Abstract:
A disclosed example camera module includes a substrate, an integrated circuit image capture device (ICD) mounted on the substrate, the image capture device having an array of light sensors on its top surface, a first lens unit rigidly fixed to the top surface of the image capture device, a second lens unit, and a lens actuator mounted on the substrate. The lens actuator adjustably supports the second lens unit over the first lens unit. The first lens unit includes a stacked plurality of lenses. Optionally, the second lens unit also includes a stacked plurality of lenses. Movement of the second lens unit with respect to the first lens unit provides a focus and/or zoom function.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of copending U.S. Provisional Patent Application No. 60/925,947, filed Apr. 24, 2007 by the same inventor, which is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    This invention relates generally to electronic devices, and more particularly to digital camera modules. Even more particularly, this invention relates to camera modules incorporating variable focus/zoom devices. 
         [0004]    2. Description of the Background Art 
         [0005]    Digital camera modules are currently being incorporated into a variety of host devices. Such host devices include cellular telephones, personal data assistants (PDAs), computers, and so on. Therefore, consumer demand for digital camera modules in host devices continues to grow. 
         [0006]    Host device manufacturers prefer digital camera modules to be small, so that they can be incorporated into the host device without increasing the overall size of the host device. Further, host device manufacturers prefer camera modules that minimally affect host device design. In meeting these requirements the host device manufacturers prefer camera modules that capture images of the highest possible quality. Of course, it is an ongoing goal for camera module manufacturers to design camera modules that meet these requirements at minimal manufacturing cost. 
         [0007]    A conventional digital camera module generally includes a lens assembly, a housing, a printed circuit board (PCB), and an integrated image capture device (ICD). Typically, the components are formed separately and later assembled to create the digital camera module. That is, the ICD is attached to the PCB, and then the housing is attached to the PCB so that the ICD is covered by the bottom of the housing. Then, the lens assembly is mounted to the opposite end of the housing to focus incident light onto an image capture surface of the ICD. The ICD is electrically coupled to the PCB, which includes a plurality of electrical contacts for the ICD to communicate image data to the host device for processing, display, and storage. 
         [0008]    It is also common for digital cameras, although not necessarily miniature camera modules, to include a variable focus/zoom device for enhancing the quality of images captured at various focal fields. Typically, the variable focus/zoom device includes an electronic actuator coupled to one or more lenses of the lens assembly for changing the displacement of the lens(s) with respect to the image capture surface of the ICD and with respect to each other. 
         [0009]    In manufacturing miniature camera modules, many problems are encountered by the camera module manufacturers. As one example, bare ICD dies are extremely vulnerable to contamination before and during assembly. When the image capture surface is exposed to dust and/or other particulate debris, these contaminants can block incident light, resulting in visible defects in the images captured. Such contamination often results in the discarding of the defective image capture devices, which can be extremely expensive, especially when yield losses are high. In efforts to minimize contamination, the camera modules have to be carefully assembled in a class  100  clean room. Although the image capture devices of assembled camera modules are protected against contaminants from outside of the camera module, they are still vulnerable to internally generated contaminants. Such internal contaminants are usually the result of dust, component adhesives (e.g., epoxy), and/or particulates formed by frictional wear within the camera module. Frictional wear is typical when components are assembled or after the assembly, such as when movable components (e.g., variable zoom/focus devices) within the camera modules are actuated. Contamination of an image sensor after the camera is assembled can be especially expensive because the entire camera module may have to be discarded. 
         [0010]    Another problem is that variable focus/zoom devices typically include multiple moving optical elements, which have to be extremely small to be incorporated into miniature camera modules and, therefore, require extremely delicate processes for fabrication, assembly, and alignment. Indeed, the alignment process becomes increasingly more difficult as the number of required camera module components is increased. This is because the lenses have to be positioned with respect to the ICD within a predetermined tolerance. The overall tolerance is an accumulation of other intermediate component tolerances. Ideally, the lenses should all be coaxially perpendicular to the center of the planar image capture surface. However, this is typically only achieved within a predetermined overall tolerance defined by the sum of: the tolerance of the ICD with respect to the PCB, the tolerance of the PCB with respect to the housing, the tolerance of the housing with respect to the focus/zoom device, and the tolerances of the lenses with respect to the focus/zoom device. 
         [0011]    One prior art method for minimizing the contamination of the ICD during the assembly of the camera module includes fixing a transparent protective substrate (e.g., a glass plate) over the image capture surfaces. Typically, this is achieved by adhering the transparent substrate directly over the image capture surface via a transparent adhesive. Another common method includes forming an annular element around the peripheral surface of the image capture device, then adhering the transparent substrate to the annular element so as to form a space between the image capture surface and the transparent substrate. 
         [0012]    Although a transparent cover may protect the image capture surface from some contaminants before the camera module is assembled, the camera module is still extremely vulnerable to contamination and the resulting image quality degradation. For example, contaminants can still collect on the transparent substrate which itself is vulnerable to contamination. As another example, the process of applying the transparent cover to the ICD could itself cause contamination. Further, the additional components are likely to increase the overall costs of the manufacturing the camera modules and increase the manufacturing time. 
         [0013]    What is needed, therefore, is a camera module that is less vulnerable to contamination. What is also need is a camera module that can be assembled with a more forgiving tolerances. What is also needed is a camera module that requires fewer components and fewer manufacturing steps. What is also needed is a method of assembling a miniature camera module with an autofocus and/or zoom feature. 
       SUMMARY 
       [0014]    The present invention overcomes the problems associated with the prior art by providing a camera module with an autofocus and/or zoom feature that is less vulnerable to contamination, requires fewer components and manufacturing steps, and can be assembled with more forgiving manufacturing tolerances. A disclosed example camera module includes a substrate, an integrated circuit image capture device (ICD) mounted on the substrate, the image capture device having an array of light sensors on its top surface, a first lens unit rigidly fixed to the top surface of the image capture device, a second lens unit, and a lens actuator mounted on the substrate. The lens actuator adjustably supports the second lens unit over the first lens unit. The first lens unit includes a stacked plurality of lenses. Optionally, the second lens unit also includes a stacked plurality of lenses. Movement of the second lens unit with respect to the first lens unit provides a focus and/or zoom function. 
         [0015]    In the disclosed example embodiment, the first lens unit includes a first lens element having a bottom surface and a second lens element having a top surface and a bottom surface. The top surface of the second lens element is adhered to the bottom surface of the first lens element, and the bottom surface of the second lens element is adhered to said top surface of said image capture device. 
         [0016]    The first lens unit is adhered to the top surface of the image capture device such that the array of light sensors is sealed between the image capture device and the first lens unit. The first lens unit includes a mounting surface having a cavity formed therein, and the mounting surface is fixed to the top surface of the image capture device at an area surrounding the sensor array such that the cavity is disposed over the sensor array. In a particular embodiment, a top surface of the first lens unit is at least 1-2 mm from the top surface of the image capture device. 
         [0017]    A method of manufacturing camera modules is also disclosed. The example method disclosed includes providing an integrated circuit ICD including a sensor array on its top surface, providing a first lens unit, rigidly attaching the first lens unit to the top surface of the ICD, mounting the image capture device on a substrate, providing an electromechanical actuator assembly having a second lens unit adjustably mounted therein, and mounting the electro-mechanical actuator assembly on the substrate with the second lens unit disposed a spaced distance above the first lens unit. In a particular method, the step of providing the first lens unit includes providing a first lens substrate having a plurality of individual lenses formed therein, providing a second lens substrate having a plurality of individual lenses formed therein, adhering at least a portion of a bottom surface of the first lens substrate to at least a portion of a top surface of the second lens substrate. The step of rigidly attaching the first lens unit to the top surface of the image capture device includes providing an integrated circuit substrate including the image capture device and a plurality of other image capture devices, providing a lens substrate having a plurality of individual lenses formed therein, at least one of the lenses forming a portion of the first lens unit and others of the lenses forming portions of other lens units, and adhering at least a portion of a bottom surface of the lens substrate to the top surface of the image capture device, thereby attaching said first lens unit to said image capture device and attaching said other lens units to said other image capture devices. The method further includes dividing the lens substrate and the integrated circuit substrate to produce a plurality of separate image capture devices, each having one of the lens units attached thereto. 
         [0018]    In an alternative method, the step of providing an integrated circuit ICD includes providing an integrated circuit ICD having a transparent cover (e.g., a glass plate) over the top surface. The step of rigidly attaching a first lens unit to the top surface of the image capture device includes fixing the first lens unit to the transparent cover. 
         [0019]    In the example method, the first lens unit includes a stacked plurality of lens elements. Optionally, at least one element of the stacked plurality of lens elements includes an infrared filter integrated therein. 
         [0020]    As another option, the method further includes programming the image capture device with data indicative of at least one optical characteristic of the first lens unit. 
         [0021]    A disclosed example camera module can also be described as including a substrate, an integrated circuit ICD mounted on said substrate, the ICD having an array of light sensors on its top surface, a first lens unit, means for mounting the first lens unit with respect to the image capture device, a second lens unit, and a lens actuator mounted on the substrate, the actuator adjustably positioning the second lens unit with respect to the first lens unit. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0022]    The present invention is described with reference to the following drawings, wherein like reference numbers denote substantially similar elements: 
           [0023]      FIG. 1  is a perspective view of a camera module of the present invention mounted on a printed circuit board (PCB) of a host device; 
           [0024]      FIG. 2  is a partially sectioned, perspective view of the camera module of  FIG. 1 ; 
           [0025]      FIG. 3  is a partially sectioned, perspective view of internal components of the camera module of  FIG. 1 ; 
           [0026]      FIG. 4  is an exploded perspective view of a plurality of glass wafers used to manufacture optical component stacks of the camera module shown in  FIG. 2 ; 
           [0027]      FIG. 5  is a cross sectional view of a portion of the glass wafers of  FIG. 4  after an alignment and bonding process; and 
           [0028]      FIG. 6  is a flow chart summarizing one particular method of manufacturing camera modules according to the present invention. 
       
    
    
     DETAILED DESCRIPTION  
       [0029]    The present invention overcomes the problems associated with the prior art, by providing a novel method of manufacturing a miniature camera module with an autofocus and/or zoom feature. In the following description, numerous specific details are set forth (e.g., number of lens elements in an optical stack, 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 electronic assembly practices and components have been omitted, so as not to unnecessarily obscure the present invention. 
         [0030]      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 component) 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. 
         [0031]      FIG. 2  is a partially sectioned, perspective view of camera module  100  including an integrated circuit image capture device (ICD)  200 , PCB  202 , focus/zoom device  204 , base  206 , and a housing  208 . ICD  202  is mounted and electrically coupled to PCB  202  by means commonly known to those in the art (e.g., wire bonding, reflow soldering, etc.). Focus/zoom device  204  includes an optical stack  210 , lens carrier  212 , and an actuator  214 . Optical stack  210  and lens carrier  212  are coaxially positioned along an optical axis  216  which is perpendicular to and centered with respect to an image capture surface of ICD  200 . Optical stack  210  is rigidly fixed onto the top surface of ICD  200 , while lens carrier  212  is movable along axis  216 . Actuator  214  is an electromechanical device (e.g., MEMS, piezoelectric, voice coil, etc.) that is operative to position lens carrier  212  with respect to optical stack  210  responsive to an electronic control signal. In particular, when actuator  214  receives a signal indicative of a particular focal/zoom field, actuator  214  positions lens carrier  212  a corresponding distance from optical stack  210 . 
         [0032]    Base  206  is a rigid substrate formed directly over PCB  202  and the peripheral edges of ICD  202 , so as to provide support to actuator  214  and housing  208 . Base  206  can be formed by any of several means. For example, base  206  can be preformed then attached to PCB  202 . Alternatively, base  206  can be molded directly onto PCB  202  after ICD  200  and optical stack  210  are fixed to PCB  202 . As yet another alternative, base  206  and actuator  214  can be integrated as a single component. As yet even another alternative, ICD  200  (with optical stack  210  attached) can be flip-chip mounted to base  206 , which can then be mounted to PCB  202  by, for example, a reflow soldering process. 
         [0033]    Housing  208  is formed directly over base  206  and actuator  214  so as to provide protection to the internal components of camera module  100 . Housing  208  includes an aperture  218 , which allows light to enter camera module  100 . Aperture  218  can be covered by a transparent material (e.g., lens, IR filter, etc.) to further prevent external debris from entering camera module  100 . The formation of housing  208  can be achieved by any of several means. For example, housing  208  can be prefabricated then attached to base  206  and actuator  214 . As another example, housing  208  can be overmolded onto base  206  and actuator  214 . It should be noted that the alignment of optical stack  210  and lens carrier  212  with respect to ICD  202  does not depend on the alignment of housing  208  with respect to ICD  200  because housing  208  is not an intermediate component. Therefore, housing  208  does not contribute to problems associated with lens alignment tolerance accumulation. 
         [0034]      FIG. 3  is a partially sectioned perspective view of ICD  200 , optical stack  210 , and lens carrier  212 . ICD  200  includes a planar image capture surface  300  which is perpendicular to optical axis  216 . As can be seen, optical axis  216  passes through the center of optical stack  210 , lens carrier  212 , and image capture surface  300 . 
         [0035]    Optical stack  210  includes a stack of four lenses  302 ,  304 ,  306 , and  308  fixed to one another and mounted over image capture surface  300 . In particular, the bottom surface of lens  302  is directly fixed to ICD  200 , lens  304  is fixed to lens  302 , lens  306  is fixed to lens  304 , and lens  308  is fixed to lens  306 . Further, the bottom surface of lens  302  defines an opening into a cavity  310 , the opening having an area slightly greater than the area of image capture surface  300  so as to prevent contact between lens  302  and image capture surface  300 . It is important to recognize that after optical stack  210  is fixed to ICD  200 , contamination or image degradation due to post assembly processes is very unlikely. This is because debris collecting on the top surface of lens  308  is too far away from the image focal plane to cause blemish related yield loss. In addition, the bonding of lens  302  to ICD  200  effectively seals image capture surface  300  within cavity  310 , thereby preventing contaminants from reaching image capture surface  300 . 
         [0036]    Lens carrier  212  defines a cavity  312  and an optical aperture  314 . Cavity  312  fixably seats a second optical stack  316 , which includes a stack of four lenses  318 ,  320 ,  322 , and  324  fixed to one another. In particular, lens  320  is fixed to lens  318 , lens  322  is fixed to lens  320 , and lens  324  is fixed to lens  322 . Lens  324  defines a convex surface  326  which is seated within aperture  314 . Although not shown, lens carrier  212  includes a feature (e.g., ferrous element, magnet, guide rails, rigid lip, etc.) which reacts to an electrical or mechanical force (e.g., magnetic force, piezoelectric biasing force, etc.) provided by actuator  214  for moving lens carrier  212  with respect to optical stack  210 . In response to an actuating force, lens carrier  212  and optical stack  316  are displaced with respect to image capture surface  300  along axis  216 , thereby changing the focal/zoom field. 
         [0037]    In addition, ICD  200  includes data indicative of the optical characteristics of at least one of optical stack  210  and optical stack  316 . Providing this information in the programming code of ICD  200  facilitates the use of software such as enhanced depth of field (EDOF) and optical fault correction (OFC). Optical features created in the wafer level optics can then be used by the software for image enhancement. This feature can also improve module yield by correcting image artifacts. 
         [0038]      FIG. 4  is an exploded perspective view of four glass wafers  400 ,  402 ,  404 , and  406  used in forming optical stack  210 . Glass wafers  400 ,  402 ,  404 , and,  406  include lens arrays  408 ,  410 ,  412 , and  414 , respectively, which are individually formed by some suitable means such as etching/replication technology. After the lens arrays are formed, the glass wafers are vertically aligned such that each individual lens is coaxially aligned with three other individual lenses. The glass wafers are then adhered to one another in a stacked relationship in preparation for a separation process which will yield several individual optical stacks  210 . 
         [0039]    Alternatively, glass wafers  400 ,  402 ,  404 , and  406  can be bonded to a wafer including a like plurality of integrated circuit image capture devices, before separation of the wafers into individual ICDs with attached lens stacks. However, it can be more difficult to separate the lens wafers and the ICD wafer at the same time, because separation may require the dicing of the glass wafers over the active areas of the silicon ICD wafer. In addition, bonding the lenses to the wafers prior to separation reduces the yield of lenses from the glass wafers, because the lens stacks occupy a smaller area than the ICDs. Therefore, if the glass wafers are diced prior to attachment to the ICD wafer, the lenses can be positioned closer together rather than having a spacing that must match the spacing of the ICDs. 
         [0040]      FIG. 5  is a cross-sectional view of a small portion of glass wafers  400 ,  402 ,  404 , and  406  aligned and adhered to one another. After the glass wafers are adhered to one and other, the lenses are tested for quality and then diced along lines  500  forming multiple individual optical stacks  210 . After individual optical stacks  210  are formed, they are cleaned and prepared to be mounted on ICDs. Note that optical stack  316  is formed using the same general process used to form optical stack  210 , but of course with differently shaped lens elements. 
         [0041]      FIG. 6  is a flowchart summarizing one method  600  of manufacturing an autofocus/zoom camera module according to the present invention. In a first step  602 , an image capture device (ICD) is provided. Then, in a second step  604 , a first lens unit is provided. Next, in a third step  606 , the first lens unit is rigidly attached to the ICD. Optionally, steps  602 ,  604 , and  606  occur at the wafer level. That is, these steps occur while the ICD is still incorporated in a wafer with other ICDs, and while the lens elements are still incorporated in glass wafers with other lens elements. 
         [0042]    Next, in a fourth step  608 , the ICD (with first lens unit attached) is mounted on a substrate (e.g., a PCB of a host device). Then, in a fifth step  610  an actuator with a second lens unit is provided, and in a sixth step  612 , the actuator is mounted on the substrate over the ICD and the first lens unit. 
         [0043]    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 lens units may be substituted for the optical stacks shown. As another example, different electronic mounting processes can be used to assemble the camera modules. 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.