JP7737893B2 - printed wiring board - Google Patents

Description

This disclosure relates to printed wiring boards.

Printed wiring boards are required to achieve a specific circuit impedance for via conductors within the circuit. To achieve this, a structure is 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 the central conductor, the signal via conductor, and these are arranged coaxially (see, for example, Patent Document 1).

Japanese Patent Application Laid-Open No. 2005-311338

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

When multiple via conductors are arranged in a coaxial configuration, the impedance 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 conductor. 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 tangent lines connecting the insides of the multiple ground via conductors arranged around the signal via conductor changes on the front and back of the board, resulting in a large change in impedance.

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 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.

A printed wiring board according to one embodiment of the present disclosure can reduce the change in impedance between the front and back sides when multiple ground via conductors are arranged circumferentially around a signal via conductor.

FIG. 1 is a plan view of an example of a printed wiring board according to a first embodiment, as viewed from above. FIG. 2 is a plan view of the printed wiring board of FIG. 1 as seen from below. FIG. 2 is a cross-sectional view taken along line III-III in FIG. FIG. 1 is a perspective view showing an imaginary truncated cone formed on a printed wiring board. 4 is a graph showing impedance changes in the thickness direction of the printed wiring board according to the first embodiment. 3A to 3C are cross-sectional views showing steps in a method for manufacturing a printed wiring board according to the first embodiment. 3A to 3C are cross-sectional views showing steps in a method for manufacturing a printed wiring board according to the first embodiment. FIG. 10 is a cross-sectional view of an example of a printed wiring board according to a second embodiment. FIG. 10 is a cross-sectional view of a modified example of the printed wiring board according to the second embodiment. FIG. 10 is a cross-sectional view of a modified example of the printed wiring board according to the second embodiment.

Below, a detailed description is given of a form for implementing 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 this embodiment. Furthermore, the embodiments can be combined as appropriate to the extent that the processing content is not contradictory.

Furthermore, in the embodiments described below, 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.

Furthermore, the figures referenced below are schematic diagrams for the convenience of explanation. Therefore, details may be omitted from each figure, and the dimensions and dimensional ratios of the components in each figure do not faithfully represent the dimensions and dimensional ratios of the actual components.

[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.

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

Printed wiring board 10A has an insulating layer 1 and a plurality of via conductors that penetrate insulating layer 1. In the following description, the plurality of via conductors that penetrate insulating layer 1 will be designated by the number "2." In printed wiring board 10A, via conductors 2 include one signal via conductor 21 and a plurality (e.g., eight) of 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 a number other than eight, as long as the ground via conductors 22 can be viewed as being arranged in a circumferential or circular pattern around signal via conductor 21.

When the insulating layer 1 is viewed in plan, the positional relationship between the signal via conductors 21 and the ground via conductors 22 is such that eight ground via conductors 22 are arranged in a circular pattern around the signal via conductor 21. "Arranged in a circular pattern" here refers to, for example, a configuration in which multiple ground via conductors 22 are arranged on the circumference of a circle that is concentric with or similar to the signal via conductor 21.

The signal via conductor 21 and the ground via conductor 22 both have a large diameter at one end and a small diameter at the other end. Furthermore, the signal via conductor 21 and the ground via conductor 22 are oriented in opposite directions, from the large diameter side to the small diameter side. Having a large diameter at one end and a small diameter at the other end means that the diameters at both ends are different, with the diameter at one end being smaller than the diameter at the other end. In other words, it means that the diameter at one end is larger than the diameter at the other end.

Here, one end and the other end refer to positions when viewing the insulating layer 1 in the Z-axis direction, and are the positions from the halfway point in the thickness of the insulating layer 1 shown in FIG. 1 to the surface in the +Z direction, and the positions from the halfway point in the thickness of the insulating layer 1 shown in FIG. 1 to the surface of the insulating layer 1 in the -Z direction. The one end and the other end are not limited to the +Z direction and -Z direction of the insulating layer 1. For example, if a specific position in the + direction of the via conductor 2 in the thickness direction of the insulating layer 1 is defined as one end, then a specific position in the - direction of the via conductor 2 in the thickness direction of the insulating layer 1 is defined as the other end. In this case, the positions in the + direction and the - direction of the one end and the other end in the thickness direction of the insulating layer 1 may be reversed.

Specifically, for the signal via conductor 21, the diameter d11 on the top surface Sa side of the insulating layer 1 is larger than the diameter d12 on the bottom surface Sb side. Conversely, for the eight ground via conductors 22, the diameter d31 on the top surface Sa side of the insulating layer 1 is smaller than the diameter d32 on the bottom surface Sb side. In other words, the relationships are d11 > d12 and d31 < d32.

In the via conductors 2 of the printed wiring board 10A, the positions of the signal via conductors 21 and the ground via conductors 22 where the diameters are large and small may be opposite to the orientation shown in Figures 1 to 3. Alternatively, the orientation from the large diameter side to the small diameter side may be opposite to the orientation 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 may be smaller than the diameter d12 on the bottom surface Sb side. Conversely, for the eight ground via conductors 22, the diameter 31 on the top surface Sa side of the insulating layer 1 may be larger than the diameter d32 on the bottom surface Sb side. That is, the relationship d11 < d12 and d31 > d32 may be satisfied.

In addition, 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. In other words, 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 is the same among the multiple ground via conductors 22, the diameters of the large diameter side and the small diameter side may be the same or different.

The printed wiring board 10A shown in Figures 1 to 3 has the above-described configuration of via conductors 2 as its basic unit. However, in this embodiment, the printed wiring board 10A may have, for example, multiple combinations of one signal via conductor 21 and multiple ground via conductors 22. Furthermore, it may also include via conductors other than the signal via conductor 21 and the ground via conductor 22. Furthermore, in combinations of a signal via conductor and multiple ground via conductors, it is considered desirable to minimize signal leakage if the gap between the ground via conductors is positioned so that it is 1/10 or less of the wavelength λ of the highest frequency of the signal passing through the signal via conductor, and is typically positioned so that it is 1/20.

In the printed wiring board 10A, the signal via conductors 21 and 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 ground via conductors 22 preferably decrease continuously from the larger diameter side to the smaller diameter side. In this case, the slope 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 for a continuous change in impedance 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 designated as one end above and the surface designated as the other end above).

The external shape of the signal via conductor 21 and the ground via conductor 22 is preferably a truncated cone. In this case, the signal via conductor 21 is preferably arranged so that, when viewed as a truncated cone, the bottom surface (21a) is close to the upper surface Sa of the insulating layer 1 and the top surface (21b) is close to the lower surface Sb of the insulating layer 1. In this case, the bottom surface 21a of the signal via conductor 21 preferably coincides with the upper surface Sa of the insulating layer 1. The top surface 21b of the signal via conductor 21 preferably coincides with the lower surface Sb of the insulating layer 1.

The ground via conductor 22 is preferably positioned so that its bottom surface 22a is close to the lower surface Sb of the insulating layer 1 and its top surface (22b) is close to the upper surface Sa of the insulating layer 1. In this case, the bottom surface 22a of the ground via conductor 22 preferably coincides with the lower surface Sb of the insulating layer 1. The top surface 22b of the ground via conductor 22 preferably coincides with the upper surface Sa of the insulating layer 1.

The top surface of printed wiring board 10A is formed in an XY plane consisting of the top surface Sa of insulating layer 1 and the top surfaces of signal via conductors 21 and ground via conductors 22. The bottom surface of printed wiring board 10A is formed in an XY plane consisting of the bottom surface Sb of insulating layer 1 and the bottom surfaces of signal via conductors 21 and ground via conductors 22.

In this embodiment, it is preferable that 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 circular.

The bottom surfaces 22a of the multiple ground via conductors 22 arranged around the signal via conductor 21 should preferably have the same shape. The top surfaces 22b of the multiple ground via conductors 22 should also preferably have the same shape.

Furthermore, it is preferable that the multiple ground via conductors 22 arranged around the signal via conductor 21 have similar changes in the longitudinal direction (Z direction) of the side surface 22s (change from diameter d32 to diameter d31). This makes it possible to reduce the change 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) (change from diameter d32 to diameter d31) of all of the multiple ground via conductors 22 arranged around the signal via conductor 21 are the same.

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 diameter d11 of the signal via conductor 21 and the center PC1c of an imaginary circle PC1 inscribed in the diameter 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 diameter d12 of the signal via conductor 21 and the center PC2c of an imaginary circle PC2 inscribed in the diameter d32 of the eight ground via conductors 22 preferably coincide.

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 becomes a truncated cone (hereinafter referred to as "imaginary truncated cone PC1D"). As shown in FIG. 4, imaginary truncated cone PC1D is a truncated cone with its bottom surface at imaginary circle PC1 on the top surface Sa of printed wiring board 10A and its top surface at imaginary circle PC2 on the bottom surface Sb of printed wiring board 10A. As described above, 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. Therefore, on printed wiring board 10A, the axis of signal via conductor 21 coincides with the axis of imaginary truncated cone PC1D and is coaxial.

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

In this case, the ground via conductors 22 are arranged circumferentially, surrounding the signal via conductors and dividing the circumference equally. This has the effect of suppressing changes in impedance between the front and back of the printed wiring board. In addition, by arranging the ground via conductors 22 so that they divide the circumference equally, the signals flowing through the signal via conductors 21 are less susceptible to the influence of noise generated around the ground via conductors 22.

The longitudinal length (Z direction) of the signal via conductors 21 and ground via conductors 22 should preferably correspond to the thickness t of the insulating layer 1. The thickness t of the insulating layer 1 is selected appropriately depending on 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, the diameter d11 on the top side and the diameter d12 on the bottom side of the signal via conductor 21, and the diameter d31 on the top side and the diameter d32 on the bottom side of the ground via conductor 22, may be, for example, the following sizes, while satisfying the relationships d11 > d12 and d31 < d32.

For example, the diameter d11 of the signal via conductor 21 may be 100 to 250 μm and the diameter d12 may be 60 to 150 μm, and typically, the diameter d11 may be 130 to 180 μm and the diameter d12 may be 70 to 100 μm. For example, the diameter d31 of the ground via conductor 21 may be 60 to 150 μm and the diameter d32 may be 100 to 250 μm, and typically, the diameter d31 may be 70 to 100 μm and the diameter d32 may be 130 to 180 μm.

Here, the impedance of via conductors arranged in a coaxial structure in a specified XY plane can be calculated using the following formula (I):

In formula (I), each symbol has the following meaning.
Z ₀ : Impedance ε _r : Relative permittivity of inter-conductor insulator d1 : Diameter of signal via conductor d2 : Diameter of imaginary circle inscribed in ground via conductor

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

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

Example 1 shows a case where the signal via conductors 21 and 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 ground via conductors 22) are opposite to each other.

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 impedance on the top and bottom surfaces is 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 to the bottom of the printed wiring board 10A is greater than the rate at which the diameter of the ground via conductor 22 increases. In this case, it is preferable that the diameters of the multiple ground vias 22 are the same on both the top and bottom sides.

As a comparative example, we also calculated the impedance of the top and bottom surfaces of a printed wiring board with the same configuration as printed wiring board 10A, 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 impedance calculation results for Examples 1 to 4 and the comparative example are shown in Table 1.

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

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

The rate of diameter change for each via conductor in each example can be adjusted by adjusting the conditions for forming the through holes in the insulating layer when manufacturing the via conductors. Methods for forming the through holes include, for example, using a laser or a reamer, with the laser method being preferred.

(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.

The 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 step is to form 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-hole 21h and the second through-hole 22h formed in the second step with a conductor.

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, and polyphenylene sulfide (PPS) resin.

In addition to the resin materials mentioned above, the substrate 1P may also contain inorganic fillers such as silica, barium sulfate, talc, clay, glass, calcium carbonate, titanium oxide, and aluminum hydroxide, or organic fillers made of phenolic resin or methacrylic resin. Furthermore, the insulator may also 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 also be used in combination.

As shown in Figure 6B, the first through hole 21h is formed, for example, by irradiating a laser from the side of the substrate 1P that would become the upper surface Sa when it is made into the insulating layer 1 toward the side that would become the lower surface Sb. 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 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.

Similarly, as shown in FIG. 6B, the second through holes 22h are formed, for example, by irradiating a laser from the lower surface Sb toward the upper surface Sa of the substrate 1P. In this case, the second through holes 22h are preferably formed so as to be arranged in a circular pattern around the first through hole 21h. Preferably, they are arranged so as to equally divide the circumference around the first through hole 21h. The second through holes 22h are, for example, truncated cone-shaped through holes with a smaller diameter d31 on the upper surface Sa side and a larger diameter d32 on the lower surface Sb side. In this way, through holes can be formed in which the relationship between diameters d31 and d32 is d31<d32. The specific size is set appropriately depending on the design. Laser irradiation conditions corresponding to the design are set, and through holes that match the design can be obtained.

The first through hole 21h and the second through hole 22h may be formed using a reamer instead of a laser.

In the third step, the conductive material used for the first through hole 21h and the second through hole 22h may be, for example, a metal such as copper, and the method for filling the conductor may be, for example, electrolytic plating.

Note that while a via conductor in which a conductor is filled in a through hole is shown here, the via conductor is not necessarily limited to a form in which a through hole is filled with a conductor, and may also be a form in which a conductor layer is formed on the side of the through hole with a predetermined layer thickness.

The signal via conductors 21 and ground via conductors 22 that make up the printed wiring board 10A described above are used by being electrically connected to the signal terminals and ground terminals, respectively, of a semiconductor element mounted on a semiconductor device or the like.

[Configuration of the printed wiring board according to the second embodiment]
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 a 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.

Printed wiring board 10Ba, the cross section of which is shown in FIG. 7, has a core layer C having a configuration similar to that of printed wiring board 10A shown in FIGS. 1 to 3, and has a buildup layer B1 on the upper surface Sa of core layer C, which is composed of internal ground wiring conductors 41, internal signal wiring conductors 51, and an insulating layer 31, and a buildup layer B2 on the lower surface Sb of core layer C, which is composed of internal ground wiring conductors 42, internal signal wiring conductors 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 extend in the XY plane direction while maintaining an appropriate distance between them so that the top surface Sa and the bottom surface Sb of the core layer C can be impedance matched.

In multilayer printed wiring boards with a configuration such as printed wiring boards 10Ba-10Bc, the area where conductor wiring is concentrated is often the core layer C, which is an inner layer. 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 increases the effectiveness 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 build-up layers B1 and B2, respectively, the change in impedance can be further reduced, thereby further enhancing the effectiveness of improving electrical properties.

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

As described above, when a through hole is formed in an insulating layer using a laser, the diameter of the through hole is larger 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, a method is used in which laser processing is performed from one surface or the other depending on the position of the through hole, as shown in Figure 6B, for example.

When manufacturing a multilayer printed wiring board by stacking buildup layers B1 and B2 sequentially one above the other on a core layer C, through holes can only be formed on the surfaces (top and bottom) of buildup layers B1 and B2, so it is not possible to form two types of through holes in which the diameter of the through hole decreases 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 diameter of the through hole decreases in opposite directions.

The printed wiring board 10Bb, the cross section of which is shown in Figure 8, has the same configuration as the printed wiring board 10Ba, including the core layer C and the build-up layer B2 formed on the lower surface Sb of the core layer C.

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

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

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

Printed wiring board 10Bc, the cross section of which is shown in Figure 9, has buildup layers formed on both sides of core layer C, each with a configuration similar to that of buildup layer B1 of printed wiring board 10Bb. Buildup layer B2, formed on the lower surface Sb of core layer C, also has a configuration similar to that of buildup layer B1 described for printed wiring board 10Bb. However, while buildup layer B1 has components stacked sequentially upward, buildup layer B2 has components stacked sequentially downward.

That is, buildup layer B2 has internal ground wiring conductors 42 and internal signal wiring conductors 52 that connect to ground via conductors 22 and signal via conductors 21, respectively, of core layer C. Buildup layer B2 also has ground wiring conductors 72 and signal wiring conductors 92. Buildup layer B2 further has ground via conductors 62 that connect internal ground wiring conductors 42 and 72, and signal via conductors 82 that connect internal signal wiring conductors 52 and 92.

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

Printed wiring board 10Bc is configured so that components mounted on the top surface of buildup layer B1 and the bottom surface of buildup layer B2 can exchange signals.

The above describes a printed wiring board according to the second embodiment, taking as an example a printed wiring board with a multilayer structure including build-up layers B1 and B2 in a core layer C. However, printed wiring boards 10Ba-10Bc having the configurations shown in Figures 7-9 may also be formed using a simultaneous 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 conforms to the configuration of this embodiment.

The specific details of the configuration, structure, positional relationships, and shape shown in the above embodiments may be modified as appropriate without departing from the spirit of this disclosure. Furthermore, the configurations, structures, positional relationships, and shapes shown in the above embodiments may be combined as appropriate without departing from the spirit of this disclosure.

10A, 10Ba to 10Bc Printed wiring board 1 Insulating layer 21 Signal via conductor 21h First through hole 22 Ground via conductor 22h Second through hole C Core layers B1, B2 Build-up layers 31, 32 Insulating layer (for build-up layer)
41, 42: Ground internal wiring conductors 51, 52: Signal internal wiring conductors 61, 62: Ground via conductors (for build-up layers)
71, 72 Ground wiring conductors 81, 82 Signal via conductors (for build-up layers)
91, 92 Signal wiring conductor

Claims (6)

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 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. 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 . The printed wiring board according to claim 1 or 2, which has a multilayer structure including a core layer, the core layer comprising the insulating layer and the plurality of via conductors. The printed wiring board according to any one of claims 1 to 3, wherein the axis of the signal via conductor and the axis of the truncated cone obtained by connecting an imaginary circle inscribed within the diameter of the ground via conductors between both ends of the ground via conductors are coaxial. The printed wiring board according to any one of claims 1 to 4, wherein the plurality of ground via conductors are arranged at positions that equally divide the circumference surrounding the signal via conductor. The printed wiring board of any one of claims 1 to 5, wherein the rate at which the diameter of the signal via conductor decreases from its large diameter side to its small diameter side is greater than the rate at which the diameter of the ground via conductors increases from its large diameter side to its small diameter side.