JP7563124B2 - Graphene Joints - Google Patents

Description

This invention relates to a graphene joint having a structure in which a graphene-containing carbonaceous member containing graphene aggregates is joined to a member to be joined.

A graphene-containing carbonaceous member that contains graphene aggregates has excellent thermal conductivity and is therefore particularly suitable as a member that constitutes a heat dissipation member or a heat conduction member.
For example, by forming an insulating layer made of ceramics or the like on the surface of the graphene-containing carbonaceous member containing the above-mentioned graphene aggregates, it becomes possible to use the graphene-containing carbonaceous member as an insulating substrate.

In addition, by forming a metal layer on the surface of the graphene-containing carbonaceous material, it becomes possible to use it as a heat-conducting plate. This heat-conducting plate is disposed between the heat-generating element (the element, the substrate on which the element is mounted, etc.) and the heat sink in various devices equipped with the heat-generating element (power semiconductor element and LED element), such as a power module and an LED module.

For example, Patent Document 1 discloses an anisotropic heat conduction element having a structure in which graphene sheets are stacked along a first direction, and an intermediate member (metal or ceramic) joined to an end face of the structure in a second direction intersecting the first direction, and the intermediate member (metal or ceramic) is pressure-bonded to the end face via an insert material containing at least titanium.

JP 2012-238733 A

Incidentally, the insulating substrate may be subjected to thermal cycles in the environment in which it is used. In particular, in recent years, the insulating substrate may be used in harsh environments such as engine compartments, and may be subjected to thermal cycles under severe conditions with large temperature differences.
In the above-mentioned Patent Document 1, the intermediate member made of a metal or ceramic and the graphene structure are joined via an insert material containing titanium. However, depending on the joining conditions, the intermediate member made of a metal or ceramic and the graphene structure may not be firmly joined, and peeling may occur when subjected to severe thermal cycles.

This invention has been made in consideration of the above-mentioned circumstances, and aims to provide a graphene joint in which a joined material and a graphene-containing carbonaceous member containing graphene aggregates are firmly joined, and peeling does not occur even when subjected to a thermal cycle load, resulting in excellent thermal cycle reliability.

In order to solve these problems and achieve the above-mentioned object, the graphene conjugate of the present invention is a graphene conjugate having a structure in which a graphene-containing carbonaceous member containing graphene aggregates is bonded to a member to be joined, and is characterized in that at the bonding interface between the graphene-containing carbonaceous member and the member to be joined, an active metal compound layer is formed on the bonding surface of the graphene-containing carbonaceous member, and an Sn-enriched layer having an Sn concentration of 1 mass% or more is formed on the graphene-containing carbonaceous member side, and the thickness of the active metal compound layer is within the range of 0.05 μm to 3 μm.

In the graphene conjugated body having this configuration, at the joining interface between the graphene-containing carbonaceous member and the joined member, an active metal compound layer containing one or both of an active metal oxide and an active metal carbide is formed on the joining surface of the graphene-containing carbonaceous member. Therefore, the joining surface of the graphene-containing carbonaceous member is sufficiently reacted with the active metal, and the graphene-containing carbon member and the joined member can be firmly joined together.
Furthermore, at the joining interface between the graphene-containing carbonaceous member and the joined member, an Sn-concentrated layer having an Sn concentration of 1 mass % or more is formed on the graphene-containing carbonaceous member side. This makes it possible to suppress peeling between the graphene-containing carbonaceous member and the joined member when subjected to a thermal cycle load, thereby improving thermal cycle reliability.
In addition, since a joining material containing Sn is used, it becomes possible to firmly join the graphene-containing carbonaceous member and the joined member under a relatively low temperature condition.
Furthermore, since the thickness of the active metal compound layer is set to be 0.05 μm or more, the graphene-containing carbonaceous member and the joined member can be joined more firmly. Meanwhile, since the thickness of the active metal compound layer is limited to be 3 μm or less, the occurrence of cracks in the active metal compound layer during thermal cycle loading can be suppressed.

In the graphene joined body of the present invention, the Sn-enriched layer preferably has a thickness in the range of 0.2 μm to 10 μm.
In this case, since the thickness of the Sn-enriched layer is set to 0.2 μm or more, the thermal cycle reliability can be further improved, while since the thickness of the Sn-enriched layer is limited to 10 μm or less, the occurrence of cracks in the Sn-enriched layer during thermal cycle loading can be suppressed.

Furthermore, in the graphene conjugate of the present invention, it is preferable that the graphene-containing carbonaceous member includes the graphene aggregates formed by depositing single or multiple layers of graphene and flat graphite particles, the flat graphite particles are stacked using the graphene aggregates as a binder such that their basal surfaces are folded over, and the flat graphite particles have a structure in which the basal surfaces are oriented in one direction.
In this case, it is possible to further improve the thermal conductivity characteristics of the graphene-containing carbonaceous member.

In the graphene joined body of the present invention, the joined members may be ceramic members made of ceramics.
In this case, since the member to be joined is made of ceramics having excellent insulating properties, it can be used as an insulating substrate.

Furthermore, in the graphene joined body of the present invention, the joined members may be metal members made of metal.
In this case, since the members to be joined are made of a metal having excellent thermal conductivity, they can be used as a heat conductive plate.

According to the present invention, the material to be joined and the graphene-containing carbonaceous member containing graphene aggregates are firmly joined, and no peeling occurs even when subjected to thermal cycles, making it possible to provide a graphene joint with excellent thermal cycle reliability.

FIG. 1 is a schematic explanatory diagram of a power module using a graphene joint (thermal conductive plate) according to a first embodiment of the present invention. FIG. 1 is a schematic explanatory diagram of a graphene composite (thermal conductive plate) according to a first embodiment of the present invention. 1 shows the results of observation of a bonding interface between a graphene-containing carbonaceous member and a metal member in a graphene bonded body (thermal conductive plate) according to a first embodiment of the present invention. FIG. 2 is an element mapping diagram of a bonding interface between a graphene-containing carbonaceous member and a metal member in the graphene bonded body (thermal conduction plate) according to the first embodiment of the present invention. FIG. 1 is a flow diagram showing an example of a method for producing a graphene bonded body (thermal conductive plate) according to a first embodiment of the present invention. FIG. 2 is a schematic explanatory diagram of a graphene composite (insulating substrate) according to a second embodiment of the present invention. 13 shows observation results of a bonding interface between a graphene-containing carbonaceous member and a ceramic member in a graphene bonded body (insulating substrate) according to a second embodiment of the present invention. FIG. 4 is a flow diagram showing an example of a method for producing a graphene joint (insulating substrate) according to a second embodiment of the present invention. FIG. 11 is a schematic explanatory diagram of another power module using a graphene composite (thermal conductive plate) according to an embodiment of the present invention. FIG. 11 is a schematic explanatory diagram of another power module using a graphene composite (thermal conductive plate) according to an embodiment of the present invention. FIG. 11 is a schematic explanatory diagram of another power module using a graphene composite (thermal conductive plate) according to an embodiment of the present invention.

Embodiments of the present invention will be described below with reference to the attached drawings. Note that each embodiment shown below is specifically described to provide a better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified. Also, the drawings used in the following description may show essential parts enlarged for the sake of convenience in order to make the features of the present invention easier to understand, and the dimensional ratios of each component may not necessarily be the same as the actual ones.

First Embodiment
First, a graphene composite according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 5. FIG.
The graphene composite in the present embodiment is a heat conductive plate 20 having a structure in which a metal plate is joined as a joined member to a graphene-containing carbonaceous member containing graphene aggregates.

First, a power module using a graphene joint body (thermal conductive plate 20) according to the present embodiment will be described.
A power module 1 shown in FIG. 1 includes an insulating circuit board 10, a semiconductor element 3 joined to one surface side (upper side in FIG. 1) of the insulating circuit board 10 via a solder layer 2, a heat conduction plate 20 disposed on the other surface side (lower side in FIG. 1) of the insulating circuit board 10, and a heat sink 30 disposed on the other surface side of the heat conduction plate 20.

The insulating circuit board 10 comprises an insulating layer 11, a circuit layer 12 disposed on one surface (the upper surface in FIG. 1) of the insulating layer 11, and a metal layer 13 disposed on the other surface (the lower surface in FIG. 1) of the insulating layer 11.
The insulating layer 11 prevents electrical connection between the circuit layer 12 and the metal layer 13, and in this embodiment is made of highly insulating ceramics such as aluminum nitride (AlN), aluminum oxide (Al ₂ O ₃ ), silicon nitride (Si ₃ N ₄ ), etc. The thickness of the insulating layer 11 is set within the range of 0.2 to 1.5 mm, and in this embodiment is set to 0.635 mm.

The circuit layer 12 is formed by bonding a metal plate having excellent electrical conductivity to one surface of the insulating layer 11. In this embodiment, a copper plate made of copper or a copper alloy, specifically a rolled plate of oxygen-free copper, is used as the metal plate constituting the circuit layer 12. A circuit pattern is formed on this circuit layer 12, and one surface thereof (the upper surface in FIG. 1 ) serves as a mounting surface on which the semiconductor element 3 is mounted.
The thickness of the metal plate (copper plate) that becomes the circuit layer 12 is set within a range of 0.1 mm to 1.0 mm, and in this embodiment, it is set to 0.6 mm.
The method for joining the metal plate (copper plate) that will become the circuit layer 12 and the insulating layer 11 is not particularly limited, and they can be joined using an active metal brazing material or the like.

The metal layer 13 is formed by joining a metal plate having excellent thermal conductivity to the other surface of the insulating layer 11. In this embodiment, a copper plate made of copper or a copper alloy, specifically a rolled plate of oxygen-free copper, is used as the metal plate constituting the metal layer 13.
The thickness of the metal plate (copper plate) that becomes the metal layer 13 is set within a range of 0.1 mm to 1.0 mm, and in this embodiment, it is set to 0.6 mm.
The method for joining the metal plate (copper plate) that will become the metal layer 13 to the insulating layer 11 is not particularly limited, and they can be joined using an active metal brazing material or the like.

The heat sink 30 is for cooling the insulating circuit board 10 described above, and has a structure in which a plurality of flow paths 31 are provided for circulating a cooling medium (for example, cooling water).
The heat sink 30 is preferably made of a material having good thermal conductivity, such as aluminum or an aluminum alloy, copper or a copper alloy, and in this embodiment, is made of oxygen-free copper.

The semiconductor element 3 is made of a semiconductor material such as Si or SiC. The semiconductor element 3 is mounted on the circuit layer 12 via a solder layer 2 made of a solder material such as Sn-Ag, Sn-In, or Sn-Ag-Cu.

The graphene bonded body (thermal conductive plate 20 ) of this embodiment is interposed between the insulating circuit board 10 and the heat sink 30 .
As described later, the outermost layers of both main surfaces of the thermally conductive plate 20 are made of oxygen-free copper, and are joined to the metal layer 13 of the insulating circuit board 10 made of copper and the heat sink 30 made of copper via, for example, a Sn--Ag based, Sn--In based, or Sn--Ag--Cu based solder material.

As shown in FIG. 2, the heat conductive plate 20 of this embodiment includes a carbon plate 21 made of a graphene-containing carbonaceous material containing graphene aggregates, and a metal member layer 25 bonded to both main surfaces of the carbon plate 21.

The graphene-containing carbonaceous material constituting the carbon plate 21 preferably contains graphene aggregates formed by the deposition of single or multiple layers of graphene and flat graphite particles, and the flat graphite particles are preferably stacked with the graphene aggregates as a binder so that their basal surfaces overlap.

The flat graphite particles have a basal surface on which the hexagonal carbon mesh plane appears and an edge surface on which the end of the hexagonal carbon mesh plane appears. As the flat graphite particles, flake graphite, flaky graphite, earthy graphite, flaky graphite, kish graphite, pyrolytic graphite, highly oriented pyrolytic graphite, etc. can be used.
Here, the average particle size of the graphite particles as viewed from the basal plane is preferably in the range of 10 μm to 1000 μm, and more preferably in the range of 50 μm to 800 μm. By setting the average particle size of the graphite particles within the above range, the thermal conductivity is improved.
Furthermore, the thickness of the graphite particles is preferably in the range of 1 μm to 50 μm, and more preferably in the range of 1 μm to 20 μm. By setting the thickness of the graphite particles within the above range, the orientation of the graphite particles can be appropriately adjusted.
The thickness of the graphite particles is preferably within a range of 1/1000 to 1/2 of the particle diameter as viewed from the basal plane. By setting the thickness of the graphite particles within the above range, excellent thermal conductivity and the orientation of the graphite particles can be appropriately adjusted.

The graphene aggregate is formed by depositing single-layer or multi-layer graphene, and the number of layers of the multi-layer graphene is, for example, not more than 100, and preferably not more than 50. This graphene aggregate can be produced, for example, by dropping a graphene dispersion in which single-layer or multi-layer graphene is dispersed in a solvent containing a lower alcohol or water onto a filter paper, and depositing the graphene aggregate while separating the solvent.
Here, the average particle size of the graphene aggregates is preferably within a range of 1 μm to 1000 μm. By setting the average particle size of the graphene aggregates within the above range, the thermal conductivity is improved.
Furthermore, the thickness of the graphene aggregate is preferably within a range of 0.05 μm or more and less than 50 μm. By setting the thickness of the graphene aggregate within the above range, the strength of the carbonaceous member is ensured.
The thickness of the carbon plate 21 is preferably within a range of 0.3 mm to 3 mm.

The metal member layer 25 is formed by bonding a metal plate to the main surface of the carbon plate 21 .
The metal plate constituting the metal member layer 25 is preferably made of a metal having excellent thermal conductivity, and the metal plate in this embodiment is made of copper or a copper alloy, and more specifically, is a rolled plate of oxygen-free copper.
The lower limit of the thickness of the metal member layer 25 (thickness of the metal plate) is preferably 50 μm or more, and more preferably 100 μm or more, whereas the upper limit of the thickness of the metal member layer 25 (thickness of the metal plate) is preferably 5000 μm or less, and more preferably 3000 μm or less.

FIG. 3 shows an observation photograph of the bonding interface between the carbon plate 21 made of a graphene-containing carbonaceous material and the metal member layer 25, and FIG. 4 shows an element mapping diagram of the bonding interface between the carbon plate 21 made of a graphene-containing carbonaceous material and the metal member layer 25.
In FIG. 3, the upper black portion is the carbon plate 21 (graphene-containing carbonaceous member), and the gray portion located below it is the metal member layer 25 (member to be joined).

3 and 4(a) to 4(d), at a bonding interface 40 between a carbon plate 21 made of a graphene-containing carbonaceous material and a metal member layer 25, an active metal compound layer 41 containing one or both of an active metal oxide and an active metal carbide is formed on the bonding surface of the carbon plate 21. In FIG. 4(a), the region where the active metal (Ti) is present is the active metal compound layer 41.
In addition, a Sn-concentrated layer 42 having a Sn concentration of 1 mass % or more is formed on the carbon plate 21 side of the joint interface 40. In FIG.
Furthermore, an alloy layer 43 containing Ag and Cu is formed on the metal member layer 25 side of the joint interface 40. In Figures 4(c) and 4(d), the region where Ag and Cu coexist is the alloy layer 43.

The active metal compound layer 41 is formed by the reaction of the active metal contained in the bonding material interposed between the carbon plate 21 and the metal plate with oxygen and carbon during bonding.
For example, one or more selected from Ti, Zr, Hf, and Nb can be used as the active metal constituting the active metal compound layer 41. In this embodiment, the active metal is Ti, and the active metal compound layer 41 contains one or two of titanium oxide (Ti-O) and titanium carbide (Ti-C).

Here, if the thickness t1 of the active metal compound layer 41 is 0.05 μm or more, the reaction between the bonding material and the carbon plate 21 is promoted, and sufficient bonding strength of the carbon plate 21 is ensured. On the other hand, if the thickness t1 of the active metal compound layer 41 is 3 μm or less, the occurrence of cracks in the active metal compound layer 41 during thermal cycle loading can be suppressed.
Therefore, in this embodiment, the thickness t1 of the active metal compound layer 41 is set to be within the range of 0.05 μm or more and 3 μm or less.
The lower limit of the thickness t1 of the active metal compound layer 41 is preferably 0.1 μm or more, and more preferably 0.2 μm or more. On the other hand, the upper limit of the thickness t1 of the active metal compound layer 41 is preferably 2 μm or less, and more preferably 1.8 μm or less.

The Sn-enriched layer 42 is formed when Sn contained in the bonding material interposed between the carbon plate 21 and the metal plate during bonding is segregated toward the carbon plate 21 .
The Sn-enriched layer 42 can be identified by taking a cross-sectional observation sample near the bonded interface of the graphene/ceramic bonded body and obtaining EPMA mapping using an EPMA (for example, JXA-8530F manufactured by JEOL Ltd., acceleration voltage: 15 kV, spot diameter: 1 μm or less).

Here, if the thickness t2 of the Sn-enriched layer 42 is 0.2 μm or more, the thermal cycle reliability can be reliably improved. On the other hand, if the thickness t2 of the Sn-enriched layer 42 is limited to 10 μm or less, it is possible to suppress the occurrence of cracks in the Sn-enriched layer 42 during thermal cycle loading.
Therefore, in this embodiment, the thickness t2 of the Sn-enriched layer 42 is preferably set within a range of 0.2 μm to 10 μm.
The lower limit of the thickness t2 of the Sn-enriched layer 42 is more preferably 0.5 μm or more, and even more preferably 0.7 μm or more. On the other hand, the upper limit of the thickness t2 of the Sn-enriched layer 42 is more preferably 5 μm or less, and even more preferably 3 μm or less.

The alloy layer 43 is formed by a reaction between Ag and Cu contained in the bonding material interposed between the carbon plate 21 and the metal plate during bonding. In this embodiment, the metal member layer 25 (metal plate) is made of oxygen-free copper, so that the Ag of the bonding material diffuses to the metal member layer 25 (metal plate) side to form the alloy layer 43. Therefore, a concentration gradient of Ag exists in the alloy layer 43 and the metal member layer 25. Note that if Ag diffuses sufficiently to the metal member layer 25 side and forms a solid solution within the metal member layer 25, the alloy layer 43 may not be formed.

Here, if the thickness t3 of the alloy layer 43 is 1 μm or more, the reaction of the bonding material is sufficiently promoted, and sufficient bonding strength is ensured between the carbon plate 21 and the metal member layer 25. On the other hand, if the thickness t3 of the alloy layer 43 is 20 μm or less, the occurrence of cracks in the alloy layer 43 during thermal cycle loading can be suppressed.
Therefore, in this embodiment, the thickness t3 of the alloy layer 43 is preferably within the range of 1 μm to 20 μm.
The lower limit of the thickness t3 of the alloy layer 43 is more preferably 2 μm or more, and even more preferably 3 μm or more. On the other hand, the upper limit of the thickness t3 of the alloy layer 43 is more preferably 10 μm or less, and even more preferably 8 μm or less.

Next, the manufacturing method of the graphene joint body (thermal conductive plate 20) according to this embodiment will be described with reference to the flow diagram shown in FIG. 5.

(Carbon plate forming step S01)
First, the above-mentioned flat graphite particles and graphene aggregates are weighed to have a predetermined blend ratio, and then mixed using an existing mixer such as a ball mill.
The mixture thus obtained is filled into a mold having a given shape and pressed to obtain a molded product. Heating may be performed during the pressing.
The resulting molded body is then cut to obtain the carbon plate 21 .

The pressure during molding is preferably in the range of 20 MPa to 1000 MPa, and more preferably in the range of 100 MPa to 300 MPa.
The molding temperature is preferably within the range of 50°C or higher and 300°C or lower.
Furthermore, the pressurization time is preferably within a range of 0.5 to 10 minutes.

(Metal plate lamination process S02)
Next, metal plates that will become the metal member layers 25 are laminated on both main surfaces of the carbon plate 21 via a bonding material.
The bonding material used herein contains Ag, Cu, Sn, and an active metal (Ti in this embodiment). The bonding material may be in the form of a paste or a foil. Alternatively, for example, a Cu-Ag-Sn alloy and an active metal may be laminated.
In this embodiment, the bonding material contains Cu in a range of 18 mass% to 34 mass%, Sn in a range of 3 mass% to 10 mass%, Ti in a range of 0.3 mass% to 7 mass%, and the balance is Ag and The composition used is considered to be an unavoidable impurity.

(Metal plate joining process S03)
Next, the metal plate and the carbon plate 21 laminated with the bonding material therebetween are pressed in the lamination direction and heated, and then cooled to bond the metal plate and the carbon plate 21 together, thereby forming a metal member layer 25. do.
Here, the heating temperature is preferably within a range of 740° C. to 900° C. In addition, the holding time at the heating temperature is preferably within a range of 20 minutes to 180 minutes. The pressure is preferably in the range of 0.1 MPa to 3.5 MPa. The atmosphere is preferably a non-oxidizing atmosphere such as a reduced pressure atmosphere or a nitrogen gas atmosphere.

In this metal plate bonding step S03, the active metal (Ti in this embodiment) contained in the bonding material reacts with oxygen and carbon to form an active metal compound layer 41 on the bonding surface of the carbon plate 21.
Furthermore, Sn contained in the bonding material segregates toward the carbon plate 21 side, forming an Sn-concentrated layer 42 .
Furthermore, Cu and Ag contained in the bonding material react with each other, and Ag diffuses toward the metal plate (metal member layer 25 ), forming an alloy layer 43 on the metal member layer 25 side.

The above steps produce the graphene joint (thermal conduction plate 20) of this embodiment.

According to the graphene conjugate (thermal conductive plate 20) of this embodiment configured as described above, an active metal compound layer 41 containing one or both of active metal oxide (Ti-O) and active metal carbide (Ti-C) is formed on the bonding surface of the carbon plate 21 at the bonding interface between the carbon plate 21 and the metal member layer 25. Therefore, the bonding surface of the carbon plate 21 made of the graphene-containing carbonaceous material is sufficiently reacted with the active metal (Ti in this embodiment), and the carbon plate 21 and the metal member layer 25 (metal plate) are firmly bonded.

Furthermore, at the joint interface between the carbon plate 21 and the metal member layer 25, Sn contained in the joint material segregates on the carbon plate 21 side to form an Sn-concentrated layer 42 with a Sn concentration of 1 mass% or more. This makes it possible to suppress peeling between the carbon plate 21 and the metal member layer 25 when subjected to a thermal cycle, thereby improving thermal cycle reliability.
Furthermore, since a bonding material containing Sn is used, it becomes possible to firmly bond the carbon plate 21 and the metal member layer 25 (metal plate) under relatively low temperature conditions.

In addition, in this embodiment, the thickness of the active metal compound layer 41 is set to 0.05 μm or more, so that the carbon plate 21 made of the graphene-containing carbonaceous material and the metal member layer 25 can be firmly bonded. On the other hand, the thickness of the active metal compound layer 41 is limited to 3 μm or less, so that the occurrence of cracks in the active metal compound layer 41 during thermal cycle loading can be suppressed.

Furthermore, in this embodiment, when the thickness of the Sn-enriched layer 42 is set to 0.2 μm or more, it is possible to reliably improve thermal cycle reliability. On the other hand, when the thickness of the Sn-enriched layer 42 is limited to 10 μm or less, it is possible to suppress the occurrence of cracks in the Sn-enriched layer 42 during thermal cycle loading.

Furthermore, in this embodiment, when the graphene-containing carbonaceous material constituting the carbon plate 21 includes graphene aggregates formed by the deposition of single or multiple layers of graphene and flat graphite particles, and the flat graphite particles are stacked with the graphene aggregates as a binder so that their basal surfaces are folded over, and the basal surfaces of the flat graphite particles are oriented in one direction, it is possible to further improve the thermal conductivity characteristics of the carbon plate 21 (graphene-containing carbonaceous material).

Furthermore, in this embodiment, since the heat conducting plate 20 is disposed between the insulating circuit board 10 and the heat sink 30, the heat from the insulating circuit board 10 can be spread in the planar direction in the metal member layer 25 formed on one main surface side of the heat conducting plate 20, and this heat can be efficiently transferred in the thickness direction and dissipated in the heat sink 30. Therefore, a power module 1 with excellent heat dissipation characteristics can be configured.

Second Embodiment
Next, a graphene composite according to a second embodiment of the present invention will be described with reference to FIGS.
The graphene bonded body in this embodiment is an insulating substrate 120 having a structure in which a ceramic plate is bonded as a bonded member to a graphene-containing carbonaceous member containing graphene aggregates.

As shown in FIG. 6, the insulating substrate 120 of this embodiment has a structure in which a ceramic plate 125 and carbon plates 121 made of a graphene-containing carbonaceous material containing graphene aggregates are bonded to both sides of the ceramic plate 125.

The graphene-containing carbonaceous member constituting the carbon plate 121 preferably has a structure in which, similarly to the first embodiment, the graphene aggregates formed by depositing single or multiple layers of graphene and flat graphite particles are stacked with the basal planes of the flat graphite particles folded over each other using the graphene aggregates as a binder.
The thickness of the carbon plate 121 is preferably within a range of 0.3 mm to 3 mm.

The ceramic plate 125 is made of ceramics with excellent insulating properties, such as aluminum nitride (AlN), aluminum oxide (Al ₂ O ₃ ), silicon nitride (Si ₃ N ₄ ), or the like.
The lower limit of the thickness of the ceramic plate 125 is preferably 100 μm or more, and more preferably 250 μm or more, while the upper limit of the thickness of the ceramic plate 125 is preferably 1500 μm or less, and more preferably 1000 μm or less.

FIG. 7 shows an observation photograph of the bonding interface between the carbon plate 121 made of a graphene-containing carbonaceous material and the ceramic plate 125.
In FIG. 7, the upper black portion is a carbon plate 121 (graphene-containing carbonaceous member), and the gray portion located below is a ceramic plate 125 (member to be joined).

At the bonding interface 140 between the carbon plate 121 made of a graphene-containing carbonaceous material and the ceramic plate 125, an active metal compound layer containing one or both of an active metal oxide and an active metal carbide is formed on the bonding surface of the carbon plate 121, as in the first embodiment.
In addition, a Sn-enriched layer having a Sn concentration of 1 mass % or more is formed on the carbon plate 121 side of the joint interface 140 .
Furthermore, an alloy layer containing Ag and Cu is formed on the bonding interface 140 on the ceramic plate 125 side.

The active metal compound layer is formed when an active metal (Ti in this embodiment) contained in the bonding material interposed between the carbon plate 121 and the ceramic plate 125 reacts with oxygen and carbon during bonding.
Here, the active metal compound layer in this embodiment has the same structure as that in the first embodiment.
The thickness t11 of the active metal compound layer is set to be within the range of 0.05 μm to 3 μm.

The Sn-enriched layer is formed when Sn contained in the bonding material interposed between the carbon plate 121 and the ceramic plate 125 segregates toward the carbon plate 121 during bonding.
Here, the Sn-enriched layer in this embodiment has the same configuration as that in the first embodiment.
The thickness t12 of the Sn-enriched layer is preferably within a range of 0.2 μm to 10 μm.

The alloy layer is formed by a reaction between Ag and Cu contained in the bonding material interposed between the carbon plate 121 and the ceramic plate 125 during bonding. In this embodiment, Ag of the bonding material does not diffuse to the ceramic plate 125 side, and the alloy layer tends to be formed thicker than in the first embodiment.
In this embodiment, the thickness t13 of the alloy layer is preferably within the range of 1 μm to 20 μm.
The lower limit of the thickness t13 of the alloy layer is more preferably 2 μm or more, and even more preferably 3 μm or more. On the other hand, the upper limit of the thickness t13 of the alloy layer is more preferably 10 μm or less, and even more preferably 8 μm or less.

Next, the manufacturing method of the graphene conjugate (insulating substrate 120) according to this embodiment will be described with reference to the flow diagram shown in FIG.

(Carbon plate forming step S101)
First, similarly to the first embodiment, flat graphite particles and graphene aggregates are weighed to have a predetermined compounding ratio and mixed by an existing mixer such as a ball mill. The obtained mixture is filled into a mold of a predetermined shape and pressurized to form a molded body, and the obtained molded body is cut out.
This makes it possible to obtain a graphene-containing carbonaceous member (carbon plate 121) having a structure including graphene aggregates formed by the accumulation of single or multiple layers of graphene and flat graphite particles, in which the flat graphite particles are stacked using the graphene aggregates as a binder such that their basal surfaces are folded over, and the basal surfaces of the flat graphite particles are oriented in one direction.

(Ceramic plate lamination process S102)
Next, the carbon plates 121 are laminated on both main surfaces of the ceramic plate 125 via bonding materials.
As the bonding material, a material containing Ag, Cu, Sn, and an active metal (Ti in this embodiment) is used, as in the first embodiment.

(Ceramic plate bonding process S103)
Next, the ceramic plate 125 and the carbon plate 121 laminated with the bonding material therebetween are pressed in the lamination direction and heated, and then cooled, thereby bonding the ceramic plate 125 and the carbon plate 121 together.
Here, the heating temperature is preferably within a range of 750° C. to 900° C. The holding time at the heating temperature is preferably within a range of 20 minutes to 180 minutes. The pressurizing pressure is preferably within a range of 0.1 MPa to 3.5 MPa. The atmosphere is preferably a non-oxidizing atmosphere such as a reduced pressure atmosphere or a nitrogen gas atmosphere.

In this ceramic plate bonding step S103, the active metal (Ti in this embodiment) contained in the bonding material reacts with oxygen and carbon to form an active metal compound layer on the bonding surface of the carbon plate 121.
Furthermore, Sn contained in the bonding material segregates toward the carbon plate 121, forming an Sn-enriched layer.
Furthermore, Cu and Ag contained in the bonding material react with each other to form an alloy layer on the ceramic plate 125 side.

The above steps produce the graphene junction (insulating substrate 120) of this embodiment.

According to the graphene joint (insulating substrate 120) of this embodiment configured as described above, an active metal compound layer is formed on the joint surface of the carbon plate 121 at the joint interface between the carbon plate 121 and the ceramic plate 125, so that the joint surface of the carbon plate 121 made of the graphene-containing carbonaceous material reacts sufficiently with the active metal (Ti in this embodiment), and the carbon plate 121 and the ceramic plate 125 are firmly joined.

Furthermore, at the joint interface between the carbon plate 121 and the ceramic plate 125, Sn contained in the joint material segregates on the carbon plate 121 side, forming an Sn-concentrated layer with an Sn concentration of 1 mass% or more. This makes it possible to suppress peeling between the carbon plate 121 and the ceramic plate 125 when subjected to a thermal cycle, thereby improving thermal cycle reliability.
Furthermore, since a bonding material containing Sn is used, it becomes possible to bond the carbon plate 121 and the ceramic plate 125 firmly under a relatively low temperature condition.

In addition, in this embodiment, the thickness t11 of the active metal compound layer is set to 0.05 μm or more, so that the carbon plate 121 made of the graphene-containing carbonaceous material and the ceramic plate 125 can be firmly bonded. On the other hand, the thickness t11 of the active metal compound layer is limited to 3 μm or less, so that the occurrence of cracks in the active metal compound layer during thermal cycle loading can be suppressed.

Furthermore, in this embodiment, when the thickness t12 of the Sn-enriched layer is set to 0.2 μm or more, it is possible to reliably improve thermal cycle reliability. On the other hand, when the thickness t12 of the Sn-enriched layer is limited to 10 μm or less, it is possible to suppress the occurrence of cracks in the Sn-enriched layer during thermal cycle loading.

Furthermore, in this embodiment, when the graphene-containing carbonaceous material constituting the carbon plate 121 includes graphene aggregates formed by the deposition of single or multiple layers of graphene and flat graphite particles, and the flat graphite particles are stacked with the graphene aggregates as a binder so that their basal surfaces are folded over, and the basal surfaces of the flat graphite particles are oriented in one direction, it is possible to further improve the thermal conductivity characteristics of the carbon plate 121 (graphene-containing carbonaceous material).

Furthermore, the insulating substrate 120 of this embodiment has excellent insulating properties because it is provided with a ceramic plate 125. In addition, it has excellent thermal conductivity because it is provided with a carbon plate 121 made of a graphene-containing carbonaceous material. Therefore, for example, it can be used as the insulating layer 11 of the power module 1 (insulated circuit substrate 10) shown in FIG. 1.

Although the embodiment of the present invention has been described above, the present invention is not limited to this, and can be modified as appropriate without departing from the technical concept of the invention.
For example, in the present embodiment, a power module is configured by mounting a semiconductor element (power semiconductor element) on the circuit layer of an insulating circuit board, but the present invention is not limited to this. For example, an LED module may be configured by mounting an LED element on an insulating circuit board, or a thermoelectric module may be configured by mounting a thermoelectric element on the circuit layer of an insulating circuit board.

In addition, in this embodiment, as shown in FIG. 1, a power module 1 having a structure in which a thermally conductive plate 20 is disposed between an insulating circuit board 10 and a heat sink 30 has been described as an example, but the present invention is not limited to this, and there is no particular restriction on the method of using the graphene composite of the present invention.

For example, a power module 201 may be configured such that a thermally conductive plate 220 is disposed between a circuit layer 212 of an insulating circuit board 210 and a semiconductor element 3, as in the graphene composite (thermally conductive plate 220) shown in FIG.
Furthermore, a power module 301 may be formed using a heat conductive plate 320 as a metal layer of an insulating circuit board 310, such as a graphene composite (heat conductive plate 320) shown in FIG.
In addition, like the graphene composite (thermal conductive plate 420) shown in FIG. 11, a power module 401 may be formed using a thermal conductive plate 420 as the circuit layer and the metal layer of an insulating circuit board 410.

A power module 201 shown in Fig. 9 differs from the power module 1 shown in Fig. 1 in that a heat conductive plate 220 is used instead of the solder layer 2, and a solder layer 32 is used instead of the heat conductive plate 20. The other configurations are similar to those of the power module 1 shown in Fig. 1, and the same configurations are denoted by the same reference numerals and will not be described.
The heat conduction plate 220 includes a carbon plate 221 made of a graphene-containing carbonaceous material containing graphene aggregates, and a metal member layer 225 bonded to both main surfaces of the carbon plate 221. The heat conduction plate 220, the carbon plate 221, and the metal member layer 225 may have the same configurations as the heat conduction plate 20, the carbon plate 21, and the metal member layer 25 of the first embodiment, respectively.
In the power module 201, the metal layer 213 and the heat sink 30 are joined via a solder layer 32 made of, for example, a Sn--Ag based, Sn--In based, or Sn--Ag--Cu based solder material.
In the power module 201, the heat conductive plate 220 is disposed between the circuit layer 212 of the insulating circuit board 10 and the semiconductor element 3, so that the heat from the insulating circuit board 10 can be spread in the planar direction and can be efficiently transferred in the thickness direction to be dissipated in the heat sink 30. Thus, the power module 201 with excellent heat dissipation characteristics can be configured.

A power module 301 shown in Fig. 10 is an insulating circuit board 310 in which a carbon plate 321 is used as the metal layer instead of the metal layer 13, and differs from the power module 1 shown in Fig. 1 in that the insulating circuit board 310 and the heat sink 30 are joined using an active metal brazing material or the like. The other configurations are the same as those of the power module 1 shown in Fig. 1, and the same configurations are denoted by the same reference numerals and will not be described.
The carbon plate 321 has a configuration similar to that of the carbon plate 21 of the first embodiment or the carbon plate 121 of the second embodiment. The insulating layer 311 and the carbon plate 321 are joined in a configuration similar to that of the second graphene joined body (insulating substrate 120). The carbon plate 321 and the heat sink 30 are joined in a configuration similar to that of the first graphene joined body (thermal conduction plate 20).
In the power module 301, a carbon plate 321 is used as a metal layer of an insulating circuit board 310, the insulating layer 311 and the carbon plate 321 are joined in a configuration similar to that of the second graphene conjugate (insulating substrate 120), and the carbon plate 321 and the heat sink 30 are joined in a configuration similar to that of the first graphene conjugate (thermal conduction plate 20), so that heat from the insulating circuit board 301 can be spread in the planar direction and efficiently transferred in the thickness direction to be dissipated in the heat sink 30. Thus, a power module 301 with excellent heat dissipation characteristics can be configured.

A power module 401 shown in Fig. 11 is an insulating circuit board 410 using a heat conductive plate 420 instead of the circuit layer 12 and the metal layer 13, and other configurations are similar to those of the power module 1 shown in Fig. 1, and the same configurations are given the same reference numerals and will not be described. The heat conductive plate 420, which is the circuit layer, and the semiconductor element 3 are bonded via a solder layer 2. The heat conductive plate, which is the metal phase, and the heat sink 30 are bonded via a solder layer 32.
The heat conduction plate 420 includes a carbon plate 421 made of a graphene-containing carbonaceous material containing graphene aggregates, and a metal member layer 425 bonded to one surface of the carbon plate 421. The ceramic substrate 411 and the carbon plate 421 are bonded in the same manner as in the second embodiment. The heat conduction plate 420, the carbon plate 421, and the metal member layer 425 may have the same configurations as the heat conduction plate 20, the carbon plate 21, and the metal member layer 25 of the first embodiment, respectively.
In the power module 401, the heat conductive plate 420 is used as the circuit layer and the metal layer of the insulating circuit board 410, so that the heat from the semiconductor element 3 and the insulating circuit board 10 can be spread in the planar direction and the heat can be efficiently transferred in the thickness direction and dissipated in the heat sink 30. Therefore, the power module 401 having excellent heat dissipation characteristics can be configured.

We will now explain the confirmation experiments we conducted to verify the effectiveness of this invention.

As disclosed in this embodiment, flat graphite particles and graphene aggregates were mixed in a predetermined ratio and molded under pressure and heat to obtain a molded body in which flat graphite particles were laminated with the graphene aggregates as a binder so that their basal surfaces were folded over. The obtained molded body was cut out to obtain a carbon plate (40 mm x 40 mm x 1.5 mm thick).

A copper plate (40 mm×40 mm×0.3 mm thick) made of rolled oxygen-free copper or a ceramic plate (40 mm×40 mm×0.3 mm thick) was laminated on one surface of the carbon plate via a bonding material (variable thickness) having a composition of Ag-28 mass% Cu-5 mass% Sn-3 mass% Ti, and the carbon plate and the copper plate were bonded under the conditions shown in Table 1.
The bonded interface between the carbon plate and the copper plate was then observed to confirm the thickness of the active metal compound layer and the thickness of the Sn-enriched layer.

Specifically, the thickness of the active metal compound layer was measured by taking an observation sample from the center of the graphene/copper bonded body, observing the bonded interface with a scanning transmission electron microscope (Titan ChemiSTEM (with EDS detector) manufactured by FEI) at a magnification of 40,000 times and an acceleration voltage of 200 kV, and mapping was performed using energy dispersive X-ray analysis (NSS7 manufactured by Thermo Scientific). The area of the region where the active metal was present was measured, and the value obtained by dividing the value by the width of the measurement field of view was the average value of the five fields of view, which was taken as the thickness of the active metal compound layer. The measurement points observed were the center point of the insulating circuit board and the four vertices of a 20 mm x 20 mm square centered on that point, for a total of five points.

Regarding the thickness of the Sn-enriched layer, a cross-sectional observation sample was taken near the bonded interface of the graphene/copper bonded body, and EPMA mapping was performed using an EPMA (JXA-8530F manufactured by JEOL Ltd., acceleration voltage: 15 kV, spot diameter: 1 μm or less). The area of the Sn-enriched layer was measured by regarding the area where Sn was 1 mass% or more as the Sn-enriched layer, and the area was divided by the width of the measurement field to obtain the average value of the five fields of view as the thickness of the Sn-enriched layer. A total of five points were observed as the measurement points: the area at the center point of the insulating circuit board and the areas at the four vertices of a 20 mm x 20 mm rectangle centered on that point.

The obtained bonded body was subjected to 2000 cycles of a thermal cycle of -55°C x 30 minutes ←→ 175°C x 30 minutes. The bonding rate of the interface between the carbon plate and the copper plate was evaluated using an ultrasonic inspection device (FineSAT200 manufactured by Hitachi Power Solutions Co., Ltd.) and calculated from the following formula. Here, the initial bonding area was defined as the area to be bonded before bonding. In the image obtained by binarizing the ultrasonic inspection image, peeling is indicated by a white area in the bonded portion, so the area of this white area was defined as the peeled area (non-bonded portion area).
(Bonding rate) = {(Initial bonding area) - (Non-bonding area)}/(Initial bonding area) x 100

In Comparative Examples 1 and 2 in which no Sn-enriched layer was formed, the bonding rates after the thermal cycle test were low at 71% and 73%, respectively.
In Comparative Examples 3 and 4, in which the thickness of the active metal compound layer was outside the range of 0.05 μm or more and 3 μm or less, the bonding rates after the thermal cycle test were low at 75% and 74%, respectively.
In contrast, in Example 1-6 of the present invention, in which an Sn-enriched layer was formed and the thickness of the active metal compound layer was in the range of 0.05 μm or more and 3 μm or less, the bonding rate after the thermal cycle test was 80% or more, and the thermal cycle reliability was excellent.

The above experimental results confirm that, according to the present invention, the materials to be joined and the graphene-containing carbonaceous member containing graphene aggregates are firmly joined, and no peeling occurs even when subjected to thermal cycles, making it possible to provide a graphene joint with excellent thermal cycle reliability.

20, 220, 320 Heat conductive plate (graphene joint)
21, 121, 221, 321 Carbon plate (graphene-containing carbonaceous material)
25, 225, 325 Metal member layer (member to be joined)
40, 140 Bonding interface 41, 141 Active metal compound layer 42, 142 Sn-enriched layer 120 Insulating substrate (graphene bonded body)
125 Ceramic plate (member to be joined)

Claims (5)

A graphene joined body having a structure in which a graphene-containing carbonaceous member containing graphene aggregates and a joined member are joined,
a graphene joined body, characterized in that, at a joining interface between the graphene-containing carbonaceous member and the joined member, an active metal compound layer is formed on the joining surface of the graphene-containing carbonaceous member, and a Sn-concentrated layer having a Sn concentration of 1 mass % or more is formed on the graphene-containing carbonaceous member side, and a thickness of the active metal compound layer is within a range of 0.05 μm or more and 3 μm or less. The graphene joint described in claim 1, characterized in that the thickness of the Sn-enriched layer is in the range of 0.2 μm to 10 μm. The graphene-containing carbonaceous member according to claim 1 or 2, characterized in that it includes the graphene aggregates formed by the deposition of single or multiple layers of graphene and flat graphite particles, the flat graphite particles are stacked with the graphene aggregates as a binder so that their basal surfaces are folded over, and the basal surfaces of the flat graphite particles are oriented in one direction. The graphene joint body according to any one of claims 1 to 3, characterized in that the members to be joined are ceramic members made of ceramics. The graphene joint body according to any one of claims 1 to 3, characterized in that the joined members are metal members made of metal.

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