Patent Description:
Conventionally, a shunt resistor is widely used in current detecting applications. Such a shunt resistor includes a plate-shaped resistance element and plate-shaped electrodes joined to both ends of the resistance element. The resistance element is made of alloy, such as copper-nickel alloy, copper-manganese alloy, iron-chromium alloy, or nickel-chromium alloy. The electrodes are made of highly conductive metal, such as copper.

The shunt resistor is required to have a small temperature coefficient of resistance (TCR) in order to detect current with little temperature fluctuation. The temperature coefficient of resistance (TCR) is an index that indicates a rate of change in resistance due to temperature change. In order to improve the TCR of the shunt resistor, an alloy with a low TCR, such as Manganin (registered trademark), has been used as a material of the resistance element.

<CIT> shows an example of a shunt resistor. <CIT> relates to a hybrid integrated circuit having a resistor and an electrode connected to two opposite sides of the resistor. A notch is provided in the region in parallel with the connection surface with the resistor. Resistance measurement terminal positions are located on the outer edge of the electrodes, viewed from the resistor. Furthermore, <CIT> relates to a shunt resistance type current detection device comprising two wiring members consisting of metal members having a conductivity, and a resistive element consisting of a metal member whose resistance temperature coefficient is smaller than those of the metal members used in these wiring members and to which both wiring members are fixed. In one embodiment, cuts are provided in the wiring members. <CIT> relates to a metal plate resistor including a plate-like resistor, a pair of plate-like electrodes joined with both ends of the resistor, and bolt holes formed on the electrode. The electrodes are respectively provided with electrode deformation portions allowed to be deformed by bolting between outside portions having the bolt holes and inside portions having junction portions with the resistor. <CIT> relates to a resistor being provided with a resistive element, a current terminal having a conductivity that is higher than that of the resistive element, and a voltage detection terminal shunted from the current terminal, said resistive element being provided with a protruding section protruding in the direction substantially orthogonal to the disposition direction of the current terminal.

However, there is a limit to adjusting (improving) the TCR by selecting the material of the resistance element. It is therefore an object of the present invention to provide a shunt resistor allowing for easy adjustment of TCR regardless of a material of a resistance element, i.e., capable of achieving a desired TCR.

In accordance with the invention, a shunt resistor as set forth in the appended claims is provided. In particular, , there is provided a shunt resistor inter alia comprising: a resistance element having a plate shape; and electrodes connected to both end surfaces of the resistance element, wherein the electrodes have cut portions, respectively, the cut portions extending parallel to joint portions of the resistance element and the electrodes, and each of the cut portions is located at a position where a relationship Y≤<NUM>. 80X-<NUM> holds, where Y is a distance from each joint portion to each cut portion, and X is a length of the joint portions in a width direction of the electrodes.

In an embodiment, the shunt resistor further comprises voltage detection terminals provided on voltage detecting portions located between the joint portions and the cut portions. A width of the electrodes at positions where the cut portions are formed is <NUM>/<NUM> or more of the length of the joint portions in the width direction of the electrodes.

Each cut portion is formed at a position where the relationship Y ≦ <NUM>. 80X-<NUM> holds, where Y is the distance from the joint portion to the cut portion, and X is the length of the joint portion in the width direction of the electrodes. The cut portions extend parallel to the joint portions. As a result, a desired TCR can be satisfied with a simple configuration. In addition, the TCR of the shunt resistor can be easily adjusted by the adjustment of the length of the cut portions.

<FIG> is a perspective view schematically showing an embodiment of a shunt resistor <NUM>, and <FIG> is a plan view of the shunt resistor <NUM> shown in <FIG>. White arrows shown in <FIG> indicate a direction of an electric current flowing through the shunt resistor <NUM>. As shown in <FIG>, the shunt resistor <NUM> includes a plate-shaped resistance element <NUM> made of an alloy having a predetermined thickness and a predetermined width, and electrodes <NUM> and <NUM> made of a highly conductive metal connected to both end surfaces 5a and 5b of the resistance element <NUM>. Specifically, the electrode <NUM> is connected to the end surface 5a, and the electrode <NUM> is connected to the end surface 5b. Configurations of the electrode <NUM>, which will not be particularly described, are the same as configurations of the electrode <NUM>. The electrodes <NUM> and <NUM> are arranged symmetrically with respect to the resistance element <NUM>. The width of the electrode <NUM> and the width of the electrode <NUM> are the same, and are represented by a width W2. A width direction of the electrodes <NUM> and <NUM> is a direction perpendicular to the current direction. An example of an alloy forming the resistance element <NUM> is a nickel-chromium alloy. An example of the highly conductive metal forming the electrodes <NUM> and <NUM> is copper.

Specifically, inner end surfaces 6a and 7a of the electrodes <NUM> and <NUM> are joined to the both end surfaces 5a and 5b of the resistance element <NUM>, respectively, by means of welding (for example, electron beam welding, laser beam welding, or brazing). The inner end surfaces 6a and 7a are joint surfaces joined to the resistance element <NUM>. Hereinafter, in this specification, the inner end surfaces 6a and 7a may be referred to as joint surfaces 6a and 7a.

The inner end surface 6a of the electrode <NUM> and the end surface 5a of the resistance element <NUM> constitute a joint portion <NUM> of the resistance element <NUM> and the electrode <NUM>. The inner end surface 7a of the electrode <NUM> and the end surface 5b of the resistance element <NUM> constitute a joint portion <NUM> of the resistance element <NUM> and the electrode <NUM>.

The electrodes <NUM> and <NUM> have cut portions <NUM> and <NUM>, respectively. The cut portions <NUM> and <NUM> extend parallel to the joint portions <NUM> and <NUM> (i.e., the joint surfaces 6a and 7a and both end surfaces 5a and 5b), respectively. The cut portions <NUM> and <NUM> of this embodiment have a slit shape extending linearly. The cut portion <NUM> extends linearly from a side surface 6b of the electrode <NUM> toward the center of the electrode <NUM>, and the cut portion <NUM> extends linearly from a side surface 7b of the electrode <NUM> toward the center of the electrode <NUM>.

Configurations of the cut portion <NUM>, which will not be particularly described, are the same as those of the cut portion <NUM>. The cut portion <NUM> and the cut portion <NUM> are arranged symmetrically with respect to the resistance element <NUM>. In this embodiment, the cut portion <NUM> has the same width W1 as the width of the cut portion <NUM>. A length of the cut portion <NUM> in a width direction of the electrodes <NUM> and <NUM> (i.e., a direction parallel to the joint surfaces 6a and 7a and perpendicular to the current direction) is the same as a length of the cut portion <NUM> in the width direction of the electrodes <NUM> and <NUM>, and both lengths are denoted by t1.

The cut portions <NUM> and <NUM> formed in the electrodes <NUM> and <NUM> causes the electric current flowing through the shunt resistor <NUM> to avoid the cut portions <NUM> and <NUM>. As a result, a state of the electric current flowing through the shunt resistor <NUM> is different from a state of electric current flowing through a shunt resistor without the cut portions. As a result, a TCR (temperature coefficient of resistance) of the shunt resistor <NUM> is different from a TCR (temperature coefficient of resistance) of a shunt resistor without cut portions in electrodes.

In this embodiment, a length of the joint portion <NUM> (or the joint surface 6a and the end surface 5a) in the width direction of the electrode <NUM> is the same as a length of the joint portion <NUM> (or the joint surface 7a and the end surface 5b) in the width direction of the electrode <NUM>. A distance from the joint portion <NUM> (or the joint surface 6a) to the cut portion <NUM> is the same as a distance from the joint portion <NUM> (or the joint surface 7a) to the cut portion <NUM>. In the present embodiment, the cut portions <NUM> and <NUM> are located such that a relationship expressed by a formula (<NUM>) Y≤<NUM>. 80X-<NUM> holds, where Y represents the distance from each of the joint portions <NUM> and <NUM> to each of the cut portions <NUM> and <NUM>, and X represents the length of the joint portions <NUM> and <NUM> in the width direction of the electrodes <NUM> and <NUM>.

The TCR of the shunt resistor <NUM> can be adjusted by forming the cut portions <NUM> and <NUM> at positions where the relationship of the above formula (<NUM>) holds. Specifically, when the cut portions <NUM> and <NUM> are formed at positions where the relationship of the above formula (<NUM>) is established, the TCR of the shunt resistor <NUM> can be adjusted by changing the length t1 of the cut portions <NUM> and <NUM>. In other words, the temperature coefficient of resistance of the shunt resistor <NUM> can be adjusted by forming the cut portions <NUM> and <NUM> having an adjusted length t1 at positions where the relationship of the above formula (<NUM>) holds.

Voltage detection terminals <NUM> and <NUM> are provided on surfaces of the electrodes <NUM> and <NUM>, respectively. The voltage detection terminals <NUM> and <NUM> are used for measuring a voltage generated across the resistance element <NUM> (i.e., generated between both end surfaces 5a and 5b). For example, aluminum wires are coupled to the voltage detection terminals <NUM> and <NUM>, so that the voltage generated between both end surfaces of the resistance element <NUM> is detected. The voltage detection terminal <NUM> is provided on a voltage detecting portion <NUM> of the electrode <NUM>, and the voltage detection terminal <NUM> is provided on a voltage detecting portion <NUM> of the electrode <NUM>. The voltage detecting portion <NUM> is located between the joint portion <NUM> and the cut portion <NUM>, and the voltage detecting portion <NUM> is located between the joint portion <NUM> and the cut portion <NUM>.

The voltage detection terminals <NUM> and <NUM> provided on the voltage detecting portions <NUM> and <NUM> (i.e., the voltage detecting portions <NUM> and <NUM> located in voltage detecting positions) can allow for measuring of the voltage reflecting the adjusted TCR. Specifically, the voltage of the resistance element <NUM> can be measured while the TCR of the shunt resistor <NUM> is affected by the cut portions <NUM> and <NUM>. The arrangements of the voltage detection terminals <NUM> and <NUM> adjacent to the resistance element <NUM> make it possible to measure the voltage that more reflects the adjusted TCR.

<FIG> is a graph showing a rate of change in a resistance value of the shunt resistor <NUM> due to temperature change. <FIG> shows the rate of change in the resistance value of the shunt resistor <NUM> according to the change in temperature when the resistance element <NUM> is made of a nickel-chromium alloy and the electrodes <NUM> and <NUM> are made of copper. The cut portions <NUM> and <NUM> are formed at positions where the relationship of the above formula (<NUM>) holds. In <FIG>, the width W1 (see <FIG>) of the cut portions <NUM> and <NUM> is <NUM>, the width W2 (see <FIG>) of the electrodes <NUM> and <NUM> is <NUM>, the width W3 of the resistance element <NUM> (see <FIG>) is <NUM>, and the distance Y (see <FIG>) from each of the joint portions <NUM> and <NUM> (or the joint surfaces 6a and 7a) to each of the cut portions <NUM> and <NUM> is <NUM>.

<FIG> shows the rate of change in the resistance value of the shunt resistor <NUM> with the temperature change when the length t1 of the cut portions <NUM> and <NUM> is <NUM>, <NUM>, <NUM>, and <NUM>. For comparison, <FIG> further shows a rate of change in a resistance value of a shunt resistor in which the cut portions <NUM> and <NUM> are not formed. Other configurations of the shunt resistor in which the cut portions <NUM> and <NUM> are not formed are the same as those of the shunt resistor <NUM>.

<FIG> shows that, when the cut portions <NUM> and <NUM> having the width W1 of <NUM> are formed in the electrodes <NUM> and <NUM>, a ratio of the rate of change in the resistance value to an amount of change in temperature of the shunt resistor <NUM> is reduced. The ratio of the rate of change in the resistance value to the amount of change in temperature of the shunt resistor <NUM> corresponds to the temperature coefficient of resistance (TCR) of the shunt resistor <NUM>. Furthermore, <FIG> shows that the temperature coefficient of resistance of the shunt resistor <NUM> depends on the length t1 of the cut portions <NUM> and <NUM>. Specifically, <FIG> shows that the adjustment of the length t1 of the cut portions <NUM> and <NUM> when the cut portions <NUM> and <NUM> are formed at the positions where the relationship of the above formula (<NUM>) holds, i.e., the cut portions <NUM> and <NUM> having the adjusted length t1 formed at the positions where the relationship of the above formula (<NUM>) holds, allows for the adjustment of the temperature coefficient of resistance (TCR) of the shunt resistor <NUM>.

As shown in <FIG>, as the length t1 of the cut portions <NUM> and <NUM> increases, the temperature coefficient of resistance of the shunt resistor <NUM> decreases. When the length t1 is <NUM>, an absolute value of the temperature coefficient of resistance of the shunt resistor <NUM> is minimized. When the length t1 is <NUM>, the temperature coefficient of resistance of the shunt resistor <NUM> has a negative slope. Therefore, by adjusting the length t1 of the cut portions <NUM> and <NUM>, i.e., by forming the cut portions <NUM> and <NUM> having an adjusted length t1 at the positions where the relationship of the above formula (<NUM>) holds, the temperature coefficient of resistance (TCR) of the shunt resistor <NUM> can be adjusted over a wide range (i.e., a desired TCR can be achieved). As a result, an optimum TCR adjustment can be achieved not only when a nickel-chromium alloy is used for the resistance element <NUM>, but also when various alloys are used for the resistance element <NUM>. According to the present embodiment, the desired temperature coefficient of resistance can be achieved with a simple structure in which the cut portions <NUM> and <NUM> having an adjusted length t1 are formed at positions where the above formula (<NUM>) holds.

In this embodiment, the width W3 of the resistance element <NUM> is <NUM>, and the width W1 of the cut portions <NUM> and <NUM> is <NUM>. It should be noted, however, the widths W3 and W1 are not limited to this embodiment. The TCR of the shunt resistor <NUM> can be adjusted by the adjustment of the length t1 of the cut portions <NUM> and <NUM> regardless of the magnitudes of the width W3 and the width W1. When the cut portions <NUM> and <NUM> are formed at positions where the relationship of the above formula (<NUM>) holds and the cut portions <NUM> and <NUM> extend parallel to the joint portions <NUM> and <NUM>, the temperature coefficient of resistance (TCR) of the shunt resistor <NUM> can be adjusted easily (i.e., a desired TCR can be achieved) by adjusting the length t1 of the cut portions <NUM> and <NUM>, i.e., by forming the cut portions <NUM> and <NUM> having an adjusted length t1 at the positions where the relationship of the above formula (<NUM>) holds.

As shown in <FIG>, a width W4 of the electrode <NUM> (and the electrode <NUM>) narrowed by the formation of the cut portion <NUM> (and the cut portion <NUM>) is preferably <NUM>/<NUM> or more of a length X of the joint portions <NUM> and <NUM>. In other words, the width W4 of the electrodes <NUM> and <NUM> is a width of the electrodes <NUM> and <NUM> at positions where the cut portions <NUM> and <NUM> are formed with respect to a direction perpendicular to the width direction of the electrodes <NUM> and <NUM>. The width W4 having <NUM>/<NUM> or more of the length X allows the electrodes <NUM> and <NUM> to have sufficient mechanical strength, and can prevent a decrease in high-frequency characteristics of the shunt resistor <NUM> that can occur due to the decrease in the width W4. The results of <FIG> show that, when the cut portions <NUM> and <NUM> are formed at positions where the relationship of the above formula (<NUM>) holds, the TCR can vary widely while the width W4 is <NUM>/<NUM> or more of the length X.

<FIG> is a plan view showing another embodiment of the shunt resistor <NUM>. Configurations of this embodiment, which will not be particularly described, are the same as those of the embodiments described with reference to <FIG>, and redundant descriptions thereof will be omitted. In this embodiment, the cut portion <NUM> extends from a side surface 7c of the electrode <NUM> toward the center of the electrode <NUM>. Side surfaces 6c and 7c shown in <FIG> are opposite surfaces from the side surfaces 6b and 7b.

In this embodiment also, when the cut portions <NUM> and <NUM> are formed at positions where the relationship of the above formula (<NUM>) holds, the temperature coefficient of resistance (TCR) of the shunt resistor <NUM> can be adjusted (i.e., a desired TCR can be achieved) by adjusting the length t1 of the cut portions <NUM> and <NUM>, i.e., by forming the cut portions <NUM> and <NUM> having an adjusted length t1 at the positions where the relationship of the above formula (<NUM>) holds. In an embodiment, the cut portion <NUM> may be formed so as to extend from the side surface 6c of the electrode <NUM> toward the center of the electrode <NUM>, and the cut portion <NUM> may be formed so as to extend from the side surface 7b of the electrode <NUM> to the center of the electrode <NUM>.

<FIG> is a plan view showing still another embodiment of the shunt resistor <NUM>. Configurations of this embodiment, which will not be particularly described, are the same as those of the embodiments described with reference to <FIG>, and redundant descriptions thereof will be omitted. In this embodiment, the electrode <NUM> further has a cut portion <NUM>, and the electrode <NUM> further has a cut portion <NUM>.

The cut portions <NUM> and <NUM> extend parallel to the joint portions <NUM> and <NUM> (or the joint surfaces 6a and 7a and both end surfaces 5a and 5b), respectively. The cut portions <NUM> and <NUM> of this embodiment have a slit shape extending linearly. The cut portion <NUM> extends linearly from the side surface 6c of the electrode <NUM> toward the center of the electrode <NUM>, and the cut portion <NUM> extends linearly from the side surface 7c of the electrode <NUM> toward the center of the electrode <NUM>. The cut portion <NUM> is formed on an extension line of the cut portion <NUM>, and the cut portion <NUM> is formed on an extension line of the cut portion <NUM>. Specifically, the cut portions <NUM> and <NUM> are arranged at the same positions as the cut portions <NUM> and <NUM>, respectively, in the direction perpendicular to the width direction of the electrodes <NUM> and <NUM>.

Configurations of the cut portion <NUM>, which will not be particularly described, are the same as those of the cut portion <NUM>. The cut portion <NUM> and the cut portion <NUM> are arranged symmetrically with respect to the resistance element <NUM>. In this embodiment, the cut portion <NUM> has a width W5 which is the same as a width of the cut portion <NUM>. A length of the cut portion <NUM> in the width direction of the electrodes <NUM> and <NUM> is the same as a length of the cut portion <NUM> in the width direction of the electrodes <NUM> and <NUM>, and both of these lengths are represented by length t2.

In this embodiment, voltage detection terminals <NUM> and <NUM> are provided on the surfaces of the electrodes <NUM> and <NUM>, respectively. The voltage detection terminal <NUM> is provided on a voltage detecting portion <NUM> of the electrode <NUM>, and the voltage detection terminal <NUM> is provided on a voltage detecting portion <NUM> of the electrode <NUM>. The voltage detecting portion <NUM> is located between the joint portion <NUM> and the cut portion <NUM>. The voltage detecting portion <NUM> is located between the joint portion <NUM> and the cut portion <NUM>. Configurations of the voltage detection terminals <NUM> and <NUM> and the voltage detecting portions <NUM> and <NUM>, which are not specifically described, are the same as those of the voltage detection terminals <NUM> and <NUM> and the voltage detecting portions <NUM> and <NUM>, respectively.

Also in this embodiment, when the cut portions <NUM>, <NUM>, <NUM>, and <NUM> are formed at positions where the relationship of the above formula (<NUM>) holds, the temperature coefficient of resistance (TCR) of the shunt resistor <NUM> can be adjusted (i.e., a desired TCR can be achieved) by adjusting the length t1 of the cut portions <NUM> and <NUM> and the length t2 of the cut portions <NUM> and <NUM>, i.e., by forming the cut portions <NUM>, <NUM>, <NUM> and <NUM> having adjusted lengths t1 and t2 at the positions where the relationship of the above formula (<NUM>) holds. The length t1 and the length t2 may be the same or different. The width W1 and the width W5 may be the same or different. Also in the present embodiment, the width W4 of the electrodes <NUM> and <NUM> narrowed by the formation of the cut portions <NUM>, <NUM>, <NUM> and <NUM> is preferably <NUM>/<NUM> or more of the length X of the joint portions <NUM> and <NUM>.

<FIG> is a perspective view schematically showing still another embodiment of a shunt resistor <NUM>, and <FIG> is an exploded perspective view of the shunt resistor <NUM> of <FIG>. Configurations of this embodiment, which will not be particularly described, are the same as those of the embodiments described with reference to <FIG>, and redundant descriptions thereof will be omitted. The shunt resistor <NUM> of this embodiment further includes a substrate <NUM> which is made of insulating material, and a pedestal <NUM>. Conductors <NUM> and <NUM> and voltage detection terminals <NUM> and <NUM> are provided on a surface of substrate <NUM>. White arrows shown in <FIG> indicate the direction of electric current flowing through the shunt resistor <NUM>. The pedestal <NUM> has electrical contacts <NUM>, <NUM> on its surface.

As shown in <FIG> and <FIG>, the cut portion <NUM> of this embodiment has a first surface 11a extending parallel to the joint portion <NUM> and a second surface 11b extending in a direction perpendicular to the first surface 11a. The cut portion <NUM> has a first surface 12a extending parallel to the joint portion <NUM> and a second surface 12b extending in a direction perpendicular to the first surface 12a. An outer end surface 6d of the electrode <NUM> and the first surface 11a are coupled by the second surface 11b, and an outer end surface 7d of the electrode <NUM> and the first surface 12a are coupled by the second surface 12b.

The electrode <NUM> is folded at a position between the first surface 11a and the joint surface 6a, and the electrode <NUM> is folded at a position between the first surface 12a and the joint surface 7a. The electrodes <NUM>, <NUM> are symmetrically bent with respect to the resistance element <NUM>. The outer end faces 6d and 7d are in contact with the conductors <NUM> and <NUM>, respectively. With such configurations, the electric current flows from the conductor <NUM> through the electrode <NUM>, the resistance element <NUM>, and the electrode <NUM> to the conductor <NUM>.

The first surfaces 11a, 12a are in contact with the electrical contacts <NUM>, <NUM>, respectively. The pedestal <NUM> further includes a plurality of conductive wires (not shown). The electrical contact <NUM> is coupled to the voltage detection terminal <NUM> via one of the plurality of conductive wires, and the electrical contact <NUM> is coupled to the voltage detection terminal <NUM> via another conductive wire. With such configurations, the voltage generated across the resistance element <NUM> (i.e., generated between the end surfaces 5a and 5b) can be measured via the voltage detection terminals <NUM> and <NUM>. For example, the voltage generated across the resistance element <NUM> is detected via aluminum wires coupled to the voltage detection terminals <NUM> and <NUM>.

Also in this embodiment, the electric current flows from the conductor <NUM> to the conductor <NUM> while avoiding the cut portions <NUM> and <NUM>. Therefore, as well as the embodiments described with reference to <FIG>, the temperature coefficient of resistance (TCR) of the shunt resistor <NUM> can be adjusted (i.e., a desired TCR can be achieved) by adjusting the length t1 of the cut portions <NUM> and <NUM> in the width direction of the electrodes <NUM> and <NUM>, i.e., by forming the cut portions <NUM> and <NUM> having an adjusted length t1 at the positions where the relationship of the above formula (<NUM>) holds. Also in this embodiment, the width W4 of the electrode <NUM> (and the electrode <NUM>) narrowed by the formation of the cut portion <NUM> (and the cut portion <NUM>) is preferably <NUM>/<NUM> or more of the length X of the joint portions <NUM> and <NUM>.

The previous description of embodiments is provided to enable a person skilled in the art to make and use the present invention. Moreover, various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles and specific examples defined herein may be applied to other embodiments. Therefore, the present invention is not intended to be limited to the embodiments described herein but is to the appended claims.

Claim 1:
A shunt resistor (<NUM>) comprising:
a resistance element (<NUM>) having a plate shape; and
electrodes (<NUM>, <NUM>) connected to both end surfaces (5a, 5b) of the resistance element (<NUM>),
wherein the electrodes (<NUM>, <NUM>) have cut portions (<NUM>,<NUM>), respectively, the cut portions (<NUM>,<NUM>) extending parallel to joint portions (<NUM>,<NUM>) of the resistance element (<NUM>) and the electrodes (<NUM>, <NUM>),
the cut portions (<NUM>, <NUM>) have a slit shape extending linearly from side surfaces (6a, 7b) of the electrodes (<NUM>, <NUM>) toward centers of the electrodes (<NUM>, <NUM>) parallel to the resistance element (<NUM>),
voltage detection terminals (<NUM>, <NUM>) provided on voltage detection portions (<NUM>, <NUM>) located between the joint portions (<NUM>, <NUM>) and the cut portions (<NUM>,<NUM>),
each of the cut portions (<NUM>,<NUM>) is located at a position where a relationship Y≤<NUM>.80X-<NUM> holds, where Y is a distance from each joint portion (<NUM>,<NUM>) to each cut portion (<NUM>,<NUM>), and X is a length of the joint portions (<NUM>,<NUM>) in a width direction of the electrodes (<NUM>,<NUM>),
a narrowed width (W4) of the electrodes (<NUM>,<NUM>) at positions where the cut portions (<NUM>, <NUM>) are formed is <NUM>/<NUM> or more of the length (X) of the joint portions (<NUM>,<NUM>) in the width direction of the electrodes (<NUM>, <NUM>).