Abstract:
A camera module having a ground dummy board, the camera module including: a lens holder having at least one lens; an image sensor having an image region where light passed through the lens is imaged; a board having the image sensor mounted at one side assembled to a lower surface of the lens holder; and a ground dummy board disposed on an outer surface of the board to electrically connect to ground via holes exposed to the outer surface of the board. The camera module minimally experiences electromagnetic interference and electrostatic discharge, thereby improved in electrical properties thereof.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the priority of Korean Patent Application No. 2006-127130 filed on Dec. 13, 2006, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a camera module, and more particularly, to a camera module having a ground dummy board which minimally undergoes electromagnetic interference and electrostatic discharge resulting from a board during operation, thereby improved in electrical properties thereof. 
         [0004]    2. Description of the Related Art 
         [0005]      FIG. 1  is an exploded perspective view illustrating a general camera module. The camera module  1  includes a lens barrel having at least one lens disposed therein, and has a male thread  12  formed on an outer surface of the lens barrel  10  with an exposure hole  14  formed in a top surface thereof. 
         [0006]    A housing  20  is threadably assembled to the lens barrel  10 , and has an opening with a female thread  22  formed on an inner circumferential surface thereof to be threadably engaged with the male thread  12 . The opening has an infrared (IR) cut filter  25  for blocking infrared rays contained in light passed through the lens. 
         [0007]    An image sensor  30  is disposed under the housing  20  and has an image region where an image of an object passed through the lens of the lens barrel  10  is formed. The image sensor  30  is flip-chip bonded to one side of the board  40  to be electrically connected thereto. The side of the board  40  where the image sensor  30  is mounted is assembled to a lower surface of the housing  20 . 
         [0008]    The board  40  has a window  44  formed at the one side to expose the image region of the image sensor  30 , and connection terminals  41  electrically connected to bumps  31  formed on a top of the image sensor  30 . The board  40  has a connector  45  disposed at another side for electrical connection with an unillustrated display unit. 
         [0009]    Here, the image sensor  30  is flip-chip bonded to a bottom of the one side of the board  40 , but not limited thereto. The image sensor  30  may be wire-bonded to a top of the one side of the board  40  by a plurality of wires. 
         [0010]    The board  40  is a flexible printed circuit board (FPCB). As a way to manufacture the board  40 , conductive layers are thermo-compressed on a top and bottom of an insulating layer of the board  40 , and dry films are laminated on the conductive layers to form circuit patterns. Subsequently, the dry films laminated are exposed and etched to form predetermined circuit patterns  42  electrically connecting the image sensor  30  with the connector  45 . Moreover, coverlays (not shown), i.e., board protective films are formed on a top and bottom of the board  40  to protect the circuit patterns from external environment. 
         [0011]    Meanwhile, during operation of the camera module  1 , an analogue electrical signal of the image obtained from the image region of the image sensor  30  is converted into a digital electrical signal by a converter (not shown) and then transmitted to the connector  45  through the circuit patterns  42 . 
         [0012]    In this process, electromagnetic waves are generated from the circuit patterns  42  of the board  40 . The electronic magnetic waves are then radiated outside to electromagnetically interfere with neighboring electronic parts, thereby triggering electromagnetic interference (EMI). Furthermore, electromagnetic waves generated from other electronic parts may affect the board  40  to induce electromagnetic interference. In addition, static electricity may be discharged in an electro-static discharge (ESD) phenomenon. These problems disadvantageously degrade electrical properties of the camera module. 
       SUMMARY OF THE INVENTION 
       [0013]    An aspect of the present invention provides a camera module having a ground dummy board in which electromagnetic interference and electro-static discharge are maximally suppressed to improve electrical properties of the camera module. 
         [0014]    According to an aspect of the present invention, there is provided a camera module having a ground dummy board, the camera module including: a lens holder having at least one lens therein; an image sensor having an image region where light passed through the lens is imaged; a board having the image sensor mounted at one side assembled to a lower surface of the lens holder; and a ground dummy board disposed on an outer surface of the board to electrically connect to ground via holes exposed to the outer surface of the board. 
         [0015]    The ground dummy board may include: a ground layer having both ends electrically connected to the ground via holes exposed to the board, by a conductive adhesive; and protective layers disposed on a top and bottom of the ground layer, respectively. 
         [0016]    The ground dummy board may be bonded to at least one of a top and a bottom of the board by an adhesive. 
         [0017]    The ground via holes may be formed of one of a through via hole and a blind via hole electrically connected to a ground line out of circuit patterns formed on the board. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The above and other aspects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
           [0019]      FIG. 1  is an exploded perspective view illustrating a general camera module; 
           [0020]      FIG. 2  is an exploded perspective view illustrating a camera module having a ground dummy board according to an exemplary embodiment of the invention; and 
           [0021]      FIG. 3  is a cross-sectional view illustrating a dummy board and a board which are connected together in a camera module having a dummy board according to an exemplary embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0022]    Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. 
         [0023]      FIG. 2  is an exploded perspective view illustrating a camera module having a ground dummy board according to an exemplary embodiment of the invention. The camera module  100  includes a lens holder  101 , an image sensor  130 , a board  140  and a ground dummy board  150 . 
         [0024]    The lens holder  101  includes a lens barrel  110  and a housing  120 . The lens barrel  110  is a hollow with at least one lens disposed therein and has a male thread  112  formed on an outer surface thereof. The housing  120  has a female thread  122  formed on an inner circumferential surface thereof corresponding to the male thread  112  and is threadably assembled to the lens barrel  110 . 
         [0025]    The lens barrel  110  is a hollow having a predetermined dimension of inner space so that at least one lens is arranged therein along an optical axis. An opening  114  of a predetermined size is formed in a top of the lens barrel  110  to have its center aligned with the optical axis. 
         [0026]    The plurality of lenses are disposed at a predetermined interval in the lens barrel  110  with spacers (not shown) provided therebetween. 
         [0027]    The housing  120  includes a tubular portion having the female thread  122  threadably engaged with the male thread  112  of the lens barrel  110 , and a square portion assembled with the board  140 . 
         [0028]    With this threadable engagement with the housing  120 , the lens barrel  110  can be disposed movable back and forth in an optical axis direction, thereby varying a focal length between the lens and the image sensor  130 . 
         [0029]    Meanwhile, an infrared (IR) cut filter  125  is disposed in the housing, i.e., between the lenses arranged in the lens barrel  110  and the image sensor  130  to block infrared rays contained in light incident on the image region. 
         [0030]    The image sensor  130  has the image region  132  where an image is formed, on a top surface onto which a focal point of the lens is directed. The image sensor  130  is electrically connected to the board  140  so that the image formed is converted into an electrical signal and then transmitted to a display through the board  140 . 
         [0031]    A plurality of bumps  131  are formed on an outer periphery of the image region  132  of the image sensor  130  to facilitate flip-chip bonding between the image sensor  130  and the board  140 . The image sensor  130  is disposed on a lower surface of one side of the board  140  via a conductive adhesive (not shown) such as an Anisotropic conductive film (ACF) and an Anisotropic conductive paste (ACP). 
         [0032]    Here, the image sensor  130  is flip-chip bonded to the one side of the board  140 , but not limited thereto. The image sensor  130  may be wire-bonded onto a top of the board  140  by a plurality of wires. 
         [0033]    The board  140  has a window  144  formed at the side where the image sensor  130  is mounted to have a size substantially identical to the image area of the image sensor  130 . 
         [0034]    A plurality of connection terminals  141  are formed on the side of the board where the window  144  is formed to be electrically connected in correspondence with the bumps  131  formed on the image sensor  130 . 
         [0035]    A connector  145  is disposed at another side of the board  140  to be connected thereto so that an electrical signal fed from the image sensor  130  is transmitted to the board  140 . Circuit patterns  142  are formed on a portion of the board  140  between the side where the image sensor  130  is mounted and the side where the connector  45  is disposed, thereby enabling transmission and reception of various electrical signals. 
         [0036]    The board  140 , as shown in  FIG. 3 , includes an insulating layer  140   a  made of a resin-based material such as polyimide and polyester, and conductive layers  140   b  applied and thermo-compressed on a top and bottom of the insulating layer  140   b.    
         [0037]    Conductive films are laminated on the conductive layers  140   b  and then exposed and etched to form predetermined circuit patterns  142  electrically connecting the image sensor  130  with the connector  145 . Coverlays  140   c , i.e., board protective films are formed on the top and bottom of the board  140  to protect the circuit patterns  142  from external environment. 
         [0038]    The ground dummy board  150  is provided on an outer surface of the board  140  to be electrically connected to ground via holes  151  exposed to the outer surface of the board  140 . 
         [0039]    The ground dummy board  150  includes a ground layer  152  and protective layers  153 . The ground layer  152  is electrically connected to the ground via holes  151  exposed through the outer surface of the board  140 , by a conductive adhesive  154 . The protective layers  153  are formed on a top and bottom of the ground layer  152 . 
         [0040]    The ground layer  152  is a ground line exposed to the outside at both sides of the ground dummy board  150  to be electrically connected to the ground via holes  151  of the board  140 . The protective layers  153  are made of an insulating resin which is applied on the top and bottom of the insulating layer to protect the ground layer  152 . 
         [0041]    The ground dummy board  150  may be bonded to one of a top and bottom of the board  140  by an adhesive  159 , but not limited thereto. The ground dummy boards  150  may be bonded to the top and bottom of the board  140 , respectively, by an adhesive. 
         [0042]    The ground via holes  151  connected to the ground dummy board  150  are configured as one of a through via hole and a blind via hole electrically connected to a ground line out of the circuit patterns  142  formed on the board  140 . 
         [0043]    Also, the connection terminals  141  of the board  140  connected to the bumps  131  of the image sensor  130  by a solder ball B may be formed of a terminal connecting via hole  149 . 
         [0044]    Meanwhile, to ground-connect the ground dummy board  150  to the top of the board  140 , first, some portions of the coverlays  140   c  applied on the outer surface of the board  140  are removed to expose the ground via holes  151  to the outside and a conductive adhesive  154  is applied on one of an upper end and a lower end of the exposed ground via holes  151 . 
         [0045]    Moreover, portions of the protective layers  153  of the ground dummy board  150  corresponding to the ground via holes  151  of the board are removed to expose both sides of the ground layer  152  to the outside. 
         [0046]    Then, the ground dummy board  150  is attached onto the outer surface of the board  140  and the ground via holes  151  are bonded to the ground layer  152  of the ground dummy board  150  by the conductive adhesive  154 . With heat and pressure applied to portions corresponding to the conductive adhesive  154 , the ground via holes and the ground layer are electrically connected to each other. 
         [0047]    As a result, when an electrical signal of the image obtained from the image region of the image sensor  130  is converted into a digital electrical signal and then transmitted to the connector  145  through the circuit patterns  142  of the board  140 , electromagnetic waves are generated, without being radiated outward, but absorbed in the ground layer  152  electrically connected to the ground via holes  151 . Subsequently, the electromagnetic waves are radiated through the ground line. This prevents noises from occurring in the electrical signal. 
         [0048]    Furthermore, the electromagnetic waves generated outside are blocked from affecting the board through the circuit patterns and electro-static discharge (ESD) in which static electricity is discharged is suppressed. 
         [0049]    As set forth above, according to exemplary embodiments of the invention, a ground dummy board is provided on an outer surface of a board electrically connecting an image sensor with a connector to be electrically connected to ground via holes of the board. This prevents electromagnetic waves generated from circuit patterns of the board from being radiated outward, thereby affecting neighboring electronic parts, or electromagnetic waves generated outside from being induced into the board. This as a result enhances electrical properties of the camera module and prevents noises from occurring in an electrical signal, thereby achieving a high-quality image. 
         [0050]    While the present invention has been shown and described in connection with the exemplary embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.