JP6473599B2 - Ceramic metal bonded body and circuit board using the same - Google Patents

Description

  The present invention relates to a ceramic metal bonded body and a circuit board using the same.

  In recent years, insulated gate bipolar transistor (IGBT) devices, metal oxide field effect transistor (MOSFET) devices, light emitting diode (LED) devices, freewheeling diode (FWD) devices, giant transistor (GTR) devices, etc. 2. Description of the Related Art An electronic device in which various electronic components such as a semiconductor element, a sublimation thermal printer head element, a thermal ink jet printer head element, and a Peltier element are mounted on a circuit member of a circuit board is used.

  As a circuit board provided with a circuit member for mounting an electronic component, for example, a laminated material in which a plurality of metal layers are laminated on both main surfaces of an insulating ceramic substrate is used.

And as an example of the circuit board using such a laminated material, for example, in Patent Document 1, a group consisting of AlN, Al ₂ O ₃ , Si ₃ N ₄ , SiC, Y ₂ O ₃ , CaO, BN and BeO. A substrate made of one kind of ceramic selected from the following (hereinafter referred to as a ceramic substrate), Al powder, Cu powder, Ag powder, Au powder, Al alloy powder, Cu A first sintered body layer made of one kind of metal powder selected from the group consisting of alloy powder, Ag alloy powder and Au alloy powder, and a mixed powder of Cu powder and Mo powder formed on the other surface of the substrate , Mixed powder of Cu powder and W powder, mixed powder of Al powder and SiC powder, mixed powder of Al powder and AlN powder, mixed powder of Si powder and SiC powder, mixed of Al and short carbon fiber And a second sintered body layer made of one kind of mixed powder selected from the group consisting of a mixed powder of Al and carbon particles, the first and second sintered body layers comprising the above powder and Insulating laminates formed by using a green sheet formed by mixing a resin and a plasticizer and sintering the powder in the green sheet by a discharge plasma sintering method have been proposed.

JP 2011-71260 A

  However, in the insulating laminated material proposed in Patent Document 1, the outer peripheral surfaces of the first sintered body layer and the second sintered body layer are perpendicular to the substrate in a sectional view and flush with the outer peripheral surface of the ceramic substrate. Since it is comprised, the stress accompanying expansion | swelling or shrinkage | contraction of a 1st sintered compact layer or a 2nd sintered compact layer tends to act on the outer peripheral surface of a ceramic substrate directly. For this reason, if heat is repeatedly applied to the ceramic substrate over a long period of time, there is a problem that the ceramic substrate is likely to be cracked starting from the outer peripheral surface.

  The present invention has been devised in view of the above-described problems, and an object of the present invention is to provide a ceramic metal joined body and a circuit board that are unlikely to crack even when heat is repeatedly applied.

A ceramic metal bonded body according to an aspect of the present invention includes a disk-shaped ceramic substrate, a first metal member bonded to one main surface side of the ceramic substrate via a first metal layer, and the other of the ceramic substrates. A ceramic metal joined body having a second metal member joined to a main surface side via a second metal layer, wherein the first metal member is a circular shape facing the one main surface of the ceramic substrate. A first main surface and a circular second main surface opposite to the first main surface, wherein the first main surface has a smaller area than the second main surface; member is composed mainly of copper, the first metal layer is a brazing material, characterized by being arranged a first coupling layer comprising copper foil between the first metal member and the first metal layer And A disk-shaped ceramic substrate; a first metal member bonded to one main surface of the ceramic substrate via a first metal layer; and a second metal layer interposed to the other main surface of the ceramic substrate. A first metal member having a circular first main surface facing the one main surface of the ceramic substrate, and the first main member. and a surface opposite to circular second main surface side of said second small area of said first major surface than the main surface, the second metal member is a main component of copper, the first 2 the metal layer is a brazing material, characterized by comprising placing a second coupling layer comprising copper foil between the second metal member and the second metal layer.

  A circuit board according to an aspect of the present invention is characterized in that the ceramic metal joined body according to the present invention having the above-described configuration is used.

  The ceramic metal bonded body and the circuit board according to one embodiment of the present invention can suppress damage such as cracks generated in the ceramic substrate.

An example of the ceramic metal joined body of this embodiment is shown, (a) is a plan view, (b) is a cross-sectional view taken along line A-A 'in (a), and (c) is a bottom view. The other example of the ceramic metal joined body of this embodiment is shown, (a) is a top view, (b) is sectional drawing in C-C 'of (a), (c) is a bottom view. The other example of the ceramic metal joined body of this embodiment is shown, (a) is a top view, (b) is sectional drawing in D-D 'of (a), (c) is a bottom view. The other example of the ceramic metal joined body of this embodiment is shown, (a) is a top view, (b) is sectional drawing in E-E 'of (a), (c) is a bottom view. The other example of the ceramic metal joined body of this embodiment is shown, (a) is a top view, (b) is sectional drawing in F-F 'of (a), (c) is a bottom view. The other example of the ceramic metal joined body of this embodiment is shown, (a) is a top view, (b) is sectional drawing in G-G 'of (a), (c) is a bottom view. The other example of the ceramic metal joined body of this embodiment is shown, (a) is a top view, (b) is sectional drawing in H-H 'of (a), (c) is a bottom view.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, in all the drawings in this specification, the same parts are denoted by the same reference symbols unless the confusion occurs, and the description thereof is omitted as appropriate.

  1A and 1B show an example of a ceramic-metal bonded body according to the present embodiment, in which FIG. 1A is a plan view, FIG. 1B is a cross-sectional view taken along line A-A ′ in FIG.

  A ceramic metal bonded body 10a shown in FIG. 1 includes a disk-shaped ceramic substrate 1, a first metal member 3 bonded to one main surface 1A side of the ceramic substrate 1 via a first metal layer 2, and a ceramic substrate. And a second metal member 5 bonded to the other main surface 1B side of the first metal via a second metal layer 4. The first metal member 3 has a circular first main surface P1 facing the one main surface 1A of the ceramic substrate 1 and a circular second main surface P2 opposite to the first main surface P1. The area of the first main surface P1 is smaller than that of the second main surface P2.

  FIG. 1 shows an example in which both the first metal member 3 and the second metal member 5 are disk-shaped, but at least one of the first metal member 3 and the second metal member 5 is cylindrical. Also good.

In the ceramic-metal bonded body 10a described above, the first main surface P1 and the second main surface P2 of the first metal member 3 are circular, so that the first main surface P1 and the second main surface P2 are somewhat large. While having a large area, the length of the peripheral line is relatively short. When the first metal member 3 is thermally expanded or contracted,
The peripheral line portion of the first main surface P1 and the peripheral line portion of the second main surface P2 serve as a starting point portion of a force for peeling or compressing the first metal layer 2. In particular, when there is a horn portion in the peripheral line portion, stress is easily applied to the horn portion so as to concentrate thermal expansion and contraction, and the ceramic substrate 1 is easily damaged. In the ceramic-metal bonded body 10a of the present embodiment, since the first main surface P1 and the second main surface P2 of the first metal member 3 are circular, there is no portion where these stresses tend to concentrate, and the first metal layer The force for peeling or compressing 2 is difficult to be applied to the first metal layer 2 and the ceramic substrate 1. Further, by reducing the area of the first main surface P1 as compared with the second main surface P2 of the first metal member 3, the degree of thermal expansion and contraction in the vicinity of the first main surface P1 can be reduced. It is smaller than the degree of thermal expansion and contraction in P2, and the thermal stress itself applied to the ceramic substrate 1 from the first main surface P1 on the side that restrains the ceramic substrate 1 is relatively small. In the ceramic metal bonded body 10a, damage such as cracks applied to the ceramic substrate 1 is suppressed. The second main surface P2 of the first metal member 3 also functions as a heat radiating surface that radiates the heat of the ceramic substrate 1. In the ceramic metal bonded body 10a, the extent of the thermal expansion and the thermal contraction of the first metal member 3 itself is suppressed by keeping the area on the second main surface P2 side relatively large. Damage is more reliably suppressed.

  2A and 2B show another example of the ceramic-metal bonded body of the present embodiment. FIG. 2A is a plan view, FIG. 2B is a sectional view taken along the line CC ′ of FIG. is there. 2, the same reference numerals as those in FIG. 1 are used for the same configurations as those in FIG. Also in the ceramic metal joined body 10c of the example shown in FIG. 2, the first metal member 3 has a circular third main surface P3 facing the one main surface 1A of the ceramic substrate 1 and a side opposite to the third main surface P3. It has a circular fourth main surface P4, and the area of the third main surface P3 is smaller than that of the fourth main surface P4. The ceramic metal joined body 10c of the example shown in FIG. 2 has a slit portion 3A provided in the first metal member 3, and the first metal member 3 is divided into a plurality of portions via the slit 3A. 1 is different from the ceramic-metal bonded body 10a shown in FIG. The first metal member 3 may be divided into a plurality of parts in this way, for example, when the first metal member 3 is desired to be divided into a plurality of electrically independent parts. Also in this case, each part of the metal member 3 has a shape in which the peripheral line part of the first main surface P1 and the peripheral line part of the second main surface P2 have arc-shaped parts, and the peripheral line has a plurality of corners. Compared to a certain case, the peripheral line is relatively short, and there are relatively few portions where stress or the like is likely to concentrate. Although not shown, the second metal member 5 may also be divided into a plurality of portions. 2 is an example in which the first metal member 3 is divided into two parts, but at least one of the first metal member 3 and the second metal member 5 is divided into three or more parts. May be.

  3A and 3B show another example of the ceramic-metal bonded body of the present embodiment, in which FIG. 3A is a plan view, FIG. 3B is a cross-sectional view taken along line DD ′ in FIG. . In the ceramic metal joined body 10d shown in FIG. 3, the first metal member 3 includes a first step 12 on the outer peripheral surface in the vicinity of the first main surface P1. Specifically, the first metal member 3 has a step 12 having a shape in which a part of the outer peripheral surface in the vicinity of the first main surface P1 is continuously cut out in the circumferential direction. By providing the step 12, the area of the outer peripheral surface of the first metal member 3 in the vicinity of the ceramic substrate 1 can be made relatively large. The area of the outer peripheral surface of the 1st metal member 3 means all the areas including the part corresponding to the level | step difference 12 including the part which faces the lower direction in FIG.3 (b). The vicinity of the first main surface P1 is a case where the space between the first main surface P1 and the second main surface P2 is divided into two along a plane parallel to the first main surface P1 and the second main surface P2. The part of the side including the first main surface P1. In the embodiment of FIG. 3, since the heat dissipation characteristics of the first metal member 3 in the vicinity of the ceramic substrate 1 are relatively high due to the stepped portion 12, the degree of thermal expansion and contraction in the vicinity of the first main surface P1 is The degree of thermal expansion and thermal contraction on the second main surface P2 can be further reduced.

FIG. 4 shows another example of the ceramic-metal bonded body of the present embodiment, (a) is a plan view, (b) is a sectional view taken along line EE ′ of (a), and (c) is a bottom view. is there. The ceramic metal joined body 10e shown in FIG. 4 is a ceramic metal joined body having the basic structure of the ceramic metal joined body 10a shown in FIG. 1, and the second metal member 5 is the other main body of the ceramic substrate 1. The third main surface has a circular third main surface P3 facing the surface 1B and a circular fourth main surface P4 opposite to the third main surface P3, as compared to the fourth main surface P4. The area of P3 is small.

  With such a configuration, not only in the first metal member 3 but also in the second metal member 5, the degree of thermal expansion and contraction in the vicinity of the third main surface P3 of the second metal member 5 is set to the fourth main surface. Compared with the degree of thermal expansion and thermal contraction in P4, the ceramic substrate 1 can be more reliably suppressed from being damaged.

  FIG. 5 shows another example of the ceramic-metal bonded body of the present embodiment, (a) is a plan view, (b) is a sectional view taken along line FF ′ in (a), and (c) is a bottom view. is there. In the ceramic metal joined body 10f of the example shown in FIG. 5, the second metal member 5 includes a second step 13 on the outer peripheral surface in the vicinity of the third main surface P3. Specifically, the second metal member 5 has a step 13 having a shape such that a part of the outer peripheral surface in the vicinity of the third main surface P3 is continuously cut out in the circumferential direction. By providing the step 13, the area of the outer peripheral surface of the second metal member 5 in the vicinity of the ceramic substrate 1 can be made relatively large. The area of the outer peripheral surface of the second metal member 5 refers to the entire area including the part corresponding to the step 13 and the part facing the lower side in FIG. The vicinity of the third main surface P3 is a case where the space between the third main surface P3 and the fourth main surface P4 is divided into two along a plane parallel to the third main surface P3 and the fourth main surface P4. This refers to the portion including the third main surface P3. In the embodiment of FIG. 5, since the heat dissipation characteristics of the second metal member 5 in the vicinity of the ceramic substrate 1 are relatively high due to the stepped portion 13, the degree of thermal expansion and contraction in the vicinity of the third main surface P <b> 3 is The degree of thermal expansion and contraction on the fourth main surface P4 can be further reduced.

  FIG. 6 shows another example of the ceramic-metal bonded body of the present embodiment, (a) is a plan view, (b) is a cross-sectional view at GG ′ in (a), and (c) is a bottom view. It is. The ceramic metal joined body 10g of the example shown in FIG. 6 has the ceramic metal joined body 10f of the example shown in FIG. 5 as a basic configuration, the first metal member 3 is mainly composed of copper, and the first metal layer 2 and the first metal Between the member 3, the 1st coupling layer 6 which has copper as a main component is arrange | positioned. With such a configuration, the first metal layer 2 and the first metal member 3 can be bonded at a low temperature (for example, 325 ° C.). It can be increased and high heat dissipation characteristics can be obtained.

  FIG. 7 shows another example of the ceramic-metal bonded body of the present embodiment, (a) is a plan view, (b) is a cross-sectional view at HH ′ of (a), and (c) is a bottom view. is there. The ceramic metal joined body 10n of the example shown in FIG. 7 has the ceramic metal joined body 10g of the example shown in FIG. 6 as a basic configuration, the second metal member 5 is mainly composed of copper, the second metal layer 2 and the second metal A second bonding layer 7 mainly composed of copper is disposed between the member 5 and the member 5. With such a configuration, since the second metal layer 4 and the second metal member 5 can be joined at a low temperature (for example, 325 ° C.), the second metal member 5 is less likely to warp, so the thickness thereof is reduced. It can be increased and higher heat dissipation characteristics can be obtained.

In addition, it is preferable that the copper which is a main component of the 1st coupling layer 2 and the 2nd coupling layer 4 is 1 or more types chosen from an oxygen free copper, a tough pitch copper, and phosphorus deoxidation copper. In particular, among oxygen-free copper, it is preferable to use any of linear crystalline oxygen-free copper, single-crystal high-purity oxygen-free copper, and vacuum-dissolved copper having a copper content of 99.995% by mass or more.

1 to 7, for example, the main component is silicon nitride, aluminum nitride, or aluminum oxide, and the first metal member 3 and the second metal member 5 are mainly composed of copper or aluminum. . In the case where the main component of the ceramic substrate 1 is aluminum oxide, it is preferably an aluminum oxide single crystal (sapphire) in terms of high heat dissipation characteristics. The main component in the present embodiment is a component occupying 60% by mass or more, more preferably 80% by mass or more, out of 100% by mass of all the components constituting each of the above members. For identification of the main component, an X-ray diffraction method may be used, and the content of the main component may be determined by fluorescent X-ray analysis or ICP emission spectroscopic analysis. Regarding a specific method for determining the content of the main component, when the main component of the ceramic substrate 1 is silicon nitride, the content of silicon is determined by fluorescent X-ray analysis or ICP emission spectroscopic analysis and converted to nitride. Thus, the content of silicon nitride may be obtained. Further, when the main component of the ceramic substrate 1 is aluminum nitride, the aluminum content may be obtained by the same method as described above, and the aluminum nitride content may be obtained in terms of nitride. . When the main component of each of the first metal member 3, the second metal member 5, the first bonding layer 6 and the second bonding layer 7 is copper, the electric resistance is low, the thermal conductivity is high, and the heat dissipation characteristics are excellent. Therefore, it is preferable to use at least one selected from oxygen-free copper, tough pitch copper, and phosphorus deoxidized copper having a high copper content. In particular, among oxygen-free copper, it is preferable to use any of linear crystalline oxygen-free copper, single-crystal high-purity oxygen-free copper, and vacuum-dissolved copper having a copper content of 99.995% by mass or more.

  Here, the ceramic substrate 1 has, for example, a diameter of 50 mm to 100 mm and a thickness of 0.3 mm to 12 mm. In addition, the first metal member 3 has, for example, a diameter of the first main surface P1 and the second main surface P2 of 30 mm to 38 mm, 40 mm to 48 mm, and a thickness of 2 mm to 20 mm. The second metal member 5 has, for example, a diameter of the third main surface P3 and the fourth main surface P4 of 30 mm to 38 mm and 40 mm to 48 mm, respectively, and a thickness of 2 mm to 20 mm.

  The first metal layer 2 and the second metal layer 4 both have a thickness of, for example, 0.1 mm or more and 0.6 mm or less.

  The first metal layer 2 and the second metal layer 4 are selected from, for example, silver and copper, at least one element A selected from indium, zinc and tin, and titanium, zirconium, hafnium and niobium. Including at least one element B and at least one element C selected from molybdenum, osmium, rhenium and tungsten, and a total content of 100% by mass of silver, copper, elements A, B and C, Copper content is 35% by mass or more and 50% by mass or less, and each content of elements A, B and C is 2% by mass or more and 22% by mass or less, 1% by mass or more and 8% by mass or less, 1% by mass or less 8% by mass, respectively. % Or less, and the balance is preferably made of silver.

  Moreover, as for the 1st coupling layer 6 and the 2nd coupling layer 7, all are 0.02 mm or more and 0.1 mm or less in thickness, for example.

  The circuit board of the present embodiment uses the above-described ceramic metal joined body, and one of the first metal member 3 and the second metal member 5 is connected to the circuit member on which the electronic component is mounted. The other of the one metal member or the second metal member 5 (the metal member different from the above one) corresponds to a heat dissipating member that dissipates the heat of the generated electronic component. As described above, the circuit board of the present embodiment is unlikely to crack at least from the outer peripheral surface of the ceramic substrate 1 on the first metal member 3 side, and can maintain reliability over a long period of time.

  Next, an example of the manufacturing method of the ceramic metal joined body of this embodiment is demonstrated.

  First, the disk-shaped ceramic substrate 1 is heat-treated at 800 ° C. or higher and 900 ° C. or lower in an air atmosphere to remove organic substances and residual carbon adhering to the surface of the ceramic substrate 1.

  Next, a paste-like brazing material is arranged on substantially the entire surface of the one main surface 1A and the other main surface 1B of the heat-treated ceramic substrate 1 in accordance with the arrangement of the first metal member 3 and the second metal member 5, and the screen printing method, After applying by any method such as pressure printing method and brush coating method, it is dried at 120 ° C. or higher and 150 ° C. or lower.

  Here, the component of the brazing material is a component constituting each of the first metal layer 2 and the second metal layer 4. And the 1st metal member 3 of the shape shown in either of FIGS. 1-8 is arrange | positioned, for example on the brazing material apply | coated and dried to one main surface 1A of the ceramic substrate 1, and the other main surface 1B By placing the second metal member 5 having the shape shown in any of FIGS. 1 to 8 on the brazing material applied and dried on the substrate, and heating in a vacuum atmosphere in the range of 800 ° C. or more and 900 ° C. or less. The first metal member 3 and the second metal member 5 can be bonded to the ceramic substrate 1 via the first metal layer 2 and the second metal layer 4, respectively.

  Then, a resist is printed on the surfaces of the first metal member 3 and the second metal member 5 that are joined, and the resist is dried at 120 ° C. or higher and 150 ° C. or lower. Etching using an aqueous iron solution or the like removes unnecessary portions of the first metal layer 2 and the second metal layer 4 on which the resist is not printed around the first metal member 3 and the second metal member 5, respectively. be able to. And any one of ceramic metal joined bodies 10a-10k can be obtained by removing a resist using alkaline aqueous solution, such as sodium hydroxide aqueous solution and potassium hydroxide aqueous solution.

  In order to obtain the ceramic-metal bonded body 10g shown in FIG. 6, a metal foil mainly composed of copper is applied to the second main surface on the brazing material applied to the first main surface of the ceramic substrate 1 and dried. The second metal member 5 having the shape shown in FIG. 6 is placed on the brazing material applied and dried on the metal, and heated in the range of 800 ° C. or more and 900 ° C. or less in a vacuum atmosphere, so that the metal foil and The two metal members 5 can be bonded to the ceramic substrate 1 via the first metal layer 2 and the second metal layer 4, respectively.

  And after grind | polishing the main surface of metal foil, the 1st metal member 3 is arrange | positioned, and it heats at 300-500 degreeC in the atmosphere chosen from hydrogen, nitrogen, neon, argon, etc., and 30 MPa After pressurizing with the above pressure, it cools to the temperature (50 degreeC) which copper does not oxidize, and after becoming below this temperature, a pressurization is complete | finished through the 1st metal layer 2 and the 1st coupling layer 6. Thus, the first metal member 3 can be bonded to the ceramic substrate 1.

  Then, a resist is printed on the surfaces of the first metal member 3 and the second metal member 5 that are joined, and the resist is dried at 120 ° C. or higher and 150 ° C. or lower. Etching using an aqueous iron solution or the like allows the first metal layer 2, the first bonding layer 6, and the second metal layer 4 on which the resist around each of the first metal member 3 and the second metal member 5 is not printed. Unnecessary portions can be removed. And 10 g of ceramic metal joined bodies can be obtained by removing a resist using alkaline aqueous solution, such as sodium hydroxide aqueous solution and potassium hydroxide aqueous solution.

  Further, in order to obtain the ceramic-metal bonded body 10h shown in FIG. 7, metal foils mainly composed of copper on the brazing material coated and dried on the first main surface and the second main surface of the ceramic substrate 1, respectively. The metal foil can be bonded to the ceramic substrate 1 via the first metal layer 2 and the second metal layer 4 respectively by heating in a range of 800 ° C. or higher and 900 ° C. or lower in a vacuum atmosphere. .

And after grind | polishing the main surface of both metal foil, the 1st metal member 3 and the 2nd metal member 5 are arrange | positioned, and in the atmosphere chosen from hydrogen, nitrogen, neon, argon, etc., 300
The first metal is heated at a temperature not lower than 500 ° C. and pressurized at a pressure of 30 MPa or higher, then cooled to a temperature at which copper does not oxidize (50 ° C.). The first metal member 3 can be bonded to the ceramic substrate 1 via the layer 2 and the first bonding layer 6, and the second metal member 5 can be bonded to the ceramic substrate 1 via the second metal layer 4 and the second bonding layer 7. .

  Then, a resist is printed on the surfaces of the first metal member 3 and the second metal member 5 that are joined, and the resist is dried at 120 ° C. or higher and 150 ° C. or lower. Etching using an aqueous iron solution or the like allows the first metal layer 2, the first bonding layer 6, the second metal layer 4 and the first metal member 3 and the second metal member 5 not to be printed with resist around each of them. Unnecessary portions of the second bonding layer 7 can be removed. Then, the ceramic metal joined body 10h can be obtained by removing the resist using an aqueous alkali solution such as an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution.

The ceramic-metal bonded body 10 obtained by the manufacturing method as described above has the above-described characteristics in which the constraint on the outer peripheral portion on the first metal member 3 side is reduced even when heat is repeatedly applied to the ceramic substrate 1. In the circuit board using the ceramic metal joined body of the present embodiment, since cracks starting from the outer peripheral surface on the first metal member 3 side in the ceramic substrate 1 are difficult to enter, reliability is maintained over a long period of time. can do.

1: Ceramic substrate 2: First metal layer 3: First metal member 4: Second metal layer 5: Second metal member 6: First bonding layer 7: Second bonding layer
10: Ceramics metal joint

Claims (6)

A disk-shaped ceramic substrate, a first metal member bonded to one main surface side of the ceramic substrate via a first metal layer, and a second metal layer bonded to the other main surface side of the ceramic substrate A ceramic metal joined body having a second metal member formed,
The first metal member has a circular first main surface facing the one main surface of the ceramic substrate, and a circular second main surface on the side opposite to the first main surface, The area of the first main surface is smaller than that of the second main surface,
Wherein the first metal member is a main component of copper, the first metal layer is a brazing material, by disposing the first coupling layer comprising copper foil between the first metal member and the first metal layer A ceramic metal joined body characterized by comprising:   2. The ceramic metal bonded body according to claim 1, wherein the first metal member includes a first step on an outer peripheral surface in a vicinity of the first main surface.   The second metal member has a circular third main surface facing the other main surface of the ceramic substrate, and a circular fourth main surface opposite to the third main surface, The ceramic metal joined body according to claim 1 or 2, wherein an area of the third main surface is smaller than that of the fourth main surface.   4. The ceramic metal bonded body according to claim 3, wherein the second metal member includes a second step on an outer peripheral surface in a vicinity of the third main surface. 5. A disk-shaped ceramic substrate, a first metal member bonded to one main surface side of the ceramic substrate via a first metal layer, and a second metal layer bonded to the other main surface side of the ceramic substrate A ceramic metal joined body having a second metal member formed,
The first metal member has a circular first main surface facing the one main surface of the ceramic substrate, and a circular second main surface on the side opposite to the first main surface, The area of the first main surface is smaller than that of the second main surface,
The second metal member is a main component of copper, said second metal layer is a brazing material, by placing a second coupling layer comprising copper foil between the second metal member and the second metal layer A ceramic metal joined body characterized by comprising:   A circuit board using the ceramic-metal bonded body according to any one of claims 1 to 5.

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