Wiring board and method of manufacturing the same

Abstract

To improve the performance of a wiring board.SOLUTION: The printed circuit board SUB1 includes a ceramic substrate 10 having an upper surface 10t and a lower surface 10b, and a conductive pattern 10t formed on the upper surface 20A of the ceramic substrate 10. The conductive pattern 20A includes an underlying metallic layer 21 formed on the 10t of the upper surface of the ceramic substrate 10, and a metallic layer 22 formed on the 10t of the upper surface of the ceramic substrate 10 so as to cover the entire underlying metallic layer 21. The underlying metal layer 21 contains at least one of titanium and chromium in addition to copper and silver. The metal layer 22 contains copper as a main component, and the weight ratio of silver contained in the metal layer 22 is smaller than the weight ratio of silver contained in the underlying metal layer 21. The side 21s of the base metal layer 21 is covered with the metallic layer 22.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] One technique for forming a wiring pattern on a ceramic substrate involves the use of an underlying metal layer made of copper. For example, Japanese Patent Application Laid-Open No. 2009-253196 (Patent Document 1) describes a method for forming a wiring pattern by applying a high-melting-point metal paste to an aluminum nitride sintered substrate, firing the paste, and then laminating a copper paste on the wiring pattern made of the high-melting-point metal and firing the paste. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-253196 Summary of the Invention [Problem to be solved by the invention]

[0004] When forming a conductor pattern on a ceramic substrate, it is necessary to improve the adhesion between the ceramic substrate and the conductor pattern. If a conductor pattern whose main component is copper contains a silver component, the adhesion between the ceramic substrate and the conductor pattern can be improved. However, if the conductor pattern contains a silver component, silver migration may occur. From the viewpoint of improving the reliability of the wiring substrate, it is necessary to prevent migration caused by silver. [Means for solving the problem]

[0005] A wiring board according to one embodiment includes a ceramic substrate having a first surface and a second surface opposite the first surface, and a first conductor pattern formed on the first surface of the ceramic substrate. The first conductor pattern includes a first base metal layer formed on the first surface of the ceramic substrate and a first metal layer formed on the first surface of the ceramic substrate so as to cover the entire first base metal layer. The first base metal layer contains copper, silver, and at least one of titanium and chromium. The first metal layer contains copper as a primary component, and the weight percentage of silver contained in the first metal layer is smaller than the weight percentage of silver contained in the first base metal layer. The side surfaces of the first base metal layer are covered by the first metal layer.

[0006] Another embodiment of a method for manufacturing a wiring board includes the steps of: (a) preparing a ceramic substrate having a first surface and a second surface opposite the first surface; (b) applying a first base metal paste to the first surface of the ceramic substrate; (c) firing the first base metal paste to form a first base metal layer; (d) after step (c), applying the first metal paste to cover the entire first base metal layer; and (e) after step (d), firing the first metal paste to form a first metal layer. The first base metal paste contains copper particles, silver particles, and at least one of titanium particles and chromium particles. The weight percentage of the copper particles contained in the first metal paste is greater than the weight percentage of the copper particles contained in the first base metal paste, and the weight percentage of the silver particles contained in the first metal paste is less than the weight percentage of the copper particles contained in the first base metal paste. In the step (d), the side surfaces of the first metal underlayer are covered with the first metal paste. [Effects of the Invention]

[0007] According to the above embodiment, the performance of the wiring board can be improved. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 2 is a top view of the wiring substrate according to the embodiment; [Figure 2] FIG. 2 is an enlarged cross-sectional view taken along line AA in FIG. [Figure 3] FIG. 2 is an enlarged cross-sectional view taken along line BB in FIG. [Figure 4] 3 is an enlarged cross-sectional view of a wiring board that is a study example of FIG. 2. [Figure 5] 4 is an enlarged transparent plan view showing the planar positional relationship between the base metal layer and the metal layer covering the base metal layer shown in FIGS. 2 and 3. FIG. [Figure 6] 3 is an enlarged cross-sectional view showing an example of the detailed structure of each layer constituting the conductor pattern shown in FIG. 2. FIG. [Figure 7] 6 is a perspective enlarged plan view of a wiring board which is a modified example of the wiring board shown in FIG. 5. [Figure 8] FIG. 8 is an enlarged cross-sectional view taken along line CC in FIG. 7. [Figure 9] FIG. 8 is an enlarged cross-sectional view taken along line DD in FIG. 7. [Figure 10] 9 is an enlarged cross-sectional view showing an example of the detailed structure of each layer constituting the conductor pattern shown in FIG. 8. [Figure 11] 1. FIG. 4 is a bottom view of a wiring board which is a modified example of the wiring board shown in FIG. [Figure 12] FIG. 12 is a cross-sectional view taken along line EE in FIG. [Figure 13] 1A to 1C are explanatory diagrams illustrating an example of a manufacturing process for a wiring substrate according to an embodiment. [Figure 14] FIG. 14 is an enlarged cross-sectional view showing the first base metal paste applying step shown in FIG. [Figure 15] 14 is an enlarged cross-sectional view showing the second base metal paste applying step shown in FIG. 13. FIG. [Figure 16] 14 is an enlarged cross-sectional view showing a state in which an underlayer is formed by the underlayer firing step shown in FIG. 13. FIG. [Figure 17] 14 is an enlarged cross-sectional view showing the first metal paste application step shown in FIG. 13. FIG. [Figure 18] 14 is an enlarged cross-sectional view showing a state in which a metal layer has been formed by the first metal layer firing step shown in FIG. 13. FIG. [Figure 19] 14 is an explanatory diagram showing an example of a manufacturing process of a wiring board which is a modified example of the wiring board shown in FIG. 13. [Figure 20] 20 is an enlarged cross-sectional view showing a second metal paste application step shown in FIG. 19. FIG. [Figure 21] FIG. 20 is an enlarged view showing the second metal layer firing step shown in FIG. 19. [Figure 22] FIG. 16 is an enlarged cross-sectional view showing a second base metal paste applying step, which is a modified example of the step shown in FIG. [Figure 23] FIG. 23 is an enlarged cross-sectional view of a conductor pattern obtained by the modified example shown in FIG. 22. DETAILED DESCRIPTION OF THE INVENTION

[0009] (Explanation of the description format, basic terms and usage in this application) In this application, the description of the embodiments will be divided into multiple sections, etc., for convenience, as necessary. However, unless otherwise expressly stated, these are not mutually independent and separate, and regardless of the order of description, they are each part of a single example, one being a partial detail of the other, or a partial or complete modification, etc. Furthermore, as a general rule, repeated explanations of similar parts will be omitted. Furthermore, each component in the embodiments is not essential unless otherwise expressly stated, there is a theoretical limit to the number, or it is clearly not essential from the context.

[0010] In each drawing of the embodiment, the same or similar parts are indicated by the same or similar symbols or reference numerals, and the description thereof will not be repeated as a general rule.

[0011] In the following description, a wiring board refers to a component in which a conductor pattern is formed on a base material such as a ceramic substrate made of ceramics. The conductor pattern includes not only a linear (strip-like) wiring pattern but also a terminal pattern for ensuring electrical connection with external devices such as electronic components and semiconductor components. The conductor pattern may also include a bonding pad for mounting external devices, or a large-area conductor pattern such as a ground plane or power plane.

[0012] In the following description, the term "main component" may be used to describe the metal element that constitutes the metal layer. For example, a "metal layer containing copper as a main component" means that the metal material that constitutes the metal layer contains at least 90 wt % or more, preferably 99 wt % or more, of copper.

[0013] Furthermore, when describing the metal elements that make up a metal layer, the term "weight proportion" may be used. The "weight proportion of an element" is the value obtained by dividing the weight value of the target element contained per unit volume by the total weight value per unit volume. For example, the "weight proportion of silver in component A" is the value obtained by dividing the weight value of silver contained in a part (or all) of component A by the weight value of said part (or all) of component A. Furthermore, the "weight proportion of silver particles in component A" is the value obtained by dividing the weight value of silver particles contained in a part (or all) of component A by the weight value of said part (or all) of component A.

[0014] In the following description, directions such as the X direction, the Y direction, and the Z direction may be used. For example, the X direction and the Y direction are shown in FIG. 1, which will be described later. The X direction and the Y direction intersect with each other. In the example described below, the X direction is orthogonal to the Y direction. In the following description, the XY plane including the X direction and the Y direction is assumed to be a plane parallel to the main surface of the wiring board.

[0015] Furthermore, a surface that intersects the XY plane (for example, a surface parallel to the XZ plane including the X and Z directions, and a surface parallel to the YZ plane including the Y and Z directions) is called a side surface. In the following description, unless otherwise specified, "planar view" refers to the view of a surface parallel to the XY plane. Furthermore, the normal direction to the XY plane will be referred to as the "Z direction" or thickness direction. Unless otherwise specified, "thickness" and "height" refer to the length in the "Z direction." The X, Y, and Z directions are directions that intersect with each other, and more specifically, are directions that are perpendicular to each other.

[0016] <Wiring board> FIG. 1 is a top view of a wiring board according to this embodiment. FIG. 2 is an enlarged cross-sectional view taken along line AA in FIG. 1. FIG. 3 is an enlarged cross-sectional view taken along line BB in FIG. 1. FIG. 4 is an enlarged cross-sectional view of a wiring board that is an example of consideration in relation to FIG. 2. FIG. 5 is an enlarged transparent plan view showing the planar positional relationship between the underlying metal layer and the metal layer covering the underlying metal layer shown in FIGS. 2 and 3. In FIG. 5, the outline of the underlying metal layer 21 shown in FIGS. 2 and 3 is shown by a dotted line.

[0017] As shown in Figure 2, the wiring board SUB1 of this embodiment has a ceramic substrate 10 having an upper surface (face) 10t and a lower surface (face) 10b opposite the upper surface 10t, and a conductive pattern 20A formed on the upper surface 10t of the ceramic substrate 10.

[0018] 1, in addition to the conductor pattern 20A, conductor patterns 20B, 20C, and 20D, which are spaced apart from the conductor pattern 20A, are formed on the upper surface 10t of the ceramic substrate 10. The conductor patterns 20A to 20D are electrically isolated from each other.

[0019] The multiple conductor patterns 20 include patterns with different planar areas and shapes. Each of the multiple conductor patterns 20 has a similar layer structure. Below, the detailed structure of the conductor pattern 20A shown in FIG. 2 will be described as a representative example of the conductor pattern 20.

[0020] The ceramic substrate 10 is made of, for example, silicon nitride or aluminum nitride. The conductor pattern 20 is a metal layer containing copper as the main material. The wiring board SUB1, in which the conductor pattern 20 made of a metal layer containing copper as the main material is bonded onto the ceramic substrate 10, is used, for example, as a wiring board for a power module incorporated into a power supply circuit.

[0021] From the viewpoint of electrical conductivity or heat dissipation characteristics, it is preferable to use a metal layer whose main material is copper for the conductive pattern 20A. However, because copper does not have a very high adhesion to the ceramic substrate 10, measures must be taken to improve the bonding strength between the ceramic substrate 10 and the conductive pattern 20A.

[0022] 2 and 3, in this embodiment, a metal base layer 21 is interposed between the metal layer 22 and the upper surface 10t of the ceramic substrate 10. The metal base layer 21 contains at least one of titanium and chromium in addition to copper and silver. The metal base layer 21 functions as a bonding layer for improving the bonding strength between the metal layer 22, which is mainly made of copper, and the ceramic substrate 10.

[0023] 2 and 3 are porous metal layers in which a plurality of metal particles are bonded to one another, as will be described in detail later. The size of the voids in the metal layer can be adjusted by the average particle size of the plurality of metal particles and the degree of sintering (the firing temperature and the firing time).

[0024] However, from the viewpoint of simply improving the bonding strength between the copper layer and the ceramic substrate 10, it is sufficient to have a structure in which a metal layer 22 is laminated on a base metal layer 21, and the side surface 21s of the base metal layer 21 is not covered by the metal layer 22, as shown in Figure 4 as an example wiring substrate SUB1.

[0025] However, according to the investigations of the present inventors, it was found that the structure of the wiring board SUB2 has a problem caused by electromigration of silver contained in the base metal layer 21. For example, the weight percentage of silver contained in the base metal layer 21 is greater than the weight percentage of copper contained in the base metal layer 21. By increasing the weight percentage of silver contained in the base metal layer 21, the bonding strength between the base metal layer 21 and the ceramic substrate 10 can be improved.

[0026] However, if electromigration occurs in the silver contained in the base metal layer 21, the silver component contained in the base metal layer 21 spreads around the conductor pattern 20A along the upper surface 10t of the ceramic substrate 10. In this case, the electrical characteristics of the current flowing through the conductor pattern 20A become unstable.

[0027] Alternatively, as shown in FIG. 1, when conductive patterns 20A and 20B are adjacent to each other, depending on the degree of diffusion due to electromigration, there is a concern that conductive patterns 20A and 20B may be short-circuited via the diffused silver component.

[0028] Therefore, the inventors of the present invention have investigated methods for improving the bonding strength between the metal layer 22 and the ceramic substrate 10 while suppressing the electromigration of the silver component, and have found the structure of this embodiment.

[0029] 2 and 3, the conductive pattern 20A includes a metal base layer 21 formed on the upper surface 10t of the ceramic substrate 10, and a metal layer 22 formed on the upper surface 10t of the ceramic substrate 10 so as to cover the entire metal base layer 21. The metal base layer 21 contains copper, silver, and at least one of titanium and chromium. The metal layer 22 contains copper as a main component, and the weight percentage of silver contained in the metal layer 22 is smaller than the weight percentage of silver contained in the metal base layer 21. It is particularly preferable that the metal layer 22 does not contain silver. The side surface 21s of the metal base layer 21 is covered with the metal layer 22.

[0030] 4, the metal base layer 21 has a quadrangle shape in a plan view and has four side surfaces 21s. As shown in FIGS. 2 to 4, all of the four side surfaces 21s of the metal base layer 21 are covered with the metal layer 22.

[0031] Furthermore, the expression "the weight percentage of silver contained in the metal layer 22 is smaller than the weight percentage of silver contained in the base metal layer 21" also includes the case where the metal layer 22 does not contain silver. Furthermore, the "weight percentage of silver" means the weight percentage of silver contained per unit volume. In this embodiment, the weight percentage of silver in the metal layer 22 is at least 10% by weight or less, preferably 5% by weight or less, and particularly preferably 1% by weight or less. The lower the weight percentage of silver contained in the metal layer, the better, and as described above, it is particularly preferable that the metal layer 22 does not contain silver. In this way, when the side surface 21s of the base metal layer 21 is covered with the metal layer 22 having a small weight percentage of silver, electromigration of silver does not progress. Therefore, the wiring board SUB1 has higher electrical reliability than the wiring board SUB2 shown in FIG.

[0032] On the other hand, the base metal layer 21 contains silver and titanium, or silver and chromium, thereby improving the bonding strength with the ceramic substrate 10. For this reason, the weight percentage of silver contained in the base metal layer 21 is high, for example, about 20 to 30% by weight. Also, the weight percentage of titanium or chromium contained in the base metal layer 21 is, for example, about 1 to 5% by weight.

[0033] Therefore, the weight percentage of copper contained in the base metal layer 21 is lower than the weight percentage of copper contained in the metal layer 22. For example, the weight percentage of copper contained in the base metal layer 21 is about 30 to 50% by weight. On the other hand, the weight percentage of copper contained in the metal layer 22 is 90% or more.

[0034] 5, the area of ​​the contact surface between the base metal layer 21 and the ceramic substrate 10 is larger than the area of ​​the contact surface between the metal layer 22 and the ceramic substrate 10. As described above, the base metal layer 21 is a layer for strengthening the bonding strength between the ceramic substrate 10 and the conductive pattern 20A, and therefore the bonding strength is strengthened in proportion to the area of ​​the contact surface between the base metal layer 21 and the ceramic substrate 10.

[0035] On the other hand, if the contact surface area between the metal layer 22 and the ceramic substrate 10 is large enough, electromigration can be prevented from occurring on the side surface 21s of the base metal layer 21. Therefore, as long as the contact surface area between the metal layer 22 and the ceramic substrate 10 is larger than a certain value, the electromigration suppression effect remains almost constant. For example, in FIG. 2, the width W22F of the portion of the metal layer 22 that is in direct contact with the ceramic substrate 10 is approximately 30 μm to 50 μm. If the width W22F is 30 μm or more, electromigration can be suppressed.

[0036] Therefore, from the viewpoint of strengthening the bonding strength between the conductor pattern 20A and the ceramic substrate 10 and suppressing electromigration, it is preferable that the area of ​​the contact surface between the base metal layer 21 and the ceramic substrate 10 is larger than the area of ​​the contact surface between the metal layer 22 and the ceramic substrate 10, as shown in Figure 5.

[0037] Next, a detailed description will be given of the structure of each layer shown in Fig. 2 and Fig. 3. Fig. 6 is an enlarged cross-sectional view showing an example of the detailed structure of each layer constituting the conductor pattern shown in Fig. 2.

[0038] As shown in Figure 6, each of the metal base layer 21 and the metal layer 22 is a porous metal layer in which a plurality of metal particles 20P are bonded to one another. The density of the plurality of metal particles 22P in the metal layer 22 is higher than the density of the plurality of metal particles 21P in the metal base layer 21. The "density of the plurality of metal particles" is the value obtained by dividing the total weight of the plurality of metal particles per unit volume by the unit volume. Therefore, the larger the volume of the gaps contained in the metal layer, the lower the density of the plurality of metal particles.

[0039] Therefore, the above expression "the density of the plurality of metal particles 22P in the metal layer 22 is higher than the density of the plurality of metal particles 21P in the metal base layer 21" can be rephrased as "the average value of the volume of gaps existing per unit volume of the metal base layer 21 is larger than the average value of the volume of gaps existing per unit volume of the metal layer 22." Such a state can be determined as follows based on an image taken by a microscope such as an SEM (Scanning Electron Microscope).

[0040] That is, when a predetermined number (for example, about 3 to 10) of arbitrary cross sections of the conductor pattern 20 (cross sections obtained by cutting the conductor pattern 20 in the thickness direction) are photographed, the average value of the gap area per unit area of ​​the base metal layer 21 is larger than the average value of the gap area per unit area of ​​the metal layer 22. In this case, it is estimated that the average value of the volume of gaps existing per unit volume of the base metal layer 21 is larger than the average value of the volume of gaps existing per unit volume of the metal layer 22.

[0041] The plurality of metal particles 21P constituting the metal base layer 21 includes copper particles and silver particles, and also includes at least one of titanium particles and chromium particles.

[0042] On the other hand, the majority (e.g., 90% by weight or more) of the plurality of metal particles 22P constituting the metal layer 22 is copper particles. In the example shown in FIG. 6, all of the plurality of metal particles 22P are copper particles. As a variation of this embodiment, the plurality of metal particles 22P may contain metal particles other than copper particles. For example, with the aim of improving the characteristics of the metal layer 22, metal particles made of a metal other than copper may be contained in the plurality of metal particles 22P constituting the metal layer 22. However, as described above, from the viewpoint of suppressing electromigration, it is preferable that the weight ratio of silver particles contained in the plurality of metal particles 22P is a small value including zero.

[0043] The weight ratio of copper contained in metal layer 22 and base metal layer 21 can also be expressed as follows: The weight ratio of copper contained in metal layer 22 is greater than the weight ratio of copper contained in base metal layer 21.

[0044] That is, the metal layer 22 contains more copper than the underlying metal layer 21. Therefore, the electrical properties of the metal layer 22 are higher than the electrical properties of the underlying metal layer 21. Alternatively, the thermal conductivity of the metal layer 22 is higher than the thermal conductivity of the underlying metal layer 21. That is, the metal layer 22 conducts heat more easily than the underlying metal layer 21.

[0045] 2, in the region overlapping with the metal base layer 21, the thickness T22 of the metal layer 22 is greater than the thickness T21 of the metal base layer 21. In other words, the thickness T21 of the metal base layer 21 is smaller than the thickness T22 of the metal layer 22. In this case, the electrical characteristics of the conductor pattern 20A are determined mainly by the electrical characteristics of the metal layer 22, and therefore, degradation of the electrical characteristics due to the use of the metal base layer 21 can be suppressed.

[0046] For example, the thickness T21 of the base metal layer 21 is, for example, about 10 μm to 20 μm. On the other hand, the thickness T22 of the metal layer 22 is, for example, about 100 μm to 300 μm. As will be described in detail later, the upper limit of the thickness T22 is set to 300 μm due to constraints in the manufacturing process. If a method described later as a modified example of the method for manufacturing the wiring board is used, the value of the thickness T22 can exceed 300 μm, for example, about 1 mm.

[0047] Alternatively, the following can be said from the viewpoint of thermal conductivity: By reducing the thickness T21 of the base metal layer 21, which has a lower thermal conductivity than the metal layer 22, the distance between the metal layer 22 and the ceramic substrate 10 is shortened in the portion where the metal layer 22 and the base metal layer 21 are stacked. In other words, the section occupied by the base metal layer 21 in the heat conduction path from the metal layer 22 to the ceramic substrate 10 can be shortened, thereby improving the thermal conductivity of the conductor pattern 20A as a whole.

[0048] As explained using Fig. 1, the wiring board SUB1 has a plurality of conductor patterns 20 spaced apart from one another. While the structure of conductor pattern 20A has been explained as a representative example in Figs. 1 to 3, 5, and 6, each of conductor patterns 20B, 20C, and 20D shown in Fig. 1 has a similar structure to conductor pattern 20A. Therefore, the wiring board SUB1 shown in Fig. 1 can be expressed, for example, as follows:

[0049] That is, the wiring board SUB1 further includes a conductor pattern 20B formed on the upper surface 10t of the ceramic substrate 10 so as to be spaced apart from the conductor pattern 20A. In a plan view, the conductor pattern 20A and the conductor pattern 20B are adjacent to each other. The conductor pattern 20B includes a base metal layer 21 and a metal layer 22, similar to the conductor pattern 20A shown in FIGS. 1 to 3, 5, and 6.

[0050] The wiring board SUB1 also has a plurality of conductor patterns 20 spaced apart from one another on the upper surface 10t of the ceramic substrate 10. Each of the plurality of conductor patterns 20 includes a base metal layer 21 and a metal layer 22, similar to the conductor pattern 20A shown in FIGS.

[0051] In this way, in a structure in which multiple conductor patterns 20 are arranged so as to be spaced apart from each other in a planar view, if the above-mentioned electromigration occurs, there is a concern that a short circuit may occur between adjacent conductor patterns 20 depending on the degree of diffusion of the silver component.

[0052] 2 to 5, the side surfaces 21s of the metal base layer 21 of each of the plurality of metal base patterns 20 are covered with the metal layer 22 having a small weight percentage of silver, thereby suppressing electromigration of the silver component contained in the metal base layer 21. Therefore, short circuits between adjacent metal base patterns 20 can be prevented.

[0053] <Modifications of the Conductor Pattern Structure> Next, modified examples of the conductor pattern 20A shown in Fig. 2 will be described. Fig. 7 is an enlarged transparent plan view of a wiring board which is a modified example of the wiring board shown in Fig. 5. Fig. 8 is an enlarged cross-sectional view taken along line CC in Fig. 7. Fig. 9 is an enlarged cross-sectional view taken along line DD in Fig. 7. Fig. 10 is an enlarged cross-sectional view showing a detailed structural example of each layer constituting the conductor pattern shown in Fig. 8.

[0054] 7 to 10 can be applied by replacing one or more of the plurality of conductor patterns 20 shown in Fig. 1. Therefore, the wiring board SUB3 shown in Fig. 7 to 10 has a plurality of conductor patterns 20 formed on the upper surface 10t, similar to the wiring board SUB1 shown in Fig. 1. Furthermore, each of the plurality of conductor patterns 20 has a structure similar to that of the conductor pattern 20E described below.

[0055] The wiring board SUB3 shown in FIGS. 7 to 10 differs from the wiring board SUB1 shown in FIGS. 1 to 3, 5, and 6 in the following points.

[0056] First, the conductor pattern 20E of the wiring board SUB3 includes, in addition to the already-described base metal layer 21 and metal layer 22, a base metal layer 23 formed on the base metal layer 21. Each of the base metal layer 21 and the base metal layer 23, including the side surface 21s of the base metal layer 21 and the side surface 23s of the base metal layer 23, is entirely covered with the metal layer 22.

[0057] The wiring board SUB1 has a structure including a single metal base layer 21. However, the metal base layer may be a single layer, or, as in the wiring board SUB3, may be a laminated film including multiple layers. When the metal base layer is a laminated film including multiple layers, as shown in FIG. 7, if the metal base layer 21 and the metal base layer 23 each form a quadrangle in plan view, the metal base layer 21 has four side surfaces 21s, and the metal base layer 23 has four side surfaces 23s. In this case, even if the metal base layer 23 contains silver, electromigration due to the silver contained in the metal base layer 23 can be prevented.

[0058] In this modification, the base metal layer 23 contains copper as a main component. Specifically, 90% by weight or more of the metal elements constituting the base metal layer 23 are copper elements. The weight percentage of silver contained in the base metal layer 23 is smaller than the weight percentage of silver contained in the base metal layer 21. For example, the weight percentage of silver per unit volume of the base metal layer 23 is 1% by weight or less.

[0059] As will be described in more detail later, in the manufacturing process of a wiring board, when a metal film such as silver, titanium, or chromium is formed on the upper surface of the base metal layer and metal layer 22 is laminated on top of the base metal layer, it may be difficult to bond the metal film other than copper formed on the upper surface of the base metal layer to metal layer 22.

[0060] In this modified example, the base metal layer 23, which has a higher copper purity than the base metal layer 21, is interposed between the base metal layer 21 and the metal layer 22, resulting in a good bond between the metal layer 22 and the base metal layer 23. Furthermore, by forming the base metal layer 21 and the base metal layer 23 together, a good bond is obtained at the boundary between the base metal layer 21 and the base metal layer 23. As a result, the multiple metal layers that make up the conductor pattern 20A are firmly bonded to each other and to the ceramic substrate 10.

[0061] 10 , each of the metal base layer 21, the metal base layer 23, and the metal layer 22 is a porous metal layer in which a plurality of metal particles 20P are bonded to one another. The density of the plurality of metal particles 22P in the metal layer 22 is higher than the density of the plurality of metal particles 21P in the metal base layer 21. The density of the plurality of metal particles 23P in the metal base layer 23 is higher than the density of the plurality of metal particles in the metal layer 22.

[0062] When a dense base metal layer 23 is interposed between the base metal layer 21 and the metal layer 22 as in this modification, the bonding strength between the metal layers is improved compared to the example described with reference to Fig. 6. In other words, according to this modification, the base metal layer 23 and the metal layer 22 are less likely to peel from the base metal layer 21 that constitutes the conductor pattern 20E. As a result, the conductor pattern 20E of the wiring board SUB3 is less likely to peel from the ceramic substrate 10, thereby improving reliability.

[0063] Incidentally, the base metal layer 23 contains copper as a main component and has a small weight percentage of silver. For this reason, a modified embodiment is one in which the base metal layer 23 itself is used in place of the metal layer 22 shown in Figures 2 and 3. In this case, the base metal layer 23 is denser than the metal layer 22, and therefore the electrical properties and thermal conductivity properties are improved compared to the conductor pattern 20A shown in Figure 2.

[0064] However, the dense base metal layer 23 is difficult to thicken compared to the metal layer 22. Therefore, even when the base metal layer 23 contains copper as a main component and the weight percentage of silver is small, as in this modified example, it is preferable that the metal layer 22 be formed so as to cover the base metal layer 23.

[0065] 8 and 9, in the region overlapping with the metal base layer 21, the thickness T22 of the metal layer 22 is greater than the sum of the thickness T21 of the metal base layer 21 and the thickness T23 of the metal base layer 23. Therefore, the electrical characteristics or heat conduction characteristics of the conductor pattern 20A are determined mainly by the characteristics of the metal layer 22.

[0066] For example, the thickness T21 of the metal base layer 21 and the thickness T23 of the metal base layer 23 are each, for example, about 10 μm to 20 μm, while the thickness T22 of the metal layer 22 is about 100 μm to 300 μm.

[0067] Since the weight proportion of silver in the base metal layer 23 is small, as a modified example of Figures 8 and 9, a structure can be used in which each of the multiple side surfaces 21s of the base metal layer 21 is covered with the base metal layer 23 and a portion of the base metal layer 23 is in contact with the ceramic substrate 10.

[0068] However, it is necessary to increase the thickness T23 of the metal base layer 23 in order to reliably cover each of the multiple side surfaces 21s of the metal base layer 21. In this case, it is necessary to solve the problem of difficulty in increasing the thickness of the metal base layer 23, as described above.

[0069] Therefore, even if the weight proportion of silver in the base metal layer 23 is small, as in this modified example, it is preferable that the base metal layer 23 is formed only on the base metal layer 21, and each of the multiple side surfaces 21s of the base metal layer 21 is covered with the metal layer 22. Except for the differences described above, the wiring board SUB3 shown in Figures 7 to 10 is similar to the wiring board SUB1 described with reference to Figures 1 to 3, 5, and 6. Therefore, a duplicated description will be omitted.

[0070] <Other Modified Examples of Wiring Board> Next, another modified example of the wiring board SUB1 will be described. Fig. 11 is a bottom view of a wiring board which is a modified example of the wiring board shown in Fig. 1. Fig. 12 is a cross-sectional view taken along line EE in Fig. 11.

[0071] 1 to 3, 5, and 6 in that the wiring board SUB4 shown in Figures 11 and 12 has a conductor pattern 20F formed on the lower surface 10b in addition to the plurality of conductor patterns 20 formed on the upper surface 10t as shown in Figure 12. In other words, the wiring board SUB4 further has a conductor pattern 20F formed on the lower surface 10b of the ceramic substrate 10 in addition to the conductor pattern 20A shown in Figure 2.

[0072] Let us consider the case where a temperature cycle load is applied to the wiring board SUB4. When a temperature cycle load is applied to the wiring board SUB4, the linear expansion coefficients of the plurality of conductor patterns 20 made of a metal layer and the ceramic substrate 10 are different. Therefore, from the viewpoint of reducing the stress applied to the wiring board SUB4 due to the temperature cycle load, it is preferable to form conductor patterns with similar linear expansion coefficients on both the top surface 10t and the bottom surface 10b, as in the wiring board SUB4.

[0073] The conductor pattern 20F formed on the lower surface 10b may not be used as a terminal or wiring. Even in this case, it is preferable that the bond between the conductor pattern 20F and the ceramic substrate 10 is strong. Therefore, the conductor pattern 20F includes a base metal layer 21A and a metal layer 22A laminated on the base metal layer 21A. The base metal layer 21A is a member similar to the base metal layer 21 already described, except that the metal layer 22A does not cover the side surfaces 21s of the base metal layer 21A. Furthermore, the metal layer 22A is a member similar to the metal layer 22 already described, except that the metal layer 22A does not cover the side surfaces 21s of the base metal layer 21A.

[0074] If the conductive pattern 20F is not used as a terminal or wiring, even if electromigration occurs in the conductive pattern 20F, it may not cause a deterioration in the performance of the wiring board SUB4. For this reason, in the example shown in FIG. 12, each of the multiple side surfaces 21s of the base metal layer 21A is not covered with the metal layer 22. In this case, the manufacturing process for forming the conductive pattern 20F is simpler than the process for forming the multiple conductive patterns 20 on the upper surface 10t of the ceramic substrate 10.

[0075] 12, a modified example of the conductor pattern 20F may include a metal base layer 21A and a metal layer 22A, similar to the conductor pattern 20A. In other words, each of the side surfaces 21s of the metal base layer 21A of the conductor pattern 20F may be covered with a metal layer 22A. In this case, electromigration caused by the silver component contained in the metal base layer 21A can be suppressed, and the conductor pattern 20F can be used as a terminal or a conductive path such as wiring.

[0076] As a modification of FIG. 11, a plurality of conductor patterns 20F spaced apart from one another may be formed on the lower surface 10b.

[0077] <Method of manufacturing wiring board> Next, a method for manufacturing a wiring board will be described. The method for manufacturing the wiring board SUB3 shown in Figures 7 to 10 will be described as an example. In the case of the method for manufacturing the wiring board SUB1 shown in Figures 1 to 3, 5 and 6, some of the manufacturing steps described below can be omitted. Below, steps that can be omitted in the case of the method for manufacturing the wiring board SUB1 will be explained accordingly.

[0078] In the method for manufacturing a wiring board described below, which will be described in detail later, when forming each of the plurality of conductor patterns 20 shown in Fig. 1, for example, a paste material containing a plurality of metal particles is applied and then fired to form the pattern. This method has the following advantages compared to a method of forming a conductor pattern by removing a portion of a metal film by etching.

[0079] In the wiring board manufacturing method described below, etching is not required, so undercutting due to overetching or residue of the underlying metal layer due to underetching does not occur. Furthermore, in the present embodiment, since etching is not required, many steps can be omitted, including the step of forming an etching mask. As a result, manufacturing efficiency is improved.

[0080] Fig. 13 is an explanatory diagram showing an example of a manufacturing process for a wiring board according to an embodiment of the present invention. In Fig. 13, manufacturing steps that can be omitted in the manufacturing method for the wiring board SUB1 shown in Figs. 1 to 3, 5, and 6 are shown in parentheses.

[0081] 13, the method for manufacturing a wiring board includes a ceramic substrate preparation step, a first base metal paste application step, a second base metal paste application step, a base layer firing step, a first metal paste application step, and a first metal layer firing step. Each step will be described in detail below.

[0082] First, in the ceramic substrate preparation step, a ceramic substrate 10 is prepared before application of a base metal paste 21PS, as shown in FIG. 14, which will be described later. The ceramic substrate 10 has an upper surface 10t and a lower surface 10b opposite to the upper surface 10t. The ceramic substrate 10 is made of, for example, silicon nitride or aluminum nitride.

[0083] Even when the ceramic substrate 10 is made of, for example, silicon nitride or aluminum nitride, it may contain elements other than silicon or aluminum. For example, other elements may be added to improve the characteristics of the ceramic substrate 10. Alternatively, the ceramic substrate 10 may contain elements that are inevitably mixed in during the manufacturing process.

[0084] Next, in the first base metal paste application step, a base metal paste 21PS is applied to the upper surface 10t of the ceramic substrate 10, as shown in Fig. 14. Fig. 14 is an enlarged cross-sectional view showing the first base metal paste application step shown in Fig. 13. The base metal paste 21PS is a paste-like material containing a plurality of metal particles 21P and a binder material 21B made of an organic material. The plurality of metal particles 21P are dispersed in the binder material 21B.

[0085] The metal particles 21P include at least one of titanium particles and chromium particles in addition to copper particles and silver particles, i.e., the metal base paste 21PS includes at least one of titanium particles and chromium particles in addition to copper particles and silver particles.

[0086] In this process, for example, the base metal paste 21PS is ejected onto the upper surface 10t of the ceramic substrate 10 from a dispenser not shown, thereby obtaining a state in which the base metal paste 21PS is applied onto the upper surface 10t, as shown in Figure 14.

[0087] Next, in the second base metal paste application step, a base metal paste 23PS is applied onto the base metal paste 21PS, as shown in FIG. 15. FIG. 15 is an enlarged cross-sectional view showing the second base metal paste application step shown in FIG. 13. The base metal paste 23PS is a paste-like material containing a plurality of metal particles 23P and a binder material 23B made of an organic material. The plurality of metal particles 23P are dispersed in the binder material 23B. Note that the binder material 23B is made of the same organic material as the binder material 21B shown in FIG. 14, for example.

[0088] The weight percentage of copper particles contained in base metal paste 23PS is greater than the weight percentage of copper particles contained in base metal paste 21PS, and the weight percentage of silver particles contained in base metal paste 23PS is preferably smaller than the weight percentage of silver particles contained in base metal paste 21PS.

[0089] The weight percentage of copper particles contained in the base metal paste 21PS is, for example, about 30 to 50% by weight. The weight percentage of silver particles contained in the base metal paste 21PS is, for example, about 20 to 40% by weight. The weight percentage of titanium particles or chromium particles contained in the base metal paste 21PS is, for example, about 1 to 5% by weight. The weight percentage of copper particles contained in the base metal paste 23PS is, for example, 90% by weight or more. The weight percentage of silver particles contained in the base metal paste 23PS is, for example, 5% by weight or less.

[0090] In this process, for example, the base metal paste 23PS is ejected onto the base metal paste 21PS from a dispenser not shown, thereby obtaining a state in which the base metal paste 23PS is applied onto the base metal paste 21PS, as shown in FIG.

[0091] 1 to 3, 5, and 6, the second base metal paste application step can be omitted. In this case, the base layer firing step is carried out after the first base metal paste application step.

[0092] Next, in the base layer firing step, the base metal paste 21PS and the base metal paste 23PS shown in Fig. 15 are fired to form a laminate of the base metal layer 21 and the base metal layer 23 shown in Fig. 16. Fig. 16 is an enlarged cross-sectional view showing the state in which the base metal layer 21 and the base metal layer 23 have been formed by the base layer firing step shown in Fig. 13.

[0093] In this process, for example, the ceramic substrate 10 coated with the base metal paste 21PS and the base metal paste 23PS is placed in a firing furnace (not shown), and then fired under preset firing conditions (firing temperature and firing time). In this process, the binder material 21B shown in Fig. 14 and the binder material 23B shown in Fig. 15 evaporate.

[0094] In this step, the plurality of metal particles 21P shown in FIG. 14 and the plurality of metal particles 23P shown in FIG. 15 are bonded (connected) to each other, and the sintered metal base layer 21 (see FIG. 16) and the metal base layer 23 (see FIG. 16) are obtained. In addition, the metal particles 21P and the metal particles 23P are partially bonded at the boundary between the metal base layer 21 and the metal base layer 23. This results in an underlying layer that is an integrally formed laminated structure.

[0095] If the firing temperature in this step is excessively high, only the surface of the paste will be fired rapidly. As a result, firing will proceed at uneven speeds between the surface and the interior of the paste, resulting in a large difference in shrinkage rate, which may cause cracks to form in the metal layer. In this case, there is a concern that cracks may occur in parts of the base metal layer 21 and base metal layer 23 shown in FIG. 16. Therefore, it is preferable to fire at a firing temperature of 1000°C or less, for example, about 600 to 900°C.

[0096] In the example shown in Fig. 13, the base layer firing step is not included between the first base metal paste application step and the second base metal paste application step, but are performed consecutively. Since the thickness of the base metal paste 21PS and the thickness of the base metal paste 23PS shown in Fig. 15 are each thin, about 10 to 20 µm, if the base layer firing step is performed after the two layers are stacked, the organic components contained in the paste material can be removed all at once.

[0097] Furthermore, as shown in FIG. 13, a manufacturing process in which the first base metal paste application step and the second base metal paste application step are successively performed, and then the base layer firing step is performed, is preferable in the following respects.

[0098] As already explained, the base metal paste 21PS shown in FIG. 14 contains a large number of silver particles in addition to copper particles. The base metal paste 21PS also contains titanium particles or chromium particles. The inventors of the present application have found that when the base metal paste 21PS is fired alone, a metal thin film made of silver, titanium, or chromium may be formed on the surface of the resulting base metal layer 21 (see FIG. 16). In this way, when a metal thin film containing a large number of metals other than copper is formed on the surface of the base metal layer 21, it may be difficult to bond the base metal layer 21 and the base metal layer 23 shown in FIG. 16 together.

[0099] On the other hand, when the base metal paste 21PS and the base metal paste 23PS shown in Figure 15 are fired together as in this embodiment, they are sintered without forming a thin metal film on the surface of the base metal layer 21, so the bonding state between the base metal layer 21 and the base metal layer 23 shown in Figure 16 is good.

[0100] Furthermore, as described above, since the base metal layer 23 is a metal layer containing copper as its main component, it is difficult to form a metal film made of a metal other than copper, such as silver, titanium, or chromium, on its surface. Therefore, in the first metal layer firing step shown in Fig. 13, the bonding state between the base metal layer 23 and the metal layer 22 shown in Fig. 18, which will be described later, is also good.

[0101] If the manufacturing process includes the second base metal paste application step shown in Figure 13, the number of steps will increase compared to omitting this step, but from the perspective of improving the reliability of the conductor pattern, it is preferable to include the second base metal paste application step.

[0102] Next, in the first metal paste application step, as shown in Fig. 17, metal paste 22PS is applied so as to entirely cover base metal layer 21 and base metal layer 23. Fig. 17 is an enlarged cross-sectional view showing the first metal paste application step shown in Fig. 13.

[0103] The metal paste 22PS is a paste-like material containing a plurality of metal particles 22P and a binder material 22B made of an organic material. The plurality of metal particles 22P are dispersed in the binder material 22B. The binder material 22B is made of the same organic material as the binder material 21B shown in FIG. 14, for example.

[0104] The weight ratio of copper particles contained in metal paste 22PS is greater than the weight ratio of copper particles contained in base metal paste 21PS, and the weight ratio of silver particles contained in base metal paste 21PS is smaller than the weight ratio of silver particles contained in the base metal layer.

[0105] In this step, for example, the metal paste 22PS is discharged onto the metal base layer 23 from a dispenser (not shown), thereby obtaining a state in which the metal paste 22PS is applied onto the metal base layer 23, as shown in Fig. 17. In the case of the method for manufacturing the wiring board SUB1 shown in Figs. 1 to 3, 5 and 6, the metal paste 22PS is applied to the metal base layer 21.

[0106] As shown in FIG. 17 , in the present embodiment, in the first metal paste application step, the side surface 21s of the metal base layer 21 is covered with the metal paste 22PS. Similarly, the side surface 23s of the metal base layer 23 is covered with the metal paste 22PS. While FIG. 17 illustrates only one side surface 21s of the metal base layer 21 and one side surface 23s of the metal base layer 23, in this step, all of the side surfaces 21s of the metal base layer 21 and all of the side surfaces 23s of the metal base layer 23 are covered with the metal paste 22PS. Furthermore, a portion of the metal paste 22PS is applied so as to contact the upper surface 10t of the ceramic substrate 10. As a result, the metal base layer 21 and the metal base layer 23 are sealed with the metal paste 22PS.

[0107] In this step, all side surfaces 21s of the metal base layer 21 and all side surfaces 23s of the metal base layer 23 are covered with the metal paste 22PS, so that, as already explained, occurrence of electromigration caused by the metal base layer 21 can be suppressed.

[0108] Next, in the first metal layer firing step, the metal paste 22PS shown in Fig. 17 is fired to form the metal layer 22 shown in Fig. 18. Fig. 18 is an enlarged cross-sectional view showing the state in which the metal layer has been formed by the first metal layer firing step shown in Fig. 13.

[0109] In this process, for example, the ceramic substrate 10 coated with the metal paste 22PS is placed in a firing furnace (not shown), and then fired under preset firing conditions (firing temperature and firing time). In this process, the binder material 22B shown in FIG. 17 evaporates.

[0110] In this step, the plurality of metal particles 22P shown in Fig. 17 are bonded (connected) to one another, and a metal layer 22 (see Fig. 18) is obtained as a sintered body. Furthermore, at the boundary between the metal layer 22 and the metal base layer 23, a portion of the metal particles 22P is bonded to the metal base layer 23. This results in a conductor pattern 20E (see Fig. 18) that is an integrally formed laminated structure.

[0111] As already explained, if the firing temperature in the firing step is excessively high, cracks may occur in the paste during firing, which may cause deformation of the applied paste. Therefore, in this step as well, similarly to the above-mentioned underlayer firing step, the firing temperature is preferably 1000°C or less, for example, about 600 to 900°C.

[0112] As shown in Fig. 13, in this embodiment, the base layer firing step is performed before the first metal paste application step. In other words, the base layer and metal layer 22 are not formed at the same time. Since metal layer 22 is the main layer of conductive pattern 20, it needs to have a certain thickness. Therefore, when base metal paste 21PS and base metal paste 23PS shown in Fig. 15 are sealed with metal paste 22PS shown in Fig. 17 and then fired together, binder material 21B (see Fig. 14) and binder material 23B (see Fig. 15) may not be sufficiently removed.

[0113] In the present embodiment, the base layer firing step is performed before the first metal paste application step, so that the binder material 21B (see FIG. 14) and the binder material 23B (see FIG. 15) can be reliably removed.

[0114] Through the above steps, the wiring board SUB3 described with reference to Figures 7 to 10 or the wiring board SUB1 shown in Figures 1 to 3, 5, and 6 is obtained. Note that if the multiple conductor patterns 20 have similar structures, the multiple conductor patterns 20 can be formed at the same time. This makes it possible to avoid a decrease in manufacturing efficiency due to a large number of conductor patterns 20.

[0115] <Modification of manufacturing method> Next, a modified example of the method for manufacturing a wiring board will be described. Fig. 19 is an explanatory diagram showing an example of a manufacturing process for a wiring board which is a modified example of Fig. 13. Fig. 20 is an enlarged cross-sectional view showing the second metal paste application step shown in Fig. 19. Fig. 21 is an enlarged view showing the second metal layer firing step shown in Fig. 19.

[0116] The modified example shown in FIG. 19 differs from the wiring board manufacturing method shown in FIG. 13 in that it includes a second metal paste applying step and a second metal layer firing step after the first metal layer firing step.

[0117] As already explained, if the thickness of the paste to be fired at one time is large, the binder material contained in the base metal paste 21PS and the base metal paste 23PS may not be sufficiently removed. According to the study by the inventors of the present application, from the viewpoint of removing the binder material, the thickness T22 of the metal layer 22 shown in Figures 2 and 8 is preferably 300 μm or less.

[0118] On the other hand, the thickness of the conductive pattern 20 (see FIG. 2) is not limited to 300 μm or less, and may require a thickness of, for example, about 1 mm. In this modification, by repeating the first metal paste application step and the first metal layer firing step already described, a conductive pattern 20 with a thickness exceeding 300 μm can be obtained.

[0119] In the second metal paste application step shown in FIG. 19, a metal paste 24PS is applied onto the metal layer 22 as shown in FIG. 20. The metal paste 24PS contains a plurality of metal particles 24P and a binder material 24B. The metal paste 24PS is made of the same material as the metal paste 22PS shown in FIG. 17. For example, the plurality of metal particles 24P contain copper particles in the same weight ratio as the plurality of metal particles 22P shown in FIG. 17. The binder material 24B is made of the same organic material as the binder material 22B shown in FIG. 17.

[0120] When the metal paste 22PS shown in FIG. 17 and the metal paste 24PS shown in FIG. 20 are made of the same material, the boundary between the metal layer 22 and the metal layer 24 shown in FIG. 21 can be joined well.

[0121] Next, in the second metal layer firing step shown in Fig. 19, after the second metal paste application step, the metal paste 24PS shown in Fig. 20 is fired to form the metal layer 24 shown in Fig. 21. In this step, the multiple metal particles 24P shown in Fig. 20 are bonded (connected) to each other, and the metal layer 24 (see Fig. 21) is obtained as a sintered body.

[0122] Furthermore, at the boundary between metal layer 24 and metal layer 22, a portion of metal particles 24P is bonded to metal layer 22. When metal paste 24PS shown in Fig. 21 is made of the same material as metal PS shown in Fig. 17, the boundary between metal layer 22 and metal layer 24 is apparently bonded to an extent that it is difficult to visually recognize.

[0123] The firing temperature in this step is preferably 1000°C or less, for example, about 600 to 900°C, as in the above-mentioned underlayer firing step and first metal layer firing step.

[0124] The thickness T24 of the metal layer 24 obtained by this step (see FIG. 21) is 300 μm or less. If the thickness T22 and the thickness T24 shown in FIG. 21 are each 300 μm, the resulting conductive pattern 20 has a total thickness of 600 μm.

[0125] 19 shows the process up to the second metal layer firing step, but if the thickness of the conductive pattern 20 is to be increased further, the second metal paste application step and the second metal layer firing step are repeated after the second metal layer firing step, thereby obtaining a conductive pattern 20 with a thickness exceeding 600 μm.

[0126] Metal layer 22 (see FIG. 21) and metal layer 24 (see FIG. 21) are layers thicker than the underlying metal layer (underlying metal layer 21 and underlying metal layer 23 shown in FIG. 21). Therefore, if metal paste 22PS (see FIG. 17) and metal paste 24PS (see FIG. 20) are fired together, just as underlying metal layer 21 and underlying metal layer 23 are formed together in the manufacturing process of the underlying metal layer, there is a concern that the weight of the laminated metal pastes themselves will cause the shape of the wiring to collapse before firing. Therefore, by applying metal paste 24PS after firing metal paste 22PS to form metal layer 22, a thick wiring layer can be formed without collapsing the shape.

[0127] Fig. 22 is an enlarged cross-sectional view showing a second base metal paste applying step which is a modification of Fig. 15. Fig. 23 is an enlarged cross-sectional view of a conductor pattern obtained by the modification shown in Fig. 22.

[0128] The modified example shown in FIG. 22 differs from the wiring board manufacturing method shown in FIG. 15 in that in the second base metal paste application step, side surfaces 21s of base metal paste 21PS are covered with base metal paste 23PS.

[0129] 23, the wiring board SUB5 manufactured by the wiring board manufacturing method shown in Fig. 22 differs from the wiring board SUB3 shown in Fig. 8 in the following respects: In other words, the conductive pattern 20A of the wiring board SUB5 has a side surface 21s of the base metal layer 21 covered with the base metal layer 23, and a side surface 23s of the base metal layer 23 covered with the metal layer 22.

[0130] As already explained, when the base metal paste 21PS and the base metal paste 23PS shown in FIG. 22 are fired together in the manufacturing process of a wiring board, they are sintered before a metal film is formed on the surface of the base metal paste 21PS, so that the bonding state between the base metal layer 21 and the base metal layer 23 shown in FIG. 23 is good.

[0131] Therefore, in this modification, the bonding strength between the side surface 21s of the underlying metal layer 21 and the underlying metal layer 23 is better than the bonding strength between the side surface 21s of the underlying metal layer 21 and the metal layer 22 shown in FIG.

[0132] Although several representative embodiments have been described above using the drawings, there are various other variations of the above-described embodiments and variations. Parts of the embodiments can be modified as appropriate within the scope of the above-described explanation. Furthermore, for example, parts of the above-described embodiments and variations can be combined with parts of other embodiments. [Explanation of symbols]

[0133] 10 Ceramic substrate 10b Bottom surface (side) 10t top surface (side) 20, 20A, 20B, 20C, 20D, 20E, 20F Conductor pattern 20P,21P,22P,23P,24P metal particles 21,21A,23 Base metal layer 21B, 22B, 23B, 24B Binder material 21PS, 23PS Base metal paste 21s,23s side 22,22A,24 Metal layer 22PS, 24PS metal paste SUB1, SUB2, SUB3, SUB4, SUB5 wiring board T21, T22, T23, T24 thickness W22F width

Claims

1. a ceramic substrate having a first surface and a second surface opposite to the first surface; a first conductor pattern formed on the first surface of the ceramic substrate; and The first conductor pattern is a first base metal layer formed on the first surface of the ceramic substrate; a first metal layer formed on the first surface of the ceramic substrate so as to cover the entire first base metal layer; Including, the first metal underlayer contains at least one of titanium and chromium in addition to copper and silver; the first metal layer contains copper as a main component, and the weight percentage of silver contained in the first metal layer is smaller than the weight percentage of silver contained in the first base metal layer; A wiring board, wherein a side surface of the first base metal layer is covered with the first metal layer.

2. In claim 1, each of the first base metal layer and the first metal layer is a porous metal layer in which a plurality of metal particles are bonded to one another; A wiring board, wherein the density of the plurality of metal particles in the first metal layer is higher than the density of the plurality of metal particles in the first base metal layer.

3. In claim 2, a thickness of the first metal layer greater than a thickness of the first underlying metal layer in a region where the first metal layer and the first underlying metal layer overlap;

4. In claim 1, The first conductor pattern is a second metal underlayer formed on the first metal underlayer, A wiring board, wherein each of the first and second underlying metal layers is entirely covered with the first metal layer, including the side surfaces of the first and second underlying metal layers.

5. In claim 4, the second underlying metal layer contains copper as a main component, each of the first underlying metal layer, the second underlying metal layer, and the first metal layer is a porous metal layer in which a plurality of metal particles are bonded to one another; a density of the plurality of metal particles in the first metal layer is higher than a density of the plurality of metal particles in the first metal base layer; A wiring board, wherein the density of the plurality of metal particles in the second underlying metal layer is higher than the density of the plurality of metal particles in the first metal layer.

6. In claim 4, A wiring board, wherein in the region where the first metal layer, the first underlying metal layer, and the second underlying metal layer overlap, the thickness of the first metal layer is greater than the sum of the thickness of the first underlying metal layer and the thickness of the second underlying metal layer.

7. In claim 1, The first conductor pattern is a second metal underlayer formed on the first metal underlayer, A wiring board, wherein a side surface of the first underlying metal layer is covered with the second underlying metal layer, and a side surface of the second underlying metal layer is covered with the first metal layer.

8. In claim 1, A wiring board, wherein the area of ​​the contact surface between the first base metal layer and the ceramic substrate is larger than the area of ​​the contact surface between the first metal layer and the ceramic substrate.

9. In claim 1, a second conductor pattern formed on the first surface of the ceramic substrate and spaced apart from the first conductor pattern; In a plan view, the first conductor pattern and the second conductor pattern are arranged adjacent to each other, The second conductor pattern is the first underlying metal layer; the first metal layer; a wiring board including:

10. In claim 1, The ceramic substrate is a wiring substrate made of silicon nitride or aluminum nitride.

11. In claim 1, The wiring board further comprises a third conductor pattern formed on the second surface of the ceramic substrate.

12. (a) providing a ceramic substrate having a first surface and a second surface opposite the first surface; (b) applying a first base metal paste onto the first surface of the ceramic substrate; (c) firing the first undercoat metal paste to form a first undercoat metal layer; (d) after the step (c), applying a first metal paste to cover the entire first base metal layer; (e) after the step (d), firing the first metal paste to form a first metal layer; Including, the first metal base paste contains at least one of titanium particles and chromium particles in addition to copper particles and silver particles; a weight ratio of copper particles contained in the first metal paste is greater than a weight ratio of copper particles contained in the first base metal paste, and a weight ratio of silver particles contained in the first metal paste is less than a weight ratio of silver particles contained in the first base metal paste; In the step (d), the side surface of the first metal underlayer is covered with the first metal paste.

13. In claim 12, (f) applying a second base metal paste onto the first base metal paste after the step (b) and before the step (c); Further comprising: In the step (c), the first base metal paste and the second base metal paste are fired together to form the first base metal layer and the second base metal layer laminated on the first base metal layer together; A method for manufacturing a wiring substrate, wherein the weight ratio of copper particles contained in the second base metal paste is greater than the weight ratio of copper particles contained in the first metal paste.

14. In claim 13, (g) applying a second metal paste onto the first metal layer after the step (e); (h) after the step (g), firing the second metal paste to form a second metal layer; The method for manufacturing a wiring board further comprises:

15. In claim 14, The method for manufacturing a wiring substrate, wherein the second metal paste is made of the same material as the first metal paste.

16. In claim 13, In the step (f), the side surfaces of the first base metal paste are covered with a second base metal paste.

Images