Patent Publication Number: US-2022238783-A1

Title: Electronic device and method for manufacturing electronic device

Description:
The present application is based on, and claims priority from JP Application Serial Number 2021-009356, filed Jan. 25, 2021, and JP Application Serial Number 2021-103914, filed Jun. 23, 2021, the disclosures of which are hereby incorporated by reference herein in their entirety. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to an electronic device and a method for manufacturing an electronic device. 
     2. Related Art 
     For example, in a vibration device described in JP-A-2013-239947, a pair of lid bodies are bonded to upper and lower surfaces of a frame portion coupled to an outer edge of a vibration portion and provided so as to surround the outer edge of the vibration portion in a plan view, so that the vibration portion is accommodated. In addition, a shield plate is provided on the lid body on the upper surface via an insulating layer, and a terminal for electrically coupling to an external circuit is formed on the lid body on the upper surface and the shield plate. 
     However, in the vibration device described in JP-A-2013-239947, a notch is provided in the shield plate bonded to an upper surface of the lid body in order to form a terminal electrically coupled to the external circuit. For this reason, a strength becomes insufficient, and when the vibration device is resin-molded, there is a problem that the lid body together with the shield plate is bent and vibration characteristics are changed due to a pressure received from a molten resin at the time of molding. In particular, in a case of an electronic device including a sensor element or the like, there is a concern that deterioration of characteristics of the sensor element and breakage of the sensor element may occur due to deformation of the lid body. 
     SUMMARY 
     An electronic device includes: an electronic component including an inertial element, a base including a substrate to which the inertial element is fixed and a frame portion provided to surround the inertial element in a plan view, a first lid bonded to the frame portion so as to accommodate the inertial element between the first lid and the base, a second lid provided to face the first lid and having an outer edge flush with or protruding from an outer edge of the first lid, and a rigid member disposed between the first lid and the second lid; and a molded portion covering the electronic component. 
     A method for manufacturing an electronic device includes: disposing an inertial element in a region surrounded by a frame portion of a base, and fixing the inertial element to a substrate of the base; bonding a first lid to the frame portion of the base so as to accommodate the inertial element between the first lid and the base; disposing a second lid such that the second lid faces the first lid via a rigid member and an outer edge of the second lid is flush with or protrudes from an outer edge of the first lid; mounting an electronic component including the rigid member and the second lid on a printed substrate including a lead terminal; and forming a molded portion covering the electronic component by a transfer molding method. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view showing a schematic structure of an electronic device according to a first embodiment. 
         FIG. 2  is a side view showing the schematic structure of the electronic device according to the first embodiment. 
         FIG. 3  is a cross-sectional view showing deformation of a lid that occurs in a configuration of the related art. 
         FIG. 4  is a cross-sectional view showing the deformation of the lid that occurs in the configuration of the related art. 
         FIG. 5  is a cross-sectional view showing a schematic structure of an electronic component included in the electronic device. 
         FIG. 6  is an enlarged view of a portion A in  FIG. 5 . 
         FIG. 7  is a flowchart showing a method for manufacturing the electronic device according to the first embodiment. 
         FIG. 8  is a cross-sectional view showing a schematic structure of an electronic component included in an electronic device according to a second embodiment. 
         FIG. 9  is an enlarged view of a portion B in  FIG. 8 . 
         FIG. 10  is a cross-sectional view showing a schematic structure of an electronic component included in an electronic device according to a third embodiment. 
         FIG. 11  is a cross-sectional view showing a schematic structure of an electronic component included in an electronic device according to a fourth embodiment. 
         FIG. 12  is a flowchart showing a method for manufacturing an electronic device according to a fifth embodiment. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     1. First Embodiment 
     1.1. Electronic Device 
     First, an electronic device  1  according to a first embodiment will be described with reference to  FIGS. 1 to 6 . 
     In order to make a structure of the electronic device  1  easier to understand, a molded portion  9  in FIGS. and  2  is illustrated as being translucent. For convenience of the description, in the following drawings, an X axis, a Y axis, and a Z axis are shown as three axes orthogonal to one another. A direction along the X axis is referred to as an “X direction”, a direction along the Y axis is referred to as a “Y direction”, and a direction along the Z axis is referred to as a “Z direction”. An arrow side in each axis is also referred to as a “plus side”, a side opposite to the arrow is also referred to as a “minus side”. A plus side in the Z direction is also referred to as “upper”, and a minus side in the Z direction is also referred to as “lower”. 
     The electronic device  1  includes a printed substrate  2  having a plurality of lead terminals  3 , electronic components  5 ,  6  disposed on an upper surface of the printed substrate  2 , an IC chip  7  disposed on a lower surface of the printed substrate  2 , and the molded portion covering the printed substrate  2 , the electronic components  5 ,  6 , and the IC chip  7 . 
     Each of the electronic components  5 ,  6  is a sensor component. Specifically, the electronic component  5  is an X-axis angular velocity sensor that detects an angular velocity around the X axis, and the electronic component  6  is a three-axis acceleration sensor that independently detects an acceleration in the X-axis direction, an acceleration in the Y-axis direction, and an acceleration in the Z-axis direction. In the present embodiment, the electronic component  5  is the X-axis angular velocity sensor, but the present disclosure is not limited thereto, and the angular velocity sensor may be a Y-axis angular velocity sensor that detects an angular velocity around the Y axis or a Z-axis angular velocity sensor that detects an angular velocity around the Z axis. 
     The configuration of the electronic device  1  may be a six-axis composite sensor including three angular velocity sensors, that is, the X-axis angular velocity sensor, the Y-axis angular velocity sensor, and the Z-axis angular velocity sensor, and the three-axis acceleration sensor. The electronic components  5 ,  6  are not limited to sensor components, and may be, for example, vibration components such as vibrators. 
     The lead terminals  3  provided on the printed substrate  2  are electrically coupled to the electronic components  5 ,  6  and the IC chip  7  by wirings (not shown) provided on the upper and lower surfaces of the printed substrate  2 . The electronic components  5 ,  6  and the IC chip  7  are electrically coupled to each other by through wirings (not shown) or the like provided in the printed substrate  2 . 
     The molded portion  9  molds, that is, resin-seals, the printed substrate  2 , the two electronic components  5 ,  6 , and the IC chip  7 , so that the printed substrate  2 , the two electronic components  5 ,  6 , and the IC chip  7  are protected from moisture, dust, impact, and the like. A mold material forming the molded portion  9  is not particularly limited, for example, a thermosetting epoxy resin can be used, and the molded portion  9  can be molded by a transfer molding method. 
     Here, in the transfer molding method, the electronic components  5 ,  6  and the IC chip  7  are disposed in a molding die in a state of being mounted on the printed substrate  2 , the molding die is filled with a molten or softened mold material M via a gate, and then the mold material M is cured or solidified to form the mold portion covering the printed substrate  2 , the electronic components  5 ,  6 , and the IC chip  7 . However, since a space shape of the inside of the molding die becomes complicated, it is difficult to uniformly fill the molten or softened mold material M into the molding die. In particular, it is difficult to fill the mold material M on back sides of each of the electronic components  5 ,  6  and the IC chip  7  and spaces between each of the electronic components  5 ,  6  and the IC chip  7  and side surfaces of the molding die, and there is a chance that voids, which are air bubbles, are generated in such portions, which causes deterioration of characteristics of the electronic device  1  and breakage of the electronic device  1 . 
     In order to prevent the generation of such voids, a method for filling the molding die with the molten or softened mold material M at a higher pressure is considered. As a result, the molding material M can be more reliably filled even in a portion in which the mold material M is difficult to be filled, and the generation of the voids can be effectively prevented. However, in such a method, as shown in  FIGS. 3 and 4 , in an electronic component having a structure of the related art, a first lid  20  bonded to a base  10  is bent inward due to a pressure received from the mold material M, and an inertial element  30  may fail or characteristics of the electronic component may deteriorate. 
     In particular, as shown in  FIG. 3 , the first lid  20  may come into contact with the inertial element  30 , and the inertial element  30  may be damaged or the inertial element  30  cannot be appropriately driven. Further, as shown in  FIG. 4 , even when the first lid  20  does not contact with the inertial element  30 , an electrostatic capacitance is formed between the inertial element  30  and the first lid  20  or a magnitude of the originally formed electrostatic capacitance changes due to the first lid  20  approaching the inertial element  30 . Therefore, characteristics of the inertial element  30  change, in particular, zero-point drift occurs, and an angular velocity detection characteristic of the electronic component deteriorates. 
     Therefore, in the present embodiment, in order to prevent the deformation of the first lid  20  due to the pressure from the mold material M caused by the forming of the molded portion  9 , a double lid structure in which a second lid  22  is bonded to an upper surface of the first lid  20  via a rigid member  21  and a bending strength of the first lid  20  is increased is adopted. 
     Next, configurations of the electronic components  5 ,  6  will be described in detail. Since the electronic component  5  and the electronic component  6  have substantially the same configuration except that the electronic component  5  and the electronic component  6  are different in a shape of the inertial element  30  accommodated in the base  10  or the like, the electronic component  5  will be described as a representative, and the description of the electronic component  6  will be omitted. 
     As shown in  FIG. 5 , the electronic component  5  includes the base  10 , the first lid  20 , and the inertial element  30  that is an angular velocity sensor element accommodated in an internal space S formed by the base  10  and the first lid  20 . 
     The base  10  has a rectangular shape in a plan view from the Z direction, and includes a substrate  11  including a convex portion  14  for fixing the inertial element  30 , and a frame portion  12  provided so as to surround the inertial element  30  in the plan view, and the substrate  11  and the frame portion  12  are integrally formed. The inertial element  30  is fixed to an upper surface of the convex portion  14  via a bonding member  31 . Further, a seam ring  15  is provided on the upper surface of the frame portion  12 , and the first lid  20  is bonded to the seam ring  15 , so that the inner space S for accommodating the inertial element  30  is formed by the first lid  20  and a concave portion  13  of the base  10 . An external terminal  16  for electrically coupling the inertial element  30  and the IC chip  7  is provided on a lower surface of the substrate  11 . 
     The base  10  is made of, for example, various ceramics such as alumina and titania, but a constituent material of the base  10  is not particularly limited. 
     The first lid  20  has a rectangular shape in the plan view from the Z direction, the second lid  22  having a rectangular shape in the plan view is disposed on an upper surface side which is a surface of the first lid  20  opposite to an inertial element  30  side, the rigid member  21  is disposed between the first lid  20  and the second lid  22 , and the first lid  20  and the second lid  22  are bonded to each other by the rigid member  21 . Therefore, it is possible to prevent the deformation of the first lid  20  due to the pressure from the mold material M caused by the forming of the molded portion  9 . 
     The first lid  20  and the second lid  22  are made of, for example, a metal material such as Kovar, but constituent materials of the first lid  20  and the second lid  22  are not particularly limited. 
     An outer edge  201  of the first lid  20  is provided on a side closer to an outer edge  122  of the frame portion  12  with respect to a center of an upper surface  121  of the frame portion  12  of the base  10 , and is provided on an outer side with respect to the center of the upper surface  121  of the frame portion  12  and on an inner side with respect to the outer edge  122  of the upper surface  121  of the frame portion  12 . Specifically, as shown in  FIG. 6 , the outer edge  201  of the first lid  20  on a minus side in the X direction is disposed on the minus side in the X direction with respect to a center line CL of the frame portion  12  of the base  10  in the X direction, and is disposed on a plus side in the X direction with respect to the outer edge  122  of the upper surface  121  of the frame portion  12 . The outer edge  201  of the first lid  20  on the plus side in the X direction is disposed on the plus side in the X direction with respect to the center line CL of the frame portion  12  of the base  10  in the X direction, and is disposed on the minus side in the X direction with respect to the outer edge  122  of the upper surface  121  of the frame portion  12 . Further, the outer edge  201  of the first lid  20  in the Y direction is disposed on an outer side with respect to the center line CL of the frame portion  12  of the base  10  in the Y direction, and is provided on an inner side with respect to the outer edge  122  of the upper surface  121  of the frame portion  12 . 
     The second lid  22  is provided so as to face the first lid  20 , and an outer edge  221  of the second lid  22  protrudes from the outer edge  201  of the first lid  20 . Specifically, as shown in  FIG. 6 , a distance L 2  between the outer edge  221  of the second lid  22  and the center line CL of the frame portion  12  of the base  10  in the X direction is longer than a distance L 1  between the outer edge  201  of the first lid  20  and the center line CL of the frame portion  12  of the base  10  in the X direction. In the plan view from the Z direction, an outer shape of the second lid  22  is larger than an outer shape of the first lid  20 , that is, a length of the second lid  22  in the X direction is longer than a length of the first lid  20  in the X direction, and a length of the second lid  22  in the Y direction is longer than a length of the first lid  20  in the Y direction. 
     The rigid member  21  is disposed between the first lid  20  and the second lid  22 , and has a function of bonding the second lid  22  to the first lid  20 . The rigid member  21  protrudes from the outer edge  201  of the first lid  20  and is in contact with the upper surface  121  of the frame portion  12  of the base  10 . Therefore, it is possible to further prevent the deformation of the first lid  20  due to the pressure from the mold material M caused by the forming of the molded portion  9 . 
     As a constituent material of the rigid member  21 , an epoxy resin, a polyimide resin, a polyamide resin, or the like is suitable. A glass transition temperature Tg of the rigid member  21  is lower than a molding temperature T of the molded portion  9  by not more than 40° C. Specifically, when the molding temperature T of the molded portion  9  is 150° C., the glass transition temperature Tg of the rigid member  21  is 110° C. or higher, and when the molding temperature T of the molded portion  9  is 175° C., the glass transition temperature Tg of the rigid member  21  is 135° C. or higher. The glass transition temperature Tg of the rigid member  21  is preferably lower than the molding temperature T of the molded portion  9  by not more than 25° C. A flexural modulus FS of the rigid member  21  is preferably 10 GPa or more. 
     As described above, in the electronic device  1  according to the present embodiment, the second lid  22  is bonded, via the rigid member  21 , to the upper surface of the first lid  20  bonded to the frame portion  12  so as to accommodate the inertial element  30 , and thus the bending strength of the first lid  20  is increased, so that it is possible to prevent the bending deformation of the first lid  20  toward the inertial element  30  side due to the pressure from the mold material M caused by the forming of the molded portion  9 . 
     Since the outer edge  201  of the first lid  20  is provided on the side closer to the outer edge  122  of the frame portion  12  with respect to the center of the upper surface  121  of the frame portion  12  of the base  10 , it is possible to make it difficult for the first lid  20  to be deformed and bend toward the inertial element  30  side. 
     The rigid member  21  protrudes from the outer edge  201  of the first lid  20  and is in contact with the upper surface  121  of the frame portion  12  of the base  10 , and thus the bending strength of the first lid  20  is further increased, so that it is possible to further prevent the bending deformation of the first lid  20  toward the inertial element  30  side due to the pressure from the mold material M caused by the forming of the molded portion  9 . 
     The glass transition temperature Tg of the rigid member  21  is lower than the molding temperature of the molded portion  9  by not more than 40°, and thus when the molded portion  9  is formed, the rigid member  21  is less likely to be liquefied, and the second lid  22  can be prevented from being peeled off. 
     1.2. Manufacturing Method 
     Next, a method for manufacturing the electronic device  1  according to the first embodiment will be described with reference to  FIG. 7 . 
     As shown in  FIG. 7 , the method for manufacturing the electronic device  1  according to the present embodiment includes an inertial element fixing step, a first lid bonding step, a second lid bonding step, an electronic component mounting step, and a molded portion forming step. 
     1.2.1. Inertial Element Fixing Step 
     First, in step S 101 , the inertial element  30  is formed by a silicon substrate being vertically processed by a Bosch process which is a deep etching technique, the inertial element  30  is disposed in a region surrounded by the frame portion  12  of the base  10 , and the inertial element  30  is fixed to the upper surface of the convex portion  14  of the substrate  11  via the bonding member  31 . 
     1.2.2. First Lid Bonding Step 
     In step S 102 , the first lid  20  is welded and bonded to the upper surface  121  of the frame portion  12  of the base  10  via the seam ring  15  so as to accommodate the inertial element  30  between the first lid  20  and the base  10 . 
     1.2.3. Second Lid Bonding Step 
     In step S 103 , the second lid  22  is disposed such that the second lid  22  faces the first lid  20  via the rigid member  21  and the outer edge  221  protrudes from the outer edge  201  of the first lid  20 , and the second lid  22  is bonded to the first lid  20  by the rigid member  21 . 
     1.2.4. Electronic Component Mounting Step 
     In step S 104 , the electronic components  5 ,  6  manufactured in steps S 101  to S 103  and the IC chip  7  including a circuit for driving the electronic components  5 ,  6  are mounted on the printed substrate  2  having the lead terminals  3 . 
     1.2.5. Molded Portion Forming Step 
     In step S 105 , the printed substrate  2  on which the electronic components  5 ,  6  and the IC chip  7  are mounted is placed in the molding die, and the molded portion  9  covering the printed substrate  2 , the electronic components  5 ,  6 , and the IC chip  7  is formed by a transfer molding method in which the molding die is filled with the molten or softened mold material M at a high pressure. The molding temperature of the molded portion  9  is 150° C. to 175° C. 
     In the present manufacturing method, after the first lid  20  is bonded to the base  10 , the second lid  22  is bonded onto the first lid  20  via the rigid member  21 , but the present disclosure is not limited thereto. After the second lid  22  is bonded onto the first lid  20  via the rigid member  21 , the first lid  20  on which the second lid  22  is bonded may be bonded to the base  10 . 
     According to the method for manufacturing the electronic device  1  described above, it is possible to reduce the voids generated at the time of forming the molded portion  9 , and to prevent the bending deformation of the first lid  20  toward the inertial element  30  side due to the pressure from the mold material M caused by the forming of the molded portion  9 . Therefore, it is possible to obtain the electronic device  1  in which the breakage of the inertial element  30  and the deterioration of the characteristics of the electronic component  5 ,  6  are less likely to occur. 
     2. Second Embodiment 
     Next, an electronic device  1   a  according to a second embodiment will be described with reference to  FIGS. 8 and 9 . 
     The electronic device  1   a  according to the present embodiment is the same as the electronic device  1  according to the first embodiment except that a size of the second lid  22   a  of the electronic component  5   a  and the configuration of the rigid member  21   a  are different from those of the electronic device  1  according to the first embodiment. Differences from the first embodiment described above will be mainly described, the same elements will be denoted by the same reference numerals, and description thereof will be omitted. 
     As shown in  FIGS. 8 and 9 , a second lid  22   a  of the electronic component  5   a  is disposed such that the outer edge  221  is flush with the outer edge  201  of the first lid  20 . Specifically, a distance L 2  between the outer edge  221  of the second lid  22   a  and the center line CL of the frame portion  12  of the base  10  in the X direction is equal to the distance L 1  between the outer edge  201  of the first lid  20  and the center line CL of the frame portion  12  of the base  10  in the X direction. 
     The rigid member  21   a  is disposed between the first lid  20  and the second lid  22   a , and does not protrude outward from the outer edge  201  of the first lid  20  and the outer edge  221  of the second lid  22   a.    
     According to such a configuration, the outer edge  122  of the base  10  can be easily seen in the plan view from the Z direction, mounting on the printed substrate  2  can be performed with high positional accuracy, and the same effects as those of the electronic device  1  according to the first embodiment can be obtained. 
     3. Third Embodiment 
     Next, an electronic device  1   b  according to a third embodiment will be described with reference to  FIG. 10 . 
     The electronic device  1   b  according to the present embodiment is the same as the electronic device  1  according to the first embodiment except that a lid structure of an electronic component  5   b  is different from that of the electronic device  1  according to the first embodiment. Differences from the first embodiment described above will be mainly described, the same elements will be denoted by the same reference numerals, and description thereof will be omitted. 
     As shown in  FIG. 10 , the lid structure of the electronic component  5   b  is a triple lid structure including the first lid  20 , the second lid  22 , and a third lid  24 . That is, the third lid  24  is bonded onto the second lid  22  via a rigid member  23 . 
     In addition, an area of an XY plane, which is a size of each lid, has a relationship of an area of the first lid  20 ≤an area of the second lid  22 ≤an area of the third lid  24 . By increasing the areas of the lids from a lower lid to an upper lid, it is possible to make it more difficult for the first lid  20 , which is the first lid, to be deformed and bend toward the inertial element  30  side. In addition, a thickness of each of the second and subsequent lids may be thicker or thinner than a thickness of the first lid  20  which is the first lid. When the thickness of each of the second and subsequent lids is thicker than the thickness of the first lid  20 , strengths of the lids are increased and the lids are not easily deformed, and when the thickness of each of the second and subsequent lids is thinner than the thickness of the first lid  20 , the strength of the lids is easily finely adjusted, and a size of the electronic device  1   b  can be reduced. It should be noted that overlapping displacement caused by the bonding of the second lid  22  and the third lid  24  is within an allowable range as long as a part of the outer edge  221  of the second lid  22  and a part of an outer edge  241  of the third lid  24  overlap the outer edge  122  of the base  10  in a plan view from the Z direction, so that the deformation of the first lid  20  can be sufficiently prevented. 
     According to such a configuration, the bending strength of the first lid  20  can be further increased, and the same effects as those of the electronic device  1  according to the first embodiment can be obtained. 
     4. Fourth Embodiment 
     Next, an electronic device  1   c  according to a fourth embodiment will be described with reference to  FIG. 11 . 
     The electronic device  1   c  according to the present embodiment is the same as the electronic device  1  according to the first embodiment except that a lid structure of an electronic component  5   c  is different from that of the electronic device  1  according to the first embodiment. Differences from the first embodiment described above will be mainly described, the same elements will be denoted by the same reference numerals, and description thereof will be omitted. 
     As shown in  FIG. 11 , the lid structure of the electronic component  5   c  is a quadruple lid structure including the first lid  20 , the second lid  22 , a third lid  24 , and a fourth lid  26 . That is, the third lid  24  is bonded onto the second lid  22  via the rigid member  23 , and the fourth lid  26  is bonded onto the third lid  24  via a rigid member  25 . 
     In addition, the area of the XY plane, which is the size of each lid, has a relationship of an area of the first lid  20 ≤an area of the second lid  22 ≤an area of the third lid  24 ≤an area of the fourth lid  26 . By increasing the areas of the lids from a lower lid to an upper lid, it is possible to make it more difficult for the first lid  20 , which is the first lid, to be deformed and bend toward the inertial element  30  side. In addition, a thickness of each of the second and subsequent lids may be thicker or thinner than the thickness of the first lid  20  which is the first lid. When the thickness of each of the second and subsequent lids is thicker than the thickness of the first lid  20 , strengths of the lids are increased and the lids are not easily deformed, and when the thickness of each of the second and subsequent lids is thinner than the thickness of the first lid  20 , the strength of the lids is easily finely adjusted, and a size of the electronic device  1   c  can be reduced. It should be noted that overlapping displacement caused by the bonding of the second lid  22 , the third lid  24  and the fourth lid  26  is within an allowable range as long as a part of the outer edge  221  of the second lid  22 , a part of the outer edge  241  of the third lid  24 , and a part of an outer edge  261  of the fourth lid  26  overlap the outer edge  122  of the base  10  in the plan view from the Z direction, so that the deformation of the first lid  20  can be sufficiently prevented. 
     According to such a configuration, the bending strength of the first lid  20  can be further increased, and the same effects as those of the electronic device  1  according to the first embodiment can be obtained. 
     5. Fifth Embodiment 
     Next, a method for manufacturing the electronic device  1  according to a fifth embodiment will be described with reference to  FIG. 12 . 
     The method for manufacturing the electronic device  1  according to the present embodiment is the same as the method for manufacturing the electronic device  1  according to the first embodiment except that an order of the second lid bonding step and the electronic component mounting step is different from that of the method for manufacturing the electronic device  1  according to the first embodiment. Differences from the first embodiment described above will be mainly described, the same elements will be denoted by the same reference numerals, and description thereof will be omitted. 
     As shown in  FIG. 12 , the method for manufacturing the electronic device  1  according to the present embodiment is performed in the following order: the inertial element fixing step of step S 201 ; the first lid bonding step of step S 202 ; the electronic component mounting step of step S 203 ; the second lid bonding step of step S 204 ; and the molded portion forming step of step S 205 . 
     That is, after the electronic components  5 ,  6  manufactured in steps S 201  and S 202  and the IC chip  7  for driving the electronic components  5 ,  6  are mounted on the printed substrate  2 , the second lid  22  is bonded onto the first lid  20  via the rigid member  21 . 
     According to such a manufacturing method, the same effects as those of the method for manufacturing the electronic device  1  according to the first embodiment can be obtained.