7 mm or less.

10. The ceramic circuit board according to claim 8, wherein the metal circuit is made of either copper or a copper alloy.

11. The aforementioned activated metal brazing layer is At least one selected from the group consisting of titanium, zirconium, hafnium, and niobium, At least one selected from the group consisting of silver, copper, tin, indium, zinc, aluminum, silicon, carbon, and magnesium, A ceramic circuit board according to claim 8, including the following:

12. A step of placing an activated metal brazing material on at least one first surface of a ceramic substrate, The steps include: arranging a metal circuit having through holes on the first surface via the activated metal brazing material; A step of joining the metal circuit to the ceramic substrate using the activated metal brazing material, The steps include inserting a metal pin into the through hole of the joined metal circuit, A method for manufacturing a ceramic circuit board, comprising the step of joining the metal pins to the ceramic substrate using the activated metal brazing material.

13. A step of placing an activated metal brazing material on at least one first surface of a ceramic substrate, The first surface is arranged with a metal circuit having a through hole and a metal pin inserted into the through hole via the activated metal brazing material. A method for manufacturing a ceramic circuit board, comprising the step of joining the metal circuit and the metal pins to the ceramic substrate using the activated metal brazing material.

14. The aforementioned through hole is The first end located on the surface of the metal circuit, The second end facing the active metal brazing layer, Includes, A method for manufacturing a ceramic circuit board according to claim 12 or 13, wherein the ratio (D2 / D1) of the dimension of the second end in the second direction to the dimension of the first end in the second direction parallel to the first surface (D1) is greater than 1.00 and less than or equal to 1.10.