Abstract:
In a module in which a circuit board is integrally insert molded with a housing while semiconductor parts mounted on the circuit board are exposed, deformation of the circuit board caused by pressure on the circuit board by a mold for blocking the molding resin is reduced. In the module in which the circuit board is integrally insert molded with the housing while the semiconductor parts mounted on the circuit board are exposed, the deformation of the circuit board is reduced by placing a material, which has an elastic modulus smaller than the elastic modulus of the printed circuit board, in the projection area of the mold holding portion on the circuit board.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a circuit board mounting structure and a sensor using the same. 
       BACKGROUND ART 
       [0002]    By way of background of the art, there is Japanese Unexamined Patent Application Publication No. 2012-163504 (Patent Literature 1), which describes as follows: “In an air flow measurement device with a structure in which a sensing element for measuring the physical quantity, such as temperature and humidity, is provided on a circuit board in which an electronic circuit is formed, the electronic drive circuit is placed in a housing and the sensing element is exposed to the intake air. At least one or more insulating layers are provided between the circuit board and a glass or resin coated layer. Further, a conductor wiring for connecting the sensing element to the electronic drive circuit is provided below the insulating layer”. 
       CITATION LIST 
     Patent Literature 
       [0003]    Patent Literature 1: Japanese Unexamined Patent Application 
         [0004]    Publication No. 2012-163504 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0005]    An object of the present invention is to provide a circuit board structure that can reduce deformation of a circuit board in insert molding of the circuit board. 
       Solution to Problem 
       [0006]    A structure formed by insert molding according to the present invention is an insert molded article that includes a printed circuit board mounted with semiconductor parts, in which the area where the semiconductor parts on the printed circuit board are not mounted is covered with a first resin. A second resin with an elastic modulus smaller than the elastic modulus of the material of the printed circuit board is placed on the outside of the area where the main surface of the printed circuit board overlaps the first resin. 
       Advantageous Effects of Invention 
       [0007]    According to the present invention, it is possible to suppress deformation and crack of a circuit board when the circuit board is formed by insert molding. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0008]      FIG. 1  is a view of a mounting structure of a circuit module according to a first embodiment of the present invention. 
           [0009]      FIG. 2  is a cross-sectional view taken along line A-A of  FIG. 1  with respect to the circuit module according to the first embodiment of the present invention. 
           [0010]      FIG. 3  is a cross-sectional view showing a mold structure for forming a housing in the circuit module to secure the circuit module according to the first embodiment of the present invention. 
           [0011]      FIG. 4  is a cross-sectional view showing a mounting structure of a circuit board in which the housing is formed in the circuit module according to the first embodiment of the present invention. 
           [0012]      FIG. 5  is a view of a mounting structure of a circuit module according to a second embodiment of the present invention. 
           [0013]      FIG. 6  is a cross-sectional view taken along line A-A of  FIG. 5  with respect to the circuit module according to the second embodiment of the present invention. 
           [0014]      FIG. 7  is a cross-sectional view showing a mold structure for forming a housing in the circuit module to secure the circuit module according to the second embodiment of the present invention. 
           [0015]      FIG. 8  is a view of a mounting structure of a circuit module according to a third embodiment of the present invention. 
           [0016]      FIG. 9  is a cross-sectional view taken along line A-A of  FIG. 8  with respect to the circuit module according to the third embodiment of the present invention. 
           [0017]      FIG. 10  is a cross-sectional view showing a mold structure for forming a housing in the circuit module to secure the circuit module according to the third embodiment of the present invention. 
           [0018]      FIG. 11  is a cross-sectional view of a mounting structure of the circuit board in which the housing is formed in the circuit module according to the third embodiment of the present invention. 
           [0019]      FIG. 12  is a view of a mounting structure of a circuit module according to a fourth embodiment of the present invention. 
           [0020]      FIG. 13  is a cross-sectional view taken along line A-A of  FIG. 12  with respect to the circuit module according to the fourth embodiment of the present invention. 
           [0021]      FIG. 14  is a cross-sectional view showing a mold structure for forming a housing in the circuit module to secure the circuit module according to the fourth embodiment of the present invention. 
           [0022]      FIG. 15  is a cross-sectional view showing a mounting structure of the circuit board in which the housing is formed in the circuit module according to the fourth embodiment of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0023]    Currently, the internal combustion engine of a car or vehicle is provided with modules including an electronic circuit, such as a sensor, an engine control unit, and an electronic control throttle. For these modules, a circuit board on which semiconductor parts are mounted is used. The circuit board is accommodated within a housing. In the conventional approach, the circuit board on which the semiconductor parts are mounted has been secured to a plastic housing by bonding with an adhesive. However, this method requires a process of applying and curing the adhesive, which reduces the throughput of the module manufacturing process. Thus, there is also another method called insert molding. 
         [0024]    Insert molding is the method of placing a circuit board within a mold in such a way that the circuit board is secured by pouring resin around the perimeter of the circuit board to form a plastic housing. In the method of insert molding, melting resin is directly brought into contact with the circuit board, so that the circuit board can be bonded to the housing simultaneously when the resin is solidified. In this way, it is possible to simplify the bonding process. Here, when the housing resin is brought into contact with the semiconductor parts on the circuit board, a load due to shrinkage of the resin can be easily applied to the semiconductor as well as the joint portion of the semiconductor parts and the circuit board. For this reason, the housing should be formed by pouring resin in such a way that the mounting area of the semiconductor parts is enclosed by the mold so that the mounting area and the peripheral board are not covered with the resin. However, this method blocks the resin by pressing the mold against the board. Thus, there is a risk that the board may be deformed by stress from the mold and deformation and crack may occur in the board. 
       First Embodiment 
       [0025]    In the following embodiment, as an example of the insert molding using a board, an intake air flow sensor is described which is mounted on the internal combustion engine of a car. The intake air flow sensor is the flow sensor for measuring the flow rate of gas (air), which is provided to help control the intake air flow by an electronic fuel injector that is mounted on the internal combustion engine. The intake air flow sensor uses a sensor chip with a thin-walled diaphragm, in which the data measured by the sensor chip is collected and adjusted by a control chip and is output to the outside. 
         [0026]    Hereinafter, the first embodiment will be described with reference to the drawings. 
         [0027]      FIG. 1  shows a circuit module mounted with a semiconductor chip having a control circuit and the like.  FIG. 2  is a cross-sectional view of the semiconductor chip taken along line A-A of  FIG. 1 , showing the mounting structure of the circuit module. 
         [0028]    In  FIG. 2 , the circuit module is mounted with a first semiconductor chip  3  including a diaphragm  2  on a printed circuit board  1  of a material which is, for example, a lamination of Glass fiber and resin, as well as a second semiconductor chip  4  including a control circuit. The printed circuit board  1  and the first semiconductor chip  3  are attached with an adhesive  5 . Further, the printed circuit board  1  and the second semiconductor chip  4  are attached with a second adhesive  6 . Inside the printed circuit board  1 , a conductor wiring  8  and a wire pad  9  for the conductor wiring are formed. The first semiconductor chip  3  and the second conductor chip  4  are connected by a wire  7 , the conductive wiring  8 , and the wire pad  9 . Further, the second semiconductor chip  4  is connected to the conductor wiring  8  by the wire  7 . A potting  10  is provided in order to protect the wire  7 . 
         [0029]    For example, thermosetting resin such as epoxy resin and polyurethane resin, as well as thermoplastic resin such as polyimide and acrylic resin can be used for the first adhesive  5  bonding the printed board  1  to the first semiconductor chip  3 , the second adhesive  6  bonding the printed circuit board  1  to the second semiconductor chip  4 , and the potting  9  for the protection of the wire  7 . At the same time, a filler such as glass or mica can be mixed in the resin. 
         [0030]    With respect to the mounting structure of the circuit module described above, a manufacturing method for bonding the circuit module to the housing while the area where the semiconductor parts are mounted is exposed. 
         [0031]      FIG. 3  shows the mold structure for molding the circuit module while exposing the area where the semiconductor parts are mounted. The mounted circuit module and a connector lead  13  are placed into a mold including an upper mold  11  and a lower mold  12 , in which a hollow portion  14  is formed by clamping the circuit module by a clamp Portion  15  of the mold. Then, a resin  16  is injected into the hollow portion  14 . 
         [0032]    Next, as shown in  FIG. 14 , the wire pad  9  of the circuit module is connected to the connector lead  13  by a wire  17 . Further, in order to protect a circuit chamber  18  which is a space including the wire  17 , an upper cover  19  and a lower cover  20  are bonded to the top and bottom of the circuit chamber  18 , respectively. By the process described above, the circuit module and the housing are bonded together while the semiconductor parts on the circuit module are exposed, to complete the sensor module capable of outputting the detected signal from the circuit module to the outside. 
         [0033]    Here, the problem of the conventional insert molding as well as the features of the present embodiment will be described. When the circuit module is insert molded, the printed circuit board  1  should be clamped in the clamp portion  15  of the mold so that the resin  16  does not flow to the semiconductor parts. At this time, if the load of the clamp portion  15  is excessive, deformation will occur in the printed circuit board  1 . Further, if the thickness of the printed circuit board  1  varies and increases in the manufacturing process, the deformation could be further increased. In the conventional approach, nothing is placed in the position of the clamp portion  15 , and the molding resin is injected into the mold that is in direct contact with the printed circuit board  1 . In the present embodiment, as shown in  FIGS. 3 and 4 , a member  21  with an elastic modulus smaller than the average elastic modulus of the printed circuit board  1  is added to the mold clamp portion  15  on the printed circuit board  1 . As shown in  FIG. 3 , the housing is formed by injecting the resin  17  into the hollow portion  14  while clamping the area where the member  21  of the circuit module by the clamp portion  15  using the upper mold  11  and the lower mold  12 . At the same time, the circuit module and the housing are bonded together. 
         [0034]    The elastic modulus herein is the proportionality constant E when Hooke&#39;s law stating that the stress in an elastic body and the deformation are proportional to each other is expressed such that “the stress σ is proportional to the deformation ε, i.e., σ=Eε. 
         [0035]    For example, it is desirable to compare the elastic modulus of the member  21  with the elastic modulus of the printed circuit board  1  at the temperature 25° C. (room temperature). Further, the comparison of the elastic modulus can be performed between the elastic modulus of the member  21  and the elastic modulus of the base material of the printed circuit board  1 . 
         [0036]    In the above description, the comparison of the elastic modulus is made between the member  21  and the printed circuit board  1 , the principle of which is that the member  21  whose hardness is softer than that of the printed circuit board  1  is used. The hardness herein can be compared with Vickers hardness, Micro Vickers hardness, Brinell hardness, or Rockwell hardness at room temperature. 
         [0037]    For the member  21 , for example, thermosetting resin such as epoxy resin and polyurethane resin or thermoplastic resin such as polyimide and acrylic resin can be used as long as it satisfies the requirement described above. At the same time, a filler such as glass or mica can be mixed in the resin. 
         [0038]    In this manner, it is possible to reduce the load applied by the mold to the circuit board by the member  21  in the insert molding process. As a result, it is possible to reduce the occurrence of deformation in the printed circuit board  1 . 
       Second Embodiment 
       [0039]    Next, a description is given of a case where a wiring protective resist is placed on the wiring in the printed circuit board  1  of the first embodiment. 
         [0040]    In  FIG. 5 , the wiring  8  embedded in the printed circuit board  1  in  FIG. 1  is formed on the board, in which a wiring protective resist  23  is provided in order to protect the wiring  8 . 
         [0041]    The member  21  can also be applied to the configuration of the circuit board shown in  FIG. 5 . In this case, it is possible to use the same material as the wiring protective resist  23  as long as it satisfies the requirement that the elastic modulus of the member  21  is lower than the elastic modulus of the circuit board. In this embodiment, the member  21  can be placed at one time in the installation process of the wiring protective resist  23 . As a result, the bonding process can be simplified 
       Third Embodiment 
       [0042]    The mounting structure of a circuit module of a third embodiment is shown in  FIG. 8 . The third embodiment significantly differs from the first and second embodiments in that a member  24 , which corresponds to the member  21  in the first and second embodiments, is also added to the area of the joint portion  27  shown in  FIGS. 8 to 11 . 
         [0043]    In  FIG. 8 , a third semiconductor chip  25  is connected to the wire pad  9  by an outer lead  26  that is derived from the third semiconductor chip  25 . With respect to this mounting structure, insert modeling is performed in order to bond the circuit module to the housing while exposing the area where the semiconductor parts of the circuit module are mounted. The member  24  is placed on the main surface of the circuit board  1  in the area where the circuit board  1  overlaps the mold clamp portion  15  as well as the area including the joint portion  27  of the circuit board and the resin. 
         [0044]    According to this embodiment, there is no need to accurately place the member  24  in the contact area of the mold, so that the placement of the member  25  is easy compared to the first and second embodiments. Thus, it is possible to improve deterioration of the yield. In addition, it is possible to reduce the thermal stress generated after molding due to the difference in the linear expansion coefficient between the circuit board  1  and the resin  16  by placing the member  21  in the joint portion  27 . As a result, it is possible to reduce the deformation of the circuit board and to prevent separation of the joint portion. 
       Fourth Embodiment 
       [0045]    The present embodiment illustrates a circuit board in which a conductor wiring  22  is placed also in the clamp portion  15  and the joint portion  27 , to which the present invention is applied. 
         [0046]    Like the second and third embodiments, the wiring protective resist  23  is placed in the area except the wire pad  9  of the conductor wiring  22  and in the area  28  where the conductor wiring is exposed. In addition, in the present embodiment, the conductor wiring  22  is also placed in the cramp portion  15  and the joint portion  27 . Further, the member  24  is also placed over the conductor wiring  22  that is placed in the clamp portion  15  and the joint portion  27 . 
         [0047]    With respect to such a mounting structure, insert modeling is performed in order to bond the circuit module to the housing while exposing the area  28  where the semiconductor parts of the circuit module are mounted. The procedure of the insert molding using the mold is the same as the procedure described in the first to third embodiments. According to this embodiment, since the member  24  is placed over a wide range like the third embodiment, there is no need to accurately place the member  24  in the contact area of the mold, so that the placement of the member  25  is easy compared to the first and second embodiments. Thus, it is possible to improve deterioration of the yield. In addition, it is possible to reduce the thermal stress generated after molding due to the difference in the linear extension coefficient between the printed circuit board  1  and the resin  16 . As a result, it is possible to reduce the deformation of the circuit board and to prevent separation of the joint portion. 
         [0048]    The above description illustrates an example of the component in which the intake air flow sensor is insert molded. However, the present invention is not limited only to this example, and it can be used for any component in which a circuit board, especially, a printed circuit board is insert molded. 
         [0049]    The invention made by the present inventors has been concretely described based on the embodiments. However, it is needless to say that the present invention is not limited to the above embodiments and various modifications and alterations can be made within the scope of the present invention. 
       LIST OF REFERENCE SINGS 
       [0050]      1  . . . printed circuit board,  2  . . . diaphragm ,  3  . . . first semiconductor chip,  4  . . . second semiconductor chip,  5  . . . first adhesive,  6  . . . second adhesive,  7  . . . wire,  8  . . . conductor wiring,  9  . . . wire pad,  10  . . . potting,  11  . . . upper mold,  12  . . . lower mold,  13  . . . connector lead,  14  . . . hollow portion,  15  . . . clamp portion,  16  . . . resin,  17  . . . wire,  18  . . . circuit chamber,  19  . . . upper cover,  20  . . . lower cover,  21  . . . member,  22  . . . conductor wiring,  23  . . . wiring protective resist,  24  . . . member,  25  . . . third semiconductor chip,  26  . . . outer lead,  27  . . . joint portion,  28  . . . area where the conductor wiring is exposed