Electric device

Abstract

This electric device comprises: a multilayer substrate (10) provided with a plurality of conductive layers; power supply wiring (13) formed across the plurality of conductive layers; capacitors (14); and a circuit element (12) serving as a generation source of noise that propagates through the power supply wiring (13). A path from a power supply position of the power supply wiring (13) to the circuit element (12) includes: a first section (13-1) connected to the circuit element (12); a second section (13-2) adjacent to the first section; and a third section (13-3) connected to the power supply position. The power supply wiring (13) in the first section (13-1) is formed at least in an inner layer of the plurality of conductive layers, and the power supply wiring (13) in the second section (13-2) is formed in an outer layer of the plurality of conductive layers and is not formed in the inner layer. The capacitors (14) are connected to the power supply wiring (13) in the second section (13-2).

Description

Electrical Equipment

[0001] The present invention relates to an electrical device including a multilayer substrate.

[0002] Multilayer boards, which have conductive layers not only on the outside (front and back) but also inside the board, are known as a type of printed circuit board. Power supply wiring is formed on such multilayer boards to supply power to various circuit elements mounted on the multilayer board. In particular, when a large-capacity power supply is required, the power supply wiring may be formed across multiple conductive layers, including inner layers.

[0003] When a circuit element such as a DC-DC converter is connected to a power supply wiring, the circuit element may become a noise source, and the noise may propagate through the power supply wiring. One possible solution to suppress this noise propagation is to connect a capacitor to the power supply wiring. However, particularly when the power supply wiring is formed on an inner layer of a multilayer board, such a solution may be difficult to implement or may not be sufficiently effective.

[0004] The present invention has been made in consideration of the above-mentioned circumstances, and one of its objects is to provide an electrical device that can effectively suppress the propagation of noise through power supply wiring when power supply wiring spanning multiple conductive layers is formed on a multilayer substrate.

[0005] The electrical device of the present invention comprises a multilayer substrate having a plurality of conductive layers, power supply wiring formed across the plurality of conductive layers, a capacitor connected to the power supply wiring, and a circuit element that is a source of noise propagating via the power supply wiring, wherein the plurality of conductive layers include an outer layer formed on the outside of the multilayer substrate and an inner layer formed on the inside of the multilayer substrate, and a path from a power supply position of the power supply wiring to the circuit element includes a first section connected to the circuit element, a second section adjacent to the first section on the side of the power supply position, and a third section connected to the power supply position, wherein the power supply wiring of the first section is formed at least on the inner layer, and the power supply wiring of the second section is formed on the outer layer and not on the inner layer, and the capacitor is connected to the power supply wiring in the second section.

[0006] It is a diagram showing a schematic diagram of main components of an electric device according to an embodiment of the present invention. It is a diagram showing a schematic diagram of a cross section of a part of a multilayer substrate. It is a diagram showing a schematic diagram of a planar shape of power supply wiring formed on a plurality of conductive layers of a multilayer substrate. It is a graph showing the noise suppression effect of an electric device according to an embodiment of the present invention.

[0007] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0008] 1 is a diagram illustrating the main components of an electrical device 1 according to an embodiment of the present invention. As shown in the diagram, the electrical device 1 includes a multilayer substrate 10, a power supply unit 20, and an AC power cable 21.

[0009] The multilayer substrate 10 is a printed circuit board on which various circuit elements for realizing the functions of the electrical device 1 are mounted, and in this embodiment, includes ten conductive layers. Hereinafter, the ten conductive layers included in the multilayer substrate 10 will be referred to as conductive layers L1-L10 in order from the back surface side of the multilayer substrate 10. Power supply wiring for supplying power to each circuit element arranged on the multilayer substrate 10 is formed on these conductive layers. Details of this power supply wiring will be described later.

[0010] Among the multiple conductive layers included in the multilayer substrate 10, those that are formed on the outside (front or back side) of the multilayer substrate 10 and have a portion exposed on the front or back side of the multilayer substrate 10 are hereinafter referred to as outer layers. In this embodiment, the conductive layers L1 and L10 are the outer layers. More specifically, the conductive layer L1 is formed on the back side of the multilayer substrate 10, and the conductive layer L10 is formed on the front side of the multilayer substrate 10.

[0011] Among the multiple conductive layers included in the multilayer substrate 10, the conductive layers formed inside the multilayer substrate 10 other than the outer layers are referred to as inner layers. In this embodiment, eight layers, namely, conductive layers L2-L9, are inner layers.

[0012] Furthermore, among the inner layers, a conductive layer adjacent to an outer layer in the thickness direction of the multilayer substrate 10 will be referred to as an adjacent layer hereinafter. In this embodiment, conductive layers L2 and L9 are adjacent layers. More specifically, among the inner layers, conductive layer L2 is closest to the back surface of the multilayer substrate 10 and is adjacent to conductive layer L1 in the thickness direction of the multilayer substrate 10. Furthermore, among the inner layers, conductive layer L9 is closest to the front surface of the multilayer substrate 10 and is adjacent to conductive layer L10 in the thickness direction of the multilayer substrate 10.

[0013] Furthermore, the conductive layers among the inner layers other than the adjacent layers (here, the six conductive layers L3-L8) are hereinafter referred to as deep layers. Deep layers are conductive layers among the inner layers that are adjacent only to other inner layers in the thickness direction of the multilayer substrate 10 and are not adjacent to any outer layers.

[0014] The power supply unit 20 includes a power supply circuit for supplying power supplied from an external commercial power source to the multilayer substrate 10. Specifically, the power supply unit 20 rectifies AC current input from outside the electric device 1 via an AC power cable 21 to DC current of a given voltage, and supplies the DC current to the multilayer substrate 10 via a power connector 11 (described later). The AC power cable 21 is a power cable for connecting the electric device 1 to a commercial power source external to the electric device 1, and is connected upstream of the power supply unit 20.

[0015] The power supply wiring formed on the multilayer substrate 10 in this embodiment will be described below. Power supplied from the power supply unit 20 to the multilayer substrate 10 is first input to a power connector 11, which functions as a power supply location on the multilayer substrate 10, and then supplied to each circuit element mounted on the multilayer substrate 10 via power supply wiring formed on the conductive layers of the multilayer substrate 10. More specifically, the power connector 11 is disposed on the multilayer substrate 10, and its power terminal is connected to the power supply unit 20. Furthermore, multiple DC-DC converters are disposed on the multilayer substrate 10, and the power supply wiring extending from the power connector 11 branches off midway and is connected to each of these multiple DC-DC converters. The DC power supplied from the power supply unit 20 is transformed to a given voltage by each of these DC-DC converters before being supplied to each circuit element on the multilayer substrate 10.

[0016] Here, a DC-DC converter may be a noise source that generates noise that propagates through the power supply wiring. Below, we will focus on one DC-DC converter that can be a noise source among the multiple DC-DC converters arranged on multilayer substrate 10, and explain noise countermeasures for that DC-DC converter. Below, this one DC-DC converter, which is a circuit element that can be a noise source, will be referred to as target converter 12. Furthermore, the entire power supply wiring connecting target converter 12 and power connector 11 will be referred to as power supply wiring 13.

[0017] As a result of research, the inventors of the present application have found that noise propagating from converter 12 is not only radiated directly into the air from power supply wiring 13, but may also propagate to power supply unit 20 via power connector 11 and be radiated into the air from power supply unit 20 or AC power cable 21. In such cases, shielding multilayer substrate 10 on which power supply wiring 13 is formed is not sufficient as a noise countermeasure, and it is necessary to suppress the radiation current itself propagating from power supply wiring 13 to power supply unit 20.

[0018] Generally, connecting a capacitor to the power supply wiring is considered to suppress noise propagating through the power supply wiring. In particular, because DC-DC converters require the connection of a capacitor for their function, connecting a capacitor near the DC-DC converter to also suppress noise is effective. However, if at least a portion of the power supply wiring runs through an inner layer of the multilayer substrate 10, connecting a capacitor directly to the power supply wiring on the inner layer is difficult, making it impossible to achieve sufficient noise suppression. On the other hand, arranging power supply wiring only on the outer layer of the multilayer substrate 10 is often difficult due to circuit layout constraints, etc. In particular, when a large-capacity power supply is required, the area of ​​the power supply wiring must be large, and there may not be room to place the power supply wiring on the outer layer of the multilayer substrate 10.

[0019] Therefore, in this embodiment, in some sections of the entire path of the power supply wiring 13, the power supply wiring 13 passes only through the outer layers (i.e., conductive layer L1 and / or conductive layer L10) of the multiple conductive layers of the multilayer substrate 10, and a capacitor is connected to at least that section of the power supply wiring 13. In this embodiment, the power supply wiring 13 from the power connector 11 to the target converter 12 is configured, in a plan view, to include a first section 13-1 directly connected to the target converter 12, a second section 13-2 adjacent to one end of the first section 13-1 on the power connector 11 side, and a third section 13-3 adjacent to one end of the second section 13-2 on the power connector 11 side and directly connected to the power connector 11.

[0020] FIG. 2 is a diagram showing the arrangement of the power supply wiring 13, and schematically illustrates a cross section of a portion of the multilayer substrate 10. Note that in FIG. 2, the portion of the conductive layers of the multilayer substrate 10 that constitutes the power supply wiring 13 is indicated by hatching. Furthermore, the conductive portion extending along the thickness direction of the multilayer substrate 10 indicates a portion where multiple conductive layers are electrically connected by vias or the like. Also, FIG. 3 is a diagram showing an example of the shape of the power supply wiring 13 in plan view, and particularly schematically illustrates the shape of conductive layers L1, L2, L3, L9, and L10 in plan view. Note that while conductive layers L4-L8 are not shown, they may have the same shape as conductive layer L3.

[0021] 2, the multiple conductive layers that make up the power supply wiring 13 are electrically connected to each other at least at the boundary positions of each section (i.e., the position where the first section 13-1 and the second section 13-2 are adjacent, and the position where the second section 13-2 and the third section 13-3 are adjacent) and the position where the target converter 12 is connected (the end of the first section 13-1 on the opposite side from the second section 13-2). As a result, the power supply wiring 13 is formed across the multiple conductive layers, and the current input from the power supply unit 20 to the power connector 11 flows to the target converter 12 while branching into the multiple conductive layers.

[0022] 2, in the second section 13-2, the power supply wiring 13 is not present on the conductive layers L2-L9, which are the inner layers of the multilayer substrate 10, and the power supply wiring 13 is arranged only on the conductive layers L1 and L10, which are the outer layers of the multilayer substrate 10. Therefore, the current flowing through the power supply wiring 13 is detoured to flow on the outer layers of the multilayer substrate 10 at least in this second section 13-2.

[0023] In contrast, in the first section 13-1, power supply wiring 13 is arranged not only on the conductive layers L1 and L10, which are the outer layers of the multilayer substrate 10, but also on the adjacent conductive layers L2 and L9. On the other hand, power supply wiring 13 is not arranged on the conductive layers L3-L8, which are deeper layers further inward than these conductive layers. Therefore, in this first section 13-1, the current flows branching into four conductive layers.

[0024] In the third section 13-3, the power supply wiring 13 is not arranged on the adjacent conductive layers L2 and L9, but is arranged on the conductive layers L1 and L10 as well as on the deeper conductive layers L3-L7. In this embodiment, the third section 13-3 shares at least a portion with the power supply wiring for supplying power to DC-DC converters other than the target converter 12, and includes a portion branching off to other power supply wiring (not shown). In contrast, the first section 13-1 and the second section 13-2 do not branch off to other power supply wiring within those sections, and only the current input to the target converter 12 flows.

[0025] The power supply wiring 13 in the third section 13-3 has a wide width in a plan view in a direction intersecting the direction of current flow and is arranged across many conductive layers in order to pass a large amount of current for supplying power to the multiple DC-DC converters. In contrast, in the first section 13-1 and the second section 13-2, it is sufficient to pass a current for supplying power to the target converter 12, so the width of the power supply wiring 13 in each layer in a plan view may be relatively narrower than that of the third section 13-3.

[0026] Furthermore, the power supply wiring 13 in the second section 13-2 is formed only on the conductive layers L1 and L10, which are outer layers of the multilayer substrate 10. Therefore, compared to the power supply wiring 13 in the first section 13-1, which is formed on a total of four layers, the width in a plan view in a direction intersecting the direction of current flow is wider. Specifically, as shown in Figure 3, the width w2 of the power supply wiring 13 in the second section 13-2 is approximately twice the width w1 of the power supply wiring 13 in the first section 13-1.

[0027] With this configuration, the current output by the power supply unit 20 is input to the power connector 11, and then first flows in the third section 13-3 of the power supply wiring 13, branching off into other power supply wiring and then dispersing through eight layers (conductive layers L1, L3-L8, and L10). Then, in the second section 13-2, the current flows only through the outer layers (two layers: conductive layers L1 and L10). Then, in the first section 13-1, the current flows through four layers (conductive layers L1, L2, L9, and L10) and is finally input to the target converter 12.

[0028] Furthermore, a plurality of capacitors 14 are connected to the portion of the power supply wiring 13 that is formed on the conductive layers L1 and L10, which are the outer layers, in order to suppress noise propagation through the power supply wiring 13. Specifically, the capacitors 14 are connected to the power supply wiring 13 in the second section 13-2, where the power supply wiring 13 is arranged at least only on the outer layers. This ensures that noise propagating from the target converter 12 passes through the power supply wiring 13 in the second section 13-2 to which the capacitors 14 are connected.

[0029] However, it is not necessary to place capacitors 14 only in the second section 13-2; capacitors 14 may also be placed in other sections. In particular, in this embodiment, because it is difficult to place a sufficient number of capacitors 14 in the second section 13-2 due to space constraints, capacitors 14 are also connected to the power supply wiring 13 on conductive layers L1 and L10 in the first section 13-1. Here, in the first section 13-1, unlike the third section 13-3, the power supply wiring 13 running through the inner layers of the multilayer substrate 10 is placed on adjacent layers (conductive layers L2 and L9) that are relatively close to the outer layers. This allows for a greater noise suppression effect by the capacitors 14 than when the power supply wiring 13 is placed on the conductive layers L3-L8 in the deeper layers.

[0030] Specifically, in this embodiment, power supply wiring 13 is arranged on both conductive layer L1, which is an outer layer on the back surface side of multilayer substrate 10, and conductive layer L10, which is an outer layer on the front surface side of multilayer substrate 10, in second section 13-2. Therefore, capacitors 14 are arranged on both the back surface side and the front surface side of multilayer substrate 10. Furthermore, on both the back surface side and the front surface side, a plurality of capacitors 14 are connected from first section 13-1 to second section 13-2. These plurality of capacitors 14 may include capacitors with different capacitances.

[0031] As described above, the first section 13-1 and second section 13-2 of the power supply wiring 13 to which the capacitor 14 is connected are sections through which current flows that is input only to the target converter 12 after the power supply wiring 13 connected to the power connector 11 branches off from other power supply wiring. Therefore, connecting the capacitor 14 to the power supply wiring 13 in this section can efficiently suppress noise propagating from the target converter 12. Here, if the length of the power supply wiring 13 along the direction in which the current flows in a planar view is defined as the power supply path length, the total power supply path length of the first section 13-1 and second section 13-2 adjacent to the target converter 12 is less than half the overall power supply path length of the power supply wiring 13.

[0032] The placement positions of the capacitors connected to the power supply wiring 13 do not need to be limited to the first section 13-1 and the second section 13-2, and a capacitor may also be connected to the power supply wiring 13 in the third section 13-3. In particular, by connecting a capacitor to the power supply wiring 13 on the conductive layer L1 or L10 located relatively close to the power connector 11, before the power supply wiring for supplying power to the multiple DC-DC converters branches, it is possible to expect the effect of suppressing noise propagating from the multiple power supply wiring to the power supply unit 20. In this embodiment, as shown in FIG. 2, multiple capacitors 15 are connected to the power supply wiring 13 on the conductive layer L1 near the power connector 11 in the third section 13-3.

[0033] 4 is a graph showing the results of a simulation verifying the noise suppression effect of the electrical device 1 according to the embodiment of the present invention. The horizontal axis of this graph represents frequency (unit: MHz), and the vertical axis represents the magnitude of the noise component contained in the power supply voltage at the power connector 11 (unit: dBV). The solid line in the graph represents the results for the electrical device 1 according to this embodiment, while the dashed line represents the results for a comparative example configuration in which the power wiring 13 is arranged to the inner layer in both the first section 13-1 and the second section 13-2. As shown in the figure, it has been confirmed that the configuration of this embodiment can suppress noise propagating to the power connector 11.

[0034] As described above, according to the electrical device 1 of this embodiment, a second section 13-2 is provided midway along the power supply wiring 13 up to the target converter 12, in which the power supply wiring 13 is formed only on the outer conductive layers L1 and / or L10, and a capacitor 14 is connected to the power supply wiring 13 in this section, thereby making it possible to effectively suppress noise propagating from the target converter 12 via the power supply wiring 13.

[0035] Furthermore, in this embodiment, the power supply wiring 13 is formed only on the outer conductive layer in the second section 13-2 adjacent to the first section 13-1, rather than in the first section 13-1 directly connected to the target converter 12. This allows the width of the power supply wiring 13 in the first section 13-1 close to the target converter 12 to be relatively narrow, making it less subject to restrictions on the circuit layout.

[0036] The present invention is not limited to the above-described embodiment, and various modifications are possible.

[0037] For example, the planar shape of the power supply wiring 13, the length of each section, and the conductive layer on which the power supply wiring 13 is arranged in each section are all merely illustrative and may differ from the above description without departing from the spirit of the present invention. As an example, in the second section 13-2, the power supply wiring 13 may be formed on only one of the conductive layers L1 and L10. Furthermore, in the first section 13-1 and / or the third section 13-3, the power supply wiring 13 may be formed only on an inner layer. Furthermore, the power supply wiring 13 may not have a portion branching off into other power supply wiring along the way, and all of the current input to the power connector 11 may be input to the target converter 12.

[0038] Furthermore, in the above description, one DC-DC converter is described as a noise source, but this is not limiting, and the configuration of the present invention may be employed in cases where various circuit elements become noise sources and there is a risk of noise being propagated along the power supply wiring 13. Furthermore, the configuration of the present invention may be employed for each of multiple power supply wirings that branch off along the way and supply power to different circuit elements. Furthermore, in the above description, the electrical device 1 is described as operating using power supplied from an external AC power source, but the electrical device according to the embodiment of the present invention is not limited to this, and the configuration of the present invention can be applied to various electrical devices in which power supply wiring for supplying power is arranged on a multilayer substrate.

[0039] 1 Electrical equipment, 10 Multilayer board, 11 Power connector, 12 Target converter, 13 Power wiring, 14, 15 Capacitor, 20 Power supply unit, 21 AC power cable

Claims

1. An electrical device comprising: a multilayer substrate having a plurality of conductive layers; power supply wiring formed across the plurality of conductive layers; a capacitor connected to the power supply wiring; and a circuit element that is a source of noise propagating via the power supply wiring, wherein the plurality of conductive layers include an outer layer formed on the outside of the multilayer substrate and an inner layer formed on the inside of the multilayer substrate, wherein a path from a power supply position of the power supply wiring to the circuit element includes a first section connected to the circuit element, a second section adjacent to the first section on the side of the power supply position, and a third section connected to the power supply position, wherein the power supply wiring of the first section is formed on at least the inner layer, and the power supply wiring of the second section is formed on the outer layer and not on the inner layer, and wherein the capacitor is connected to the power supply wiring in the second section.

2. An electrical device according to claim 1, wherein the power supply wiring of the first section is formed on the outer layer and the inner layer, and the width in a plan view in a direction intersecting the direction of current flow is narrower than that of the second section.

3. An electrical device according to claim 2, wherein the plurality of conductive layers include a plurality of inner layers, and the plurality of inner layers include adjacent layers adjacent to the outer layers in the thickness direction of the multilayer board, and deep layers that are not adjacent to the outer layers and are adjacent only to other inner layers, and the power supply wiring of the first section is formed in the outer layers and the adjacent layers, but not in the deep layers.

4. An electric device according to claim 2, wherein a capacitor other than the capacitor is connected to the power supply wiring formed on the outer layer in the first section.

5. An electrical device according to claim 1, wherein the power supply wiring branches off into other power supply wiring in the third section, and in the first and second sections, the power supply wiring does not branch off into other power supply wiring, and only the current input to the circuit element flows.

6. An electric device according to claim 1, wherein the circuit element is a DC-DC converter that transforms the voltage of the current flowing through the power supply wiring.

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