Abstract:
In one embodiment, an image sensor module having an auto-aligned lens includes: a substrate on which an image sensor chip is mounted; a housing which has an opening to expose an upper surface of the image sensor chip, and which is attached onto the substrate; a lens holder which extends the opening vertically and upwardly; and a lens unit incorporating spacers which is fixed to an inner sidewall of the lens holder and is aligned automatically. Friction-caused particles are not produced, and focal alignment is readily automated.

Description:
BACKGROUND OF THE INVENTION 
     This application claims the priority of Korean Patent Application No. 2004-28628 filed on Apr. 26, 2004 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     1. Field of the Invention 
     The present invention relates to an image sensor module and a method of fabricating the same, and more particularly, to an image sensor module in which a focal length of a lens can be automatically aligned, and a method of fabricating the same, and a method of automatically controlling a focus of the lens. 
     2. Description of the Related Art 
     Due to the recent popularity of various mobile electronic products such as cellular phones, Portable Digital Assistants (PDA), and digital cameras, digital photography has become very important. Specifically, a palm-sized apparatus having a digital camera such as PDA and cellular phone employs a key technique for photographing and transmitting an image. Accordingly, an image sensor module for processing an external image into a digital signal is of importance. 
       FIG. 1  is a cross-sectional view schematically illustrating a conventional image sensor module. 
     Referring to  FIG. 1 , an image sensor chip  12  is mounted on and electrically connected with the substrate  10  by a bonding wire  14 . A digital signal processor (DSP) chip  16  can be mounted onto the other surface of the substrate  10  opposite to the image sensor chip  12 . The DSP chip  16  is attached to the substrate  10  and electrically thereto to the substrate  10  through the bonding wire  14 . After that, the DSP chip  16  is encapsulated by a mold  18 . A housing  20  is attached onto the substrate  10  and has an opening  22  for exposing an upper surface of the image sensor chip  12 . A lens holder  24  is provided on the housing  20 . The lens holder  24  extends the opening  22  vertically and upwardly and has a lens assembly unit  26  affixed to an inner sidewall thereof. The lens assembly unit  26  has a plurality of lenses and is threaded into the lens holder  24 . 
     The lens assembly unit  26  includes a toothed connection unit on an outer side surface thereof for threaded engagement with the toothed connection unit corresponding to an inner sidewall of the lens holder  24 . The lens assembly unit  26  is affixed to manually control a vertical distance (d) between an upper surface of the image sensor chip  12  and the lowermost end of a lens  28 . That is, the vertical distance (d) is controlled to be consistent with the focal length provided by the plurality of lenses  28 . An infrared screen filter  30  can be provided between the lens  28  and the image sensor chip  12  to screen against infrared radiation. 
     However, a conventional method of fabricating the image sensor module including the lens assembly unit  26  has several drawbacks. First, because the vertical distance (d) is controlled in a screw manner, impurity particles are generated due to the friction between the screw threads of the lens assembly unit  26  and those of the lens holder  24  formed of a polymer material, for example, polycarbonate and polyphenylsulfide. Further, due to the manual alignment control of the lens  28 , a separate process is required for manually controlling the focal length. Furthermore, since a diameter or a width (W 1 ) of the lens holder  24  is determined including the lens assembly unit  26 , it is disadvantageous when the image sensor module is to be miniaturized. 
     To solve the above drawbacks, U.S. Pat. No. 6,483,652 discloses an image sensor module in which a predetermined jaw is provided at an inner sidewall of the lens holder  24  without a lens assembly unit  26  to affix a lens. However, since the U.S. patent has the limitation to single-lens optics, it has a difficulty in the application of optics employing a plurality of lenses. In detail, to affix the plurality of lenses, a plurality of jaws are provided at an inner sidewall of the lens holder. However, the plurality of jaws have each a different radius to affix the plurality of lenses to the lens holder  24 . Accordingly, the lenses also need to have different radiuses. Therefore, it has been very difficult to control the focal lengths of the lenses. Further, because the lens needs to be inserted into the lens holder one-by-one, the process of inserting the lens is complicated, thereby increasing the manufacturing costs. Also, it has been difficult to employ injection molding since the lens holder should be made very precisely. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention provide an image sensor module in which a lens is automatically aligned to have a focal length consistent with a focal length of a plurality of lenses, and an image sensor chip module can be miniaturized. 
     Also, embodiments of the present invention provide a method of fabricating an image sensor module in which a lens is automatically aligned to have a focal length consistent with a focal length of a plurality of lenses, and an image sensor chip module can be miniaturized. 
     Further, embodiments of the present invention provide a method of automatically controlling a focal length of a plurality of lens. 
     According to an embodiment of the present invention, there is provided an image sensor module having an auto-aligned lens, the module including: a substrate for mounting an image sensor chip; a housing which has an opening for exposing an upper surface of the image sensor chip, and which is attached onto the substrate; a lens holder which extends the opening vertically and upwardly; and a lens unit having a plurality of lenses with a spacer disposed therebetween. The lens unit is affixed to an inner sidewall of the lens holder and is aligned automatically. 
     In one aspect, the image sensor module, the lens holder has a fixing jaw extending into a portion of the extended opening. 
     The lens unit can include: a plurality of spheric or aspheric lenses; and a ring-shaped spacer which is closely attached to a sidewall of the lens holder, for controlling a distance between the lenses. 
     The lens and the spacer can be integral-typed. 
     The distance between the lenses can be controlled by a variation of a thickness of the spacer. 
     The spacer may have a width less than or the same width as a flat portion of the lens. 
     The module can further have a ring-shaped screen film on an uppermost lens of the lens unit to screen light incident from the external. 
     The module can further have a fixing jaw, which has an upper surface parallel with an upper surface of the image sensor chip, on a lower inner sidewall of the lens holder. 
     The module can further include a digital image processor chip on a lower surface of the substrate. 
     The module can further include a digital image processor chip between the substrate and the image sensor chip. 
     According to another embodiment of the present invention, there is provided a method of fabricating an image sensor module having an auto-aligned lens, the method including: mounting an image sensor chip on a substrate; attaching a housing and a lens holder onto the substrate, the housing having an opening which exposes the image sensor chip, and the lens holder extending the opening vertically and upwardly; fabricating a lens unit which is installed in the lens holder and automatically aligned; and assembling the lens unit to an inner sidewall of the lens holder. 
     The fabricating of the lens unit includes: coating a binder resin on an upper surface of a first lens; pressing a spacer onto the first lens having the coated binder resin; coating the binder resin on an upper surface of the pressed spacer; and pressing a second lens onto the spacer having the coated binder resin. 
     The coating of the binder resin includes: placing a droplet of the binder resin at a predetermined area of an upper surface of the first lens or the spacer by using a fiber having a small diameter; and pressing the dropped droplet by using the spacer or the second lens to spread the placed droplet in a film type. 
     The binder resin can be formed of an ultraviolet-radiation curing material. 
     After the pressing of the second lens, the method can further include: curing the binder resin by using ultraviolet radiation; and heating the cured results for heat-treatment. 
     A screen film can be further provided on an uppermost lens of the lens unit. 
     A fixing jaw having an upper surface parallel with an upper surface of the image sensor chip can be further provided on a lower inner sidewall of the lens holder. 
     According to a yet another embodiment of the present invention, there is provided an automatic focus controlling method using an auto-aligned lens, the method including: preparing a reference object; storing a reference image, which is provided as an optimal image by the reference object, in a separate measurement unit; preparing a vacuum holder to which the reference object is attached; holding the lens unit by using the vacuum holder; descending the vacuum holder vertically to insert the lens unit into the lens holder; comparing a matching degree of the reference image and a comparative image, which is an image of the reference object formed by the lens unit, by using the measurement unit; stopping to descend the vacuum holder in case where the matching degree of the reference image and the comparative image is reliably satisfied; and fixing the lens unit to the lens holder by using the binder resin. 
     The fixing using the binder resin can further include: curing the binder resin by using ultraviolet ray; and heating the cured results for heat-treatment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
         FIG. 1  is a cross-sectional view schematically illustrating a conventional image sensor module; 
         FIG. 2  is a cross-sectional view schematically illustrating an image sensor module according to one embodiment of the present invention; 
         FIGS. 3A and 3B  are cross-sectional views illustrating a lens unit according to one embodiment of the present invention; 
         FIGS. 4A and 4B  are plan views illustrating a procedure of fabricating a lens unit of  FIG. 3A  according to one embodiment of the present invention; 
         FIGS. 4C and 4D  are plan views illustrating a procedure of fabricating the lens unit of  FIG. 3A  according to one embodiment of the present invention; 
         FIG. 5  is a schematic view illustrating a procedure of installing a lens unit in a lens holder according to one embodiment of the present invention; 
         FIG. 6  is a flowchart illustrating a procedure of  FIG. 5 ; and 
         FIGS. 7 through 9  are cross-sectional views illustrating an image sensor module according to another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. The invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art. 
       FIG. 2  is a cross-sectional view schematically illustrating an image sensor module according to one embodiment of the present invention. 
     As shown in  FIG. 2 , an image sensor chip  102 , for example, a CMOS Image Sensor (CIS) chip is mounted on and electrically connected with a substrate  100  by a bonding wire  104 . A DSP chip  106  can be fixed on the other surfaces of the substrate  100  to face with the image sensor chip  102 , as shown in the embodiment of  FIG. 2 . The DSP chip  106  is attached and connected to the substrate  100  by the bonding wire  104 . After that, a mold  108  is formed. A housing  110  having an opening  112  to expose an upper surface of the image sensor chip  102  is attached onto the substrate  100 . A lens holder  114  is connected to the housing  110 . The lens holder  114  extends the opening  112  vertical upwardly. The lens holder  114  has a fixing jaw  116  disposed on an inner sidewall thereof and having an upper surface substantially parallel with the upper surface of the image sensor chip  102 . At this time, a lens unit  120  is assembled at the upper side of the fixing jaw  116  within the lens holder  114 . 
     The housing  110  and the lens holder  114  can be integrally connected with each other, and can be also connected with each other using a predetermined connection unit (not shown) disposed at each of ends thereof. The housing  110  and the lens holder  114  may be formed of insulating material, for example, polycarbonate and polyphenylsulfide. 
     However, since the embodiment of the present invention does not have a lens assembly unit ( 26  of  FIG. 1 ) connected to the lens holder  114 , impurity particles are not generated. Further, since the lens assembly unit ( 26  of  FIG. 1 ) is not provided, the lens holder  114  has a smaller diameter or width (W 2 ). Accordingly, the embodiment of the present invention can be effectively applied if the sizes of the substrate  100  and several chips mounted thereon are reduced. Accordingly, embodiments of the present invention are advantageous when the image sensor module is miniaturized. 
       FIGS. 3A and 3B  are cross-sectional views illustrating a lens unit according to one embodiment of the present invention. 
     Referring to  FIG. 3A , a ring-shaped spacer  120   b  is provided on a first spherical or aspherical lens  120   a  to be closely attached to an inner sidewall of the lens holder  114 . A second lens  120   c  is disposed on the spacer  120   b , and a ring shaped screen film  120   d  can be disposed on the second lens  120   c  to screen light incident from outside. 
     The spacer  120   b  has a thickness of about to about, and has an upper surface substantially parallel with the upper surface of the image sensor chip  102 . The thickness of the spacer  120   b  can be controlled adaptively to the focal length of the lenses  120   a  and  120   b . Because the focal length generally depends on a slope at a center of the lens as well as a distance between lenses, the thickness of the lens  120   b  can be different depending on a state of the lens. 
     The width of the spacer  120   b  may be less than or equal to the widths of flat portions of the lenses  120   a  and  120   c . This is to prevent the spacer  120   b  from being sloped by the lenses  120   a  and  120   c . If the lenses  120   a  and  120   c  are sloped, the centers of the lenses  120   a  and  120   c  can be sloped. Accordingly, the focal length of the lens becomes irregular. 
     According to an embodiment of the present invention, since the distance between the lenses is automatically controlled by the thickness of the spacer  120   b , a separate process for manually controlling the focal length is not required. 
       FIG. 3B  illustrates an integral spacer  121 , which is a combination of the second lens  120   c  and the spacer  120   b . The lens unit  120  having the integral spacer  121  has the same function as the lens unit  120  having the spacer  120   b  of  FIG. 3A . 
       FIG. 4A  is a plan view of the lens unit  120  of  FIG. 3A . 
       FIG. 4B  is a plan view of the internal spacer  121  of  FIG. 3B . 
     A screen film  120   d  controls an amount of light incident on the image sensor chip  102 , and prevents light loss such as scattering from being generated due to light transmission of a screened portion. The screen film  120   d  can be formed of opaque material, for example, ink, carbon black, and metal. This material is called a light screen material. The light screen material can be coated or adhered on or to the second lens to form the screen film  120   d . The width of the screen film  120   d  may be greater than or equal to the width of a lower flat portion of the second lens  120   c . This is to prevent unnecessary light loss from being generated at the flat portion. 
       FIGS. 4C and 4D  are plan views illustrating a procedure of fabricating the lens unit of  FIG. 3A  according to one embodiment of the present invention. 
     Referring to  FIGS. 4C and 4D , a binder resin  124  is coated on the first lens  120   a . In detail, a droplet of the binder resin  124  is dropped at a predetermined region of an upper surface of the first lens  120   a  by using a fiber having a small diameter. After that, the spacer  120   b  is placed and pressed on the coated first lens  120   a . If the spacer  120   b  is pressed, the droplet of the binder resin  124  is spread on the upper surface of the first lens  120   a  to have a film shape. 
     Next, the droplet of the binder resin  124  is provided on the upper surface of the spacer  120   b  in the same manner as aforementioned, and then pressed using the second lens  120   c . The ring-shaped screen film  120   d  can be additionally formed on the second lens  120   c  to screen light incident from outside. 
     The binder resin can be an ultraviolet-radiation curing material, for example, an epoxy resin. At this time, the binder resin  124  is cured using ultraviolet between the first resin  120   a  and the spacer  120   b  and the second lens  120   c , and then the lens unit  120  is heated. 
     The lens unit  120  can be formed using a suitable jig for precise engagement with the lens holder  114 . 
     A method of fabricating the image sensor module according to one embodiment of the present invention is now described. 
     First, the image sensor chip  102  is mounted on the substrate  100 . After that, the housing  110  and the lens holder  114  are attached to the substrate  100 . The housing  110  has the opening  112  to expose the image sensor chip  102 , and the lens holder  114  has the fixing jaw  116  disposed on the inner sidewall thereof. The fixing jaw  116  may have the upper surface substantially parallel with the upper surface of the image sensor chip  102 . The lens unit  120  installed in the lens holder  114  is fabricated as shown in  FIGS. 4A through 4D . And then, the lens unit  120  is assembled on the fixing jaw within the lens holder  114 . 
       FIG. 5  is a schematic view illustrating a procedure of installing the lens unit  120  in the lens holder  114  according to one embodiment of the present invention.  FIG. 6  is a flowchart of the process illustrated in  FIG. 5 . 
     Referring to  FIGS. 5 and 6 , a reference image is stored in a separate measurement unit  216  (S 10 ). Here, the reference image refers to an optimal image provided by a reference object  204 , for example, a patterned substrate. After that, a vacuum holder  200  having the reference object  204  is prepared (S 20 ). The lens unit  120  is held using the vacuum from the vacuum holder  200  (S 30 ). The vacuum is provided through a vacuum passage  202 . Next, the vacuum holder  200  is vertically descended so that the lens unit  120  is inserted into the lens holder  114  (S 40 ). The term “vertically descended” may mean that the vacuum holder  200  approach the lens holder  114  along any axial direction to the opening of the lens holder  114 , vertically or otherwise. 
     At this time, a comparative image of the reference object  204  is formed in the lens unit  120  to be digitalized in the image sensor chip  102  and the DSP chip  106 . The digitalized image is transmitted to the measurement unit  216  along a connection terminal  212  and a signal line  214  via a substrate, for example, a soft printed circuit board  210  connected with the substrate  100 . 
     Next, the measurement unit  216  compares the comparative image of the reference object  204  with the stored reference image (S 50 ). The comparing of the images is to determine whether or not the images are matched with each other to some degree. At a high matching degree, the comparative image and the reference image are well matched. At this time, if the compared images have a reliable matching degree, the vacuum holder  200  stops the descent (S 60 ). After that, the ultraviolet curing binder resin, for example, the epoxy resin is coated between the lens unit  120  and the lens holder  114  (S 70 ). After the binder resin is cured using the ultraviolet ray (S 80 ), a predetermined heat-treatment is performed (S 90 ). 
       FIGS. 7 through 9  are cross-sectional views illustrating the image sensor module according to other embodiments of the present invention. These embodiments are substantially the same as the above-mentioned embodiment in a procedure of fabricating and assembling the lens unit  120  in the lens holder  114 . However, the embodiments are different from each other in a method of mounting the image sensor chip and the DSP chip on the substrate  100 . 
     Referring to  FIG. 7 , after the DSP chip  106  is attached on the substrate  100 , the image sensor chip  102  is connected on the DSP chip  106  by using an inter-chip binder  107  such as epoxy. The image sensor chip  102  and the DSP chip  106  are respectively electrically connected to the substrate  100  by the wire  104 . 
     Referring to  FIG. 8 , a multi chip  300 , which is a combination of the image sensor chip  102  and the DSP chip  106 , is attached onto the substrate  100 , and is connected by the wire  104 . 
     Referring to  FIG. 9 , a multi chip  300  is disposed over an opening provided at a central lower side of the substrate  100  to perform the same function as that of  FIG. 8 . That is, a bump  302  is disposed on a lower surface of the substrate  100  to electrically connect the multi chip  300  with the substrate  100 . Next, an infrared-ray screen filter  118  is disposed to cover the opening of the substrate  100 . 
     In the automatically optically aligned image sensor module and the method of fabricating the same according to embodiments of the present invention, when the lens assembly unit is connected, the impurity particles are not generated. 
     Further, the diameter or the width of the lens holder is small-sized to reduce the sizes of the substrate and several chips mounted thereon. Therefore, the present invention can also contribute to the miniaturization of the image sensor module. 
     Furthermore, since the distance between the lenses is controlled by the thickness of the spacer, a separate additional process for automatically controlling the focal length is not required. 
     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.