Composite wiring board, package, and electronic device

A terminal substrate includes a signal terminal disposed on a terminal surface of an insulation ceramic layer. An insulation resin layer of a flexible substrate includes a first surface facing the terminal surface, and a second surface on an opposite side of the first surface. A first signal pad disposed on the first surface is joined to the signal terminal. A first penetration conductive part penetrates the insulation resin layer from the first signal pad. A first signal line is disposed on the second surface. A second penetration conductive part penetrates the insulation resin layer from the first signal line. A second signal line is disposed on the first surface. A third penetration conductive part penetrates the insulation resin layer from the second signal line. A second signal pad is disposed on the second surface.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a composite wiring board, a package, and an electronic device, and more particularly to a composite wiring board, a package including the composite wiring board, and an electronic device including the package.

Description of the Background Art

In recent years, in the field of electronic devices for information communication, enhancing a bandwidth (that is, enhancing communication speed) and downsizing of an apparatus size have been carried out rapidly. At the same time, low loss transmission of high-frequency signals and smaller sizes have been required for packages that accommodate the electronic device for information communication at a high standard. To meet the requirements, a flexible substrate is in some cases used instead of a metal pin, which is widely used as a high-frequency signal transmission path between the package and its outside. The flexible substrate includes an insulation sheet made of resin having flexibility, and a plurality of metal films attached to a surface of the insulation sheet. In comparison to the metal pin, the metal films can be easily disposed at smaller intervals. Thus, the size of the package can be made smaller.

According to WO 2019/050046, a package for electronic component accommodation is disclosed. According to an example thereof, the package for electronic component accommodation includes a heat dissipation plate, an electronic component mounting part provided on a surface of the heat dissipation plate, a frame part provided to surround the electronic component mounting part, and a connection structure. The connection structure includes a wiring board, and a flexible substrate joined to the wiring board. The wiring board is inserted into the frame part or constitutes a part of the frame part. The wiring board includes an insulation member made of ceramics, a conductive layer for a signal line provided at least on a main surface of the insulation member, and a ground layer provided on a back surface or inside of the insulation member. The flexible substrate includes an insulation sheet made of resin, and a metal film provided at least on a main surface of the insulation sheet. The metal film includes a signal line pad that is provided on the main surface side of the flexible substrate, and that is joined to the conductive layer for a signal line using a joining member.

In manufacture of the electronic device using the package, an electronic component is mounted on the electronic component mounting part of the package. Subsequently, a lid for maintaining an airtight state of a space in the frame part is joined to the opening of the frame part.

The package includes a composite wiring board including the wiring board (terminal substrate) and the flexible substrate. In manufacture of the electronic device, typically, the electronic component is electrically connected to the wiring board, and a printed circuit board (PCB) is joined to the flexible substrate. With this configuration, the electronic component and the PCB are electrically connected to each other by the composite wiring board. Further, in many cases, a heat dissipation plate (base plate) of the package is joined to the top of the PCB. Meanwhile, in a case of an electronic device with a large heat generation amount, such as an optical transmitter, performance of heat dissipation from the base plate is required in particular. Thus, it is conceivable to dispose a lid, instead of the base plate, on the PCB, with the aim of enhancing the heat dissipation performance. Selection of the disposition as above has influence on a configuration of the wiring board (terminal substrate). Specifically, as a result of the selection of the disposition, the positional relationship between the lid and the base plate on which the electronic component is mounted is inversed, and therefore there is a need to dispose the conductive layer for a signal line for electrical connection with the electronic component, specifically, the signal terminal of the terminal substrate, on a surface on the opposite side of the main surface of the insulation member. In this case, the signal terminal of the terminal substrate and the PCB face each other. Thus, the flexible substrate needs to include a signal path between the first surface facing the signal terminal of the terminal substrate and the second surface that is located on the opposite side of the first surface and that faces the PCB (in a more general term, some member). A method of stably enhancing a bandwidth of the above-described signal path of the flexible substrate used in combination with the terminal substrate has not yet been fully studied so far.

SUMMARY

The present invention is made in view of the problem as described above, and has an object to provide a composite wiring board that can stably enhance a bandwidth of a signal path of a flexible substrate electrically joining a signal terminal of a terminal substrate facing a first surface of the flexible substrate and a member facing a second surface of the flexible substrate.

A composite wiring board according to one aspect includes a terminal substrate, and a flexible substrate. The terminal substrate includes an insulation ceramic layer, and a signal terminal. The insulation ceramic layer has a terminal surface having an edge, an opposite surface on an opposite side of the terminal surface, and a side surface connecting the edge of the terminal surface and the opposite surface to each other. The signal terminal is disposed on the terminal surface of the insulation ceramic layer. The flexible substrate includes an insulation resin layer, a first signal pad, a first penetration conductive part, a first signal line, a second penetration conductive part, a second signal line, a third penetration conductive part, and a second signal pad. The insulation resin layer has a first surface facing the terminal surface of the insulation ceramic layer, and a second surface on an opposite side of the first surface. The first signal pad is disposed on the first surface of the insulation resin layer, and is joined to the signal terminal of the terminal substrate. The first penetration conductive part penetrates the insulation resin layer from the first signal pad so as to extend to the second surface of the insulation resin layer. The first signal line is connected to the first signal pad through the first penetration conductive part, and is disposed on the second surface of the insulation resin layer. The second penetration conductive part penetrates the insulation resin layer from the first signal line so as to extend to the first surface of the insulation resin layer. The second signal line is connected to the first signal line through the second penetration conductive part, and is disposed on the first surface of the insulation resin layer so as to be separated away from the first signal pad. The third penetration conductive part penetrates the insulation resin layer from the second signal line so as to extend to the second surface of the insulation resin layer. The second signal pad is connected to the second signal line through the third penetration conductive part, and is disposed on the second surface of insulation resin layer so as to be separated away from the first signal line.

Preferably, the composite wiring board includes a resin adhesive agent connecting the flexible substrate and the side surface of the insulation ceramic layer to each other.

Preferably, the terminal substrate includes a ground terminal disposed on the terminal surface of the insulation ceramic layer, and the flexible substrate includes a first ground pattern disposed on the first surface of the insulation resin layer, and joined to the ground terminal of the terminal substrate, and a second ground pattern disposed on the second surface of the insulation resin layer, and electrically connected to the first ground pattern. Preferably, the terminal surface of the insulation ceramic layer includes a margin region between the edge of the terminal surface and the signal terminal, and the first ground pattern enters a gap between the margin region and the insulation resin layer. Preferably, the second signal line includes an end portion connected to the second penetration conductive part and an extending portion extending from the end portion toward the third penetration conductive part, and an interval between the first ground pattern and the end portion is smaller than an interval between the first ground pattern and the extending portion.

A package according to one aspect includes the composite wiring board, and a frame part constituting a space for accommodating an electronic component, together with the terminal substrate. Preferably, the package includes a base plate for supporting the electronic component. The base plate faces the opposite surface of the terminal substrate.

An electronic device according to one aspect includes the package, the electronic component, and a circuit substrate. The electronic component is supported by the base plate of the package, and is electrically connected to the signal terminal of the package. The circuit substrate includes a circuit joined to the second signal pad of the package.

According to one aspect, a member (typically, a PCB) to be joined to the second signal pad of the flexible substrate faces the second surface, not the first surface, of the flexible substrate, while the signal terminal of the terminal substrate faces the first surface of the flexible substrate. In the composite wiring board, primarily, with a signal path of the flexible substrate being guided to the second surface of the flexible substrate by the first penetration conductive part, adverse influence on characteristic impedance of the signal path due to a configuration near the terminal substrate faced by the first surface can be reduced. Secondarily, with the signal path of the flexible substrate being guided to the first surface of the flexible substrate by the second penetration conductive part, adverse influence on characteristic impedance of the signal path due to a configuration near the member faced by the second surface can be reduced. Based on these advantages, both of the adverse influence on characteristic impedance of the signal path due to the configuration near the terminal substrate faced by the first surface and the adverse influence on characteristic impedance of the signal path due to the configuration near the member faced by the second surface can be reduced. With this configuration, characteristic impedance of the signal path of the flexible substrate can be more easily maintained at a desired value. From the above, it is possible to stably enhance a bandwidth of the signal path of the flexible substrate electrically joining the signal terminal of the terminal substrate facing the first surface of the flexible substrate and the member facing the second surface of the flexible substrate to each other.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described below with reference to the drawings. Note that, in the following description, terms related to directions, such as “up”, “down”, “right”, “left”, and “bottom”, are used. Unless otherwise specifically noted, however, these terms are used to distinguish directions, and are not to indicate relation to the gravity direction. Specifically, unless otherwise specifically noted, the orientation of each configuration described in the following description with reference to the gravity direction is arbitrary.

FIG.1andFIG.2are a cross-sectional diagram and a block diagram, respectively, schematically illustrating a configuration of an electronic device700according to an embodiment. The electronic device700includes a package600(package with a flexible substrate), an electronic component710, a bonding wire711(electrical connection member), an optical component720, an optical fiber721(light transmission path), a lid730, and a PCB770(circuit substrate). In the present embodiment, the electronic device700is an optical transmission apparatus, and is, for example, an optical transmitter, an optical receiver, or an optical transmitter/receiver. The optical component720and the electronic component710are electrically connected to each other. The electronic component710is, typically, a semiconductor device such as an integrated circuit (IC). The optical component720is, for example, a photodiode or a semiconductor laser. The optical component720is optically connected to the optical fiber721. The PCB770includes an insulation layer771, and a circuit772(metal pattern) that is provided on the insulation layer771. The circuit772of the PCB770is electrically connected to the electronic component710through the package600and the bonding wire711.

FIG.3is a cross-sectional diagram schematically illustrating a configuration of the package600included in the electronic device700(FIG.1). The package600includes a composite wiring board500, a frame part610, and a base plate620. The composite wiring board500includes a terminal substrate100and a flexible substrate200.

The terminal substrate100and the frame part610constitute a cavity CV (space) for accommodating the electronic component710(FIG.1). The cavity CV is a space that is surrounded by the terminal substrate100and the frame part610. In the package600(FIG.3), the cavity CV includes a side wall surface configured by the terminal substrate100and the frame part610, and a bottom surface configured by the base plate620. The terminal substrate100includes an insulation ceramic layer110, and a plurality of terminals120made of a conductive material. Note that fine insulator particles may be distributed in the conductive material.

The base plate620is provided to support the electronic component710, and supports the electronic component710in the electronic device700(FIG.1). The base plate620has a function as a heat dissipation plate as well as a function as a support plate. It is preferable that the base plate620be made of metal.

In the example illustrated inFIG.3, the frame part610includes a through hole portion611for allowing the optical fiber721(FIG.1) to pass through. As a modification, a light blocking portion may be provided instead of the through hole portion611. The light blocking portion is a window portion made of a light blocking material.

FIG.4is a cross-sectional diagram schematically illustrating a configuration of the composite wiring board500included in the package600(FIG.3). Note that, inFIG.1,FIG.3, andFIG.4, illustration of conductive members included in the flexible substrate200is omitted.FIG.5is a plan view schematically illustrating each of the terminal substrate100and the flexible substrate200with a solid line and an imaginary line, respectively, as seen in the direction of the arrow V (FIG.4).

The insulation ceramic layer110of the terminal substrate100includes a terminal surface ST including an edge ED (lower surface inFIG.4), an opposite surface SP on the opposite side of the terminal surface ST (upper surface inFIG.4), and a side surface SS that connects the edge ED of the terminal surface ST and the opposite surface SP to each other (right surface inFIG.4). In the package600(FIG.3), the base plate620faces the opposite surface SP of the terminal substrate100.

It is preferable that the composite wiring board500include a resin adhesive agent300. The resin adhesive agent300connects the flexible substrate200and the side surface SS of the insulation ceramic layer110to each other.

The plurality of terminals120of the terminal substrate100are disposed on the terminal surface ST of the insulation ceramic layer110. The plurality of terminals120include a plurality of signal terminals121and ground terminals122. The signal terminals121(FIG.5) include a signal terminal121aand a signal terminal121bas a pair of signal terminals constituting one differential line in the terminal surface ST of the insulation ceramic layer110. The ground terminals122are disposed to two-dimensionally shield the differential line. In the electronic device700(FIG.1andFIG.2), the electronic component710is electrically connected to each of the signal terminals121and the ground terminals122through the bonding wire711. Thus, the electronic component710is electrically connected to the signal terminals121and the ground terminals122.

FIG.6is an enlarged view of a region VI illustrated inFIG.1.FIG.7andFIG.8are a top view and a bottom view, respectively, schematically illustrating a configuration of the flexible substrate200(FIG.6). The flexible substrate200is a substrate having high flexibility in the thickness direction (vertical direction inFIG.6), and is bent as illustrated inFIG.6in a state of being attached to the PCB770.

The flexible substrate200includes an insulation resin layer210, and a plurality of conductive members attached to the insulation resin layer210. The plurality of conductive members include a plurality of upper signal pads231(first signal pad), a plurality of lower signal pads232(second signal pad), a plurality of lower signal lines251(first signal line), a plurality of upper signal lines252(second signal line), an upper ground pattern221(first ground pattern), a lower ground pattern222(second ground pattern), a plurality of signal penetration conductive parts241(first penetration conductive part), a plurality of signal penetration conductive parts242(second penetration conductive part), a plurality of signal penetration conductive parts243(third penetration conductive part), and a ground penetration conductive part224.

The insulation resin layer210includes an upper surface S1(first surface) that faces the terminal surface ST of the insulation ceramic layer110, and a lower surface S2(second surface on the opposite side of the first surface). The upper surface S1and the lower surface S2are substantially in parallel to each other. In a state where the flexible substrate200is attached to the PCB770, each of the upper surface S1and the lower surface S2is a curved surface. The insulation resin layer210has such high flexibility as to be able to secure flexibility that is required for the flexible substrate200, and is made of polyimide, for example.

The upper ground pattern221and the lower ground pattern222are disposed on the upper surface S1and the lower surface S2of the insulation resin layer210, respectively. The ground penetration conductive part224penetrates the insulation resin layer210, and electrically connects the upper ground pattern221and the lower ground pattern222to each other.

The upper signal pads231are disposed on the upper surface S1of the insulation resin layer210. The upper signal pads231include an upper signal pad231aand an upper signal pad231bas a pair of signal pads constituting a differential line.

The signal penetration conductive parts241penetrate the insulation resin layer210from the upper signal pads231so as to extend to the lower surface S2of the insulation resin layer210. The signal penetration conductive parts241include a signal penetration conductive part241aand a signal penetration conductive part241b. The signal penetration conductive part241aand the signal penetration conductive part241bare connected to the upper signal pad231aand the upper signal pad231bon the upper surface S1, respectively.

The lower signal lines251are disposed on the lower surface S2of the insulation resin layer210. The lower signal lines251include a lower signal line251aand a lower signal line251bas a pair of signal lines constituting a differential line. The lower signal line251ais connected to the upper signal pad231athrough the signal penetration conductive part241a. The lower signal line251bis connected to the upper signal pad231bthrough the signal penetration conductive part241b.

The signal penetration conductive parts242penetrate the insulation resin layer210from the lower signal lines251so as to extend to the upper surface S1of the insulation resin layer210. The signal penetration conductive parts242include a signal penetration conductive part242aand a signal penetration conductive part242b. The signal penetration conductive part242aand the signal penetration conductive part242bare connected to the lower signal line251aand the lower signal line251bon the lower surface S2, respectively.

The upper signal lines252are disposed on the upper surface S1of the insulation resin layer210so as to be separated away from the upper signal pads231. The upper signal lines252include an upper signal line252aand an upper signal line252bas a pair of signal lines constituting a differential line. The upper signal line252ais connected to the lower signal line251athrough the signal penetration conductive part242a. The upper signal line252bis connected to the lower signal line251bthrough the signal penetration conductive part242b.

The signal penetration conductive parts243penetrate the insulation resin layer210from the upper signal lines252so as to extend to the lower surface S2of the insulation resin layer210. The signal penetration conductive parts243include a signal penetration conductive part243aand a signal penetration conductive part243b. The signal penetration conductive part243aand the signal penetration conductive part243bare connected to the upper signal line252aand the upper signal line252bon the upper surface S1, respectively.

The lower signal pads232are disposed on the lower surface S2of the insulation resin layer210so as to be separated away from the lower signal lines251. The lower signal pads232include a lower signal pad232aand a lower signal pad232bas a pair of signal pads constituting a differential line. The lower signal pad232ais connected to the upper signal line252athrough the signal penetration conductive part243a. The lower signal pad232bis connected to the upper signal line252bthrough the signal penetration conductive part243b.

The upper signal pad231aand the upper signal pad231bare joined to the signal terminal121aand the signal terminal121bof the terminal substrate100, respectively. The upper ground pattern221is joined to the ground terminal122of the terminal substrate100. The lower signal pad232a, the lower signal pad232b, and the lower ground pattern222are joined to the circuit772of the PCB770. The above joining may be performed using a connection member (not illustrated), such as a solder layer.

The terminal surface ST (FIG.5) of the insulation ceramic layer110includes a margin region RM between the edge ED of the terminal surface ST and the signal terminal121. Specifically, the edge ED of the terminal surface ST is separated away from the signal terminal121. Between the margin region RM on the terminal surface ST of the insulation ceramic layer110and the insulation resin layer210, a gap is formed in the thickness direction (direction perpendicular to the drawing sheet ofFIG.5, vertical direction inFIG.6). The upper ground pattern221enters the gap. Thus, in plan view (FIG.5), the upper ground pattern221overlaps a part of the margin region RM and the edge ED.

Each of the upper signal lines252(FIG.7) includes an end portion PA connected to the signal penetration conductive part242, and an extending portion PB extending from the end portion PA toward the signal penetration conductive part243It is preferable that an interval LA between the upper ground pattern221and the end portion PA be smaller than an interval LB between the upper ground pattern221and the extending portion PB. Each of the lower signal lines251(FIG.8) includes an end portion PC connected to the signal penetration conductive part242, and an extending portion PD extending from the end portion PC toward the signal penetration conductive part241. It is preferable that an interval LC between the lower ground pattern222and the end portion PC be smaller than an interval LD between the lower ground pattern222and the extending portion PD.

Note that the surface of the flexible substrate200illustrated inFIG.7and FIG.8may be covered by an insulation coating layer (not illustrated) in so far as electrical connection between the flexible substrate200and each of the terminal substrate100and the PCB770is not interfered. Further, the number of each of the signal penetration conductive part241aand the signal penetration conductive part241bis one inFIG.7andFIG.8; however, as a modification, the number may be two or more. With this configuration, contribution of thermal conduction by the signal penetration conductive part241aand the signal penetration conductive part241bcan be enhanced in heating for a joining process between the upper signal pads231and the signal terminals121in manufacture of the composite wiring board500. With this configuration, the joining process is further facilitated. Similarly, the number of each of the signal penetration conductive part243aand the signal penetration conductive part243bis one inFIG.7andFIG.8; however, as a modification, the number may be two or more. With this configuration, contribution of thermal conduction by the signal penetration conductive part243aand the signal penetration conductive part243bcan be enhanced in heating for a joining process between the lower signal pads232and the circuit772in manufacture of the electronic device700. With this configuration, the joining process is further facilitated.

FIG.9is a cross-sectional diagram schematically illustrating a configuration of the flexible substrate200and the resin adhesive agent300taken along the line IX-IX ofFIG.6. The resin adhesive agent300is separated from the lower signal lines251by the upper ground pattern221in the thickness direction of the flexible substrate200(vertical direction inFIG.9). In other words, the upper ground pattern221is disposed between the resin adhesive agent300and the lower signal lines251.

FIG.10is a cross-sectional diagram of an electronic device700C1according to the first comparative example, shown in a view similar toFIG.6.FIG.11is a cross-sectional diagram schematically illustrating a configuration of a flexible substrate200C1and the resin adhesive agent300taken along the line XI-XI (FIG.10). Unlike the above embodiment (FIG.6), in the present comparative example (FIG.10), the upper signal lines252extend from the top of the signal terminals121beyond the edge ED of the terminal surface ST in the horizontal direction (horizontal direction inFIG.10). As a result, the resin adhesive agent300(FIG.11) is disposed on the upper signal lines252, and conductive members to be given the ground potential are not disposed between the resin adhesive agent300and the upper signal lines252. Accordingly, capacitance through the resin adhesive agent300is formed between the upper signal line252aand the upper signal line252bconstituting a pair of differential lines. Thus, as the first phenomenon, the capacitance varies due to variation of a formation process of the resin adhesive agent300, which results in variation of characteristic impedance of the differential lines. As the second phenomenon, because a material of the resin adhesive agent300is typically a material having relatively high dielectric loss, capacitance attributable to the material is formed, which causes increase of the dielectric loss of the differential lines. From the above, in the present comparative example, it is difficult to stably form a differential line having a wideband.

Note that, in the electronic device700C1, if the resin adhesive agent300is omitted, strength of fixing between the flexible substrate200C1and the terminal substrate100becomes insufficient, which makes it difficult to secure sufficient reliability. In addition, the position of the upper signal lines252with respect to the edge ED of the terminal surface ST is liable to be unstable, and this thus causes characteristic impedance of the differential line to be liable to vary.

FIG.12is a cross-sectional diagram of an electronic device700C2according to the second comparative example, shown in a view similar toFIG.6. Unlike the above embodiment (FIG.6), in the present comparative example (FIG.12), the lower signal lines251extend from the signal penetration conductive parts241to the top of the circuit772of the PCB770in the horizontal direction (horizontal direction in the figure). As a result, characteristic impedance of the lower signal lines251varies depending on relative disposition between the flexible substrate200C2and the PCB770, in particular an angle AG formed between the flexible substrate200C2and the PCB770. Thus, it is difficult to stably form a differential line having a wideband. Note that, if a resin adhesive agent is filled in a space having the angle AG in order to stabilize the angle AG in the electronic device700C2, characteristic impedance of the differential line varies due to variation of the formation process of the resin adhesive agent.

According to the composite wiring board500(FIG.6) of the present embodiment, the PCB770to be joined to the lower signal pads232of the flexible substrate200faces the lower surface S2, not the upper surface S1, of the flexible substrate200, while the signal terminals121of the terminal substrate100face the upper surface S1of the flexible substrate200. In the composite wiring board500, primarily, with a signal path of the flexible substrate200being guided to the lower surface S2of the flexible substrate200by the signal penetration conductive parts241, adverse influence on characteristic impedance of the signal path due to a configuration near the terminal substrate100faced by the upper surface S1, in particular the resin adhesive agent300, can be reduced. Secondarily, with the signal path of the flexible substrate200being guided to the upper surface S1of the flexible substrate200by the signal penetration conductive parts242, adverse influence on characteristic impedance of the signal path due to a configuration near the PCB770faced by the lower surface S2, in particular the angle AG, can be reduced. Based on these advantages, both of the adverse influence on characteristic impedance of the signal path due to the configuration near the terminal substrate100faced by the upper surface S1and the adverse influence on characteristic impedance of the signal path due to the configuration near the PCB770faced by the lower surface S2can be reduced. With this configuration, characteristic impedance of the signal path of the flexible substrate200can be more easily maintained at a desired value. From the above, it is possible to stably enhance a bandwidth of the signal path of the flexible substrate200electrically joining the signal terminals121of the terminal substrate100which faces the upper surface S1of the flexible substrate200and the PCB770which is to face the lower surface S2of the flexible substrate200to each other.

The electronic device700(FIG.6) according to the present embodiment includes the composite wiring board500. With this configuration, the signal terminals121of the terminal substrate100and the circuit772of the PCB770can be electrically connected to each other by the flexible substrate200.

Preferably, the composite wiring board500(FIG.4) includes the resin adhesive agent300that connects the flexible substrate200and the side surface SS of the insulation ceramic layer110to each other. With this configuration, the flexible substrate200can be rigidly fixed to the terminal substrate100. Here, according to the present embodiment, adverse influence on characteristic impedance of the signal path of the flexible substrate200due to the resin adhesive agent300located near the terminal substrate100is reduced for the reasons described above. In addition, adverse influence on dielectric loss of the signal path of the flexible substrate200can also be reduced.

The terminal substrate100(FIG.5) includes the ground terminal122, and the flexible substrate200(FIG.6) includes the upper ground pattern221and the lower ground pattern222. With this configuration, the composite wiring board500consisting of the terminal substrate100and the flexible substrate200can be provided with a part maintained at the ground potential. The part has an effect of shielding electric fields. By using the effect, transmission characteristics can be enhanced.

Preferably, the upper ground pattern221(FIG.5) enters a gap between the margin region RM (FIG.5) on the terminal surface ST of the insulation ceramic layer110and the insulation resin layer210in the thickness direction (direction perpendicular to the drawing sheet ofFIG.5, vertical direction inFIG.6). With this configuration, primarily, strength of the flexible substrate200can be enhanced. Secondarily, entry of the resin adhesive agent300into the gap can be reduced in manufacture of the composite wiring board500. With this configuration, variation of characteristic impedance of the differential line of the composite wiring board500due to variation of the formation process of the resin adhesive agent300can be reduced.

Preferably, the interval LA (FIG.7) between the upper ground pattern221and the end portion PA is smaller than the interval LB (FIG.7) between the upper ground pattern221and the extending portion PB. With this configuration, local increase of characteristic impedance near the end portion PA due to no formation of the lower ground pattern222near the end portion PA in plan layout can be at least partially cancelled out. Therefore, the signal path of the flexible substrate200can be caused to have a wider bandwidth. Similarly, the interval LC (FIG.8) between the lower ground pattern222and the end portion PC is smaller than the interval LD (FIG.8) between the lower ground pattern222and the extending portion PD. With this configuration, local increase of characteristic impedance near the end portion PC due to no formation of the upper ground pattern221near the end portion PC in plan layout can be at least partially cancelled out. Therefore, the signal path of the flexible substrate200can be caused to have a wider bandwidth.

The package600(FIG.1) according to the present embodiment includes the frame part610. With this configuration, the frame part610together with the terminal substrate100constitutes the cavity CV for accommodating the electronic component710. In addition, an electrical path between the inside and the outside of the cavity CV can be provided by the terminal substrate100.

Preferably, the package600(FIG.1) includes the base plate620that promotes heat dissipation while supporting the electronic component710. With this configuration, heat dissipation efficiency to the outside of the package600can be enhanced. Further, the base plate620faces the opposite surface SP (FIG.3), not the terminal surface ST, of the terminal substrate100. Thus, a heat dissipation surface (upper surface inFIG.1) of the base plate620does not face the PCB770. With this configuration, performance of heat dissipation from the base plate620can be enhanced. Heat dissipation performance can further be enhanced by attaching a heat dissipation fin, a water cooling mechanism, or the like to the base plate620.

The terminal120(FIG.1) to which each of the electronic component710and the flexible substrate200is electrically connected is disposed on the terminal surface ST (FIG.3) of the insulation ceramic layer110. With this configuration, the formation process of the signal terminals121(FIG.5) of the terminal120can be performed as formation of conductive patterns on the terminal surface ST (typically, printing and firing of a conductive paste on the terminal surface ST). Thus, there is no need to perform overlaying of a plurality of conductive patterns in the formation process of the signal terminals121. Note that, when such overlaying is required, characteristic impedance of the signal terminals varies due to variation of overlay accuracy.

Note that the above embodiment specifically describes the composite wiring board500including one differential line. However, the composite wiring board may include a plurality of differential lines.

FIG.13andFIG.14are graphs showing simulation results of transmission characteristics regarding the composite wiring board according to the above embodiment. Specifically,FIG.13shows an example of a relationship between frequency and differential insertion, andFIG.14shows an example of a relationship between frequency and differential return from the PCB side. Based on these results, by applying the above embodiment as appropriate, a bandwidth as wide as approximately at least 80 GHz is expected.

While the invention has been shown and described in detail, the foregoing description is in all aspects illustrative and not restrictive. It is therefore understood that numerous unillustrated modifications can be devised without departing from the scope of the present invention. For example, the above embodiment specifically describes the electronic device including the optical component in addition to the electronic component. However, the electronic device need not include the optical component.