Patent Publication Number: US-2022238259-A1

Title: Resistor

Description:
TECHNICAL FIELD 
     The present disclosure relates to a resistor mainly used in current detection. 
     BACKGROUND ART 
     A known resistor is provided with a resistive element made of a metal plate. Such a resistor is mainly used in current detection. In Patent Document 1, an example is described of a resistor provided with a resistive element made of a metal plate. This resistor is provided with a resistive element and a pair of electrodes formed on the ends of a surface of the resistive element facing one direction in a thickness direction. 
     There is a need for resistors provided with a resistive element made of a metal plate to have a lower resistance value in order to improve the accuracy of current detection. However, as described in Patent Document 1, the resistive element is provided with a slit for adjusting the resistance value of the resistor. In this case, when a slit is provided near either one of the pair of electrodes of the resistor, the value of the temperature coefficient of resistance (TCR) is confirmed to be relatively higher. Also, it is confirmed that there is a tendency for the value of the temperature coefficient of resistance to rise further when the resistance value of the resistor is low. With high values for the temperature coefficient of resistance, variation increases in the resistance value of the resistor caused by heat generated from the resistive element when the resistor is in use. This causes the accuracy of the current detection using the resistor to be reduced. Accordingly, there is a need to suppress an increase of the temperature coefficient of resistance in a resistor provided with a resistive element including a slit. 
     PRIOR ART DOCUMENTS 
     Patent Document 
     Patent Document 1: JP-A-2013-225602 
     SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
     In light of the foregoing, the present disclosure is directed at providing a resistor that enables an increase in temperature coefficient of resistance to be suppressed. 
     Means for Solving the Problem 
     A resistor provided according to an aspect of the present disclosure includes: a resistive element including a first surface and a second surface facing opposite sides in a thickness direction; a protective film disposed on the first surface and having electrical insulating properties; and a pair of electrodes spaced apart from each other in a first direction perpendicular to the thickness direction, where the pair of electrodes are held in contact with the resistive element. The protective film includes a first outer edge and a second outer edge that are spaced apart from each other in the first direction and each extend in a second direction perpendicular to the thickness direction and the first direction. The resistive element includes a first slit and a second slit each extending from the first surface through to the second surface and extending in the second direction. The first slit is located closest to the first outer edge, and the second slit is located closest to the second outer edge. As viewed in the thickness direction, a first distance between the first outer edge and the first slit and a second distance between the second outer edge and the second slit together have a length 15% or greater of a dimension of the protective film in the first direction. 
     Preferably, as viewed in the thickness direction, the first distance and the second distance are equal to each other. 
     Preferably, each one of the pair of electrodes includes a bottom portion opposite to the resistive element with respect to the protective film in the thickness direction. The bottom portion of each one of the pair of electrodes includes a portion overlapping with a portion of the protective film as viewed in the thickness direction. 
     Preferably, the protective film is made of a material including a synthetic resin. 
     Preferably, the protective film includes a filler made of a material including a ceramic. 
     Preferably, the first slit overlaps with the bottom portion of one of the pair of electrodes as viewed in the thickness direction. The second slit overlaps with the bottom portion of the other one of the pair of electrodes as viewed in the thickness direction. 
     Preferably, as viewed in the thickness direction, the first distance and the second distance together have a length 30% or less of the dimension of the protective film in the first direction. 
     Preferably, the resistive element includes a pair of first end surfaces spaced apart from each other in the first direction and connected to both the first surface and the second surface. Each one of the pair of electrodes includes a side portion jutting out in the thickness direction and connected to the bottom portion of one of the pair of electrodes. The side portion of each one of the pair of electrodes is in contact with one of the pair of first end surfaces. 
     Preferably, the resistor further includes an insulating plate disposed on the second surface and made of a material including a synthetic resin. The resistive element includes a pair of second end surfaces spaced apart from each other in the second direction and connected to both the first surface and the second surface; and the pair of second end surfaces are covered by the insulating plate. 
     Preferably, the side portions of the pair of electrodes are in contact with the insulating plate. 
     Preferably, the first slit extends in the second direction from one surface of the pair of second end surfaces. The second slit extends in the second direction from the other surface of the pair of second end surfaces. 
     Preferably, the insulating plate includes a portion extending into the first slit and the second slit in the thickness direction. 
     Preferably, the first slit and the second slit each include a pair of side walls spaced apart from each other in the first direction, where each one of the pair of side walls includes a portion recessed in the first direction. 
     Preferably, the resistive element includes a projection projecting in the second direction from one of the pair of second end surfaces, where the projection is connected to one of the pair of first end surfaces. The bottom portion of one of the pair of electrodes is in contact with the projection. 
     Preferably, the resistive element includes a plurality of grooves recessed in the first surface and each extending in a predetermined direction. The protective film meshes with the plurality of grooves. 
     Preferably, the resistor further includes a pair of intermediate layers located between the resistive element and the bottom portion of the pair of electrodes in the thickness direction. Each one of the pair of intermediate layers includes a cover portion covering a portion of the protective film. The bottom portion of each one of the pair of electrodes is in contact with the cover portion of one of the pair of intermediate layers. 
     Preferably, the first outer edge and the second outer edge are located between the pair of first end surfaces as viewed in the thickness direction. The first surface includes a first region and a second region not covered by any one of the protective film and the pair of intermediate layers. The first region is located between the first outer edge and one of the pair of first end surfaces located closest to the first outer edge. The second region is located between the second outer edge and one of the pair of first end surfaces located closest to the second outer edge. Each of the first region and the second region are in contact with the bottom portion of one of the pair of electrodes. 
     According to the above-described configurations of the resistor, an increase in the temperature coefficient of resistance can be suppressed. 
     Other features and advantages of the present disclosure will be apparent from the following detailed description with reference to the attached diagrams. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a plan view of a resistor according to a first embodiment. 
         FIG. 2  is a plan view of the resistor illustrated in  FIG. 1 , with an insulating plate made transparent. 
         FIG. 3  is a bottom view of the resistor illustrated in  FIG. 1 . 
         FIG. 4  is a bottom view corresponding to  FIG. 3 , with a pair of electrodes made transparent. 
         FIG. 5  is a bottom view corresponding to  FIG. 4 , with a pair of intermediate layers made transparent. 
         FIG. 6  is a right side view of the resistor illustrated in  FIG. 1 . 
         FIG. 7  is a front view of the resistor illustrated in  FIG. 1 . 
         FIG. 8  is a cross-sectional view taken along line VIII-VIII of  FIG. 2 . 
         FIG. 9  is an enlarged view of a portion of  FIG. 8 . 
         FIG. 10  is an enlarged view of a portion of  FIG. 8 . 
         FIG. 11  is an enlarged view of a portion of  FIG. 8 . 
         FIG. 12  is a cross-sectional view for describing a manufacturing process of the resistor illustrated in  FIG. 1 . 
         FIG. 13  is a cross-sectional view for describing a manufacturing process of the resistor illustrated in  FIG. 1 . 
         FIG. 14  is a cross-sectional view for describing a manufacturing process of the resistor illustrated in  FIG. 1 . 
         FIG. 15  is a cross-sectional view for describing a manufacturing process of the resistor illustrated in  FIG. 1 . 
         FIG. 16  is a cross-sectional view for describing a manufacturing process of the resistor illustrated in  FIG. 1 . 
         FIG. 17  is a cross-sectional view for describing a manufacturing process of the resistor illustrated in  FIG. 1 . 
         FIG. 18  is a graph showing the temperature coefficient of resistance of the resistor illustrated in  FIG. 1  and a resistor of a comparative example. 
         FIG. 19  is a plan view of a resistor according to a second embodiment, with the insulating plate made transparent. 
         FIG. 20  is a bottom view of the resistor illustrated in  FIG. 19 , with the pair of electrodes made transparent. 
         FIG. 21  is a front view of the resistor illustrated in  FIG. 19 . 
         FIG. 22  is a cross-sectional view taken along line XXII-XXII of  FIG. 19 . 
         FIG. 23  is a cross-sectional view for describing a manufacturing process of the resistor illustrated in  FIG. 19 . 
         FIG. 24  is a cross-sectional view for describing a manufacturing process of the resistor illustrated in  FIG. 19 . 
         FIG. 25  is a cross-sectional view for describing a manufacturing process of the resistor illustrated in  FIG. 19 . 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     Various embodiments of the present disclosure are described below with reference to the attached drawings. 
     A resistor A 10  according to a first embodiment will now be described with reference to  FIGS. 1 to 11 . The resistor A 10  is an example of a shunt resistor used in current detection. The resistor A 10  has a main resistance value of 5 mΩ. The resistor A 10  may be surface mounted on a circuit board of various electronic devices. The resistor A 10  is provided with a resistive element  10 , an insulating plate  20 , a protective film  30 , a pair of intermediate layers  40 , and a pair of electrodes  50 . Note that in  FIG. 2 , to facilitate understanding, the insulating plate is shown as being transparent. In  FIG. 4 , to facilitate understanding, the pair of electrodes  50  are shown as being transparent. In  FIG. 5 , the pair of intermediate layers  40  and the pair of electrodes  50  are shown as being transparent. In these diagrams, the transparent pair of intermediate layers  40  and the pair of electrodes  50  are indicated by an imaginary line (two-dot chain line). 
     In the description of the resistor A 10 , the direction along the thickness of the resistive element  10  is referred to as “thickness direction z”. A direction perpendicular to the thickness direction z is referred to as “first direction x”. A direction perpendicular to both the thickness direction z and the first direction x is referred to as “second direction y”. The “thickness direction z”, the “first direction x”, and the “second direction y” are also used in describing a resistor A 20  described below. As illustrated in  FIG. 1 , the resistor A 10  is rectangular as viewed in the thickness direction z. The first direction x corresponds to the length direction of the resistor A 10 . The second direction y corresponds to the width direction of the resistor A 10 . 
     The resistive element  10  forms the functional core of the resistor A 10 . The resistive element  10  is a metal plate. The material of the metal plate may be, for example, an alloy of copper (Cu), manganese (Mn), and nickel (Ni) (Manganin®) or an alloy of copper, manganese, and tin (Sn) (ZERANIN®). The thickness of the resistive element  10  ranges from 50 μm to 150 μm. 
     As illustrated in  FIGS. 7 and 8 , the resistive element  10  includes a first surface  10 A, a second surface  10 B, a pair of first end surfaces  10 C, and a pair of second end surfaces  10 D. The first surface  10 A faces one direction in the thickness direction z. The second surface  10 B facing the opposite direction to the first surface  10 A. Thus, the first surface  10 A and the second surface  10 B face opposite sides in the thickness direction z. The pair of first end surfaces  10 C are spaced apart from each other in the first direction x. Each one of the pair of first end surfaces  10 C is connected to both the first surface  10 A and the second surface  10 B. The pair of second end surfaces  10 D are spaced apart from each other in the second direction y. Each one of the pair of second end surfaces  10 D is connected to both the first surface  10 A and the second surface  10 B. 
     As illustrated in  FIGS. 2 to 8 , the resistive element  10  includes a first slit  111  and a second slit  112 . The first slit  111  and the second slit  112  are provided for adjusting the resistance value of the resistive element  10  to a predetermined value. The first slit  111  and the second slit  112  are spaced apart from each other in the first direction x. The first slit  111  and the second slit  112  extend through the resistive element  10  from the first surface  10 A toward the second surface  10 B. The first slit  111  extends in the second direction y from one surface of the pair of second end surfaces  10 D. The second slit  112  extends in the second direction y from the other surface of the pair of second end surfaces  10 D. 
     As illustrated in  FIG. 9 , the first slit  111  includes a pair of side walls  11 A. Note that, though omitted from the drawings, the second slit  112  also includes a pair of side walls  11 A in a similar manner to the first slit  111 . The pair of side walls  11 A are spaced apart from each other in the first direction x. Each one of the pair of side walls  11 A is connected to both the first surface  10 A and the second surface  10 B. Each side wall  11 A includes a portion recessed in the first direction x. 
     As illustrated in  FIGS. 5 and 10 , the resistive element  10  is provided with a plurality of grooves  12  for adjusting the resistance value of the resistive element  10  to a predetermined value, together with the first slit  111  and the second slit  112 . The plurality of grooves  12  are recessed from the first surface  10 A and extend in a predetermined direction. In illustrated example of the resistor A 10 , the plurality of grooves  12  extend in the second direction y. The plurality of grooves  12  are located between the first slit  111  and the second slit  112  in the first direction x. As illustrated in  FIG. 10 , a maximum width bmax of the plurality of grooves  12  is less than a minimum width Bmin (see  FIG. 9 ) of the first slit  111  and the second slit  112 . 
     As illustrated in  FIGS. 2, 4, and 7 , the resistive element  10  includes four projections  14 . As viewed in the thickness direction z, the four projections  14  are located at the four corners of the resistive element  10 . The four projections  14  each project in the second direction y from one of the pair of second end surfaces  10 D. Each one of the four projections  14  is connected to one of the pair of first end surfaces  10 C. 
     The shape of the resistive element  10  has point symmetry as viewed in the thickness direction z. Point symmetry in this case indicates the point symmetrical relationship with respect to a center C of two divided sections formed by dividing the resistive element  10  into two via a boundary N that passes through the center C of the resistive element  10  illustrated in  FIG. 2  and extends in the second direction y. 
     As illustrated in  FIG. 8 , the insulating plate  20  is disposed on the second surface  10 B of the resistive element  10 . The insulating plate  20  is made of a material including a synthetic resin. In the illustrated example of the resistor A 10 , the insulating plate  20  is a synthetic resin sheet including an epoxy resin. As illustrated in  FIGS. 1 and 7 , the pair of second end surfaces  10 D of the resistive element  10  are covered by the insulating plate  20 . As illustrated in  FIGS. 1, 6, and 8 , the insulating plate  20  includes a pair of end surfaces  20 A. The pair of end surfaces  20 A face opposite sides in the first direction x and are spaced apart from each other in the first direction x. Each one of the pair of end surfaces  20 A is flush with one of the pair of first end surfaces  10 C. As illustrated in  FIG. 8 , a portion of the insulating plate  20  is disposed extending through the first slit  111  and the second slit  112  of the resistive element  10  in the thickness direction z. 
     As illustrated in  FIG. 8 , the protective film  30  is disposed on the first surface  10 A of the resistive element  10 . The protective film  30  has electrical insulating properties and is made of a material including a synthetic resin. In the illustrated example of the resistor A 10 , the protective film  30  is made of a material including an epoxy resin. As illustrated in  FIGS. 9 and 10 , the protective film  30  includes a filler  31 . The filler  31  is made of a material including a ceramic. The ceramic is preferably one with a relatively high thermal conductivity, such as alumina (Al 2 O 3 ) or boron nitride (BN). The protective film  30  covers a portion of the first surface  10 A and the portion of the insulating plate  20  disposed extending through the first slit  111  and the second slit  112  of the resistive element  10 . As illustrated in  FIG. 10 , the protective film  30  meshes with the plurality of grooves  12  of the resistive element  10 . 
     As illustrated in  FIGS. 2, 5, and 8 , the protective film  30  includes a first outer edge  30 A and a second outer edge  30 B. The first outer edge  30 A and the second outer edge  30 B are spaced apart from each other in the first direction x and extend in the second direction y. The first outer edge  30 A is located closest to the first slit  111  of the resistive element  10 . The second outer edge  30 B is located closest to the second slit  112  of the resistive element  10 . As viewed in the thickness direction z, a first distance L 1  from the first outer edge  30 A to the first slit  111  and a second distance L 2  from the second outer edge  30 B to the second slit  112  together occupy from 15% to 30% of a dimension L 0  of the protective film  30  in the first direction x. The first distance L 1  indicates the least distance from the boundary between the pair of side walls  11 A of the first slit  111  and the first surface  10 A of the resistive element  10  to the first outer edge  30 A. In a similar manner, the second distance L 2  indicates the least distance from the boundary between the pair of side walls  11 A of the second slit  112  and the first surface  10 A to the second outer edge  30 B. Note that the dimension L 0  is equal to the distance from the first outer edge  30 A and the second outer edge  30 B. As viewed in the thickness direction z, the first distance L 1  and the second distance L 2  are equal. 
     In  FIG. 2 , the first distance L 1  and the second distance L 2  equal to 15% of the dimension L 0  of the protective film  30  in the first direction x are indicated by a first distance L 1 min and a second distance L 2 min. Also, the first distance L 1  and the second distance L 2  equal to 30% of the dimension L 0  of the protective film  30  in the first direction x are indicated by a first distance L 1 max and a second distance L 2 max. 
     As illustrated in  FIGS. 4, 5, and 8 , the first outer edge  30 A and the second outer edge  30 B of the protective film  30  are located between the pair of first end surfaces  10 C of the resistive element  10  as viewed in the thickness direction z. The first surface  10 A of the resistive element  10  includes a first region  131  and a second region  132  not covered by the protective film  30  or the pair of intermediate layers  40 . The first region  131  is located between the first outer edge  30 A and one of the pair of first end surfaces  10 C located closest to the first outer edge  30 A. The second region  132  is located between the second outer edge  30 B and one of the pair of first end surfaces  10 C located closest to the second outer edge  30 B. 
     As illustrated in  FIG. 8 , the pair of intermediate layers  40  are located between the resistive element  10  and a bottom portion  51  (details described below) of the pair of electrodes  50  in the thickness direction z. The pair of intermediate layers  40  are spaced apart from each other in the first direction x. The pair of intermediate layers  40  have electrical conductivity. In the resistor A 10 , the pair of intermediate layers  40  have electrical conductivity and are made of a material including a synthetic resin. The pair of intermediate layers  40  include metal particles. The metal particles include silver (Ag). In the illustrated example of the resistor A 10 , the synthetic resin included in the pair of intermediate layers  40  is an epoxy resin. The electric resistivity of the pair of intermediate layers  40  is approximately ten times the electric resistivity of the resistive element  10 . Accordingly, the electric resistivity of the pair of intermediate layers  40  is greater than the electric resistivity of the resistive element  10 . 
     As illustrated in  FIGS. 4 and 8 , each one of the pair of intermediate layers  40  includes a cover portion  41  and an extension portion  42 . The cover portion  41  is located on the opposite side of the protective film  30  to the resistive element  10  in the thickness direction z. The cover portion  41  covers a portion of the protective film  30 . The extension portion  42  extends from one of the cover portions  41  of the pair of intermediate layers  40  towards one of the pair of first end surfaces  10 C of the resistive element  10 . The extension portion  42  is in contact with the first surface  10 A of the resistive element  10 . In this manner, the pair of intermediate layers  40  are electrically connected to the resistive element  10 . 
     As illustrated in  FIGS. 2, 4, and 8 , each one of the pair of intermediate layers  40  includes a first layer  40 A and a second layer  40 B. The first layer  40 A includes the extension portion  42  and is in contact with the first surface  10 A of the resistive element  10 . The dimension in the thickness direction z of the first layer  40 A is substantially uniform throughout the first layer  40 A. The second layer  40 B includes the cover portion  41 . The second layer  40 B is in contact with the first layer  40 A of one of the pair of intermediate layers  40 . The second layer  40 B is configured to cover over a portion of the first layer  40 A. 
     As illustrated in  FIG. 4 , a cutout  421  is formed in the extension portion  42  of each one of the pair of intermediate layers  40 . The cutout  421  is recessed in the first direction x from one of the pair of first end surfaces  10 C. The first region  131  and the second region  132  including the pair of projections  14  of the resistive element  10  are exposed from the cutouts  421 . 
     As illustrated in  FIG. 11 , the first layer  40 A of each one of the pair of intermediate layers  40  includes an interposed portion  43  extending from the extension portion  42  toward the protective film  30 . The interposed portion  43  includes a portion located between the resistive element  10  and the protective film  30 . Accordingly, both ends in the first direction x of the protective film  30  are covered over by the first layers  40 A of the pair of intermediate layers  40 . The interposed portions  43  are in contact with both the resistive element  10  and the protective film  30 . 
     As illustrated in  FIGS. 1 to 3, 6, and 8 , the pair of electrodes  50  are disposed spaced apart from each other in the first direction x. Each one of the pair of electrodes  50  is in contact with the resistive element  10 . In this manner, the pair of electrodes  50  are electrically connected to the resistive element  10 . Each one of the pair of electrodes  50  is formed of a plurality of metal layers. In the illustrated example of the resistor A 10 , the plurality of metal layers include a copper layer, a nickel layer, and a tin layer stacked in this order from the side closest to the resistive element  10 . 
     As illustrated in  FIGS. 3 and 6 to 8 , each one of the pair of electrodes  50  includes the bottom portion  51 . The bottom portion  51  is located on the opposite side of the protective film  30  to the resistive element  10  in the thickness direction z. The bottom portion  51  of each one of the pair of electrodes  50  includes a portion that overlaps with a portion of the protective film  30  as viewed in the thickness direction z. As illustrated in  FIG. 2 , the first slit  111  of the resistive element  10  overlaps with the bottom portion  51  of one of the pair of electrodes  50  as viewed in the thickness direction z. Also, the second slit  112  of the resistive element  10  overlaps with the bottom portion  51  of the other one of the pair of electrodes  50  as viewed in the thickness direction z. 
     As illustrated in  FIGS. 6 and 8 , the bottom portion  51  of each one of the pair of electrodes  50  is in contact with both the cover portion  41  and the extension portion  42  of one of the pair of intermediate layers  40 . Also, as illustrated in  FIGS. 7 and 8 , the bottom portion  51  of one of the pair of electrodes  50  is in contact with either the first region  131  or the second region  132  of the resistive element  10  and the two projections  14  adjacent to one of the pair of first end surfaces  10 C of the resistive element  10 . 
     As illustrated in  FIGS. 1 to 3 and 6 to 8 , each one of the pair of electrodes  50  includes a side portion  52 . The side portion  52  is connected to the bottom portion  51  of one of the pair of electrodes  50  and juts out extending in the thickness direction z. The side portion  52  of each one of the pair of electrodes  50  is in contact with one of the pair of first end surfaces  10 C of the resistive element  10 . Also, the side portion  52  of each one of the pair of electrodes  50  is in contact with one of the pair of end surfaces  20 A of the insulating plate  20 . 
     Next, an example of a method of manufacturing the resistor A 10  will be described with reference to  FIGS. 12 to 17 . Note that the cross-section location illustrated in  FIGS. 12 to 17  is the same as the cross-section location illustrated in  FIG. 8 . 
     As illustrated in  FIG. 12 , first, a resistive element  81  including a first surface  81 A and a second surface  81 B facing opposite sides in the thickness direction z is bonded to a base material  82  via thermocompression bonding. The resistive element  81  is formed of a plurality of resistive elements  10  of the resistor A 10  contiguous in the first direction x and the second direction y. The first surface  81 A corresponds to the first surface  10 A of the resistive element  10 . The second surface  81 B corresponds to the second surface  10 B of the resistive element  10 . The base material  82  is formed of a plurality of insulating plates  20  of the resistor A 10  contiguous in the first direction x and the second direction y. First, a plurality of slits  811  are formed in the resistive element  81  extending from the first surface  10 A through to the second surface  81 B. The plurality of slits  811  correspond to the first slit  111  and the second slit  112  of the resistive element  10 . The plurality of slits  811  are formed via wet etching. Next, the base material  82  is bonded to the second surface  81 B via thermocompression bonding using a laminating press. When the base material  82  is bonded to the second surface  81 B via thermocompression bonding, a portion of the base material  82  extends through the plurality of slits  811  in the thickness direction z. Lastly, with a probe for measuring the resistance value of the resistive element  81  brought into contact with the first surface  10 A, a plurality of grooves  812  recessed from the first surface  10 A are formed in the resistive element  81 . The plurality of grooves  812  correspond to the plurality of grooves  12  of the resistive element  10 . The plurality of grooves  12  are formed via laser irradiation, for example. When the resistance value of the resistive element  81  reaches a predetermined value, the formation of the plurality of grooves  812  ends. 
     Next, as illustrated in  FIG. 13 , the first layers  40 A of the pair of intermediate layers  40  that cover a portion of the first surface  81 A of the resistive element  81  are formed. The first layers  40 A of the pair of intermediate layers  40  are applied to the first surface  81 A by screen printing a material including silver particles and an epoxy resin. Here, the material is applied at positions spaced apart from each other in the first direction x. Then, the material is thermally cured, and the first layers  40 A of the pair of intermediate layers  40  are formed. 
     Next, as illustrated in  FIG. 14 , the protective film  30  covering a portion of the first surface  81 A of the resistive element  81  and a portion of the base material  82  extending through the plurality of slits  811  of the resistive element  81  is formed. First, a material including an epoxy resin is applied via screen printing to a portion of the first surface  81 A so as to completely cover the portion of the base material  82  extending through the plurality of slits  811 . Here, each end of the material in the first direction x covers over the first layer  40 A of one of the pair of intermediate layers  40 . Then, the material is thermally cured, and the protective film  30  is formed. 
     Next, as illustrated in  FIG. 15 , the second layers  40 B of the pair of intermediate layers  40  that cover a portion of the protective film  30  are formed. First, a material including silver particles and an epoxy resin are applied to the protective film  30  via screen printing. Here, the material is applied at positions spaced apart from each other in the first direction x. Also, each portion of the material spaced apart from each other is applied so as to cover over a portion of the first layer  40 A of one of the pair of intermediate layers  40 . Then, the material is thermally cured, and the second layers  40 B of the pair of intermediate layers  40  are formed. 
     Next, as illustrated in  FIG. 16 , a dicing blade is used to cut the resistive element  81  and the base material  82  along a cutting line CL to divide the resistive element  81  and the base material  82  into a piece including the protective film  30  and the pair of intermediate layers  40  (the first layers  40 A and the second layers  40 B). This piece corresponds to the component of the resistor A 10  minus the pair of electrodes  50 . In other words, the resistive element  81  divided into pieces corresponds to the resistive element  10  of the resistor A 10 . Also, the base material  82  divided into pieces corresponds to the insulating plate  20  of the resistor A 10 . Note that the pair of first end surfaces  10 C of the resistive element  10  correspond to the cut surfaces of the resistive element  81  formed in this process. Also, the pair of end surfaces  20 A of the insulating plate  20  correspond to the cut surfaces of the base material  82  formed in this process. 
     Lastly, as illustrated in  FIG. 17 , the pair of electrodes  50  that come into contact with the resistive element  10  are formed. The pair of electrodes  50  are formed by electrolytic barrel plating of the copper layer, the nickel layer, and the tin layer in this order. Each one of the pair of intermediate layers  40  is covered by the bottom portion  51  of one of the pair of electrodes  50 . The bottom portion  51  of each one of the pair of electrodes  50  is in contact with either the first region  131  or the second region  132  of the resistive element  10  and the protective film  30 . Also, each one of the pair of first end surfaces  10 C of the resistive element  10  and a portion of each one of the pair of end surfaces  20 A of the insulating plate  20  are covered by the side portion  52  of one of the pair of electrodes  50 . Next, the pair of electrodes  50  are heat treated at a temperature of 170° C. for two hours. In this manner, the bonds between the bottom portions  51  of the pair of electrodes  50  and the resistive element  10  are improved. With the process described above complete, the resistor A 10  is manufactured. 
     Next, the effects of the resistor A 10  will be described. 
     The resistor A 10  is provided with the resistive element  10 , the protective film  30  disposed on the first surface  10 A of the resistive element  10 , and the pair of electrodes  50  disposed in contact with the resistive element  10  and spaced apart from each other in the first direction x. The resistive element  10  includes the first slit  111  and the second slit  112 . The protective film  30  includes the first outer edge  30 A located closest to the first slit  111  and the second outer edge  30 B located closest to the second slit  112 . In the resistor A 10 , as viewed in the thickness direction z, the first distance L 1  from the first outer edge  30 A to the first slit  111  and the second distance L 2  from the second outer edge  30 B to the second slit  112  together occupy 15% or greater of the dimension L 0  of the protective film  30  in the first direction x. 
       FIG. 18  is a diagram illustrating the coefficient of variation of resistance (unit: 10 −6 /° C.) of the resistor A 10  and a resistor of a comparative examples when the temperature of the resistive element  10  varies within a range from 20° C. to 60° C. In comparative example  1  indicated in  FIG. 18 , the first slit  111  and the second slit  112  have the same length as the first slit  111  and the second slit  112  of the resistor A 10 - 1 . In a similar manner, in comparative example  2 , the first slit  111  and the second slit  112  have the same length as the first slit  111  and the second slit  112  of the resistor A 10 - 2 . In comparative example  1  and comparative example  2 , as viewed in the thickness direction z, the first distance L 1  from the first outer edge  30 A to the first slit  111  and the second distance L 2  from the second outer edge  30 B to the second slit  112  together occupy less than 15% of the dimension L 0  of the protective film  30  in the first direction x. 
     As illustrated in  FIG. 18 , the coefficient of variation of resistance of the resistor A 10 - 1  is approximately 50% of the coefficient of variation of resistance of the comparative example  1 . In a similar manner, the coefficient of variation of resistance of the resistor A 10 - 2  is approximately 50% of the coefficient of variation of resistance of the comparative example  2 . Thus, according to the resistor A 10 , an increase in the temperature coefficient of resistance can be suppressed. 
     Also, in the resistor A 10 , as viewed in the thickness direction z, the first distance L 1  from the first outer edge  30 A to the first slit  111  and the second distance L 2  from the second outer edge  30 B to the second slit  112  together occupy 30% or less of the dimension L 0  of the protective film  30  in the first direction x. In a case where the distance between the first slit  111  and the second slit  112  is too small, when the resistor A 10  is in use, the increase in the temperature of the region of the resistive element  10  between the first slit  111  and the second slit  112  is significant. In this state, variation in the resistance value of the resistor A 10  may occur. Thus, with the present configuration, an excessive increase in the temperature of the region of the resistive element  10  between the first slit  111  and the second slit  112  can be prevented, and thus variation of the resistance value of the resistor A 10  caused by an increase in the temperature of the resistive element  10  can be suppressed. 
     In the resistor A 10 , the first slit  111  overlaps with the bottom portion  51  of one of the pair of electrodes  50  as viewed in the thickness direction z. Also, the second slit  112  overlaps with the bottom portion  51  of the other one of the pair of electrodes  50 . In the regions of the resistive element  10  adjacent to the first slit  111  and the second slit  112  in the second direction y, the resistance value increases locally relative to other regions. Thus, when the resistor A 10  is in use, the temperature of these regions increases more than other regions. Accordingly, with the present configuration, because the heat generated from these regions is transferred to the pair of bottom portions  51 , an excessive increase in the temperature of these regions can be prevented. 
     The resistive element  10  includes the plurality of grooves  12  recessed from the first surface  10 A and extending in a predetermined direction. The protective film  30  meshes with the plurality of grooves  12 . In this manner, because an anchoring effect is displayed by the protective film  30  with respect to the resistive element  10 , the bond between the resistive element  10  and the protective film  30  can be improved. 
     The protective film  30  includes the filler  31  made of a material including a ceramic. In this manner, the mechanical strength of the protective film  30  can be increased. Furthermore, a ceramic with a relatively high thermal conductivity such as alumina, boron nitride, or the like can be selected as the ceramic, allowing the protective film  30  to have a high thermal conductivity. In this manner, the heat dissipation of the resistor A 10  can be further improved. 
     The insulating plate  20  is made of a material including a synthetic resin. Accordingly, in the process illustrated in  FIG. 11 , the base material  82  can be bonded to the second surface  81 B of the resistive element  81  via thermocompression bonding using a laminating press. Also, a portion of the insulating plate  20  is disposed extending through the first slit  111  and the second slit  112  in the thickness direction z. In this manner, because an anchoring effect is displayed by the insulating plate  20  with respect to the resistive element  10 , the bond between the resistive element  10  and the insulating plate  20  can be improved. Furthermore, the first slit  111  and the second slit  112  each include the pair of side walls  11 A separated in the first direction x. Each side wall  11 A includes a portion recessed in the first direction x. In this manner, because the anchoring effect displayed by the insulating plate  20  with respect to the resistive element  10  is increased, the bond between the resistive element  10  and the insulating plate  20  can be further improved. 
     The insulating plate  20  includes the pair of end surfaces  20 A facing opposite sides in the first direction x and spaced apart from each other in the first direction x. The side portion  52  of each one of the pair of electrodes  50  is in contact with one of the pair of end surfaces  20 A. In this manner, the dimension in the thickness direction z of the side portions  52  of pair of electrodes  50  can be further lengthened. When mounting the resistor A 10  on the circuit board, a solder fillet is formed at the side portions  52  of the pair of electrodes  50 . Thus, according to the present configuration, because the volume of the solder fillet is larger, the mountability of the resistor A 10  on the circuit board is further improved. 
     The resistor A 10  is further provided with the pair of intermediate layers  40  spaced apart from each other in the first direction x and each including the cover portion  41  covering a portion of the protective film  30 . The pair of intermediate layers  40  are electrically connected to the resistive element  10 . In the resistor A 10 , the pair of intermediate layers  40  are made of a metal thin film. The cover portion  41  of each one of the pair intermediate layers  40  is located between the protective film  30  and the bottom portion  51  of one of the pair of electrodes  50 . In this manner, in the process illustrated in  FIG. 16 , the bottom portions  51  of the pair of electrodes  50  covering a portion of the protective film  30  can be formed via electrolytic barrel plating. 
     The first outer edge  30 A and the second outer edge  30 B of the protective film  30  are located between the pair of first end surfaces  10 C of the resistive element  10  as viewed in the thickness direction z. The first surface  10 A of the resistive element  10  includes the first region  131  and the second region  132  not covered by the protective film  30  or the pair of intermediate layers  40 . The first region  131  and the second region  132  are each in contact with the bottom portion  51  of one of the pair of electrodes  50 . In this manner, when the resistor A 10  is in use, the current running through the resistive element  10  is made easier to run from the first region  131  and the second region  132  to the bottom portions  51  of the pair of electrodes  50 . Thus, because the length of the current path in the resistor A 10  is shortened, the variance of the resistance value of the resistor A 10  can be suppressed. 
     The resistive element  10  includes the projections  14  projecting in the second direction y from one of the pair of second end surfaces  10 D. Each one of the projections  14  is connected to one of the pair of first end surfaces  10 C. In this manner, in the process illustrated in  FIG. 15 , the cutting line CL can be set with the projections  14  as the target. Also, the area of the first region  131  or the second region  132  of the resistive element  10  can be increased via the projections  14 . In this manner, the bonds between the bottom portion  51  of one of the pair of electrodes  50  and the resistive element  10  can be improved. In forming the pair of electrodes  50  by electrolytic barrel plating via the process illustrated in  FIG. 16 , the bonding is improved, thus making it less likely that the bottom portion  51  of either one of the pair of electrodes  50  is defective. 
     The shape of the resistive element  10  has point symmetry as viewed in the thickness direction z. Thus, the resistance value of the resistor A 10  is constant irrespective of the polarity of the pair of electrodes  50 . Accordingly, it is not necessary to check the polarity of the pair of electrodes  50  when mounting the resistor A 10  on the circuit board. 
     In the resistor A 10 , the pair of intermediate layers  40  are made of a material including a synthetic resin including metal particles. Accordingly, the protective film  30  and the pair of intermediate layers  40  have a configuration including the same type of material. This allows the bond between the protective film  30  and the cover portions  41  of the pair of intermediate layers  40  can be improved. Also, because the physical properties of the pair of intermediate layers  40  includes electrical conductivity, the pair of intermediate layers  40  can be electrical conductive with the resistive element  10 . 
     In the resistor A 10 , the electric resistivity of the pair of intermediate layers  40  is greater than the electric resistivity of the resistive element  10 . Thus, when the resistor A 10  is in use, the current running through the resistive element  10  is made more difficult to run to the pair of intermediate layers  40 . Accordingly, variation of the resistance value of the resistor A 10  due to the effects of the pair of intermediate layers  40  can be suppressed. 
     The resistor A 20  according to a second embodiment will now be described with reference to  FIGS. 19 to 22 . In these diagrams, elements the same or similar to those of the resistor A 10  described above are given the same reference sign, and redundant descriptions are omitted. Note that in  FIG. 19 , the insulating plate  20  is shown as being transparent. In  FIG. 20 , the pair of electrodes  50  are shown as being transparent. In  FIG. 20 , the transparent pair of electrodes  50  are indicated by an imaginary line. 
     The resistor A 20  has a different configuration to the resistor A 10  described above in terms of the configuration of the pair of intermediate layers  40 . 
     In the resistor A 20 , the pair of intermediate layers  40  are made of a metal thin film. The metal thin film is made of a nickel-chromium (Cr) alloy, for example. As illustrated in  FIGS. 19, 20, and 22 , each one of the pair of intermediate layers  40  includes the cover portion  41  and the extension portion  42 . The cover portion  41  is located on the opposite side of the protective film  30  to the resistive element  10  in the thickness direction z. The cover portion  41  covers a portion of the protective film  30 . The extension portion  42  extends from one of the cover portions  41  of the pair of intermediate layers  40  towards one of the pair of first end surfaces  10 C of the resistive element  10 . The extension portion  42  is in contact with the first surface  10 A of the resistive element  10 . In this manner, the pair of intermediate layers  40  are electrically connected to the resistive element  10 . Note that in the resistor A 20 , each one of the pair of intermediate layers  40  does not include the first layer  40 A and the second layer  40 B. Accordingly, each one of the pair of intermediate layers  40  are an integral member. 
     Next, an example of a method of manufacturing the resistor A 20  will be described with reference to  FIGS. 12, 16, 17, and 23 to 25 . Note that the cross-section location illustrated in  FIGS. 23 to 25  is the same as the cross-section location illustrated in  FIG. 22 . 
     As illustrated in  FIG. 12 , first, the resistive element  81  including the first surface  81 A and the second surface  81 B facing opposite sides in the thickness direction z is bonded to the base material  82  via thermocompression bonding. Note that the present process is the same as the process in the method of manufacturing the resistor A 10 , and thus description thereof will be omitted. 
     Next, as illustrated in  FIG. 23 , the protective film  30  covering a portion of the first surface  81 A of the resistive element  81  and a portion of the base material  82  extending through the plurality of slits  811  of the resistive element  81  is formed. A material including an epoxy resin is applied via screen printing to a portion of the first surface  81 A so as to completely cover the portion of the base material  82  entering through the plurality of slits  811 , and then the material is thermally cured to form the protective film  30 . 
     Next, as illustrated in  FIG. 24 , a metal thin film  83  is formed overlapping with the entire first surface  81 A of the resistive element  81  and the entire protective film  30  as viewed in the direction y. To form the metal thin film  83 , first, a mask layer  89  is formed covering a portion of the first surface  81 A of the resistive element  81  and a portion of the protective film  30 . The mask layer  89  is formed via screen printing. After the mask layer  89  is formed, the metal thin film  83  is formed. The metal thin film  83  is made of a nickel-chromium alloy. The metal thin film  83  is formed via a sputtering method. In the present process, the entire mask layer  89  is covered by the metal thin film  83 . 
     Next, as illustrated in  FIG. 25 , the mask layer  89  and a portion of the metal thin film  83  covering the mask layer  89  are removed (lift off). In the present process, the pair of intermediate layers  40  are formed covering a portion of the first surface  81 A of the resistive element  81  and a portion of the protective film  30 . In other words, the pair of intermediate layers  40  are formed from the metal thin film  83  remaining on the protective film  30  and the like. 
     Next, as illustrated in  FIG. 16 , a dicing blade is used to cut the resistive element  81  and the base material  82  along the cutting line CL to divide the resistive element  81  and the base material  82  into a piece including the protective film  30  and the pair of intermediate layers  40 . Note that the present process is the same as the process in the method of manufacturing the resistor A 10 , and thus description thereof will be omitted. 
     Lastly, as illustrated in  FIG. 17 , the pair of electrodes  50  that come into contact with the resistive element  10  are formed. Note that the present process is the same as the process in the method of manufacturing the resistor A 10 , and thus description thereof will be omitted. With the process described above complete, the resistor A 20  is manufactured. 
     Next, the effects of the resistor A 20  will be described. 
     The resistor A 20  is provided with the resistive element  10 , the protective film  30  disposed on the first surface  10 A of the resistive element  10 , and the pair of electrodes  50  disposed in contact with the resistive element  10  and spaced apart from each other in the first direction x. The resistive element  10  includes the first slit  111  and the second slit  112 . The protective film  30  includes the first outer edge  30 A located closest to the first slit  111  and the second outer edge  30 B located closest to the second slit  112 . In the resistor A 10 , as viewed in the thickness direction z, the first distance L 1  from the first outer edge  30 A to the first slit  111  and the second distance L 2  from the second outer edge  30 B to the second slit  112  together occupy 15% or greater of the dimension L 0  of the protective film  30  in the first direction x. Thus, also according to the resistor A 20 , an increase in the temperature coefficient of resistance can be suppressed. 
     The present disclosure is not limited to the embodiments described above. Also, variation design modifications can be made to the specific configurations of the various components in these embodiments. 
     REFERENCE NUMERALS 
     A 10 , A 20  Resistor 
       10  Resistive element 
       10 A First surface 
       10 B Second surface 
       10 C First end surface 
       10 D Second end surface 
       111  First slit 
       112  Second slit 
       11 A Side wall 
       12  Groove 
       131  First region 
       132  Second region 
       14  Projection 
       20  Insulating plate 
       20 A End surface 
       30  Protective film 
       30 A First outer edge 
       30 B Second outer edge 
       31  Filler 
       40  Intermediate layer 
       40 A First layer 
       40 B Second layer 
       41  Cover portion 
       42  Extension portion 
       421  Cutout 
       43  Interposed portion 
       50  Electrode 
       51  Bottom portion 
       52  Side portion 
       81  Resistive element 
       81 A First surface 
       81 B Second surface 
       811  Slit 
       812  Groove 
       82  Base material 
       83  Metal thin film 
       89  Mask layer 
     L 1 , L 1 min, L 1 max First distance 
     L 2 , L 2 min, L 2 max Second distance 
     L 0  Dimension 
     C Center 
     N Boundary 
     Bmin, bmax Width 
     CL Cutting line 
     z Thickness direction 
     x First direction 
     y Second direction