Cu/ceramic bonded body, method for manufacturing Cu/ceramic bonded body, and power module substrate

A Cu/ceramic bonded body according to the present invention is formed by bonding a copper member made of copper or a copper alloy and a ceramic member made of AlN or Al2O3 using a bonding material containing Ag and Ti, in which a Ti compound layer made of a Ti nitride or a Ti oxide is formed at a bonding interface between the copper member and the ceramic member, and Ag particles are dispersed in the Ti compound layer.

CROSS REFERENCE TO RELATED APPLICATIONS

This Application is a 35 U.S.C. § 371 National Phase Application of International PCT Patent Application No. PCT/JP2014/075339, filed on Sep. 25, 2014, which claims the benefit of and priority to Japanese Patent Application Serial No. JP 2013-204060, filed Sep. 30, 2013, the entire contents of each of which are hereby incorporated by reference herein in their entirety.

TECHNICAL FIELD

The present invention relates to a Cu/ceramic bonded body formed by bonding a copper member made of copper or a copper alloy and a ceramic member made of AlN or Al2O3, a method for manufacturing the Cu/ceramic bonded body, and a power module substrate made of the Cu/ceramic bonded body.

Priority is claimed on Japanese Patent Application No. 2013-204060, filed Sep. 30, 2013, the content of which is incorporated herein by reference.

BACKGROUND ART

A semiconductor device such as an LED or a power module has a structure in which a semiconductor element is bonded to a circuit layer made of a conductive material.

A power semiconductor element for controlling higher amounts of power used to control wind power generation, electric automobiles, hybrid automobiles, and the like generates a large amount of heat. Therefore, as a substrate on which such a power semiconductor element is mounted, for example, a power module substrate including a ceramic substrate made of AlN (aluminum nitride), Al2O3(alumina), and the like, and a circuit layer formed by bonding a metal plate having excellent conductivity to one surface of the ceramic substrate has been widely used until now. As the power module substrate, a substrate having a metal layer formed by bonding a metal plate to the other surface of the ceramic substrate is also provided.

For example, PTL 1 proposes a power module substrate in which a first metal plate and a second metal plate which constitute a circuit layer and a metal layer are copper plates, and these copper plates are directly bonded to a ceramic substrate using a DBC method. In the DBC method, by utilizing a eutectic reaction between copper and a copper oxide, a liquid phase is formed at the interface between the copper plate and the ceramic substrate to bond the copper plate to the ceramic substrate.

Further, PTL 2 proposes a power module substrate in which a circuit layer and a metal layer are formed by bonding copper plates to one surface and the other surface of a ceramic substrate. In the power module substrate, the copper plates are bonded to the ceramic substrate by performing a heating treatment in a state in which the copper plates are arranged on one surface and the other surface of the ceramic substrate via a Ag—Cu—Ti-based brazing filler metal (a so-called active metal brazing method). In the active metal brazing method, since a brazing filler metal containing Ti which is an active metal is used, the wettability between the melted brazing filler metal and the ceramic substrate is improved and the ceramic substrate and the copper plates are bonded in a satisfactory manner.

CITATION LIST

Patent Documents

DISCLOSURE OF INVENTION

Technical Problem

However, as disclosed in PTL 1, in the case in which a ceramic substrate and copper plates are bonded by a DBC method, it is required to set the bonding temperature to 1,065° C. or higher (the eutectic point temperature of copper and a copper oxide or higher). Therefore, in the DBC method, there is a concern of deterioration of the ceramic substrate at the time of bonding.

In addition, as disclosed in PTL 2, in the case in which a ceramic substrate and copper plates are bonded by an active metal brazing method, it is required to set the bonding temperature to a relatively high temperature of 900° C. Therefore, there is also a problem of deterioration of the ceramic substrate in the active metal brazing method. Herein, when the bonding temperature is lowered, the brazing filler metal does not sufficiently react with the ceramic substrate and the bonding rate at the interface between the ceramic substrate and the copper plate is decreased. Thus, it is not possible to provide a power module substrate having high reliability.

The present invention has been made in consideration of the aforementioned circumstances, and an object thereof is to provide a Cu/ceramic bonded body in which a copper member and a ceramic member are reliably bonded, a method for manufacturing the Cu/ceramic bonded body, and a power module substrate made of the Cu/ceramic bonded body.

Solution to Problem

In order to solve such problems and achieve the aforementioned object, there is provided a Cu/ceramic bonded body according to a first aspect of the present invention formed by bonding a copper member made of copper or a copper alloy and a ceramic member made of AlN or Al2O3using a bonding material containing Ag and Ti, in which a Ti compound layer made of a Ti nitride or a Ti oxide is formed at a bonding interface between the copper member and the ceramic member, and Ag particles are dispersed in the Ti compound layer.

The Cu/ceramic bonded body having the configuration has a structure in which a copper member made of copper or a copper alloy and a ceramic member made of AlN or Al2O3are bonded using a bonding material containing Ag and Ti, and a Ti compound layer is formed at a bonding interface between the copper member and the ceramic member. Here, when the ceramic member is made of AlN, a Ti compound layer made of a Ti nitride is formed at the bonding interface between the copper member and the ceramic member. In addition, when the ceramic member is made of Al2O3, a Ti compound layer made of a Ti oxide is formed at the bonding interface between the copper member and the ceramic member. These Ti compound layers are formed by the reaction of Ti in the boding material with oxygen or nitrogen in the ceramic member.

In the Cu/ceramic bonded body according to the first aspect of the present invention, Ag particles are dispersed in the Ti compound layer. It is assumed that the Ag particles are formed in the process of forming the aforementioned Ti compound layer by the reaction of Ti with nitrogen or oxygen in a liquid phase formed by the eutectic reaction Ag between Al. That is, by holding a temperature under a low temperature condition in which the temperature is equal to or higher than the eutectic point temperature of Ag and Al (567° C.), the Ti compound is easily formed and the aforementioned Ti compound layer is sufficiently formed. As a result, it is possible to obtain a Cu/ceramic bonded body in which the copper member and the ceramic member are reliably bonded.

In the Cu/ceramic bonded body according to the first aspect of the present invention, the concentration of Ag in a near interface region from the interface with the ceramic member to 500 nm in the Ti compound layer may be 0.3 atomic % or more.

In this case, since the Ag particles are sufficiently dispersed in the Ti compound layer, formation of the Ti compound is promoted and the Ti compound layer is sufficiently formed. As a result, the copper member and the ceramic member are bonded strongly together.

In addition, in the Cu/ceramic bonded body according to the first aspect of the present invention, the particle size of the Ag particles dispersed in the Ti compound layer may be in a range from 10 nm to 100 nm.

In this case, since the Ag particles dispersed in the Ti compound layer have a relatively fine particle size of 10 nm or more and 100 nm or less and are formed in the process of forming the aforementioned Ti compound layer by the reaction of Ti with nitrogen or oxygen, formation of the Ti compound is promoted and the Ti compound layer is sufficiently formed. As a result, it is possible to obtain a Cu/ceramic bonded body in which a copper member and a ceramic member are reliably bonded.

Further, in the Cu/ceramic bonded body according to the first aspect of the present invention, the bonding material may further contain Cu and Cu particles may be dispersed in the Ti compound layer.

In this case, since the bonding material contains Cu in addition to Ag and Ti, and Cu particles are dispersed in the Ti compound layer, the Ti compound layer is sufficiently formed on the surface of the ceramic member. As a result, it is possible to obtain a Cu/ceramic bonded body in which a copper member and a ceramic member are reliably bonded.

A method for manufacturing a Cu/ceramic bonded body according to a second aspect of the present invention is a method for manufacturing the aforementioned Cu/ceramic bonded body and the method includes a low temperature holding step of holding a temperature in a temperature range from a eutectic point temperature of Ag and Al to a temperature lower than a eutectic point temperature of Ag and Cu in a state in which a bonding material containing Ag and Ti is interposed between the copper member and the ceramic member, a heating step of, after the low temperature holding step, performing heating to a temperature equal to or higher than the eutectic point temperature of Ag and Cu to melt the bonding material, and a cooling step of, after the heating step, performing cooling and solidifying the melted bonding material to bond the copper member to the ceramic member.

According to the method for manufacturing a Cu/ceramic bonded body having the configuration, since the method includes a low temperature holding step of holding a temperature in a temperature range from a eutectic point temperature of Ag and Al to a temperature lower than a eutectic point temperature of Ag and Cu in a state in which a bonding material containing Ag and Ti is interposed between the copper member and the ceramic member, a liquid phase is formed at the interface between the copper member and the ceramic member by a eutectic reaction between Al and Ag through the low temperature holding step. Al used in the reaction is supplied from AlN or Al2O3constituting the ceramic member and Ti contained in the bonding material reacts with nitrogen or oxygen to form a Ti compound layer on the surface of the ceramic member. In the process, Ag particles are dispersed in the Ti compound layer.

Here, since the holding temperature in the low temperature holding step is set to the eutectic point temperature of Ag and Al or higher, a liquid phase can be reliably formed at the interface between the copper member and the ceramic member by a eutectic reaction between Al and Ag. In addition, since the holding temperature in the low temperature holding step is set to a temperature lower than the eutectic point temperature of Ag and Cu, Ag which reacts with Al can be secured without consuming Ag by the reaction with Cu. As a result, it is possible to reliably form a liquid phase by the eutectic reaction between Al and Ag.

After the low temperature holding step, the method includes a heating step of performing heating to a temperature equal to or higher than the eutectic point temperature of Ag and Cu to melt the bonding material, and a cooling step of performing cooling and solidifying the melted bonding material to bond the copper member to the ceramic member. As a result, even when the heating temperature in the heating step is a low temperature, in a state in which the Ti compound layer is sufficiently formed, the bonding material is melted and thus the ceramic member and the copper member can be reliably bonded.

In the method for manufacturing a Cu/ceramic bonded body according to the second embodiment of the present invention, it is preferable that the holding time in the low temperature holding step be in a range from 30 minutes to 5 hours.

In this case, since the holding time in the low temperature holding step is set to 30 minutes or more, the Ti compound layer is sufficiently formed and the ceramic member and the copper member can be reliably bonded.

On the other hand, since the holding time in the low temperature holding step is 5 hours or less, the amount of energy consumed can be reduced.

In the method for manufacturing a Cu/ceramic bonded body according to the second embodiment of the present invention, it is preferable that the heating temperature in the heating step be in a range from 790° C. to 830° C.

In this case, since the heating temperature in the heating step is set to a relatively low temperature in a range from 790° C. to 830° C. thermal load on the ceramic member at the time of bonding can be reduced and deterioration of the ceramic member can be limited. In addition, as described above, the method includes the low temperature holding step, even in the case in which the heating temperature in the heating step is a relatively low temperature, the ceramic member and the copper member can be reliably bonded.

A power module substrate according to a third aspect of the present invention is a power module substrate formed by bonding a copper plate made of copper or a copper alloy to a surface of a ceramic substrate made of AlN or Al2O3and includes the Cu/ceramic bonded body.

According to the power module substrate having the configuration, since the substrate includes the Cu/ceramic bonded body, thermal load on the ceramic substrate can be reduced by performing bonding under a low temperature condition and deterioration of the ceramic substrate can be limited. In addition, even when bonding is performed under a low temperature condition, the ceramic substrate and the copper plate are reliably bonded and thus bonding reliability can be secured. The copper plate bonded to the surface of the ceramic substrate is used as a circuit layer or a metal layer.

Advantageous Effects of Invention

According to the present invention, it is possible to provide a Cu/ceramic bonded body in which a copper member and a ceramic member are reliably bonded, a method for manufacturing the Cu/ceramic bonded body, and a power module substrate made of the Cu/ceramic bonded body.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described below with reference to the appended drawings.

A Cu/ceramic bonded body according to the embodiment includes a power module substrate10formed by bonding a ceramic substrate11which is a ceramic member and a copper plate22(circuit layer12) which is a copper member.

InFIG. 1, the power module substrate10according to the first embodiment of the present invention and a power module1using the power module substrate10are shown.

The power module1includes the power module substrate10, a semiconductor element3that is bonded to one side (upper side inFIG. 1) of the power module substrate10via a solder layer2, and a heat sink51that is arranged on the other side (lower side inFIG. 1) of the power module substrate10.

Here, for example, the solder layer2is made of a Sn—Ag-based, Sn—In-based, or Sn—Ag—Cu-based solder material.

The power module substrate10includes the ceramic substrate11, the circuit layer12that is arranged on one surface (upper surface inFIG. 1) of the ceramic substrate11, and a metal layer13that is arranged on the other surface (lower surface inFIG. 1) of the ceramic substrate11.

The ceramic substrate11prevents electrical connection between the circuit layer12and the metal layer13, and is made of AlN (aluminum nitride) having high insulating properties in the embodiment. Here, the thickness of the ceramic substrate11is set to be in a range from 0.2 mm to 1.5 mm and is set to 0.635 mm in the embodiment.

As shown inFIG. 4, the circuit layer12is formed by bonding the copper plate22made of copper or a copper alloy to one surface of the ceramic substrate11. In the embodiment, as the copper plate22constituting the circuit layer12, a rolled sheet of oxygen-free copper is used. A circuit pattern is formed on the circuit layer12and one surface (upper surface inFIG. 1) of the circuit layer is a surface on which the semiconductor element3is mounted. Here, the thickness of the circuit layer12is set to be in a range from 0.1 mm to 1.0 mm and is set to 0.6 mm in the embodiment.

As shown inFIG. 4, the metal layer13is formed by bonding an aluminum plate23to the other surface of the ceramic substrate11. In the embodiment, the metal layer13is formed by bonding an aluminum plate23made of a rolled sheet of aluminum with a purity of 99.99 mass % or more (so-called 4N aluminum) to the ceramic substrate11.

The aluminum plate23has a 0.2% proof stress of 30 N/mm2or less. Here, the thickness of the metal layer13(aluminum plate23) is set to be in a range from 0.5 mm to 6 mm, and is set to 2.0 mm in the embodiment.

The heat sink51cools the aforementioned power module substrate10and is configured to have a top plate portion52which is bonded to the power module substrate10and a channel53through which a cooling medium (for example, cooling water) is circulated. The heat sink51(top plate portion52) is preferably made of a material having good thermal conductivity and is made of A6063 (an aluminum alloy) in the embodiment.

In the embodiment the heat sink51(top plate portion52) is directly bonded to the metal layer13of the power module substrate10by brazing.

Here, as shown inFIG. 4, the ceramic substrate11and the circuit layer12(copper plate22) are bonded using a Ag—Cu—Ti-based brazing filler metal24.

A Ti compound layer31made of TiN (titanium nitride) and a Ag—Cu eutectic layer32are formed at the bonding interface between the ceramic substrate11and the circuit layer12(copper plate22) as shown inFIG. 2. The Cu content of the Ag—Cu—Ti-based brazing filler metal24is preferably 18 mass % to 34 mass % and the Ti content is preferably 0.3 mass % to 7 mass %. However, there is no limitation thereto. In addition, in the embodiment, a foil is used as the Ag—Cu—Ti-based brazing filler metal24and the thickness may be set to be in a range from 3 μm to 50 μm.

Ag particles35are dispersed in the Ti compound layer31.

A large amount of the Ag particles35is distributed in the Ti compound layer31on the side close to the ceramic substrate11, and the concentration of Ag in a near interface region31A from the interface with the ceramic substrate11to 500 nm in the Ti compound layer31is 0.3 atomic % or more and preferably set to be in a range from 0.3 atomic % to 15 atomic %. In the embodiment, 90% or more of the Ag particles35observed in the Ti compound layer31is distributed in the aforementioned near interface region31A. The ratio of the Ag particles35distributed in the aforementioned near interface region31A is preferably 95% or more and the upper limit is 100%. However, there is no limitation thereto.

In addition, in the embodiment, the particle size of the Ag particles35dispersed in the Ti compound layer31is set to be in a range from 10 nm to 100 nm. The particle size of the Ag particles35may be set to be in a range from 10 nm to 50 nm.

Further, in the embodiment, Cu particles36are dispersed in the Ti compound layer31other than the Ag particles35.

Next, a method for manufacturing the power module substrate10of the aforementioned embodiment will be described with reference toFIGS. 3 to 5.

As shown inFIGS. 3 and 4, the copper plate22which becomes the circuit layer12is bonded to the ceramic substrate11(copper plate bonding step S01). In the copper plate bonding step S01of the embodiment, the copper plate22made of a rolled sheet of oxygen-free copper and the ceramic substrate11made of AlN are bonded by using the Ag—Cu—Ti-based brazing filler metal24. The copper plate bonding step S01will be described in detail later.

Next, the aluminum plate23which becomes the metal layer13is bonded to the other surface of the ceramic substrate11(aluminum plate bonding step S02).

In the aluminum plate bonding step S02, the ceramic substrate11and the aluminum plate23are laminated via a brazing filler metal25, and the ceramic substrate and the aluminum plate are put into a vacuum furnace and subjected to brazing while being compressed in the lamination direction. Thus, the ceramic substrate11and the aluminum plate23are bonded. At this time, as the brazing filler metal25, for example, an Al—Si-based brazing filler metal foil can be used and the brazing temperature is preferably set to 600° C. to 650° C.

Thus, the power module substrate10of the embodiment is manufactured.

Next, the heat sink51is bonded to the other surface (lower side inFIG. 1) of the metal layer13of the power module substrate10(heat sink bonding step S03).

In the heat sink bonding step S03, the power module substrate10and the heat sink51are laminated via a brazing filler metal26and this laminated body is put into a vacuum furnace and subjected to brazing while being compressed in the lamination direction. Thus, the metal layer13of the power module substrate10and the top plate portion52of the heat sink51are bonded. At this time, as the brazing filler metal26, for example, an Al—Si-based brazing filler metal foil having a thickness of 20 μm to 110 μm can be used. It is preferable that the brazing temperature be set to a temperature lower than the brazing temperature in the aluminum bonding step S02.

Next, the semiconductor element3is bonded to one surface of the circuit layer12of the power module substrate10by soldering (semiconductor element mounting step S04).

Through the above steps, the power module1shown inFIG. 1is produced.

Here, the copper plate bonding step S01that is the method for manufacturing the Cu/ceramic bonded body according to the embodiment will be described in detail.

In the copper plate bonding step S01, first, the copper plate22which becomes the circuit layer12is laminated on one surface of the ceramic substrate11via the Ag—Cu—Ti-based brazing filler metal24(laminating step S11).

Next, in a state in which the ceramic substrate11and the copper plate22are compressed in the lamination direction under pressure in a range from 0.5 kgf/cm2to 35 kgf/cm2(4.9×104Pa to 343×104Pa), the ceramic substrate and the copper plate are put into a heating furnace in a vacuum or argon atmosphere and heated and the temperature is held (low temperature holding step S12). Here, the holding temperature in the low temperature holding step S12is set to be in a range from the eutectic point temperature of Ag and Al to a temperature lower than the eutectic point temperature of Ag and Cu, and specifically set to be in a range from 570° C. to 770° C. In addition, the holding time in the low temperature holding step S12is set to be in a range from 30 minutes to 5 hours. The holding temperature in the low temperature holding step S12is preferably set to be in a range from 590° C. to 750° C. Further, the holding time in the low temperature holding step S12is preferably set to be in a range from 60 minutes to 3 hours.

Since the temperature equal to or higher than the eutectic point temperature of Ag and Al is held in the low temperature holding step S12, as shown inFIG. 5, Ag in the Ag—Cu—Ti-based brazing filler metal24, and Al formed by the reaction of the ceramic substrate11made of AlN with Ti undergo a eutectic reaction to form a liquid phase38. In the liquid phase38, Ti in the Ag—Cu—Ti-based brazing filler metal24reacts with N (nitrogen) in the ceramic substrate11to form TiN. Thus, the Ti compound layer31made of TiN is formed in the form of corrosion of the surface of the ceramic substrate11.

After the low temperature holding step S12, in the state in which the copper plate22and the ceramic substrate11are compressed, the copper plate and the ceramic substrate are heated in a heating furnace in a vacuum atmosphere to melt the Ag—Cu—Ti-based brazing filler metal24(heating step S13). Here, the heating temperature in the heating step S13is set to the eutectic point temperature of Ag and Cu or higher and specifically is set to be in a range from 790° C. to 830° C. In addition, the holding time in the heating step S13is set to be in a range from 5 minutes to 60 minutes. The heating temperature in the heating step S13is preferably set to be in a range from 800° C. to 820° C. Further, the holding time in the heating step S13is preferably set to be in a range from 10 minutes to 30 minutes.

After the heating step S13, cooling is performed to solidify the melted Ag—Cu—Ti-based brazing filler metal24(cooling step S14). The cooling rate in the cooling step S14is not particularly limited and is preferably set to be in a range from 2° C./min to 10° C./min.

As described above, the copper plate bonding step S01includes the laminating step S11, the low temperature holding step S12, the heating step S13, and the cooling step S14and the ceramic substrate11which is a ceramic member and the copper plate22which is a copper member are bonded.

The Ag particles35and the Cu particles36are dispersed in the Ti compound layer31made of TiN.

According to the Cu/ceramic bonded body (power module substrate10) having the above configuration of the embodiment, the copper plate22(circuit layer12) made of oxygen-free copper and the ceramic substrate11made of AlN are bonded using the Ag—Cu—Ti-based brazing filler metal24, the Ti compound layer31made of TiN is formed at the bonding interface of the ceramic substrate11, and since the Ag particles35and the Cu particles36are dispersed in the Ti compound layer31, the Ti compound layer31is sufficiently formed at the time of bonding. As a result, it is possible to obtain the power module substrate10in which the copper plate22(circuit layer12) and the ceramic substrate11are reliably bonded.

In addition, since the concentration of Ag in the aforementioned near interface region31A of the Ti compound layer31is set to 0.3 atomic % or more in the embodiment, the Ti compound layer31is sufficiently formed at the bonding interface of the ceramic substrate11. As a result, the copper plate22(circuit layer12) and the ceramic substrate11are bonded strongly together.

Further, in the embodiment, the Ag particles35dispersed in the Ti compound layer31have a relatively fine particle size in a range from 10 nm to 100 nm and are assumed to be formed in the process of forming the aforementioned Ti compound layer31by the reaction between Ti and N. Thus, the Ti compound layer31is sufficiently formed at the interface of the ceramic substrate11, and thus it is possible to obtain the power module substrate10in which the copper plate22(circuit layer12) and the ceramic substrate11are reliably bonded.

In addition, in the embodiment, the copper plate bonding step S01includes the laminating step S11of laminating the copper plate22and the ceramic substrate11via the Ag—Cu—Ti-based brazing filler metal24, the low temperature holding step S12of holding a temperature in a temperature range from the eutectic point temperature of Ag and Al to a temperature lower than the eutectic point temperature of Ag and Cu in a state in which the laminated copper plate22and ceramic substrate11are compressed in the lamination direction, the heating step S13of, after the low temperature holding step S12, performing heating to the eutectic point temperature of Ag and Cu or higher to melt the Ag—Cu—Ti-based brazing filler metal24, and the cooling step S14of, after the heating step S13, performing cooling to solidify the melted Ag—Cu—Ti-based brazing filler metal24. Therefore, the copper plate22and the ceramic substrate11can be reliably bonded.

That is, in the low temperature holding step S12of holding the temperature in a temperature range from the eutectic point temperature of Ag and Al to a temperature lower than the eutectic point temperature of Ag and Cu, the liquid phase38is formed at the interface between the copper plate22and the ceramic substrate11by the eutectic reaction between Al and Ag. In the liquid phase38, Ti reacts with N to form the Ti compound layer31at the interface of the ceramic substrate11. In this process, the Ag particles35are dispersed in the Ti compound layer31. Thus, even when the heating temperature in the heating step S13is set to a relatively low temperature, the copper plate22and the ceramic substrate11can be reliably bonded.

Here, in the embodiment, the holding temperature in the low temperature holding step S12is set to the eutectic point temperature of Ag and Al or higher and specifically set to 570° C. or higher. Therefore, the liquid phase38can be reliably formed at the interface between the copper plate22and the ceramic substrate11by the eutectic reaction between Al and Ag.

In addition, since the holding temperature in the low temperature holding step S12is set to a temperature lower than the eutectic point temperature of Ag and Cu and is specifically set to be lower than 770° C., Ag which reacts with Al can be secured without consuming Ag by the reaction with Cu. As a result, it is possible to reliably form the liquid phase38by the eutectic reaction between Al and Ag.

In the embodiment, since the holding time in the low temperature holding step S12is set to 30 minutes or more, the Ti compound layer31made of TiN is sufficiently formed and even when the heating temperature in the heating step S13is set to a relatively low temperature, the copper plate22and the ceramic substrate11can be reliably bonded. In addition, since the holding time in the low temperature holding step S12is set to 5 hours or less, the amount of energy consumed can be reduced.

Further, in the embodiment, since the heating temperature in the heating step S13is set to a relatively low temperature in a range from 790° C. to 830° C., the thermal load on the ceramic substrate11at the time of bonding can be reduced and deterioration of the ceramic substrate11can be limited. Since the copper plate bonding step includes the low temperature holding step S12as described above, even in the case in which the heating temperature in the heating step S13is set to a relatively low temperature, the ceramic substrate11and the copper plate22can be reliably bonded.

Next, a second embodiment of the present invention will be described with reference toFIGS. 6 to 10.

A Cu/ceramic bonded body according to the embodiment includes a power module substrate110formed by bonding a copper plate122(circuit layer112) and a copper plate123(metal layer113) which are copper members to a ceramic substrate111which is a ceramic member.

InFIG. 6, the power module substrate110according to the second embodiment of the present invention and a power module101using the power module substrate110are shown.

The power module101includes the power module substrate110, a semiconductor element103that is bonded to one side (upper side inFIG. 6) of the power module substrate110via a first solder layer102, and a heat sink151that is arranged on the other side (lower side inFIG. 6) of the power module substrate110.

The power module substrate110includes the ceramic substrate111, the circuit layer112that is arranged on one surface (upper surface inFIG. 6) of the ceramic substrate111, and the metal layer113that is arranged on the other surface (lower surface inFIG. 6) of the ceramic substrate111.

The ceramic substrate111prevents electrical connection between the circuit layer112and the metal layer113and is made of alumina (Al2O3) having high insulating properties in the embodiment. Here, the thickness of the ceramic substrate111is set to be in a range from 0.2 mm to 1.5 mm and is set to 0.635 mm in the embodiment.

As shown inFIG. 9, the circuit layer112is formed by bonding the copper plate122made of copper or a copper alloy to one surface of the ceramic substrate111. In the embodiment, as the copper plate122constituting the circuit layer112, a rolled sheet of tough pitch copper is used. A circuit pattern is formed on the circuit layer112and one surface (upper surface inFIG. 6) of the circuit layer is a surface on which the semiconductor element103is mounted. Here, the thickness of the circuit layer112is set to be in a range from 0.1 mm to 1.0 mm and is set to 0.6 mm in the embodiment.

As shown inFIG. 9, the metal layer113is formed by bonding the copper plate123made of copper or a copper alloy to the other surface of the ceramic substrate111. In the embodiment, as the copper plate123constituting the metal layer113, a rolled sheet of tough pitch copper is used. Here, the thickness of the metal layer113is set to be in a range from 0.1 mm to 1.0 mm and is set to 0.6 mm in the embodiment.

The heat sink151cools the aforementioned power module substrate110and is configured to have a heat radiation plate152which is bonded to the power module substrate110, and a cooler153which is arranged to be laminated on the heat radiation plate152.

The heat radiation plate152causes heat from the aforementioned power module substrate110to spread in a plane direction, and is made of copper or a copper alloy having excellent thermal conductivity. The heat radiation plate152and the metal layer113of the power module substrate110are bonded via a second solder layer108.

As shown inFIG. 6, the cooler153includes a channel154through which a cooling medium (for example, cooling water) is circulated. The cooler153is preferably made of a material having good thermal conductivity and is made of A6063 (an aluminum alloy) in the embodiment.

As shown inFIG. 6, the heat radiation plate152is fastened to the cooler153by a fixing screw156via a grease layer (not shown).

Here, the ceramic substrate111and the circuit layer112(copper plate122), and the ceramic substrate111and the metal layer113(copper plate123) are bonded using a Ag—Ti-based brazing filler metal124as shown inFIG. 9.

A Ti compound layer131made of TiO2(titanium oxide) and a Ag—Cu eutectic layer132are respectively formed at the bonding interface between the ceramic substrate111and the circuit layer112(copper plate122) and the bonding interface between the ceramic substrate111and the metal layer113(copper plate123) as shown inFIG. 7. The Ti content of the Ag—Ti-based brazing filler metal124is preferably 0.4 mass % to 75 mass %. However, there is no limitation thereto. In addition, in the embodiment, as the Ag—Ti-based brazing filler metal124, a foil is used and the thickness may be set to be in a range from 3 μm to 25 μm.

Ag particles135are dispersed in the Ti compound layer131.

A large amount of the Ag particles135is distributed in the Ti compound layer131on the side close to the ceramic substrate111, and the concentration of Ag in a near interface region131A from the interface with the ceramic substrate111to 500 nm in the Ti compound layer131is 0.3 atomic % or more and is preferably set to be in a range from 0.3 atomic % to 15 atomic %. In the embodiment, 90% or more of the Ag particles135observed in the Ti compound layer131is distributed in the aforementioned near interface region131A. The ratio of the Ag particles135distributed in the near interface region131A is more preferably 95% or more and the upper limit is 100%. However, there is no limitation thereto.

In addition, in the embodiment, the particle size of the Ag particles135dispersed in the Ti compound layer131is set to be in a range from 10 nm to 100 nm. The particle size of the Ag particles135may be set to be in a range from 10 nm to 50 nm.

Next, a method for manufacturing the power module substrate110of the aforementioned embodiment will be described with reference toFIGS. 8 to 10.

As shown inFIGS. 8 and 9, the copper plate122which becomes the circuit layer112and the ceramic substrate111, and the copper plate123which becomes the metal layer113and the ceramic substrate111are bonded (copper plate bonding step S101). In the embodiment, the copper plates122and123made of rolled sheets of tough pitch copper and the ceramic substrate111made of Al2O3are bonded by the Ag—Ti-based brazing filler metal124. The copper plate bonding step S101will be described in detail later.

The power module substrate110of the embodiment is manufactured by the copper plate bonding step S101.

Next, the heat radiation plate152is bonded to the other surface (lower side inFIG. 6) of the metal layer113of the power module substrate110(heat radiation plate bonding step S102).

The power module substrate110and the heat radiation plate152are solder-bonded by laminating the power module substrate110and the heat radiation plate152via a solder material and putting the substrate and the heat radiation plate into a heating furnace.

Next, the cooler153is arranged on the other surface of the heat radiation plate152(lower side inFIG. 6) (cooler arranging step S103).

The heat radiation plate152and the cooler153are coupled by the fixing screw156by applying grease (not shown) between the heat radiation plate152and the cooler153.

Next, the semiconductor element103is bonded to one surface of the circuit layer112of the power module substrate110by soldering (semiconductor element mounting step S104).

Through the above steps, the power module101shown inFIG. 6is produced.

Here, the copper plate bonding step S101which is the method for manufacturing the Cu/ceramic bonded body of the embodiment will be described in detail.

First, in the copper plate bonding step S101, the copper plate122which becomes the circuit layer112is laminated on the one surface of the ceramic substrate111via the Ag—Ti-based brazing filler metal124and the copper plate123which becomes the metal layer113is laminated on the other surface of the ceramic substrate111via the Ag—Ti-based brazing filler metal124(laminating step S111).

Next, in a state in which the copper plate122, the ceramic substrate111, and the copper plate123are compressed in the lamination direction under pressure in a range from 0.5 kgf/cm2to 35 kgf/cm2(4.9×104Pa to 343×104Pa), the copper plates and the ceramic substrate are put into a heating furnace in a vacuum or argon atmosphere and heated and the temperature is held (low temperature holding step S112). Here, the holding temperature in the low temperature holding step S112is set to be in a range from the eutectic point temperature of Ag and Al to a temperature lower than the eutectic point temperature of Ag and Cu and specifically set to be in a range from 570° C. to 770° C. In addition, the holding time in the low temperature holding step S112is set to be in a range from 30 minutes to 5 hours. The holding temperature in the low temperature holding step S112is preferably set to be in a range from 590° C. to 750° C. Further, the holding time in the low temperature holding step S112is preferably set to be in a range from 60 minutes to 3 hours.

Since the temperature equal to or higher than the eutectic point temperature of Ag and Al is held in the low temperature holding step S112, as shown inFIG. 10, Ag in the Ag—Ti-based brazing filler metal124, and Al formed by the reaction of the ceramic substrate111made of Al2O3with Ti undergo a eutectic reaction to form a liquid phase138. In the liquid phase138, Ti in the Ag—Ti-based brazing filler metal124reacts with O (oxygen) in the ceramic substrate111to form TiO2. Thus, the Ti compound layer131made of TiO2is formed in the form of corrosion of the surface of the ceramic substrate111.

After the low temperature holding step S112, in the state in which the copper plate122, the ceramic substrate111, and the copper plate123are compressed, the copper plates and the ceramic substrate are heated in the heating furnace in a vacuum atmosphere to melt the Ag—Ti-based brazing filler metal124(heating step S113). At this time, Cu is supplied from the copper plates122and123to the Ag—Ti-based brazing filler metal124and the melting point is lowered due to a eutectic reaction between Ag and Cu. Thus, melting of the Ag—Ti-based brazing filler metal124is promoted. Here, the heating temperature in the heating step S113is set to the eutectic point temperature of Ag and Cu or higher and specifically set to be in a range from 790° C. to 830° C. In addition, the holding time in the heating step S113is set to be in a range from 5 minutes to 60 minutes. The heating temperature in the heating step S113is preferably set to be in a range from 800° C. to 820° C. Further, the holding time in the heating step S113is preferably set to be in a range from 10 minutes to 30 minutes.

After the heating step S113, cooling is performed to solidify the melted Ag—Ti-based brazing filler metal124(cooling step S114). The cooling rate in the cooling step S114is not particularly limited and is preferably set to be in a range from 2° C./min to 10° C./min.

As described above, the copper plate bonding step S101includes the laminating step S111, the low temperature holding step S112, the heating step S113, and the cooling step S114and the ceramic substrate111which is a ceramic member and the copper plates122and123which are copper members are bonded.

The Ag particles135are dispersed in the Ti compound layer131made of TiO2.

According to the Cu/ceramic bonded body (power module substrate110) having the above configuration of the embodiment, the copper plate122(circuit layer112) and the copper plates123(metal layer113) made of tough pitch copper and the ceramic substrate111made of Al2O3are bonded using the Ag—Ti-based brazing filler metal124, and the Ti compound layer131made of TiO2is formed at the bonding interface of the ceramic substrate111. Since the Ag particles135are dispersed in the Ti compound layer131, the Ti compound layer131is sufficiently formed at the time of bonding. As a result, it is possible to obtain the power module substrate110in which the copper plate122(circuit layer112), the copper plate123(metal layer113), and the ceramic substrate111are reliably bonded.

In addition, in the embodiment, the copper plate bonding step S101includes the laminating step S111of laminating the copper plates122and123and the ceramic substrate111via the Ag—Ti-based brazing filler metal124, the low temperature holding step S112of holding a temperature in a temperature range from the eutectic point temperature of Ag and Al to a temperature lower than the eutectic point temperature of Ag and Cu in a state in which the laminated copper plates122and123and ceramic substrate111are compressed in the lamination direction, the heating step S113of, after the low temperature holding step S112, performing heating to the eutectic point temperature of Ag and Cu or higher to melt the Ag—Ti-based brazing filler metal124, and the cooling step S114of, after the heating step S113, performing cooling to solidify the melted Ag—Ti-based brazing filler metal124. As a result, the copper plates122and123, and the ceramic substrate111can be reliably bonded.

That is, in the low temperature holding step S112, the liquid phase138is formed at each interface between the copper plates122and123, and the ceramic substrate111by the eutectic reaction between Al and Ag, and the Ti compound layer131is formed at the interface with the ceramic substrate111in the liquid phase138by a reaction between Ti and O. In the process, the Ag particles135are dispersed in the Ti compound layer131. Thus, even in the case in which the heating temperature in the heating step S113is set to a relatively low temperature, the copper plates122and123, and the ceramic substrate111can be reliably bonded.

Here, since the heating temperature in the heating step S113is set to a relatively low temperature in a range from 790° C. to 830° C. in the embodiment, the thermal load on the ceramic substrate111at the time of bonding can be reduced and deterioration of the ceramic substrate111can be limited. Since the copper plate bonding step includes the low temperature holding step S112as described above, even in the case in which the heating temperature in the heating step S113is set to a relatively low temperature, the ceramic substrate111and the copper plates122and123can be reliably bonded.

Next, a third embodiment of the present invention will be described with reference toFIGS. 11 to 15.

A Cu/ceramic bonded body according to this embodiment includes a power module substrate210formed by bonding a copper plate222(circuit layer212) which is a copper member to a ceramic substrate211which is a ceramic member as shown inFIG. 11.

The ceramic substrate211is made of Al2O3(alumina) having high insulating properties and has the same configuration as that of the second embodiment.

The circuit layer212is formed by bonding a copper plate222made of copper or a copper plate to one surface of the ceramic substrate211as shown inFIG. 14and has the same configuration as that of the second embodiment.

Here, the ceramic substrate211and the circuit layer212(copper plate222) are bonded using a Ag—Ti-based brazing filler metal paste224as shown inFIG. 14.

A Ti compound layer231made of TiO2(titanium oxide) and a Ag—Cu eutectic layer232are formed at the bonding interface between the ceramic substrate211and the circuit layer212(copper plate222) as shown inFIG. 12.

Then, Ag particles235are dispersed in the Ti compound layer231.

A large amount of the Ag particles235is distributed in the Ti compound layer231on the side close to the ceramic substrate211and the concentration of Ag in a near interface region231A from the interface with the ceramic substrate211to 500 nm in the Ti compound layer231is set to 0.3 atomic % or more and preferably set to be in a range from 0.3 atomic % to 15 atomic %. In the embodiment, 90% or more of the Ag particles235observed in the Ti compound layer231is distributed in the aforementioned near interface region231A. The ratio of the Ag particles235distributed in the near interface region231A is more preferably 95% or more and the upper limit is 100%. However, there is no limitation thereto.

In addition, in the embodiment, the particles size of the Ag particles235dispersed in the Ti compound layer231is set to be in a range from 10 nm to 100 nm. The particle size of the Ag particles235may be set to be in a range from 10 nm to 50 nm.

Next, a method for manufacturing the power module substrate210of the aforementioned embodiment will be described with reference toFIGS. 13 to 15.

First, the Ag—Ti-based brazing filler metal paste224is applied to one surface of the ceramic substrate211by screen printing (brazing filler metal paste application step S211). The thickness of the Ag—Ti-based brazing filler metal paste224is set to 20 μm to 300 μm after drying.

Here, the Ag—Ti-based brazing filler metal paste224includes a powder component containing Ag and Ti, a resin, a solvent, a dispersing agent, a plasticizer, and a reducing agent.

In the embodiment, the content of the powder component is set to 40 mass % to 90 mass % with respect to the total amount of the Ag—Ti-based brazing filler metal paste224. In addition, in the embodiment, the viscosity of the Ag—Ti-based brazing filler metal paste224is adjusted to 10 Pa·s to 500 Pa·s and more preferably to 50 Pa·s to 300 Pa·s.

As the composition of the powder component, the Ti content is 0.4 mass % to 75 mass % and the balance is Ag and inevitable impurities. In the embodiment, the powder component includes 10 mass % of Ti and the balance being Ag and inevitable impurities.

Further, in the embodiment, as the powder component containing Ag and Ti, an alloy powder of Ag and Ti is used. The alloy powder is prepared by an atomizing method and the prepared alloy powder is sieved. Thus, the particle size is set to 40 μm or less, preferably set to 20 μm or less, and still more preferably set to 10 μm or less.

Next, the copper plate222which becomes the circuit layer212is laminated on one surface of the ceramic substrate211(laminating step S212).

Further, in a state in which the copper plate222and the ceramic substrate211are compressed in the lamination direction under pressure in a range from 0.5 kgf/cm2to 35 kgf/cm2(4.9×104Pa to 343×104Pa), the copper plate and the ceramic substrate are put into a heating furnace in a vacuum or argon atmosphere and heated, and the temperature is held (low temperature holding step S213). Here, the holding temperature in the low temperature holding step S213is set to be in a range from the eutectic point temperature of Ag and Al to a temperature lower than the eutectic point temperature of Ag and Cu and specifically set to be in a range from 570° C. to 770° C. In addition, the holding time in the low temperature holding step S213is set to be in a range from 30 minutes to 5 hours. The holding temperature in the low temperature holding step S213is preferably set to be in a range from 590° C. to 750° C. Further, the holding time in the low temperature holding step S213is preferably set to be from 60 minutes to 3 hours.

Since the temperature equal to or higher than the eutectic point temperature of Ag and Al is held in the low temperature holding step S213, as shown inFIG. 15, Ag in the Ag—Ti-based brazing filler metal paste224, and Al formed by the reaction of the ceramic substrate211made of Al2O3with Ti undergo a eutectic reaction to form a liquid phase238. In the liquid phase238, Ti in the Ag—Ti-based brazing filler metal paste224reacts with O (oxygen) in the ceramic substrate211to form TiO2. Thus, the Ti compound layer231made of TiO2is formed in the form of corrosion of the surface of the ceramic substrate211.

After the low temperature holding step S213, in the state in which the copper plate222and the ceramic substrate211are compressed, the copper plate and the ceramic substrate are heated in the heating furnace in a vacuum atmosphere to melt the Ag—Ti-based brazing filler metal paste224(heating step S214). At this time, Cu is supplied from the copper plate222to the Ag—Ti-based brazing filler metal paste224and the melting point is lowered due to a eutectic reaction between Ag and Cu. Thus, melting of the Ag—Ti-based brazing filler metal paste224is promoted. Here, the heating temperature in the heating step S214is set to the eutectic point temperature of Ag and Cu or higher and specifically set to be in a range from 790° C. to 830° C. In addition, the holding time in the heating step S214is set to be in a range from 5 minutes to 60 minutes. The heating temperature in the heating step S214is preferably set to be in a range from 800° C. to 820° C. Further, the holding time in the heating step S214is preferably set to be 10 minutes to 30 minutes.

After the heating step S214, cooling is performed to solidify the melted Ag—Ti-based brazing filler metal paste224(cooling step S215). The cooling rate in the cooling step S215is not particularly limited and is preferably set to be from 2° C./min to 10° C./min.

As described above, the power module substrate210of the embodiment is manufactured by bonding the copper plate222which is a copper member and the ceramic substrate211which is a ceramic member.

The Ag particles235are dispersed in the Ti compound layer231made of TiO2.

The Cu/ceramic bonded body (power module substrate210) having the above configuration of the embodiment exhibits the same effect as that of the second embodiment.

In addition, in the embodiment, the method includes the brazing filler metal paste application step S211of applying the Ag—Ti-based brazing filler metal paste224to one surface of the ceramic substrate211, the laminating step S212of laminating the copper plate222and the ceramic substrate211via the applied Ag—Ti-based brazing filler metal paste224, the low temperature holding step S213of holding a temperature in a temperature range from the eutectic point temperature of Ag and Al to a temperature lower than the eutectic point temperature of Ag and Cu in a state in which the laminated copper plate222and ceramic substrate211are compressed in the lamination direction, the heating step S214of, after the low temperature holding step S213, performing heating to the eutectic point temperature of Ag and Cu or higher to melt the Ag—Ti-based brazing filler metal paste224, and the cooling step S215of, after the heating step S214, performing cooling to solidify the melted Ag—Ti-based brazing filler metal paste224. As a result, the copper plate222and the ceramic substrate211can be reliably bonded.

That is, in the low temperature holding step S213, the liquid phase238is formed at the interface between the copper plate222and the ceramic substrate211by the eutectic reaction between Al and Ag and in the liquid phase238, Ti reacts with O to form the Ti compound layer231at the interface of the ceramic substrate211. In the process, the Ag particles235are dispersed in the Ti compound layer231. Thus, even in the case in which the heating temperature in the heating step S214is set to a relatively low temperature, the copper plate222and the ceramic substrate211can be reliably bonded.

Here, in the embodiment, since the heating temperature in the heating step S214is set to a relatively low temperature in a range from 790° C. to 830° C., thermal load on the ceramic substrate211at the time of bonding can be reduced and deterioration of the ceramic substrate211can be limited. In addition, as described above, the method includes the low temperature holding step S213, even in the case in which the heating temperature in the heating step S214is a relatively low temperature, the ceramic substrate211and the copper plate222can be reliably bonded.

While embodiments of the present invention have been described above, the present invention is not limited to these embodiments and modifications can be appropriately made without departing from the technical ideas of the invention.

For example, the copper plate constituting the circuit layer or the metal layer using a rolled sheet of oxygen-free copper or tough pitch copper is described. However, the embodiments are not limited thereto and sheets made of other types of copper or other copper alloys may be used.

In addition, in the first embodiment, the aluminum plate constituting the metal layer using a rolled sheet of pure aluminum having a purity of 99.99 mass % is described. However, the embodiment is not limited thereto and sheets made of other types of aluminum such as aluminum having a purity of 99 mass % (2N aluminum), or other aluminum alloys may be used.

Furthermore, in the embodiment, the concentration of Ag in the near interface region is set to 0.3 atomic % or more. However, the embodiment is not limited thereto.

In addition, in the embodiment, the particle size of the Ag particles dispersed in the Ti compound layer is set to be in a range from 10 nm to 100 nm. However, Ag particles having particle sizes out of the above range may be dispersed.

Furthermore, the heat sink or the heat radiation plate is not limited to the examples of the embodiment and the structure of the heat sink is not particularly limited.

In addition, a buffer layer made of aluminum, an aluminum alloy, or a composite material including aluminum (for example, AlSiC) may be provided between the top plate portion of the heat sink or the heat radiation plate and the metal layer.

Furthermore, in the third embodiment, the ceramic substrate and the copper plate are bonded using the Ag—Ti-based brazing filler metal paste. However, the embodiment is not limited thereto and a Ag—Cu—Ti-based paste may be used. In this case, the third embodiment has the same interface structure as that of the first embodiment.

In addition, the Ag—Ti-based brazing filler metal paste is applied to the ceramic substrate. However, the embodiment is not limited thereto and the Ag—Ti-based brazing filler metal paste or the like may be applied to the copper plate.

Furthermore, the Ag—Ti-based brazing filler metal paste is applied by screen printing but the application method is not limited.

In addition, before the laminating step (S212), a step of drying the Ag—Ti-based brazing filler metal paste may be provided.

Further, in the third embodiment, as the powder component containing Ag and Ti, the alloy powder of Ag and Ti is used. However, the embodiment is not limited thereto and a mixed powder of a Ag powder and a Ti powder can be used. In this case, the particle size of the Ag powder to be used may be 40 μm or less, preferably 20 μm or less, and still more preferably 10 μm or less.

In addition, instead of using the Ti powder, a TiH2powder can be used. In the case of using the TiH2powder, as the composition of the powder component, the TiH2content may be 0.4 mass % to 50 mass % and the balance may be Ag and inevitable impurities. The particle size of the TiH2powder to be used may be preferably 15 μm or less and more preferably 5 μm or less. Further, in the case of a paste using the TiH2powder, the thickness of the applied paste may be 20 μm to 300 μm after drying.

In addition, a paste made of a mixed powder of a Ag powder, a Cu powder, and a Ti powder, or a TiH2powder can be used.

In addition, one or two or more elements selected from In, Sn, Al, Mn and Zn can be added to the Ag—Cu—Ti-based brazing filler metal and the Ag—Ti-based brazing filler metal described in the embodiments. In this case, the bonding temperature can be further lowered.

Further, as the Ag—Ti-based brazing filler metal paste, a paste including Ti, one or two or more elements selected from In, Sn, Al, Mn and Zn, and the balance being Ag and inevitable impurities can be used. In this case, the bonding temperature can be further lowered.

In addition, in the second embodiment, instead of using the foil of the Ag—Ti-based brazing filler metal, the Ag—Ti-based brazing filler metal paste described in the third embodiment can be used.

EXAMPLES

Hereinafter, the results of a confirmation test performed to check the effectiveness of the embodiments according to the present invention will be described.

Cu/ceramic bonded bodys were formed by using ceramic substrates, brazing filler metals, and copper plates shown in Table 1. Specifically, each Cu/ceramic bonded body was formed by bonding a copper plate having a size of 38 mm square and a thickness of 0.6 mm to one surface of a ceramic substrate having a size of 40 mm square and a thickness of 0.635 mm using a brazing filler metal foil containing Ag and Ti and having a thickness of 20 μm under the conditions shown in Table 1. In addition, as the brazing filler metal, in the case of Ag—Cu—Ti, a Ag-28 mass % Cu-3 mass % Ti brazing filler metal was used, and in the case of Ag—Ti, a Ag-10 mass % Ti brazing filler metal was used. The applied pressure (load) in the lamination direction was set to 1.5 kgf/cm2.

In addition, Cu/ceramic bonded bodies were formed by using ceramic substrates, brazing filler metals, and copper plates shown in Table 2. Specifically, each Cu/ceramic bonded body was formed by bonding a copper plate having a size of 38 mm square and a thickness of 0.6 mm to one surface of a ceramic substrate having a size of 40 mm square and a thickness of 0.635 mm using a brazing filler metal paste containing Ag and Ti under the conditions shown in Table 2. The applied pressure (load) in the lamination direction was set to 1.5 kgf/cm2.

As the brazing filler metal paste, in the case of Ag—Cu—Ti, a paste containing a brazing filler metal powder including, a powder component (having a particle size of 20 μm) having a composition of Ag-28 mass % Cu-3 mass % Ti, an acrylic resin, and texanol was used and the thickness of the applied paste was set to the values shown in Table 2.

In the case of Ag—Ti, a paste containing a brazing filler metal powder including a powder component (having a particle size of 20 μm) having a composition of Ag-10 mass % Ti, an acrylic resin, and texanol was used and the thickness of the applied paste was set to the values shown in Table 2.

In the case of Ag—TiH2, a paste containing a mixed powder of a Ag powder (having a particle size of 5 μm) and a TiH2powder (having a particle size of 5 μm), an acrylic resin, and texanol was used. As the composition of the mixed powder, the TiH2content was 20 mass % and the balance was Ag and inevitable impurities. The thickness of the applied paste was set to the values shown in Table 2.

In the case of Ag—Cu—TiH2, a paste containing a mixed powder of a Ag powder (having a particle size of 5 μm), a Cu powder (having a particle size of 2.5 μm), and a TiH2powder (having a particle size of 5 μm), an acrylic resin, and texanol was used. As the composition of the mixed powder, the Cu content was 27 mass %, the TiH2content was 3 mass %, and the balance was Ag and inevitable impurities. The thickness of the applied paste was set to the values shown in Table 2.

In Examples, after the paste was applied, the paste was dried at 150° C. The coating thickness shown in Table 2 was set to a value after drying.

In each Cu/ceramic bonded body obtained in the above-described manner, the presence of Ag particles and Cu particles in the Ti compound layer, the concentration of Ag in the near interface region in the Ti compound layer, and the bonding rate of the copper plate and the ceramic substrate were evaluated.

(Presence of Ag Particles and Cu Particles in Ti Compound Layer)

5 visual fields of the bonding interface between the copper plate and the ceramic substrate were observed using a scanning electron microscope (ULTRA 55 manufactured by Carl Zeiss NTS GmbH) at a magnitude of 15,000 times (measurement range: 6 μm×8 μm) and the presence of Ag particles and Cu particles in the Ti compound layer was confirmed.

(Concentration of Ag in Near Interface Region in Ti Compound Layer)

A line analysis was performed on the bonding interface between the copper plate and the ceramic substrate (the section parallel to the lamination direction) using an energy dispersive X-ray detector (SDD detector manufactured by Thermo Fisher Scientific Inc. and Norton System Six) and the concentration of Ag in the near interface region in the Ti compound layer was measured.

The bonding rate of the copper plate and the ceramic substrate was obtained by the following expression using an ultrasonic flow detector (Fine SAT 200 manufactured by Hitachi Power Solutions Co., Ltd.). Here, the initial bonding area was the area of the copper plate (38 mm square) which is an area to be bonded before bonding. In an image obtained by performing a binarization treatment on an ultrasonic flaw image, peeling was indicated by white parts in the bonding portion and thus the area of the white parts was set to a peeled area.
(Bonding Rate)={(Initial bonding area)−(Peeled area)}/(Initial bonding area)×100

The evaluation results are show in Tables 3 and 4. In addition, the backscattercd electron image of Example 1 is shown inFIG. 16.

In Conventional Example 1, when a copper plate made of OFC was bonded to a ceramic substrate made of AlN using a Ag—Cu—Ti brazing filler metal, a low temperature holding step of holding a temperature in a temperature range from the eutectic point temperature of Ag and Al to the eutectic point temperature of Ag and Cu was not performed. In such Conventional Example 1, formation of a Ti compound layer made of TiN was confirmed at the interface between the ceramic substrate and the copper plate, but the presence of Ag particles and Cu particles was not confirmed in the Ti compound layer. In addition, the concentration of Ag in the near interface region between the ceramic substrate and the Ti compound layer was 0.00 atomic %. In such Conventional Example 1, the bonding rate was 83.7%.

In contrast, in Examples 2 to 7, when a copper plate made of OFC was bonded to a ceramic substrate made of AlN using a Ag—Cu—Ti brazing filler metal, a low temperature holding step of holding a temperature in a temperature range from the eutectic point temperature of Ag and Al to the eutectic point temperature of Ag and Cu was performed. In such Examples 2 to 7, formation of a Ti compound layer made of TiN was confirmed at the interface between the ceramic substrate and the copper plate and Ag particles and Cu particles in the Ti compound layer were observed. In addition, the concentration of Ag in the near interface region between the ceramic substrate and the Ti compound layer was 0.15 atomic % to 12.28 atomic %. In such Examples 2 to 7, the bonding rate was 92.1% to 97.6% and an improvement in the bonding rate was confirmed compared to Conventional Examples.

In Examples 1 and 8, when a copper plate made of TPC or OFC was bonded to a ceramic substrate made of AlN using a Ag—Ti brazing filler metal, a low temperature holding step of holding a temperature in a temperature range from the eutectic point temperature of Ag and Al to the eutectic point temperature of Ag and Cu was performed. In such Examples 1 and 8, formation of a Ti compound layer made of TiN was confirmed at the interface between the ceramic substrate and the copper plate and Ag particles were observed in the Ti compound layer. In addition, the concentration of Ag in the near interface region between the ceramic substrate and the Ti compound layer was 0.13 atomic % to 10.56 atomic %. In such Examples 1 and 8, the bonding rate was 93.3% and 98.0% respectively and an improvement in the bonding rate was confirmed compared to Conventional Examples.

In Examples 9, 10, and 13 to 16, when a copper plate made of OFC was bonded to a ceramic substrate made of Al2O3using a Ag—Ti brazing filler metal, a low temperature holding step of holding a temperature in a temperature range from the eutectic point temperature of Ag and Al to the eutectic point temperature of Ag and Cu was performed. In such Examples 9, 10, and 13 to 16, formation of a Ti compound layer made of TiO2was confirmed at the interface between the ceramic substrate and the copper plate and Ag particles were observed in the Ti compound layer. In addition, the concentration of Ag in the near interface region between the ceramic substrate and the Ti compound layer was 0.21 atomic % to 11.12 atomic %. In such Examples 9, 10, and 13 to 16, the bonding rate was 91.1% to 98.8% and an improvement in the bonding rate was confirmed compared to Conventional Examples.

In Examples 11 and 12, when a copper plate made of OFC was bonded to a ceramic substrate made of Al2O3using a Ag—Cu—Ti brazing filler metal, a low temperature holding step of holding a temperature in a temperature range from the eutectic point temperature of Ag and Al to the eutectic point temperature of Ag and Cu was performed. In such Examples 11 and 12, formation of a Ti compound layer made of TiO2was confirmed at the interface between the ceramic substrate and the copper plate and Ag particles and Cu particles were observed in the Ti compound layer. In addition, the concentration of Ag in the near interface region between the ceramic substrate and the Ti compound layer was 9.08 atomic % and 11.36 atomic %. In such Examples 11 and 12, the bonding rate was 97.5% and 98.7% respectively and an improvement in the bonding rate was confirmed compared to Conventional Examples.

As shown in Tables 2 and 4, even in the cases of using the Ag—Ti-based paste, the Ag—Cu—Ti-based paste, and the Ag—TiH2-based paste, as in the case of using a brazing filler metal foil, as a result, an improvement in the bonding rate was confirmed compared to Conventional Examples.

INDUSTRIAL APPLICABILITY

According to the present invention, it is possible to provide a Cu/ceramic bonded body in which a copper member and a ceramic member are reliably bonded, a method for manufacturing the Cu/ceramic bonded body, and a power module substrate made of the Cu/ceramic bonded body. The Cu/ceramic bonded body and the power module substrate according to the present invention are suitable for power semiconductor elements for controlling higher amounts of power used to control wind power generation, electric automobiles, hybrid automobiles, and the like.

REFERENCE SIGNS LIST

10,110,210: POWER MODULE SUBSTRATE

12,112,212: CIRCUIT LAYER

13,113: METAL LAYER

22,122,123,222: COPPER PLATE

31,131,231: Ti COMPOUND LAYER

31A,131A,231A: NEAR INTERFACE REGION