Abstract:
An image sensor module includes a lens member, a resin frame that holds the lens member, a diaphragm formed on the lens member, an image sensor chip that receives light converged by the lens member, and a supporting board upon which the image sensor chip is mounted. The board is fixed to the bottom side of the resin frame. The diaphragm includes an opening for allowing the passage of light, and a light-shielding portion which is entirely held in contact with the lens member. The lens member is glued to the frame so that any additional fixing element such as a lens cap is unnecessary.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image sensor module incorporated in a device having an image capturing function, such as a digital camera, mobile phone or camera-integrated watch. The present invention also relates to a method of making such an image sensor module. 
     2. Description of the Related Art 
     Conventionally, an image capturing device such as a digital camera incorporates an image sensor module for converting optical image data of an object into electric signals. An example of prior art image sensor module is illustrated in  FIG. 8 . In the prior art image sensor module  200  shown in the figure, an image sensor chip  1  and internal terminals Ta electrically connected to the image sensor chip  1  are enclosed in a package  209 . The image sensor chip  1  is formed, at the upper surface thereof, with a light receiving portion  11 . When the light receiving portion  11  receives light, image signals with output levels corresponding to the received amount of light are generated by photoelectric conversion elements and outputted from electrode pads. The package  209 , which protects the image sensor chip  1 , is formed with an opening which is closed with a cover glass  291 . Each of the internal terminals Ta is connected to a corresponding external terminal Tb projecting outward of the package  209 , thereby providing a connection terminal T′. 
     As shown in  FIG. 9 , the image sensor module  200  is used in combination with a lens  103  for converging light reflected by an object onto the image receiving portion  11 . Specifically, for using the image sensor module  200 , a lens mount  204  for supporting the lens  103  is prepared. As shown in the figure, the lens mount  204  is so disposed as to cover the image sensor module  200 . 
     In the above prior art, a lens mount  204  need be separately prepared from the image sensor module  200 . Therefore, the number of parts and the process steps for the manufacturing are increased as a whole, which results in a high manufacturing cost. Further, since the lens mount  204  need be larger than the image sensor module  200 , the entire size is inevitably increased. 
       FIG. 10  illustrates another prior art image sensor module disclosed in JP-A-10-41492. As shown in the figure, the image sensor module  100  includes an image sensor chip  1  and a lens  103  which are supported by a frame  104 . 
     The image sensor chip  1  is mounted on an upper surface of a substrate  2 . The substrate  2  has a lower surface formed with connection terminals T, which are electrically connected to the image sensor chip  1 . The frame  104  includes a chip case portion  104   a  for covering the image sensor chip  1  and a lens mount portion  104   b  located above the chip case portion  104   a . The frame  104  is formed of a resin so that the chip case portion  104   a  and the lens mount portion  104   b  are integral with each other to provide a generally cylindrical configuration as a whole. The chip case portion  104   a  has a flat lower end surface to which the substrate  2  is attached. 
     The lens mount portion  104   b  is internally formed with a stepped portion  140  upon which the lens  103  is placed. Thus, the inner space of the frame  104  is sealed by the substrate  1  and the lens  103 . Use is made of a lens cap  108  for holding the lens  103  in place relative to the stepped portion  140  so that the lens  103  does not come out of the lens mount portion  104   b . More specifically, the lens cap  108  is fitted outwardly to the lens mount portion  104   b  from above, so that the peripheral portion of the lens  103  is sandwiched between a thick wall portion  108   a  of the lens cap  108  and the stepped portion  140 . At this time, the lens  103  and the image sensor chip  1  are so arranged that the optical axis of the lens  103  is perpendicular to the light receiving portion  11 . Further, the distance between the lens  103  and the image sensor chip  1  is so set that parallel light entering the lens portion  103  forms a proper image on the light receiving portion  11 . 
     An image sensor module often includes a diaphragm for increasing the depth of field so that the precise focusing is unnecessary. In this image sensor module  100 , the lens cap  108  is formed with an aperture  107  as a diaphragm. 
     Unlike the image sensor module  200 , the image sensor module  100  incorporates the lens  103 , so that any external lens or lens support is not necessary. Further, since the lens  103  is fixed to the frame  104  just by fitting the lens cap  108  to the frame  104 , the module can be assembled at a relatively low cost. Moreover, unlike the image sensor module  200 , the image sensor chip  1  is used as it is (i.e., without being packaged). Therefore, the image sensor module  100  can be made smaller in entire area surface than the image sensor module  200 . 
     However, since the image sensor module  100  utilizes the lens cap  108 , the overall cost of the structural parts will be high accordingly. 
     Further, recently, there is a demand for thickness reduction of an image sensor module for incorporation in a thin device such as a mobile phone or a watch for example. However, due to the additional thickness of the lens cap  108 , the image sensor module  100  is not a suitable unit to provide a device that should be compact. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide an image sensor module which is relatively small in overall size and which can be manufactured at a relatively low cost. Another object of the present invention is to provide a method for making such an image sensor module. 
     According to a first aspect of the present invention, there is provided an image sensor module that includes: a lens member including a first surface and a second surface opposite to the first surface; a frame that holds the lens member; a diaphragm formed on the first surface of the lens member, the diaphragm including an opening and a light-shielding portion; an image sensor chip that receives light converged by the lens member; and a board upon which the image sensor chip is mounted, and which is fixed to the frame. The light-shielding portion of the diaphragm is entirely held in contact with the lens member. 
     Preferably, the first surface of the lens member may be provided with a retreated portion corresponding in position to the opening of the diaphragm. 
     Preferably, the frame may be internally provided with a lens holding space that accommodates the lens member in a manner such that the lens member avoids protruding from the frame. 
     Preferably, the inner diameter of the lens holding space may be smaller than the outer diameter of the lens member, so that the lens member is press-fitted into the lens holding space. 
     Preferably, the second surface of the lens member may be provided with a convex light-emitting portion. 
     Preferably, the lens member may include a cylindrical wall surrounding the convex light-emitting portion. 
     Preferably, the cylindrical wall may include a flat reference contact surface for positioning the lens member relative to the frame, wherein the convex light-emitting portion avoids protruding beyond the reference contact surface. 
     Preferably, the reference contact surface may be perpendicular to an optical axis of the lens member. 
     Preferably, the module of the present invention may further include a bonding layer for fixing the lens member to the frame. 
     Preferably, the lens member may be fixed to the frame by ultrasonic bonding. 
     Preferably, the module of the present invention may further include an optical filter disposed between the lens member and the image sensor chip. 
     Preferably, the frame may be internally provided with a chip accommodating space that accommodates the image sensor chip. The chip accommodating space may be hermetically closed by the board and the optical filter. 
     Preferably, the diaphragm may be made of light-shielding ink. 
     According to a second aspect of the present invention, there is provided a method of making an image sensor module. This method includes the steps of: mounting an image sensor chip onto a supporting board; forming an intermediate assembly by fixing the board to a lens holding frame; fixing the intermediate assembly to an external element by reflow soldering; and fixing a lens member to the lens holding frame. 
     Preferably, the fixing of the lens member may be performed by using a glue, or by press-fitting the lens member into the lens holding frame, or by ultrasonic bonding. 
     Other features and advantages of the present invention will become clearer from the detailed description given below with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic sectional view illustrating an image sensor module embodying the present invention; 
         FIG. 2  is an exploded view of the image sensor module of  FIG. 1 ; 
         FIG. 3  is a schematic sectional view illustrating a lens member and a resin package of an image sensor module according to another embodiment of the present invention; 
         FIGS. 4A and 4B  are schematic sectional views illustrating process steps for fixing a lens member to a resin package according to another embodiment of the present invention; 
         FIGS. 5A and 5B  are schematic sectional views illustrating process steps for fixing a lens member to a resin package according to another embodiment of the present invention; 
         FIGS. 6A-6C  are sectional views illustrating the process steps for making the image sensor module of  FIG. 1 ; 
         FIG. 7  is a schematic sectional view showing another example of lens member according to the present invention; 
         FIG. 8  is a schematic sectional view illustrating an example of prior art image sensor module; 
         FIG. 9  is a schematic sectional view illustrating the image sensor module of  FIG. 8  in use; and 
         FIG. 10  is a schematic sectional view illustrating another example of prior art image sensor module. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Preferred embodiments of the present invention will be described below in detail with reference to the  FIGS. 1-7  and  9 . In these figures, the elements or portions which are identical or similar to those of the prior art image sensor module shown in  FIGS. 8 and 10  are designated by the same reference signs as those used for the prior art module. 
     As shown in  FIGS. 1 and 2 , an image sensor module A according to the present invention includes a substrate  2  on which an image sensor chip  1  is mounted, a lens member  3 A, and a resin frame  4 A for accommodating the image sensor chip  1  and the lens member  3 A. 
     The image sensor chip  1  may be a solid state image sensor of a CCD type or a MOS type for example, and has a flat and rectangular configuration, as seen from  FIG. 2 . The image sensor chip  1  is provided with a light receiving portion  11  under which a plurality of photoelectric conversion elements (not shown) are arranged in a matrix. Further, a plurality of electrode pads  12  are formed on the upper surface of the image sensor chip. Upon receiving light at the light receiving portion  11 , each of the photoelectric conversion elements generates an electric signal with a level corresponding to the received amount of light and outputs the signal from a corresponding one of the electrode pads  12 . 
     As shown in  FIG. 2 , the substrate  2 , which may be a flat rectangular printed circuit board, is large enough to close the lower opening of a chip case portion  42 . The substrate  2  has an obverse surface formed with a wiring pattern (not shown) provided with a plurality of conductor pads  21 . Each of the conductor pads  21  is connected to a corresponding one of the electrode pads  12  of the image sensor chip  1  via a wire W. The substrate  2  has a reverse surface provided with a plurality of electrode terminals T for surface-mounting the image sensor module A to an external device. The electrode terminals T are electrically connected to the wiring pattern on the obverse surface of the substrate  2  via non-illustrated through holes. 
     As shown in  FIG. 1 , the lens member  3 A includes an effective lens portion  31  for converging the light reflected by an object, and a support portion  32 A surrounding the lens portion  31 . The lens portion  31  and the support portion  32 A are formed of a light-permeable material such as acryl or PMMA (polymethyl methacrylate) and integral with each other. 
     The lens portion  31  has a downwardly convex lower surface  30   a  for facing the image sensor chip  1 . The lens portion  31  has an upper surface which consists of a central concave region  30   b  and a flat region  30   c  surrounding the concave region  30   b.    
     The support portion  32 A includes, at the lower end thereof, a flat support surface S perpendicular to the optical axis Ax of the lens portion  31 . The support surface S, in other words, is parallel to a reference plane (not shown) of the lens portion  31 , wherein the “reference plane” is perpendicular to the axis Ax. 
     Further, the support portion  32 A has a flat upper surface  33  connected to the flat region  30   c  of the lens portion  31 . The support portion  32 A is cylindrical to surround the lens portion  31 . The lower end of the support portion  32 A serves as the support surface S. The thickness Sd of the support portion  32 A is larger than the thickness Ld of the lens portion  31  so that the convex lower surface  30   a  of the lens portion  31  does not project downward beyond the support surface S. With this structure, the flattening process of the support surface S can be performed without damaging the lens portion  31 . 
     As shown in  FIG. 2 , the flat region  30   c  of the upper surface of the lens member  3 A is covered with a light shielding layer  5 , so that light is prevented from passing through portions other than the concave region  30   b . Specifically, the light shielding layer  5  includes a circular aperture  51  at a portion corresponding to the concave region  30   b , thereby serving as a diaphragm. The aperture  51  is relatively small in diameter to increase the depth of field. Thus, the image sensor module A or a device incorporating the module need not include any focusing mechanism, which is advantageous to reducing the size of the module or the device. The diameter of the aperture  51  is set to the smallest value so long as it allows light of the amount necessary for capturing images to reach the image sensor chip  1 . 
     The light shielding layer  5  may be formed by printing a light-resistant coating material (e.g. black coating) on the upper surface of the lens member  3 A. For this printing, use may be made of a printing roller carrying such a coating material. Simply by running the roller over the lens member  3 A, the aperture  51  is readily made due to the concave region  30   b  with which the roller does not come into contact. 
     The resin frame  4 A is made of a light shielding resin such as a black epoxy resin. As shown in  FIG. 2 , the resin frame  4 A includes a chip case portion  42  and a lens mount portion  41 A disposed above the chip case portion  42 . As shown in FIG.  1 , the chip case portion  42  and the lens mount portion  41 A are integral with each other so that the respective inner spaces communicate with each other. 
     As shown in  FIG. 2 , the chip case portion  42  is shaped like a box having an upper opening and a lower opening. The lens mount portion  41 A is generally cylindrical to receive the lens member  3 A. As shown in  FIG. 1 , the chip case portion  42  has a flat substrate base surface BS 1  coming into contact with the substrate  2 , whereas the lens mount portion  41 A has a flat lens base surface BS 2  for supporting the lens member  3 A. 
     As shown in  FIG. 2 , the lens mount portion  41 A is formed with a stepped portion  40 A projecting radially inward from the inner wall surface of the lens mount portion  41 A. The stepped portion  40 A has an upper surface serving as the lens base surface BS 2 . With this structure, when the substrate  2  and the lens member  31  are assembled with the resin frame  4 A as shown in  FIG. 1 , the resin frame  4 A is closed by the substrate  2  and the lens member  3 A. 
     As shown in  FIG. 1 , the thickness Sd of the support portion  32 A is smaller than a depth Wd measured between the top of the lens mount portion  41 A and the stepped portion  40 A. Thus, the lens member  3 A does not protrude upward beyond the top of the lens mount portion  41 A. 
     The substrate base surface BS 1  and the lens base surface BS 2  are parallel to each other. Thus, when the substrate  2  and the lens member  31  are mounted to the resin frame  4 A, the non-illustrated reference plane of the lens portion  31  is parallel to the light receiving portion  11  of the image sensor chip  1 . Further, the distance between the substrate base surface BS 1  and the lens base surface BS 2  is so set that parallel light entering the lens portion  31  forms a proper image on the light receiving portion  11 . 
     The image sensor module A is assembled as follows. The substrate  2  is attached to the chip case portion  42  of the resin frame  4 A by bringing the upper surface of the substrate  2  into contact with the substrate base surface BS 1 . The substrate  2  is fixed to the resin frame  4 A with an adhesive for example. In mounting the lens member  3 A to the lens mount portion  41 A of the resin frame  4 A, the lens member  3 A is properly positioned relative to the image sensor chip  1  just by bringing the support surface S of the lens member  3 A into contact with the lens base surface BS 2 . 
     In the above embodiment, the lens member  3 A is bonded to the lens mount portion  41 A with an adhesive. According to the present invention, as shown in  FIG. 3 , the lens member  3 A may simply be fitted into the lens mount portion  41 B. For this purpose, the inner diameter of the lens mount portion  41 B is slightly smaller than the outer diameter of the lens member  3 A. With this structure, when the lens member  3 A is inserted into the lens mount portion  41 B, the lens mount portion  41 B elastically presses the outer circumferential surface of the lens member  3 A, thereby fixing the lens member  3 A. Since the support portion  32 A of the lens member  3 A is generally cylindrical, a relatively large contact area is provided between the lens member  3 A and the lens mount portion  41 B. Therefore, the lens member  3 A can be reliably secured to the resin frame  4 B. 
       FIGS. 4A and 4B  illustrate another embodiment of the present invention, in which a lens member  3 C is fixed to a lens mount  41 C of a resin frame  4 C by ultrasonic bonding. Specifically, as shown in  FIG. 4A , the lens member  3   c  has a support portion  32 C which includes a thin peripheral portion. The thin peripheral portion has a flat lower surface serving as a support surface S. Unlike the lens mount portion  41 A or  41 B of the foregoing embodiments, the lens mount portion  41 C is not formed with a stepped portion  40 A. Instead, the lens mount portion  41 C has an inner circumferential surface including a bonding surface  40 C. The lens mount portion  41 C has an upper end surface serving as the lens base surface BS 2 . For fixing the lens member  3 C to the resin frame  4 C, the lens member  3 C is pressed against the lens mount portion  41 C while vibrating the lens member  3 C by application of ultrasonic waves. As a result, a lower corner portion  31   c  of the lens member  3 C is melted due to the friction with the bonding surface  40 C. As the corner portion gradually deforms to fit to the bonding surface  40 C, the support surface S gradually approaches the lens support surface BS 2  of the resin frame  4 C and finally comes into complete contact with the surface BS 2 , as shown in  FIG. 4B . Then, the melted corner portion  31   c  is cooled for hardening, so that the lens member  3 C is fixed to the resin frame  4 C. 
     For performing the ultrasonic bonding, a lens member  3 D and a resin frame  4 D as shown in  FIGS. 5A and 5B  may also be utilized. Specifically, the lens member  3 D includes a support portion  32 D of a constant thickness. The support portion  32 D has a lower surface serving as a support surface S. The lower surface is formed with projections  39 . The resin frame  4 D includes a lens mount portion  41 D having an upper surface formed with a circumferentially extending recess  49  at a location corresponding to the projections  39 . Portions of the upper surface of the resin frame  4 D other than the recess  49  serves as the lens base surface BS 2 . For fixing the lens member  3 D to the resin frame  4 D, the lens member  3 D is pressed against the lens mount portion  41 D while applying ultrasonic vibration to the lens member  3 D, so that the projections  39  melt due to the friction with the bottom surface of the recess  49 . As a result, the support surface S of the lens member  4 D finally contacts the lens base surface BS 2  of the resin frame  4 D, as shown in  FIG. 4B . Thereafter, the melted projections  39  are cooled for hardening, thereby fixing the lens member  3 D to the resin frame  4 D. 
     Referring back to  FIG. 1 , the image sensor module A is provided with an optical filter  7  disposed between the chip case portion  42  and the lens mount portion. The optical filter  7  is provided for forming an image with high quality. Specifically, when an infrared-shielding filter is utilized as the optical filter  7 , the image sensor chip  1  receives light containing no or small amount of infrared component. Therefore, the contour and the color of the object are clearly represented in the formed image. Such a filter may also be provided in the other image sensor modules shown in  FIGS. 3 ,  4 A˜ 4 B and  5 A˜ 5 B. 
     The resin frame  4 A shown in  FIG. 1  is provided with a stepped portion (or filter mount portion)  43  to which the optical filter  7  is attached. As a result, the upper opening and the lower opening of the chip case portion  42  are closed by the optical filter  7  and the substrate  2 , respectively. Similarly, the resin frame  4 B,  4 C and  4 D are provided with a filter mount portion  43  (see  FIGS. 3-5 ). Alternatively, the flat lower end surface of the lens mount portion  41  may be utilized as it is for the filter mount portion. 
     Next, a method for making an image sensor module A shown in  FIG. 1  will be described with reference to  FIGS. 6A-6C . 
     As shown in  FIG. 6A , an optical filter  7  is fixed to a filter mount portion  43  of a resin frame  4 A with an adhesive for example. Mean while, an image sensor chip  1  is mounted on an obverse surface of a substrate  2 , and the electrode pads of the image sensor chip  1  are connected to the conductor pads of the substrate  2  via wires W. The wire bonding may be performed using a capillary in a known manner. Since the substrate  2  is a flat board as described above, there are no objects for hindering the movement of the capillary so that the wire bonding can be easily performed. Subsequently, the substrate  2  carrying the image sensor chip  1  is fixed to the resin frame  4 A, thereby providing an intermediate assembly A′. The positioning of the substrate  2  is performed by bringing the upper surface of the substrate  2  into contact with the base surface BS 1  of the chip case portion  42 . 
     In the above manner, the chip case portion  42  is sealed by the substrate  2  and the optical filter  7 . Therefore, in the subsequent process steps, it is possible to prevent dust or moisture from entering the chip case portion  42 . Thus, even when the intermediate assembly A′ is temporarily stored in a certain place or transported to another place as it is in the manufacturing process of the module A, the breakage of the image sensor chip  1  or the wires W due to dust or moisture can be prevented. 
     Then, as shown in  FIG. 6B , the intermediate assembly A′ is mounted to an external device C (e.g. a printed circuit board) by reflow soldering. Specifically, solder paste is applied to predetermined portions of the external device C. Then, the intermediate assembly A′ is disposed on the external device C so that electrode terminals T on the reverse surface of the substrate  2  lie on the solder deposits on the external device C. Then, the solder deposits are melted by heating in a reflow oven and cooled for hardening. Thus, the intermediate assembly A′ is fixed to the external device C. 
     Then, as shown in  FIG. 6C , a lens member  3 A with a light shielding layer  5  formed thereon is attached to the resin frame  4 A. As described before, the lens member  3 A is accurately positioned by bringing the support surface S into contact with the lens base surface BS 2 . The lens member  3 A is glued to the lens mount portion  41 A of the resin frame  4 A. 
     In the step of reflow soldering, the temperature in the reflow oven is raised to about 220° C., which is higher than the melting point (170° C.) of the lens member  3 A. However, since the lens member  3 A is attached to the resin frame  4 A after the reflow soldering is over, the lens member  3 A is not adversely affected by the heating. 
     The image sensor module A having the above-described structure has the following advantages. 
     The image sensor module A has incorporated a lens member as an integral part. The positioning of the lens member  3 A relative to the image sensor chip  1  is easily performed by bringing the lens member  3 A,  3 C or  3 D into contact with the lens base surface BS 2  of a resin frame  4 A. Therefore, unlike the prior art image sensor module  200  there is no need to prepare an additional lens, a lens support or the like in using the image sensor module A. Thus, otherwise troublesome work of positioning an external lens relative to the image sensor chip  1  can be eliminated. Thus, the number of parts required to fabricate the module is prevented from increasing and the manufacturing process of the module is not complicated. 
     Further, unlike the prior art image sensor module  200 , the image sensor chip  1  is used as it is (i.e., without being packaged) Therefore, as compared with the prior art module  200 , the image sensor module A can be made compact. 
     Moreover, unlike the prior art image sensor module  100  in which the lens is fixed using the lens cap  108 , the lens member  3 A is fixed to the resin frame  4 A without using any fixing member. Therefore, the image sensor module A of the present invention can be made compact. Moreover, by the elimination of the lens cap  108 , the number of structural parts can be reduced, resulting in a cost reduction. 
     In the embodiment described above, the lens portion  31  has an upper surface including a concave region  30   b  and a flat region  30   c  surrounding the concave region  30   b . However, as shown in  FIG. 7 , a lens portion  31 ′ may have an upper surface including a convex region  30   b ′ and a flat region  30   c  surrounding the convex region  30   b ′. In this case, it is preferable that the flat region  30   c  is above the apex of the convex region  30   b′.    
     The light shielding layer  5  may be formed by attaching a light shielding film to the lens member instead of applying and printing a coating material to the lens member.