Metal-ceramic bonded substrate and manufacturing method thereof

Abstract

To provide a metal-ceramic bonded substrate having good partial discharge characteristics and excellent heat cycle resistance and heat resistance.SOLUTION: In a metal-ceramic bonded substrate 1 in which a metal circuit board 12 is bonded to one surface of a ceramic substrate 10 via a brazing material layer 11, a protruding portion 11a of the brazing material layer 11 protrudes outward from the lower end of the side surface of the metal circuit board 12 by 80 μm or more, and the side surface of the metal circuit board 12 has an inclination angle θ of 75° or more with respect to the surface of the ceramic substrate 10, and the side surface of metal circuit board 12 and protruding portion 11a of the brazing material layer 11 is covered with an insulating layer 13.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a metal-ceramic bonding (circuit) substrate and a method for manufacturing the same, and more particularly to a metal-ceramic bonding substrate in which a metal circuit is bonded to a ceramic substrate with a brazing material, and a method for manufacturing the same. [Background technology]

[0002] Power modules have traditionally been used to control large amounts of power in electric vehicles, trains, machine tools, etc. As insulating substrates for such power modules, metal-ceramic bonding substrates have been used, in which plating is applied to areas requiring soldering of chip components and terminals on a metal circuit plate bonded to one side of a ceramic substrate.

[0003] For example, in applications for trains, the operating voltage is high, at 6 to 9 kV, and therefore the metal-ceramic bonded substrates used are required to be highly reliable and able to withstand such voltages with ease. When high voltage is applied, the amount of partial discharge charge increases, which can lead to dielectric breakdown. While partial discharge can be suppressed by increasing the insulation distance (distance between circuit patterns, creepage distance), this requires increasing the size of the metal-ceramic bonded substrate, which poses the challenge of making it difficult to miniaturize the metal-ceramic bonded substrate and power module. Furthermore, in such a metal-ceramic bonding substrate, cracks are likely to occur in the ceramic substrate due to thermal stress generated by the difference in thermal expansion between the ceramic substrate and the metal circuit plate caused by thermal shock after bonding.

[0004] Known methods for alleviating such thermal stress include thinning the surface of the metal circuit board, i.e., forming a stepped structure or a fillet of brazing filler metal (an overhanging portion of brazing filler metal for joining the metal circuit board to the ceramic substrate) on the peripheral edge of the metal circuit board.

[0005] Furthermore, in order to suppress partial discharge, for example, the technology disclosed in Japanese Patent Laid-Open No. 2002-76190 (Patent Document 1) places a solid insulator on the upper surface of the insulating substrate in contact with the outer peripheral edge of the conductive film of the circuit board, thereby preventing partial discharge from occurring at the outer peripheral edge of the conductive film and preventing the outer peripheral edge from becoming the starting point of dielectric breakdown, thereby improving reliability.

[0006] Furthermore, the technology disclosed in JP 2005-116602 A (Patent Document 2) is said to provide sufficient durability against dielectric strength and partial discharge characteristics even at high voltages such as 6 to 9 kV by applying a coating material to a bonded substrate with a solder fillet. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-76190 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-116602 Summary of the Invention [Problem to be solved by the invention]

[0008] However, as operation at even higher voltages is expected in the future, there is a problem of insulation degradation due to partial discharge. In recent years, power modules are required to have higher withstand voltage and partial discharge characteristics, as well as excellent heat cycle resistance, due to improvements in the withstand voltage of chips, etc. The technology disclosed in Patent Document 1 has good partial discharge characteristics by inserting an insulating substrate into a mold and filling it with resin, but it has poor heat cycle resistance and is costly to fill the resin. Furthermore, the technology disclosed in Patent Document 2 has partial discharge characteristics of up to about 9 kV, which is not sufficient.

[0009] Furthermore, according to the investigations of the present inventors, it has been found that the partial discharge characteristics deteriorate due to the thermal history when the circuit board is assembled into the power module, i.e., when the chip components and the heat sink are formed on the circuit board by soldering or the like.

[0010] The present invention aims to solve these problems and to provide a metal / ceramic bonding substrate that has good partial discharge characteristics and is excellent in heat cycle resistance and heat resistance, and a method for producing the same. [Means for solving the problem]

[0011] In order to solve the above problems, according to the present invention, there is provided a metal-ceramic bonding substrate in which a metal circuit plate is bonded to one surface of a ceramic substrate via a brazing material layer, the metal circuit plate being 80 μm or more outward from the lower end of a side surface of the metal circuit plate. , 300μm or less A protruding portion of the brazing material layer is formed, and the side surface of the metal circuit plate is at an angle of 75° or more with respect to the surface of the ceramic substrate. , 100° or less and the side surfaces of the metal circuit plate and the protruding portion of the brazing material layer are covered with an insulating layer.

[0012] A heat-dissipating-side metal plate may be bonded to the other surface of the ceramic substrate. The heat-dissipating-side metal plate may be copper or a copper alloy. The metal circuit plate may be copper or a copper alloy. Nickel plating or nickel alloy plating may be formed on the surfaces of the metal circuit plate and the protruding portion of the brazing material layer. The insulating layer may be a resin. In this case, the resin may be mainly composed of polyimide resin.

[0013] According to the present invention, in a metal-ceramic bonded body in which a metal plate is bonded to one surface of a ceramic substrate via a brazing filler metal layer, an unnecessary portion of the metal plate is removed to form a metal circuit plate, and the brazing filler metal layer is removed from the lower end of the side of the metal circuit plate by 80 μm or more. , 300μm or lessThe side of the metal circuit plate is at an angle of 75° or more to the surface of the ceramic substrate. , 100° or less and then forming an insulating layer to cover the side surface of the metal circuit plate and the protruding portion of the brazing material layer.

[0014] In a metal-ceramic bonded body having a metal plate bonded to one surface of a ceramic substrate via a brazing filler metal layer and a metal plate bonded to the other surface via a heat-dissipation-side brazing filler metal layer, unnecessary portions of the metal plate on one surface and the metal plate on the other surface may be removed to form a metal circuit plate on one surface of the ceramic substrate and a heat-dissipation-side metal plate on the other surface. The heat-dissipation-side metal plate may be copper or a copper alloy. The metal circuit plate may be copper or a copper alloy. Nickel or nickel alloy plating may be formed on the surfaces of the metal circuit plate and the protruding portion of the brazing filler metal. The insulating layer may be formed by applying a coating material made of insulating resin and then curing it. In this case, the resin may be primarily composed of polyimide resin. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a metal / ceramic bonding substrate having good partial discharge characteristics and excellent heat cycle resistance and heat resistance, and a method for producing the same. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a cross-sectional view showing a metal-ceramic bonding substrate according to an embodiment of the present invention. [Figure 2] FIG. 2 is an enlarged cross-sectional view of a portion A in FIG. [Figure 3] FIG. 2 is an explanatory diagram showing an example of a method for manufacturing a metal-ceramic bonding substrate according to an embodiment of the present invention, showing a state in which a paste-like active metal-containing brazing material is applied to both sides of a ceramic substrate by screen printing. [Figure 4] FIG. 2 is an explanatory view showing an example of a method for manufacturing a metal-ceramic bonding substrate according to an embodiment of the present invention, showing a state in which a ceramic substrate and a metal plate are bonded via an active metal-containing brazing filler metal. [Figure 5] FIG. 1 is an explanatory diagram showing an example of a method for manufacturing a metal-ceramic bonding substrate according to an embodiment of the present invention, showing a state in which resist having a desired circuit pattern shape and a heat-dissipating-side metal plate shape is applied to the surfaces of metal plates bonded to the upper and lower surfaces of a ceramic substrate. [Figure 6] FIG. 2 is an explanatory view showing an example of a method for manufacturing a metal / ceramic bonding substrate according to an embodiment of the present invention, showing a state in which unnecessary portions of a metal plate have been removed by etching. [Figure 7] FIG. 2 is an explanatory view showing an example of a method for manufacturing a metal / ceramic bonding substrate according to an embodiment of the present invention, showing a state in which the resist has been removed after unnecessary portions of the metal plate have been removed by etching. [Figure 8] FIG. 2 is an explanatory view showing an example of a method for producing a metal / ceramic bonding substrate according to an embodiment of the present invention, showing a state in which an unnecessary portion of an active metal-containing brazing filler metal has been removed. [Figure 9] FIG. 2 is an explanatory view showing an example of a method for manufacturing a metal / ceramic bonding substrate according to an embodiment of the present invention, showing a state in which a resist is applied to substantially the entire upper surface (front surface) of a metal plate. [Figure 10] FIG. 1 is an explanatory diagram showing an example of a method for manufacturing a metal-ceramic bonding substrate according to an embodiment of the present invention, illustrating a state in which the side surface (periphery of the metal plate) of the metal plate is etched away to cause the active metal-containing brazing material to protrude from the side surface of the metal plate. [Figure 11] FIG. 1 is an explanatory diagram showing an example of a method for manufacturing a metal-ceramic bonding substrate according to an embodiment of the present invention, showing a state in which the side surface (periphery of the metal plate) of the metal plate is etched away to cause the active metal-containing brazing material to protrude from the side surface of the metal plate, and then the resist is removed. [Figure 12]FIG. 1 is an explanatory diagram showing an example of a method for manufacturing a metal-ceramic bonding substrate according to an embodiment of the present invention, in which an insulating resin solution is dropped so as to cover the side surface of a metal circuit board and the protruding portion of a brazing material layer, and then the insulating resin solution is hardened by heating in an inert gas atmosphere to form an insulating layer. [Figure 13] FIG. 2 is an explanatory diagram of the substrate dimensions and the shape of the metal circuit plate (circuit pattern dimensions) of Examples 1 to 4 and Comparative Examples 1 to 6. [Figure 14] 1 is a cross-sectional photograph showing the shapes of metal circuit plates and fillets of metal-ceramic bonding substrates of Examples 1 and 4 and Comparative Examples 2 and 5. DETAILED DESCRIPTION OF THE INVENTION

[0017] An embodiment of the present invention will now be described with reference to the accompanying drawings. In this specification, substantially similar components are designated by the same reference numerals, and redundant description will be omitted.

[0018] <Metal-ceramic bonded substrate> 1, a metal-ceramic bonding substrate 1 according to an embodiment of the present invention has a structure in which one or more metal circuit plates 12 are bonded to at least one surface of a (for example, substantially rectangular) ceramic substrate 10 via a brazing filler metal layer 11. In the illustrated embodiment, two (for example, substantially rectangular) metal circuit plates 12 are bonded to the upper surface of the ceramic substrate 10 via a brazing filler metal layer 11. A (for example, substantially rectangular) heat-dissipating metal plate 16 is bonded to the lower surface of the ceramic substrate 10 via a brazing filler metal layer 15, and a heat-dissipating member (not shown), such as a metal or composite heat-dissipating plate called a base plate, or a metal heat-dissipating fin or cooling jacket, is attached to the lower surface of the heat-dissipating metal plate 16.

[0019] The ceramic substrate 10 is preferably made of an oxide whose main component is alumina or silica, or a non-oxide whose main component is aluminum nitride, silicon nitride, silicon carbide, or the like, and can be a substrate having a length of approximately 5 to 200 mm (preferably, 10 to 100 mm) x width of 5 to 200 mm (preferably, 10 to 100 mm) and a thickness of 0.25 to 3.0 mm (preferably, 0.3 to 1.0 mm).

[0020] The brazing filler metal layers 11, 15 are made of a brazing filler metal containing, for example, an active metal, and the silver content of the brazing filler metal (metal component) is preferably 30% by mass or more. When the total metal components of this active metal-containing brazing filler metal are taken as 100% by mass, an active metal-containing brazing filler metal can be used, which contains 1.0 to 7.0% by mass (preferably 1.5 to 6.5% by mass) of active metal, 30 to 95% by mass (preferably 50 to 90% by mass, more preferably 60 to 80% by mass) of silver, and the remainder as copper. Titanium, zirconium, and hafnium can be used as the active metal of this active metal-containing brazing filler metal. The brazing filler metal may further contain, for example, 10% by mass or less of an element such as Sn or In.

[0021] Since chip components such as semiconductor elements are mounted on the metal circuit plate 12, the metal circuit plate 12 is preferably made of a metal with excellent electrical conductivity and thermal conductivity, and is preferably made of, for example, a single metal such as copper or aluminum, or an alloy such as a copper alloy or an aluminum alloy.

[0022] The heat-dissipating metal plate 16 is preferably made of, for example, copper or a copper alloy, aluminum or an aluminum alloy, in order to dissipate heat generated from chip components such as semiconductor elements mounted on the metal circuit plate 12 . In addition, heat dissipation components such as a base plate, heat dissipation fins, and cooling jacket made of materials such as copper or copper alloy, aluminum or aluminum alloy, or Al-SiC composite material (not shown) are attached to the surface of the heat dissipation side metal plate 16 (the surface opposite to the surface bonded to the ceramic substrate) by soldering or bolting.

[0023] As shown in FIG. 2, an enlarged view of portion A in FIG. 1 shows, on the upper surface of the ceramic substrate 10, a protruding portion (fillet) 11a is formed so that the brazing material layer 11 protrudes outward from the lower end of the side surface of the metal circuit plate 12. To effectively relieve thermal stress caused by the difference in thermal expansion between the ceramic substrate 10 and the metal circuit plate 12, the protruding length (fillet length) L of the protruding portion 11a is 80 μm or more. Furthermore, by setting the protruding length to this value, the insulating layer 13 (described below) is well formed on the side surface 12a of the metal circuit plate 12, the protruding portion 11a, and the upper surface of the ceramic substrate 10, suppressing gaps such as voids, which is thought to improve partial discharge characteristics. The protruding length L is the protruding length of the protruding portion 11a protruding outward from the lower end of the side surface of the metal circuit plate 12. It is more preferable that the protruding length L be 90 μm or more. Furthermore, if the protrusion length L is made too large, it becomes necessary to enlarge the outer dimensions of the metal-ceramic bonding substrate 1 in order to ensure an insulating distance between the patterns, which hinders miniaturization of the metal-ceramic bonding substrate 1. Therefore, the protrusion length L is preferably set to 300 μm or less, and more preferably set to 200 μm or less.

[0024] The side surfaces and protruding portion 11a of the metal circuit plate 12 are covered with an insulating layer 13. The insulating layer 13 is made of, for example, an insulating resin such as polyimide resin.

[0025] The side surface 12a of the metal circuit plate 12 has a shape that is inclined so as to gradually widen outward as it goes downward from the upper end 12b of the side surface of the metal circuit plate 12 (upper corner portion of the metal circuit plate 12), or a shape that is perpendicular to the upper surface of the ceramic substrate 10. The inclination angle θ of the side surface 12a of the metal circuit plate 12 with respect to the upper surface of the ceramic substrate 10 is 75° or more, preferably 80° or more, preferably 100° or less, more preferably 90° or less, and preferably has a shape without an overhang. In the present invention, when observing a cross section of the metal-ceramic bonding substrate 1, the inclination angle θ is defined as the angle between the upper surface of the ceramic substrate 10 and a line (12b-P) connecting the upper end (upper corner) 12b of the metal circuit plate 12 and a position P on the side surface 12a of the metal circuit plate 12 that is halfway through the thickness of the metal circuit plate 12 (a position halfway through the height from the upper surface of the ceramic substrate 10 to the upper surface of the metal circuit plate 12). When measuring the tilt angle θ, for convenience, the angle formed by the lines M and N may be measured when the line passing through P and parallel to the surface of the ceramic substrate 10 in FIG. 2 is defined as line N.

[0026] <Method for manufacturing metal-ceramic bonded substrate> Next, an example of a method for manufacturing a metal-ceramic bonding substrate 1 according to an embodiment of the present invention will be described. Note that, as shown in Fig. 1, a method for manufacturing a metal-ceramic bonding substrate 1 in which two metal circuit plates 12 are bonded to the upper surface of a ceramic substrate 10 via a brazing layer 11 will be described as an example.

[0027] 3 and 4, paste-like active metal-containing brazing filler metal 20 and active metal-containing brazing filler metal 25 are applied to the upper and lower surfaces of ceramic substrate 10 by a known method such as screen printing, spraying, or a roll coater. Metal plates 21 and 26 are then placed in contact with active metal-containing brazing filler metal 20 and active metal-containing brazing filler metal 25, and are heated in a vacuum or a non-oxidizing atmosphere and then cooled, thereby joining metal plates 21 and 26 to the upper and lower surfaces of ceramic substrate 10. The active metal-containing brazing material 20 may be a metal foil of a brazing material having a predetermined composition, and may be disposed on the upper and lower surfaces of the ceramic substrate 10 .

[0028] Next, as shown in Fig. 5, resist 22 having a desired circuit pattern and resist 22 having a shape of a (substantially rectangular) heat-dissipating metal plate are applied to the surfaces of metal plates 21 and 26 bonded to the upper and lower surfaces of ceramic substrate 10. Then, as shown in Fig. 6, unnecessary portions of metal plates 21 and 26 are etched away using a cupric chloride etching solution or an iron chloride etching solution. Thereafter, resist 22 is removed as shown in Fig. 7.

[0029] 8, unnecessary portions of the active metal-containing brazing filler metal 20 and the active metal-containing brazing filler metal 25 (which remain between the circuit patterns, around the circuit patterns, and around the heat dissipation side metal plate 16) are removed using, for example, an aqueous solution containing hydrofluoric acid or an aqueous solution containing a compound that forms a complex with an active metal, such as ethylenediaminetetraacetic acid (EDTA). By removing the unnecessary portions of the active metal-containing brazing filler metal 20 and the active metal-containing brazing filler metal 25 in this manner, the brazing filler metal layers 11 and 15 are formed in the predetermined shapes (with protruding portions 11a protruding outward from the side surfaces of the metal plates 21 and 26 not yet appearing).

[0030] 9, resist 23 is applied to metal plates 21 and 26 over substantially the entire surfaces thereof. Resist 23 is preferably applied so that it has the exact same shape as the surfaces of metal plates 21 and 26, or so that the peripheral edges of the surfaces are exposed (for example, approximately 500 μm or less). Resist 23 has substantially the same shape as metal circuit plate 12 and heat-dissipating-side metal plate 16. Then, as shown in FIG. 10, unnecessary portions of metal plates 21 and 26 (the side surfaces and peripheral edges of metal plates 21 and 26) are etched and removed using an etching solution or chemical polishing solution containing cupric chloride or iron chloride, so that the peripheral portions of brazing filler metal layer 11 and brazing filler metal layer 15 extend beyond the side surfaces of metal plates 21 and 26. By etching away unnecessary portions of the metal plates 21 and 26 (peripheral portions of the metal plates 21 and 26) in this manner, the metal circuit plate 12 and the heat-dissipation-side metal plate 16 are formed in a predetermined shape. In addition, by making the peripheral portions of the brazing material layer 11 protrude from the side portions of the metal plates 21 and 26, protruding portions 11a, 15a having a predetermined protruding length (fillet length) L are formed. When etching away unnecessary portions of the metal plate 21 (the side surfaces and peripheral edges of the metal plate 21), the etching conditions (size of the resist 23, etching solution, etching temperature and time) are adjusted so that the protrusion length (fillet length) L of the protruding portion 11a is 80 μm or more.

[0031] Furthermore, by forming the resist 23 and then etching the metal circuit plate 12, the fillet length L can be controlled to a predetermined length, and the inclination angle θ of the side surface 12a of the metal circuit plate 12 can be set to 75° or more, preferably 80° or more and 100° or less, more preferably 90° or less, and can be set to a shape without overhangs. In particular, by forming the resist 23 on almost the entire surface of the metal plate 21 as described above and adjusting the etching conditions to obtain the target fillet length L, the fillet width L and inclination angle θ of the present invention can be obtained.

[0032] 11, the resist 23 is then removed. In this way, the metal plate 21, the metal plate 26, the active-metal-containing brazing filler metal 20, and the active-metal-containing brazing filler metal 25 are formed into a predetermined shape, forming the metal circuit plate 12, the heat-dissipating-side metal plate 16, the brazing filler metal layer 11, and the brazing fillet layer 15, and also forming a protruding portion (fillet) 11a in which the brazing filler metal layer 11 protrudes outward from the side surface 12a of the metal circuit plate 12. Similarly, on the lower surface of the ceramic substrate 10, it is preferable to form a protruding portion (fillet) 15a in which the brazing material layer 15 protrudes from the side surface 16a of the heat-dissipating side metal plate 16 using the same manufacturing method as for the metal circuit plate 12.

[0033] 12, an insulating resin solution (insulating layer 13) is dripped onto the side surface 12a of the metal circuit plate 12, the protruding portion 11a of the brazing material layer 11, and the surface of the ceramic substrate 10. The insulating resin solution can be dripped using a resin dispenser or the like. After that, the insulating resin solution is heated in an inert gas atmosphere to harden it, thereby forming the insulating layer 13.

[0034] The insulating resin is preferably a polyimide resin, etc. For example, it is preferable to dilute the polyimide resin with a solvent such as N-methyl-2-pyrrolidone (NMP) to prepare a polyimide resin solution having a viscosity (measured with an E-type viscometer) of 50 to 1000 mPa·s (preferably 70 to 900 mPa·s) at room temperature (25°C), and then drop this polyimide resin solution onto or around the spaces between the metal circuit plates 12 (between the circuit patterns) using a resin dispenser or the like to form the insulating layer 13.

[0035] If necessary, a Ni plating film may be formed on the metal circuit plate 12 and the protruding portion (fillet) 11a by, for example, electrolytic Ni plating or electroless Ni plating. Also, a base plate made of a metal plate or composite material, heat dissipation fins, or a cooling jacket for water cooling (not shown) can be attached to the lower surface of the heat-dissipating-side metal plate 16 via, for example, solder or brazing material.

[0036] In the metal-ceramic bonding substrate 1 according to the embodiment of the present invention thus manufactured, the side surface 12a of the metal circuit plate 12 at a predetermined angle and the protruding portion 11a of the brazing fillet layer 11 having a predetermined protruding width are covered with the insulating layer 13, thereby providing a metal-ceramic bonding substrate with good partial discharge characteristics and excellent heat cycle resistance. Furthermore, the large inclination of the side surface 12a of the metal circuit plate 12 increases adhesion to the resin, and the protruding portion (fillet) 11a provides a stress relief effect even after thermal history, thereby suppressing cracking of the ceramic substrate 10. As an example of an embodiment of the present invention, a form in which two metal circuit plates 12 are bonded to the upper surface of a ceramic substrate 10 via a brazing material layer 11 has been shown, but the number of metal circuit plates 12 may be one or three or more, and it is sufficient that a metal circuit plate 12 is bonded to at least one surface of the ceramic substrate 10, and it is preferable that a heat dissipation side metal plate 16 is bonded to the other surface of the ceramic substrate 10. [Example]

[0037] Examples of metal-ceramic bonded (circuit) substrates and manufacturing methods thereof according to the present invention are described in detail below. In Examples 1 to 4 and Comparative Examples 1 to 6, the metal circuit board and heat-dissipating metal plate (metal plate) were oxygen-free copper (length 20 mm, width 14 mm, thickness 0.25 mm), the ceramic substrate was aluminum nitride (length 19.8 mm, width 13.8 mm, thickness 0.635 mm), and the active metal-containing brazing filler metal paste was a brazing filler metal containing titanium with silver as the main component. The active metal-containing brazing filler metal paste (Ag:Cu:Sn:Ti=83:10:5:2) contained 83% by weight of silver, 10% by weight of copper, 5% by weight of tin, and 2% by weight of titanium (as the active metal component) as the metal components.

[0038] [Examples 1 to 4] Similar to the manufacturing method of the metal-ceramic bonding substrate described above, a paste-like active metal-containing brazing filler metal was applied to the top and bottom surfaces of the ceramic substrate by screen printing to a thickness of 20 μm, and a metal plate was placed in contact with the active metal-containing brazing filler metal. The substrate was heated to 850°C in a vacuum furnace and then cooled, thereby bonding the metal plate to the top and bottom surfaces of the ceramic substrate.

[0039] Next, an ultraviolet-curable alkali-peelable resist in the shape of a circuit pattern was applied by screen printing to the surface of the metal plate bonded to one side of the ceramic substrate, and the same resist in the shape of a heat-dissipating metal plate was applied to the surface of the metal plate bonded to the other side. After these resists were hardened by irradiation with ultraviolet light, unnecessary portions of the metal plate (copper plate) were etched with an etching solution consisting of copper chloride, hydrochloric acid, and the remainder water, and the resist was removed with an aqueous sodium hydroxide solution to form a metal circuit plate and a heat-dissipating metal plate made of copper plate.

[0040] Next, the substrate was immersed in a chelating aqueous solution containing 1.6 mass% EDTA·4Na (sodium salt of ethylene diamine tetraacetic acid), 3 mass% ammonia water, and 5 mass% hydrogen peroxide water, and then in a known brazing filler metal etching solution consisting of a chelating aqueous solution containing 2 mass% ethylene triamine pentaacetic acid (DTPA)·5Na and 5 mass% hydrogen peroxide water, thereby removing unnecessary portions of the active metal-containing brazing filler metal remaining between the copper circuit patterns on the surface of the ceramic substrate and around the copper plate on the heat dissipation side, and an intermediate product was obtained.

[0041] Next, the resist was applied to the entire surface of the intermediate product metal circuit plate and heat dissipation side metal plate by screen printing, and then immersed in an etching solution (chemical polishing solution) at a liquid temperature of 45°C consisting of 14 mass% sulfuric acid, 3.2 mass% hydrogen peroxide, and the remainder water to etch (chemically polish) the sides of the metal circuit plate and heat dissipation side metal plate, causing the active metal-containing brazing filler metal to protrude by a predetermined length from the side portions of the circuit side copper plate and heat dissipation side copper plate, forming protruding portions of the brazing filler metal (brazing fillet), and thereby obtaining a metal-ceramic bonding substrate. In Examples 1 to 4, the target fillet length was approximately 100 μm.

[0042] Next, a 4 μm thick Ni—P alloy plating film was formed by electroless plating on the surfaces of the metal circuit board and the heat-radiating metal plate and on the protruding portions of the brazing filler metal. Next, the polyimide resin solution was applied dropwise between the metal circuit plates (between the circuit patterns) and around them using a resin dispenser (discharge pressure: 0.25 MPa, discharge time: 2 msec, discharge interval: 0.5 mm / shot), and then heated and cured at 250°C for 30 minutes to form an insulating layer, which was used as the evaluation sample. The substrate dimensions and metal circuit plate shapes (circuit pattern dimensions) of Examples 1 to 4 and Comparative Examples 1 to 6 are shown in FIG.

[0043] [Comparative Examples 1 to 3] As in the Examples, a paste-like active metal-containing brazing filler metal was applied by screen printing to the upper and lower surfaces of the ceramic substrate, a metal plate was placed so that it was in contact with the active metal-containing brazing filler metal, and the metal plate was bonded to the upper and lower surfaces of the ceramic substrate by heating and then cooling. The metal-ceramic bonding substrates of Comparative Examples 1 to 3 were then obtained by the following process: resist printing → etching → resist removal → brazing filler layer removal → electroless Ni-P plating → polyimide application. That is, the substrates were fabricated using the same manufacturing method as in the Examples, except for the process of fillet formation (and simultaneous control of the side surface inclination angle of the metal circuit plate), and no fillets were used in Comparative Examples 1 to 3.

[0044] [Comparative Examples 4 to 6] As in the Examples, a paste-like active metal-containing brazing filler metal was applied by screen printing to the upper and lower surfaces of the ceramic substrate, and a metal plate was placed so that it was in contact with the active metal-containing brazing filler metal. After heating, the metal plate was bonded to the upper and lower surfaces of the ceramic substrate by cooling. The metal-ceramic bonded substrates of Comparative Examples 4 to 6 were then obtained by the following process: resist printing → etching → resist removal → brazing filler layer removal → chemical polishing → electroless Ni plating → polyimide coating. In Comparative Examples 4 to 6, the metal-ceramic bonded substrates were different from the Examples in that, after brazing filler removal, chemical polishing (fillet formation) was performed without forming a resist on the surface of the metal plate, and the process aimed for a fillet length of approximately 50 μm. In Comparative Examples 4 to 6, the thickness of the metal circuit plate was reduced, and the upper surface of the metal circuit plate was rounded.

[0045] Fig. 14 shows the cross-sectional shapes of the metal circuit plates and fillets of Examples 1 and 4 and Comparative Examples 2 and 5. Fig. 14 shows a cross section of an evaluation sample, a metal-ceramic bonding substrate on which Ni-P plating was formed, taken along a plane perpendicular to the surface of the ceramic substrate and perpendicular to the side (periphery) of the circuit pattern. Partial discharge in the metal-ceramic bonded substrate was measured using the following method. First, aluminum wire was ultrasonically bonded to the surface of each of the multiple metal circuit plates, thereby electrically connecting the metal circuit plates. Next, with the metal-ceramic bonded substrate immersed in insulating oil, the voltage between the metal circuit plate and the heat-dissipating metal plate was increased in 0.5 kV increments and then decreased in 0.5 kV increments using a partial discharge meter (DAC-PD-3, manufactured by Soken Denki Co., Ltd.), and the amount of partial discharge charge at each voltage was measured. The discharge charge thresholds were set to 10 pC (picocoulomb) and 5 pC (picocoulomb). The voltages that exceeded each discharge charge threshold were recorded as the initiation voltage, and the voltages that fell below each discharge charge threshold were recorded as the extinction voltage. In addition, the heat cycle resistance of the metal-ceramic bonding substrate was evaluated by holding it at -40°C for 30 minutes and then at 150°C for 30 minutes, with the substrate being returned to room temperature every 50 cycles and checking for the occurrence of cracks in the ceramic. The evaluation samples of Comparative Examples 1 to 3, which do not have fillets, have good partial discharge properties, and maintain these properties even after heat treatment at 380°C. However, cracks appear in the ceramic substrate after 50 heat cycles, and the heat cycle (HC) resistance is poor. The heat treatment was performed by passing the sample through an oven (nitrogen:hydrogen 80:20) in which the temperature was raised from room temperature to 380°C in 10 minutes, held at that temperature for 10 minutes, and then returned to room temperature in 5 minutes. In Comparative Examples 4 to 6, in which the angle of the side surface (Cu side surface) of the metal circuit plate was 75° or less and the fillet length was 70 μm or less, the partial discharge extinction voltage after heat treatment was sometimes 10 kV or less, and it was found that the partial discharge characteristics were poor. On the other hand, in Examples 1 to 4, in which the angle of the side surface of the metal circuit plate (Cu plate side surface) in the cross section was 80° or more and the fillet was more than 90 μm, the partial discharge inception and partial discharge extinction voltages after polyimide application before heat treatment were 13 kV or more, and in the partial discharge measurement after heat treatment, even under the condition that the discharge charge amount was less than 5 pC, the partial discharge extinction voltage was 12 kV or more, and it was possible to obtain a metal-ceramic bonding substrate with good partial discharge characteristics and excellent heat cycle resistance.

[0046] [Table 1] [Explanation of symbols]

[0047] 1. Metal-ceramic bonded substrate 10 Ceramic substrate 11 Brazing material layer 11a Protruding part (fillet) 12 Metal circuit board 12a side 12b Top edge (top corner) 13 Insulating layer 15 Brazing material layer 15a Protruding part (fillet) 16 Heat radiation side metal plate 20 Active metal-containing brazing filler metal 21 Metal plate 22, 23 Resist

Claims

1. A metal-ceramic bonding substrate in which a metal circuit plate is bonded to one surface of a ceramic substrate via a brazing material layer, a protruding portion of the brazing material layer is formed so as to protrude outward from a lower end of a side surface of the metal circuit plate by 80 μm or more and 300 μm or less; the side surface of the metal circuit plate has an inclination angle of 75° or more and 100° or less with respect to the surface of the ceramic substrate, The metal-ceramic bonding substrate has a side surface of the metal circuit plate and an extended portion of the brazing material layer covered with an insulating layer.

2. 2. The metal / ceramic bonding substrate according to claim 1, wherein a heat-dissipating metal plate is bonded to the other surface of said ceramic substrate.

3. 3. The metal / ceramic bonding substrate according to claim 2, wherein the heat-radiating metal plate is made of copper or a copper alloy.

4. 4. The metal / ceramic bonding substrate according to claim 1, wherein said metal circuit plate is made of copper or a copper alloy.

5. 5. The metal / ceramic bonding substrate according to claim 1, wherein the surfaces of the metal circuit plate and the protruding portions of the brazing material layer are plated with nickel or nickel alloy.

6. 6. The metal / ceramic bonding substrate according to claim 1, wherein said insulating layer is made of a resin.

7. 7. The metal / ceramic bonding substrate according to claim 6, wherein the resin is mainly composed of a polyimide resin.

8. In a metal-ceramic bonded body in which a metal plate is bonded to one surface of a ceramic substrate via a brazing filler metal layer, an unnecessary portion of the metal plate is removed to form a metal circuit plate, the brazing filler metal layer is caused to protrude from the lower end of the side surface of the metal circuit plate by 80 μm or more and 300 μm or less to form an overhanging portion of the brazing filler metal layer, and the side surface of the metal circuit plate is etched so that the side surface of the metal circuit plate has an inclination angle of 75° or more and 100° or less with respect to the surface of the ceramic substrate, and forming an insulating layer so as to cover the side surfaces of the metal circuit plate and the protruding portion of the brazing material layer;

9. 9. The method for producing a metal-ceramic bonding substrate according to claim 8, wherein a metal plate is bonded to one surface of a ceramic substrate via a brazing filler metal layer and a metal plate is bonded to the other surface of the ceramic substrate via a heat-dissipation-side brazing filler metal layer, and unnecessary portions of the metal plate on one surface and the metal plate on the other surface are removed to form a metal circuit plate on one surface of the ceramic substrate and a heat-dissipation-side metal plate on the other surface.

10. 10. The method for producing a metal / ceramic bonding substrate according to claim 9, wherein the heat-radiating metal plate is made of copper or a copper alloy.

11. The method for producing a metal / ceramic bonding substrate according to any one of claims 8 to 10, wherein the metal circuit plate is made of copper or a copper alloy.

12. 12. The method for producing a metal / ceramic bonding substrate according to claim 8, wherein nickel or nickel alloy plating is formed on the surfaces of the metal circuit plate and the protruding portion of the brazing material layer.

13. 13. The method for producing a metal / ceramic bonding substrate according to claim 8, wherein the insulating layer is formed by applying a coating material made of an insulating resin and then curing the coating material.

14. 14. The method for producing a metal / ceramic bonding substrate according to claim 13, wherein the resin is mainly composed of a polyimide resin.

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