Patent Publication Number: US-2018054884-A1

Title: Circuit module

Description:
CLAIM OF PRIORITY 
     This application claims benefit of Japanese Patent Application No. 2016-161867 filed on Aug. 22, 2016, which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a circuit module, and more specifically, it relates to a circuit module on which a heat generating component is mounted. 
     2. Description of the Related Art 
     There have been circuit modules in which a heat generating component is mounted. For example, in a circuit module having a communication function, a communication integrated circuit is mounted. In the case of a communication integrated circuit, since transmission power is required, power consumption is large, and heat is generated. Therefore, it is necessary to radiate the heat generated from this integrated circuit, that is, heat generating component in order to cause the heat generating component to operate normally. Various heat radiating structures have been developed for this heat radiation. For example, a heat radiating structure is known in which, on the lower surface of a circuit board, part of a housing such as a cover member is deformed, and heat is radiated to the housing side. 
     An electronic control unit  900  having such a heat radiating structure is disclosed in Japanese Unexamined Patent Application Publication No. 2006-054481. The electronic control unit  900  will be described below with reference to  FIG. 7 . 
     In the electronic control unit  900 , a printed board  979  is sandwiched between a case  935  and a cover  971  and is fixed to a housing with screws that pass through the printed board  979 . Thermally conductive thin film layers made of copper foil are formed in parallel on a mounting surface and an opposite mounting surface  979   b  of the printed board  979  and inside the printed board  979 , and these layers are thermally separated from each other. The cover  971  is provided with a protrusion  973  that protrudes from the bottom of the cover  971  toward the mounting position of an electronic component  925  that is a heat generating component. A flexible thermally conductive material  975  is disposed between the top surface  973   a  of the protrusion  973  and the opposite mounting surface  979   b  of the printed board  979  corresponding to the mounting position of the electronic component  925  (that is, the projection region of the electronic component  925 ). A movement-preventing portion  977  for effectively preventing a thermally conductive material  975  from flowing out is provided around the top surface  973   a  of the protrusion  973 . 
     In the electronic control unit  900 , by such a heat radiating structure, heat generated from the electronic component  925  is radiated through the printed board  979  to the cover  971 . 
     In general, a heat generating component generates heat from both upper and lower surfaces thereof. However, in the case of a heat radiating structure such as that of the electronic control unit  900 , since heat can be radiated only on the lower surface side of the heat generating component, sufficient heat radiation performance cannot be obtained. It is possible to provide a similar heat radiating structure on the upper surface side of the heat generating component. However, when the heat generating component has a different shape, it is necessary to change the shape and/or dimensions of the housing such as the case according to the shape of the heat generating component, and the housing cannot be standardized. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of such a situation of the conventional art, and provides a circuit module that has improved heat radiation performance and that permits the standardization of the housing. 
     In an aspect of the present invention, a circuit module includes a circuit board on a first surface of which electronic components including at least one heat generating component are mounted, a plate member attached to the first surface of the circuit board so as to cover the heat generating component, and a cover member made of metal provided so as to face a second surface of the circuit board. The plate member includes a plane portion that extends so as to face the heat generating component, and leg portions that extend from the outer periphery of the plane portion, pass through the circuit board, protrude to the second surface side of the circuit board, and are connected to the cover member. 
     With this configuration, since heat on the upper surface side of the heat generating component is radiated through the plane portion and the leg portions of the plate member to the cover member, heat radiation performance can be improved. When the heat generating component has a different shape, it is only necessary to change the dimensions of each part of the plate member according to the shape of the heat generating component, and therefore the change in the shape and dimensions of the housing such as the case is not required. Therefore, the housing can be standardized while maintaining heat radiation performance. 
     It is preferable that the second surface of the circuit board be provided with a first pattern land disposed at a position corresponding to the heat generating component, that the cover member be provided with a protruding portion that protrudes toward the circuit board at a position corresponding to the first pattern land, and that a first heat radiating member be disposed between the protruding portion and the first pattern land. 
     With this configuration, since heat on the lower surface side of the heat generating component is radiated through the first pattern land of the circuit board and the first heat radiating member to the cover member, heat radiation performance can be further improved. 
     It is preferable that the second surface of the circuit board be provided with second pattern lands disposed at positions corresponding to the leg portions, and the first pattern land and the second pattern lands be connected, that a second heat radiating member be disposed between the plane portion and the heat generating component, and that the leg portions be connected to the second pattern lands and the protruding portion. 
     With this configuration, since heat on the upper surface side of the heat generating component is transferred through the second heat radiating member to the plane portion of the plate member, heat radiation performance can be improved. Since the leg portions are connected to the protruding portion of the cover member and are connected to the second pattern lands of the circuit board, heat on the upper surface side of the heat generating component can be radiated through the first pattern land connected to the second pattern lands and the first heat radiating member to the cover member. Therefore, heat radiation performance can be further improved. 
     It is preferable that the first heat radiating member and the second heat radiating member be both formed of silicone grease. 
     With this configuration, since the first heat radiating member and the second heat radiating member are both formed of silicone grease, the distance between the circuit board and the protruding portion of the cover member and the distance between the heat generating component and the plane portion of the plate member can be reduced compared to the case where the first heat radiating member and the second heat radiating member are silicone sheets, while filling the gap between the circuit board and the protruding portion of the cover member and the gap between the heat generating component and the plane portion of the plate member. Therefore, heat can be transferred more easily. 
     It is preferable that the plane portion be provided with an opening. 
     With this configuration, since the plane portion of the plate member is provided with the opening, silicone grease can be filled through the opening, and the check of the application of silicone grease and the control of the amount of application can be easily performed. 
     It is preferable that the plate member be formed of metal. 
     With this configuration, by forming the plate member of a highly thermally conductive metal such as copper or iron, heat can be transferred more easily. 
     It is preferable that the leg portions be provided at a plurality of places so as to surround the heat generating component. 
     With this configuration, since the leg portions are provided at a plurality of places, the plate member can be stably attached, and heat transferred to the plate member can be equally transferred to the leg portions. Therefore, heat can be radiated efficiently. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing the appearance of a circuit module according to an embodiment of the present invention; 
         FIG. 2  is a plan view of the circuit module; 
         FIG. 3  is an exploded perspective view showing main components of the circuit module; 
         FIG. 4  is a plan view of the lower surface of a circuit board; 
         FIG. 5  is an enlarged perspective view showing the appearance of the heat radiating structure of the circuit module; 
         FIG. 6  is an enlarged sectional view showing the heat radiating structure of the circuit module; and 
         FIG. 7  is a sectional view of an electronic control unit relating to a conventional example. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The circuit module of the present invention will be described below with reference to the drawings. The circuit module of the present invention is, for example, a small circuit module having a communication circuit used in wireless LAN (Local Area Network), Bluetooth (trademark), or the like, and is mounted and used in an electronic device such as a smartphone. The use of the circuit module of the present invention is not limited to the embodiment described below, and can be appropriately changed. In this specification, in the description with reference to the drawings, the words “right,” “left,” “rear,” front,” “upper,” and “lower” respectively designate the +X side, −X side, +Y side, −Y side, +Z side, and −Z side in the drawings. 
     EMBODIMENT 
     First, an outline of the structure of a circuit module  100  according to an embodiment of the present invention and main components of the circuit module  100  will be described with reference to  FIGS. 1 to 4 .  FIG. 1  is a perspective view showing the appearance of the circuit module  100 , and  FIG. 2  is a plan view of the circuit module  100 .  FIG. 3  is an exploded perspective view showing main components of the circuit module  100 , and  FIG. 4  is a plan view of the lower surface (second surface  30   b ) of a circuit board  30 . 
     As shown in  FIGS. 1 and 2 , the circuit module  100  includes a circuit board  30  that has a first surface  30   a  (upper surface) and a second surface  30   b  (lower surface) and has a rectangular shape, a case  17  that serves as a housing that houses the circuit board  30 , and a cover member  15  that is provided so as to face the second surface  30   b  of the circuit board  30  and that is made of metal. 
     Electronic components  41  including at least one heat generating component  41   a  and a non-heat generating component  41   b  are mounted on the first surface  30   a  of the circuit board  30 . The heat generating component  41   a  is, for example, a communication integrated circuit, and has a low cuboid shape that is square in plan view. The shape of the heat generating component  41   a  is not limited to a square shape, and may be, for example, a rectangular shape. A wiring pattern  39  is formed on the circuit board  30 , and the wiring pattern  39  and the plurality of electronic components  41  form an electronic circuit  40 . 
     A plate member  10  is attached to the first surface  30   a  of the circuit board  30  so as to cover the above-described heat generating component  41   a . The plate member  10  is attached in order to transfer heat generated from the heat generating component  41   a  to the cover member  15  made of metal. 
     As shown in  FIG. 3 , the plate member  10  includes a plane portion  10   a  that extends so as to face the heat generating component  41   a  that is square in plan view, a frame portion  10   b  that is formed so as to surround the plane portion  10   a  and that is substantially square in plan view, connecting portions  10   d  that connect the plane portion  10   a  and the frame portion  10   b , and leg portions  10   c  that extend from the outer periphery of the plane portion  10   a  through the connecting portions  10   d  and the frame portion  10   b . An opening  10   e  that is circular in plan view is formed in the center of the plane portion  10   a . The shape of the frame portion  10   b  is not limited to a substantially square shape, and may be, for example, a substantially rectangular shape. 
     The leg portions  10   c  of the plate member  10  are provided at a plurality of places so as to surround the heat generating component  41   a , and are formed so as to extend downward. In the circuit module  100 , the leg portions  10   c  are provided one in the center of each side of the substantially square frame portion  10   b.    
     The height of the plane portion  10   a  from the frame portion  10   b  corresponds to the vertical height of the heat generating component  41   a , and the dimensions of the frame portion  10   b  in the left-right direction and the front-rear direction correspond to the width and the depth of the heat generating component  41   a . The length of the leg portions  10   c  corresponds to the thickness of the circuit board  30  and the thickness of the protruding portion  15   a  of the cover member  15 . That is, the plate member  10  can be formed easily corresponding to the size of the heat generating component  41   a  and the thicknesses of the circuit board  30  and the cover member  15 . 
     The plate member  10  is formed of metal, for example, a highly thermally conductive, easily punchable and bendable, and solderable metal such as copper or iron. The plate member  10  may be formed of a highly thermally conductive material other than metal, such as ceramic. When the plate member  10  is formed of metal, processing such as providing the leg portions  10   c  is easy. 
     The circuit board  30  has, at positions corresponding to the plurality of leg portions  10   c  of the plate member  10 , a plurality of attachment holes  35  into which the plurality of leg portions  10   c  are inserted and attached. The attachment holes  35  are formed so as to function also as via holes  35   a  for electrically connecting the first surface  30   a  and the second surface  30   b  of the circuit board  30 . 
     As shown in  FIG. 4 , the second surface  30   b  of the circuit board  30  is provided with a first pattern land  31  disposed at a position corresponding to the heat generating component  41   a , and second pattern lands  32  disposed at positions corresponding to the leg portions  10   c  of the plate member  10 . The first pattern land  31  and the second pattern lands  32  are connected by connecting pattern lands  33 . 
     The first pattern land  31  is formed on the second surface  30   b  of the circuit board  30 , according to the shape and area of the heat generating component  41   a . In the circuit module  100 , the first pattern land  31  is formed in a square shape in plan view according to the shape of the heat generating component  41   a . The first pattern land  31  is provided with a plurality of via holes  37  for electrically connecting the first surface  30   a  and the second surface  30   b  of the circuit board  30 . By providing the plurality of via holes  37  in the first pattern land  31 , heat generated from the heat generating component  41   a  can be transferred from the first surface  30   a  to the second surface  30   b  of the circuit board  30 . 
     The second pattern lands  32  are provided so as to surround the above-described attachment holes  35 , and are formed in such a size that the leg portions  10   c  of the plate member  10  can be reliably attached to them by soldering. 
     The connecting pattern lands  33  are provided to connect the first pattern land  31  and the second pattern lands  32 . When the size of the first pattern land  31  is set large, the first pattern land  31  and the second pattern lands  32  may be provided so as to be directly in contact with each other without the interposition of the connecting pattern lands  33  therebetween. 
     As with the plate member  10 , the cover member  15  is formed of metal, for example, a highly thermally conductive metal such as cupper, iron, or aluminum. The cover member  15  forms the housing together with the case  17 . As shown in  FIG. 3 , the cover member  15  is provided with a protruding portion  15   a  that protrudes toward the circuit board  30  at a position corresponding to the first pattern land  31  of the circuit board  30 . The upper surface of the protruding portion  15   a  is flat, and is formed so as to be parallel to the second surface  30   b  of the circuit board  30 . 
     The protruding portion  15   a  of the cover member  15  is provided with a plurality of connection holes  15   b . The connection holes  15   b  are formed at a plurality of (four) positions corresponding to the attachment holes  35  provided in the circuit board  30 , for inserting the leg portions  10   c  of the plate member  10 . 
     The portion other than the protruding portion  15   a  of the cover member  15  is formed parallel to the circuit board  30 , is the same size as the case  17 , and is formed so as to cover the second surface  30   b  of the circuit board  30  as shown in  FIG. 1 . 
     Next, the heat radiating structure in the circuit module  100  will be described with reference to  FIGS. 5 and 6 .  FIG. 5  is an enlarged perspective view showing the appearance of the heat radiating structure of the circuit module  100 , and  FIG. 6  is an enlarged sectional view showing the heat radiating structure of the circuit module  100  as seen from line VI-VI of  FIG. 2 . 
     The heat radiating structure for the heat generating component  41   a  in the circuit module  100  includes the plate member  10 , the circuit board  30 , the cover member  15 , a first heat radiating member  21 , and a second heat radiating member  22  as shown in  FIGS. 5 and 6 . 
     The heat generating component  41   a  is mounted on the first surface  30   a  of the circuit board  30 . The plate member  10  is attached to the circuit board  30  so as to cover the heat generating component  41   a . The plane portion  10   a  of the plate member  10  is located over the upper surface of the heat generating component  41   a , and the plurality of leg portions  10   c  are inserted into the attachment holes  35  of the circuit board  30  and are connected to the circuit board  30 . 
     As shown in  FIG. 6 , the second heat radiating member  22  is disposed between the lower surface of the plane portion  10   a  of the plate member  10  and the upper surface of the heat generating component  41   a . The second heat radiating member  22  is formed of silicone grease  22   a , and is provided in close contact with each of the lower surface of the plane portion  10   a  of the plate member  10  and the upper surface of the heat generating component  41   a . The second heat radiating member  22  may not be formed of silicone grease  22   a  but may be a silicone sheet. By forming the second heat radiating member  22  of silicone grease  22   a , the distance between the plane portion  10   a  of the plate member  10  and the heat generating component  41   a  can be reduced, and heat radiation performance can be further improved. 
     Silicone grease  22   a  forming the second heat radiating member  22  is filled through the opening  10   e  of the plate member  10 . When the plate member  10  is attached to the first surface  30   a  of the circuit board  30 , a predetermined gap is provided between the plane portion  10   a  of the plate member  10  and the upper surface of the heat generating component  41   a . After the attachment of the heat generating component  41   a  and the plate member  10  to the circuit board  30 , silicone grease  22   a  is filled into the gap through the opening  10   e  of the plate member  10 . 
     By disposing the second heat radiating member  22  formed of silicone grease  22   a  between the plane portion  10   a  of the plate member  10  and the upper surface of the heat generating component  41   a , and filling the gap between the plane portion  10   a  of the plate member  10  and the upper surface of the heat generating component  41   a , heat from the upper surface of the heat generating component  41   a  can be efficiently transferred to the plate member  10 . 
     The gap between the circuit board  30  and the protruding portion  15   a  of the cover member  15 , and the gap between the heat generating component  41   a  and the plane portion  10   a  of the plate member  10  are for absorbing the variation in dimensions and the variation in attachment position of each member. When these variations are very small, and the protruding portion  15   a  of the cover member  15  and the first pattern land  31  of the circuit board  30  can be brought into close contact with each other, the first heat radiating member  21  may not be necessary. Likewise, when the plane portion  10   a  of the plate member  10  and the upper surface of the heat generating component  41   a  can be brought into close contact with each other, the second heat radiating member  22  may not be necessary. 
     The plurality of leg portions  10   c  are connected to the second pattern lands  32  of the circuit board  30  by soldering at first connecting places S 1  shown in  FIG. 6 . As a result, heat from the heat generating component  41   a  can be transferred through the second pattern lands  32  and the connecting pattern lands  33  of the circuit board  30  to the first pattern land  31 . 
     As shown in  FIGS. 5 and 6 , the cover member  15  made of metal is provided so as to face the second surface  30   b  of the circuit board  30 . The plurality of leg portions  10   c  pass through the circuit board  30 , protrude to the second surface  30   b  side of the circuit board  30 , and are connected to the protruding portion  15   a  of the cover member  15 . 
     The leg portions  10   c  are connected to the protruding portion  15   a  of the cover member  15  at second connecting places S 2  in the connection holes  15   b  of the cover member  15  shown in  FIG. 6 . When the cover member  15  is formed of a solderable metal such as copper or iron, the leg portions  10   c  are connected to the cover member  15  by soldering. 
     When the cover member  15  is formed of aluminum, since soldering cannot be performed, the leg portions  10   c  are connected to the cover member  15  by press-fitting the leg portions  10   c  into the connection holes  15   b  or bringing the leg portions  10   c  into strong contact with the cover member  15  by caulking the leg portions  10   c.    
     Even when the cover member  15  is formed of a metal such as copper or iron, the leg portions  10   c  may be connected to the cover member  15  by press-fitting the leg portions  10   c  into the connection holes  15   b  or caulking the leg portions  10   c . Alternatively, the leg portions  10   c  may be connected to the cover member  15  by filling silicone grease into the connection holes  15   b  of the cover member  15  in which the leg portions  10   c  are inserted. 
     By connecting the plurality of leg portions  10   c  to the cover member  15 , heat from the upper surface of the heat generating component  41   a  can be easily transferred through the plate member  10  to the cover member  15 . 
     As shown in  FIG. 6 , the first heat radiating member  21  is disposed between the protruding portion  15   a  of the cover member  15  and the first pattern land  31  of the circuit board  30 . As with the second heat radiating member  22 , the first heat radiating member  21  is formed of silicone grease  21   a , is provided in close contact with each of the upper surface of the protruding portion  15   a  of the cover member  15  and the first pattern land  31  of the circuit board  30 , and fills the gap between the protruding portion  15   a  of the cover member  15  and the first pattern land  31  of the circuit board  30 . 
     As with the second heat radiating member  22 , the first heat radiating member  21  may not be formed of silicone grease  21   a  but may be a silicone sheet. By forming the first heat radiating member  21  of silicone grease  21   a , the distance between the protruding portion  15   a  of the cover member  15  and the first pattern land  31  of the circuit board  30  can be reduced, and heat radiation performance can be further improved. 
     By disposing the first heat radiating member  21  between the protruding portion  15   a  of the cover member  15  and the first pattern land  31  of the circuit board  30 , heat transferred from the lower surface of the heat generating component  41   a  through the circuit board  30  and the first pattern land  31 , and heat transferred from the upper surface of the heat generating component  41   a  through the plate member  10  and the first pattern land  31  can be efficiently transferred to the cover member  15 . 
     The advantageous effects of this embodiment will be described below. 
     In the circuit module  100 , since heat on the upper surface side of the heat generating component  41   a  is radiated through the plane portion  10   a  and the leg portions  10   c  of the plate member  10  to the cover member  15 , heat radiation performance can be improved. When the heat generating component  41   a  has a different shape, it is only necessary to change the dimensions of each part of the plate member  10  according to the shape of the heat generating component  41   a , and therefore the change in the shape and dimensions of the housing such as the case  17  is not required. Therefore, the housing can be standardized while maintaining heat radiation performance. 
     Since heat on the lower surface side of the heat generating component  41   a  is radiated through the first pattern land  31  of the circuit board  30  and the first heat radiating member  21  to the cover member  15 , heat radiation performance can be further improved. 
     Since heat on the upper surface side of the heat generating component  41   a  is transferred through the second heat radiating member  22  to the plane portion  10   a  of the plate member  10 , heat radiation performance can be improved. Since the leg portions  10   c  are connected to the protruding portion  15   a  of the cover member  15  and are connected to the second pattern lands  32  of the circuit board  30 , heat on the upper surface side of the heat generating component  41   a  can be radiated through the first pattern land  31  connected to the second pattern lands  32  and the first heat radiating member  21  to the cover member  15 . Therefore, heat radiation performance can be further improved. 
     Since the first heat radiating member  21  and the second heat radiating member  22  are formed of silicone grease  21   a  and silicone grease  22   a , the distance between the circuit board  30  and the protruding portion  15   a  of the cover member  15  and the distance between the heat generating component  41   a  and the plane portion  10   a  of the plate member  10  can be reduced compared to the case where the first heat radiating member  21  and the second heat radiating member  22  are silicone sheets, while filling the gap between the circuit board  30  and the protruding portion  15   a  of the cover member  15  and the gap between the heat generating component  41   a  and the plane portion  10   a  of the plate member  10 . Therefore, heat can be transferred more easily. 
     Since the plane portion  10   a  of the plate member  10  is provided with the opening  10   e , silicone grease  22   a  can be filled through the opening  10   e , and the check of the application of silicone grease  22   a  and the control of the amount of application can be easily performed. 
     By forming the plate member  10  of a highly thermally conductive metal such as copper or iron, heat can be transferred more easily. 
     Since the leg portions  10   c  are provided at a plurality of places, the plate member  10  can be stably attached, and heat transferred to the plate member  10  can be equally transferred to the leg portions  10   c . Therefore, heat can be radiated efficiently. 
     As described above, in the circuit module of the present invention, since heat on the upper surface side of the heat generating component is radiated through the plane portion and the leg portions of the plate member to the cover member, heat radiation performance can be improved. When the heat generating component has a different shape, it is only necessary to change the dimensions of each part of the plate member according to the shape of the heat generating component, and therefore the change in the shape and dimensions of the housing such as the case is not required. Therefore, the housing can be standardized while maintaining heat radiation performance. 
     The present invention is not limited to the above-described embodiment, and various changes may be made without departing from the spirit of the present invention.