Ceramic wiring board, method for manufacturing ceramic wiring board, and brazing material for ceramic wiring board

Abstract

A ceramic wiring board (100) comprising a ceramic substrate (10) and a metal wiring part (11) formed on the ceramic substrate (10), wherein the metal wiring part (11) is composed of a thermally conductive particle / metal composite film including thermally conductive particles (30) containing at least one of diamond and cBN, and a metal layer (20) containing Cu and Mg and further containing at least one active metal element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W, the content of Cu being the highest among the elements constituting the metal layer (20).

Description

Ceramic wiring board, method for manufacturing ceramic wiring board, and brazing material for ceramic wiring board

[0001] The present disclosure relates to a ceramic wiring substrate, a method for manufacturing a ceramic wiring substrate, and a brazing filler metal for a ceramic wiring substrate.

[0002] Ceramic wiring substrates are known in which metal wiring is formed by applying a metal paste to the surface of a ceramic substrate and then sintering it. Such ceramic wiring substrates preferably have high thermal conductivity and excellent heat dissipation properties.

[0003] For example, Patent Document 1 discloses a method for manufacturing a metallized substrate, comprising the steps of: laminating a first paste layer containing copper powder and titanium hydride powder on a nitride ceramic sintered substrate to manufacture a first laminate; laminating a second paste layer containing silver-copper alloy powder on the first paste layer of the first laminate to manufacture a second laminate; and firing the second laminate to form the titanium nitride layer and the metal layer on the nitride ceramic sintered substrate.

[0004] Patent No. 5731476

[0005] An object of the present disclosure is to provide a ceramic wiring substrate that is expected to have improved thermal conductivity.

[0006] According to one aspect of the present disclosure, there is provided a ceramic wiring substrate comprising: a ceramic substrate; and a metal wiring portion formed on the ceramic substrate, wherein the metal wiring portion comprises a thermally conductive particle / metal composite film having thermally conductive particles containing at least one of diamond and cBN; and a metal layer containing Cu and Mg and further containing at least one active metal element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W, wherein the metal layer has the highest Cu content among the elements constituting the metal layer.

[0007] According to another aspect of the present disclosure, there is provided a method for manufacturing a ceramic wiring substrate, comprising the steps of: preparing a brazing filler metal containing Cu and Mg, and further containing at least one active metal element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W, with Cu being the highest among the contained elements; mixing thermally conductive particles containing at least one of diamond and cBN with the brazing filler metal; placing the brazing filler metal mixed with the thermally conductive particles on a ceramic substrate; and heating and maintaining the ceramic substrate on which the brazing filler metal has been placed at a temperature equal to or higher than the melting point of the brazing filler metal and equal to or lower than 800°C.

[0008] According to another aspect of the present disclosure, there is provided a brazing filler metal for ceramic wiring substrates, comprising: thermally conductive particles including at least one of diamond and cBN; Cu; Mg; and at least one active metal element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W, wherein the Cu content is the highest among the elements contained in the Cu, Mg, and the active metal.

[0009] According to the present disclosure, it is possible to provide a ceramic wiring substrate that is expected to have improved thermal conductivity.

[0010] FIG. 1 is a partial cross-sectional schematic diagram of a ceramic wiring substrate 100 according to one embodiment of the present disclosure. FIG. 2 is a schematic diagram illustrating a method for manufacturing a ceramic wiring substrate 100 according to one embodiment of the present disclosure. FIG. 3 is a cross-sectional SEM photograph of Sample 2 according to an embodiment of the present disclosure. FIG. 4 is a cross-sectional SEM photograph of Sample 2 according to an embodiment of the present disclosure. FIG. 5 is an enlarged cross-sectional SEM photograph (left side of the figure) of Sample 2 according to an embodiment of the present disclosure, and the results of EDX analysis (right side of the figure).

[0011] <One Aspect of the Present Disclosure> One aspect of the present disclosure will be described below with reference to the above-mentioned drawings. Note that all drawings used in the following description are schematic. The dimensions and proportions of each element shown in the drawings do not necessarily correspond to the actual dimensions. Furthermore, the dimensions and proportions of each element do not necessarily correspond between drawings. Note that in this specification, "A to B" means a numerical range of "greater than or equal to A and less than or equal to B."

[0012] (1) Structure of Ceramic Wiring Substrate: FIG. 1 is a partial cross-sectional schematic diagram of a ceramic wiring substrate 100 according to one embodiment of the present disclosure. As shown in FIG. 1, the ceramic wiring substrate 100 includes a ceramic substrate 10 and a metal wiring portion 11 formed on the ceramic substrate 10. The metal wiring portion 11 is a thermally conductive particle / metal composite film including thermally conductive particles 30 containing at least one of diamond and cBN (cubic boron nitride), and a metal layer 20 containing copper (Cu) and magnesium (Mg) and further containing at least one active metal element selected from the group consisting of titanium (Ti), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), and tungsten (W). In other words, the thermally conductive particle / metal composite film is a composite film composed of the thermally conductive particles 30 and the metal layer 20.

[0013] The ceramic substrate 10 is, for example, a ceramic plate material obtained by pressure-molding and sintering ceramic granules, and is preferably made of aluminum nitride (AlN), silicon nitride (Si ３ N ４ ), alumina (Al ２ O ３ The shape and size of the plate are not particularly limited.

[0014] The metal layer 20 is a layer of the metal wiring portion 11 that is responsible for electrical conductivity and contains, for example, Cu and Mg, and further contains at least one active metal element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W. The metal layer 20 may further contain at least one element selected from tin (Sn), antimony (Sb), and bismuth (Bi). The metal layer 20 may further contain at least one element selected from silver (Ag) and indium (In). In this embodiment, Ti is used as the active metal element, and the metal layer 20 mainly contains Cu, Mg, Sn (Sb, Bi), and Ti.

[0015] As described below, the metal layer 20 is formed by heat-treating a brazing filler metal 50 containing Cu, Mg, Sn (Sb, Bi), and the aforementioned active metal element Ti in predetermined proportions. The brazing filler metal 50 used in this embodiment is a Cu-Mg brazing filler metal that does not contain silver (Ag) as a primary component. Among the elements constituting the brazing filler metal 50 (here, Cu, Mg, and the active metal elements), the Cu content (at %) is the highest. Therefore, the Cu content (at %) is the highest among the elements constituting the metal layer 20. The brazing filler metal 50 contains, for example, 40 to 85 at % Cu, 1 to 25 at % Mg, 1 to 25 at % total of at least one element selected from Sn, Sb, and Bi, and 0.1 to 10 at % total of the active metal element (Ti in this embodiment). By using such a brazing filler metal 50, the heat treatment temperature during formation of the metal layer 20 can be lowered (e.g., 800°C or lower), thereby suppressing thermal denaturation and reliability degradation of the thermally conductive particles 30 and improving the thermal conductivity of the ceramic wiring substrate 100. The brazing filler metal 50 used in this embodiment may further contain at least one element selected from Ag and In, for example, to further lower the melting point. However, from the viewpoints of electrical conductivity and electromigration, the total content of the element selected from Ag and In is preferably 0 to 50 at% (less than 40 at% for each element alone). Even when at least one element selected from Ag and In is contained in the brazing filler metal 50, it is preferable that the brazing filler metal 50 contains at least one element selected from Ag and In, and that Cu has the highest content among the elements constituting the brazing filler metal 50. In other words, it is preferable that the element selected from Ag and In is contained so that the content of each of the elements Ag and In is lower than the content of Cu.

[0016] The thermally conductive particles 30 contain at least one of diamond and cBN, which are materials with higher thermal conductivity than Cu, which is the main component (e.g., a content of more than 50 at%) of the metal layer 20. The presence of such thermally conductive particles 30 in the metal wiring portion 11 can improve the thermal conductivity of the ceramic wiring substrate 100.

[0017] However, simply introducing diamond or cBN into the metal wiring portion 11 does not necessarily improve the thermal conductivity of the ceramic wiring substrate 100. For example, mixing diamond or cBN into an Ag-Cu paste (brazing material) as described in Patent Document 1 requires heat treatment at temperatures exceeding 800°C, which can result in thermal denaturation of the thermally conductive particles 30 (e.g., graphitization in the case of diamond) or a decrease in the reliability of the thermally conductive particles 30 (e.g., cleavage in diamond and cBN), potentially reducing the thermal conductivity. Furthermore, the use of expensive Ag can increase costs. Furthermore, for example, if voids or the like exist at the interface between the thermally conductive particles 30 and the metal layer 20, heat transfer between the thermally conductive particles 30 and the metal layer 20 becomes difficult, potentially reducing the thermal conductivity.

[0018] In contrast, in this embodiment, the use of the brazing filler metal 50 described above allows the heat treatment temperature to be lowered when forming the metal layer 20, so that the thermally conductive particles 30 can remain in an un-thermally denatured state (for example, in the case where the thermally conductive particles 30 are diamond, in an un-graphitized state), thereby improving the thermal conductivity of the ceramic wiring substrate 100.

[0019] 1, it is preferable that an interface reaction layer 21 containing an active metal element exists between the thermally conductive particles 30 and the metal layer 20. The interface reaction layer 21 is, for example, a layer formed by a reaction between a part of the thermally conductive particles 30 and a part of the active metal element contained in the brazing material 50. In this embodiment in which the brazing material 50 contains Ti as the active metal element, if the thermally conductive particles 30 are diamond, the interface reaction layer 21 contains TiC, and if the thermally conductive particles 30 are cBN, the interface reaction layer 21 contains TiN, TiB, TiB ２The interfacial reaction layer 21 contains at least one of the following active metal elements: carbides of the active metal element if the thermally conductive particles 30 are diamond; and nitrides or boron compounds of the active metal element if the thermally conductive particles 30 are cBN. The other active metal element may be at least one of the active metal carbides, nitrides, or borides, which have a low standard free energy of formation and readily react with the thermally conductive particles 30. In addition to Ti, at least one element selected from the group consisting of Zr, Hf, V, Nb, Ta, Cr, Mo, and W may be used. The presence of the interfacial reaction layer 21 formed by the reaction of a portion of the thermally conductive particles 30 with a portion of the active metal element thus improves the thermal conductivity of the interface between the thermally conductive particles 30 and the metal layer 20. Furthermore, the wettability of the metal layer 20 to the thermally conductive particles 30 is improved, allowing for the formation of a dense composite film.

[0020] 1, it is also preferable that an interface reaction layer 21 containing an active metal element exists between the ceramic substrate 10 and the metal layer 20. This can improve the thermal conductivity of the interface between the ceramic substrate 10 and the metal layer 20.

[0021] As shown in FIG. 1, the metal layer 20 includes a solid solution phase 22 in which other metal elements are dissolved in Cu, and a solid solution phase 23 in which Cu is dissolved in Cu. ４ and a compound phase 23 having at least one intermetallic compound selected from MgSn, CuMgSb, and CuMgBi.

[0022] The solid solution phase 22 is mainly composed of, for example, a solid solution of Mg dissolved in Cu crystals, and may also contain other metal elements and active metal elements that were contained in the brazing filler metal 50. When other metal elements are dissolved in Cu, the strength of the solid solution phase 22 (the strength of the metal layer 20) can be improved by solid solution strengthening.

[0023] In the solid solution phase 22, the amount of each metal element dissolved in Cu is, for example, preferably 5 at% or less for Mg, 5 at% or less for Sn, 4 at% or less for Sb, and 1 at% or less for Bi. The amount of each metal element dissolved can be measured, for example, by energy dispersive X-ray analysis (EDX).

[0024] In the solid solution phase 22, when Mg and Sn are dissolved in Cu, the ratio A / B is preferably 0.1 or more and 2.0 or less, where A is the amount of dissolved Mg and B is the amount of dissolved Sn. When Mg and Sn are dissolved in Cu at such a ratio, the strength of the metal layer 20 can be further increased.

[0025] The compound phase 23 is, for example, Cu ４ The metal layer 20 is formed by the precipitation of at least one intermetallic compound selected from MgSn, CuMgSb, and CuMgBi. The compound phase 23 may also contain other intermetallic compounds composed of Cu, Mg, Sn, Sb, Bi, and active metal elements. The presence of a trace amount of the compound phase 23 in the metal layer 20 can improve the strength of the metal layer 20 through precipitation strengthening. From this perspective, it is preferable that the compound phase 23 be uniformly dispersed in the solid solution phase 22. Furthermore, the presence of an appropriate amount of the compound phase 23 reduces the amount of other metal elements dissolved in Cu in the solid solution phase 22, thereby improving thermal conductivity.

[0026] The average particle size d of the thermally conductive particles 30 is preferably greater than 0.5 times the film thickness a of the metal layer 20 but less than 1 time the film thickness a (i.e., 0.5a<d<a). As a result, as shown in FIG. 1 , the thermally conductive particles 30 are more likely to overlap in the thickness direction of the metal wiring portion 11, forming paths of the thermally conductive particles 30 and improving thermal conductivity. Specifically, the average particle size d of the thermally conductive particles 30 is preferably, for example, 10 to 50 μm, and the film thickness a of the metal layer 20 is preferably, for example, 20 to 100 μm. The average particle size d is determined by observing the cross-sectional structure using an SEM and randomly selecting 30 thermally conductive particles 30 and averaging their major axes.

[0027] The proportion of the thermally conductive particles 30 in the metal wiring portion 11 is preferably 5 to 60 vol. %. If the proportion of the thermally conductive particles 30 is less than 5 vol. %, it may be difficult to achieve an improvement in thermal conductivity. In contrast, by setting the proportion of the thermally conductive particles 30 to 5 vol. % or more, the improvement in thermal conductivity is more easily achieved. On the other hand, if the proportion of the thermally conductive particles 30 exceeds 60 vol. %, it becomes difficult for the metal layer 20 to fill the spaces between the thermally conductive particles 30 without leaving any gaps. In contrast, by setting the proportion of the thermally conductive particles 30 to 60 vol. % or less, the metal layer 20 is filled without any gaps, thereby suppressing the occurrence of voids. It is advisable to adjust the ratio of the brazing filler metal 50 to the thermally conductive particles 30 so that the proportion of the thermally conductive particles 30 in the metal wiring portion 11 is within the above range.

[0028] The metal layer 20 is formed using the brazing filler metal 50 described above, thereby suppressing the occurrence of voids. When a brazing filler metal containing Mg is used, there is a concern that evaporation of the Mg contained in the brazing filler metal may cause voids or pinholes (hereinafter, collectively referred to as voids) to occur in the metal layer. The presence of such voids can reduce the strength of the metal layer 20. In this regard, in the present embodiment, the brazing filler metal 50 contains at least one element selected from Sn, Sb, and Bi, which is an element that suppresses evaporation of Mg, thereby suppressing the evaporation of Mg and the occurrence of voids in the metal layer 20.

[0029] Specifically, when the cross section of the metal layer 20 of this embodiment is observed, the thickness is approximately 10,000 μm. ２ In other words, when observing the cross section of the metal layer 20, the number of voids having a circular equivalent diameter of 8 μm or more is 1 or less, and more preferably, no voids are observed in an arbitrary field of view of the metal layer 20. ２ It is preferable that the number of voids having a circular equivalent diameter of 4 μm or more is one or less per 10,000 μm. ２ It is more preferable that the number of voids having a circular equivalent diameter of 1 μm or more is 1 or less per 10,000 μm. ２It is more preferable that there is one or less per molecule.

[0030] By having these various features, this embodiment succeeds in improving the thermal conductivity of the ceramic wiring substrate 100.

[0031] (2) Method for Manufacturing Ceramic Wiring Substrate Next, a method for manufacturing the above-mentioned ceramic wiring substrate 100 will be described.

[0032] First, a brazing filler metal 50 for forming the metal layer 20 is prepared. As described above, the brazing filler metal 50 of this embodiment is a Cu-Mg brazing filler metal containing Cu as the primary component (e.g., a Cu content of 40 at% or more, with Cu being the highest among the elements constituting the brazing filler metal 50). Specifically, the brazing filler metal 50 contains 40 to 85 at% Cu, 1 to 25 at% Mg, 1 to 25 at% Sn, Sb, and Bi in total, and 0.1 to 10 at% active metal elements (Ti in this embodiment). The use of such a brazing filler metal 50 allows the heat treatment temperature during the formation of the metal layer 20 to be reduced (e.g., 800°C or less), thereby suppressing thermal denaturation and reliability degradation of the thermally conductive particles 30 and improving the thermal conductivity of the ceramic wiring substrate 100. The brazing filler metal 50 used in this embodiment may contain 0 to 50 at % in total of elements selected from Ag and In (less than 40 at % of each element alone) from the viewpoint of further lowering the melting point, etc. Even when at least one element selected from Ag and In is contained in the brazing filler metal 50, the brazing filler metal 50 still contains at least one element selected from Ag and In, and among the elements constituting the brazing filler metal 50, the content of Cu is the highest.

[0033] Cu is an element that forms a solid solution that mainly constitutes the metal layer 20 when the brazing filler metal 50 is heat-treated. Cu also contributes to the ductility and malleability of the metal layer 20.

[0034] Mg acts to lower the melting point of Cu and thereby lower the heat treatment temperature of the brazing filler metal 50. Furthermore, Mg acts to increase the wettability of the brazing filler metal 50 with respect to the thermally conductive particles 30.

[0035] At least one element selected from Sn, Sb, and Bi is an element that easily reacts with Mg when the brazing filler metal 50 is heated, and forms a ternary intermetallic compound with, for example, Cu or Mg. Therefore, these elements act to suppress evaporation of Mg.

[0036] When the brazing filler metal 50 is heated, the active metal element reacts with a portion of the thermally conductive particles 30 to form a compound, which acts to improve the thermal conductivity of the interface between the thermally conductive particles 30 and the metal layer 20. The active metal element also acts to increase the wettability of the metal layer 20 to the thermally conductive particles 30, forming a dense composite film. Therefore, the content of the active metal element may be changed depending on the amount of the thermally conductive particles 30, which will be described later.

[0037] Each metal element constituting the brazing filler metal 50 may be in the form of a powder containing at least one of an element, a hydride, or an intermetallic compound with another metal element, and a mixture of these powders can be used as the brazing filler metal 50. The form after mixing may be any form, and details thereof will be described later.

[0038] In the brazing material 50 , the particle size of the powder containing each metal element can be changed as appropriate depending on the type of ceramic substrate 10 and the thickness of the metal layer 20 .

[0039] The brazing filler metal 50 may be in the form of a powder, foil, or paste. When the brazing filler metal 50 is in the form of a paste, the main solvent may be an alcohol such as terpineol or butanediol, or a toluene, the binder may be polyvinyl alcohol, ethyl cellulose, polymethacrylic acid, polyacrylic, or the like, and the surfactant may be a cationic, anionic, or nonionic activator. A plasticizer or a dispersant may also be included. The method for preparing the brazing filler metal 50 is not particularly limited, and any known method may be used.

[0040] After preparing the brazing filler metal 50, a predetermined amount of thermally conductive particles 30 (e.g., diamond or cBN) is mixed into the brazing filler metal 50 to prepare a brazing filler metal 50 containing the thermally conductive particles 30 (also referred to as a brazing filler metal for ceramic wiring substrates). The amount of thermally conductive particles 30 mixed is preferably such that the proportion of the thermally conductive particles 30 in the brazing filler metal 50 is 5 to 60 vol. %. The method for mixing the thermally conductive particles 30 is not particularly limited, and known methods can be used. When the brazing filler metal 50 is foil-shaped, as described below, the foil-shaped brazing filler metal 50 may be placed on the ceramic substrate 10, and then the thermally conductive particles 30 may be sprinkled on the brazing filler metal 50. Furthermore, another foil-shaped brazing filler metal 50 may be placed on the brazing filler metal 50 with the thermally conductive particles 30, or a paste-like brazing filler metal 50 may be applied on top of the brazing filler metal 50.

[0041] After preparing the brazing filler metal 50 containing the thermally conductive particles 30, the brazing filler metal 50 is placed on the ceramic substrate 10 as shown in Fig. 2. The brazing filler metal 50 can be placed by any known method such as screen printing, transfer, dispensing, inkjet printing, spray coating, sputtering, or vapor deposition.

[0042] After the brazing filler metal 50 is placed, the ceramic substrate 10 and the brazing filler metal 50 are heated and held in a predetermined atmosphere. The predetermined atmosphere may be any one of a vacuum atmosphere (reduced pressure atmosphere), an inert gas atmosphere, and a reducing atmosphere. ２ The oxygen concentration can be adjusted by introducing an inert gas such as toluene.

[0043] The heat treatment temperature is preferably set to, for example, the melting point of the brazing filler metal 50 or higher and 800°C or lower. This makes it possible to suppress thermal denaturation and a decrease in reliability of the thermally conductive particles 30. It also improves the diffusibility of the active metal element, making it easier to form the interface reaction layer 21. Note that as the heat treatment furnace used to bond the ceramic substrate 10 and the metal layer 20, known furnaces such as a stationary batch furnace, a multi-chamber furnace, a belt conveyor furnace, and a roller hearth kiln can be used.

[0044] Other conditions for bonding are exemplified as follows: Oxygen concentration: 0.01 volume ppm or more and 1000 volume ppm or less Holding time: Not particularly limited, but for example, 30 minutes or more and 180 minutes or less

[0045] After the heat treatment, the temperature of the ceramic substrate 10 is lowered. Through the above steps, the ceramic wiring substrate 100 of this embodiment can be manufactured.

[0046] Other Aspects of the Present Disclosure The above describes specific aspects of the present disclosure. However, the present disclosure is not limited to the above aspects and can be modified in various ways without departing from the spirit and scope of the present disclosure.

[0047] The thermally conductive particle / metal composite film according to the present disclosure has both high electrical conductivity and heat transfer properties, and therefore can be used in applications other than the metal wiring portion of a ceramic wiring substrate, such as heat sinks and processing tools.

[0048] (Preparation of Samples 1 to 5) A 10 mm x 10 mm x 0.32 mm alumina plate and a 10 mm x 10 mm x 0.65 mm aluminum nitride plate were prepared as ceramic substrates 10. Diamond particles with the particle sizes shown in Table 1 were prepared as thermally conductive particles. A brazing filler metal 50 was prepared by mixing each metal element and diamond in the ratios shown in Table 1 to form a paste. Terpineol was used as the solvent and polyisobutyl methacrylate as the binder, with the total solvent and binder content in the paste being 17 mass%. This paste was applied to the ceramic substrate 10 by screen printing. Samples 1 to 5 were then prepared by performing a 120-minute heat treatment at the predetermined heat treatment temperature and atmosphere shown in Table 1. The particle diameters of the thermally conductive particles in Table 1 were determined by SEM observation of the cross-sectional structure, randomly selecting 30 thermally conductive particles 30, and averaging their major axes. The heat treatment temperature was higher than the melting point of each brazing filler metal 50. In this example, diamond was selected as the thermally conductive particles because it has a higher thermal conductivity than cBN, but the present invention is not limited to diamond.

[0049]

[0050] The cross-sectional structures of Samples 1 to 5 were observed using an SEM. Cross-sectional SEM photographs of Sample 2 are shown in Figures 3 and 4. As shown in Figures 3 and 4, a thermally conductive particle / metal composite film having thermally conductive particles 30 and a metal layer 20 was confirmed to have been formed on a ceramic substrate 10. It was also confirmed that no noticeable voids with a circle-equivalent diameter of 20 μm or more were present in the metal layer 20. The black grains indicated by the arrows in Figure 4 are fragments of diamond broken during cross-section processing and are not voids. It was also confirmed that there were no cleavages in the thermally conductive particles 30. Furthermore, Figure 5 shows an enlarged SEM photograph of Sample 2 (left side of the figure) and the results of EDX analysis (right side of the figure). As shown in Figure 5, it was confirmed that an interfacial reaction layer 21 containing an active metal element (here, Ti) was present between the thermally conductive particles 30 and the metal layer 20. The same was true for Samples 1 and 3 to 5. In addition, samples in which there were no noticeable voids in the metal layer 20 with a circle equivalent diameter of 20 μm or more, there were no cleavage in the thermally conductive particles 30, and an interfacial reaction layer 21 was confirmed between the thermally conductive particles 30 and the metal layer 20 were marked with ``O'' in the cross-sectional structure column of Table 1.

[0051] For Samples 1 to 5, an X-ray diffractometer (XRD) was used to check whether or not the thermally conductive particles 30 had been altered. As a result, it was confirmed that the thermally conductive particles 30 of Samples 1 to 5 were not thermally altered.

[0052] From the above, it has been confirmed that the use of the brazing filler metal 50 described above can be expected to suppress thermal denaturation of the thermally conductive particles 30 and improve the thermal conductivity of the ceramic wiring substrate 100. It has also been confirmed that the formation of the interface reaction layer 21 between the metal layer 20 and the thermally conductive particles 30 can be expected to improve the thermal conductivity of the interface between the thermally conductive particles 30 and the metal layer 20.

[0053] <Preferred Aspects of the Present Disclosure> Preferred aspects of the present disclosure are described below. Note that any combination of the technical matters described in the following supplementary notes is possible and will bring about useful effects.

[0054] According to one aspect of the present disclosure, there is provided a ceramic wiring substrate comprising: a ceramic substrate; and a metal wiring portion formed on the ceramic substrate, wherein the metal wiring portion comprises a thermally conductive particle / metal composite film having thermally conductive particles containing at least one of diamond and cBN, and a metal layer containing Cu and Mg and further containing at least one active metal element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W, wherein the metal layer has the highest Cu content among the elements constituting the metal layer.

[0055] Preferably, the metal layer further contains at least one element selected from the group consisting of Sn, Sb, and Bi.

[0056] Preferably, the metal layer further contains at least one element selected from Ag and In.

[0057] Preferably, an interface reaction layer containing the active metal element exists between the thermally conductive particles and the metal layer.

[0058] Preferably, an interface reaction layer containing the active metal element exists between the ceramic substrate and the metal layer.

[0059] Preferably, the metal layer comprises a solid solution phase in which another metal element is dissolved in Cu, and a solid solution phase in which Cu ４ and a compound phase having at least one intermetallic compound selected from MgSn, CuMgSb, and CuMgBi.

[0060] Preferably, the average particle size d of the thermally conductive particles is greater than 0.5 times the film thickness a of the metal layer and smaller than 1 time the film thickness a.

[0061] According to another aspect of the present disclosure, there is provided a method for manufacturing a ceramic wiring substrate, comprising the steps of: preparing a brazing filler metal containing Cu and Mg, and further containing at least one active metal element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W, with Cu being the highest among the contained elements; mixing thermally conductive particles containing at least one of diamond and cBN with the brazing filler metal; placing the brazing filler metal mixed with the thermally conductive particles on a ceramic substrate; and heating and maintaining the ceramic substrate on which the brazing filler metal has been placed at a temperature equal to or higher than the melting point of the brazing filler metal and equal to or lower than 800°C.

[0062] Preferably, in the step of preparing the brazing filler metal, a brazing filler metal containing 40 to 85 at % Cu, 1 to 25 at % Mg, 1 to 25 at % in total of at least one element selected from Sn, Sb, and Bi, and 0.1 to 10 at % in total of the active metal elements is prepared.

[0063] Preferably, in the step of preparing the brazing filler metal, a brazing filler metal is prepared which further contains at least one element selected from Ag and In in a total amount of 50 at% or less, and in which the content of each of Ag and In is lower than the content of Cu.

[0064] According to another aspect of the present disclosure, there is provided a brazing filler metal for ceramic wiring substrates, comprising: thermally conductive particles including at least one of diamond and cBN; and Cu, Mg, and at least one active metal element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W, wherein Cu has the highest content among the elements contained in the Cu, Mg, and the active metal element.

[0065] Preferably, the alloy contains 40 to 85 at % Cu, 1 to 25 at % Mg, 1 to 25 at % in total of at least one element selected from Sn, Sb and Bi, and 0.1 to 10 at % in total of the active metal elements.

[0066] Preferably, the alloy further contains at least one element selected from Ag and In in a total amount of 50 at % or less, and the content of each of Ag and In is lower than the content of Cu.

[0067] REFERENCE SIGNS LIST 10 Base material 11 Metal wiring portion 20 Metal layer 21 Interface reaction layer 22 Solid solution phase 23 Compound phase 30 Thermally conductive particles 50 Brazing filler metal 100 Ceramic wiring substrate

Claims

1. A ceramic wiring substrate comprising: a ceramic substrate; and a metal wiring portion formed on the ceramic substrate, wherein the metal wiring portion comprises a thermally conductive particle / metal composite film having thermally conductive particles containing at least one of diamond and cBN; and a metal layer containing Cu and Mg, and further containing at least one active metal element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W, wherein the metal layer has the highest Cu content among the elements constituting the metal layer.

2. The ceramic wiring substrate according to claim 1, wherein the metal layer further contains at least one element selected from the group consisting of Sn, Sb, and Bi.

3. The ceramic wiring substrate according to claim 2, wherein the metal layer further contains at least one element selected from the group consisting of Ag and In.

4. The ceramic wiring substrate according to claim 1, wherein an interface reaction layer containing the active metal element exists between the thermally conductive particles and the metal layer.

5. The ceramic wiring board according to claim 1, wherein an interface reaction layer containing the active metal element exists between the ceramic substrate and the metal layer.

6. The ceramic wiring substrate according to claim 1, wherein the average particle size d of said thermally conductive particles is greater than 0.5 times the film thickness a of said metal layer and smaller than 1 time the film thickness a.

7. A method for manufacturing a ceramic wiring substrate, comprising the steps of: preparing a brazing filler metal containing Cu and Mg, and further containing at least one active metal element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W, with Cu being the highest among the contained elements; mixing thermally conductive particles containing at least one of diamond and cBN into the brazing filler metal; placing the brazing filler metal mixed with the thermally conductive particles on a ceramic substrate; and heating and maintaining the ceramic substrate on which the brazing filler metal has been placed at a temperature equal to or higher than the melting point of the brazing filler metal and equal to or lower than 800°C.

8. A method for manufacturing a ceramic wiring substrate according to claim 7, wherein in the step of preparing the brazing filler metal, a brazing filler metal containing 40 to 85 at % of Cu, 1 to 25 at % of Mg, 1 to 25 at % in total of at least one element selected from Sn, Sb, and Bi, and 0.1 to 10 at % in total of the active metal elements is prepared.

9. A method for manufacturing a ceramic wiring substrate as described in claim 8, wherein in the step of preparing the brazing filler metal, a brazing filler metal is prepared which further contains an element selected from Ag and In in a total amount of 50 at% or less, and in which the content of each of Ag and In is lower than the content of Cu.

10. A brazing filler metal for ceramic wiring substrates, comprising thermally conductive particles including at least one of diamond and cBN, Cu, Mg, and at least one active metal element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W, wherein the Cu content is the highest among the Cu, Mg, and active metal elements.

11. The brazing filler metal for ceramic wiring substrates according to claim 10, containing 40 to 85 at % of Cu, 1 to 25 at % of Mg, 1 to 25 at % in total of at least one element selected from Sn, Sb, and Bi, and 0.1 to 10 at % in total of the active metal elements.

12. The brazing filler metal for ceramic wiring substrates according to claim 11, further containing an element selected from Ag and In in a total amount of 50 at% or less, and the content of each of Ag and In is lower than the content of Cu.

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