Patent Description:
Priority is claimed on <CIT>, and <CIT>.

In power modules, LED modules, and thermoelectric modules, there are structures in which power semiconductor elements, LED elements, and thermoelectric elements are bonded with an insulated circuit substrate on which a circuit layer formed of a conductive material is formed on one surface of an insulating layer.

For example, power semiconductor elements for controlling large amounts of power, which are used to control wind power generation, electric vehicles, hybrid vehicles, and the like, generate a large amount of heat during operation, thus, as a substrate for mounting the above, for example, insulated circuit substrates provided with a ceramic substrate formed of silicon nitride or the like, and a circuit layer formed by bonding a metal sheet with excellent electrical conductivity to one surface of the ceramic substrate are widely used in the related art. Here, there are also insulated circuit substrates on which a metal layer is formed by bonding a metal sheet to the other surface of the ceramic substrate.

For example, Patent Document <NUM> proposes an insulated circuit substrate in which a circuit layer and a metal layer are formed by bonding copper sheets to one surface and the other surface of a ceramic substrate. In this insulated circuit substrate, copper sheets are arranged to interpose an Ag-Cu-Ti-based brazing material on one surface and the other surface of the ceramic substrate and the copper sheets are bonded by performing a heat treatment (the so-called active metal brazing method).

In addition, Patent Document <NUM> proposes an insulated circuit substrate in which a copper sheet formed of copper or a copper alloy is bonded with the surface of a ceramic substrate formed of silicon nitride. In this insulated circuit substrate, an active metal and a Mg are arranged between the copper sheet and the ceramic substrate and the ceramic substrate and the copper sheet are bonded by heating the copper sheet and the ceramic substrate in a state of being pressed in the laminating direction.

Patent Document <NUM> discloses a copper/ceramic joined body in which a copper member made of copper or a copper alloy and a ceramic member made of silicon nitride are joined.

Here, in a case where a ceramic substrate and a copper sheet are bonded by the active metal brazing method, as disclosed in Patent Document <NUM>, a compound layer of an active metal (Ti) is formed at the bonded interface between the ceramic substrate and the copper sheet. For example, in a case where a ceramic substrate including nitrogen is bonded using an active brazing material including Ti as the active metal, a TiN layer is formed at the bonded interface between the ceramic substrate and the copper sheet.

In addition, in Patent Document <NUM>, an active metal nitride layer including one or two or more active metal nitrides selected from Ti, Zr, Nb, and Hf is formed on the ceramic substrate side between the copper sheet and the ceramic substrate.

Here, in the insulated circuit substrate described above, when a terminal material or the like was ultrasonically welded with the surface of the circuit layer (copper sheet), there were concerns that the copper sheet may be plastically deformed, the active metal nitride layer, such as the hard TiN layer, may be destroyed, and the bonding reliability may be decreased. In addition, there was a concern that breaking starting from the destruction of the TiN layer may occur in the ceramic substrate.

This invention was created in consideration of circumstances described above and has an objective of providing a copper/ceramic bonded body in which a copper member, which is formed of copper or a copper alloy, and a ceramic member are reliably bonded and in which the bonding reliability is excellent even when ultrasonic waves are applied thereto, as well as an insulated circuit substrate.

In order to solve these problems and achieve the objective, the present inventors obtained the following findings as a result of intensive investigation. The invention is defined in the appended claims <NUM>-<NUM>.

When a ceramic substrate and a copper sheet are heated to be bonded, the crystal grains of the copper sheet are coarsened. In a case where the crystal grains are coarsened in a region adjacent to an active metal nitride layer such as a TiN layer, it is understood that the region in the vicinity of the bonded interface of the copper sheet is easily deformed when ultrasonic waves are applied thereto and active metal nitride layers such as a TiN layer are destroyed.

The present invention was created based on the findings described above and a copper/ceramic bonded body of an aspect of the present invention is a copper/ceramic bonded body formed by bonding a copper member, which is formed of copper or a copper alloy, and a ceramic member, in which, a ratio D1/D0 is <NUM> or less, D0 being an average crystal grain size of the entire copper member, D1 being an average crystal grain size of the copper member at a position <NUM> from a bonding surface with the ceramic member, D0 and D1 being obtained by observing a cross-section of the copper member along a laminating direction.

In the copper/ceramic bonded body with this configuration, when a cross-sectional surface of the copper member in a laminating direction is observed, a ratio D1/D0 of an average crystal grain size D1 at a position of <NUM> in the laminating direction from the bonding surface between the copper member and the ceramic member to an average crystal grain size D0 of the entire copper member is <NUM> or less, thus, the crystal grain size in the vicinity of the bonded interface is suppressed to be comparatively small, it is possible to suppress deformation of the copper member in the region in the vicinity of the bonded interface when ultrasonic waves are applied thereto, and it is possible to suppress the destruction of the active metal nitride layer such as a TiN layer. In addition, the crystal grain size is not significantly different between the entire copper member and in the vicinity of the bonded interface and it is possible to suppress the hardening of the entire copper member.

Here, in the copper/ceramic bonded body of the present aspect, preferably, Mg is diffused in a region in the copper member, the region being at least <NUM> from the bonding surface with the ceramic member in the laminating direction, and Mg concentration decreases with increasing a distance from the bonding surface.

In such a case, Mg is sufficiently diffused in a region of the copper member from the bonding surface with the ceramic member to at least <NUM> in the laminating direction and it is possible to make the crystal grain size in the vicinity of the bonded interface comparatively small.

An insulated circuit substrate of an aspect of the present invention is an insulated circuit substrate formed by bonding a copper sheet, which is formed of copper or a copper alloy, with a surface of a ceramic substrate, in which, a ratio D1/D0 is <NUM> or less, D0 being an average crystal grain size of the entire copper sheet, D1 being an average crystal grain size of the copper sheet at a position <NUM> from a bonding surface with the ceramic substrate, D0 and D1 being obtained by observing a cross-section of the copper sheet along a laminating direction.

In the insulated circuit substrate with this configuration, when a cross-sectional surface of the copper sheet in a laminating direction is observed, a ratio D1/D0 of an average crystal grain size D1 at a position of <NUM> in the laminating direction from the bonding surface between the copper sheet and the ceramic substrate to an average crystal grain size D0 of the entire copper sheet is <NUM> or less, thus, it is possible to suppress the crystal grain size in the vicinity of the bonded interface to be comparatively small, to suppress deformation of the copper sheet in the region in the vicinity of the bonded interface when ultrasonic waves are applied thereto, and to suppress destruction of the active metal nitride layer such as a TiN layer. In addition, the crystal grain size does not differ significantly between the entire copper sheet and in the vicinity of the bonded interface and it is possible to suppress the hardening of the entire copper sheet.

Here, in the insulated circuit substrate of the present aspect, preferably, Mg is diffused in a region in the copper sheet, the region being at least <NUM> from the bonding surface with the ceramic substrate in the laminating direction, and Mg concentration decreases with increasing a distance from the bonding surface.

In such a case, Mg is sufficiently diffused in a region of the copper sheet from the bonding surface with the ceramic substrate to at least <NUM> in the laminating direction and it is possible to make the crystal grain size in the vicinity of the bonded interface comparatively small.

According to the present invention, it is possible to provide a copper/ceramic bonded body in which a copper member, which is formed of copper or a copper alloy, and a ceramic member are reliably bonded and in which the bonding reliability is excellent even when ultrasonic waves are applied thereto, as well as an insulated circuit substrate.

A description will be given below of embodiments of the present invention with reference to the accompanying drawings.

A description will be given of embodiments of the present invention with reference to <FIG>.

The copper/ceramic bonded body according to the present embodiment is an insulated circuit substrate <NUM> formed by bonding a ceramic substrate <NUM>, which is a ceramic member, with a copper sheet <NUM> (a circuit layer <NUM>) and a copper sheet <NUM> (a metal layer <NUM>), which are copper members.

<FIG> shows the insulated circuit substrate <NUM> of an embodiment of the present invention and a power module <NUM> using this insulated circuit substrate <NUM>.

The power module <NUM> is provided with the insulated circuit substrate <NUM>, a semiconductor element <NUM> bonded with one side of the insulated circuit substrate <NUM> (the upper side in <FIG>) via a first solder layer <NUM>, and a heat sink <NUM> bonded with the other side of the insulated circuit substrate <NUM> (the lower side in <FIG>) via a second solder layer <NUM>.

The insulated circuit substrate <NUM> is provided with the ceramic substrate <NUM>, the circuit layer <NUM> arranged on one surface (the upper surface in <FIG>) of the ceramic substrate <NUM>, and the metal layer <NUM> arranged on the other surface (the lower surface in <FIG>) of the ceramic substrate <NUM>.

The ceramic substrate <NUM> prevents electrical connection between circuit layer <NUM> and metal layer <NUM> and is formed of AlN (aluminum nitride), Si<NUM>N<NUM> (silicon nitride), Al<NUM>O<NUM> (alumina), or the like with excellent insulation properties. In particular, the ceramic substrate <NUM> is preferably formed of Si<NUM>N<NUM> (silicon nitride), which has excellent strength. Here, the thickness of the ceramic substrate <NUM> is preferably in a range of <NUM> or more and <NUM> or less and, in the present embodiment, may be set to <NUM>, for example.

As shown in <FIG>, the circuit layer <NUM> is provided by bonding the copper sheet <NUM> formed of copper or a copper alloy with one surface of the ceramic substrate <NUM>. In the present embodiment, a rolled sheet of oxygen-free copper is used as the copper sheet <NUM> forming the circuit layer <NUM>. A circuit pattern is provided on this circuit layer <NUM> and one surface thereof (the upper surface in <FIG>) is the mounting surface on which the semiconductor element <NUM> is mounted. Here, the thickness of the circuit layer <NUM> is preferably in a range of <NUM> or more and <NUM> or less and, in the present embodiment, for example, may be set to <NUM>.

As shown in <FIG>, the metal layer <NUM> is formed by bonding the copper sheet <NUM> formed of copper or a copper alloy with the other surface of the ceramic substrate <NUM>. In the present embodiment, a rolled sheet of oxygen-free copper is used as the copper sheet <NUM> forming the metal layer <NUM>. Here, the thickness of the metal layer <NUM> is preferably in a range of <NUM> or more and <NUM> or less and, in the present embodiment, for example, may be set to <NUM>.

The heat sink <NUM> is for cooling the insulated circuit substrate <NUM> described above and, in the present embodiment, is a heat-dissipating sheet formed of a material with favorable thermal conductivity. In the present embodiment, the heat sink <NUM> is formed of copper or a copper alloy with excellent thermal conductivity. The heat sink <NUM> and the metal layer <NUM> of the insulated circuit substrate <NUM> are bonded via the second solder layer <NUM>.

Here, the ceramic substrate <NUM> and the circuit layer <NUM> (copper sheet <NUM>) as well as the ceramic substrate <NUM> and the metal layer <NUM> (copper sheet <NUM>) are bonded via a Mg-Ti-based bonding material <NUM> as shown in <FIG>.

At the bonded interface between the ceramic substrate <NUM> and the circuit layer <NUM> (the copper sheet <NUM>) and the bonded interface between the ceramic substrate <NUM> and the metal layer <NUM> (the copper sheet <NUM>), a TiN layer <NUM> is provided as shown in <FIG>. This TiN layer <NUM> is created by a reaction between the Ti included in the Mg-Ti-based bonding material <NUM> and the nitrogen (N) included in the ceramic substrate <NUM>.

In the present embodiment, when a cross-sectional surface of the circuit layer <NUM> (the copper sheet <NUM>) and the metal layer <NUM> (the copper sheet <NUM>) in a laminating direction is observed, a ratio D1/D0 of an average crystal grain size D1 at a position of <NUM> in the laminating direction from the bonding surface with the ceramic substrate <NUM> to an average crystal grain size D0 of the entirety of the circuit layer <NUM> (the copper sheet <NUM>) and the metal layer <NUM> (the copper sheet <NUM>) is <NUM> or less and preferably in a range of <NUM> or more and <NUM> or less.

That is, the crystal grain size of the circuit layer <NUM> (the copper sheet <NUM>) and metal layer <NUM> (the copper sheet <NUM>) is locally smaller at a position of <NUM> in the laminating direction from the bonding surface of ceramic substrate <NUM>.

In the present embodiment, the bonding surface of the circuit layer <NUM> with the ceramic substrate <NUM> is the uppermost surface of the circuit layer <NUM> side of the ceramic substrate <NUM> in the laminating direction.

In addition, in the present embodiment, the bonding surface of the metal layer <NUM> with the ceramic substrate <NUM> is the uppermost surface of the metal layer <NUM> side of the ceramic substrate <NUM> in the laminating direction.

In the region from the bonding surface with ceramic substrate <NUM> to <NUM> in the laminating direction, the TiN layer <NUM> is interposed between the ceramic substrate <NUM> and the circuit layer <NUM> and between the ceramic substrate <NUM> and the metal layer <NUM>, but the TiN layer <NUM> is sufficiently thin compared to the circuit layer <NUM> and the metal layer <NUM>.

The circuit layer <NUM> and the metal layer <NUM> are bonded with the ceramic substrate <NUM> via the TiN layer <NUM>.

The average crystal grain sizes D0 and D1 in the present embodiment are the average crystal grain sizes of the crystal grains including twin crystals.

Here, in the present embodiment, preferably, Mg is diffused in a region of the circuit layer <NUM> (the copper sheet <NUM>) and the metal layer <NUM> (the copper sheet <NUM>) from the bonding surface of the ceramic substrate <NUM> to at least <NUM> in the laminating direction and the Mg concentration decreases with increasing a distance from the bonding surface. That is, preferably, the Mg in the Mg-Ti-based bonding material <NUM> is sufficiently diffused to the circuit layer <NUM> (the copper sheet <NUM>) side and the metal layer <NUM> (the copper sheet <NUM>) side. The concentration of Mg in this region is preferably <NUM> wt% or more and <NUM> wt% or less.

Next, a description will be given of the method for manufacturing the insulated circuit substrate <NUM> of the present embodiment described above and the power module <NUM> with reference to <FIG> and <FIG>.

As shown in <FIG>, the Mg-Ti-based bonding material <NUM> is arranged between the copper sheet <NUM> which is the circuit layer <NUM> and the ceramic substrate <NUM> and between the copper sheet <NUM> which is the metal layer <NUM> and the ceramic substrate <NUM> and the above are laminated. In the present embodiment, a paste material including titanium hydride powder and magnesium hydride powder is used as the Mg-Ti-based bonding material <NUM>. Since titanium and magnesium are active metals, the use of titanium hydride powder and magnesium hydride powder makes it possible to suppress oxidation and the like of titanium and magnesium.

Here, the Mg-Ti-based bonding material <NUM> to be arranged preferably has a Ti amount in a range of <NUM> or more and <NUM> or less in terms of thickness and an Mg amount in a range of <NUM> or more and <NUM> or less.

Next, the copper sheet <NUM>, the ceramic substrate <NUM>, and the copper sheet <NUM>, which are laminated, are pressed in the laminating direction, charged into a heating furnace, heated, and held at a predetermined holding temperature for a set time.

Here, in the present embodiment, the pressing load in the holding step S02 is preferably in a range of <NUM> MPa or more and <NUM> MPa or less. In addition, the inside of the heating furnace is preferably an inert gas atmosphere such as Ar.

The holding temperature is preferably in a range of <NUM> or higher and <NUM> or lower and the holding time at the holding temperature is preferably in a range of <NUM> minutes or more and <NUM> minutes or less.

By this holding step S02, the Mg of the Mg-Ti-based bonding material <NUM> is sufficiently diffused toward the copper sheet <NUM> that will become the circuit layer <NUM> and the copper sheet <NUM> that will become the metal layer <NUM>.

Next, after the holding step S02, the copper sheet <NUM>, the ceramic substrate <NUM>, and the copper sheet <NUM>, which are laminated, are further heated in a state of being pressed in the laminating direction to bond the copper sheet <NUM>, the ceramic substrate <NUM>, and the copper sheet <NUM>. In this bonding step S03, it is preferable to create a vacuum atmosphere in the heating furnace.

Here, the pressing load in the bonding step S03 is set in a range of <NUM> MPa or more and <NUM> MPa or less.

In addition, the heating temperature in the bonding step S03 is preferably in a range of <NUM> or higher and <NUM> or lower.

Furthermore, the holding time at the heating temperature is preferably in a range of <NUM> minutes or more and <NUM> minutes or less.

In addition, the vacuum level in the bonding step S03 is preferably in a range of <NUM> × <NUM>-<NUM> Pa or more and <NUM> × <NUM>-<NUM> Pa or less.

As described above, the insulated circuit substrate <NUM> of the present embodiment is manufactured by the laminating step S01, the holding step S02, and the bonding step S03.

Next, the heat sink <NUM> is bonded with the other surface side (the opposite side to the ceramic substrate <NUM>) of the metal layer <NUM> of the insulated circuit substrate <NUM>. In the present embodiment, the insulated circuit substrate <NUM> and the heat sink <NUM> are laminated via the solder material and charged into a heating furnace and the insulated circuit substrate <NUM> and the heat sink <NUM> are solder-bonded via the second solder layer <NUM>.

Next, the semiconductor element <NUM> is bonded with one surface side (the opposite side to the ceramic substrate <NUM>) of the circuit layer <NUM> of the insulated circuit substrate <NUM> by soldering.

The power module <NUM> shown in <FIG> is produced by the above steps.

According to the insulated circuit substrate <NUM> (the copper/ceramic bonded body) of the present embodiment formed as described above, when a cross-sectional surface of the circuit layer <NUM> and the metal layer <NUM> in a laminating direction is observed, a ratio D1/D0 of an average crystal grain size D1 at a position of <NUM> in the laminating direction from the bonding surface with the ceramic substrate <NUM> to an average crystal grain size D0 of the entirety of the circuit layer <NUM> and the metal layer <NUM> is <NUM> or less. Therefore, it is possible to suppress the crystal grain size in the vicinity of the bonded interface to be comparatively small, to suppress deformation of the circuit layer <NUM> and metal layer <NUM> in the region in the vicinity of the bonded interface when ultrasonic waves are applied thereto, and to suppress destruction of the TiN layer <NUM>. In addition, the crystal grain size is not significantly different in the vicinity of the bonded interface between the entire circuit layer <NUM> and the metal layer <NUM> and it is possible to suppress the hardening of the entire circuit layer <NUM> and metal layer <NUM>.

Furthermore, in the present embodiment, Mg is sufficiently diffused in a region of the circuit layer <NUM> and metal layer <NUM> from the bonding surface of the ceramic substrate <NUM> to at least <NUM> in the laminating direction and it is possible to make the crystal grain size in the vicinity of the bonded interface of the circuit layer <NUM> and metal layer <NUM> comparatively small.

Although the embodiments of the present invention were described above, the present invention is not limited thereto and appropriate modification is possible in a range not departing from the scope of the invention.

For example, the copper sheet forming the circuit layer or metal layer was described as a rolled sheet of oxygen-free copper, but is not limited thereto and may be formed of other copper or copper alloys.

In addition, it is also possible to carry out the manufacturing using a foil material as the bonding material instead of a paste material.

Furthermore, a description was given of a heat sink with a heat-dissipating sheet as an example; however, the heat sink is not limited thereto and there is no particular limitation on the structure of the heat sink. For example, the heat sink may have a passage through which a refrigerant circulates or may be provided with cooling fins. In addition, it is also possible to use a composite material (for example, AlSiC or the like) including aluminum or aluminum alloys as a heat sink.

In addition, a buffer layer formed of aluminum or a composite material (for example, AlSiC or the like) including aluminum alloys or aluminum may be provided between the top plate portion of the heat sink or the heat-dissipating sheet, and the metal layer.

In addition, in the present embodiment, a description was given of forming a power module by mounting a power semiconductor element on the circuit layer of the insulated circuit substrate; however, the power module is not limited thereto. For example, an LED module may be formed by mounting an LED element on the insulated circuit substrate, or a thermoelectric module may also be formed by mounting a thermoelectric element on the circuit layer of an insulated circuit substrate.

A description will be given of confirmatory experiments performed to confirm the effectiveness of the present invention.

A copper sheet (<NUM> × <NUM>, thickness of <NUM>) was bonded with both surfaces of a ceramic substrate (<NUM> × <NUM>, thickness of <NUM>) shown in Table <NUM> using the bonding material shown in Table <NUM> and an insulated circuit substrate (copper/ceramic bonded body) on which a circuit layer and metal layer were formed was obtained. The holding step and bonding step were carried out under the conditions shown in Table <NUM>. In addition, the vacuum level of the vacuum furnace during bonding was <NUM> × <NUM>-<NUM> Pa.

The insulated circuit substrates (copper/ceramic bonded bodies) obtained in this manner were observed in a cross-sectional surface in the laminating direction and the crystal grain sizes of the circuit layer and metal layer were measured. In addition, ultrasonic waves were applied thereto and peeling at the bonded interface and cracking of the ceramic substrate were evaluated.

In the cross-sectional surface in the laminating direction of the insulated circuit substrate (circuit layer and metal layer), an average crystal grain size D0 of the entire circuit layer and the entire metal layer was measured using an EBSD measuring device. <FIG> shows the observation results of the crystal structure.

In addition, the average crystal grain size D1 at a position of <NUM> from the uppermost surface of the ceramic substrate to the circuit layer side and the metal layer side was calculated using the equation below by drawing a reference line parallel to the bonded interface at a position separated by <NUM> in the laminating direction from the bonded interface of the circuit layer and the metal layer with the ceramic substrate and using the number of particles N touching the reference line and the length L of the reference line. The length L of the reference line was as shown in Table <NUM>.

This measurement was performed for each of the circuit layer and the metal layer and the average values thereof are shown in Table <NUM>.

Terminal materials were ultrasonically welded under conditions of a bonding area of <NUM> × <NUM><NUM>, a bonding time of approximately <NUM> seconds, and a sinking amount of <NUM> and the presence or absence of peeling at the copper/ceramic substrate bonded interface and cracking in the ceramic substrate was confirmed by ultrasonic flaw detection (SAT).

This confirmation was performed for each of the circuit layer and the metal layer and a case in which peeling of the bonded interface and cracking of the ceramic substrate were confirmed in either was set as "Yes" and a case in which neither was confirmed was set as "No" and listed in Table <NUM>.

For the insulated circuit substrate (copper/ceramic bonded body), line analysis of Mg was performed using EPMA for a cross-sectional surface in the laminating direction from the bonding surface of the circuit layer (metal layer) with the ceramic substrate to the surface side of the circuit layer (metal layer). The distance from the bonding surface of the circuit layer (metal layer) with the ceramic substrate to the location where the concentration of Mg was <NUM> wt% was set as the Mg diffusion distance. This measurement was performed at five locations in each of the circuit layer and metal layer and the average values are listed in Table <NUM>.

In the Comparative Example, the ratio D1/D0 of the average crystal grain size D1 at a position of <NUM> in the laminating direction from the bonding surface of the circuit layer and the metal layer with the ceramic substrate to the average crystal grain size D0 of the entire circuit layer and metal layer was <NUM> and cracking was generated at the bonded interface when ultrasonic waves were applied thereto. This is assumed to be because Ag-Ti paste was used as the bonding material, the crystal grains in the vicinity of the bonded interface were not sufficiently refined, and it was not possible to suppress deformation in the region in the vicinity of the bonded interface in the circuit layer and metal layer when ultrasonic waves were applied thereto.

In Invention Examples <NUM> to <NUM>, the ratio D1/D0 of the average crystal grain size D1 at a position of <NUM> in the laminating direction from the bonding surface of the ceramic substrate with the circuit layer and the metal layer to the average crystal grain size D0 of the entire circuit layer and metal layer was <NUM> or less and it was possible to suppress the generation of cracking at the bonded interface when ultrasonic waves were applied thereto. This is assumed to be because material containing Mg was used as the bonding material, Mg was diffused to the circuit layer side and metal layer side by further carrying out the holding step and bonding step shown in Table <NUM> such that the crystal grains in the vicinity of the bonded interface were sufficiently refined and it was possible to suppress deformation in the region in the vicinity of the bonded interface in the circuit layer and metal layer when ultrasonic waves were applied thereto.

Claim 1:
A copper/ceramic bonded body formed by bonding a copper member, which is formed of copper or a copper alloy, and a ceramic member,
wherein a ratio D1/D0 is <NUM> or less, D0 being an average crystal grain size of the entire copper member, D1 being an average crystal grain size of the copper member at a position <NUM> from a bonding surface with the ceramic member, D0 and D1 being obtained by observing a cross-section of the copper member along a laminating direction.