Ceramic composite substrate

Abstract

To achieve both heat cycle characteristics and insulation.SOLUTION: A ceramic composite substrate according to an embodiment of the present disclosure includes a ceramic plate having a first main surface and a second main surface, a first bonding layer provided on the first main surface, a first metal body bonded to the first main surface via the first bonding layer, a second bonding layer spaced apart from the first bonding layer on the first main surface, and a second metal body bonded to the first main surface via the second bonding layer, and the first bonding layer has an extension extending from between the first main surface and the first metal body toward the second bonding layer. The average value of the thickness D of the extension in the first direction orthogonal to the first main surface is 10 μm or less. The ratio of the average value of the length L of the extension in the second direction in which the first bonding layer and the second bonding layer face each other to the average value of the thickness D is greater than 3 and 15 or less.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present disclosure relates to a ceramic composite substrate.

Background Art

[0002] Patent Documents 1 to 3 disclose a circuit board or the like including a ceramic substrate and a metal plate formed on the upper surface of the ceramic substrate.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] The present disclosure provides a ceramic composite substrate useful for achieving both heat cycle characteristics and insulation properties.

Means for Solving the Problems

[0005] A ceramic composite substrate according to one aspect of the present disclosure includes a ceramic plate having a first main surface and a second main surface, a first bonding layer provided on the first main surface, a first metal body bonded to the first main surface via the first bonding layer, a second bonding layer provided on the first main surface with a space from the first bonding layer, and a second metal body bonded to the first main surface via the second bonding layer. The first bonding layer has an extending portion that protrudes from between the first main surface and the first metal body toward the second bonding layer. The average value of the thickness D of the extending portion in a first direction orthogonal to the first main surface is 10 μm or less. The ratio of the average value of the length L of the extending portion in a second direction in which the first bonding layer and the second bonding layer face each other to the average value of the thickness D is greater than 3 and less than or equal to 15.

[0006] In this ceramic composite substrate, the ratio of the average value of the length L to the average value of the thickness D is greater than 3 and equal to or less than 15, and the average value of the thickness D of the extending portion is 10 μm or less, so the volume of the extending portion is small. Also, by setting the above ratio to 15 or less, the extending portion does not approach the second metal body too much. Therefore, the insulation between the extending portion and the second metal body or the second bonding layer is improved. On the other hand, by making the above ratio greater than 3, the thermal stress applied near the end of the lower surface of the first metal body due to the heat cycle is easily dispersed. Therefore, the heat cycle characteristics are improved. Accordingly, this ceramic composite substrate is useful for achieving both heat cycle characteristics and insulation.

[0007] The average value of the thickness D may be 1 μm to 8 μm. By setting the average value of the thickness D to 1 μm or more, the formation of the first bonding layer becomes easy. Also, by setting the average value of the thickness D to 8 μm or less, the insulation with the second metal body or the second bonding layer is further improved. Therefore, it is useful for achieving both ease of manufacturing of the ceramic composite substrate and insulation.

[0008] The average value of the length L may be 25 μm to 80 μm. If the length L is short, thermal stress may concentrate near the end of the lower surface of the first metal body due to the heat cycle. On the other hand, if the length L is increased to relieve the thermal stress, the distance to the second metal body or the second bonding layer becomes short, and the insulation may deteriorate. In the above configuration, by setting the length L to 25 μm or more, the thermal stress due to the heat cycle can be relieved, and by setting the length L to 80 μm or less, the insulation with the second metal body or the second bonding layer can be maintained.

[0009] In a cross-section including the first direction and the second direction, the connecting portion between the upper surface of the first metal body and the side surface facing the second metal body may have a rounded shape that is inscribed in the tip of the upper surface and has an average value of the maximum radius of a virtual circle that can be formed inside the upper surface and the side surface in the range of 5.5 μm to 10.0 μm. By setting the rounded shape with the average value of the maximum radius of the virtual circle in the range of 5.5 μm to 10.0 μm, the discharge from the tip of the upper surface of the first metal body is suppressed. Therefore, it is useful for improving the insulation between the first metal body and the second metal body.

Effect of the Invention

[0010] According to the present disclosure, a ceramic composite substrate useful for achieving both heat cycle characteristics and insulation is provided.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0012] Hereinafter, an embodiment will be described with reference to the drawings. The following embodiments are examples for explaining the present disclosure and are not intended to limit the present disclosure to the following content. In the description, the same reference numerals are given to the same elements or elements having the same function, and redundant descriptions are omitted. The positional relationships such as up, down, left, and right are based on the positional relationships shown in the drawings unless otherwise specified. The dimensional ratios of the respective elements are not limited to the ratios shown in the drawings. The drawings show a rectangular coordinate system defined by the X-axis, Y-axis, and Z-axis.

[0013] [Ceramic Composite Substrate] FIG. 1 schematically shows an example of a ceramic composite substrate according to an embodiment. The ceramic composite substrate 10 is a substrate used as a component such as a power module, for example. The ceramic composite substrate 10 includes a ceramic plate 20 and a metal circuit board 30.

[0014] The ceramic plate 20 is formed in a flat plate shape. The ceramic plate 20 has a pair of main surfaces facing each other. Hereinafter, one of the pair of main surfaces is referred to as "front surface 20A", and the other is referred to as "back surface 20B". The shape of the outer edge of the front surface 20A may be a quadrilateral. Among the outer edges of the front surface 20A, the direction in which a set of sides parallel to each other extends is defined as the "X-axis direction", and the direction in which another set of sides parallel to each other extends is defined as the "Y-axis direction". The thickness direction of the ceramic plate 20 (the direction perpendicular to the front surface 20A) is defined as the "Z-axis direction".

[0015] The material (ceramic) forming the ceramic plate 20 is not particularly limited. The ceramic plate 20 is, for example, a silicon nitride plate or an aluminum nitride plate. The thickness of the ceramic plate 20 may be 0.1 mm to 1.0 mm, may be 0.1 mm to 0.6 mm, or may be 0.2 mm to 0.4 mm.

[0016] The metal circuit board 30 is provided on the front surface 20A (the first main surface) of the ceramic plate 20. A chip (electronic component) may be mounted on at least a part of the metal circuit board 30. The metal circuit board 30 may be a copper plate. The metal circuit board 30 has, for example, a metal body 30a, a metal body 30b, and a metal body 30c. The metal body 30a, the metal body 30b, and the metal body 30c are arranged on the front surface 20A in a state of being separated from each other. For example, when the metal body 30a constitutes the first metal body, the metal body 30b constitutes the second metal body. When three or more metal bodies are provided, among a plurality of sets of adjacent metal bodies, a set of metal bodies with the smallest distance between the metal bodies may be selected as the first metal body and the second metal body.

[0017] Each of the metal bodies 30a, 30b, and 30c is, for example, a copper plate. The thicknesses of the metal bodies 30a, 30b, and 30c may be substantially the same as each other. The thickness of each of the metal bodies 30a, 30b, and 30c may be 0.1 mm to 2.0 mm, may be 0.2 mm to 1.5 mm, or may be 0.3 mm to 1.2 mm. Each of the metal bodies 30a, 30b, and 30c is disposed inside the outer edge of the surface 20A.

[0018] The ceramic composite substrate 10 includes a bonding layer 40. The bonding layer 40 is a layer that bonds the metal circuit board 30 to the surface 20A. The bonding layer 40 has, for example, a bonding layer 40a (first bonding layer), a bonding layer 40b (second bonding layer), and a bonding layer 40c. Each of the bonding layers 40a, 40b, and 40c is provided on the surface 20A. The lower surface of each of the bonding layers 40a, 40b, and 40c is in contact with the surface 20A.

[0019] The bonding layer 40a is provided at a position corresponding to the metal body 30a, and the metal body 30a is bonded to the surface 20A via the bonding layer 40a. The region near the outer edge of the bonding layer 40a is exposed from the outer edge of the metal body 30a. The region near the outer edge of the bonding layer 40a protrudes outward from between the metal body 30a and the surface 20A, for example, over its entire circumference. The outer edge of the bonding layer 40a surrounds the outer edge of the metal body 30a. In the present disclosure, a part of the bonding layer that protrudes outward from between the metal body and the surface 20A is referred to as an "extension portion".

[0020] The bonding layer 40b is provided at a position corresponding to the metal body 30b, and the metal body 30b is bonded to the surface 20A via the bonding layer 40b. The bonding layer 40c is provided at a position corresponding to the metal body 30c, and the metal body 30c is bonded to the surface 20A via the bonding layer 40c. The relationship between the size of the bonding layer 40b and the metal body 30b and the relationship between the size of the bonding layer 40c and the metal body 30c may be the same as the relationship between the size of the bonding layer 40a and the metal body 30a.

[0021] The bonding layer 40 (each of the bonding layers 40a, 40b, and 40c) may be composed of an Ag-Cu-Sn based solder material. The Ag-Cu-Sn based solder material contains silver, copper, tin, and an active metal. The silver content in the bonding layer 40 may be 70% by mass or more, may be 80% by mass or more, or may be 85% by mass or more. The silver content in the bonding layer 40 may be 98% by mass or less. The tin in the bonding layer 40 may be 0.5 to 10 parts by mass, may be 0.5 to 5.0 parts by mass, or may be 1 to 5 parts by mass with respect to 100 parts by mass in total of silver and copper. The copper content in the bonding layer 40 may be 5 to 20 parts by mass with respect to 100 parts by mass of silver.

[0022] The above active metal includes at least one selected from the group consisting of titanium, zirconium, hafnium, and niobium. The active metal in the bonding layer 40 may be 0.5 to 10 parts by mass, may be 0.5 to 5 parts by mass, or may be 2 to 5 parts by mass with respect to 100 parts by mass in total of silver and copper. The active metal may be contained as a hydride, for example, may contain titanium hydride (TiH2). The content of TiH2 in the bonding layer 40 may be 0.5 to 10 parts by mass, may be 1 to 5 parts by mass, or may be 2 to 5 parts by mass with respect to 100 parts by mass in total of silver and copper.

[0023] The content of various components constituting the bonding layer 40 may be determined by measuring the concentration in the vicinity of the bonding interface between the metal body and the ceramic plate using a scanning electron microscope and an EDS (Energy Dispersive X-ray Spectroscopy) detector. The content of various components constituting the bonding layer 40 may also be specified by measuring the mixing ratio in the raw material when preparing the bonding layer 40. Components contained in the solder material constituting the bonding layer 40 often do not contain components that volatilize at the heating temperature during bonding (for example, about 800°C). In this case, the mixing ratio in the raw material of the solder material substantially coincides with the composition ratio of various components contained in the solder material after bonding.

[0024] FIG. 2 shows a cross-section taken along line II-II in FIG. 1. The metal bodies 30a and 30b are arranged side by side along one direction along the surface 20A. The metal bodies 30a and 30b face each other in the direction in which one side of the surface 20A extends (for example, the X-axis direction). The metal bodies 30a and 30b are arranged at intervals. The distance between the metal bodies 30a and 30b is set in consideration of the insulation (electrical insulation) between these metal bodies. The distance (shortest distance) between the metal bodies 30a and 30b is, for example, 0.3 mm to 1.5 mm.

[0025] The bonding layer 40b is arranged at an interval from the bonding layer 40a on the surface 20A. The bonding layers 40a and 40b are arranged side by side along one direction (for example, the X-axis direction) along the surface 20A, similar to the relationship between the metal bodies 30a and 30b. The bonding layers 40a and 40b face each other in the above one direction (for example, the X-axis direction). Hereinafter, it will be described assuming that the direction in which the bonding layers 40a and 40b face each other is the X-axis direction. FIG. 3 shows an enlarged view of the range surrounded by line III in FIG. 2.

[0026] As described above, the bonding layer 40a includes an extension portion that protrudes outward from between the metal body 30a and the surface 20A. The extension portion located on the outer periphery of the bonding layer 40a includes an extension portion 42a that protrudes from between the surface 20A and the metal body 30a toward the bonding layer 40b (or the metal body 30b) as shown in FIG. 3. The extension portion 42a is located between the metal bodies 30a and 30b in the X-axis direction (second direction). The extension portion 42a extends along the surface 20A and along the Y-axis direction perpendicular to the X-axis direction.

[0027] The average value of the thickness D of the extending portion 42a is 10 μm or less. The thickness D of the extending portion 42a is the thickness (size) of the extending portion 42a in the direction orthogonal to the surface 20A (the above-mentioned thickness direction: the first direction). From the viewpoint of insulation between the metal body 30b or the bonding layer 40b, the average value of the thickness D may be 9 μm or less, may be 8 μm or less, or may be 7 μm or less. From the viewpoint of manufacturing the ceramic composite substrate 10, the average value of the thickness D may be 1.0 μm or more, may be 1.5 μm or more, or may be 2.0 μm or more. The average value of the thickness D may be 1 μm to 8 μm, or may be 2 μm to 7 μm.

[0028] The average value of the thickness D is the arithmetic average value of the thickness D of the extending portion 42a measured at the observation cross-sections of 5 arbitrarily selected locations (5 fields of view) in the extending portion 42a. In the Y-axis direction, the positions of the above 5 locations are different from each other. Each of the 5 locations is selected, for example, in each region when the extending portion 42a is evenly divided into 5 parts in the Y-axis direction. The observation cross-section at each of the 5 locations is a cross-section (X-Z plane) perpendicular to the Y-axis direction. When observing the ceramic composite substrate 10 at the observation cross-section, the thickness D at that cross-section is defined by the maximum value of the thickness of the extending portion 42a.

[0029] The ratio of the average value of the length L of the extending portion 42a in the X-axis direction to the average value of the thickness D of the extending portion 42a (hereinafter, simply referred to as "ratio L / D") is greater than 3 and 15 or less. From the viewpoint of the adhesiveness of the bonding layer 40a to the surface 20A, the ratio L / D may be 4 or more, may be 4.5 or more, may be 5 or more, or may be 6 or more. From the viewpoint of insulation between the metal body 30b or the bonding layer 40b, the ratio L / D may be 18 or less, may be 16 or less, or may be 15 or less.

[0030] The average value of the length L of the extended portion 42a may be 25 μm or more, may be 30 μm or more, and may be 35 μm or more from the viewpoint of the adhesiveness to the surface 20A of the bonding layer 40a. The average value of the length L may be 80 μm or less, may be 70 μm or less, and may be 60 μm or less from the viewpoint of the insulation between the metal body 30b or the bonding layer 40b. The length L may be 25 μm to 80 μm, or may be 30 μm to 80 μm.

[0031] The average value of the length L is the arithmetic mean value of the length L along the X-axis direction of the extended portion 42a measured at the observation cross-sections of 5 locations (5 fields of view) arbitrarily selected in the extended portion 42a, similar to the average value of the thickness D. The observation cross-section when measuring the length L may be the same as or different from the observation cross-section when measuring the thickness D. When observing the ceramic composite substrate 10 at the observation cross-section, the length L in that cross-section is defined as the maximum value of the length along the X-axis direction of the extended portion 42a.

[0032] In the X-axis direction, the position of the tip 38a of the upper surface 32a of the metal body 30a closest to the metal body 30b and the position of the tip 39a of the lower surface of the metal body 30a closest to the metal body 30b are offset from each other (see also FIG. 1). In the X-axis direction, the distance between the tip 44a of the extended portion 42a that protrudes most outward and the tip 38a is larger than the distance between the tip 44a and the tip 39a of the extended portion 42a. The side surface 34a connecting the tip 38a and the tip 39a is the surface facing the metal body 30b and is curved so as to be recessed in the direction away from the metal body 30b. In the present disclosure, the upper surface 32a and the side surface 34a are separated with the tip 38a as the boundary. According to this definition, the upper surface 32a may have a shape that slopes downward toward the tip 38a in the vicinity of the tip 38a.

[0033] FIG. 4 shows an enlarged view of the area surrounded by line IV in FIG. 3. In FIG. 4, the connecting portion 36a that connects the upper surface 32a and the side surface 34a of the metal body 30a is enlarged. The connecting portion 36a (connecting part) may have a rounded shape from the viewpoint of ensuring insulation between the metal body 30b. In the above observation cross-section (a cross-section including the X-axis direction and the Z-axis direction), the connecting portion 36a may have a rounded shape in which the average value of the maximum radius of the virtual circle IC that can be formed inside the upper surface 32a and the side surface 34a and is inscribed in the tip 38a of the upper surface 32a is 5.5 μm to 10.0 μm. Inscribing in the tip 38a means that the virtual circle IC passes through the tip 38a in a state where it is located inside the upper surface 32a and the side surface 34a. The average value of the maximum radius of the virtual circle IC may be 5.7 μm to 9.8 μm, or may be 5.9 μm to 9.6 μm.

[0034] The average value of the maximum radius of the virtual circle IC is the arithmetic average value of the maximum radius of the virtual circle IC when observing the ceramic composite substrate 10 in the observation cross-section of 5 locations (5 fields of view). The maximum radius of the virtual circle IC is defined, for example, as the radius of the circle with the largest radius among the circles that can be formed inside the upper surface 32a and the side surface 34a and are inscribed in the tip 38a in the observed cross-section when performing a 3000-fold SEM observation on the cross-section of the ceramic composite substrate 10.

[0035] Returning to FIG. 2, the ceramic composite substrate 10 includes a metal plate 50 and a bonding layer 60. The metal plate 50 is provided on the back surface 20B (the second main surface). Different from the metal circuit board 30, the metal plate 50 may not be divided into a plurality of metal bodies. The bonding layer 60 is located between the metal plate 50 and the back surface 20B, and the metal plate 50 is bonded to the back surface 20B via the bonding layer 60.

[0036] The material constituting the metal plate 50 may be the same as the material constituting the metal circuit board 30, and the thickness of the metal plate 50 may be substantially the same as the thickness of the metal circuit board 30. The material constituting the bonding layer 60 may be the same as the material constituting the bonding layer 40. In the ceramic composite substrate 10, while the metal circuit board 30 has a function of transmitting an electrical signal or electric power, the metal plate 50 may have a function of dissipating heat without transmitting an electrical signal.

[0037] Other extending portions other than the extending portion 42a may be formed in the same manner as the extending portion 42a, and other connecting portions other than the connecting portion 36a may be formed in the same manner as the connecting portion 36a. The other extending portions may have the same dimensions (thickness D and length L) as the extending portion 42a. The other connecting portions may have the same rounded shape as the connecting portion 36a. In one example, in the extending portion protruding from between the metal body 30b and the surface 20A toward the metal body 30a, the average value of the thickness may be 10 μm or less, and the ratio of the average value of the length along the X-axis direction to the average value of the thickness may be greater than 3 and 15 or less.

[0038] [Manufacturing Method] Subsequently, an example of a manufacturing method of the ceramic composite substrate 10 will be described. First, a step of forming a slurry containing ceramic powder, a sintering aid, a binder resin, and a solvent to obtain a green sheet is performed. The slurry may contain a plasticizer, a dispersant, and the like.

[0039] The ceramic powder is, for example, silicon nitride powder or aluminum nitride powder. Examples of the sintering aid include rare earth metals, alkaline earth metals, metal oxides, fluorides, chlorides, nitrates, and sulfates. These may be used alone or in combination of two or more. Examples of the binder resin include methyl cellulose, ethyl cellulose, polyvinyl alcohol, polyvinyl butyral, and (meth)acrylic resins.

[0040] Examples of plasticizers include purified glycerin, glycerin trioleate, diethylene glycol, phthalic acid-based plasticizers such as di-n-butyl phthalate, dibasic acid-based plasticizers such as di-2-ethylhexyl sebacate, and the like. Examples of dispersants include poly(meth)acrylate and (meth)acrylic acid-maleic acid copolymer. Examples of solvents include organic solvents such as ethanol and toluene.

[0041] Examples of the forming method of the slurry include the doctor blade method and the extrusion molding method. Next, a step of degreasing and sintering the obtained green sheet is performed. The degreasing may be carried out, for example, by heating at 400 to 800 °C for 0.5 to 20 hours. By this, while suppressing the oxidation and deterioration of the inorganic compound, the residual amount of the organic substance (carbon) can be reduced. The sintering is carried out by heating to 1700 to 1900 °C in a non-oxidizing gas atmosphere such as nitrogen, argon, ammonia or hydrogen. Thereby, the ceramic plate 20 can be obtained.

[0042] The above-mentioned degreasing and sintering may be carried out in a state where a plurality of green sheets are laminated. When laminating and performing degreasing and sintering, in order to smoothly separate the base materials after firing, a release layer using a release agent may be provided between the green sheets. As the release agent, for example, boron nitride (BN) can be used. The number of green sheets to be laminated may be, for example, 5 to 100 sheets, or may be 10 to 70 sheets.

[0043] Next, a step of obtaining a joined body using the ceramic plate 20 and a pair of metal plates is performed. Specifically, first, a joining material (for example, a brazing material) is applied to each of the front surface 20A and the back surface 20B of the ceramic plate 20, and a pair of metal plates are bonded to the front surface 20A and the back surface 20B. The pair of metal plates may have the same flat plate shape as the ceramic plate 20.

[0044] The bonding material is applied to the front surface 20A and the back surface 20B of the ceramic plate 20 by a method such as a roll coater method, a screen printing method, or a transfer method. When the bonding material is a solder, the solder contains, for example, silver powder, copper powder, tin powder, and powders of an active metal or its compound (hydride), an organic solvent, a binder, and the like. The content of tin powder with respect to a total of 100 parts by mass of silver powder and copper powder may be 0.5 to 5.0 parts by mass. The content of the metal hydride powder with respect to a total of 100 parts by mass of silver powder and copper powder may be 1 to 8 parts by mass. The viscosity of the solder may be, for example, 5 to 20 Pa·s. The content of the organic solvent in the solder may be, for example, 5 to 25% by mass, and the content of the binder amount may be, for example, 2 to 15% by mass.

[0045] A pair of metal plates are superposed on the front surface 20A and the back surface 20B of the ceramic plate 20 to which the bonding material is applied to obtain a laminate. Next, a firing step of firing this laminate in a heating furnace is performed. The temperature inside the furnace (firing temperature) during firing is, for example, 750°C or higher. The firing temperature may be 750°C to 950°C, or may be 780°C to 900°C. The time (firing time) held at the above firing temperature may be 10 minutes to 180 minutes, or may be 15 minutes to 90 minutes. The atmosphere inside the heating furnace during firing may be an inert gas such as nitrogen, or may be under a reduced pressure of less than atmospheric pressure (1.0×10 -3 Pa or less), or may be under vacuum. Through the above steps, a bonded body in which metal plates are bonded to the front surface 20A and the back surface 20B of the ceramic plate 20 via bonding layers can be obtained.

[0046] Next, a step of removing a part of each of the pair of metal plates in the above bonded body to form a metal circuit board 30 and a metal plate 50 is performed. This step may be performed, for example, by photolithography. Specifically, first, a resist (etching resist) having photosensitivity is printed on the surface of the bonded body (the surface of the metal plate). Then, a resist pattern having a predetermined shape is formed using an exposure apparatus. The resist may be a negative type or a positive type. The uncured resist is removed, for example, by washing.

[0047] After forming the resist pattern, the portions of the metal plate that are not covered by the resist pattern are removed by etching. As a result, on the surface 20A of the ceramic plate 20, a metal circuit board 30 including metal bodies 30a, 30b, and 30c is formed, and a metal plate 50 is formed on the back surface 20B. The etching solution is not particularly limited, and for example, ferric chloride solution, cupric chloride solution, sulfuric acid, hydrogen peroxide water, etc. can be used. Etching can be performed in any manner, and an immersion method or a spray method can be used.

[0048] By adjusting the etching conditions (for example, etching time or number of etching times), the contour shape of the metal body 30a in the observed cross-section can be adjusted. Specifically, in the X-axis direction (the direction in which the metal body 30a and the metal body 30b face each other), the positional relationship between the tip 38a of the upper surface 32a of the metal body 30a and the tip 39a of the lower surface of the metal body 30a can be adjusted. By adjusting the etching conditions, the metal body 30a may be formed such that the tip 39a approaches the metal body 30b compared to the tip 38a.

[0049] After etching a part of the metal body, a bonding layer (solder layer) may remain at the location where the metal body is removed. Therefore, the remaining bonding layer is removed by etching different from the etching of the metal body. As a result, bonding layers 40a, 40b, and 40c corresponding to the metal bodies 30a, 30b, and 30c, respectively, are formed, and a bonding layer 60 corresponding to the metal plate 50 is formed. The size of the extending portion (protrusion) included in the bonding layer 40 is adjusted according to the conditions in the etching of the bonding layer.

[0050] As an etching solution for removing the bonding layer, for example, a solution containing at least one selected from the group consisting of an aqueous ammonium halide solution, inorganic acids such as sulfuric acid and nitric acid, and hydrogen peroxide water is used. As the etching solution for removing the bonding layer, a mixed solution containing a fluorine-based chemical solution and hydrogen peroxide water may be used. The concentration of hydrogen peroxide water in the above mixed solution may be 5% by mass to 30% by mass. From the viewpoint of easily adjusting the size of the extending portion, the concentration of hydrogen peroxide water may be 8% by mass to 28% by mass, or may be 10% by mass to 23% by mass. The bonding layer can be etched by an immersion method or a spray method. For example, from the viewpoint of easily adjusting the size of the extending portion, the spray method is used.

[0051] After etching a part of the bonding layer, chemical polishing is performed on the surface of a metal body such as the metal body 30a. By chemical polishing, foreign substances attached to the surface of the metal body and the oxide film formed on the surface can be removed, and furthermore, a roundness can be additionally imparted to the contour of the connecting portion of the metal body. The chemical solution used for chemical polishing may be a mixed solution containing hydrogen peroxide and sulfuric acid. The processing time for performing chemical polishing may be set to a time such that the thickness of the metal body is reduced by about several μm to several tens of μm. Through the above steps, the ceramic composite substrate 10 as shown in FIG. 1 can be obtained.

[0052] By adjusting various conditions including the etching conditions of the metal plate and the conditions for performing chemical polishing, the roundness (degree of roundness) of the connecting portion 36a connecting the upper surface 32a and the side surface 34a can be adjusted. Specifically, the maximum radius of the virtual circle IC that can be inscribed in the tip 38a of the upper surface 32a and can be formed inside the upper surface 32a and the side surface 34a can be adjusted. By adjusting various conditions including the etching conditions of the metal plate, the metal body 30a may be formed such that the average value of the maximum radius of the virtual circle IC is 5.5 μm to 10.0 μm.

[0053] By adjusting various conditions including the etching conditions of the metal plate and the etching conditions of the bonding layer, the thickness D and the length L of the extending portion 42a can be adjusted to a predetermined setting range. By adjusting various conditions including the etching conditions of the bonding layer (for example, the concentration of hydrogen peroxide), the ratio (ratio L / D) of the average value of the length L of the extending portion 42a in the X-axis direction to the average value of the thickness D of the extending portion 42a is greater than 3 and not more than 15, and the bonding layer 40a may be formed.

[0054] The thickness D depends on the thickness of the bonding layer applied before etching rather than the etching conditions of the bonding layer. Before etching, a bonding layer (solder layer) may be applied to the surface 20A of the ceramic plate 20 so that the thickness D is 10 μm or less, or 1 μm to 8 μm. By forming the metal body 30a so that the average value of the maximum radius of the virtual circular IC is 5.5 μm to 10.0 μm, it becomes easy to adjust the ratio L / D (or the length L) to a desired range.

[0055] [Effects of the Embodiment] In the ceramic composite substrate 10 described above, the ratio L / D of the average value of the length L to the average value of the thickness D is greater than 3 and not more than 15, and the average value of the thickness D of the extending portion 42a is 10 μm or less, so the volume of the extending portion 42a is small. Also, by setting the ratio L / D to 15 or less, the extending portion 42a does not approach the metal body 30b too much. Therefore, the insulation between the extending portion 42a and the metal body 30b or the bonding layer 40b is improved. On the other hand, by setting the ratio L / D to be greater than 3, the thermal stress applied near the end of the lower surface of the metal body 30b due to the heat cycle is easily dispersed. Therefore, the heat cycle characteristics are improved. Therefore, the ceramic composite substrate 10 is useful for achieving both heat cycle characteristics and insulation.

[0056] In the ceramic composite substrate 10 described above, the average value of the thickness D may be 1 μm to 8 μm. By setting the thickness D to 1 μm or more, the formation of the bonding layer 40a becomes easy. Further, by setting the thickness D to 8 μm or less, the insulation between the metal body 30b or the bonding layer 40b is further improved. Therefore, it is useful for achieving both ease of manufacturing and insulation of the ceramic composite substrate 10.

[0057] In the ceramic composite substrate 10 described above, the average value of the length L may be 25 μm to 80 μm. If the length L is short, thermal stress may concentrate in the vicinity of the end of the lower surface of the metal body 30a due to heat cycles. On the other hand, if the length L is increased to relieve the thermal stress, the distance between the metal body 30b or the bonding layer 40b becomes short, and the insulation may deteriorate. In the above configuration, by setting the length L to 25 μm or more, the thermal stress due to heat cycles can be relieved, and by setting the length L to 80 μm or less, the insulation between the metal body 30b or the bonding layer 40b can be maintained.

[0058] In the above observation cross-section, the connecting portion (connecting portion 36a) between the upper surface 32a of the metal body 30a and the side surface 34a facing the metal body 30b may have a rounded shape with an average value of the maximum radius of the virtual circle IC that can be formed inside the upper surface 32a and the side surface 34a and inscribed in the tip 38a of the upper surface 32a being 5.5 μm to 10.0 μm. By setting the rounded shape with the average value of the maximum radius of the virtual circle IC being 5.5 μm to 10.0 μm, discharge from the tip of the upper surface 32a of the metal body 30a is suppressed. Therefore, it is useful for improving the insulation between the metal body 30a and the metal body 30b.

Example

[0059] Subsequently, the content of the present disclosure will be described in more detail with reference to examples and comparative examples, but the present disclosure is not limited to the following examples.

[0060] (Example 1) [Fabrication of bonded body] A brazing material used as a bonding layer was prepared. First, the following raw material powders were prepared. Silver powder: manufactured by Fukuda Metal Foil & Powder Co., Ltd., Ag-HWQ (trade name), average particle diameter D50: 2.5 μm, specific surface area 0.4 m 2 / g Copper powder: manufactured by Fukuda Metal Foil & Powder Co., Ltd., Cu-HWQ (trade name), average particle diameter D50: 3.0 μm, specific surface area: 0.4 m 2 / g Tin powder: manufactured by Fukuda Metal Foil & Powder Co., Ltd., Sn-HPN (trade name), average particle diameter D50: 3.0 μm, specific surface area 0.1 m 2 / g Titanium hydride powder: manufactured by Toho Titanium Co., Ltd., TCH-100 (trade name)

[0061] Based on a total of 100 parts by mass of silver powder (90 parts by mass) and copper powder (10 parts by mass), 1 part by mass of tin powder and 3.5 parts by mass of titanium hydride powder were blended, and an organic solvent, a binder, etc. were added to prepare a brazing material. The brazing material was applied to both main surfaces of a commercially available silicon nitride substrate (thickness: 0.32 mm) by screen printing so that the coating amount was 8 mg / cm 2 and then dried.

[0062] Copper plates (oxygen-free copper plate with a thickness of 0.8 mm (JIS H 3100, C 1020)) were stacked on both main surfaces of the silicon nitride plate to obtain a laminate. Using an electric furnace, the laminate was heated in a vacuum atmosphere at a furnace temperature of 800 °C for 40 minutes to melt the brazing material powder and join the ceramic substrate and the metal plate (firing process). Then, the furnace temperature was cooled to 600 °C at an average cooling rate of 10 °C / min. Then, the heating was stopped and it was naturally cooled to room temperature in a nitrogen atmosphere. In this way, a joined body in which the ceramic plate and a pair of metal plates were joined via a brazing material layer was produced.

[0063] [Fabrication of Ceramic Composite Substrate] An etching resist was printed on predetermined locations on both main surfaces of the copper plate in the fabricated bonded body. After forming a resist pattern having a predetermined shape on the main surface of the copper plate using an exposure apparatus, etching of the metal plate was performed using a ferric chloride solution. Further, etching was performed using a mixed solution of ammonium fluoride and hydrogen peroxide to remove the bonding layer and the like formed at the locations where unnecessary metal portions were removed. As a result, an extension portion protruding from one metal body toward the other metal body was formed between one circuit pattern (metal body) and the other circuit pattern (metal body) adjacent to each other.

[0064] Next, chemical polishing was performed to remove foreign matter and oxide films on the surface of the metal body. In this way, a ceramic composite substrate in which a ceramic plate and a metal circuit board are joined via a brazing material layer as shown in FIG. 1 was obtained.

[0065] [Measurement of the thickness T and length L of the extension portion] One extension portion of the brazing material layer in the ceramic composite substrate was observed using a scanning electron microscope (SU6600 type, manufactured by Hitachi High-Technologies Corporation). Reflection electron image observation (magnification: 200 times) was performed in 5 fields of view (each field of view is 400 μm in length × 600 μm in width), and the thickness D and length L of the extension portion for each field of view were measured. The thickness D for each field of view was taken as the maximum thickness of the extension portion, and the length L for each field of view was taken as the maximum length of the extension portion. The average value of the thickness D and the average value of the length L in 5 fields of view were obtained. The results were as shown in Table 1.

[0066] [Evaluation of insulation] The insulation between the first metal body corresponding to the extension portion and the second metal body adjacent to the first metal body was evaluated. Specifically, a substrate (more specifically, a substrate with a comb-shaped electrode) on which a first electrode including the first metal body and a second electrode including the second metal body were formed was prepared. In the above substrate, the distance between the first metal body and the second metal body was 0.5 mm. In a high-temperature and high-humidity chamber, a DC (direct current) voltage of 1 kV was continuously applied between the first electrode and the second electrode in an atmosphere of 85 °C and 93% RH, and the insulation resistance value between the first metal body and the second metal body was 1×10 6The time when it becomes Ω or less was measured. The upper limit of the measurement time was set to 500 hours. The results were as shown in Table 1. In the insulation evaluation column of Table 1, the meanings of "A", "B", and "C" are as follows. A: Even after 500 hours had elapsed since the start time of voltage application, the insulation resistance value remained at 1×10 6 Ω or more. B: Between 100 hours and 500 hours from the start time of voltage application, the insulation resistance value decreased to 1×10 6 Ω or less. C: In less than 100 hours from the start time of voltage application, the insulation resistance value decreased to 1×10 6 Ω or less.

[0067] [Evaluation of Heat Cycle Characteristics] A heat cycle test of the fabricated ceramic composite substrate was conducted. Specifically, a series of steps of holding at -50°C for 15 minutes and at 150°C for 15 minutes was defined as one cycle, and this was repeated 2000 times. After the test, the copper plate and the brazing material layer of the ceramic composite substrate were peeled off by copper chloride solution, ammonium fluoride, and hydrogen peroxide etching. Using a scanner, an image of the main surface of the ceramic plate from which the copper plate and the brazing material layer had been removed was acquired at a resolution of 600 dpi × 600 dpi. Binary processing of the image was performed using image analysis software GIMP2 (threshold value 140) to calculate the crack area. The calculated crack area was divided by the area of the circuit pattern to obtain the crack rate for evaluation. The results were as shown in Table 1. In the heat cycle characteristic evaluation column of Table 1, the meanings of "A", "B", and "C" are as follows. A: The crack area ratio is 0.5% or less. B: The crack area ratio is greater than 0.5% and less than 1.0%. C: The crack area ratio is 1.0% or more.

[0068] (Examples 2 to 5) Before etching, the thickness of the brazing material applied and various etching conditions (for example, the etching time of the metal plate and the concentration of hydrogen peroxide in the solution for etching the brazing material) were changed, and a ceramic composite substrate was obtained in the same procedure as in Example 1. The various conditions were adjusted such that the average value of the thickness D was 10 μm or less and the average value of the length L was greater than 3 and 15 or less.

[0069] (Comparative Examples 1 to 3) Before etching, the thickness of the brazing material applied and various etching conditions were changed, and a ceramic composite substrate was obtained in the same procedure as in Example 1. In Comparative Examples 1 and 3, the various conditions were adjusted such that the average value of the thickness D was greater than 10 μm. In Comparative Example 2, the various conditions were adjusted such that the ratio L / D exceeded 15, and in Comparative Example 3, the various conditions were adjusted such that the ratio L / D was less than 3.

[0070]

Table 1

[0071] As shown in Table 1, it can be seen that by making the thickness D 10 μm or less and the ratio L / D 15 or less, the insulation between adjacent metal bodies is maintained. Also, by making the ratio L / D greater than 3, it can be seen that the crack generation rate is reduced and the heat cycle characteristics are excellent.

Explanation of Reference Numerals

[0072] 10…Ceramic composite substrate, 20…Ceramic plate, 20A…Front surface, 20B…Back surface, 30a, 30b…Metal bodies, 32a…Upper surface, 34a…Side surface, 36a…Connection part, 38a…Tip, 40a, 40b…Bonding layer, 42a…Extended part, D…Thickness of the extended part 42a, L…Length of the extended part 42a.

Claims

1. A ceramic plate having a first main surface and a second main surface, a first bonding layer provided on the first main surface, a first metal body bonded to the first main surface via the first bonding layer, a second bonding layer provided on the first main surface at a distance from the first bonding layer, a second metal body bonded to the first main surface via the second bonding layer, and comprising: the first bonding layer has an extending portion that protrudes from between the first main surface and the first metal body toward the second bonding layer, the average value of the thickness D of the extending portion in a first direction orthogonal to the first main surface is 1 μm to 8 μm, the ratio of the average value of the length L of the extending portion in a second direction in which the first bonding layer and the second bonding layer face each other to the average value of the thickness D is greater than 3 and less than or equal to 15, the average value of the length L is 25 μm to 80 μm, a ceramic composite substrate, wherein the distance between the first metal body and the second metal body in the second direction is 0.3 mm to 1.5 mm.

2. In a cross section including the first direction and the second direction, a connecting portion between an upper surface of the first metal body and a side surface facing the second metal body has a rounded shape that is inscribed in a tip of the upper surface and has an average value of a maximum radius of a virtual circle that can be formed inside the upper surface and the side surface of 5.5 μm to 10.0 μm. The ceramic composite substrate according to Claim 1.

Images