Abstract:
An image pickup device mounting structure includes an image pickup device, a reinforcing plate, and a flexible circuit board having at least one electrical component mounted thereon, wherein the reinforcing plate; the image pickup device and a part of the flexible circuit board are superimposed on each other, the reinforcing plate includes at least one cutout portion; and the electrical component is positioned on the part of the flexible circuit board and within the cutout portion.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a mounting structure of an image pickup device (installed in an optical device) to which a flexible printed circuit board is mounted. 
     2. Description of the Related Art 
     Optical devices such as digital cameras and cellular phones in which a flexible printed circuit board (hereinafter referred to as a flexible PCB) to which an image pickup device is mounted are known in the art. Electrical components are also mounted to the flexible printed circuit board around the image pickup device as needed. Among such electrical components, it is desirable for transistors, resistors, capacitors, and other specific electrical components, to be arranged in the vicinity of the image pickup device for the sake of noise reduction. On the other hand, when a flexible PCB to which an image pickup device is mounted is installed in an optical device, the image pickup device is superimposed with a reinforcing plate (mounting plate) and the flexible printed circuit board. The reinforcing plate possesses high stiffness and is fastened to the back of a portion of the flexible PCB to which the image pickup device is mounted to reinforce this portion of the flexible PCB to prevent the flexible PCB, which is poor in maintaining planarity, from bending. An example of such a structure is disclosed in Japanese unexamined patent publication No. 2002-330358. 
     However, in the above described configuration in which a mounting board is fastened to the back of a flexible PCB, the aforementioned electrical components (transistors, resistors, capacitors, and other specific electrical components) that are desirably arranged in the vicinity of the image pickup device cannot be arranged behind the image pickup device, and accordingly, these electrical components have to be arranged on the front of the flexible PCB around the image pickup device, which becomes a cause of an increase in size of the flexible PCB. 
     SUMMARY OF THE INVENTION 
     The present invention provides a mounting structure of an image pickup device to a flexible printed circuit board, wherein one or more electrical components can be mounted to the flexible printed circuit board in the close vicinity of the image pickup device in a space-saving manner in order to miniaturize the optical device which employs the mounting structure. 
     According to an aspect of the present invention, an image pickup device mounting structure is provided, including an image pickup device, a reinforcing plate, and a flexible circuit board having at least one electrical component mounted thereon, wherein the reinforcing plate, the image pickup device and a part of the flexible circuit board are superimposed on each other. The reinforcing plate includes at least one cutout portion. The electrical component is positioned on the part of the flexible circuit board and within the cutout portion. 
     It is desirable for the reinforcing plate to be bonded to the flexible printed circuit board to be integral with the flexible printed circuit board. 
     It is desirable for the reinforcing plate to be bonded to the flexible printed circuit board with a UV cure adhesive. 
     It is desirable for the reinforcing plate to be bonded to the flexible printed circuit board with an electrical insulating bonding agent. 
     It is desirable for the electrical component to be mounted on a side of the flexible printed circuit board on which the image pickup device is mounted. 
     Alternatively, the electrical component and the image pickup device can be mounted on opposite sides of the flexible printed circuit board, respectively. 
     It is desirable for the image pickup device and the flexible printed circuit board are bonded to each other. 
     It is desirable for the cutout portion to be a through-hole which extends through the reinforcing plate in a direction of thickness thereof. 
     It is desirable for the cutout portion to be a recess which is formed in the reinforcing plate in a direction of thickness thereof. 
     It is desirable for the image pickup device to be one of a CCD image sensor and a CMOS image sensor. 
     It is desirable for the reinforcing plate and the electrical component substantially to lie in a common plane. 
     It is desirable for the cutout portion to be one of a through-hole and a recess which is formed within the outer edge of the reinforcing plate. 
     In an embodiment, a mounting structure of an image pickup device to a front surface of a flexible printed circuit board is provided, the mounting structure including a reinforcing plate fixed to a back surface of the flexible printed circuit board so that the flexible printed circuit board is sandwiched between the reinforcing plate and the image pickup device, the reinforcing plate including at least one through-hole through which at least a part of the back surface of the flexible printed circuit board is exposed rearwardly; and at least one electrical component mounted on the part of the back surface of the flexible printed circuit board within the through hole in a manner to prevent the electrical component from interfering with the reinforcing plate. 
     It is desirable for the reinforcing plate and the electrical component to substantially lie in a common plane. 
     In an embodiment, a mounting structure of an image pickup device to a front surface of the flexible printed circuit board is provided, the mounting structure including a reinforcing plate fixed to the front surface of the flexible printed circuit board with the reinforcing plate sandwiched between the image pickup device and the flexible printed circuit board, the reinforcing plate including at least one through-hole through which at least a part of the front surface of the flexible printed circuit board is communicatively connected to a back surface of the image pickup device; and at least one electrical component mounted on the part of the front surface of the flexible printed circuit board so that the electrical component is aligned with the through-hole of the reinforcing plate so as to be prevented from interfering with the reinforcing plate. 
     It is desirable for the reinforcing plate and the electrical component to substantially lie in a common plane. 
     In an embodiment, a mounting structure of an image pickup device to a flexible printed circuit board is provided, the mounting structure including a reinforcing plate fixed to one of front and back surfaces of the flexible printed circuit board at a position corresponding to a position at which the image pickup device is mounted on the other of the front and back surfaces of the flexible printed circuit board; and at least one electrical component mounted on the flexible printed circuit board. The reinforcing plate includes at least one cutout portion which prevents the reinforcing plate from interfering with the electrical component. 
     According to the present invention, one or more electrical components can be arranged behind the image pickup device, which makes it possible to reduce the surface area of the flexible PCB to thereby achieve miniaturization of the optical device. 
     The present disclosure relates to subject matter contained in Japanese Patent Application No.2005-318983 (filed on Nov. 2, 2005), which is expressly incorporated herein by reference in its entirety. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be described below in detail with reference to the accompanying drawings in which: 
         FIG. 1  is an exploded perspective view of a lens unit which adopts a first embodiment of a mounting structure of an image pickup device to a flexible printed circuit board according to the present invention, showing the overall structure of the lens unit; 
         FIG. 2A  is an exploded perspective view of a portion of the lens unit shown in  FIG. 1  which includes an image pickup device, a flexible PCB and a reinforcing plate, showing a state before the image pickup device, the flexible PCB and the reinforcing plate are integrated in a superimposed manner; 
         FIG. 2D  is an exploded perspective view of the elements shown in  FIG. 2A , showing a state where the image pickup device, the flexible PCB and the reinforcing plate have been integrated in a superimposed manner; 
         FIG. 3A  is an exploded perspective view of a second embodiment of the mounting structure according to the present invention, showing structures of an image pickup device, a flexible PCB and a reinforcing plate of the lens unit; 
         FIG. 3B  is an exploded perspective view of the elements shown in  FIG. 3A , viewed from a different angle; and 
         FIG. 3C  is a perspective view of the elements shown in  FIGS. 3A and 3B , showing a state where the image pickup device, the flexible PCB and the reinforcing plate have been integrated in a superimposed manner. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
       FIG. 1  shows main elements of a lens unit  100  which adopts a first embodiment of a mounting structure of an image pickup device to a flexible printed circuit board. The first embodiment of the mounting structure is provided with an image pickup device  20 , a flexible PCB  30  and a reinforcing plate (mounting plate)  40 . Light which emerges from a lens module  10  is incident on the image pickup device  20  to be focused thereon. The flexible PCB  30  is fixed to the image pickup device  20  and is electrically connected thereto. The lens module  10  is provided with a housing (not shown) and a plurality of lens elements  11  which are housed in the housing and supported thereby. 
     For instance, a surface-mount type of CCD (charge-coupled device) or CMOS (complementary metal oxide semiconductor), image sensor having a substantially rectangular shape in plan configuration, can be adopted as the image pickup device  20 . The lens unit  100  is provided, in front of a front surface (imaging surface)  20   a  of the image pickup device  20 , with an aperture plate  21 , an optical low-pass filter  22  and a cover frame  23 , in that order from the lens module  10  side. 
     The flexible PCB  30  is provided with a flexible substrate made of, e.g., polyester film or a polyimide film, and a plurality of conductor traces formed on one surface (front surface)  31  of the flexible PCB  30  (e.g., a plurality of copper traces bonded to the front surface  31 ). A plurality of contacts  25  which project from the image pickup device  20  are soldered to a corresponding plurality of conductor traces of the flexible PCB  30 , respectively, thereby fixing a back surface  20   b  of the image pickup device  20  to the front surface  31  of the flexible PCB  30 . The strength of this fixation can be enhanced by bonding the image pickup device  20  and the flexible PCB  30  to each other. Using the flexible PCB  30  as a printed circuit board in this manner makes it possible to enhance the degree of freedom in placement of the lens module  10 . 
     Electrical components (e.g., transistors, resistors and capacitors)  35  which are to be arranged in the vicinity of the image pickup device  20  are mounted to a portion of the other surface (back surface)  32  of the flexible PCB  30  on the opposite side of the flexible PCB  30  from the image pickup device  20  (a portion of the back surface  32  of the flexible PCB  30  on which an orthogonal projection of the image pickup device  20  is formed when the image pickup device  20  and the flexible PCB  30  are positioned parallel to each other). For instance, each terminal of the electrical components  35  is inserted into a corresponding through hole of the flexible PCB  30 , which is made in the flexible PCB  30  to extend therethrough from the front surface  31  to the back surface  32 , to be electrically connected to a corresponding conductor trace on the front surface  31  of the flexible PCB  30 . By arranging the electrical components  35  on a portion of the back surface  32  which corresponds to the portion of the front surface  31  to which the image pickup device  20  is mounted in this manner, the electrical components  35  no longer need to be conventionally arranged around the image pickup device  20  on the same side surface of the flexible PCB  30 , which makes it possible to make the outside shape of the flexile PCB  30  smaller than that of the prior art, to thereby achieve miniaturization of the lens unit  100 . 
     The reinforcing plate  40  is made of a metal plate which possesses high stiffness (e.g., an aluminum or SUS plate), and is provided with an opening (cutout portion/through-hole)  41  which extends through the reinforcing plate  40  in the direction of the thickness thereof at a substantially central portion of the reinforcing plate  40 . The size and shape of the opening  41  are determined so that the electrical components  35  and the reinforcing plate  40  do not interfere with each other when the image pickup device  20 , the flexible PCB  30  and the reinforcing plate  40  are superimposed on each other and fixed to the lens module  10 . The reinforcing plate  40  is adhered to the flexible PCB  30  with a bonding agent which is dripped onto an inner edge  41   a  of the opening  41 . It is desirable that an electrical insulating bonding agent be used as this bonding agent, e.g., a UV cure adhesive can be used. The shape and the position of the opening  41  on the reinforcing plate  40  are optional and more than one of the opening  41  can be made in the reinforcing plate  40  so long as the electrical components  35  and the reinforcing plate  40  do not contact each other when the flexible PCB  30  and the reinforcing plate  40  are overlaid on each other. For instance, the opening  41  of the reinforcing plate  40  can be replaced by a recess or a groove which does not extend completely through the reinforcing plate  40  in the direction of the thickness thereof. However, it is desirable that the opening  41  (or such a recess or groove) not be in the shape of a regular polygon to ensure adequate adhesive strength between the flexible PCB  30  and the reinforcing plate  40 . 
     As described above, the image pickup device  20 , the flexible PCB  30  and the reinforcing plate  40  are superimposed as shown in  FIG. 2B  by mounting the image pickup device  20  on the front surface  31  of the flexile PCB  30  and bonding the flexile PCB  30  and the reinforcing plate  40  to each other. The image pickup device  20 , the flexible PCB  30  and therein forcing plate  40  which are thus integrated in a superimposed manner are fixed to the lens module  10  with the image pickup device  20  being positioned on the lens module by three set screws (not shown) which are inserted into three through holes  43 ,  44  and  45  of the reinforcing plate  40  to be screwed into three female screw holes (not shown) of the aforementioned housing (not shown) of the lens module  10 , respectively, which completes the lens unit  100 . In this manner, the electrical components  35  are arranged on the back surface  32  of the flexible PCB  30  so as to substantially lie in a common plane with that of the reinforcing plate  40 , to thereby achieve miniaturization of the lens unit  100  by providing the reinforcing plate  40 , that supports the image pickup device  20 , with the opening  41 , while the image pickup device  20 , the flexible PCB  30  and the reinforcing plate  40  are superimposed so as to be detachably attached to the lens module  10 , Accordingly, the position of the superimposed combination of the image pickup device  20 , the flexible PCB  30  and the reinforcing plate  40  can be easily readjusted and each of the lens module  10  and the superimposed combination of the image pickup device  20 , the flexible PCB  30  and the reinforcing plate  40  can be easily repaired or replaced. Moreover, the relative positions among the lens module  10 , the image pickup device  20 , the flexible PCB  30  and the reinforcing plate  40  can be easily readjusted. 
     Second Embodiment 
     A second embodiment of the mounting structure will be discussed hereinafter. The second embodiment of the mounting structure shown in  FIGS. 3A ,  3 B and  3 C is different from the first embodiment of the mounting structure shown in  FIGS. 1 ,  2 A and  2 B in that the second embodiment of the mounting structure is provided with an image pick up device  120 , a flexible PCB  130  and a reinforcing plate  140  instead of the image pick up device  20 , the flexible PCB  30  and the reinforcing plate  40  that are arranged from the lens module side, respectively. Apart from this difference, the second embodiment of the mounting structure has the same structure as the first embodiment of the mounting structure. 
     Similar to the flexible PCB  30 , the flexible PCB  130  is provided with a flexible substrate and a plurality of conductor traces formed on one surface (front surface)  131  of the flexible PCB  130 . A plurality of contacts  125  which project from the image pickup device  120  are soldered to a corresponding plurality of conductor traces of the flexible PCB  130 , respectively, thereby fixing a back surface  120   b  of the image pickup device  120  to the front surface  131  of the flexible PCB  130 . 
     Electrical components (e.g., transistors, resistors and capacitors)  135  which are to be arranged in the vicinity of the image pickup device  120  are mounted to a portion of the front surface  131  of the flexible PCB  130  which faces the back surface  120   b  of the image pickup device  120  (a portion of the front surface  131  of the flexible PCB  130  on which an orthogonal projection of the image pickup device  120  is formed when the image pickup device  120  and the flexible PCB  130  are positioned parallel to each other). For instance, each terminal of the electrical components  135  is soldered to a corresponding conductor trace on the front surface  131  of the flexible PCB  130  to thereby be electrically connected thereto. By arranging the electrical components  135  on a portion of the front surface  131  which faces the image pickup device  120  in this manner, the electrical components  135  no longer need to be conventionally arranged around the image pickup device  120  on the same side surface of the flexible PCB  130 , which makes it possible to make the outside shape of the flexile PCB  130  smaller than before to thereby achieve miniaturization of the lens unit  100 . 
     The reinforcing plate  140  is made of a metal plate which also possesses a high stiffness like that of the reinforcing plate  40 , and is provided with two openings (cutout portions/through-holes)  141  and  142 , each of which extends through the reinforcing plate  140  in the direction of the thickness thereof. The shapes and sizes of the two opening  141  and  142  are determined so that the electrical components  135  and the reinforcing plate  140  do not interfere with each other when the image pickup device  120 , the flexible PCB  130  and the reinforcing plate  140  are superimposed on each other and fixed to the lens module  10 . The reinforcing plate  140  is further provided at a substantially center thereof with a circular opening (through-hole)  148  which extends through the reinforcing plate  140  in the direction of the thickness thereof. The reinforcing plate  140  is adhered to the back surface  120   b  of the image pickup device  120  with a bonding agent which is dripped into the circular opening  148 . After the completion of this fastening of the reinforcing plate  140  to the image pickup device  120 , the image pickup device  120  is mounted to the flexible PCB  130  with the reinforcing plate  140  sandwiched between the image pickup device  120  and the flexible PCB  130 . It is desirable that an electrical insulating bonding agent be used as the bonding agent, e.g., a UV cure adhesive can be used. The shapes and the positions of the two openings  141  and  142  of the reinforcing plate  140  on the reinforcing plate  140  are optional. More than two openings corresponding to the two openings  141  and  142  can be made in the reinforcing plate  140  so long as the electrical components  135  and the reinforcing plate  140  do not contact each other when the flexible PCB  130  and the reinforcing plate  140  are overlaid on each other. For instance, each of the two openings  141  and  142  of the reinforcing plate  140  can be replaced by a recess or a groove which does not extend completely through the reinforcing plate  140  and which is recessed in a direction away from the flexible PCB  130 . 
     As described above, the image pickup device  120 , the flexible PCB  130  and the reinforcing plate  140  are superimposed on each other as shown in  FIG. 3C  by bonding the flexile PCB  130  and the reinforcing plate  140  to each other, and subsequently mounting the image pickup device  120  to the flexible PCB  130 . The image pickup device  120 , the flexible PCB  130  and the reinforcing plate  140  which are thus integrated in a superimposed manner are fixed to the lens module  10  with the image pickup device  120  being positioned on the lens module by four set screws (not shown) which are inserted into four through holes  133 ,  132 ,  134  and  136  of the flexible PCB  130  and corresponding four through holes  143 ,  144 ,  145  and  146  of the reinforcing plate  140  to be screwed into four female screw holes (not shown) of the aforementioned housing (not shown) of the lens module  10 , respectively, which completes the lens unit  100 . In this manner, the electrical components  135  can be arranged on the front surface  131  of the flexible PCB  130  so as to substantially lie in a common plane with that of the reinforcing plate  140   r  to thereby achieve miniaturization of the lens unit  100  by providing the reinforcing plate  140  that supports the image pickup device  120  with the two openings  141  and  142 , while the image pickup device  120 , the flexible PCB  130  and the reinforcing plate  140  are superimposed to become capable of being detachably attached to the lens module  10 . Accordingly, the position of the superimposed combination of the image pickup device  120 , the flexible PCB  130  and the reinforcing plate  140  can be easily readjusted and each of the lens module  10  and the superimposed combination of the image pickup device  120 , the flexible PCB  130  and the reinforcing plate  140  can be easily repaired or replaced. Moreover, the relative positions among the lens module  10 , the image pickup device  120 , the flexible PCB  130  and the reinforcing plate  140  can be easily readjusted. Note that other effects and functions are identical to those in the first embodiment of the mounting structure. 
     Obvious changes may be made in the specific embodiments of the present invention described herein, such modifications being within the spirit and scope of the invention claimed. It is indicated that all matter contained herein is illustrative and does not limit the scope of the present invention.