JP7725907B2 - Copper/ceramic bonded body and insulated circuit board - Google Patents

Description

This invention relates to a copper/ceramic bonded body formed by bonding a copper member made of copper or a copper alloy to a ceramic member, and to an insulated circuit board formed by bonding a copper plate made of copper or a copper alloy to the surface of a ceramic substrate.

In the power module, LED module, and thermoelectric module, a power semiconductor element, an LED element, and a thermoelectric element are bonded to an insulating circuit board having a circuit layer made of a conductive material formed on one surface of an insulating layer.
For example, power semiconductor elements for controlling large amounts of electric power used to control wind power generation, electric vehicles, hybrid vehicles, etc. generate a large amount of heat during operation. Therefore, as the substrate on which these elements are mounted, an insulated circuit board has been widely used that includes a ceramic substrate, a circuit layer formed by bonding a metal plate with excellent conductivity to one surface of the ceramic substrate, and a metal layer for heat dissipation formed by bonding a metal plate to the other surface of the ceramic substrate.

For example, Patent Document 1 proposes an insulated circuit board in which a circuit layer and a metal layer are formed by bonding copper plates to one side and the other side of a ceramic substrate. In Patent Document 1, copper plates are placed on one side and the other side of the ceramic substrate with an Ag-Cu-Ti brazing material interposed between them, and the copper plates are bonded by heat treatment (the so-called active metal brazing method).

Furthermore, Patent Document 2 proposes a power module substrate in which a copper plate made of copper or a copper alloy and a ceramic substrate made of AlN or Al ₂ O ₃ are bonded together using a bonding material containing Ag and Ti.
Furthermore, Patent Document 3 proposes a power module substrate in which a copper plate made of copper or a copper alloy and a ceramic substrate made of silicon nitride are bonded together using a bonding material containing Ag and Ti.
As described above, when a copper plate and a ceramic substrate are joined using a bonding material containing Ti, Ti, which is an active metal, reacts with the ceramic substrate, improving the wettability of the bonding material and increasing the bonding strength between the copper plate and the ceramic substrate.

Patent No. 3211856 Patent No. 5757359 Japanese Patent Application Laid-Open No. 2018-008869

Recently, there has been a trend toward higher heat generation temperatures from semiconductor elements mounted on insulated circuit boards, and insulated circuit boards are being required to have higher thermal cycle reliability than ever before, so that they can withstand severe thermal cycles.
Here, as mentioned above, when a copper plate and a ceramic substrate are joined using a joining material containing Ti, Ti, which is an active metal, diffuses to the copper plate side, and an intermetallic compound containing Cu and Ti precipitates, which hardens the vicinity of the joining interface, causing cracks in the ceramic member when subjected to thermal cycling, which could reduce thermal cycling reliability.

This invention was made in consideration of the above-mentioned circumstances, and aims to provide a copper/ceramic bonded body that can suppress the occurrence of cracks in the ceramic member even when subjected to severe thermal cycling and has excellent thermal cycling reliability, as well as an insulated circuit board made of this copper/ceramic bonded body.

As a result of extensive research conducted by the inventors to solve the aforementioned problems, they discovered that when a ceramic member and a copper member are joined using a joining material containing Ag and an active metal, the joining layer formed at the joining interface contains an Ag-enriched phase with a high Ag concentration and active-metal-containing precipitates containing the active metal, and that the joining interface hardens due to precipitation hardening caused by the active-metal-containing precipitates. Therefore, they discovered that by optimizing the amount of active-metal-containing precipitates present, it is possible to suppress the occurrence of cracks in ceramic members when subjected to thermal cycles.

The present invention has been made based on the above-mentioned findings, and the copper/ceramic joined body of the present invention is a copper/ceramic joined body obtained by joining a copper member made of copper or a copper alloy to a ceramic member, wherein an active metal compound layer is formed on the ceramic member side at the joining interface between the ceramic member and the copper member, and an area A of active metal-containing precipitates is 360 μm2 or less within a field of view of 200 μm in the width direction of the joining interface in a cross section along the lamination direction of the ceramic member and the copper member and 10 μm from the surface of the active metal compound layer toward the copper member, and ^a ratio A/B of the area A of the active metal-containing precipitates to an area B of an Ag-enriched phase having an Ag concentration of 10 atomic % or more is within a range of 0.03 to 0.8.

In the copper/ceramic joined body of the present invention, within a field of view of 200 μm in the width direction of the joining interface in a cross section taken along the lamination direction of the ceramic member and the copper member and 10 μm from the surface of the active metal compound layer toward the copper member, the ratio A/B of the area A of the active metal-containing precipitates to the area B of the Ag-enriched phase having an Ag concentration of 10 atomic % or more is 0.03 or more. This ensures that the active metal reacts sufficiently, and the ceramic member and the copper member are firmly joined together.
Furthermore, the area A of the active metal-containing precipitate is set to 360 ^μm2 or less, and the ratio A/B of the area A of the active metal-containing precipitate to the area B of the Ag-enriched phase having an Ag concentration of 10 atomic % or more is set to 0.8 or less. This makes it possible to prevent the bonding interface from becoming hard, and to prevent the ceramic members from cracking when subjected to thermal cycles.

In the copper/ceramic bonded body of the present invention, the thickness t1 of the active metal compound layer is preferably in the range of 0.05 μm to 1.2 μm.
In this case, the thickness t1 of the active metal compound layer is set within the range of 0.05 μm or more and 1.2 μm or less, so that the active metal reliably and firmly bonds the ceramic member and the copper member, and hardening of the bonding interface is further suppressed.

In the copper/ceramic joined body of the present invention, it is preferable that an Ag—Cu alloy layer is formed on the copper member side at the joining interface between the ceramic member and the copper member, and that the Ag—Cu alloy layer has a thickness t2 in the range of 1 μm to 30 μm.
In this case, Ag of the bonding material reacts sufficiently with the copper member to reliably and firmly bond the ceramic member and the copper member, and hardening of the bonding interface is further suppressed.

The insulated circuit board of the present invention is an insulated circuit board obtained by bonding a copper plate made of copper or a copper alloy to the surface of a ceramic substrate, wherein an active metal compound layer is formed on the ceramic substrate side at the bonding interface between the ceramic substrate and the copper plate, and the area A of active metal-containing precipitates is 360 ^μm2 or less within a field of view of 200 μm in the width direction of the bonding interface in a cross section along the lamination direction of the ceramic substrate and the copper plate and 10 μm from the surface of the active metal compound layer toward the copper plate, and the ratio A/B of the area A of the active metal-containing precipitates to the area B of an Ag-enriched phase having an Ag concentration of 10 atomic % or more is within a range of 0.03 to 0.8.

According to the insulating circuit board of the present invention, within a field of view of 200 μm in the width direction of the bonding interface in a cross section along the lamination direction of the ceramic substrate and the copper plate and 10 μm from the surface of the active metal compound layer toward the copper member, the ratio A/B of the area A of the active metal-containing precipitates to the area B of the Ag-enriched phase having an Ag concentration of 10 atomic % or more is 0.03 or more, so that the active metal has reacted sufficiently and the ceramic substrate and the copper plate are firmly bonded together.
Furthermore, the area A of the active metal-containing precipitate is set to 360 ^μm2 or less, and the ratio A/B of the area A of the active metal-containing precipitate to the area B of the Ag-enriched phase having an Ag concentration of 10 atomic % or more is set to 0.8 or less. This makes it possible to prevent the bonding interface from becoming hard, and to prevent the ceramic substrate from cracking when subjected to thermal cycles.

In the insulating circuit board of the present invention, the thickness t1 of the active metal compound layer is preferably within the range of 0.05 μm to 1.2 μm.
In this case, the thickness t1 of the active metal compound layer is set within the range of 0.05 μm or more and 1.2 μm or less, so that the active metal reliably and firmly bonds the ceramic substrate and the copper plate, and further prevents the bonding interface from hardening.

In addition, in the insulating circuit board of the present invention, it is preferable that an Ag-Cu alloy layer is formed on the copper plate side at the bonding interface between the ceramic substrate and the copper plate, and that the thickness t2 of the Ag-Cu alloy layer is in the range of 1 μm or more and 30 μm or less.
In this case, Ag in the bonding material reacts sufficiently with the copper plate to reliably and firmly bond the ceramic substrate and the copper plate, and hardening of the bonding interface is further suppressed.

The present invention provides a copper/ceramic bonded body that can suppress the occurrence of cracks in ceramic members even when subjected to severe thermal cycles, and has excellent thermal cycle reliability, as well as an insulated circuit board made of this copper/ceramic bonded body.

1 is a schematic explanatory diagram of a power module using an insulating circuit board according to an embodiment of the present invention. FIG. 3 is an enlarged explanatory view of the bonding interface between the circuit layer and the metal layer of the insulating circuit board according to the embodiment of the present invention and the ceramic substrate. FIG. 1 is a flowchart of a method for manufacturing an insulating circuit board according to an embodiment of the present invention. 1A to 1C are schematic explanatory views of a method for manufacturing an insulating circuit board according to an embodiment of the present invention. FIG. 2 is an explanatory diagram showing a method for calculating the area A of the active metal-containing precipitate and the area B of the Ag-enriched phase in an example of the present invention. 1 is a photograph showing an example of the observation result of a bonding interface in this example.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
The copper/ceramic joined body according to this embodiment is an insulating circuit board 10 formed by joining a ceramic substrate 11 as a ceramic member made of ceramic to a copper plate 42 (circuit layer 12) and a copper plate 43 (metal layer 13) as copper members made of copper or a copper alloy. Fig. 1 shows a power module 1 including the insulating circuit board 10 according to this embodiment.

This power module 1 includes an insulated circuit board 10 on which a circuit layer 12 and a metal layer 13 are arranged, a semiconductor element 3 bonded to one surface of the circuit layer 12 (the upper surface in Figure 1) via a bonding layer 2, and a heat sink 5 arranged on the other side of the metal layer 13 (the lower side in Figure 1).

The semiconductor element 3 is made of a semiconductor material such as Si. The semiconductor element 3 and the circuit layer 12 are bonded together via the bonding layer 2.
The bonding layer 2 is made of, for example, a Sn--Ag based, Sn--In based, or Sn--Ag--Cu based solder material.

The heat sink 5 is used to dissipate heat from the insulating circuit board 10. The heat sink 5 is made of copper or a copper alloy, and in this embodiment, is made of phosphorus-deoxidized copper. The heat sink 5 is provided with a flow path for a cooling fluid to flow.
In this embodiment, the heat sink 5 and the metal layer 13 are joined together by a solder layer 7 made of a solder material. The solder layer 7 is made of, for example, a Sn—Ag-based, Sn—In-based, or Sn—Ag—Cu-based solder material.

As shown in FIG. 1, the insulating circuit board 10 of this embodiment comprises a ceramic substrate 11, a circuit layer 12 disposed on one surface (the upper surface in FIG. 1) of the ceramic substrate 11, and a metal layer 13 disposed on the other surface (the lower surface in FIG. 1) of the ceramic substrate 11.

The ceramic substrate 11 is made of a ceramic such as _{silicon nitride} ( _Si3N4 ), aluminum nitride (AlN), or alumina ( _Al2O3 ), which has excellent insulating and heat dissipation properties. In this embodiment, the ceramic substrate 11 is made of aluminum nitride (AlN), which has particularly excellent heat dissipation properties. The thickness of the ceramic substrate 11 is set, for example, within a range of 0.2 mm to 1.5 mm, and in this embodiment, it is set to 0.635 mm.

As shown in FIG. 4, the circuit layer 12 is formed by joining a copper plate 42 made of copper or a copper alloy to one surface (the upper surface in FIG. 4) of the ceramic substrate 11 .
In this embodiment, the circuit layer 12 is formed by bonding a rolled sheet of oxygen-free copper to the ceramic substrate 11 .
The thickness of the copper plate 42 that becomes the circuit layer 12 is set within a range of 0.1 mm to 2.0 mm, and in this embodiment, it is set to 0.6 mm.

As shown in FIG. 4, the metal layer 13 is formed by joining a copper plate 43 made of copper or a copper alloy to the other surface (the lower surface in FIG. 4) of the ceramic substrate 11 .
In this embodiment, the metal layer 13 is formed by bonding a rolled sheet of oxygen-free copper to the ceramic substrate 11 .
The thickness of the copper plate 43 that becomes the metal layer 13 is set within a range of 0.1 mm to 2.0 mm, and in this embodiment, it is set to 0.6 mm.

As shown in FIG. 2, at the bonding interface between the ceramic substrate 11 and the circuit layer 12 and metal layer 13, an active metal compound layer 21 and an Ag—Cu alloy layer 22 are formed in this order from the ceramic substrate 11 side.
In this embodiment, the bonding material 45 contains Ti as an active metal, and the ceramic substrate 11 is made of aluminum nitride, so the active metal compound layer 21 is made of titanium nitride (TiN).

In the insulating circuit board 10 of this embodiment, active metal-containing precipitates are present at the bonding interface between the ceramic substrate 11 and the circuit layer 12 and at the bonding interface between the ceramic substrate 11 and the metal layer 13 .
Here, the area A of the active metal-containing precipitate is set to 360 μm2 or less within a field of view of 200 μm in the width direction of the bonding interface in a cross section along the stacking direction of the ceramic substrate 11 and the circuit layer 12 and metal layer ¹³ , and 10 μm from the surface of the active metal compound layer 21 toward the circuit layer 12 and metal layer 13. This prevents the bonding interface from hardening, and suppresses the occurrence of cracks in the ceramic substrate 11 when subjected to thermal cycles. The area A of the active metal-containing precipitate is preferably set to ¹⁰ μm2 or more. It is difficult to manufacture an insulating circuit board 10 in which the area A of the active metal-containing precipitate is less than ¹⁰ μm2.
Furthermore, the ratio A/B of the area A of the active metal-containing precipitate to the area B of the Ag-enriched phase having an Ag concentration of 10 atomic % or more is set to a range of 0.03 to 0.8, thereby preventing the bonding interface from becoming hard and suppressing the occurrence of cracks in the ceramic substrate 11 when subjected to thermal cycles.

Furthermore, in this embodiment, it is preferable that the thickness t1 of the active metal compound layer 21 formed at the bonding interface between the circuit layer 12 and the metal layer 13 be within the range of 0.05 μm to 1.2 μm.
In this embodiment, the thickness t2 of the Ag--Cu alloy layer 22 formed at the bonding interface between the circuit layer 12 and the metal layer 13 is preferably 1 μm or more and 30 μm or less.

The manufacturing method for the insulating circuit board 10 according to this embodiment will be described below with reference to Figures 3 and 4.

(Joint material disposing step S01)
A copper plate 42 that will become the circuit layer 12 and a copper plate 43 that will become the metal layer 13 are prepared.
Then, a bonding material 45 is applied to the bonding surfaces of the copper plate 42 that will become the circuit layer 12 and the copper plate 43 that will become the metal layer 13, and then dried. The thickness of the applied paste bonding material 45 is preferably in the range of 10 μm to 50 μm after drying.
In this embodiment, the paste-like bonding material 45 is applied by screen printing.

The bonding material 45 contains Ag and active metals (Ti, Zr, Nb, Hf). In this embodiment, an Ag-Ti brazing filler metal (Ag-Cu-Ti brazing filler metal) is used as the bonding material 45. It is preferable to use an Ag-Ti brazing filler metal (Ag-Cu-Ti brazing filler metal) that contains, for example, Cu in the range of 0% by mass to 45% by mass, Ti (the active metal) in the range of 0.5% by mass to 20% by mass, with the remainder being Ag and unavoidable impurities.

The bonding material 45 uses Ag powder as the Ag and active metal powder as the active metal. The specific surface area of the Ag powder contained therein is preferably 0.15 m ² /g or more, more preferably 0.25 m ² /g or more, and even more preferably 0.40 m ² /g or more. On the other hand, the specific surface area of the Ag powder contained in the bonding material 45 is preferably 1.40 m ² /g or less, more preferably 1.00 m ² /g or less, and even more preferably 0.75 ^{m 2} /g or less.

In this embodiment, the particle size distribution [ _D90 - _D10 ] of Ag powder contained in the bonding material 45 and the ratio [ _D90 - _D10 ] _Ag /[ _D90 - _D10 ] active _{metal of the particle size distribution of the active} metal _powder [ _D90 - _D10 ] _{active metal} are adjusted to adjust the area A of the active metal-containing precipitate at the bonding interface and the ratio A/B of the area A of the active metal-containing precipitate to the area B of the Ag-enriched phase having an Ag concentration of 10 atomic % or more.

By setting the particle size distribution ratio [ _D90 - _D10 ] _Ag /[ _D90 - _D10 ] _{active metal} to 0.01 or more, the area A and area ratio A/B of the active metal-containing precipitate are prevented from becoming unnecessarily high. On the other hand, by setting the particle size distribution ratio [ _D90 - _D10 ] _Ag /[ _D90 - _D10 ] _{active metal} to 1.00 or less, the area A and area ratio A/B of the active metal-containing precipitate are prevented from becoming unnecessarily low.
The particle size distribution ratio [D ₉₀ -D ₁₀ ] _Ag /[D ₉₀ -D ₁₀ ] _{active metal} is more preferably 0.05 or more, and even more preferably 0.15 or more, and the particle size distribution ratio [D ₉₀ -D ₁₀ ] _Ag /[D ₉₀ -D ₁₀ ] _{active metal} is more preferably 0.80 or less, and even more preferably 0.50 or less.

(Lamination step S02)
Next, a copper plate 42 that will become the circuit layer 12 is laminated on one surface (top surface in Figure 4) of the ceramic substrate 11 via a bonding material 45, and a copper plate 43 that will become the metal layer 13 is laminated on the other surface (bottom surface in Figure 4) of the ceramic substrate 11 via a bonding material 45.

(Pressure and heating step S03)
Next, the copper plate 42, the ceramic substrate 11, and the copper plate 43 are heated in a heating furnace in a vacuum atmosphere while being pressed together, to melt the bonding material 45.
Here, the heating temperature in the pressurizing and heating step S03 is preferably within a range of 800° C. to 850° C. The total temperature integral value in the temperature increasing step from 780° C. to the heating temperature and the holding step at the heating temperature is preferably within a range of 7° C.-h to 120° C.-h.
The pressure load in the pressurizing and heating step S03 is preferably set within a range of 0.029 MPa or more and 2.94 MPa or less.
Furthermore, the degree of vacuum in the pressurizing and heating step S03 is preferably set to a range of 1×10 ⁻⁶ Pa or more and 5×10 ⁻² Pa or less.

(Cooling process S04)
Then, after the pressurizing and heating step S03, the molten bonding material 45 is solidified by cooling, bonding the copper plate 42 that will become the circuit layer 12 to the ceramic substrate 11, and the ceramic substrate 11 to the copper plate 43 that will become the metal layer 13.
The cooling rate in the cooling step S04 is preferably within a range of 2° C./min to 20° C./min, inclusive, from the heating temperature to 780° C., the Ag—Cu eutectic temperature.

As described above, the insulating circuit board 10 of this embodiment is manufactured through the bonding material application process S01, the lamination process S02, the pressure and heating process S03, and the cooling process S04.

(Heat sink bonding step S05)
Next, the heat sink 5 is bonded to the other surface of the metal layer 13 of the insulating circuit board 10 .
The insulating circuit board 10 and the heat sink 5 are stacked with a solder material interposed therebetween and placed in a heating furnace, where the insulating circuit board 10 and the heat sink 5 are solder-joined via the solder layer 7 .

(Semiconductor element bonding step S06)
Next, the semiconductor element 3 is joined to one surface of the circuit layer 12 of the insulating circuit board 10 by soldering.
Through the above-described steps, the power module 1 shown in FIG. 1 is manufactured.

In the insulating circuit board 10 (copper/ceramic bonded body) of the present embodiment configured as described above, within a field of view of 200 μm in the width direction of the bonded interface in a cross section along the stacking direction of the ceramic substrate 11, and the circuit layer 12 and the metal layer 13, and 10 μm from the surface of the active metal compound layer 21 toward the circuit layer 12 and the metal layer 13, the ratio A/B of the area A of the active metal-containing precipitates to the area B of the Ag-enriched phase having an Ag concentration of 10 atomic % or more is 0.03 or more. Therefore, the active metal has sufficiently reacted, and the ceramic substrate 11 is firmly bonded to the circuit layer 12 and the metal layer 13.
Furthermore, the area A of the active metal-containing precipitate is set to 360 ^μm2 or less, and the ratio A/B of the area A of the active metal-containing precipitate to the area B of the Ag-enriched phase having an Ag concentration of 10 atomic % or more is set to 0.8 or less. This prevents the bonding interface from becoming hard, and prevents cracks from occurring in the ceramic substrate 11 when subjected to thermal cycles.

Furthermore, in this embodiment, an active metal compound layer 21 is formed at the bonding interface between the ceramic substrate 11 and the circuit layer 12 and metal layer 13. When the thickness t1 of the active metal compound layer 21 is within the range of 0.05 μm or more and 1.2 μm or less, the active metal reliably and firmly bonds the ceramic substrate 11 to the circuit layer 12 and metal layer 13, and further prevents the bonding interface from hardening.

In order to further improve thermal cycle reliability, the thickness t1 of the active metal compound layer 21 is preferably set to 0.08 μm or less, and more preferably set to 0.15 μm or less.
In order to further prevent the bonding interface from becoming harder than necessary, the thickness t1 of the active metal compound layer 21 is preferably set to 1.0 μm or less, and more preferably set to 0.6 μm or less.

Furthermore, in this embodiment, an Ag-Cu alloy layer 22 is formed at the bonding interface between the ceramic substrate 11 and the circuit layer 12 and metal layer 13. When the thickness t2 of this Ag-Cu alloy layer 22 is within the range of 1 μm or more and 30 μm or less, the Ag of the bonding material reacts sufficiently with the circuit layer 12 and metal layer 13, reliably and firmly bonding the ceramic substrate 11 to the circuit layer 12 and metal layer 13, and further suppressing hardening of the bonding interface.

In order to further firmly bond the ceramic substrate 11 to the circuit layer 12 and the metal layer 13, the thickness t2 of the Ag--Cu alloy layer 22 is preferably 3 μm or more, and more preferably 5 μm or more.
In order to further prevent the bonding interface from becoming harder than necessary, the thickness t2 of the Ag--Cu alloy layer 22 is preferably set to 25 μm or less, and more preferably set to 15 μm or less.

Although the embodiment of the present invention has been described above, the present invention is not limited to this and can be modified as appropriate within the scope of the technical idea of the invention.
For example, in the present embodiment, a power module is described as being configured by mounting a semiconductor element on an insulating circuit board, but the present invention is not limited to this. For example, an LED module may be configured by mounting an LED element on a circuit layer of an insulating circuit board, or a thermoelectric module may be configured by mounting a thermoelectric element on a circuit layer of an insulating circuit board.

Furthermore, in the insulating circuit board of this embodiment, the ceramic substrate has been described as being made of aluminum nitride (AlN), but the present invention is not limited to this, and other ceramic substrates such as alumina (Al ₂ O ₃ ) and silicon nitride (Si ₃ N ₄ ) may also be used.

Furthermore, in this embodiment, Ti has been used as an example of the active metal contained in the joining material, but this is not limited to this, and it is sufficient if the joining material contains one or more active metals selected from Ti, Zr, Hf, and Nb. Note that these active metals may also be contained as hydrides.

Furthermore, in this embodiment, the circuit layer is described as being formed by bonding a rolled sheet of oxygen-free copper to a ceramic substrate, but this is not limited thereto, and the circuit layer may be formed by bonding copper pieces punched out of a copper plate in a circuit pattern to a ceramic substrate. In this case, it is sufficient that each copper piece has the interface structure with the ceramic substrate as described above.
In addition, in this embodiment, the bonding material is described as being disposed on the bonding surface of the copper plate, but this is not limited to this, and it is sufficient that the bonding material is disposed between the ceramic substrate and the copper plate, and the bonding material may also be disposed on the bonding surface of the ceramic substrate.

Below, we will explain the results of confirmation experiments conducted to confirm the effectiveness of this invention.

First, ceramic substrates (40 mm x 40 mm) were prepared as shown in Table 1. The thicknesses were 0.635 mm _for AlN and _Al2O3 , and 0.32 _mm for _Si3N4 .
Furthermore, copper plates made of oxygen-free copper and measuring 37 mm x 37 mm and having the thickness shown in Table 1 were prepared as copper plates to be used as circuit layers and metal layers.

A bonding material containing Ag powder and active metal powder shown in Table 1 was applied to a copper plate that would become a circuit layer and a metal layer so that the target thickness after drying would be the value shown in Table 1.
The bonding material used was a paste material, and the amounts of Ag, Cu, and active metal were as shown in Table 1.
The BET value (specific surface area) of the Ag powder was measured using AUTOSORB-1 manufactured by QUANTACHRROME, with pretreatment of vacuum degassing by heating at 150°C for 30 minutes, followed by N ₂ adsorption, liquid nitrogen at 77K, and the BET multipoint method.

Particle size distribution of Ag powder [D ₉₀ -D ₁₀ ] The particle size distribution of _Ag and active metal powder [D ₉₀ -D ₁₀ ] _{active metal} was measured as follows.
Particle size distribution was measured using a laser diffraction/scattering particle size distribution analyzer (MT3300EXII) manufactured by Microtrac. The powder was dispersed in an aqueous sodium hexametaphosphate solution and subjected to US dispersion for 1 minute. The measurement was performed three times, and the average value was used. In the measurement results, the particle size at which the cumulative frequency was 10% on a volume basis was defined as D10, and the particle size at which the cumulative frequency was 90% was defined as D90. The particle size of D90-D10 for Ag powder was defined as [ _D90 - _D10 ] _Ag , and the particle size of D90-D10 for active metal powder was defined as [ _D90 - _D10 ] _{active metal} . The ratio of [ _D90 - _D10 ] _Ag to [ _D90 - _D10 ] _{active metal} ([ _D90 - _D10 ] _Ag / _D90 - _D10 ] _{active metal} ) is shown in Table 1.

A copper plate, which will serve as the circuit layer, was laminated on one side of the ceramic substrate. Furthermore, a copper plate, which will serve as the metal layer, was laminated on the other side of the ceramic substrate.

The laminate was heated while being pressed in the stacking direction to generate an Ag—Cu liquid phase. The pressure load was 0.294 MPa, and the temperature integral values were as shown in Table 2.
The heated laminate was then cooled to bond the copper plate that would become the circuit layer, the ceramic substrate, and the metal plate that would become the metal layer together, thereby obtaining an insulated circuit board (copper/ceramic bonded body).

The resulting insulated circuit board (copper/ceramic bonded body) was evaluated for the area A of the active metal-containing precipitate, the area B of the Ag-enriched phase, the thickness t1 of the active metal compound layer, the thickness t2 of the Ag-Cu alloy layer, and thermal cycle reliability as follows:

(Area A of active metal-containing precipitate)
The cross sections of the bonding interfaces between the circuit layer and the metal layer and the ceramic substrate were observed using an EPMA device, and element maps (50 μm wide×30 μm high) of the active metal were obtained from five fields of view for each, for a total of 10 fields of view.
As shown in Figure 5, in the region from the active metal compound layer to 10 µm toward the surface of the circuit layer (metal layer), when Ag + Cu + active metal = 100 atomic %, the region where the active metal concentration was in the range of 30 atomic % to 70 atomic % was defined as the active metal-containing precipitate, and the area A of the active metal-containing precipitate was calculated. The average value of these 10 fields of view is shown in Table 2. If waviness occurs in the active metal compound layer, the region is set along the waviness.

(Area B of Ag-enriched phase)
As with the area A of the active metal-containing precipitate, the cross section of the bonding interface between the circuit layer and the metal layer and the ceramic substrate was observed using an EPMA device, and element maps (width 50 μm × height 30 μm) for Ag were obtained from five fields of view each, for a total of 10 fields of view.
5, in the region from the active metal compound layer to 10 μm toward the surface of the circuit layer (metal layer), when Ag + Cu + active metal = 100 atomic %, the region where the Ag concentration was 10 atomic % or more was defined as the Ag-enriched phase, and the area B of the Ag-enriched phase was calculated. The average values of these 10 fields of view are shown in Table 2.
Furthermore, the ratio A/B of the area A of the active metal-containing precipitate to the area B of the Ag-enriched phase was calculated and shown in Table 2.
An example of the observation result of the bonded interface is shown in Fig. 6. Active metal-containing precipitates and an Ag-enriched phase are observed at the bonded interface.

(Active metal compound layer)
The cross sections of the bonding interface between the circuit layer and the ceramic substrate and the bonding interface between the ceramic substrate and the metal layer were measured at a magnification of 30,000 times using a scanning electron microscope (ULTRA55 manufactured by Carl Zeiss NTS, accelerating voltage 1.8 kV), and elemental mapping of N, O, and active metal elements was obtained by energy dispersive X-ray analysis. The presence of an active metal compound layer was determined when the active metal element and N or O were present in the same region.
Observation was performed in five fields of view for each sample, and the area in which the active metal element and N or O were present in the same region was divided by the measured width, and the average value was recorded in Table 2 as the "thickness of the active metal compound layer."

(Ag-Cu alloy layer)
The cross sections of the bonding interface between the circuit layer and the ceramic substrate, and the bonding interface between the ceramic substrate and the metal layer were subjected to elemental mapping of Ag, Cu, and active metals using an EPMA device. Elemental mapping was performed in five fields of view for each.
When Ag + Cu + active metal = 100% by mass, the region where the Ag concentration was 15% by mass or more was defined as the Ag—Cu alloy layer, and the area of the layer was calculated and divided by the width of the measurement region (200 μm) to obtain the value (area/width of measurement region (200 μm)). The average of these values is shown in Table 2 as the thickness of the Ag—Cu alloy layer.

(Cold-heat cycle reliability)
The insulating circuit boards described above were subjected to the following thermal cycles depending on the material of the ceramic substrate, and the presence or absence of ceramic cracks was determined by SAT testing. The evaluation results are shown in Table 2.
For AlN and Al ₂ O ₃ : -40°C x 5 min ←→ 150°C x 5 min, SAT inspection every 50 cycles up to 500 cycles.
For Si ₃ N ₄ : -40°C x 5 min ←→ 150°C x 5 min, SAT inspection every 200 cycles up to 2000 cycles.

First, invention examples 1-3 and comparative example 1, which use AlN as the ceramic substrate, will be compared.
In Comparative Example 1, in a field of view of 200 μm in the width direction of the bonding interface in a cross section along the lamination direction of the ceramic substrate and the copper plate and 10 μm from the surface of the active metal compound layer toward the copper plate, the ratio A/B of the area A of the active metal-containing precipitate to the area B of the Ag-enriched phase having an Ag concentration of 10 atomic % or more was 0.007, and the number of times cracks occurred in a thermal cycle test was 50.

In contrast, in Examples 1-3 of the present invention, the area A of the active metal-containing precipitate was 360 ^μm2 or less, and the ratio A/B of the area A of the active metal-containing precipitate to the area B of the Ag-enriched phase having an Ag concentration of 10 atomic % or more was in the range of 0.03 to 0.8, and the number of crack occurrences in the thermal cycling test was 350 to 500, indicating excellent thermal cycling reliability.

Next, invention examples 4-6 and comparative examples 2 and 3, which use Si ₃ N ₄ as the ceramic substrate, will be compared.
In Comparative Example 2, in a field of view of 200 μm in the width direction of the bonding interface in a cross section along the lamination direction of the ceramic substrate and the copper plate and 10 μm from the surface of the active metal compound layer toward the copper plate, the area A of the active metal-containing precipitate was 395.7 ^μm2 , and the ratio A/B of the area A of the active metal-containing precipitate to the area B of the Ag-enriched phase having an Ag concentration of 10 atomic % or more was 1.256, and the number of cracks that occurred in a thermal cycle test was 1,200.
In Comparative Example 3, in a field of view of 200 μm in the width direction of the bonding interface in a cross section along the lamination direction of the ceramic substrate and the copper plate and 10 μm from the surface of the active metal compound layer toward the copper plate, the ratio A/B of the area A of the active metal-containing precipitate to the area B of the Ag-enriched phase having an Ag concentration of 10 atomic % or more was 1.305, and the number of times cracks occurred in a thermal cycle test was 1,200.

In contrast, in Examples 4-6 of the present invention, the area A of the active metal-containing precipitate was 360 ^μm2 or less, and the ratio A/B of the area A of the active metal-containing precipitate to the area B of the Ag-enriched phase having an Ag concentration of 10 atomic % or more was 0.03 or more and 0.8 or less. In the thermal cycling test, the number of crack occurrences exceeded 1,800 to 2,000, and the thermal cycling reliability was excellent.

Next, invention examples 7 and 8, which use Al ₂ O ₃ as the ceramic substrate, will be compared with comparative example 4.
In Comparative Example 4, in a field of view of 200 μm in the width direction of the bonding interface in a cross section along the lamination direction of the ceramic substrate and the copper plate and 10 μm from the surface of the active metal compound layer toward the copper plate, the ratio A/B of the area A of the active metal-containing precipitate to the area B of the Ag-enriched phase having an Ag concentration of 10 atomic % or more was 0.018, and the number of times cracks occurred in a thermal cycle test was 50.

In contrast, in Examples 7 and 8 of the present invention, the area A of the active metal-containing precipitate was 360 ^μm2 or less, and the ratio A/B of the area A of the active metal-containing precipitate to the area B of the Ag-enriched phase having an Ag concentration of 10 atomic % or more was in the range of 0.03 to 0.8, and the number of times cracks occurred in the thermal cycling test exceeded 300 to 450, indicating excellent thermal cycling reliability.

The results of the above confirmatory experiments confirmed that the present invention can suppress the occurrence of cracks in the ceramic substrate even when subjected to severe thermal cycling, making it possible to provide an insulated circuit board (copper/ceramic bonded body) with excellent thermal cycling reliability.

10 Insulated circuit board (copper/ceramic bonded body)
11 Ceramic substrate (ceramic member)
12 Circuit layer (copper member)
13 Metal layer (copper member)
21 Active metal compound layer 22 Ag-Cu alloy layer

Claims (6)

A copper/ceramic bonded body obtained by bonding a copper member made of copper or a copper alloy to a ceramic member,
an active metal compound layer is formed on the ceramic member side at the bonding interface between the ceramic member and the copper member,
In a field of view of 200 μm in the width direction of the bonding interface in a cross section along the lamination direction of the ceramic member and the copper member and 10 μm from the surface of the active metal compound layer toward the copper member,
The area A of the active metal-containing precipitate is 360 μm ² or less, and
a ratio A/B of an area A of the active metal-containing precipitate to an area B of an Ag-enriched phase having an Ag concentration of 10 atomic % or more, which is in the range of 0.03 to 0.8. The copper/ceramic bonded body according to claim 1, characterized in that the thickness t1 of the active metal compound layer is in the range of 0.05 μm or more and 1.2 μm or less. an Ag—Cu alloy layer is formed on the copper member side at the bonding interface between the ceramic member and the copper member;
3. The copper/ceramic joined body according to claim 1, wherein the thickness t2 of the Ag--Cu alloy layer is in the range of 1 μm to 30 μm. An insulating circuit board having a copper plate made of copper or a copper alloy bonded to the surface of a ceramic substrate,
an active metal compound layer is formed on the ceramic substrate side at the bonding interface between the ceramic substrate and the copper plate;
In a field of view of 200 μm in the width direction of the bonding interface in a cross section along the lamination direction of the ceramic substrate and the copper plate and 10 μm from the surface of the active metal compound layer toward the copper plate,
The area A of the active metal-containing precipitate is 360 μm ² or less, and
an area ratio A/B of the area A of the active metal-containing precipitate to the area B of the Ag-enriched phase having an Ag concentration of 10 atomic % or more, which is in the range of 0.03 to 0.8. The insulating circuit board described in claim 4, characterized in that the thickness t1 of the active metal compound layer is in the range of 0.05 μm or more and 1.2 μm or less. an Ag—Cu alloy layer is formed on the copper plate side at the bonding interface between the ceramic substrate and the copper plate;
6. The insulating circuit board according to claim 4, wherein the thickness t2 of the Ag--Cu alloy layer is within the range of 1 μm to 30 μm.