Double-sided circuit non-oxide-based ceramic substrate and method for manufacturing same

The object of the invention is to provide a double-sided circuit non-oxide-based ceramic substrate excellent in radiation property and low in cost, and a method for manufacturing the same. A double-sided circuit non-oxide-based ceramic substrate related to the present invention includes a high heat-conductive non-oxide-based ceramic substrate that includes a through hole, a holding layer that is formed on a wall surface of the through hole, and an electro-conductive metal section that is held inside the through hole by the holding layer and does not include an active metal. The double-sided circuit non-oxide-based ceramic substrate related to the present invention preferably includes electrodes (thin film electrodes) that shield end surfaces of the holding layer and end surfaces of the electro-conductive metal section which are exposed to front and back surfaces of the ceramic substrate.

TECHNICAL FIELD

The present invention relates to a double-sided circuit non-oxide-based ceramic substrate and a method for manufacturing the same.

BACKGROUND ART

In Patent Literature 1, there is described a method for manufacturing a ceramic via substrate that includes an electro-conductive via in a through hole of a ceramic sintered compact substrate, the through hole being for electrical conduction, the electro-conductive via being obtained by closest-packing electro-conductive metal paste in the through hole, the metal paste including a metal having a melting point of 600° C. or above and 1,100° C. or below, a metal having a melting point higher than that of the said metal, and an active metal (titanium). In the method, an active layer is formed in the interface between the electro-conductive via and the ceramic sintered compact substrate.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

High power laser devices have been used for the usage of healthcare, machining, wavelength conversion, and the like for example. The laser output of the high power laser device has risen year by year, and the heat generation amount has been increasing accompanying it. Therefore, with respect to the ceramic substrate used for the high power laser device, high heat radiation performance is required.

Also, according to the manufacturing method described in Patent Literature 1, because the electro-conductive metal paste including an active metal (titanium) is used as described above, it is required to execute baking under a vacuum environment by using a high vacuum furnace and so on in constructing the electro-conductive via. Therefore, it is concerned that the cost increases in the manufacturing method described in Patent Literature 1.

The present invention has been achieved in view of the circumstances described above, and its object is to provide a double-sided circuit non-oxide-based ceramic substrate excellent in heat radiation performance and low in cost, and a method for manufacturing the same.

Solution to Problem

The double-sided circuit non-oxide-based ceramic substrate related to the present invention includes a high heat-conductive non-oxide-based ceramic substrate, a holding layer, and an electro-conductive metal section. The ceramic substrate includes a through hole, the holding layer is formed on a wall surface of the through hole by oxide of silicon or alumina, and the electro-conductive metal section is held inside the through hole by the holding layer and does not include an active metal.

Advantageous Effects of Invention

According to the present invention, it is possible to provide a double-sided circuit non-oxide-based ceramic substrate excellent in heat radiation performance and low in cost, and a method for manufacturing the same.

Problems, configurations (means), and effects other than those described above will be clarified by explanation of embodiments described below.

DESCRIPTION OF EMBODIMENTS

Below, embodiments of the present invention will be explained in detail referring to the drawings. Also, in each drawing, common constituent elements will be marked with a same reference sign, and duplicated explanation will be omitted. Further, there is a case that the size and the shape of a member may be modified or exaggerated to be expressed schematically for the sake of convenience of explanation.

FIG.1is a cross-sectional view that shows a double-sided circuit non-oxide-based ceramic substrate (may be hereinafter described simply as “double-sided circuit substrate” in the present description) related to the present embodiment. A double-sided circuit substrate1related to the present embodiment shown inFIG.1is applied to an integrated circuit that is mounted on a high power laser device for the usage of healthcare, machining, wavelength conversion, and the like for example. Also, in the present embodiment, a high power laser device means one having the laser output of 1 W or more for example.

As shown inFIG.1, the double-sided circuit substrate1includes a high heat-conductive non-oxide-based ceramic substrate (may be hereinafter described simply as “high heat-conductive substrate in the present description)10, a holding layer20, and an electro-conductive metal section30S, the ceramic substrate10including a through hole11that is for electrical conduction, the holding layer20being formed on a wall surface11aof the through hole11, the electro-conductive metal section30S being held inside the through hole11by the holding layer20, being arranged so as to fill the entirety of the through hole11, and not including an active metal. Also, with respect to the double-sided circuit substrate1, both ends of the through hole11are exposed to the surfaces (the front surface and the back surface) of the high heat-conductive substrate10and are shielded by electrodes (thin film electrodes41and42). Also, with regard to “not including an active metal”, although it is ideal not to include an active metal (the content is 0 mass %), an active metal may be contained if the content is in a degree of inevitable impurities. Here, inevitable impurities mean impurities that exist in the raw material or are inevitably mixed in the manufacturing process in the electro-conductive metal section30S, are essentially unnecessary, but are permitted because they are in a minute quantity and do not adversely affect the property of the electro-conductive metal section30S. As the upper limit of the content (allowable quantity of an active metal) of a degree of inevitable impurities, 0.05 mass % can be cited for example. As an active metal, titanium, chromium, and the like can be cited for example.

The high heat-conductive substrate10is one that becomes a base of the double-sided circuit substrate1, and is formed using non-oxide-based ceramic material. Such non-oxide-based ceramic material (“high heat-conductive non-oxide-based ceramic substrate” referred to in claims) forming the high heat-conductive substrate10can be formed using at least one kind selected from a group consisting of aluminum nitride (AlN), silicon nitride (SiN), silicon carbide (SiC), and diamond for example. Particularly, in the present embodiment, it is preferable to be the high heat-conductive substrate10that is formed using AlN, SiC, diamond, and the like because the heat conductivity is high and the mechanical strength and the insulation performance are also high. Here, the heat conductivity of the high heat-conductive substrate10is preferable to be 80 W/(m·K) or more, is more preferable to be 100 W/(m·K) or more, is further more preferable to be 140 W/(m·K) or more, is still more preferable to be 250 W/(m·K) or more, and is most preferable to be 1,000 W/(m·K) or more. By doing so, the heat radiation performance of the double-sided circuit substrate1becomes surely excellent. On the other hand, when the substrate is formed using oxide-based ceramic material, because the heat conductivity is low, the substrate is inferior in the heat radiation performance.

Also, with respect the method for manufacturing the high heat-conductive substrate10, generally known manufacturing method for a sintered compact can be used. For example, in the case of the high heat-conductive substrate10made of AlN, raw material powder whose main component is AlN powder is mixed by a wet process, is thereafter added with a binder, and is mixed and dried to obtain granulated powder. Thereafter, the granulated powder is formed into a compact by a known press forming method, a CIP (Cold Isostatic Pressing) forming method, or a known forming method such as a doctor blade method that is suitable to form a sheet, an extrusion forming method, and an injection molding method. Thereafter, by subjecting the compact to degreasing of the forming binder and baking, the high heat-conductive substrate10can be obtained (refer to the substrate baking step S1described below).

Also, the high heat-conductive substrate10includes the through holes11that penetrate a sheet-like member of the high heat-conductive substrate10from one surface side (the front surface side) to the other surface side (the back surface side). Further, the number of forming the through holes11is not limited to the number shown inFIG.1(2 positions), and may be 1 position or 3 positions or more. For example, when the high heat-conductive substrate10is applied to an integrated circuit of a high power laser device, the through holes11having the diameter of approximately 0.1 mm are formed.

The holding layer20is formed on the wall surface (the peripheral wall surface, the inner wall surface)11aof the through hole11. Also, it is preferable that the holding layer20is formed on the entire wall surface11aof the through hole11so that one end in the axial direction of the through hole11extends to one surface side (the front surface side10a) of the high heat-conductive substrate10and that the other end in the axial direction of the through hole11extends to the other surface side (the back surface side10b) of the high heat-conductive substrate10. Further, the holding layer20is formed so as to closely adhere to the wall surface11aof the through hole11.

Also, it is preferable to form the holding layer20using oxide of silicon for example. In concrete terms, it is preferable to form the holding layer20using silicon dioxide (SiO2). Thus, the wall surface11aof the through hole11becomes in an oxygen-rich state, and the bonding force of the holding layer20and the electro-conductive metal section30S can be enhanced. Also, the holding layer20can be formed by optional material as far as the holding layer20can be formed so as to closely adhere to the wall surface11aof the through hole11and the oxygen-rich state that allows to join with the electro-conductive metal section30S can be formed on the surface. From such viewpoint, the holding layer20can be formed using oxide of aluminum for example, or, to be more specific, alumina (Al2O3).

The electro-conductive metal section30S is obtained by baking an electro-conductive metal paste30(refer toFIG.3D,FIG.4D) that contains tin (Sn) for example. As the electro-conductive metal paste30, it is possible to use a paste including an Ag—Sn-based alloy having the main component of silver (Ag) and containing Sn, a paste including a Cu—Sn-based alloy having the main component of copper (Cu) and containing Sn, and so on. In terms of the electro-conductivity, a paste including Ag and Cu is preferable. When the electro-conductive metal paste30is a paste including an Ag—Sn-based alloy for example, it is preferable to use one with 90 mass % of Ag and 3-8 mass % of Sn. Also, the electro-conductive metal paste30is not limited to those described above, and can also use an alloy that contains at least one of Au, Ag, and Cu and Sn of a paste including an Au—Sn-based alloy, a paste including an Ag—Cu—Sn-based alloy, and so on. Further, the electro-conductive metal paste30does not include an active metal such as titanium and chromium in order to prevent oxidation at the time of baking.

As described above, with respect to the double-sided circuit substrate1, both ends of the holding layer20and both ends of the electro-conductive metal section30S formed on the wall surface11aof the through hole11are exposed to the surfaces (the front surface and the back surface) of the high heat-conductive substrate10and are shielded by the electrodes (the thin film electrodes41and42). Also, the thin film electrodes41and42are arranged so as to be in contact with the electro-conductive metal section30S. Further, the surface of the high heat-conductive substrate10, the both ends of the holing layer20, and both end surfaces of the electro-conductive metal section30S are formed so as to be flush with each other, and are configured to form a flat surface (a smooth surface). Thus, it is easy to overlay the thin film electrodes41and42so as to be in contact with the electro-conductive metal section30S on the surface of the high heat-conductive substrate10, and to form a circuit pattern.

Also, the thin film electrodes41and42are formed of 3 layers of a titanium thin film, a platinum thin film, and a gold thin film for example. Further, the thin film electrodes41and42are not limited to have 3 layers, and may have 2 layers or less, or 4 layers or more. The thin film electrodes41and42can be formed to have the thickness of 0.1 to 5 μm for example. However, the present embodiment is not limited to it, and it is also possible to employ electrodes thicker than the thin film electrodes41and42(the thickness of 5 to 100 μm for example).

As described above, the double-sided circuit substrate1related to the present embodiment includes the high heat-conductive substrate10, the holing layer20, and the electro-conductive metal section30S, the high heat-conductive substrate10including the through hole11, the holing layer20being formed on the wall surface11aof the through hole11, the electro-conductive metal section30S being held inside the through hole11by the holding layer20and not including an active metal. Thus, with respect to the double-sided circuit substrate1, because the holing layer20is formed on the wall surface11aof the through hole11, when the through hole11is filled with the electro-conductive metal paste30and baking is performed, the electro-conductive metal section30S and the high heat-conductive substrate10can be bonded to each other. Also, with respect to the double-sided circuit substrate1related to the present embodiment, because the electro-conductive metal paste30does not include an active metal, baking under a high vacuum environment using a high vacuum furnace and so on is not required, and manufacturing is possible at a low cost (this point will be described below).

Next, a method for manufacturing a double-sided circuit substrate related to the present embodiment will be explained.

FIG.2is a flowchart that explains contents of a method for manufacturing the double-sided circuit substrate related to the present embodiment.FIGS.3A to3Gare process drawings that show an aspect of the method for manufacturing the double-sided circuit substrate related to the present embodiment.FIGS.4A to4Gare process drawings that show another aspect of the method for manufacturing the double-sided circuit substrate related to the present embodiment.

As shown inFIG.2, the present manufacturing method includes a substrate baking step S1, a piercing step S2, and a holding layer forming step S3. By executing the steps up to here in this order, it is possible to manufacture the double-sided circuit substrate1related to an intermediate material10C (refer toFIG.3CandFIG.4C) described below.

Also, continuing to the holding layer forming step S3described above, the present manufacturing method includes a filling step S4, an electro-conductive metal section forming step S5, and a polishing step S6. By executing the steps up to here in this order, it is possible to manufacture the double-sided circuit substrate1of a stage before forming electrodes.

Also, continuing to the polishing step S6described above, the present manufacturing method includes an electrode shielding step S7. By executing this step, it is possible to manufacture the double-sided circuit substrate1that is formed with the electrodes.

Here, with respect to the aspect of piercing by the piercing step S2, because the contents up to completion of the double-sided circuit substrate1differs to some extent according to whether the high heat-conductive substrate10has the penetrated through holes11(refer toFIGS.3A to3G) or the non-penetrated through holes11(non-penetrated holes12, refer toFIGS.4A to4G), explanation will be made individually referring toFIGS.3A to3GandFIGS.4A to4G.

First, an aspect of piercing by the piercing step S2will be explained for a case of the penetrated through holes11referring toFIGS.3A to3G.

In the process drawings ofFIGS.3A to3G, the process is executed in the order of3A→3B→3C→3D→3E→3F→3G. Also, explanation will be hereinafter made with the definition that the upper side in the drawing of the high heat-conductive substrate10as the front side and the lower side in the drawing as the back side.

FIG.3Ashows the substrate baking step S1that is shown inFIG.2. In the substrate baking step S1, non-oxide-based ceramic material formed into a sheet shape is baked, and the high heat-conductive substrate10is manufactured. This high heat-conductive substrate10is in a state before forming the through holes11. With respect to the non-oxide-based ceramic material, one described above can be used, and the non-oxide-based ceramic material can be formed into a sheet shape by a general method. The sheet thickness of the high heat-conductive substrate10may be approximately 0.5 mm for example.

FIG.3Bshows the piercing step S2that is shown inFIG.2. In this piercing step S2, predetermined positions of the high heat-conductive substrate10are pierced, and the penetrated through holes11are formed. The through holes11shown inFIG.3Bare formed by laser machining or blast machining. In the laser machining, the diameter of the through hole11can be made smaller compared to the blast machining. Also, in the laser machining, the diameter of the through hole11can be made equal from the front surface to the back surface of the high heat-conductive substrate10. With respect to the blast machining, shot blast, sand blast, and the like can be applied. Also, a dummy sheet (fitting plate)100inFIG.3Bis a sheet that is fitted to the back surface of the high heat-conductive substrate10which is on the opposite side of the laser irradiation side in the laser machining.

FIG.3Cshows the holding layer forming step S3that is shown inFIG.2. In the holding layer forming step S3, the holding layer20is formed at least on the wall surface11aof the through hole11. By executing this holding layer forming step S3, the double-sided circuit substrate1related to intermediate material10C can be manufactured. Although it is preferable to form the holding layer20using oxide of silicon as described above, the holding layer20can be formed also using oxide of aluminum and so on.

As the method for forming the holding layer20on the wall surface11a, a known gas-phase process such as sputtering, CVD (Chemical Vapor Deposition), ion plating, and the like for example can be applied. Also, the film thickness of the holding layer20is not particularly limited, and only has to be of such degree that oxygen is attached to the wall surface11a, namely approximately 1 μm for example.

Further, by performing sputtering, CVD, ion plating, and the like from the both surfaces (the front surface and the back surface) of the high heat-conductive substrate10, the holding layer20can be formed on the entire wall surface11aof the through hole11. Also, inFIGS.3A to3G, such aspect is shown that the holding layer20is formed by sputtering, CVD, ion plating, and the like not only on the wall surface11abut also in a position other than the through hole11of the high heat-conductive substrate10.

FIG.3Dshows the filling step S4that is shown inFIG.2. In the filling step S4, the through hole11where the holding layer20is formed in the holding layer forming step S3is filled with the electro-conductive metal paste30. As a method for filling the through hole11with the electro-conductive metal paste30, it is possible to apply a general method such as a screen printing method for example. Also, when the diameter of the through hole11is small, the viscosity of the electro-conductive metal paste30is high, and it is hard to fill the through hole11with the electro-conductive metal paste30, at the time of screen printing, a mesh-shape sheet material is fitted to the opposite side of the side for printing the through hole11, the electro-conductive metal paste30is sucked by a suction device through the mesh-shape sheet material, and thereby the electro-conductive metal paste30can be filled to the entire hole from one end to the other end in the axial direction of the through hole11. Further, by printing the electro-conductive metal paste30, filling is executed in a state the electro-conductive metal paste30slightly protrudes from the through hole11.

FIG.3Eshows the electro-conductive metal section forming step S5that is shown inFIG.2. In the electro-conductive metal section forming step S5, the high heat-conductive substrate10after the filling step S4is baked, and the electro-conductive metal paste30is made the electro-conductive metal section30S. Baking of the high heat-conductive substrate10is executed under an atmospheric environment using a reflow furnace for example. In the reflow furnace, when the high heat-conductive substrate10shown inFIG.3Dis charged, the high heat-conductive substrate10is discharged from the reflow furnace after going through a pre-heating step, a reflow step, and a cooling step which are not illustrated. Also, in the present embodiment, because an active metal such as titanium is not included in the electro-conductive metal paste30, the high heat-conductive substrate10is not required to be baked under a vacuum environment, and can be baked using a device that is used under an atmospheric environment, the device being of lower cost compared to a high vacuum furnace. Further, the heating condition is properly set according to the kind of the high heat-conductive substrate10, the kind of the electro-conductive metal paste30, and so on. As the heating condition, when the electro-conductive metal paste30is a paste including an Ag—Sn-based alloy for example, setting to approximately 860° C. can be cited. By doing so, solvent, binder and the like included in the electro-conductive metal paste30can be vaporized/removed.

Here, because the high heat-conductive substrate10is formed of a non-oxide-based ceramic material such as AlN, the high heat-conductive substrate10does not basically adhere to the electro-conductive metal paste30(the electro-conductive metal section30S) of an Ag—Sn-based alloy and the like. However, in the present embodiment, because the holding layer20is formed on the wall surface11aof the through hole11in the step ofFIG.3C, predetermined atoms included in the holding layer20and predetermined atoms in the electro-conductive metal paste30are combined to each other to form a chemical compound. For example, an oxygen atom (O) included in the holding layer20and Sn for example in the electro-conductive metal paste30are combined to each other to form tin oxide (SnO). Because a tight interface by inter-atom bonding of the chemical compound (SnO) thus formed is formed, the electro-conductive metal section30S is adhered (bonded) to the high heat-conductive substrate10, and is held within the through hole11.

FIG.3Fshows the polishing step S6that is shown inFIG.2. In the polishing step S6, one side surface (a front side surface10a) and the other side surface (a back side surface10b) of the high heat-conductive substrate10including the electro-conductive metal section30S are polished. Also, in the polishing step S6, end surfaces20aand20bof the holding layer20and end surfaces30aand30bof the electro-conductive metal section30S held inside the through hole11by the holding layer20are exposed to the front side surface10aand the back side surface10bof the high heat-conductive substrate10respectively (are preferably polished so as to become smooth). In the polishing step S6, mechanical polishing is executed in both front and back surfaces of the high heat-conductive substrate10. Also, in the polishing step S6, for example, after executing rough grinding of both of the front and back surfaces of the high heat-conductive substrate10having been baked before, polishing is executed for finishing the front side surface10aand the back side surface10bof the high heat-conductive substrate10(the holding layer20and the electro-conductive metal section30S) having been ground to become smooth. Further, this polishing step S6is executed to such degree that the holding layer20having been shielded by the surfaces (the front side surface10aand the back side surface10b) of the high heat-conductive substrate10is removed and the high heat-conductive substrate10is exposed. Also, in the polishing step S6, as the grinding agent, powder of the diamond slurry, the alumina slurry, and the like for example is used.

By this polishing step S6, as shown inFIG.3F, a smooth surface1sis formed which includes the front side surface10aof the high heat-conductive substrate10, the end surface20aof one end side of the holding layer20, and the end surface30aof one end side of the electro-conductive metal section30S. In a similar manner, by this polishing step S6, as shown inFIG.3F, a smooth surface1tis formed which includes the back side surface10bof the high heat-conductive substrate10, the end surface20bof the other end side of the holding layer20, and the end surface30bof the other end side of the electro-conductive metal section30S.

FIG.3Gshows the electrode shielding step S7that is shown inFIG.2. In the electrode shielding step S7, thin film metallization is executed. That is to say, in this step, after the polishing step S6, the end surfaces20a,20bof the holding layer20and the end surfaces30a,30bof the electro-conductive metal section30S having been exposed are shielded by the electrodes (the thin film electrodes41and42). To be more specific, the end surface30aof one end side of the electro-conductive metal section30S exposed to the smooth surface1sof the front side of the high heat-conductive substrate10is shielded by the thin film electrode41along with the end surface20aof one end side of the holding layer20and a part of the front side surface10aof the high heat-conductive substrate10. Also, the end surface30bof the other end side of the electro-conductive metal section30S exposed to the smooth surface1tof the back side is shielded by the thin film electrode42along with the end surface20bof the other end side of the holding layer20and a part of the back side surface10bof the high heat-conductive substrate10. The thin film electrodes41and42are formed of 3 layers of a titanium thin film, a platinum thin film, and a gold thin film for example as described above. Thus, the thin film electrode41of the front side and the thin film electrode42of the back side can be made conductive to each other through the electro-conductive metal section30S that is formed in the through hole11. Also, known methods that can execute thin film metallization can be applied to the electrode shielding step S7.

Next, referring toFIGS.4A to4G, an aspect of piercing by the piercing step S2will be explained for a case of non-penetrated through hole11(a non-penetrated hole12).

In the process drawings ofFIGS.4A to4G, the process is executed in the order of4A→4B→4C→4D→4E→4F→4G.

FIG.4Ashows the substrate baking step S1that is shown inFIG.2. The substrate baking step S1can be executed similarly to the explanation that was made referring toFIG.3A, and a high heat-conductive substrate10A is thereby manufactured.

FIG.4Bshows the piercing step S2that is shown inFIG.2. In the piercing step S2, the non-penetrated hole12is formed in the high heat-conductive substrate10A. The non-penetrated hole12is formed by laser machining and blast machining. In the laser machining, by controlling the output (W) and the irradiation time, the hole12is formed which has a peripheral surface (side surface)12aand a bottom surface12band not penetrates to the back side surface10b(refer toFIG.4F) of the high heat-conductive substrate10A. Also, by applying the laser machining, the diameter of the non-penetrated hole12can be made small, and the diameter of the non-penetrated hole12can be formed to be equal from the opening to the bottom. On the other hand, as the blast machining, shot blast, sand blast, and the like can be applied. Also, as shown inFIG.4B, when piercing is executed by this aspect, because it is not required to penetrate the hole, the dummy plate100that was required inFIG.3Bcan be made unnecessary, and the cost incurred in manufacturing can be reduced.

FIG.4Cshows the holding layer forming step S3that is shown inFIG.2. By executing this holding layer forming step S3, the double-sided circuit substrate1related to the intermediate material10C can be manufactured. The holding layer forming step S3can be executed similarly to the explanation that was made referring toFIG.3C. However, in this holding layer forming step S3, the holding layer20is formed on the peripheral surface12aand the bottom surface12bof the non-penetrated hole12. Also, since the bottom surface12bis to be removed by the polishing step S6described below, it is also possible to be configured that the holding layer20is formed only on the peripheral surface12aexcluding the bottom surface12b.

FIG.4Dshows the filling step S4that is shown inFIG.2. The filling step S4can be executed similarly to the explanation that was made referring toFIG.3D. However, in an example shown inFIG.4D, the non-penetrated hole12is formed. Accordingly, because fitting of the mesh-shape member from the opposite side of the hole and the suction device as explained inFIG.3Dare not required, the cost incurred in manufacturing can be reduced. Also, in an example shown inFIG.4D, since the electro-conductive metal paste30does not leak from the opposite side of the non-penetrated hole12, it is easier to fill the non-penetrated hole12with the electro-conductive metal paste30. Further, in an example shown inFIG.4D, the filling step S4can be executed quickly by ordinary screen printing that does not use the mesh and the suction device. Also, a range T shown by a single dot chain line inFIG.4Dshows a range used as the product.

FIG.4Eshows the electro-conductive metal section forming step S5that is shown inFIG.2. The electro-conductive metal section forming step S5can be executed similarly to the explanation that was made referring toFIG.3E.

FIG.4Fshows the polishing step S6that is shown inFIG.2. In the polishing step S6, similarly to the explanation that was made referring toFIG.3F, the front side surface10aand the back side surface10bof the high heat-conductive substrate10A including the electro-conductive metal section30S are polished. However, here, with respect to the back side surface10bwhere the non-penetrated hole12is not formed, the high heat-conductive substrate10A is polished until the electro-conductive metal section30S is exposed. In the polishing step S6, after executing rough grinding of both of the front and back surfaces of the high heat-conductive substrate10A, polishing is executed for finishing the front side surface10aand the back side surface10bof the high heat-conductive substrate10A (including the holding layer20and the electro-conductive metal section30S) having been ground to become smooth. Also, this polishing step S6is executed until the holding layer20shielding the surface (the front side surface10aand the back side surface10b) of the high heat-conductive substrate10A is removed and the surface of the high heat-conductive substrate10A is exposed in the front side surface10a, and until the electro-conductive metal section30S is exposed in the back side surface10b.

By this polishing step S6, as shown inFIG.4F, the smooth surface1sis formed which includes the front side surface10aof the high heat-conductive substrate10A, the end surface20aof one end side of the holding layer20, and the end surface30aof one end side of the electro-conductive metal section30S. In a similar manner, by this polishing step S6, as shown inFIG.4F, the smooth surface1tis formed which includes the back side surface10bof the high heat-conductive substrate10A, the end surface20bof the other end side of the holding layer20, and the end surface30bof the other end side of the electro-conductive metal section30S.

FIG.4Gshows the electrode shielding step S7that is shown inFIG.2. The electrode shielding step S7can be executed similarly to the explanation that was made referring toFIG.3G.

According to the method for manufacturing the double-sided circuit substrate1shown inFIGS.4A to4G, since the dummy sheet100(refer toFIG.3B) is not required in the step for piercing the non-penetrated hole12shown inFIG.4B, the cost incurred in manufacturing can be reduced. Also, in the manufacturing method shown inFIGS.4A to4G, since the electro-conductive metal paste30does not leak from the opposite side of the non-penetrated hole12, it is easier to fill the non-penetrated hole12with the electro-conductive metal paste30. Further, in the manufacturing method shown inFIGS.4A to4G, the filling step S4can be executed quickly by ordinary screen printing that does not use the mesh and the suction device.

By both of the contents shown inFIGS.3A to3Gand the contents shown inFIGS.4A to4G, the double-sided circuit substrate1related to the present embodiment can be manufactured properly. The double-sided circuit substrate1includes the high heat-conductive substrate10(10A) having the through hole11, the holding layer20formed on the wall surface11aof the through hole11, and the electro-conductive metal section30S held inside the through hole11by the holding layer20.

Also, the double-sided circuit substrate1has excellent radiation property because the high heat-conductive substrate10(10A) is formed using the high heat-conductive non-oxide-based ceramic material. Further, the double-sided circuit substrate1can rigidly hold the electro-conductive metal section30S within the through hole11by arranging the holding layer20in the through hole11. Since this electro-conductive metal section30S does not include an active metal, it is not required to be baked under a vacuum environment using a high vacuum furnace and the like in the manufacturing step, and the electro-conductive metal section30S can be manufactured at a low cost.

Also, according to the present embodiment, there are provided the smooth surfaces1s,1twhich are obtained by polishing the end surfaces30a,30bof both ends of the electro-conductive metal section30S and the end surfaces20a,20bof both ends of the holding layer20, and the electro-conductive metal section30S exposed to the smooth surfaces1s,1tis shielded by the thin film electrodes41and42(refer toFIG.1,FIG.3G, andFIG.4G). Thus, by forming the smooth surfaces1s,1t, the double-sided circuit substrate1can be used as a ceramic substrate for double-sided mounting. Particularly, the double-sided circuit substrate1can be used properly for a high power laser device.

The present invention is not limited to the embodiments described above, and various modifications are further included. For example, although explanation was made exemplifying the high heat-conductive substrate10and10A for double-sided mounting in the embodiments described above, it may also be configured to use the double-sided circuit substrate1in a multi-layered style.

LIST OF REFERENCE SIGNS