Abstract:
A novel digital camera module includes an image capture device, a lens unit, a housing including an opening for receiving the lens unit and positioning the lens unit with respect to the image capture device, and a boot coupled the lens unit and the housing. In a particular embodiment, the boot includes an upper end and a lower end, each of which has a different outer perimeter. In another particular embodiment, a portion of the inner surface of the boot remains free of contact from the outer surface of the lens unit. In another particular embodiment, the lower end of the boot extends beyond the lower end of the lens unit.

Description:
RELATED APPLICATIONS 
   This application claims the benefit of prior U.S. Provisional Patent Application Ser. No. 60/864,348, filed on Nov. 3, 2006 by at least one common inventor, which is incorporated herein by reference in its entirety. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to electronic devices, and more particularly to digital camera modules. Even more particularly, the present invention relates to a system for focusing a digital camera module that prevents debris and particulate matter produced by the focusing process from contaminating the sensor array of an image capture device. 
   2. Description of the Background Art 
   Digital camera modules are currently being incorporated into a variety of electronic devices. Such camera hosting devices include, but are not limited to, cellular telephones, personal data assistants (PDAs), and computers. The demand for digital camera modules continues to grow as the ability to incorporate the camera modules into host devices expands. Therefore, one design goal of digital camera modules is to make them as small as possible so that they will fit into an electronic device without substantially increasing the overall size of the device. Means for achieving this goal must, of course, preserve the quality of the image captured by the camera modules. 
   Such digital camera modules typically include a substrate, an image capture device, a housing, and a lens unit. The substrate is typically a printed circuit board (PCB) that includes circuitry to facilitate data exchange between the image capture device and the host device. The image capture device is mounted and electrically coupled to the circuitry of the PCB. The housing is then mounted on the PCB over the image capture device. The housing includes an opening that receives and centers the lens unit with respect the image capture device. Typically, the opening includes a set of threads and the lens unit includes a complementary set of threads that facilitate the factory focusing of the camera module. During a factory focus operation, for example, focusing equipment rotates the lens unit with respect to the housing, which adjusts the distance between the lens unit and the image capture device. When the lens unit is properly focused, it is fixed in position with respect to the housing with an adhesive, a thermal weld, or the like. 
   Although camera modules that are focused via thread sets provide for relatively accurate focal adjustments, they still have disadvantages. For example, as the lens unit is rotated within the housing, sliding friction between threads creates particulate debris that could easily contaminate the image sensor and/or other optical components (e.g., infra-red filters, protective covers, other lenses, etc.). Consequently, these contaminants accumulate and noticeably degrade the quality of images captured by, for example, blocking light to the image sensor. 
   It should be noted that although threaded components are used here as an example, other types of focusing components can similarly produce particulate debris that reduces the quality of the captured images. For example, U.S. Pat. No. 6,426,839 issued to Dou et al. discloses a camera module including a plurality of ramps formed directly on a stationary lens located inside the camera module. A rotatable lens carrier (having a separate lens) includes a plurality of legs that engage the ramped surfaces of the stationary lens. Rotating the lens carrier causes the legs of the lens carrier to move up or down the ramped surfaces of the lens, thereby moving the second lens closer to or further from the stationary lens, depending on the direction of rotation. Because the legs of the lens carrier slide over the ramped surfaces of the stationary lens, particulate debris can still be produced and collect on the imaging components of the camera module. 
   In addition to particulate debris produced by friction, ramped housings are also susceptible to other contaminants. For example, adhesives used to fix lens units to housings can easily run down into the camera module and contaminate the imaging components. Ramped modules are particularly susceptible to fluid contamination because the interface between the lens unit and the housing is typically not as tight as that of threaded camera modules. Generally, the walls of the lens unit and the housing are smooth, as opposed to having threads formed thereon. In addition to providing a path for contaminant entry, the loose fit between the lens unit and the housing can allow the lens barrel to fall out of the housing during steps of the manufacturing process that occur prior to fixing the lens unit to the housing, thereby reducing yield. 
   In efforts to minimize the accumulation of such contaminants, manufacturers have employed contaminant collecting surfaces within camera modules. For example, U.S. 2006/0103953 (Lee et al.) discloses a camera module that includes a particle collecting groove defined within the housing. In particular, the groove is formed around the peripheral surface of the light receiving aperture of the housing. The groove collects some the debris before it can reach the image sensor or other optical components within the camera module. 
   Although the groove formed on the camera module disclosed in U.S.2006/0103953 reduces the amount of debris that collects on the image sensor, there are still some disadvantages. For example, debris is still free to move out of the groove because the groove is not entirely isolated. Further, it is unlikely that the camera module will remain upright during use, thus debris is free to fall back out of the groove and obstruct the image sensor and/or optics. 
   What is needed, therefore, is a camera module design that minimizes the contamination of optical components during assembly and focusing processes. What is also needed is a camera module design that isolates contaminants before they collect on components within the camera module. 
   SUMMARY 
   The present invention overcomes the problems associated with the prior art by providing a camera module that includes a contaminant trap for collecting any contaminants that enter the camera module. 
   According to an example embodiment of the invention, a camera module includes an image capture device, a lens unit, a housing, and a boot disposed between the lens unit and the housing. The body of the lens unit extends perpendicularly with respect to an image capture surface of the image capture device (e.g., along an optical axis of the lens unit). The housing includes a mounting portion coupled to the image capture device and a receiving portion including an opening to receive the lens unit. The boot has a first end coupled to the lens unit and a second end coupled to the housing. Each end of the boot includes an inner and outer surface. The outer surfaces of the ends of the boot each have perimeters that form at least a portion of a particle trap. In one embodiment, the outer perimeter of one end of the boot is different (e.g., larger, smaller, shaped differently, etc.) than the outer perimeter of the other end of the boot. Alternatively, in at least one disclosed embodiment, the outer perimeters of the ends of the boot are the same size, such that the boot is a cylindrical tube with a uniform outer perimeter. In an example embodiment, the boot is formed from a resilient material and is shaped as an annulus. 
   The boot and the receiving portion of the housing function together as a means of limiting contaminants that might otherwise reach the image capture surface of the image capture device. The receiver portion of the housing includes a first inner surface and a second inner surface. The inner perimeter of the first inner surface is smaller than the perimeter of the second inner surface, with the first inner surface being disposed between the second inner surface and the image capture device. The boot extends from a position surrounded by the first inner surface of the housing to a position surrounded by the second inner surface of the housing. For example, in some embodiments, the boot extends past the end (e.g., bottom surface) of the lens unit, so that at least a portion of the inner surface of the second end of the boot is spaced apart from the lens unit (e.g., closer to the image capture device). A contaminant collection surface (e.g., a ledge with a V-shaped channel) joins the first inner surface and the second inner surface. The outer surface of the second end of the boot engages (e.g., slidably abuts) the first inner surface of the opening in the housing. The second end of the boot remains in contact with the first inner surface of the housing is moved with respect to the image capture device (e.g., along the optical axis during a focus operation). The contact between the second end of the boot and the first inner surface of the housing reduces the passage of contaminants between the lens unit and the housing to the image capture device. 
   The first end of the boot contacts the lens unit. For example, the boot can be stretched over the end of the lens unit so as to remain in place via frictional engagement. Optionally, the first end of the boot can be fixed to the lens unit with an adhesive or a mechanical attachment device. Alternatively, the boot can be fixed to the housing and slidably contact the lens unit, but this approach may be less effective at reducing contamination of the image capture device. 
   In an example embodiment, the receiver portion of the housing includes a first cylindrical wall and a second cylindrical wall, which are coaxial. The first cylindrical wall has an inner diameter that is smaller than the inner diameter of the second cylindrical wall and is disposed closer to the image capture device than the second cylindrical wall. The second end of the boot is coupled to the housing by an exterior surface of the second end of the boot slidably engaging the first cylindrical wall. The top edge of the first cylindrical wall is joined to the bottom edge of the second cylindrical wall by a ledge, which serves as a particle trap. In a particular embodiment, the ledge defines a channel that enhances its functionality as a particle trap. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention is described with reference to the following drawings, wherein like reference numbers denote substantially similar elements: 
       FIG. 1  is a perspective view of a camera module according to one embodiment of the present invention; 
       FIG. 2  is a partially exploded, perspective view of the camera module of  FIG. 1 ; 
       FIG. 3  is a bottom perspective view of the lens unit of  FIG. 2 ; 
       FIG. 4  is cross-sectional view of the boot of  FIG. 2 ; 
       FIG. 5  is a cross-sectional perspective view of the housing of  FIG. 2 ; 
       FIG. 6   a  is a cross-sectional side view of the camera module of  FIG. 1  in a raised position; 
       FIG. 6   b  is a cross-sectional side view of the camera module of  FIG. 1  in a lowered position; 
       FIG. 7  is a cross-sectional side view of an alternate camera module according to another embodiment of the present invention. 
       FIG. 8  is a cross-sectional side view of another alternate camera module according to yet another embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   The present invention overcomes the problems associated with the prior art by providing a digital camera module including a boot disposed between the lens unit and the housing, so as to reduce contaminants entering the camera module, which might degrade the quality of images captured. In the following description, numerous specific details are set forth (e.g., particular examples of focus devices, substrate types, attachment devices, etc.) in order to provide a thorough understanding of the invention. Those skilled in the art will recognize, however, that the invention may be practiced apart from these specific details. In other instances, details of well known camera module manufacturing practices (e.g., automated focus processes, materials selection, molding processes, etc.) and components (e.g., electronic circuitry, device interfaces, etc.) have been omitted, so as not to unnecessarily obscure the present invention. 
     FIG. 1  is a perspective view of a camera module  100  according to one embodiment of the present invention. Camera module  100  is shown mounted on a portion of a printed circuit board (PCB)  102  that represents a PCB of a camera hosting device. Camera module  100  communicates electronically with other components of the hosting device via a plurality of conductive traces  104 . Device  106  represents an electronic component (e.g., passive device, etc.) that may be mounted directly on PCB  102 . Those skilled in the art will recognize that the particular design of PCB  102  will depend on the particular application, and is not particularly relevant to the present invention. Therefore, PCB  102 , traces  104 , and device  106  are representational in character only. 
   Camera module  100  includes an image capture device  108  (not visible in the view of  FIG. 1 ), a circuit substrate  110 , a housing  112 , and a lens unit  114 . Circuit substrate  110  is mounted to one end (e.g., the bottom) of housing  112  and lens unit  114  is mounted to the other end (e.g., the top) of housing  112 . Image capture device  108  ( FIG. 2 ) is mounted on the top surface of circuit substrate  110 , so as to position image capture device  108  between substrate  110  and housing  112 . 
     FIG. 2  is a partially exploded view of camera module  100 , showing some additional details not visible in the view of  FIG. 1 . In this particular embodiment, camera module  100  further includes a boot  200  disposed between housing  112  and lens unit  114 . Note that the components of camera module  100  are aligned along an optical axis  202 . In particular, housing  112 , boot  200 , and lens unit  114  are coaxial with respect to optical axis  202 . Additionally, image capture device  108  includes an image capture surface  204  that is perpendicularly centered with respect to optical axis  202 . Proper optical alignment of lens unit  114  with respect to image capture surface  204  facilitates proper focusing of images onto image capture surface  204 . 
   Image capture surface  204  provides a substantially flat planar surface whereon images are focused and converted into electrical data that is processed by the processing circuitry of image capture device  108  and/or the host device. Data communication between image capture device  108  and substrate  110  can be achieved by any suitable means known to those skilled in the art. For example, image capture device  108  can include a set of contact pads electrically coupled to a complementary set of contact pads of substrate  110  via wire bonding, soldering, or the like. Image capture device  108  can be fixed to substrate  110  by any suitable means known to those skilled in the art (e.g., adhesive). Alternatively, camera module  100  can be assembled without substrate  110  by coupling image capture device  108  directly to housing  112 . 
   Housing  112  includes a mounting portion  206  and a receiver portion  208 . Mounting portion  206  is adapted to mount to substrate  110  so as to enclose image capture device  108  between substrate  110  and housing  112 . Receiver portion  208  includes an opening  210  that receives lens unit  114 . Opening  210  defines a set of threads  212  formed to engage a complementary set of threads  214  formed on lens unit  114  so as to facilitate the focusing of camera module  100 . In particular, rotating lens unit  114  in a clockwise direction raises lens unit  114  with respect to housing  112 , thereby increasing the distance between lens unit  114  and image capture surface  204 . Conversely, rotating lens unit  114  in a counter-clockwise direction lowers lens unit  114  with respect to housing  112 , thereby decreasing the distance between lens unit  114  and image capture surface  204 . Thus, an image focused by lens unit  114  can be properly adjusted to lie in the focal plane of image capture surface  204 . After lens unit  114  is positioned correctly, lens unit  114  is fixed with respect to housing  112  by some suitable means (e.g., adhesive, thermal weld, etc.). 
     FIG. 3  shows is a bottom perspective view of lens unit  114 , showing additional features not visible in previously described figures. Lens unit  114  includes a body  300 , a flange  302 , and a lower end  304 . Body  300  extends along optical axis  202  and is functional to carry the optical components (not shown) of lens unit  114 . Flange  302  provides a surface for a user and/or machine (e.g., automatic focusing machines) to engage during the focusing of camera module  100 . Lower end  304  includes a cylindrical portion  306  adapted to engage boot  200 . 
     FIG. 4  shows a cross-sectional side view of boot  200 . Boot  200  is a resilient annular-shaped element, which forms a seal for preventing contaminants from reaching image capture device  108 . Boot  200  includes an upper end  400 , a lower end  402 , an inner surface  404 , and an outer surface  406 . Upper end  400  and inner surface  404  of boot  200  receive cylindrical portion  306  of lens unit  114  ( FIG. 3 ). Lower end  402  and outer surface  406  of boot  200  engage the inner surface of housing  112 , which will be described below in greater detail with reference to  FIG. 5 . Before boot  200  is flexed outward and coupled to lens unit  114 , the perimeter of inner surface  404  of upper end  400  is slightly less than the outer perimeter of cylindrical portion  306  of lens unit  114 . Therefore, the elastic retraction force of upper end  400  is sufficient to fix boot  200  to cylindrical portion  306  of lens unit  114 . 
     FIG. 5  shows a cross-sectional view of housing  112  showing some additional features not visible in previous figures. In particular, housing  112  includes a recess  500 , a first inner surface  502 , a second inner surface  504 , and a channel  506 . Recess  500  provides a space to receive image capture device  108 . Inner surface  502  is contoured to engage outer surface  406  of boot  200  so as to prevent contaminants from entering recess  500 . Inner surface  504  forms the outside wall of a contaminant trap  508  ( FIG. 6 ). As shown, the perimeter of first inner surface  502  is smaller than the perimeter of second inner surface  504 , such that surfaces  502  and  504  form a pair of concentric cylindrical walls. Channel  506  is formed in a ledge that connects the top edge of inner surface  502  with the bottom edge of surface  504 , and is operative to collect any contaminants that move past thread set  212 . Examples of such contaminants include dust and/or other particulate debris caused by frictional contact between thread set  212  and complementary thread set  214  of lens unit  114 . Channel  506  can also trap excess adhesive that is used to fix lens unit  114  to housing  112  during focusing processes. 
     FIG. 6   a  is a cross-sectional view of assembled lens module  100  in a raised position. In this particular embodiment, boot  200  is disposed between lens unit  114  and housing  112 . In particular, inner surface  404  of upper end  400  of boot  200  engages cylindrical portion  306  of lens unit  114 , and outer surface  406  of lower end  402  slidably contacts inner surface  502  of housing  112 . Together, boot  200 , inner surfaces  502 ,  504  and channel  506  form contaminant trap  508  which, as described above, collects and isolates any contaminants that advance past threads  212  and threads  214 . Note that contaminant trap  508  is an isolated space enclosed by inner surface  504  of housing  112 , outer surface  406  of boot  200 , channel  506  of housing  112 , and lower end  304  of lens unit  114 . 
     FIG. 6   b  is a cross-sectional view of assembled lens module  100  in a lowered position. As lens unit  114  is displaced downward towards image capture device  108 , outer surface  406  of boot  200  slides within inner surface  502 , while inner surface  404  of upper end  400  remains fixed to cylindrical portion  306  of lens unit  114 . Alternatively, outer surface  406  can remain fixed to inner surface  502  while cylindrical portion  306  of lens unit  114  slides within inner surface  404  of boot  200 . 
   Note that contaminant trap  508  remains sealed as lens unit  114  is moved up and down with respect to image capture device  108 . In particular, the lower end  402  of boot  200  extends a sufficient distance past the bottom of lens unit  114  to remain in contact with inner surface  502  as lens unit  114  is moved up and down a predetermined distance required to achieve proper focus. Maintaining this contact during both rotational and translational movement of lens unit  114  and boot  200  is facilitated by the physical characteristics of boot  200 . In particular, boot  200  is made from a soft, compressible material and is sized to fit into inner surface  502  under slight compression. Boot  200  then exerts a slight outward force and, thereby, maintains contact with inner surface  502 . The inventors have found that forming boot  200  from various materials including, but not limited to, rubber, polyurethane/PPU, silicone, polytetrafluoroethylene, and/or plastic, provides acceptable results. 
     FIG. 7  shows a cross-sectional view of an alternative camera module  700 . Camera module  700  includes a circuit substrate  702 , an image capture device  704 , a housing  706 , a boot  708 , and a lens unit  710 . Apart from the alternate sealing mechanism described below, the components of camera module  700  are substantially similar to the respective components of camera module  100 . 
   Boot  708  includes an upper end  712 , a lower end  714 , an inner surface  716 , and an outer surface  718 . In this particular embodiment, the outer perimeter of upper end  712  is smaller than the outer perimeter of lower end  714 . Upper end  712  and lower end  714  are coupled to lens unit  710  and housing  706 , respectively. In particular, inner surface  716  contacts an outer cylindrical surface  720  of lens unit  710 , while outer surface  718  of boot  708  contacts an inner cylindrical surface  722  of housing  706 . In this embodiment, boot  708  is fixed with respect to lens unit  710  and slidably engages housing  706 . Alternatively, boot  708  can be fixed with respect to housing  706  and slidably engage lens unit  710 . 
     FIG. 8  shows a cross-sectional view of yet another alternative camera module  800 . Camera module  800  includes a circuit substrate  802 , an image capture device  804 , a housing  806 , a boot  808 , and a lens unit  810 . Apart from the alternate sealing mechanism described below, the components of camera module  800  are substantially similar to the respective components of camera module  100 . 
   In this particular embodiment, boot  808  is a resilient cylindrical tube having an approximately uniform outer perimeter along its length. Boot  808  includes an upper end  812 , a lower end  814 , an inner surface  816 , and an outer surface  818 . As shown, the outer perimeter of boot  808  is uniform from upper end  812  to lower end  814 . Upper end  812  of boot  808  is coupled to lens unit  810  and lower end  814  is coupled to housing  806 . In particular, inner surface  816  of boot  808  contacts an outer cylindrical surface  820  of lens unit  810  while outer surface  818  of boot  808  contacts an inner cylindrical surface  822  of housing  806 . As lens unit  810  is displaced vertically with respect to image capture device  804 , outer surface  818  and inner surface  816  of boot  808  remain in contact with inner cylindrical surface  822  and outer cylindrical surface  820 , respectively. As in the previous embodiment, boot  808  can be fixed to either lens unit  810  or housing  806 . However, the inventors expect superior results will be achieved by fixing boot  808  to the lower end of lens unit  810 . 
   The description of particular embodiments of the present invention is now complete. Many of the described features may be substituted, altered or omitted without departing from the scope of the invention. For example, alternate focus mechanisms (e.g., complementary opposing ramps on lens unit  114  and the top of housing  112 ) may be substituted for those described above. Indeed, the inventors believe that the combination of the contamination reduction features described herein with such alternate focus mechanisms will provide a significant improvement over the devices of the prior art. As another example, alternate materials can be used to form the boot, depending on the particular application. These and other deviations from the particular embodiments shown will be apparent to those skilled in the art, particularly in view of the foregoing disclosure.