Patent ID: 12249448

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Explanation of Resistor

A resistor1of the present embodiment of the present disclosure will be described in detail with reference toFIGS.1and2.FIG.1is a perspective view of the resistor1of the present embodiment.FIG.2is a perspective view of the resistor1of the present embodiment viewed from the side of a mounting surface for a circuit board.

The resistor1is provided with a resistance body10, a first electrode body11(an electrode), and a second electrode body12(the electrode), and the resistor1is formed by bonding the first electrode body11, the resistance body10, and the second electrode body12in this order. The resistor1is mounted on the circuit board, etc., which is not shown inFIG.1. For example, the resistor1is arranged on a pair of electrodes that are formed on a land pattern of the circuit board. In the present embodiment, the resistor1is used as a current sensing resistor (a shunt resistor).

In the present embodiment, the direction in which the first electrode body11and the second electrode body12are arranged (the longitudinal direction of the resistor1) is referred to as the X direction (the direction towards the first electrode body11is referred to as the +X direction, and the direction towards the second electrode body12is referred to as the −X direction), the width direction of the resistor1is referred to as the Y direction (the front side with respect to the plane ofFIG.1is referred to as the +Y direction, and the back side with respect to the plane ofFIG.1is referred to as the −Y direction), and the thickness direction of the resistor1is referred to as the Z direction (the direction towards the circuit board is referred to as the −Z direction, and the direction away from the circuit board is referred to as the +Z direction). The X direction, the Y direction, and the Z direction are orthogonal with each other. In addition, the mounting surface of the resistor1means a surface of the resistor1that opposes to the circuit board when the resistor1is mounted on the circuit board, and the mounting surface includes respective surfaces of the first electrode body11, the resistance body10, and the second electrode body12that oppose to the circuit board.

In the present embodiment, the resistance body10is formed to have a cuboid shape (or a cube shape).

For the resistance body10, it is possible to use materials having low to high resistances according to the application. In the present embodiment, from the view point of sensing a large current at a high accuracy, it is preferable that the resistance body10be formed of a resistance body material having a low specific resistance and a small temperature coefficient of resistance (TCR). As examples, a copper-manganese-nickel alloy, a copper-manganese-tin alloy, a nickel-chromium alloy, a copper-nickel alloy, and so forth can be used.

The first electrode body11is provided with a main body portion21that is bonded to the resistance body10and a leg portion22that is formed integrally with the main body portion21so as to extend towards the circuit board. In addition, the second electrode body12is provided with a main body portion31that is bonded to the resistance body10and a leg portion32that is formed integrally with the main body portion31so as to extend towards the circuit board.

The first electrode body11(the main body portion21and the leg portion22) and the second electrode body12(the main body portion31and the leg portion32) are preferably be formed of an electrically conductive material having a good electrical conductivity and thermal conductivity from the view point of ensuring a stable sensing accuracy. As one example, copper, a copper alloy, and so forth may be used as the first electrode body11and the second electrode body12. An oxygen-free copper (C1020) may preferably be used as the copper. The same material can be used for the first electrode body11and the second electrode body12.

The main body portion21of the first electrode body11has an end surface having substantially the same shape as an end surface of the resistance body10on the +X direction side, and the end surface of the main body portion21is bonded to the end surface of the resistance body10on the +X direction side so as to be abutted thereto. At a bonded portion13that is a boundary portion between the main body portion21and the resistance body10, a boundary between the resistance body10and the main body portion21has no step and is flat, and so, the resistance body10and the main body portion21form a smooth continuous surface. In other words, a surface of the bonded portion13is formed so as to be flat over the entire circumference of the boundary between the resistance body10and the main body portion21(the state in which the step is not formed).

The main body portion31of the second electrode body12has an end surface having substantially the same shape as an end surface of the resistance body10on the −X direction side, and the end surface of the main body portion31is bonded to the end surface of the resistance body10on the −X direction side so as to be abutted thereto. At a bonded portion14that is the boundary portion between the main body portion31and the resistance body10, the boundary of the resistance body10and the main body portion31has no step and is flat, and so, the resistance body10and the main body portion31form a smooth continuous surface. In other words, a surface of the bonded portion14is formed so as to be flat over the entire circumference of the boundary between the resistance body10and the main body portion31(the state in which the step is not formed).

The leg portion22is a member that extends towards the −Z direction from the mounting surface of the resistor1, in other words, from the circuit board side of the main body portion21. Although the length of the leg portion22in the X direction is shorter than that of the main body portion21, a side surface of the leg portion22on the +X direction side forms the same flat surface with a side surface of the main body portion21on the +X direction side.

The leg portion32is a member that extends towards the −Z direction from the mounting surface of the resistor1, in other words, from the circuit board side of the main body portion31. Although the length of the leg portion32in the X direction is shorter than that of the main body portion31, a side surface of the leg portion32on the −X direction side forms the same flat surface with a side surface of the main body portion31on the −X direction side.

In the present embodiment, the bonded portion13between the resistance body10and the first electrode body11and the bonded portion14between the resistance body10and the second electrode body12are each bonded by a cladding (a solid phase bonding). In other words, the bonded surfaces respectively form a diffusion bonded surface in which metal atoms in the resistance body10and the first electrode body11are mutually diffused and the diffusion bonded surface in which metal atoms in the resistance body10and the second electrode body12are mutually diffused.

The resistor1is mounted on the circuit board such that the leg portion22and the leg portion32project out towards the circuit board, and thereby, the resistance body10is mounted on the circuit board so as to be separated from the circuit board.

A portion of the main body portion21that is protruded towards the −X direction side is a protruded portion211, and the protruded portion211is bonded to the resistance body10. Similarly, a portion of the main body portion31that is protruded towards the +X direction side is a protruded portion311, and the protruded portion311is bonded to the resistance body10.

When the length L of the resistor1in the longitudinal direction (the X direction) (seeFIG.1) is set constant, by arbitrarily adjusting the length of the protruded portion211in the X direction (the length of the main body portion21, seeFIG.1) or the length of the protruded portion311in the X direction (the length of the main body portion31in the X direction, seeFIG.1), it is possible to adjust the length L0of the resistance body10in the X direction (seeFIG.1) so as to satisfy L0=L−(L1+L2). Therefore, it is possible to arbitrarily adjust the resistance value of the resistor1without changing the dimension L of the resistor1and without changing the shapes of the leg portions22and32. Alternatively, even if the protruded amount of each the protruded portions211and311is increased without changing the dimension L of the resistor1, the distance between the leg portion22and the leg portion32can be ensured, and so, it is possible to increase the degree of freedom for designing the resistor1while ensuring the distance between the land patterns.

In the above, the ratio of the length L0of the resistance body10in the longitudinal direction of the resistance body10(the X direction), the length L1of the first electrode body11in the X direction, and the length L2of the second electrode body12in the X direction can be set arbitrarily. However, from the view point of reducing the resistance value while suppressing the increase in the TCR (the temperature coefficient of resistance [ppm/° C.]), it is preferable that the ratio be set so as to be L1:L0:L2=1:2:1 or about 1:2:1.

Furthermore, from the view point of increasing a heat radiation property and reducing the resistance value, it is preferable that the ratio of the length L0of the resistance body10relative to the length L of the resistor1(=L1+L0+L2) be equal to or less than 50%.

In the present embodiment, the resistor1has, on its surface, stripe-patterned grooves and ridges15(seeFIG.1(enlarged view) andFIG.2(enlarged view)). In this embodiment, the stripe-patterned grooves and ridges15are formed so as to extend along the Y direction on other side surfaces than the side surface facing the +Y direction and the side surface facing the −Y direction of the resistor1.

The surface roughness caused by the groove portions and the ridge portions of the stripe-patterned grooves and ridges15can be about from 0.2 to 0.3 μm in terms of arithmetic average roughness (Ra).

In the present embodiment, the length L of the resistor1in the X direction is formed so as to be equal to or shorter than 3.2 mm. In addition, the resistance value of the resistor1is adjusted so as to be equal to or lower than 2 mΩ.

In this embodiment, from the view point of applying the resistor1to the high density circuit board, the length L of the resistor1in the X direction can be set equal to or shorter than 3.2 mm, and the length W of the resistor1in the Y direction (the width) can be set equal to or shorter than 1.6 mm (product standard 3216 size). Thus, as the size of the resistor1in this embodiment, the resistor1can also be applied to product standard 2012 size (L: 2.0 mm, W: 1.2 mm), product standard 1608 size (L: 1.6 mm, W: 0.8 mm), and product standard 1005 size (L: 1.0 mm, W: 0.5 mm). From the view point of achieving a handling property in a manufacturing method, which will be described below, for example, from the view point of preventing failure of a resistor base material100forming a base of the resistor1(seeFIG.14), the length L of the resistor1in this embodiment can be set to have the size equal to or larger than the above-described product standard 1005 size.

In this embodiment, from the view point of realizing the small size and the low resistance, it is possible to adjust the resistance value of the resistor1so as to be equal to or lower than 2 mΩ in any of the above-described sizes, and for example, it is possible to adjust the resistance value so as to be equal to or lower than 0.5 mΩ. In the above, the low resistance is a concept including the resistance value that is lower than the resistance value assumed from the dimension of a general resistor (for example, the resistor of the type disclosed in JP2002-57009A).

In this embodiment, all of corner portions P each serving as an edge side extending in the Y direction of the resistor1have chamfered shapes. In this embodiment, it is preferred that a radius of curvature of each corner portion P be set so as to be R=0.1 mm or less.

In addition, as shown inFIG.2, oxide films5(5a,5b,5c,5d) are respectively formed on the bonded portion13and the bonded portion14of the resistor1on the mounting surface side (this includes not only the mounting surface, but also a region near the mounting surface on the side surface of the resistor1facing the Y direction). This will be described below with reference toFIGS.3to6.

Oxide Film5

FIG.3is a diagram showing an oxide film5(5a) formed on the resistor1of the present embodiment.FIG.4is a diagram showing a first modification of the oxide film5(5b) formed on the resistor1of the present embodiment.FIG.5is a diagram showing a second modification of the oxide film5(5c) formed on the resistor1of the present embodiment.FIG.6is a diagram showing a third modification of the oxide film5(5d) formed on the resistor1of the present embodiment.

As shown inFIGS.3to6, the oxide film5(5a,5b,5c,5d) is formed on the mounting surface side of the resistor1of the present embodiment. The oxide film5(5a,5b,5c,5d) is a thermal oxide film that is formed on a mounting-surface-side surface of any of the resistance body10, the first electrode body11, and the second electrode body12by heating it by irradiating laser.

InFIG.3, on the mounting surface side of the resistor1, the oxide film5a(5) is formed on the resistance body10side of the bonded portion13between the resistance body10and the first electrode body11so as to have a predetermined width in the X direction and so as to extend over the entirety thereof in the Y direction. In addition, although illustration is omitted, on the mounting surface side of the resistor1, the oxide film5a(5) is formed on the resistance body10side of the bonded portion14between the resistance body10and the second electrode body12so as to have a predetermined width in the X direction and so as to extend over the entirety thereof in the Y direction.

In the first modification shown inFIG.4, on the mounting surface side of the resistor1, the oxide film5b(5) is formed on the first electrode body11side of the bonded portion13between the resistance body10and the first electrode body11so as to have a predetermined width in the X direction and so as to extend over the entirety thereof in the Y direction. In addition, although illustration is omitted, on the mounting surface side of the resistor1, the oxide film5b(5) is formed on the second electrode body12side of the bonded portion14between the resistance body10and the second electrode body12so as to have a predetermined width in the X direction and so as to extend over the entirety thereof in the Y direction.

In the second modification shown inFIG.5, on the mounting surface side of the resistor1, the oxide film5c(5) is formed so as to cover the bonded portion13between the resistance body10and the first electrode body11, so as to have a predetermined width in the X direction, and so as to extend over the entirety thereof in the Y direction. In addition, although illustration is omitted, on the mounting surface side of the resistor1, the oxide film5c(5) is formed so as to cover the bonded portion14between the resistance body10and the second electrode body12, so as to have a predetermined width in the X direction, and so as to extend over the entirety thereof in the Y direction.

The oxide film5d(5) in the third modification shown inFIG.6is formed by extending the oxide film5c(5) in the above-described second modification to the side surface of the resistor1(the surface facing the +Y direction and the surface facing the −Y direction). In addition, the oxide film5d(5) may be formed so as to extend over the entire circumference of the bonded portion13and/or the bonded portion14. The third modification may also be applied to the oxide film5a(5) shown inFIG.3and the oxide film5b(5) shown inFIG.4.

A reason why the oxide film5(5a,5b,5c,5d) is to be formed as described above will be described.

When the resistor1is mounted on the circuit board and a reflowing step is performed, the solder tends to creep up to the mounting surface side of the resistance body10along the leg portion22of the first electrode body11and along the leg portion32of the second electrode body12. However, the oxide film5(5a,5b,5c,5d) has a low wettability to the solder. Thus, even if the gap between the resistance body10and the circuit board is narrow, it is difficult for the solder to creep up on the oxide film5(5a,5b,5c,5d). Therefore, it is possible to prevent the solder from creeping over the oxide film5(5a,5b,5c,5d) and up to the resistance body10.

By forming the oxide film5a(5) as shown inFIG.3, it is possible to prevent further creeping of the solder at the edge side of the oxide film5a(5) on the leg portion22side, in other words, at a position where the protruded portion211of the first electrode body11overlaps with the bonded portion13. In addition, although illustration is omitted, it is possible to prevent further creeping of the solder at the edge side of the oxide film5a(5) on the leg portion32side, in other words, at a position where the protruded portion311of the second electrode body12overlaps with the bonded portion14.

By forming the oxide film5b,5c,5d(5) as shown inFIGS.4,5, and6, it is possible to prevent further creeping of the solder at the edge side of the oxide film5b,5c,5d(5) on the leg portion22side, in other words, at a position on the leg portion22side of the protruded portion211of the first electrode body11that is an intermediate position to which the solder has moved in the −X direction. In addition, although illustration is omitted, it is possible to prevent further creeping of the solder at the edge side of the oxide film5b,5c,5d(5) on the leg portion32side, in other words, at a position on the main body portion31that is an intermediate position to which the solder has moved in the +X direction from a position of a joint of the leg portion32.

In the arrangement of the oxide film5a(5) shown inFIG.3, the creeping of the solder reaches the bonding position of the first electrode body11with the resistance body10on the mounting surface (the bonded portion13) and reaches the bonding position of the second electrode body12with the resistance body10on the mounting surface (the bonded portion14). Thus, temperature variation of the TCR of the first electrode body11and the second electrode body12can be compensated more effectively compared with the arrangement of the oxide film5b,5c,5d(5) respectively shown inFIG.4toFIG.6.

FIG.7is a sectional photograph in which the resistor1of the present embodiment is mounted by using the solder. Similarly to the case described above, the resistor1shown inFIG.7is formed by performing the cladding by abutting the end surface of the resistance body10with the end surface of the first electrode body11and by abutting the end surface of the resistance body10with the end surface of the second electrode body12. In the above, on the mounting surface side of the resistor1, although the oxide film5(seeFIG.2, etc.) is formed on the boundary portion extending over the bonded portion14between the second electrode body12and the resistance body10, the oxide film5is not formed on the boundary portion extending over the bonded portion13between the first electrode body11and the resistance body10.

By performing the reflowing step, the resistor1was mounted on the circuit board7via a solder9. As a result, the solder9that came into contact with the leg portion22of the first electrode body11shown on the right side creeped up the leg portion22and also creeped up to the resistance body10via the protruded portion211on the mounting surface, thereby coming into contact with the resistance body10. On the other hand, although the solder9that came into contact with the leg portion32of the second electrode body12creeped up the leg portion32and also creeped up to the protruded portion311on the mounting surface, the creeping of the solder9was prevented at the position where the solder9came into contact with the oxide film5. Therefore, in actual resistor1, the oxide films5are respectively formed on the boundary portion extending over the bonded portion14between the second electrode body12and the resistance body10and formed on the boundary portion extending over the bonded portion13between the first electrode body11and the resistance body10. With such a configuration, it is possible to easily understand that the creeping of the solder9up to the resistance body10can be prevented.

Trimming

FIG.8is a schematic view of a case in which a trimming is performed on the resistor1of the present embodiment.FIG.9is a diagram showing the mounting surface of the resistor1after the trimming.FIG.10is a side view of the resistor1after the trimming.

In the resistor1of the present embodiment, it is possible to adjust the resistance value by performing the trimming on the resistance body10. The trimming is performed by irradiating laser beam onto the resistance body10to cut off a part of the resistance body10. In addition, the above-described oxide film5is formed on the part of the resistance body10that has subjected to the trimming. Thus, by devising parts to be subjected to the trimming, it is possible to perform adjustment of the resistance value and processing for preventing the creeping of the solder at the same time. Although the irradiation of the laser is also performed when the oxide film5shown inFIGS.3to6is to be formed, an intensity of the laser is suppressed to a level that will not cause trimming in such a case.

As shown inFIG.8, on the mounting surface of the resistor1, the laser is irradiated to the bonded portion13and the bonded portion14.

Incidentally, as described below (seeFIGS.11and12), the resistor1of the present embodiment is formed by inserting the resistor base material100, which has been obtained by subjecting a resistance body base material10A sandwiched between electrode body base materials11A and12A to the cladding (the solid phase bonding), through a die300such that the cross-sectional shape thereof is deformed to achieve the cross-sectional shape of the resistor1while reducing the cross-sectional area, and by cutting the resistor base material100that is obtained after being inserted through the die300. Thus, although the bonded portion13(the boundary portion) and the bonded portion14(the boundary portion) are normally formed to have a flat surface (a straight line), they may be slightly curved. In such a case, it is difficult to focus only on the bonded portion13and the bonded portion14when the irradiation of the laser is to be performed.

Therefore, as shown in an enlarged view inFIG.8, the laser is irradiated to the resistance body10and the first electrode body11on the bonded portion13. At this time, an irradiation area51(the width in the X direction: 0.1 mm to 0.15 mm) of the laser is set such that the laser is to be irradiated to the resistance body10and the second electrode body12on the bonded portion14.

As shown by arrows (tracing paths of irradiated positions of the laser) in the enlarged view inFIG.8, for example, the laser is moved from a position on an end portion of the irradiation area51on the −X direction side, which is the position away from the resistor1when viewed in a planar view, towards the +Y direction, irradiated to the resistor1, and is moved to the position away from the resistor1when viewed in a planar view. Subsequently, the laser is moved in the +X direction by a small distance (the moved distance is smaller than the spot size of the laser on the resistor1), moved towards the −Y direction, irradiated to the resistor1, and moved to the position away from the resistor1when viewed in a planar view. Thereafter, the operation is repeated in a similar manner to irradiate the laser to the entire surface of the irradiation area51.

The output power of the laser is unstable and may become excessively high or low soon after occurrence of lasing. Thus, as described above, it is desirable that the lasing of the laser be started at the position away from the resistor1when viewed in a planar view (the position at which the laser is not irradiated to the resistor1), and then, the laser, the output power of which has been stabilized, be irradiated to the resistor1. In addition, it is desirable that the laser be irradiated from the end portion of the irradiation area51on the +Y direction (the −Y direction) side to the end portion on the −Y direction (the +Y direction) side without interruption.

In addition, the resistance value is not stable during the irradiation of the laser to the resistor1, and so, the resistance value needs to be measured after the irradiation of the laser. Thus, the irradiation of the laser and the measurement of the resistance value will be repeated until the desired resistance value is achieved.

By irradiating the laser to the entire surfaces of the irradiation areas51as described above, recessed portions6are respectively formed so as to extend along the bonded portion13and the bonded portion14as shown inFIGS.9and10. The recessed portions6are each formed to extend in the Y direction and to have a substantially semicircular cross-sectional shape when viewed from the Y direction (alternatively, rectangular or indefinite shape). By forming the recessed portions6as described above, the resistance value of the resistor1is shifted to the higher resistance side. In addition, by forming each recessed portion6from the end portion to the end portion of the irradiation area51as described above, the oxide film5, which is a surface modified by a thermal reaction, is formed so as to be centered at an inner wall thereof, and therefore, it is possible to prevent the creeping of the solder up to the resistance body10at the reflowing step. Thus, for the resistance body10positioned between the pair of oxide films5, even in a state in which the resistance body10forming a base material is exposed, there is no concern that the solder creeps up to the resistance body10.

Modification

FIG.11is a diagram showing a modification of the resistor1of the present embodiment. In the modification of the resistor1of the present embodiment, the leg portion22of the first electrode body11and the leg portion32of the second electrode body12are not provided, and the mounting surface of the resistor1is flat. On the other hand, electrodes71and72are arranged on the circuit board7, and the electrodes71and72are arranged so as to project out from the circuit board7. The first electrode body11is mounted on the electrode71with the solder (not shown), and the second electrode body12is mounted on the electrode72with the solder (not shown). At this time, the resistance body10is arranged so as to be separated away from the circuit board7.

Similarly to the configuration described above, on the mounting surface of the resistor1, the oxide films5are arranged so as to respectively cover the bonded portions13and14, for example. Therefore, at the reflowing step, it is possible to prevent the solder that has flown along the first electrode body11from flowing beyond the oxide film5formed on the bonded portion13and creeping up to the resistance body10. Furthermore, it is also possible to prevent the solder that has flown along the second electrode body12from flowing beyond the oxide film5formed on the bonded portion14and creeping up to the resistance body10. In this modification, the recessed portion6(the oxide film5) described above may also be formed.

Effect of Present Embodiment

Next, operational advantages of the present embodiment will be described.

According to the resistor1of the present embodiment, the resistor1is provided with the resistance body10and the pair of electrodes connected to the resistance body10(the first electrode body11, the second electrode body12), the resistance body10being arranged so as to be at least separated away from a substrate board (the circuit board) when mounted on the substrate board (the circuit board), wherein the resistor1has the oxide film5on at least one of the resistance body10and each of the electrodes (the first electrode body11, the second electrode body12) at the boundary portion (the bonded portion13, the bonded portion14) between the resistance body10and each of the electrodes (the first electrode body11, the second electrode body12) on the mounting surface of the resistor1(the mounting surface side).

With the above-described configuration, because the resistor1is configured of the resistance body10and the pair of electrodes (the first electrode body11and the second electrode body12) connected to the resistance body10, it is possible to realize the resistor1having a small size and a low resistance. In addition, the oxide film5has the low wettability to the solder. Thus, even if the gap between the resistance body10and the substrate board (the circuit board) is small, it is difficult for the solder to creep up because of the presence of the oxide film5, and so, it is possible to prevent the solder from creeping up beyond the oxide film5and creeping up to the resistance body10. Therefore, compared with a case in which the resistance body10is covered by a resin, it is possible to improve a manufacturing yield and to suppress a manufacturing cost.

In the present embodiment, the oxide film5is formed at least on the resistance body10(seeFIGS.3and5). With such a configuration, because the creeping of the solder reaches the bonding position (the bonded portion13, the bonded portion14) of the electrode (the first electrode body11, the second electrode body12) to the resistance body10, the temperature variation of the TCR of the electrode (the first electrode body11, the second electrode body12) can be compensated effectively.

In the present embodiment, on the surface of the resistance body10, the resistance body forming the base material is exposed except for the part formed with the oxide film5. In other words, in a case in which the oxide film5is formed on the electrode (the first electrode body11, the second electrode body12) (seeFIG.4, etc.), the metal material that is the resistance body forming the base material is exposed on the surface of the resistance body10. With such a configuration, it is possible to prevent the creeping of the solder up to the resistance body10without covering the surface of the resistance body10, especially, the mounting surface of the resistance body10, furthermore, for example, the mounting surface side of the side surfaces of the resistance body10with the resin.

In the present embodiment, the electrodes (the first electrode body11, the second electrode body12) each has the main body portion21,31connected to the resistance body10and the leg portion22,32protruded towards the substrate board (the circuit board), the boundary portion (the bonded portion13, the bonded portion14) being formed by the resistance body10and the main body portion21,31(the protruded portion211,311), and the oxide film5is formed at least on the main body portion21,31(seeFIG.4) at the boundary portion (the bonded portion13, the bonded portion14) between the resistance body10and the main body portion21,31(the protruded portion211,311). With such a configuration, it is possible to prevent the creeping of the solder up to the resistance body10while ensuring the bonding between the leg portions22and32and the solder.

In the present embodiment, the resistor1has the recessed portion6at the boundary portion (the bonded portion13, the bonded portion14), and the oxide film5is formed in the recessed portion6or in the vicinity of the recessed portion6centered at the inner wall of the recessed portion6. With such a configuration, it is possible to perform the adjustment of the resistance value and the processing for preventing the creeping of the solder at the same time.

In the present embodiment, the resistor1has the recessed portion6at the boundary portion (the bonded portion13, the bonded portion14), and the oxide film5is formed in the recessed portion6or in the vicinity of the recessed portion6centered at the inner wall of the recessed portion6, the recessed portion6being formed so as to extend over both of the main body portion21,31(the protruded portion211,311) and the resistance body10. With such a configuration, it is possible to perform the adjustment of the resistance value and the processing for preventing the creeping of the solder at the same time and in a stable manner.

A manufacturing method of the resistor1of the present embodiment is a method for manufacturing the resistor1provided with the resistance body10and the pair of electrodes (the first electrode body11and the second electrode body12) connected to the resistance body10, the resistance body10being arranged so as to be at least separated away from the substrate board (the circuit board) when mounted on the substrate board (the circuit board), the method comprising a step of forming the oxide film5on at least one of the resistance body10and each of the electrodes (the first electrode body11, the second electrode body12) by irradiating the laser to the boundary portion (the bonded portion13, the bonded portion14) between the resistance body10and each of the electrodes (the first electrode body11, the second electrode body12) on the mounting surface side of the resistor1.

With the above-described method, because the resistor1is configured of the resistance body10and the pair of electrodes (the first electrode body11and the second electrode body12) connected to the resistance body10, it is possible to realize the resistor1having a small size and a low resistance. In addition, the oxide film5has the low wettability to the solder. Thus, even if the gap between the resistance body10and the substrate board (the circuit board) is small, it is difficult for the solder to creep over the oxide film5, and so, it is possible to prevent the solder from creeping up beyond the oxide film5and creeping up to the resistance body10. Therefore, compared with a case in which the resistance body10is covered by a resin, it is possible to improve the manufacturing yield and to suppress the manufacturing cost.

Besides, the resistor1of the present embodiment has configurations, operations, and effects as described below.

According to the resistor1of the present embodiment, the resistor1is provided with the resistance body10and the pair of electrodes (the first electrode body11and the second electrode body12) connected to the resistance body10, the end surfaces of the resistance body10are respectively abutted to and bonded to the end surfaces of the electrodes (the first electrode body11and the second electrode body12), the electrodes (the first electrode body11and the second electrode body12) respectively include the main body portions21and31and the leg portions22and32respectively protruded from the main body portions21and31towards the mounting surface, the length dimension (L) of a long side of the resistor1is equal to or shorter than 3.2 mm, and the resistance value is equal to or lower than 2 mΩ.

With the above-described configuration, the leg portions22and32that respectively protrude from the main body portions21and31towards the mounting surface are configured by the resistance body10and the pair of electrodes (the first electrode body11and the second electrode body12) connected to the resistance body10. With such a configuration, because lines can be drawn out from sensing terminals between the leg portions22and32, it is possible to realize the resistor1having the small size. In addition, because the electrodes (the first electrode body11and the second electrode body12) are bonded on both ends of the resistance body10, the dimension of the resistance body10(in the X direction) becomes smaller than the dimension of the resistor1(in the X direction). With such a configuration, it is possible to realize the resistor1having a lower resistance than resistors of the type in which the pair of electrodes are bonded to the lower surface of the resistance body10. As described above, it is possible to obtain the resistor1capable of realizing further lower resistance (2 mΩ or lower), which has not been realized with general resistors, while realizing the smaller size (the long side dimension 3.2 mm or shorter, 3216 size or smaller).

In a case of a resistor that is formed by welding the resistance body and the electrode bodies by using, electron beam, etc., it is required to consider influence on the resistance value caused by the beads formed by the welding in a case of the resistor of this size scale. However, with the resistor1of the present embodiment, as described below, because the resistance body10can be bonded to the first electrode body11, and the resistance body10can be bonded to the second electrode body12by the diffusion bonding, it is possible to stabilize properties such as the resistance value, etc. even if the resistor is designed to have such a small size.

In the present embodiment, in the mounting surface of the resistor1, the boundary portions (the bonded portions13and14) between the resistance body10and the respective main body portions21and31are flat. Because the welding beads caused by the electron beam welding, etc. are not formed, the boundaries between the resistance body10and the respective main body portions21and31become obvious, and so, it is possible to perform a judgement as being acceptable or defective with ease. In addition, when the resistor1is used as a shunt resistor, it is possible to suppress deterioration of the sensing accuracy of the current generated due to formation of the step at the boundaries between the resistance body10and the respective main body portions21and31(the bonded portions13and14). Furthermore, it is possible to improve a stability of the resistance value and a thermal property.

In the present embodiment, the resistance body10is bonded to the main body portions21and31by the solid phase bonding. Thus, the resistance body10and the first electrode body11are firmly bonded with each other, and the resistance body10and the second electrode body12are firmly bonded with each other, and therefore, a good electrical property can be obtained. In addition, in the resistor1, the electron beam welding, etc., is not used for the bonding between the resistance body10and the first electrode body11and the bonding between the resistance body10and the second electrode body12, and therefore, the bonded portions13and14do not have the welding beads (a welding mark having an irregular shape). Therefore, a bondability is not deteriorated even in a case in which wire bonding, etc. is performed on the surface of the resistor1.

In the present embodiment, the main body portions21and31respectively have the protruded portions211and311protruded towards the resistance body side. With such a configuration, when the length (L) of the resistor1in the longitudinal direction (the X direction) is set constant, by arbitrarily adjusting the length of the protruded portion211in the X direction (the length L1of the main body portion21) or the length of the protruded portion311in the X direction (the length L2of the main body portion31in the X direction), it is possible to adjust the length (L0) of the resistance body10in the X direction so as to satisfy L0=L−(L1+L2). Therefore, it is possible to arbitrarily adjust the resistance value of the resistor1without changing the shapes of the leg portions22and32.

In the present embodiment, in the direction in which the resistance body10and the electrodes (the first electrode body11and the second electrode body12) of the resistor1are arranged (the X direction), end portions of the leg portions22and32on the mounting surface side each has the chamfered shape.

In general resistors, the resistors tend to be damaged due to occurrence of a phenomenon called an electromigration that is caused as a current density is increased in a non-chamfered corner portion, or due to concentration of thermal stress to such a corner portion in a similar manner. In addition, because the electromigration has a non-negligible influence as the circuit size is decreased, there was a concern that the smaller the resistor is, the more pronounced the electromigration becomes.

In contrast, in the resistor1, because the corner portions P are chamfered, deviation of the current density in the corner portions P is reduced. Thus, it is possible to suppress occurrence of the electromigration. In addition, in a similar manner, because the concentration of the thermal stress can be reduced, it is possible to improve a heat cycle resistance.

In the present embodiment, the direction orthogonal to the direction in which the resistance body10and the electrodes (the first electrode body11and the second electrode body12) of the resistor1are arranged (the X direction) as well as to the mounting direction of the resistor1(the Z direction) is set as the width direction (the Y direction), and the surface of the resistance body10and/or the surfaces of the electrodes (the first electrode body11and the second electrode body12) is/are formed with the stripe-patterned grooved and ridged surface (the stripe-patterned grooves and ridges15) extending in the width direction (the Y direction). With such a configuration, the surface area of the resistor1can be increased to improve the heat radiation property, and in addition, when the grooves and ridges are formed on the electrodes (the first electrode body11and the second electrode body12), it is possible to increase a bonding strength for a solder for fixing the resistor1to the circuit board.

In the present embodiment, the resistance body10is formed to have the cuboid shape (or the cube shape). In a case in which the resistance body10has the cuboid shape (or the cube shape), the first electrode body11and the second electrode body12are respectively formed to have substantially the same shapes as the end surfaces of the resistance body10and are respectively bonded to the end surfaces of the resistance body10, and a path of the current flowing from the first electrode body11and the second electrode body12through the resistance body10is formed linearly, and therefore, it is possible to stabilize the resistance value. In addition, in the resistor1, because the resistance body10is bonded between the first electrode body11and the second electrode body12, it is possible to adjust the resistance value while setting the volume of the resistance body10to the minimum required volume.

Explanation of Manufacturing Method of Resistor

FIG.12is a schematic view for explaining the manufacturing method of the resistor1of the present embodiment.

The manufacturing method of the resistor1of the present embodiment includes: Step (a) of preparing materials; Step (b) of bonding the materials; Step (c) of processing the shape; Step (d) of cutting out individual resistors1(separation into pieces); and Step (e) of adjusting the resistance value of the resistor1by using a laser.

In Step (a) of preparing the materials, a resistance body base material10A serving as a base material of the resistance body10, an electrode body base material11A serving as the base material of the first electrode body11, and an electrode body base material12A serving as the base material of the second electrode body12are prepared. The resistance body base material10A and the electrode body base materials11A and12A are each a long wire rod having a flat rectangular shape. In the present embodiment, from the view point of the size, the resistance value, and a processability of the resistor1, it is preferable to use a copper-manganese alloy as the material of the resistance body base material10A (the resistance body10) and to use the oxygen-free copper (C1020) as the material of the electrode body base materials11A and12A (the first electrode body11and the second electrode body12).

In Step (b) of bonding the materials, the electrode body base material11A, the resistance body base material10A, and the electrode body base material12A are stacked in this order, and the materials are bonded by applying pressure in the stacked direction, and thereby, the resistor base material100is formed.

In other words, in Step (b), a so-called cladding (the solid phase bonding) between dissimilar metal materials is performed. The bonded surface between the electrode body base material11A and the resistance body base material10A subjected to the cladding, and the bonded surface between the electrode body base material12A and the resistance body base material10A subjected to the cladding are each the diffusion bonded surface in which metal atoms from both materials are diffused to each other.

Thus, it is possible to perform firm mutual bonding at the bonded surface between the resistance body base material10A and the electrode body base material11A and at the bonded surface between the resistance body base material10A and the electrode body base material12A, without performing a common electron beam welding. In addition, a good electrical property is obtained at the bonded surface between the resistance body base material10A (the resistance body10) and the electrode body base material11A (the first electrode body11) and at the bonded surface between the resistance body base material10A (the resistance body10) and the electrode body base material12A (the second electrode body12).

FIG.13is a front view of a die300used in Step (c) shown inFIG.12viewed from the upstream side in the drawing direction F.FIG.14is a sectional view taken along line B-B inFIG.14and is a schematic view for explaining the step of processing the shape in the manufacturing method of the resistor1of the present embodiment. In Step (c), the resistor base material100obtained by the cladding is passed through the die300. When the resistor1of the present embodiment is to be manufactured, as one example, it is possible to use the die300shown inFIG.13.

An opening portion301is formed in the die300. The opening portion301has an inlet opening302that is set to have the dimension that allows the insertion of the resistor base material100, an outlet opening303that is set to have the dimension smaller than the outer dimension of the resistor base material100, and an insertion portion304that is formed to have a tapered shape from the inlet opening302towards the outlet opening303. In the present embodiment, the opening portion301is formed to have a rectangular shape in which corner portions are processed to have the chamfered shapes.

By passing the resistor base material100through the die300having such a shape, it is possible to compressively deform the resistor base material100from all directions. Thus, a cross-sectional shape of the resistor base material100is processed to the shape that imitates the outer shape of the die300(the outlet opening303).

In addition, in the present embodiment, in Step (c), when the resistor base material100is passed through the die300, a drawing method in which the resistor base material100is drawn out by a holding tool400is applied.

In Step (c), it may be possible to perform a drawing processing by preparing a plurality of dies300respectively having the opening portions301with different sizes and by passing the resistor base material100through the plurality of dies300in a consecutive manner.

In addition, in Step (c), by changing the shape of the opening portion301of the die300, it is possible to manufacture the resistor1of the present embodiment.

When the resistor1is to be manufactured, as one example, the die300, in which a protruded portion300ahaving a rectangular shape protruded towards the center of the opening is formed on a part of one side of the opening portion301(the inlet opening302, the outlet opening303), is applied. Because of the protruded shape provided on the rectangular outlet opening303, a rectangular groove105extending continuously in the drawing direction is formed in the resistor base material100.

As the resistor base material100is cut into separate pieces, the rectangular groove105forms a recessed portion that is surrounded by the resistance body10, the main body portion21and the leg portion22of the first electrode body11, and the main body portion31and the leg portion32of the second electrode body12.

Returning toFIG.12, in Step (d) following Step (c), the resistor1is cut out from the resistor base material100so as to achieve the length W in the Y direction as designed. In addition, in the present embodiment, in Step (d), it is preferred that the resistor base material100be cut from a surface100aof the resistor base material100, in which the rectangular groove105is formed, towards an opposite surface100b. By doing so, a burr of the metal is formed to have a shape that extends upwards from the upper surface of the resistor1, and the burr extending in the −Z direction (FIGS.1and2) (the burr extending towards a circuit substrate) is not formed on the leg portions22and32. By doing so, it is possible to surely perform mounting of the resistor1onto the circuit board.

By following the above-described steps, it is possible to obtain an individual piece of the resistor1from the resistor base material100. Furthermore, in Step (e), the resistance value of the resistor1is set at a desired resistance value by performing the trimming of the resistance body10by irradiating laser. A detail of the trimming is as described above (seeFIGS.8to10).

The corner portions P shown inFIGS.1and2are formed so as to imitate the shape of the opening portion301of the die300, and the stripe-patterned grooves and ridges15are a stripe-patterned sliding mark formed so as to extend in the length-wise direction of the resistor base material100when the resistor base material100is slid in a state in which the resistor base material100is compressed against an inner wall of the die300(the outlet opening303).

Effect of Manufacturing Method of Resistor1Using Die300according to Present Embodiment

Next, operational advantages of the present embodiment will be described.

According to the manufacturing method of the resistor1using the die300of the present embodiment, the pressure is applied after stacking the electrode body base material11A, the resistance body base material10A, and the electrode body base material12A in parallel, and the cladding (the solid phase bonding) is performed, and thereby, the resistor base material100(the resistor1) having an integrated structure (in other words, a parallel structure) is obtained. Thus, without using the electron beam welding, etc., it is possible to increase the bonding strength between the resistance body base material10A (the resistance body10) and the electrode body base material11A (the first electrode body11) and the bonding strength between the resistance body base material10A (the resistance body10) and the electrode body base material12A (the second electrode body12).

In addition, according to the above-described manufacturing method of the present embodiment, by compressing the resistor base material100from all directions by passing it through the die300, it is possible to form the external shape of the resistor base material100. Therefore, after the resistor base material100is formed, it is possible to manufacture the individual resistor1only by performing Step (d). Therefore, it is possible to suppress individual differences caused by the manufacture of the resistor1. In addition, by passing the resistor base material100through the die300, it is possible to further increase the bonding strength between the resistance body10and the first electrode body11and the bonding strength between the resistance body10and the second electrode body12.

As a method to compress the resistor base material100from all directions, if the resistor base material100is of a square shape, for example, there has been a method in which the resistor base material100is subjected to a first pressure welding by using a pair of rollers that apply the pressure in the thickness direction (Z), and thereafter, the resistor base material100is subjected to a second pressure welding by using a pair of rollers that apply the pressure in the width direction (Y).

However, with such a method, in the first pressure welding step, although the resistor base material100is compressed in the thickness direction (Z), the resistor base material100is expanded in the width direction (Y). In addition, in the following second pressure welding step, although the resistor base material100is compressed in the width direction (Y), the resistor base material100is expanded in the thickness direction (Z). As a result, the dimensional accuracy is deteriorated, and individual variation for the resistor, variation in a temperature distribution when power is applied to the resistor, and so forth are increased.

In contrast, according to the above-described manufacturing method in the present embodiment, by performing the drawing step in which the resistor base material100is passed through the die300, it is possible to uniformly compress the resistor base material100in the length-wise direction (X) and in the thickness direction (Z).

Therefore, compared with a resistor base material obtained by repeating the compression from one direction and the compression from the other direction by using the rollers, it is considered that an electrically advantageous bonding interface is formed in the resistor base material100. Therefore, it is possible to suppress differences in properties for the resistor1as an end product.

With the above-described manufacturing method according to the present embodiment, especially, by using the plurality of dies300respectively having the opening portions301of different types in a consecutive manner, a compression forming is performed such that the size of the resistor base material100is reduced in a consecutive manner. By doing so, it is possible to uniformly compress the resistor base material100in the length-wise direction (X) and the thickness direction (Z) while reducing a load to the resistor base material100and the die300. Thus, it is possible to suppress the variations in properties for the resistor1as the end product.

In addition, with the above-described manufacturing method according to the present embodiment, in Step (c) in which the resistor base material100is passed through the die300, by applying the drawing step, it is possible to increase the accuracy of the end product compared with an extruding method. By using this manufacturing method, it is possible to realize a stabilization of the properties as the resistor1.

Especially, at least the outlet opening303of the opening portion301of the die300is formed with continuous curves. With such a configuration, it is possible to relieve a stress imparted to the resistor base material100while the resistor base material100is being passed through the opening, and so, it is possible to reduce the load to the resistor base material100and the die300. Thus, it is possible to suppress the variations in properties for the resistor1as the end product.

In addition, because at least the outlet opening303is formed with the continuous curves, the corner portions P (the edge sides) of the resistor1, which are obtained by being passed through the die300, are chamfered. Thus, it is possible to suppress the electromigration caused in the resistor1at the corner portions P. In addition, it is possible to increase the heat cycle resistance of the resistor1.

In addition, according to the above-described manufacturing method of the present embodiment, because the first electrode body11, the resistance body10, and the second electrode body12are mutually bonded by the diffusion bonding (the solid phase bonding), the welding beads are not formed. When the bonding is performed by the welding, such as the common electron beam welding, etc., there may have been a risk in that, as the size of the resistor is reduced, the non-negligible influence is imparted to the resistance value property by the welding beads. However, there is no such a concern for the resistor1obtained by the above-described manufacturing method according to the present embodiment.

As described above, in the above-described manufacturing method according to the present embodiment, the resistor base material100is obtained by cladding (the solid phase bonding) the resistance body base material10A and the electrode body base materials11A and12A, and the resistor base material100is passed through the die300to perform the forming. Thus, because the bonding strength between the materials can be increased without employing the electron beam welding for example, and at the same time, because the high dimensional accuracy can be ensured, the manufacturing method is suitable for the manufacture of the small resistor1.

When the resistor1is to be manufactured, in Step (d), it is preferred that the resistor base material100be cut from the surface100aof the resistor base material100, in which the rectangular groove105is formed, towards the opposite surface100b. By doing so, it is possible to prevent, at the mounting surface side, the formation of the burr caused by the cutting.

In addition, in the above-described manufacturing method according to the present embodiment, before performing Step (c) of processing the shape, a step of adjusting the size of the resistor base material100, which has been subjected to the cladding, to the size that allows the insertion into the die300may be performed.

In addition, in the above-described manufacturing method according to the present embodiment, although the irradiation of the laser is used for the formation of the oxide film5, there is no intention to limit the means of forming the oxide film5to the laser as long as it is possible to form the oxide film5by modifying a metal surface, and for example, the oxide film5may be formed by supplying an oxidizing agent.

Although the embodiments of the present disclosure have been described in the above, the above-mentioned embodiments merely illustrate a part of application examples of the present disclosure, and the technical scope of the present disclosure is not intended to be limited to the specific configurations in the above-mentioned embodiments. For example, in the present embodiment, although a description has been given of the resistor1that is obtained by passing the resistor base material100through the die300and by separating it into individual pieces, the present disclosure may also be applied to the resistor that is obtained by cladding the resistance body and the electrode bodies without passing them through the die300or to the resistor that is formed by press working.

The present application claims a priority based on Japanese Patent Application No. 2020-011196 filed on Jan. 27, 2020 in the Japan Patent Office, the entire contents of which are incorporated herein by reference.