Circuit board and manufacturing method thereof

Abstract

To provide a manufacturing method of a circuit board capable of efficiently obtaining a circuit board improved in junction reliability of a junction layer and a metal plate.SOLUTION: A manufacturing method of a circuit board includes: a lamination step of obtaining a laminate by arranging a plurality of metal plates in a distributed manner on one surface of a brazing material layer provided on a principal face of a ceramic plate; a junction step of heating the laminate and obtaining a conjugate in which the ceramic plate and the plurality of metal plates are joined by junction layers; and a removal step of electrically insulating the plurality of adjacent metal plates from each other by removing the junction layer between the plurality of metal plates adjacent to each other along the principal face of the ceramic plate.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present disclosure relates to a circuit board and a method for manufacturing the same. [Background technology]

[0002] As industrial equipment such as robots and motors become more sophisticated, power modules that control large currents and high voltages are being used. Circuit boards in such power modules include a ceramic substrate and a copper plate, which are joined together via a brazing material containing an active metal. An etching method is known as a method for manufacturing a joint used in such circuit boards.

[0003] On the other hand, Patent Document 1 proposes a method for manufacturing an insulating circuit board, which includes a laminate formation step of forming a laminate by arranging a brazing material on one side of a ceramic substrate to form a laminate, and a bonding step of forming a circuit layer by bonding a metal plate for a circuit layer to one side of the ceramic substrate by pressurizing and heating the laminate in the stacking direction. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-155444 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the technology for producing a bonded body using an etching method, resist printing and etching processes are required to process the metal plate to a predetermined size. On the other hand, the mounting method of bonding the circuit layer as in Patent Document 1 does not require such processes, and production efficiency can be improved. However, when arranging multiple metal plates side by side on the main surface of a ceramic plate using the mounting method, it is necessary to first form a brazing material layer at each position where the multiple metal plates are to be bonded, and then bond the multiple brazing material layers and the multiple metal plates while aligning them. This makes the process complicated, and there is a problem that the brazing material layer and the metal plate are likely to be misaligned. If a misalignment occurs, there is a concern that the bonding reliability between the ceramic plate and the metal plate and the distance between the bonding layers bonding the adjacent metal plates will change, thereby impairing the insulation reliability.

[0006] The present disclosure provides a method for efficiently producing a circuit board having excellent bonding reliability between a bonding layer and a metal plate, and also provides a circuit board having excellent bonding reliability between a bonding layer and a metal plate. [Means for solving the problem]

[0007] One aspect of the present disclosure provides the following method for manufacturing a circuit board.

[0008] [1] A lamination step in which a plurality of metal plates are arranged so as to be dotted on one surface of a brazing material layer provided on a main surface of a ceramic plate to obtain a laminate; a bonding step of heating the laminate to obtain a bonded body in which the ceramic plate and the plurality of metal plates are bonded together with a bonding layer; a removal step of removing the bonding layer between the plurality of metal plates adjacent to each other along the main surface of the ceramic plate to electrically insulate the plurality of adjacent metal plates from each other. [2] The method for manufacturing a circuit board according to [1], wherein all of the plurality of metal plates are provided on the one surface of the brazing material layer. [3] The method for manufacturing a circuit board according to [1] or [2], further comprising a coating step of coating a brazing material on the main surface of the ceramic plate to provide the brazing material layer on the main surface. [4] The plurality of metal plates include Cu; The method for producing a circuit board according to any one of [1] to [3], wherein the brazing material layer contains Ag, and a ratio of Ag to a total of Ag and Cu in the brazing material layer is 91 mass % or more. [5] When the circuit board is viewed in a plan view, the outer edges of the plurality of metal plates each include a plurality of sides, and in at least one of the plurality of metal plates, a minimum value L of the protrusion distance of the bonding layer on the plurality of sides is min Maximum value L for max The method for producing a circuit board according to any one of [1] to [4], wherein the ratio is 4.0 or less. [6] The maximum value of the protrusion distance L max and the minimum value L min The method for manufacturing a circuit board according to [5], wherein the difference is 0.3 mm or less.

[0009] The method for manufacturing a circuit board according to [1] above includes a lamination step in which a laminate is obtained by arranging a plurality of metal plates in a dotted manner on one surface of a brazing material layer. Then, after forming a bonding layer in a bonding step, a removal step is included in which the bonding layer between the plurality of metal plates is removed to electrically insulate the adjacent plurality of metal plates from each other. Therefore, compared to a method in which each of the plurality of metal plates is bonded to each of the plurality of brazing material layers while being aligned, it is possible to reduce the labor required for alignment and suppress misalignment. Therefore, according to this method for manufacturing a circuit board, a circuit board in which misalignment between the bonding layer and the metal plate is suppressed can be efficiently obtained. The circuit board obtained in this manner has excellent bonding reliability between the ceramic plate and the metal plate.

[0010] According to the method for manufacturing a circuit board described above in [2], all of the metal plates arranged on one main surface are arranged on one surface of the brazing material layer, which further simplifies the process and makes it possible to manufacture the circuit board more efficiently.

[0011] In the method for manufacturing a circuit board described above in [3], the formation of the brazing filler metal layer by coating can be performed relatively easily, and therefore the positioning of the brazing filler metal layer on the main surface of the ceramic board can be simplified, thereby enabling the circuit board to be manufactured more efficiently.

[0012] In the method for manufacturing a circuit board described above in [4], the melting speed of the brazing material in the bonding process is slowed down, thereby preventing the brazing material from creeping up onto the metal plate and preventing voids from being generated in the bonding layer, thereby further improving the bonding reliability of the circuit board and also improving the insulation reliability.

[0013] In the circuit board obtained by the manufacturing method [5] or [6] above, the positional deviation between the bonding layer and the metal plate is sufficiently suppressed. Such a circuit board has sufficiently excellent bonding reliability. The circuit board can be suitably used in a power module that controls a large current and a high voltage.

[0014] One aspect of the present disclosure provides a circuit board comprising:

[0015] [7] A ceramic plate, a plurality of metal plates, and a plurality of bonding layers bonding the ceramic plate and each of the plurality of metal plates, When viewed in a plan view, each of the outer edges of the plurality of metal plates includes a plurality of sides, In at least one of the plurality of metal plates, the minimum protrusion distance L of the bonding layer on the plurality of sides min Maximum value L for max A circuit board having a ratio of 4.0 or less. [8] The maximum value of the protrusion distance L max and the minimum value L min The circuit board according to [7], wherein the difference is 0.3 mm or less. [9] The circuit board according to [7] or [8], wherein the standard deviation of the protrusion distance is 0.05 mm or less.

[0016] The circuit board in [7] above has a minimum protrusion distance of L min Maximum value L for maxSince the ratio is equal to or less than the predetermined value, misalignment between at least one of the plurality of metal plates and the bonding layer that bonds the metal plate and the ceramic plate is sufficiently suppressed. Such a circuit board has excellent bonding reliability between the ceramic plate and the metal plate.

[0017] The circuit board in [8] above has a maximum protrusion distance of L max and the minimum value L min Since the difference between the above is equal to or less than a predetermined value, misalignment between the multiple metal plates and the bonding layers that bond each of the metal plates to the main surface of the ceramic plate is sufficiently suppressed. Such a circuit board has excellent bonding reliability between the ceramic plate and the metal plate.

[0018] In the circuit board of [9], the standard deviation of the protrusion distance is equal to or less than a predetermined value, so that the variation in the positional deviation between the multiple metal plates and the bonding layer that bonds each of them to the main surface of the ceramic plate is sufficiently suppressed. Such a circuit board can further improve the bonding reliability between the ceramic plate and the metal plate. Effect of the Invention

[0019] According to the present disclosure, it is possible to provide a method for manufacturing a circuit board that can efficiently obtain a circuit board having excellent bonding reliability between a bonding layer and a metal plate. It is also possible to provide a circuit board having excellent bonding reliability between a bonding layer and a metal plate. [Brief description of the drawings]

[0020] [Figure 1] FIG. [Diagram 2] FIG. 2 is a perspective view showing a state in which a brazing material layer is provided on a main surface of a ceramic plate. [Diagram 3] FIG. [Figure 4] FIG. 2 is a cross-sectional view in the lamination direction showing a cross-sectional structure of a bonded body. [Diagram 5] FIG. [Figure 6] FIG. 2 is a diagram illustrating a part of a circuit board when viewed from above. [Figure 7] FIG. 7 is a cross-sectional view taken along line VII-VII in FIG. [Figure 8] FIG. 2 is a diagram illustrating a part of a circuit board when viewed from above. [Figure 9] Photographs showing images observed by an ultrasonic flaw detection device, (A), (B), and (C) are photographs of the images observed in Examples 1, 4, and 5, respectively. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings as needed. However, the following embodiments are merely examples for explaining the present disclosure, and are not intended to limit the present disclosure to the following contents. In the description, the same elements or elements having the same functions will be designated by the same reference numerals, and redundant descriptions will be omitted as the case may be. In addition, positional relationships such as up, down, left, and right will be based on the positional relationships shown in the drawings unless otherwise specified. Furthermore, the dimensional ratios of each element are not limited to those shown in the drawings.

[0022] In this disclosure, each numerical range indicated with the symbol "~" includes the lower limit and the upper limit. That is, a numerical range indicated with "A to B" means A or more and B or less. The upper limit or lower limit of each numerical range may be replaced with the numerical value of any of the examples, and this disclosure is also included. When multiple materials are exemplified, one of them may be used alone, or multiple materials may be used in combination.

[0023] A method for manufacturing a circuit board according to one embodiment includes a coating step of coating a brazing material onto a main surface of a ceramic plate to provide a brazing material layer on the main surface; a lamination step of arranging a plurality of metal plates so as to be dotted on one surface of the brazing material layer provided on the main surface of the ceramic plate to obtain a laminate; a bonding step of heating the laminate to obtain a bonded body in which the ceramic plate and the plurality of metal plates are bonded with a bonding layer; and a removal step of removing the bonding layers between the plurality of adjacent metal plates along the main surface of the ceramic plate to electrically insulate the adjacent plurality of metal plates from each other.

[0024] The material of the ceramic plate is not particularly limited, and examples thereof include silicon nitride sintered body, aluminum nitride sintered body, aluminum oxide sintered body, and silicon carbide sintered body. The shape of the ceramic plate is not particularly limited as long as it is plate-like. The thickness of the ceramic plate may be, for example, 0.2 to 2 mm, or 0.25 to 1.5 mm.

[0025] A ceramic plate 10 in Fig. 1, which is an example of a ceramic plate, has a flat plate shape. A first main surface 10A of the ceramic plate 10 is divided into a plurality of areas by scribe lines. A metal plate may be provided for each of the areas thus divided by the scribe lines. The first main surface 10A is provided with a plurality of scribe lines SL1 extending along a first direction and arranged at equal intervals, and a plurality of scribe lines SL2 extending along a second direction perpendicular to the first direction and arranged at equal intervals. The scribe lines SL1 and SL2 are perpendicular to each other.

[0026] The scribe lines SL1 and SL2 are composed of a plurality of holes formed by a laser beam. Examples of the laser source include a carbon dioxide gas laser and a YAG laser. The scribe lines can be provided by forming a plurality of holes along a predetermined direction by intermittently irradiating a laser beam from such a laser source. The scribe lines SL1 and SL2 do not have to be arranged at equal intervals, and are not limited to being perpendicular to each other. Moreover, they may be curved or bent instead of being straight. The scribe lines SL1 and SL2 may also be formed on the second main surface 10B of the ceramic plate 10 opposite to the first main surface 10A. It is not necessary to provide a scribe line on the ceramic plate.

[0027] The brazing material may contain Ag in the form of a metal element or a metal compound (alloy), and may contain, in addition to Ag, one or more metals selected from the group consisting of Cu, Sn, and active metals. Each metal may be included as an alloy or a compound. The active metal may contain one or more metals selected from the group consisting of Ti, Hf, Zr, and Nb. The brazing material may have a ratio of Ag to the total of Ag and Cu of 80 mass% or more, 91 mass% or more, 95 mass% or more, 98 mass% or more, or 100 mass%. In other words, the brazing material may not contain Cu. By sufficiently increasing the ratio of Ag to Cu in this way, the timing of melting of the brazing material can be delayed when the temperature of the laminate is raised in the bonding process. Therefore, the brazing material can be suppressed from creeping up onto the metal plate, and the occurrence of voids in the bonding layer can be sufficiently suppressed. Therefore, the bonding reliability between the metal plate and the ceramic plate can be further improved. In addition, the insulation between adjacent metal plates in the circuit board can be improved.

[0028] The metal plate may contain Cu. Ag and Cu have a eutectic point near a mass ratio of 72:28. Therefore, the molten brazing material reacts smoothly with Cu contained in the metal plate to form a eutectic alloy. Therefore, the contact area between the bonding layer and the ceramic plate and the metal plate can be sufficiently and smoothly increased.

[0029] The content of the active metal in the brazing material may be 0.5 to 8 parts by mass relative to 100 parts by mass of the total of Ag and Cu. By making the content of the active metal 0.5 parts by mass or more, it is possible to improve the bondability between the ceramic plate and the brazing material. On the other hand, by making the content of the active metal 8 parts by mass or less, it is possible to suppress the formation of a brittle alloy layer at the bonded interface.

[0030] The active metals contained in the brazing material may be present as nitrides, oxides, carbides or hydrides. As an example, the brazing material may be titanium nitride and / or titanium hydride (TiH 2This allows the bonding strength between the ceramic plate and the metal plate to be sufficiently high. 2 The content may be, for example, 1 to 8 parts by mass.

[0031] The brazing material may contain, in addition to the above-mentioned metal or metal compound, an organic solvent, a binder, etc. The viscosity of the brazing material may be, for example, 5 to 20 Pa·s. The content of the organic solvent in the brazing material may be, for example, 5 to 25 mass %, and the content of the binder may be, for example, 2 to 15 mass %.

[0032] In the coating step, a brazing material layer may be formed by coating a brazing material on at least one of the first main surface 10A and the second main surface 10B of the ceramic plate 10. In FIG. 2, a brazing material layer 20 is provided on a portion of the first main surface 10A excluding the end portion. The brazing material layer 20 may be provided so as to cover the entire first main surface 10A, or may be provided so as to cover a portion of the first main surface 10A as shown in FIG. 2. Examples of the coating method include a roll coater method, a screen printing method, and a transfer method. The brazing material layers 20 provided on both the first main surface 10A and the second main surface 10B may have the same shape or may be different from each other.

[0033] In the lamination process, a plurality of metal plates 30 are arranged in a dotted manner on the surface 20A of the brazing material layer 20 provided on the first main surface 10A of the ceramic plate 10 to obtain a laminate 100. The plurality of metal plates 30 may be pressed against one surface of the brazing material layer 20 for adhesion. At this time, a support plate to which the plurality of metal plates 30 are temporarily fixed may be used. The support plate and the ceramic plate 10 may be overlapped with each other so that the plurality of metal plates 30 and the brazing material layer 20 face each other, and the metal plates 30 may be laminated on the brazing material layer 20.

[0034] 3, all of the multiple metal plates 30 bonded to the first main surface 10A of the ceramic plate 10 via the brazing material layer 20 are disposed on the front surface 20A (one surface) of one brazing material layer 20. In this example, the coating process can be simplified compared to the case where multiple brazing material layers are provided on the first main surface 10A.

[0035] The metal plate 30 may contain Cu and may be a copper plate. The side of the metal plate 30 may be formed of a cut surface. The metal plate 30 may have a sag (sag surface) and a burr (burr surface). Such a metal plate is obtained by, for example, punching. In this case, the metal plate may be joined to the ceramic plate via the brazing material layer 20 so that the burr is located closer to the ceramic plate than the sag. This makes it difficult for voids to occur in the joint (joint layer) at the end of the metal plate, and the end of the metal plate 30 can be firmly fixed to the ceramic plate 10. The shape of the metal plate 30 is not particularly limited, and may be a square prism shape or a prism shape other than a square prism. At least some corners of the metal plate 30 may be chamfered. The thickness of the metal plate may be, for example, 0.1 to 2.0 mm, or 0.2 to 1.5 mm. The metal plate 30 may have a plating film on its surface.

[0036] In the laminate 100, a brazing material layer 20 may also be provided on the second main surface 10B of the ceramic plate 10, and a plurality of metal plates 30 may be arranged so as to be dotted on the surface 20A of the brazing material layer 20. The shape and number of the metal plates 30 on the second main surface 10B side may be the same as those on the first main surface 10A side, or may be different from each other. In a modified example, a plurality of metal plates 30 may be arranged on the surface of different brazing material layers on the second main surface 10B of the ceramic plate 10. In another modified example, no metal plate 30 may be provided on the second main surface 10B side of the ceramic plate 10.

[0037] In the bonding step, the laminate 100 is heated to obtain a bonded body in which the ceramic plate and the multiple metal plates are bonded with a bonding layer. In the bonding step, the laminate 100 may be heated using a heating furnace. The heating may be performed while pressing the laminate in the stacking direction. The heating bonds the ceramic plate 10 and the multiple metal plates 30 via the bonding layer 22. The heating temperature may be, for example, 700 to 900°C. The atmosphere in the heating furnace may be an inert gas such as nitrogen, and may be performed under reduced pressure below atmospheric pressure or under vacuum.

[0038] The heating may melt the components contained in the brazing material layer 20 and the components contained in the metal plate 30 to form a bonding layer. The heating furnace may be a continuous type that continuously produces a plurality of bonded bodies, or may be a batch type that produces one or a plurality of bonded bodies. Heating may be performed by heating a plurality of laminates together to obtain a plurality of bonded bodies. Heating may be performed while pressing the laminates in the stacking direction using a fixture or the like. The bonded body obtained by heating may have the same appearance as the laminate 100 in FIG. 3.

[0039] 4 is a cross-sectional view of a bonded body 110 obtained by heating the laminate 100, cut along the lamination direction. A plurality of metal plates 30 are bonded to the first main surface 10A (second main surface 10B) of the ceramic plate 10 in the bonded body 110 via a bonding layer 22. The bonding layer 22 is provided not only on the portion of the first main surface 10A (second main surface 10B) where the metal plate 30 is bonded, but also on the portion of the first main surface 10A (second main surface 10B) where the metal plate 30 is not bonded. Since the bonding layer 22 is electrically conductive, the metal plates 31, 32, and 33 bonded to the first main surface 10A are electrically connected to each other. The metal plates 31, 32, and 33 bonded to the second main surface 10B are also electrically connected to each other.

[0040] In the removal step, the exposed portion 23 of the bonding layer 22 between the metal plates 31, 32 adjacent to each other along the first main surface 10A and the second main surface 10B of the ceramic plate, and the exposed portion 24 of the bonding layer 22 between the metal plates 32, 33 adjacent to each other are removed. At this time, the exposed portion 25 of the bonding layer 22 on the outer side of the metal plates 31, 33 bonded to the outermost edge of the ceramic plate 10 may also be removed. The exposed portions 23, 24, 25 are part of the bonding layer 26. By removing the exposed portions 23, 24, the adjacent metal plates 31, 32 and the adjacent metal plates 32, 33 are electrically insulated from each other. The method of removing the exposed portions 23, 24, 25 that are part of the bonding layer 26 is not particularly limited, and may be performed using an etching solution, sandblasting, or a laser. By removing the exposed portions 23 and 24, the scribe line SL1 (SL2) that was covered by the bonding layer 22 (exposed portions 23 and 24) is exposed.

[0041] The etching solution may be an aqueous solution containing an inorganic acid such as an aqueous solution of ammonium halide, sulfuric acid, or nitric acid, and hydrogen peroxide. Such an aqueous solution may be sprayed from a nozzle onto the exposed portions 23, 24, and 25 to remove them. The protruding distance of the bonding layer 26, which will be described later, can be adjusted by changing the spray time, the concentration of the inorganic acid and hydrogen peroxide in the aqueous solution, and / or the discharge pressure (spray pressure) of the aqueous solution.

[0042] After the removing step, a surface treatment may be performed as necessary. In the surface treatment, a plating film may be formed on the surface of the metal plate 30. In this manner, for example, a circuit board 120 having a shape as shown in FIG. 5 can be obtained. In the circuit board 120, each of the first main surface 10A and the second main surface 10B of the ceramic plate 10 is bonded to the metal plate 30 by a bonding layer 26 obtained by removing the exposed portions 23, 24, and 25 from the bonding layer 22.

[0043] In the removal step, it is not necessary to completely remove the exposed portions 23, 24, and 25 of the bonding layer 22. The exposed portions 23, 24, and 25 may be removed to the extent that adjacent metal plates 30 are electrically insulated from each other. By reducing the remaining amount of the exposed portions 23, 24, and 25, the insulation between the metal plates 30 can be improved.

[0044] According to the above-mentioned method for manufacturing a circuit board, it is possible to obtain a circuit board in which misalignment between the bonding layer 26 and the metal plate 30 is suppressed. Compared to a method in which a plurality of metal plates and a plurality of brazing layers are bonded together while being aligned, the labor required for alignment can be reduced. Therefore, a circuit board with excellent bonding reliability can be efficiently manufactured.

[0045] The circuit board 120 shown in FIG. 5 includes a ceramic plate 10, a plurality of metal plates 30, and a plurality of bonding layers 26 that bond the first main surface 10A (second main surface 10B) of the ceramic plate 10 to each of the plurality of metal plates 30. The adjacent metal plates 31, 32 and the adjacent metal plates 32, 33 are all electrically insulated from each other. That is, the plurality of metal plates 30 are all electrically insulated from the adjacent metal plates 30. If the circuit board 120 is divided along SL1 and SL2, a plurality of circuit boards (individualized boards) can be obtained. The metal plate 30 on the first main surface 10A side of the circuit board 120 may form a circuit, and the metal plate 30 on the second main surface 10B side may form a heat transfer layer.

[0046] In the circuit board 120, when the first main surface 10A side or the second main surface 10B side of the ceramic plate 10 is viewed in plan, the outer edges of the multiple metal plates 30 each include multiple sides, and in at least one of the multiple metal plates 30 (in one example, it may be all of the multiple metal plates 30), the minimum protrusion distance L of the bonding layer on the multiple sides is min Maximum value L for max may be 4.0 or less. The ratio may be 3.0 or less, 2.0 or less, or 1.7 or less. In such a circuit board 120, positional deviation between the multiple metal plates 30 and the bonding layer 26 that bonds each of them to the first main surface 10A (second main surface 10B) of the ceramic plate 10 is suppressed. In such a circuit board 120, the bonding reliability between the ceramic plate 10 and the metal plate 30 is excellent. In addition, the variation in the interval between the bonding layers 26 that bond adjacent metal plates 30 can be reduced, and the insulation reliability can also be improved.

[0047] In the circuit board 120, when the first main surface 10A side or the second main surface 10B side of the ceramic plate 10 is viewed in plan, the outer edges of the multiple metal plates 30 each include multiple sides, and in at least one of the multiple metal plates 30 (in one example, it may be all of the multiple metal plates 30), the maximum protrusion distance L of the bonding layer on the multiple sides is max and the minimum value L minmay be 0.3 mm or less. The difference may be 0.2 mm or less, 0.1 mm or less, or 0.08 mm or less. In such a circuit board 120, positional deviation between the multiple metal plates 30 and the bonding layer 26 that bonds each of them to the first main surface 10A (second main surface 10B) of the ceramic plate 10 is suppressed. In such a circuit board 120, the bonding reliability between the ceramic plate 10 and the metal plate 30 is excellent. In addition, the variation in the interval between the bonding layers 26 that bond adjacent metal plates 30 can be reduced, and the insulation reliability can also be improved.

[0048] The protrusion distance of the bonding layer 26 can be measured as shown in FIG. 6, FIG. 7, and FIG. 8. As shown in FIG. 6, when the first main surface 10A of the circuit board is viewed in a plane, the outer edge of the metal plate 30 includes a plurality of sides S1, S2, S3, and S4. The side S1 in FIG. 6 corresponds to the side of the metal plate 30 shown in FIG. 7. The sides S2, S3, and S4 also correspond to the side of the metal plate 30, as well as the side S1. As shown in FIG. 6, in the plan view of the circuit board, a position where the distance from the side S1 to the outer edge 26E of the bonding layer 26 is the longest is identified along a direction perpendicular to the side S1 of the metal plate 30. The length from the side S1 (side surface of the metal plate 30) at that position to the outer edge 26E is defined as the protrusion distance L1 at the side S1 of the bonding layer 26. When the side S1 and the outer edge 26E are not parallel in the plan view as in FIG. 6, the maximum length from the side S1 to the outer edge 26E is defined as the protrusion distance L1.

[0049] The protrusion distance L1 can be measured by cutting the circuit board along the thickness direction of the metal plate 30 (the lamination direction of the metal plate 30, the bonding layer 26, and the ceramic plate 10) and observing the cut surface using a scanning electron microscope (SEM). When such a cut surface is observed with an SEM, a structure as shown in FIG. 7 can be observed. Using an SEM image or an SEM photograph, the length from the side S1 (side surface) of the metal plate 30 to the outer edge 26E of the bonding layer 26 is measured. This is the protrusion distance L1. Similarly, for the sides S2, S3, and S4, the lengths at the positions where the distances from the sides S2, S3, and S4 to the outer edge 26E of the bonding layer 26 are the longest are measured. The lengths obtained in this manner are the protrusion distances L1, L2, L3, and L4 measured for each of the multiple sides S1, S2, S3, and S4.

[0050] In the example of FIG. 6, the protrusion distances L1, L2, L3, and L4 measured on the four sides S1, S2, S3, and S4 included in the outer edge of the metal plate 30 are all equal. That is, L1=L2=L3=L4. Therefore, the minimum protrusion distance L of the bonding layer 26 is min = Maximum L max The minimum protrusion distance L min Maximum value L for max The ratio is 1. In addition, the maximum value L of the protruding distance of the bonding layer 26 max and the minimum value L min The difference is 0 mm.

[0051] 8, in a plan view of the circuit board 120, the protrusion distances L1, L2, L3, and L4 measured on the four sides S1, S2, S3, and S4 included in the outer edge of the metal plate 30 are all different. That is, L1>L2>L4>L3. In this example, the minimum protrusion distance L min = L3, and the maximum protrusion distance of the bonding layer 26 is L max = L1. The minimum protrusion distance L min Maximum value L for max The ratio is calculated as L1 / L3. The maximum protrusion distance L max and the minimum value L minThe difference between these values ​​is calculated as L1-L3. When the bonding layer 26 does not protrude from the circuit board in a plan view, the protrusion distance is 0.

[0052] Minimum protrusion distance L of the bonding layer 26 min From the viewpoint of obtaining a circuit board having sufficiently excellent bonding reliability, the maximum protrusion distance L of the bonding layer 26 (L3 in the example of FIG. 8) may exceed 0, may be 0.001 mm or more, or may be 0.005 mm or more. max From the viewpoint of obtaining a circuit board with sufficiently excellent insulation reliability, (L1 in the example of FIG. 8) may be 2.0 mm or less, 1.5 mm or less, or 0.8 mm or less.

[0053] In all of the plurality of metal plates 30 on the first main surface 10A and the second main surface 10B of the ceramic plate 10, the minimum protruding distance L of the bonding layer 26 on the plurality of sides min Maximum value L for max and the maximum value L of the protruding distance of the bonding layer 26 on the multiple sides max and the minimum value L min The "difference" between the bonding layers 26 is obtained by the above-mentioned procedure. It is not essential that the "ratio" and the "difference" are within the above-mentioned numerical range for all of the plurality of metal plates 30. For example, the average value of the "ratio" of the protruding distance of the bonding layer 26 in the plurality of metal plates 30 obtained by the above-mentioned procedure in at least one of the first main surface 10A and the second main surface 10B of the ceramic plate 10 may be 4.0 or less, 3.0 or less, 2.0 or less, or 1.7 or less. Similarly, the average value of the "difference" of the protruding distance of the bonding layer 26 in the plurality of metal plates 30 obtained by the above-mentioned procedure in at least one of the first main surface 10A and the second main surface 10B of the ceramic plate 10 may be 0.3 mm or less, 0.2 mm or less, 0.1 mm or less, or 0.08 mm or less. Even such a circuit board 120 has excellent bonding reliability.

[0054] For all of the multiple metal plates 30 on at least one of the first main surface 10A and the second main surface 10B, the “ratio” and / or “difference” of the protrusion distance of the bonding layer 26 obtained by the above-mentioned procedure may be within the above-mentioned numerical range.

[0055] In the examples of FIG. 6 and FIG. 8, the standard deviation of the protrusion distance of the bonding layer 26 is obtained as the standard deviation of the protrusion distances L1, L2, L3, and L4. The standard deviation thus obtained may be 0.05 mm or less, and may be 0.04 mm or less. In such a circuit board 120, the variation in the positional deviation between the multiple metal plates 30 and the bonding layer 26 that bonds each of them to the first main surface 10A of the ceramic plate 10 is sufficiently reduced. Such a circuit board 120 has sufficiently excellent bonding reliability and insulation reliability. The above-mentioned standard deviation may exceed 0 mm, for example, and may be 0.003 mm or more. In all of the multiple metal plates 30 on at least one of the first main surface 10A and the second main surface 10B, the average value of the standard deviation of the protrusion distance of the bonding layer 26 obtained by the above-mentioned procedure may be within the numerical range of the above-mentioned standard deviation.

[0056] In the examples of FIGS. 6 and 8, the metal plate 30 is rectangular in plan view of the circuit board 120. However, even if the corners of the metal plate 30 are chamfered, the minimum protrusion distance L min Maximum value L for max Ratio and maximum protrusion distance L max and the minimum value L min The metal plate 30 may have a polygonal shape other than a rectangle. When the brazing material is present on the entire side surface and upper surface of the metal plate 30, the interface between the side surface of the metal plate 30 and the brazing material is examined in a cross section such as that shown in FIG. 7, and the length from the interface to the outer edge 26E can be obtained as the protrusion distance.

[0057] In FIG. 7, the metal plate 30 is bonded only to the first main surface 10A of the ceramic plate 10, but a metal plate may also be bonded to the second main surface 10B. The protruding distance of the bonding layer on the second main surface 10B side can be measured in the same manner as the first main surface 10A side. The maximum protruding distance L of the bonding layer on the second main surface 10B side is max , minimum value L min , the ratio of the maximum value to the minimum value (L max / L min), the difference between the maximum and minimum values ​​(L max -L min ) and the standard deviation may or may not be included in the respective numerical ranges on the first main surface 10A side.

[0058] The circuit board 120 may be divided along the scribe lines SL1 and SL2. Such a circuit board (singulated board) may be mounted on a power module. The metal plate 30 may function as a circuit board having a function of transmitting an electric signal, or as a heat sink having a function of transmitting heat. The metal plate 30 may also have both a function of transmitting heat and a function of transmitting an electric signal. In the circuit board 120, the positional deviation between the bonding layer 26 and the metal plate 30 is suppressed at least on the first main surface 10A side of the ceramic plate 10. Therefore, the bonding reliability between the bonding layer 26 and the metal plate 30 is excellent. Such a circuit board is also excellent in connection reliability with an external circuit such as a semiconductor element. Therefore, it is suitable as a component to be mounted on a power module that requires high reliability. The power module may be manufactured by mounting a semiconductor element on the circuit board (singulated board) using solder and wire bonding, etc., and housing the circuit board and the semiconductor element in the housing space of the housing, and then sealing with a resin.

[0059] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above embodiments. For example, the number of brazing material layers 20 provided on the first main surface 10A of the ceramic plate 10 is not limited to one, but may be two or more. For example, two metal plates 30 may be bonded to each of three brazing material layers 20. The number of multiple metal plates 30 bonded to one brazing material layer 20 is also not particularly limited. EXAMPLES

[0060] The present disclosure will be described in more detail with reference to examples and comparative examples, but the present disclosure is not limited to the following examples.

[0061] Example 1 [Creating a circuit board] The copper base material was punched out with a die to obtain 15 copper plates (material: oxygen-free copper, size: length x width x thickness = 17 mm x 38 mm x 0.5 mm). Separately, a silicon nitride ceramic plate (length x width x thickness = 20 mm x 41 mm x 0.25 mm) was prepared.

[0062] Ag, Sn, and TiH 2 The brazing filler metal was prepared by mixing 3 parts by mass of Sn and TiH 2 This brazing filler metal did not contain Cu.

[0063] One of the main surfaces of the ceramic plate was divided into 15 areas (3 × 5) by scribe lines. A brazing material was applied to the main surface, except for the end (width 1 mm), by screen printing to form a brazing material layer. The amount of brazing material applied was 8 mg / cm. 2 It was decided.

[0064] Fifteen copper plates were attached to the brazing layer so as to be aligned along the main surface of the ceramic plate, thereby obtaining a laminate in which the copper plates were stacked on one brazing layer, one for each area defined by the scribe lines.

[0065] The obtained laminate was pressurized in the lamination direction at 0.015 MPa using a pressure tool while being heated in a vacuum (1.0 × 10 -3 The copper plates were heated at 1000 K and 790°C for 1 hour. In this way, a bonded body was obtained in which 15 copper plates were bonded to one main surface of the ceramic plate via a bonding layer containing a brazing material component. An etching solution containing ammonium halide, sulfuric acid, nitric acid, and hydrogen peroxide was sprayed toward the surface of the bonded body to which the copper plates were bonded. This etched and removed the bonding layer between the adjacent copper plates. The spray discharge pressure was 0.26 MPa. After etching, electroless plating was performed using a Ni-P plating solution (phosphorus concentration: 8 to 12 mass%) to cover the copper plates with a plating film. In this way, a circuit board was obtained in which multiple copper plates were bonded to one main surface of the ceramic plate with bonding layers.

[0066] [Circuit board evaluation] <Measurement of protruding distance> As shown in Figure 6, the main surface of the ceramic plate to which the copper plate was bonded was viewed in plan view, and the portion on each side (each side) of the copper plate where the protruding distance of the bonding layer was the longest was identified. The bonded body was cut along the lamination direction at that portion, and the cut surface was observed under an SEM (magnification: 80x). Using the SEM photographs taken, the protruding distances L1, L2, L3, and L4 on each side of the copper plate were measured. The arithmetic mean value, standard deviation, and maximum value L of L1, L2, L3, and L4 were calculated. max , minimum value L min , the difference between the maximum and minimum values ​​(L max -L min ), and the ratio of the maximum value to the minimum value (L max / L min The same procedure was used to measure each of the 15 copper plates (No. 1 to 15), and each value was calculated. The results are shown in Table 1.

[0067] Example 2 A circuit board was manufactured and evaluated in the same manner as in Example 1, except that the spray discharge pressure when etching the bonding layer between adjacent copper plates was set to 0.21 MPa. The results are shown in Table 2.

[0068] Example 3 A circuit board was manufactured and evaluated in the same manner as in Example 1, except that the spray discharge pressure when etching the bonding layer between adjacent copper plates was 0.14 MPa. The results are shown in Table 3.

[0069] Comparative Example 1 A ceramic plate was obtained with one main surface divided into 15 regions by scribe lines using the same procedure as in Example 1. The brazing filler metal used in Examples 1 to 3 was applied to each region by screen printing to form 15 brazing filler metal layers. The application area of ​​each brazing filler metal layer was the same as the area of ​​the main surface of the copper plate to be joined to the ceramic plate. The application amount of brazing filler metal per unit area in the portion where the brazing filler metal was applied was 8 mg / cm2. 2 It was decided.

[0070] The brazing material layer and the copper plate were aligned, and the copper plate was attached to the brazing material layer. Each brazing material layer was attached to a copper plate to obtain a laminate. A circuit board was manufactured and evaluated in the same manner as in Example 1, except that the laminate obtained in this manner was used. The results are shown in Table 4.

[0071] [Table 1]

[0072] [Table 2]

[0073] [Table 3]

[0074] [Table 4]

[0075] In Tables 1 to 4, the arithmetic mean values ​​of each value are shown in the bottom columns. The difference between the maximum value and the minimum value (L max -L min ), and the ratio of the maximum value to the minimum value (L max / L min ) was sufficiently small. Thus, in Examples 1 to 3, it is possible to suppress misalignment between the bonding layer and the metal plate without aligning the brazing material layer and the copper plate as in Comparative Example 1. That is, in Examples 1 to 3, it was possible to efficiently manufacture a circuit board in which misalignment between the bonding layer and the metal plate was suppressed. From the results of Examples 1 to 3, it was confirmed that the protruding distance of the bonding layer could be reduced by increasing the discharge pressure of the spray.

[0076] Example 4 Ag, Cu, Sn, and TiH 2The brazing filler metal was prepared. The mass ratio of Ag and Cu in this brazing filler metal was 90:10. This brazing filler metal contained 3 parts by mass of Sn and TiH 2 A circuit board was produced in the same manner as in Example 1, except that this brazing material was used.

[0077] Example 5 Ag, Cu, Sn, and TiH 2 The brazing filler metal was prepared. The mass ratio of Ag and Cu in this brazing filler metal was 69:31. This brazing filler metal contained 3 parts by mass of Sn and TiH 2 A circuit board was produced in the same manner as in Example 1, except that this brazing material was used.

[0078] The joints between the ceramic plate and the copper plate in Examples 1, 4, and 5 were observed by ultrasonic testing (SAT). Specifically, the presence or absence of voids between the ceramic plate and the copper plate was examined using an ultrasonic testing device (device name: Fine SAT V) manufactured by Hitachi Power Solutions Co., Ltd. Photographs of SAT images are shown in FIG. 9. In FIG. 9, (A) is an SAT image of Example 1, (B) is an SAT image of Example 4, and (C) is an SAT image of Example 5. As shown in FIG. 9, the ratio of voids in the joint was the lowest in Example 1 and the highest in Example 5. The width of the voids obtained from each photograph in FIG. 9 was less than 1 mm in Example 4 and 1 mm or more in Example 5. The presence of voids could not be confirmed in Example 1. Among Examples 1, 4, and 5, Example 5 had the most creeping up to the upper surface of the copper plate (creeping width of the brazing filler metal on the upper surface of the copper plate: 3 mm or more), and Example 1 had the least (creeping width of the brazing filler metal on the upper surface of the copper plate: less than 1 mm).

[0079] The reason why the proportion of voids is higher in Example 4 than in Example 1, and the width of the brazing material rising is larger in Example 5 than in Example 4, is considered to be as follows. That is, since the ratio of Ag and Cu in the brazing material in Example 5 is a eutectic composition of Ag and Cu, the melting speed of the brazing material is faster when heated in the joining process. Since Example 4 is also closer to the above eutectic composition than Example 1, the melting speed of the brazing material is faster than Example 1. When the melting speed of the brazing material increases, the width of the brazing material rising increases, and the brazing material forming the joining layer becomes insufficient, making it easier for voids to form. However, even in Examples 4 and 5, the positional deviation between the joining layer and the copper plate is sufficiently suppressed, and the positional deviation is suppressed. Therefore, the joining reliability is improved compared to the manufacturing method such as Comparative Example 1. [Industrial Applicability]

[0080] The present invention provides a method for manufacturing a circuit board that can efficiently obtain a circuit board in which misalignment between a bonding layer and a metal plate is suppressed. Also, a circuit board in which misalignment between a bonding layer and a metal plate is suppressed is provided. [Explanation of symbols]

[0081] 10...ceramic plate, 10A...first main surface, 10B...second main surface, 20...solder layer, 20A...surface, 22, 26...joint layer, 23, 24, 25...exposed portion, 26E...outer edge, 30, 31, 32, 33...metal plate, 100...laminated body, 110...joint, 120...circuit board, L1, L2, L3, L4...overhang distance, S1, S2, S3, S4...side, SL1, SL2...scribe line.

Claims

1. a lamination step of arranging a plurality of metal plates in a dotted manner on one surface of a brazing material layer provided on a main surface of a ceramic plate to obtain a laminate; a bonding step of heating the laminate to obtain a bonded body in which the ceramic plate and the plurality of metal plates are bonded together with a bonding layer; a removal step of removing the bonding layer between the plurality of metal plates adjacent to each other along the main surface of the ceramic plate to electrically insulate the plurality of adjacent metal plates from each other.

2. The method for manufacturing a circuit board according to claim 1 , wherein all of the plurality of metal plates are provided on the one surface of the brazing material layer.

3. 3. The method for manufacturing a circuit board according to claim 1, further comprising a coating step of coating the main surface of the ceramic plate with a brazing material to provide the brazing material layer on the main surface.

4. The plurality of metal plates include Cu, The method for manufacturing a circuit board according to claim 1 , wherein the brazing material layer contains Ag, and a ratio of Ag to a total of Ag and Cu in the brazing material layer is 91 mass % or more.

5. When the circuit board is viewed in plan, each of the outer edges of the plurality of metal plates includes a plurality of sides, and in at least one of the plurality of metal plates, a minimum value L of the protrusion distance of the bonding layer on the plurality of sides is ｍｉｎ Maximum value L for ｍａｘ The method for producing a circuit board according to claim 1 or 2, wherein the ratio is 4.0 or less.

6. The maximum protrusion distance L ｍａｘ and the minimum value L ｍｉｎ The method for manufacturing a circuit board according to claim 5 , wherein the difference is 0.3 mm or less.

7. a ceramic plate, a plurality of metal plates, and a plurality of bonding layers bonding the ceramic plate to each of the plurality of metal plates, When viewed in a plan view, each of the outer edges of the plurality of metal plates includes a plurality of sides, In at least one of the plurality of metal plates, the minimum value L of the protrusion distance of the bonding layer on the plurality of sides ｍｉｎ Maximum value L for ｍａｘ The circuit board has a ratio of 4.0 or less.

8. The maximum protrusion distance L ｍａｘ and the minimum value L ｍｉｎ The circuit board according to claim 7 , wherein the difference is 0.3 mm or less.

9. 9. The circuit board according to claim 7, wherein a standard deviation of the protrusion distance is 0.05 mm or less.

Images