JP2015076836A - Waveguide substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a waveguide substrate capable of achieving electrical connection and signal transmission between a post wall waveguide and an external device without causing deterioration in transmission loss of the post wall waveguide.SOLUTION: In a waveguide substrate 10, a transmission line 20 is laminated on a post wall waveguide 14 comprising: a pair of ground conductor layers 12, 13 formed on facing both surfaces of a dielectric substrate 11; and a pair of post walls 18, 18 comprising posts 15 configured to penetrate through the dielectric substrate 11 so as to connect the pair of ground conductor layers 12, 13. In the waveguide substrate 10, (1) Rz3>Rz0 is satisfied, where Rz0 represents a ten point average roughness Rz on a surface of the ground conductor layers between the ground conductor layers 12, 13 and the dielectric substrate 11, and Rz3 represents a ten point average roughness Rz on a surface of the transmission line between a dielectric layer 22 in contact with the transmission line 20 and the transmission line 20, or (2) the dielectric substrate 11 is made of a liquid crystal polymer or a fluororesin, and the dielectric layer 22 in contact with the transmission line 20 is made of a polyimide-based resin.

Description

  The present invention relates to a waveguide substrate including a transmission line and a post wall waveguide.

  In recent years, high-speed and large-capacity communication of several Gbps using the millimeter wave band has been proposed, and a part thereof is being realized. In particular, wireless communication devices operating in the 60 GHz band are becoming more important. In Japan, a wide frequency band of 59 to 66 GHz can be used with specific low power, so that it is expected to spread to the consumer field, and the realization of an inexpensive and small millimeter-wave communication module is an urgent need. Yes.

  As a form for realizing an inexpensive and small millimeter-wave communication module, a millimeter-wave module using a post-wall waveguide (hereinafter abbreviated as “PWW”) is disclosed as a waveguide by a printed circuit board ( For example, see Patent Document 1 and Non-Patent Document 1). PWW can be interpreted as replacing the side wall (metal wall) of a conventional waveguide with a through hole group (post group) of a printed circuit board. A wireless communication IC (CMOS-IC) mounted on a PWW is connected to a transmission line (such as a microstrip line, a coplanar line, or a strip line) using a planar circuit by a method such as wire bonding or bump connection. The millimeter wave signal output from the wireless communication IC is once transmitted through the transmission line, and is finally guided to the waveguide structure (PWW) through the planar circuit / waveguide conversion structure (converter).

JP 2011-109438 A

R. Suga, et al. “Cost-Effective 60-GHz Antenna-Package with End-Fire Radiation from Open-Ended Post-Wall Waveguide for Wire-Trans-E-T11”. 348-351

  In this PWW, transmission loss due to the constituent material occurs. The loss is roughly divided into a conductor loss and a dielectric loss. The conductor loss is caused by the waveguiding mode of the electromagnetic wave inside the PWW, and a large proportion is occupied by Joule loss generated in the upper and lower waveguide wide walls. In addition, the skin effect becomes significant in a high frequency band such as a millimeter wave band. For example, when the metal material of the conductor is copper (Cu), the skin depth at 60 GHz is 270 nm, and current flows only on the very surface layer of the conductor. For this reason, when the conductor surface is rough, the conductor loss increases as compared with a flat case. Therefore, in the waveguide, it is preferable that the upper and lower waveguide wide walls and the close contact portion of the dielectric material inside are flat.

  However, if the adhesion portion between the waveguide wide wall and the dielectric material is flat, the high-frequency characteristics are good, but the adhesion strength between the waveguide wide wall and the dielectric material is lost. The decrease in adhesion strength has a serious adverse effect on the result, such as causing damage to the connection part due to the construction method when the waveguide is connected to a component or device outside the waveguide by a connecting means such as a bonding wire or a bump. In the worst case, it causes the obstacle of loss of conduction function. The tendency that the adhesion strength is likely to be impaired if the adhesion portion between the waveguide wide wall and the dielectric material is flat is attributed to the molecular structure of the dielectric material. For example, a liquid crystal polymer or a polymer such as Teflon (registered trademark) is used. Tetrafluoroethylene (PTFE, fluororesin) has a low dielectric loss tangent, and is a material with good high-frequency characteristics.

  The present invention has been made in view of the above circumstances, and a waveguide substrate that enables electrical connection and signal transmission between the post wall waveguide and an external device without deteriorating the transmission loss of the post wall waveguide. The issue is to provide.

In order to solve the above-mentioned problems, the present invention provides a waveguide substrate including a transmission line and a post wall waveguide, and the post wall waveguide is a pair of ground conductors formed on both opposing surfaces of a dielectric substrate. And a pair of post walls including posts penetrating the dielectric substrate so as to connect the pair of ground conductor layers, and the transmission line is connected to any one of the pair of ground conductor layers. The surface of the pair of ground conductor layers between the pair of ground conductor layers and the dielectric substrate is stacked on the post wall waveguide via one or more dielectric layers therebetween. The point average roughness Rz is Rz0, and the ten-point average roughness Rz of the surface of the transmission line between the one or two or more dielectric layers in contact with the transmission line and the transmission line is Rz3. When Rz3> Rz0, Providing a waveguide substrate, wherein.
In this case, the Rz0 is preferably 0.8 μm or less.

In order to solve the above-mentioned problems, the present invention provides a waveguide substrate including a transmission line and a post wall waveguide, and the post wall waveguide is a pair of ground conductors formed on both opposing surfaces of a dielectric substrate. And a pair of post walls including posts penetrating the dielectric substrate so as to connect the pair of ground conductor layers, and the transmission line is connected to any one of the pair of ground conductor layers. 1 or 2 or more dielectric layers in between, and is laminated on the post wall waveguide, and the dielectric substrate is made of a liquid crystal polymer or a fluorine-based resin, of the 1 or 2 or more dielectric layers A waveguide substrate is provided in which a dielectric layer in contact with the transmission line is made of a polyimide resin.
In this case, the ten-point average roughness Rz of the surface of the pair of ground conductor layers between the pair of ground conductor layers and the dielectric substrate, and between the dielectric layer in contact with the transmission line and the transmission line. The ten-point average roughness Rz of the surface of the transmission line is preferably 0.8 μm or less.

The waveguide substrate may include a high frequency signal injection structure for injecting a high frequency signal from the transmission line to the post wall waveguide.
The high-frequency signal injection structure may have a pin structure formed from the transmission line toward the inside of the dielectric substrate.
The high-frequency signal injection structure may be a through-conductor type waveguide excitation structure that penetrates the dielectric substrate.
A part of the high-frequency signal injection structure may be formed of an aggregate of conductive particles, a conductive band assembly, or a sintered body of conductive particles having fine pores.

The waveguide substrate may include connection means for connecting the transmission line and an external device, and the connection means may be made of a gold wire or a gold ribbon.
The waveguide substrate may include a connection means for connecting the transmission line and an external device, and the connection means may be a stud bump.
Preferably, the stud bump is an Au stud bump, and an AuSn material is provided between the Au stud bump and the transmission line.

  According to the present invention, the surface roughness between the transmission line and the dielectric layer in contact with the transmission line is larger than that between the ground conductor layer of the post-wall waveguide and the dielectric substrate, or the dielectric substrate is liquid crystal. Since the dielectric layer in contact with the transmission line is made of polyimide resin and made of polymer or fluorine resin, it is possible to suppress a decrease in the adhesion strength of the transmission line without deteriorating the transmission loss of the post wall waveguide. As a result, electrical connection and signal transmission between the post wall waveguide and the external device become possible.

It is a perspective view which shows an example of a waveguide board | substrate. (A), (b) is sectional drawing which shows an example of a waveguide board | substrate. (A)-(d) is sectional drawing which shows an example of the manufacturing process of a post wall waveguide. (A)-(e) is sectional drawing which shows an example of the manufacturing process of a transmission line. It is sectional drawing which shows an example of the manufacturing process of a planar circuit / waveguide conversion structure. It is sectional drawing which shows another example of a planar circuit / waveguide conversion structure. FIG. 7 is a perspective view of the planar circuit / waveguide conversion structure of FIG. 6. It is sectional drawing which shows an example of a connection means with a semiconductor element. It is sectional drawing which shows another example of a connection means with a semiconductor element. It is a graph which shows an example of the relationship between the surface roughness of a conductor layer, and the attenuation constant (alpha) of a transmission line. It is a graph which shows an example of the relationship between the surface roughness of a conductor layer, and the transmission loss of a post wall waveguide.

Hereinafter, based on a preferred embodiment, the present invention will be described with reference to the drawings.
1 and 2 show an example of a waveguide substrate. The waveguide substrate 10 has a structure in which a transmission line 20 is provided on a post wall waveguide 14. The post wall waveguide 14 has a plurality of ground conductor layers 12 and 13 formed on opposite surfaces of the dielectric substrate 11, and a large number of through the dielectric substrate 11 so as to connect the pair of ground conductor layers 12 and 13. It has a structure in which a pair of post walls 18, 18 are formed from the posts 15, 15,. The pair of ground conductor layers 12 and 13 and the pair of post walls 18 and 18 function as a wide wall and a narrow wall of the waveguide, respectively.

  The transmission line 20 is laminated on the post wall waveguide 14 with an insulating layer 22 interposed between the transmission line 20 and one ground conductor layer 13. In the case of FIG. 2A, the insulating layer 22 has an adhesive layer 23 on the opposite surface of the transmission line 20. The adhesion strength between the insulating layer 22 and the ground conductor layer 13 is ensured through the adhesive layer 23. The post 15 of the post wall 18 and the transmission line 20 do not exist on the same plane as shown in FIG. 1, but in FIG. 2A, they are shown in the same cross-sectional view for convenience.

  Such a waveguide substrate 10 includes at least three conductor layers (L1, L2, L3). The first conductor layer (L1) and the second conductor layer (L2) are the ground conductor layers 12 and 13 corresponding to the wide wall of the waveguide, and the third conductor layer (L3) includes the transmission line 20. This is a conductor layer 21. The waveguide substrate 10 includes at least three dielectric layers (D1, D2, D3) as shown in FIG. The first dielectric layer (D1) is the dielectric substrate 11 that constitutes the post wall waveguide 14. The second dielectric layer (D2) is an adhesive layer 23 having a function of bonding the transmission line 20 and the post wall waveguide 14 together. The third dielectric layer (D3) is an insulating layer 22 in contact with the transmission line 20.

  The transmission line 20 composed of a planar circuit is a TEM line that propagates a signal in a TEM mode (a mode in which the vibration directions of an electric field and a magnetic field are perpendicular to each other and both vibration directions are perpendicular to the propagation direction). On the other hand, the post wall waveguide 14 propagates a signal in a TE mode (a mode in which only the electric field vibrates in the cross-sectional direction and the magnetic field has a component in the transmission direction). The transmission line 20 can be composed of, for example, a microstrip line, a coplanar line, a strip line, or the like.

(First aspect of the present invention)
Regarding the surface roughness, in the TE mode in the post wall waveguide 14, the influence of the surface roughness of the upper and lower ground conductor layers 12 and 13 on the high frequency characteristics (increase in conductor loss) is large. For this reason, it is preferable to reduce the surface roughness of the conductor layer between the ground conductor layers 12 and 13 and the dielectric substrate 11 as much as possible. In addition, the surface roughness of the conductor layer between the dielectric layer (insulating layer) 22 in contact with the transmission line 20 and the transmission line 20 has an influence on high-frequency characteristics (increased conductor loss in the transmission line), but is closely attached. In order to ensure the properties, it is preferable to increase the surface roughness.

For reference, FIG. 10 shows that the surface roughness Rz of the conductor layer (copper foil) constituting the transmission line (microstrip line) is 0.8 μm (chain line), 1.3 μm (dashed line), or 2.0 μm (solid line). An example of the attenuation constant α (dB / mm) of the transmission line in each case is shown. As shown in this graph, when Rz is 0.8 μm or more, it can be seen that α increases as Rz increases and there is a clear difference in transmission loss of the transmission line.
FIG. 11 shows the transmission loss of the post wall waveguide in each case where the surface roughness Rz of the ground conductor layer (copper foil) of the post wall waveguide is 0.5 μm (broken line) or 0.8 μm (solid line). An example of (dB) is shown. As shown in this graph, it can be seen that there is no clear difference in the transmission loss of the post wall waveguide between Rz of 0.5 μm and 0.8 μm.

  Therefore, in the first aspect of the present invention, the surface roughness R3 of the transmission line 20 between the insulating layer 22 in contact with the transmission line 20 and the transmission line 20 is set to the ground conductor layers 12 and 13 and the dielectric substrate 11. Is larger than the surface roughness R0 of the ground conductor layers 12 and 13 (R3> R0). For example, if the surface roughness is expressed by an index of the ten-point average roughness Rz, the ten-point average roughness Rz of the surface of the ground conductor layers 12 and 13 between the ground conductor layers 12 and 13 and the dielectric substrate 11 is assumed. Is Rz0, and the ten-point average roughness Rz of the surface of the transmission line 20 between the dielectric layer (insulating layer) 22 in contact with the transmission line 20 and the transmission line 20 is Rz3, Rz3> Rz0. Rz0 is preferably 0.8 μm or less. Rz3 is preferably larger than 0.8 μm (Rz3> 0.8 μm). The range (numerical value) of Rz0 is not limited to 0.8 μm, for example, and may be 0.5 μm. Examples of the range (numerical value) of Rz3 include 1.3 μm and 2.0 μm.

  The ten-point average roughness Rz of the surface of the ground conductor layer 12 between the ground conductor layer 12 and the dielectric substrate 11 is Rz1, and the surface of the ground conductor layer 13 between the ground conductor layer 13 and the dielectric substrate 11 is ten. When the point average roughness Rz is Rz2, if both are smaller than Rz3, Rz1> Rz2, Rz1 = Rz2, or Rz1 <Rz2 may be satisfied. That is, Rz3> Rz1 = Rz2, Rz3> Rz1> Rz2, or Rz3> Rz2> Rz1 may be sufficient.

  “The surface roughness of the ground conductor layer between the ground conductor layer and the dielectric substrate (10-point average roughness)” means the ground conductor layer on the side where the ground conductor layer is laminated on the dielectric substrate. It is the surface roughness (ten point average roughness) of the conductor layer (copper foil etc.) which comprises. In addition, “surface roughness of the transmission line between the dielectric layer in contact with the transmission line and the transmission line (10-point average roughness)” means the transmission line on the side where the transmission line is laminated on the dielectric layer. It is the surface roughness (ten point average roughness) of the conductor layer (copper foil etc.) which comprises. It can be seen that the surface roughness of the conductor layer does not change in the normal lamination direction even after the conductor layer is laminated on the dielectric substrate or the dielectric layer. When confirming the surface roughness (ten-point average roughness) of the conductor layer after lamination, for example, by cutting the waveguide substrate, photographing the section, and observing the surface shape of the conductor layer in the section, the surface Roughness can be measured.

  In the first aspect, in order to reduce the transmission loss of the waveguide, L1 and L2 for which a flat surface is required are not provided with a function of connecting to the outside of the waveguide, but L3 provided on the upper portion thereof is provided outside the waveguide. Have a connection function. That is, a relatively large surface roughness is not imparted to the conductor surface between L1 and D1 and between D1 and L2 which affects the loss of the waveguide, and instead, a relatively large surface roughness is imparted to the conductor surface between L3 and D3. By providing the above, it is possible to achieve both an external connection and a signal transmission function without deteriorating the loss of the waveguide. However, since a large surface roughness is imparted to the conductor surface between L3 and D3, in order to avoid loss deterioration of the TEM line due to this, the length of the transmission line 20 (in FIG. 2A). It is preferable to shorten L).

  In the case of the first aspect, the material of the dielectric substrate 11 and the insulating layer 22 may be the same. It is preferable to use a liquid crystal polymer (LCP) or a fluororesin such as polytetrafluoroethylene (PTFE) as a material having good high-frequency characteristics (small dielectric loss tangent).

(Second aspect of the present invention)
Regarding the dielectric material, in the TE mode in the post wall waveguide 14, the high frequency characteristics (dielectric loss tangent, etc.) of the dielectric substrate 11 greatly affect the high frequency characteristics (increase in dielectric loss). For this reason, as a dielectric material constituting the dielectric substrate 11, a high-frequency characteristic (low dielectric loss tangent), a liquid crystal polymer (LCP), or a fluorine resin such as polytetrafluoroethylene (PTFE)) is used. preferable. Moreover, it is preferable to use a polyimide resin having excellent adhesion to a conductor material such as a metal constituting the transmission line 20 as a dielectric material constituting the dielectric layer (insulating layer) 22 in contact with the transmission line 20.

  In this case, the surface roughness of the conductor layer between the conductor layer and the dielectric layer is preferably as small as possible from the viewpoint of the conductor loss described above. For example, if the surface roughness is expressed by an index of the ten-point average roughness Rz, the ten-point average roughness Rz of the surface of the ground conductor layers 12 and 13 between the ground conductor layers 12 and 13 and the dielectric substrate 11 is assumed. Is Rz0, Rz0 is preferably 0.8 μm or less. Further, when the ten-point average roughness Rz of the surface of the transmission line 20 between the dielectric layer (insulating layer) 22 in contact with the transmission line 20 and the transmission line 20 is Rz3, Rz3 is 0.8 μm or less. Is preferred. The range (numerical value) of Rz0 and Rz3 is not limited to 0.8 μm, for example, and may be 0.5 μm. The definition of the surface roughness (ten-point average roughness) in this aspect is the same as that in the first aspect.

  In the second aspect, in order to reduce the transmission loss of the waveguide, L1 and L2, which are required to have a flat surface, are not provided with a function of connecting to the outside of the waveguide. Have a connection function. In addition, by using a polyimide resin with excellent adhesion to the conductor layer as the dielectric material of D3, it is possible to achieve both external connection and signal transmission function without deteriorating the waveguide loss. Can do. However, since a material having a relatively large dielectric loss tangent than the dielectric material of D1 constituting the waveguide is used for D3 that is in contact with L3, in order to avoid loss deterioration of the TEM line due to this, transmission is performed. It is preferable to shorten the length of the line 20 (L in FIG. 2A).

(Configuration example of waveguide substrate)
The transmission line 20 and the post wall waveguide 14 are connected by a planar circuit / waveguide conversion structure (converter) for providing a high-frequency signal injection structure. The converter shown in FIGS. 1 and 2 is a converter 50 having a pin structure inserted from the transmission line 20 toward the inside of the dielectric substrate 11. 1 to 5, the converter 50 is configured by a combination of a lower conductor 16 formed on the dielectric substrate 11 and an upper conductor 24 formed on the insulating layer 22. A gap 17a is provided between the ground conductor layer 13 and the lower conductor 16 (the land 17 around the lower conductor 16 in FIG. 2A), and a dielectric (between the lower conductor 16 and the ground conductor layer 12). Insulation is performed at part of the adhesive layer 23 in FIG.

  In FIG. 1, the conductor layer 21 on the insulating layer 22 including the transmission line 20 (hereinafter referred to as “upper conductor layer”) includes a GSG pad 28 having a GSG (ground-signal-ground) structure and a signal pad 25 of the GSG pad 28. Including a signal transmission line 21b for connecting the pad to the pad 21a of the lower conductor 16, an open stub 21c that can be trimmed. The ground pad 26 of the GSG pad 28 is connected to the ground conductor layer 13 by a ground via 27 penetrating the insulating layer 22 and the adhesive layer 23 as shown in FIG. Although not shown, the ground conductor layers 12 and 13 are connected to the outside so as to have a ground (ground) potential. The planar circuit formed by the upper conductor layer 21 may include an impedance matching element or the like. For example, by adjusting the width and length of the signal transmission path 21b, the width and length (overhang) of the open stub 21c, the distance between the open stub 21c and the ground pad 26, the amount of phase rotation, and inductance Impedance matching can be achieved by controlling the size of the component or the capacitive component.

  The pin structure of the high-frequency signal injection structure (converter) for injecting a high-frequency signal from the transmission line 20 to the post wall waveguide 14 includes a lower conductor 16 formed on the dielectric substrate 11 and a dielectric on the ground conductor layer 13. You may comprise from the two bodies of the upper conductor 24 which penetrates a body layer (the insulating layer 22 and the contact bonding layer 23). The pin may be formed of one type of conductor, or may be configured by stacking two or more types of conductors. The interior of the pin may be a cavity, filled with a conductor, or filled with a dielectric. The tip shape of the pin may be rounded or pointed.

  In the case of a converter having a pin structure, the length of the pin can be freely adjusted, and reflection loss can be suppressed without adjustment by other circuit elements or the like. The lower conductor 16 can be formed of a conductor such as copper (Cu), silver (Ag), or gold (Au). In order to improve the adhesion between the lower conductor 16 and the dielectric substrate, it is preferable to provide a film such as titanium (Ti) or chromium (Cr) as an adhesion layer (not shown) between them. The adhesion layer is preferably as thin as possible so long as the adhesion between the lower conductor 16 and the dielectric substrate 11 is not impaired. For example, when the Cu film is 300 nm or more, the Ti or Cr film is preferably about 40 nm.

  The post wall waveguide 14 has a short wall 19 orthogonal to the post wall 18. The short wall is composed of one or more posts 15 penetrating the dielectric substrate 11 so as to connect the ground conductor layers 12 and 13. The signal radiated from the converter 50 to the dielectric substrate 11 is transmitted in a direction away from the short wall 19 in the post wall waveguide 14.

  Each post 15 is formed to be a columnar conductor by laminating a conductor on the inner surface of a through hole formed in the dielectric substrate 11 or filling the through hole with a conductor. The cross-sectional shape of the through hole is not limited to a circle, but may be a quadrangle, a polygon, or other shapes. The arrangement and interval of the adjacent posts 15 are set so that the high frequency signal does not leak outside the post wall waveguide 14. For example, the center-to-center distance between adjacent posts 15 and 15 can be set to be twice or less the diameter of the post 15.

  A method for manufacturing the waveguide substrate 10 shown in FIGS. 1 and 2 will be described with reference to FIGS. 3A to 3D are cross-sectional views showing the main part of the substrate in the manufacturing process of the post wall waveguide 14 step by step in the order of the manufacturing process. 4A to 4E are cross-sectional views showing the main part of the substrate in the manufacturing process of the transmission line 20 step by step in the order of the manufacturing process. FIG. 5 is a cross-sectional view showing a stage of combining the post wall waveguide 14 of FIG. 3D and the transmission line 20 of FIG. 3 and 5, the post 15 and the transmission line 20 are shown in the same sectional view as in FIG.

  In the manufacturing process of the post wall waveguide 14, first, as a preparation process, as shown in FIG. 3A, a laminated substrate having conductor layers 12 and 13 on both surfaces of a dielectric substrate 11 is prepared as a base material. The conductor layers 12 and 13 in the manufacturing process may not be grounded. For example, as the laminated substrate, a flexible substrate having a thickness of about 100 to 500 μm can be given. The conductor layers 12 and 13 are preferably copper foil films such as copper foil. The thicknesses of the conductor layers 12 and 13 are desirably greater than at least the skin depth of the millimeter wave band. At a frequency of 60 GHz, since the skin depth of the signal current is 270 nm, it is sufficient that the thickness is about 2 μm.

  Next, as shown in FIG. 3B, as the drilling step, the concave shape of the through hole 15a and the bottomed hole 16a is formed on the laminated substrate of FIG. 3A by processing means such as laser ablation or drill. . These recess shapes are formed so as to correspond to the post 15 and the lower conductor 16 in FIG. The through hole 15 a is formed so as to penetrate the dielectric substrate 11 corresponding to the position of the post 15. The bottomed hole 16a is formed with a desired depth corresponding to the length of the lower conductor 16 and a thickness corresponding to the diameter.

When the laminated substrate is a flexible substrate, for example, a liquid crystal polymer substrate (LCP substrate) is formed with a concave shape by irradiating the laser with a UV-YAG laser, CO ₂ laser, etc. with adjusted laser intensity. can do. The diameters of the through hole 15a and the bottomed hole 16a are not particularly limited, but can be appropriately set within a range of 10 to 300 μm, for example. In a mode converter using a thin substrate, the length (pin length) of the lower conductor 16 becomes a transmission characteristic as the thickness of the post wall waveguide 14 is reduced, that is, as the dielectric substrate 11 is reduced. The degree of influence increases. Therefore, it is necessary to design the pin length more precisely. For example, when the thickness of the dielectric substrate is 300 μm or less, it is desirable to control the pin length at the 10 μm level.

  Next, as shown in FIG. 3C, a conductor layer constituting the post 15 and the lower conductor 16 is formed inside the through hole 15a and the bottomed hole 16a. The conductor layer preferably has a laminated structure in which a plating layer such as Cu is formed on a seed layer such as Cr / Cu or Ti / Cu. The thickness of the seed layer is, for example, 10 nm to 500 nm, and can be formed by sputtering. The thickness of the plating layer is preferably at least greater than the skin depth of the millimeter wave band. At a frequency of 60 GHz, since the skin depth of the signal current is 270 nm, a thickness of about 2 μm is sufficient. At this time, conductor layers such as a seed layer and a plating layer may be simultaneously formed on the conductor layers 12 and 13 on the front and back surfaces of the dielectric substrate 11.

  Next, as shown in FIG. 3 (d), a region corresponding to the gap 17 a around the lower conductor 16 is removed by etching to form a land 17. At this time, by forming and etching a resist having an opening at the position that becomes the gap 17a, the conductor layer 13 at the position that becomes the gap 17a can be selectively removed. When etching a copper foil, wet etching using an acid solution such as ferric chloride solution or cupric chloride solution can be used.

  After the formation of the lower conductor 16, the bottomed hole 16a having the lower conductor 16 may be filled with a paste-like conductive material (conductive paste) by means such as screen printing. In this case, first, a sheet-like cover is attached to the entire surface of the substrate, and only a portion corresponding to the bottomed hole 16a is removed to form a through hole. In this state, when the conductive paste is applied to the entire surface of the substrate by screen printing, the bottomed hole 16a can be filled through the through hole of the cover. Thereafter, the sheet can be removed, and only the inside of the lower conductor 16 can be filled with the paste. As the cover, for example, a metal mask made of stainless steel or aluminum alloy can be used. As a method of forming the through hole in the cover, laser processing with adjusted energy can be used as in the case of forming the through hole 15a in the laminated substrate of the dielectric substrate 11 and the conductor layers 12 and 13.

  In the manufacturing process of the transmission line 20, first, as a preparation process, as shown in FIG. 4A, a laminated substrate having a conductor layer 21 on one side of an insulating layer 22 is prepared as a base material. The conductor layer 21 is preferably a copper foil film such as a copper foil. The thickness of the conductor layer 21 is desirably at least greater than the skin depth of the millimeter wave band. At a frequency of 60 GHz, since the skin depth of the signal current is 270 nm, it is sufficient that the thickness is about 2 μm.

Next, as shown in FIG. 4B, the conductor layer 21 is etched to form planar circuits such as the pad 21a, the signal transmission path 21b, the open stub 21c, the signal pad 25, and the ground pad 26 of FIG. At this time, these planar circuits can be formed by forming a resist patterned in the shape of a planar circuit and removing the other conductor layers 21 by etching. Thereafter, the resist is removed with a resist stripping solution. Furthermore, a reactive ion etching (RIE) process using CF ₄ gas or O ₂ gas can be performed. At this time, as described above, each dimension in each planar circuit can be set for impedance matching. In FIG. 4, only the pad 21a and the signal transmission path 21b are shown as a planar circuit.

  Next, as shown in FIG. 4C, an adhesive layer 23 is formed on the entire back surface of the insulating layer 22. As the adhesive layer 23, an adhesive layer made of an epoxy or acrylic adhesive or a liquid crystal polymer (LCP) is used. Since the adhesive layer 23 may be made of a material having inferior high-frequency characteristics, it is preferable to make the thickness of the adhesive layer 23 thinner than that of the insulating layer 22. By making the insulating layer 22 thicker than the adhesive layer 23, loss can be reduced.

  Next, as shown in FIG. 4D, an opening 24a is formed in the dielectric layer (the insulating layer 22 and the adhesive layer 23) by processing means such as laser ablation. The opening 24a is provided at a position corresponding to the upper conductor 24 and the ground via 27 in FIG. On the insulating layer 22, the opening 24 a is formed through the insulating layer 22 and the adhesive layer 23 so as to be electrically connected to a planar circuit such as the pad 21 a and the ground pad 26 of the signal transmission path 21 b. By adjusting the laser irradiation conditions, it is possible to form an opening 24 a that does not penetrate the conductor layer 21 and penetrates the insulating layer 22 and the adhesive layer 23. In FIG. 4D, only the opening 24a under the pad 21a is shown.

  Next, as shown in FIG. 4E, in the filling step, the opening 24a may be filled with a paste-like conductive material (conductive paste) by means such as screen printing. At this time, the conductive paste serving as the upper conductor 24 can be filled in the opening 24a by applying the conductive paste to the entire surface of the adhesive layer 23 and then pressing it with a squeegee or the like. The conductive paste does not have to be completely filled in the opening 24a, but it is desirable that the inside of the opening 24a be completely filled when airtightness is required.

  In order to combine the post wall waveguide 14 of FIG. 3D and the transmission line 20 of FIG. 4E, as shown in FIG. 5, the positions of the lower conductor 16 and the upper conductor 24 and other positions are aligned and pasted. It can adhere | attach by the contact bonding layer 23 by combining and heat-pressing. The heat and pressure treatment is performed so that the adhesive layer 23 is adhered to the conductor layer 13 of the post-wall waveguide 14 and the lower conductor 16 and the upper conductor 24 are connected, and the planar circuit is not deformed. . As described above, it is preferable to fill the inside of the lower conductor 16 with a conductive paste because the connection is ensured.

  The conductive paste contains conductive particles (conductive particles) such as copper (Cu), silver (Ag), gold (Au), tin (Sn), and bismuth (Bi). Flux etc. can be included. When a conductive paste is filled into fine recesses using a printing method, it becomes easy to form a conductor in a recess with a high aspect ratio. Thereby, in order to reduce the size and thickness of the waveguide substrate, a pin having a desired length can be stably formed even when the pin structure of the converter is formed small. The transducer (high-frequency signal injection structure) manufactured in this way includes, in a part thereof, an aggregate of conductive particles, a collection zone of conductive particles, or a sintered body of conductive particles having fine pores. It will be a thing.

  The high-frequency signal injection structure is not limited to a pin structure that does not penetrate the dielectric substrate, and may be a through-conductor type waveguide excitation means that penetrates the dielectric substrate. 6 and 7 show an example of a through-conductor type waveguide excitation means. In this through conductor type converter 60, the lower conductor 16 penetrates the dielectric substrate 11, and the lands 17 and 17 at both ends are separated from the ground conductor layers 12 and 13 by gaps 17a and 17b, respectively. The through-conductor type converter can be manufactured in the same manner as the manufacturing method shown in FIGS. The main change is that the bottomed hole 16a is formed until it reaches the ground conductor layer 12 in the step of FIG. 3B, and the ground conductor layers 12 and 13 are formed in the step of FIG. As shown in FIG. 6, the gaps 17a and 17b are formed.

  As an advantage of the through-conductor type converter, for example, when the thickness of the dielectric substrate 11 is relatively thin (for example, less than 300 μm), or when it is desired to achieve impedance matching of 50Ω, the length of the transmission line 20 (see FIG. 2 (a) L) can be shortened, and loss in the TEM line portion can be reduced.

(Connection with external device)
On the waveguide substrate provided with the post wall waveguide, a connection means between the transmission line and the external device can be provided. An example of the external device is a semiconductor device such as an integrated circuit (IC).
In the configuration of FIG. 8, the semiconductor device 30 is disposed on the waveguide substrate 10. The transmission line 20 and the semiconductor device 30 are electrically connected by bumps 31. The high-frequency signal output from the semiconductor device 30 is converted into a signal of the post wall waveguide 14 through the transmission line 20 and the converter 50, and an outlet 14 a is provided at the end of the post wall waveguide 14 opposite to the short wall 19. The high frequency signal W is radiated from the outside. The semiconductor device 30 of this example is arranged at a position different from the post wall waveguide 14 in the waveguide substrate 10.

  The waveguide substrate 10 includes a direct current (DC) circuit 32, and the direct current circuit 32 and the semiconductor device 30 are electrically connected by another bump 31. The DC circuit 32 reaches the back surface of the waveguide substrate 10 through the through hole 33. The circuit formed on the mother substrate 40 and the DC circuit 32 on the back surface of the waveguide substrate 10 are electrically connected by the bump 31 by the bump 42. The bumps 42 for fixing the waveguide substrate 10 on the mother substrate 40 and the bumps 31 for fixing the semiconductor device 30 on the waveguide substrate 10 are located in places where electrical connection is required in the circuit or transmission path. Without limitation, a desired number and arrangement can be provided.

  Examples of the bump include a stud bump, a plating bump, and a solder (solder) bump since miniaturization is possible. The stud bump is a bump formed by cutting a ball formed by melting the tip of a wire, and an apparatus similar to wire bonding can be used. An Au stud bump is suitable as the stud bump, and an AuSn material is preferably provided between the Au stud bump and the transmission line. The Au stud bump can be formed from a thin Au wire and can be miniaturized. Gold-tin alloy (AuSn) is suitable as a bonding material because it is lead-free and has a relatively low melting point.

  FIG. 9 shows an example different from FIG. In this configuration, the semiconductor device 30 is disposed in a recess provided in the waveguide substrate 10, and the connection between the semiconductor device 30, the transmission line 20, and the DC circuit 32 is replaced by the bumps 31 of FIG. Is used. As these connection means, a gold wire or a gold ribbon is preferable. Gold (Au) has excellent conductivity, corrosion resistance, and reliability, and can be connected without being oxidized even in the air, so that it is excellent in workability.

  The connection means is not limited to the bumps 31 and the wires 34 by surface mounting, but includes pin terminals by through-hole mounting. In the case of surface mounting, the semiconductor device 30 can be mounted on one side of the waveguide substrate 10.

As mentioned above, although this invention has been demonstrated based on suitable embodiment, this invention is not limited to the above-mentioned embodiment, A various change is possible in the range which does not deviate from the summary of this invention.
As a high-frequency signal, a millimeter wave can be cited, but a signal having a higher frequency such as a terahertz wave (sub-millimeter wave) may be used as long as propagation by a waveguide structure is possible.

DESCRIPTION OF SYMBOLS 10 ... Waveguide board | substrate, 11 ... Dielectric board | substrate, 12, 13 ... Ground conductor layer, 14 ... Post wall waveguide, 15 ... Post, 16 ... Lower conductor, 18 ... Post wall, 20 ... Transmission line, 21 ... Conductor layer , 22 ... insulating layer (dielectric layer), 23 ... adhesive layer (dielectric layer), 24 ... upper conductor, 30 ... semiconductor device, 31 ... bump, 34 ... wire, 50, 60 ... transducer.

Claims (10)

A waveguide substrate comprising a transmission line and a post wall waveguide,
The post wall waveguide includes a pair of ground walls formed of a pair of ground conductor layers formed on opposite surfaces of the dielectric substrate, and posts penetrating the dielectric substrate so as to connect the pair of ground conductor layers. And consists of
The transmission line is laminated on the post wall waveguide via one or more dielectric layers between any one of the pair of ground conductor layers,
The ten-point average roughness Rz of the surface of the pair of ground conductor layers between the pair of ground conductor layers and the dielectric substrate is Rz0, and the one or more dielectric layers are in contact with the transmission line. A waveguide substrate characterized by Rz3> Rz0, where Rz3 is the ten-point average roughness Rz of the surface of the transmission line between the dielectric layer and the transmission line.   The waveguide substrate according to claim 1, wherein Rz0 is 0.8 μm or less. A waveguide substrate comprising a transmission line and a post wall waveguide,
The post wall waveguide includes a pair of ground walls formed of a pair of ground conductor layers formed on opposite surfaces of the dielectric substrate, and posts penetrating the dielectric substrate so as to connect the pair of ground conductor layers. And consists of
The transmission line is laminated on the post wall waveguide via one or more dielectric layers between any one of the pair of ground conductor layers,
The waveguide substrate, wherein the dielectric substrate is made of a liquid crystal polymer or a fluorine resin, and the dielectric layer in contact with the transmission line among the one or more dielectric layers is made of a polyimide resin.   The ten-point average roughness Rz of the surface of the pair of ground conductor layers between the pair of ground conductor layers and the dielectric substrate, and the transmission between the dielectric layer in contact with the transmission line and the transmission line The waveguide substrate according to claim 3, wherein the ten-point average roughness Rz of the surface of the line is 0.8 μm or less.   The waveguide substrate according to any one of claims 1 to 4, wherein the waveguide substrate includes a high-frequency signal injection structure for injecting a high-frequency signal from the transmission line to the post wall waveguide. .   6. The waveguide substrate according to claim 5, wherein the high-frequency signal injection structure is a through-conductor-type waveguide excitation structure that penetrates the dielectric substrate.   The part of the high-frequency signal injection structure is composed of an aggregate of conductive particles, a conductive band assembly, or a sintered body of conductive particles having fine pores. Waveguide substrate.   The waveguide substrate according to any one of claims 1 to 7, wherein the waveguide substrate includes a connection unit between the transmission line and an external device, and the connection unit includes a gold wire or a gold ribbon. .   The waveguide substrate according to any one of claims 1 to 7, wherein the waveguide substrate includes a connection unit between the transmission line and an external device, and the connection unit includes a stud bump.   10. The waveguide substrate according to claim 9, wherein the stud bump is an Au stud bump, and an AuSn material is provided between the Au stud bump and the transmission line.

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