Patent Publication Number: US-2023140922-A1

Title: Current detection resistor and current detection apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to a current detection resistor and a current detection apparatus. 
     BACKGROUND ART 
     Recent years have seen an increase in electric currents used in electronic devices. This has stimulated efforts to develop modules referred to as power modules for performing conversion and control of electric power by switching a power semiconductor. The power semiconductor requires a current detection element for detecting current, such as a current-detection shunt resistor. 
     Also, in order to address an increase in electric power while minimizing the volume of the module, which tends to be large in size due to being a power module, intense research and development is being conducted to achieve higher power and higher density. Thus, the demand for minimizing the mounting area for components is increasing year after year. 
     Against the above background, there is a need for reducing the mounting area for a shunt resistor for power modules. 
     For example, Patent Literature 1 proposes an example in which a resistor is mounted directly on an upper surface of a transistor. 
     Semiconductors such as insulated-gate bipolar transistors (IGBT) adopted in power modules have a complex structure due to, for example, electrodes disposed on the upper surface being partitioned by an insulating film (insulating protection film). Accordingly, it is difficult to obtain a mounting structure in which the structure of such a vertical shunt resistor is provided on the upper surface of a power semiconductor (see FIG. 8 of Patent Literature 1, for example). 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: JP 2018-170478 A 
     SUMMARY OF INVENTION 
     Technical Problem 
       FIG.  6    is a perspective view of an example of a substrate mounting structure X of a conventional resistor and a power module. 
     As illustrated in  FIG.  6   , in a semiconductor (for example, an IGBT device)  121  used in the power module, on a first surface (upper surface) opposite to a second surface (lower surface) mounted on a substrate  101 , divided portions  127   a  are formed, forming emitter electrodes  127  comprising a comb-shaped electrical conductor. The emitter electrodes  127  may be configured such that at least a part of the electrodes is separated. 
     An IGBT device is a device of which the input portion has a MOSFET structure and the output portion has a bipolar structure. The device is a transistor which, despite being a bipolar-type device that uses the two types of carriers of electron and hole, achieves both a low saturation voltage (corresponding to a low on-resistance of a power MOSFET) and a relatively fast switching characteristic. A semiconductor layer  131  has an n + −p + −n − −p +  series structure, for example. 
     As illustrated in  FIG.  6   , the IGBT device  121  has four divided electrodes (emitter electrodes in contact with the first conductivity-type semiconductor (n + ))  127  on the first surface. Each divided electrode  127  is exposed from an insulating region comprising an insulating film  133 . On the first surface, a gate electrode  131   a  exposed from the insulating film  133  is formed in a region different from the emitter electrodes  127 . 
     On the second surface, a collector electrode (not illustrated) is formed. 
     In the IGBT device  121 , a current is controlled by a voltage signal to the gate electrode  131   a,  and flows from the collector electrode disposed on the second surface of the IGBT device toward the emitter electrodes  127  disposed on the first surface. 
     On the mounting substrate  101 , the IGBT device  121  and a shunt resistor  111  provided adjacent thereto are connected. The shunt resistor  111  is formed of a structure in which a first electrode  115   a  and a second electrode  115   b  are disposed on either side of a resistive body  113  with, for example, end faces of the resistive body  113  abutting one end face of each of the first electrode  115   a  and the second electrode  115   b.  A voltmeter  117  is used to measure a voltage between the first electrode  115   a  and the second electrode  115   b  via bonding wires  118 , whereby the emitter current of the IGBT device  121  can be detected. 
     Reference signs  116 ,  119 ,  125  refer to metal pads provided on the substrate  101 . 
     For example, in the conventional mounting structure X illustrated in  FIG.  6   , the emitter electrodes  127  and the pads on which the shunt resistor  111  are mounted are connected by bonding wires  141  to construct current paths. In this case, by providing a plurality of the bonding wires  141  corresponding to the number of the emitter electrodes  127 , it is possible to lower the electric resistance of the bonding wires  141  and to accommodate to an application of large currents. 
     However, the conventional shunt resistor  111  illustrated in  FIG.  6    is mounted around a semiconductor device such as the IGBT device  121 , resulting in a correspondingly greater footprint of the module (mounting structure). 
     It is an objective of the present invention to reduce the mounting area for an electronic component, such as a semiconductor device, and a resistor for current detection. 
     Solution to Problem 
     According to an aspect of the present invention, there is provided a current detection resistor for detecting current. The current detection resistor includes a plate-like resistive body, and a first electrode and an opposite second electrode which are stacked in a thickness direction of the resistive body and are disposed so as to sandwich the resistive body. The first electrode has a groove portion. 
     In this way, when a resistor for current detection is integrated with an electronic component, such as a semiconductor device, in the thickness (vertical) direction, the mounting area for the integrated circuit can be reduced. 
     Further, a volume of reservoir for an adhesive for adhering the electronic component, such as a semiconductor device, to the resistor for current detection can be secured. 
     Preferably, the groove portion may have a depth less than or equal to ½ of a thickness of the first electrode. Preferably, the groove portion may have a depth greater than a thickness of a connecting material applied between the resistor for current detection and the electronic component connected thereto. 
     Preferably, the first electrode may have formed thereon a surface processing film including an Ni material. Preferably, the second electrode may have formed thereon a surface processing film of an Ni material, an Al material, or an Au material. 
     The first electrode and the resistive body of the current detection resistor may be cut to form an exposed region in which the second electrode is exposed for wire bonding. 
     According to another aspect of the present invention, there is provided a current detection apparatus including a stacked-structure electronic component disposed on a mounting substrate, and a current detection resistor for detecting a current in the electronic component. The current detection resistor includes a resistive body having an area smaller than an electrode region on a first surface of the electronic component on which the current detection resistor is disposed, and a first electrode and a second electrode which are stacked in a thickness direction of the resistive body and are disposed so as to sandwich the resistive body, the first electrode being disposed on a second surface side and the second electrode being disposed on a first surface side opposite to the second surface side, the first electrode having a groove portion. 
     Preferably, the groove portion on the first surface of the current detection resistor may be provided in a position avoiding an insulating film separating the electrode region on the first surface of the stacked-structure electronic component into a plurality of portions. 
     The present description incorporates the contents disclosed in JP Patent Application No. 2020-070184, from which the present application claims priority. 
     Advantageous Effects of Invention 
     According to the present invention, the mounting area for an electronic component, such as a semiconductor device, and a resistor for current detection can be reduced. 
     Further, a volume of reservoir for an adhesive adhering the electronic component, such as a semiconductor device, to the resistor for current detection can be secured. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a perspective view of a resistor according to a first embodiment of the present invention, and an example of a mounting structure therefor. 
         FIG.  2    illustrates a vertical shunt resistor before being mounted on a first surface of an IGBT device. 
         FIG.  3    illustrates the vertical shunt resistor after being mounted on the first surface of the IGBT device. 
         FIG.  4    is a perspective view of a resistor according to a second embodiment of the present invention, and an example of a mounting structure therefor. 
         FIG.  5    illustrates a modification of groove portions of a second electrode according to the present embodiment. 
         FIG.  6    is a perspective view of an example of a substrate mounting structure of a conventional resistor and power module. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     In the following, a resistor according to an embodiment of the present invention and a mounting structure therefor will be described with reference to the drawings. 
     First Embodiment 
       FIG.  1    is a perspective view of the resistor according to a first embodiment of the present invention and an example of a mounting structure therefor. As a power semiconductor device, an IGBT having a structure similar to that of  FIG.  6    will be described by way of example. 
     Specifically, an IGBT device  21  includes a collector electrode (not illustrated), a gate electrode  31   a,  emitter electrodes  27 , a semiconductor layer  31 , and an insulating film  33 . 
     A vertical shunt resistor  11  includes a first electrode  15   a /a resistive body  13 /a second electrode  15   b.  Reference signs  19 ,  25  designate metal pads provided on the substrate. 
     In the example described below, the object of measurement by the current detection device is a current that flows through the IGBT device. However, the object of measurement by the current detection device may be a current that flows through any vertical electronic component, including a transistor, a capacitor, and an inductor. Structures for detecting currents in such electronic components are also within the scope of the present invention. 
     A mounting surface of the mounting substrate  1  is referred to as a first surface, and a surface opposite thereto is referred to as a second surface. 
     1) Regarding Vertical Shunt Resistor 
     The IGBT device  21  has a first surface on which the vertical shunt resistor  11  is disposed. The shunt resistor  11  is sized to fit within an area in which a plurality of emitter electrodes  27  are disposed. The vertical shunt resistor  11  has a stacked structure comprising a plate-like first electrode  15   a /a plate-like resistive body  13 /a plate-like second electrode  15   b.  The first electrode  15   a  and the second electrode  15   b  are formed on first and second surfaces of the resistive body  13  from a material having a smaller electric resistance than the resistive body  13 . 
     The electrode material is an electrically conductive metal material, such as Cu. The resistive body material is a metal material, such as a Cu—Ni-based, a Cu—Mn-based, or a Ni—Cr-based metal material, or a composite material of such a metal material and ceramics. 
       FIG.  2    and  FIG.  3    are cross-sectional views taken along line Ia-Ib of  FIG.  1   .  FIG.  2    illustrates the vertical shunt resistor  11  before being connected to the first surface of the IGBT device  21  by soldering or the like.  FIG.  3    illustrates the vertical shunt resistor  11  after being connected to the first surface of the IGBT device  21  by soldering or the like. Besides soldering, other connecting materials may be used, such as a paste of nano-silver or nano-copper, or a resin silver paste. That is, the connecting material is not limited to solder. 
     By means of the configuration of 1) above, the vertical shunt resistor  11  can be mounted on the first surface of the IGBT device  21 . Accordingly, it is possible to eliminate the footprint that would be required on the module for mounting the mounting substrate vertical shunt resistor  11 . This also eliminates the need for bonding wires and the like for connecting the power semiconductor device and the shunt resistor together. 
     2) Regarding Mounting Structure 
     As illustrated in  FIG.  2    and  FIG.  3   , on the first surface of the IGBT device  21 , the emitter electrodes  27  are formed with a comb-shaped electrical conductor, the emitter electrodes  27  having gap regions  27   a  separating the plurality of electrodes in a plane. The emitter electrodes  27  may be configured such that at least one part thereof is separated. The insulating film  33  is exposed from the gap regions  27   a.    
     In the mounting structure, the first electrode  15   a  of the vertical shunt resistor  11  has groove portions  43  formed therein, corresponding to the gap regions  27   a.  In this way, it is possible to keep a distance between the surface of the insulating film  33  and the facing surfaces (bottom surfaces) of the groove portions on the first surface side. 
     The gap regions  27   a  have a width W 1  and the groove portions  43  have a width W 2 , where W 2 &gt;W 1 , such as W 2 &gt;2W 1 . In this way, the gap regions  27   a  can be located within the width of the groove portions  43 . 
     The groove portions  43  have a depth t 2 , and the first electrode  15   a  has a thickness t 1 , where t 2  is preferably less than a remaining thickness (t 2 &lt;(t 1 −t 2 )). Preferably, the relationship may be t 1 /2&gt;t 2 , for example. 
     In addition, the depth t 2  of the groove portions  43  may preferably be greater than a coating thickness t 3  of the bonding material between the vertical shunt resistor  11  and the IGBT device  21 , such as solder paste  61 . 
     In this way, the solder paste  61  can be contained within the groove portions  43 . Thus, the solder paste  61  can be prevented from extending beyond the device region. 
     The groove portions  43  may have an interval equal to the interval of the gap regions  27   a.  The width and depth of the gap regions  27   a  are parameters that may be changed depending on a predetermined process. 
     A second surface of the vertical shunt resistor  11  is desirably provided with a surface processing layer  41   b  for enhancing adhesiveness, which is formed by performing surface treatment prior to bonding, in order to improve adhesion with the bonding material  61 . 
     From 2) described above, when the IGBT device  21  and the vertical shunt resistor  11  are bonded together with solder, for example, the groove portions  43  provided in the first electrode  15   a  serve as a solder reservoir. Thus, with the groove portions  43 , it is possible to suppress attachment of excess solder to the first surface of the IGBT device or to the sides of the vertical shunt resistor  11  (see  FIG.  3   ). 
     In addition, the insulating film  33  of the IGBT device  21  and the first electrode  15   a  of the vertical shunt resistor  11  not contacting each other provides the effect of preventing destruction of the insulating film  33 . 
     Because the resistance value of a shunt resistor is often very low, such as about 1 mΩ or 50 μΩ, it is important to make the potential distribution of an electrode, such as the first electrode  15   a,  uniform. Thus, the thickness of the electrode remaining portion (t 1 −t 2 ) after the groove portions are formed in the first electrode  15   a  is made greater than the depth t 2  of the groove portions  43 , whereby the potential distribution in the electrode can be made uniform. 
     The thickness t 3  of the solder paste  61  as the bonding material is typically about 50 μm. Thus, in this case, the groove depth is desirably greater than or equal to 50 μm, and the thickness of the first electrode  15   a  is desirably twice as thick, or greater than or equal to 100 μm. 
     The interval of metal terminals of a power semiconductor is about 0.1 mm to 0.2 mm. Thus, the width of the grooves on the shunt lower surface needs to be greater than that interval, and is in this case desirably about 0.2 mm to 0.4 mm. 
     3) Regarding Electrode Surface Treatment for Vertical Shunt Resistor 
     Further, the second electrode  15   b  of the vertical shunt resistor  11  is connected by means of bonding wires  51 , a lead frame, and the like. Thus, in order to provide surface treatment to facilitate such connections and improve connectivity, it is preferable to form a surface processing layer  41   a  by plating the surface with Ni or Sn, for example. 
     In 3) described above, it is necessary to secure a current path and to connect the bonding wires  41  for voltage signal detection. Thus, it is preferable to perform electrode surface processing by Ni plating or Au plating, or by means of an Al pad or the like. Further, as illustrated in  FIG.  1   , for voltage signal detection, it is necessary to perform wire bonding on the emitter electrodes  27  of the IGBT device  21 , in addition to on the second electrode  15   b  of the vertical shunt resistor  11 . 
     As described above, according to the present embodiment, it is possible to reduce the mounting area in the current detection resistor in which a power module and a resistor are mounted. 
     It is to be noted that the vertical resistor is not limited to an IGBT device as a semiconductor device, but may be mounted on other semiconductor devices, such as a MOSFET device. It will be appreciated that the dimensions of the vertical resistor, the shape of the groove portions of the first electrode and the like may require design changes, depending on the shape of the semiconductor device. 
     Second Embodiment 
     A second embodiment of the present invention will be described.  FIG.  4    is a perspective view of a resistor according to the second embodiment of the present invention, and an example of a mounting structure therefor. 
     In the mounting structure illustrated in  FIG.  2   , if the vertical shunt resistor  11  is smaller than the region of the first surface of the IGBT device  21 , it is possible to provide a region, on the insulating film  33  on the first surface of the IGBT device  21 , in which the gate electrode  31   a  for connecting bonding wires  53  is exposed. 
     However, in some cases, it may be impossible to secure a sufficient region in the emitter electrodes  27  of the IGBT device  21  for connecting the bonding wires  53 . 
     In such cases, as illustrated in  FIG.  4   , a part of a corner of the vertical shunt resistor  11  may be cut to form a cut shape  11   a . In this way, a partial region  27   b  of the emitter electrodes  27  of the IGBT device  21  can be exposed to secure a location for connecting the bonding wires  53  to the emitter electrodes  27 . 
     Third Embodiment 
     Next, a third embodiment of the present invention will be described. The shape of the grooves of the second electrode  15   b  of the vertical shunt resistor  11  may be any shape that avoids contact with the insulating film  33  of the semiconductor. 
       FIG.  5    illustrates a modification of the groove portions of the first electrode  15   a  according to the present embodiment. Reference will also be made to  FIG.  1    as needed.  FIG.  5    shows an inverted view of  FIG.  1   , where the first electrode  15   a  and the second electrode  15   b  are formed on the first and second surfaces of the resistive body  13  from a material having a smaller electric resistance than the resistive body  13 . 
     As illustrated in  FIG.  5   , groove portions  45   a  are formed in the first electrode  15   a  corresponding to the regions between the emitter electrodes  27  of the IGBT device  21  in which the insulating film  33  is exposed. Groove portions  45   b  may be provided extending in a direction intersecting, such as orthogonal to, the groove portions  45   a.  The groove portions  45   b  are not provided in positions corresponding to the regions exposing the insulating film  33 . However, in this way, the volume of the groove portions  45   b  can be added to the volume of the groove portions  45   a  to obtain a volume of the solder reservoir. Thus, the volume of the solder reservoir can be increased and a necessary volume can be secured. 
     In the foregoing embodiments, the illustrated configurations and the like are not limiting and may be modified, as appropriate, as long as the effects of the present invention can be obtained. The embodiments may otherwise be modified and implemented, as appropriate, without departing from the range of the objective of the present invention. The respective constituent elements of the present invention may be selectively added or omitted as needed, and an invention comprising a selectively added or omitted configuration is also included in the present invention. 
     INDUSTRIAL APPLICABILITY 
     The present invention may be utilized for a current detection resistor and a mounting structure for a current detection resistor. 
     REFERENCE SIGNS LIST 
     
         
           1  Mounting substrate 
           11  Vertical shunt resistor 
           13  Resistive body 
           15   a  First electrode 
           15   b  Second electrode 
           21  IGBT device 
           27  Emitter electrode 
           27   a  Gap region 
           31  Semiconductor layer 
           31   a  Gate electrode 
           33  Insulating film 
           41   a,    41   b  Surface processing layer 
           43 ,  45   a,    45   b  Groove portion 
           51 ,  53  Bonding wire 
           61  Bonding material (solder paste) 
       
    
     All publications, patents and patent applications cited in the present description are incorporated herein by reference in their entirety.