Abstract:
A method for manufacturing camera modules for use in portable electronic devices, such as mobile phones, is provided. More specifically, in camera modules utilizing lens motion type auto focus actuation, permanent magnets associated with voice coil motors utilized in the auto focus system, generate magnetic flux that can interfere with the process of bonding image sensors to camera modules if the permanent magnets of different voice coil motors are positioned too closely. Incorporating a magnetic shield into the manufacturing process to restrain or control the magnetic flux generated by the permanent magnets permits voice coil motors to be positioned closer together during the manufacturing process. This increases manufacturing throughput and reduces cost.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a method of manufacturing an electromagnetically actuated lens driving device used in a camera module of electronic devices such as mobile phones, personal digital assistants and other similar devices. 
       BACKGROUND OF THE INVENTION 
       [0002]    There is growing market demand for handheld and portable electronic devices to include cameras. Mobile phones, personal digital assistants (PDAs), tablets and other portable electronic devices routinely include at least one camera and, in some instances, multiple cameras. There is a consumer demand to increase the presence of cameras in portable electronic devices. Accordingly, there is also a demand to increase the manufacture of camera modules for such devices. Simultaneously, there is incentive to reduce the cost of manufacturing camera modules while improving the yield of the manufacturing process. 
         [0003]    In addition, consumer demand requires improved image quality with such cameras. Generally speaking, image quality improves by increasing pixels within image sensors and, with increased pixels, there is a need for an autofocus function associated with the camera module in order to output quality images. Virtually all camera modules used in handheld electronic devices now include an autofocus feature. In general there are two types of auto focusing actuators used in cameras for mobile electronic devices. One is a lens motion type auto focus actuation which utilizes a voice coil motor, piezoelectrics or micro electromechanical system (MEMs) technologies. A second is a lens modification type auto focus actuation which utilizes liquid lens and solid state electro-optical devices. The present invention relates to lens motion type auto focus actuation systems and more specifically those that utilize permanent magnets in connection with the auto focus system such as are used in voice coil motors. 
         [0004]      FIG. 1  is a perspective view of a representative example of voice coil motor (VCM)  10  with lens motion type auto focus actuation.  FIG. 2  is an exploded view of the VCM  10 . In general terms, the VCM  10  includes an axially movable lens  12 , a frame member  14 , a voice coil motor top spring  16 , an electromagnetic interference (EMI) shield  18 , a yoke  20  and a base  22 . A representative example of a VCM  10  is shown in cross section in  FIG. 3 . A voice coil motor serves to adjust the position of the lens  12 . In general terms, and with respect to adjustment of the lens  12  position, the VCM includes one or more permanent magnets  24  fixed to the yoke  20  and a wire coil  26  associated with the lens housing  28 . The coil  26  comprises a number of turns of wire and is positioned radially inwardly from the permanent magnet  24 . By driving current through the coil  26 , an electromagnetic field is created which interacts with the magnetic field of the permanent magnet  24  to move the lens  12  and drive the lens  12  outwardly or inwardly along its optical axis  30 . Changing direction of the current flowing in the coil  26  causes the lens to move in opposite directions. Moving the lens along its optical access  30 , towards or away from an image sensor (not shown), focuses a target image on the image sensor. One or more springs  16  are utilized to assist in maintaining the orientation of the lens  12  within the VCM  10  and relative to an image sensor (not shown) and to provide a known resistive or opposing force to the movement imparted by the voice coil motor on the lens  12 . 
         [0005]    The permanent magnet  24  is generally in the form of a ring or cylinder or may comprise a plurality of arc-shaped magnets which are arranged around the perimeter of the inner wall of the yoke  20 . The permanent magnet or magnets generate or create a magnetic flux field that is always present. In contrast, the coil in combination with the yoke also creates a flux field when current flows through the coil. This latter flux field creates what is known as electromagnetic interference (EMI), which may adversely affect nearby or adjacent electrical circuits. The EMI shield  18  is designed to reduce the adverse effects of EMI on surrounding electronics once the VCM is installed in an electronic device and is in operation with current flowing through the coil. 
         [0006]    However, during manufacture, the magnetic flux field created by the permanent magnet adversely affects the manufacturing process and, potentially, the acceptable production yield of camera modules containing the VCMs. More specifically, the repelling force or magnetic interference from the permanent magnet(s) inside voice coil motors in adjacent or proximally located voice coil motors or camera assemblies can cause the voice coil motors or camera assemblies to physically shift or move. This is particularly problematic during the manufacturing step of adhering VCMs to image sensors on a printed circuit board or substrate where an adhesive is used to bond these two components to a printed circuit board to create camera modules. Alignment of the VCM relative to the image sensor is a critical step in achieving a camera that outputs acceptable images. If the image sensor and VCM are not properly aligned, the resulting image quality is adversely affected and the camera module formed with the misaligned VCM and image sensor will not pass quality testing and will not be assembled into an electronic device. Thus care must be taken to separate VCMs and associated image sensors a sufficient distance apart from adjacent or proximately positioned VCMs and associated image sensors such that, during the time period before the bonding adhesive fully cures, the repelling force or magnetic interference of nearby permanent magnets does not cause the position of a voice coil motor to shift relative to its associated image sensor. Because of the need for adequate spacing between adjacent or proximate VCMs and associated image sensors, the maximum number of VCMs and associated image sensors that can be processed at one time in any particular manufacturing process is physically limited. Moreover, the existing EMI shields  18  are not designed to resolve this problem, but are designed solely to restrict electromagnetic flux created by the coil and yoke when current is flowing in the coil. 
       SUMMARY OF THE INVENTION 
       [0007]    According to one embodiment of the present invention, a method of manufacturing camera modules is provided comprising providing a plurality of image sensors affixed to a substrate, applying an adhesive to the substrate generally around the perimeter of each image sensor, providing a first voice coil motor and associated movable lens, associating a magnetic shield with the first voice coil motor and lens, positioning the first voice coil motor, lens and associated magnetic shield on the adhesive associated with a first image sensor, providing a second voice coil motor and associated movable lens, associating a second magnetic shield with the second voice coil motor and lens, and positioning the second voice coil motor, lens and associated magnetic shield closely adjacent the first voice coil motor, lens and associated first magnetic shield, wherein the distance separating the first and second voice coil motors is reduced due to the presence of the magnetic shields. As a result, the number of camera modules assembled on the substrate may be increased compared to the number of camera modules that could be assembled on the substrate in the absence of the magnetic shields. 
         [0008]    According to a second embodiment of the invention, the magnetic shield associated with each voice coil motor and lens may be reused with a different voice coil motor and lens after the adhesive is cured to bond the first voice coil motor to the first image sensor. 
         [0009]    According to another embodiment of the invention, the magnetic shield is associated with a voice coil motor after the voice coil motor is positioned on adhesive associated with an image sensor. Alternatively, the magnetic shield is associated with the voice coil motor before the voice coil motor is positioned on adhesive associated with an image sensor. 
         [0010]    In a further embodiment of the invention, the magnetic shield remains associated with the voice coil motor and is included in the final electronic device as part of the camera module. 
         [0011]    In a further embodiment of the invention, multiple magnetic shields comprise a single, integral structure. 
         [0012]    In yet another embodiment of the invention, the electromagnetic shield of the voice coil motor is eliminated from the voice coil motor assembly and is replaced by the magnetic shield. 
         [0013]    As used herein, the term camera module refers to an individual voice coil motor lens and associated image sensor bonded to a printed circuit board or substrate. Multiple voice coil motors and associated lens and image sensors mounted on a single printed circuit board or substrate is referred to as a camera assembly on a printed circuit board. 
         [0014]    The Summary of the Invention is neither intended nor should it be construed as being representative of the full extent and scope of the present invention. Moreover, reference made herein to “the present invention” or aspects thereof should be understood to mean certain embodiments of the present invention and should not necessarily be construed as limiting all embodiments to a particular description. The present invention is set forth in various levels of detail in the Summary of the Invention as well as in the attached drawings and the Detailed Description of the Invention and no limitation as to the scope of the present invention is intended by either the inclusion or non-inclusion of elements, components, etc. in this Summary of the Invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and together with the general description of the invention given above and the detailed description of the drawings given below, serve to explain the principles of these inventions. 
           [0016]      FIG. 1  is a perspective view of a voice coil motor having lens motion auto focus actuation. 
           [0017]      FIG. 2  is an exploded perspective view of a voice coil motor of  FIG. 1 . 
           [0018]      FIG. 3  is a cross-section of the voice coil motor of  FIG. 1 . 
           [0019]      FIG. 4  is a top view of a portion of a printed circuit board, further depicting image sensors and adhesive patterns. 
           [0020]      FIG. 5  is a cross-section plan view of a pair of adjacent camera assemblies on a printed circuit board or substrate. 
           [0021]      FIG. 6  is a perspective view of the repelling force generated by permanent magnets of two adjacent voice coil motors. 
           [0022]      FIG. 7  is a top plan view schematic of a layout of camera assemblies on a printed circuit board or substrate for adhesive curing. 
           [0023]      FIG. 8  is an exploded view of a voice coil motor and magnetic shield cap. 
           [0024]      FIG. 9  is a top plan view of schematic layout of camera assemblies on a printed circuit board or substrate and including a magnetic shield cap, and showing a more compact arrangement of the camera assemblies for adhesive curing. 
           [0025]      FIG. 10  is a cross sectional view of a single magnetic shield cap used with multiple voice coil motors. 
       
    
    
       [0026]    It should be understood that the drawings are not necessarily to scale. In certain instances, details that are not necessary for an understanding of the invention or that render other details difficult to perceive may have been omitted. It should be understood, of course, that the invention is not necessarily limited to the particular embodiments illustrated herein. 
       DETAILED DESCRIPTION 
       [0027]    Turning to  FIG. 4 , a top view of a portion of a printed circuit board or substrate panel  32  is shown. Six discrete areas are also shown for camera assemblies. Three image sensors  34 , such as a complementary metal oxide semiconductor (CMOS) or a charge couple device (CCD), are affixed to the substrate  32 . As is further shown, an epoxy or other adhesive  36  is positioned around each of the sensors  34 . 
         [0028]    As part of the manufacturing process, voice coil motors  10  are affixed to the substrate  32  by positioning the VCM  10  on the adhesive pattern  36  associated with each individual image sensor  34 . This may be accomplished with robotics, such as a pick and place machine, or manually. The entire substrate  32  is then positioned within an oven to cause curing of the adhesive  36  such that the VCM and image sensor are effectively bonded together to form a camera assembly. As part of the positioning and curing steps, and as best illustrated in  FIG. 5 , it is critical that the optical axis  30  of the lens  12  align with the optical axis  38  of the image sensor  34 . If the optical axes  30  and  38  are skewed or not aligned, the finished camera module may not pass quality testing. Positioning of the VCM  10  relative to the image sensor  30  can directly affect the ability of the camera module to provide an appropriately focused image. It is, therefore, an essential step that the relative positioning of the VCM relative to the sensor not change prior to or during the curing period. 
         [0029]    Following curing the adhesive, the camera assemblies are separated or singulated resulting in individual camera modules. Apertures or holes  40  are formed in the substrate panel  32  and define each of the discrete areas. The apertures  40  assist in singulating the camera assemblies  10  from each other for subsequent testing and assembly into a finished electronic device. 
         [0030]    During the curing process, it is possible that the permanent magnets  24  within each VCM interact with the permanent magnets  24  in adjacent VCMs due to their proximity on the substrate  32 . This is diagrammatically represented in  FIG. 6  showing the repelling force between two adjacent VCMs  10 . Because of the repelling force or magnetic interference, it is possible for permanent magnets in adjacent VCMs to interact and cause physical movement of one or more lenses  12  relative to the associated image sensor  34  before the adhesive  36  is cured. As a result, it is possible that the optical axis  30  of the lens  12  and the optical axis  38  of the image sensor  34  become skewed or misaligned, thereby adversely degrading the image quality of the resulting camera module. To avoid this type of adverse interaction and to avoid a reduction or loss in manufacturing yield, the individual image sensors  34  are positioned a safe distance apart on the printed circuit board  32  to reduce this adverse interaction between VCMs when the VCMs are positioned on the printed circuit board. A representative example of a printed circuit board having 64 discrete locations  42  for adhering image sensors  34  relative to VCMs  10  to create camera assemblies is shown in  FIG. 7 . As illustrated, the substrate  32  includes four 4×4 arrays of camera assemblies  10 . In this embodiment, the substrate  32  is approximately 62 millimeters by 237 millimeters, and the individual VCMs  10  are typically 8.5 millimeters by 8.5 millimeters. As shown in  FIGS. 5 and 7 , the VCMs are separated by a distance “d.” To avoid or substantially reduce the repelling action of the permanent magnets in adjacent VCMs, the distance “d” in the array shown in  FIG. 7  is approximately 4.5 millimeters. With this orientation and layout, the VCMs  10  cover approximately 32% of the surface area of the printed circuit board  32 , and  64  camera assemblies may be cured simultaneously on the single substrate  32  without magnetic interference causing undesired movement of adjacent VCMs. According to the present invention, the repelling force of the permanent magnets  22  can be substantially constrained or controlled by adding a magnetic shield cap  44  to each VCM  10 . An illustration of such a magnetic shield is shown in  FIG. 8 . The magnetic shield cap  44  is positioned over the camera module prior to the VCM being positioned on the adhesive pattern  36  laid out on the substrate  32 . The magnetic shield cap  44  constrains and controls the flux generated by the permanent magnet. As shown, the shield comprises four side wall panels  46  that generally match the size of the side walls  48  of the VCM. The upper panel  50  is shown with an opening  52  such that it does not interfere with the optical functioning of the lens  12 . An example of material used for the magnetic shield cap  44  is a Co-Netic® foil product, Model AA6F006-4, made by Magnetic Shield Corporation of Bensenville, Ill., having a thickness of 0.15 millimeters. Foil ranging in thickness from approximately 0.05 millimeters to 0.25 millimeters can provide effective shielding with minimum tooling costs. As should be appreciated, many alternative versions of this material will work, with thicker shielding providing a higher shielding effect. 
         [0031]    Set forth below in Table 1 is a comparison of repelling distance in millimeters of two adjacent VCMs of the same construction. Fifteen tests were performed involving 30 VCMs of the same construction. In the first test, the repelling distance was determined without a magnetic shield cap  44  in place. In the second test, the repelling distance was determined with a magnetic shield cap  44  in place. For purposes of this test, the foregoing identified Co-Netic Foil AA6F006-4 having a thickness of 0.15 millimeters. 
         [0000]    
       
         
               
               
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                   
                 Repel Distance (mm) 
               
             
          
           
               
                   
                   
                 W/O Magnetic-Shield Cap 
                 W/ Magnetic-Shield Cap 
               
               
                   
                   
               
             
          
           
               
                   
                  1 
                 4.8213 
                 0.1198 
               
               
                   
                  2 
                 5.7235 
                 0.1403 
               
               
                   
                  3 
                 5.4433 
                 0.1252 
               
               
                   
                  4 
                 4.8012 
                 0.1353 
               
               
                   
                  5 
                 4.2124 
                 0.1461 
               
               
                   
                  6 
                 5.4456 
                 0.1551 
               
               
                   
                  7 
                 4.5100 
                 0.1538 
               
               
                   
                  8 
                 5.3185 
                 0.2207 
               
               
                   
                  9 
                 5.1448 
                 0.1589 
               
               
                   
                 10 
                 5.1197 
                 0.1641 
               
               
                   
                 11 
                 4.5456 
                 0.1609 
               
               
                   
                 12 
                 5.6894 
                 0.1490 
               
               
                   
                 13 
                 4.3446 
                 0.1253 
               
               
                   
                 14 
                 4.4460 
                 0.1461 
               
               
                   
                 15 
                 5.2325 
                 0.1765 
               
               
                   
                 Max 
                 5.7235 
                 0.2207 
               
               
                   
                 Min 
                 4.2124 
                 0.1198 
               
               
                   
                 Average 
                 4.9866 
                 0.1518 
               
               
                   
                   
                 Total QTY (units) 
                 30 
               
               
                   
                   
               
             
          
         
       
     
         [0032]    As can be seen, without a magnetic shield cap  44  in place, the average repelling distance was slightly under 5 millimeters, specifically 4.9866 millimeters. In comparison, with a magnetic shield cap  44  in place, the average repelling distance was reduced by a factor of 33 to 0.1518 millimeters. The resulting effect is that by using magnetic shield caps during the adhesive curing stage of the manufacturing process, adjacent VCMs  10  may be positioned closer together to increase the through-put of the manufacturing process and reduce costs without sacrificing quality or yield. As shown in  FIG. 9 , using a magnetic shield, the same substrate  32  as depicted in  FIG. 7  may comfortably hold 100 VCMs  10  during the curing process with the distance “d” separating the VCM camera assemblies approximately 1.75 millimeters. As a result, the number of camera assemblies increases by more than 50% using a substrate of the same size. The data in Table 1 shows that the VCMs  10  may be positioned even closer together utilizing a magnetic shield cap. However, the limiting factor is the ability for other tooling to cut the substrate and singulate the individual camera modules from each other. Smaller or more precise tooling may allow even more camera assemblies to be utilized within the same area. 
         [0033]    In one embodiment the magnetic shield caps  44  are removed from the camera assemblies  10  following curing of the adhesive, either prior to or following singulation. The removed magnetic cap shields may then be reused during the curing process of a subsequent batch of VCMs, thereby achieving further savings from re-use of the magnetic shield caps. Alternatively, it should be appreciated that the magnetic cap shields may remain in place and be included into the final electronic device. In such circumstances, the electromagnetic interference shield  18  may be completely removed from the VCM assembly and replaced by the magnetic shield cap  44 . The magnetic shield cap  44  will control both the magnetic flux generated by the permanent magnets during the manufacturing process and also the EMI shielding needed to control the magnetic flux generated by the electromagnetics sufficient to meet applicable standards. In another embodiment, illustrated in  FIG. 10 , multiple magnetic shield caps may be formed in a single integral piece  54 . Such a structure may reduce the manufacturing through put time and increase efficiencies in the manufacturing process. 
         [0034]    While various embodiments of the present invention have been described in detail, it is apparent that modifications and alterations of those embodiments will occur to those skilled in the art. However, it is to be expressly understood that such modifications and alterations are within the scope and spirit of the present invention, as set forth in the following claims. 
         [0035]    Other modifications or uses for the present invention will also occur to those of skill in the art after reading the present disclosure. Such modifications or uses are deemed to be within the scope of the present invention.