Printed wiring board

Abstract

This printed wiring board comprises: a first ground conductor; a first insulating layer positioned on the first ground conductor and having a first surface on a side opposite the first ground conductor; a wire extending over a first region of the first surface; a second insulating layer covering the wire and having a second surface on a side opposite the first insulating layer; and a second ground conductor positioned on the second surface. The first insulating layer has a groove that is open along a direction in which the wire extends on the first surface in a transparent plan view. The second insulating layer has a first portion in the groove. The relative permittivity of the second insulating layer is smaller than the relative permittivity of the first insulating layer.

Description

printed wiring board

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

[0002] In printed wiring boards, the thickness of the insulating layer covering the signal lines is specified to appropriately determine the characteristic impedance and reduce the electrostatic capacitance and crosstalk between the wiring. Meanwhile, there is a demand for miniaturization of printed wiring boards and higher density of stripline structures. Japanese Patent No. 7180781 discloses a method for suppressing transmission loss by arranging a stripline between an insulating layer having a first relative dielectric constant and an insulating layer having a second relative dielectric constant lower than the first relative dielectric constant.

[0003] One aspect of a printed wiring board according to the present disclosure includes: (1) a first ground conductor; a first insulating layer located on the first ground conductor and having a first surface opposite the first ground conductor; wiring extending over a first region of the first surface; a second insulating layer located on the first surface, covering the wiring, and having a second surface opposite the first insulating layer; and a second ground conductor located on the second surface, wherein the first insulating layer has a groove having an opening that is aligned at least along the direction in which the wiring on the first surface extends in a planar perspective view; the second insulating layer has a first portion located within the groove; and the dielectric constant of the second insulating layer is smaller than the dielectric constant of the first insulating layer.

[0004] (2) In the printed wiring board described in (1) above, the groove is located around the wiring, and an opening edge of the groove is located along the outline of the wiring in a planar perspective. (3) In the printed wiring board described in (1) above, at least a portion of the groove is a through groove penetrating the first insulating layer, and the first portion of the second insulating layer is in contact with the first ground conductor. (4) In the printed wiring board described in (1) above, the wiring includes differential signal wiring in which a first signal wiring conductor and a second signal wiring conductor are located side by side, and the groove is located around the first signal wiring conductor and the second signal wiring conductor in a planar perspective. (5) In the printed wiring board described in (1) above, the first surface includes a second region in which the wiring is not located, and the first region and the second region are located on either side of the opening. (6) In the printed wiring board described in (2) above, in a cross-sectional view perpendicular to the direction in which the wiring extends, a sidewall surface of the groove that follows the outline of the wiring is perpendicular to the first ground conductor. (7) In the printed wiring board described in (1) above, in a cross-sectional view perpendicular to the direction in which the wiring extends, a width of the wiring that contacts the first region is equal to a width of the first surface of the first insulating layer that contacts the wiring. (7) In the printed wiring board described in (1) above, in a cross-sectional view perpendicular to the direction in which the wiring extends, a width of the wiring that contacts the first region is equal to a width of the first surface of the first insulating layer that contacts the wiring.

[0005] FIG. 1 is a plan view parallel to the upper surface of a printed wiring board. FIG. 2 is a cross-sectional view perpendicular to the upper surface of a printed wiring board. FIG. 3 is a view showing another example 1 of the cross-sectional shape of a printed wiring board. FIG. 4 is a view showing another example 2 of the cross-sectional shape of a printed wiring board. FIG. 5 is a view showing another example 3 of the cross-sectional shape of a printed wiring board. FIG. 6 is a view showing another example 4 of the cross-sectional shape of a printed wiring board. FIG. 7 is a table showing the results of calculating differential impedance in a printed wiring board by numerical simulation. FIG. 8 is a view showing another example 5 of the cross-sectional shape of a printed wiring board. FIG. 9 is a view showing another example 6 of the cross-sectional shape of a printed wiring board.

[0006] Hereinafter, an embodiment will be described with reference to the drawings. FIG. 1A is a plan view parallel to the upper surface of a printed wiring board 1 of this embodiment. FIG. 1B is a cross-sectional view perpendicular to the upper surface of the printed wiring board 1. FIG. 1A is a plan view taken along the cross-sectional line BB in FIG. 1B. FIG. 1B is a cross-sectional view taken along the cross-sectional line AA in FIG. 1A, and includes a conductor layer not shown in FIG. 1A. Note that these figures may show only a portion of the printed wiring board 1. Furthermore, the scale and aspect ratio of each component in these figures are for illustrative purposes and do not necessarily reflect the optimal configuration.

[0007] As shown in FIGS. 1A and 1B , the printed wiring board 1 includes a first ground conductor 11 located on the bottom side, a second ground conductor 14 located on the top side, and wiring 12 and an insulating layer 13 located between the first ground conductor 11 and the second ground conductor 14.

[0008] The first ground conductor 11 and the second ground conductor 14 are solid conductor layers made of metal or the like that include positions in a planar perspective corresponding to at least the wiring 12. The first ground conductor 11 and the second ground conductor 14 may be made of, for example, copper, aluminum, or gold.

[0009] The insulating layer 13 is located on the first ground conductor 11 on the side of the second ground conductor 14. The insulating layer 13 includes a first insulating layer 131 and a second insulating layer 132. The bottom surface of the first insulating layer 131 is in contact with the first ground conductor 11. The first insulating layer 131 has a groove D1 that opens along the extension direction of the wiring 12 in a planar perspective view. At least a portion of the groove D1 may be a through groove that vertically penetrates the first insulating layer 131. The sidewall surface of the groove D1 may be perpendicular to the top surface of the first ground conductor 11. Here, "perpendicular" includes a tilt within the range of tolerance that may occur during manufacturing, for example, a tilt range of approximately ±5%, i.e., ±4.5 degrees or less. The first ground conductor 11 may be made of, for example, copper, aluminum, gold, or the like.

[0010] In a portion 1311 of the first insulating layer 131, the wiring 12 extends in a first region S1, which is a region on the surface (first surface f1) opposite to the surface in contact with the first ground conductor 11. The wiring 12 is not particularly limited, but may be a differential signal wiring in which a first signal wiring conductor 121 and a second signal wiring conductor 122 are positioned parallel to each other. In the differential signal wiring, the distance between the wirings 12 may be, for example, 250 μm. Both ends of the wiring 12 in the extension direction may be connected to through conductors such as through holes or vias. The wiring 12 may also be curved and / or bent along the way. The wiring 12 may be made of a material with high electrical conductivity, excellent processability, and corrosion resistance, such as copper.

[0011] The wiring 12 has a slightly flattened trapezoidal shape in a cross section perpendicular to the direction of extension, but is not limited to this. The wiring 12 may have a rectangular cross section, a rounded corner shape, an elliptical shape, or the like. The width of the wiring 12 may be 50 μm.

[0012] In the printed wiring board 1, the opening edge of the groove D1 on the first surface f1 may be located along the contours of the first signal wiring conductor 121 and the second signal wiring conductor 122 in a planar perspective. "Located along the contours" means that the width of the wiring 12 (first region S1) may be equal to the width of the first surface f1, which is the upper surface of a portion 1311 of the first insulating layer 131 that is in contact with the wiring 12, or the width of the first insulating layer 131 that is in contact with the wiring 12 may be greater than the width of the wiring 12. The entire area between the first signal wiring conductor 121 and the second signal wiring conductor 122 may be the groove D1. The groove D1 does not need to be within a fixed distance from the first signal wiring conductor 121 and the second signal wiring conductor 122. In the first insulating layer 131, a portion 1312 corresponding to the second region S2 is located at a position sandwiching the groove D1 from the portion 1311 that corresponds to the first region S1 in a planar perspective. That is, the second region S2 (part 1312) is located surrounding the wiring 12 and the trench D1.

[0013] The second insulating layer 132 is located on the first surface f1 of the first insulating layer 131 (portion 1311) so as to cover the wiring 12. The second insulating layer 132 also includes a first portion 1322 located in the groove D1. That is, the portion 1321 of the second insulating layer 132 covering the side of the first insulating layer 131 opposite to the first ground conductor 11 (the upper surface side) is connected to the first portion 1322 filling the groove D1. As a result, the second insulating layer 132 is in direct contact with the first ground conductor 11 at the first portion. The dielectric constant of the second insulating layer 132 is smaller than the dielectric constant of the first insulating layer 131 (e.g., approximately 3.5 to 5.0). For example, the second insulating layer 132 may be a liquid crystal polymer (e.g., having a dielectric constant of approximately 2.8 to 3.3).

[0014] The top surface of the second insulating layer 132, i.e., the side opposite the wiring 12 (second surface f2), is in contact with the second ground conductor. The first insulating layer 131 and the second insulating layer 132 may each include a glass cloth (not shown). The glass cloth extends in the direction of extension of each layer, corresponding to the front-to-back and left-to-right directions in FIG. 1B . However, the glass cloth in the first insulating layer 131 is interrupted at the groove D1, which corresponds to the first portion 1322 in a planar perspective. The glass cloth increases the rigidity of the printed wiring board 1 and reduces the thermal expansion coefficient, but has a higher dielectric constant than resin. The first insulating layer 131 may be, for example, R-5670 (GC) or R-5670 (GF) of MEGTRON6 manufactured by Panasonic® Corporation, and may have a thickness of 0.06 mm. The second insulating layer 132 may be, for example, R-1551 (MD) manufactured by Panasonic Corporation, and may have a thickness of 0.055 mm. Furthermore, the first insulating layer 131 and the second insulating layer 132 may contain an inorganic filler in addition to the above.

[0015] As described above, in the insulating layer 13 of this embodiment, the second insulating layer 132 (first portion 1322) is located within the groove D1 of the first insulating layer 131. On the other hand, the conventional insulating layer 13 does not have the groove D1. That is, the insulating layer 13 between the wiring 12 and the first ground conductor 11 is only the first insulating layer 131, which is an uninterrupted glass cloth. Therefore, in the present disclosure, the volume ratio of the insulating material with a low relative dielectric constant around the wiring 12 can be increased compared to the conventional embodiment in the cross-sectional view of FIG. 1B . Therefore, this embodiment can mitigate the decrease in the characteristic impedance of the wiring 12 more effectively than the conventional embodiment.

[0016] Such a printed wiring board 1 may be obtained, for example, by the following manufacturing procedure. A first insulating layer 131 is uniformly formed on the first ground conductor 11, and the wiring 12 is then arranged. After that, unnecessary portions of the first insulating layer 131 are removed by laser processing to match the shape of the required groove D1. At this time, the glass cloth in the corresponding area of ​​the first insulating layer 131 is also removed. Then, a second insulating layer is laminated to cover the wiring 12, and at the same time, the groove D1 is filled with resin from the second insulating layer 132. Next, the second ground conductor 14 is arranged on the second insulating layer 132.

[0017] 2A, 2B, 3A, and 3B are diagrams showing other examples of the cross-sectional shape shown in FIG. 1B. As in Example 1 shown in FIG. 2A, a portion 1311a of the first insulating layer 131 corresponding to the first region S1 may have a width that gradually decreases from the side of the first ground conductor 11 toward the side of the wiring 12. With this first insulating layer 131 (portion 1311a), the volume ratio of the insulating material with a low dielectric constant around the wiring 12 is reduced compared to the case of FIG. 1B. Therefore, the printed wiring board 1 can structurally support the wiring 12 more stably while reducing an increase in characteristic impedance.

[0018] 2B , a portion 1311b of the first insulating layer 131 corresponding to the first region S1 may have a width that gradually increases from the side of the first ground conductor 11 toward the side of the wiring 12. With such a first insulating layer 131 (portion 1311b), the volume ratio of the insulating material with a low relative dielectric constant around the wiring 12 increases compared to the case of FIG. 1B , which further reduces the decrease in characteristic impedance.

[0019] 3A , the width, i.e., the area in a plan view, of a portion 1311c of the first insulating layer 131 including the first surface f1 may be larger than the first region S1, which is the contact surface of the wiring 12 with the first insulating layer 131. In other words, the width of the wiring 12 and the width of the first surface in contact with the wiring 12 may not be the same.

[0020] 3B , a portion 1312d of the first insulating layer 131 corresponding to the second region S2d may be present near the center between the first signal wiring conductor 121 and the second signal wiring conductor 122. In other words, the groove D11 around the first signal wiring conductor 121 and the groove D12 around the second signal wiring conductor 122 may have a bifurcated portion. When the width of the groove D1 is narrower than in the above embodiment, a range at a certain distance from the outline of the first signal wiring conductor 121 and a range at a certain distance from the outline of the second signal wiring conductor 122 are separated. In other words, a portion 1312d of the first insulating layer 131 where no wiring 12 is disposed may be located near the center between the first signal wiring conductor 121 and the second signal wiring conductor 122.

[0021] The bond between the insulating materials of the first insulating layer 131 and the second insulating layer 132 tends to be weaker than the bond between the insulating material and the ground conductor. By providing an uneven surface between the first insulating layer 131 and the second insulating layer 132, the bond area can be increased, thereby improving the bond strength. Furthermore, in this case, the glass cloth in the insulating layer 13 remains unremoved in the area where the second insulating layer 132 overlaps with the central portion 1312d of the first insulating layer 131 in a planar perspective view. Therefore, compared to Examples 1 to 3 above, the resin flow during the formation of the printed wiring board 1 can be reduced, and misalignment between the wiring in each layer and a decrease in rigidity due to the presence of the groove D12 can be suppressed.

[0022] 4 is a table showing the results of calculating the characteristic (differential) impedance of the printed wiring board 1 of this embodiment by numerical simulation. In this example, the wiring 12, which is a differential wiring, has a first signal wiring conductor 121 and a second signal wiring conductor 122, each with a circuit width of 50 μm, and a circuit gap between the first signal wiring conductor 121 and the second signal wiring conductor 122, which is 250 μm. The thickness of the wiring 12 is 16 μm.

[0023] The thickness of the first insulating layer 131 was 60 μm, and the dielectric constant of the entire first insulating layer 131 made of resin and glass cloth was set to 4.40. The thickness of the second insulating layer 132 excluding the first portion filling the groove D1 was 54 μm, and the dielectric constant of the entire second insulating layer 132 made of resin and glass cloth was set to 3.26, and the dielectric constant of the resin of the second insulating layer 132 was set to 3.07.

[0024] The groove D1 is located around each of the wirings 12 along its contour in a planar perspective view. The width of the groove D1 is 150 μm at the opening and 130 μm at the lower end where the groove D1 contacts the first ground conductor 11. That is, the first portion 1322 of the second insulating layer 132 between the first signal wiring conductor 121 and the second signal wiring conductor 122 does not have the portion 1312d of the first insulating layer 131 in Example 4. The groove D1 has a tapered shape as a whole, as in Example 1. The depth of the groove D1 is the same as the thickness of the first insulating layer 131, i.e., 60 μm. The simulation was performed using Electronics Pro 2D by ANSYS.

[0025] As shown in the examples, under the above conditions, the differential impedance of the wiring 12 in the printed wiring board 1 can be set to approximately the target of 100 Ω. Since the differential impedance varies by approximately ±9% during manufacturing, the resulting printed wiring board 1 falls within the range of 90 Ω to 110 Ω, which is ±10% of the target of 100 Ω. Therefore, the yield during manufacturing of the printed wiring board 1 can be improved.

[0026] Comparative Example 1 is a case where the first insulating layer 131 does not have the groove D1. That is, with a plane including the underside of the wiring 12 as the boundary, all of the insulating layers 13 on the side closer to the first ground conductor 11 are the first insulating layers 131, and all of the insulating layers 13 on the side closer to the second ground conductor 14 are the second insulating layers 132. In this case, the differential impedance does not reach the target of 100 Ω, resulting in a low overall value. Within the range of manufacturing variation, it is possible to produce products whose differential impedance is less than 90 Ω, which is -10% of 100 Ω. This can result in a decrease in yield, increased manufacturing costs, and waste of material resources.

[0027] In Comparative Example 2, the circuit width is narrowed to 46 μm, but the rest of the design is the same as in the Example. In this case, the median differential impedance is approximately 100 Ω, and the variation is limited to 90 Ω to 110 Ω, which is ±10% of 100 Ω. However, with the current subtractive method, which removes unnecessary conductors by etching, it is difficult to fabricate a printed wiring board 1 with a circuit width of 50 μm or less. Even if it were possible to fabricate it, it could lead to increased manufacturing costs.

[0028] In Comparative Example 3, the circuit gap is widened to 950 μm, with the other design values ​​being the same as in the Example. Simply widening the circuit gap does not sufficiently increase the differential impedance. Therefore, the median is slightly lower than 100 Ω, and within the range of variation, products may be produced that fall below 90 Ω, which is -10% of 100 Ω. Furthermore, as the circuit gap increases, the circuit accommodation capacity deteriorates and the size of the printed wiring board 1 also increases, leading to increased costs and required space.

[0029] 5A and 5B are diagrams showing other examples of the cross-sectional shape of the printed wiring board 1. As in the printed wiring board 1a of Example 5 shown in FIG. 5A , multiple stripline structures may be stacked. The stacking order (upper-lower relationship) of the first insulating layer 131 and the second insulating layer 132 may be different among the insulating layers 13 associated with the multiple stripline structures. While the wiring 12 is shown overlapping and positioned at the same position in a planar perspective, this is not a limitation. The positions of the wiring 12 may also be different among the multiple insulating layers 13. Furthermore, the insulating layer 15 positioned between the multiple stripline structures may be made of the same material as the first insulating layer 131 or the same material as the second insulating layer 132, which has a low dielectric constant.

[0030] 5B , wiring 16 connected to the stripline structure or separate from it may be exposed on the outer surface of printed wiring board 1. This wiring 16 may be covered with a protective film or the like.

[0031] Furthermore, the printed wiring board 1 may be used as a core substrate, with build-up layers or the like located on one or both sides thereof. Also, a solder resist layer may be located on the outer surface of the printed wiring board 1.

[0032] As described above, the printed wiring board 1 of this embodiment includes the first ground conductor 11, the first insulating layer 131 located on the first ground conductor 11 and having a first surface f1 opposite the first ground conductor 11, the traces 12 extending over a first region S1 on the first surface f1, the second insulating layer 132 located on the first surface f1 to cover the traces 12 and having a second surface f2 opposite the first insulating layer 131, and the second ground conductor 14 located on the second surface f2. The first insulating layer 131 has a groove D1 having an opening extending along at least the direction in which the traces 12 extend on the first surface f1 in a planar perspective view. The second insulating layer 132 has a first portion 1322 located within the groove D1. The second insulating layer 132 has a dielectric constant smaller than that of the first insulating layer 131. With this structure, the printed wiring board 1 can mitigate the decrease in characteristic impedance of the wiring 12 even if the printed wiring board 1 is thin and the interlayer distance between the wiring 12 and the first ground conductor 11 and the second ground conductor 14 is 60 μm or less.

[0033] Moreover, the groove D1 may be located around the wiring 12, and the opening edge of the groove D1 may be located, in a plan view perspective, along the outline of the wiring 12. By positioning the groove D1 so as to surround the wiring in this way and positioning the second insulating layer 132 with a low relative dielectric constant within the groove D1, the printed wiring board 1 can control the characteristic impedance over a wider range.

[0034] Furthermore, at least a portion of the groove D1 may be a through groove penetrating the first insulating layer 131. The first portion 1322 of the second insulating layer 132 may be in contact with the first ground conductor 11. This allows the printed wiring board 1 to control the characteristic impedance over a wider range even when it is small and thin. Furthermore, because the second insulating layer 132 is in direct contact with the first ground conductor 11, it is easier to increase the bonding strength than when the second insulating layer 132 is bonded to the first insulating layer 131. Therefore, the robustness and durability of the structure of the printed wiring board 1 can be improved.

[0035] Furthermore, the wiring 12 may include a differential signal wiring in which a first signal wiring conductor 121 and a second signal wiring conductor 122 are positioned side by side. In a planar perspective, the groove D1 is positioned around and between the first signal wiring conductor 121 and the second signal wiring conductor 122. In this way, by positioning the second insulating layer 132, which has a relatively low dielectric constant, between the two differential signal wirings, the characteristic impedance of the wiring 12 can be set to a value within an appropriate range even if the interlayer distance is small.

[0036] The first surface f1 may also include a second region S2 (the upper surface of a portion 1312 of the first insulating layer 131) where the wiring 12 is not located. The first region S1 and the second region S2 may be located with an opening (groove D1) sandwiched between them. Therefore, the first portion 1322, which has a low dielectric constant, is surrounded by the portion 1312 of the first insulating layer 131, improving the bonding strength between the insulating layers, and allowing the printed wiring board 1 to have a stable shape.

[0037] Furthermore, in a cross-sectional view perpendicular to the direction in which the wiring 12 extends, the sidewall surface of the groove D1 that follows the outline of the wiring 12 may be perpendicular to the first ground conductor 11. That is, by preventing the portion 1311 of the first insulating layer 131 from becoming thicker than necessary, it is possible to obtain a more stable and appropriate characteristic impedance. On the other hand, by preventing the portion 1311 from becoming thinner than necessary, it is possible to reliably support the wiring 12 and make it less likely for the wiring to collapse during manufacturing.

[0038] Furthermore, in a cross-sectional view perpendicular to the direction in which the wiring 12 extends, the width of the wiring 12 in contact with the first region S1 may be equal to the width of the first surface, which is the upper surface of a portion 1311 of the first insulating layer 131 in contact with the wiring 12. In this case, too, an appropriate characteristic impedance can be obtained by preventing the portion 1311 of the first insulating layer 131 from becoming unnecessarily thick. Note that "equal" here includes the range of error that may occur during manufacturing, for example, a difference between the width of the wiring 12 in contact with the first region S1 and the width of the first insulating layer 131 in contact with the wiring 12 of approximately ±30% or less.

[0039] The above embodiment is merely an example, and various modifications are possible. For example, the wiring 12 does not have to be a differential signal wiring. It may be a wiring that transmits one or more signals independently, such as a signal or power.

[0040] In the above embodiment, the entire periphery of the wiring 12 is surrounded by the opening of the groove D1, but this is not limiting. The wiring 12 may have portions at both ends, etc., that do not necessarily have the groove D1.

[0041] In the above embodiment, the groove D1 is described as a through groove, but it does not necessarily have to be a through groove. Also, only a portion of the groove may be a through groove, with the remaining portion being a non-through groove. As described above, it is difficult to increase the bonding strength between different insulating layers, but increasing the unevenness of the contact surface can improve the overall bonding strength.

[0042] In the above embodiment, the first insulating layer 131 has been described as having a portion 1312 corresponding to the second region S2, but this portion may be omitted. The first insulating layer 131 may have only a portion 1311 corresponding to the first region S1.

[0043] Furthermore, the cross-sectional shape of the sidewall surface may be different between a portion 1311 and another portion 1312 of the first insulating layer 131. Alternatively, the same portion may have a portion with a different cross-sectional shape of the sidewall surface. Furthermore, each cross-sectional shape does not have to be linear. In addition, the specific configuration, structure, materials, size, manufacturing procedure, etc. shown in the above embodiment can be appropriately changed without departing from the spirit of the present invention. The scope of the present invention includes the scope of the invention described in the claims and their equivalents.

[0044] The present disclosure can be used in printed wiring boards.

[0045] 1, 1a, 1b Printed wiring board 11 First ground conductor 12, 16 Wiring 13 Insulating layer 14 Second ground conductor 15 Insulating layer 16 Wiring 100 Printed wiring 131 First insulating layer 132 Second insulating layer D1, D11, D12 Groove f1 First surface f2 Second surface S1 First region S2, S2d Second region

Claims

1. a first ground conductor; a first insulating layer positioned on the first ground conductor and having a first surface opposite the first ground conductor; a wiring extending over a first region of the first surface; a second insulating layer located on the first surface to cover the wiring and having a second surface on the opposite side to the first insulating layer; a second ground conductor located on the second surface; Equipped with the first insulating layer has a groove having an opening that is aligned along at least the direction in which the wiring extends on the first surface in a planar perspective view; the second insulating layer has a first portion located in the groove; the second insulating layer has a dielectric constant smaller than that of the first insulating layer; Printed wiring board.

2. the groove is positioned around the wiring, and an opening edge of the groove is positioned along the outline of the wiring in a plan view perspective; The printed wiring board according to claim 1.

3. At least a portion of the groove is a through groove that penetrates the first insulating layer, the first portion of the second insulating layer is in contact with the first ground conductor; The printed wiring board according to claim 1.

4. the wiring includes differential signal wiring in which a first signal wiring conductor and a second signal wiring conductor are positioned side by side; the groove is located around and between the first signal wiring conductor and the second signal wiring conductor in a planar perspective view; The printed wiring board according to claim 1.

5. the first surface includes a second region in which the wiring is not located; The first region and the second region are located on either side of the opening. The printed wiring board according to claim 1.

6. 3. The printed wiring board according to claim 2, wherein a sidewall surface of the groove that follows the outline of the wiring is perpendicular to the first ground conductor in a cross-sectional view perpendicular to the direction in which the wiring extends.

7. 2. The printed wiring board according to claim 1, wherein, in a cross-sectional view perpendicular to the direction in which the wiring extends, the width of the wiring contacting the first region is equal to the width of the first surface of the first insulating layer contacting the wiring.