Wiring substrate and method of making wiring substrate

Abstract

A wiring substrate includes a core layer having a hole penetrating therethrough in a thickness direction thereof, and having a projecting part projecting from an inner wall of the hole toward an inner space of the hole, the projecting part being situated at a border that divides a plurality of areas in the hole, a plurality of electronic components disposed in the areas, respectively, the electronic components being arranged at a spaced interval with the projecting part therebetween, and a resin layer filling the hole and supporting the electronic components, wherein a thickness of the projecting part in the thickness direction of the core layer decreases toward a tip of the projecting part.

Claims

What is claimed is: 1 . A wiring substrate, comprising: a core layer having a hole penetrating therethrough in a thickness direction thereof, and having a projecting part projecting from an inner wall of the hole toward an inner space of the hole, the projecting part being situated at a border that divides a plurality of areas in the hole; a plurality of electronic components disposed in the areas, respectively, the electronic components being arranged at a spaced interval with the projecting part therebetween; and a resin layer filling the hole and supporting the electronic components, wherein a thickness of the projecting part in the thickness direction of the core layer decreases toward a tip of the projecting part. 2 . The wiring substrate as claimed in claim 1 , wherein the hole has a rectangular shape in a plan view perpendicular to the thickness direction, and the projecting part situated at the border projects from each of two respective opposite inner walls, among the inner walls, situated sideways relative to a direction in which the areas are arranged side by side. 3 . The wiring substrate as claimed in claim 2 , wherein a gap between the projecting parts projecting from the two respective opposite inner walls is shorter than a width of the electronic components in a direction perpendicular to the direction in which the areas are arranged side by side. 4 . The wiring substrate as claimed in claim 1 , wherein a width of the projecting part in the direction in which the areas are arranged side by side decreases toward a tip of the projecting part. 5 . The wiring substrate as claimed in claim 1 , wherein each of the electronic components has a cuboid shape with electrodes disposed on opposite ends thereof opposite to each other in a longitudinal direction of the cuboid shape. 6 . The wiring substrate as claimed in claim 1 , wherein each of the electronic components has a cuboid shape, and the electronic components are arranged side by side in a longitudinal direction of the cuboid shape. 7 . The wiring substrate as claimed in claim 1 , wherein each of the electronic components has a cuboid shape, and the electronic components are arranged side by side in a direction perpendicular to a longitudinal direction of the cuboid shape. 8 . The wiring substrate as claimed in claim 1 , wherein the electronic components are capacitor chips.
CROSS-REFERENCE TO RELATED APPLICATIONS [0001] The present application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2014-043317 filed on Mar. 5, 2014, with the Japanese Patent Office, the entire contents of which are incorporated herein by reference. FIELD [0002] The disclosures herein relate to a wiring substrate and a method of making a wiring substrate. BACKGROUND [0003] A certain type of wiring board is known in the art that has a substrate having a cavity formed therein and an electronic component disposed in the cavity. The wiring board further includes an insulating layer formed to cover the opening of the cavity (see Japanese Patent Application Publication No. 2011-216740, for example). [0004] As described above, a related-art wiring board has a single electronic component disposed in a single cavity. [0005] Placing a plurality of electronic components in a single cavity may give rise to a risk of causing the electronic components to be displaced at the time of filling an insulating layer in the cavity. Such displacement of the electronic components is associated with a risk of having short-circuit caused by physical contact or a risk of having a failure to secure connection with a wiring layer, thereby creating a problem regarding electrical reliability. [0006] Accordingly, it may be desirable to provide a wiring substrate and a method of making the wiring substrate that ensure improved electrical reliability with respect to a plurality of electronic components disposed in a single penetrating hole. SUMMARY [0007] According to an aspect of the embodiment, a wiring substrate includes a core layer having a hole penetrating therethrough in a thickness direction thereof, and having a projecting part projecting from an inner wall of the hole toward an inner space of the hole, the projecting part being situated at a border that divides a plurality of areas in the hole, a plurality of electronic components disposed in the areas, respectively, the electronic components being arranged at a spaced interval with the projecting part therebetween, and a resin layer filling the hole and supporting the electronic components, wherein a thickness of the projecting part in the thickness direction of the core layer decreases toward a tip of the projecting part. [0008] The object and advantages of the embodiment will be realized and attained by means of the elements and combinations particularly pointed out in the claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. BRIEF DESCRIPTION OF DRAWINGS [0009] FIG. 1 is a cross-sectional view of a wiring substrate according to an embodiment; [0010] FIGS. 2A through 2C are cross-sectional views of the core; [0011] FIGS. 3A and 3B are drawings illustrating an arrangement in which capacitor chips are disposed in a penetrating hole of the core; [0012] FIGS. 4A through 4E are drawings illustrating a method of making the wiring substrate of the embodiment; [0013] FIGS. 5A through 5C are drawings illustrating a method of making the wiring substrate of the embodiment; [0014] FIG. 6 is a drawing illustrating the wiring substrate and an LSI chip formed thereon; [0015] FIGS. 7A through 7G are drawings illustrating variations of the penetrating hole of the embodiment; [0016] FIGS. 8A and 8B are drawings illustrating processes for forming a penetrating hole by use of a laser beam; and [0017] FIGS. 9A through 9D illustrate the penetrating hole formed through the core by a laser process. DESCRIPTION OF EMBODIMENTS [0018] In the following, a description will be given of embodiments of a wiring substrate and a method of making a wiring substrate. [0019] FIG. 1 is a cross-sectional view of a wiring substrate 100 according to an embodiment. In the following, a description will be given by using an XYZ coordinate system having an XY plane parallel to a wiring substrate 100 wherein such a coordinate system is an example of an orthogonal coordinate system. FIG. 1 illustrates a cross-section of the wiring substrate 100 taken along a plane parallel to the XZ plane and taken at the center point of the wiring substrate 100 in the Y-axis direction. [0020] The wiring substrate 100 includes a core 110 , a wiring layer 111 A, through electrodes 120 A and 120 B, insulating layers 130 A and 130 B, and capacitor chips 200 . [0021] The wiring substrate 100 further includes vias 140 A 1 , 140 A 2 , 140 A 3 , 140 A 4 , 140 A 5 , 140 A 6 , 140 B 1 , 140 B 2 , 140 B 3 , 140 B 4 , 140 B 5 , and 140 B 6 . [0022] The wiring substrate 100 further includes wiring layer segments 150 A 1 , 150 A 2 , 150 A 3 , 150 A 4 , 150 A 5 , 150 A 6 , 150 B 1 , 150 B 2 , 150 B 3 , 150 B 4 , 150 B 5 , and 150 B 6 , and also includes solder resist layers 160 A and 160 B. [0023] In the following, for the sake of convenience of explanation, a surface facing upward in the drawings will be referred to as an upper surface, and a surface facing downward will be referred to as a lower surface. Moreover, terms “upward” and “downward” will be used for the sake of convenience of explanation. It may be noted, however, that terms such as “upper surface”, “lower surface”, “upward”, “downward”, “upper”, and “lower” used in the description are not intended to indicate the permanent nature of upper and lower positions, but are simply used for the purpose of referring to upper and lower positions temporarily set in the drawings. [0024] The core (i.e., core layer) 110 may be a glass cloth base material impregnated with epoxy resin having copper foils attached to the surfaces thereof, and serves as a core for a buildup substrate. One of the copper foils formed on the upper surface of the core 110 is patterned to form the wiring layer 111 A. The other one of the copper foils formed on the lower surface of the core 110 may be patterned to form another wiring layer. If no wiring layer is necessary on the lower surface of the core 110 , a copper foil suffices to be attached only to the upper surface of the core 110 . [0025] The core 110 has a penetrating hole 110 H formed therein. The penetrating hole 110 H penetrates through the core 110 in the thickness direction thereof (i.e., in the Z-axis direction in FIG. 1 ). The inner wall of the penetrating hole 110 H of the core 110 has a projecting part 110 A that projects inwardly inside the penetrating hole 110 H. The projecting part 110 A is not situated on the cross-section illustrated in FIG. 1 , so that dashed lines are used to depict the position of the projecting part 110 A. The projecting part 110 A will be explained later in connection with FIG. 2 and FIG. 3 . [0026] The wiring layer 111 A is a metal layer formed on the upper surface of the core 110 . The wiring layer 111 A may be formed by patterning the copper foil attached to the upper surface of the core 110 , for example. The wiring layer 111 A has a hollow rectangular shape (i.e., rectangular loop shape) surrounding the opening of the penetrating hole 110 H in a plan view (i.e., as viewed from above). [0027] The through electrodes 120 A and 120 B are electrodes penetrating the core 110 in the thickness direction thereof. The through electrodes 120 A and 120 B are situated on opposite sides of the penetrating hole 110 H, respectively. The through electrodes 120 A and 120 B are formed by filling with copper plating the through holes formed through the core 110 on the opposite sides of the penetrating hole 110 H. [0028] In this example, the through electrodes 120 A and 120 B have the configuration in which the through holes are filled with copper plating. Alternatively, through hole vias may be made by forming copper plating in a cylindrical shape on the inner wall of the through holes. [0029] The insulating layer 130 A is formed to cover the upper surfaces of the core 110 , the wiring layer 111 A, the through electrodes 120 A and 120 B, and the capacitor chips 200 . The insulating layer 130 A is formed by thermally curing a resin material such as an epoxy-based material or polyimide-based material through heating and application of pressure. It may be noted that the insulating layer 130 A is formed after the insulating layer 130 B is formed in the arrangement that is upside down relative to the arrangement illustrated in FIG. 1 . [0030] The insulating layer 130 B may be made by using the same resin material as the resin material such as an epoxy-based or polyimide-based material that is used to form the insulating layer 130 A. The insulating layer 130 B is formed to cover the lower surfaces of the core 110 , the through electrodes 120 A and 120 B, and the capacitor chips 200 after filling the penetrating hole 110 H with molten resin. The insulating layer 130 B is formed by thermally curing a resin material such as an epoxy-based material or polyimide-based material through heating and application of pressure. [0031] The vias 140 A 1 , 140 A 2 , 140 A 3 , 140 A 4 , 140 A 5 , and 140 A 6 are formed inside via holes formed through the insulating layer 130 A. The vias 140 A 1 , 140 A 2 , and 140 A 3 are connected to the through electrode 120 A, an electrode 202 of the left-hand-side capacitor chip 200 on the left-hand side thereof, and another electrode 202 of the left-hand-side capacitor chip 200 on the right-hand side thereof, respectively. [0032] The vias 140 A 4 , 140 A 5 , and 140 A 6 are connected to an electrode 202 of the right-hand-side capacitor chip 200 on the left-hand side thereof, another electrode 202 of the right-hand-side capacitor chip 200 on the right-hand side thereof, and the through electrode 120 B, respectively. The vias 140 A 1 , 140 A 2 , 140 A 3 , 140 A 4 , 140 A 5 , and 140 A 6 are formed by copper plating films, for example. [0033] The vias 140 B 1 , 140 B 2 , 140 B 3 , 140 B 4 , 140 B 5 , and 140 B 6 are formed inside via holes formed through the insulating layer 130 B. The vias 140 B 1 , 140 B 2 , and 140 B 3 are connected to the through electrode 120 A, an electrode 202 of the left-hand-side capacitor chip 200 on the left-hand side thereof, and another electrode 202 of the left-hand-side capacitor chip 200 on the right-hand side thereof, respectively. [0034] The vias 140 B 4 , 140 B 5 , and 140 B 6 are connected to an electrode 202 of the right-hand-side capacitor chip 200 on the left-hand side thereof, another electrode 202 of the right-hand-side capacitor chip 200 on the right-hand side thereof, and the through electrode 120 B, respectively. The vias 140 B 1 , 140 B 2 , 140 B 3 , 140 B 4 , 140 B 5 , and 140 B 6 are formed by copper plating films, for example. [0035] The wiring layer segments 150 A 1 , 150 A 2 , 150 A 3 , 150 A 4 , 150 A 5 , and 150 A 6 are formed on the upper surface of the insulating layer 130 A, and are connected to the vias 140 A 1 , 140 A 2 , 140 A 3 , 140 A 4 , 140 A 5 , and 140 A 6 , respectively. The wiring layer segments 150 A 1 , 150 A 2 , 150 B 3 , 150 A 4 , 150 A 5 , and 150 A 6 are formed by copper plating films, for example. [0036] The wiring layer segments 150 B 1 , 150 B 2 , 150 B 3 , 150 B 4 , 150 B 5 , and 150 B 6 are formed on the lower surface of the insulating layer 130 B, and are connected to the vias 140 B 1 , 140 B 2 , 140 B 3 , 140 B 4 , 140 B 5 , and 140 B 6 , respectively. The wiring layer segments 150 B 1 , 150 B 2 , 150 B 3 , 150 B 4 , 150 B 5 , and 150 B 6 are formed by copper plating films, for example. [0037] The solder resist layer 160 A is formed on the insulating layer 130 A and on the wiring layer segments 150 A 1 , 150 A 2 , 150 A 3 , 150 A 4 , 150 A 5 , and 150 A 6 . Portions of the wiring layer segments 150 A 1 , 15012 , 15013 , 15014 , 15015 , and 15016 that are exposed through the solder resist layer 160 A are employed as terminals. [0038] The solder resist layer 160 B is formed beneath the insulating layer 130 B and beneath the wiring layer segments 150 B 1 , 150 B 2 , 150 B 3 , 15034 , 150 B 5 , and 150 B 6 . Portions of the wiring layer segments 150 B 1 , 150 B 2 , 150 B 3 , 15034 , 150 B 5 , and 150 B 6 that are exposed through the solder resist layer 160 B are employed as terminals. [0039] The capacitor chips 200 are an example of electronic components, and two of them are disposed inside the penetrating hole 110 H. Each of the two capacitor chips 200 has a main body 201 and a pair of electrodes 202 . The main body 201 is made of ceramic, for example, and supports the electrodes 202 disposed on opposite sides thereof, respectively. The permittivity of the capacitor chips 200 is determined by the material of the main body 201 . [0040] Each of the electrodes 202 is larger than the main body 201 in the YZ-plan view (i.e., as viewed from the X-axis direction), such that the electrode projects from the main body 201 in the positive Y direction and the negative Y direction as well as in the positive Z direction and the negative Z direction. Further, the electrodes 202 are formed to cover the surface of the main body 201 facing toward the positive X direction and the surface of the main body 201 facing toward the negative X direction, respectively. Namely, the electrodes 202 are formed in a cap shape to cover the main body 201 of a cuboid shape in the positive X direction and the negative X direction, respectively. [0041] One of the two capacitor chips 200 is disposed in such an area of the penetrating hole 110 H as is situated further toward the negative X direction than a pair of projecting parts 110 A. The other one of the two capacitor chips 200 is disposed in such an area of the penetrating hole 110 H as is situated further toward the positive X direction than the pair of projecting parts 110 A. [0042] Further, each of the capacitor chips 200 is supported on the side surfaces and lower surface thereof by the insulating layer 130 B, and are supported on the upper surface thereof by the insulating layer 130 A. [0043] The two capacitor chips 200 are arranged side by side in the X-axis direction such that the two electrodes 202 of each of the capacitor chips 200 face toward the positive X direction and the negative X direction, respectively. The capacitor chips 200 are spaced apart and insulated from each other. [0044] In the following, FIGS. 2A through 2C and FIGS. 3A and 3B will be referred to in order to describe the penetrating hole 110 H of the core 110 . [0045] FIGS. 2A through 2C are cross-sectional views of the core 110 . FIG. 2A illustrates a plan view (i.e., a view of the XY plane). FIGS. 2B and 2C illustrate cross-sections taken along planes parallel to the XZ plane. [0046] FIG. 2B depicts a cross-section taken along a line A 1 -A 1 illustrated in FIG. 2A as viewed from the negative Y direction. FIG. 2C depicts a cross-section taken along a line A 2 -A 2 illustrated in FIG. 2A as viewed from the negative Y direction. The cross-section illustrated in FIG. 2C is parallel to the XZ plane and corresponds to the view illustrated in FIG. 1 . Specifically, the cross-section illustrated in FIG. 2C is parallel to the XZ plane and taken at the center point of the core 110 in the Y-axis direction. FIGS. 2A through 2C illustrate the core 110 together with the wiring layer 111 A and the through electrodes 120 A and 120 B. [0047] As was previously described, the core 110 is formed of a glass-cloth base material impregnated with epoxy resin, and serves as a core for a buildup substrate. The core 110 has the penetrating hole 110 H penetrating therethrough in the thickness direction. [0048] The penetrating hole 110 H has the inner wall thereof having the projecting parts 110 A. The projecting parts 110 A extend inwardly in the penetrating hole 110 H, from both the inner wall facing toward the positive Y direction and the inner wall facing toward the negative Y direction, at such a center point of the penetrating hole 110 H as defined in the X-axis direction (i.e., in the longitudinal direction of the penetrating hole 110 H). The projecting parts 110 A taper toward the tips thereof in the plan view as illustrated in FIG. 2A . [0049] The inner walls of the penetrating hole 110 H extend vertically in parallel to the Z axis. In the plan view, the two projecting parts 110 A extend inwardly in the penetrating hole 110 H and taper toward the tips thereof in the plan view. [0050] The two penetrating holes 110 H are provided for the purpose of suppressing positional displacement of the two capacitor chips 200 when the capacitor chips 200 are placed inside the penetrating hole 110 H. The inner space of the penetrating hole 110 H is divided by the two opposing projecting parts 110 A into the area situated toward the positive X direction and the area situated toward the negative X direction. These two areas accommodate the two capacitor chips 200 , respectively. Each of the two areas is an example of a placement area. [0051] Each of the projecting parts 110 A is formed by retaining a portion of the core 110 that is not removed when the penetrating hole 110 H is formed by routing. [0052] FIGS. 3A and 3B are drawings illustrating an arrangement in which the capacitor chips 200 are disposed in the penetrating hole 110 H of the core 110 . In reality, the capacitor chips 200 are supported by the insulating layers 130 A and 130 B and the like as illustrated in FIG. 1 . In FIG. 3 , the positions of the two capacitor chips 200 as would be arranged inside the penetrating hole 110 H are illustrated without the insulating layers 130 A and 130 B. [0053] FIGS. 3A and 3B are a plan view and a cross-sectional view corresponding to FIGS. 2A and 2C , respectively. FIG. 3B illustrates a cross-sectional view that is taken along a line A 3 -A 3 in FIG. 3A and that is viewed from the negative Y direction. The cross-section illustrated in FIG. 3B is parallel to the XZ plane and corresponds to the view illustrated in FIG. 1 . Specifically, the cross-section illustrated in FIG. 3B is parallel to the XZ plane and taken at the center point of the core 110 in the Y-axis direction. [0054] The two capacitor chips 200 are placed in the area situated toward the positive X direction and the area situated toward the negative X direction, respectively, which are demarcated as areas distinct from each other by the two opposing projecting parts 110 A in the penetrating hole 110 H as illustrated in FIG. 3A . [0055] The length of the area of the penetrating hole 110 H situated on the positive X side of the projecting parts 110 A and the length of the area of the penetrating hole 110 H situated on the negative X side are each set longer than the length of a capacitor chip 200 in the X-axis direction. Further, the width of the penetrating hole 110 H in the Y-axis direction other than the position at which the projecting parts 110 A are situated is set wider than the width of a capacitor chip 200 in the Y-axis direction. [0056] The gap in the Y-axis direction between the two opposing projecting parts 110 A is set narrower than the width of a capacitor chip 200 in the Y-axis direction. [0057] This arrangement is made for the purpose of suppressing the displacement, in the X-axis direction, of the capacitor chips 200 placed in the penetrating hole 110 H, thereby preventing the capacitor chips 200 from intruding into each other's territory. [0058] Since the capacitor chips 200 are arranged side by side in the X-axis direction, movement in the X-axis direction may cause the electrodes 202 to come in contact with each other, or may prevent the electrodes 202 from being properly connected to the vias 140 A 2 through 140 A 5 and 140 B 2 through 140 B 5 . [0059] As described above, the wiring substrate 100 of the present embodiment is provided with the projecting parts 110 A projecting from the inner walls of the penetrating hole 110 H situated sideways relative to the direction in which the two capacitor chips 200 are arranged side by side. With this arrangement, movement of any one of the capacitor chips 200 toward the other one of the capacitor chips 200 results in the capacitor chip 200 coming in contact with the projecting parts 110 A so that the displacement thereof is suppressed. [0060] Further, the difference between the length of a capacitor chip 200 in the X-axis direction and the length of the area of the penetrating hole 110 H situated further toward the positive X direction than the projecting parts 110 A and the difference between the length of a capacitor chip 200 in the X-axis direction and the length of the area of the penetrating hole 110 H situated further toward the negative X direction than the projecting parts 110 A are set smaller than the tolerable positional displacement of the electrodes 202 of the capacitor chips 200 relative to the vias 140 A 2 through 140 A 5 and 140 B 2 through 140 B 5 . [0061] Similarly, the difference between the width of the capacitor chips 200 in the Y-axis direction and the width of the penetrating hole 110 H in the Y-axis direction at positions other than the position of the projecting parts 110 A is set smaller than the tolerable positional displacement of the electrodes 202 of the capacitor chips 200 relative to the vias 140 A 2 through 140 A 5 and 140 B 2 through 140 B 5 . [0062] This arrangement is made for the purpose of ensuring connection between the electrodes 202 and the vias 140 A 2 through 140 A 5 and 140 B 2 through 140 B 5 . [0063] In the following, a method of making the wiring substrate 100 of the present embodiment will be described by referring to FIGS. 4A through 4E and FIGS. 5A through 5C . Further, a method of mounting an LSI (large scale integrated) circuit chip on the wiring substrate 100 will be described by referring to FIG. 6 . [0064] FIGS. 4A through 4E and FIGS. 5A through 5C illustrate the method of making the wiring substrate 100 of the present embodiment. Cross-sections described in the following correspond to the cross-sections illustrated in FIG. 1 , FIG. 2C , and FIG. 3B . Namely, these cross-sections correspond to the plane parallel to the XZ plane and situated at the center of the wiring substrate 100 in the Y-axis direction. [0065] As illustrated in FIG. 4A , the penetrating hole 110 H is formed through the core 110 by routing, and, then, with the core 110 placed upside down, a tentative tape 300 is attached to the surface of the core 110 on which the wiring layer 111 A is formed. The tentative tape 300 has an adhesive layer on a surface thereof that is the upper surface in FIG. 4A . The tentative tape 300 may be made of a resin film such as PET (Polyethylene terephthalate). [0066] As illustrated in FIG. 4B , the capacitor chips 200 are inserted into the penetrating hole 110 H of the core 110 . In this state, the capacitor chips 200 are bonded to the tentative tape 300 . This serves to secure the capacitor chips 200 tentatively. [0067] As illustrated in FIG. 4C , molten resin material is used to fill the penetrating hole 110 H and also to cover the core 110 , the through electrodes 120 A and 120 B, and the capacitor chips 200 . In so doing, a resin film is placed on the core 110 to cover the penetrating hole 110 H, and is melted by heat. The resin material is then heated and subjected to pressure to thermally cure, thereby forming the insulating layer 130 B. [0068] In this process step, the positional displacement of the capacitor chips 200 in the X-axis direction is suppressed by the projecting parts 110 A, and the capacitor chips 200 are tentatively secured by the tentative tape 300 , so that the positional displacement of the capacitor chips 200 are sufficiently reduced. Physical contact between the capacitor chips 200 is thus prevented to ensure insulation between the capacitor chips 200 . [0069] The wiring layer 111 A has a hollow rectangular shape (i.e., rectangular loop shape) in the plan view to surround the penetrating hole 110 H, so that the insulating layer 130 B is prevented from entering areas outside the wiring layer 111 A. If the intrusion of the insulating layer 130 B is not a problem or does not occur, the wiring layer 111 A fully circling around the penetrating hole 110 H does not have to be provided. [0070] Subsequently, the tentative tape 300 is removed, followed by flipping over the core 110 again as illustrated in FIG. 4D . [0071] As illustrated in FIG. 4E , the insulating layer 130 A is formed to cover the upper faces of the core 110 , the wiring layer 111 A, the through electrodes 120 A and 120 B, and the capacitor chips 200 . The insulating layer 130 A is formed by heating and applying pressure to the same resin material as that of the insulating layer 130 B for thermal curing. [0072] In this process step, the positional displacement of the capacitor chips 200 in the X-axis direction is suppressed by the projecting parts 110 A, and the capacitor chips 200 are supported by the insulating layer 130 B, so that the positional displacement of the capacitor chips 200 are sufficiently reduced. Physical contact between the capacitor chips 200 is thus prevented to ensure insulation between the capacitor chips 200 . In the process steps illustrated in FIG. 4C through 4E , the capacitor chips 200 are encapsulated in the insulating layers 130 A and 130 B. [0073] Subsequently, via holes 131 A and 131 B are formed as illustrated in FIG. 5A . The via holes 131 A are formed by a laser process, for example, at the positions where the vias 140 A 1 through 140 A 6 will be formed later. With the core 110 being flipped over, the via holes 131 B are formed by a laser process, for example, at the positions where the vias 140 B 1 through 140 B 6 will be formed later. [0074] As illustrated in FIG. 5B , the vias 140 A 1 through 140 A 6 , the vias 140 B 1 through 140 B 6 , the wiring layer segments 150 A 1 through 150 A 6 , and the wiring layer segments 150 B 1 through 150 B 6 are formed. [0075] The vias 140 A 1 through 140 A 6 and the vias 140 B 1 through 140 B 6 may be formed inside the via holes 131 A and 131 B, respectively, by use of a semi-additive process, for example, The vias 140 A 1 through 140 A 6 are formed simultaneously, and the vias 140 B 1 through 140 B 6 are formed simultaneously. [0076] The wiring layer segments 150 A 1 through 150 A 6 and the wiring layer segments 150 B 1 through 150 B 6 are formed integrally with the vias 140 A 1 through 140 A 6 and the vias 140 B 1 through 140 B 6 , respectively, by use of a semi-additive method performed immediately after the plating process forming these vias. [0077] Subsequently, the solder resist layers 160 A and 160 B are formed as illustrated in FIG. 5C . [0078] The solder resist layer 160 A is formed by placing resist material all over the insulating layer 130 A and the wiring layer segments 150 A 1 through 150 A 6 and by exposing through exposure and development processes the portions of the wiring layer segments 150 A 1 through 150 A 6 that are to be used as terminals. The resist material is photosensitive epoxy resin or photosensitive acrylic resin. [0079] Similarly, the solder resist layer 160 B is formed by placing resist material all over the insulating layer 130 B and the wiring layer segments 150 B 1 through 150 B 6 and by exposing through exposure and development processes the portions of the wiring layer segments 150 B 1 through 150 B 6 that are to be used as terminals. [0080] With this, the process of making the wiring substrate 100 of the present embodiment comes to an end. [0081] FIG. 6 is a drawing illustrating the wiring substrate 100 and an LSI chip 400 formed thereon. [0082] As illustrated in FIG. 6 , the LSI chip 400 may be mounted through bumps 401 on the portions of the wiring layer segments 150 A 1 through 150 A 6 that are used as terminals. Underfill resin 402 may be placed to fill the gap under the LSI chip 400 . [0083] According to the present embodiment, the insulating layers 130 A and 130 B and the solder resist layers 160 A and 160 B are formed while the positional displacement of the capacitor chips 200 is suppressed by the projecting parts 110 A of the inner walls of the penetrating hole 110 H. [0084] This arrangement suppresses the positional displacement of the capacitor chips 200 arranged side by side in the X-axis direction, thereby preventing short-circuiting caused by physical contact between the electrodes 202 , and also preventing the electrodes 202 from failing to be properly connected to the vias 140 A 2 through 140 A 5 and the vias 140 B 2 through 140 B 5 . [0085] Accordingly, the wiring substrate 100 and a method of making the wiring substrate 100 are provided that improve electrical reliability with respect to the two capacitor chips 200 disposed in the single penetrating hole 110 H. [0086] It may be noted that mounting a semiconductor chip such as a CPU operating at high frequency on the wiring substrate 100 may require a large number of capacitor chips 200 to be used for the purpose of improving electrical characteristics. [0087] Each capacitor chip 200 may be disposed in a different penetrating hole 110 H when providing a large number of capacitor chips 200 . Such an arrangement, however, ends up having a large number of penetrating holes 110 H, which occupy a large area in the wiring substrate 100 . The presence of such penetrating holes 110 H means reduced freedom in wiring placement. Further, since a large number of penetrating holes 110 H are provided, the horizontal area size of the wiring substrate 100 may need to be increased. [0088] In order to obviate the problems noted above, the present embodiment uses a single penetrating hole 110 H to accommodate a plurality of capacitor chips 200 . [0089] Provision may be made such that a plurality of penetrating holes 110 H are provided. [0090] The description provided heretofore has been directed to a case in which the two capacitor chips 200 are disposed in the single penetrating hole 110 H. This is not a limiting example, and the number of capacitor chips 200 disposed in the single penetrating hole 110 H may be any number that is two or more. In the case of three or more capacitor chips 200 being disposed in a single penetrating hole 110 H, it suffices to form projecting parts 110 A at each border between areas in which the capacitor chips 200 are disposed. [0091] The description provided heretofore has also been directed to a case in which the capacitor chips 200 are disposed in the penetrating hole 110 H. This is not a limiting example. What is disposed in the penetrating hole 110 H is not limited to the capacitor chips 200 , and may be any electronic components that have terminals or the like on an outer face thereof. For example, a plurality of CPU (central processing unit) chips or memory chips may be disposed in the penetrating hole 110 H. [0092] Further, the description provided heretofore has been directed to a case in which the penetrating hole 110 H is formed by routing, and the projecting parts 110 A are portions of the core 110 remaining after the routing. This is not a limiting example, and the penetrating hole 110 H may be formed by a laser process or by another mechanical process. [0093] Further, the description provided heretofore has been directed to the wiring substrate 100 in which only the insulating layers 130 A and 130 B are formed on the upper surface and lower surface of the core 110 , respectively, as insulating layers. This is not a limiting example, and the wiring substrate 100 may include one or more other insulating layers in addition to the insulating layers 130 A and 130 B, and may also include a plurality of wiring layers. [0094] FIGS. 7A through 7G are drawings illustrating variations of the penetrating hole of the embodiment. Penetrating holes 110 H 1 through 110 H 7 illustrated in FIGS. 7A through 7G , respectively, may be used in place of the penetrating hole 110 H illustrated in FIG. 2A and FIG. 3A . FIGS. 7A through 7G also illustrate the capacitor chips 200 . [0095] As in the case of the penetrating hole 110 H 1 illustrated in FIG. 7A , the penetrating hole may be formed to have a prolonged length in the X-axis direction so as to accommodate three capacitor chips 200 , with two pairs of projecting parts 110 A that divide the penetrating hole into three areas. [0096] As in the case of the penetrating hole 110 H 2 illustrated in FIG. 7B , the penetrating hole may be formed to have a shortened length in the X-axis direction and a broadened width in the Y-axis direction so as to accommodate two capacitor chips 200 arranged side by side in their width direction (i.e., short-side direction), with a pair of projecting parts 110 A that divides the penetrating hole into two areas. [0097] As in the case of the penetrating hole 110 H 3 illustrated in FIG. 7C , the penetrating hole may be formed to accommodate three capacitor chips 200 arranged side by side in their width direction (i.e., short-side direction), with two pairs of projecting parts 110 A that divide the penetrating hole into three areas. [0098] As in the case of the penetrating hole 110 H 4 illustrated in FIG. 7D , the penetrating hole may be formed to have the width thereof in the Y-axis direction substantially equal to the width of capacitor chips 200 in the Y-axis direction, such that the two capacitor chips 200 are engaged with the inner walls of the penetrating hole facing toward each other in the Y-axis direction. [0099] As in the case of the penetrating hole 110 H 5 illustrated in FIG. 7E , the penetrating hole 110 H 4 illustrated in FIG. 7D may be elongated in the X-axis direction to accommodate three capacitor chips 200 , with two pairs of projecting parts 110 A being formed that divide the penetrating hole into three areas. [0100] As in the case of the penetrating hole 110 H 6 illustrated in FIG. 7F , the penetrating hole H 4 illustrated in FIG. 7D may be modified to have a shortened length in the X-axis direction and a broadened width in the Y-axis direction so as to accommodate two capacitor chips 200 arranged side by side in their width direction (i.e., short-side direction). [0101] As in the case of the penetrating hole 110 H 7 illustrated in FIG. 7G , the penetrating hole 110 H 6 illustrated in FIG. 7F may be elongated in the X-axis direction to accommodate three capacitor chips 200 , with two pairs of projecting parts 110 A being formed that divide the penetrating hole into three areas. [0102] A description provided heretofore is directed to an example in which the penetrating holes 110 H and 110 H 1 through 110 H 7 are formed by a mechanical process such as routing. Alternatively, such holes may be formed by a laser process. A relevant description will be given by referring to FIGS. 8A and 8B and FIGS. 9A through 9C . [0103] FIGS. 8A and 8B are drawings illustrating processes for forming a penetrating hole 110 HX by use of a laser beam. [0104] As illustrated in FIGS. 8A and 8B , a core 110 X having the wiring layer 111 A and the through electrodes 120 A and 120 B is provided, and, then, a laser process is utilized to form the penetrating hole 110 HX. [0105] For example, the diameter and power of the laser beam are set such that one laser shot creates a hole 110 HX 1 as illustrated in FIGS. 8A and 8B . The hole 110 HX 1 may be approximately one third of the width of the penetrating hole 110 HX in the Y-axis direction as illustrated in FIG. 8A , and may have a depth slightly deeper than half the thickness of the core 110 X. As illustrated in FIG. 8B , the hole 110 HX 1 has a cross-section thereof whose horizontal span decreases toward the bottom. Such a shape of the hole 110 HX 1 is made by a laser process. [0106] The position of a laser shot is shifted successively as illustrated by chain-line circles illustrated in FIG. 8A in the area where the penetrating hole 110 HX is created, and, then, the core 110 X is flipped over for a similar laser process to be performed, thereby creating the penetrating hole 110 HX. [0107] When laser shots impact on the core 110 from both surfaces thereof, the diameter and power of the laser beam may be adjusted to leave projecting part 110 AX on the inner walls of the penetrating hole 110 HX. With this arrangement, the penetrating hole 110 HX having the projecting part 110 AX is formed in the core 110 X. [0108] In the example described above, the penetrating hole 110 HX is formed through the core 110 X having the wiring layer 111 A and the through electrodes 120 A and 120 B. Alternatively, the penetrating hole 110 HX may be formed first through the core 110 X, and, then, the wiring layer 111 A and the through electrodes 120 A and 120 B may be formed. [0109] The penetrating hole 110 HX and the projecting parts 110 AX formed by a laser process as described above have shapes as illustrated in FIGS. 9A through 9C . [0110] FIGS. 9A through 9C illustrate the penetrating hole 110 HX formed through the core 110 X by a laser process. FIG. 9A is a plan view (i.e., a view of the XY plane), and FIG. 9B illustrates a cross-section taken along a line X 1 -X 1 in FIG. 9A as viewed from the negative Y direction. FIG. 9C depicts a cross-section taken along a line X 2 -X 2 illustrated in FIG. 9A as viewed from the negative Y direction. The cross-section illustrated in FIG. 9C is parallel to the XZ plane and corresponds to the view illustrated in FIG. 1 . Specifically, the cross-section illustrated in FIG. 9C is parallel to the XZ plane and taken at the center point of the core 110 X in the Y-axis direction. FIGS. 9A through 9C illustrates the core 110 X together with the wiring layer 111 A and the through electrodes 120 A and 120 B. [0111] The inner walls 110 BX of the penetrating hole 110 HX of the core 110 X project toward the inner space of the penetrating hole 110 HX in the plan view, and has a cross-section thereof formed in a tapered shape as illustrated in FIG. 9B and FIG. 9C . The inner walls 110 BX projecting in a tapered shape are formed along the perimeter of the penetrating hole 110 HX to form a rectangular loop. The inner walls 110 BX have the most projecting part thereof at the center point of the core 110 X as defined in the thickness direction (i.e., in the Z-axis direction), so that the most projecting part forms ridges. [0112] The inner wall 110 BX facing toward the negative Y direction and the inner wall 110 BX facing toward the positive Y direction project further toward the inner space of the penetrating hole 110 HX at the center of the penetrating hole 110 HX as defined in the X-axis direction than at any other parts of these inner walls 110 BX, thereby forming the projecting parts 110 AX. [0113] As illustrated in FIGS. 9B and 9C , each projecting part 110 AX has a rhombus shape as defined in the XZ plane, and has both the span in the X-axis direction and the span in the Z-axis direction decreasing toward the tip thereof. Namely, each projecting part 110 AX has a tapered shape in the cross-section parallel to the YZ plane, and also has a tapered shape in the cross-section parallel to the XY plane. [0114] As illustrated in FIG. 9D , the projecting part 110 AX having a tapered shape is configured such that the inner walls of the penetrating hole 110 HX are not vertical to extend in the Z-axis direction, but are formed at an angle smaller than 90 degrees relative to the upper surface and lower surface of the core 110 X, and such that the inner walls have the most projecting part at a general center thereof in the thickness direction of the core 110 X projecting toward the inner space of the penetrating hole 110 HX. A thickness of the projecting part 110 AX in the thickness direction of the core 110 X decreases toward a tip of the projecting part. [0115] The descriptions of a wiring substrate and a method of making the wiring substrate according to exemplary embodiments have been provided heretofore. The present invention is not limited to these embodiments, but various variations and modifications may be made without departing from the scope of the present invention. [0116] According to at least one embodiment, a wiring substrate and a method of making the wiring substrate are provided that ensure improved electrical reliability with respect to a plurality of electronic components disposed in a single penetrating hole. [0117] All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiment(s) of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention. [0118] The disclosures herein include the following configurations. [0119] Clause 1) A method of making a wiring substrate, comprising: [0120] forming a hole penetrating through a core layer in a thickness direction thereof, such that a projecting part projects from an inner wall of the hole toward an inner space of the hole, the projecting part being situated at a border that divides a plurality of areas in the hole; [0121] placing a plurality of electronic components in the areas, respectively, the electronic components being arranged at a spaced interval with the projecting part therebetween; and [0122] filling the hole with resin material to form a resin layer that supports the electronic components. [0123] Clause 2) The method as recited in Clause 1, wherein the step of forming the hole forms the hole such that a thickness of the projecting part in the thickness direction of the core layer decreases toward a tip of the projecting part. [0124] Clause 3) The method as recited in Clause 1, wherein the step of forming the hole forms the hole such that a width of the projecting part in the direction in which the areas are arranged side by side decreases toward a tip of the projecting part.

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