High-frequency multilayer substrate

Abstract

A high-frequency multilayer substrate according to the present disclosure is characterized by comprising a first layer, a second layer, and a third layer, a first wire connecting the first layer and the second layer, a first wiring pad formed in the first layer and connected to the first wire, and a second wire connecting the second layer and the third layer, wherein at least the first layer includes a ground surface, the center of the second wire is deviated in a first direction with respect to the center of the first wire in the second layer, and the center of the first wiring pad is disposed with a predetermined value of deviation toward the second wire with respect to the center of the first wire in the plane of the first layer.

Description

High frequency multilayer board

[0001] This application claims priority to Japanese Patent Application No. 2023-156580, filed on September 22, 2023, the contents of which are incorporated herein by reference.

[0002] Conventionally, printed wiring boards have been disclosed.

[0003] For example, Patent Document 1 discloses a circuit board having a laminated structure in which a ground layer and a conductor layer are stacked with an electrically insulating layer interposed therebetween, and the ground layer has a removed area obtained by removing at least the projection area of ​​the conductor layer when orthogonally projected. The technology disclosed in Patent Document 1 can achieve a configuration in which the conductor layer is less likely to be electrically affected by the ground layer, even when the electrically insulating layer is thin and the distance between the ground layer and the conductor layer is short. Therefore, the impedance of the conductor layer can be reduced, and a circuit board in which the impedance of the conductor layer can be easily matched can be realized with a simple configuration.

[0004] JP 2012-238848 A

[0005] However, the circuit board in Patent Document 1 aims to eliminate the influence of the ground layer, and does not enable impedance adjustment by coupling the ground surface of an adjacent layer to the destination of electromagnetic field coupling.

[0006] In view of the above problems, the present disclosure aims to provide a high-frequency multilayer substrate that allows impedance adjustment by using the ground plane of an adjacent layer as a destination for electromagnetic field coupling, thereby improving transmission characteristics.

[0007] The high-frequency multilayer substrate according to the present disclosure comprises a first layer, a second layer, and a third layer, a first wiring connecting the first layer and the second layer, a first wiring pad formed on the first layer and connected to the first wiring, and a second wiring connecting the second layer and the third layer, wherein at least the first layer includes a ground plane, and in the second layer, the center of the second wiring is shifted in a first direction from the center of the first wiring, and the center of the first wiring pad is positioned shifted by a predetermined value toward the second wiring from the center of the first wiring within the first layer plane.

[0008] As described above, according to the present disclosure, it is possible to provide a high-frequency multilayer substrate with improved transmission characteristics, in which impedance can be adjusted by using the ground plane of an adjacent layer as a destination of electromagnetic field coupling.

[0009] FIG. 1 is a cross-sectional view of a high-frequency multilayer substrate according to the present disclosure. FIG. 2 is an enlarged view of A shown in FIG. 1. FIG. 3 is an image of a conductor (wiring) near A in FIG. 1 viewed obliquely. FIG. 4 is a diagram showing the electromagnetic field distribution in a conventional structure. FIG. 5 is a diagram showing the reflection loss S11 when the center of the first wiring pad is shifted by a predetermined value toward the second wiring from the center of the first wiring for configurations in which the diameter of the first wiring pad is 100 μm, 150 μm, and 200 μm. FIG. 6 is a diagram showing the transmission loss S21 when the center of the first wiring pad is shifted by a predetermined value toward the second wiring from the center of the first wiring for configurations in which the diameter of the first wiring pad is 100 μm, 150 μm, and 200 μm. FIG. 7 is a diagram showing the reflection loss S11 versus the first anti-pad diameter for configurations in which the first wiring pad is shifted by 0 μm, −50 μm, and −100 μm. FIG. 8 is a diagram showing the transmission loss S21 versus the first anti-pad diameter for configurations in which the first wiring pad is shifted 0 μm, −50 μm, and −100 μm. FIG. 9 is a cross-sectional view of a high-frequency multilayer substrate according to the present disclosure. FIG. 10 is an image diagram of the conductor (wiring) near B in FIG. 9 viewed from an oblique direction. FIG. 11 is a diagram showing the reflection loss S11 versus the second anti-pad diameter for configurations in which the first wiring pad is shifted 0 μm, −50 μm, and −100 μm. FIG. 12 is a diagram showing the transmission loss S21 versus the second anti-pad diameter for configurations in which the first wiring pad is shifted 0 μm, −50 μm, and −100 μm. FIG. 13 is an image diagram of the conductor shown in FIG. 3 viewed from the −Z direction.

[0010] Preferred embodiments of the present disclosure will be described in detail below with reference to the drawings. Note that the present embodiments described below do not unduly limit the content of the present disclosure as defined in the claims, and not all of the configurations described in the present embodiments are necessarily essential to the solution of the present disclosure. In addition, the X-axis direction in the drawings is defined as the first direction, the Y-axis direction as the second direction, and the Z-axis direction as the third direction. That is, the stacking direction from L1 to L4 (described later) is defined as the Z-axis direction, and the direction from the center of the second wiring 10 to the center of the first wiring 11 as viewed from the +Z axis (above) is defined as the +X-axis direction, and the Y-axis is determined according to a right-handed coordinate system.

[0011] FIG. 1 is a cross-sectional view of a high-frequency multilayer substrate 100 according to the present disclosure. The high-frequency multilayer substrate 100 according to the present disclosure includes several wiring layers. The high-frequency multilayer substrate 100 shown in FIG. 1 includes a first layer (hereinafter simply referred to as L1), a second layer (hereinafter simply referred to as L2) above L1, a third layer (hereinafter simply referred to as L3) above L2, and a fourth layer (hereinafter simply referred to as L4) above L3. Note that the layers above L1 are the layers L2, L3, and L4 onward, which are in the Z-axis direction (+Z direction) of the third direction. The high-frequency multilayer substrate 100 according to the present disclosure also includes at least one signal circuit, such as a signal circuit that is electrically connected from L1 through L2 and L3 to L4 on the opposite side of L1.

[0012] L1, L2, L3, L4, etc. are wiring layers in which conductor circuits are formed on the insulating layer core P1 or insulating layer P2. The high-frequency multilayer substrate 100 according to the present disclosure is formed by laminating these layers. The insulating layers P1 and P2 are made of, for example, a core substrate or prepreg. The conductors are made of, for example, copper, silver, palladium, gold, etc.

[0013] Although the high frequency multilayer substrate 100 in FIG. 1 is illustrated as a four-layer substrate, it may be a multilayer substrate having six or more layers.

[0014] 1 , the high-frequency multilayer substrate 100 according to the present disclosure includes a first wiring 11, first wiring pads 21 and 22, a second wiring 10, a second wiring pad 20, a ground plane 30, and a first anti-pad 41. Regarding the reference symbols for the first wiring pads, the pad for L1 is indicated as 21, and the pad for L2 is indicated as 22.

[0015] The first wiring 11 is, for example, a so-called via in which a conductor is formed in a hole formed by a laser. The first wiring 11 may be in a form in which the conductor is formed only on the side surface of the hole, or in which the hole is filled with the conductor. The shape of the via is, for example, a cylinder or a truncated cone.

[0016] The first wiring pad 21 is a pad formed on L1 and connected to the first wiring 11. The shape of the first wiring pad 21 is, for example, circular.

[0017] The second wiring 10 is, for example, a so-called through-hole in which a conductor is formed in a hole formed by a drill. The second wiring 10 may have a conductor formed only on the side surface of the hole, or may have a hole filled with a conductor. The shape of the through-hole is, for example, a cylinder or a truncated cone.

[0018] The second wiring pad 20 is a pad formed on L2 and connected to the second wiring 10. The shape of the second wiring pad 20 is, for example, circular.

[0019] The high frequency multilayer substrate 100 according to the present disclosure has at least a ground plane 31 (30) in L1, but may also have a ground plane 32 (30) in one or more of the other L2, L3, and L4.

[0020] The first antipad 41 is formed outside the first wiring pad 21 to insulate it from the ground plane 31, and is a region centered on the center 11a of the first wiring 11. The first antipad 41 is a hollowed-out portion of the ground plane 31 around the first wiring 11, and is a portion where no conductor exists. The second antipad, which will be described later, has a similar configuration.

[0021] Fig. 2 is an enlarged view of A shown in Fig. 1. Fig. 3 is an image diagram of the conductor (wiring) near A in Fig. 1 viewed from an oblique direction. For convenience, Fig. 3 omits the insulating layer core P1 or insulating layer P2 and the ground plane 31 (30), and shows only the first wiring 11, the first wiring pad 21, and the second wiring pad 20. In Fig. 3, the first anti-pad 41 is indicated by a dashed circle.

[0022] As shown in FIGS. 2 and 3 , the high-frequency multilayer substrate 100 according to the present disclosure is characterized in that the center 10a of the second wiring 10 is offset in the X-axis direction (first direction) from the center 11a of the first wiring 11. The center 21a of the first wiring pad 21 is offset by a predetermined value M toward the second wiring 10 in the X-axis direction (first direction) from the center 11a of the first wiring 11 in the L1 plane. The first wiring 11 and the second wiring 10 are not coaxial. That is, the center 11a of the first wiring 11 and the center 10a of the second wiring 10 do not overlap when viewed from the ±Z direction and are not on the same point when projected onto the XY plane. The center 11a of the first wiring 11 refers to the central axis of the first wiring 11, and the center 10a of the second wiring 10 refers to the central axis of the second wiring 10. The predetermined value is a value determined in a certain manner.

[0023] The center 11 a of the first wiring 11 is coaxial with the center 41 a of the first anti-pad 41 .

[0024] However, during manufacturing, if the area of ​​the wiring material (remaining copper ratio) of each wiring layer differs significantly between the wiring layers, warping can occur. Furthermore, providing a ground plane 31 around the wiring improves resistance to external noise. Therefore, it is preferable to fill the empty spaces other than the wiring of each wiring layer with wiring material.

[0025] The first anti-pad 41, which is a hollowed-out portion of the ground plane 31 around the first wiring 11, is set to a diameter that matches impedance with the diameter of the first wiring and the diameter 21R of the first wiring pad 21, if it is a single piece. The same applies to the portion where the second wiring 10 and the second wiring pad 20 are connected.

[0026] Here, Figure 4 shows the electromagnetic field in a conventional structure. In the conventional structure, the distance between the L1 ground plane 31 (30) (not shown) and the through-hole pad 20 in L2 becomes short, resulting in electromagnetic field coupling. This results in deviation from the impedance set in each wiring layer. Furthermore, unnecessary electromagnetic fields are generated from this portion. Note that locating the via 11 and the through-hole 10 farther apart leads to an increase in the size of the board and a more complicated wiring design, so it is preferable to place them close to each other.

[0027] Therefore, by using the structure of the high-frequency multilayer substrate 100 according to the present disclosure, it is possible to adjust the impedance by using the ground plane 31 of the adjacent layer as the electromagnetic field coupling destination, thereby improving the transmission characteristics and reducing the size of the substrate.

[0028] FIG. 5 shows the reflection loss S11 when the center 21a of the first wiring pad 21 is shifted by a predetermined value M (Via Pad Shift) toward the second wiring 10 relative to the center 11a of the first wiring 11 for configurations in which the diameter 21R of the first wiring pad 21 is 100 μm, 150 μm, or 200 μm. Hereinafter, the first wiring pad 21 is referred to as port 1, and the wiring on the L3 layer is referred to as port 2. Reflection loss is evaluated using S11, an element of the S-parameter, and transmission loss is evaluated using S21. FIG. 6 shows the transmission loss S21 when the center 21a of the first wiring pad 21 is shifted by a predetermined value M toward the second wiring 10 relative to the center 11a of the first wiring 11. Note that a minus (-) sign indicates that the center 21a is closer to the second wiring 10. This is a configuration at a frequency of 28 GHz when the radius of the first wiring 11 is 50 μm, the thickness between L1 and L2 is 65 μm (interlayer thickness), the diameter of the second wiring pad is 175 μm, and the conductor thickness is 15 μm, and the thickness between L2 and L3 is a thickness that is not affected by L3. No ground plane 32 (30) is installed on L2. This configuration can be used, for example, in an antenna feeder line.

[0029] 5 and 6 show that when the diameter 21R of the first wiring pad 21 is 100 μm, the predetermined value M does not fall below −100 μm because the first wiring pad 21 and the first wiring 11 only contact at a single point. When the diameter 21R of the first wiring pad 21 is 200 μm, the optimum predetermined value M is −100 μm to −50 μm, indicating that the optimum configuration varies depending on the balance between impedance matching and electromagnetic field coupling with the second wiring pad 20. In any case, by shifting the first wiring pad 21 toward the second wiring 10, both the reflection loss S11 and the transmission loss S21 can be reduced. Furthermore, compared to when the diameter of the first wiring is 100 μm and the predetermined value M is 0 μm, the values ​​when the diameter of the first wiring is 200 μm and the predetermined value M is −50 μm are not significantly worse. This is effective when warping and external noise must be reduced.

[0030] Therefore, in the configuration shown in FIG. 1, by taking into consideration not only L1 or only L2 but also the entire L1 and L2, the center 21a of the first wiring pad 21 is positioned at a predetermined value M toward the second wiring 10 relative to the center 11a of the first wiring 11 within the first layer plane, making it possible to adjust the impedance by using the ground plane 31 of the adjacent layer as the electromagnetic field coupling destination, and improving the transmission characteristics.

[0031] Furthermore, it is preferable that the predetermined value M is smaller than the radius 21r of the first wiring pad 21. However, the positional relationship between the first wiring 11 and the second wiring pad 20 is such that they contact each other at only one point, excluding cases where they are in contact. In this way, it is possible to adjust the impedance by using the ground plane 31 of the adjacent layer as the electromagnetic field coupling destination, and the transmission characteristics can be further improved.

[0032] FIG. 7 shows the reflection loss S11 versus the diameter 41R of the first anti-pad 41 for a configuration in which the first wiring pad 21 is shifted 0 μm, −50 μm, and −100 μm in the X-axis direction. FIG. 8 shows the transmission loss S21 versus the diameter 41R of the first anti-pad 41 for a configuration in which the first wiring pad 21 is shifted 0 μm, −50 μm, and −100 μm in the X-axis direction. The figure shows a configuration at a frequency of 28 GHz in which the diameter 21R of the first wiring pad 21 is 100 μm, the radius of the first wiring 11 is 50 μm, the thickness between L1 and L2 is 65 μm (interlayer thickness), the diameter of the second wiring pad is 175 μm, and the conductor thickness is 15 μm. The thickness between L2 and L3 is a thickness that is not affected by L3. No ground plane 32 (30) is installed on L2.

[0033] Generally, in a coaxial wiring structure consisting of a core wire that is a signal line and a ground wire that surrounds it in a circular shape, the impedance can be calculated using the following equation (1), where er is the dielectric constant between the signal line and the ground wire, d1 is the diameter of the core wire, and d2 is the inner diameter of the ground wire.

[0034]

[0035] Considering only L1, the first wiring pad 21 as the core portion, and the ground plane 31 (30) as the ground line, from equation (1), the radius 41r of the first anti-pad 41 is preferably 465 μm to adjust the impedance to 50 Ω.

[0036] 7 and 8, it can be seen that the larger the radius 41r of the first antipad 41, the more the return loss S11 and the transmission loss S21 improve. This result is because, in order to reduce electromagnetic field coupling between the second wiring pad 20 and the ground plane 31 of L1, increasing the radius 41r of the first antipad 41 makes it possible to bring the impedance of the system shown in FIG. 3 closer to 50Ω. Furthermore, for each radius 41r of the first antipad 41, shifting the first wiring pad 21 toward the second wiring 10 in the X-axis direction improves the characteristics.

[0037] Therefore, by taking into consideration not only L1 or L2 but the entire L1 and L2, the center 21a of the first wiring pad 21 is positioned by a predetermined value M toward the second wiring 10 relative to the center 11a of the first wiring 11 in the first layer plane, and by widening the first anti-pad 41, the reflection loss S11 and transmission loss S21 can be reduced.

[0038] The theoretical value of diameter 41R of first antipad 41 in a configuration with only L1 can be found by equation (1) as described above. When the influence of L2 is also taken into consideration, it is preferable to modify equation (1) above to satisfy the following equation (2) when the diameter of first antipad 41 is d12, the diameter of first wiring pad 21 is d11, the dielectric constant of the dielectric around first wiring pad 21 is e1, the impedance of the signal wave input to first wiring pad 21 is Z1, or the output impedance to first wiring pad 21 is Z1 (usually 50Ω).

[0039]

[0040] This makes it possible to suppress electromagnetic field coupling, making it possible to adjust impedance taking into account electromagnetic field coupling between adjacent layers, and further improving transmission characteristics.

[0041] 9 is a cross-sectional view of a high-frequency multilayer substrate 100 according to the present disclosure. The structure shown in FIG. 9 differs from that shown in FIG. 1 in that L2 also has a ground plane 32 (30) and a second anti-pad 40. The second anti-pad 40 is formed outside the second wiring pad 20 to insulate it from the ground plane 32 (30) of L2, and is a region centered on the center 10a of the second wiring 10.

[0042] FIG. 10 is an image diagram of the conductor (wiring) near B in FIG. 9 viewed from an oblique direction. In FIG. 10, the second antipad 40 is indicated by a dashed line. FIG. 11 is a diagram showing the reflection loss S11 versus the radius 40r of the second antipad 40 for a configuration in which the first wiring pad 21 is shifted by a predetermined value M (0 μm, −50 μm, −100 μm) in the X-axis direction. FIG. 12 is a diagram showing the transmission loss S21 versus the radius 40r of the second antipad 40 for a configuration in which the first wiring pad 21 is shifted by a predetermined value M (0 μm, −50 μm, −100 μm) in the X-axis direction. This diagram shows a configuration at a frequency of 28 GHz where the radius of the first wiring 11 is 50 μm, the thickness between L1 and L2 is 65 μm, the diameter of the second wiring pad is 175 μm, and the conductor thickness is 15 μm. From equation (1), in order to adjust the impedance to 50Ω, it is preferable that the radius 41r of the first antipad 41 is 465 μm. Furthermore, considering only L2, from equation (1), in order to adjust the impedance to 50Ω, it is preferable that the center 40a of the second antipad 40 is located at the center 10a of the second wiring 10 and that the radius is 815 μm.

[0043] The center 10 a of the second wiring 10 is coaxial with the center 40 a of the second anti-pad 40 .

[0044] 11 and 12, it can be seen that the smaller the radius 40r (Anti Pad TH_radius) of the second antipad 40, the more the return loss S21 and the transmission loss S21 improve. Furthermore, for each radius 40r of the second antipad 40, the characteristics improve when the first wiring pad 21 is shifted toward the second wiring 10.

[0045] This is because the first wiring 11 is electromagnetically coupled not only to the ground plane 31 of L1 but also to the ground plane 32 of L2. When the second anti-pad 40 is circular as shown in Fig. 11, the electromagnetic coupling between the second wiring 10 and the first wiring 11 and the ground planes 32 of L1 and L2 can be balanced by making the second anti-pad 40 smaller.

[0046] Furthermore, if the second anti-pad 40 can be made smaller, the ground via can be placed closer to the via or through-hole, increasing the degree of freedom in arranging the ground via. This makes it easier to reduce the transmission loss S21 between L1 and L2 and also increases the degree of freedom in design.

[0047] Therefore, when the diameter of the second antipad 40 is d22, the diameter of the second wiring pad 20 is d21, the dielectric constant of the dielectric around the second wiring pad 20 is e2, the impedance of the signal wave input to the second wiring pad 20 is Z2, or the output impedance to the second wiring pad 20 is Z2 (usually 50Ω), it is preferable to modify the above formula (1) to satisfy the following formula (3):

[0048]

[0049] This makes it possible to adjust the impedance taking into consideration electromagnetic coupling with the ground plane 30 of the adjacent layer, thereby further improving the transmission characteristics. Alternatively, the shape of the second anti-pad 40 can be adjusted by forming it into a shape in which two circles are partially overlapped, an ellipse, an oval, or the like, instead of a circle.

[0050] Fig. 13 is a conceptual diagram of the conductor shown in Fig. 3 as viewed from above. As shown in Fig. 13, the first wiring pad 21 is made up of a first region A1 which is a region closer to the second wiring 10 than the first wiring 11, and a second region A2 which is a region on the opposite side of the first wiring 11 from the second wiring 10.

[0051] The first region A1 is a region on the left side of the area of ​​the first wiring pad 21 shown in Fig. 13, which is divided by a line parallel to the Y-axis direction and passing through the center 11a of the first wiring 11. The second region A2 is a region on the right side of the area of ​​the first wiring pad 21 shown in Fig. 13, which is divided by a line parallel to the Y-axis direction and passing through the center 11a of the first wiring 11, which is opposite to the second wiring 10.

[0052] The area of ​​the first region A1 is preferably larger than the area of ​​the second region A2, which increases the overlapping area between the first wiring pad 21 and the second wiring pad 20, thereby further suppressing electromagnetic field coupling.

[0053] Moreover, the transmission loss S21 can be improved by increasing the diameter 21R of the first wiring pad 21. Furthermore, by increasing the diameter 21R of the first wiring pad 21, the area occupied by the first wiring pad region in the first anti-pad 41 region increases, thereby reducing warpage.

[0054] As described above, the high-frequency multilayer substrate 100 according to the present disclosure makes it possible to adjust impedance by using the ground plane 30 of an adjacent layer as a destination of electromagnetic field coupling, thereby improving transmission characteristics.

[0055] Although each embodiment and each example of the present disclosure have been described in detail above, it will be readily apparent to those skilled in the art that many modifications are possible without substantially departing from the novel features and effects of the present disclosure. Therefore, all such modifications are intended to be included within the scope of the present disclosure.

[0056] For example, a term that is described at least once in the specification or drawings together with a different term having a broader or equivalent meaning can be replaced with that different term anywhere in the specification or drawings. Furthermore, the configuration and operation of the high frequency multilayer substrate are not limited to those described in the embodiments and examples of the present disclosure, and various modifications are possible.

Claims

1. A high frequency multilayer board comprising: a first layer, a second layer and a third layer; a first wiring connecting the first layer and the second layer; a first wiring pad formed on the first layer and connecting to the first wiring; and a second wiring connecting the second layer and the third layer, wherein at least the first layer includes a ground plane, and in the second layer, the center of the second wiring is offset in a first direction from the center of the first wiring, and the center of the first wiring pad is positioned offset by a predetermined value toward the second wiring side from the center of the first wiring within the first layer plane.

2. A high frequency multilayer board as described in claim 1, characterized in that the first layer is provided with a first anti-pad formed outside the first wiring pad and centered on the center of the first wiring to insulate it from the ground plane.

3. The high frequency multilayer board according to claim 1, wherein the predetermined value is smaller than the radius of the first wiring pad.

4. The high frequency multilayer board according to claim 2, characterized in that the following formula is satisfied when the diameter of the first antipad is d12, the diameter of the first wiring pad is d11, the dielectric constant of the dielectric around the first wiring pad is e1, the impedance of a signal wave input to the first wiring pad is Z1, or the output impedance to the first wiring pad is Z1.

5. The high frequency multilayer board according to claim 2, further comprising: a second wiring pad formed on the second layer and connected to the second wiring; wherein the second layer includes a ground plane, and a second anti-pad is provided which is formed outside the second wiring pad and centered on the center of the second wiring to insulate it from the ground plane of the second layer, and wherein the following formula is satisfied when the diameter of the second anti-pad is d22, the diameter of the second wiring pad is d21, the dielectric constant of the dielectric around the second wiring pad is e2, the impedance of the signal wave input to the second wiring pad is Z2, or the output impedance to the second wiring pad is Z2.

6. A high frequency multilayer board comprising: a first layer, a second layer and a third layer; a first wiring connecting the first layer and the second layer; a first wiring pad formed on the first layer and connecting to the first wiring; and a second wiring connecting the second layer and the third layer, wherein at least the first layer includes a ground plane, and in the second layer, the center of the second wiring is offset in a first direction from the center of the first wiring, and the first wiring pad comprises: a first region which is a region on the second wiring side of the first wiring, and a second region which is a region on the opposite side of the first wiring to the second wiring, and wherein the area of ​​the first region is larger than the area of ​​the second region.

7. A high frequency multilayer board comprising: a first layer, a second layer, and a third layer including a ground plane; a first wiring connecting the first layer and the second layer; a first wiring pad formed on the first layer and connecting to the first wiring; and a second wiring connecting the second layer and the third layer, wherein the first layer is provided with a first anti-pad formed outside the first wiring pad and centered on the center of the first wiring in order to insulate it from the ground plane, wherein the following formula is satisfied when the diameter of the first anti-pad is d12, the diameter of the first wiring pad is d11, the dielectric constant of the dielectric around the first wiring pad is e1, the impedance of a signal wave input to the first wiring pad is Z1, or the output impedance to the first wiring pad is Z1:

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