Abstract:
A voice-coil motor for picking up chips is disclosed. Through the electromagnetic force generated from the voice-coil motor, the invention can accurately control its strength when picking up a chip. The procedure of picking a chip is as follows: first, a chip is separated from a blue film due to the force of a rising ejectpin; then a pickup head is used to suck the chip to an assigned place. In particular, when the ejectpin pushes the chip up, the pickup head is controlled to rise together with the ejectpin so that the ejectpin also raises the pickup head. Through the above-mentioned control, the stress on the chip can be reduced, preventing the chip from being broken.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of Invention  
           [0002]    The invention relates to a chip picking mechanism and, in particular, to a voice-coil motor for picking up chips.  
           [0003]    2. Related Art  
           [0004]    The conventional chip picking mechanism mainly uses the force due to a rising ejectpin to separate the chip from the blue film. A pickup head is then used to suck the chip to an assigned place. During this process, however, the pickup head cannot control to rise together with the ejectpin when the ejectpin pushes the chip upwards. The ejectpin has to push the pickup head too. Thus, the chip undertakes the extra burden from the pickup head.  
           [0005]    The explicit operations are shown in FIGS. 1A to  1 D. Such a conventional chip picking mechanism utilizes a spring to control the pickup head for picking up chips. The state of the pickup head  10  before action is shown in FIG. 1A. When it starts its action, the pickup head  10  lowers down to the surface of the chip  20 , as shown in FIG. 1B. Afterwards, the ejectpin  30  goes up to separate the chip  20  from the blue film  40 . This process requires the spring force of the spring  11 , as shown in FIG. 1C. Finally, the pickup head  10  uses the vacuum force at its tip to hold and raise the chip  20 , as shown in FIG. 1D.  
           [0006]    In fact, this kind of picking action cannot accurately control the strength. Moreover, since the force is mechanical (positive spring force), the force to pick up the chip is nonlinear. Therefore, it is not easy to control.  
           [0007]    In the precision semiconductor industry, chips are thinner and smaller. Conventional chip picking mechanisms are therefore not sufficient in use. That is, once the picking force cannot be accurately controlled, the chip may be broken or have cracks. It is thus highly desirable to design a mechanism that is able to accurately control the force for picking chips.  
         SUMMARY OF THE INVENTION  
         [0008]    In view of the foregoing, the invention provides a voice-coil motor for picking up chips. The motor is designed to accurately control the force imposed on the chips through a magnetic force, preventing the chips from being broken during the process.  
           [0009]    To achieve the above objective, the disclosed voice-coil motor contains: a yoke support, an annular magnet, a moving coil, a first linear bearing, positioning pins, stop pins, a main axis, a fixture cover, a pickup head, a connection axis, and a second linear bearing. The annular magnet is used to generate homogeneous closed magnetic lines. The yoke support connects and holds on to the annular magnet. The moving coil is coiled between the annular magnet and the yoke support for generating a magnetic force by allowing a current to flow through. The fixture cover is used to fix the moving coil. The main axis and the fixture cover are connected. When the moving coil generates a force, it makes vertical motion relative to the yoke support. Its top is installed with an air-pressure connector for producing an air pressure difference. The pickup head is connected to the bottom of the main axis for sucking the chip pump under the generated air pressure difference. The positioning pins are installed inside the fixture cover and the yoke support for limiting the downward motion of the main axis and to prevent the fixture cover from spinning.  
           [0010]    Furthermore, the yoke support can be installed with a linear bearing for guiding the moving direction of the main axis. An additional stop pin can be installed on the yoke support as the stop point of the positioning pin. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    The invention will become more fully understood from the detailed description given hereinbelow illustration only, and thus are not limitative of the present invention, and wherein:  
         [0012]    [0012]FIGS. 1A to  1 D are schematic diagrams showing the procedure of picking a chip in the prior art that uses springs as pickup heads;  
         [0013]    [0013]FIG. 2 is a schematic view of the disclosed voice-coil motor structure;  
         [0014]    [0014]FIG. 3A shows the force output in the prior art;  
         [0015]    [0015]FIG. 3B shows the force output of the invention;  
         [0016]    [0016]FIG. 4A shows the appearance of the voice-coil motor in the first embodiment;  
         [0017]    [0017]FIG. 4B shows a quarter cross-section of the voice-coil motor in the first embodiment;  
         [0018]    [0018]FIG. 5A shows the appearance of the voice-coil motor in the second embodiment;  
         [0019]    [0019]FIG. 5B shows a quarter cross section of the voice-coil motor in the second embodiment; and  
         [0020]    [0020]FIGS. 6A to  6 D are schematic views showing the procedure of picking a chip using the disclosed voice-coil motor. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]    The voice-coil motor  50  according to the invention is shown in FIG. 2. An annular magnet  51  is fixed on a yoke shell  52 , generating homogeneous closed magnetic lines, as indicated by the arrows. A coil  53  is fixed on a coil base  54 , placed inside the annular magnet  51 . When there is a current flowing perpendicular to the magnetic flux, a vertical force is generated.  
         [0022]    According to the Fleming&#39;s Left Hand Rule, the magnetic force generated by the voice-coil motor is F=N×I×L×B, where N is the number of turns of the coil, I is the current flowing through the coil, B is the magnetic field, and L is the effective length. Therefore, the force generated by the voice-coil motor varies with the current, the number of coil turns, and the magnetic field. Since the number of turns of the coil  53  and the magnetic field of the annular magnet are both fixed, only the current is an adjustable variable. The invention changes the magnitude of the magnetic force by varying the current. Reversing the current flowing direction (reversing charge poles) can generate forces in the opposite direction.  
         [0023]    [0023]FIG. 3A and FIG. 3B show the relation between the output force and the displacement in a conventional pickup head that uses a spring and the disclosed pickup head that uses a voice-coil motor as the picking mechanism, respectively. As seen in FIG. 3, the picking force of the invention is a constant in the distance. Therefore, it has a better picking performance.  
         [0024]    On the other hand, the voice-coil motor utilizes an annular magnet and, therefore, one has to take into account the problem of the generation of a rotational torque by the voice-coil motor. To avoid the voice-coil motor from rotating due to the generated rotational torque, it is necessary to provide a rotation-free mechanism. We use two embodiments hereinafter to illustrate the invention.  
         [0025]    [0025]FIG. 4A shows a first embodiment of the voice-coil motor  200 . From its appearance, one sees the rotation-free mechanism, which consists of a first positioning pin  205  and a second positioning pin  206 , and a stop mechanism for the vertical motion of the motor, which consists of a stop pin  211  and a main axis  207 . Please refer to FIG. 4B, a quarter cross-section of the first embodiment, for a more detailed explanation. The main parts of the first embodiment include: a yoke support  201 , an annular magnet  202 , a moving coil  203 , a linear bearing  204 , a first positioning pin  205 , a second positioning pin  206 , a main axis  207 , a fixture cover  208 , a pickup head  209 , a connection axis  210 , a first stop pin  211 , and a second stop pin  212 .  
         [0026]    The annular magnet  202  is installed on the yoke support  201  to generate homogeneous closed magnetic field lines in the yoke support  201 . The moving coil  203  coils between the annular magnet  202  and the yoke support  201 , and combines with the fixture cover  208 . When the moving coil  203  is imposed with an electric current, its flowing direction is perpendicular to the magnetic field lines generated by the magnet  202 , generating a force parallel to the moving direction. This force drags the moving coil  203  and the fixture cover  208  to make vertical motion. Moreover, the invention accurately controls the output force by tuning the input current, offering a standard linear output force. This output force control can be achieved through a current control module.  
         [0027]    The main axis  207  has an air-pressure connector is provided at its top and is connected to a pickup head  209  through a connection axis  210 . Through the air pressure difference generated by the air pressure connector, the pickup head can pick up or put down a chip. The main axis  207  and the fixture cover  208  are connected by a screw. Therefore, when the moving coil  203  is provided with a current and generates a force, the force is also imposed on the main axis and the fixture cover. When the stress on the chip is greater than the force generated by the coil, the main axis  207  rises. Since it has the property of a negative spring, the force imposed on the chip becomes smaller when the main axis  207  ascends, preventing the chip from being broken due to the stress. The first and second positioning pins  205 ,  206  are used to guide the vertical motion of the fixture cover without making rotations. The linear bearing  204  is fixed on the yoke support  201 , guiding the main axis  207  to make vertical motion without too much friction.  
         [0028]    The first stop pin  211  is installed on the fixture cover  208 , whereas the second stop pin  212  is installed on the second stop pin  212 . The first stop pin  211  and the second stop pin  212  are designed to limit the vertical motion range of the moving coil  203 , the fixture cover  208 , and the main axis  207 . The bottom of the main axis  207 , the first stop pin  205 , and the second stop pin  206  are all provided with stop mechanisms to restrict the upward motion of the main axis. Such a design can protect the whole structure from falling apart.  
         [0029]    With reference to FIG. 5A, the second embodiment of the invention has a simpler voice-coil motor structure  300 . The rotation-free mechanism and the downward motion stop mechanism are combined together, i.e. the positioning pin  305  and the stop pin  306 . Similarly, the upward motion stop mechanism of the motor is achieved with the help of the main axis  307 . A detailed cross section is shown in FIG. 5B. Essential parts include: a yoke support  301 , an annular magnet  302 , a moving coil  303 , a first linear bearing  304 , a positioning pin  305 , a stop pin  306 , a main axis  307 , a fixture cover  308 , a pickup head  309 , a connection axis  310 , and a second linear bearing  311 .  
         [0030]    Comparing FIGS. 4A, 4B with FIGS. 5A, 5B, one easily sees that the main difference between the second embodiment and the first embodiment is on the design of the positioning pins and the stop pins. The first embodiment employs the design of separate positioning pins and stop pins, whereas the second embodiment combines both types of pins together as one. That is, a single positioning pin  305  can achieve both the stopping and positioning functions. Moreover, the later embodiment has the second linear bearing  311  installed on the yoke support  301  for guiding the vertical motion of the positioning pin  305  and reducing the friction. The rest parts in the second embodiment are the same as in the first embodiment and, therefore, are not explained again.  
         [0031]    Finally, please refer to FIGS. 6A through 6D. FIG. 6A shows the state of the motor before action. In FIG. 6B. the voice-coil motor  10   a  lowers to the surface of a chip  20   a . Afterwards, the ejectpin  30   a  rises to separate the chip  20   a  from the blue film  40   a . At the moment, the voice-coil motor  10   a  uses its negative spring force to absorb the force from the rising ejectpin  30   a , as shown in FIG. 6C. Finally, the pickup head of the voice-coil motor  10   a  sucks the chip  20   a  using the vacuum at its tip and rises to pick up the chip  20   a , as shown in FIG. 6D.  
       EFFECTS OF THE INVENTION  
       [0032]    Using the disclosed voice-coil motor can accurately control the picking force, preventing the chip from being broken during the picking process. This is because the stress on the chip is reduced.  
         [0033]    The invention uses a magnetic force to control the force imposed on the chip by the pickup head. It has the advantages of being able to accurately controlling the force, having a standard linear output, being easy to control and acting like a negative spring.  
         [0034]    While the invention has been described by way of example and in terms of the preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements as would be apparent to those skilled in the art. Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.