Patent ID: 12213244

DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present disclosure will be described in detail below with reference to drawings.

First Embodiment

FIG.1is an explanatory diagram of a digital camera600that is an image pickup apparatus serving as an example of an electronic device according to a first embodiment. The digital camera600that is an image pickup apparatus is a digital camera of a lens-replacing type, and includes a camera body601. A lens unit (lens barrel)602including a lens is attachable to and detachable from the camera body601. The camera body601includes a casing611, and an electronic unit500disposed inside the casing611.

The electronic unit500includes an image pickup module200serving as an example of a first electronic module, an image processing module300serving as an example of a second electronic module, and a transmission module100. The image pickup module200transmits a digital signal D2indicating an image signal to the image processing module300via the transmission module100. The image pickup module200transmits the digital signal D2to the image processing module300via the transmission module100by multilevel transmission of 3 or more levels, which is 4-level transmission in the first embodiment. As a result of this, the transmission speed of data can be increased.

FIGS.2A and2Bare explanatory diagrams of an electronic unit500according to the first embodiment.FIG.2Ais a schematic plan view of the electronic unit500, andFIG.2Bis a schematic side view of the electronic unit500. InFIGS.2A and2B, the transmission module100is stretched straight.

The image pickup module200serves as an example of a printed circuit board, and also serves as an example of a semiconductor module. The image pickup module200includes a printed wiring board201, an image sensor202serving as an example of a semiconductor device, a conversion circuit203serving as an example of a semiconductor device, and a connector204.

The printed wiring board201is a rigid printed wiring board. The image sensor202, the conversion circuit203, and the connector204are mounted on the printed wiring board201.

The image sensor202is, for example, a complementary metal oxide semiconductor CMOS image sensor, or a charge coupled device: CCD image sensor. The image sensor202includes a circuit that converts light incident via the lens unit602into an analog signal that is an electric signal, and a circuit that converts the analog signal into a digital signal D1. As a result of this, the image sensor202outputs a digital signal D1. The digital signal D1is an image signal. In the first embodiment, the digital signal D1is a binary signal.

The conversion circuit203converts the digital signal D1that is a binary signal to a multilevel signal, which is the digital signal D2that is a 4-level signal in the first embodiment. As described above, the conversion circuit203modulates the digital signal D1that is a binary signal to the digital signal D2that is a 4-level signal, and outputs the digital signal D2to the connector204subsequent thereto.

The connector204is an interface through which the digital signal D2is output from the conversion circuit203to the transmission module100, and is electrically connected to the conversion circuit203.

To be noted, although a case where the conversion circuit203is constituted by a semiconductor device different from the image sensor202has been described, the configuration is not limited to this, and the image sensor202may be configured to output the digital signal D2that is a 4-level signal as an image signal. For example, the conversion circuit203may be included in the image sensor202.

The image processing module300serves as an example of a printed circuit board, and also serves as an example of a semiconductor module. The image processing module300includes a printed wiring board301, and as examples of semiconductor devices, an image processing device302, a memory device303, and a conversion circuit304.

The printed wiring board301is a rigid printed wiring board. The image processing device302, the memory device303, and the conversion circuit304are mounted on the printed wiring board301.

A connector305is an interface through which input of the digital signal D2from the transmission module100is received, and is electrically connected to the conversion circuit304subsequent thereto. In the first embodiment, the connector305has substantially the same configuration as the connector204.

The conversion circuit304converts the digital signal D2that is a 4-level signal into the digital signal D1that is a binary signal, and outputs the digital signal D1to the image processing device302. That is, the conversion circuit304demodulates the digital signal D2that is a 4-level signal into the digital signal D1that is a binary signal.

The image processing device302is, for example, a digital signal processor, obtains the digital signal D1, and performs correction processing on the digital signal D1to generate image data. The memory device303stores the image data.

To be noted, although a case where the conversion circuit304is constituted by a semiconductor device different from the image processing device302has been described, the configuration is not limited to this, and the conversion circuit304may be included in the image processing device302. That is, the image processing device302may be configured to obtain the digital signal D2that is a 4-level signal.

The transmission module100is an example of a flexible printed circuit board. The transmission module100is used for transmitting the digital signal D2from the image pickup module200to the image processing module300. The digital signal D2is preferably a differential signal that enables high-speed transmission.

The transmission module100includes a flexible printed wiring board101, and connectors109and120mounted on the flexible printed wiring board101. The connectors109and120are each electrically connected to the flexible printed wiring board101. The connector109is detachably attached to the connector204, and the connector120is detachably attached to the connector305. The connector109is electrically connected to the connector204when attached to the connector204. In addition, the connector120is electrically connected to the connector305when attached to the connector305. In the first embodiment, the connector120has substantially the same configuration as the connector109.

As a result of the configuration described above, the image sensor202is capable of communicating data with the image processing device302via the conversion circuit203, the connector204, the connector109, the flexible printed wiring board101, the connector120, the connector305, and the conversion circuit304.

Here, in the case of transmitting a digital signal by multilevel transmission, the transmission speed is improved but the S/N ratio to the noise of the same voltage amplitude becomes low as compared with a case of transmitting a digital signal by binary transmission.FIG.3is an explanatory diagram comparing a case where a digital signal DA is transmitted by binary transmission and a case where a digital signal DB is transmitted by 4-level transmission. The maximum voltage amplitudes of the digital signals DA and DB are set to be equal. In addition, the voltage amplitudes of a noise N superimposed on the digital signals DA and DB are also set to be equal. Even in the case where the noise N of the same amplitude is superimposed on the digital signals DA and DB, the S/N ratio of the digital signal DB that is a 4-level signal is lower than the S/N ratio of the digital signal DA that is a binary signal. One cause of the noise N is inconsistency of a characteristic impedance. When there is inconsistency of the characteristic impedance, a reflection wave of the signal is generated as the noise N at an inconsistent portion.

FIG.4Ais a plan view of the transmission module100according to the first embodiment.FIG.4Bis a longitudinal section view of the transmission module100according to the first embodiment.FIGS.4A and4Bschematically illustrate the transmission module100. To be noted, inFIGS.4A and4B, the flexible printed wiring board101is stretched straight.

The flexible printed wiring board101includes a plurality of signal lines110used for transmission of the digital signal D2. Further, the flexible printed wiring board101may include lines other than the signal line110such as a control line, a power line, and a ground line. Among the plurality of signal lines110, pairs of adjacent signal lines110each constitute a differential line pair111that is a transmission path used for transmitting a differential signal. In the example ofFIG.4A, eight signal lines110constitute four differential line pairs111. Due to increase in the size of the image data, the digital signal D2is transmitted at a transmission speed of 10 Gbps or more per one differential line pair111. Gbps stands for giga bits per second. The signal lines110are each formed from a metal foil such as a copper foil.

FIG.5Ais a partial plan view of the transmission module100according to the first embodiment.FIG.5Bis a partial section view of the transmission module100according to the first embodiment. To be noted, inFIG.5A, illustration of the connector109is omitted.FIG.6Ais a cross-section view of the transmission module100taken along a line VIA-VIA ofFIG.4A.FIG.6Bis a cross-section view of the transmission module100taken along a line VIB-VIB ofFIG.4A.FIG.6Cis a cross-section view of the transmission module100taken along a line VIC-VIC ofFIG.4A. To be noted, inFIG.6C, illustration of the connector109is omitted.

The flexible printed wiring board101includes an insulating layer1014that is electrically insulating and supports the plurality of signal lines110. The insulating layer1014includes a base layer1011and a cover layer1013. The plurality of signal lines110are disposed in a conductor layer1012on the base layer1011. The conductor layer1012is covered by the cover layer1013. The base layer1011and the cover layer1013are formed from, for example, polyimide.

The transmission module100includes a reinforcing member130disposed at a position opposing the connector109with the flexible printed wiring board101therebetween. In addition, the transmission module100includes a reinforcing member140disposed at a position opposing the connector120with the flexible printed wiring board101therebetween. The reinforcing member130includes an insulating layer135that is electrically insulating. The reinforcing member140includes an insulating layer145that is electrically insulating. The reinforcing member130is a member for reinforcing the flexible printed wiring board101to suppress breakage of the signal lines110when attaching or detaching the connector109to or from the connector204. Therefore, the insulating layer135is thicker than the flexible printed wiring board101. Similarly, the reinforcing member140is a member for reinforcing the flexible printed wiring board101to suppress breakage of the signal lines110when attaching or detaching the connector120to or from the connector305. Therefore, the insulating layer145is thicker than the flexible printed wiring board101. As viewed in a Z direction perpendicular to a main surface1010of the flexible printed wiring board101, the reinforcing member130is disposed in a region including the entirety of the connector109. In addition, as viewed in the Z direction, the reinforcing member140is disposed in a region including the entirety of the connector120.

Here, a transmission module of a comparative example will be described.FIG.7Ais a plan view of a transmission module100X of a comparative example.FIG.7Bis a longitudinal section view of the transmission module IMX of the comparative example.FIGS.7A and7Bschematically illustrate the transmission module100X.FIG.8Ais a cross-section view of the transmission module100X taken along a line VIIIA-VIIIA ofFIG.7AFIG.8Bis a cross-section view of the transmission module100X taken along a line VIIIB-VIIIB ofFIG.7A.FIG.8Cis a cross-section view of the transmission module100X taken along a line VIIIC-VIIIC ofFIG.7A. To be noted, inFIG.8C, illustration of the connector109is omitted.

The transmission module100X includes a flexible printed wiring board101X. The flexible printed wiring board101X includes a plurality of signal lines110X. The plurality of signal lines110X are disposed in one conductor layer1012X. Among the plurality of signal lines110X, a pair of adjacent signal lines110X constitute a differential line pair111X that is a transmission path used for transmitting a differential signal. The flexible printed wiring board101X includes an insulating layer1014that has a configuration having substantially the same configuration as in the first embodiment and supports the plurality of signal lines110X. The insulating layer1014includes the base layer1011and the cover layer1013.

In addition, the transmission module100X includes the connector109mounted on the flexible printed wiring board101X and having substantially the same configuration as in the first embodiment, and a reinforcing member130X disposed at a position opposing the connector109with the flexible printed wiring board101X therebetween. The reinforcing member130X is constituted by only an insulating layer having substantially the same configuration as the insulating layer135of the first embodiment. The flexible printed wiring board101X is a one-sided flexible printed wiring board including one conductor layer1012X. Therefore, there is no planar ground conductor having a stable potential around the plurality of signal lines110X.

The signal lines110X each include a pad104X bonded to a terminal1091of the connector109, and wiring portions102X and103X. As viewed in the Z direction, the pad104X and the wiring portion103X overlap the reinforcing member130X, and the wiring portion102X does not overlap the reinforcing member130X. A width W103X of the wiring portion103X is equal to a width W102X of the wiring portion102X. In addition, in the differential line pair111X, a distance S103X between two adjacent wiring portions103X is equal to a distance S102X between two adjacent wiring portions102X A width W104X of the pad104X is larger than each of the width W102X of the wiring portion102X and the width W103X of the wiring portion103X. In addition, in the differential line pair111X, a distance S104X between two adjacent pads104X is larger than each of the distance S102X between two adjacent wiring portions102X and the distance S103X between two adjacent wiring portions103X.

Here, a differential signal is transmitted through the pair of signal lines110X of the differential line pair111X. Therefore, a characteristic impedance Z1X of the wiring portion102X described below is a differential impedance of the pair of wiring portions102X in the differential line pair111X. In addition, a characteristic impedance Z2X of the wiring portion103X is a differential impedance of the pair of wiring portions103X in the differential line pair111X. In addition, a characteristic impedance Z3X of the pad104X is a differential impedance of the pair of pads104X in the differential line pair111X.

In the configuration described above, the characteristic impedance Z3X of the pad104X is higher than the characteristic impedance Z1X of the wiring portion102X, and the characteristic impedance Z2X of the wiring portion103X is lower than the characteristic impedance Z1X of the wiring portion102X. Specifically, the characteristic impedance Z2X of the wiring portion103X overlapping the reinforcing member130X having a higher relative permittivity than the air, is lower than the characteristic impedance Z1X of the wiring portion102X not overlapping the reinforcing member130X. In addition, since the distance S104X between the two pads104X is larger than each of the distance S102X between the two wiring portions102X and the distance S103X between the two wiring portions103X, the characteristic impedance Z3X of the pad104X is higher than each of the characteristic impedances Z1X and Z2X. Therefore, there is a difference between the characteristic impedances Z1X and Z2X, and there is a difference between the characteristic impedances Z2X and Z3X. Due to these differences between the characteristic impedances, particularly the difference between the characteristic impedances Z2X and Z3X, a reflection wave of the digital signal is generated as a noise in the signal line110X. That is, a slight difference between the widths W103X and W104X of the signal line110X, a slight difference between the distances S103X and S104X between a pair of the signal lines110X, difference in the relative permittivity around the signal line110X, and the like make the characteristic impedance of the signal line110X inconsistent.

When the characteristic impedance is inconsistent in the signal line110X, a reflection wave, that is, a noise is generated in the signal line110X, and thus the quality of the digital signal transmitted through the signal line110X is likely to deteriorate. Further, as the transmission speed of the digital signal increases, the deterioration of the quality of the digital signal transmitted through the signal line110X becomes greater.

Therefore, in the first embodiment, the reinforcing member130is configured in a different manner from the reinforcing member130X of the comparative example, and the signal line110is configured in a different manner from the signal line110X of the comparative example.

With reference toFIGS.4A to6C, the signal line110includes wiring portions102and103as a main line, and a pad104. The wiring portion102serves as an example of a first wiring portion, and is disposed at a position not overlapping the reinforcing member130as viewed in the Z direction. The wiring portion103serves as a second wiring portion, and is disposed between the wiring portion102and the pad104. The wiring portion103and the pad104are disposed in a region overlapping the reinforcing member130as viewed in the Z direction. The pad104is bonded to the terminal1091of the connector109via solder or the like.

In addition, the signal line110includes a wiring portion105and a pad106. The wiring portion105is disposed between the wiring portion102and the pad106. The wiring portion105and the pad106are disposed in a region overlapping the reinforcing member140as viewed in the Z direction. The pad106is bonded to a terminal1201of the connector120via solder or the like.

In the first embodiment, the reinforcing member130includes a conductive member136disposed on the insulating layer135. In addition, in the first embodiment, the reinforcing member140includes a conductive member146disposed on the insulating layer145.

The configuration of the reinforcing member140is substantially the same as the reinforcing member130. In addition, the positional relationship of the reinforcing member140with the connector120, the wiring portion105, and the pad106is substantially the same as the positional relationship of the reinforcing member130with the connector109, the wiring portion103, and the pad104. Therefore, detailed description of the reinforcing member140will be omitted.

The insulating layer135of the reinforcing member130is formed in a uniformly constant thickness in a direction parallel to the main surface1010. Examples of the material of the insulating layer135of the reinforcing member130include resins such as polyimide, polyethylene terephthalate: PET, and glass epoxy, and among the resins, glass epoxy, which has high rigidity, is particularly preferable. The conductive member136of the reinforcing member130is disposed on the insulating layer135. The conductive member136is a metal foil such as a copper foil. The conductive member136may be electrically connected to an unillustrated ground terminal of the connector109.

Among the plurality of pads104, description will be given focusing on one pad104. As viewed in the Z direction, the reinforcing member130includes a first portion P1disposed in a region including at least part of the pad104, and a second portion P2disposed around the first portion P1as viewed in the Z direction. It is preferable that the region of the first portion P1includes 90% or more of the area of the pad104as viewed in the Z direction. In the first embodiment, as viewed in the Z direction, the first portion P1is disposed in a region including the entirety of the pad104.

Focusing on the plurality of the pads104, that is, all the pads104, the first portion P1is disposed in a region including the entirety of the plurality of pads104as viewed in the Z direction. Further, the second portion P2is disposed around the first portion P1so as to surround the first portion P1as viewed in the Z direction.

Here, a differential signal is transmitted through the pair of signal lines110of the differential line pair111. Therefore, the characteristic impedance Z1of the wiring portion102described below is a differential impedance of the pair of wiring portions102in the differential line pair111. In addition, the characteristic impedance Z2of the wiring portion103is a differential impedance of the pair of wiring portions103in the differential line pair111. In addition, the characteristic impedance Z3of the pad104is a differential impedance of the pair of pads104in the differential line pair111.

In the first embodiment, a member constituting the first portion P1is a member having a nature that reduces the characteristic impedance Z3of the pad104more than a member constituting the second portion P2does.

Specifically, the first portion P1is constituted by an insulating member1351that is part of the insulating laver135, and the conductive member136disposed on the insulating member1351. As viewed in the Z direction, the insulating member1351and the conductive member136each have the same shape and size as the first portion P1. In addition, the second portion P2is constituted by an insulating member1352that is part of the insulating layer135and disposed around the insulating member1351. As viewed in the Z direction, the insulating member1352has the same shape and size as the second portion P2. The insulating member1351serves as an example of a first insulating member. The insulating member1352serves as an example of a second insulating member. The insulating member1351is formed from the same material as the insulating member1352and in the same thickness as the insulating member1352, and has the same relative permittivity as the insulating member1352.

As described above, in the first embodiment, the insulating member1351and the conductive member136are members constituting the first portion P1. In addition, in the first embodiment, the insulating member1352having the same relative permittivity and the same thickness as the insulating member1351is a member constituting the second portion P2. The member constituted by the insulating member1351and the conductive member136has a nature that reduces the characteristic impedance of an opposing conductor more than the member constituted by the insulating member1352does. Since the reinforcing member130X of the comparative example has substantially the same configuration as the insulating layer135, the characteristic impedance Z3of the first embodiment is reduced more than the characteristic impedance Z3X of the comparative example. That is, since the conductive member136is disposed to oppose the pad104with the insulating member1351therebetween, the characteristic impedance Z3of the pad104is reduced. As a result of this, the absolute value of the difference (Z3-Z2) between the characteristic impedance Z2of the wiring portion103and the characteristic impedance Z3of the pad104can be reduced. Therefore, in the signal line110, generation of the reflection wave of the digital signal D2, that is, generation of the noise can be reduced, and thus the quality of the digital signal D2transmitted through the signal line110can be improved.

A width W104of the pad104is preferably larger than each of a width W102of the wiring portion102and a width W103of the wiring portion103for bonding the terminal1091of the connector109thereto. In addition, a distance S104between the pair of pads104is preferably larger than each of a distance S102between a pair of wiring portions102and a distance S103between a pair of wiring portions103for bonding the terminal1091of the connector109thereto.

In addition, the width W103of the wiring portion103is preferably equal to or less than the width W102of the wiring portion102. As viewed in the Z direction, the wiring portion103overlaps the second portion P2of the reinforcing member130having a higher relative permittivity than the air. Therefore, the width W103of the wiring portion103may be equal to the width W102of the wiring portion102not overlapping the reinforcing member130, but is preferably smaller than the width W102. As a result of this, the characteristic impedance Z2of the wiring portion103is higher than the characteristic impedance Z2X of the wiring portion103X of the comparative example. Therefore, the absolute value of the difference (Z2-Z1) between the characteristic impedance Z1of the wiring portion102and the characteristic impedance Z2of the wiring portion103can be reduced. In addition, the absolute value of the difference (Z3-Z2) between the characteristic impedance Z2of the wiring portion103and the characteristic impedance Z3of the pad104can be reduced. Therefore, in the signal line110, generation of the reflection wave of the digital signal D2, that is, generation of the noise can be more effectively reduced, and the quality of the digital signal D2transmitted through the signal line110can be more effectively improved.

In addition, the distance S103between a pair of the wiring portions103is preferably equal to or larger than the distance S102between a pair of the wiring portions102. As viewed in the Z direction, the pair of the wiring portions103overlaps the second portion P2of the reinforcing member130having a higher relative permittivity than the air. Therefore, the distance S103between the pair of the wiring portions103may be equal to the distance S102of the pair of the wiring portions102not overlapping the reinforcing member130, but is preferably larger than the distance S102. As a result of this, the characteristic impedance Z2is higher than the characteristic impedance Z2X of the comparative example. Therefore, the absolute value of the difference (Z2-Z1) between the characteristic impedance Z1and the characteristic impedance Z2and the absolute value of the difference (Z3-Z2) between the characteristic impedance Z2and the characteristic impedance Z3can be reduced. Therefore, in the signal line110, generation of the reflection wave of the digital signal D2, that is, generation of the noise can be more effectively reduced, and the quality of the digital signal D2transmitted through the signal line110can be more effectively improved.

In addition, as viewed in the Z direction, although the wiring portion103may partially overlap the first portion P1, since the first portion P1has a nature that reduces the characteristic impedance of an opposing conductor, it is preferable that the wiring portion103does not overlap the first portion P1. As a result of this, reduction of the characteristic impedance Z2of the wiring portion103can be suppressed, and the absolute value of the difference (Z2-Z1) and the absolute value of the difference (Z3-Z2) can be reduced. Therefore, in the signal line110, generation of the reflection wave of the digital signal D2, that is, generation of the noise can be more effectively reduced, and the quality of the digital signal D2transmitted through the signal line110can be more effectively improved.

In addition, although the reinforcing member130has been described, since the reinforcing member140has substantially the same configuration as the reinforcing member130, the quality of the digital signal D2transmitted through the signal line110can be more effectively improved.

Example 1

Simulation of differential impedance was performed for the transmission module100according to the first embodiment. HyperLynx available from Mentor Graphics was used for the simulation of the differential impedance.

The thickness of the base layer1011is denoted by T1011, the thickness of the conductor layer1012is denoted by T1012, the thickness of a portion of the cover layer1013overlapping the signal line110on the conductor layer1012is denoted by T1013. In addition, the thickness of the insulating laver135is denoted by T105, and the thickness of the conductive member136is denoted by T106. In the simulation, parameter values of the respective thicknesses were as follows: T1011=12.5 μm; T1012=12 μm; T1013=27.5 μm; T105=265 μm and T106=115 μm. To be noted, the thickness T105of the insulating layer135includes a thickness of 15 μm of an adhesive between the insulating layer135and the base layer1011. In addition, the thickness T106of the conductive member136includes a thickness of 15 μm of an adhesive between the conductive member136and the insulating layer135. The relative permittivity of the base layer1011was set to 3.3, the relative permittivity of the cover layer1013was set to 3.6, the relative permittivity of the insulating layer135of the reinforcing member130was set to 4.7, and the relative permittivity of the adhesive was set to 4.0. The conductivity of the signal line110and the conductivity of the conductive member136were set to 1.724×10−8Ωm.

In addition, in the simulation, the parameter values of the width W104and the distance S104were as follows: W104=250 μm; and S104=150 μm.

As Example 1, simulation was performed for three patterns while changing the magnitude relationship between the width W102and the width W103, and the magnitude relationship between the distance S102and the distance S103. The simulation results of the three patterns are shown in the following Table 1 as Examples 1-1, 1-2, and 1-3.

TABLE 1Z1 = 103.8ΩMAGNITUDERELATIONSHIPW102W103S102S103Z2Example 1-1W102 > W103150 μm130 μm45 μm65 μm100.5ΩS102 < S103Z2 − Z1 = −3.3ΩExample 1-2W102 > W103150 μm65 μm45 μm45 μm100.1ΩS102 = S103Z2 − Z1 = −3.7ΩExample 1-3W102 = W103150 μm150 μm45 μm70 μm100.3ΩS102 < S103Z2 − Z1 = −3.5Ω

To be noted, in Example 1-1, W104>W102>W103and S104>S103>S102held. In Example 1-2, W104>W102>W103and S104>S103=S102held. In Example 1-3, W104>W102=W103and S104>S103>S102held.

In each of Examples 1-1, 1-2, and 1-3, the characteristic impedance (differential impedance) Z1of the wiring portion102was 103.8Ω The characteristic impedance (differential impedance) Z3of the pad104was 102.2Ω.

Comparative Example 1

In addition, the simulation of differential impedance was also performed for the transmission module100X of the comparative example illustrated inFIGS.7A to8C. HyperLynx available from Mentor Graphics was used for the simulation of the differential impedance.

The thickness of the base layer1011is denoted by T1011X, the thickness of the conductor layer1012X is denoted by T1012X, the thickness of a portion of the cover layer1013overlapping the signal line110X on the conductor layer1012X is denoted by T1013X In addition, the thickness of the reinforcing member130X is denoted by T105X. In the simulation, parameter values of the respective thicknesses were as follows, similarly to Example 1: T1011X=12.5 μm; T1012X=12 μm; T1013X=27.5 μm; and T105X=265 μm. To be noted, the thickness T105X of the reinforcing member130X includes a thickness of 15 μm of an adhesive between the reinforcing member130X and the base layer1011. The relative permittivity of the base layer1011was set to 3.3, the relative permittivity of the cover layer1013was set to 3.6, the relative permittivity of the reinforcing member130X was set to 4.7, and the relative permittivity of the adhesive was set to 4.0.

The simulation results of the differential impedance of Comparative Example 1 will be described. The characteristic impedance (differential impedance) Z1X of the wiring portion102X was 103.8Ω. The characteristic impedance (differential impedance) Z2X of the wiring portion103X was 85.5Ω. The characteristic impedance (differential impedance) Z3X of the pad104X was 118.2Ω.

The distance S104X between a pair of the pads104X is larger than each of the distance S102X between a pair of the wiring portions102X and the distance S103X between a pair of the wiring portions103X. Therefore, in the configuration of Comparative Example 1 not including the conductive member136, the characteristic impedance (differential impedance) Z3X of the pad104X was higher than the characteristic impedance Z2X of the wiring portion103X. The difference (Z3X-Z2X) between the characteristic impedances was 32.7Ω.

In contrast, in Examples 1-1, 1-2, and 1-3, the difference (Z3-Z2) in the characteristic impedance were respectively 1.7 Ω, 2.1Ω, and 1.9Ω. Therefore, in all of Examples 1-1, 1-2, and 1-3, the absolute value |Z3-Z2| of the difference in the characteristic impedance was smaller than the absolute value |Z3X-Z2X| of the difference in the characteristic impedance of Comparative Example 1. Therefore, in each of Examples 1-1, 1-2, and 1-3, the characteristic impedance was more consistent than in Comparative Example 1. Therefore, in Examples 1-1, 1-2, and 1-3, the generation of the reflection wave can be reduced

Particularly, in Example 1-1, the absolute value |Z3-Z2| of the difference in the characteristic impedance was smaller than in Examples 1-2 and 1-3. Therefore, in Example 1-1, the generation of the reflection wave can be reduced as compared with Examples 1-2 and 1-3.

In addition, in Example 1-3, the absolute value |Z3-Z2| of the difference in the characteristic impedance was smaller than in Example 1-2. Therefore, in Example 1-3, the generation of the reflection wave can be reduced as compared with Example 1-2.

In addition, the effective permittivity of the surroundings of the wiring portion103X was higher than the effective permittivity of the surroundings of the wiring portion102X. Therefore, the characteristic impedance Z2X of the wiring portion103X was lower than the characteristic impedance Z1X of the wiring portion102X, and the difference (Z2X-Z1X) in the characteristic impedance was −18.3Ω.

Meanwhile, as shown in Table 1, the difference (Z2-Z1) in the characteristic impedance in Examples 1-1, 1-2, and 1-3 were respectively −3.3 Ω, −3.7Ω, and −3.5Ω. Therefore, in all of Examples 1-1, 1-2, and 1-3, the absolute value |Z2-Z1| of the difference in the characteristic impedance was smaller than the absolute value |Z2X-Z1X| of the difference in the characteristic impedance of Comparative Example 1. Therefore, in each of Examples 1-1, 1-2, and 1-3, the characteristic impedance was more consistent than in Comparative Example 1. Therefore, in Examples 1-1, 1-2, and 1-3, the generation of the reflection wave can be effectively reduced.

Particularly, in Example 1-1, the absolute value |Z2-Z1| of the difference in the characteristic impedance was smaller than in Examples 1-2 and 1-3. Therefore, in Example 1-1, the generation of the reflection wave can be reduced as compared with Examples 1-2 and 1-3.

In addition, in Example 1-3, the absolute value |Z2-Z1| of the difference in the characteristic impedance was smaller than in Example 1-2. Therefore, in Example 1-3, the generation of the reflection wave can be reduced as compared with Example 1-2.

In Example 1, the effect of the consistency of the characteristic impedance increases as the transmission speed increases. For example, in the case where the length of the pads104and104X in the wiring direction is 1 mm, the transmission time of the signal is about 7 ps. In the case where the transmission speed is 5 Gbps (signal period: 200 ps), the rising time of the signal is about 40 ps to 66 ps (about ⅕ to ⅓ of the period). Therefore, in the pads104and104X, the rising time of the signal is longer than the transmission time of the signal. Therefore, even in the case of Comparative Example 1, the deterioration of the signal waveform caused by the inconsistency of the impedance in the pad104X is small.

However, in the case where the transmission speed is 10 Gbps (signal period: 100 ps), the rising time of the signal is about 20 ps to 33 ps. Therefore, in Comparative Example 1, deterioration of the signal waveform caused by the inconsistency of the impedance of the pad104starts becoming apparent in Comparative Example 1. In the case where the transmission speed is 20 Gbps (signal period: 50 ps), the rising time of the signal is about 10 ps to 17 ps. Therefore, in Comparative Example 1, the deterioration of the signal wavelength caused by the inconsistency of the impedance of the pad104X becomes prominent.

In addition, in the case of multilevel transmission such as 4-level or 16-level transmission, waveforms of different signal amplitudes are mixed, and therefore the S/N ratio of a signal of a low amplitude is lower than the S/N ratio of a signal of a high amplitude. Therefore, the deterioration of the waveform caused by the inconsistency of the impedance is likely to occur in a signal of a low amplitude.

In contrast, in Example 1, since the impedance is consistent between the pad104and the wiring portion103, the deterioration of the signal waveform is less likely to occur no matter whether the transmission speed of the signal is 10 Gbps or 20 Gbps, and the quality of the signal is improved.

Second Embodiment

Next, a transmission module of a second embodiment will be described.FIG.9Ais a plan view of a transmission module100A according to the second embodiment.FIG.9Bis a longitudinal section view of the transmission module100A according to the second embodiment.FIGS.9A and9Bschematically illustrate the transmission module100A. In the second embodiment, the transmission module100A is applied to the electronic unit500in place of the transmission module100of the first embodiment. Therefore, description of elements substantially the same as in the first embodiment will be omitted.

The transmission module100A of the second embodiment includes the flexible printed wiring board101, the connector109, and the connector120described in the first embodiment. To be noted, inFIGS.9A and9B, the flexible printed wiring board101is stretched straight.FIG.10Ais a cross-section view of the transmission module100A taken along a line XA-XA ofFIG.9A.FIG.10Bis a cross-section view of the transmission module100A taken along a line XB-XB ofFIG.9A.FIG.10Cis a cross-section view of the transmission module100A taken along a line XC-XC ofFIG.9A. To be noted, inFIG.10C, illustration of the connector109is omitted.

The flexible printed wiring board101includes a plurality of signal lines110used for transmission of the digital signal D2. Among the plurality of signal lines110, pairs of adjacent signal lines110each constitute a differential line pair111that is a transmission path used for transmitting a differential signal. The signal lines110each include the wiirng portion102, the wiring portion103, the pad104, the wiring portion105, and the pad106.

The transmission module100A of the second embodiment includes a reinforcing member130A disposed at a position opposing the connector109with the flexible printed wiring board101therebetween. In addition, the transmission module100A includes a reinforcing member140A disposed at a position opposing the connector120with the flexible printed wiring board101therebetween.

The reinforcing member130A includes insulating members1351A and1352A that are electrically insulating. The relative permittivity of the insulating member1351A is higher than the relative permittivity of the insulating member1352A. The reinforcing member140A includes insulating members1451A and1452A that are electrically insulating. The relative permittivity of the insulating member1451A is higher than the relative permittivity of the insulating member1452A.

The reinforcing member130A is a member for reinforcing the flexible printed wiring board101to suppress breakage of the signal lines110when attaching or detaching the connector109to or from the connector204. Therefore, the reinforcing member130A is thicker than the flexible printed wiring board101. Similarly, the reinforcing member140A is a member for reinforcing the flexible printed wiring board101to suppress breakage of the signal lines110when attaching or detaching the connector120to or from the connector305. Therefore, the reinforcing member140A is thicker than the flexible printed wiring board101. As viewed in the Z direction perpendicular to the main surface1010of the flexible printed wiring board101, the reinforcing member130A is disposed in a region including the entirety of the connector109. In addition, as viewed in the Z direction, the reinforcing member140A is disposed in a region including the entirety of the connector120.

The configuration of the reinforcing member140A is substantially the same as the configuration of the reinforcing member130A. In addition, the positional relationship of the reinforcing member140A with the connector120, the wiring portion105, and the pad106is substantially the same as the positional relationship of the reinforcing member130A with the connector109, the wiring portion103, and the pad104. Therefore, detailed description of the reinforcing member140A will be omitted.

The insulating member1351A of the reinforcing member130A serves as an example of a first insulating member. The insulating member1352A of the reinforcing member130A serves as an example of a second insulating member.

The insulating member1352A is formed in a uniformly constant thickness in a direction parallel to the main surface1010. Examples of the material of the insulating member1352A include resins such as polyimide, PET, and glass epoxy, and among the resins, glass epoxy, which has high rigidity, is particularly preferable. The insulating member1351A is formed in the same thickness as the insulating member1352A. The material of the insulating member1351A is, for example, alumina.

Among the plurality of pads104, description will be given focusing on one pad104. As viewed in the Z direction, the reinforcing member130A includes a first portion P1A disposed in a region including at least part of the pad104, and a second portion P2A disposed around the first portion P1A as viewed in the Z direction. It is preferable that the region of the first portion P1A includes 90% or more of the area of the pad104as viewed in the Z direction. In the second embodiment, as viewed in the Z direction, the first portion P1A is disposed in a region including the entirety of the pad104.

Focusing on the plurality of the pads104, that is, all the pads104, the first portion P1A is disposed in a region including entirety of the plurality of pads104as viewed in the Z direction. Further, the second portion P2A is disposed around the first portion PIA so as to surround the first portion P1A as viewed in the Z direction.

Here, a differential signal is transmitted through the pair of signal lines110of the differential line pair111. Therefore, a characteristic impedance Z1A of the wiring portion102described below is a differential impedance of the pair of wiring portions102in the differential line pair111. In addition, a characteristic impedance Z2A of the wiring portion103is a differential impedance of the pair of wiring portions103in the differential line pair111. In addition, a characteristic impedance Z3A of the pad104is a differential impedance of the pair of pads104in the differential line pair111.

In the second embodiment, a member constituting the first portion P1A is a member having a nature that reduces the characteristic impedance Z3A of the pad104more than a member constituting the second portion P2A does.

Specifically, the first portion P1A is constituted by the insulating member1351A described above. As viewed in the Z direction, the insulating member1351A has the same shape and size as the first portion P1A. In addition, the second portion P2A is constituted by the insulating member1352A disposed around the insulating member1351A. As viewed in the Z direction, the insulating member1352A has the same shape and size as the second portion P2A. The insulating member1351A is formed from a different material from the insulating member1352A but in the same thickness as the insulating member1352A, and has a higher relative permittivity than the insulating member1352A.

As described above, in the second embodiment, the insulating member1351A is a member constituting the first portion P1A. In addition, in the second embodiment, the insulating member1352A formed from a different material from the insulating member1351A is a member constituting the second portion P2A. The insulating member1351A has a nature that reduces the characteristic impedance of an opposing conductor more than the insulating member1352A does. The reinforcing member130X of the comparative example is formed from the same material as and in the same thickness as the insulating member1352A. Therefore, the characteristic impedance Z3A of the second embodiment is reduced more than the characteristic impedance Z3X of the comparative example. That is, since the insulating member1351A is disposed to oppose the pad104, the characteristic impedance Z3A of the pad104is reduced. As a result of this, the absolute value of the difference (Z3A-Z2A) between the characteristic impedance Z2A of the wiring portion103and the characteristic impedance Z3A of the pad104can be reduced. Therefore, in the signal line110, generation of the reflection wave of the digital signal D2, that is, generation of the noise can be reduced, and thus the quality of the digital signal D2transmitted through the signal line110can be improved.

A width W204of the pad104is preferably larger than each of A width W202of the wiring portion102and a width W203of the wiring portion103for bonding the terminal1091of the connector109thereto. In addition, a distance S204between the pair of pads104is preferably larger than each of a distance S202between a pair of wiring portions102and a distance S203between a pair of wiring portions103for bonding the terminal1091of the connector109thereto.

In addition, the width W203of the wiring portion103is preferably equal to or less than the width W202of the wiring portion102. As viewed in the Z direction, the wiring portion103overlaps the second portion P2A of the reinforcing member130A having a higher relative permittivity than the air. Therefore, the width W203of the wiring portion103may be equal to the width W202of the wiring portion102not overlapping the reinforcing member130A, but is preferably smaller than the width W202. As a result of this, the characteristic impedance Z2A of the wiring portion103is higher than the characteristic impedance Z2X of the wiring portion103X of the comparative example. Therefore, the absolute value of the difference (Z2A-ZIA) between the characteristic impedance Z1A of the wiring portion102and the characteristic impedance Z2A of the wiring portion103can be reduced. In addition, the absolute value of the difference (Z3A-Z2A) between the characteristic impedance Z2A of the wiring portion103and the characteristic impedance Z3A of the pad104can be reduced. Therefore, in the signal line110, generation of the reflection wave of the digital signal D2, that is, generation of the noise can be more effectively reduced, and the quality of the digital signal D2transmitted through the signal line110can be more effectively improved.

In addition, the distance S203between a pair of the wiring portions103is preferably equal to or larger than the distance S202between a pair of the wiring portions102. As viewed in the Z direction, the pair of the wiring portions103overlaps the second portion P2A of the reinforcing member130A having a higher relative permittivity than the air. Therefore, the distance S203between the pair of the wiring portions103may be equal to the distance S202of the pair of the wiring portions102not overlapping the reinforcing member130A, but is preferably larger than the distance S202. As a result of this, the characteristic impedance Z2A is higher than the characteristic impedance Z2X of the comparative example. Therefore, the absolute value of the difference (Z2A-Z1A) between the characteristic impedance Z1A and the characteristic impedance Z2A and the absolute value of the difference (Z3A-Z2A) between the characteristic impedance Z2A and the characteristic impedance Z3A can be reduced. Therefore, in the signal line110, generation of the reflection wave of the digital signal D2, that is, generation of the noise can be more effectively reduced, and the quality of the digital signal D2transmitted through the signal line110can be more effectively improved.

In addition, as viewed in the Z direction, although the wiring portion103may partially overlap the first portion P1A, since the first portion P1A has a nature that reduces the characteristic impedance of an opposing conductor, it is preferable that the wiring portion103does not overlap the first portion P1A. As a result of this, reduction of the characteristic impedance Z2A of the wiring portion103can be suppressed, and the absolute value of the difference (Z2A-Z1A) and the absolute value of the difference (Z3A-Z2A) can be reduced. Therefore, in the signal line110, generation of the reflection wave of the digital signal D2, that is, generation of the noise can be more effectively reduced, and the quality of the digital signal D2transmitted through the signal line110can be more effectively improved.

To be noted, although the reinforcing member130A has been described, since the reinforcing member140A has substantially the same configuration as the reinforcing member130A, the quality of the digital signal D2transmitted through the signal line110can be more effectively improved.

In addition, the first portion PIA may further include the conductive member136having substantially the same configuration as in the first embodiment.

Example 2

Simulation of differential impedance was performed for the transmission module100A according to the second embodiment. HyperLynx available from Mentor Graphics was used for the simulation of the differential impedance.

The thickness of the base layer1011is denoted by T2011, the thickness of the conductor layer1012is denoted by T2012, and the thickness of a portion of the cover layer1013overlapping the signal line110on the conductor layer1012is denoted by T2013. In addition, the thickness of the reinforcing member130A, that is, the thickness of the insulating member1351A and1352A is denoted by T205. In the simulation, parameter values of the respective thicknesses were as follows: T2011=12.5 μm; T2012=12 μm; T2013=27.5 μm; and T205=430 μm. To be noted, the thickness1205of the reinforcing member130A includes a thickness of 30 μm of an adhesive between the reinforcing member130A and the base layer1011. The relative permittivity of the base layer1011was set to 3.3, the relative permittivity of the cover layer1013was set to 3.6, the relative permittivity of the insulating member1352A of the reinforcing member130A was set to 4.7, and the relative permittivity of the adhesive was set to 4.0. The relative permittivity of the insulating member1351A was set to 9.8. The conductivity of the signal line110was set to 1.724×10−8Ωm.

The width of the wiring portion102is denoted by W202, the width of the wiring portion103is denoted by W203, and the width of the pad104is denoted by W204. In addition, the distance between a pair of the wiring portions102in the differential line pair111is denoted by S202, the distance between a pair of the wiring portions103in the differential line pair111is denoted by S203, and the distance between a pair of the pads104in the differential line pair111is denoted by S204. In the simulation, the values of the widths and the distances were as follows: W202=150 μm; S202=45 μm; W203=120 μm; S203=75 μm; W204=250 μm: and S204=150 μm. As described above, in Example 2, W204>W202>W203and S204>S203>S202hold.

In Example 2, the characteristic impedance (differential impedance) ZIA of the wiring portion102was 103.8Ω. The characteristic impedance (differential impedance) Z2A of the wiring portion103was 99.2Ω. The characteristic impedance (differential impedance) Z3A of the pad104was 100.8Ω.

In Comparative Example 1, the difference (Z3X-Z2X) in the characteristic impedance was 32.7Ω. In contrast, in Example 2, the difference (Z3A-Z2A) in the characteristic impedance was 1.6Ω. Therefore, the absolute value |Z3A-Z2A| of the difference in the characteristic impedance of Example 2 was smaller than the absolute value |Z3X-Z2X| of the difference in the characteristic impedance of Comparative Example 1, which indicates that the characteristic impedance was more consistent in Example 2 than in Comparative Example 1. Therefore, in Example 2, generation of the reflection wave can be reduced.

In Comparative Example 1, the difference (Z2X-Z1X) in the characteristic impedance was −18.3Ω. In contrast, in Example 2, the difference (Z2A-Z1A) in the characteristic impedance was −4.6Ω. Therefore, the absolute value |Z2A-Z1A| of the difference in the characteristic impedance of Example 2 was smaller than the absolute value |Z2X-Z1X| of the difference in the characteristic impedance of Comparative Example 1, which indicates that the characteristic impedance was more consistent in Example 2 than in Comparative Example 1. Therefore, in Example 2, generation of the reflection wave can be reduced.

Third Embodiment

Next, a transmission module of a third embodiment will be described.FIG.11Ais a plan view of a transmission module100B according to the third embodiment.FIG.11Bis a longitudinal section view of the transmission module100B according to the third embodiment.FIGS.11A and11Bschematically illustrate the transmission module100B. In the third embodiment, the transmission module100B is applied to the electronic unit500in place of the transmission module100of the first embodiment. Therefore, description of elements substantially the same as in the first embodiment will be omitted.

The transmission module10B of the third embodiment includes the flexible printed wiring board101, the connector109, and the connector120described in the first embodiment. To be noted, inFIGS.11A and11B, the flexible printed wiring board101is stretched straight.FIG.12Ais a cross-section view of the transmission module100B taken along a line XIIA-XIIA ofFIG.11A.FIG.12Bis a cross-section view of the transmission module100B taken along a line XIIB-XIIB ofFIG.1A.FIG.12Cis a cross-section view of the transmission module100B taken along a line XIIC-XIIC ofFIG.11A. To be noted, inFIG.12C, illustration of the connector109is omitted.

The flexible printed wiring board101includes a plurality of signal lines110used for transmission of the digital signal D2. Among the plurality of signal lines110, a pair of adjacent signal lines110constitute a differential line pair III that is a transmission path used for transmitting a differential signal. The signal lines110each include the wiring portion102, the wiring portion103, the pad104, the wiring portion105, and the pad106.

The transmission module100B of the third embodiment includes a reinforcing member130B disposed at a position opposing the connector109with the flexible printed wiring board101therebetween. In addition, the transmission module100B includes a reinforcing member140B disposed at a position opposing the connector120with the flexible printed wiring board101therebetween.

The reinforcing member130B includes insulating members1351B,1352B, and1353B that are electrically insulating. The relative permittivity of the insulating member1351B is higher than the relative permittivity of the insulating member1352B. The insulating member1353B is formed from the same material as the insulating member1352B and has the same relative permittivity as the insulating member1352B, but is thinner than the insulating member1352B.

The reinforcing member140B includes insulating members1451B,1452B, and1453B that are electrically insulating. The relative permittivity of the insulating member1451B is higher than the relative permittivity of the insulating member1452B. The insulating member1453B is formed from the same material as the insulating member1452B and has the same relative permittivity as the insulating member1452B, but is thinner than the insulating member1452B.

The reinforcing member130B is a member for reinforcing the flexible printed wiring board101to suppress breakage of the signal lines110when attaching or detaching the connector109to or from the connector204. Therefore, the reinforcing member130B is thicker than the flexible printed wiring board101. Similarly, the reinforcing member140B is a member for reinforcing the flexible printed wiring board101to suppress breakage of the signal lines110when attaching or detaching the connector120to or from the connector305. Therefore, the reinforcing member140B is thicker than the flexible printed wiring board101. As viewed in the Z direction perpendicular to the main surface1010of the flexible printed wiring board101, the reinforcing member130B is disposed in a region including the entirety of the connector109. In addition, as viewed in the Z direction, the reinforcing member140B is disposed in a region including the entirety of the connector120.

The configuration of the reinforcing member140B is substantially the same as the configuration of the reinforcing member130B. In addition, the positional relationship of the reinforcing member140B with the connector120, the wiring portion105, and the pad106is substantially the same as the positional relationship of the reinforcing member130B with the connector109, the wiring portion103, and the pad104. Therefore, detailed description of the reinforcing member140B will be omitted.

The insulating member1351B of the reinforcing member130B serves as an example of a first insulating member. The insulating member1352B of the reinforcing member130B serves as an example of a second insulating member. The insulating member1353B of the reinforcing member130B serves as an example of a third insulating member.

The insulating member1352B is formed in a uniformly constant thickness in a direction parallel to the main surface1010. Examples of the material of the insulating member1352B include resins such as polyimide, PET, and glass epoxy, and among the resins, glass epoxy, which has high rigidity, is particularly preferable. The material of the insulating member1351B is, for example, titanium oxide. The material of the insulating member1353B is different from that of the insulating member1351B, and is the same as that of the insulating member1352B.

Among the plurality of pads104, description will be given focusing on one pad104. As viewed in the Z direction, the reinforcing member130B includes a first portion P1B disposed in a region including at least part of the pad104, and a second portion P2B disposed around the first portion P1B as viewed in the Z direction. It is preferable that the region of the first portion P1B includes 90% or more of the area of the pad104as viewed in the Z direction. In the third embodiment, as viewed in the Z direction, the first portion P1B is disposed in a region including the entirety of the pad104.

Focusing on the plurality of the pads104, that is, all the pads104, the first portion P1B is disposed in a region including entirety of the plurality of pads104as viewed in the Z direction. Further, the second portion P2B is disposed around the first portion P1B so as to surround the first portion P1B as viewed in the Z direction.

Here, a differential signal is transmitted through the pair of signal lines110of the differential line pair111. Therefore, the characteristic impedance Z1B of the wiring portion102described below is a differential impedance of the pair of wiring portions102in the differential line pair111. In addition, the characteristic impedance Z2B of the wiring portion103is a differential impedance of the pair of wiring portions103in the differential line pair111. In addition, the characteristic impedance Z3B of the pad104is a differential impedance of the pair of pads104in the differential line pair111.

In the third embodiment, a member constituting the first portion P1B is a member having a nature that reduces the characteristic impedance Z3B of the pad104more than a member constituting the second portion P2B does.

Specifically, the first portion P1B is constituted by the insulating members1351B and1353B described above. As viewed in the Z direction, the insulating members1351B and1353B are laminated in the thickness direction of the flexible printed wiring board101, that is, the Z direction. As viewed in the Z direction, the insulating members1351B and1353B each have the same shape and size as the first portion P1B.

In addition, the second portion P2B is constituted by the insulating member1352B disposed around the insulating member1351B. As viewed in the Z direction, the insulating member1352B has the same shape and size as the second portion P2B. The relative permittivity of the insulating member1353B is equal to the relative permittivity of the insulating member1352B, and is different from the relative permittivity of the insulating member1351B. In the third embodiment, the insulating member1351B has a higher relative permittivity than the insulating members1352B and1353B.

As described above, in the third embodiment, the insulating members1351B and1353B formed from different materials are members constituting the first portion P1B. In addition, in the third embodiment, the insulating member1352B formed from a different material from the insulating member1351B is a member constituting the second portion P2B. The insulating member1351B has a nature that reduces the characteristic impedance of an opposing conductor more than the insulating member1352B does. The reinforcing member130X of the comparative example is formed from the same material as and in the same thickness as the insulating member1352B. Therefore, a characteristic impedance Z3B of the third embodiment is reduced more than the characteristic impedance Z3X of the comparative example. That is, since the laminate of the insulating members1351B and1353B is disposed to oppose the pad104, the characteristic impedance Z3B of the pad104is reduced. As a result of this, the absolute value of the difference (Z3B-Z2B) between a characteristic impedance Z2B of the wiring portion103and the characteristic impedance Z3B of the pad104can be reduced. Therefore, in the signal line110, generation of the reflection wave of the digital signal D2, that is, generation of the noise can be reduced, and thus the quality of the digital signal D2transmitted through the signal line110can be improved.

A width W304of the pad104is preferably larger than each of a width W302of the wiring portion102and a width W303of the wiring portion103for bonding the terminal1091of the connector109thereto. In addition, a distance S304between the pair of pads104is preferably larger than each of a distance S302between a pair of wiring portions102and a distance S303between a pair of wiring portions103for bonding the terminal1091of the connector109thereto.

In addition, the width W303of the wiring portion103is preferably equal to or less than the width W302of the wiring portion102. As viewed in the Z direction, the wiring portion103overlaps the second portion P2B of the reinforcing member130B having a higher relative permittivity than the air. Therefore, the width W303of the wiring portion103may be equal to the width W302of the wiring portion102not overlapping the reinforcing member130B, but is preferably smaller than the width W302. As a result of this, the characteristic impedance Z2B of the wiring portion103is higher than the characteristic impedance Z2X of the wiring portion103X of the comparative example. Therefore, the absolute value of the difference (Z2B-Z1B) between a characteristic impedance Z1B of the wiring portion102and the characteristic impedance Z2B of the wiring portion103can be reduced. In addition, the absolute value of the difference (Z3B-Z2B) between the characteristic impedance Z2B of the wiring portion103and the characteristic impedance Z3B of the pad104can be reduced. Therefore, in the signal line110, generation of the reflection wave of the digital signal D2, that is, generation of the noise can be more effectively reduced, and the quality of the digital signal D2transmitted through the signal line110can be more effectively improved.

In addition, the distance S303between a pair of the wiring portions103is preferably equal to or larger than the distance S302between a pair of the wiring portions102. As viewed in the Z direction, the pair of the wiring portions103overlaps the second portion P2B of the reinforcing member130B having a higher relative permittivity than the air. Therefore, the distance S303between the pair of the wiring portions103may be equal to the distance S302of the pair of the wiring portions102not overlapping the reinforcing member130B, but is preferably larger than the distance S302. As a result of this, the characteristic impedance Z2B is higher than the characteristic impedance Z2X of the comparative example. Therefore, the absolute value of the difference (Z2B-Z1B) between the characteristic impedance Z1B and the characteristic impedance Z2B and the absolute value of the difference (Z3B-Z2B) between the characteristic impedance Z2B and the characteristic impedance Z3B can be reduced. Therefore, in the signal line110, generation of the reflection wave of the digital signal D2, that is, generation of the noise can be more effectively reduced, and the quality of the digital signal D2transmitted through the signal line110can be more effectively improved.

In addition, as viewed in the Z direction, although the wiring portion103may partially overlap the first portion P1B, since the first portion P1B has a nature that reduces the characteristic impedance of an opposing conductor, it is preferable that the wiring portion103does not overlap the first portion P1B. As a result of this, reduction of the characteristic impedance Z2B of the wiring portion103can be suppressed, and the absolute value of the difference (Z2B-Z1B) and the absolute value of the difference (Z3B-Z2B) can be reduced. Therefore, in the signal line110, generation of the reflection wave of the digital signal D2, that is, generation of the noise can be more effectively reduced, and the quality of the digital signal D2transmitted through the signal line110can be more effectively improved.

To be noted, although the reinforcing member130B has been described, since the reinforcing member140B has substantially the same configuration as the reinforcing member130B, the quality of the digital signal D2transmitted through the signal line110can be more effectively improved.

In addition, the first portion P1B may further include the conductive member136having substantially the same configuration as in the first embodiment.

Example 3

Simulation of differential impedance was performed for the transmission module100B according to the third embodiment. HyperLynx available from Mentor Graphics was used for the simulation of the differential impedance.

The thickness of the base layer1011is denoted by T3011, the thickness of the conductor layer1012is denoted by T3012, and the thickness of a portion of the cover layer1013overlapping the signal line110on the conductor layer1012is denoted by T3013. In addition, the thickness of the reinforcing member130B, that is, the thickness of the insulating member1352B is denoted by T305. The thickness of the insulating member1351B is denoted by T3051, and the thickness of the insulating member1353B is denoted by T3053. The sum of the thickness T3051and the thickness T3053equals to the thickness T305. In the simulation, parameter values of the respective thicknesses were as follows: T3011=12.5 μm; T3012=12 μm; T3013=27.5 μm; T305=415 μm; T3053=100 μm; and T3051=315 μm. To be noted, the thickness T305of the reinforcing member130B and the thickness T3053of the insulating member1353B includes a thickness of 15 μm of an adhesive between the reinforcing member130B and the base layer1011. The relative permittivity of the base layer1011was set to 3.3, the relative permittivity of the cover layer1013was set to 3.6, the relative permittivity of the insulating members1352B and1353B was set to 4.7, and the relative permittivity of the adhesive was set to 4.0. The relative permittivity of the insulating member1351B was set to 30. The conductivity of the signal line110was set to 1.724×10−8Ωm.

The width of the wiring portion102is denoted by W302, the width of the wiring portion103is denoted by W303, and the width of the pad104is denoted by W304. In addition, the distance between a pair of the wiring portions102in the differential line pair111is denoted by S302, the distance between a pair of the wiring portions103in the differential line pair111is denoted by S303, and the distance between a pair of the pads104in the differential line pair111is denoted by S304. In the simulation, the values of the widths and the distances were as follows: W302=150 μm; S302=45 μm: W303=130 μm: S303=65 μm; W304=250 μm; and S304=150 μm. As described above, in Example 3. W304>W302>W303and S304>S303>S302hold.

In Example 3, the characteristic impedance (differential impedance) Z1B of the wiring portion102was 103.8Ω. The characteristic impedance (differential impedance) Z2B of the wiring portion103was 100.0Ω. The characteristic impedance (differential impedance) Z3B of the pad104was 100.8Ω.

In Comparative Example 1, the difference (Z3X-Z2X) in the characteristic impedance was 32.7Ω. In contrast, in Example 3, the difference (Z3B-Z2B) in the characteristic impedance was 0.8Ω. Therefore, the absolute value |Z3B-Z2B| of the difference in the characteristic impedance of Example 3 was smaller than the absolute value |Z3X-Z2X| of the difference in the characteristic impedance of Comparative Example 1, which indicates that the characteristic impedance was more consistent in Example 3 than in Comparative Example 1. Therefore, in Example 3, generation of the reflection wave can be reduced.

In Comparative Example 1, the difference (Z2X-Z1X) in the characteristic impedance was −18.3Ω. In contrast, in Example 3, the difference (Z2B-Z1B) in the characteristic impedance was −3.8Ω. Therefore, the absolute value |Z2B-Z1B| of the difference in the characteristic impedance of Example 3 was smaller than the absolute value |Z2X-Z1X| of the difference in the characteristic impedance of Comparative Example 1, which indicates that the characteristic impedance was more consistent in Example 3 than in Comparative Example 1. Therefore, in Example 3, generation of the reflection wave can be reduced.

Fourth Embodiment

Next, a transmission module of a fourth embodiment will be described.FIG.13Ais a plan view of a transmission module100C according to the fourth embodiment.FIG.13Bis a longitudinal section view of the transmission module100C according to the fourth embodiment.FIGS.13A and13Bschematically illustrate the transmission module100C. In the fourth embodiment, the transmission module100C is applied to the electronic unit500instead of the transmission module100of the first embodiment. Therefore, description of elements substantially the same as in the first embodiment will be omitted.

The transmission module100C of the fourth embodiment includes the flexible printed wiring board101, the connector109, and the connector120described in the first embodiment. To be noted, inFIGS.13A and13B, the flexible printed wiring board101is stretched straight.FIG.14Ais a cross-section view of the transmission module100C taken along a line XIVA-XIVA ofFIG.13A.FIG.14Bis a cross-section view of the transmission module100C taken along a line XIVB-XIVB ofFIG.13A.FIG.14Cis a cross-section view of the transmission module100C taken along a line XIVC-XIVC ofFIG.13A. To be noted, inFIG.14C, illustration of the connector109is omitted.

The flexible printed wiring board101includes a plurality of signal lines110used for transmission of the digital signal D2. Among the plurality of signal lines110, pairs of adjacent signal lines110each constitute a differential line pair111that is a transmission path used for transmitting a differential signal. The signal lines110each include the wiring portion102, the wiring portion103, the pad104, the wiring portion105, and the pad106.

The transmission module100C of the fourth embodiment includes a reinforcing member130C disposed at a position opposing the connector10) with the flexible printed wiring board101therebetween. In addition, the transmission module100C includes a reinforcing member140C disposed at a position opposing the connector120with the flexible printed wiring board101therebetween.

The reinforcing member130C includes insulating members1351C and1352C that are electrically insulating. The relative permittivity of the insulating member1351C is equal to the relative permittivity of the insulating member1352C. The insulating member1351C is disposed at a position opposing the plurality of pads104. The insulating member1351C is thicker than the insulating member1352C.

The reinforcing member140C includes insulating members1451C and1452C that are electrically insulating. The relative permittivity of the insulating member1451C is equal to the relative permittivity of the insulating member1452C. The insulating member1451C is disposed at a position opposing the plurality of pads106. The insulating member1451C is thicker than the insulating member1452C.

The reinforcing member130C is a member for reinforcing the flexible printed wiring board101to suppress breakage of the signal lines110when attaching or detaching the connector109to or from the connector204. Therefore, the insulating member1352C of the reinforcing member130C is thicker than the flexible printed wiring board101. Similarly, the reinforcing member140C is a member for reinforcing the flexible printed wiring board101to suppress breakage of the signal lines110when attaching or detaching the connector120to or from the connector305. Therefore, the insulating member1452C of the reinforcing member140C is thicker than the flexible printed wiring board101. As viewed in the Z direction perpendicular to the main surface1010of the flexible printed wiring board101, the reinforcing member130C is disposed in a region including the entirety of the connector109. In addition, as viewed in the Z direction, the reinforcing member140C is disposed in a region including the entirety of the connector120.

The configuration of the reinforcing member140C is substantially the same as the configuration of the reinforcing member130C. In addition, the positional relationship of the reinforcing member140C with the connector120, the wiring portion105, and the pad106is substantially the same as the positional relationship of the reinforcing member130C with the connector109, the wiring portion103, and the pad104. Therefore, detailed description of the reinforcing member140C will be omitted.

The insulating member1351C of the reinforcing member130C serves as an example of a first insulating member. The insulating member1352C of the reinforcing member130C serves as an example of a second insulating member.

The insulating member1352C is formed in a uniformly constant thickness in a direction parallel to the main surface1010. Examples of the material of the insulating member1352C include resins such as polyimide. PET, and glass epoxy, and among the resins, glass epoxy, which has high rigidity, is particularly preferable. The insulating member1351C is formed from the same material as the insulating member1352C. By using the same material for the insulating members1351C and1352C, the manufacturing cost can be reduced.

Among the plurality of pads104, description will be given focusing on one pad104. As viewed in the Z direction, the reinforcing member130C includes a first portion P1C disposed in a region including at least part of the pad104, and a second portion P2C disposed around the first portion P1C as viewed in the Z direction. It is preferable that the region of the first portion P1C includes 90% or more of the area of the pad104as viewed in the Z direction. In the fourth embodiment, as viewed in the Z direction, the first portion P1C is disposed in a region including the entirety of the pad104.

Focusing on the plurality of the pads104, that is, all the pads104, the first portion P1C is disposed in a region including the entirety of the plurality of pads104as viewed in the Z direction. Further, the second portion P2C is disposed around the first portion P1C so as to surround the first portion P1C as viewed in the Z direction.

Here, a differential signal is transmitted through the pair of signal lines110of the differential line pair111. Therefore, a characteristic impedance Z1C of the wiring portion102described below is a differential impedance of the pair of wiring portions102in the differential line pair111. In addition, a characteristic impedance Z2C of the wiring portion103is a differential impedance of the pair of wiring portions103in the differential line pair111. In addition, a characteristic impedance Z3C of the pad104is a differential impedance of the pair of pads104in the differential line pair111.

In the fourth embodiment, a member constituting the first portion P1C is a member having a nature that reduces the characteristic impedance Z3C of the pad104more than a member constituting the second portion P2C does.

Specifically, the first portion P1C is constituted by the insulating member1351C described above. As viewed in the Z direction, the insulating member1351C has the same shape and size as the first portion P1C. In addition, the second portion P2C is constituted by the insulating member1352C disposed around the insulating member1351C. As viewed in the Z direction, the insulating member1352C has the same shape and size as the second portion P2C. The insulating member1351C has the same relative permittivity as the insulating member1352C.

To be noted, although the insulating member1351C may be formed integrally with the insulating member1352C, the insulating member1351C may be divided into two portions1351C-1and1351C-2in view of ease of manufacture thereof. In this case, the portions1351C-1and1351C-2may be joined using an adhesive. In addition, in this case, the insulating member1352C may be integrally formed with the portion1351C-1.

As described above, in the fourth embodiment, the insulating member1351C is a member constituting the first portion P1C. In addition, in the fourth embodiment, the insulating member1352C is a member constituting the second portion P2C. In addition, the insulating member1351C is thicker than the insulating member1352C. Therefore, the insulating member1351C has a nature that reduces the characteristic impedance of an opposing conductor more than the insulating member1352C does. The reinforcing member130X of the comparative example is formed from the same material as and in the same thickness as the insulating member1352C. Therefore, the characteristic impedance Z3C of the fourth embodiment is reduced more than the characteristic impedance Z3X of the comparative example. That is, since the insulating member1351C is disposed to oppose the pad104, the characteristic impedance Z3C of the pad104is reduced. As a result of this, the absolute value of the difference (Z3C-Z2C) between the characteristic impedance Z2C of the wiring portion103and the characteristic impedance Z3C of the pad104can be reduced. Therefore, in the signal line110, generation of the reflection wave of the digital signal D2, that is, generation of the noise can be reduced, and thus the quality of the digital signal D2transmitted through the signal line110can be improved.

A width W404of the pad104is preferably larger than each of a width W402of the wiring portion102and a width W403of the wiring portion103for bonding the terminal1091of the connector109thereto. In addition, a distance S404between the pair of pads104is preferably larger than each of a distance S402between a pair of wiring portions102and a distance S403between a pair of wiring portions103for bonding the terminal1091of the connector109thereto.

In addition, the width W403of the wiring portion103is preferably equal to or less than the width W402of the wiring portion102. As viewed in the Z direction, the wiring portion103overlaps the second portion P2C of the reinforcing member130C having a higher relative permittivity than the air. Therefore, the width W403of the wiring portion103may be equal to the width W402of the wiring portion102not overlapping the reinforcing member130C, but is preferably smaller than the width W402. As a result of this, the characteristic impedance Z2C of the wiring portion103is higher than the characteristic impedance Z2X of the wiring portion103X of the comparative example. Therefore, the absolute value of the difference (Z2C-Z1C) between the characteristic impedance Z1C of the wiring portion102and the characteristic impedance Z2C of the wiring portion103can be reduced. In addition, the absolute value of the difference (Z3C-Z2C) between the characteristic impedance Z2C of the wiring portion103and the characteristic impedance Z3C of the pad104can be reduced. Therefore, in the signal line110, generation of the reflection wave of the digital signal D2, that is, generation of the noise can be more effectively reduced, and the quality of the digital signal D2transmitted through the signal line110can be more effectively improved.

In addition, the distance S403between a pair of the wiring portions103is preferably equal to or larger than the distance S402between a pair of the wiring portions102. As viewed in the Z direction, the pair of the wiring portions103overlaps the second portion P2C of the reinforcing member130C having a higher relative permittivity than the air. Therefore, the distance S403between the pair of the wiring portions103may be equal to the distance S402of the pair of the wiring portions102not overlapping the reinforcing member130C, but is preferably larger than the distance S402. As a result of this, the characteristic impedance Z2C is higher than the characteristic impedance Z2X of the comparative example. Therefore, the absolute value of the difference (Z2C-Z1C) between the characteristic impedance Z1C and the characteristic impedance Z2C and the absolute value of the difference (Z3C-Z2C) between the characteristic impedance Z2C and the characteristic impedance Z3C can be reduced. Therefore, in the signal line110, generation of the reflection wave of the digital signal D2, that is, generation of the noise can be more effectively reduced, and the quality of the digital signal D2transmitted through the signal line110can be more effectively improved.

In addition, as viewed in the Z direction, although the wiring portion103may partially overlap the first portion P1C, since the first portion P1C has a nature that reduces the characteristic impedance of an opposing conductor, it is preferable that the wiring portion103does not overlap the first portion P1C. As a result of this, reduction of the characteristic impedance Z2C of the wiring portion103can be suppressed, and the absolute value of the difference (Z2C-Z1C) and the absolute value of the difference (Z3C-Z2C) can be reduced. Therefore, in the signal line110, generation of the reflection wave of the digital signal D2, that is, generation of the noise can be more effectively reduced, and the quality of the digital signal D2transmitted through the signal line110can be more effectively improved.

To be noted, although the reinforcing member130C has been described, since the reinforcing member140C has substantially the same configuration as the reinforcing member130C, the quality of the digital signal D2transmitted through the signal line110can be more effectively improved.

In addition, the first portion P1C may further include the conductive member136having substantially the same configuration as in the first embodiment. In addition, part or the entirety of the insulating member1351C included in the first portion P1C may be formed from a material having a higher relative permittivity than the insulating member1352C.

Example 4

Simulation of differential impedance was performed for the transmission module100C according to the fourth embodiment. HyperLynx available from Mentor Graphics was used for the simulation of the differential impedance.

The thickness of the base layer1011is denoted by T4011, the thickness of the conductor layer1012is denoted by T4012, and the thickness of a portion of the cover layer1013overlapping the signal line110on the conductor layer1012is denoted by T4013. In addition, the thickness of the insulating member1352C of the reinforcing member130C is denoted by T405. The thickness of the portion1351C-1is also denoted by T405. The thickness of the insulating member1351C is denoted by T4051. The thickness of the portion1351C-2, which is a projecting portion, that is obtained by subtracting the thickness T405from the thickness T4051of the insulating member1351C is denoted by T406. In the simulation, parameter values of the respective thicknesses were as follows: T4011=12.5 μm; T4012=12 μm; T4013=27.5 μm; T405=415 μm, and T406=415 μm. To be noted, the thickness T405of the insulating member1352C includes a thickness of 15 μm of an adhesive between the insulating member1352C and the base layer1011. The thickness T406of the portion1351C-2includes a thickness of 15 μm between the portion1351C-1and the portion1351C-2. The relative permittivity of the base layer1011was set to 3.3, the relative permittivity of the cover layer1013was set to 3.6, the relative permittivity of the portions1351C-1and1351C-2and the insulating member1352C was set to 4.7, and the relative permittivity of the adhesive was set to 4.0. The conductivity of the signal line110was set to 1.724×10−8Ωm.

The width of the wiring portion102is denoted by W402, the width of the wiring portion103is denoted by W403, and the width of the pad104is denoted by W404. In addition, the distance between a pair of the wiring portions102in the differential line pair111is denoted by S402, the distance between a pair of the wiring portions103in the differential line pair111is denoted by S403, and the distance between a pair of the pads104in the differential line pair111is denoted by S404. In the simulation, the values of the widths and the distances were as follows: W402=150 μm: S402=45 μm; W403=130 μm; S403=65 μm; W404=290 μm: and S404=110 μm. As described above, in Example 4, W404>W402>W403and S404>S403>S402hold.

In Example 4, the characteristic impedance (differential impedance) Z1C of the wiring portion102was 103.8Ω. The characteristic impedance (differential impedance) Z2C of the wiring portion103was 100.0Ω. The characteristic impedance (differential impedance) Z3C of the pad104was 99.7Ω.

In Comparative Example 1, the difference (Z3X-Z2X) in the characteristic impedance was 32.7Ω. In contrast, in Example 4, the difference (Z3C-Z2C) in the characteristic impedance was −0.3Ω. Therefore, the absolute value |Z3C-Z2C| of the difference in the characteristic impedance of Example 4 was smaller than the absolute value |Z3X-Z2X| of the difference in the characteristic impedance of Comparative Example 1, which indicates that the characteristic impedance was more consistent in Example 4 than in Comparative Example 1. Therefore, in Example 4, generation of the reflection wave can be reduced.

In Comparative Example 1, the difference (Z2X-Z1X) in the characteristic impedance was −18.3Ω. In contrast, in Example 4, the difference (Z2C-Z1C) in the characteristic impedance was −3.8Ω. Therefore, the absolute value |Z2C-Z1C| of the difference in the characteristic impedance of Example 4 was smaller than the absolute value |Z2X-Z1X| of the difference in the characteristic impedance of Comparative Example 1, which indicates that the characteristic impedance was more consistent in Example 4 than in Comparative Example 1. Therefore, in Example 4, generation of the reflection wave can be reduced.

Fifth Embodiment

Next, a transmission module of a fifth embodiment will be described.FIG.15Ais a plan view of a transmission module100D according to the fifth embodiment.FIG.15Bis a longitudinal section view of the transmission module100D according to the fifth embodiment.FIGS.15A and15Bschematically illustrate the transmission module100D. In the fifth embodiment, the transmission module100D is applied to the electronic unit500instead of the transmission module100of the first embodiment. Therefore, description of elements substantially the same as in the first embodiment will be omitted.

The transmission module100D of the fifth embodiment includes a flexible printed wiring board101D, and the connector109and the connector120described in the first embodiment. To be noted, inFIGS.15A and15B, the flexible printed wiring board101D is stretched straight.FIG.16Ais a cross-section view of the transmission module100D taken along a line XVIA-XVIA ofFIG.15A.FIG.16Bis a cross-section view of the transmission module100D taken along a line XVIB-XVIB ofFIG.15A. To be noted, inFIG.16B, illustration of the connector109is omitted.

The flexible printed wiring board101D includes a plurality of signal lines110D used for transmission of the digital signal D2. Among the plurality of signal lines110D, pairs of adjacent signal lines110D each constitute a differential line pair111D that is a transmission path used for transmitting a differential signal. Due to increase in the size of the image data, the digital signal D2is transmitted at a transmission speed of 10 Gbps or more per one differential line pair111D. The signal lines110D are each formed from a metal foil such as a copper foil.

The flexible printed wiring board101D includes the insulating layer1014that is described in the first embodiment that supports the plurality of signal lines110D. The insulating layer1014includes the base layer1011and the cover layer1013. The plurality of signal lines110D are disposed in a conductor layer1012D on the base layer1011. The base layer1011and the cover layer1013are formed from, for example, polyimide.

The transmission module100D of the fifth embodiment includes a reinforcing member130D disposed at a position opposing the connector109with the flexible printed wiring board101D therebetween. In addition, the transmission module100D includes a reinforcing member140D disposed at a position opposing the connector120with the flexible printed wiring board101D therebetween. The reinforcing member130D includes an insulating layer135D that is electrically insulating. The reinforcing member140D includes an insulating layer145D that is electrically insulating. The reinforcing member130D is a member for reinforcing the flexible printed wiring board101D to suppress breakage of the signal lines110D when attaching or detaching the connector109to or from the connector204. Therefore, the insulating layer135D of the reinforcing member130D is thicker than the flexible printed wiring board101D. Similarly, the reinforcing member140D is a member for reinforcing the flexible printed wiring board101D to suppress breakage of the signal lines110D when attaching or detaching the connector120to or from the connector305. Therefore, the insulating layer145D of the reinforcing member140D is thicker than the flexible printed wiring board101D. As viewed in the Z direction perpendicular to a main surface1010D of the flexible printed wiring board101D, the reinforcing member130D is disposed in a region including the entirety of the connector109. In addition, as viewed in the Z direction, the reinforcing member140D is disposed in a region including the entirety of the connector120.

The signal line110D includes a wiring portion102D as a main line, and a pad104D connected to the wiring portion102D. The wiring portion102D serves as an example of a first wiring portion, and is disposed at a position not overlapping the reinforcing member130D as viewed in the Z direction. The pad104D is disposed in a region overlapping the reinforcing member130D as viewed in the Z direction. The pad104D is bonded to the terminal1091of the connector109via solder or the like.

In addition, the signal line110D includes a pad106D connected to the wiring portion102D. The pad106D is disposed in a region overlapping the reinforcing member140D as viewed in the Z direction. The pad106D is bonded to the terminal1201of the connector120via solder or the like.

In the fifth embodiment, the reinforcing member130D includes a conductive member136D disposed on the insulating layer135D. In addition, in the fifth embodiment, the reinforcing member140D includes a conductive member146D disposed on the insulating layer145D.

The configuration of the reinforcing member140D is substantially the same as the reinforcing member130D. In addition, the positional relationship of the reinforcing member140D with the connector120, the wiring portion102D, and the pad106D is substantially the same as the positional relationship of the reinforcing member130D with the connector109, the wiring portion102D, and the pad104D. Therefore, detailed description of the reinforcing member140D will be omitted.

The insulating layer135D of the reinforcing member130D is formed in a uniformly constant thickness in a direction parallel to the main surface1010D. Examples of the material of the insulating layer135D include resins such as polyimide, PET, and glass epoxy, and among the resins, glass epoxy, which has high rigidity, is particularly preferable. The conductive member136D of the reinforcing member130D is disposed on the insulating layer135D. The conductive member136D is a metal foil such as a copper foil. The conductive member136D may be electrically connected to an unillustrated ground terminal of the connector109.

Among the plurality of pads104D, description will be given focusing on one pad104D. As viewed in the Z direction, the reinforcing member130D includes a first portion P1D disposed in a region including at least part of the pad104D, and a second portion P2D disposed around the first portion P1D as viewed in the Z direction. It is preferable that the region of the first portion PID includes 90% or more of the area of the pad104D as viewed in the Z direction. In the fifth embodiment, as viewed in the Z direction, the first portion P1D is disposed in a region including the entirety of the pad104D.

Focusing on the plurality of the pads104D, that is, all the pads104D, the first portion P1D is disposed in a region including entirety of the plurality of pads104D as viewed in the Z direction. Further, the second portion P2D is disposed around the first portion P1D so as to surround the first portion P1D as viewed in the Z direction.

Here, a differential signal is transmitted through the pair of signal lines110D of the differential line pair111D. Therefore, a characteristic impedance Z1D of the wiring portion102D described below is a differential impedance of the pair of wiring portions102D in the differential line pair111D. In addition, a characteristic impedance Z3D of the pad104D is a differential impedance of the pair of pads104D in the differential line pair111D.

In the fifth embodiment, a member constituting the first portion P1D is a member having a nature that reduces the characteristic impedance Z3D of the pad104D more than a member constituting the second portion P2D does.

Specifically, the first portion P1D is constituted by an insulating member1351D that is part of the insulating layer135D, and the conductive member136D disposed on the insulating member1351D. As viewed in the Z direction, the insulating member1351D and the conductive member136D each have the same shape and size as the first portion P1D. In addition, the second portion P2D is constituted by an insulating member1352D that is part of the insulating layer135D and disposed around the insulating member1351D. As viewed in the Z direction, the insulating member1352D has the same shape and size as the second portion P2D. The insulating member1351D serves as an example of a first insulating member. The insulating member1352D serves as an example of a second insulating member. The insulating member1351D is formed from the same material as the insulating member1352D and in the same thickness as the insulating member1352D, and has the same relative permittivity as the insulating member1352D.

As described above, in the fifth embodiment, the insulating member1351D and the conductive member136D are members constituting the first portion PID. In addition, in the fifth embodiment, the insulating member1352D having the same relative permittivity and the same thickness as the insulating member1351D is a member constituting the second portion P2D. The member constituted by the insulating member1351D and the conductive member136D has a nature that reduces the characteristic impedance of an opposing conductor more than the member constituted by the insulating member1352D does. Since the reinforcing member130X of the comparative example has substantially the same configuration as the insulating laver135D, the characteristic impedance Z3D of the fifth embodiment is reduced more than the characteristic impedance Z3X of the comparative example. That is, since the conductive member136D is disposed to oppose the pad104D with the insulating member1351D therebetween, the characteristic impedance Z3D of the pad104D is reduced. As a result of this, the absolute value of the difference (Z3D-Z1D) between the characteristic impedance Z1D of the wiring portion102D and the characteristic impedance Z3D of the pad104D can be reduced. Therefore, in the signal line110D, generation of the reflection wave of the digital signal D2, that is, generation of the noise can be reduced, and thus the quality of the digital signal D2transmitted through the signal line110D can be improved.

A width W504of the pad104D is preferably larger than the width W502of the wiring portion102D for bonding the terminal1091of the connector109thereto. In addition, a distance S504between the pair of pads104D is preferably larger than a distance S502between a pair of wiring portions102D for bonding the terminal1091of the connector109thereto.

To be noted, although a case where the first portion P1D of the fifth embodiment has substantially the same configuration as the first portion P1of the first embodiment has been described, the configuration is not limited to this. For example, the first portion P1D of the fifth embodiment may be configured in substantially the same manner as one of the first portions P1A to P1C of the second to fourth embodiments.

In addition, whereas the reinforcing member130D has been described, the reinforcing member140D has substantially the same configuration as the reinforcing member130D, and therefore the quality of the digital signal D2transmitted through the signal line110D can be more effectively improved.

Example 5

Simulation of differential impedance was performed for the transmission module100D according to the fifth embodiment. HyperLynx available from Mentor Graphics was used for the simulation of the differential impedance.

The thickness of the base layer1011is denoted by T5011, the thickness of the conductor layer1012D is denoted by T5012, the thickness of a portion of the cover layer1013overlapping the signal line110D on the conductor layer1012D is denoted by T5013. In addition, the thickness of the insulating layer135D of the reinforcing member130D is denoted by T505, and the thickness of the conductive member136D is denoted by T506. In the simulation, parameter values of the respective thicknesses were as follows: T5011=12.5 μm; T5012=12 μm; T5013=27.5 μm: T505=265 μm: and T506=115 μm. To be noted, the thickness T505of the insulating layer135D includes a thickness of 15 μm of an adhesive between the insulating layer135D and the base layer1011. In addition, the thickness T506of the conductive member136D includes a thickness of 15 μm of an adhesive between the conductive member136D and the insulating layer135D. The relative permittivity of the base layer1011was set to 3.3, the relative permittivity of the cover layer1013was set to 3.6, the relative permittivity of the insulating layer135D of was set to 4.7, and the relative permittivity of the adhesive was set to 4.0. The conductivity of the signal line110D and the conductivity of the conductive member136D were set to 1.724×10−8Ωm.

The width of the wiring portion102D is denoted by W502, and the width of the pad104D is denoted by W504. In addition, the distance between a pair of the wiring portions102D in the differential line pair111D is denoted by S502, and the distance between a pair of the pads104D in the differential line pair111D is denoted by S504. In the simulation, the values of the widths and the distances were as follows: W502=150 μm; S502=45 μm; W504=250 μm; and S504=150 μm. As described above, in Example 5, W504>W502and S504>S502hold.

In Example 5, the characteristic impedance (differential impedance) Z1D of the wiring portion102D was 103.8Ω. The characteristic impedance (differential impedance) Z3D of the pad104D was 102.2Ω.

In Comparative Example 1, the difference (Z3X-Z2X) in the characteristic impedance was 32.7Ω. In addition, in Comparative Example 1 the difference (Z2X-Z1X) in the characteristic impedance was −18.3Ω. In contrast, in Example 5, the difference (Z3D-Z1D) in the characteristic impedance was −1.6Ω. Therefore, the absolute value |Z3D-Z1D| of the difference in the characteristic impedance of Example 5 was smaller than the absolute values |Z3X-Z2X| and |Z2X-Z1X| of the difference in the characteristic impedance of Comparative Example 1, which indicates that the characteristic impedance was more consistent in Example 5 than in Comparative Example 1. Therefore, in Example 5, generation of the reflection wave can be reduced.

As described above, according to the present disclosure, the quality of the digital signal that is transmitted is improved.

The present invention is not limited to the embodiments described above, and can be modified in many ways within the technical concept of the present disclosure. In addition, the effects described in the embodiments are merely enumeration of the most preferable effects that can be achieved by the present invention, and the effects of the present invention are not limited to those described in the embodiments.

Although the digital signal D2is a 4-level signal in the first to fifth embodiments, the configuration is not limited to this. In addition, a configuration in which the image signal transmitted from the image sensor202to the image processing device302as the digital signal D1that is a binary signal is not transmitted through the conversion circuits203and204may be employed. In the case of transmitting a binary signal, the conversion circuits203and204can be omitted. Even in these cases, the present disclosure is applicable when the digital signals D1and D2are transmitted at a high speed.

Although a case where the electronic unit of the present disclosure is applied to an image pickup apparatus such as a digital camera has been described in the first to fifth embodiments, the configuration is not limited to this. For example, the electronic unit of the present disclosure is applicable to electronic devices capable of incorporating the electronic unit, such as mobile communication devices, wearable devices, and image forming apparatuses. Examples of the mobile communication devices include devices such as smartphone, tablet PCs, and gaming devices. Examples of the image forming apparatuses include printers, copiers, facsimile machines, and multifunctional apparatuses having functions of these.

In addition, although a case where the first electronic module is configured to transmit a digital signal to the second electronic module via the transmission module has been described in the first to fifth embodiments, the configuration is not limited to this. Further, the second electronic module may be configured to transmit a digital signal to the first electronic module via the transmission module.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

This application claims the benefit of Japanese Patent Application No. 2021-178495, filed Nov. 1, 2021, which is hereby incorporated by reference herein in its entirety.