Printed wiring boards

Abstract

To provide a printed-circuit board in which a change of an impedance is suppressed in a front and a back of a printed-circuit board.SOLUTION: A printed-circuit board includes: an insulation layer; and a plurality of via conductors penetrated with the insulation layer. The plurality of via conductors contain a combination of a via conductor for one signal and a plurality of via conductor for grounding. When viewing the insulation layer in a plan view, the plurality of via conductors for grounding is arranged in parallel in a circle shape to the circumference of the via conductor for a signal. In both of the via conductor for a signal and the plurality of via conductors for grounding, one end is a large diameter, and the other end is a small diameter. A direction of both of the via conductor for a signal and the plurality of via conductors for grounding is inverse from the large diameter to the small diameter.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to printed wiring boards. [Background technology]

[0002] In a printed wiring board, it is required to realize a specific circuit impedance for via conductors in a circuit. To achieve this, a structure has been adopted in which ground-connected via conductors (hereinafter also referred to as "ground via conductors") are arranged as peripheral conductors at a certain distance from a signal via conductor, which is a central conductor, and these are arranged coaxially (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-311338 Summary of the Invention [Problem to be solved by the invention]

[0004] Via conductors are typically manufactured by forming through holes in a substrate and then forming conductors in the through holes. Conventionally, through holes in substrates have generally been formed by drilling, but in recent years, as via conductors have become smaller in diameter, laser processing has become increasingly common. However, due to the nature of lasers, through holes formed by laser processing tend to have smaller diameters on the protruding side as the processing depth increases.

[0005] The impedance of multiple via conductors arranged in a coaxial configuration is proportional to the natural logarithm of the ratio between the inner diameter of the imaginary circle formed by the ground via conductors and the outer diameter of the signal via conductors. When through holes are formed by laser processing as described above, the resulting via conductors have a problem in that the distance between the outer diameter of the signal via conductor and the inner diameter of the imaginary circle formed by tangents connecting the insides of the multiple ground via conductors arranged around the signal via conductor changes on the front and back sides of the substrate, resulting in a large change in impedance. [Means for solving the problem]

[0006] A printed wiring board according to one aspect of the present disclosure includes: The substrate has an insulating layer and a plurality of via conductors that penetrate the insulating layer. The plurality of via conductors includes a combination of one signal via conductor and a plurality of ground via conductors. When the insulating layer is viewed from above, the ground via conductors are arranged in a circular pattern around the signal via conductor. The signal via conductor and the plurality of ground via conductors each have a large diameter at one end and a small diameter at the other end. All The ground via conductors are arranged in opposite directions from the large diameter side to the small diameter side. [Effects of the Invention]

[0007] According to a printed wiring board according to an embodiment of the present disclosure, it is possible to reduce the change in impedance between the front and back sides when a plurality of ground via conductors are arranged circumferentially around a signal via conductor. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a plan view of an example of a printed wiring board according to a first embodiment, as viewed from above. [Figure 2] 2 is a plan view of the printed wiring board of FIG. 1 as seen from below. [Figure 3] FIG. 2 is a cross-sectional view taken along line III-III in FIG. [Figure 4]FIG. 1 is a perspective view showing an imaginary truncated cone formed on a printed wiring board. [Figure 5] 4 is a graph showing impedance changes in the thickness direction of the printed wiring board according to the first embodiment. [Figure 6A] 2A to 2C are cross-sectional views showing steps in a method for manufacturing a printed wiring board according to the first embodiment. [Figure 6B] 2A to 2C are cross-sectional views showing steps in a method for manufacturing a printed wiring board according to the first embodiment. [Figure 7] FIG. 10 is a cross-sectional view of an example of a printed wiring board according to a second embodiment. [Figure 8] FIG. 10 is a cross-sectional view of a modified example of the printed wiring board according to the second embodiment. [Figure 9] FIG. 10 is a cross-sectional view of a modified example of the printed wiring board according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, a detailed description will be given of a printed wiring board according to the present disclosure (hereinafter referred to as an "embodiment") with reference to the drawings. Note that the printed wiring board according to the present disclosure is not limited to the embodiment. Furthermore, the embodiments can be appropriately combined within the scope of not causing any contradiction in the processing content.

[0010] In addition, in the following embodiments, expressions such as "constant," "orthogonal," "perpendicular," or "parallel" may be used, but these expressions do not necessarily mean "constant," "orthogonal," "perpendicular," or "parallel" in the strict sense. In other words, the above expressions allow for deviations due to, for example, manufacturing precision, installation precision, etc.

[0011] The drawings referred to below are schematic diagrams for the sake of convenience, and therefore some details may be omitted, and the dimensions and dimensional ratios of the components in the drawings do not faithfully represent the dimensions and dimensional ratios of the actual components.

[0012] [Configuration of the printed wiring board according to the first embodiment] Fig. 1 is a plan view of a printed wiring board 10A, which is an example of a printed wiring board according to the first embodiment, as viewed from above, and Fig. 2 is a plan view of the printed wiring board 10A as viewed from below. Fig. 3 is a cross-sectional view of the printed wiring board 10A taken along line III-III in Fig. 1. Fig. 4 is a perspective view showing a virtual truncated cone formed on the printed wiring board 10A. Fig. 5 is a graph showing the change in impedance in the thickness direction of the printed wiring board 10A.

[0013] In this specification, the orientation of each part of printed wiring board 10A is described in an XYZ Cartesian coordinate system, with the thickness direction of printed wiring board 10A being the Z direction. In this specification, the direction facing the +Z direction of printed wiring board 10A and each layer that constitutes printed wiring board 10A may be expressed as "up" or "top surface." The direction facing the -Z direction may be expressed as "down" or "bottom surface." Unless otherwise specified, a plan view or plan perspective view refers to a view in the z direction.

[0014] Printed wiring board 10A has an insulating layer 1 and a plurality of via conductors penetrating insulating layer 1. In the following description, the plurality of via conductors penetrating insulating layer 1 will be denoted by the reference numeral "2." In printed wiring board 10A, via conductor 2 includes one signal via conductor 21 and a plurality of (e.g., eight) ground via conductors 22. While eight ground via conductors 22 have been given as an example, the present disclosure is not limited to this. Needless to say, the number of ground via conductors 22 may be any number other than eight, as long as the ground via conductors 22 can be considered to be arranged circumferentially or circularly around signal via conductor 21.

[0015] The positional relationship between the signal via conductor 21 and the ground via conductors 22 is such that, when the insulating layer 1 is viewed in a plane, eight ground via conductors 22 are arranged in a circular pattern around the signal via conductor 21. Here, "arranged in a circular pattern" refers to, for example, a configuration in which a plurality of ground via conductors 22 are arranged on the circumference of a circle that is concentric with or has a shape similar to that of the signal via conductor 21.

[0016] Both the signal via conductor 21 and the ground via conductor 22 have a large diameter at one end and a small diameter at the other end. Also, the direction from the large-diameter side to the small-diameter side of the signal via conductor 21 is opposite to that of the ground via conductor 22. Here, having a large diameter at one end and a small diameter at the other end means that the diameters at both ends are different, and the diameter at the other end is smaller than the diameter at one end. In other words, it means that the diameter at one end is larger than the diameter at the other end.

[0017] Here, one end and the other end are positions when viewing the insulating layer 1 in the Z-axis direction, the position from the mid-thickness position of the insulating layer 1 shown in FIG. 1 to the surface in the +Z direction, and the position from the mid-thickness position of the insulating layer 1 shown in FIG. 1 to the surface of the insulating layer 1 in the -Z direction. One end and the other end are not limited to the +Z direction and -Z direction of the insulating layer 1. For example, in the thickness direction of the insulating layer 1, when a specific position in the + direction of the via conductor 2 is taken as one end, then in the thickness direction of the insulating layer 1, a specific position in the - direction of the via conductor 2 becomes the other end. In this case, one end and the other end may be reversed in the + direction position and - direction position in the thickness direction of the insulating layer 1.

[0018] Specifically, for the signal via conductor 21, the diameter d11 on the upper surface Sa side of the insulating layer 1 is larger than the diameter d12 on the lower surface Sb side, and for the eight ground via conductors 22, conversely, the diameter d31 on the upper surface Sa side of the insulating layer 1 is smaller than the diameter d32 on the lower surface Sb side. That is, the relationship is d11 > d12 and d31 < d32.

[0019] In the via conductors 2 of the printed wiring board 10A, the positions of the large diameter and the small diameter for the signal via conductors 21 and the ground via conductors 22 may be opposite to the directions shown in Figures 1 to 3. Alternatively, the direction from the large diameter side to the small diameter side may be opposite to the directions shown in Figures 1 to 3. That is, for the signal via conductor 21, the diameter d11 on the top surface Sa side of the insulating layer 1 is smaller than the diameter d12 on the bottom surface Sb side, and for the eight ground via conductors 22, the diameter 31 on the top surface Sa side of the insulating layer 1 is larger than the diameter d32 on the bottom surface Sb side, that is, d11<d12かつd31> It may also be a d32 relationship.

[0020] The direction from the large diameter side to the small diameter side of each of the multiple ground via conductors 22 is opposite to the direction from the large diameter side to the small diameter side of the signal via conductors 21. That is, the direction from the large diameter side to the small diameter side is the same among the multiple ground via conductors 22. As long as the direction from the large diameter side to the small diameter side of the multiple ground via conductors 22 is the same, the diameters of the large diameter side and the small diameter side may be the same or different.

[0021] 1 to 3 has the above-described configuration of the via conductor 2 as a basic unit, but in this embodiment, the printed wiring board 10A may have, for example, a plurality of combinations of one signal via conductor 21 and a plurality of ground via conductors 22. Furthermore, the printed wiring board 10A may include via conductors other than the signal via conductor 21 and the ground via conductor 22. In addition, in a combination of a signal via conductor and a plurality of ground via conductors, it is considered preferable to minimize signal leakage by arranging the gap between the ground via conductors so that it is 1 / 10 or less of the wavelength λ of the highest frequency of the signal passing through the signal via conductors, and the gap is typically 1 / 20 of the wavelength λ.

[0022] In the printed wiring board 10A, the signal via conductors 21 and the ground via conductors 22 preferably have a circular shape in the XY plane of the insulating layer 1. Furthermore, as shown in FIG. 3, the diameters of both the signal via conductors 21 and the ground via conductors 22 preferably continuously decrease from the larger diameter side to the smaller diameter side. In this case, the inclination of the side surface 22s of the via conductor 2 from the larger diameter side to the smaller diameter side is preferably constant. This allows the impedance to change continuously in the thickness direction of the printed wiring board 10A. Here, the side surface 22s of the via conductor 2 refers to the surface of the via conductor 2 that is in contact with the insulating layer 1. In other words, the side surface 22s refers to the surface that intersects with the surfaces of the via conductor 2 along both main surfaces of the insulating layer 1 (the surface at the one end and the surface at the other end).

[0023] The outer shapes of the signal via conductors 21 and the ground via conductors 22 are preferably truncated cones. In this case, when the signal via conductor 21 is viewed as a truncated cone, the signal via conductor 21 is preferably arranged so that its bottom surface (21a) is close to the top surface Sa of the insulating layer 1 and its top surface (21b) is close to the bottom surface Sb of the insulating layer 1. In this case, the bottom surface 21a of the signal via conductor 21 is preferably aligned with the top surface Sa of the insulating layer 1. The top surface 21b of the signal via conductor 21 is preferably aligned with the bottom surface Sb of the insulating layer 1.

[0024] The ground via conductors 22 are preferably arranged so that the bottom surfaces 22a are close to the lower surface Sb of the insulating layer 1 and the top surfaces (22b) are close to the upper surface Sa of the insulating layer 1. In this case, the bottom surfaces 22a of the ground via conductors 22 preferably coincide with the lower surface Sb of the insulating layer 1. The top surfaces 22b of the ground via conductors 22 preferably coincide with the upper surface Sa of the insulating layer 1.

[0025] The upper surface of printed wiring board 10A is formed on an XY plane consisting of upper surface Sa of insulating layer 1 and upper surfaces of signal via conductors 21 and ground via conductors 22. The lower surface of printed wiring board 10A is formed on an XY plane consisting of lower surface Sb of insulating layer 1 and lower surfaces of signal via conductors 21 and ground via conductors 22.

[0026] In this embodiment, the shape of the bottom surface 21a of the signal via conductor 21 and the shape of the bottom surface 22a of the ground via conductor 22 are preferably circular.

[0027] The bottom surfaces 22a of the plurality of ground via conductors 22 arranged around the signal via conductor 21 preferably have the same shape, and the top surfaces 22b of the plurality of ground via conductors 22 preferably have the same shape.

[0028] Furthermore, it is preferable that the plurality of ground via conductors 22 arranged around the signal via conductor 21 have similar changes in the longitudinal direction (Z direction) of the side surfaces 22s (changes from diameter d32 to diameter d31). This makes it possible to reduce changes in impedance in the thickness direction (Z direction) of the printed wiring board 10A. In particular, it is preferable that the shape of the bottom surface 22a, the shape of the top surface 22b, and the change in diameter in the longitudinal direction (Z direction) (changes from diameter d32 to diameter d31) of all of the plurality of ground via conductors 22 arranged around the signal via conductor 21 are the same.

[0029] Furthermore, the positional relationship between the signal via conductor 21 and the eight ground via conductors 22 is preferably concentric when the printed wiring board 10A is viewed in a plan view or a planar perspective view. For example, as shown in Fig. 1, when the printed wiring board 10A is viewed in the -Z direction from the top surface Sa, the center d11c of the signal via conductor 21 and the center PC1c of an imaginary circle PC1 inscribed in the diameters d31 of the eight ground via conductors 22 preferably coincide or nearly coincide. Similarly, when the printed wiring board 10A is viewed in the +Z direction from the bottom surface Sb, the center d12c of the signal via conductor 21 and the center PC2c of an imaginary circle PC2 inscribed in the diameters d32 of the eight ground via conductors 22 preferably coincide.

[0030] When an imaginary circle inscribed in the diameter of ground via conductor 22 is connected between both ends of the ground via conductor, the shape of a truncated cone (hereinafter referred to as "imaginary truncated cone PC1D"). As shown in Fig. 4, imaginary truncated cone PC1D is a truncated cone whose bottom surface is an imaginary circle PC1 on the top surface Sa of printed wiring board 10A and whose top surface is an imaginary circle PC2 on the bottom surface Sb of printed wiring board 10A. As described above, since the center of diameter d11 of signal via conductor 21 coincides with the center of imaginary circle PC1 and the center of diameter d12 of signal via conductor 21 coincides with the center of imaginary circle PC2, in printed wiring board 10A, the axis of signal via conductor 21 coincides with the axis of imaginary truncated cone PC1D and is coaxial.

[0031] Furthermore, in printed wiring board 10A, it is preferable that, in a plan view, eight ground via conductors 22 are arranged at positions that equally divide the circumference surrounding signal via conductor 21. This satisfies the condition that signal via conductor 21 and ground via conductor 22 both have a large diameter at one end and a small diameter at the other end, and that signal via conductor 21 and ground via conductor 22 are oriented in opposite directions from the large diameter side to the small diameter side.

[0032] In this case, the ground via conductor 22 is arranged in a circular shape while surrounding the signal via conductor and equally dividing the circumference. As a result, an effect of suppressing a change in impedance between the front and back of the printed wiring board can be obtained. In addition, by arranging the ground via conductor 22 in an equally divided configuration of the circumference, the signal flowing through the signal via conductor 21 is less likely to be affected by the noise generated around the ground via conductor 22.

[0033] The length of the signal via conductor 21 and the ground via conductor 22 in the longitudinal direction (Z direction) is preferably equivalent to the thickness t of the insulating layer 1. The thickness t of the insulating layer 1 is appropriately selected according to the design of the printed wiring board 10A. The thickness t of the insulating layer 1 is, for example, 30 to 200 μm. In the printed wiring board 10A, as the sizes of the upper surface side diameter d11 and the lower surface side diameter d12 of the signal via conductor 21, and the upper surface side diameter d31 and the lower surface side diameter d32 of the ground via conductor 22, while satisfying the relationship of d11 > d12 and d31 < d32, specifically, the following sizes can be mentioned.

[0034] For example, for the signal via conductor 21, the diameter d11 may be 100 to 250 μm, and the diameter d12 may be 60 to 150 μm. Typically, the diameter d11 may be 130 to 180 μm, and the diameter d12 may be 70 to 100 μm. Also, for example, for the ground via conductor 21, the diameter d31 may be 60 to 150 μm, and the diameter d32 may be 100 to 250 μm. Typically, the diameter d31 may be 70 to 100 μm, and the diameter d32 may be 130 to 180 μm.

[0035] Here, the impedance in a predetermined XY plane of the via conductors arranged in a coaxial structure can be calculated by the following formula (I).

[0036]

Equation

[0037] In formula (I), each symbol represents the following meaning. Z0: Impedance εr ;Relative permittivity of the inter-conductor insulator d1: Diameter of signal via conductor d2: Diameter of an imaginary circle inscribed in the ground via conductor

[0038] From formula (I), it can be seen that by keeping the ratio (d2 / d1) of the diameter of the imaginary truncated cone to the diameter of the signal via conductor constant in the thickness direction of printed wiring board 10A, it is possible to obtain printed wiring board 10A with no change in impedance between the front and back. Furthermore, in order to keep d2 / d1 in formula (I) constant in the thickness direction of printed wiring board 10A, for example, one method can be to make the rate at which the diameter of ground via conductor 22 increases from the small diameter side to the large diameter side greater than the rate at which the diameter of signal via conductor 21 decreases from the large diameter side to the small diameter side from the top surface to the bottom surface of printed wiring board 10A.

[0039] Specifically, in printed wiring board 10A shown in FIGS. 1 to 3, the diameter d11 of the top surface of signal via conductor 21, the diameter d12 of the bottom surface, the diameter d31 of the top surface of ground via conductor 22, the diameter d32 of the bottom surface, the diameter d21 of imaginary circle PC1 on the top surface, and the diameter d22 of imaginary circle PC2 on the bottom surface were designed as shown in Examples 1 to 4 in Table 1. Furthermore, the impedances of the top and bottom surfaces of printed wiring board 10A, in which each diameter is continuously changed from the top surface to the bottom surface, were calculated. In printed wiring board 10A configured as described above, signal via conductor 21 and ground via conductor 22 are frustum-shaped. Furthermore, the shape connecting imaginary circle PC1 on the top surface and imaginary circle PC2 on the bottom surface of printed wiring board 10A is a frustum-shaped cone.

[0040] Example 1 shows a case where the signal via conductors 21 and the ground via conductors 22 are the same size, but the directions in which their diameters decrease in the thickness direction of the printed wiring board 10A (the longitudinal direction of the signal via conductors 21 and the ground via conductors 22) are opposite to each other.

[0041] In Examples 2 to 4, when the signal via conductor 21 is the same size as in Example 1, the diameters of the imaginary circles PC1 and PC2 are set so that the impedances on the top and bottom surfaces are equal to 50 Ω. In Examples 2 to 4, the ground via conductors 22 are designed to have different sizes. In Examples 2 to 4, the rate at which the diameter of the signal via conductor 21 decreases from the top surface to the bottom surface of the printed wiring board 10A is greater than the rate at which the diameter of the ground via conductors 22 increases. In this case, it is preferable that the diameters on the top surface and the bottom surface of the multiple ground vias 22 are the same.

[0042] As a comparative example, the impedances of the top and bottom surfaces of a printed wiring board having the same configuration as printed wiring board 10A were calculated, except that both signal via conductors 21 and ground via conductors 22 were designed so that their diameters continuously decreased from the top surface to the bottom surface. The calculation results of the impedances of Examples 1 to 4 and the comparative example are shown in Table 1.

[0043] In the above formula (I), the relative permittivity of the inter-conductor insulator is the relative permittivity of the material constituting the insulating layer 1. In calculating the impedance, the material was assumed to be a PPE-based material (Panasonic Corporation Industries Company, copper-clad laminate R-5775(N)), and a relative permittivity of 3.5 was introduced into formula (I). Also, assuming that the thickness t of the printed wiring board 10A is 200 μm, a graph showing the change in impedance in the thickness direction (see FIG. 5) was created. The graph shows the change in impedance in the thickness direction for Example 1, Example 2, and the comparative example in Table 1.

[0044] [Table 1]

[0045] The above results show that in the comparative example, in which the diameters of both the signal via conductors and the ground via conductors are designed to continuously decrease from the top surface to the bottom surface of the printed wiring board, the change in impedance is large between the top and bottom surfaces of the printed wiring board. In contrast, in the printed wiring board of this embodiment, the change in impedance is small between the top and bottom surfaces of the printed wiring board, and it is possible to reduce the change in impedance to "0" by design.

[0046] The rate of change in diameter of each via conductor in each example can be adjusted by adjusting the conditions for forming a through hole in the insulating layer when manufacturing the via conductor. The through hole can be formed, for example, by a method using a laser or a reamer, and the method using a laser is preferred.

[0047] (Method for manufacturing printed wiring board according to the first embodiment) Next, a method for manufacturing the printed wiring board of the first embodiment will be described. 6A and 6B are cross-sectional views illustrating a method for manufacturing printed wiring board 10A according to the first embodiment.

[0048] Printed wiring board 10A is manufactured, for example, by a method including the following first to third steps. The first step is to prepare a substrate 1P made of an insulator that will become the insulating layer 1 (see FIG. 6A). 6B, the second process is a process of forming through holes 21h and 22h for forming via conductors at predetermined positions on the substrate 1P. The through hole designated by reference numeral 21h is a first through hole 21h for forming the signal via conductor 21. The through hole designated by reference numeral 22h is a second through hole 22h for forming the ground via conductor 22. The third step is a step of filling the first through holes 21h and the second through holes 22h formed in the second step with a conductor.

[0049] The resin material for the substrate 1P prepared in the first step may be, for example, one selected from the group consisting of epoxy resin, bismaleimide-triazine resin, polyimide resin, polyphenylene ether (PPE) resin, phenolic resin, polytetrafluoroethylene (PTFE) resin, silicon resin, polybutadiene resin, polyester resin, melamine resin, urea resin, polyphenylene sulfide (PPS) resin, etc.

[0050] In addition to the resin materials described above, the substrate 1P may contain inorganic fillers such as silica, barium sulfate, talc, clay, glass, calcium carbonate, titanium oxide, and aluminum hydroxide, or organic fillers such as phenolic resin and methacrylic resin. Furthermore, the insulator may contain a reinforcing material. Examples of reinforcing materials include glass fiber and glass nonwoven fabric, aramid nonwoven fabric and aramid fiber, and polyester fiber. Two or more of these fillers or reinforcing materials may be used in combination.

[0051] As shown in FIG. 6B, the first through hole 21h is formed, for example, by irradiating a laser from the side of the substrate 1P that will become the upper surface Sa toward the side that will become the lower surface Sb when the substrate 1P is made into the insulating layer 1. The first through hole 21h is, for example, a truncated cone-shaped through hole with a diameter d11 on the upper surface Sa side and a diameter d12 on the lower surface Sb side. The relationship between the diameters d11 and d12 is d11>d12, and the specific size is set appropriately depending on the design. Laser irradiation conditions corresponding to the design are set, and a through hole that matches the design is obtained.

[0052] Similarly, as shown in FIG. 6B, the second through-hole 22h is formed by irradiating a laser, for example, from the lower surface Sb side to the upper surface Sa side of the substrate 1P. In this case, the second through-holes 22h are preferably formed so as to be arranged circumferentially around the first through-hole 21h. Preferably, an arrangement that equally divides the circumference around the first through-hole 21h is good. The second through-hole 22h is, for example, a through-hole having a frustum shape in which the upper surface Sa side has a diameter d31 that is small and the lower surface Sb side has a diameter d32 that is larger than the diameter d31. In this way, a through-hole in which the relationship between the diameter d31 and the diameter d32 is d31 < d32 can be formed. Note that the specific size is appropriately set according to the design. The irradiation conditions of the laser corresponding to the design are set, and through-holes conforming to the design are obtained.

[0053] For the formation of the first through-hole 21h and the second through-hole 22h, a reamer may be used in addition to the laser.

[0054] In the third step, examples of the conductor material used for the first through-hole 21h and the second through-hole 22h include metals such as copper, and examples of the conductor filling method include electrolytic plating.

[0055] Here, although a via conductor in which the through-hole is filled with a conductor is shown, the via conductor is not necessarily limited to a form in which the through-hole is filled with a conductor, and a form in which a conductor layer is formed with a predetermined layer thickness on the side surface of the through-hole may also be used.

[0056] The signal via conductor 21 and the ground via conductor 22 that constitute the printed wiring board 10A described above are electrically connected to the signal terminals and ground terminals of semiconductor elements mounted on semiconductor devices and the like, respectively, and are used.

[0057] 〔Configuration of Printed Wiring Board According to Second Embodiment〕 FIGS. 7 to 9 are cross-sectional views of printed wiring boards 10Ba to 10Bc according to the second embodiment, respectively. Printed wiring boards 10Ba to 10Bc are multilayer printed wiring boards configured with printed wiring board 10A shown in Figures 1 to 3 as core layer C, and build-up layers B1 and B2 formed on the upper surface Sa and lower surface Sb of printed wiring board 10A, respectively.

[0058] The printed wiring board 10Ba, the cross section of which is shown in Figure 7, has a core layer C having a configuration similar to that of the printed wiring board 10A shown in Figures 1 to 3, and has a buildup layer B1 on the upper surface Sa of the core layer C, which is composed of an internal wiring conductor for ground 41, an internal wiring conductor for signal 51, and an insulating layer 31, and a buildup layer B2 on the lower surface Sb of the core layer C, which is composed of an internal wiring conductor for ground 42, an internal wiring conductor for signal 52, and an insulating layer 32. The ground internal wiring conductor 41 and the signal internal wiring conductor 51 are connected to the top surface Sa of the core layer C, and the ground internal wiring conductor 42 and the signal internal wiring conductor 52 are connected to the bottom surface Sb of the core layer C, respectively, and are configured to extend in the XY plane direction while maintaining an appropriate distance from each other so that the top surface Sa and the bottom surface Sb of the core layer C can be impedance matched.

[0059] In multilayer printed wiring boards having a configuration such as printed wiring boards 10Ba to 10Bc, the core layer C, which is an inner layer, is often the location where conductor wiring is concentrated. For this reason, it is preferable to apply the configuration described in the first embodiment, such as printed wiring board 10A, to core layer C. This enhances the effect of improving electrical properties, such as impedance matching, even when the printed wiring board has a multilayer structure. Furthermore, if the thickness t of such core layer C is made thicker than the thicknesses t1 and t2 of buildup layers B1 and B2, respectively, the change in impedance can be further reduced, thereby further enhancing the effect of improving electrical properties.

[0060] In the printed wiring board 10Ba, a core layer C is prepared, and the ground internal wiring conductors 41 and the signal internal wiring conductors 51 are formed on its upper surface Sa in the above-described configuration, with the insulating layer 31 formed thereon. The ground internal wiring conductors 42 and the signal internal wiring conductors 52 are formed on the lower surface Sb of the core layer C in the above-described configuration, with the insulating layer 32 formed thereon. The thicknesses t1 and t2 of the insulating layers 31 and 32 are typically smaller than the thickness t of the insulating layer 1 of the core layer. The constituent materials of the insulating layers 31 and 32 can be the same as the constituent material of the insulating layer 1 of the core layer. These internal wiring conductors 41, 42, 51, and 52 are made of a metal such as copper.

[0061] As described above, when a through hole is formed in an insulating layer using a laser, the diameter of the through hole is large on the incident surface and decreases toward the opposite surface. When forming through holes in the same insulating layer in which the diameter decreases in opposite directions, for example, as shown in Figure 6B, a method is used in which laser processing is performed from one surface or the other depending on the position of the through hole.

[0062] Here, when manufacturing a multilayer printed wiring board by stacking buildup layers B1 and B2 one on top of the other on a core layer C, because through holes can only be formed from the surfaces (top and bottom) of the buildup layers B1 and B2, it is not possible to form two types of through holes in which the diameters of the through holes decrease in opposite directions. In this way, only the core layer can form two types of through holes in the same insulating layer in which the diameters of the through holes decrease in opposite directions.

[0063] Printed wiring board 10Bb, the cross section of which is shown in FIG. 8, has the same configuration as printed wiring board 10Ba in terms of core layer C and buildup layer B2 formed on the lower surface Sb side of core layer C.

[0064] The printed wiring board 10Bb has a buildup layer B1 formed on the top surface Sa of the core layer C. The buildup layer B1 has internal ground wiring conductors 41 and internal signal wiring conductors 51 that connect to the ground via conductors 22 and signal via conductors 21 of the core layer C, respectively. The buildup layer B1 located on the top side of the core layer C is an insulating layer 31. The buildup layer B1 has ground wiring conductors 71 and signal wiring conductors 91 on its top surface. The buildup layer B1 also has ground via conductors 61 that connect the internal ground wiring conductors 41 and 71, and signal via conductors 81 that connect the internal signal wiring conductors 51 and 91. In the printed wiring board 10Bb, the layer of insulating material that constitutes the buildup layer B1 is represented as the insulating layer 31.

[0065] In the printed wiring board 10Bb, the signal wiring conductor 91 and the ground wiring conductor 71 formed on the upper surface B1a of the insulating layer 31 constituting the buildup layer B1 are connected in an impedance-matched state to components mounted on the upper surface B1a of the buildup layer B1.

[0066] The ground via conductors 61 and the signal via conductors 81 can be formed in the insulating layer 31 by forming corresponding through holes with a laser or a reamer and filling the through holes with a conductor such as copper. Examples of the conductors that make up the ground wiring conductors 71 and the signal wiring conductors 91 include metals such as copper.

[0067] 9 has buildup layers formed on both sides of a core layer C, each having a configuration similar to that of the buildup layer B1 of printed wiring board 10Bb. The buildup layer B2 formed on the lower surface Sb of the core layer C also has a configuration similar to that of the buildup layer B1 described for printed wiring board 10Bb. However, while the components of buildup layer B1 are stacked in an upward direction, the components of buildup layer B2 are stacked in a downward direction.

[0068] That is, the buildup layer B2 has internal ground wiring conductors 42 and internal signal wiring conductors 52 that are respectively connected to the ground via conductors 22 and signal via conductors 21 of the core layer C. The buildup layer B2 also has a ground wiring conductor 72 and a signal wiring conductor 92. The buildup layer B2 further has a ground via conductor 62 that connects the internal ground wiring conductors 42 and 72, and a signal via conductor 82 that connects the internal signal wiring conductors 52 and 92.

[0069] Such buildup layer B2 can be formed in the same manner as buildup layer B1 in printed wiring board 10Bb.

[0070] The printed wiring board 10Bc is configured so that components mounted on the upper surface of the buildup layer B1 and the lower surface of the buildup layer B2 can exchange signals with each other.

[0071] The above describes the second embodiment of the printed wiring board as an example of a multilayer printed wiring board including build-up layers B1 and B2 in a core layer C. However, the printed wiring boards 10Ba to 10Bc having the configurations shown in Figures 7 to 9 may be formed by a batch lamination process in which the core layer and the upper and lower outer layers are integrated in a single lamination (thermocompression bonding) as long as the configuration of the core layer is compatible with the configuration of this embodiment.

[0072] Here, the specific details of the configuration, structure, positional relationship, shape, etc. shown in the above embodiment can be appropriately changed without departing from the spirit of the present disclosure. Furthermore, the configurations, structures, positional relationship, and shapes shown in the above embodiment can be appropriately combined without departing from the spirit of the present disclosure. [Explanation of symbols]

[0073] 10A, 10Ba~10Bc printed wiring board 1. Insulation layer 21 Signal via conductor 21h 1st through hole 22 Ground via conductor 22h 2nd through hole C Core layer B1, B2 build-up layers 31, 32 Insulation layer (for build-up layer) 41, 42 Internal wiring conductor for ground 51, 52 Internal signal wiring conductors 61, 62 Ground via conductor (for build-up layer) 71, 72 Ground wiring conductor 81, 82 Signal via conductor (for build-up layer) 91, 92 Signal wiring conductors

Claims

1. an insulating layer; a plurality of via conductors penetrating the insulating layer; the plurality of via conductors include a combination of one signal via conductor and a plurality of ground via conductors, When the insulating layer is viewed from above, the plurality of ground via conductors are arranged circumferentially around the signal via conductor, A printed wiring board, wherein the signal via conductor and the plurality of ground via conductors both have a large diameter at one end and a small diameter at the other end, and the signal via conductor and all of the plurality of ground via conductors are oriented in opposite directions from the large diameter side to the small diameter side.

2. The printed wiring board of claim 1, wherein the ratio (d2 / d1) of the diameter d1 of the signal via conductor to the diameter d2 of an imaginary circle inscribed in the plurality of ground via conductors is constant on the upper and lower surfaces of the insulating layer.

3. 3. The printed wiring board according to claim 1, which has a multilayer structure including a core layer, the core layer including the insulating layer and the plurality of via conductors.

4. A printed wiring board as described in any one of claims 1 to 3, wherein the axis of the signal via conductor and the axis of a truncated cone obtained by connecting a virtual circle inscribed in the diameter of the multiple ground via conductors between both ends of the multiple ground via conductors are coaxial.

5. 5. The printed wiring board according to claim 1, wherein the plurality of ground via conductors are arranged at positions that equally divide a circumference surrounding the signal via conductor.

6. The printed wiring board according to any one of claims 1 to 5, wherein the rate at which the diameter of the signal via conductor decreases from the large diameter side to the small diameter side is greater than the rate at which the diameter of the ground via conductor increases from the large diameter side to the small diameter side.

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