Wiring board and method for manufacturing conductive layer

Abstract

To improve the smoothness and uniformity of the film thickness of a conductive film provided on a wiring substrate.SOLUTION: A wiring board includes a base material and a conductive film disposed inside the base material and having electrical conductivity, and the conductive film has a coefficient of variation of thickness of 0.05 or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Conventionally, known methods for patterning metal wiring in electronic components and the like include printing methods using a screen mask, photolithography, and laser patterning (see, for example, Patent Documents 1 to 4). Patent Document 1 describes a screen printing plate on which an anti-reflection film that reduces light reflectance is formed. Patent Document 2 describes a method for manufacturing a wiring structure that enables high-precision, fine patterning. Patent Document 3 describes a patterning process that uses laser processing technology. Patent Document 4 describes a manufacturing method in which an intermediate transfer material with a weaker surface adhesive strength than the green sheet is used to transfer a metal plating film from a green sheet to an intermediate transfer material. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-334058 [Patent Document 2] Japanese Patent Application Publication No. 2017-224645 [Patent Document 3] Patent Publication No. 2021-111744 [Patent Document 4] Japanese Patent Application Laid-Open No. 2008-130607 Summary of the Invention [Problem to be solved by the invention]

[0004] To achieve component miniaturization and precise temperature control, a patterning method capable of forming a more accurate and uniform film thickness is required. The so-called conventional screen printing method described in Patent Document 1 enables patterning at low cost. However, bleeding and blurring occur during printing, resulting in poor film thickness uniformity of the manufactured conductor. The manufacturing method described in Patent Document 2 can achieve high-precision and fine patterning, but requires a complex process, resulting in high cost and a long process time. Furthermore, there are issues such as disposal of chemical solutions generated during the process, and there is room for improvement in the uniformity of the manufactured film thickness. The patterning using laser processing described in Patent Document 3 forms wiring with a highly accurate and stable cross-sectional shape using a relatively simple process. Since the surface that was in contact with the smooth PET (Poly Ethylene Terephthalate) appears as the surface of the conductor film after transfer, a surface with higher smoothness is formed compared to screen printing. However, the smoothness of the surface not in contact with the PET is not as high. In Patent Document 4, the smoothness of both surfaces of the gold plating film is improved by transferring the green sheet and the intermediate transfer material twice, but there is room for further improvement in the transfer process and smoothness.

[0005] The present invention has been made to solve at least part of the above-mentioned problems, and has an object to improve the smoothness and uniformity of the film thickness of a conductive film provided on a wiring board. [Means for solving the problem]

[0006] The present invention has been made to solve at least part of the above-mentioned problems, and can be realized in the following forms.

[0007] (1) According to one aspect of the present invention, there is provided a wiring board including a base material and a conductive film disposed inside the base material and having electrical conductivity, wherein the coefficient of variation of the thickness of the conductive film is 0.05 or less.

[0008] This configuration provides a wiring substrate having a conductor film with a thickness variation coefficient of 0.05 or less, i.e., improved film thickness uniformity and smoothness. The improved film thickness uniformity and smoothness of the conductor film provide a wiring substrate that can be used for miniaturizing components and precise temperature control.

[0009] (2) In the wiring board of the above aspect, the average thickness of the conductive film may be 0.5 μm or more and 30 μm or less. This configuration improves the uniformity and smoothness of the film thickness, and also controls the average thickness of the conductive film to 0.5 μm or more and 30 μm or less, providing a wiring substrate that is even more suitable for miniaturization of components and precise temperature control.

[0010] (3) In the wiring board of the above aspect, the average particle size of the raw material powder of the conductive film may be 0.5 μm or more and 4.0 μm or less. According to this configuration, a conductive film with improved film thickness uniformity and smoothness is manufactured using raw material powder of 0.5 μm to 4.0 μm, which is generally used as a raw material for a conductive film.

[0011] (4) In the wiring board of the above aspect, the conductive film may have a pair of main surfaces in the thickness direction, and each of the pair of main surfaces may have a surface roughness Rz of 1.6 μm or less before firing. This configuration suppresses the coefficient of variation of the thickness of the conductive film and the surface roughness Rz of each surface of the conductive film to 1.6 μm or less, thereby providing a wiring board provided with a conductive film with improved film thickness uniformity and smoothness.

[0012] (5) According to another aspect of the present invention, there is provided a method for manufacturing a conductive layer, comprising: a coating step of forming a conductive paste layer by coating a first substrate with a conductive paste containing metal powder having an average particle size of 0.5 μm or more and 4.0 μm or less; a laser processing step of processing the shape of the conductive paste layer by irradiating the conductive paste layer with laser light; a first transfer step of transferring the conductive paste layer formed on the first substrate to a second substrate; and a second transfer step of transferring the conductive paste layer transferred to the second substrate to a green sheet. According to this configuration, the conductive paste layer is formed using a conductive paste containing metal powder with an average particle size of 0.5 μm or more and 4.0 μm or less. The conductive paste layer formed on the first substrate is transferred to the second substrate in a first transfer process, and then transferred to a green sheet in a second transfer process. Therefore, both sides of the conductive paste layer are in contact with the first substrate or the second substrate during the manufacturing process, improving the smoothness of both sides of the conductive paste after sintering. The improved smoothness improves the uniformity of the film thickness of the conductive paste after sintering. According to this configuration, the smoothness of both sides of the conductive paste layer and the uniformity of the film thickness of the conductive paste layer are improved even if no additional processing is performed on the conductive paste after sintering.

[0013] The present invention can be realized in various forms, for example, a wiring board, a conductive film, an electronic component, and a system including these, a method for manufacturing a conductive film, a method for manufacturing a conductive layer, a method for manufacturing a wiring board, and a system including these. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a schematic cross-sectional view of a wiring board according to an embodiment of the present invention; [Figure 2] 3 is a flowchart of a method for manufacturing a wiring board according to the present embodiment. [Figure 3] FIG. 4 is a schematic cross-sectional view of a first substrate and a conductive paste layer after a coating step. [Figure 4] FIG. 4 is a schematic cross-sectional view of the first substrate and the conductive layer after a laser processing step. [Figure 5] FIG. 4 is a schematic cross-sectional view of the first substrate and the conductive layer after the marginal portion has been removed. [Figure 6] FIG. 3 is a schematic cross-sectional view of a first substrate, a second substrate, and a conductive layer during a first transfer step. [Figure 7] FIG. 4 is a schematic cross-sectional view of the second substrate and the conductive layer after the first transfer step. [Figure 8] FIG. 10 is a schematic cross-sectional view of a second substrate, a conductive layer, and a green sheet during a second transfer step. [Figure 9] FIG. 10 is a schematic cross-sectional view of a laminate including a green sheet and a conductive layer after a second transfer step. [Figure 10] FIG. 2 is a schematic cross-sectional view of a laminate in which a plurality of laminates are stacked after a stacking step. [Figure 11] FIG. 2 is an explanatory diagram of a cross section of the wiring board of the present embodiment. [Figure 12] FIG. 2 is an explanatory diagram of a cross section of the wiring board of the present embodiment. [Figure 13] FIG. 10 is an explanatory diagram of a cross section of a wiring board of a comparative example. [Figure 14] 10 is a flowchart of a direct laser method of a comparative example. [Figure 15] FIG. 10 is a schematic cross-sectional view of a conductive layer during a first transfer step in a comparative example. [Figure 16] 1 is an explanatory diagram of each parameter of the conductive film of the embodiment and comparative examples 1 and 2. FIG. [Figure 17] FIG. 10 is an explanatory diagram for evaluating the resistance values ​​of the present embodiment and a comparative example. [Figure 18] FIG. 2 is an explanatory diagram of the relationship between the average particle size of the raw material powder and the film thickness of the conductor film after firing. [Figure 19] FIG. 2 is an explanatory diagram of the particle size of Mo powder used as a raw material powder for a conductive film. [Figure 20] FIG. 2 is an explanatory diagram of the particle size of W powder as a raw material powder of a conductive film. [Figure 21] FIG. 2 is an explanatory diagram of the particle size of a mixed powder of Ag and Pd as a raw material powder for a conductive film. [Figure 22]FIG. 2 is an explanatory diagram of the particle size of Cu powder as a raw material powder for a conductive film. [Figure 23] FIG. 4 is an explanatory diagram of the surface roughness of a conductive paste layer before firing. [Figure 24] FIG. 4 is an explanatory diagram of the surface roughness of a conductive layer before firing. [Figure 25] FIG. 4 is an explanatory diagram of the surface roughness of a conductive layer before firing. [Figure 26] FIG. 4 is an explanatory diagram of the surface roughness of a conductive paste layer before firing. [Figure 27] FIG. 4 is an explanatory diagram of the surface roughness of a conductive layer before firing. [Figure 28] FIG. 4 is an explanatory diagram of the surface roughness of a conductive layer before firing. DETAILED DESCRIPTION OF THE INVENTION

[0015] <Embodiment> FIG. 1 is a schematic cross-sectional view of a wiring board 100 according to one embodiment of the present invention. The wiring board 100 of this embodiment is used for forming circuits in electronic components, IC packages, sensor devices, semiconductor manufacturing equipment, and the like. The wiring board 100 shown in FIG. 1 includes four substrates 10 and three conductive layers (conductor films) 20 disposed inside each of the four substrates 10. While a detailed manufacturing method for the wiring board 100 will be described later, the wiring board 100 is manufactured by stacking the four substrates 10 and the three conductive layers 20. The substrates 10 are made of a ceramic material and have a rectangular, flat plate shape. The Cartesian coordinate system CS shown in FIG. 1 has two axes, X and Y, that are orthogonal to the Z-axis direction, with the Z-axis direction being the stacking direction of the substrates 10 and the conductive layers 20. The X and Y axes are axes parallel to each side of the rectangular substrate 10. The Cartesian coordinate system CS shown in FIG. 1 corresponds to the Cartesian coordinate system CS shown in FIG. 3 and subsequent figures.

[0016] Each of the three conductive layers 20 is formed from a plurality of conductive films 21. The plurality of conductive films 21 included in each conductive layer 20 are processed into a predetermined wiring pattern by laser trimming. As shown in FIG. 1 , the conductive film 21 of this embodiment has a first main surface F1 and a second main surface F2 that form a pair of main surfaces in the stacking direction, and end surface portions EP1 and EP2 that connect the ends of the first main surface F1 and the second main surface F2. The end surface portions EP1 and EP2 form slopes that move away from each other on the X-axis as they move toward the negative Z-axis direction. Therefore, the cross section of the conductive film 21 shown in FIG. 1 is substantially trapezoidal. The conductive film 21 is made from a conductive paste containing metal powder such as copper, aluminum, silver, gold, platinum, nickel, titanium, iron, chromium, molybdenum, and tungsten. Note that the dashed line in FIG. 1 represents the boundary between the two stacked substrates 10. The boundary line may not be distinguishable in the cross section of the wiring board 100.

[0017] FIG. 2 is a flowchart of a manufacturing method for a wiring board 100 including a conductive layer 20 according to this embodiment. The manufacturing flow for the wiring board 100 shown in FIG. 2 begins with a coating process (step S1) in which a conductive paste containing metal powder with an average particle size of 0.5 μm or more and 4.0 μm or less is applied to the first base material MA1. FIG. 3 is a schematic cross-sectional view of the first base material MA1 and the conductive paste layer 20A after the coating process. As shown in FIG. 3, in the coating process, the conductive paste layer 20A containing metal powder and resin is applied to the surface of the first base material MA1 by screen printing, a coater method, a doctor blade method, or the like. The metal used for the metal powder is appropriately selected depending on the purpose, and examples thereof include copper, aluminum, silver, gold, platinum, nickel, titanium, iron, chromium, molybdenum, tungsten, and alloys thereof. The thickness of the conductive paste layer 20A formed on the surface of the first base material MA1 is approximately 0.5 to 100 μm. A known resin (binder) is used as the resin contained in the conductive paste. The conductive paste may contain other components (solvent, filler, etc.) in addition to the metal powder and resin, as long as the object of the present invention is not impaired.

[0018] The first base material MA1 is a film-like or sheet-like member. The thickness of the first base material MA1 is such that it will not be cut by the laser processing step described below, for example, about 25 to 200 μm. Examples of materials for the first base material MA1 include rigid films of polyester resins such as PET and polybutylene terephthalate (PBT).

[0019] After the coating step (step S1), a drying step is performed to dry the conductive paste layer 20A formed on the first substrate MA1 (step S2 in FIG. 2). In the drying step, the conductive paste layer 20A coated on the first substrate MA1 is placed in, for example, a batch dryer and dried with hot air. The temperature inside the dryer is, for example, 80 to 90 degrees Celsius (°C). The drying time is, for example, 5 to 15 minutes. The drying conditions (heating temperature, drying time, etc.) in the drying step may be set appropriately depending on the material (resin, etc.) used in the conductive paste. For example, if the conductive paste layer 20A dries naturally at room temperature, the drying step may not be performed.

[0020] After the drying step (step S2), a laser processing step is performed in which the conductive layer 20B, on which the conductive paste layer 20A has dried, is irradiated with laser light to cut the conductive layer 20B into a pattern (step S3). In the laser processing step, the laser light is irradiated from a substantially perpendicular direction onto the conductive layer 20B on the first base material MA1.

[0021] FIG. 4 is a schematic cross-sectional view of the first base material MA1 and conductive layer 20B after the laser processing step. The cut surface of the conductive layer 20B processed by the laser beam LA irradiated from the positive direction of the Z axis rises substantially vertically, forming a trapezoidal shape as shown in FIG. 4. In this trapezoidal shape, the long side LS is located on the first base material MA1 side, and the short side SS is located on the side irradiated by the laser beam LA. The conductive layer 20B irradiated by the laser beam LA is vaporized and disappears. In addition to cutting the conductive layer 20B, the irradiation of the laser beam LA also forms a V-shaped groove in the first base material MA1. Note that the conductive layer 20B shown in FIG. 4 includes a margin 29 that will not be used as a wiring pattern in the finished wiring board 100.

[0022] As the laser light LA, for example, a green laser (wavelength: 532 nm) is used. The output of the laser light LA ​​is, for example, 1 W to 6 W. Note that the conditions of the laser light LA ​​in the laser processing step (for example, wavelength, output, scanning speed, number of passes, etc.) are appropriately set within a range in which the conductive layer 20B can be cut without cutting the first base material MA1.

[0023] A laser beam having a higher transmittance of the laser beam LA through the first base material MA1 than through the conductive layer 20B is used. The transmittance of the laser beam LA through the first base material MA1 is, for example, preferably 50% or more, more preferably 60% or more, and even more preferably 70% or more. In contrast, the transmittance of the laser beam LA through the conductive layer 20B is, for example, preferably 20% or less, more preferably 10% or less. When the transmittances of the first base material MA1 and the conductive layer 20B are within these ranges, the first base material MA1 is not cut even when irradiated with the laser beam LA. Furthermore, heat accumulates in the first base material MA1, and the accumulated heat prevents cracks and the like from occurring in the conductive layer 20B. Note that, as shown in FIG. 3, the conductive layer 20B after the laser processing step includes a margin 29 that is not used as wiring.

[0024] After the laser processing step (step S3 in FIG. 2), a marginal portion removing step is performed to remove marginal portions 29 included in conductive layer 20B (step S4). FIG. 5 is a schematic cross-sectional view of first base material MA1 and conductive layer 20C after marginal portions 29 have been removed. In the marginal portion removing step, marginal portions 29 are removed from conductive layer 20B shown in FIG. 4 so that conductive layer 20C has a desired wiring pattern. For example, marginal portions 29 may be removed using adhesive tape or a sheet. Alternatively, a film may be placed on conductive layer 20B from the side opposite to the first base material MA1 (positive Z-axis direction side), and marginal portions 29 are pressed against the film from the back side of first base material MA1 (negative Z-axis direction side). Only marginal portions 29 are transferred to the film. When marginal portions 29 are transferred to the film, the positions of first base material MA1 and the film may be reversed upside down. In addition to these methods, the margin 29 may be removed by using a known method used in forming this type of conductive layer. In the conductive layer 20C shown in Fig. 5, the short side SS is in contact with the smooth PET, and therefore the smoothness of the short side SS is superior to that of the long side LS, which is not in contact with the PET or the like.

[0025] After the margin removal process (step S4 in FIG. 2), a first transfer process is performed in which the conductive layer 20C is transferred from the first substrate MA1 to the second substrate MA2 (step S5). FIG. 6 is a schematic cross-sectional view of the first substrate MA1, the second substrate MA2, and the conductive layer 20C during the first transfer process. As shown in FIG. 6, in the first transfer process, the conductive layer 20C and the first substrate MA1 are placed on the second substrate MA2 so that the conductive layer 20C faces the second substrate MA2. The second substrate MA2 is a film-like or sheet-like member. Examples of materials that can be used for the second substrate MA2 include synthetic resin films made of polyester resins such as PET and PBT.

[0026] After the conductive layer 20C and the first substrate MA1 are stacked on the second substrate MA2, the conductive layer 20C is pressed against the second substrate MA2 using a jig or the like from the side of the first substrate MA1 on which the conductive layer 20C is not formed (the positive Z-axis side). In this embodiment, the peel strength when the conductive layer 20C is peeled off from the first substrate MA1 is smaller than the peel strength when the conductive layer 20C is peeled off from the second substrate MA2. Therefore, after the conductive layer 20C is pressed against the second substrate MA2, when the conductive layer 20C and the first substrate MA1 are peeled off from the second substrate MA2, the conductive layer 20C is transferred to the second substrate MA2.

[0027] 7 is a schematic cross-sectional view of the second substrate MA2 and the conductive layer 20C after the first transfer step. As shown in Fig. 7, the conductive layer 20C transferred onto the second substrate MA2 is formed on the second substrate MA2 so that the short side SS of the trapezoidal cross section faces the second substrate MA2.

[0028] After the first transfer step (step S5 in FIG. 2), the second transfer step (step S6) is performed to transfer the conductive layer 20C from the second substrate MA2 to the green sheet GS. FIG. 8 is a schematic cross-sectional view of the second substrate MA2, conductive layer 20C, and green sheet GS during the second transfer step. As shown in FIG. 8, in the second transfer step, the conductive layer 20C and the second substrate MA2 are placed on the green sheet GS so that the conductive layer 20C faces the green sheet GS. The green sheet GS is produced, for example, by kneading a mixture of material powders in a ball mill and forming the resulting mixture into a sheet using a doctor blade method. The material powder mixture is a mixture containing appropriate amounts of aluminum nitride powder, yttrium oxide powder, acrylic resin (binder), dispersant, plasticizer, etc., to which an organic solvent such as toluene is added. Note that other known green sheets GS may also be used.

[0029] After the conductive layer 20C and the second base material MA2 are stacked on the green sheet GS, the conductive layer 20C is pressed against the second base material MA2 using a jig or the like from the side of the second base material MA2 where the conductive layer 20C is not formed (the positive Z-axis side). After being pressed in this manner, the conductive layer 20C has a stronger adhesive force to the green sheet GS than to the second base material MA2. Therefore, by peeling the second base material MA2 from the green sheet GS side, the conductive layer 20C is peeled off from the second base material MA2 and transferred to the green sheet GS.

[0030] 9 is a schematic cross-sectional view of a laminate 31 including a green sheet GS and a conductive layer 20C after the second transfer step. In the laminate 31 shown in FIG. 9, the conductive layer 20C transferred onto the green sheet GS is formed on the green sheet GS so that the long side LS of the trapezoidal cross section faces the green sheet GS. In the conductive layer 20C shown in FIG. 9, the long side LS side is in contact with the smooth green sheet GS, and therefore the long side LS side has the same degree of smoothness as the short side SS side.

[0031] After the second transfer step (step S6 in FIG. 2), a lamination step is performed in which a plurality of laminates 31 are laminated (step S7). FIG. 10 is a schematic cross-sectional view of a laminate 30 in which a plurality of laminates 31 are laminated after the lamination step. The laminate 30 shown in FIG. 10 is formed by laminating three laminates 31 (FIG. 9) and one green sheet GS. The laminate 30 is formed by applying pressure from the positive Z-axis direction after lamination. Note that the laminate 30 shown in FIG. 10 is just an example, and for example, four or more laminates may be laminated.

[0032] After the lamination step (step S7 in FIG. 2), a firing step (step S8) is performed to sinter the laminate 30 to manufacture the wiring board 100 shown in FIG. 1, thereby completing the manufacturing flow for the wiring board 100. The firing step is performed, for example, by firing the laminate 30 in a humidified hydrogen-nitrogen atmosphere at a predetermined temperature (e.g., 1900°C) for a predetermined time (e.g., 4 hours). The firing step sinters the green sheets GS in the laminate 30 to form the substrate 10. The conductive layer 20C is then sintered to form the conductive layer 20. Note that, prior to the firing step, a degreasing step may be performed, if necessary, in which the laminate 30 is degreased by heating in a nitrogen atmosphere (e.g., at 550°C for 12 hours).

[0033] 11 and 12 are explanatory diagrams of cross sections of wiring boards 100A and 100B manufactured by the manufacturing method of this embodiment. Fig. 13 is an explanatory diagram of a cross section of wiring board 100X manufactured by the direct laser method of Comparative Example 1. Each of Figs. 11 to 13 shows an enlarged SEM image of the cross section of wiring boards 100A, 100B, and 100X taken by a scanning electron microscope.

[0034] FIG. 14 is a flowchart of the direct laser method of Comparative Example 1. As shown in FIG. 14, wiring board 100X of Comparative Example 1 is a board manufactured by removing the second transfer step of step S6 of FIG. 2 from wiring board 100 of the embodiment. In the direct laser flow of Comparative Example 1 of FIG. 14, the same steps as steps S1 to S4 of FIG. 2 are performed, and then a first transfer step is performed to transfer conductive layer 20C from first base material MA1 to green sheet GS (step S5y). In Comparative Example 1, conductive layer 20C is transferred from first base material MA1 to green sheet GS without transferring second base material MA2.

[0035] Fig. 15 is a schematic cross-sectional view of the green sheet GS, conductive layer 20C, and first substrate MA1 during the first transfer step of Comparative Example 1. The conductive layer 20C transferred onto the green sheet GS after the first transfer step (S5y) shown in Fig. 15 is formed on the green sheet GS so that the short side SS of the trapezoidal cross section faces the green sheet GS.

[0036] After the first transfer step (step S5y), a lamination step of laminating a plurality of laminates 31y (step S7y) is performed, and a firing step (step S8) is performed, thereby manufacturing the wiring board 100X of Comparative Example 1.

[0037] In this embodiment, the coefficient of variation CV of the conductor films 21A, 21B, and 21X included in the wiring boards 100A, 100B, and 100X was evaluated. FIG. 16 is an explanatory diagram of the parameters of the conductor films 21A, 21B, and 21X and the four types of conductor films 21YA, 21YB, 21YC, and 21YD manufactured by screen printing in Comparative Example 2. FIG. 16 shows a table of parameters calculated from film thicknesses measured at 10 locations on the conductor films 21A and 21B of this embodiment and the conductor films 21X, 21YA, 21YB, 21YC, and 21YD of Comparative Examples 1 and 2. The 10 locations where film thicknesses were measured in this embodiment and Comparative Example 1 are indicated by straight lines in each of FIGS. 11 to 13. In other words, the length indicated by the straight lines parallel to the Z-axis direction in FIGS. 11 to 13 corresponds to the film thickness of the conductor films 21A and 21B. FIG. 16 also shows parameters calculated from film thicknesses measured at 10 locations on the conductive films 21A, 21B, 21X, 21YA, 21YB, 21YC, and 21YD of this embodiment and comparative examples 1 and 2, which are formed by screen printing.

[0038] The table shown in FIG. 16 lists the following parameters: the average film thickness (μm), the maximum film thickness (μm) among the 10 measured values, the minimum film thickness (μm) among the 10 measured values, 3σ (σ: standard deviation) calculated from the film thickness measurements at the 10 measured values, and 3CV calculated as the coefficient of variation corresponding to 3σ. The coefficient of variation CV is calculated by dividing the standard deviation σ by the average film thickness. The coefficient of variation CV of each of the conductor films 21A, 21B, 21X, 21YA, 21YB, 21YC, and 21YD is calculated from the 3CV values ​​shown in FIG. 13. As shown in FIG. 16, the coefficients of variation CV of the conductor films 21A and 21B of this embodiment are 0.0412 and 0.0499, both of which are less than 0.05. On the other hand, the coefficients of variation CV of the conductive films 21X, 21YA, 21YB, 21YC, and 21YD of Comparative Examples 1 and 2 were 0.0851, 0.0653, 0.0933, 0.0582, and 0.1289, respectively, all of which were greater than 0.05.

[0039] FIG. 17 is an explanatory diagram illustrating the evaluation of resistance values ​​of the present embodiment and Comparative Example 2. FIG. 17 shows a table listing the average film thickness before firing, the average resistance value of the film thickness after firing, σ, 3σ, coefficient of variation CV, and coefficient of variation 3CV for the conductive film of the embodiment manufactured by the manufacturing method of the present embodiment shown in FIG. 2 and the conductive film of Comparative Example 2 manufactured by screen printing. The coefficient of variation CV of the thickness of the conductive film 21 of the embodiment shown in FIG. 17 is 0.05 or less. On the other hand, the coefficient of variation CV of the thickness of the conductive film of Comparative Example 2 shown in FIG. 17 is greater than 0.05. Note that the coefficients of variation CV and 3CV shown in FIG. 17 represent coefficients of variation of resistance values ​​and are different from the coefficients of variation of film thickness.

[0040] The parameters of the embodiment and comparative example 2 shown in FIG. 17 are the average value, σ (3σ), and coefficient of variation CV (3CV) calculated from measurements at four locations for each of three samples. As shown in FIG. 17, the 3σ of the resistance value of the conductive film manufactured by the manufacturing method of this embodiment is 0.076, which is smaller than 0.095 for comparative example 2. The coefficient of variation CV of the resistance value of the conductive film manufactured by the manufacturing method of this embodiment is 0.044, which is smaller than 0.65 for comparative example 2. In other words, because the coefficient of variation CV of the thickness of the conductive film 21 manufactured by the manufacturing method of this embodiment is 0.05 or less, the variation in the resistance value of the conductive film 21 is suppressed more than the variation in comparative example 2.

[0041] FIG. 18 is an explanatory diagram of the relationship between the average particle size of the raw material powder for the conductive film and the film thickness of the conductive film after firing. FIG. 18 shows a table of the relationship between the average particle size of the raw material powder and the 3CV, which is the coefficient of variation of the conductive film after firing. Five samples were prepared for each particle size, and the 3CV of the film thickness shown in FIG. 18 was calculated from the average value of the film thickness measured at 10 points on the five samples. FIG. 18 shows the results of the judgment for each sample, with the coefficient of variation 3CV of 0.15 or less (CV of 0.05 or less) being used as a threshold, and the judgment results for each sample being classified as "A" if the threshold is met, and "B" if the threshold is not met. In other words, when the average particle size of the raw material powder for the conductive film is 0.5 μm or more and 4.0 μm or less, the coefficient of variation CV was the threshold of 0.05 or less. The numerical range of "0.5 to 1.0" shown in FIG. 18 represents 0.5 or more and less than 1.0.

[0042] Each of Figures 19 to 22 is an explanatory diagram of materials with an average particle size of 0.5 μm or more and 4.0 μm or less used as raw material powders for conductive films. Figure 19 lists Mo powders (samples A-1 to A-7) as seven types of raw material powders differing in particle size range. Figure 20 lists W powders (samples B-1 to B-13) as 13 types of raw material powders differing in particle size range. Figure 21 lists mixed powders of Ag powder and Pd powder (samples C-1 to C-3) as three types of raw material powders differing in powder size. The mass ratio of Ag:Pd in ​​the mixed powder is 70:30. Figure 22 lists Cu powders (samples D-1 to D-9) as nine types of raw material powders differing in powder size.

[0043] 23 to 28 are explanatory diagrams of the surface roughness of the conductive paste layer 20A and the conductive layer 20C, which are the conductive films of this embodiment before firing. Each of FIGS. 23 to 28 shows the surface roughness of two locations on one sample: the short side SS before the laser processing step (step S3) in FIG. 2, the long side LS after the first transfer step (step S5), and the short side SS after the second transfer step (step S6). Each of FIGS. 23 to 28 uses a line graph to show the change in the surface height of the conductive paste layer 20A and the conductive layer 20C when the height of the reference surface is set to zero. Each of FIGS. 23 to 28 also shows the numerical values ​​of the arithmetic mean roughness Ra and the ten-point mean roughness Rz calculated from the line graph. The graphs shown in FIGS. 23 to 25 show the surface roughness at one of the two locations, and the graphs shown in FIGS. 26 to 28 show the surface roughness at the other of the two locations.

[0044] The surface roughness shown in Figures 23 and 26 is the value of the upper surface of the conductive paste layer 20A shown in Figure 3, which will be the surface on the short side SS side after laser processing. The surface roughness shown in Figures 24 and 27 is the value of the long side LS side of the conductive layer 20C shown in Figure 7, i.e., the upper surface where the conductive layer 20C is not in contact with the second substrate MA2. The surface roughness shown in Figures 25 and 28 is the value of the short side SS side of the conductive layer 20C shown in Figure 9. Therefore, the surface roughness shown in Figure 24 and the surface roughness shown in Figure 25 are the surface roughness of each of the pair of main surfaces in the thickness direction of the conductive layer 20C before firing. Similarly, the surface roughness shown in Figure 27 and the surface roughness shown in Figure 28 are the surface roughness of each of the pair of main surfaces in the thickness direction of the conductive layer 20C before firing. Note that the two locations where the surface roughness was measured correspond to each other in the thickness direction of the sample.

[0045] Comparing the arithmetic mean roughness Ra and ten-point mean roughness Rz of the short side SS side shown in Figures 23 and 26 with the arithmetic mean roughness Ra and ten-point mean roughness Rz of the short side SS side shown in Figures 25 and 28, the arithmetic mean roughness Ra and ten-point mean roughness Rz in Figures 25 and 28 are smaller. The reason for this is thought to be that the surface of the conductive layer 20C shown in Figure 7 is smoothed by the application of pressure to the short side SS side of the conductive paste layer 20A (Figure 3) before laser processing while it is in contact with the second substrate MA2. The arithmetic mean roughness Ra and ten-point mean roughness Rz of the long side LS side shown in Figures 24 and 27 are smaller than the arithmetic mean roughness Ra and ten-point mean roughness Rz of the short side SS side before it comes into contact with the second substrate MA2 shown in Figures 23 and 26 due to the application of pressure during the laser processing process while the conductive paste layer 20A is in contact with the first substrate MA1. The arithmetic mean roughness Ra at two locations on the short side SS shown in Figures 25 and 28 is 0.4284 μm and 0.4161 μm. The ten-point mean roughness Rz at two locations on the short side SS shown in Figures 25 and 28 is 1.5535 μm (<1.6 μm) and 1.5576 μm (<1.6 μm). The arithmetic mean roughness Ra at two locations on the long side LS shown in Figures 24 and 27 is 0.1004 μm and 0.0903 μm. The ten-point mean roughness Rz at two locations on the long side LS shown in Figures 24 and 27 is 0.462 μm (<1.6 μm) and 0.4058 μm (<1.6 μm).

[0046] As described above, the coefficients of variation CV of the conductive films 21A, 21B in this embodiment are approximately 0.0412 and approximately 0.0499, both of which are 0.05 or less, as shown in FIG. 16 . In this embodiment, a wiring substrate is manufactured that includes conductive films 21A, 21B with thickness variation coefficients of 0.05 or less, i.e., with improved film thickness uniformity and smoothness. The improved film thickness uniformity and smoothness of the conductive films 21A, 21B provides a wiring substrate 100 that can be used for component miniaturization and precise temperature control.

[0047] In addition, in this embodiment, the coefficient of variation CV is equal to or less than the threshold value when the average particle size of the raw material powder of the conductive film is 0.5 μm or more and 4.0 μm or less, as shown in Figure 18. In this embodiment, a conductive film with improved film thickness uniformity and smoothness is manufactured using raw material powder of 0.5 μm or more and 4.0 μm or less, which is commonly used as a raw material for conductive films.

[0048] As shown in FIGS. 25 and 28 of this embodiment, the ten-point mean roughness Rz of the short side SS of the conductive layer 20C before firing is 1.5535 μm (<1.6 μm) and 1.5576 μm (<1.6 μm). As shown in FIGS. 24 and 27, the ten-point mean roughness Rz of the long side LS of the conductive layer 20C before firing is 0.462 μm (<1.6 μm) and 0.4058 μm (<1.6 μm). Therefore, in addition to the coefficient of variation CV of the thickness of the conductive layer 20C of this embodiment, the surface roughness Rz of each main surface of the conductive layer 20C is suppressed to 1.6 μm or less. In other words, a wiring substrate 100 is provided that includes a conductive film 21 with improved film thickness uniformity and smoothness.

[0049] In the manufacturing flow of the wiring board 100 of this embodiment shown in FIG. 2, the conductive paste layer 20A is formed in the coating process using a conductive paste containing metal powder with an average particle size of 0.5 μm or more and 4.0 μm or less. The conductive paste layer 20A formed on the first substrate MA1 is transferred to the second substrate MA2 in the first transfer process, and then transferred to the green sheet GS in the second transfer process. Because both sides of the conductive layer 20C are in contact with the first substrate MA1 or the second substrate MA2 in the manufacturing flow, the smoothness of both sides of the conductive film 21 after sintering is improved. The improved smoothness improves the thickness uniformity of the conductive film 21 after sintering. According to the manufacturing flow of this embodiment, the smoothness of both sides of the conductive film 21 and the uniformity of the film thickness of the conductive film 21 are improved even if no additional processing is performed on the conductive film 21 after sintering.

[0050] <Modification of this embodiment> The present invention is not limited to the above-described embodiment, and can be embodied in various forms without departing from the spirit of the invention. For example, the following modifications are also possible.

[0051] The manufacturing method of the wiring board 100 and the conductive layer 20 in the above embodiment is an example and can be modified. Furthermore, the manufacturing method of the conductive layer 20 can be modified as long as both the first transfer step (S5) and the second transfer step (S6) are performed. The materials of the base material 10, the conductive layer 20, the first base material MA1, and the second base material MA2 in the above embodiment are an example and well-known materials can be used. The number of layers of base material 10 and conductive layer 20 stacked to form the wiring board 100 may be one layer or two or more layers. A layer other than the conductive layer 20 may be formed between two base materials 10, or when three or more base materials 10 are stacked, there may be a layer between the base materials 10 where the conductive layer 20 is not stacked.

[0052] In the above embodiment, the average thickness of the conductor film 21 after firing is preferably 0.5 μm or more and 30 μm or less. When the average thickness of the conductor film 21 is within this range, a wiring substrate 100 is provided that is more suitable for component miniaturization and precise temperature control. In the above embodiment, the so-called two-step transfer manufacturing method shown in FIG. 2 is used as an example of a method for manufacturing the conductor film 21 having a thickness with a coefficient of variation CV of 0.05 or less, but other methods may also be used.

[0053] This aspect has been described above based on embodiments and modifications. However, the above-described embodiments are intended to facilitate understanding of this aspect and are not intended to limit this aspect. This aspect may be modified or improved without departing from the spirit and scope of the claims, and equivalents thereof are included in this aspect. Furthermore, if a technical feature is not described as essential in this specification, it may be deleted as appropriate.

[0054] The present invention can also be realized in the following forms. [Application example 1] A wiring board, A substrate; a conductive film disposed inside the base material and having electrical conductivity; Equipped with A wiring board characterized in that the coefficient of variation of the thickness of the conductive film is 0.05 or less. [Application example 2] The wiring board according to Application Example 1, The wiring board is characterized in that the average thickness of the conductive film is 0.5 μm or more and 30 μm or less. [Application example 3] The wiring board according to Application Example 1 or Application Example 2, The wiring substrate is characterized in that the average particle size of the raw material powder of the conductive film is 0.5 μm or more and 4.0 μm or less. [Application example 4] The wiring board according to any one of Application Examples 1 to 3, the conductive film has a pair of main surfaces in a thickness direction, A wiring board characterized in that the surface roughness Rz of each of the pair of main surfaces before firing is 1.6 μm or less. [Application example 5] A method for manufacturing a conductive layer, comprising: a coating step of coating a conductive paste containing metal powder having an average particle size of 0.5 μm or more and 4.0 μm or less onto a first substrate to form a conductive paste layer; a laser processing step of processing the shape of the conductive paste layer by irradiating the conductive paste layer with laser light; a first transfer step of transferring the conductive paste layer formed on the first substrate to a second substrate; a second transfer step of transferring the conductive paste layer transferred to the second substrate onto a green sheet; A manufacturing method comprising: [Explanation of symbols]

[0055] 10...Base material 20,20B,20C…conductive layer 20A...Conductive paste layer 21,21A,21B,21X,21YA~21YD…Conductor film 29...Margin 30...Laminate 31, 31y...Laminate 100, 100A, 100X...wiring board CS...Cartesian coordinate system CV...coefficient of variation F1...First principal surface (principal surface) F2...Second principal surface (principal surface) GS...Green Sheet LA...laser light LS...long side SS...short side MA1...first base material MA2…Second base material

Claims

1. A wiring board, A substrate; a conductive film disposed inside the base material and having electrical conductivity; Equipped with A wiring substrate, characterized in that the coefficient of variation of the thickness of the conductive film is 0.05 or less.

2. 2. The wiring board according to claim 1, The wiring substrate, wherein the average thickness of the conductive film is 0.5 μm or more and 30 μm or less.

3. 2. The wiring board according to claim 1, The wiring substrate is characterized in that the average particle size of the raw material powder of the conductive film is 0.5 μm or more and 4.0 μm or less.

4. 2. The wiring board according to claim 1, the conductive film has a pair of main surfaces in a thickness direction, A wiring board characterized in that the surface roughness Rz of each of the pair of main surfaces before firing is 1.6 μm or less.

5. A method for manufacturing a conductive layer, comprising: a coating step of coating a conductive paste containing metal powder having an average particle size of 0.5 μm or more and 4.0 μm or less on a first substrate to form a conductive paste layer; a laser processing step of processing the shape of the conductive paste layer by irradiating the conductive paste layer with laser light; a first transfer step of transferring the conductive paste layer formed on the first substrate to a second substrate; a second transfer step of transferring the conductive paste layer transferred to the second substrate onto a green sheet; A manufacturing method comprising:

Images