Wiring boards and vehicle display devices

Abstract

In a wiring board with a high-frequency transmission line, the impedance increase and disturbance caused by reflections, etc., of the return current flowing to the ground plane due to the AC signal flowing through the high-frequency transmission line is reduced without requiring major changes to the wiring pattern. [Solution] The ground plane has a first cutout BR1 for electronic components and a second cutout SL as a slit formed at a position corresponding to the electronic component. In the perspective view, the first and second cutouts are arranged so that at least a portion of them overlap. The ground pattern 42 for electronic components extends across the second cutout SL as a slit in the direction of AC signal transmission. Each of the first and second ground planes 10a and 10b is electrically connected to the ground pattern 42 for electronic components by through conductors 40a to 40c, and a bypass path is formed that allows the return current 29 to flow around the second cutout SL.

Description

Technical Field

[0001] The present invention relates to a wiring board and a vehicle display device mounted on a vehicle such as an automobile.

Background Art

[0002] Patent Document 1 discloses a circuit board having a first ground layer and a second ground layer connected to the first ground layer via a bypass capacitor and serving as an AC ground that allows only AC noise components to flow to the first ground layer. As described in

[0031] of Patent Document 1, a portion where no ground layer is formed (generally referred to as a slit) is provided between the first ground layer and the second ground layer, and the DC potentials of the respective ground layers are separated by this slit. In the circuit board of FIG. 4B of Patent Document 1, signal lines for transmitting differential current signals are wired so as to cross the above-described slit (portion without formation).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a circuit board as in Patent Document 1, when a signal line in the nth layer (n is a natural number of 2 or more) is wired across a slit (portion without formation) provided in the ground layer, when a high-frequency signal (microwave) is transmitted via the signal line, eddy currents are generated in the signal wiring, and due to electromagnetic induction caused by these eddy currents, a return current (return current: when the high-frequency signal is regarded as a microwave, it can be referred to as a "reflected wave" generated at the termination) flows in the ground plane (ground surface) provided in the (n - 1)th layer, which is the layer immediately below, in the direction opposite to the direction in which the high-frequency signal flows. This return current attempts to flow through the ground plane from the receiving end to the transmitting end of a high-frequency signal. However, slits (ground cutouts) in the ground plane prevent it from traveling along the shortest path. As a result, the return current has to take a long detour through a chaotic current path through which it can flow. This increases unwanted reflections in the return current, causing waveform distortion. The transmitted high-frequency signal and the return current are in a paired relationship; an increase in reflection or waveform distortion in the return current directly leads to an increase in the characteristic impedance of the transmitted high-frequency signal. An increase in characteristic impedance in a high-frequency signal transmission path can lead to signal reflection and waveform distortion, degrading signal quality and potentially making it impossible to maintain acceptable signal quality.

[0005] Furthermore, a deterioration in signal quality has a significant impact on electromagnetic compatibility (EMC). To keep electromagnetic compatibility (EMC) within a specified tolerance range, it is important to reduce the adverse effects of external noise on the circuit and to reduce the emission of unwanted electromagnetic waves from the circuit itself as a noise source (in other words, to suppress unwanted radiation). However, the increased reflection and waveform distortion of high-frequency signals mentioned above can cause unwanted electromagnetic waves to be emitted to the outside, leading to a decrease in electromagnetic compatibility (EMC). However, if the slits (cutouts in the ground layer) in the ground plane are removed, when different circuits are operating, the operation of one circuit will cause the potential of the ground plane at the position corresponding to that circuit to fluctuate. This fluctuation is then transmitted to the other circuit through the solid ground plane without cutouts, causing the operation of the other circuit to become unstable, resulting in a crosstalk problem. Therefore, a slit (a cutout in the ground plane) has to be added to the ground plane. However, this slit blocks the flow of return current caused by high-frequency signals that flow across the slit, or in other words, longitudinally. As a result, the characteristic impedance of the high-frequency signal increases, leading to a deterioration of electromagnetic compatibility (EMC). In other words, the challenges of separating DC potentials between different ground planes using slits and blocking return currents caused by high-frequency signals routed across (longitudinally through) the slits are in a trade-off relationship, and achieving both simultaneously is difficult with current technology. While it is possible to significantly alter the wiring pattern from conventional designs to address the above issues, this would increase the burden on designers and lead to higher costs. The aforementioned Patent Document 1 does not describe such problems, nor does it mention any means of solving them.

[0006] One of the objectives of the present invention is to reduce the increase in impedance and disturbances due to reflection, etc., of the return current flowing to the ground plane caused by the AC signal flowing through the high-frequency transmission line, without requiring major changes to the wiring pattern, in a wiring board having a high-frequency transmission line where the ground plane is DC-separated by a slit to provide two ground planes.

[0007] Other objects of the present invention will become apparent to those skilled in the art by referring to the embodiments and best embodiments described below, as well as the accompanying drawings. [Means for solving the problem]

[0008] The following are examples of embodiments of the present invention to facilitate understanding of its outline.

[0009] In a first embodiment, the wiring board has a wiring layer provided on a first surface of an insulating substrate having a predetermined thickness and being flat, and a ground plane provided on a second surface facing the first surface via the insulating substrate, wherein the wiring layer comprises a signal transmission pattern as a transmission path for transmitting high-frequency signals, a first ground pattern as a first ground surface that defines a reference potential on the wiring board, and a second ground pattern as a second ground surface that is DC-separated from the first ground pattern and functions as an AC ground for AC signals flowing through the signal transmission pattern, wherein the second ground pattern includes a ground pattern for an electronic component connected to the other pole of an electronic component mounted with one pole connected to the signal transmission pattern, and the ground plane has a first cutout, which is a cutout for the electronic component, where the conductor layer constituting the second ground pattern is removed at a position facing the electronic component mounted on the wiring layer via the insulating substrate, and a first ground plane corresponding to the first ground pattern on the wiring layer and the front of the wiring layer A second cutout is formed as a slit portion that electrically separates the second ground plane corresponding to the second ground pattern, and in a perspective view of the insulating substrate as seen from the first surface, the first and second cutouts are arranged so that at least a portion of them overlap, and in a perspective view of the insulating substrate as seen from the first surface, the ground pattern for the electronic component included in the second ground pattern extends across the second cutout portion as a slit portion in the direction of transmission of the AC signal, the first ground plane is electrically connected to the ground pattern for the electronic component by a first through conductor that penetrates the insulating substrate, and the second ground plane is electrically connected to the ground pattern for the electronic component by a second through conductor that penetrates the insulating substrate, and the first through conductor, the ground pattern for the electronic component, and the second through conductor constitute a bypass path that allows the return current generated in the ground pattern in response to the AC signal flowing in the signal transmission path to flow around the second cutout portion as a slit portion.

[0010] In the first embodiment, a bypass path for a bridge structure (bridge structure) that efficiently carries back current is easily constructed by making effective use of existing ground wiring patterns. Even if the return current path is interrupted by the slits in the ground plane, the return current can still flow efficiently via the shortest and least disturbed linear path through the bypass path provided by the bridge structure described above. Therefore, reflections and waveform distortions in the return current are sufficiently suppressed, which in turn suppresses the increase in the characteristic impedance of the high-frequency signal transmission line, ensuring signal quality within acceptable limits, and also suppressing a decrease in the electromagnetic compatibility (EMC) of the wiring board (or circuit board if mounted components are included). The bypass route for the bridge structure described above can be easily realized by arranging (laying out) a first cutout formed in the ground pattern directly beneath an electronic component mounted on the wiring layer (one pole of which is connected to the ground pattern for the electronic component), and a second cutout, also formed in the ground pattern, which serves as a slit to electrically separate two ground patterns with different DC potentials, such that at least a portion of them overlap in a perspective plan view seen from the side of the upper wiring pattern. The following explains this point. The first cutout formed in the ground plane directly beneath the electronic component is formed to suppress the occurrence of large parasitic capacitance between the electronic component and the ground plane directly beneath it, which would otherwise hinder the high-speed transmission of high-frequency signals. In other words, because electronic components have a large mounting area, a large parasitic capacitance is formed between the bottom surface of the electronic component and the ground plane region directly beneath it. As a result, the electronic component functions as a capacitive component, which blunts the waveform of high-frequency signals and hinders the high-speed transmission of high-frequency signals. To prevent this, a first cutout is provided in the ground plane directly beneath the electronic component, removing the ground conductor layer. This prevents the formation of the aforementioned parasitic capacitance, thereby suppressing a decrease in the transmission speed of high-frequency signals and waveform distortion. In this embodiment, the first cutout is positioned to overlap the slit portion, which is the second cutout. As mentioned above, the first cutout is located directly beneath the electronic component. Conversely, this means that an electronic component is always located directly above the first cutout. Furthermore, the electronic component is placed between the signal line extending across the slit and the ground pattern for the electronic component; therefore, a ground pattern for the electronic component is always present in the vicinity of the electronic component. Furthermore, since electronic components are connected to high-frequency signal transmission lines, high-speed potential fluctuations constantly occur at one pole of the electronic component. Therefore, the ground pattern for electronic components needs to absorb these potential fluctuations and stabilize the ground potential. Consequently, the ground pattern for electronic components has a relatively larger area compared to ordinary wiring. Having a large surface area means, in other words, that the ground pattern for the electronic component extends in the direction of signal transmission, crossing (vertically traversing) the slit portion, which acts as a second cutout formed in the ground plane directly below. Therefore, when the first cutout is positioned to overlap the second cutout, an electronic component is always located directly above it, and a large ground pattern for that electronic component extends across the slit area in the vicinity of that electronic component. This automatically creates a wiring and ground plane layout (this can be described as a kind of self-alignment automatic positioning of wiring patterns, etc.). Then, one of the ground patterns separated by the slit is connected via a first through-conductor (such as a through-via) to the ground pattern for the upper electronic component, at a location in front of the slit, using the shortest possible path. The other ground plane separated by the slit is connected via a second through-conductor (such as a through-via) to the ground pattern for the upper electronic component, at a location behind the slit, using the shortest possible path. This allows the first through-conductor, the ground pattern for the electronic components, and the second through-conductor to construct a bridge-like bypass path that efficiently allows the return current to flow around the second cutout, which acts as a slit. In this embodiment, since the existing ground patterns for electronic components are effectively utilized, there is no need to add new ground patterns for electronic components. Furthermore, by changing the layout so that the first and second cutouts overlap, the ground pattern for electronic components can be automatically positioned (self-aligned positioning) so that it straddles (crosses) the slit section. This allows for easy implementation of a bypass path for the return current without major changes to the wiring pattern, requiring only minor layout changes as needed (for example, slightly changing the shape of the ground pattern for electronic components, or adding a few through-conductors (through-vias, etc.)). Therefore, the burden on designers can be reduced, and cost increases can be suppressed.

[0011] In a second embodiment dependent on the first embodiment, the first and second ground patterns may be DC-separated high-resistance, with one pole connected to the electronic component and the signal transmission pattern and the other pole connected to the ground pattern for the electronic component, or a diode used to suppress overcurrent or overvoltage in the signal transmission pattern, with one pole connected to the signal transmission pattern and the other pole connected to the ground pattern for the electronic component.

[0012] In the second embodiment, the electronic component may be a high-resistance component that DC-separates two ground planes connected to a high-frequency signal transmission pattern, or a diode that constitutes an overcurrent (overvoltage) protection circuit, etc. These electronic components are not special; they are commonly used in high-frequency circuits, and large-area ground patterns for other electronic components are always laid out near them to stabilize the ground potential. In this aspect, by using the ground pattern for existing electronic components present in this normal high-frequency circuit as a conductor that is a component of the return current path, it is possible to effectively suppress an increase in the characteristic impedance of the high-frequency transmission line and a degradation in signal quality without requiring special wiring pattern changes or the like.

[0013] In a third aspect dependent on the first or second aspect, the AC signal may be a differential current signal.

[0014] In this aspect, an AC signal (high-frequency signal) is transmitted as a differential current signal. Differential current transmission is a transmission method that uses two signal lines, flows currents of opposite phases to each other, and transmits using the potential difference between the signal lines. According to this transmission method, even if the same noise is added to each signal line, in differential current transmission, since the potential difference between the signal lines is observed, the noise is canceled, and thus malfunction of the circuit or the like can be suppressed. Also, an effect of improving electromagnetic interference (EMI) can be expected.

[0015] In a fourth aspect dependent on any of the first to third aspects, in a perspective plan view seen from the side of the first surface of the insulating base material, the first cutout portion that is the cutout portion for the electronic component overlaps with the ground pattern on the receiving end side of the high-frequency signal and the second cutout portion among the ground patterns divided by the slit portion, or the first cutout portion that is the cutout portion for the electronic component overlaps with the ground pattern on the transmitting end side of the high-frequency signal and the second cutout portion among the ground patterns divided by the slit portion, or the first cutout portion that is the cutout portion for the electronic component may overlap with both of the two ground patterns divided by the second cutout portion and the slit portion.

[0016] In the fourth aspect, layout examples of the allowable overlap of the first and second cutouts are shown. In this aspect, three overlapping layout examples are shown, but any layout is acceptable because separation of the ground pattern by the slit portion is achieved, so any layout may be used. In other words, when aligning the first and second cutouts, even if a slight deviation occurs due to the alignment error, any of the above layouts is acceptable, so the overlapping alignment is facilitated and the burden of layout design can be reduced.

[0017] In a fifth aspect dependent on any one of the first to fourth aspects, in a perspective plan view seen from the side of the first surface of the insulating base material, the first and second ground patterns face each other in parallel through the second cutout as the slit portion, or, in a perspective plan view seen from the side of the first surface of the insulating base material, each of the first and second ground patterns may have a corner at a corresponding position to each other through the second cutout as the slit portion and face each other. In this aspect, the first and second ground patterns separated by the second cutout as the slit portion may be arranged to face each other in parallel through the second cutout (when considering the thickness of each ground pattern, they are arranged to face each other in parallel planes). In this case, no local electric field concentration occurs in each ground pattern, and a ground pattern with a more stable ground potential can be obtained. Also, each of the first and second ground patterns may be arranged to face each other with corners at corresponding positions through the second cutout as the slit portion (when considering the thickness of each ground pattern, they are arranged to face each other with corners). In this case, a slight localized electric field concentration occurs at the opposing corners of each ground pattern, and it is expected that the return current flows through this area, overcoming the second slit-like opening. In this case, in addition to the bridge-like bypass path described above, a current path is also created that flows over the second slit, which contributes to suppressing the rise in impedance of the return current and suppressing reflection and waveform distortion.

[0018] In a sixth embodiment dependent on any of the first to fifth embodiments, the wiring board may be a multilayer wiring board in which a plurality of insulating substrates having the wiring layers and the ground plane are laminated together.

[0019] In the sixth embodiment, a multilayer wiring board is used as the wiring board. As the number of layers increases, the wiring patterns and other elements become more complex, making it difficult to keep electromagnetic compatibility (EMC) within acceptable limits. By applying the present invention, it becomes easier to keep electromagnetic compatibility (EMC) within acceptable limits even for multilayer substrates with a large number of layers, thereby reducing the burden of designing wiring boards.

[0020] In a seventh embodiment dependent on any of the first to fifth embodiments, the wiring board may be a vehicle wiring board that is mounted on a vehicle and supplies the AC signal to an in-vehicle display device mounted on the vehicle via the signal transmission pattern.

[0021] In the seventh embodiment, a vehicle-mounted wiring board is used as the wiring board. Vehicle-mounted wiring boards are required to have strict noise immunity or noise emission reduction characteristics. By applying the present invention, it becomes easier to keep electromagnetic compatibility (EMC) within acceptable limits, improving the quality of the wiring board (circuit board) and reducing the burden of wiring board (circuit board) design.

[0022] In the eighth embodiment, the vehicle display device comprises a wiring board in any of the first to fifth forms mounted on a vehicle, a vehicle display device mounted on the vehicle, and a vehicle display control device mounted on the vehicle that supplies AC signals necessary for display on the vehicle display device to the wiring board.

[0023] By applying the present invention to a vehicle display device, the deterioration of the display quality of vehicle displays (including instrument displays, traffic guide displays, etc.) can be suppressed, and for example, accurate and easy-to-read vehicle displays can be realized.

[0024] In a ninth embodiment dependent on the eighth embodiment, the vehicle display device may be an instrument display device that displays information indicating the status of the vehicle.

[0025] Instrument displays show important information such as vehicle speed and engine RPM, and therefore require accurate and easy-to-read information. By applying the present invention, the deterioration of instrument display quality can be suppressed, and accurate and easy-to-read instrument displays can be realized.

[0026] Those skilled in the art will readily understand that the embodiments of the present invention illustrated can be further modified without departing from the spirit of the invention. [Brief explanation of the drawing]

[0027] [Figure 1] Figures 1(A) to 1(D) illustrate the problems before applying the present invention, and Figure 1(E) illustrates why the problems are solved by applying the present invention. [Figure 2] Figure 2(A) shows an example of the transmission path of a differential current signal in a 4-layer wiring board, Figure 2(B) shows an example of the return current path before the application of the present invention, and Figure 2(C) shows an example of the return current path after the application of the present invention. [Figure 3] Figure 3 shows an example of a circuit mounted on a circuit board in which electronic components are mounted on a wiring board. [Figure 4]Figure 4 shows an example of the layout patterns for each of the first to fourth layers (L1 to L4) when the circuit in Figure 3 is mounted on a four-layer multilayer substrate using the present invention. [Figure 5] Figures 5(A) to 5(E) show examples of overlapping configurations of the first cutout for electronic components and the second cutout as a slit, as well as the layout shapes of the ground patterns in the first and second cutouts. [Modes for carrying out the invention]

[0028] The best embodiments described below are used to facilitate understanding of the present invention. Therefore, those skilled in the art should note that the present invention is not unduly limited by the embodiments described below.

[0029] (First Embodiment) Refer to Figure 1. Figures 1(A) to (D) illustrate the problems before applying the present invention, and Figure 1(E) illustrates why the problems are solved by applying the present invention.

[0030] The wiring board shown in Figure 1(A) has a predetermined thickness and is flat, and comprises a wiring layer 14 provided on the upper, first surface of an insulating substrate (in the case of a rigid substrate, for example, an insulating substrate made of glass epoxy) 17, and a ground plane 10 provided on the lower, second surface that faces the upper, first surface via the insulating substrate 17.

[0031] The wiring layer 14, although not shown in Figure 1(A), includes a signal transmission pattern that serves as a transmission path for transmitting high-frequency signals.

[0032] In Figure 1(A), when the high-frequency signal (microwave) indicated by arrow 21 flows from the left end (transmitting end) to the right end (receiving end) in the figure, eddy currents are generated in the signal pattern, and electromagnetic coupling occurs between it and the lower ground plane 10 due to these eddy currents. The figure shows a combination of an ellipse and an arrow, which indicates that electromagnetic coupling is occurring between the upper wiring layer 14 and the lower ground pattern 10.

[0033] As a result of this electromagnetic coupling, a return current (a reflected wave if the high-frequency signal is considered a transmitted wave such as a microwave) 19 is generated in the lower ground plane 10, directly beneath the transmission path of the high-frequency signal, in the opposite direction to the flow of the high-frequency signal.

[0034] In the figure, the symbols CX1 and CX2 indicate parasitic capacitances formed between the wiring layer 14 and the ground plane 10. Furthermore, electronic circuits constructed by mounting electronic components on the wiring layers of a wiring board have the properties of distributed-parameter circuits.

[0035] Furthermore, the circuit board itself functions as a microstrip line for transmitting microwaves (a microwave transmission line having a structure in which a coaxial cable is cut into sections and half of each section is extended in a planar shape).

[0036] In Figure 1(B), two different circuits G1 and G2 are mounted on the wiring layer 14. As a result, a return current 19 corresponding to circuit G1 and a return current 25 corresponding to circuit G2 flow through the lower ground plane 10.

[0037] In Figure 1(B), the ground plane 10 is a continuous (solid) ground pattern used in common for circuits G1 and G2. Therefore, when circuits G1 and G2 operate independently, the operation of one circuit causes the potential of the ground plane 10 at the position corresponding to that circuit to fluctuate. This fluctuation is transmitted to the other circuit via the solid ground plane 10, causing the operation of the other circuit to become unstable, resulting in a crosstalk problem. In Figure 1(B), two dashed arrows are shown, indicating that crosstalk is occurring.

[0038] In Figure 1(C), a slit section SL (a section where the conductor layer is removed) is provided in the ground plane 10 to prevent crosstalk, thereby separating the ground plane 10 into two ground planes 10a and 10b, which correspond to circuits G1 and G2, respectively. By providing the slit section SL, the return current corresponding to one circuit does not flow into the region of the ground plane corresponding to the other circuit, thereby preventing crosstalk.

[0039] In Figure 1(D), in a structure where the ground plane 10 is separated into two ground planes 10a and 10b by a slit SL, the high-frequency signal (microwave) indicated by arrow 27 flows from the left end (transmitting end) to the right end (receiving end) in the upper wiring layer 14. In this case, the return current 29 first flows through the ground plane 10b, but its flow is then blocked by the slit (removal) section SL. Therefore, the return current 29 has to take a large detour through the disordered current path J1, which is capable of carrying current, resulting in significant reflections and waveform distortion. In Figure 1(D), this disorder of the return current is represented by arrows 30 with inconsistent directions. Disruptions in the return current result in an increase in the characteristic impedance of the high-frequency signal 27 in the wiring layer 14, leading to a problem of degraded signal quality.

[0040] As a countermeasure, Figure 1(E) shows how to easily construct a bypass path using a bridge structure (bridge configuration) that efficiently carries back current, by making effective use of the existing ground wiring pattern. According to the structure shown in Figure 1(E), even if the return current path is interrupted by the slit section SL, the return current can efficiently flow through the shortest and least disturbed linear path via the bypass path provided by the bridge structure described above. This point will be explained below.

[0041] In Figure 1(E), the lower ground pattern is separated into two ground patterns (ground pattern regions) 10a and 10b by the slit portion SL, similar to Figures 1(C) and (D).

[0042] What is noteworthy here is that, in the perspective plan view from the upper wiring layer 14 side (in other words, from above), a layout is adopted in which the cutout BR corresponding to the electronic component 50 is superimposed on the slit SL.

[0043] In the following explanation, the cutout portion BR corresponding to the electronic component 50 may be referred to as the "first cutout portion," and the slit portion SL may be referred to as the "second cutout portion."

[0044] The first cutout BR1 formed in the ground plane directly beneath the electronic component 50 is formed to suppress the occurrence of a large parasitic capacitance between the electronic component 50 and the ground plane directly beneath it, which would otherwise hinder the high-speed transmission of high-frequency signals.

[0045] In other words, because the electronic component 50 has a larger mounting area compared to a normal wiring pattern, a large parasitic capacitance is formed between the bottom surface of the electronic component 50 and the ground plane region directly below it. As a result, the electronic component 50 functions as a capacitive component, which blunts the waveform of high-frequency signals and hinders the high-speed transmission of high-frequency signals.

[0046] To prevent this, a first cutout is provided in the ground plane directly beneath the electronic component 50, removing the ground conductor layer. This prevents the formation of the aforementioned parasitic capacitance, thereby suppressing a decrease in the transmission speed of high-frequency signals and waveform distortion.

[0047] Prior to the application of the present invention, there were no layout rules regarding the relative positional relationship between the first and second cutouts, and each cutout could be freely positioned.

[0048] In contrast, the present invention employs a layout rule in which the first cutout portion BR1 is positioned to overlap the second cutout portion, which is the slit portion SL.

[0049] As described above, the first cutout BR1 is located directly below the electronic component 50. Alternatively, this means that the electronic component 50 is always located directly above the first cutout BR1.

[0050] Furthermore, the electronic component 50 is installed between the signal line extending across the slit portion SL and the ground pattern for the electronic component. Therefore, a ground pattern for the electronic component (reference numeral 42 in Figure 1(E)) is always present in the vicinity of the electronic component 50.

[0051] Furthermore, in the ground pattern 42 for electronic components, a cutout BW is provided in the area where the electronic component 50 is mounted, where no conductor is formed.

[0052] Furthermore, since the electronic component 50 is connected to a high-frequency signal transmission path, high-speed potential fluctuations constantly occur at one pole of the electronic component 50. The ground pattern 42 for the electronic component needs to absorb these potential fluctuations and stabilize the ground potential. Therefore, the ground pattern 42 for the electronic component has a relatively large area compared to ordinary wiring.

[0053] Having a large area means, in other words, that the ground pattern 42 for the electronic component extends in the direction of signal transmission, straddling (vertically traversing) the slit portion SL, which is a second cutout formed in the ground plane directly below, as shown in Figure 1(E).

[0054] Therefore, when the first cutout BR1 is positioned to overlap the second cutout SL, an electronic component 50 is always directly above it, and a large ground pattern 42 for the electronic component extends across the slit SL in the vicinity of the electronic component 50. This wiring and ground plane layout is automatically realized (this can be described as automatic positioning of wiring patterns, etc., by a kind of self-alignment).

[0055] Then, as shown in Figure 1(E), one of the ground patterns 10b separated by the slit SL is connected via a first through-conductor (through-via, etc.) 40a to the ground pattern 42 for the upper electronic components, on the side closer to the receiving end of the signal transmission line (in front of the slit SL), using the shortest possible path. The other ground plane separated by the slit SL is connected via second through-conductors (through-via, etc.) 40b and 40b' to the ground pattern 42 for the upper electronic components, on the side further from the slit (in front of the transmitting end of the signal transmission line), using the shortest possible path.

[0056] This allows the first through-conductor 40a, the ground pattern 42 for electronic components, and the second through-conductors 40b and 40b' to construct a bridge-like bypass path that efficiently allows the return current to flow around the second cutout SL, which acts as a slit.

[0057] In Figure 1(E), the flow of return current through this bypass path is indicated by dashed arrows, and each part is labeled with the symbols J1, J2, J2', J3, and J3'. As a result, the return current 29 flowing through the ground plane 10b can flow efficiently through the ground plane 10a with almost no waveform distortion.

[0058] In Figure 1(E), since the existing ground patterns for electronic components are effectively utilized, there is no need to add new ground patterns for new electronic components.

[0059] Furthermore, by changing the layout so that the first and second cutouts BR and SL overlap, the ground pattern 42 for electronic components can be automatically positioned (self-aligned positioning) to straddle (longitudinally traverse) the slit SL. This allows for easy implementation of a bypass path for the return current without major changes to the wiring pattern, requiring only minor layout changes as needed (for example, slightly changing the shape of the ground pattern 42 for electronic components, or adding a few through-conductors (through-vias, etc.: indicated by labels 40a, 40b, and 40b' in Figure 1(E))). Thus, the burden on designers is reduced, and cost increases can be suppressed.

[0060] (Second embodiment) Next, refer to Figure 2. Figure 2(A) shows an example of the transmission path of a differential current signal in a four-layer wiring board, Figure 2(B) shows an example of the return current path before the application of the present invention, and Figure 2(C) shows an example of the return current path after the application of the present invention.

[0061] Figure 2(A) shows an example of the structure of a differential current signal transmission path on a 4-layer wiring board (or "4-layer circuit board" if the mounted electronic components are considered; the term "4-layer wiring board" will be used in the following explanation).

[0062] The 4-layer wiring board 100 includes a first wiring layer 101, ground planes 103 and 105 for the second and third layers, a fourth wiring layer 107, and electrical insulating substrates (here, glass epoxy resin) 102, 104, and 106.

[0063] The four-layer wiring board 100 in Figure 2(A) is a multilayer wiring board for vehicle use (onboard) that is mounted in a vehicle.

[0064] This four-layer wiring board 100 has the function of transmitting a pair of differential current signals S1 and S2 output by the vehicle display control device 195 to a connector 170 for connecting to a vehicle display device (here, an instrument display device that displays vehicle information such as vehicle speed) 173 via a high-frequency signal transmission path 165 contained in the fourth wiring layer 107, which is the uppermost layer.

[0065] The differential current signals S1 and S2 output from the connector 170 are supplied to the vehicle display device 173, which then displays instrument information (such as vehicle speed) indicating the vehicle status.

[0066] The high-frequency signal transmission path 165 included in the fourth wiring layer 107 is connected to an IC (Integrated Circuit) 140 having a high-frequency signal transmission function (and reception function), and electronic components 160 such as capacitors and diodes.

[0067] In the figure, reference numeral 151 indicates a through-conductor structure for VBB, which is connected to the AC ground electrode 205 of IC140 and consists of multiple through-conductors (through-vias) for supplying AC ground VBB to IC140. Reference numerals 152 and 153 indicate through-conductor structures for S1 and S2, which are supplied to IC140 with differential current signals S1 and S2, and consist of multiple through-conductors (through-vias).

[0068] Figure 2(B) shows an example of the structure of the return current path in a 4-layer wiring board before the application of the present invention. In Figure 2(B), the same reference numerals are used for the same parts as in Figure 2(A).

[0069] In Figure 2(B), the uppermost fourth layer, wiring layer 107, includes a wiring region 205 for the AC ground VBB, which is the potential of the AC ground VBB, and a wiring region 206 for the DC ground GND, which is the potential of the DC ground GND.

[0070] Furthermore, the third-layer ground plane 105 is provided with three ground plane regions 181, 182, and 183.

[0071] Furthermore, the ground plane region 182 of the third layer and the wiring region 205 of the fourth layer are electrically connected via through conductors (through vias) 203. The third layer's ground plane region 183 is electrically connected via through-conductors (through-vias) 204.

[0072] In addition, in the figure, reference numeral 155 indicates a through-conductor structure for the AC ground VBB that is connected to the ground plane region 182 and consists of multiple through-conductors (through-vias).

[0073] Furthermore, reference numeral 156 indicates a through-conductor structure for DC ground GND, which is connected to the DC ground electrode 206 of connector 170 and supplies DC ground GND to connector 170, and consists of multiple through-conductors (through-vias).

[0074] As explained earlier, the ground plane region 181 for DC ground GND and the ground plane region 182 for AC ground VBB are separated by a slit (second cutout) SL.

[0075] Furthermore, a cutout (first cutout) BR for the electronic component is provided in the ground plane 105 located directly below (below) the electronic component 160.

[0076] As explained earlier in Figure 1(D), the presence of the slit SL prevents the return current 191 from flowing through the shortest path. In this case, the return current flows through a large detour path J2, resulting in significant reflection and waveform distortion. In Figure 2(B), this disturbance in the return current is shown by multiple arrows 192 pointing in different directions.

[0077] Figure 2(C) shows an example of the structure of the return current path after applying the present invention to a four-layer wiring board. In Figure 2(C), the same reference numerals are used for the same parts as in Figure 2(B).

[0078] In Figure 2(C), the wiring layout has been slightly modified. As explained earlier in Figure 1(E), in the perspective plan view from above (the wiring side of the fourth layer), the cutout for electronic components (first cutout) BR overlaps with the slit (second cutout) SL in at least part.

[0079] As explained earlier, when the first cutout BR1 is positioned to overlap the second cutout SL, an electronic component 160 is always directly above it, and a large ground pattern 207 for the electronic component is always located near the electronic component 160, extending across the slit SL when viewed in a perspective plan view. This wiring and ground plane layout is automatically realized (this can be described as a kind of self-alignment automatic positioning of wiring patterns, etc.).

[0080] Furthermore, the ground pattern region 181 on the receiving end side of the high-frequency signal, separated by the slit portion SL (referred to as the front side), is connected via a through-conductor (through-via, etc.) 203 to the ground pattern 207 for the upper electronic components, at a position on the front side of the slit portion SL, via the shortest path. The other ground pattern region 184, separated by the slit portion SL, is connected via a through-conductor (through-via, etc.) 204 to the ground pattern 207 for the upper electronic components, at a position on the transmitting end side of the high-frequency signal, viewed from the perspective plan view, beyond the slit portion SL (referred to as the back side), via the shortest path.

[0081] This allows for the construction of a bridge-like bypass path through the through-conductor 203, the ground pattern 207 for electronic components, and the through-conductor 204, which efficiently directs the return current around the second cutout SL, which acts as a slit. In Figure 2(C), the flow of the return current through this bypass path is indicated by a dashed arrow.

[0082] In the four-layer wiring board shown in Figure 2(C), the existing ground pattern 207 for electronic components is effectively utilized, eliminating the need to add new ground patterns for electronic components.

[0083] Furthermore, by changing the layout so that the first and second cutouts BR and SL overlap, the ground pattern 207 for electronic components can be automatically positioned (self-aligned positioning) so that it straddles (crosses) the slit SL when viewed in a perspective plan view. This allows for easy implementation of a bypass path for the return current without major changes to the wiring pattern, requiring only minor layout changes as needed (for example, slightly changing the shape of the ground pattern 207 for electronic components, or adding a few through-conductors (through-vias, etc.)). Therefore, the burden on designers is reduced, and cost increases can be suppressed.

[0084] Next, refer to Figure 3. Figure 3 shows an example of a circuit mounted on a circuit board in which electronic components are mounted on a wiring board. In Figure 3, parts common to the previously shown diagram are denoted by the same reference numerals.

[0085] In Figure 3, four transmission lines LS1 to LS4 (collectively referred to as LS in the figure) are provided as transmission lines for transmitting high-frequency signals of differential current signals.

[0086] An IC140 (having a transmitter 301 and a receiver 302) is connected to one end of the transmission lines LS1 to LS4 as a high-frequency signal communication device, and a connector 170 (having a transmitter 305 and a receiver 306) is connected to the other end.

[0087] Furthermore, a DC blocking capacitor C100 is interposed in the transmission lines (transmission lines) LS1 to LS4 to allow the DC potential to be different at one end and the other end.

[0088] In the figure, the symbol D100 indicates the diode section where diodes D1, D2, etc., for overcurrent (overvoltage) protection are provided.

[0089] Furthermore, the symbol R100 indicates a resistor (including high-resistance R1 to R4) used to maintain a high impedance between the AC ground VBB and the DC ground GND.

[0090] Furthermore, reference numeral 307 denotes a relay section that relays the AC ground VBB and the DC ground GND. The relay section 307 can be, for example, a conductive structure composed of through-conductors (through-vias) provided through multiple insulating substrates.

[0091] Reference numeral 309 indicates the AC ground VBB / DC ground GND separation section, which separates the AC ground VBB from the DC ground GND. Multiple bypass capacitors CA1 to CA20 and a high resistance RH are connected between the wiring LX and the DC ground GND. As a result, AC noise components superimposed on the wiring LX are discharged to the DC ground GND via the bypass capacitors CA1 to CA20. Therefore, the wiring LX functions as the AC ground VBB.

[0092] Reference numeral 311 indicates the AC ground VBB / DC ground GND generation section. Reference numerals CX1 to CX4 indicate bypass capacitors, and RX2 indicates a high resistance that suppresses the flow of large currents into the AC ground VBB.

[0093] Furthermore, the symbol RX1 indicates a resistor that grounds the DC ground (GND), and the symbol CX3 indicates a capacitor that stabilizes the DC ground potential (ground potential) by diverting AC noise components superimposed on the DC ground (GND) to the ground.

[0094] Next, refer to Figure 4. Figure 4 shows an example of the layout patterns for each of the first to fourth layers (L1 to L4) when the circuit of Figure 3 is mounted on a four-layer multilayer substrate using the present invention.

[0095] In Figure 4, the notations L1 to L4 represent the first to fourth layers. In Figure 4, the first layer (L1) is shown at the bottom, and as the hierarchy increases to the second, third, and fourth layers, the position of the notation moves upwards.

[0096] Each of the first to fourth layers (L1 to L4) is provided with AC ground (VBB) patterns and DC ground (GND) patterns. As shown in Figure 2, the same types of patterns in each layer are connected by through conductors (through vias) in each layer and maintained at the same potential.

[0097] First, the wiring pattern of the first layer (L1) will be explained. As shown in the figure, the first layer (L1) is provided with the wiring pattern for IC140 (including the pattern for high-frequency signals and the AC ground (VBB) pattern) ICP-L1, the AC ground (VBB) pattern 403-L1, and the DC ground (GND) pattern 405-L1. Also, in the figure, the area indicated by the symbol CN1 (the roughly rectangular area indicated by the dashed line) corresponds to the mounting area of ​​the connector 170. Furthermore, the wiring pattern of the first layer is provided with terminal areas TA1 and TA2 corresponding to through conductors (through vias).

[0098] Furthermore, through conductors (held at the potential of VBB and GND; not shown) inserted through terminal regions TA1 and TA2 of the first layer (L1) are connected to through conductors (through vias; not shown) of terminal regions TA3 and TA4 of the fourth layer (L4).

[0099] The wiring pattern of the second layer (L2) includes the ground plane pattern ICP-L2 for IC140, the AC ground (VBB) pattern 403-L2, and the DC ground (GND) pattern 405-L2.

[0100] For the third layer (L3), both the ground plane pattern before the application of the present invention (left side) and the ground plane pattern after the application of the present invention (right side) are shown for ease of understanding.

[0101] In the third layer (L3), similar to the second layer, there are patterns ICP-L3 for the ground plane of IC140, 403-L3 for the AC ground (VBB), and 405-L3 for the DC ground (GND). In addition, there are cutouts (first cutouts) BR1 and BR2 and a slit (second cutout) SL for electronic components (here, the resistor section R100 (high resistance R1~R4) in Figure 3).

[0102] In the pattern prior to the application of the present invention (the pattern shown on the left in the figure), as explained earlier, the cutouts for electronic components (first cutouts) BR1 and BR2 do not overlap with the slit (second cutout) SL in a perspective view from above. Therefore, the return current flows by taking a large detour, for example, through a disordered bypass path (indicated by a thick arrow in the figure) J3, which causes large reflections and large waveform distortions, increasing the characteristic impedance of the high-frequency signal transmission path and degrading the signal quality.

[0103] In the pattern prior to the application of the present invention (the pattern shown on the left in the figure), as explained earlier, the cutouts for electronic components (first cutouts) BR1 and BR2 do not overlap with the slit (second cutout) SL in a perspective plan view from above. Therefore, the return current flows in a large detour, for example, through a disordered bypass path (indicated by the thick arrow in the diagram) J3, which causes large reflections and significant waveform distortion, increasing the characteristic impedance of the high-frequency signal transmission path and degrading signal quality.

[0104] In the pattern after applying the present invention (the pattern shown on the right in the figure), as previously explained, the cutouts for electronic components (first cutouts) BR1 and BR2 are arranged to overlap with the slit (second cutout) SL in a perspective view from above.

[0105] Furthermore, in the third layer ground plane, there are cutouts (first cutouts) BR-D100 corresponding to the diode section D100 where diodes D1, D2, etc. for overcurrent (overvoltage) protection are provided, and cutouts (first cutouts) BR-R100 corresponding to the resistor section R100 are provided.

[0106] In the third layer (L3), the slit section (second cutout) SL is essentially formed, including the first and second cutout sections BR1 and BR2, and the potential separation of the AC ground VBB and the DC ground GND is achieved. However, when viewed in the perspective plan view, it appears that there is no slit in the slit section SL (where the second cutout overlaps). Also, through conductors (through vias) VA1 and VA2 are provided in the pattern of the third layer.

[0107] In the wiring pattern of the fourth layer (L4), similar to the second and third layers, a ground pattern ICP-L4 for IC140, an AC ground (VBB) pattern 403-L4, and a DC ground (GND) pattern 405-L4 are provided.

[0108] Furthermore, there are cutouts (first cutouts) BR1 and BR2 for electronic components (here, the resistor section R100 (high resistance R1 to R4) in Figure 3), and a slit section (second cutout) SL.

[0109] Furthermore, the fourth layer (L4) is provided with high-frequency signal transmission lines (transmission lines) LS (LS1 to LS4 in Figure 3; shown as bent solid lines in Figure 4) and an AC ground pattern (AC ground pattern region) for electronic components (here, high-resistance R1 to R4) that is connected to one pole of the electronic components.

[0110] The dashed rectangle in the upper center of Figure 4 shows a magnified view of a portion of the pattern, including the AC ground pattern (AC ground pattern region) for electronic components. The AC ground pattern (AC ground pattern region) for electronic components is the region indicated by the symbols EG1 to EG3 in the figure.

[0111] Furthermore, the fourth layer (L4) contains high-resistor components R1 to R4 and the diode section D100 (including diodes D1, D2, etc.). Furthermore, terminal regions TA3 and TA4, and through conductors (through vias) VA3 and VA4 are provided.

[0112] As can be seen from Figures 3 and 4, according to the pattern to which the present invention is applied, the shortest bypass path of the bridge structure that can efficiently carry the return current is automatically configured, as explained earlier.

[0113] Specifically, this detour path is a current path that passes through, for example, the through-conductor (through-via) VA1 of the third layer (L3), the through-conductor (through-via) VA3 of the fourth layer (L4), the AC ground pattern (AC ground pattern region) EG2 for electronic components in the fourth layer (L4), the through-conductor (through-via) VA4 of the fourth layer (L4), and the through-conductor (through-via) VA2 of the third layer (L3). The return current flows through paths J4a, J4b, and J4c (indicated by dashed arrows in the figure).

[0114] Because the return current flows through the shortest bypass path, the increase in the characteristic impedance of the high-frequency signal transmission line is sufficiently suppressed. Therefore, the degradation of the signal quality of the high-frequency signal can be effectively suppressed.

[0115] (Third embodiment) Next, refer to Figure 5. Figures 5(A) to (E) show examples of the overlapping configuration of the first cutout for electronic components and the second cutout as a slit, and the layout shape of the ground pattern in each cutout.

[0116] Figures 5(A) to (C) show examples of acceptable overlapping configurations of the first and second cutouts BR and SL.

[0117] In Figure 5(A), in the perspective plan view from the first surface side (upper side, or wiring layer side) of the insulating substrate, in other words, in the perspective plan view from the wiring layer side (upper side), the first cutouts BR1 and BR2, which are cutouts for electronic components, overlap with the ground pattern 205 on the high-frequency signal receiving end side of the ground patterns 205 and 206 separated by the slit (second cutout) SL, and with the second cutout SL, which is the slit.

[0118] In Figure 5(B), the first cutouts BR1 and BR2, which are cutouts for electronic components, overlap with the ground pattern 206 on the high-frequency signal transmission end side and the second cutout SL, which is a slit, of the ground patterns 205 and 206 separated by the slit (second cutout) SL.

[0119] In Figure 5(C), the first cutouts BR1 and BR2, which are cutouts for electronic components, overlap with both the second cutout SL, which is a slit, and the two ground patterns 205 and 206 that are separated by the slit (second cutout).

[0120] Figures 5(A) to (C) show three overlapping layout examples, but any of these layouts is acceptable because the separation of ground patterns 205 and 206 by the slit section SL is achieved in any of them.

[0121] In other words, even if a slight misalignment occurs due to alignment errors when aligning the first and second cutout sections BR and SL, it is acceptable in any of the above layouts, thus simplifying overlapping alignment and potentially reducing the burden of layout design.

[0122] Figures 5(D) and (E) show examples of ground pattern layouts in the first and second cutout sections.

[0123] In Figure 5(D), in a perspective plan view from the first surface side (upper side, or wiring layer side) of the insulating substrate, the first and second ground patterns 205 and 206, separated by the slit portion (second cutout) SL, are arranged parallel to each other via the second cutout SL, which acts as the slit portion. If the thickness of each ground pattern 205 and 206 is also taken into consideration, it can be said that they are arranged parallel to each other.

[0124] In this case, localized electric field concentrations do not occur in each ground pattern, resulting in a ground pattern with a more stable ground potential.

[0125] In Figure 5(E), in a perspective plan view seen from the first surface side (upper side, or wiring layer side) of the insulating substrate, the first and second ground patterns 205 and 206 each face each other with corners at corresponding positions, via the second cutout portion SL which serves as a slit. If the thickness of each ground pattern 205 and 206 is also taken into consideration, this can be rephrased as them being arranged face-to-face with corners.

[0126] In this case, a slight localized electric field concentration occurs at the opposing corners of each ground pattern 205 and 206, and it can be expected that the return current flows through this area, overcoming the second slit portion SL.

[0127] In Figures 5(D) and (E), the paths of the current flowing in this manner are shown by dashed arrows.

[0128] In the examples of Figures 5(D) and (E), in addition to the bridge-like bypass path described above, a current path is also created that flows over the second extraction section SL described above. This contributes to suppressing the rise in impedance of the return current, as well as suppressing reflections and waveform distortions.

[0129] (Fourth embodiment) In the example shown in Figure 4, the cutouts BR1 and BR2 for the high-resistance electronic components R1 to R4 were superimposed on the slit SL, which served as the second cutout. However, depending on the circuit configuration, it may not be possible to provide the high-resistance components R1 to R4.

[0130] In such cases, for example, the cutout BR-D100 for the diode section D100 may be superimposed on the slit section SL, which serves as a second cutout. Such modifications and applications can be made as appropriate.

[0131] (Experimental results) The target characteristic impedance of the differential current signal transmission line is 100 ohms, and the design standard allows for a tolerance of 90 to 110 ohms, taking into account variations. Before the application of this invention, the characteristic impedance was 10⁹ ohms. The allowable variation margin was small. On the other hand, after applying the present invention, the characteristic impedance became 10⁶.5 ohms. The allowable variation margin is expanded, and thus the design is simplified.

[0132] As described above, according to the embodiments of the present invention, in a wiring board having a high-frequency transmission line, the increase in impedance and disturbances due to reflection, etc., of the return current flowing to the ground plane caused by the AC signal flowing through the high-frequency transmission line can be reduced without requiring major changes to the wiring pattern.

[0133] Furthermore, according to embodiments of the present invention, the first cutouts in electronic components such as high-resistance components that DC-separate two ground planes connected to a high-frequency signal transmission pattern, or diodes that constitute an overcurrent (overvoltage) protection circuit, can be effectively utilized. These electronic components are not special; they are commonly used in high-frequency circuits, and large-area ground patterns for other electronic components are always laid out near them to stabilize the ground potential. Therefore, by using this material as a conductor that is a component of the bypass path for the return current in the ground pattern for existing electronic components in a typical high-frequency circuit, it is possible to effectively suppress the increase in characteristic impedance and the degradation of signal quality in the high-frequency transmission line without requiring any special changes to the wiring pattern.

[0134] Furthermore, in the embodiments of the present invention, a differential current signal can be used as the transmitted AC signal. Differential current transmission is a transmission method that uses two signal lines, through which currents with opposite phases flow, and transmits the signal using the potential difference between the signal lines. With this transmission method, even if the same noise is applied to each signal line, differential current transmission cancels out the noise by considering the potential difference between the signal lines, thus suppressing circuit malfunctions. Furthermore, it is expected to improve electromagnetic interference (EMI).

[0135] Furthermore, in the embodiments of the present invention, a multilayer wiring board can be used as the wiring board. As the number of layers increases on a circuit board (a circuit board on which electronic components are mounted), the complexity of the wiring patterns and other elements increases, making it more difficult to keep electromagnetic compatibility (EMC) within acceptable limits. By applying the present invention, it becomes easier to keep electromagnetic compatibility (EMC) within acceptable limits even for multilayer substrates with a large number of layers, thereby reducing the burden of designing wiring boards.

[0136] Furthermore, in embodiments of the present invention, the wiring board may be a vehicle wiring board that is mounted on a vehicle and supplies AC signals to an in-vehicle display device mounted on the vehicle via a signal transmission pattern (see Figure 2(A)). Vehicle wiring boards require stringent noise immunity and noise emission reduction characteristics. By applying the present invention, it becomes easier to keep electromagnetic compatibility (EMC) within acceptable limits, improving the quality of the wiring board (circuit board) and reducing the burden of wiring board (circuit board) design.

[0137] Furthermore, in embodiments of the present invention, the vehicle display device may include a wiring board mounted on a vehicle, a vehicle display device mounted on a vehicle, and a vehicle display control device mounted on a vehicle that supplies AC signals necessary for display in the vehicle display device to the wiring board (see Figure 2(A)). By applying the present invention to a vehicle display device, the deterioration of the display quality of vehicle displays (including instrument displays, traffic guide displays, etc.) can be suppressed, and for example, accurate and easy-to-read vehicle displays can be realized.

[0138] Furthermore, in embodiments of the present invention, the vehicle display device may be an instrument display device that displays information indicating the status of the vehicle. Instrument displays show important information such as vehicle speed and engine RPM, and therefore require accurate and easy-to-read information. By applying the present invention, the deterioration of instrument display quality can be suppressed, and accurate and easy-to-read instrument displays can be realized.

[0139] The present invention is not limited to the exemplary embodiments described above, and those skilled in the art will be able to easily modify the exemplary embodiments described above to the extent included in the claims. [Explanation of symbols]

[0140] 10...Ground plane, 14...Wiring layer, 17...Insulating substrate, 19, 29, 30...Return current, 21, 23, 27...High frequency signal (microwave), 42...Ground pattern for electronic components, 40a~40c...Through conductor (through via), 50...Electronic component, 100...4-layer wiring board, 101...First layer wiring, 104, 105...Ground planes for the second and third layers, 107...Fourth layer wiring, 102, 104, 106...Insulating substrate (glass epoxy resin, etc.), 140...IC, 151...Through conductor structure for VBB, No. 152 ,153... is a through-conductor structure for differential current signals, 160... electronic components, 170... connectors, 173... vehicle display devices (instrument display devices), 195... vehicle display control devices, CX1, CX2... parasitic capacitance formed between the wiring layer and the ground plane, BW... cutout in the area directly below where the electronic component 50 is mounted (a place in the fourth layer where no conductor is formed), BR (BR1, BR2)... cutouts corresponding to electronic components (first cutouts), SL... second cutout as a slit, J1, J2, J2', J3, J3'... return current flow through bypass paths.

Claims

1. A wiring board having a wiring layer provided on a first surface of an insulating substrate having a predetermined thickness and being flat, and a ground plane provided on a second surface facing the first surface via the insulating substrate, The aforementioned wiring layer is A signal transmission pattern as a transmission path for transmitting high-frequency signals, A first ground pattern, which serves as a first ground plane for determining the reference potential on the aforementioned wiring board, The system comprises a second ground pattern which is DC-separated from the first ground pattern and functions as an AC ground for AC signals flowing through the signal transmission pattern, wherein the second ground pattern includes a ground pattern for an electronic component connected to the other pole of an electronic component mounted with one pole connected to the signal transmission pattern. The aforementioned ground plane includes, A first cutout, which is a cutout for the electronic component, is provided, where the conductor layer constituting the second ground pattern is removed at a position facing the electronic component mounted on the wiring layer via the insulating substrate, A second cutout portion, which serves as a slit portion for electrically separating a first ground plane corresponding to the first ground pattern in the wiring layer from a second ground plane corresponding to the second ground pattern in the wiring layer, A structure has been formed, Furthermore, in the perspective plan view of the insulating substrate as seen from the first surface, the first and second cutouts are arranged so that at least a portion of them overlap, In the perspective plan view of the insulating substrate as seen from the first surface, the ground pattern for the electronic component included in the second ground pattern extends across the second cutout portion, which serves as the slit portion, in the direction of transmission of the AC signal. The first ground plane is electrically connected to the ground pattern for the electronic component by a first through-conductor that penetrates the insulating substrate. and, The second ground plane is electrically connected to the ground pattern for the electronic component by a second through-conductor that penetrates the insulating substrate. The first through conductor, the ground pattern for the electronic component, and the second through conductor constitute a bypass path that allows the return current generated in the ground pattern in response to the AC signal flowing through the signal transmission line to flow around the second cutout, which serves as the slit. Wiring board.

2. The aforementioned electronic component is One pole is connected to the signal transmission pattern, and the other pole is connected to the ground pattern for the electronic component, and the high resistance DC-separates the first and second ground patterns. Or, A diode used to suppress overcurrent or overvoltage in the signal transmission pattern, wherein one pole is connected to the signal transmission pattern and the other pole is connected to the ground pattern for the electronic component. The wiring board according to claim 1.

3. The aforementioned AC signal is a differential current signal. The wiring board according to claim 1.

4. In the perspective plan view seen from the first surface of the insulating substrate, The first cutout, which is a cutout for the electronic component, overlaps with the ground pattern on the receiving end side of the high-frequency signal, which is part of the ground pattern separated by the slit, and the second cutout. Or, The first cutout, which is a cutout for the electronic component, overlaps with the ground pattern on the transmitting end side of the high-frequency signal, which is separated by the slit, and the second cutout. Or, The first cutout, which is a cutout for the electronic component, overlaps with both of the two ground patterns separated by the second cutout and the slit. The wiring board according to claim 1.

5. In the perspective plan view of the insulating substrate as seen from the first surface, the first and second ground patterns are parallel to each other, separated by the second cutout which serves as the slit. Or, In the perspective plan view of the insulating substrate as seen from the first surface, each of the first and second ground patterns faces each other at corresponding positions, with corners, via the second cutout which serves as the slit portion. The wiring board according to claim 1.

6. The aforementioned wiring board is The multilayer wiring board is constructed by stacking multiple insulating substrates, each having the aforementioned wiring layer and the aforementioned ground plane. The wiring board according to claim 1.

7. The aforementioned wiring board is mounted in the vehicle, This is a vehicle wiring board that supplies the AC signal to an in-vehicle display device mounted on the vehicle via the signal transmission pattern. The wiring board according to claim 1.

8. A wiring board according to any one of claims 1 to 6, which is mounted on a vehicle, A vehicle display device mounted on the aforementioned vehicle, A vehicle display control device is mounted on the vehicle and supplies AC signals necessary for display in the vehicle display device to the wiring board, A vehicle display device having the following features.

9. The vehicle display device is an instrument display device that displays information indicating the status of the vehicle. The vehicle display device according to claim 8.

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