Printed circuit board and printed circuit board assembly

Abstract

To provide a printed board that can suppress more effectively the deterioration in signal waveform in a conductive junction part and its peripheral structure.SOLUTION: A printed board includes a first wiring layer including a first terminal and a first signal wire connected to the first terminal, a second wiring layer including a second terminal for conductive junction, which faces the first terminal, a first dielectric layer existing between the first wiring layer and the second wiring layer and having an edge extending in a direction intersecting with a first direction and a thickness direction, and a plurality of veers provided along the first direction between the first terminal and the second terminal and electrically connecting the first terminal and the second terminal. The first veers include a first veer closest to one end of the first terminal on the edge side, and a second veer closest to one end of the second terminal on the side opposite to the edge. The first veer is a half veer provided so that the inside of the first veer is exposed to the outside on the edge. The distance between the second veer and one end on the opposite side of the edge of the second terminal is less than or equal to 1 / 8 of the signal wavelength.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to printed circuit boards and printed circuit board assemblies. [Background technology]

[0002] Patent Document 1 discloses a technique related to a flexible wiring board. This flexible wiring board includes a first wiring layer including at least one signal wiring, a second wiring layer including a ground conductor pattern, and a terminal electrically connected to the signal wiring and for electrically connecting to an external conductive element. The signal wiring includes a transmission line portion disposed along the ground conductor pattern, and a wiring portion connecting the transmission line portion and the terminal to each other. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2010-212617 A Summary of the Invention [Problem to be solved by the invention]

[0004] A configuration is known in which a terminal of a printed circuit board, such as a flexible wiring board, and a terminal of a connected body, such as a package of an optical communication module, are conductively connected to each other. When the printed circuit board and the connected body have signal wiring for transmitting high-frequency signals, the terminals connected to the signal wiring are conductively connected to each other to connect the signal wirings to each other. Then, impedance matching is performed at the conductive joint and its surrounding structure to suppress deterioration of the signal waveform. However, when transmitting a signal of an extremely high frequency, for example, exceeding 30 GHz, impedance matching alone may not be sufficient to suppress deterioration of the signal waveform. The present disclosure aims to provide a printed circuit board and a printed circuit board assembly that can more effectively suppress deterioration of the signal waveform at the conductive joint and its surrounding structure. [Means for solving the problem]

[0005] The printed circuit board of the present disclosure has a connection part at an end in a first direction and is for transmitting a high-frequency signal. The printed circuit board includes a first wiring layer having a first terminal provided at the connection part and a first signal wiring connected to the first terminal, a second wiring layer having a second terminal for conductive bonding facing the first terminal in a thickness direction of the printed circuit board intersecting with the first direction, a first dielectric layer interposed between the first wiring layer and the second wiring layer and having an edge extending at an end in a direction intersecting with the first direction and the thickness direction, and a plurality of vias provided between the first terminal and the second terminal along the first direction and electrically connecting the first terminal and the second terminal. The plurality of vias include a first via closest to one end on the edge side of the first terminal in the first direction and a second via closest to one end opposite the edge of the second terminal in the first direction. The distance between the first via and one end on the edge side of the first terminal is 1 / 8 or less of the signal wavelength of the high-frequency signal at the first terminal. Alternatively, the first via is a half via provided such that the inside of the first via is exposed to the outside at the edge. The distance between the second via and one end of the second terminal opposite to the edge is 1 / 8 or less of the signal wavelength of the high frequency signal at the second terminal. Effect of the Invention

[0006] According to the present disclosure, it is possible to provide a printed circuit board and a printed circuit board assembly that can more effectively suppress degradation of signal waveforms in conductive joints and their surrounding structures. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a plan view showing the external appearance of a flexible wiring board as a printed circuit board according to an embodiment of the present disclosure, as viewed from the front side. [Diagram 2] FIG. 2 is a bottom view showing the appearance of the flexible wiring board as seen from the back side. [Diagram 3] FIG. 3 is an enlarged cutaway perspective view showing a part of the flexible wiring board. [Figure 4] FIG. 4 is a perspective view showing the appearance of an optical module to which the flexible wiring board is to be joined. [Diagram 5] FIG. 5 is a plan view of the optical module. [Figure 6] FIG. 6 is a perspective view showing a state in which the flexible wiring board is joined to a package. [Figure 7] FIG. 7 is a side view showing the same state. [Figure 8] FIG. 8 is an enlarged perspective view of a part of FIG. [Figure 9] FIG. 9 is an enlarged perspective view showing, as a comparative example, a configuration in which the via farthest from the edge of the dielectric substrate is omitted from the multiple vias between the signal terminals shown in FIGS. 3 and 8. In FIG. [Figure 10] FIG. 10 is a graph showing a simulation result of the relationship between the signal frequency and the differential transmission characteristic Sdd21 in the configuration of the embodiment shown in FIG. 8 and the configuration of the comparative example shown in FIG. [Figure 11] FIG. 11 is a diagram showing a model used in the simulation. [Figure 12] FIG. 12 is a perspective view showing a model in which the distance in the X direction between the via farthest from the edge of the dielectric substrate and one end of the signal terminal is the shortest in the simulation. [Figure 13] FIG. 13 is a perspective view showing a model in which the distance in the X direction between the via farthest from the edge of the dielectric substrate and one end of the signal terminal is the greatest in the simulation. [Figure 14] FIG. 14 is a graph showing the results of the simulation. [Figure 15] FIG. 15 is a diagram showing a circuit model used in the simulation. [Figure 16] FIG. 16 is a graph showing the results of a simulation using the circuit model of FIG. [Figure 17] FIG. 17 is a cross-sectional view showing a configuration of a printed board assembly according to a first modified example. [Figure 18]FIG. 18 is a cross-sectional view showing a configuration of a printed board assembly according to a second modified example. [Figure 19] FIG. 19 is a partially enlarged perspective view of a printed board assembly according to a third modified example. [Figure 20] FIG. 20 is a partial side view of a printed board assembly according to a third modified example. [Figure 21] FIG. 21 is a partially enlarged perspective view of a flexible wiring board according to a fourth modified example. [Figure 22] FIG. 22 is a partially enlarged perspective view of a flexible wiring board according to a fifth modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] [Description of the embodiments of the present disclosure] First, the embodiments of the present disclosure will be listed and described. A printed circuit board according to one embodiment has a connection portion at an end in a first direction and is for transmitting a high-frequency signal. The printed circuit board includes a first wiring layer having a first terminal provided at the connection portion and a first signal wiring connected to the first terminal, a second wiring layer having a second terminal for conductive bonding facing the first terminal in a thickness direction of the printed circuit board intersecting with the first direction, a first dielectric layer interposed between the first wiring layer and the second wiring layer and having an edge extending at an end in a direction intersecting with the first direction and the thickness direction, and a plurality of vias provided between the first terminal and the second terminal along the first direction and electrically connecting the first terminal and the second terminal. The plurality of vias include a first via closest to one end on the edge side of the first terminal in the first direction and a second via closest to one end opposite the edge of the second terminal in the first direction. The distance between the first via and one end on the edge side of the first terminal is 1 / 8 or less of the signal wavelength of the high-frequency signal at the first terminal. Alternatively, the first via is a half via provided such that the inside of the first via is exposed to the outside at the edge. The distance between the second via and one end of the second terminal opposite to the edge is 1 / 8 or less of the signal wavelength of the high frequency signal at the second terminal.

[0009] For example, when transmitting a high-frequency signal such as 30 GHz, if an open stub with a length of 1 / 4 or less of the signal wavelength is present in the middle of the signal transmission path, the open stub appears capacitive, and the reflection of the high-frequency signal at the open stub increases, degrading the signal waveform of the high-frequency signal. In the above-mentioned printed circuit board, one end of the first terminal protruding from the position of the first via toward the edge of the first dielectric layer and one end of the second terminal protruding from the position of the second via toward the opposite side of the edge act as open stubs for the high-frequency signal propagating through the first signal wiring. According to the inventor's simulation, when the length of this open stub is 1 / 8 or less of the signal wavelength, degradation of the signal waveform of the high-frequency signal is effectively suppressed. That is, as in the above-mentioned printed circuit board, the distance between one end of the first terminal in the first direction that is on the edge side of the first dielectric layer and the first via is 1 / 8 of the signal wavelength or the first via is a half via provided at the edge of the first dielectric layer, and the distance between one end of the second terminal in the first direction that is on the opposite side to the edge of the first dielectric layer and the second via is 1 / 8 of the signal wavelength or less, thereby effectively suppressing degradation of the signal waveform of the high-frequency signal.

[0010] In the above-mentioned printed circuit board, the signal wavelength of the high frequency signal at the first terminal and the signal wavelength of the high frequency signal at the second terminal may be determined for a high frequency signal having a frequency of 30 GHz or more. When the signals supplied to the first terminal and the second terminal are such high frequency signals, the above-mentioned printed circuit board is particularly useful.

[0011] In the printed circuit board, the distance between the first via and one end of the first terminal may be 1 / 16 or less of the signal wavelength of the high frequency signal at the first terminal, in which case deterioration of the signal waveform of the high frequency signal is more effectively suppressed.

[0012] In the printed circuit board, the distance between the second via and one end of the second terminal may be 1 / 16 or less of the signal wavelength of the high frequency signal at the second terminal, thereby more effectively suppressing deterioration of the signal waveform of the high frequency signal.

[0013] In the above printed circuit board, the first dielectric layer may be a flexible resin film.

[0014] A printed circuit board assembly according to one embodiment includes any one of the printed circuit boards described above, and a bonded body having a third wiring layer including a third terminal conductively bonded to the second terminal. When the third terminal is conductively bonded to the second terminal, the distance between one end of the third terminal opposite the edge of the first dielectric layer and the second via in the first direction is 1 / 8 or less of the signal wavelength of the high-frequency signal at the third terminal. This printed circuit board assembly includes any one of the printed circuit boards described above, so that deterioration of the signal waveform of the high-frequency signal can be suppressed. In addition, since the distance between one end of the third terminal opposite the edge of the first dielectric layer and the second via is 1 / 8 or less of the signal wavelength, an open stub generated by the third terminal can be made smaller, so that deterioration of the signal waveform of the high-frequency signal can be further suppressed.

[0015] In the above-mentioned printed circuit board assembly, the signal wavelength of the high frequency signal at the third terminal may be determined for a high frequency signal having a frequency of 30 GHz or more. When the signal supplied to the third terminal is such a high frequency signal, the above-mentioned printed circuit board is particularly useful.

[0016] In the above printed circuit board assembly, the joined object may further include a positioning portion for positioning the printed circuit board and the joined object in the first direction. In this case, the second via and the third terminal can be positioned relative to each other in the first direction with high accuracy. This makes it possible to prevent an open stub due to the third terminal from becoming large due to an assembly error.

[0017] In the above printed circuit board assembly, the positioning portion may abut against the edge. In this case, the positioning of the printed circuit board and the joined object in the first direction can be easily performed with a simple configuration. In this case, when the positioning portion abuts against the edge, a position of one end of the second terminal opposite to the edge in the first direction may be equal to a position of one end of the third terminal opposite to the edge.

[0018] In the above-mentioned printed circuit board assembly, the joined object may be a package that houses at least one of a light receiving element and a light emitting element of an optical module having at least one of the elements. In this case, it is possible to provide an optical module that can effectively suppress deterioration of the signal waveforms of the high frequency signal output from the light receiving element or the high frequency signal input to the light emitting element.

[0019] In the above printed circuit board assembly, the joined object may include a fourth wiring layer including a second signal wiring facing the third terminal in the thickness direction of the printed circuit board, a second dielectric layer interposed between the third wiring layer and the fourth wiring layer, and a plurality of third vias provided along the first direction between the third terminal and the second signal wiring and electrically connecting the third terminal and the second signal wiring. The distance in the first direction between one end of the second signal wiring on the printed circuit board side and a third via that is closest to one end of the second signal wiring among the plurality of third vias between the third terminal and the second signal wiring may be ⅛ or less of the signal wavelength of the high frequency signal in the second signal wiring. In this case, the open stub generated in the second signal wiring can be made small, and deterioration of the signal waveform of the high frequency signal can be further suppressed.

[0020] [Details of the embodiment of the present disclosure] Specific examples of the printed circuit board and printed circuit board assembly of the present disclosure will be described below with reference to the drawings. Note that the present invention is not limited to these examples, but is indicated by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims. In the following description, the same elements in the description of the drawings are given the same reference numerals, and duplicated descriptions are omitted. In each drawing, an XYZ Cartesian coordinate system is shown as necessary for the purpose of explanation.

[0021] FIG. 1 is a plan view showing the appearance of a flexible wiring board (FPC) 3A as a printed circuit board according to an embodiment of the present disclosure, as viewed from the front side. FIG. 2 is a bottom view showing the appearance of the flexible wiring board 3A as viewed from the back side. FIG. 3 is a cutaway perspective view showing an enlarged portion of the flexible wiring board 3A. The flexible wiring board 3A of this embodiment is a thin plate-like member with the X direction (first direction) as the longitudinal direction and the Y direction perpendicular to the X direction as the transverse direction. In one example, the planar shape of the flexible wiring board 3A is rectangular. The flexible wiring board 3A has a connection portion 30 at an end in the X direction. The connection portion 30 is a portion for electrically connecting a bonded body described later and the flexible wiring board 3A. The connection portion 30 is provided at an end of the flexible wiring board 3A, from one end to the other end of the flexible wiring board 3A in the Y direction. Note that the figure shows the connection portion 30 provided at one end of the flexible wiring board 3A, but a connection portion having a similar structure may also be provided at the other end of the flexible wiring board 3A.

[0022] The flexible wiring board 3A includes a dielectric layer 31, a first wiring layer 32 and a protective film 34 (both see FIG. 1), a second wiring layer 35 and a protective film 36 (both see FIG. 2), and a plurality of vias (also called through holes or via holes) 33.

[0023] The dielectric layer 31 is interposed between the first wiring layer 32 and the second wiring layer 35. The dielectric layer 31 extends along the XY plane and is a flexible resin film made of a resin material such as polyimide, liquid crystal polymer (LCP), or fluorine-based resin. The thickness of the dielectric layer 31 in the Z direction is, for example, 0.05 mm. The dielectric layer 31 has a flat first surface 31a and a flat second surface 31b facing away from the first surface 31a. The first surface 31a is parallel to the second surface 31b. The planar shape of the dielectric layer 31 is a rectangle with the X direction as the longitudinal direction, and has an edge 31c in the X direction. The edge 31c is included in an end (connection portion 30) of the flexible wiring board 3A. The edge 31c extends along a direction intersecting the X direction, which is the longitudinal direction of the flexible wiring board 3A, for example, along the Y direction.

[0024] The first wiring layer 32 is a wiring layer including a conductive film provided on the first surface 31a of the dielectric layer 31. The first wiring layer 32 has signal terminals 32a and 32b which are conductive films, a ground terminal 32c which is a conductive film, and signal wires 32d and 32e which are conductive films. These conductive films are metal films such as copper plating. The signal terminals 32a and 32b correspond to the first terminals in the present disclosure. The planar shape of the signal terminals 32a and 32b is a rectangle with the X direction as the longitudinal direction. The signal wires 32d and 32e correspond to the first signal wires in the present disclosure.

[0025] The signal terminals 32a, 32b and the ground terminal 32c are arranged in line in the Y direction in the connection part 30. Specifically, a plurality of ground terminals 32c are arranged in line in the Y direction. A set of signal terminals 32a, 32b arranged adjacent to each other in the Y direction is arranged between these ground terminals 32c. In other words, the ground terminals 32c and the sets of signal terminals 32a, 32b are arranged alternately along the Y direction. The signal wirings 32d, 32e extend along the X direction from one end to the other end of the flexible wiring board 3A. One end of the signal wiring 32d is connected to the signal terminal 32a, and one end of the signal wiring 32e is connected to the signal terminal 32b. The length of the signal wirings 32d, 32e in the X direction is greater than the length of the signal terminals 32a, 32b in the same direction. The width of the signal wirings 32d, 32e in the Y direction is smaller than the width of the signal terminals 32a, 32b in the same direction.

[0026] A high-frequency differential signal is supplied to the signal wirings 32d, 32e. The frequency of the signal supplied to the signal wirings 32d, 32e is, for example, 30 GHz or more, or 50 GHz or more. The signal wirings 32d, 32e form a microstrip line together with a ground wiring 35d, which will be described later. The signal wirings 32d, 32e are covered with a protective film 34. The protective film 34 is an insulating film provided over the entire surface of the first surface 31a except for the connection portion 30. The protective film 34 mainly contains a resin material, for example, a solder resist or a coverlay.

[0027] The second wiring layer 35 is a wiring layer including a conductive film provided on the second surface 31b of the dielectric layer 31. The second wiring layer 35 has signal terminals 35a and 35b which are conductive films, a ground terminal 35c which is a conductive film, and a ground wiring 35d which is a conductive film. These conductive films are metal films such as copper plating. The signal terminals 35a and 35b are terminals for conductive bonding with a bonded body described later, and correspond to the second terminals in the present disclosure. The planar shape of the signal terminals 35a and 35b is a rectangle with the X direction as the longitudinal direction.

[0028] The signal terminals 35a, 35b and the ground terminal 35c are arranged in line in the Y direction in the connection portion 30. The specific aspect is the same as the signal terminals 32a, 32b and the ground terminal 32c of the first wiring layer 32. The signal terminals 35a, 35b face the signal terminals 32a, 32b, respectively, with the dielectric layer 31 interposed therebetween in the thickness direction (Z direction) of the flexible wiring board 3A. The ground terminal 35c is arranged at a position facing the ground terminal 32c with the dielectric layer 31 interposed therebetween. The ground wiring 35d extends from one end to the other end of the flexible wiring board 3A in the X direction, except for the connection portion 30. One end of the ground wiring 35d is connected to the ground terminal 35c. The width of the ground wiring 35d in the Y direction is approximately equal to the width of the dielectric layer 31 in the same direction.

[0029] The ground wiring 35d is covered with a protective film 36. The protective film 36 is an insulating film provided over the entire second surface 31b except for the connection portion 30. As a constituent material of the protective film 36, for example, those exemplified as the constituent material of the protective film 34 are used.

[0030] The vias 33 are conductive wirings extending from the first surface 31a to the second surface 31b of the dielectric layer 31. Some of the vias 33 are provided between the signal terminals 32a and 35a, and electrically connect the signal terminals 32a and 35a. At least two vias 33 are provided side by side in the X direction between each of the signal terminals 32a and 35a. Other vias 33 are provided between the signal terminals 32b and 35b, and electrically connect the signal terminals 32b and 35b. At least two vias 33 are provided side by side in the X direction between each of the signal terminals 32b and 35b. The remaining vias 33 are provided between the ground terminals 32c and 35c, and electrically connect the ground terminals 32c and 35c. At least one via 33 is provided between each of the ground terminals 32c and 35c.

[0031] The multiple vias 33 include multiple vias 33a and multiple half vias 33b. The vias 33a are arranged away from the edge 31c of the dielectric layer 31 in the X direction. The vias 33a are metal films formed in holes penetrating the dielectric layer 31 from the first surface 31a to the second surface 31b. The half vias 33b are provided on the edge 31c of the dielectric layer 31. The half vias 33b are metal films formed in grooves formed on the edge 31c. The half vias 33b are the vias closest to the edge 31c among the multiple vias 33 between each signal terminal 32a (32b) and each signal terminal 35a (35b), and correspond to the first vias in this disclosure.

[0032] In the illustrated example, two vias 33a and one half via 33b are arranged side by side in the X direction between the signal terminal 32a and the signal terminal 35a. Similarly, two vias 33a and one half via 33b are arranged side by side in the X direction between the signal terminal 32b and the signal terminal 35b. Three vias 33a and one half via 33b are arranged side by side in the X direction between the ground terminal 32c and the ground terminal 35c. In this way, the number of vias 33 between the ground terminal 32c and the ground terminal 35c may be greater than the number of vias 33 between the signal terminal 32a and the signal terminal 35a and between the signal terminal 32b and the signal terminal 35b.

[0033] As shown in FIG. 3, one end 35aa of the signal terminal 35a opposite to the edge 31c in the X direction is separated from the via 33a (second via) closest to the one end 35aa of the signal terminal 35a among the vias 33 between each signal terminal 32a and each signal terminal 35a by a distance Da1. The one end 35aa is the end of the signal terminal 35a farthest from the edge 31c in the X direction. In one example, the one end 35aa is one end in the X direction of a circular land pattern around a hole required for forming the via 33a. The distance between the via 33a and the one end 35aa specifically refers to the distance between the part of the via 33a closest to the one end 35aa and the one end 35aa. The magnitude of the distance Da1 is 1 / 8 or less, more preferably 1 / 16 or less, of the signal wavelength of the high-frequency signal propagating through the signal terminal 35a. The signal terminal 35b has a configuration similar to that of the signal terminal 35a described above.

[0034] FIG. 4 is a perspective view showing the appearance of the optical module 1A to which the flexible wiring board 3A is joined. FIG. 5 is a plan view of the optical module 1A. The optical module 1A includes at least one of a light receiving element and a light emitting element for optical communication. The light receiving element is, for example, a photodiode, and converts a high-frequency optical signal input from the outside into an electrical receiving signal and outputs the signal. The light emitting element is, for example, a laser diode, and converts a high-frequency electrical transmitting signal input from the outside into an optical signal and outputs the signal. When the optical module 1A includes a light receiving element, the optical module 1A is used as an optical receiving module. When the optical module 1A includes a light emitting element, the optical module 1A is used as an optical transmitting module. When the optical module 1A includes both a light receiving element and a light emitting element, the optical module 1A is used as an optical transmitting module.

[0035] The optical module 1A has a package 10A as a bonded body to be bonded to the flexible wiring board 3A. The package 10A accommodates a light receiving element and a light emitting element provided in the optical module 1A, and an electronic circuit connected to the light receiving element and the light emitting element. The package 10A has a rectangular parallelepiped shape and includes a bottom plate 11, a rectangular frame-shaped side wall 12 provided on the bottom plate 11, and a top plate 13 provided on the side wall 12. The bottom plate 11, the side wall 12, and the top plate 13 form an internal space of the package 10A. The side wall 12 has a front surface 12a and a back surface 12b that face each other in the X direction and extend along a plane intersecting the X direction, and side surfaces 12c and 12d that face each other in the Y direction and extend along a plane intersecting the Y direction. The side surface 12c connects the front surface 12a and the back surface 12b on one side in the Y direction. The side surface 12d connects the front surface 12a and the rear surface 12b on the other side in the Y direction.

[0036] The package 10A further includes a feedthrough 20. The feedthrough 20 is a plate-shaped member provided at the front end of the package 10A in the X direction. The feedthrough 20 is disposed so as to cover an opening provided in the side wall 12, and penetrates between the inner space and the outer space of the package 10A. The feedthrough 20 includes a plate-shaped dielectric member 22 and a wiring layer 27. The dielectric member 22 is made of a dielectric material such as alumina. The three-dimensional shape of the dielectric member 22 is a rectangular parallelepiped with the Y direction as the longitudinal direction. The dielectric member 22 has a main surface 21 facing upward in the Z direction, side surfaces 23a and 23b located at one end and the other end in the Y direction, respectively, and an end surface 24 facing forward in the X direction.

[0037] The wiring layer 27 is a layer including a conductive film provided on the main surface 21 of the dielectric member 22, and corresponds to the third wiring layer in the present disclosure. The conductive film is a metal film such as an Au film. The wiring layer 27 includes signal terminals 25a, 25b and a ground terminal 26. The signal terminals 25a, 25b correspond to the third terminal in the present disclosure. The signal terminals 25a, 25b and the ground terminal 26 each have a planar shape that is rectangular with the X direction as the longitudinal direction.

[0038] The signal terminals 25a, 25b and the ground terminal 26 are arranged side by side in the Y direction on the main surface 21. Specifically, a plurality of ground terminals 26 are arranged side by side in the Y direction. A set of signal terminals 25a, 25b arranged adjacent to each other in the Y direction is arranged between these ground terminals 26. In other words, the ground terminals 26 and the set of signal terminals 25a, 25b are arranged alternately along the Y direction. The signal terminals 25a, 25b are electrically connected to the electronic circuit in the package 10A through wiring provided in the feedthrough 20. The ground terminal 26 is electrically connected to the ground potential pattern in the package 10A through wiring provided in the feedthrough 20. The arrangement pitch of the signal terminals 25a, 25b and the ground terminal 26 is equal to the arrangement pitch of the signal terminals 32a, 32b and the ground terminal 32c of the flexible wiring board 3A.

[0039] Fig. 6 is a perspective view showing a state in which the flexible wiring board 3A is joined to the package 10A, and Fig. 7 is a side view showing the same state. Fig. 8 is a perspective view showing an enlarged portion of Fig. 6. As shown in these figures, the flexible wiring board 3A and the package 10A are joined to each other to form a printed board assembly 5A.

[0040] In this printed circuit board assembly 5A, the signal terminals 35a, 35b and the ground terminal 35c of the flexible wiring board 3A are conductively joined to the signal terminals 25a, 25b and the ground terminal 26 of the package 10A, respectively, by solder or the like. As shown in FIG. 8, when the signal terminal 25a is conductively joined to the signal terminal 35a, one end 25aa of both ends of the signal terminal 25a in the X direction on the opposite side to the edge 31c (i.e., the end face 24 side) is separated by a distance Db1 from the via 33a (second via) closest to the one end 25aa among the multiple vias 33 between each signal terminal 32a and each signal terminal 35a. The one end 25aa is the front end of the signal terminal 25a. In one example, the position of the one end 25aa in the X direction coincides with the position of the one end 35aa (see FIG. 3) in the same direction. Moreover, the distance between the via 33a and the one end 25aa specifically refers to the distance between the one end 25aa and the part of the via 33a that is closest to the one end 25aa. The signal terminal 25b has a configuration similar to the above-described configuration of the signal terminal 25a.

[0041] The distance Da1 is equal to or less than 1 / 8, and more preferably equal to or less than 1 / 16, of the signal wavelength of the high frequency signal propagating through the signal terminal 32a. The distance Db1 is equal to or less than 1 / 8, and more preferably equal to or less than 1 / 16, of the signal wavelength of the high frequency signal propagating through the signal terminals 35a and 25a.

[0042] The effects obtained by the flexible wiring board 3A and the printed circuit board assembly 5A of the present embodiment described above will be described. For example, when transmitting a high-frequency signal of 30 GHz or more, if an open stub with a length of 1 / 4 or less of the signal wavelength is present in the middle of the signal transmission path, the open stub appears capacitive. In particular, when the open stub is close to 1 / 4 of the signal wavelength, the reflection of the high-frequency signal at the open stub increases, and the signal waveform of the high-frequency signal deteriorates. In particular, when the dielectric constant of the dielectric member 22 (e.g., alumina) of the feedthrough 20 is large compared to the dielectric constant of the material (e.g., polyimide) of the dielectric layer 31 of the flexible wiring board 3A, the effective dielectric constant of the capacitive open stub becomes larger than that of the flexible wiring board 3A alone. Therefore, deterioration of the signal waveform of the high-frequency signal becomes noticeable. In FIG. 3, the propagation path of the high-frequency signal Sg is indicated by an arrow. 3, in the flexible wiring board 3A of this embodiment, one end of the signal terminals 35a, 35b (one end 35aa in the case of the signal terminal 35a) protruding from the position of the via 33a toward the opposite side to the edge 31c acts as an open stub for the high-frequency signal propagating through the signal wirings 32d, 32e. By shortening the length of the open stub, the frequency at which the effect of the capacitive property of the open stub becomes large can be increased.

[0043] 9 is an enlarged perspective view showing a comparative example in which the via 33a closest to one end 35aa of the signal terminal 35a is omitted from the two vias 33a between the signal terminal 32a and the signal terminal 35a shown in FIGS. 3 and 8. In this case, the distance Da1 between the via 33a closest to the one end 35aa of the signal terminal 35a and the one end 35aa of the signal terminal 35a is greater than the distance Da1 shown in FIG. 3. Also, the distance Db1 between the via 33a closest to the one end 25aa of the signal terminal 25a and the one end 25aa of the signal terminal 25a is greater than the distance Db1 shown in FIG. 8.

[0044] FIG. 10 is a graph showing a simulation result of the relationship between the signal frequency and the differential transmission characteristic Sdd21 in the configuration of this embodiment shown in FIG. 8 and the configuration of the comparative example shown in FIG. 9. In FIG. 10, the vertical axis represents the differential transmission characteristic Sdd21 (unit: dB), and the horizontal axis represents the signal frequency (unit: GHz). Moreover, graph G11 shows the characteristics of the configuration of this embodiment shown in FIG. 8 (distance Db1=60 μm), and graph G12 shows the characteristics of the configuration of the comparative example shown in FIG. 9 (distance Db1=275 μm). Referring to FIG. 10, in the configuration of this embodiment, the differential transmission characteristic Sdd21 gradually decreases as the signal frequency increases, but in the configuration of the comparative example, the degree of decrease in the differential transmission characteristic Sdd21 increases in the band of 30 GHz or more, and further, the differential transmission characteristic Sdd21 rapidly decreases in the band of 50 GHz or more. From this result, it is found that in the band of 30 GHz or more, the distance Da1 between the end 35aa and the via 33a closest to the end 35aa has a large effect on the signal passing characteristics.

[0045] The inventor further performed a simulation using the model shown in FIG. 11 in order to grasp the tendency of the signal passing characteristics depending on the distance Da1 between the one end 35aa and the via 33a closest to the one end 35aa. In this model, a flexible wiring board 3D and a bonded body 5 were connected to each other. The flexible wiring board 3D has one signal wiring 32d and one signal terminal 32a on one surface of the dielectric layer 31, and has one signal terminal 35a on the other surface of the dielectric layer 31, and the signal terminal 32a and the signal terminal 35a are connected by one via 33a and one half via 33b. The bonded body 5 has a wiring 52 extending in the X direction provided on one surface of the dielectric substrate 50. The wiring 52 is conductively bonded to the signal terminal 35a. The position of one end 35aa of the signal terminal 35a in the X direction is aligned with the position of one end of the wiring 52 in the same direction.

[0046] FIG. 12 shows a model in which the distance Da1 between the via 33a and the one end 35aa in the X direction is the smallest in this simulation. In this case, the one end 35aa is one end in the X direction of the annular land pattern around the via 33a. Also, FIG. 13 shows a model in which the distance Da1 is the largest in this simulation. In this simulation, the distance Da1 was set to 60 μm, 160 μm, 260 μm, 360 μm, 460 μm, and 560 μm. The calculation was performed with the relative dielectric constant of the dielectric layer 31 set to 3.2 (i.e., the relative dielectric constant of polyimide) and the relative dielectric constant of the dielectric substrate 50 set to 9.0 (i.e., the relative dielectric constant of alumina). Note that the case where the distance Da1 is 60 μm corresponds to the case where the one end 35aa is one end in the X direction of the annular land pattern around the via 33a.

[0047] In the study using this simulation, calculations are performed assuming that the relative dielectric constant of dielectric layer 31 is 3.2, the relative dielectric constant of dielectric substrate 50 is 9.0, and the effective relative dielectric constant of signal terminal 32a and signal terminal 35a, i.e., connection portion 30, is 6.1.

[0048] The effective dielectric constant of the signal terminals 32a and 35a, i.e., the connection portion 30, may be calculated based on the dielectric constant of the dielectric layer 31 and the dielectric substrate 50. For example, the effective dielectric constant of the signal terminals 32a and 35a, i.e., the connection portion 30, may be calculated as an average of the dielectric constant of the dielectric layer 31 and the dielectric substrate 50. Furthermore, the effective dielectric constant of the connection portion 30 may be calculated in consideration of the shapes of the signal terminals 32a, 35a, the dielectric layer 31 and the dielectric substrate 50 in addition to the dielectric constant of the dielectric layer 31 and the dielectric substrate 50.

[0049] In addition, since the signal terminals 32a and 35a are considered to have the same propagation characteristics when connected to the dielectric substrate 50, the signal wavelength of the high-frequency signal propagating through the signal terminal 32a is approximately equal to the signal wavelength of the high-frequency signal propagating through the signal terminal 35a. In other words, the signal wavelength of the high-frequency signal at the signal terminal 32a is approximately equal to the signal wavelength at the signal terminal 35a.

[0050] For example, if the frequency of the high-frequency signal propagating through the signal terminals 32a and 35a is 50 GHz, the distance Da1 is preferably 304 μm or less, more preferably 152 μm or less. Note that 304 μm corresponds to 1 / 8 of the signal wavelength of the high-frequency signal with a frequency of 50 GHz in the signal terminals 32a and 35a. Also, 152 μm corresponds to 1 / 16 of the signal wavelength of the high-frequency signal with a frequency of 50 GHz in the signal terminals 32a and 35a.

[0051] If the frequency of the high-frequency signal propagating through the signal terminals 32a and 35a is 70 GHz, the distance Da1 is preferably 216 μm, more preferably 108 μm or less. Note that 221 μm corresponds to 1 / 8 of the signal wavelength of the high-frequency signal having a frequency of 70 GHz in the signal terminals 32a and 35a. Furthermore, 110 μm corresponds to 1 / 16 of the signal wavelength of the high-frequency signal having a frequency of 70 GHz in the signal terminals 32a and 35a.

[0052] Fig. 14 is a graph showing the results of this simulation. In Fig. 14, the vertical axis represents the differential transmission characteristic Sdd21 (unit: dB) and the horizontal axis represents the signal frequency (unit: GHz). Graphs G21 to G26 show the cases where the distance Da1 is 60 μm, 160 μm, 260 μm, 360 μm, 460 μm, and 560 μm, respectively.

[0053] Referring to FIG. 14, it can be seen that the smaller the distance Da1, ie, the length of the open stub, the more the degradation of the differential transmission characteristic Sdd21 is suppressed in the signal frequency band of 30 GHz or more, and the better the signal passing characteristic becomes.

[0054] For example, at a frequency of 50 GHz, the graphs G21, G22, and G23, in which the distance Da1 is less than 303 μm, which is 1 / 8 of the signal wavelength, show a significant suppression of the decrease in the differential transmission characteristic Sdd21 compared to the graphs G24, G25, and G26. Also, at a frequency of 70 GHz, the graphs G21 and G22, in which the distance Da1 is less than 216 μm, which is 1 / 8 of the signal wavelength, show a significant suppression of the decrease in the differential transmission characteristic Sdd21 compared to the graphs G23, G24, G25, and G26.

[0055] In this way, in particular, when the distance Da1 is 1 / 8 or less of the signal wavelength, the decrease in the differential transmission characteristic Sdd21 is significantly suppressed compared to when the distance Da1 is greater than 1 / 8 of the signal wavelength. Also, since the decrease in the differential transmission characteristic Sdd21 is further suppressed as the distance Da1 becomes smaller, the decrease in the differential transmission characteristic Sdd21 is more significantly suppressed when the distance Da1 is 1 / 16 or less of the signal wavelength compared to when the distance Da1 is greater than 1 / 16 of the signal wavelength.

[0056] Moreover, in order to examine the relationship between the distance Da1 and the signal wavelength, a simulation was performed on the circuit model of Fig. 15 to examine the transmission characteristic S21. The circuit model of Fig. 15 includes a stub 63 of a predetermined length between two ideal transmission lines 61 and 62. The length of the ideal transmission lines 61 and 62 is set to a value (e.g., 100 µm) that is sufficiently short with respect to the signal wavelength, and the length of the ideal transmission lines 61 and 62 is set to have no effect on the transmission characteristic.

[0057] Fig. 16 is a graph showing the results of a simulation of the circuit model of Fig. 15. In Fig. 16, the vertical axis represents the transmission characteristic S21 (unit: dB) and the horizontal axis represents the value (unit: dimensionless) obtained by dividing the length of stub 63 by the signal wavelength. The graph also shows the case where the length of stub 63 is 300 μm.

[0058] From the results in FIG. 16, when the length of the stub 63 is 1 / 8 or less of the signal wavelength, the loss is −0.5 dB or less. Also, when the length of the stub 63 is 1 / 16 or less of the signal wavelength, the loss is −0.1 dB or less. Therefore, in this embodiment, when the distance Da1 (see FIG. 3) is 1 / 8 or less of the signal wavelength, the loss due to the stub is suppressed. Also, when the distance Da1 (see FIG. 3) is 1 / 16 or less of the signal wavelength, the loss due to the stub is further suppressed.

[0059] From this, it can be seen that in this embodiment, when the distance Da1 (see FIG. 3) is 1 / 8 or less of the signal wavelength, degradation of the signal waveform of the high frequency signal is effectively suppressed. Also, it can be seen that when the distance Da1 is 1 / 16 or less of the signal wavelength, degradation of the signal waveform of the high frequency signal is more effectively suppressed.

[0060] In addition, for the signal terminal 32a of this embodiment, since the via 33 closest to the edge 31c is the half via 33b, the distance between the other end of the signal terminal 32a closest to the edge 31c and the via 33 closest to the other end can be said to be zero. In this case, as is clear from the propagation path of the high-frequency signal shown in Figure 3, no open stub is generated in the signal terminal 32a. Therefore, degradation of the signal waveform of the high-frequency signal due to the open stub does not occur in the signal terminal 32a.

[0061] As described above, the frequency of the signals supplied to the signal wirings 32d and 32e may be 30 GHz or higher, or 50 GHz or higher. When the signals supplied to the signal wirings 32d and 32e are such high-frequency signals, the flexible wiring board 3A of the present embodiment is particularly useful.

[0062] As described above, in a state where the signal terminal 25a is conductively joined to the signal terminal 35a, the distance Db1 between the end 25aa of the signal terminal 25a opposite the edge 31c of the dielectric layer 31 and the via 33a closest to the end 25aa may be ⅛ of the signal wavelength or less. Since the signal terminal 25a is conductively joined to the signal terminal 35a while facing the signal terminal 35a, the portion of the signal terminal 25a protruding from the via 33a also acts as an open stub for the high-frequency signal. Therefore, by making the distance Db1 ⅛ of the signal wavelength or less, the open stub generated by the signal terminal 25a can be made small, and deterioration of the signal waveform of the high-frequency signal can be further suppressed.

[0063] As described above, the object to be joined to the flexible wiring board 3A may be the package 10A that houses at least one of a light receiving element and a light emitting element of the optical module 1A having at least one of the elements. In this case, it is possible to provide the optical module 1A that can effectively suppress deterioration of the signal waveforms of the high frequency signal output from the light receiving element or the high frequency signal input to the light emitting element.

[0064] (First Modification) FIG. 17 is a cross-sectional view showing a configuration of a printed circuit board assembly 5B according to a first modified example of the above embodiment. The printed circuit board assembly 5B of this modified example includes a printed circuit board 4A as a bonded body instead of the optical module 1A of the above embodiment. The printed circuit board 4A has a dielectric substrate 40 and a wiring layer 41. The dielectric substrate 40 is a plate-shaped member having a main surface 40a and a back surface 40b, and mainly contains a dielectric material such as epoxy resin. The thickness direction of the dielectric substrate 40 coincides with the Z direction. The wiring layer 41 is a layer including a metal film provided on the main surface 40a. The wiring layer 41 corresponds to the third wiring layer in this disclosure.

[0065] The wiring layer 41 includes a signal terminal 41a and a signal wiring 41b. The signal terminal 41a extends along the X direction near an end of the dielectric substrate 40 in the X direction. The signal terminal 41a faces the signal terminal 35a of the flexible wiring substrate 3A and is conductively joined to the signal terminal 35a by solder or the like. The signal wiring 41b is connected to the signal terminal 41a and extends on the main surface 40a. The wiring layer 41 further includes a signal terminal (not shown) that faces the signal terminal 35b of the flexible wiring substrate 3A and is conductively joined to the signal terminal 35b by solder or the like, and a signal wiring connected to the signal terminal. The wiring layer 41 further includes a ground terminal (not shown) that faces the ground terminal 35c of the flexible wiring substrate 3A and is conductively joined to the ground terminal 35c by solder or the like, and a ground wiring connected to the ground terminal. The arrangement and shape of these terminals, including the signal terminal 41a, may be similar to the arrangement and shape of the signal terminals 25a, 25b and the ground terminal 26 in the above embodiment.

[0066] In this modification, the distance Db1 in the X direction between one end 41aa of the signal terminal 41a on the flexible wiring board 3A side and the via 33a closest to the one end 41aa is equal to or less than 1 / 8 of the signal wavelength, more preferably equal to or less than 1 / 16 of the signal wavelength. In this case, the open stub caused by the signal terminal 41a is made small, the signal passing characteristics are improved, and deterioration of the signal waveform of the high-frequency signal can be suppressed.

[0067] (Second Modification) FIG. 18 is a cross-sectional view showing a configuration of a printed circuit board assembly 5C according to a second modified example of the embodiment. The printed circuit board assembly 5C of this modified example includes a printed circuit board 4B as a bonded body instead of the optical module 1A of the embodiment. The printed circuit board 4B has a dielectric substrate 40, a wiring layer 41, and a wiring layer 42. The dielectric substrate 40 is a plate-shaped member having a main surface 40a and a back surface 40b, and mainly contains a dielectric material such as epoxy resin. The thickness direction of the dielectric substrate 40 coincides with the Z direction. The wiring layer 41 is a layer including a metal film provided on the main surface 40a. The wiring layer 42 is a layer including a metal film provided inside the dielectric substrate 40, i.e., between the main surface 40a and the back surface 40b. The wiring layer 42 is not limited to this form, and may be provided on the back surface 40b. The dielectric substrate 40 is interposed between the wiring layer 41 and the wiring layer 42. The wiring layer 41 corresponds to the third wiring layer in this disclosure. The wiring layer 42 corresponds to the fourth wiring layer in the present disclosure. The portion of the dielectric substrate 40 located between the wiring layer 41 and the wiring layer 42 corresponds to the second dielectric layer in the present disclosure.

[0068] The wiring layer 41 includes a signal terminal 41a. The signal terminal 41a extends along the X direction near an end of the dielectric substrate 40 in the X direction. The signal terminal 41a faces the signal terminal 35a of the flexible wiring substrate 3A and is conductively joined to the signal terminal 35a by solder or the like. The signal terminal 41a corresponds to a third signal terminal in the present disclosure. The wiring layer 41 further includes a signal terminal (not shown) that faces the signal terminal 35b of the flexible wiring substrate 3A and is conductively joined to the signal terminal 35b by solder or the like. The wiring layer 41 further includes a ground terminal (not shown) that faces the ground terminal 35c of the flexible wiring substrate 3A and is conductively joined to the ground terminal 35c by solder or the like.

[0069] The wiring layer 42 includes a signal wiring 42a. The signal wiring 42a extends in a plane along the main surface 40a inside the dielectric substrate 40. An end of the signal wiring 42a faces the signal terminal 41a in the Z direction across a part of the dielectric substrate 40. The signal wiring 42a corresponds to a second signal wiring in the present disclosure. The wiring layer 42 further includes a signal wiring (not shown) facing the signal terminal of the wiring layer 41 connected to the signal terminal 35b of the flexible wiring substrate 3A, and a ground wiring (not shown) facing the ground terminal of the wiring layer 41 connected to the ground terminal 35c of the flexible wiring substrate 3A.

[0070] The printed circuit board 4B further includes a plurality of vias 43. The plurality of vias 43 are conductive internal wiring extending in the Z direction, and are arranged in the X direction between the signal terminal 41a and the signal wiring 42a, and electrically connect the signal terminal 41a and the signal wiring 42a. A distance Dc1 between an end 42aa of the signal wiring 42a on the flexible wiring board 3A side in the X direction and a via 43 (third via) closest to the end 42aa of the signal wiring 42a among the plurality of vias 43 between the signal terminal 41a and the signal wiring 42a is ⅛ or less of the signal wavelength. In this case, the open stub generated in the signal wiring 42a can be made small, and the deterioration of the signal waveform of the high-frequency signal can be further suppressed. Note that a plurality of vias are also provided between the signal terminal of the wiring layer 41 connected to the signal terminal 35b and the signal terminal of the wiring layer 42 facing the signal terminal. Similarly, a plurality of vias are provided between the ground terminal of the wiring layer 41 connected to the ground terminal 35c and the ground terminal of the wiring layer 42 opposed to the ground terminal.

[0071] (Third Modification) Fig. 19 is a partially enlarged perspective view of a printed board assembly 5D according to a third modified example of the above embodiment. Fig. 20 is a partial side view of the printed board assembly 5D of this modified example. The printed board assembly 5D of this modified example includes a package 10B as a bonded object instead of the package 10A of the above embodiment. The package 10B further includes a pair of protrusions 14 in addition to the configuration of the package 10A of the above embodiment. The pair of protrusions 14 are convex portions provided at both ends of the front surface 12a in the Y direction, and extend in the Z direction from the main surface 21 of the feedthrough 20 to the top plate 13. The pair of protrusions 14 protrude from the front surface 12a toward the front in the X direction (i.e., toward the flexible wiring board 3A).

[0072] The top surfaces of the pair of protrusions 14 come into contact with the edge 31c of the flexible wiring board 3A. This allows the flexible wiring board 3A and the package 10B to be positioned relative to each other in the X direction. The pair of protrusions 14 correspond to the positioning portion in the present disclosure. According to this modification, the relative position in the X direction between the via 33a closest to the one end 35aa of the signal terminal 35a and the one end 25aa of the signal terminal 25a can be accurately determined. This makes it possible to prevent the open stub caused by the signal terminal 25a from becoming large due to assembly errors.

[0073] Also, as in this modification, the positioning portion may be a portion provided on the package 10B as the joined object, which abuts against the edge 31c. In this case, the positioning of the flexible wiring board 3A and the package 10B in the X direction can be easily performed with a simple configuration.

[0074] (Fourth Modification) 21 is a partially enlarged perspective view of a flexible wiring board 3B according to a fourth modified example of the embodiment. In the flexible wiring board 3B of this modified example, the position of one end 35aa of the signal terminal 35a in the X direction coincides with the edge of the via 33a closest to the one end 35aa. In other words, the distance between the one end 35aa and the via 33a closest to the one end 35aa is zero. The signal terminal 35b also has a similar configuration to the signal terminal 35a. In this case, the open stub generated in the signal terminals 35a and 35b is eliminated, and deterioration of the signal waveform of the high-frequency signal can be significantly suppressed.

[0075] (Fifth Modification) 22 is a partially enlarged perspective view of a flexible wiring board 3C according to a fifth modified example of the embodiment. This flexible wiring board 3C is different from the flexible wiring board 3A of the embodiment in that it does not include the half via 33b. The distance Dd1 between one end 32aa of the signal terminal 32a on the edge 31c side among both ends of the signal terminal 32a in the X direction and the via 33a (first via) closest to the one end 32aa of the signal terminal 32a among the multiple vias 33a between the signal terminal 32a and the signal terminal 35a is 1 / 8 or less, more preferably 1 / 16 or less, of the signal wavelength propagating through the signal wiring 32d. The signal terminal 32b also has the same configuration as the signal terminal 32a.

[0076] In the flexible wiring board 3C of this modification, one end of the signal terminals 32a, 32b (one end 32aa in the case of the signal terminal 32a) protruding from the position of the via 33a toward the edge 31c acts as an open stub for the high-frequency signal propagating through the signal wirings 32d, 32e. Therefore, by making the distance Dd1 equal to or less than 1 / 8 (more preferably equal to or less than 1 / 16) of the signal wavelength, the open stub generated in the signal terminals 32a, 32b can be made small, the signal passing characteristics can be improved, and deterioration of the signal waveform of the high-frequency signal can be suppressed.

[0077] The printed circuit board and printed circuit board assembly according to the present disclosure are not limited to the above-described embodiment, and various other modifications are possible. For example, in the above-described embodiment and each modification, the optical module packages 10A and 10B and the printed circuit boards 4A and 4B are exemplified as the objects to be joined, but the objects to be joined in the present disclosure are not limited to these, and various devices having signal terminals similar to the signal terminals 35a or 41a can be the objects to be joined.

[0078] In addition, in the above embodiment and each modified example, a flexible wiring board has been exemplified as the printed circuit board of the present disclosure, but the printed circuit board of the present disclosure may be a so-called rigid board in which the dielectric layer does not have flexibility. [Explanation of symbols]

[0079] 1A...Optical module 3A, 3B, 3C, 3D... Flexible wiring board 4A, 4B...Printed circuit board 5…Object to be joined 5A, 5B, 5C, 5D...Printed circuit board assembly 10A, 10B…Package 11...Bottom plate 12…Side wall 12a...Front 12b…Back 12c,12d…side 13…Tabletop 14...Protrusion 20…Feedthrough 21…Main surface 22...Dielectric member 23a, 23b…side 24…End face 25a, 25b…Signal terminal 25aa…one end 26...Ground terminal 27...Wiring layer 30…Connection 31...Dielectric layer 31a…First page 31b…Second side 31c...Edge 32...1st wiring layer 32a…Signal terminal 32aa…one end 32b…Signal terminal 32c...ground terminal 32d,32e…Signal wiring 33,33a…Via 33b...Half via 34...Protective film 35…Second wiring layer 35a,35b…Signal terminal 35aa…one end 35c...ground terminal 35d…Ground wiring 36…Protective film 40...Dielectric substrate 40a…Main surface 40b…Back 41...Wiring layer 41a…Signal terminal 41aa…one end 41b…Signal wiring 42...Wiring layer 42a…Signal wiring 42aa…one end 43…Beer 61,62…Ideal transmission line 63…Stub Da1,Db1,Dc1,Dd1…Distance Sg…High frequency signal

Claims

1. A printed circuit board for transmitting a high-frequency signal, the printed circuit board having a connection portion at an end portion in a first direction, a first wiring layer having a first terminal provided on the connection portion and a first signal wiring connected to the first terminal; a second wiring layer having a second terminal for conductive connection facing the first terminal in a thickness direction of the printed circuit board that intersects with the first direction; a first dielectric layer interposed between the first wiring layer and the second wiring layer and having an edge at the end portion thereof extending in a direction intersecting the first direction and the thickness direction; a plurality of vias provided along the first direction between the first terminal and the second terminal, electrically connecting the first terminal and the second terminal; Equipped with the plurality of vias include a first via that is closest to one end of the first terminal on the edge side in the first direction, and a second via that is closest to one end of the second terminal on an opposite side to the edge in the first direction, a distance between the first via and one end of the first terminal on the edge side is equal to or less than 1 / 8 of a signal wavelength of the high frequency signal in the first terminal, or the first via is a half via provided such that an inside of the first via is exposed to the outside at the edge, A printed circuit board, wherein the distance between the second via and one end of the second terminal opposite the edge is 1 / 8 or less of the signal wavelength of the high frequency signal at the second terminal.

2. 2. The printed circuit board according to claim 1, wherein the signal wavelength of the high frequency signal at the first terminal and the signal wavelength of the high frequency signal at the second terminal are determined for the high frequency signal having a frequency of 30 GHz or higher.

3. 3. The printed circuit board according to claim 1, wherein a distance between the first via and the one end of the first terminal is equal to or less than 1 / 16 of a signal wavelength of the high frequency signal at the first terminal.

4. 4. The printed circuit board according to claim 1, wherein a distance between the second via and the one end of the second terminal is equal to or less than 1 / 16 of a signal wavelength of the high frequency signal at the second terminal.

5. The printed circuit board according to claim 1 , wherein the first dielectric layer is a flexible resin film.

6. A printed circuit board according to any one of claims 1 to 5; a bonded body having a third wiring layer including a third terminal that is conductively bonded to the second terminal; Equipped with a printed circuit board assembly, wherein when the third terminal is conductively joined to the second terminal, a distance between one end of the third terminal in the first direction opposite the edge and the second via is 1 / 8 or less of a signal wavelength of the high frequency signal at the third terminal.

7. 7. The printed circuit board assembly according to claim 6, wherein a signal wavelength of the high frequency signal at the third terminal is determined for the high frequency signal having a frequency of 30 GHz or higher.

8. 8. The printed circuit board assembly according to claim 6, wherein the object further comprises a positioning portion that positions the printed circuit board and the object in the first direction.

9. The printed circuit board assembly according to claim 8 , wherein the positioning portion abuts against the edge.

10. 10. The printed circuit board assembly of claim 9, wherein when the positioning portion abuts against the edge, in the first direction, the position of one end of the second terminal opposite the edge is equal to the position of one end of the third terminal opposite the edge.

11. 11. The printed circuit board assembly according to claim 6, wherein the object to be joined is a package of an optical module including at least one of a light receiving element and a light emitting element, the package housing the at least one element.

12. The object to be joined is a fourth wiring layer including a second signal wiring that faces the third terminal in a thickness direction of the printed circuit board; a second dielectric layer interposed between the third wiring layer and the fourth wiring layer; a plurality of third vias provided along the first direction between the third terminals and the second signal wirings, the third vias electrically connecting the third terminals and the second signal wirings; Equipped with 12. The printed circuit board assembly according to claim 6, wherein a distance between an end of the second signal wiring on the printed circuit board side in the first direction and a third via among the plurality of third vias between the third terminal and the second signal wiring that is closest to the end of the second signal wiring is 1 / 8 or less of a signal wavelength of the high frequency signal in the second signal wiring.

Images