WO2020040072A1

WO2020040072A1 - Wiring board, package, and module

Info

Publication number: WO2020040072A1
Application number: PCT/JP2019/032221
Authority: WO
Inventors: 正人石▲崎▼; 久保　昇
Original assignee: Ｎｇｋエレクトロデバイス株式会社; 日本碍子株式会社
Priority date: 2018-08-21
Filing date: 2019-08-19
Publication date: 2020-02-27
Also published as: CN112119489B; JPWO2020040072A1; JP7026804B2; CN112119489A

Abstract

According to the present invention, a second wiring path (52) is separated from a first ground pattern (41) by means of a first wiring path (51), and extends parallel to the first wiring path (51). A second ground pattern (42) is separated from the first wiring path (51) by means of the second wiring path (52). A first pad pair (61) for mounting a capacitor is provided in the middle of the first wiring path (51), and has a width that is greater than the width of the first wiring path (51). A second pad pair (62) for mounting a capacitor is provided in the middle of the second wiring path (52), and has a width that is greater than the width of the second wiring path (52). A ceramic base (10) has: a first recess portion (RC1) provided between the first ground pattern (41) and the first pad pair (61); and a second recess portion (RC2) provided between the second ground pattern (42) and the second pad pair (62).

Description

Wiring boards, packages and modules

The present invention relates to a wiring board, a package, and a module.

高周波 WO 2017/170389 discloses a high frequency module. The high-frequency module has a high-frequency package, a semiconductor element, and a lid. The high-frequency package includes a frame having a through-hole and a high-frequency board attached to the through-hole. The high-frequency substrate has an insulating base, a first line conductor, a second line conductor, a capacitor, a first bonding material, and a second bonding material. By providing a capacitor between the first line conductor and the second line conductor, the DC current component of the high-frequency signal can be removed.

The insulating base has a concave portion on the upper surface. The first electrode pad is provided at an end of the recess on the upper surface of the insulating base. The first line conductor is provided on the upper surface of the insulating base so as to extend from the first electrode pad. The second electrode pad is provided on the upper surface of the insulating base so as to face the first electrode pad with the concave portion interposed therebetween. The second line conductor is provided on the upper surface of the insulating base so as to extend from the second electrode pad. The capacitor overlaps the recess. The first bonding material bonds the capacitor and the first electrode pad. The second joining material joins the capacitor and the second electrode pad, and is provided with a space between the first joining material.

Even when the amounts of the first bonding material and the second bonding material are increased due to the provision of the concave portion in the high-frequency substrate, the gap between the first bonding material and the second bonding material is maintained by the concave portion. Can be. Thereby, the possibility that the first bonding material and the second bonding material come into contact with each other can be reduced. Further, since a space is provided between the electrode portions of the capacitor by the concave portion, between the electrode portions of the capacitor, between the first electrode pad and the second electrode pad, and between the first bonding material and the second bonding material. Can be reduced, and the characteristic impedance of the transmission line for the high-frequency signal can be adjusted to a desired value.

WO 2017/170389

According to the technique described in the above publication, as described above, the characteristic impedance of the transmission line for the high-frequency signal can be adjusted by the concave portion arranged to overlap the capacitor. However, according to the study of the present inventors, if it is attempted to ensure sufficient matching of the characteristic impedance mainly by relying on the concave portion, a local sudden change in the characteristic impedance at a portion where the concave portion is provided becomes remarkable. . Local sudden changes in characteristic impedance result in higher return losses at higher frequencies. In recent years, there has been a demand for broadening the band of a high-frequency package, and thus it has been required to obtain good pass characteristics even in a higher frequency region.

The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a wiring board, a package, and a module that can obtain good transmission characteristics in a high-frequency region.

A wiring board according to the present invention includes a ceramic base, a first ground pattern, a first wiring path, a second wiring path, a second ground pattern, a first pad pair, and a second pad. Have a pair. The first ground pattern is provided on the ceramic base. The first wiring path is provided on the ceramic base, is disposed apart from the first ground pattern, and has a portion extending in one direction on the ceramic base. The second wiring path is provided on the ceramic base, is separated from the first ground pattern by the first wiring path on the ceramic base, and extends in one direction alongside the first wiring path. Has a part. The second ground pattern is provided on the ceramic base, is separated from the first wiring path by the second wiring path on the ceramic base, and is separated from the second wiring path on the ceramic base. . The first pad pair is for mounting a capacitor, is provided in the middle of the first wiring path, and has a width larger than the width of the first wiring path. The second pad pair is for mounting a capacitor, is provided in the middle of the second wiring path, and has a width larger than the width of the second wiring path. The first pad pair includes a pair of first pads opposed in one direction. The second pad pair includes a pair of second pads opposed in one direction. The first pad pair and the second pad pair face each other in a direction orthogonal to one direction. The ceramic base includes a first concave portion provided between the first ground pattern and the first pad pair, and a second concave portion provided between the second ground pattern and the second pad pair. And

パッケージ The package of the present invention includes a wiring board and a casing having a cavity. At least a part of the wiring board is located inside the cavity.

The module of the present invention has a package, a lid for sealing the cavity of the package, and an integrated circuit mounted in the cavity. The first wiring path and the second wiring path form a differential line electrically connected to the integrated circuit.

According to the present invention, a differential line is formed by extending the first wiring path provided with the first pad pair and the second wiring path provided with the second pad pair side by side. You. In the signal transmission using this differential line, according to the study of the present inventors, by providing the first and second concave portions in the above-described arrangement in the ceramic base, good pass characteristics in a high frequency region are obtained. Obtainable.

The objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description and the accompanying drawings.

FIG. 2 is a top view schematically illustrating a configuration of a module according to Embodiment 1 of the present invention. FIG. 2 is a top view schematically showing a configuration of the package according to the first embodiment of the present invention. FIG. 3 is a schematic partial sectional view taken along a line III-III in FIG. 2. FIG. 2 is a circuit diagram schematically showing a configuration of a wiring board according to Embodiment 1 of the present invention. FIG. 5 is a schematic diagram showing a part of the circuit of the wiring board in FIG. 4 in a view parallel to the view in FIG. 3. FIG. 5 is a schematic diagram showing a part of the circuit of the wiring board in FIG. 4 in a view parallel to the view in FIG. 3. FIG. 2 is a partial top view schematically showing a configuration of a surface wiring of the wiring board according to Embodiment 1 of the present invention. FIG. 8 is a schematic partial sectional view taken along line VIII-VIII in FIG. 7. FIG. 4 is a partial top view schematically showing a configuration of a surface wiring of a wiring board of a first comparative example. FIG. 10 is a schematic partial sectional view taken along line XX of FIG. 9. FIG. 9 is a partial top view schematically showing a configuration of a surface wiring of a wiring board of a second comparative example. FIG. 12 is a schematic partial sectional view taken along line XII-XII in FIG. 11. FIG. 13 is a partial top view schematically illustrating a configuration of a surface wiring of a wiring board of a third comparative example. FIG. 14 is a schematic partial cross-sectional view taken along a line XIV-XIV in FIG. 13. FIG. 13 is a graph showing, as time-domain reflection, simulation results of characteristic impedances of the wiring boards of the example of the present embodiment and the first to third comparative examples. FIG. 10 is a graph showing simulation results of reflection characteristics in the band of 0 to 75 GHz for the wiring boards of the example of the present embodiment and the first to third comparative examples. FIG. 14 is a graph showing simulation results of crosstalk characteristics in a band of 25 to 75 GHz for the wiring board of the example of the present embodiment and the first to third comparative examples. FIG. 10 is a graph showing simulation results of the ratio of energy loss in the band of 25 to 75 GHz for the wiring board of the example of the present embodiment and the first to third comparative examples. FIG. 14 is a graph showing simulation results of pass characteristics in the band of 25 to 75 GHz for the wiring board of the example of the present embodiment and the first to third comparative examples. FIG. 8 is a partial top view showing a modification of FIG. 7. FIG. 9 is a partial top view showing another modification of FIG. 7. FIG. 11 is a top view schematically showing a configuration of a package according to a second embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<First Embodiment>
(Constitution)
FIG. 1 is a top view schematically showing a configuration of high-frequency module 701 according to the first embodiment. Note that, for the lid 730, only the outer edge is indicated by a two-dot chain line in order to make the drawing easy to see. FIG. 2 is a top view schematically illustrating a configuration of a high-frequency package 501 used to obtain the high-frequency module 701. Note that the external terminals of the high-frequency module 701 (FIG. 1) and the high-frequency package 501 (FIG. 2) are not limited to those illustrated, and for example, power is supplied into the high-frequency module 701 (high-frequency package 501). A power supply terminal (not shown) may be provided. FIG. 3 is a schematic partial sectional view taken along line III-III of FIG.

The high-frequency module 701 (FIG. 1) includes the high-frequency package 501 (FIG. 2), the lid 730, and the internal circuit 750. The internal circuit 750 has an IC (integrated circuit) 751. Each of the high-frequency module 701 and the high-frequency package 501 is a high-frequency module and a high-frequency package, and the IC 751 may have a high operating frequency, specifically, an operating frequency of 55 GHz or more. In the present embodiment, the internal circuit 750 further has an optical component 752, and thus the high-frequency module 701 and the high-frequency package 501 are an optical module and an optical package, respectively. The optical component 752 is, for example, a photodiode.

The high-frequency package 501 includes the high-frequency board 301 (wiring board) and the casing 530. The casing 530 has a cavity CV by having a bottom 531 and a frame 532 surrounding the bottom 531. The cover 730 seals the cavity CV. The internal circuit 750 is mounted in the cavity CV. In the high-frequency package 501 of the present embodiment, a cable is provided to receive light from an optical fiber (not shown) disposed outside the high-frequency module 701 or to secure a path for transmitting light to the optical fiber. An opening 535 is provided in the frame 532 of the thing 530. A cylindrical member for fixing an optical fiber may be attached to the opening 535. A translucent material may be attached inside the cylindrical member.

(4) The high-frequency substrate 301 has a portion located inside the cavity CV and a portion located outside the cavity CV. Thus, the high-frequency substrate 301 forms an electric path connecting the inside and the outside of the cavity CV. In order to obtain this configuration, the high-frequency board 301 penetrates through holes TH provided in the frame portion 532 of the casing 530.

The high-frequency board 301 has internal terminals 71 to 74 and external terminals 81 to 84. The internal terminals 71 to 74 are arranged inside the cavity CV, and the external terminals 81 to 84 are arranged outside the cavity CV. Although the external terminals 81 to 84 are only schematically shown in the drawing, the external terminals 81 to 84 may be, for example, projecting lead terminals.

FIG. 4 is a circuit diagram schematically showing a configuration of the high-frequency board 301. The high-frequency substrate 301 constitutes at least one differential line, and in this embodiment, constitutes two differential lines CA and CB. One set of internal terminals 71 to 74 and external terminals 81 to 84 is provided corresponding to each differential line.

The first ground pattern 41 connects between the internal terminal 71 and the external terminal 81. Similarly, the second ground pattern 42 connects between the internal terminal 74 and the external terminal 84. The “ground pattern” is a conductor pattern that is normally assumed to be at a ground potential when the high-frequency module 701 is used. Therefore, it is preferable that the ground patterns on the high-frequency substrate 301 are electrically short-circuited to each other.

The high-frequency board 301 has the first wiring path 51 and the pair of

first pads

61a and 61b between the internal terminal 72 and the external terminal 82. Hereinafter, the whole of the pair of

first pads

61a and 61b is also referred to as a first pad pair 61. The first pad pair 61 is provided in the middle of the first wiring path 51. The first pad pair 61 is for mounting the capacitor 90, and is provided in the middle of the first wiring path 51. Similarly, the high-frequency substrate 301 has the second wiring path 52 and a pair of

second pads

62a and 62b between the internal terminal 73 and the external terminal 83. Hereinafter, the whole of the pair of

second pads

62a and 62b is also referred to as a second pad pair 62. The second pad pair 62 is provided in the middle of the second wiring path 52. The second pad pair 62 is for mounting the capacitor 90 and is provided in the middle of the second wiring path 52.

The specific arrangement of the first pad pair 61 and the second pad pair 62 will be described later with reference to FIG. 7, but the first pad pair 61 and the second pad pair 62 51 and the second wiring path 52 are arranged symmetrically with respect to an imaginary line extending along the extending direction. This is for the following reason. Since the capacitor 90 usually has a member having a high dielectric constant, it is assumed that the phase of the signal changes inside the capacitor 90. For example, when the phase inside the capacitor 90 mounted on the first pad pair 61 and the phase of the second wiring path 52 adjacent to the capacitor 90 are different from each other and capacitive coupling occurs between them, the impedance is changed from the design value. Shift. Therefore, when the first pad pair 61 and the second pad pair 62 are arranged so as to be shifted from each other in the extending direction of the wiring path, there is a possibility that the impedance is largely shifted from the design value. On the other hand, if the first pad pair 61 and the second pad pair 62 are arranged in line symmetry, that is, if the first pad pair 61 and the second pad pair 62 are extended If they are arranged facing each other in a direction orthogonal to the existing direction, it is possible to prevent the impedance from greatly deviating from the design value.

The first wiring path 51 and the second wiring path 52 constitute a differential line electrically connected to the IC 751. In other words, during the operation of the IC 751 (FIG. 1), signals of opposite phases are propagated through the first wiring path 51 and the second wiring path 52. By providing the capacitor 90 on the differential line, the flow of the DC component in the differential line can be inhibited. Specifically, the capacitor 90 as a blocking capacitor prevents the bias voltage used in the IC 751 from being applied to the

external terminals

82 and 83.

FIG. 5 is a schematic diagram showing a portion between the internal terminal 71 and the external terminal 81 in the circuit of the high-frequency board 301 in a view parallel to the view in FIG. The portion between the internal terminal 74 and the external terminal 84 has the same configuration. FIG. 6 is a schematic diagram showing a portion between the internal terminal 72 and the external terminal 82 in the circuit of the high-frequency board 301 in a view parallel to the view of FIG. The portion between the internal terminal 73 and the external terminal 83 has the same configuration.

(4) The wiring WR (the circuit shown in FIG. 4) in the high-frequency substrate 301 has a surface wiring WRS arranged on the surface of the high-frequency substrate 301. Further, the wiring WR may include an internal wiring WRB which is disposed in the high-frequency substrate 301 and has a portion extending in the thickness direction. The above-described capacitor 90 is mounted on the surface wiring WRS. In other words, the first pad pair 61 and the second pad pair 62 described above are provided on the surface wiring WRS. Hereinafter, a specific configuration of the surface wiring WRS will be described in detail.

FIG. 7 is a partial top view schematically showing the configuration of surface wiring WRS (FIGS. 5 and 6) of high-frequency substrate 301. FIG. 8 is a schematic partial sectional view taken along line VIII-VIII of FIG.

The high frequency substrate 301 has the ceramic base 10 made of an insulator. On the ceramic base 10, a first ground pattern 41, a first wiring path 51, a second wiring path 52, a second ground pattern 42,

first pads

61a, 61b, and a

second pad

62a , 62b. The first pad 61a and the first pad 61b face each other in one direction (the horizontal direction in FIG. 7) with an interval therebetween. The first wiring path 51 is electrically separated by this interval. The second pad 62a and the second pad 62b face each other in one direction (the horizontal direction in FIG. 7) with an interval therebetween. The second wiring path 52 is electrically separated by this interval.

The first wiring path 51 is arranged apart from the first ground pattern 41. The first wiring path 51 has a portion that extends on the ceramic base 10 in one direction (the horizontal direction in FIGS. 7 and 8). The second wiring path 52 is separated from the first ground pattern 41 by the first wiring path 51 on the ceramic base 10. The second wiring path 52 has a portion extending in one direction (the horizontal direction in FIGS. 7 and 8) alongside the first wiring path 51. The second ground pattern 42 is separated from the first wiring path 51 by a second wiring path 52 on the ceramic base 10 and is separated from the second wiring path 52 on the ceramic base 10.

The high frequency substrate 301 may further have a third ground pattern 43. The third ground pattern 43 is disposed between the first wiring path 51 and the second wiring path 52 on the ceramic base 10. The third ground pattern 43 is separated from the first wiring path 51 and the second wiring path 52. In the configuration shown in FIG. 7, the second wiring path 52 is arranged on the first wiring path 51 via the third ground pattern 43.

At a position (outside of the field of view in FIG. 7) apart from the first pad pair 61 and the second pad pair 62, a curved portion is provided in the first wiring path 51 and the second wiring path 52 running in parallel. In this case, there is a phase difference between the two signals at the curved portion. The effect of this phase difference on high-frequency transmission characteristics can be suppressed by the third ground pattern 43.

よう As shown in FIG. 7, it is preferable that the third ground pattern 43 is not arranged between the first pad pair 61 and the second pad pair 62. Thereby, the effect of the present embodiment is further increased.

The first pad pair 61 including the

first pads

61a and 61b has a width larger than the width of the first wiring path 51. The second pad pair 62 including the

second pads

62a and 62b has a width larger than the width of the second wiring path 52. Here, the width is a dimension in a direction perpendicular to the extending direction of the wiring path (horizontal direction in FIG. 7), and is a vertical dimension in FIG. Since the pad pair has a width larger than the width of the wiring path, the capacitor 90 having a width larger than the width of the wiring path can be easily mounted. For example, the width of the wiring path is about 100 μm, and the width of the pad pair is about 300 μm. The mounting of the capacitor 90 can be performed using a bonding material (for example, solder).

After the step of mounting the capacitors on the high-frequency substrate 301 is performed, the high-frequency substrate 301 includes a capacitor 90 mounted on the first pad pair 61 and a capacitor 90 mounted on the second pad pair 62. have. Conversely, before the step of mounting the capacitor on the high-frequency substrate 301 is performed, the high-frequency substrate 301 does not have the capacitor 90 yet.

(4) On the surface of the ceramic base 10, a concave portion RC1 (first concave portion) and a concave portion RC2 (second concave portion) are provided. The concave portion RC1 is arranged between the first ground pattern 41 and the first pad pair 61. The concave portion RC2 is disposed between the second ground pattern 42 and the second pad pair 62. Note that the “recess” in the present specification is a region that is clearly deeper than its periphery, and specifically, a region that has a depth of 50 μm or more.

(8) As shown in FIG. 8, the high-frequency substrate 301 has a first inner-layer ground pattern 31 and a second inner-layer ground pattern 32 inside the ceramic base 10. The second inner-layer ground pattern 32 is provided deeper than the first inner-layer ground pattern 31. That is, the depth D2 of the second inner-layer ground pattern 32 is greater than the depth D1 of the first inner-layer ground pattern 31.

The first inner-layer ground pattern 31 has a portion facing the first wiring path 51 and the second wiring path 52 (not shown in FIG. 8) in the thickness direction (vertical direction in the figure), Further, an opening OP is provided below the first pad pair 61 and the second pad pair 62 (not shown in FIG. 8). The second inner layer ground pattern 32 has a portion facing the first pad pair 61 and the second pad pair 62 (not shown in FIG. 8) via the opening OP of the first inner layer ground pattern 31. are doing. By providing the opening OP, the distance between each of the first pad pair 61 and the second pad pair 62 and the inner-layer ground pattern can be set to a depth D2 larger than the depth D1.

The first ground pattern 41 and the second ground pattern 42 (FIG. 7) are electrically short-circuited to each other. Generally, these are electrically connected to each other via a vertical portion (a portion passing through a through hole) and a horizontal portion (an inner layer ground pattern) of internal wiring WRB (FIG. 5). However, as a modification, only the surface wiring WRS (FIG. 5) may be provided, and the internal wiring WRB may not be provided. In this case, the first ground pattern 41 and the second ground pattern 42 (FIG. 7) It may be electrically short-circuited to each other by any other method.

The inner-layer ground pattern is usually a pattern parallel to the surface of the ceramic base 10, and may be a pattern arranged over substantially the entire ceramic base 10 in a planar layout, in other words, a solid pattern. In this case, a pseudo coaxial structure can be formed by surrounding the internal wiring WRB (FIG. 6) connecting the internal terminal 72 and the external terminal 82 for transmitting signals with an inner layer ground pattern.

(Comparative example)
Next, first to third comparative examples with respect to the high-frequency substrate 301 (FIGS. 7 and 8) will be described below.

FIG. 9 is a partial top view schematically showing the configuration of the surface wiring WRS (see FIGS. 5 and 6) of the high-frequency substrate 301A of the first comparative example. FIG. 10 is a schematic partial sectional view taken along line XX of FIG. In the high-frequency substrate 301A, no recess is provided in the ceramic base 10. Other configurations are the same as those of the high-frequency substrate 301 (FIGS. 7 and 8).

FIG. 11 is a partial top view schematically showing the configuration of surface wiring WRS (see FIGS. 5 and 6) of high-frequency substrate 301B of the second comparative example. FIG. 12 is a schematic partial sectional view taken along line XII-XII in FIG. In the high-frequency substrate 301B, the ceramic base 10 does not have the recesses RC1 and RC2 (FIGS. 7 and 8), but instead has the recesses RC4 (fourth recess) and the recess RC5 (fifth recess). are doing. The recess RC4 is arranged between the first pad 61a and the first pad 61b, and the recess RC5 is arranged between the second pad 62a and the second pad 62b. The recess RC4 and the recess RC5 may be connected as shown in FIG. As a variant, the recesses RC4 and RC5 may be separated from each other.

FIG. 13 is a partial top view schematically showing the configuration of surface wiring WRS (see FIGS. 5 and 6) of high-frequency substrate 301C of the third comparative example. FIG. 14 is a schematic partial cross-sectional view taken along line XIV-XIV in FIG. In the high-frequency substrate 301C, the ceramic base 10 does not have the concave portions RC1 and RC2 (FIGS. 7 and 8), but has a concave portion RC3 (third concave portion) instead. The recess RC3 is arranged between the first pad pair 61 and the second pad pair 62.

Next, with reference to FIG. 15 to FIG. 19, simulation of high frequency characteristics between high frequency substrate 301 of the example of the present embodiment and high frequency substrates 301A to 301C of the first to third comparative examples. The difference between the results will be described. 17 to 19, the range of 0 to 25 GHz is omitted for the sake of clarity, but a simulation is also performed in this range, and there is almost no difference between the substrates. That has been confirmed.

The simulation is performed with a model in which a metal block is mounted as a substitute for the capacitor 90. Further, in order to facilitate comparison of the simulation results, the size of the concave portion formed on the surface of the ceramic substrate 10 in the high-

frequency substrates

301, 301B, and 301C is described in detail with reference to FIG. The average correction of the characteristic impedance performed by the recess is selected to be approximately the same.

Specifically, the simulation is performed under the following conditions. The dimension in the extending direction of the wiring path (for example, the horizontal direction in FIG. 7) is referred to as length, and the dimension in the width direction of the wiring path (vertical direction in FIG. 7) is referred to as width. Regarding any of the high-

frequency boards

301 and 301A to 301C, the configurations of the first inner-layer ground pattern 31 and the second inner-layer ground pattern 32 are set under the same conditions. These inner-layer ground patterns are almost solid patterns.

Width of first wiring path 51 (second wiring path 52): 0.1 mm
Distance D1 (FIG. 8): 0.15 mm
Distance D2 (FIG. 8): 0.5 mm
Each pad (rectangular) width: 0.35mm
Length of each pad (rectangle): 0.25mm
Shortest distance between pads constituting each pad pair: 0.3 mm
Distance between respective center lines of first wiring path 51 and second wiring path 52: 0.8 mm
Dimensions of recesses RC1 (RC2) (FIG. 7): width 0.25 mm, length 0.80 mm, depth 0.4 mm (rectangle)
Dimensions of recess RC3 (FIG. 13): width 0.35 mm, length 0.80 mm, depth 0.2 mm (rectangle)
Overall dimensions of recesses RC4 and RC5 (FIG. 11): width 1.35 mm, length 0.20 mm, depth 0.25 mm (rectangular)
Ceramic substrate: made of alumina (dielectric constant: 8.7)
Wiring path and grounding pattern: Tungsten (with nickel and gold coating, gold on outermost layer)
Inner layer ground pattern: made of tungsten Software used for simulation: HFSS ver. 15 (manufactured by Ansys)

FIG. 15 is a graph showing the simulation result of the characteristic impedance as time domain reflection (TDR: Time Domain Reflectometry) at a frequency of 67 GHz. In the drawing, the time axis represented by the horizontal axis can be regarded as a space axis, and a pair of arrows roughly corresponds to the positions of the pair of

first pads

61a and 61b. In the high-frequency substrate 301A in which no recess is formed in the ceramic base 10, the average value of the characteristic impedance between the arrows is greatly reduced. This is due to an increase in the capacitance component due to the presence of the first pad pair 61. On the other hand, in the high-

frequency substrates

301, 301B, and 301C, since the concave portions are formed in the ceramic base 10, a decrease in the average value of the characteristic impedance between the arrows is corrected. That is, the average value of the characteristic impedance approaches the designed value of 100Ω. As described above, the sizes of the concave portions of the high-

frequency boards

301, 301B, and 301C are selected so that the effect of this correction is substantially the same. Comparing the characteristic impedances of the high-

frequency boards

301, 301B, and 301C, a local sudden change in the characteristic impedance between the arrows is remarkable in the high-frequency boards 301B.

FIG. 16 is a graph showing simulation results of reflection characteristics. The high-frequency board 301B has a large reflection over a wide range from 40 GHz to 60 GHz as compared with other wiring boards. This reason is considered to be due to the sudden change in the characteristic impedance described above.

FIG. 17 is a graph showing simulation results of crosstalk characteristics. Specifically, referring to FIG. 4, the magnitude of signal energy leakage from differential line CA to differential line CB is simulated. Large crosstalk means that this undesirable leakage is large. The high-frequency substrate 301C has the poorest crosstalk characteristics in most of the band of about 40 GHz or higher. On the other hand, the high frequency substrate 301 has the most excellent crosstalk characteristics in most of the band of 40 GHz or more.

FIG. 18 is a graph showing a simulation result of an energy loss ratio. The energy loss referred to here is a difference obtained by removing a loss due to reflection (see FIG. 16) and a signal energy passing through the circuit (see FIG. 19) from the signal energy input to the circuit. Such energy loss is generally considered to be due to dielectric loss, conductor loss, radiation loss, and the like. Below 55 GHz, there is no significant difference in energy loss characteristics. On the other hand, at 55 GHz or higher, the high-frequency substrate 301 has the most excellent characteristics, and at 60 GHz or higher, the effect is more remarkable. This is presumably because radiation loss due to mode conversion into a surface wave (described later in detail) and loss due to crosstalk (FIG. 17) can be suppressed. From the results in FIG. 18, it is considered that the high-frequency substrate 301 can be used at least up to about 70 GHz in many applications. Therefore, it is considered that the high-frequency substrate 301 has excellent energy loss characteristics at least in a high-frequency region of 55 GHz or more and 70 GHz or less. In addition, it can be assumed that such a high frequency region is used particularly in an optical module (optical package).

FIG. 19 is a graph showing a simulation result of the passage characteristic. The high frequency substrate 301B has inferior transmission characteristics over a wide range from 40 GHz to 60 GHz as compared with the high frequency substrate 301A having no concave portion. This reason is considered to be due to the above-mentioned sudden change in the characteristic impedance. The high-frequency substrate 301C has a transmission characteristic similar to that of the high-frequency substrate 301A having no concave portion. Therefore, it can be seen that the concave portion RC3 of the high-frequency substrate 301C does not have the effect of widening the signal pass band from the viewpoint of the pass characteristics. The high-frequency substrate 301 has excellent transmission characteristics at a high frequency, particularly at a frequency of 60 GHz or higher, as compared with other wiring substrates. This is a result corresponding to the small energy loss (FIG. 18).

(Summary of effects)
In the signal transmission using the differential lines CA and CB (FIG. 4), as can be seen from the simulation results particularly shown in FIG. 18, the energy in the high frequency region is provided by the high frequency substrate 301 provided with the concave portions RC1 and RC2. Loss can be significantly suppressed. As a result, good pass characteristics (see FIG. 19) can be obtained.

Referring to FIG. 10, even in high-frequency substrate 301 </ b> A in which no concave portion is provided, first pad pair 61 and second pad pair 61 are formed by combining first inner layer ground pattern 31 and second inner layer ground pattern 32. The local decrease in the characteristic impedance due to the presence of the two pad pairs 62 can be suppressed to some extent. If the local decrease in the characteristic impedance, that is, the deviation from the design value of 100Ω, is sufficiently suppressed only depending on the optimization of this configuration, the width of the pad becomes larger than the width of the wiring path. The depth D2 must be increased accordingly. In other words, the distance between the second inner layer ground pattern 32 and each of the first pad pair 61 and the second pad pair 62 (not shown in FIG. 8) must be correspondingly large. In this case, as an electromagnetic phenomenon, a transverse electromagnetic field corresponding to a signal that normally propagates between the first pad 61a and the first pad 61b (and between the second pad 62a and the second pad 62b). A wave (TEM wave: Transverse @ Electromagnetic @ Wave) is easily converted to a surface wave. As a result of the increase in the conversion, the propagation loss due to the emission of the surface wave increases. According to the present embodiment, concave portions RC1 and RC2 have an effect of suppressing a local decrease in characteristic impedance (see FIG. 15). Thus, it is not necessary to increase the depth D2 excessively. Therefore, the energy loss due to the emission of the surface wave in the high frequency region can be significantly suppressed.

In the differential line, when the phase difference between the signal transmitted through the first wiring path and the signal transmitted through the second wiring path deviates from a predetermined phase difference (opposite phase), the impedance deviates from a design value. There is a risk. Therefore, it is preferable that the configuration of the surface wiring of the wiring board be as symmetrical as possible. For example, in FIG. 7, the concave portion RC1 (first concave portion) and the concave portion RC2 (second concave portion), the first pad 61a and the second pad 62a, the first pad 61b and the second pad 62b, and the first wiring The path 51 and the second wiring path 52 and the first ground pattern 41 and the second ground pattern 42 preferably have the same dimensions (including the depth of the concave portion and the thickness of the wiring path and the like). These are preferably arranged symmetrically with respect to the center line of the third ground pattern 43 (if shown in FIG. 7, the center line extending in the horizontal direction). The capacitors 90 mounted on the first pad pair 61 and the second pad pair 62 also preferably have the above-mentioned symmetry. This is the same for the differential lines in other comparative examples and modified examples.

(First Modification)
The ceramic base 10 may have a recess RC3 (FIG. 13) in addition to the recesses RC1 and RC2 (FIG. 7). Due to the design, there is an upper limit to the depth of the concave portions RC1 and RC2. Specifically, the depths of the concave portions RC1 and RC2 must be smaller than the depth D2 (FIG. 8). Due to this, there is a case where the local decrease in the characteristic impedance in the vicinity of the first pad pair 61 and the second pad pair 62 cannot be sufficiently suppressed. In such a case, by providing the concave portion RC3, it is possible to sufficiently suppress the local decrease in the characteristic impedance. Thereby, the energy loss in the high frequency region can be further suppressed. The length of the recess RC3 is preferably equal to or longer than the length LP of the first pad pair 61 (FIG. 20). Further, it is preferable that the depth of the recess RC3 is smaller than the depth of each of the recesses RC1 and RC2. Thereby, it is possible to suppress the local loss of the characteristic impedance while suppressing the energy loss due to the crosstalk in the high frequency region caused by providing the concave portion RC3.

(Second Modification)
The ceramic base 10 may have concave portions RC4 and RC5 (FIG. 11) in addition to the concave portions RC1 and RC2 (FIG. 7).

By providing the concave portions RC4 and RC5, a bonding material (typical) is provided between the first pad 61a and the first pad 61b (and between the second pad 62a and the second pad 62b) when the capacitor 90 is mounted. Is unintentionally formed between the first pad 61a and the first pad 61b (and between the second pad 62a and the second pad 62b). Thus, an electrical short circuit between the first pad 61a and the first pad 61b (and between the second pad 62a and the second pad 62b) can be prevented. In the width direction of the first wiring path 51 (and the second wiring path 52), the width of the concave portion RC4 (and RC5) is preferably equal to or larger than the width of the first pad 61a (and the second pad 62a). As a result, an electrical short circuit can be reliably prevented.

The depth of each of the recesses RC4 and RC5 is preferably smaller than the depth of each of the recesses RC1 and RC2, and is between the first pad 61a and the first pad 61b (and between the second pad 62a and the second pad 62b). ) Is sufficient to prevent an electrical short circuit. Thus, unnecessary abrupt changes in the characteristic impedance caused by the concave portions RC4 and RC5 can be avoided.

Note that the first and second modifications may be combined. That is, the ceramic base 10 may have the concave portions RC3 to RC5 in addition to the concave portions RC1 and RC2 (FIG. 7).

(Third Modification)
FIG. 20 is a partial top view showing a high-frequency board 301v (wiring board) of the third modification. In the high-frequency substrate 301v, the length LR of the recess RC1 is longer than the length LP of the first pad pair 61. Similarly, the length of the recess RC2 is longer than the length of the second pad pair 62. If the length LR is too large, the area where the first ground pattern 41 is provided is reduced. Therefore, in an actual design, the upper limit of the length LR is up to about 1.5 times the length LP of the first pad pair 61. Become. The same applies to the length of the recess RC2.

The length LP of the first pad pair 61 is the total dimension of the first pad pair 61 in the direction in which the first pad 61a and the first pad 61b face each other (the horizontal direction in FIG. 20). The length LR of the recess RC1 is the dimension of the recess RC1 in the above direction. The same applies to the length of the second pad pair 62 and the length of the recess RC2.

According to the present modification, the concave portions RC1 and RC2 can be reliably arranged in a sufficient range near the first pad pair 61 and the second pad pair 62. This makes it possible to more reliably obtain the effects of the concave portions RC1 and RC2 described above.

(Fourth modification)
FIG. 21 is a partial top view illustrating a high-frequency board 301w (wiring board) according to a fourth modification. In the high-frequency substrate 301w, the first pad pair 61 has a shape characterized by a minimum length LP1 and a maximum length LP2. Within the minimum length LP1, the first pad pair 61 has a substantially constant width. Outside this range, the first pad pair 61 has a tapered shape.

において In this modification, the minimum length LP1 is regarded as the length of the first pad pair. In this modification as well as the third modification, the length LR of the concave portion RC1 is equal to or longer than the length of the first pad pair 61, that is, the minimum length LP1. If the length LR is too large, the area in which the first ground pattern 41 is provided is reduced. Therefore, the length LR may be set to be equal to or less than the maximum length LP2 of the first pad pair 61. The length of the recess RC2 is also defined in the same manner as the length LR of the recess RC1.

<Embodiment 2>
FIG. 22 is a top view schematically showing a configuration of high-frequency package 502 according to the second embodiment. The high-frequency package 502 has a high-frequency board 302 (wiring board) instead of the high-frequency board 301 (FIG. 1: Embodiment 1). The high-frequency board 302 is different from the high-frequency board 301 and is entirely mounted in the cavity CV of the casing 530. The high-frequency board 302 may be used as a mounting area for mounting part or all of the internal circuit 750 (FIG. 1). In that case, part or all of the mounting area 550 may be omitted.

において In the present embodiment, casing 530 has external terminals 91 to 94 arranged outside cavity CV. Each of the external terminals 91 to 94 is electrically connected to the external terminals 81 to 84 of the high-frequency board 302. The specific configuration of the external terminals 91 to 94 is arbitrary, and for example, a metal pin penetrating the frame portion 532 is used.

Since the configuration other than the above is substantially the same as the configuration of the above-described first embodiment, the same or corresponding elements are denoted by the same reference characters, and description thereof will not be repeated.

高周波 Unlike the high-frequency board 301 (FIG. 1: Embodiment 1), the high-frequency board 302 of the present embodiment does not constitute external terminals of a package. Except for this point, almost the same effects as in the first embodiment can be obtained in the present embodiment.

Although the present invention has been described in detail, the above description is illustrative in all aspects, and the present invention is not limited thereto. It is understood that innumerable modifications that are not illustrated can be assumed without departing from the scope of the present invention.

CA, CB Differential line RC1 to RC5 First to fifth concave portions CV cavity TH Through hole OP Opening WR Wiring WRB Internal wiring WRS Surface wiring 10

Ceramic base

31, 32 First and second inner layer ground patterns 41 to 43 First to

third ground patterns

51, 52 First and second wiring paths 61

First pad pair

61a, 61b First pad 62

Second pad pair

62a, 62b Second pad 71-74 Internal terminal 81- 84 external terminal 90

capacitor

301, 301A to 301C, 301v, 301w, 302 high frequency substrate (wiring substrate)
501, 502 High-frequency package 530 Casing 531 Bottom 532 Frame 535 Opening 550 Mounting area 701 High-frequency module 730 Cover 750 Internal circuit 751 IC (integrated circuit)
752 Optical parts

Claims

A ceramic substrate;
A first ground pattern provided on the ceramic base;
A first wiring path which is provided on the ceramic base, is disposed apart from the first ground pattern, and has a portion extending in one direction on the ceramic base;
A second portion provided on the ceramic base, having a portion on the ceramic base separated from the first ground pattern by the first wiring path and extending in the one direction alongside the first wiring path; Wiring route,
A second ground pattern provided on the ceramic base, separated from the first wiring path by the second wiring path on the ceramic base, and separated from the second wiring path on the ceramic base; ,
A first pad pair for mounting a capacitor, provided in the middle of the first wiring path and having a width larger than the width of the first wiring path;
A second pad pair for mounting a capacitor, provided in the middle of the second wiring path and having a width larger than the width of the second wiring path;
With
The first pad pair includes a pair of first pads facing in the one direction, the second pad pair includes a pair of second pads facing in the one direction, The one pad pair and the second pad pair are opposed in a direction orthogonal to the one direction,
The ceramic base is provided between a first concave portion provided between the first ground pattern and the first pad pair, and is provided between the second ground pattern and the second pad pair. A second concave portion,
Wiring board.
A portion provided inside the ceramic base, facing the first wiring path and the second wiring path in a thickness direction, and having an opening below the first pad pair and the second pad pair; A first inner-layer ground pattern having a portion;
The first inner layer ground pattern is provided deeper inside the ceramic base than the first inner layer ground pattern, and is opposed to the first pad pair and the second pad pair via the opening of the first inner layer ground pattern. A second inner layer ground pattern having a portion
The wiring board according to claim 1, further comprising:
3. The wiring board according to claim 1, further comprising: a capacitor mounted on the first pad pair; and a capacitor mounted on the second pad pair. 4.
The length of the said 1st recessed part is more than the length of the said 1st pad pair, The length of the said 2nd recessed part is more than the length of the said 2nd pad pair. The wiring board according to claim 1.
The wiring substrate according to claim 1, wherein the ceramic base has a third recess provided between the first pad pair and the second pad pair. .
6. The wiring board according to claim 5, wherein the depth of the third recess is smaller than the depth of each of the first recess and the second recess. 7.
7. The ceramic substrate according to claim 1, wherein the ceramic base has a fourth recess provided between the first pads and a fifth recess provided between the second pads. The wiring board according to the item.
8. The wiring board according to claim 7, wherein a depth of each of the fourth recess and the fifth recess is smaller than a depth of each of the first recess and the second recess.
A wiring board according to any one of claims 1 to 8,
A casing having a cavity;
With
At least a part of the wiring board is located inside the cavity,
package.
The package according to claim 9, wherein the wiring board has a portion located outside the cavity.
A package according to claim 9 or 10,
A lid for sealing the cavity of the package;
An integrated circuit mounted in the cavity;
With
The first wiring path and the second wiring path form a differential line electrically connected to the integrated circuit.
module.
The module according to claim 11, wherein the integrated circuit has an operating frequency of 55 GHz or more.