Method for manufacturing wiring board, and wiring board

Abstract

This method for manufacturing a wiring board includes: a step for forming a first pattern sheet having at least one of a via conductor and a conductor pattern on a first green sheet; a step for preparing a second green sheet having a lower shrinkage start temperature than the first green sheet and a shrinkage end temperature equal to or lower than the shrinkage start temperature of the first green sheet; a step for forming a first laminate body by interposing the second green sheet in a middle layer portion in the lamination direction when a plurality of first pattern sheets are prepared and laminated; a step for forming a second laminate body by laminating constraint sheets, each mainly composed of an inorganic composition having a higher sintering start temperature than the first green sheet and the second green sheet, on both surfaces in the lamination direction of the first laminate body; and a step for firing the second laminate body.

Description

Method for manufacturing wiring board and wiring board

[0001] The present disclosure relates to a method for manufacturing a wiring board and a wiring board.

[0002] 2. Description of the Related Art Conventionally, a multilayer wiring board has been known in which a plurality of ceramic base materials are used to form multiple layers and wiring is disposed between the layers.

[0003] Japanese Patent Laid-Open No. 7-86743 Japanese Patent Laid-Open No. 2003-78245

[0004] The method for manufacturing a wiring board of the present disclosure includes the steps of: forming a first pattern sheet having at least one of via conductors and a conductor pattern on a first green sheet; preparing a second green sheet having a lower shrinkage start temperature than the first green sheet and a shrinkage end temperature that is the same as or lower than the shrinkage start temperature of the first green sheet; preparing and stacking a plurality of the first pattern sheets, interposing the second green sheet in the middle layer portion in the stacking direction to form a first laminate; stacking a constraint sheet mainly composed of an inorganic composition having a sintering start temperature higher than the first green sheet and the second green sheet on both sides in the stacking direction of the first laminate to form a second laminate; and firing the second laminate. Another method for manufacturing a wiring board of the present disclosure includes the steps of: forming a first pattern sheet having at least one of via conductors and a conductor pattern on a first green sheet; preparing a ceramic paste containing a ceramic composition having a shrinkage start temperature lower than that of the first green sheet and a shrinkage end temperature equal to or lower than the shrinkage start temperature of the first green sheet; preparing and stacking a plurality of the first pattern sheets, interposing a coating film of the ceramic paste in the middle layer portion in the stacking direction to form a first laminate; laminating a restraint sheet containing as its main component an inorganic composition having a sintering start temperature higher than that of the first green sheet and the coating film on both sides in the stacking direction of the first laminate to form a second laminate; and firing the second laminate.

[0005] FIG. 1 is a schematic cross-sectional view showing an example of a method for manufacturing a wiring board according to an embodiment. FIG. 2 is a schematic plan view showing a cutting line when a first laminate is produced from a matrix laminate. FIG. 3 is a schematic perspective view showing a first laminate cut out from a matrix laminate. FIG. 4 is a schematic perspective view showing a first laminate cut out from a matrix laminate. FIG. 5 is a schematic graph showing the shrinkage behavior of each sheet during firing. FIG. 6 is a schematic cross-sectional view showing the change in shape when a second laminate formed by placing constraint sheets on both sides of the first laminate is fired to obtain a wiring board. FIG. 7 is a schematic cross-sectional view showing the change in shape of each component when a laminate is fired with constraint sheets placed on both sides, to obtain a wiring board. FIG. 8 is a view showing a coated film formed in a frame-shaped pattern. FIG. 9 is a view showing a coated film formed in a grid-shaped pattern. FIG. 10A is a view showing the shape of the coated film when viewed in plan. FIG. 10B is a view showing the shape of the coated film when viewed in plan.

[0006] Hereinafter, a method for manufacturing a wiring board and a mode for carrying out a wiring board according to the present disclosure (hereinafter referred to as "embodiments") will be described in detail with reference to the drawings. Note that the present disclosure is not limited to these embodiments. Furthermore, each embodiment can be appropriately combined within a range that does not cause contradictions in the processing content. Furthermore, the same components in each of the following embodiments will be given the same reference numerals, and duplicated explanations will be omitted.

[0007] In addition, in the drawings referred to below, to make the explanation easier to understand, an orthogonal coordinate system may be shown in which the X-axis direction, Y-axis direction, and Z-axis direction, which are perpendicular to each other, are defined, and the Z-axis direction is the thickness direction of the wiring board.

[0008] A multilayer wiring board has been known in the art, in which multiple ceramic substrates are used to form multiple layers and wiring is arranged between the layers. Fig. 7 is a cross-sectional schematic diagram showing the change in shape of each component when a wiring board is obtained by placing constraint sheets on both sides of a laminate and firing it.

[0009] Such a wiring substrate 200 can be obtained, for example, by the following method: First, a pattern sheet is formed by forming a conductor pattern that will become wiring in the central region of the surface of a ceramic green sheet (hereinafter also referred to as a "green sheet" as appropriate).

[0010] Next, a plurality of pattern sheets on which conductive patterns are formed are stacked to form a laminate, that is, a first laminate 210. Next, constraining sheets 230 made of an inorganic composition having a firing start temperature higher than that of the green sheets are stacked on both sides of the first laminate 210 in the stacking direction.

[0011] Next, the second laminate 220, which is a laminate with the constraining sheet 230 laminated thereon, is fired. After firing, the constraining sheet 230 is removed from both sides of the wiring board 200, which is the fired product of the second laminate 220.

[0012] When attempting to manufacture a highly stacked wiring board as wiring board 200, the green sheet located in the middle part of the stacking direction of first laminate 210 of the pattern sheet that forms the basis of wiring board 200 is less susceptible to the restraining force of restraining sheet 230 than the green sheet that is the outermost layer in first laminate 210 or close to this position.

[0013] The more the number of pattern sheets or green sheets stacked, the less likely this restraining force will extend to the entire first laminate 210. This force becomes more pronounced in the pattern sheets or green sheets in the first laminate 210 that are located farther from the restraining sheet 230.

[0014] As a result, the shrinkage rate in the planar direction increases in the middle layer portion in the stacking direction of the first laminate 210. This may cause variations in the width and pitch of the wiring obtained from the conductor pattern formed on the green sheet, reducing the dimensional accuracy of the wiring.

[0015] Therefore, there is a need for a technology that can improve the dimensional accuracy of wiring even when manufacturing highly multi-layered wiring boards.

[0016] 1. Manufacturing Method of Wiring Board Fig. 1 is a schematic cross-sectional view showing an example of a manufacturing method of a wiring board according to an embodiment. In Fig. 1, the upper diagram is a schematic diagram showing a method of preparing and laminating a plurality of pattern sheets 3, each having a conductor pattern 2 formed on the surface of a green sheet 1. In Fig. 1, the lower diagram is a schematic diagram showing a state in which constraining sheets 4 are laminated on both sides of a first laminate 10, which is a laminate obtained through the process shown in the upper diagram.

[0017] <1-1. Fabrication of Each Sheet> A method for manufacturing a wiring board according to an embodiment will be described with reference to Fig. 1. First, as shown in the upper part of Fig. 1, a conductor pattern 2 is formed on the surface of a green sheet 1 to form a first pattern sheet 3, which is a pattern sheet. Note that hereinafter, the "first pattern sheet" may be simply referred to as the "pattern sheet."

[0018] The green sheet 1 and the first pattern sheet 3 have different areas when producing one first laminate 10 and when producing a base laminate 50 (see FIG. 2 ) from which a plurality of first laminates 10 are obtained. The first green sheet 11 used when producing one first laminate 10 has one conductive pattern 2 formed on it.

[0019] The first green sheet 11 used to prepare the base laminate 50 from which a plurality of first laminates 10 are obtained has the conductor patterns 2 formed at a plurality of locations.

[0020] The first pattern sheet 3 shown in Figure 1 simply has a conductor pattern 2 formed on the surface of the first green sheet 11, but this pattern sheet 3 may also have raw via conductors (not shown) that penetrate the first green sheet 11, if necessary.

[0021] The first pattern sheet 3 is preferably a first green sheet 11 on which at least one of the conductor pattern 2 and raw via conductors is formed.

[0022] The first green sheet 11 is, for example, a ceramic green sheet containing glass ceramics, and has a predetermined planar shape, for example, a rectangular shape.

[0023] The green sheet 1 is formed, for example, by adding and mixing inorganic particles such as silica, sintering aids, binders, solvents, dispersants, etc. to glass powder, which is the main component raw material such as borosilicate alkaline earth oxide glass, to form a slurry, and then molding this slurry using a doctor blade method.

[0024] The second green sheet 12 is also formed by the same method as the first green sheet 11. In this case, the second green sheet 12 and the first green sheet 11 preferably differ in at least one of the components (metal oxides) contained in the glass powder, the composition of the glass powder, and the type and composition of the inorganic particles.

[0025] <1-2. Conductor> The conductor pattern 3 is formed, for example, by printing a conductor paste containing copper powder on the surface of the green sheet 1. The raw via conductors are formed by forming through holes in the green sheet 1 and then filling the through holes with the conductor paste.

[0026] When required for the design of the wiring board 100 (see FIG. 6 ), at least one of the conductor pattern 3 and the raw via conductors is formed on the green sheet 1. The conductor pattern 3 and the raw via conductors may be formed on all layers of the green sheet 1 required for the design of the wiring board 100. Screen printing is a suitable method for filling the through holes with the conductor paste.

[0027] <1-3. Fabrication of First Laminate: Single-Piece Cavity> Next, the first laminate 10 is fabricated using a plurality of first pattern sheets 3 and second green sheets 12. Here, the first pattern sheets 3 have six layers. Also, here, the second green sheets 12 have one layer.

[0028] The first laminate 10 is fabricated as follows: First, a temporary laminate is fabricated as a precursor of the first laminate 10. With regard to the portion of the stacking direction of the first laminate 10, when the first laminate 10 and the wiring substrate 100 are divided into three equal parts in the stacking direction or thickness direction, the respective parts are designated as an upper layer portion, a middle layer portion, and a lower layer portion.

[0029] The stacking direction may be rephrased as the thickness direction. In this case, the upper layer portion, middle layer portion, and lower layer portion do not depend on the arrangement of the wiring of the first laminate 10 and the wiring board 100. The upper layer portion, middle layer portion, and lower layer portion refer to the portions obtained by simply dividing the wiring board 100 into thirds on a length scale in the stacking direction or thickness direction when the first laminate 10 and the wiring board 100 are placed, for example, on a desk with their two main surfaces facing up and down.

[0030] The layers may be arranged in the order of lower, middle, and upper layers from the side closest to the surface of the desk. For example, three layers of pattern sheets 3 located in the lower layers of the first laminate 10 are stacked first. Here, multiple pattern sheets 3 are referred to as a pattern sheet group. Then, one second green sheet 12 is stacked on top of these three layers of pattern sheets 3.

[0031] Next, one second green sheet 12 is placed on top of the lower group of pattern sheets, and then another group of pattern sheets is placed on top of the second green sheet 12.

[0032] Next, the temporary laminate thus produced is pressurized and heated under predetermined conditions to form the first laminate 10. By pressurizing and heating the temporary laminate, the pattern sheets 3 are adhered to each other and to the pattern sheet 3 and the second green sheet 12. By pressurizing and heating the temporary laminate, the group of pattern sheets and the second green sheet 12 are adhered to each other.

[0033] At this time, the second green sheet 12 may extend beyond the outer edges of the two pattern sheet groups that are arranged so as to sandwich it in the stacking direction.

[0034] The area of ​​the second green sheet 12 should be larger than the planar area of ​​the pattern sheet group. By forming the first laminate 10 with the area of ​​the second green sheet 12 larger than the planar area of ​​the pattern sheet group, the second green sheet 12 can exert a restraining force over the entire planar direction of the pattern sheet groups located above and below it. The second green sheet 12 only needs to extend 0.1 mm or more outside the outer edges of the two pattern sheet groups arranged to sandwich it in the stacking direction.

[0035] <1-4. Multiple First Laminates Obtained from a Base Laminate> Figure 2 is a schematic plan view showing cutting lines when producing first laminates from a base laminate. Note that the dotted areas in Figure 2 indicate the second green sheets 12 that protrude from the side surfaces of the first laminate 10. Figures 3 and 4 are schematic perspective views showing first laminates cut out from the base laminate. Figure 3 shows a first laminate 10A in the shaded area A in Figure 2. Figure 4 shows a first laminate 10B in the shaded area B in Figure 2.

[0036] As another method, the first laminate 10 may be produced by cutting the base laminate 50. In this case, the base laminate 50 is produced in advance, and then cut at predetermined positions to obtain a plurality of first laminates 10.

[0037] First, a temporary laminate is produced as a precursor of the base laminate 50 having the first laminate 10. In the case of the base laminate 50, similarly to the case of producing one first laminate 10, the base laminate 50 is divided into three equal parts in the stacking direction or thickness direction, and the respective parts are designated as an upper layer portion, a middle layer portion, and a lower layer portion.

[0038] The lamination direction may be referred to as the thickness direction. Specifically, one second green sheet 12 is laid on top of the pattern sheet group located in the lower layer portion of the base laminate 50. Thereafter, another pattern sheet group is laid on top of the second green sheet 12.

[0039] Next, the temporary laminate thus produced is pressurized and heated under predetermined conditions to obtain a base laminate 50 having a plurality of first laminates 10. By pressurizing and heating the temporary laminate, the pattern sheets 3 are adhered to each other and to the pattern sheet 3 and the second green sheet 12. By pressurizing and heating the temporary laminate, the group of pattern sheets and the second green sheet 12 are adhered to each other.

[0040] When producing the base laminate 50, the second green sheet 12 may extend beyond the outer edges of the two pattern sheet groups that are arranged to sandwich it in the stacking direction.

[0041] The area of ​​the second green sheet 12 should be larger than the planar area of ​​the pattern sheet group. By forming the first laminate 10 with the area of ​​the second green sheet 12 larger than the planar area of ​​the pattern sheet group, the second green sheet 12 can exert a restraining force over the entire planar direction of the pattern sheet groups located above and below it. The second green sheet 12 only needs to extend 0.1 mm or more outside the outer edges of the two pattern sheet groups arranged to sandwich it in the stacking direction.

[0042] As shown in Figures 3 and 4, the other side from which the second green sheet 12 does not protrude corresponds to the cut surface of the base laminate 50 (see Figure 2), so the end surfaces of the pattern sheet 3 and the second green sheet 12 may be flush.

[0043] 3 and 4, it is also possible to apply a restraining force to the entire planar direction of the group of pattern sheets located above and below the second green sheet 12. This is because, in the first laminates 10A and 10B shown in Figures 3 and 4, a portion of the second green sheet 12 is larger than the area of ​​the top or bottom surface of the first laminates 10A and 10B and protrudes from at least one side surface.

[0044] In the case of the first laminates 10A, 10B cut out from the base laminate 50 shown in Figures 3 and 4, as long as a portion of the second green sheet 12 protrudes from the side of the first laminates 10A, 10B at one point, the other portions (end faces) may have flat end faces in which the end faces of the pattern sheet group and the end faces of the second green sheet 12 form the same plane.

[0045] <1-5. Fabrication of Second Laminate: Step of Placing Constraint Sheets on Both Sides of First Laminate> Next, constraining sheets 4 are placed on both sides of the first laminate 10 in the stacking direction to fabricate the second laminate 20. As shown in the lower part of Fig. 1 , the second laminate 20 is sandwiched between the constraining sheets 4 placed on both sides of the first laminate 10 in the stacking direction.

[0046] When producing the second laminate 20, first, the constraining sheet 4 is placed on the surface of a flat table. In this case, the constraining sheet 4 placed on the surface side of the table is referred to as the lower constraining sheet 41.

[0047] The area of ​​the lower constraining sheet 41 should be larger than the area of ​​the first laminate 10 when viewed from above. The area of ​​the lower constraining sheet 41 should be larger than the area of ​​the second green sheet 12 that protrudes from the side surface of the first laminate 10. The lower constraining sheet 41 should be thick enough to bury a part of the first laminate 10.

[0048] When the first laminate 10 is placed on the lower constraining sheet 41 and degreased, it is preferable that a portion of the first laminate 10 sinks below the surface of the lower constraining sheet 41. This is because the lower constraining sheet 41 is likely to come into contact with the underside of the first laminate 10 and the side surfaces connected to this underside. When the lower constraining sheet 41 comes into contact with not only the underside but also the side surfaces of the first laminate 10, the constraining force of the lower constraining sheet 41 on the first laminate 10 can be increased.

[0049] Next, the first laminate 10 is placed on this lower constraining sheet 41. Next, another constraining sheet 4 is placed on the upper surface side of the first laminate 10. The other constraining sheet 4 placed on the upper surface side of the first laminate 10 is referred to as the upper constraining sheet 42.

[0050] The upper constraining sheet 42 placed on the upper surface of the first laminate 10 is preferably placed so as to cover the entire first laminate 10. The upper constraining sheet 42 placed on the upper surface of the first laminate 10 may have an area that extends beyond the outer edges of the first laminate 10. The outer edges of the first laminate 10 refer to the four outer edges.

[0051] The four outer edges are connected to four side surfaces that intersect with the four outer edges, respectively. The upper constraining sheet 42, which is placed on the top surface of the first laminate 10, is placed over the first laminate 10. In this state, the upper constraining sheet 42 is likely to come into contact with the top surface of the first laminate 10 and the side surfaces that connect to this top surface. When the upper constraining sheet 42 comes into contact with not only the top surface but also the side surfaces of the first laminate 10, the constraining force of the upper constraining sheet 42 on the first laminate 10 can be increased.

[0052] <1-6. Composition of Constraining Sheet> For example, alumina can be used as the inorganic composition that constitutes the constraining sheet 4. The constraining sheet 4 is formed, for example, by adding a binder to alumina powder as appropriate and mixing them to prepare a slurry, and then molding this slurry using a doctor blade method.

[0053] <1-7. Step of Firing Second Laminate> Next, the second laminate 20 is fired. The second laminate 20 is fired at a predetermined temperature (e.g., 900 to 1000°C) that is lower than the sintering start temperature of the constraining sheet 4. Then, the constraining sheet 4 is removed from the fired second laminate 20 to obtain the wiring substrate 100 (see FIG. 6).

[0054] <1-8. Firing Shrinkage Behavior of First Green Sheet and Second Green Sheet> Figure 5 is a schematic graph showing the shrinkage behavior of each sheet during firing. As shown in Figure 5, it is preferable that the second green sheet 12 begins to shrink at a lower temperature during firing than the first green sheet 11. It is preferable that the second green sheet 12 is almost completely sintered when the first green sheet 11 begins to shrink during firing.

[0055] It is preferable that the first green sheet 11 starts shrinking when the firing shrinkage of the second green sheet 12 is completed. When the second green sheet 12 tries to shrink, the second green sheet 12 is constrained by the adjacent first green sheet 11. When the first green sheet 11 tries to shrink, the first green sheet 11 is constrained by an insulating layer formed when the adjacent fired second green sheet 12 is heated.

[0056] In this case, shrinkage of the first laminate 10 in the planar direction is suppressed. The first laminate 10 tends to shrink in the thickness direction but shrink less in the planar direction. The first laminate 10 shrinks less in the planar direction but has a larger shrinkage rate in the thickness direction. The shrinkage rate of the first laminate 10 in the planar direction is smaller than the shrinkage rate in the thickness direction. The shrinkage rate may be calculated from the change in one-dimensional length, such as the length of one side of the first laminate 10 or the thickness of the first laminate 10. The method of manufacturing the disclosed wiring board 100 using the first green sheet 11 and the second green sheet 12 has been described above, but the manufacturing method of the wiring board 100 of the present disclosure is not limited to this. Another method is to replace the second green sheet 12 in the above manufacturing method with a ceramic paste coating film AF. Here, the other steps are the same as those described above except for using the ceramic paste coating film AF instead of the second ceramic green sheet 12, and therefore will not be described. The ceramic paste used contains the same ceramic composition as the second green sheet 12 described above. However, when the ceramic composition is prepared as a ceramic paste, the types and amounts of the organic binder and solvent are different. Varying the types and amounts of the organic binder and solvent adjusts the following characteristics: the viscosity of the ceramic paste, the printability of the coating film, the drying properties of the coating film after application, the volume change rate before and after drying, tensile strength, elongation, and adhesion to the first green sheet 11. The shape of the coating film AF (here, this refers to the shape when viewed in plan), similar to the second green sheet 12, can be a sheet-like shape. Furthermore, if the coating film AF is formed from the ceramic paste by, for example, screen printing, the plate pattern can be easily changed, allowing the coating film AF to be formed into a frame-like or grid-like pattern, as shown in Figures 8 to 10B. Figure 8 shows a coating film AF formed into a frame-like pattern. Figure 9 shows a coating film AF formed into a grid-like pattern. 10A and 10B are diagrams showing the shape of the coating film AF when viewed from above.Here, the terms "frame-shaped" and "grid-shaped" refer to the shape of the coating film AF when one wiring substrate 100 is viewed in plan view. When fabricating a multi-layered base laminate to simultaneously produce multiple wiring substrates 100, each region that will become a wiring substrate will have a frame-shaped pattern. However, because multiple regions that will become wiring substrates are connected, the coating film AF is connected in both the vertical and horizontal directions, which at first glance appears gritty. In this disclosure, the terms "frame-shaped" and "grid-shaped" refer to the shape of each wiring substrate 100 viewed as a single unit, even when forming a base laminate. Regarding the positioning of the coating film AF on the first green sheet 11, if the coating film AF has a frame shape, it is preferable to form it so that it follows the peripheral edge of the first laminate 10. Even if the coating film AF has a frame shape, it can be positioned near the middle layer of the first laminate 10, thereby suppressing shrinkage of the peripheral edge of the first laminate 10 when the first laminate 10 is fired. In other words, even if the coating film AF has a frame shape, the planar shrinkage rate of the middle layer in the stacking direction of the first laminate 10 can be reduced. On the other hand, if the coating film AF has a grid shape, it is preferable to form the coating film AF so as to fill the spaces between the conductor patterns 2 formed on the first green sheet 11 when the first laminate 10 is fabricated. In this case, the steps caused by the thickness of the conductor patterns 2 formed on the first green sheet 11 can be eliminated, thereby improving the flatness of each layer in the first laminate 10, thereby contributing to improving the dimensional accuracy of the final wiring board 100. Here, the grid shape does not necessarily mean a grid pattern in which the shapes of the spaces between the grids are all the same. The shapes of the spaces between the grids may be polygonal, including rectangular. The polygonal shape is not limited to shapes with sharp corners. Here, the polygonal shape also includes shapes with rounded corners. Furthermore, the areas of the spaces between the grids do not need to be the same, and may be negative shapes relative to the shapes and arrangement of the conductor patterns 2. Although I forgot to mention above, even when the shape of the coating film is frame-shaped, in the case of a laminate in which the conductive pattern 2 is formed near the peripheral edge of the first green sheet 11, it is preferable to use a negative arrangement.In this case, the inner edges of the frame-shaped coating film AF do not have to be straight. If the overall shape can be considered frame-shaped, the inner edges may have a sawtooth-like uneven shape. When the coating film AF has a lattice-like shape, shrinkage can be suppressed not only in the vicinity of the middle layer of the first laminate 10 and its peripheral portion, but also in the entire region including the central region of the first laminate 10 when the first laminate 10 is fired. Here, the peripheral portion and central region of the first laminate 10 refer to the positions when the first laminate 10 is viewed in a plane in the stacking direction. Using a ceramic paste coating film AF instead of the second green sheet 12 facilitates electrical continuity between the upper and lower layers sandwiching the coating film AF when forming the first laminate 10. This is because a frame-like or lattice-like shape of the coating film AF allows for a structure in which the upper layer conductor pattern 2 and the lower layer conductor pattern 2 are in direct contact with each other.

[0057] <1-9. Wiring board obtained by firing the second laminate> Figure 6 is a schematic cross-sectional view showing the change in shape of each component when a second laminate formed by placing constraint sheets on both sides of a first laminate is fired to obtain a wiring board. In Figure 6, the left side shows the cross-sectional shape of the first laminate 10 before firing. Also, the right side shows the cross-sectional shape of the wiring board 100 obtained after firing.

[0058] Here, the conventional manufacturing method and wiring board 200 in FIG. 7 will be described again for comparison with the manufacturing method and the shape of wiring board 100 shown in FIG. 6 . FIG. 7 is a schematic cross-sectional view showing the change in shape of each component when a wiring board is obtained by placing constraining sheets on both sides of a laminate and firing the laminate. FIG. 7 also shows the change in shape of each component when a second laminate 220 formed by placing constraining sheets 230 on both sides of a first laminate 210 is fired to obtain wiring board 200. In FIG. 7 , the left side shows the cross-sectional shape of first laminate 210 before firing. In addition, the right side shows the cross-sectional shape of wiring board 200 obtained after firing.

[0059] The wiring board 100 obtained by the above manufacturing method preferably has the shape shown in Fig. 2. The wiring board 100 shown on the right side of Fig. 6 may also have a recessed portion in the middle layer portion in the stacking direction. The wiring board 100 shown on the right side of Fig. 6 has a smaller recess on the side surface in the middle layer portion in the stacking direction compared to the wiring board 200 obtained by the conventional method shown on the right side of Fig. 7.

[0060] The wiring board 100 shown on the right side of Fig. 6 has a smaller recess depth on the side surface at the middle stage in the stacking direction compared to the wiring board 200 obtained by the conventional method shown on the right side of Fig. 7. The wiring board 100 shown on the right side of Fig. 6 has a larger radius of curvature of the recess on the side surface at the middle stage in the stacking direction compared to the wiring board 200 obtained by the conventional method shown on the right side of Fig. 7. In this case, it is preferable that the wiring board 100 shown on the right side of Fig. 6 has a larger radius of curvature obtained when an arc (curved surface) is drawn along the side surface throughout the entire thickness of the wiring board 100 compared to the wiring board 200 obtained by the conventional method shown on the right side of Fig. 7.

[0061] The wiring board 100 shown on the right side of Fig. 6 preferably has no recesses at least in the portion corresponding to the outermost layer of the side of the wiring board 100. The wiring board 100 shown on the right side of Fig. 6 may have a flat surface in the direction intersecting the surface of the outermost layer of the side of the wiring board 100, in the portion corresponding to the outermost layer. The wiring board 100 shown on the right side of Fig. 6 preferably has a flat surface perpendicular to the surface of the outermost layer of the side of the wiring board 100, in the portion corresponding to the outermost layer.

[0062] The wiring board 100 shown on the right side of Fig. 6 preferably has a recess on the side surface with a curvature radius of 10 mm or more. In the wiring board 100 shown on the right side of Fig. 6, the side surface in the middle layer preferably has a portion with a curvature radius of 5 mm or more. Note that the recess on the side surface refers to a range of recesses that can have a curvature extending from the upper layer through the middle layer to the lower layer, as shown in Fig. 6. The upper limit of the curvature radius may be 100 mm.

[0063] In the wiring substrate 100 shown on the right side of Figure 6, the radius of curvature of the recess on the side surface of the middle layer portion is preferably equal between two opposing side surfaces in the plate-like or hexahedral shape. The difference between the two radii of curvature of the two opposing side surfaces is preferably within 10%.

[0064] The difference Δr (%) between the two radii of curvature is calculated as follows. For example, in wiring substrate 100, the two opposing side surfaces are defined as a first side surface and a second side surface. The radius of curvature of the first side surface is assumed to be larger than the radius of curvature of the second side surface. The radius of curvature of the first side surface is defined as r1, and the radius of curvature of the second side surface is defined as r2.

[0065] Then, Δr (=r1-r2) obtained by subtracting the radius of curvature r2 of the second side surface from the radius of curvature r1 of the first side surface is divided by r1 and multiplied by 100 so that it can be displayed as a percentage.

[0066] Δr=((r1-r2) / r1)×100(%) (Equation 1)

[0067] When a flat surface is formed in part of the recess on the side surface of wiring substrate 100, making it difficult to determine the radius of curvature, the radius of curvature may be determined by extrapolating the curved surface between the outermost layers of wiring substrate 100. Calculating the radius of curvature by extrapolating the curved surface between the outermost layers of wiring substrate 100 means that the radius of curvature may be determined for the entirety of one side surface of wiring substrate 100 in the thickness direction.

[0068] The location for determining the radius of curvature across the thickness direction of one side surface of the wiring substrate 100 is preferably the center portion in the longitudinal direction of the side surface. Alternatively, the side surface may be divided into five or seven equal parts in the longitudinal direction, and the radii of curvature may be determined at three or five locations excluding both ends of the side surface in the longitudinal direction, and the average value may be calculated.

[0069] In wiring substrate 100, the side surfaces on which the recesses are formed may be located around the entire periphery of wiring substrate 100. In other words, wiring substrate 100 may have recesses on all four side surfaces. Even when wiring substrate 100 is formed by cutting a base laminate 50 (see FIG. 2 ) from which multiple wiring substrates 100 can be fabricated, it is preferable that a recess be formed on at least one side surface.

[0070] In the wiring board 100 shown on the right side of Figure 6, there may be a recessed portion in the middle layer in the stacking direction on the side of the wiring board 100, and there may be a portion parallel to a perpendicular flat surface on the surface of the outermost layer. Note that in the wiring board 100 shown on the right side of Figure 6, the recessed portion in the middle layer in the stacking direction on the side of the wiring board 100 may have a portion with a surface perpendicular to the surface of the outermost layer. The center of the recessed portion may have a flat portion. Here, the center of the recessed portion refers to the portion located in the center when the middle layer of the wiring board 100 is viewed in the thickness direction. The cross-sectional shape of the recess can also be described as being like a tray or basin.

[0071] The wiring board 100 shown on the right side of Figure 6 has a smaller recess on the side of the middle layer in the stacking direction compared to the wiring board 200 obtained by the conventional method shown on the right side of Figure 7, because the second green sheet 12 is interposed in the first laminate 10 before firing.

[0072] This is because, as described above, the second green sheet 12 has a sintering behavior in which the shrinkage start temperature is lower than that of the first green sheet 11 and the shrinkage end temperature is the same as or lower than the shrinkage start temperature of the first green sheet 11.

[0073] When the first laminate 10 is fired, the second green sheet 12 shrinks, but the first green sheet 11 constituting the pattern sheet 3 is in a state where shrinkage is unlikely to occur. At this time, the second green sheet 12 is sandwiched between the first green sheets 11 which have not yet started to shrink, so the second green sheet 12 is also in a state where it is unlikely to shrink compared to when the second green sheet 12 is fired alone.

[0074] On the other hand, the pattern sheet 3 including the first green sheet 11 begins to shrink after the sintering of the second green sheet 12 is almost complete, but since this first green sheet 11 is also in contact with the second green sheet 12, the shrinkage of the first green sheet 11 is now restrained by the second green sheet 12.

[0075] In this way, by placing the second green sheet 12 between the pattern sheets 3 having the first green sheets 11, the shrinkage of the first green sheets 11, which are the main green sheets 1 for forming the wiring board 100, during firing is suppressed.

[0076] As a result, it is possible to reduce the shrinkage rate in the planar direction when the wiring substrate 100 is obtained, which is mainly formed from the first green sheet 11. If the shrinkage rate in the planar direction when the wiring substrate 100 is obtained is reduced, the dimensional accuracy of the wiring formed on the wiring substrate 100 can be improved.

[0077] In particular, the above manufacturing method can improve the dimensional accuracy of wiring located in the middle of the stacking direction when manufacturing a highly multi-layer wiring board 100. Here, dimensional accuracy refers to the variation in the distance measured between wirings at specific positions formed on a plurality of wiring boards 100. The specific position refers to the distance between two pads formed on or near a diagonal line of the wiring board 100, or near two corners along one side.

[0078] Furthermore, in the above manufacturing method, when firing the first laminate 10, a restraint sheet 4 made of an inorganic composition having a higher sintering start temperature than the first green sheet 11 and the second green sheet 12 is superimposed on both sides of the first laminate 10 in the stacking direction.

[0079] In this case, by overlapping the constraining sheets 4 on both sides of the first laminate 10 in the stacking direction, it is possible to suppress firing shrinkage of the outermost layer of the first laminate 10 and the portion close to this outermost layer. According to this manufacturing method, firing shrinkage near the middle layer portion of the first laminate 10 can be suppressed, and at the same time, firing shrinkage of the outermost layer of the first laminate 10 and the portion close to this outermost layer can be suppressed, so that high dimensional accuracy can be obtained even in the inner layers of the wiring board 100, even if the wiring board 100 has a high stacking density.

[0080] As described above, the first green sheet 11 and the second green sheet 12 have different compositions, such as glass components, and this may result in different properties being obtained from the first green sheet 11 and the second green sheet 12.

[0081] For example, suppose that the first green sheet 11 is selected as the material for the main insulating layer to obtain the wiring board 100. In most cases, it is generally better to form the wiring board using only the first green sheet 11. For this reason, the above manufacturing method is advantageous for wiring boards with a large number of insulating layers.

[0082] Furthermore, in the above manufacturing method, since only one layer of green sheets with different compositions is interposed inside the first laminate 10, the properties of the wiring board obtained from the other first green sheets are less likely to be impaired.

[0083] In the case of a laminate in which the first green sheets 11 and the second green sheets 12 are alternately laminated, the dimensional accuracy of the wiring board 100 may be improved since the number of second green sheets 12 is large.

[0084] On the other hand, a reduced number of layers in the first green sheet 11 increases the probability of not achieving the characteristics of an insulating layer that is originally obtained from the first green sheet 11. In other words, a reduced number of layers in the first green sheet 11 may prevent the insulating layer from achieving the characteristics that are originally obtained from the first green sheet 11.

[0085] In contrast, the above-described manufacturing method can minimize the deterioration of the characteristics of the wiring board. Furthermore, the wiring board 100 obtained by such a manufacturing method may have a recessed middle layer in the thickness direction. In other words, the wiring board 100 obtained by the above-described manufacturing method may have a side surface including the middle layer, a portion of the upper layer, and a portion of the lower layer that contacts the middle layer, positioned more inward than the end of the outermost insulating layer.

[0086] Furthermore, in the above manufacturing method, it is preferable to use, as the first laminate 10, the second green sheets 12 arranged symmetrically above and below the middle layer portion of the first laminate 10. When the second green sheets 12 are arranged symmetrically above and below the middle layer portion of the first laminate 10, a wiring board with a highly symmetrical shape in the stacking direction can be obtained.

[0087] If the second green sheets 12 are arranged symmetrically above and below the middle layer portion of the first laminate 10, when the first laminate 10 shrinks during firing, the first laminate 10 will exhibit similar shrinkage behavior in the planar direction and thickness direction above and below the middle layer portion of the first laminate 10. This improves the flatness of the wiring board 100 on both sides.

[0088] When the first laminate 10 shrinks during firing, it tends to shrink symmetrically on both sides. This makes it possible to suppress the occurrence of warpage in the wiring board 100 due to shrinkage during firing. This makes it possible to obtain a wiring board 100 with minimal warpage.

[0089] An example of wiring board 100 having a highly symmetric shape in the stacking direction is the cross-sectional shape shown on the right side of Fig. 6. This is a state in which, when wiring board 100 has a recessed portion on its side surface, the deepest part of the curved surface forming the recessed portion is located at the center of wiring board 100 in the thickness direction.

[0090] In this case, the cross section of the curved surface should be mirror symmetrical with respect to the center position in the thickness direction. The shape of the recessed portion on the side surface of the wiring substrate 100 should be determined by observing the cross section of the wiring substrate 100 using, for example, a microscope. The microscope should be one of a stereo microscope, a scanning electron microscope, or a digital microscope.

[0091] In the above manufacturing method, it is preferable to use a layer number ratio of second green sheets 12 of 2% or more and 50% or less as the first laminate 10. As described above, when the first green sheets 11 are selected as green sheets containing materials for obtaining the basic characteristics of the wiring board 100, it is preferable that the volume ratio and the number of layers of green sheets with different compositions be small.

[0092] The ratio of the number of layers of the second green sheet 12 is preferably 2% or more and 30% or less. Expressing the ratio of the number of layers in terms of a thickness ratio, when the thickness of the second green sheet 12 is t1 and the thickness of the first laminate 10 is t0, the ratio t1 / t0 is preferably 0.02 or more and 0.3 or less.

[0093] Furthermore, in the above manufacturing method, it is preferable to use a first laminate 10 having 10 or more layers, including the pattern sheet 3 and the second green sheet 12. The above manufacturing method can obtain a wiring board with a small amount of recess on the side surface and with recessed portions that are highly symmetrical in the thickness direction, as shown on the right side of Figure 6. The number of layers that can achieve such a small amount of recess on the side surface is preferably 6 to 40, and more preferably 10 to 35.

[0094] The thickness of the wiring substrate 100 is preferably 1 mm or more and 5 mm or less, particularly 2 mm or more and 3 mm or less. The number of layers of the wiring substrate 100 is determined by polishing a cross section of the wiring substrate 100 and then observing the cross section with a digital microscope or a scanning electron microscope. A method of confirming the insulating layers based on the conductor layers formed inside the wiring substrate 100 may also be used. If the boundaries of the insulating layers constituting the wiring substrate 100 are difficult to determine, a method of determining the boundaries by measuring the distribution of specific elements using an analyzer such as EDS (Energy Dispersed Spectroscopy) may also be used.

[0095] Furthermore, in the above manufacturing method, when a virtual dividing line is formed to divide the first laminate 10 into two equal parts in the stacking direction, it is preferable that the dividing line be located within the thickness range of the second green sheet 12.

[0096] When the line dividing the thickness of the first laminate 10 is located at the center of the thickness of the first laminate 10, and the second green sheet 12 is located at the center of the thickness of the first laminate 10, the binding force of the second green sheet 12 tends to act evenly in both directions of the thickness of the first laminate 10.

[0097] This makes it possible to obtain wiring board 100 in which the shape of the recessed portion on the side surface is highly symmetric in the thickness direction. The isotope may be virtually set using a scale marked on the eyepiece or display of the digital microscope when observing the cross section of wiring board 100 with, for example, a digital microscope.

[0098] Furthermore, in the above manufacturing method, as shown in Table 1, it is preferable to use a first green sheet 11 containing silica in a proportion of 30 mass% or more and 40 mass% or less and glass in a proportion of 60 mass% or more and 70 mass% or less.

[0099] As shown in Table 1, it is preferable to use second green sheets 12 containing 5% to 15% by mass of silica and 85% to 95% by mass of glass. Furthermore, it is preferable to use constraining sheets 4 containing 85% to 95% by mass of alumina, 2% to 3% by mass of silica, and 5% to 15% by mass of glass.

[0100]

[0101] When the second laminate 20 is formed using a green sheet of the above composition, it is possible to obtain a wiring board 100 having shallow recesses on the side surfaces as shown on the right side of FIG.

[0102] The components of the organic vehicle contained in each green sheet are estimated using, for example, an FT-IR (Fourier transform infrared spectrometer). The content of the organic vehicle contained in each green sheet is determined by burning each green sheet and measuring the change in weight. The inorganic powder contained in each green sheet is identified by performing X-ray diffraction on the green sheet.

[0103] In addition, in the above manufacturing method, the first laminate 10 may be formed by laminating a second pattern sheet, which is a pattern sheet in which at least one of via conductors and a conductor pattern is formed on the second green sheet 12.

[0104] In this case, the ratio of the via conductors and the conductive patterns is preferably 0.001 to 0.5, both inclusive, when the area of ​​the second green sheet 12 is taken as 1. The via conductors and the conductive patterns are preferably located in the center of the main surface of the second green sheet, with 60% or more of their area per surface being taken as the ratio.

[0105] Here, the central portion of the main surface of the second green sheet 12 refers to the region located in the central portion when the surface of the outermost layer of the first laminate 10 is virtually divided into nine equal parts, three vertical rows and three horizontal rows, as shown in Figure 2, for example.

[0106] The central portion of the main surface of second green sheet 12 is preferably located directly below the portion where the electrical elements to be mounted on wiring board 100 will be mounted. In particular, 70% or more of the via conductors and conductor patterns are preferably located in the central portion of the main surface of the second green sheet in terms of area ratio per surface.

[0107] In the above manufacturing method, it is preferable to use, as the second laminate 20, a structure in which the constraint sheet 4 protrudes outward from the side surface of the first laminate 10, as shown in the lower part of Fig. 1. In other words, it is preferable to use, as the second laminate 20, a structure in which the constraint sheet 4 is arranged so as to form an overhang on the side surface of the first laminate 10.

[0108] As described above, the upper constraining sheet 42 placed on the top surface side of the first laminate 10 is preferably in a state in which it covers the first laminate 10, which makes it easier for the upper constraining sheet 42 to come into contact with the top surface of the first laminate 10 as well as the side surfaces connected to it. When the upper constraining sheet 42 comes into contact with not only the top surface of the first laminate 10 but also the side surfaces, the constraining force of the upper constraining sheet 42 on the first laminate 10 can be increased.

[0109] The overhanging portion formed by the constraint sheet 42 preferably has the same length (or width) in the direction of the four side surfaces of the first laminate 10. The constraint sheet 42 preferably does not contact the constraint sheet 41 disposed below the first laminate 10. This is because, when the constraint sheet 42 does not contact the constraint sheet 41 disposed below the first laminate 10, the organic vehicle contained in the first laminate 10 can more easily escape from the sides of the first laminate 10, making degreasing easier. The above describes an example of the wiring substrate 100 obtained by firing the second laminate 20, using the second green sheet 12. However, it goes without saying that the present disclosure also provides a similar second laminate 20 and wiring substrate 100 when a ceramic paste coating film AF is used instead of the second green sheet 12, as described above.

[0110] (Sample Preparation) First, a green sheet 1 measuring 200 mm x 200 mm x 200 μm thick was prepared, containing a glass ceramic raw material powder. The first green sheet 11 contained 35 mass% silica and 65 mass% glass. The second green sheet 12 contained 10 mass% silica and 90 mass% glass. The constraining sheet 4 contained 85 mass% alumina, 5 mass% silica, and 10 mass% glass.

[0111] The organic vehicle used in each of the second green sheets 12 was a polyvinyl butyral resin, toluene, and alcohols. The polyvinyl butyral resin used in the second green sheet 12 had a lower glass transition point than the polyvinyl butyral resin used in the first green sheet 11.

[0112] The conductive paste for the conductive layer was a mixture of copper powder and alkaline earth borosilicate glass powder. A cellulose-based organic resin was used as the organic vehicle. The solid content was 100 parts by mass of copper powder and 30 parts by mass of alkaline earth borosilicate glass powder.

[0113] Through holes were formed in the first green sheet 11 to form raw via conductors and conductor patterns. The area of ​​the main surface of the first laminate 10 was set to 100 mm × 100 mm. This 100 mm × 100 mm area was divided into three vertical rows and three horizontal rows, and through holes with a diameter of 100 μm were formed in the center of each of the nine equal parts.

[0114] Raw via conductors were formed in the through holes. Pad patterns with a diameter of 200 μm were formed on the surfaces of the raw via conductors. The through holes were arranged in a 100×100 grid pattern with a pitch of 400 μm.

[0115] Furthermore, one through hole of the same diameter was formed at each of the four corners of the 100 mm × 100 mm area, and raw via conductors and pad patterns were similarly formed. Twenty pattern sheets (first pattern sheets) 3 each having such a conductor pattern on the first green sheet 11 were prepared.

[0116] A conductor of the same pattern was also formed on the second green sheet 12. Ten pattern sheets 3 made from the first green sheet 11 were stacked, and then the pattern of the second green sheet 12 was laid on top of this. Ten more pattern sheets 3 made from the first green sheet 11 were laid on top of this to produce a temporary laminate that would become the first laminate 10.

[0117] The temporary laminate was pressurized and heated (30 MPa, 100°C, 10 minutes) to produce a first laminate 10. The first laminate 10 was cut into a size of approximately 100 mm x 100 mm x 4 mm. At this time, the pattern sheet 3 formed from the second green sheet 12 located in the center of the lamination direction of the first laminate 10 slightly protruded from the cut side surface. The protrusion amount was approximately 10 μm.

[0118] This is because the glass transition point of the polyvinyl butyral resin used in the second green sheet 12 is lower than the glass transition point of the polyvinyl butyral resin used in the first green sheet 11.

[0119] Next, the prepared first laminate 10 was sandwiched between constraint sheets 4 to prepare a second laminate 20. The area of ​​the upper constraint sheet 42 was slightly larger than the area of ​​the first laminate 10. The length of each side of the constraint sheet 4 was 101.5 mm.

[0120] The restraining sheet 41 placed on the lower side of the first laminate 10 had an area of ​​150 mm × 150 mm. The upper restraining sheet 42 covered the surface of the first laminate 10 and was in contact with part of the side surface.

[0121] The firing was carried out under the conditions that the samples were degreased in a moist nitrogen atmosphere, and then in a dry nitrogen atmosphere at a maximum temperature of 900°C for 2 hours. The number of samples was 15. Sample 2 was also produced as a comparative example under the same conditions except that the second green sheet 12 was not inserted.

[0122] (Evaluation of Sample) The sample after firing was evaluated. First, the binding sheet 4 on the surface of the sample (wiring board) after firing was removed by polishing to expose the surface of the wiring board.

[0123] Next, the cross section of one of the prepared samples was polished, and the shape of the side surface of the wiring substrate was observed. Sample 1 (wiring substrate 100) had the shape shown on the right side of Fig. 6, but Sample 2 (wiring substrate 200) of the comparative example had a large recess, as shown on the right side of Fig. 7.

[0124] The amount of recession in Sample 1 was one-third of that in Sample 2. The amount of recession in one sample was calculated from the average value of the four side surfaces. The dimensional accuracy of the produced Sample 1 was evaluated by measuring the length of each side of the pad pattern at the four corners formed on the insulating layer corresponding to the second green sheet 12 in the wiring substrate 100.

[0125] The dimensional accuracy of the fabricated sample 2 was evaluated by measuring the length of each side of the pad pattern at the four corners formed on the insulating layer corresponding to the first green sheet, which is the 11th layer from the top in the wiring substrate 200.

[0126] The dimensional accuracy of Sample 1 was calculated from the average (x) and standard deviation (σ) of the lengths of the four sides of each of 15 samples. σ / x of Sample 1 was 1 / 3 of the σ / x of Sample 2, a comparative example in which the second green sheet was not used.

[0127] In Sample 1, the shapes of the recesses formed on the side surfaces of the wiring substrate 100 were symmetrically arranged on the upper and lower sides with the middle layer portion at the center. Also, in Sample 1, the ratio of the number of layers of the pattern sheet 3 from the second green sheet 12 was 4.7%.

[0128] In addition, the number of layers in Sample 1 was 21. In addition, in Sample 1, when a hypothetical dividing line dividing wiring substrate 100 into two equal parts in the stacking direction was formed, the dividing line was located within the thickness range of the insulating layer formed from second green sheet 12.

[0129] It was also confirmed that the compositions of the insulating layers constituting Sample 1 were such that the insulating layer derived from first green sheet 11 contained 35 mass % silica and 65 mass % glass, and the insulating layer derived from second green sheet 12 contained 10 mass % silica and 90 mass % glass. The compositions of the insulating layers were determined from quantitative values ​​obtained by applying fluorescent X-rays to a cross section of wiring substrate 100.

[0130] 2. Wiring Board Next, a wiring board according to an embodiment will be described with reference to Fig. 1 and Fig. 6. As shown in Fig. 1 and Fig. 6, wiring board 100 is a multilayer body made up of a pattern sheet (first pattern sheet) 3 which is a first insulating layer and a second green sheet 12 which is a second insulating layer.

[0131] The pattern sheet 3 and the second green sheet 12 have different compositions. The pattern sheet 3 forms a conductor-imparting substrate layer having a conductor pattern 2. The conductor-imparting substrate layer is a glass ceramic insulating layer to which a conductor is imparted.

[0132] The pattern sheet 3 forms a conductor-imparting substrate layer laminate in which a plurality of pattern sheets 3 are laminated. The conductor-imparting substrate layer laminate is a laminate in which a plurality of pattern sheets 3, which are conductor-imparting substrate layers, are laminated. The conductor-imparting substrate layer laminate becomes the first laminate 10 described above.

[0133] The second green sheet 12 is located between the two conductor-imparting substrate layer laminates, that is, the two overlapping pattern sheets 3 .

[0134] In this way, the wiring board 100 is constructed as a multilayer body of the pattern sheet 3 and the second green sheet 12 .

[0135] In the wiring board 100, the two pattern sheets 3 may have the same thickness. This allows the first laminate 10 to shrink during firing, with the upper and lower sides of the first laminate 10, centered on the middle layer portion, to exhibit similar shrinkage behavior in the planar direction and thickness direction. This improves the flatness of the wiring board 100 on both sides.

[0136] When the first laminate 10 shrinks during firing, it tends to shrink symmetrically on both sides. This makes it possible to suppress the occurrence of warpage in the wiring board 100 due to shrinkage during firing. This makes it possible to obtain a wiring board 100 with minimal warpage.

[0137] In the wiring substrate 100, the pattern sheet 3 and the second green sheet 12 may both be glass ceramics containing a glass phase and an inorganic filler. The second green sheet 12 may have a higher glass content than the pattern sheet 3.

[0138] Furthermore, the layer number ratio of second green sheet 12 may be 2% or more and 50% or less in wiring board 100. When first green sheet 11 is selected as a green sheet containing materials for obtaining the basic characteristics of wiring board 100, it is preferable that the volume ratio or the number of layers of green sheets having different compositions be small.

[0139] The layer number ratio of the second green sheet 12 may be 2% or more and 30% or less. When the layer number ratio is expressed in terms of a thickness ratio, where t1 is the thickness of the second green sheet 12 and t0 is the thickness of the first laminate 10, t1 / t0 may be 0.02 or more and 0.3 or less.

[0140] Furthermore, in the wiring board 100, the first laminate 10 may have 10 or more layers of pattern sheets 3. This allows for a wiring board with a small side recess and high symmetry in the thickness direction of the recessed portion, as shown on the right side of FIG. 6 . The number of layers that can achieve such a side recess is preferably 6 to 40 layers, and particularly preferably 10 to 35 layers. In this case, the number of layers in the wiring board is preferably 10 or more, but with 20 to 30 or more, or 40 or more layers, the range where the restraining force of the restraining sheet 230 does not reach becomes larger, and the radius of curvature of the side tends to become larger. The upper limit of the number of layers can be 50 layers.

[0141] The thickness of wiring board 100 is preferably 1 mm or more and 5 mm or less, and particularly 2 mm or more and 3 mm or less. In other words, the thickness of the wiring board is preferably 1 mm or more, but if it is 2 mm or more, 3 mm or more, or 4 mm or more, the range where the restraining force of restraining sheet 230 does not apply becomes larger, and the radius of curvature of the side surface tends to become larger. The upper limit of the thickness can be 5 mm.

[0142] Furthermore, in the wiring board 100, when a virtual dividing line is formed that divides the second laminate 20, which is a multilayer body made of the pattern sheet 3 and the second green sheet 12, into two equal parts in the stacking direction, the dividing line may be located within the thickness range of the second green sheet 12.

[0143] When the thickness dividing line of the first laminate 10 is located at the center of the thickness of the first laminate 10, and the second green sheet 12 is located at the center of the thickness of the first laminate 10, the binding force of the second green sheet 12 tends to act equally in both directions of the thickness of the first laminate 10. A wiring board 100 using a ceramic paste coating film AF instead of the second green sheet 12 was also fabricated using a similar method. First, the same ceramic composition as the second green sheet 12 was used, and an organic vehicle containing a cellulose-based organic resin was added to it to prepare a ceramic paste. Next, this ceramic paste was used to form a coating film AF on the first green sheet by screen printing. Two types of coating film AF were fabricated for each wiring board 100: a frame-shaped pattern and a grid-shaped pattern. In this case, the frame-shaped pattern and the grid-shaped pattern were formed so as to fit between the conductor patterns 2 previously formed on the first green sheet 11 and reduce the step of the conductor patterns 2. The thickness of the coating film AF was set to about half the thickness of the second green sheet 12. The first green sheet 11 on which the coating film AF was formed was laminated so as to be at the position of the middle layer when forming the first laminate 10. The wiring boards 100 obtained by forming the frame-shaped or lattice-shaped coating film AF all had slightly greater deformation in the middle layer than the wiring boards 100 using the second green sheet 12 as a constraining layer, but the deformation in the middle layer was smaller than the wiring boards 100 not using the second green sheet 12 or the coating film AF.

[0144] The present disclosure has been described in detail above, but the present disclosure is not limited to the above-described embodiments, and various modifications, improvements, etc. are possible within the scope that does not deviate from the gist of the present disclosure.

[0145] The disclosed embodiments should be considered in all respects as illustrative and not restrictive. Indeed, the above-described embodiments may be embodied in various forms. Furthermore, the above-described embodiments may be omitted, substituted, or modified in various ways without departing from the scope and spirit of the appended claims.

[0146] The present technology can also be configured as follows: (1) A method for manufacturing a wiring board, comprising: forming a first pattern sheet having at least one of via conductors and a conductor pattern on a first green sheet; preparing a second green sheet having a shrinkage start temperature lower than that of the first green sheet and a shrinkage end temperature equal to or lower than that of the first green sheet; preparing and stacking a plurality of the first pattern sheets, interposing the second green sheet in a middle layer portion in the stacking direction to form a first laminate; laminating, on both sides of the first laminate in the stacking direction, constraining sheets mainly composed of an inorganic composition having a sintering start temperature higher than that of the first green sheet and the second green sheet to form a second laminate; and firing the second laminate. (2) The method for manufacturing a wiring board according to (1), wherein the first laminate is formed by symmetrically arranging the second green sheets above and below the middle layer portion of the first laminate. (3) The method for manufacturing a wiring board according to (1) or (2), wherein the first laminate is one in which the layer number ratio of the second green sheet is 2% or more and 50% or less. (4) The method for manufacturing a wiring board according to any one of (1) to (3), wherein the first laminate is one in which the number of layers, including the first pattern sheet and the second pattern sheet, is 10 or more. (5) The method for manufacturing a wiring board according to any one of (1) to (4), wherein the first laminate is one in which, when a virtual dividing line dividing the first laminate in half in the stacking direction is formed, the virtual dividing line is located within the thickness of the second green sheet.(6) The method for manufacturing a wiring board according to any one of (1) to (5), wherein the first green sheet contains silica at a ratio of 30% by mass to 40% by mass and glass at a ratio of 60% by mass to 70% by mass, the second green sheet contains silica at a ratio of 5% by mass to 95% by mass and glass at a ratio of 85% by mass to 95% by mass, and the constraining sheet contains alumina at a ratio of 85% by mass to 95% by mass, silica at a ratio of 20% by mass to 30% by mass and glass at a ratio of 5% by mass to 15% by mass. (7) The method for manufacturing a wiring board according to any one of (1) to (6), wherein the first laminate is formed by laminating a second pattern sheet having at least one of via conductors and a conductor pattern on the second green sheet. (8) The method for manufacturing a wiring board according to any one of (1) to (7), wherein the second laminate is one in which the constraining sheet protrudes outward from a side surface of the first laminate. (9) A method for manufacturing a wiring board, comprising: forming a first pattern sheet having at least one of via conductors and a conductor pattern on a first green sheet; preparing a ceramic paste containing a ceramic composition having a shrinkage start temperature lower than that of the first green sheet and a shrinkage end temperature equal to or lower than the shrinkage start temperature of the first green sheet; when preparing and stacking a plurality of the first pattern sheets, forming a first laminate by interposing a coating film of the ceramic paste in a middle layer portion in the stacking direction; laminating a constraining sheet containing as a main component an inorganic composition having a sintering start temperature higher than that of the first green sheet and the coating film on both sides of the first laminate in the stacking direction to form a second laminate; and firing the second laminate. (10) A method for manufacturing a wiring board according to (9), wherein the coating film is formed in a frame shape or a lattice shape.(11) A wiring board having a multilayer structure including a first insulating layer and a second insulating layer having different compositions, wherein the first insulating layer forms a conductor-imparting substrate layer having a conductor, the conductor-imparting substrate layer forms a conductor-imparting substrate layer laminate in which a plurality of the conductor-imparting substrate layers are laminated, and the second insulating layer is located between two overlapping conductor-imparting substrate layer laminates. (12) The wiring board according to (11), wherein the two conductor-imparting substrate layer laminates have the same thickness. (13) The wiring board according to (11) or (12), wherein the first insulating layer and the second insulating layer are both glass ceramics containing a glass phase and an inorganic filler, and the second insulating layer has a higher glass content than the first insulating layer. (14) The wiring board according to any one of (11) to (13), wherein the layer number ratio of the second insulating layer is 2% or more and 50% or less. (15) The wiring board according to any one of (11) to (14), wherein the conductor-imparting substrate layer laminate has 10 or more first insulating layers. (16) The wiring board according to any one of (11) to (15), wherein, when a virtual dividing line dividing the multilayer body of the first insulating layers and the second insulating layers into two equal parts in a stacking direction is formed, the dividing line is located within a thickness range of the second insulating layers.

[0147] REFERENCE SIGNS LIST 1 green sheet 2 conductive pattern 3 pattern sheet 4 constraint sheet 10 first laminate 11 first green sheet 12 second green sheet 20 second laminate 50 base laminate 100 wiring board AF coating film

Claims

1. A method for manufacturing a wiring board, comprising: a step of forming a first pattern sheet having at least one of via conductors and a conductor pattern on a first green sheet; a step of preparing a second green sheet having a shrinkage start temperature lower than that of the first green sheet and a shrinkage end temperature equal to or lower than that of the first green sheet; a step of forming a first laminate by interposing the second green sheet in a middle layer portion in the stacking direction when preparing and stacking a plurality of the first pattern sheets; a step of laminating a constraint sheet mainly composed of an inorganic composition having a sintering start temperature higher than that of the first green sheet and the second green sheet on both sides in the stacking direction of the first laminate to form a second laminate; and a step of firing the second laminate.

2. The method for manufacturing a wiring board according to claim 1, wherein the first laminate is formed by arranging the second green sheets symmetrically above and below the middle layer of the first laminate.

3. The method for manufacturing a wiring board according to claim 1 or 2, wherein the ratio of the number of layers of the second green sheet to the number of layers of the first laminate is 2% or more and 50% or less.

4. A method for manufacturing a wiring board according to any one of claims 1 to 3, wherein the first laminate has 10 or more layers, including the first pattern sheet and the second pattern sheet.

5. A method for manufacturing a wiring board according to any one of claims 1 to 4, wherein the first laminate is one in which, when a line dividing the first laminate into two equal parts in the stacking direction is formed, the line is located within the thickness range of the second green sheet.

6. A method for manufacturing a wiring board as set forth in any one of claims 1 to 5, wherein the first green sheet contains silica in a proportion of 30% by mass to 40% by mass and glass in a proportion of 60% by mass to 70% by mass, the second green sheet contains silica in a proportion of 5% by mass to 95% by mass and glass in a proportion of 85% by mass to 95% by mass, and the restraining sheet contains alumina in a proportion of 85% by mass to 95% by mass, silica in a proportion of 20% by mass to 30% by mass, and glass in a proportion of 5% by mass to 15% by mass.

7. A method for manufacturing a wiring board according to any one of claims 1 to 6, wherein the first laminate is a second pattern sheet formed by forming at least one of via conductors and a conductor pattern on the second green sheet.

8. A method for manufacturing a wiring board according to any one of claims 1 to 7, wherein the second laminate is formed by using the constraint sheet that protrudes outward from the side surface of the first laminate.

9. A method for manufacturing a wiring board, comprising: a step of forming a first pattern sheet having at least one of via conductors and a conductor pattern on a first green sheet; a step of preparing a ceramic paste containing a ceramic composition having a shrinkage start temperature lower than that of the first green sheet and a shrinkage end temperature equal to or lower than that of the first green sheet; a step of forming a first laminate by interposing a coating film of the ceramic paste in the middle layer portion in the stacking direction when preparing and stacking a plurality of the first pattern sheets; a step of forming a second laminate by laminating, on both sides in the stacking direction of the first laminate, constraint sheets mainly composed of an inorganic composition having a sintering start temperature higher than that of the first green sheet and the coating film; and a step of firing the second laminate.

10. The method for manufacturing a wiring board according to claim 9, wherein the coating film is formed in a frame or grid shape.

11. A wiring board comprising a multilayer body made of a first insulating layer and a second insulating layer having mutually different compositions, wherein the first insulating layer forms a conductor-imparting substrate layer having a conductor, the conductor-imparting substrate layer forms a conductor-imparting substrate layer laminate in which a plurality of the conductor-imparting substrate layers are laminated, and the second insulating layer is located between the layers where two of the conductor-imparting substrate layer laminates overlap.

12. The wiring board according to claim 11, wherein the two conductor-imparting substrate layer laminates have the same thickness.

13. The wiring board according to claim 11 or 12, wherein the first insulating layer and the second insulating layer are both glass ceramics containing a glass phase and an inorganic filler, and the second insulating layer has a higher glass content than the first insulating layer.

14. The wiring board according to any one of claims 11 to 13, wherein the ratio of the number of second insulating layers is 2% or more and 50% or less.

15. The wiring board according to any one of claims 11 to 14, wherein the conductor-imparting substrate layer laminate has 10 or more first insulating layers.

16. A wiring board according to any one of claims 11 to 15, wherein when a hypothetical line dividing the multilayer body made up of the first insulating layer and the second insulating layer into two equal parts in the stacking direction is formed, the line is located within the thickness of the second insulating layer.

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