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 camera modules to be positioned closer together during the manufacturing process. This increases manufacturing throughput and reduces cost.

Description:
CROSS REFERENCE 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 13/543,343 filed Jul. 6, 2012, entitled “Camera Module with Magnetic Shielding and Method of Manufacture,” which is the non-provisional of U.S. Provisional Pat. App. No. 61/504,778 filed Jul. 6, 2011, entitled “Camera Module with Magnetic Shielding and Method of Manufacture,” which are hereby incorporated in their entirety by reference. 
     
    
     BACKGROUND 
       [0002]    The disclosure herein relates generally to electronic devices, and more particularly to digital camera modules. Even more particularly, it relates to a digital camera module manufacturing technique. 
         [0003]    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 digital 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. 
         [0004]    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 to the image capture device. The housing may include a voice coil motor (VCM) module for adjusting the position of the lens unit. To save time and costs of manufacturing, a group of camera modules may be simultaneously manufactured in array form. 
         [0005]    The VCM module may include components such as a frame, permanent magnets, one or more springs, and an EMI shield. The magnets produce a strong magnetic field and will interact with another magnet nearby, such as if another VCM module is nearby. An example of this is shown in  FIG. 1 . This can present challenges in array manufacturing. Repelling forces from the magnets inside the VCM modules can cause inconsistent repelling distances, in one case in the range of 3.0-4.0 mm. Accordingly, larger spacing between image sensors on the silicon (minimum unit to unit gap 4.50 mm) may be required. This spacing increases the cost per camera module significantly. The EMI shield is designed to significantly block electromagnetic interference or flux, but does not significantly block magnetic flux. 
         [0006]    One approach to addressing this problem is to increase the unit to unit gap. That is, increase the unit to unit gap to 4.50 mm in order to minimize the repelling force between the VCM. (Refer to panel layout in  FIG. 2 ). One problem with this approach is that it results in inefficient and costly use of the silicon. Another problem is that the reduced unit quantity per silicon wafer results in a low VCM attach machine throughput (measured in units per hour, or UPH). 
         [0007]    Another approach to addressing this problem includes the singulation method illustrated in  FIG. 3 . The image sensors on the silicon can be singulated and attached onto a copper frame with greater spacing than on the silicon. The singulation method is an additional process that increases the manufacturing cost. Also, the singulation method tends to generate particulate debris that can degrade the image quality of the camera module and cause high yield loss. 
         [0008]    What is needed, therefore, is a camera module manufacturing technique that is allows for small module spacing in array processing. 
       SUMMARY 
       [0009]    Disclosed herein is a method for manufacturing camera modules that includes: providing a plurality of image sensors on a substrate, including a first and a second image sensor that are adjacent to each other; providing a plurality of VCM modules, including a first and a second VCM module, each VCM module adapted for attachment to an image sensor; providing a plurality of magnetic shields, including a first and a second magnetic shield, each shield adapted for placement over a VCM module; placing the first magnetic shield on the first VCM module and the second magnetic shield on the second VCM module; attaching the first VCM module, with the first magnetic shield thereon, to the first image sensor; and attaching the second VCM module, with the second magnetic shield thereon, to the second image sensor. 
         [0010]    The method may further include moving the first and second image sensor, with the VCM modules and magnetic shields thereon, away from each other. The method may further include removing the magnetic shields from the VCM modules. The magnetic shields may include high magnetic permeability metal alloy material. 
         [0011]    Also disclosed herein is a camera module that includes: an image sensor; a VCM module attached to the image sensor; and a magnetic shield attached to the camera module so as to surround the VCM module. The magnetic shield significantly reduces a magnetic field from the VCM module in the immediate vicinity around the exterior of the magnetic shield. 
         [0012]    The magnetic shield may include high magnetic permeability metal alloy material. 
         [0013]    According to one embodiment, 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. 
         [0014]    According to a second embodiment, 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. 
         [0015]    According to another embodiment, 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. 
         [0016]    In a further embodiment, the magnetic shield remains associated with the voice coil motor and is included in the final electronic device as part of the camera module. 
         [0017]    In a further embodiment, multiple magnetic shields comprise a single, integral structure. 
         [0018]    In yet another embodiment, the electromagnetic shield of the voice coil motor is eliminated from the voice coil motor assembly and is replaced by the magnetic shield. 
         [0019]    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. 
         [0020]    The Summary 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 as well as in the attached drawings and the Detailed Description 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. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The disclosure herein is described with reference to the following drawings, wherein like reference numbers denote substantially similar elements: 
           [0022]      FIG. 1  is a perspective view of the repelling force generated by permanent magnets of two adjacent voice coil motors; 
           [0023]      FIG. 2  is a plan view of a wafer with a plurality of image sensors defined thereon, the spacing between individual image sensors being relatively high; 
           [0024]      FIG. 3  is a process flow of a method for singulating image sensors and significantly spacing them apart from each other before assembling camera modules; 
           [0025]      FIGS. 4   a ,  4   b , and  4   c  are perspective views of portions of a camera module, with the three views showing various degrees of explosion; 
           [0026]      FIG. 5  is a schematic view of an array of image sensors, an array of VCM modules, and an array of magnetic shield caps; 
           [0027]      FIG. 6  is a schematic view of an array of image sensors and an array of VCM modules with magnetic shield caps applied thereto; 
           [0028]      FIG. 7  is a schematic view of an array of image sensors with VCM modules and magnetic shield caps applied thereto; 
           [0029]      FIG. 8  is a schematic view like  FIG. 7 , with the magnetic shield caps removed therefrom; and 
           [0030]      FIG. 9  is a plan view of a wafer with a plurality of image sensors defined thereon, the spacing between individual image sensors being relatively lower than the wafer of  FIG. 2 . 
       
    
    
       [0031]    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 
       [0032]    While the embodiments disclosed herein are susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that it is not intended to limit the invention to the particular form disclosed, but rather, the invention is to cover all modifications, equivalents, and alternatives of embodiments of the invention as defined by the claims. The disclosure is described with reference to the drawings, wherein like reference numbers denote substantially similar elements. 
         [0033]      FIGS. 4   a - 4   c  are exploded views of a VCM-based camera module  10 . In general terms, the camera module  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 , a base  22 , and an image sensor  34 . The voice coil motor (formed by the frame  14 , spring  16 , EMI shield  18 , yoke  20 , and base  22 ) serves to adjust the position of the lens  12 . In general terms, and with respect to adjustment of the lens  12  position, the voice coil motor of the camera module  10  includes one or more permanent magnets  24  fixed to the yoke  20  and a wire coil associated with the lens housing  28 . The coil comprises a number of turns of wire and is positioned radially inwardly from the permanent magnet  24 . By driving current through the coil, 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 causes the lens to move in opposite directions. Moving the lens along its optical axis  30 , towards or away from the image sensor  34 , to focus a target image on the image sensor  34 . One or more springs  16  are utilized to assist in maintaining the orientation of the lens  12  within the camera module  10  and relative to the image sensor  34  and to provide a known resistive or opposing force to the movement imparted by the voice coil motor on the lens  12 . 
         [0034]    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(s) or magnets generates or creates 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. 
         [0035]    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. More specifically, the repelling force or magnetic interference from the permanent magnet(s) inside VCMs in adjacent or proximally located camera modules can cause the camera modules to physically shift or move. This is particularly problematic during the manufacturing step of adhering the VCMs to image sensors  34  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  34  is a critical step in achieving a camera module that outputs acceptable images. If the image sensor  34  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  34  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  34  a sufficient distance apart from adjacent or proximately positioned VCMs and associated image sensors  34  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  34 . Because of the need for adequate spacing between adjacent or proximate VCMs and associated image sensors  34 , the maximum number of VCMs and associated image sensors  34  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. 
         [0036]      FIG. 5  includes a schematic view of an array of image sensors  34 , such as complementary metal oxide semiconductor (CMOS) image sensors or charge coupled device (CCD) image sensors. The image sensors  34  may be already attached to a single substrate, each attached to a separate substrate, each attached together (e.g., as part of a wafer), or otherwise arranged. Also arranged are a plurality of VCMs ready for attachment to the image sensors and a plurality of magnetic shield caps  50  ready for attachment thereto. An optical axis  38  is shown for a representative one of the image sensors  34  and an optical axis  30  for a representative one of the lenses. 
         [0037]    As is shown in  FIG. 6 , an epoxy or other adhesive  36  is positioned around the outside of the active area of each of the sensors  34 . As part of the manufacturing process, the magnetic shield caps  50  are each placed over a corresponding one of the VCMs. 
         [0038]    As shown in  FIG. 7 , the VCMs (with the magnetic shield caps thereon) are next affixed to the image sensors  34  via the adhesive associated with each individual image sensor  34 . This may be accomplished with robotics, such as a pick and place machine, or manually. The entire array of assembled camera modules (with magnetic shield caps thereon) may then be positioned within an oven to cause curing of the adhesive  36  such that the VCM camera module and image sensor  34  are effectively bonded together to form a camera module. As part of the positioning and curing steps, the optical axis  30  of the lens  12  can be kept in alignment with the optical axis  38  of the image sensor  34 , since the magnetic shield caps  50  help to prevent the magnetic flux from the permanent magnets in the VCMs from affecting the relative positioning of adjacent VCMs. Note that while the adhesive is described as having been applied to the top surface of the image sensor  34 , it may alternatively be applied to a substrate to which the image sensor  34  is applied. Alternatively, some other means of connection of the VCMs to the image sensors may be achieved. 
         [0039]    Following curing the adhesive, the assembled camera modules may be separated or singulated resulting in individual camera modules, depending on whether the image sensors were still part of a wafer or otherwise arranged. 
         [0040]    As was illustrated in  FIG. 2 , without the magnetic shield caps, the image sensors  34  were arranged in four 4×4 arrays of image sensors. In this embodiment, the illustrated area is approximately 62 millimeters by 237 millimeters, and the individual image sensors are 8.5 millimeters by 8.5 millimeters and 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. 2  is approximately 4.5 millimeters. With this orientation and layout, the image sensors cover approximately 32% of the surface area of the illustrated area, and 64 camera modules may be assembled in this space without magnetic interference causing undesired movement of adjacent VCMs. As disclosed herein, the repelling force of the permanent magnets can be substantially constrained or controlled by adding one of the magnetic shield caps  50  on top of each VCM. 
         [0041]    An illustration of four of the magnetic shield caps is shown in  FIG. 5 . As discussed above, the magnetic shield cap  50  is positioned over the VCM before it is positioned on the adhesive  36  on the image sensor  34 . The magnetic shield cap  50  constrains and controls the flux generated by the permanent magnets. As shown, the shield cap  50  includes four side wall panels  46  that generally match the size of the side walls  48  of the VCM. The upper panel  51  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  50  is a Co-Netic® foil product, Model AA6F006-4, made by Magnetic Shield Corporation of Bensenville, Ill., having a thickness of 0.15 millimeters. In one embodiment, foil ranging in thickness from approximately 0.05 millimeters to 0.25 millimeters can provide effective shielding with minimum tooling costs, although other thicknesses may also suffice. As should be appreciated, many alternative versions of this material will work, with thicker shielding providing a higher shielding effect. Further, while the caps have been shown as having an opening corresponding with the lens, but that may not be necessary in instances where the cap will be removed prior to operation. 
         [0042]    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  50  in place. In the second test, the repelling distance was determined with a magnetic shield cap  50  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 
               
               
                   
               
             
          
         
       
     
         [0043]    As can be seen, without a magnetic shield cap  50  in place, the average repelling distance was slightly under 5 millimeters, specifically 4.9866 millimeters. In comparison, with a magnetic shield cap  50  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  50  during the adhesive curing stage of the manufacturing process, adjacent VCMs 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 illustrated area as depicted in  FIG. 7  may comfortably hold 100 camera modules  10  during the curing process with the distance “d” separating the VCM camera assemblies modules approximately 1.75 millimeters. As a result, the number of camera modules  10  increases by more than 50% using a substrate of the same size. The data in Table 1 shows that the VCMs may be positioned even closer together utilizing a magnetic shield cap  50 . 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 modules to be utilized within the same area. 
         [0044]    In one embodiment the magnetic shield caps  50  are removed from the camera modules  10  following curing of the adhesive, either prior to or following singulation. The removed magnetic shield caps  50  may then be reused during the curing process of a subsequent batch of camera modules, thereby achieving further savings from re-use of the magnetic shield caps  50 . Alternatively, it should be appreciated that the magnetic shield caps  50  may remain in place and be included into the final camera module. In such circumstances, the electromagnetic interference shield  18  may be completely removed from the VCM and replaced by the magnetic shield cap  50 . The magnetic shield cap  50  will control both the magnetic flux generated by the permanent magnets during the manufacturing process and also the EMI shielding needed to control the electromagnetic flux generated by the electromagnetics sufficient to meet applicable standards. In another embodiment, not illustrated, multiple magnetic shield caps may be formed in a single integral piece. Such a structure may reduce the manufacturing through put time and increase efficiencies in the manufacturing process. 
         [0045]    As previously alluded to, for static or slowly varying magnetic fields (below about 100 kHz) the Faraday shielding of the EMI shield described above is ineffective. In these cases, shields made of high magnetic permeability metal alloys can be used, such as sheets of Permalloy and Mu-metal or with nanocrystalline grain structure ferromagnetic metal coatings. These materials do not block the magnetic field, as with electric shielding, but rather draw the field into the material, providing a path for the magnetic field lines around the shielded volume. One optimal shape for magnetic shields is thus a closed container surrounding the shielded volume. The effectiveness of this type of shielding depends on the material&#39;s permeability, which generally drops off at both very low magnetic field strengths, and also at high field strengths where the material becomes saturated. So to achieve low residual fields, magnetic shields often include several enclosures, one inside the other, each of which successively reduces the field inside it. 
         [0046]    While the embodiments of the invention have been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered as examples and not restrictive in character. For example, certain embodiments described hereinabove may be combinable with other described embodiments and/or arranged in other ways (e.g., process elements may be performed in other sequences). Accordingly, it should be understood that only example embodiments and variants thereof have been shown and described.