Patent Publication Number: US-2021195767-A1

Title: Electronic control unit and method for manufacturing electronic control unit

Description:
TECHNICAL FIELD 
     The present invention relates to an electronic control unit and a method for manufacturing the electronic control unit. 
     BACKGROUND ART 
     Vehicles are equipped with electronic control units such as an engine control unit and an automatic transmission control unit. In recent years, the electrification of automobiles has been accelerating against the background of environmental problems and energy problems, and the number of electronic control units installed has increased significantly. Accordingly, there is a limited space for installing the electronic control units, and they have to be installed in an engine room, where the conditions are particularly severe in an automobile. Meanwhile, the size of the engine room has been reduced with the increase in the size of the cabin space for improving the comfort of automobiles. Thus, a large number of electronic control units and wire harnesses for electrically connecting them are located in the engine room, whose size is being reduced, and this causes problems of a reduced degree of freedom in layout, increased weight, and hence increased cost. Therefore, size reduction, weight reduction, and cost reduction are required for the electronic control units. 
     In addition, there is a tendency to shorten the wire harnesses. Accordingly, for example, the engine control unit will be installed at a position closer to the engine, and there is a concern about the effects of high heat and high vibration from the engine. Therefore, itis necessary to improve the heat resistance and vibration resistance of the electronic control units. As a solution to this, a structure is known in which a control board on which electronic components are mounted is sealed with resin (PTL 1). By sealing the control board with resin, the effect of heat on the electronic components can be reduced, and movement of the control board can be suppressed in a vibrating environment. 
     CITATION LIST 
     Patent Literature 
     PTL 1: JP 2007-273796 A 
     SUMMARY OF INVENTION 
     Technical Problem 
     In the module of PTL 1, the electronic circuit board is screw-fixed to a metal base, and sealing resin is charged from one end of the electronic circuit board to complete the molding. However, in order to reduce the weight and cost of the electronic control units in the future, it is essential to reduce the size of the metal base, resulting in a smaller fixed area of the electronic circuit board. Therefore, there is a concern that the electronic circuit board may be warped and deformed by the molding pressure of the sealing resin when the sealing resin is charged. The warping of the electronic circuit board leads to the lowering of the reliability of the electronic control units. 
     The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an electronic control unit with improved reliability. 
     Solution to Problem 
     To solve the above-mentioned problems, an electronic control unit according to an aspect includes: a control board on which an electronic component is mounted; and an enclosure in which the control board is sealed with resin, wherein the enclosure has a shape in which a volume of resin on one surface side of the control board is larger than a volume of resin on the other surface side, a gate mark is formed in the enclosure, a length of the gate mark in a thickness direction of the control board is formed to be larger than a thickness of the control board, the control board is located such that a side surface partially overlaps a projection region of the gate mark, and the control board is arranged toward the other surface side relative to a center of the gate mark. 
     Advantageous Effects of Invention 
     According to the present invention, it is possible to provide an electronic control unit with improved reliability. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross-sectional view of an electronic control unit according to a first embodiment. 
         FIG. 2  is an explanatory diagram illustrating a process of assembling the electronic control unit according to the first embodiment. 
         FIG. 3  is a side view of the electronic control unit according to the first embodiment. 
         FIG. 4  is an explanatory diagram illustrating a process of assembling an electronic control unit of a second embodiment. 
         FIG. 5  is a side view of the electronic control unit according to the second embodiment. 
         FIG. 6  is a cross-sectional view of an electronic control unit according to a third embodiment. 
         FIG. 7  is a flow diagram illustrating a process of molding the electronic control unit according to the third embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The following describes some embodiments with reference to the drawings. It should be noted that the embodiments described below do not limit the invention defined in the claims, and all of the elements and combinations thereof described in the embodiments are not necessarily essential for the solution of the invention. 
     First Embodiment 
       FIG. 1  is a cross-sectional view showing an electronic control unit of a first embodiment.  FIG. 2  is an explanatory diagram illustrating a process of assembling the electronic control unit according to the first embodiment. 
     As shown in  FIGS. 1 and 2 , an electronic control unit  30  includes a control board  2  on which an electronic component  1  such as a microcomputer is mounted, a connector  4 , and an enclosure  3 . The enclosure  3  has a gate mark  21   a  formed on the side surface opposite to the side on which the connector is formed. A side surface of the control board  2  is provided to be partially located in the projection region of the gate mark  21   a . In other words, it is arranged such that the thickness of the control board  2  is smaller than and overlaps the height (length in the thickness direction of the control board  2 ) of the gate mark  21   a  in the thickness direction of the enclosure (the thickness direction of the control board  2 ). The enclosure  3  has a shape in which the volume of the portion on the side on which the connector  4  is formed with respect to the control board  2  is larger than the volume of the portion on the side on which the connector  4  is not formed. The control board  2  is arranged closer to the side on which the connector  4  is not formed than the center of the gate mark  21   a  in the thickness direction of the enclosure  3 . 
     As shown in  FIG. 2( a ) , the connector  4  includes terminals  10  for connecting vehicle-side harnesses and the control board  2  and a housing  11  for aligning and holding the terminals  10  at a specified pitch. The material of the terminals  10  is preferably copper or a copper alloy from the viewpoints of conductivity, size reduction, and cost. A resin such as PBT (Polybutylene Terephthalate), PA (Polyamide)  66 , or PPS (Polyphenylene Sulfide) is preferably used as the material of the housing  11  because of their light weight and excellent heat resistance. 
     Next, as shown in  FIG. 2( b ) , a plurality of electronic components  1  such as microcomputers are mounted on the front and back surfaces of the control board  2 . A resin wiring board based on glass epoxy resin or the like is used for the control board  2 . For example, lead-free solder such as Sn—Cu solder, Sn—Ag—Cu solder, or Sn—Ag—Cu—Bi solder is used for connecting the electronic components  1  to the control board  2 . 
     Next, as shown in  FIG. 2( c ) , the connector  4  is mounted to an end portion of the control board  2 . To connect the terminals  10  of the connector  4  and the control board  2 , through hole portions  12  of the control board  2  into which the terminals  10  are inserted are connected with lead-free solder such as Sn—Cu solder, Sn—Ag—Cu solder, or Sn—Ag—Cu—Bi solder. The type of the connector  4  may be either a surface-mount type or a press-fit type. 
     As shown in  FIG. 2 ( d ) , a sub-assy  20  thus prepared is set in a mold  17  for resin sealing. The mold  17  includes an upper mold  18  and a lower mold  19  covering both sides of the control board  2  in the thickness direction. In this embodiment, after the sub-assy  20  is set on the upper mold  18 , which serves as a movable mold, the upper mold  18  is moved and set on the lower mold  19 , which serves as a fixed mold. 
       FIG. 3  is a side view of the electronic control unit according to the first embodiment. 
     Referring together to  FIG. 3 , a gate portion  21 , which is an injection port of sealing resin  5  as an example of the “resin”, is provided between the upper mold  18  and the lower mold  19 . The gate portion  21  has a rectangular opening, and is provided near one end  26  of the control board  2  so as to face it. In this manner, the sealing resin  5  injected into the mold  17  from the gate  2  flows in parallel with the plane direction of the control board  2 . Further, the height (length in the thickness direction of the control board  2 ) of the opening (cross section) of the gate portion  21  is formed to be larger than the thickness of the control board  2 . Although an example is shown in which the width (length in the surface direction of the control board  2 ) of the opening of the gate portion  21  is formed to be smaller than the width of the control board  2 , there is no such limitation. 
     Referring back to  FIG. 2( d ) ,  FIG. 2( d )  illustrates a progress of charging the sealing resin  5  injected from the gate portion  21 . The height of the cross section of the gate portion  21  is larger than the thickness of the control board  2 . This allows the sealing resin  5  to smoothly flow into the mold  17 . 
     Further, the connector  4  is provided on the downstream side of a resin flow path A on the upper surface side of the control board  2 . In other words, the connector  4  is formed on the side of the control board  2  opposite to the gate mark  21   a . This can better suppress the generation of voids due to the terminals  10  than in the case where the connector  4  is provided on the upstream side of the resin flow path A. 
     Here, the connector  4  is mounted on one surface (hereinafter, upper surface) side of the control board  2 . Since the connector  4  also needs to be sealed with the sealing resin  5 , the volume of the sealing resin  5  is larger on the opposite surface (hereinafter, lower surface) side of the control board  2  than the upper surface side. In this case, the charging of the sealing resin  5  is finished at different timings between the upper and lower surface sides of the control board  2  in the mold  17 , which causes a difference in pressure from the sealing resin  5  between the upper and lower surfaces of the control board  2 . This causes the control board  2  to be warped, and if the charging of the sealing resin  5  is finished while the control board  2  is warped, a residual strain occurs in the control board  2 . This residual strain causes cracks at the solder connection portions during manufacture, resulting in a lowered yield. Thus, in this embodiment, the difference in pressure from the sealing resin  5  between the upper and lower surfaces of the control board  2  is to be reduced when the sealing resin  5  is charged into the mold  17 , in order to suppress the warping of the control board  2 . That is, the difference in time at which the charging of the sealing resin  5  is finished between the upper and lower surface sides of the control board  2  is to be reduced. More preferably, the charging of the sealing resin  5  into the mold  17  is finished at the same timing on the upper and lower surface sides of the control board  2 . 
     In this embodiment, the volume of the sealing resin  5  is larger on the upper surface side of the control board  2  than on the lower surface side. Therefore, in order to reduce the difference in timing at which the charging of the sealing resin  5  is finished between the upper and lower surface sides of the control board  2 , the cross-sectional area (S 1 ′) of the resin flow path A on the upper surface side of the control board  2  is set to be larger than the cross-sectional area (S 2 ′) of the resin flow path B on the lower surface side of the control board  2 . A substrate  5  is arranged in the mold  17  such that the relationship between the area of the gate portion  21  on the upper surface side of the control board  2  (S 1 ) and the area of the gate portion  21  on the lower surface side of the control board  2  (S 2 ) is S 2 &lt;S 1 . 
     More preferably, the charging into the mold  17  is finished at the same timing on the upper and lower sides of the control board  2 . That is, the ratio of the cross-sectional areas of both resin flow paths A and B is set such that the charging of the sealing resin  5  injected from the resin flow path A and the sealing resin  5  injected from the resin flow path B into the mold  17  is finished at the same timing on the upper and lower surface sides of the control board  2 . 
     For example, the volume ratio between the volume of the sealing resin  5  on the upper surface side of the control board  2  (V 1 ) and the volume of resin on the lower surface side of the control board  2  (V 2 &lt;V 1 ) is substantially equal to the area ratio between the cross-sectional area of the gate portion  21  on the upper surface side of the control board  2  (S 1 ) and the cross-sectional area of the gate portion  21  on the lower surface side of the control board  2  (S 2 &lt;S 1 ). That is, the control board  2  is arranged in the mold  17  such that a relationship of V 1 :V 2 ≈S 1 :S 2  holds. 
     The width of the cross section of the resin flow path A and the width of the cross section of the resin flow path B are substantially equal to each other. In this manner, the sealing resin  5  spreads equally and in a balanced manner on both sides of the control board  2  while being charged. Therefore, the height,  22 , of the cross section of the resin flow path A is higher than the height,  23 , of the cross section of the resin flow path B. 
     In order to obtain a sufficient fluidity of the sealing resin  5  and charge the sealing resin  5  finely in the mold  17 , it is preferable to preheat the mold  17 , the sub-assy  20 , and the sealing resin  5 . The sealing resin  5  may be a thermosetting epoxy resin, an unsaturated polyester resin, or a thermoplastic resin. The sealing method may be transfer molding, compression molding, injection molding, or hot melt. The sealing resin  5  preferably has a coefficient of linear expansion of 10 to 30×10 −6 /° C. and a thermal conductivity of 0.5 to 3 W/mK, depending on the physical property values of the control board  2 . This can suppress the peeling between the sealing resin  5  and the control board  2 . 
     After the charging of the sealing resin  5  into the mold  17  is finished, the sealing resin  5  is cured in the mold  17 . After the curing, the mold  17  is opened, and the resin molded product is taken out. After excess regions of the gate portion  21  are removed, the electronic control unit  30  shown in  FIG. 2( e )  is completed. The gate mark  21   a  is formed when the excess regions of the gate portion  21  are removed. 
     In this embodiment, the resin enclosure  3  has a shape in which the volume of resin on one surface side of the control board  2  is larger than the volume of resin on the other surface side, the length of the gate mark  21   a  in the thickness direction of the control board  2  is formed to be larger than the thickness of the control board  2 , the control board  2  is located such that a side surface partially overlaps the projection region of the gate mark  21   a , and the control board  2  is arranged toward one surface side relative to the center of the gate mark  21   a . With this structure, it is possible to reduce the difference in the resin charging timing between one surface side and the other surface side of the control board  2  during the molding, suppress the warping of the control board  2  during the molding, and improve the reliability of the electronic control unit  30 . Further, since the control board  2  is resin-sealed, the size reduction, weight reduction, and cost reduction of the electronic control unit  30  can be achieved. 
     In addition, more preferably, in order to make the resin charging timings the same (substantially eliminate the difference), the area ratio (S 1 /S 2 ) between the area S 1  of the gate mark  21   a  on one surface side of the control board  2  and the area S 2  of the gate mark  21   a  on the other surface side of the control board  2  and the volume ratio (V 1 /V 2 ) between the volume V 1  of the enclosure  3  on one surface side of the control board  2  and the volume V 2  of the enclosure  3  on the other surface side of the control board  2  are formed to be substantially equal to each other. In this manner, the warping of the control board  2  can be further suppressed, and the reliability can be further improved. 
     Further, since the resin flow paths A and B branch off at the one end  26  of the control board  2  toward the upper and lower surfaces of the control board  2 , the pressure of the sealing resin  5  and  5  injected into the resin flow paths A and B can be adjusted by changing the arrangement and shapes of the gate portion  21  and the control board  2 . 
     The height  22  of the cross-sectional area of the resin flow paths A and B is set to be larger than the thickness of the control board  2 , and the control board  2  is arranged such that the one end  26  faces the resin flow paths A and B. In this manner, the pressure of the sealing resin  5  and  5  charged into the resin flow paths A and B can be adjusted by changing the arrangement of the one end  26  of the control board  2 . 
     Since the cross-sectional area (S 1 ′) of the resin flow path A on the side of the control board  2  on which the connector  4  is arranged is larger than the cross-sectional area (S 2 ′) of the resin flow path B on the side of the control board  2  on which the connector  4  is not arranged, it is possible to suppress the warping of the control board  2  while sealing the connector  4 . 
     Second Embodiment 
     A second embodiment will be described in comparison with the first embodiment. A mold  27  according to the second embodiment is different from the mold  17  according to the first embodiment only in the structure of the gate portion, and the other structures are the same as those of the mold  17  according to the first embodiment. Thus, the differences from the first embodiment will be mainly described. 
       FIG. 4  is an explanatory diagram illustrating a process of assembling an electronic control unit of the second embodiment. 
     Although the gate portion  21  has a single structure as shown in  FIG. 2( d )  in the first embodiment, in the second embodiment, the gate portion  21  has a double structure in which a first gate portion  24  and a second gate portion  25  are provided as shown in  FIG. 4( d ) . 
     That is, the first gate portion  24  and the second gate portion  25  are provided to the mold  27  so as to sandwich the control board  2 . They are shaped such that the size (area) of the first gate portion  24  is larger than the size (area) of the second gate portion  25 . 
       FIG. 5  is a side view of the electronic control unit according to the second embodiment. 
     As shown in  FIG. 4( d ) , the first gate portion  24  is provided to the upper mold  18 , and the second gate portion  25  is provided to the lower mold  19 . After the charging of the sealing resin  5  into the mold  27  is finished, the sealing resin  5  is cured in the mold  27 . After the curing, the mold  27  is opened, and the resin molded product is taken out. After the excess regions of the first gate portion  24  and the second gate portion  25  are removed, an electronic control unit  40  shown in  FIG. 4( e )  is completed. Gate marks  24   a  and  25   a  are formed in the enclosure  3  in the removal step. 
     As shown in  FIG. 4 ( e ) , a first gate mark  24   a  and a second gate mark  25   a  are formed in the enclosure  3 . The first gate mark  24   a  is formed in the portion of the enclosure  3  on the surface side of the control board  2  on which the connector  4  is arranged, and the second gate mark  25   a  is formed in the portion of the enclosure  3  on the surface side of the control board  2  on which the connector  4  is not arranged. The enclosure  3  has a shape in which the volume of the portion on the side on which the connector  4  is formed with respect to the control board  4  is larger than the volume of the portion on the side on which the connector  4  is not formed with respect to the control board  2 . The size (area) of the first gate mark  24   a  is larger than the size (area) of the second gate mark  25   a.    
     In this embodiment, the resin enclosure  3  has a shape in which the volume of resin on one surface side of the control board  2  is larger than the volume of resin on the other surface side, the enclosure  3  has the first gate mark  24   a  formed on one surface side of the control board  2  and the second gate mark  25   a  formed on the other surface side of the control board  2 , and the first gate mark  24   a  is larger than the second gate mark  25   a . With this arrangement, it is possible to suppress the warping of the control board  2  and improve the reliability as in the first embodiment. Further, by dividing the gate such that the one end  26  of the control board  2  does not overlap the projection region, the sealing resin  5  is less likely to contact the one end  26  of the control board, and it becomes easier to control the flow of the sealing resin  5 . Thus, it becomes easier to suppress the warping of the control board  2  than in the first embodiment. 
     In addition, as a further preferred example, formation is performed such that the volume ratio between the volume of the enclosure  3  on one surface side of the control board  2  and the volume of the enclosure  3  on the other surface side of the control board  2  and the area ratio between the area of the first gate mark  24   a  and the area of the second gate mark  25   a  are substantially equal to each other, so that the charging timings on the upper and lower sides (one surface side and the other surface side) of the control board  2  are the same. Thus, the warping of the board can be further suppressed, and the reliability is improved. 
     In addition, the length of the first gate mark  24   a  in the thickness direction of the control board  2  is made larger than the length of the second gate mark  25   a  in the thickness direction of the control board  2 , the length of the first gate mark  24   a  in the surface direction of the control board  2  is substantially equal to the length of the second gate mark  25   a  in the surface direction of the control board  2 , and the sizes of the first gate portion  24  and the second gate portion  25  in the height direction are changed. Thus, it is possible to efficiently adjust the resin injection speeds on the upper and lower sides and reduce the height. 
     Third Embodiment 
     A third embodiment will be described in comparison with the first embodiment. A mold  37  according to the third embodiment is different from the mold  17  according to the first embodiment only in the structure of the gate portion, and the other structures are the same as those of the mold  17  according to the first embodiment. Thus, the differences from the first embodiment will be mainly described. 
       FIG. 6  is a cross-sectional view of an electronic control unit according to the third embodiment. 
     The mold  37  is additionally provided with a pair of movable pins  31  and  32 . More specifically, the upper mold  38  is provided with a through hole  33 , and a movable pin  51  is inserted into the through hole  33 . The lower mold  39  is provided with a through hole  34 , and a movable pin  52  is inserted into the through hole  34 . 
       FIG. 7  is a flow diagram illustrating a process of molding the electronic control unit according to the third embodiment. 
     A process of molding an electronic control unit  50  will now be described. First, while the pair of movable pins  31  and  32  are inserted into the pair of through holes  33  and  34 , respectively, the mold  37  is closed such that the upper and lower sides of the control board  3  are arranged between the upper mold  38  and the lower side  39  (S 701 ). Then, the pair of movable pins  31  and  32  are brought close to the control board  2 , the control board  2  is supported from above and below with the pair of movable pins  31  and  32  (S 702 ), and the injection of the sealing resin  5  is started from the gate portion  21  (S 703 ). Next, it is determined whether the injection of the sealing resin  5  has been finished (S 704 ). If the determination of S 704  is affirmative (S 704 : YES), after the sealing resin  5  is cured, the pair of movable pins  31  and  32  are separated from the control board  2  and pulled out from the upper mold  38  and the lower mold  39 . (S 705 ). Finally, the upper mold  38  and the lower mold  39  are separated (S 706 ). 
     With this arrangement, since the pair of movable pins  31  and  32  support the control board  2 , it is possible to suppress the warping of the control board  2  while the sealing resin  5  is charged. 
     Although the embodiments of the electronic control unit according to the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various design changes can be made without departing from the spirit of the present invention defined in the claims. 
     REFERENCE SIGNS LIST 
     
         
           1  electronic component 
           2  control board 
           3  enclosure 
           4  connector 
           5  sealing resin 
           10  terminal 
           17  mold 
           21  gate portion 
           21   a  gate mark 
           22  height of cross section of resin flow path A 
           23  height of cross section of resin flow path B 
           24  first gate portion 
           24   a  gate mark 
           25  second gate portion 
           25   a  gate mark 
           26  one end 
           27  mold 
           30  electronic control unit 
           31  movable pin 
           32  movable pin 
           37  mold 
           40  electronic control unit 
         A resin flow path 
         B resin flow path