Wiring board

A wiring board includes a substrate and a plurality of monolithic ceramic capacitors connected in series on the substrate. The plurality of monolithic ceramic capacitors includes a first monolithic ceramic capacitor oriented in a first direction and a second monolithic ceramic capacitor oriented in a second direction. The second direction is at an angle of 45±5 degrees relative to the first direction.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application is based on and claims priority pursuant to 35 U.S.C. § 119(a) to Japanese Patent Application No. 2019-191343, filed on Oct. 18, 2019, in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein.

BACKGROUND

Technical Field

The present disclosure relates to a wiring board.

Related Art

A capacitor is one of electronic components mounted on a wiring board. Examples of capacitors include ceramic capacitors, tantalum capacitors, and aluminum electrolytic capacitors. Since a plurality of capacitors are usually used on one wiring board, various ingenuities have been tried for the arrangement of the capacitors.

SUMMARY

According to an embodiment of this disclosure, a wiring board includes a substrate and a plurality of monolithic ceramic capacitors connected in series on the substrate. The plurality of monolithic ceramic capacitors includes a first monolithic ceramic capacitor oriented in a first direction and a second monolithic ceramic capacitor oriented in a second direction. The second direction is at an angle of 45±5 degrees relative to the first direction.

DETAILED DESCRIPTION

Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views thereof, embodiments of this disclosure are described. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.

Referring toFIG. 1, a wiring board1includes a substrate10, an active component20, and a passive component30.

The active component20and the passive component30are mounted on one side of the substrate10. However, another active component20and another passive component30can be mounted also on the other side of the substrate10as double-sided mounting.

Terminals of the active component20and the passive component30are connected to a component mounting land on the substrate10by soldering or the like. The substrate10is mounted with a wiring pattern for connecting together required portions of the terminals of the active component20and the passive component30, a power supply wiring (VDD wiring) pattern connected to the active component20, and a ground wiring (GND wiring) pattern.

The substrate10is not particularly limited, but is, for example, a resin substrate (a glass epoxy substrate, a phenolic paper substrate, etc.), a ceramic substrate, a silicon substrate, or the like. The substrate10can be any one of a single-sided substrate having a wiring pattern on one side, a double-sided substrate having wiring patterns on both sides, and a multi-layer substrate in which a plurality of wiring patterns are laminated via insulation layers.

The active component20is not particularly limited, but is, for example, a semiconductor integrated circuit, a transistor, a diode, or the like. The passive component30is not particularly limited, but is, for example, a capacitor, a resistor, an inductor, a connector, or the like.

FIG. 2is an enlarged view of a portion A inFIG. 1and illustrates an arrangement of capacitors according to the present embodiment.FIG. 3is a circuit diagram corresponding toFIG. 2. Referring toFIGS. 2 and 3, supply voltage (VDD) wiring H1having a power supply potential and ground (GND) wiring H2having a ground potential are connected to an integrated circuit (IC) IC1. Between the supply voltage wiring H1and the ground wiring H2, capacitors C1and C2(also collectively “capacitors C”), which are bypass capacitors, are connected in series.

The IC IC1is a semiconductor integrated circuit, and the capacitors C1and C2are monolithic ceramic capacitors. The IC IC1is a part of the active component20illustrated inFIG. 1. The capacitors C1and C2are a part of the passive component30illustrated inFIG. 1.

FIGS. 4A and 4Bare views illustrating an external appearance of each of the capacitors.FIG. 4Ais a perspective view, andFIG. 4Bis a plan view. As illustrated inFIGS. 4A and 4B, each of the capacitors C1and C2has a substantially rectangular parallelepiped body31, and electrodes32and33on opposite sides of the body31from each other. The body31is, for example, a dielectric made of barium titanate or the like. The electrodes32and33are electric conductors and are made of, for example, copper plated with tin.

In the present embodiment, as illustrated inFIG. 4B, in a plan view, a direction indicated by a broken line D inFIG. 4B, in which a center32aof the electrode32is connected with a center33aof the electrode33, is referred to as a mounting direction D of the capacitor C1or C2.

Returning to the description ofFIG. 2, the broken line D1indicates the mounting direction of the capacitor C1, that is, an orientation of the capacitor C1on the substrate10(hereinafter also “mounting direction D1”). In other words, the capacitor C1is mounted in the direction indicated by the broken line D1on the substrate10. A broken line D2indicates the mounting direction of the capacitor C2on the substrate10(hereinafter also “mounting direction D2”). In other words, the capacitor C2is mounted in the direction indicated by the broken line D2on the substrate10. In the capacitor arrangement illustrated inFIG. 2, an angle θ between the mounting direction D1and the mounting direction D2is 45±5 degrees. An advantage thereof is described below.

It is possible that various stresses are applied to the wiring board1. Depending on the direction of the stress, a component mounted on the wiring board1may be cracked, resulting in a short circuit.

Since a monolithic ceramic capacitor is a capacitor type in which a crack causes a short circuit, a technique being considered is connecting a plurality of monolithic ceramic capacitors in series between different direct current (DC) potentials. In such an arrangement, even when a short circuit occurs in one of the monolithic ceramic capacitors, insulation will be maintained by other serially connected monolithic ceramic capacitors. However, the plurality of monolithic ceramic capacitors connected in series is usually mounted at a short distance from each other on the wiring board. Therefore, when stress is applied to the wiring board, the same stress is applied to each monolithic ceramic capacitor, and all the monolithic ceramic capacitors may be cracked.

For example, when a short circuit occurs in the capacitors C1and C2in the circuit illustrated inFIG. 3, a short circuit may occur between the supply voltage and the ground, and a large current may flow.

Therefore, the inventors have studied the relationship between the direction in which stress is applied to a monolithic ceramic capacitor and the possibility of occurrence of a crack in the monolithic ceramic capacitor. Hereinafter, unless otherwise specified, the term “capacitor” refers to a monolithic ceramic capacitor.

According to the studies by the inventors, the possibility of occurrence of a crack is relatively low in a case where the angle of a stress F is 90 degrees (perpendicular) to the mounting direction D of the capacitor C as illustrated inFIG. 5Aand a case where the angle of the stress F is 0 degree (parallel) to the mounting direction D of the capacitor C as illustrated inFIG. 5B.

By contrast, when the angle of the stress F is 45 degrees to the mounting direction D of the capacitor C as illustrated inFIG. 5C, the possibility of occurrence of a crack is higher compared with the cases illustrated inFIGS. 5A and 5B.

From this result, as illustrated inFIG. 6A, in the arrangement in which the mounting directions D1and D2of the capacitors C1and C2are the same, it is possible that each of the capacitors C1and C2receives the stress F at an angle α1or α2of about 45 degrees relative to the mounting directions D1and D2. In this case, as illustrated inFIG. 6B, the capacitors C1and C2may be cracked, resulting a short circuit. There is a risk that a short circuit occurs between the supply voltage and the ground, and a large current flows.

On the other hand, inFIG. 6C, the mounting direction D1of the capacitor C1is deviated by the angle θ of 45 degrees from the mounting direction D2of the capacitor C2. In this arrangement, when a stress at the angle α1of 45 degrees relative to the mounting direction D1is applied to the capacitor C1, the angle α2, relative to the mounting direction D2, of the stress applied to the capacitor C2is 90 degrees. As described above with reference toFIGS. 5A to 5C, when the angle α2is 0 degrees or 90 degrees, the possibility of the occurrence of a crack by the same stress F is low. As a result, even when the capacitor C1is cracked and a short circuit occurs, the capacitor C2is not cracked and continues to operate normally as illustrated inFIG. 6D. Therefore, this arrangement can reduce the risk of the short circuit between the supply voltage and the ground and a flow of large current.

According to the consideration made by the inventors, when the angle θ between the mounting direction D1and the mounting direction D2is 45±5 degrees, the above effect can be obtained to the same extent as in the case where the angle θ is 45 degrees.

As described above, in the capacitor arrangement according to the present embodiment, the capacitor C1is mounted in the mounting direction D1(oriented in a first direction), and the capacitor C2is mounted in the mounting direction D2(oriented in a second direction) that is at an angle of 45±5 degrees relative to the mounting direction D1.

With this arrangement, the direction (relative to the mounting direction) of the applied stress differs between the capacitors C1and C2. This arrangement can prevent application of stress in the same direction to each of the capacitors and prevent a resultant crack in each of the capacitors to cause a short circuit.

The stress occurs, for example, when another connector is inserted into or removed from the connector mounted on the substrate10. Alternatively, a stress may occur when an operator pushes the wiring board1with a finger during the manufacturing of the wiring board1or after the wiring board1is manufactured.

The stress generated at this time is more easily transmitted to the capacitors C1and C2as the rigidity of the substrate used decreases. Therefore, the lower the rigidity of the substrate10is, the greater the technical significance of setting the angle between the mounting directions D1and D2to 45±5 degrees, to prevent the occurrence of cracks in the capacitors C1and C2.

That is, the technical significance of setting the angle between the mounting direction D1and the mounting direction D2to 45±5 degrees and preventing the occurrence of cracks in the capacitors C1and C2is greater in a case where a resin substrate is used for the substrate10, compared with a case where a ceramic substrate or a silicon substrate is used. In particular, when a phenolic paper substrate having a low rigidity among resin substrates is used as the substrate10, a greater technical significance is attained by setting the angle between the mounting directions D1and D2to 45±5 degrees, to prevent the occurrence of cracks in the capacitors C1and C2.

The above description concerns the example where two capacitors are connected in series between different DC potentials. However, even when three or more capacitors are connected in series between different DC potentials, the same effect as above can be obtained by shifting the mounting direction of at least two capacitors by 45±5 degrees.

Further, the different DC potentials are not limited to the power supply potential and the ground potential. For example, the different DC potentials can be a potential divided from the power supply potential and the ground potential. Further, when there is a positive power supply potential and a negative power supply potential relative to the ground potential, the capacitor arrangement according to the present embodiment can be applied to both between the positive power supply potential and the ground potential and between the negative power supply potential and the ground potential.

Further, the capacitor arrangement according to the present embodiment is applicable to, not only to the capacitors between different DC potentials, a plurality of capacitors connected in series between any two wires, regardless of direct current or alternating current. In this case, the capacitor arrangement described above can prevent the inconvenience that all capacitors are cracked and a short circuit in each capacitor occurs at the same time, causing a short circuit between the wires.