Patent Publication Number: US-2023144840-A1

Title: Semiconductor device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The disclosure of Japanese Patent Application No. 2021-181866 filed on Nov. 8, 2021 including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
     BACKGROUND 
     The present invention relates to a semiconductor device, and relates to, for example, a technology effectively applied to a semiconductor device to be a component of an inverter. 
     There are disclosed techniques listed below.
     [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2018-121035   

     Japanese Unexamined Patent Application Publication No. 2018-121035 (Patent Document 1) describes a technology relating to a package structure of a semiconductor device to be a component of an inverter. 
     SUMMARY 
     For example, as a semiconductor device in which a semiconductor chip having a power transistor formed therein is sealed, there is a semiconductor device in which a lead and an electrode called a pad formed on a surface of the semiconductor chip are connected by a plate-shaped member called a “clip”. 
     The plate-shaped member and the pad are connected via, for example, a conductive member typified by silver paste or solder. Here, peeling sometimes occurs in the conductive member due to the manufacturing process of the semiconductor device. Further, the inventors of this application have newly found that the peeling area fluctuates after the reliability test of the semiconductor device and the fluctuation of the peeling area adversely affects the performance of the semiconductor device in some cases. Therefore, based on the new finding by the inventors of this application, it is desired to devise a method capable of reducing the adverse effect on the performance of the semiconductor device even if the peeling area fluctuates. 
     A semiconductor device according to an embodiment includes a semiconductor chip having a non-overlapping region in which a first electrode and a plate-shaped member do not overlap with each other. At this time, a sense transistor is arranged in a first region of the non-overlapping region, which is located between a first portion of the plate-shaped member and a first short side of the first electrode in a plan view. 
     According to the embodiment, it is possible to suppress the deterioration of the performance of the semiconductor device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a diagram schematically showing a configuration of a 12-phase brushless DC motor control system. 
         FIG.  2    is a diagram showing a circuit configuration of an inverter circuit. 
         FIG.  3    is a diagram showing a mounting configuration of a semiconductor device that realizes an inverter circuit. 
         FIG.  4    is a diagram for describing the room for improvement newly found by the inventors of this application, and is a cross-sectional view showing a molding step for forming a sealing body. 
         FIG.  5    is a diagram showing a state in which a clip is “reversely tilted”. 
         FIG.  6 A  and  FIG.  6 B  are diagrams for describing the room for improvement existing in a related art. 
         FIG.  7    is a diagram schematically showing the “position that is less likely to be affected by the potential change due to increase or decrease of the peeled portion of silver paste”. 
       FIC.  8  is a diagram showing an embodied mode obtained from a basic idea. 
         FIG.  9    is a cross-sectional view taken along the line A-A in  FIG.  8   . 
         FIG.  10    is a diagram showing a first modification. 
         FIG.  11    is a diagram showing a second modification. 
         FIG.  12    is a diagram showing a third modification. 
         FIG.  13    is a diagram showing a fourth modification. 
         FIG.  14    is a flowchart for describing an assembly process of the semiconductor device. 
     
    
    
     DETAILED DESCRIPTION 
     In all the drawings for describing the embodiment, the same members are denoted by the same reference characters and the repetitive description thereof will be omitted. Note that hatching is applied in some cases even in a plan view so as to make the drawing easily understood. 
     &lt;12-Phase Brushless DC Motor Control System&gt; 
     In recent years, with a view to functional safety toward the practical application of automated driving of automobiles, design and development have been carried out to replace the conventional 3-phase brushless DC motor with a 6-phase or 12-phase brushless DC motor. Brushless DC motors are generally perceived as complicated to control because they are not of the self-rectifying type. Therefore, two sets of conventional three phases (U-phase. V-phase, and W-phase) are used in the 6-phase brushless DC motor control system that controls the 6-phase brushless DC motor, and four sets of conventional three phases (U phase, V phase, W phase) are used in the 12-phase brushless $0 DC motor control system that controls the 12-phase brushless DC motor, thereby preventing the problem from being apparent immediately even if the problem occurs in one set. 
     An inverter circuit is used as a circuit that controls each phase, and AC power supplied from this inverter circuit is supplied to the coils of each phase of the brushless DC motor. Therefore, in a brushless DC motor control system that controls a 6-phase brushless DC motor or a 12-phase brushless DC motor, six or twelve inverter circuits are used. 
       FIG.  1    is a diagram schematically showing a configuration of a 12-phase brushless DC motor control system. 
     A motor MOT shown in  FIG.  1    is a 12-phase brushless DC motor and has twelve coils CL. Each coil CD is connected to an inverter circuit INV. Namely, the inverter circuit INV is provided for each of the twelve coils of the motor MOT. For this reason, the 12-phase brushless DC motor control system shown in  FIG.  1    has a total of twelve inverter circuits INV. Each inverter circuit INV is connected to a control circuit CT provided in an MCU (Micro Controller Unit), and each inverter circuit is controlled by this control circuit CT. Then, AC power is supplied from each inverter circuit INV controlled by the control circuit CT to the coil CL connected to each inverter circuit INV, whereby the motor MOT is driven. 
     &lt;Configuration of Inverter Circuit&gt; 
     Next, a circuit configuration of the inverter circuit INV that is a component of the above-mentioned 12-phase brushless DC motor control system will be described. 
       FIG.  2    is a diagram showing the circuit configuration of the inverter circuit INV. 
     In  FIG.  2   , the inverter circuit INV includes a high-side switching circuit  10 , a low-side switching circuit  20 , and a control circuit  30 . 
     The high-side switching circuit  10  includes a main transistor  11  and a sense transistor  12  each composed of a power transistor. 
     On the other hand, the low-side switching circuit.  20  includes a main transistor  21  and a sense transistor  22  each composed of a power transistor. 
     In the high-side switching circuit  10  and the low-side switching circuit  20  configured in this way, the main transistor  11  included in the high-side switching circuit  10  and the main transistor  21  included in the low-side switching circuit  20  are connected in series between a power supply potential VIN and a ground potential GND. 
     Then, in  FIG.  2   , a connection node between the main transistor  11  and the main transistor  21  is “OUT”, and this connection node is connected to the coil CL shown in  FIG.  1   . 
     Subsequently, the control circuit  30  includes, for example, a predriver that applies a gate voltage to a gate electrode of the main transistor  11  and a gate electrode of the sense transistor  12  and a predriver that applies a gate voltage to a gate electrode of the main transistor  21  and a gate electrode of the sense transistor  22 . Further, the control circuit  30  includes a sense circuit  31  electrically connected to the sense transistor  22  included in the low-side switching circuit  20 . 
     In  FIG.  2   , though the sense circuit  31  electrically connected to the sense transistor  22  included in the low-side switching circuit  20  is provided, for example, the sense transistor  12  included in the high-side switching circuit  10  is not used, and a sense circuit electrically connected to the sense transistor  12  included in the high-side switching circuit  10  is not present. However, the inverter circuit INV is not limited to this, and may be configured to have, for example, the sense circuit  31  electrically connected to the sense transistor  22  included in the low-side switching circuit  20  and the sense circuit electrically connected to the sense transistor  12  included in the high-side switching circuit  10 . Further, the inverter circuit INV may have the configuration in which the sense circuit  31  electrically connected to the sense transistor  22  included in the low-side switching circuit  20  is not present and the sense circuit electrically connected to the sense transistor  12  included in the high-side switching circuit  10  is provided. 
     Also, in  FIG.  2   , an input node that inputs a control signal from the control circuit CT shown in  FIG.  1    to the control circuit  30  is “IN”, and an output node that outputs an output signal from the sense circuit  31  of the control circuit  30  is “OUT2”, This output node is electrically connected to the control circuit CT shown in  FIG.  1   . In this way, the inverter circuit INV is configured. 
     The control circuit  30  is configured to control the on/off of the main transistor  11  included in the high-side switching circuit  10  and control the on/off of the main transistor  21  included in the low-side switching circuit  20  based on the control signal from the control circuit CT shown in  FIG.  1   . Namely, the control circuit  30  controls the on/off of the main transistor  11  by switching the gate voltage applied to the gate electrode of the main transistor  11 , and also controls the on/off of the main transistor  21  by switching the gate voltage applied to the gate electrode of the main transistor  21 . 
     In this way, by the on/off control of the main transistor  11  and the on/off control of the main transistor  21 , AC power is supplied to the coil CL shown in  FIG.  1    from the connection node (“OUT”) between the main transistor  11  and the main transistor  21 . 
     Here, the sense transistor  22  included in the low-side switching circuit  20  is provided in order to detect the current value of the current flowing through the main transistor  21 . 
     For example, the main transistor  21  and the sense transistor  22  form a current mirror circuit such that the ratio between the current value of the current flowing through the main transistor  21  and the current value of the current flowing through the sense transistor  22  is equal to 12500:1 (sense ratio). 
     Also, the sense transistor  22  is electrically connected to the sense circuit  31 , and the current flowing through the sense transistor  22  is converted into a voltage by the sense circuit  31  and is then output to the control circuit CT shown in  FIG.  1    from the output node “OUT2”. At this time, in the control circuit CT shown in  FIG.  1   , the current value of the current flowing through the main transistor  21  is measured based on the voltage signal input from “0=2” and the “sense ratio”. 
     In this way, the inverter circuit INV is configured. 
     &lt;Package Structure&gt; 
     Next, a mounting configuration of the inverter circuit INV will be described. 
       FIG.  3    is a diagram showing a mounting configuration of a semiconductor device PKG that realizes an inverter circuit. 
     In  FIG.  3   , the semiconductor device PKG has a sealing body MR with a rectangular planar shape. This sealing body MR has a side S 1  that is a long side, a side S 2  that faces the side S 1 , a side S 3  that is a short side intersecting the side S 1  and the side S 2 , and a side S 4  that faces the side S 3 . Also, leads LD protrude from the long sides S 1  and S 2 . 
     In  FIG.  3   , the outline of the sealing body MR is shown by a broken line, and components sealed inside the sealing body MR are illustrated. Hereinafter, the internal configuration of the sealing body MR will be described. 
     The semiconductor device PKG includes a die pad DPC which is a chip mounting portion, a die pad DPL which is a chip mounting portion, and a die pad DPH which is a chip mounting portion. Specifically, the die pad DPL, the die pad DPC, and the die pad DPH are disposed so as to be arranged in this order in the x direction. In other words, the die pad DPL is arranged on the left side, the die pad DPC is arranged in a central portion, and the die pad DPH is arranged on the right side. 
     A semiconductor chip CPC mounted on the die pad DPC. The control circuit  30  shown in  FIG.  2    is formed in the semiconductor chip CPC. Then, on the surface of the semiconductor chip CPC, for example, a plurality of pads including a plurality of pads PDC 1  and a plurality of pads PDC 2  is formed. As described above, the semiconductor chip CPC mounted on the die pad DPC is arranged in the central portion of the semiconductor device PKG. 
     Next, a semiconductor chip CPL is mounted on the die pad DPL. The low-side switching circuit  20  shown in  FIG.  2    is formed in the semiconductor chip CPL. Namely, the main transistor  21  and the sense transistor  22  constituting the low-side switching circuit  20  are formed in the semiconductor chip CPL. The main transistor  21  and the sense transistor  22  are composed of vertical trench power transistors which flow a current in the thickness direction of the semiconductor chip CPL. Also, a plurality of pads PDL is formed on the surface of the semiconductor chip CPL together with a source pad SPL for main transistor. The plurality of pads PDL includes a source pad for sense transistor, a gate pad common to the main transistor  21  and the sense transistor  22 , and others. 
     Further, as shown in  FIG.  3   , a clip CLL which is a plate-shaped member made of copper is arranged on the source pad SPL for main transistor. Further, as shown in  FIG.  3   , the lip CLL is electrically connected to a lead LDL. On the other hand, each of the plurality of pads PDL is electrically connected to each of the plurality of pads PDC 2  formed on the surface of the semiconductor chip CPC by the bonding wire W. 
     Subsequently, a semiconductor chip CPH is mounted on the die pad DPH. The high-side switching circuit  10  shown in  FIG.  2    is formed in the semiconductor chip CPH. Namely, the main transistor  11  and the sense transistor  12  constituting the high-side switching circuit  10  are formed in the semiconductor chip CPH. The main transistor  11  and the sense transistor  12  are composed of vertical trench power transistors which flow a current in the thickness direction of the semiconductor chip CPH. Also, a plurality of pads PDH is formed on the surface of the semiconductor chip CPH together with a source pad SPH for main transistor. The plurality of pads PDH includes a source pad for sense transistor, a gate pad common to the main transistor  11  and the sense transistor  12 , and others. 
     Further, as shown in  FIG.  3   , a clip CLH which is a plate-shaped member made of copper is arranged on the source pad SPH for main transistor. Further, as shown in  FIG.  3   , the clip CLH is electrically connected to a lead LDH. On the other hand, each of the plurality of pads PDH is electrically connected to each of the plurality of pads PDC 1  formed on the surface of the semiconductor chip CPC by the bonding wire W, In the present embodiment, the planar shape of the semiconductor device PKG is a substantially rectangular shape (specifically, a rectangle in which each corner is chamfered) as shown in  FIG.  3   . Further, in the present embodiment, the planar shape of each semiconductor chip is also a rectangular shape as shown in  FIG.  3   . Then, in the present embodiment, as shown in  FIG.  3   , the semiconductor chip CPC, the semiconductor chip CPL, and the semiconductor chip CPH are arranged such that the short side of each semiconductor chip is located along the long side of the semiconductor device PKG. In this way, the size of each semiconductor chip and the size of the semiconductor device PKG are reduced. 
     In the present embodiment, the semiconductor chip CPL in which the low-side switching circuit  20  is formed and the semiconductor chip CPH in which the high-side switching circuit  10  is formed are semiconductor chips of the same type. 
     As described above, the semiconductor device PKG composed of an SiP (System in Package) in which the semiconductor chip CPC, the semiconductor chip CPL, and the semiconductor chip CPH in which circuits constituting the inverter circuit INV are formed are mounted in one package structure is implemented and configured. 
     &lt;Consideration of Improvement&gt; 
     In the following, the room for improvement in the semiconductor device PKG will be described while taking the clip CLL as the plate-shaped member. 
     In the above-mentioned semiconductor device PKG, from the viewpoint of improving heat dissipation efficiency, a configuration in which the back surface of the die pad DPL (die pad DPC, die pad DPH) is exposed from the lower surface of the sealing body MR is adopted in some cases. In the semiconductor device KG having such a configuration, the inventors of this application have newly found that there is a room for improvement shown below. 
       FIG.  4    is a diagram for describing the room for improvement newly found by the inventors of this application, and is a cross-sectional view showing a molding step for forming the sealing body MR. In  FIG.  4   , a lead  60 A and a lead  60 B in the lead frame are sandwiched between a lower mold  70 A and an upper mold  70 B. Then, the die pad DPL, the semiconductor chip CPL mounted on the die pad DPL via a silver paste  50 A, and the clip CLL mounted via a silver paste  50 B on the source pad SPL for main transistor formed on the semiconductor chip CPL are mounted in the cavity CAV. Further, the clip CLL is connected to the lead  60 A via a silver paste  50 C. Namely, the clip CLL has a function of electrically connecting the source pad SPL for main transistor and the lead  60 A. 
     Here, in the molding step shown in  FIG.  4   , the sealing body is formed by injecting a resin into the cavity CAV. At this time, if there is a gap between the lower mold  70 A and the die pad DPL in  FIG.  4   , the resin also flows into this gap. Thus, in order to prevent the formation of the gap into which the resin flows between the lower mold  70 A and the die pad DPL, for example, the molding step is performed while applying the force of pushing the die pad DPL from the lower mold  70 A toward the cavity CAV as shown in  FIG.  4   . 
     In this case, the lead  60 A and the lead  60 B are sandwiched and fixed between the lower mold  70 A and the upper mold  70 B. On the other hand, the die pad DPL is pushed toward the cavity CAV by the above-mentioned pushing force. As a result, the “offset X” indicating the height difference between the lead  60 A ( 60 B) and the die pad DPL shown in  FIG.  4    changes to be smaller. Then, a force in the direction indicated by the arrow in  FIG.  4    is applied to the clip CLL connected to both the lead  60 A and the semiconductor chip CPL. 
     This causes the deformation of the clip CLL, for example, as shown in  FIG.  5   . Specifically, the clip CLL connected to both the source pad SPL for main transistor formed on the semiconductor chip CPL and the lead  60 A is arranged in parallel to the semiconductor chip CPL in general, but the deformation in which the tip portion of the clip CLL becomes higher than the root portion of the clip occurs due to the pushing force applied to the die pad DPL described above. 
     In this specification, the shape in which the tip portion of the clip CLL is higher than the root portion of the clip CLL shown in  FIG.  5    is referred to as “reverse tilt”. 
     As described above, in the molding step for manufacturing the semiconductor device PKG in which the back surface of the die pad DPL is exposed from the lower surface of the sealing body MR, a pushing force is applied to the die pad DPL from the lower die  70 A toward the cavity CAV such that a gap into which the resin flows is not formed between the lower mold  70 A and the die pad DPL. As a result, for example, as shown in  FIG.  5   , the shape of the clip CLL becomes the “reverse tilt”. 
     Then, when the shape of the clip CLL becomes the “reverse tilt”, the portion of the silver paste  50 B in contact with the root portion  80  of the clip CLL becomes thinner than the other portion of the silver paste SOB, As a result, due to the structural stress applied to the semiconductor device, for example, a peeled portion  90  is generated in the silver paste SOB shown in  FIG.  5   . 
     In this regard, the silver paste  50 B has a function of electrically connecting the source pad SPL for main transistor formed on the semiconductor chip CPL and the clip CLL, and serves as a current path through which a current flows. For this reason, when peeling occurs in the silver paste  50 B serving as the current path, the peeled portion  90  becomes a high impedance region, so that the on-resistance of the semiconductor device becomes high. Further, in the case of a semiconductor device provided with a sense transistor, it causes the fluctuation in the sense ratio. Namely, the occurrence of peeling in the silver paste  50 B adversely affects the performance of the semiconductor device. 
     In the foregoing, the room for improvement in the semiconductor device PKG has been described while taking the clip CLL as the plate-shaped member. This is because, for example, the inverter circuit INV shown in  FIG.  2    has the sense circuit  31  electrically connected to the sense transistor  22  included in the low-side switching circuit  20  and the main transistor  21  and the sense transistor  22  constituting the low-side switching circuit  20  are formed in the semiconductor chip CPL, so that the plate-shaped member connected to the semiconductor chip CPL via the silver paste  50 B is the clip CLL. Therefore, for example, when the inverter circuit INV is configured to have the sense circuit  31  electrically connected to the sense transistor  22  included in the low-side switching circuit  20  and have the sense circuit electrically connected to the sense transistor  12  included in the high-side switching circuit  10 , since the main transistor  11  and the sense transistor  12  constituting the high-side switching circuit  10  are formed in the semiconductor chip CPH, the same room for improvement as that of the above-mentioned clip CLL is present also in the clip CLH which is a plate-shaped member connected to the semiconductor chip CPH via the silver paste. 
     Furthermore, for example, when the inverter circuit INV is configured such that the sense circuit  31  electrically connected to the sense transistor  22  included in the low-side switching circuit  20  is not provided and the sense circuit electrically connected to the sense transistor  12  included in the high-side switching circuit  10  is provided, the room for improvement described above is present for the clip CLH which is a plate-shaped member connected to the semiconductor chip CPAP: via the silver paste. 
     &lt;New Finding Found by Inventors of This Application&gt; 
     As described above, the peeling that has occurred in the silver paste  50 B serving as the current path causes the fluctuation of the sense ratio in the case of the semiconductor device in which a sense transistor is mounted. Furthermore, the inventors of this application have newly found that the occurrence of peeling itself is also a problem, but in particular, the fluctuation of the sense ratio is greatly affected by the fluctuation of the peeling area. 
     In the following, this point will be described. 
     For example, in the manufacturing process of a semiconductor device, a reliability test called HTSL (High Temperature Storage Life) is performed in some cases after the semiconductor device is manufactured. The “HTSL” is a test in which a semiconductor device is stored for a long time at a high temperature and the influence on the semiconductor device is evaluated. In the “HTSL”, since the semiconductor device is kept in a high temperature state, it is conceivable that the peeling of the silver paste  50 B due to, for example, the causes shown in  FIG.  4    and  FIG.  5    progresses. However, the inventors of this application have newly found that the peeled portion of the silver paste  50 B may not only be enlarged but also be re-adhered and reduced by the “HTSL”. Namely, according to the study by the inventors of this application, the peeling area of the silver paste  50 B is increased or decreased by the “HTSL”. Then, when the peeling area of the silver paste  50 B increases or decreases, the potential distribution on the surface of the source pad SPL for main transistor changes. As a result, the current flowing through the sense transistor changes, and the sense ratio fluctuates. 
     From the above, the finding newly found by the inventors of this application is that the peeling area of the silver paste SOB increases or decreases by performing the reliability test called “HTSL” and the potential distribution on the surface of the source pad SPL for main transistor changes due to the increase or decrease in the peeling area, so that the current (sense current) flowing through the sense transistor fluctuates and the sense ratio fluctuates. Then, since the inventors of this application have acquired the finding that the potential change due to the increase or decrease in the peeling area is large in the case of the arrangement position of the sense transistor in the related art and the sense ratio greatly fluctuates due to it, this finding will be described. 
     The “related art” referred to in this specification is not a known art, but is an art having the problem found by the inventors of this application and serving as a premise of the present invention. 
       FIG.  6 A  and  FIG.  6 B  are diagrams for describing the room for improvement existing in the related art. 
     As shown in  FIG.  6 A , a sense transistor  100  arranged near the central portion the long side direction of the semiconductor chip CPL. As a result, in the related art, the sense transistor  100  is arranged in the region close to the peeled portion  90 . Then, as shown in  FIG.  6 B , when the peeled portion.  90  increases, the sense transistor  100  comes close to the peeled portion  90 , and as a result, the sense transistor  100  is greatly affected by the potential change caused by the peeled portion  90 . Namely, in the related art, since the sense transistor  100  is formed in the region close to the growing peeled portion  90 , the current flowing through the sense transistor  100  fluctuates due to the influence of the potential change caused by the peeled portion  90 . Further, the peeled portion.  90  that has once grown is reduced by re-adhesion in some cases and a potential change occurs in this case as well, so that the current flowing through the sense transistor  100  fluctuates due to the influence of the potential change. 
     Namely, in the related art, since the sense transistor  100  is arranged in a region close to the peeled portion  90 , the current flowing through the sense transistor  100  is likely to be affected by the potential change due to the increase or decrease of the peeled portion  90 . In other words, in the related art, the sense transistor  100  is arranged at a position that is likely to be affected by the potential change due to the increase or decrease of the peeled portion  90 . For this reason, in the related art, the potential change due to the increase or decrease of the peeled portion  90  is large, and the sense ratio is greatly changed due to it. This means that the sense ratio deviates from a preset value and the detection accuracy of the current (main current) flowing through the main transistor is lowered due to it. As described above, from the viewpoint of suppressing the fluctuation of the sense ratio, the related art has the room for improvement in the point that the sense transistor  100  is arranged at the position where the potential change due to the increase or decrease of the peeled portion  90  is large. 
     Therefore, in the present embodiment, measures are taken to overcome the room for improvement existing in the related art. Hereinafter, the technical idea in the present embodiment in which the measures are taken will be described. 
     &lt;Basic Idea in Embodiment&gt; 
     The basic idea in the present embodiment is that the sense transistor is formed at the position that is less likely to be affected by the potential change due to the increase or decrease of the peeled portion of the silver paste. According to this basic idea, for example, the sense transistor becomes less likely to be affected by the potential change due to the increase or decrease of the peeled portion even if the peeled portion of the silver paste that adheres the source pad for main transistor and the clip increases or decreases by performing the reliability test called “HTSL”. As a result, according to the basic idea, since the fluctuation of the sense ratio can be suppressed, the detection accuracy of the current (main current) flowing through the main transistor can be improved. Namely, according to the basic idea, it is possible to suppress the deterioration of the performance of the semiconductor device such as the decrease in the detection accuracy of the main current due to the fluctuation of the sense ratio. 
     In the following, the embodied mode obtained from the above-mentioned basic idea will be described. 
     &lt;Embodied Mode&gt; 
     The basic idea is that a sense transistor is formed at the position that is less likely to be affected by the potential change due to the increase or decrease of the peeled portion of the silver paste, and it is important to find the “position that is less likely to be affected by the potential change due to the increase or decrease of the peeled portion of the silver paste” in order to embody the basic idea. 
     In this regard, since the inventors of this application have found the following position as the “position that is less likely to be affected by the potential change due to the increase or decrease of the peeled portion of the silver paste”, the position will be described below. 
       FIG.  7    is a diagram schematically showing the “position that is less likely to be affected by the potential change due to the increase or decrease of the peeled portion of the silver paste”. In  FIG.  7   , a region RA is located at a position away from the peeled portion  90  of the silver paste, and corresponds to the “position that is less likely to be affected by the potential change due to the increase or decrease of the peeled portion of the silver paste”. Accordingly, the sense transistor is arranged in the region RA in the present embodiment. 
     The details will be described below. 
     First, as shown in  FIG.  3   , the semiconductor device PKG includes the die pad DPL, the semiconductor chip CPL mounted on the die pad DPL, the lead LD arranged separately from the die pad DPL, and the clip CLL that electrically connects the semiconductor chip CPL and the lead LD. The clip CLL is an example of a plate-shaped member, and is made of, for example, copper. 
     Subsequently, as shown in  FIG.  2   , for example, the main transistor  21  and the sense transistor  22  constituting the low-side switching circuit  20  are formed in the semiconductor chip CPL, The main transistor  21  and the sense transistor  22  are composed of vertical trench power transistors which flow a current in the thickness direction of the semiconductor chip CPL. 
     Then, as shown in  FIG.  8   , the source pad SPL for main transistor electrically connected to the power transistor (main transistor  21  in  FIG.  2   ) and a sense pad  200  electrically connected to the sense transistor  100  (sense transistor  22  in  FIG.  2   ) are formed on the surface of the semiconductor chip CPL. 
     Here, as shown in  FIG.  8   , the source pad SPL for main transistor has a first short side SS 1 , a second short side SS 2  facing the first short side SS 1 , a first long side LS 1  intersecting the first short side SS 1 , and a second long side LS 2  facing the first long side LS 1  in a plan view. Also, the semiconductor chip CPL has an overlapping region in which the source pad SPL for main transistor and the clip CLL overlap with each other in a plan view and a non-overlapping region in which the source pad SPL for main transistor and the clip CLL do not overlap with each other. At this time, the clip CLL extends in the y direction (first direction) in which the first long side LS 1  and the second long side LS 2  extend, crosses the second short side SS 2  in a plan view, and is electrically connected to the source pad SPL for main transistor via the silver paste. Further, the non-overlapping region in which the source pad SPL for main transistor and the clip CLL do not overlap with each other includes a region sandwiched between the tip portion of the clip CLL and the first short side SS 1  of the source pad SPL for main transistor in a plan view, that is, a region in which the sense transistor  100  is arranged. 
     Namely, the non-overlapping region includes a first region which is located between a first portion PU 1  of the clip CLL (plate-shaped member) and the first short side SS 1  of the source pad SPL (first electrode) for main transistor in a plan view and in which the sense transistor  100  is arranged. In other words, the sense transistor  100  is located in the first region between the first portion PU 1  of the clip CLL (plate-shaped member) and the first short side SS 1  of the source pad SPL (first electrode) for main transistor in a plan view, in the non-overlapping region. 
     Furthermore, as shown in  FIG.  8   , a pad  300  electrically connected to the source pad SPL for main transistor is formed on the surface of the semiconductor chip CPL. At this time, the source pad SPL for main transistor and the pad  300  are connected via a first wiring WL 1  connecting the first long side LS 1  and the second long side LS 2  of the source pad SPL for main transistor and a second wiring WL 2  connecting the first wiring WL 1  and the pad  300 . 
     On the other hand, as shown in  FIG.  8   , the sense transistor  100  and the sense pad  200  are connected by a third wiring WL 3 . At this time, the third wiring WL 3  has a first portion P 1  arranged along the first short side SS 1  and a second portion P 2  arranged along the first long side LS 1 . 
     Here, in the semiconductor chip CPC (control chip) shown in  FIG.  3   , the main current flowing through the main transistor is measured based on the sense current flowing through the sense transistor  100 . Specifically, the source voltage of the sense transistor  100  is input to the semiconductor chip CPC from the sense pad  200  electrically connected to the sense transistor  100 , and the source voltage of the main transistor is input to the semiconductor chip CPC from the pad  300  electrically connected to the source pad SPL for main transistor. Then, in the semiconductor chip CPC, after correcting such that the difference between the input source voltage of the sense transistor  100  and the input source voltage of the main transistor becomes zero, in other words, after correcting such that the source voltage of the sense transistor  100  and the source voltage of the main transistor become equal to each other, the sense current input from the sense pad  200  is converted into a voltage signal. In this way, the current value of the main current flowing through the main transistor is measured based on the voltage signal and the preset “sense ratio”. In this regard, for example, if there is no increase or decrease of the peeled portion, the sense current value of the sense transistor  100  becomes a desired value, and the measurement accuracy of the main current measured from the preset “sense ratio” is good. On the other hand, if there is the increase or decrease of the peeled portion, the sense current value of the sense transistor  100  changes from a desired value, so that the measurement accuracy of the main current measured based on the preset “sense ratio” is reduced. Therefore, it is important to find the “position that is less likely to be affected by the potential change due to the increase or decrease of the peeled portion of the silver paste”, and for example, the sense transistor  100  is arranged in the region sandwiched between the tip portion of the clip CLL and the first short side SS 1  the source pad SPL for main transistor in a plan view as shown in  FIG.  8    in the present embodiment. 
     Next,  FIG.  9    is a cross-sectional view taken along the line A-A in  FIG.  8   . 
     As shown in  FIG.  9   , the main transistor and the sense transistor are composed of vertical trench power transistors which flow a current in the thickness direction of the semiconductor chip. 
     Also, the main transistor is electrically connected to the source pad. SPL for main transistor, and the source pad SPL for main transistor is connected to the clip CLL via the silver paste  50 B. On the other hand, the sense transistor is electrically connected to the sense pad  200 . 
     «Feature in Embodiment» 
     Next, the feature in the present embodiment will be described. 
     The feature in the present embodiment lies in that the sense transistor  100  is arranged in the region sandwiched between the tip portion of the clip CLL and the first short side SS 1  of the source pad SPL for main transistor in a plan view as shown in  FIG.  8   . In this way, according to the present embodiment, for example, even if the peeled portion of the silver paste that adheres the source pad SPL for main transistor and the clip CLL increases or decreases by performing the reliability test called “HTSL”, the sense transistor  100  is less likely to be affected by the potential change due to the increase or decrease of the peeled portion. This is because, according to the new finding found by the inventors of this application, the region sandwiched between the tip portion of the clip CLL and the first short side SS 1  of the source pad SPL for main transistor is located away from the peeled portion of the silver paste and is the “position that is less likely to be affected by the potential change due to the increase or decrease of the peeled portion of the silver paste”. Namely, in the present embodiment, with respect to the basic idea of forming the sense transistor  100  at the position that is less likely to be affected by the potential change due to the increase or decrease of the peeled portion of the silver past, the above-mentioned basic idea is embodied by the configuration in which the sense transistor  100  is arranged in the region sandwiched between the tip portion of the clip CLL and the first short side SS 1  of the source pad SPL for main transistor in a plan view, based on the above-mentioned new finding. As a result, according to the configuration in the present embodiment that has embodied the basic idea, the fluctuation of the sense ratio can be suppressed, so that the detection accuracy of the current flowing through the main transistor can be improved. Namely, according to the configuration in the present embodiment, it is possible to suppress the deterioration of the performance of the semiconductor device such as the decrease of the detection accuracy of the main current due to the fluctuation of the sense ratio. 
     First Modification 
       FIG.  10    is a diagram showing a first modification. 
     As shown in  FIG.  10   , in the first modification, the source pad SPL for main transistor and pad  300  are connected via the first wiring WL 1  that connects the first corner portion where the first long side LS 1  and the first short side SS 1  intersect and the second corner portion where the second long side LS 2  and the first short side SS 1  intersect and the second wiring WL 2  that connects the first wiring WL 1  and the pad  300 . 
     Further, in the first modification, the sense transistor  100  and the sense pad  200  are connected by the third wiring WL 3 , and the third wiring WL 3  has a first portion P 1  arranged along the first short side SS 1  and a second portion P 2  arranged along the first long side LS 1 . 
     Also in the first modification configured in this way, the sense transistor  100  is arranged in the region sandwiched between the tip portion of the clip CLL and the first short side SS 1  of the source pad SPL for main transistor a an view. Accordingly, also in the first modification, for example, even if the peeled portion of the silver paste that adheres the source pad SPL for main transistor and the clip CLL increases or decreases by performing the reliability test called “HTSL”, the sense transistor  100  is less likely to be affected by the potential change due to the increase or decrease of the peeled portion. As a result, it is possible to suppress the fluctuation of the sense ratio also in the first modification. 
     Second Modification 
       FIG.  11    is a diagram showing a second modification. 
     As shown in  FIG.  11   , in the second modification, the source pad SPL for main transistor and the pad  300  are connected via the first wiring WL 1  that connects the first long side LS 1  and the second long side LS 2  of the source pad SPL for main transistor and the second wiring. WL 2  that connects the first wiring WL 1  and the pad  300 . Also, the sense transistor  100  and the sense pad  200  are connected by the third wiring WL 3 , and the third wiring WL 3  has a first portion P 1  arranged along the first short side SS 1  and intersecting the second long side LS 2 , a second portion P 2  arranged along the second long side LS 2 , a third portion P 3  arranged along the first short side SS 1 , and a fourth portion P 4  arranged along the first long side LS 1  in a plan view. 
     Also in the second modification configured in this way, the sense transistor  100  is arranged in the region sandwiched between the tip portion of the clip CLL and the first short side SS 1  of the source pad SPL for main transistor in a plan view. Accordingly, also in the second modification, for example, even if the peeled portion of the silver paste that adheres the source pad SPL for main transistor and the clip CLL increases or decreases by performing the reliability test called “HTSL”, the sense transistor  100  is less likely to be affected by the potential change due to the increase or decrease of the peeled portion. As a result, it is possible to suppress the fluctuation of the sense ratio also in the second modification. 
     Third Modification 
       FIG.  12    is a diagram showing a third modification. 
     As shown in  FIG.  12   , the source pad SPL for main transistor and the pad  300  are connected via the first wiring WL 1  that connects the first long side LS 1  and the second long side LS 2  of the source pad SPL for main transistor and the second wiring WL 2  that connects the first wiring WL 1  and the pad  300 . Also, the sense transistor  100  and the sense pad  200  are connected by the third wiring WL 3 , and the third wiring WL 3  has a first portion P 1  arranged along the first long side LS 1  and intersecting the first short side SS 1 , a second portion P 2  arranged along the first short side SS 1 , and a third portion P 3  arranged along the first long side LS 1  in a plan view. 
     Also in the third modification configured in this way, the sense transistor  100  is arranged in the region sandwiched between the tip portion of the clip CLL and the first short side SS 1  of the source pad SPL for main transistor a an view. Accordingly, also in the third modification, for example, even if the peeled portion of the silver paste that adheres the source pad SPL for main transistor and the clip CLL increases or decreases by performing the reliability test called “HTSL”, the sense transistor  100  is less likely to be affected by the potential change due to the increase or decrease of the peeled portion. As a result, it is possible to suppress the fluctuation of the sense ratio also in the third modification. 
     Fourth Modification 
     In the embodiment, for example, as shown in  FIG.  8   , with respect to the basic idea of forming the sense transistor  100  at the position that is less likely to be affected by the potential change due to the increase or decrease of the peeled portion of the silver past, the above-mentioned basic idea is embodied by the configuration in which the sense transistor  100  is arranged in the region sandwiched between the tip portion of the clip CLL and the first short side SS 1  of the source pad SPL for main transistor in a plan view. However, the above-mentioned basic idea can be embodied not only by the configuration in which the sense transistor  100  is arranged in the region sandwiched between the p portion of the clip CLL and the first short side SS 1  of the source pad SPL for main transistor but also by the configuration shown in  FIG.  13   . This is because, according to the study by the inventors of this application, it has been found that the growth of the peeled portion of the silver paste is less likely to occur not only at the tip portion of the clip CLL but also at the root portion. Namely, the root portion of the clip CLL is also the position that is less likely to be affected by the potential change due to the increase or decrease of the peeled portion of the silver paste, and it is possible to suppress the fluctuation of the sense ratio also by arranging the sense transistor  100  at this position. 
     Specifically,  FIG.  13    is a diagram showing a fourth modification. 
     As shown in  FIG.  13   , the semiconductor chip CPL has an overlapping region in which the source pad SPL for main transistor and the clip CLL overlap with each other and a non-overlapping region in which the source pad SPL for main transistor and the clip CLL do not overlap with each other in a plan view. 
     Then, the clip CLL has a first portion PU 1  in contact with the silver paste  50 B, a second portion PU 2  in contact with the silver paste  50 C, and a third portion PU 3  located between the first portion PU 1  and the second portion PU 2 . Here, the overlapping region includes a region which overlaps with the third portion PU 3  of the clip CLL in a plan view and in which the sense transistor  100  is arranged. Namely, in the fourth modification, the sense transistor  100  is formed in the region overlapping with the third portion P 3  of the clip CLL in a plan view, in the semiconductor chip CPL. 
     Namely, the overlapping region includes the first region which overlaps with the third portion of the clip CLL (plate-shaped member) in a plan view and in which the sense transistor  100  is arranged. In other words, the sense transistor  100  is located in the first region of the overlapping region which overlaps with the third portion of the clip CLL (plate-shaped member) in a plan view. 
     Also in the fourth modification configured in this way, even if the peeled portion of the silver paste that adheres the source pad SPL for main transistor and the clip CLL increases or decreases by performing the reliability test called “HTSL”, the sense transistor  100  is less likely to be affected by the potential change due to the increase or decrease of the peeled portion. As a result, it is possible to suppress the fluctuation of the sense ratio also in the fourth modification, 
     &lt;Method of Manufacturing Semiconductor Device&gt; 
     Next, the method of manufacturing the semiconductor device according to the present embodiment will be described, 
     «Manufacturing Process of Semiconductor Device» 
     First, a semiconductor wafer having a plurality of chip regions is prepared. Then, by using the normal semiconductor manufacturing technology, power transistors including a main transistor and a sense transistor are formed in each chip region. At this time, for example, the main transistor and the sense transistor are formed such that the layout shown in  FIG.  8    is realized, Thereafter, a source pad for main transistor is formed on the surface of each chip region of the semiconductor wafer. The source pad for main transistor is made of, for example, aluminum. 
     Next, if necessary, a plating film such as a nickel film, a palladium film, or a gold film is formed on the exposed surface of the source pad for main transistor by using an electroless plating method or the like. Then, after performing the back surface grinding process to the semiconductor wafer, the semiconductor wafer is diced. As a result, the plurality of chip regions of the semiconductor wafer is singulated and divided into a plurality of semiconductor chips. In this way, the semiconductor chip according to the present embodiment is manufactured. 
     «Assembly Process of Semiconductor Device» 
     Next, the assembly process of the semiconductor device will be described. 
       FIG.  14    is a flowchart showing the assembly process of the semiconductor device. 
     First, a lead frame having a die pad and a lead separated from the die pad is prepared. Then, the semiconductor chip manufactured in the above-mentioned manufacturing process of the semiconductor chip is mounted on the die pad. Specifically, after applying a silver paste on the die pad, the semiconductor chip is mounted on the die pad via the silver paste (S 101 ). 
     Next, a silver paste is applied on the source pad for main transistor formed on the surface of the semiconductor chip and on the lead (S 102 ). Thereafter, the clip is arranged so as to connect the source pad for main transistor and the lead. At this time, the clip is connected to the source pad for main transistor via the silver paste and is connected to the lead via the silver paste. As a result, the source pad for main transistor and the lead are electrically connected by the clip (S 103 ). Then, a curing treatment (heat treatment at about 150° C. to 300° C.) for curing the silver paste is performed (S 104 ). 
     Subsequently, for example, the lead and other pads formed on the surface of the semiconductor chip are connected by a gold wire or a conductive wire. Namely, the wire bonding with a gold wire or a copper wire is performed to the lead and other pads formed on the surface of the semiconductor chip (S 105 ). 
     Thereafter, a sealing body is formed by performing resin sealing (molding) (S 106 ). Then, a plating layer is formed on the outer lead portion of the lead exposed from the sealing body as needed. Next, the sealing body is separated from the frame portion of the lead frame by cutting the lead at a predetermined position outside the sealing body. Subsequently, the outer lead portion of the lead protruding from the sealing body is bent. In this way, the semiconductor device can be manufactured. 
     Thereafter, the reliability test called “HTSL” is performed to the manufactured semiconductor device (S 107 ). At this time, the peeled portion of the silver paste that adheres the source pad for main transistor and the clip increases or decreases in some cases. In this regard, in the present embodiment, the sense transistor is formed at the position that is less likely to be affected by the increase or decrease of the peeled portion of the silver paste (for example, region sandwiched between the tip portion of the clip CLL and the first short side SS 1  of the source pad SPL for main transistor). As a result, in the semiconductor device according to the present embodiment, the fluctuation of the sense ratio can be suppressed, so that the detection accuracy of the current flowing through the main transistor can be improved. Namely, according to the present embodiment, it is possible to suppress the deterioration of the performance of the semiconductor device such as the decrease in the detection accuracy of the main current clue to the fluctuation of the sense ratio. Thus, according to the present embodiment, the manufacturing yield of the semiconductor device can be improved. 
     Thereafter, among the manufactured semiconductor devices, non-defective products that have passed the above-mentioned reliability test are shipped. In this way, the method of manufacturing the semiconductor device according to the present embodiment is implemented. 
     Fifth Modification 
     In the above embodiment, the configuration in which the surface of the die pad DPL (die pad DPC, die pad DPH) is exposed from the lower surface of the sealing body MR has been described as an example, but the basic idea in the embodiment is not limited to this and can be applied to, for example, the configuration in which the surface of the die pad DPL (die pad DPC, die pad DPH) is exposed from the upper surface of the sealing body MR. 
     In the case of the configuration of the fifth modification, the resin sealing step (molding step) can be performed in the configuration in which the exposed surface of the die pad. DPL is in contact with the lower mold or the configuration in which the exposed surface of the die pad DPL is in contact with the lower mold. 
     In the foregoing, the invention made by the inventors of this application has been specifically described based on the embodiment, but it goes without saying that the present invention is not limited to the embodiment described above and can be modified within the range not departing from the gist thereof. 
     In the above embodiment, as shown in  FIG.  8   , an example in which the source pad SPL for main transistor has a rectangular shape in a plan view has been described, but the basic idea in the above embodiment is not limited to this, and can be widely applied to the case in which the planar shape of the source pad SPL for main transistor has an approximately rectangular shape (deformed shape) having at least a first short side, a second short side facing the first short side, a first long side intersecting the first short side, and a second long side facing the first long side as shown in  FIG.  6 A  and  FIG.  6 B . 
     In the embodiment described above, a power MOSFET is assumed as a power transistor formed in a semiconductor chip, but the technical idea in the above embodiment is not limited to this, and can be widely applied to, for example, a semiconductor device using IGBT (insulated Gate Bipolar Transistor) as a power transistor. 
     In this case, the “source pad for main transistor” should be read as the “emitter pad for main transistor”. Also, in claims, the “first electrode” is used as the wording including the “source pad for main transistor” and the “emitter Dad for main transistor”. Namely, the “first electrode” described in claims is used with the intention of including the “source pad for main transistor” and the “emitter pad for main transistor”. 
     Further, in the above embodiment, silver paste has been described as an example, but the technical idea in the above embodiment is not limited to this, and can be widely applied to, for example, a semiconductor device using solder. Also, in claims, the “first conductive member” or the “second conductive member” is used as the wording including the “silver paste” and the “solder”. Namely, the “first conductive member” or the “second conductive member” described in claims is used with the intention of including the “silver paste” and the “solder”.