Abstract:
A COB module of an optical mouse has a controller circuit and optical components of the optical mouse integrated thereon, so as to improve the problem with conventional optical mice that light path shifting tends to occur and improve the imaging definition. By disposing a button and wheel mechanism independently outside the COB module, the optical mouse has significantly improved flexibility in design, lower cost related to design alteration, and relaxed requirements on alignment and correction during production.

Description:
FIELD OF THE INVENTION 
     The present invention is related generally to an optical mouse and, more particularly, to a chip-on-board (COB) module of an optical mouse. 
     BACKGROUND OF THE INVENTION 
     Optical components of an optical mouse are shown in  FIG. 1 , and to facilitate mass production and assembly, these components are manufactured separately. During assembly, a light source device  12  and a sensor chip  14  are soldered onto a printed circuit board (PCB)  16 , and a light source mount  10  is fixed onto the PCB  16  in a tight fit to prevent swing of the light source device  12 . The PCB  16  has an opening  162  to allow light to pass therethrough, and a lens  18  is placed beneath the opening  162  and fixed onto the PCB  16 . By means of a recess  192  and a fool-proof structure  194 , the lens  18  is in turn placed on a base  19  to align the light path with a light hole  196 . 
       FIG. 2  depicts a light path of the optical mouse shown in  FIG. 1 . The light source device  12  is generally a red LED, and the light emitted from the light source device  12  is sequentially refracted and reflected by the lens  18 , and then passes through the light hole  196  to impinge on a plane beneath the optical mouse. From there, the light is reflected back and passes through the lens  18  to be imaged onto the sensor chip  14 . Different features and roughness of the desktop surface will result in different energy intensity of the reflected light to exhibit corresponding features in the image. When the optical mouse is moved, continuous patterns will be obtained in the sensor chip  14  which then, according to difference in positions of features of the continuous images, compares and analyzes each of the images to determine the moving direction and displacement of the optical mouse. In other words, imaging quality is a key factor that dominates performance of the optical mouse. Hence, when loose engagement or misalignment among individual parts of the optical mouse occurs, light reflected from the desktop surface will fail to follow the correct light path to travel to the sensor chip  14 . Consequently, the sensor chip  14  will retrieve a drifting or blurred image, leading to incorrect recognition of the image. 
     As molds used by various manufacturers for producing the separate optical parts have non-uniform specifications, problems such as varied height of the mouse bases, poor close-fit and poor fixation effect among individual components often arise. Consequently, the resulting optical mice tend to become loose in the Z-axis (vertical) direction during operation, thereby causing shifting and out-of-focus of the light path. 
     As an effort to reduce the assembly errors during production, U.S. Pat. No. 6,462,330 to Venkat et al. suggests packaging the lens into a package of the sensor chip, U.S. Pat. No. 7,045,775 to Leong et al. suggests packaging both the lens and the LED into the package of the sensor chip, and U.S. Pat. No. 7,199,350 to Chien suggests packaging the lens, the LED and a controller chip of the optical mouse all into the package of the sensor chip. Although these arts feature a high level of integration, none of them is of a COB structure; rather, they are limited by the chip pins, and once the pin design is altered, the lead frame of the whole package must be remolded, which is labor-consuming, time-consuming and very costly. 
     On the other hand, U.S. Pat. Nos. 6,541,762 and 6,653,724 disclose an optical mouse implemented in a COB fashion, in which a sensor chip is soldered in form of a die onto a smaller secondary PCB, which is in turn fixed to a primary PCB of the optical mouse. However, this kind of optical mouse has a low level of integration because the PCB of the COB package must be fixed to another PCB (so it is also known as a secondary COB). 
     SUMMARY OF THE INVENTION 
     An objective of the present invention is to provide a COB module of an optical mouse featuring a high level of integration. Owing to the modular structure, relative positions among optical components are absolutely fixed, and loose engagement or misalignment is less likely to occur among the optical components, so the light path is made more accurate and the time required for assembly and correction during production of the optical mice are completely eliminated, thereby improving the production yield. 
     Another objective of the present invention is to provide an optical mouse that has a human-machine interface (HMI) arranged outside the COB module, thereby enhancing the flexibility in design of the optical mouse. 
     According to the present invention, a COB module of an optical mouse includes a module printed circuit board (PCB), which has a chip incorporating a sensor circuit soldered thereon in form of a COB structure and has other passive elements and a light source device also soldered thereon. A controller circuit may be integrated on the chip incorporating the sensor circuit or formed on another separate chip soldered onto the PCB. A light path formed by the lens allows light from the light source device to be imaged onto the chip incorporating the sensor circuit. 
     According to the present invention, an optical mouse includes the aforesaid COB module fixed on a mouse base, the mouse base having a light hole for the light path to pass therethrough, a button and wheel mechanism disposed on the mouse base, and a ribbon cable for connecting the button and wheel mechanism to the module PCB. 
     By integrating the optical parts and the controller circuit of the optical mouse, the present invention achieves enhanced flexibility in design, improved imaging definition and lower cost of production and design alteration. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other objects, features and advantages of the present invention will become apparent to those skilled in the art upon consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a schematic view of optical components of a conventional optical mouse; 
         FIG. 2  is a cross-sectional view of the conventional optical components when being assembled; 
         FIG. 3  is a schematic view of a first embodiment of a COB module according to the present invention; 
         FIG. 4  is a schematic view of an embodiment of an optical mouse according to the present invention; 
         FIG. 5  is a side view of a second embodiment of a COB module according to the present invention; 
         FIG. 6  is a side view of a third embodiment of a COB module according to the present invention; and 
         FIG. 7  is a schematic view of a fourth embodiment of a COB module according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In an embodiment as shown in  FIG. 3 , a COB module  30  of an optical mouse includes a module PCB  32  formed with circuits thereon. Passive elements such as resistors, capacitors and the like, in form of a dual-line package (DIP) or surface mount device (SMD) package, are fixed onto the module PCB  32  by using the card soldering or surface mounting technology (SMT). For purpose of simplicity, details of passive elements and wiring, which shall be readily appreciated by those skilled in the art, are omitted in  FIG. 3 . A module chip  42  having a sensor circuit and a controller circuit integrated therein is soldered in form of a COB structure onto the module PCB  32 . For example, an LED light source device  44  is soldered in form of a DIP or SMD package onto the module PCB  32  through card soldering or SMT soldering. A photo shield  36  fixes a lens  40  in place, and preferably is made of an opaque material. The photo shield  36  is formed with only two openings  362 ,  364  therein to allow light following a particular path to pass therethrough, thereby achieving an effect of shielding stray light. Light emitted by the light source device  44  passes through the openings  362 , refracted by the lens  40 , and passes through cutouts  384  in the enclosure  38  and light hole  463  in the mouse base  46  to impinge on a surface with which the mouse base  46  makes contact. The lens  40  images the light diffused or scattered to the module chip  42 , which then analyzes the light to obtain such information as displacement and direction of the optical mouse. In this embodiment, all the optical parts are integrated into a modular structure, so absolutely fixed relative positions among individual optical components, high precision of the light path, high definition of the resulting image, elimination of the time necessary for assembling and calibrating the optical components during production are accomplished. In this embodiment, the module chip  42  is soldered by using the COB packaging technology onto a surface of the module PCB  32  that faces downwards. By use of the COB module  30 , only a single module PCB  32  is needed for each optical mouse. In other embodiments, the image sensor circuit and the mouse controller circuit may be implemented as two separate chips soldered onto the module PCB  32  respectively, in which case the chip incorporating the sensor circuit must be aligned with the light path. 
     The COB architecture employed in the present invention makes the design more flexible. When functions of the chip pins are altered, e.g., added or deleted, what needs to be done is to alter the circuit design of the module PCB  32  and clean up the board but not need to replace the lead frame design of the package by remolding. As a result, enhanced flexibility in design is achieved and, consequently, cost related to design modification is further saved. 
       FIG. 4  is an exploded view of an optical mouse according to the present invention. A button and wheel mechanism  461  is independent from the COB module  30 , for example, is disposed on the mouse base  46 . Button signals and wheel signals generated by operating the button and wheel mechanism  461  are transmitted to an input terminal  328  of the module PCB  32  through a ribbon cable  462 . The module chip  42  makes calculations based on displacement information of the optical mouse as well as the wheel signals and button signals, so as to output a mouse control signal to the host via a USB cable  48  connected with the output terminal  326 . Referring to  FIGS. 3 and 4 , in this embodiment, the photo shield  36  serves to fix and maintain distances and relative positions among the lens  40 , the module chip  42  and the light source device  44 . The enclosure  38  covers and fixes the photo shield  36  and the lens  40 , and with a tongue  382  thereof, engages with a prefabricated engagement hole  322  on the module PCB  32 . In other embodiments, the tongue may also be disposed on the photo shield  36 , or other engagement devices and mechanisms that can engage with each other, such as slide rails and screws, may be used to replace the tongue  382  and the engagement hole  322 . Upon completion of assembly of the COB module  30 , screws  50  are threaded into female studs  465  to, in conjunction with module mounts  464 , fix the COB module  30  to the mouse module  46 . 
     In conventional optical mice, only optical components are integrated, while the mouse controller is still implemented, along with other passive elements, on a separate chip that is soldered to a primary PCB; also, the wheel and button mechanism is also disposed on the primary PCB. Consequently, once the mouse designer intends to make modification on the mouse profile which necessitates modification of positions of the buttons and the wheel, the board must be cleaned up so as to allow alteration of circuits on the primary PCB; furthermore, the button position, the wheel position and the light path must be precisely aligned with each other during assembly in order for the optical mouse to operate properly. In contrast, the optical mouse according to the present invention has the lens  40  and the mouse controller integrated into the COB module  30 , and the button and wheel mechanism  461  is disposed independently on the mouse base  46 , so the mouse designer may adjust the relative positions between the button and wheel mechanism  461  and the light hole  463  freely and also modify the profile and size of the mouse base  46  freely, so long as light exiting the COB module  30  is allowed to pass through the light hole  463 . Hence, the optical mouse according to the present invention features high flexibility in design and has lower requirements on alignment. Once the COB module according to the present invention is connected with a PC cable as well as the button signals and the wheel signals, functions of a complete optical mouse can be obtained, thereby saving more labor and time than the prior arts in practical production. 
       FIG. 5  is a side view of a second embodiment of a COB module according to the present invention. The module chip  42  and the light source device  44  are soldered onto the module PCB  32 . A photo shield  54 , which serves dual functions of blocking light and protecting a lens  55 , is formed with engagement structures  542  and  544  to engage with the lens  40  to form a COB module  50 . Light emitted from the light source device  44  passes through the photo shield  54  and reflected by the lens  40  to pass through the light hole in the mouse base  46 . The diffused or scattered light then passes through the lens  40  to be imaged onto the module chip  52 . In this embodiment, the photo shield  54  functions as a combination of the photo shield  36  and the enclosure  38  of the embodiment shown in  FIG. 3 , so the number of parts is reduced. 
       FIG. 6  is a side view of a third embodiment of a COB module according to the present invention. A lens  65  in a COB module  60  engages with the module PCB  32  and fixes a photo shield  64 . Two openings of the photo shield  64  are aligned with the module chip  42  and the light source device  44  soldered onto the module PCB  32  respectively for the light emitted from the light source device  44  to pass therethrough. In this embodiment, the lens  65  functions as a combination of the lens  40  and the enclosure  38  of the embodiment shown in  FIG. 3 , so the number of parts is reduced. 
       FIG. 7  is a schematic view of a fourth embodiment of a COB module according to the present invention. The module chip  42  and the light source device  44  are soldered onto the module PCB  32 , and the lens  74  engages with the module PCB  32  to form a COB module  70 . The lens  74 , on a portion thereof adjacent to the module chip  42 , is coated with a photoresist layer  745  to replace the function of the photo shield in the aforesaid embodiments. Light emitted from the light source device  44  is reflected by the lens  74  and passes through the light hole in the mouse base  46 . The diffused or scattered light then passes through the lens  74  to be imaged onto the module chip  42 . In this embodiment, the lens  74  not only functions as a combination of the lens  40  and the enclosure  38  of the embodiment shown in  FIG. 3 , but also allows for elimination of the independent photo shield  36 . In other embodiments, a photoresist layer may also be applied to a surface of the lens  74  adjacent to the light source device  44  to regulate the direction in which the light exits the light source device  44 . 
     While the present invention has been described in conjunction with preferred embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and scope thereof as set forth in the appended claims.