Abstract:
A housing for protecting a wafer-level camera module and fixing the wafer-level camera module to a printed circuit board (PCB) includes: four side plates, defining a quadrilateral frame; four supporting plates each fixed to a lower portion of an inner face of a corresponding one of the four side plates, each supporting plate having a top face supporting a portion of the camera module; and four bottom plates each fixed to a lower portion of an outer face of a corresponding one of the four side plates, each bottom plate having a bottom face fixed to the PCB. The housing is capable of addressing the issues of poor housing-PCB soldering, paint falling off and surface scratching and improving the efficiency in UV lamp-utilized UV adhesive curing.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims the priority of Chinese patent application number 201220471883.0, filed on Sep. 14, 2012, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to semiconductor packaging technology, and more particularly to a housing for protecting a wafer-level camera module. 
     BACKGROUND 
     Digital cameras have been widely used in a variety of applications. With the advent of some new applications, such as cellular phones, vehicles and security and medical appliances, digital cameras are miniaturized to be adapted for easy mounting. Accordingly, camera module, a component of digital cameras, is required to have low manufacturing cost and small horizontal and vertical occupation areas for its suitability for many applications. Such camera modules may be manufactured on a single wafer by using wafer-level technology and packaging technology, and then the wafer-level camera modules are singulated into individual camera modules. 
       FIG. 1  shows a conventional metal housing of a camera module. The housing includes a quadrilateral top plate  102  and four side plates  108 . The top plate  102  is adapted to protect a camera module  120 . Referring to  FIG. 2 , the camera module further includes a sensor  122  and a lens  124  that is disposed on the sensor  122 . The top plate  102  includes a light through hole  104  which allows incident light to pass through and reach the lens  124  of the camera module  120 . The light through hole  104  is covered with a film (not shown) for protecting the camera module from possible damages in subsequent processes. The side plates  108  are fixed to four sides of the quadrilateral top plate  102 , respectively, and each of them includes an opening  110  and a supporting leg  112 . Out of the four side plates  108 , oppositely disposed two have their openings that are larger than those of the other two which are also disposed opposite to each other. The metal housing is attached to the camera module  120  by ultraviolet (UV) adhesive dispensed through the openings  110 . Moreover, as shown in  FIG. 3 , the supporting legs  112  of the metal housing are soldered to solder balls  114  (not shown) attached to a bonding pad of a printed circuit board (PCB). 
     The above described design suffers from various deficiencies. One deficiency is that the metal housing is separated from the camera module by a great spacing in all three dimensions, and especially in the Z direction (along the height of the metal housing). The great spacings are highly prone to lead to positional deviations between the metal housing and the camera module during the packaging process and therefore further to a poor packaging precision between the solder balls of the PCB and the metal housing with the camera module packaged therein. This will cause cold solder joint between the metal housing and a printed circuit board assembly (PCBA) during the surface mount technology (SMT) process. Moreover, the cold solder joint will harm the reliability of the resulting housing after the assembled metal housing and camera module were soldered to the PCB. 
     Another deficiency is that the great spacing between the metal housing and the camera module in the Z direction, coupled with the existence of tolerances of their heights in the same direction, may cause the occurrence of inclination between the metal housing and the camera module during the process of assembling them together when the metal housing is not sufficiently fixed in the Z direction by the UV adhesive dispensed through the openings  110 . 
     In addition, still another deficiency is that openings of the two side plates  108  with larger openings (e.g., the two side plates  108  opposite to each other in the Y direction, i.e., along the length of the metal housing) expose signal pick-up electrodes disposed on side faces of the sensor of the camera module, leaving the camera module unprotected in the Y direction throughout the subsequent assembly processes. Considering that bumps cannot yet be totally prevented in the current manufacturing technology, once a bump occurs, the exposed signal pick-up electrodes disposed on the sensor which are not protected by the metal housing in the Y direction are very likely to be cracked, which will lead to product failure and defects. Thus, as the sensor  122  of the conventional camera module  120  with the metal housing is unprotected in the Y direction, it is vulnerable to impact in this direction. 
     Moreover, still yet another deficiency is that the great spacings between the metal housing and the camera module in the X and Y directions (i.e., along the width and the length of the metal housing, respectively) may cause deviations in alignment to a center of the light through hole  104  during the process of assembling the metal housing and the camera module together. This may lead to inaccurate alignment between the light through hole  104  and the lens  124 . 
     Furthermore, as there is a great color difference between the metal housing and the lens  124 , the metal housing is generally painted to make the outer surface color of the quadrilateral top plate  102  same with that of the lens  124 . However, outer surface of the quadrilateral top plate  102  may be scratched by a clip which is used in the assembly process to pick up the metal housing and place it to cover the camera module. Moreover, removal of the film covering the light through hole  104  after the completion of all subsequent processes may also lead to local loss (falling off) of paint applied on surface of the metal housing and hence harm its appearance. 
     Still yet another deficiency is that although UV adhesive can be conveniently dispensed through any of the four side plate openings  108 , in order to cure the dispensed UV adhesive, this design generally requires moving a point light source individually close to each opening. This practice is inefficient. 
     SUMMARY OF THE INVENTION 
     The present invention seeks to address the prior art deficiencies discussed above by presenting a modified housing for a wafer-level camera module. 
     To this end, the present invention provides a housing for protecting a wafer-level camera module and fixing the wafer-level camera module to a PCB. The housing includes: four side plates, defining a quadrilateral frame; four supporting plates each fixed to a lower portion of an inner face of a corresponding one of the four side plates, each supporting plate having a top face supporting a portion of the camera module; and four bottom plates each fixed to a lower portion of an outer face of a corresponding one of the four side plates, each bottom plate having a bottom face fixed to the PCB. 
     Preferably, the housing may have a length of 2.0 mm to 7.0 mm, a width of 2.0 mm to 7.0 mm and a height of 1.0 mm to 3.0 mm. 
     Further, each supporting plate may have a length smaller than a length of the lower portion of the corresponding side plate to which the supporting plate is fixed, and wherein each of the four supporting plates is arranged at a same end of the lower portion of the inner face of the corresponding side plate. 
     Preferably, each supporting plate may have a length of 1.0 mm to 3.0 mm and a width of 0.2 mm to 0.6 mm. 
     Further, each bottom plate may have a length smaller than a length of the lower portion of the corresponding side plate to which the bottom plate is fixed, and wherein each of the four bottom plates is arranged at a same end of the lower portion of the outer face of the corresponding side plate. 
     Preferably, each bottom plate may have a length of 1.0 mm to 3.0 mm and a width of 0.2 mm to 0.6 mm. 
     Further, the PCB may be provided with bonding pads corresponding to the bottom plates. 
     Preferably, the housing may be formed of a material selected from the group consisting of copper-nickel-zinc alloy, brass and stainless steel. 
     Preferably, each of the side plates, supporting plates and bottom plates may have a thickness of 0.06 mm to 0.1 mm. 
     Further, the camera module may include a lens and a sensor, and the lens is disposed on surface of the sensor. 
     Further, soldering points for being coupled to the supporting plates may be arranged on a bottom face of the lens of the camera module. 
     Further, the camera module may be fixed to the inner faces of the side plates by an adhesive. 
     Preferably, the adhesive may be ultraviolet adhesive. 
     In light of the above description, assembly between the housing and the camera module can be achieved by fixing the four supporting plates to lower portions of inner faces of the respective side plates, forming the quadrilateral frame with the four side plates and placing the camera module on the four supporting plates. Moreover, it can be achieved to assemble the assembly of the housing and the camera module to the PCB by fixing the bottom plates to lower portions of outer faces of the respective side plates and then the bottom plates to the PCB. 
     With such design, the four supporting plates of the housing are in direct contact with the camera module in the Z direction without any spacing left therebetweeen and the housing is separated from the camera module only in the X and Y directions. Accordingly, the housing and the camera module can be assembled with an improved accuracy. 
     Substitution of the supporting legs of the prior art which lead to a great spacing between the housing and soldering balls on the PCB for the sheet-shaped bottom plates reduces the spacing and thereby improves distance accuracy between the housing and PCB soldering balls. This can address the poor soldering problem between the housing and the PCBA in the subsequent SMT process and hence improves the reliability of the resulting housing after the assembly of the housing and the wafer-level camera module is soldered onto the PCB. 
     Additionally, as there is no spacing between the housing and the camera module in the Z direction, when an adhesive is dispensed into the open spaces between the side plates and the camera module, no issue of inclination between the housing and the camera module will arise in the process of assembling. 
     Moreover, the four side plates of the housing not only protect the camera module in the X direction, but also protect circuitry on the sensor of the camera module in the Y direction, thereby increasing impact resistance of the sensor in the Y direction. 
     In addition, the housing is a half-enclosure without a top closing plate, which exposes the camera module from the top. Accordingly, the lens of the camera module may receive incident light directly. This addresses the prior art issue of alignment inaccuracy between the center of the light through hole of the metal housing and the lens of the camera module. 
     Furthermore, non-adoption of shielding elements for the camera module  300  addresses the prior art issue of color difference between the metal housing and the lens of the camera module. It eliminates the necessity of painting the housing and protecting a central portion of the camera module lens with a film and therefore prevents the paint falling off and surface scratching issues that may occur in the assembly between the housing and the camera module. 
     Furthermore, a UV lamp can be held over the open spaces between the assembled housing and camera module to more efficiently cure adhesive dispensed in the spaces at the same time rather than in an individual manner. Separately, the house of the present invention has a simple structure which results in assembly cost reduction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic illustration of a conventional metal housing. 
         FIG. 2  shows a schematic illustration of a camera module suited to be protected by the metal housing of  FIG. 1 . 
         FIG. 3  shows a schematic illustration of the metal housing of  FIG. 1  after it has been assembled with a camera module. 
         FIG. 4  shows a schematic illustration depicting a housing for protecting a wafer-level camera module in accordance with one embodiment of the present invention. 
         FIG. 5  shows a schematic illustration of a camera module suited to be protected in accordance with one embodiment of the present invention. 
         FIG. 6  shows a schematic illustration of a wafer-level camera module protection housing with a camera module assembled therein in accordance with one embodiment of the present invention. 
         FIG. 7  schematically illustrates the dimensions of a completed wafer-level camera module protection housing in the X and Y directions in accordance with one embodiment of the present invention. 
         FIG. 8  schematically illustrates the dimension of a completed wafer-level camera module protection housing in the Z direction in accordance with one embodiment of the present invention. 
         FIG. 9  shows a schematic illustration of a PCB suited to be soldered to a wafer-level camera module protection housing in accordance with one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The above and other objectives, features and advantages of the invention will be readily apparent upon reading of following detailed description on exemplary embodiments with reference to the accompanying drawings. 
     Numerous specific details are set forth in the following description to provide a thorough understanding of the present invention. It will be apparent to those skilled in this art that the invention may be embodied in many different forms from the exemplary ones described hereunder and that various variants of the exemplary embodiments may be made without departing from the present teachings. Thus, the exemplary embodiments should not be construed to limit the scope of the invention. 
       FIG. 4  shows a schematic illustration showing a housing embodying the present invention for protecting a wafer-level camera module. The housing is also configured to fix the wafer-level camera module on a PCB. The housing includes four side plates  202 , four supporting plates  204  and four bottom plates  206 . Four side plates  202  form a quadrilateral frame. Preferably, the quadrilateral frame may have a rectangular shape. A camera module  300  may be attached to inner side faces of the quadrilateral frame with an adhesive. As shown in  FIG. 5 , the camera module may include a sensor  302  and a lens  304 , and the lens  304  is disposed on surface of the sensor  302 . Each supporting plate  204  is fixed to a lower portion of the inner face of a corresponding side plate  202 , and a top face of the supporting plate  204  supports a portion of the camera module  300 . Each bottom plate  206  is fixed to a lower portion of an outer face of a corresponding side plate  202 , and a bottom face of the bottom plate  206  is fixed to the PCB. 
     Preferably, the housing may have a length (along the X direction) of 2.0 mm to 7.0 mm, a width (along the Y direction) of 2.0 mm to 7.0 mm and a height (along the Z direction) of 1.0 mm to 3.0 mm. In a best mode, with reference to  FIG. 7  demonstrating the dimensions of the housing in the X and Y directions and  FIG. 8  demonstrating the dimension of the housing in the Z direction, the housing has a length of 3.38 mm, a width of 3.83 mm and a height of 1.23 mm. 
     As can be seen from  FIGS. 4 and 7 , as there is spacing between the housing and the camera module  300  only in the X and Y directions, it can be assembled to the camera module  300  with reduced inaccuracy. 
     Additionally, there is no spacing between the housing and the camera module  300  in the Z direction. That is, the housing is in direct contact with the camera module  300  at top faces of the four supporting plates  204 . Therefore, as shown in  FIG. 6 , when an adhesive is dispensed into the open space  208  between the quadrilateral frame and the camera module  300 , no issue of inclination between the housing and the camera module  300  will arise in the process of assembling them. Preferably, the adhesive may be ultraviolet (UV) adhesive. 
     In one variant, instead of employing the adhesive, soldering points may be prearranged on a bottom face of the lens  304  of the camera module  300  and soldered to corresponding positions of the four supporting plates  204  with soldering tin applied in advance on the soldering points. This can increase manufacturing efficiency and consistency and result in the integration as a whole of the housing and the PCB in the subsequent SMT process by PCBA soldering. 
     With further reference to  FIG. 4 , as the housing includes four side plates  202  and none of them has any opening, the housing can not only protect the camera module  300  in the X direction, but can also protect circuitry on the sensor  302  of the camera module  300  in the Y direction, thereby increasing impact resistance of the sensor  302  in the Y direction. In particular, in the variant described above where the supporting plates  204  of the housing are soldered to the lower portion of the lens  304  of the camera module  300 , the protection capability of the housing both in the X and Y directions can provide signal pick-up electrodes arranged on the sensor  302  with the most effective protection. 
     With continuing reference to  FIG. 4 , the length of each supporting plate  204  may be smaller than that of a lower side of the corresponding side plate  202  to which the supporting plate  204  is fixed, and all the supporting plates  204  are arranged at a same end, e.g., the left end, of the lower portions of the inner faces of the corresponding side plates  202 . 
     Preferably, each supporting plate  204  may have a length of 1.0 mm to 3.0 mm and a width of 0.2 mm to 0.6 mm. In a best mode, as shown in  FIG. 7 , each supporting plate  204  has a width of 0.3 mm. 
     As indicated above, after the four supporting plates  204  and the four side plates  202  that form the quadrilateral frame are assembled together, the camera module  300  may be placed on top faces of the four supporting plates  204 . That is, the camera module  300  may be assembled with the four supporting plates  204  and the quadrilateral frame at the bottom, leaving spacings and the open space  208  (as shown in  FIG. 6 ) between the quadrilateral frame and the camera module  300 . In such design, the lens  304  of the camera module  300  is directly exposed and therefore can directly receive incident light. This can address the prior art issue of alignment inaccuracy between the center of the light through hole of the metal housing and the lens of the camera module. 
     Moreover, non-adoption of shielding elements for the camera module  300  addresses the prior art issue of color difference between the metal housing and the lens of the camera module. It eliminates the necessity of painting the housing and protecting a central portion of the camera module lens with a film and therefore prevents the paint falling off and surface scratching issues that may occur in the assembly between the housing and the camera module. 
     In addition, with further reference to  FIG. 6 , the four side plates  202  may be fixed to the camera module  300  by dispensing UV adhesive into the open space  208 . A UV lamp may be held over the open space  208  to more efficiently cure the UV adhesive at the same time rather than in an individual manner. 
     With continuing reference to  FIG. 4 , the length of each bottom plate  206  may be smaller than that of a lower portion of the corresponding side plate  202  to which the bottom plate  206  is fixed, and all the bottom plates  206  are arranged at a same end, e.g., the right end, of the lower portions of the outer faces of the corresponding side plates  202 . The bottom plates  206  enable the housing  200  to be fixed on the PCB. 
     Preferably, each bottom plate  206  may have a length of 1.0 mm to 3.0 mm and a width of 0.2 mm to 0.6 mm. In a best mode, as shown in  FIG. 7 , each bottom plate  206  oriented along the X direction has a length of 1.7 mm and a width of 0.3 mm, whilst each bottom plate  206  oriented along the Y direction has a length of 2.15 mm and a width of 0.3 mm. 
     Preferably, the housing  200  may be formed of a material selected from the group consisting of copper-nickel-zinc alloy, brass and stainless steel. In a best mode, the housing  200  is made of copper-nickel-zinc alloy. 
     Preferably, each above discussed component (i.e., each side, supporting or bottom plate) of the housing  200  may have a thickness of 0.06 mm to 0.1 mm. In a best mode, each component of the housing  200  is made of copper-nickel-zinc alloy and has a thickness of 0.08 mm. 
     Preferably, the housing  200  may be manufactured by plate press technology. 
     Preferably, each component of the housing  200  has a thickness of 0.08 mm. 
     Further, referring to  FIG. 9 , the PCB may be provided with bonding pads  402  corresponding to the bottom plates  206 . Moreover, the housing  200  may be fixed to the PCB by soldering the bottom plates  206  to the corresponding bonding pads  402 . 
     Preferably, the PCB may have a length of 2.0 mm to 7.0 mm and a width of 2.0 mm to 7.0 mm. In a best mode, the PCB may have a length of 3.7 mm and a width of 4.2 mm. 
     Preferably, each bonding pad  402  may have a length of 1.0 mm to 3.0 mm and a width of 0.2 mm to 0.6 mm. In a best mode, each bonding pad  402  oriented along the X direction has a length of 2.05 mm and a width of 0.3 mm, whilst each bonding pad  402  oriented along the Y direction has a length of 2.5 mm and a width of 0.3 mm. 
     Further, with continuing reference to  FIG. 9 , the PCB may also be provided with soldering balls  404  configured to lay out sensor circuitry. Preferably, the soldering ball  404  may have a critical dimension (diameter) Ø of 0.2 mm to 0.4 mm. In a best mode, the critical dimension of the soldering balls  404  is 0.28 mm. 
     The supporting legs  112  of the prior art metal housing lead to a great spacing between housing and soldering balls on the PCB, which is prone to cause great positional deviations between the sensor of the camera module and the soldering balls during the process of soldering the housing to the bonding pads of the PCB. In contrast, employment of the sheet-shaped bottom plates enables the housing of the present invention to reduce its distance to the PCB, thereby improving distance accuracy between the housing and soldering balls of the PCB. This addresses the poor soldering issue between the housing and the PCBA in the subsequent SMT process and hence improves the reliability of the resulting structure after the assembly of the housing and the wafer-level camera module is soldered onto the PCB. 
     It will be appreciated that the sizes of the components in the best modes are provided solely for describing an approach to obtain an optimum assembly between the housing  200  and the camera module and to thereby better fix the housing onto the PCB and should not be construed as limitations on the scope of the invention. 
     Compared to the prior art housing that has a fully enclosing structure, the housing of the present invention is a half-enclosure, simple in structure and able to reduce assembly fixture cost. It is capable of achieving the purposes of protecting the camera module and fixing the camera module on the PCB even with the supporting and bottom plates not fully coupled to the side plates. 
     While preferred embodiments are described and illustrated above, they are not intended to limit the invention in any way. Those skilled in the art can make various modifications and variations without departing from the scope of the invention. Thus, it is intended that the present invention embrace all such modifications and variations as fall within the scope of the appended claims.