Patent Publication Number: US-2022238459-A1

Title: Semiconductor device, power conversion device and moving body

Description:
TECHNICAL FIELD 
     The present invention relates to a semiconductor device, a power conversion device, and a moving body. 
     BACKGROUND ART 
     A semiconductor device such as a semiconductor module includes a semiconductor chip. The semiconductor device includes a sealing body sealing the semiconductor chip to increase insulation properties and moisture resistance, for example. The sealing body includes a portion made up of epoxy resin in many cases. 
     For example, in a semiconductor device described in Patent Document 1, a semiconductor element is surrounded by a case. A sealing body is formed in a region surrounded by the case. The sealing body is made up of a first layer, a second layer, and a third layer. Silicon-series resin, for example, is used for the first layer. The second layer is a resin plate made up of a polyphenylene sulfide (PPS) material. Epoxy-series resin, for example, is used for the third layer (Paragraphs 0010-0019). 
     In a semiconductor device described in Patent Document 2, an area around a chip is sealed by a first layer resin. Next, the whole first layer resin is surrounded using a second layer resin. An upper portion of the second layer resin is sealed by a third layer resin. The first layer resin is resin such as silicone, for example. The second layer resin is resin such as polyimide, for example. The third layer resin is resin such as epoxy, for example (pp. 2, line 16 to pp. 3, line 14). 
     PRIOR ART DOCUMENTS 
     Patent Documents 
     
         
         Patent Document 1: Japanese Patent Application Laid-Open No. 2016-225449 
         Patent Document 2: Japanese Utility Model Application Laid-Open No. 58-92739 
       
    
     SUMMARY 
     Problem to be Solved by the Invention 
     However, when the sealing body includes a portion made up of epoxy resin, it is difficult to perform failure analysis of the semiconductor device. 
     A first reason for difficulty in the failure analysis of the semiconductor device when the sealing body includes the portion made up of the epoxy resin is that the portion made up of the epoxy resin needs to be separated from a remaining portion by adding a thermal history to the semiconductor device when the semiconductor device is disassembled to remove the portion made up of the epoxy resin or the semiconductor device needs to be cut off. The processing of adding the thermal history to the semiconductor device and cutting off the semiconductor device makes identification of a failure point and examination of a trace of damage difficult. 
     A second reason for difficulty in the failure analysis of the semiconductor device when the sealing body includes the portion made up of the epoxy resin is that when the semiconductor device is in actual use or after the semiconductor device is examined, impurity included in the epoxy resin penetrates elements such as silicone gel and contaminates the elements such as silicone gel, thereby causing a change of color of the elements such as silicone gel. The change of color of the elements such as silicone gel interferes analysis of the semiconductor device, for example. 
     When the sealing body includes a portion made up of epoxy resin, it is difficult to recycle the semiconductor device by a reason similar to the reason for difficulty in the failure analysis of the semiconductor device. 
     When the sealing body includes a portion made up of epoxy resin, it needs several hours to put in a fluent material which is the epoxy resin before hardened and harden the fluent material. Thus, a production efficiency of the semiconductor device decreases and a takt time for manufacturing the semiconductor device gets compressed. 
     In addition to solving these problems, the sealing body also needs to provide a semiconductor device having high insulation properties and having high moisture resistance over a long period of time. 
     The present invention is made in consideration of these problems. An object of the present invention is to facilitate failure analysis and recycle of the semiconductor device and improve a production efficiency of the semiconductor device. An object of the present invention is to provide a semiconductor device having high insulation properties and having high moisture resistance over a long period of time. 
     Means to Solve the Problem 
     The present invention is directed to a semiconductor device. 
     A semiconductor device includes an exterior, a semiconductor chip, a first sealing material, a waterproof water-repellent layer, and a second sealing material. 
     The exterior includes an inner space and an inner surface surrounding the inner space. 
     The semiconductor chip is housed in the inner space and mounted on the inner surface. 
     The first sealing material fills the inner space, is disposed on the inner surface to be overlapped on the semiconductor chip, and is made up of silicone gel. 
     The waterproof water-repellent layer is housed in the inner space, disposed on the inner surface to be overlapped on the semiconductor chip and the first sealing material, and made up of fluorine-series resin or silicone-series resin. 
     The second sealing material fills the inner space, is disposed on the inner surface to be overlapped on the semiconductor chip, the first sealing material, and the waterproof water-repellent layer, and is made up of silicone gel. 
     The present invention is also directed to a power conversion device including the semiconductor device and a moving body including the power conversion device. 
     Effects of the Invention 
     According to the present invention, the semiconductor chip is covered by the silicone gel which can easily fill the inner space or can be easily housed therein, and can be easily removed and the fluorine-series resin or the silicone-series resin. Thus, failure analysis and recycle of the semiconductor device can be facilitated. A production efficiency of the semiconductor device can be improved. 
     According to the present invention, the semiconductor chip is sealed by the first sealing material and the second sealing material. Thus, the semiconductor device having high insulation properties can be provided. According to the present invention, the waterproof water-repellent layer suppresses exposure of the semiconductor chip to moisture. Thus, the semiconductor device having high moisture resistance can be provided. According to the present invention, the second sealing material suppresses a foreign material mixed into the waterproof water-repellent layer. Thus, loss of high moisture resistance of the semiconductor device caused by the foreign material mixed into the waterproof water-repellent layer can be suppressed. According to these configurations, the semiconductor device having high insulation properties and having high moisture resistance over a long period of time can be provided. 
     These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  A cross-sectional view schematically illustrating a semiconductor device according to an embodiment 1. 
         FIG. 2  A block diagram of a power conversion system applying a power conversion device according to an embodiment 2. 
         FIG. 3  A side view schematically illustrating a moving body according to an embodiment 3. 
     
    
    
     DESCRIPTION OF EMBODIMENT(S) 
     1 Embodiment 1 
     1.1 Structure of Semiconductor Device 
       FIG. 1  is a cross-sectional view schematically illustrating a semiconductor device according to an embodiment 1. 
     A semiconductor device  1  according to the embodiment 1 illustrated in  FIG. 1  is a semiconductor module including a plurality of semiconductor chips  17 . The semiconductor device  1  may be a discrete semiconductor including one semiconductor chip  17 . 
     The semiconductor device  1  includes a chassis  11 , a heat radiation plate  12 , a cover  13 , a silicone adhesive agent  14 , a silicone adhesive agent  15 , an insulating substrate  16 , the semiconductor chip  17 , an Al wire  18 , an electrode  19 , a first sealing material  20 , a waterproof water-repellent layer  21 , and a second sealing material  22 . 
     The chassis  11 , the heat radiation plate  12 , the cover  13 , the silicone adhesive agent  14 , and the silicone adhesive agent  15  constitute an exterior  30 . Thus, the semiconductor device  1  includes the exterior  30  including the chassis  11 , the heat radiation plate  12 , the cover  13 , the silicone adhesive agent  14 , and the silicone adhesive agent  15 . 
     The chassis  11  includes an inner space  11   a . The chassis  11  includes a first opening  11   b  and a second opening  11   c . The inner space  11   a  is exposed to an outer side of the chassis  11  via the first opening  11   b  and the second opening  11   c.    
     The heat radiation plate  12  is bonded to the chassis  11  via the silicone adhesive agent  14 . The heat radiation plate  12  may be bonded to the chassis  11  via a bonding medium other than the silicone adhesive agent  14 . The heat radiation plate  12  may be directly bonded to the chassis  11  without an intervention of a bonding medium. The heat radiation plate  12  covers the first opening  11   b . The heat radiation plate  12  includes a main surface  12   a  on which the insulating substrate  16  and the semiconductor chip  17  are mounted. 
     The cover  13  is bonded to the chassis  11  via the silicone adhesive agent  15 . The cover  13  may be bonded to the chassis  11  via a bonding medium other than the silicone adhesive agent  15 . The cover  13  may be directly bonded to the chassis  11  without an intervention of a bonding medium. The cover  13  covers the second opening  11   c.    
     According to these configurations, the semiconductor device  1  includes the exterior  30  including the inner space  11   a  and an inner surface  30   a  surrounding the inner space  11   a . The main surface  12   a  of the heat radiation plate  12  constitutes a part of the inner surface  30   a  of the exterior  30 . 
     The insulating substrate  16  is housed in the inner space  11   a  of the exterior  30 . The insulating substrate  16  is disposed on the main surface  12   a  of the heat radiation plate  12 , and bonded to the main surface  12   a  of the heat radiation plate  12 . The insulating substrate  16  includes an insulator plate  41  and a conductor pattern  42 . The conductor pattern  42  is disposed on the insulator plate  41 . 
     The semiconductor chip  17  is housed in the inner space  11   a  of the exterior  30 . The semiconductor chip  17  is disposed on the main surface  12   a  of the heat radiation plate  12 , and bonded to an upper surface of the insulating substrate  16 . The semiconductor chip  17  is a switching element or a reflux diode, for example. The switching element is a metal oxide semiconductor field effect transistor (MOSFET) or an insulated gate bipolar transistor (IGBT), for example. 
     The Al wire  18  is housed in the inner space  11   a  of the exterior  30 . The Al wire  18  is connected to the semiconductor chip  17 . The Al wire  18  is connected to the conductor pattern  42 . Accordingly, the Al wire  18  electrically connects the semiconductor chip  17  and the conductor pattern  42  to each other. The Al wire  18  which is a conductor wire made of Al may be replaced with a conductor wire made of a conductor other than Al. 
     The electrode  19  is bonded to the conductor pattern  42 . The electrode  19  passes through the cover  13 . Accordingly, a signal can be inputted to the conductor pattern  42  from an outer side of the exterior  30  via the electrode  19 . A signal can be outputted from the conductor pattern  42  to the outer side of the exterior  30  via the electrode  19 . 
     The first sealing material  20  fills the inner space  11   a  of the exterior  30 . The first sealing material  20  is disposed on the main surface  12   a  of the heat radiation plate  12  to be overlapped on the insulating substrate  16  and the semiconductor chip  17 . The first sealing material  20  is made up of silicone gel. 
     The waterproof water-repellent layer  21  is housed in the inner space  11   a  of the exterior  30 . The waterproof water-repellent layer  21  is disposed on the first sealing material  20 , and disposed on the main surface  12   a  of the heat radiation plate  12  to be overlapped on the insulating substrate  16 , the semiconductor chip  17 , and the first sealing material  20 . The waterproof water-repellent layer  21  is disposed between the first sealing material  20  and the second sealing material  22 . The waterproof water-repellent layer  21  is made up of fluoride-series resin or a silicone-series resin. The waterproof water-repellent layer  21  prevents moisture, which enters the inner space  11   a  of the exterior  30  from a gap between the chassis  11  and the cover  13  and a gap between the cover  13  and the electrode  19 , from reaching the insulating substrate  16  and the semiconductor chip  17  disposed below the waterproof water-repellent layer  21 , or retards the moisture reaching the insulating substrate  16  and the semiconductor chip  17  disposed below the waterproof water-repellent layer  21 . 
     The second sealing material  22  fills the inner space  11   a  of the exterior  30 . The second sealing material  22  is disposed on the waterproof water-repellent layer  21 , and disposed on the main surface  12   a  of the heat radiation plate  12  to be overlapped on the insulating substrate  16 , the semiconductor chip  17 , the first sealing material  20 , and the waterproof water-repellent layer  21 . The second sealing material  22  is made up of silicone gel. 
     In the semiconductor device  1 , the insulating substrate  16  and the semiconductor chip  17  are covered by the silicone gel which can easily fill the inner space or can be easily housed therein, and can be easily removed and the fluorine-series resin or the silicone-series resin. Thus, failure analysis and recycle of the semiconductor device  1  can be facilitated. A production efficiency of the semiconductor device  1  can be improved. 
     In the semiconductor device  1 , the insulating substrate  16  and the semiconductor chip  17  are sealed by the first sealing material  20  and the second sealing material  22 . Thus, the insulating substrate  16  and the semiconductor chip  17  are electrically insulated from each other by the first sealing material  20  and the second sealing material  22 . In the semiconductor device  1 , a main part of the electrode  19  is sealed by the first sealing material  20  and the second sealing material  22 . Thus, the electrodes  19  are electrically insulated from each other by the first sealing material  20  and the second sealing material  22 . Thus, the semiconductor device  1  having high insulation properties can be provided. In the semiconductor device  1 , the waterproof water-repellent layer  21  suppresses exposure of the insulating substrate  16  and the semiconductor chip  17  to the moisture. Thus, the semiconductor device  1  having high moisture resistance can be provided. In the semiconductor device  1 , the second sealing material  22  suppresses a foreign material mixed into the waterproof water-repellent layer  21 . Thus, loss of high moisture resistance of the semiconductor device  1  caused by the foreign material mixed into the waterproof water-repellent layer  21  can be suppressed. According to these configurations, the semiconductor device  1  having high insulation properties and having high moisture resistance over a long period of time can be provided. 
     1.2 Fill Ration of First Sealing Material and Position of Waterproof Water-Repellent Layer 
     The first sealing material  20  preferably fills the inner space  11   a  up to an upper side of a loop top  18   a  located in an uppermost portion of the Al wire  18 , and more preferably fills the inner space  11   a  up to an immediately upper side of the loop top  18   a  of the Al wire  18  when seen from the main surface  12   a  of the heat radiation plate  12 . The waterproof water-repellent layer  21  is preferably disposed on an upper side of the loop top  18   a  of the Al wire  18 , and more preferably disposed on an immediately upper side of the loop top  18   a  of the Al wire  18  when seen from the main surface  12   a  of the heat radiation plate  12 . 
     When the first sealing material  20  only fills the inner space  11   a  halfway between the loop top  18   a  of the Al wire  18  and a junction of the Al wire  18  with the conductor pattern  42  and the waterproof water-repellent layer  21  is disposed halfway between the loop top  18   a  of the Al wire  18  and the junction of the Al wire  18  with the conductor pattern  42 , it is difficult to form a flat waterproof water-repellent layer  21 , and an effect of the waterproof water-repellent layer  21  preventing ingress of the moisture tends to decrease. Thermal stress acts on the Al wire  18  by the two silicone gel layers made up of the first sealing material  20  and the second sealing material  22 , and the Al wire  18  tends to be cut easily. Thus, the first sealing material  20  preferably fills the inner space  11   a  up to the upper side of the loop top  18   a  of the Al wire  18 . The waterproof water-repellent layer  21  is preferably disposed on the upper side of the loop top  18   a  of the Al wire  18 . 
     1.3 Hardness of First Sealing Material and Second Sealing Material 
     The second sealing material  22  preferably has higher hardness than the first sealing material  20 . For example, when penetrability of the first sealing material  20  expressing the hardness of the first sealing material  20  is 60 (mm/10), penetrability of the second sealing material  22  expressing the hardness of the second sealing material  22  is set to 40 (mm/10) smaller than that of the first sealing material  20 . Hardness of the silicones gel gets larger as penetrability thereof decreases. 
     Accordingly, even when the semiconductor device  1  is reversed when the semiconductor device  1  is in actual use, the first sealing material  20  and the waterproof water-repellent layer  21  can be held. Accordingly, the insulation properties and the moisture resistance of the semiconductor device  1  can be increased. A tolerated dose of the semiconductor device  1  against a mechanical stress such as oscillation and impact, for example, can be increased. 
     1.4 Semiconductor Constituting Semiconductor Chip 
     The semiconductor chip  17  may be a semiconductor chip including a silicon semiconductor, and is preferably a semiconductor chip including a wide bandgap semiconductor. The wide bandgap semiconductor is silicon carbide (SiC), gallium nitride (GaN), and diamond (C), for example. The wide bandgap semiconductor such as silicon carbide (SiC), gallium nitride (GaN), and diamond (C), for example, has a bandgap wider than that of a semiconductor such as silicon (Si), for example. When the semiconductor chip  17  is a semiconductor chip including a wide bandgap semiconductor, an insulation life of the semiconductor chip  17  under a high temperature environment can be stably maintained. When the semiconductor chip  17  is a semiconductor chip including a wide bandgap semiconductor, a space occupied by the semiconductor chip  17  can be reduced, thus downsizing and weight saving of the semiconductor device  1  can be achieved. 
     2 Embodiment 2 
     The semiconductor device according to the embodiment 1 described above is applied to a power conversion device, in the present embodiment. Although the application of the semiconductor device according to the embodiment 1 is not limited to a specific power conversion device, described hereinafter as the embodiment 2 is a case of applying the semiconductor device according to the embodiment 1 to a three-phase inverter. 
       FIG. 2  is a block diagram illustrating a configuration of a power conversion system applying a power conversion device according to the present embodiment. 
     The power conversion system illustrated in  FIG. 2  is made up of a power source  100 , a power conversion device  200 , and a load  300 . The power source  100 , which is a direct current power source, supplies a direct current power to the power conversion device  200 . The power source  100  can be made up of various types of components such as a direct current system, a solar battery, or a rechargeable battery, or may be also made up of a rectifying circuit connected to an alternating current system or an AC/DC converter, for example. The power source  100  may also be made up of a DC/DC converter which converts a direct current power outputted from the direct current system into a predetermined power. 
     The power conversion device  200 , which is a three-phase inverter connected between the power source  100  and the load  300 , converts the direct current power supplied from the power source  100  into the alternating current power to supply the alternating current power to the load  300 . As illustrated in  FIG. 2 , the power conversion device  200  includes a main conversion circuit  201  which converts the direct current power into the alternating current power and a control circuit  203  which outputs control signals for controlling the main conversion circuit  201  to the main conversion circuit  201 . 
     The load  300  is a three-phase electrical motor driven by the alternating current power supplied from the power conversion device  200 . The load  300  is not for specific purpose of use but is the electrical motor mounted on various types of electrical devices, thus it is used as the electrical motor for a hybrid car, an electrical car, a rail vehicle, an elevator, or an air-conditioning equipment, for example. 
     The power conversion device  200  is described in detail hereinafter. The main conversion circuit  201  includes a switching element and a reflux diode (not shown), and when a switching is performed on the switching element, the direct current power supplied from the power source  100  is converted into the alternating current power and then supplied to the load  300 . The main conversion circuit  201  includes various types of specific circuit configurations, and the main conversion circuit  201  according to the present embodiment is a three-phase full-bridge circuit having two levels, and can be made up of six switching elements and six reflux diodes being antiparallel to each switching element. Each switching element and each reflux diode of the main conversion circuit  201  are made up of a semiconductor module  202  corresponding to the embodiment 1 described above. The two switching elements among the six switching elements are series-connected to each other to constitute upper and lower arms, and each of the upper and lower arms constitutes each phase (U-phase, V-phase, and W-phase) of the full-bridge circuit. An output terminal of each of the upper and lower arms, that is to say, three output terminals of the main conversion circuit  201  are connected to the load  300 . 
     The main conversion circuit  201  includes a drive circuit (not shown) for driving each switching element, however, the drive circuit may be embedded in the semiconductor module  202  or may also have a configuration including a drive circuit separately from the semiconductor module  202 . The drive circuit generates the drive signal for driving the switching element of the main conversion circuit  201 , and supplies the drive signal to a control electrode of the switching element of the main conversion circuit  201 . Specifically, the drive circuit outputs the drive signals for switching the switching element to an ON state and the drive signals for switching the switching element to an OFF state to the control electrode of each switching element in accordance with the control signals from the control circuit  203  described hereinafter. The drive signal is a voltage signal (ON signal) equal to or higher than a threshold voltage of the switching element when the switching element is kept in the ON state, and the drive signal is a voltage signal (OFF signal) equal to or lower than the threshold voltage of the switching element when the switching element is kept in the OFF state. 
     The control circuit  203  controls the switching element of the main conversion circuit  201  to supply a desired power to the load  300 . Specifically, the control circuit  203  calculates a time when each switching element of the main conversion circuit  201  needs to enter the ON state (ON time), based on the electrical power which needs to be supplied to the load  300 . For example, the main conversion circuit  201  can be controlled by performing PWN control for modulating an ON time of the switching element in accordance with the voltage which needs to be outputted. Then, the control circuit  203  outputs a control instruction (control signals) to the drive circuit included in the main conversion circuit  201  so that the drive circuit outputs the ON signals to the switching element which needs to enter the ON state and outputs the OFF signals to the switching element which needs to enter the OFF state at each time. The drive circuit outputs the ON signals or the OFF signals as the drive signals to the control electrode of each switching element in accordance with the control signals. 
     The semiconductor module according to the embodiment 1 is applied as the switching element and the reflux diode of the main conversion circuit  201  in the power conversion device according to the present embodiment, thus failure analysis and recycle of the power conversion device can be facilitated, a production efficiency of the power conversion device can be improved, and the power conversion device having high insulation properties and having high moisture resistance over a long period of time can be provided. 
     Although the example of applying the semiconductor device according to the embodiment 1 to the three-phase inverter having the two levels is described in the present embodiment, the application of the semiconductor device according to the embodiment 1 is not limited thereto, but can be applied to the various power conversion devices. Although the power conversion device having the two levels is described in the present embodiment, a power conversion device having three or multiple levels may also applied. The semiconductor device according to the embodiment 1 may be applied to a single-phase inverter when the power is supplied to a single-phase load. The semiconductor device according to the embodiment 1 can be applied to a DC/DC converter or an AC/DC converter when the electrical power is supplied to a direct current load, for example. 
     The load of the power conversion device applying the semiconductor device according to the embodiment 1 is not limited to the electrical motor as described above, but an electrical discharge machine or a laser beam machine may also be the load. The power conversion device can also be used as a power-supply device of an induction heat cooking device or a non-contact power feeding system, and can also be further used as a power conditioner of a solar power system or an electricity storage system, for example. 
     3 Embodiment 3 
       FIG. 3  is a side view schematically illustrating a moving body according to an embodiment 3. 
     A moving body  3  illustrated in  FIG. 3  is a train. The moving body  3  may be a moving body other than the train. For example, the moving body  3  may be an automobile, a boat, a ship, an aircraft, a battery-assisted bicycle, or an electrical wheelchair. 
     The moving body  3  includes the power conversion device  200  according to the embodiment 2. The moving body  3  drives a motor, for example, by an electrical power converted by the power conversion device  200 . 
     When a downsized and light-weighted semiconductor device is applied to the power conversion device  200  according to the embodiment 2, downsizing and weight saving of the moving body  3  can be achieved, efficiency of the moving body  32  can be improved, and performance of the moving body  3  can be improved. 
     According to the present invention, the above embodiments can be arbitrarily combined, or each embodiment can be appropriately varied or omitted within the scope of the invention. 
     The present invention has been shown and described in detail, the foregoing description is in all aspects illustrative and not restrictive. It is therefore understood that numerous modifications and variations can be devised without departing from the scope of the invention. 
     EXPLANATION OF REFERENCE SIGNS 
       1  semiconductor device,  11  chassis,  11   a  inner space,  11   b  first opening,  11   c  second opening,  12  heat radiation plate,  12   a  main surface,  13  cover,  16  insulating substrate,  17  semiconductor chip,  18  Al wire,  18   a  loop top,  19  electrode,  20  first sealing material,  21  waterproof water-repellent layer,  22  second sealing material,  30  exterior,  30   a  inner surface,  41  insulator plate,  42  conductor pattern,  100  power source,  200  power conversion device,  201  main conversion circuit,  202  semiconductor module,  203  control circuit,  300  load,  3  moving body.