Abstract:
Disclosed is a method for automatically sorting LEDs (light emitting diode) according to electrostatic resistance and a system using the same. The system includes a transport carrier for laying LEDs and passing LEDs through an electrostatic discharging zone, a lightening evaluating zone, and a sorting zone in sequence. An electrostatic discharging device discharges an electrostatic power to the LED in the electrostatic discharging zone. Furthermore, a lighting device inputs a lightening power to the LED in the lightening evaluating zone. Moreover, an evaluating device in the evaluating zone generates an evaluating signal to a sorting device in the sorting zone according to the lighting condition of the LED for allowing the sorting device to sort LEDs according to electrostatic resistance. Thereby the reliability both for the failure rate and the detection rate can be raised.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Taiwanese Patent Application No. 101149907, filed Dec. 25, 2012, which is hereby incorporated by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a method for testing LEDs according to electrostatic resistance, and more particularly, to a method for automatically sorting LED according to electrostatic resistance and system using the same. 
     BACKGROUND OF THE INVENTION 
     Electrostatic discharge (ESD) is generated due to mutual contact or separation from each other of at least two articles. These kinds of phenomenon, i.e., mutual contact and separation from each other, are referred to as triboelectic charging, which is related to a rapid charge transfer between different articles respectively having different surface potential level. The so generated charge is then remained on the surface of the articles to lead to ESD. The charge imbalance of articles will create an electrostatic field. Furthermore, the electrostatic field will continue to accumulate and then cause the electrical charge transfer of articles due to the different surface potential. This phenomenon is known as ESD which is one of the main reasons for device failure in the semiconductor industry. The ESD damage for the semiconductor industry surveyed by the American National Standards Institute (ANSI) shows that, the ESD damage leads to an average loss of product in the range between 8% and 33%. 
     An electronic device will be permanently damaged when high-voltage electrostatic passes therethrough. The failure of electronic device caused by ESD includes electricity leakage, short circuit, and brightness down or burned. 
     Machine Model (MM) refers to an electrostatic discharge from a charged machine. The charged machine contacts an electronic device and discharges electrostatic from the electronic device to lead to the failure of the electronic device. The static electricity from MM is generally eliminated by a grounding process. 
     Human Body Model (HBM) is another common type of ESD that a charged human body directly transfers its accumulated electrostatic charge to an electronic device by touching it, and which is also most difficult for being completely eliminated. Electrostatic accumulated in the human body is up to 3 kV, and electrostatic accumulated in clothing is up to 8 kV in a dry environment. When a human with a positive potential or a negative potential touches one electronic device, the accumulated electrostatic is discharged and flows into the electronic device to pass a very high voltage or current to the electronic device to lead to a serious irreversible damage to the electronic device. Therefore, the staffs who have chance to touch the electronic device in a factory must be equipped with anti-static equipment for safety of device. 
     In the practice, LEDs are tested and classified, referred as sorted in the present invention, with regard to electrostatic resistance by using random sampling method. First, an electrostatic gun, handheld by the staff, discharges an electrostatic to LEDs. Then, the LEDs characteristics of brightness, electrical resistance value and so on are detected. Finally, the LEDs failure rate is estimated according to the random sampling ratio. The estimated LEDs failure rate is approximate to the LEDs real failure rate when a high percentage of random sampling ratio is achieved. When a high estimated failure rate for the LEDs is obtained, we can predict that the most of these LEDs have a weak electrostatic resistance for the testing voltage value. Conversely, when a low estimated failure rate for the LEDs is obtained, we can predict that the most of the LEDs have a strong electrostatic resistance for the testing voltage value. 
     SUMMARY OF THE INVENTION 
     The random sampling method implemented by human wastes of labor and cost. Accordingly since the random sampling ratio for testing electrostatic resistance of LEDs is hard to be increased, it leads to a difference gap between the estimated failure rate and the real failure rate, which will cause a low reliability of estimated failure rate. 
     Furthermore, the staffs in the factory may still damage the LEDs by HBM ESD although the staffs equip with anti-static equipments to cause the failure of the LEDs. 
     Therefore, the present invention has been made in view of the above circumstances and provides a method for automatically sorting LEDs according to electrostatic resistance and system using the same, and thus the random sampling ratio is increased and the labor cost is down. 
     The present invention overcomes the drawbacks of the prior art, and provides a method for automatically sorting LED according to electrostatic resistance, the method including steps of: (a) laying, on a transport carrier, a LED to be tested; (b) transporting the LED for passing the LED through an electrostatic discharging zone, a lightening evaluating zone, and a sorting zone in sequence along a detecting path by the transport carrier; (c) in the electrostatic discharging zone, discharging an electrostatic power with a detecting voltage to the LED on the transport carrier through an electric conducting member by an electrostatic discharging device during an electrostatic discharging period; (d) in the lightening evaluating zone, inputting a lightening power to the LED on the transport carrier via an electrode of the LED electrically connecting with the electric conducting member by a lighting device and transmitting an evaluating signal to a sorting device according to the lighting condition of the LED; and (e) in the sorting zone, sorting the LED for moving the LED from the transport carrier to an collecting zone by the sorting device according to the evaluating signal. 
     According to an embodiment of the present invention, in the step (c), the electrostatic power is a pulse-type electrostatic power. 
     According to an embodiment of the present invention, in the step (b) it further comprises a step of transporting the LED for passing the LED through an electrostatic eliminating zone existing between the electrostatic discharging zone and the lightening evaluating zone, and in a process between the step (c) and the step (d) it comprises a step of moving the transport carrier to the electrostatic eliminating zone for eliminating the electrostatic within the LED through the electric conducting member by means of an electrostatic eliminating device. 
     According to an embodiment of the present invention, in the step (d) it further includes a step of eliminating the electrostatic within the LED through the electric conducting member by the lighting device before inputting the lightening power to the LED. 
     According to an embodiment of the present invention, before the step (d), it further comprises a step of arranging the electrode of the LED according to the power output of the lighting device to arrange a positive electrode and a negative electrode of the LED. 
     The present invention overcomes the drawbacks of the prior art, and provides a system for automatically sorting a LED according to electrostatic resistance, comprises: a transport carrier, an electrostatic discharging device, a lighting device, an evaluating device, and a sorting device. The transport carrier, provided with an electric conducting member, for laying a LED and passing the LED through an electrostatic discharging zone, a lightening evaluating zone, and a sorting zone in sequence along a detecting path. The electrostatic discharging device provided in the electrostatic discharging zone, the electrostatic discharging device being electrically connected with the electric conducting member for discharging an electrostatic power with a detecting voltage to the LED on the transport carrier through the electric conducting member while the transport carrier is in the electrostatic discharging zone. The lighting device and an evaluating device provided in the lightening evaluating zone, the lighting device being electrically connected with the electric conducting member for inputting a lightening power to the LED on the transport carrier through the electric conducting member, and the evaluating device transmitted an evaluating signal according to the lighting result of the LED while the transport carrier is in the lightening evaluating zone. The sorting device provided in the sorting zone, the sorting device connected with the evaluating device to sort the LED for moving the LED from the sorting zone to a collecting zone according to the evaluating signal. 
     According to an embodiment of the present invention, the transport carrier further includes an insulating member, and the electric conducting member is disposed on the insulating member. 
     According to an embodiment of the present invention, the system further comprises an electrode arranging member in the electrostatic discharging zone. 
     According to an embodiment of the present invention, the system further comprises an electrode arranging member in the lightening evaluating zone. 
     The technical means adopted by the present invention are capable of detecting the electrostatic resistance for mass amount of LEDs at the same time and are capable of significantly increasing the sampling ratio to 100%. Further, the method increases the reliability of failure rate to previously prevent from the occurrence of failure after the lighting device has been bought by customers in order to meet the customer satisfaction. 
     The embodiment adopted by the present invention described with the drawings as follow. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The structure and the technical means adopted by the present invention to achieve the above and other objects can be best understood by referring to the following detailed description of the preferred embodiments and the accompanying drawings, wherein: 
         FIG. 1  is a flow chart of a method for automatically sorting LEDs with regard to electrostatic resistance according to the first embodiment of the present invention; 
         FIG. 2  is a schematic drawing of a system for automatically sorting LEDs with regard to electrostatic resistance according to the first embodiment of the present invention; 
         FIG. 3  is the first schematic drawing illustrating a operate state of a system for automatically sorting LEDs with regard to electrostatic resistance according to the first embodiment of the present invention; 
         FIG. 4  is the second schematic drawing illustrating a operate state of a system for automatically sorting LEDs with regard to electrostatic resistance according to the first embodiment of the present invention; 
         FIG. 5  is the third schematic drawing illustrating a operate state of a system for automatically sorting LEDs with regard to electrostatic resistance according to the first embodiment of the present invention; 
         FIG. 6  is a flow chart of a method for automatically sorting LEDs with based on electrostatic resistance according to the second embodiment of the present invention; 
         FIG. 7  is a schematic drawing of a system for automatically sorting LEDs with regard to electrostatic resistance according to the second embodiment of the present invention; 
         FIG. 8  is the first schematic drawing illustrating a operate state of a system for automatically sorting LEDs with regard to electrostatic resistance according to the second embodiment of the present invention; 
         FIG. 9  is the second schematic drawing illustrating a operate state of a system for automatically sorting LEDs with regard to electrostatic resistance according to the second embodiment of the present invention; 
         FIG. 10  is the third schematic drawing illustrating a operate state of a system for automatically sorting LEDs with regard to electrostatic resistance according to the second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Please refer to  FIG. 1 .  FIG. 1  is a flow chart of a method for automatically sorting LEDs with regard to electrostatic resistance according to the first embodiment of the present invention. The method includes steps of: laying LEDs on a transport carrier (step  10 ), transporting the LEDs for passing the LEDs along a detecting path by the transport carrier (step  12 ), moving the transport carrier to an electrostatic discharging zone (step  20 ), discharging an electrostatic power to the LEDs on the transport carrier (step  22 ), moving the transport carrier to a lightening evaluating zone (step  30 ), eliminating the electrostatic within the LEDs (step  31 ), arranging the electrode of the LEDs (step  32 ), inputting a lightening power to the LEDs (step  33 ), transmitting an evaluating signal to a sorting device (step  34 ), moving the transport carrier to a sorting zone (step  40 ), and sorting the LEDs by moving the LEDs to a collecting zone (step  41 ). 
     Please refer to  FIG. 2  to  FIG. 5  in light of  FIG. 1  to illustrate the detail according to the first embodiment of the present invention as below. 
     In the embodiment, the system for automatically sorting LED according to electrostatic resistance  100  includes a transport carrier  1 , an electrostatic discharging zone  2 , a lightening evaluating zone  3 , and a sorting zone  4 . The transport carrier  1  is provided with the LEDs to be tested, and passes through an electrostatic discharging zone  2 , a lightening evaluating zone  3 , and a sorting zone  4  in sequence. The amount of the LEDs  200  is only for illustration but is not limited. 
     First, the LEDs  200  are provided on the transport carrier (step  10 ). Specifically, the transport carrier  1  includes an electric conducting member  11  and an insulating member  12 . The electric conducting member  11  is disposed on the insulating member  12 . The LEDs  200  is electrically connected with the electric conducting member  11 . Next, the LEDs  200  is transported by the transport carrier  1  along a detecting path P (step  12 ). The detecting path P extends through the electrostatic discharging zone  2 , the lightening evaluating zone  3 , and the sorting zone  4  in sequence. 
     Then, the transport carrier  1  is moved to the electrostatic discharging zone  2  (step  20 ). In detail, there is an electrostatic discharging device  21  provided in the electrostatic discharging zone  2 . The electrostatic discharging device  21  are able to discharge an electrostatic power with a detecting voltage according to various parameter settings. An electrostatic conducting member  211  of the electrostatic discharging device  21  is electrically connecting with the electric conducting member  11 . Then, the electrostatic discharging device  21  discharges the electrostatic power with the detecting voltage to the LEDs  200  on the transport carrier  1  via the electric conducting member  11 . The electrostatic is remained in the LEDs  200  during an electrostatic discharging period (step  22 ). 
     Afterward, the transport carrier  1  is moved to the lightening evaluating zone  3  (step  30 ). More specifically, there is a lighting device  31 , an electrode arranging member  32 , and an evaluating device  33  provided in the lightening evaluating zone  3 . The lighting conduction member  311  of the lighting device  31  is electrically connected with the electric conducting member  11 . In the present embodiment, the system for automatically sorting LEDs according to electrostatic resistance  100  does not need to be provided with an electrostatic eliminating device, since the LEDs  200  and the lighting conduction member  311  will stabilize the electrical potential with each other, due to the potential difference between the LEDs  200  and the lighting conduction member  311 . The LEDs  200  will discharge the electrostatic to the lighting conduction member  311 , so the electrostatic within the LEDs  200  will be eliminated (step  31 ). The electrode arranging member  32  is provide to arrange the positive electrode and negative electrode of the LEDs  200  according to the direction of the electrical flow corresponding to the lighting device  31  (step  32 ). The electrode of the LEDs  200  can be previously realized in various ways, such as, reading the sign of the electrode of the LEDs  200  or measuring the electrical resistance value of the LEDs  200  by an electric meter. Therefore, the electrode of the LEDs  200  can be arranged in a way corresponding to a direction of current flow of the lighting device  31  before the LEDs  200  is disposed on the transport carrier  1 . Accordingly, the electrode arranging member  32  is not an element in necessity, and the step  32  is also a step in necessity. The lighting device  31  is able to generate a lightening power according to a setting value. The lighting conduction member  311  is provided to transmit the lightening power to the electrode of the LEDs  200  on the transport carrier  1  (step  33 ). If the LEDs  200  can be lighted by the lightening power, it means that the LEDs  200  are able to sustain the electrostatic. If the LEDs  200  can be lighted by the lightening power, but the brightness of the LEDs  200  is weak, it means that the LEDs  200  are damaged by the electrostatic. If the LEDs  200  cannot be lighted by the lightening power, it means that the LEDs  200  are not able to sustain the electrostatic. The evaluating device  33  is provided to detect the resistance value of the LEDs  200  via the lighting conduction member  311 , and then is transmitting an evaluating signal S to the sorting zone  4  according to the lighting condition of the LEDs  200  (step  34 ). For example, the evaluating signal S is excellent if the resistance value of the LEDs  200  is small, and the evaluating signal S is defective if the resistance value of the LEDs  200  is large, and the evaluating signal S is qualified if the resistance value of the LEDs  200  is medium. 
     Finally, moving the transport carrier  1  to the sorting zone  4  (step  40 ). There is a sorting device  41  provided in the sorting zone  4  and two collecting zones  421 ,  422 . The sorting device  41  is connected with the evaluating device  33 . The sorting device  41  sorts the defective LEDs  200  from the sorting zone  4  to the collecting zone  421  , sorts the qualified LEDs  200  from the sorting zone  4  to the collecting zone  422 , and holds the excellent LEDs  200  on the transport carrier  1  according to the evaluating signal S for subsequent operations (step  41 ). However, the present invention is not limited to this, the sorting zone is provide with one collecting zone or several collecting zones in other embodiment. 
     Please refer to  FIG. 6 , it is a flow chart of a method for automatically sorting LEDs based on electrostatic resistance according to the second embodiment of the present invention. The method for automatically sorting LEDs of the second embodiment is similar with the method for automatically sorting LEDs in the first embodiment. The method for automatically sorting LEDs in the second embodiment is different from the method for automatically sorting LEDs in the first embodiment as follows. First, the method further includes a step  21  of arranging the electrode of the LEDs  200  after step  20 . Second, the method further includes a step  23  of moving the transport carrier to an electrostatic eliminating zone and a step  24  of eliminating the electrostatic existing in the LEDs  200  after step  22 . Third, the method does not include the step  31  of eliminating the electrostatic existing in the LEDs  200  and the step  32  of arranging the electrode of the LED. 
     Please refer to  FIG. 7  to  FIG. 10  with corresponding to  FIG. 6 , the second embodiment of the present invention is described in detail below. 
     The system for automatically sorting LED according to electrostatic resistance  100   a  is similar with the system for automatically sorting LED according to electrostatic resistance  100  in the first embodiment. The elements in the second embodiment illustrated in these four Figs. are similar to those in the first embodiment. Thus, the elements which have the same function as in the first embodiment are labeled with the same reference numbers. 
     The first difference between the second embodiment and the first embodiment is that the system for automatically sorting LEDs according to electrostatic resistance  100   a  is further provided with an electrostatic eliminating zone  5 . The electrostatic eliminating zone is provide with an electrostatic eliminating device  51 , and the system for automatically sorting LEDs according to electrostatic resistance  100   a  is able to eliminate electrostatic faster than the system for automatically sorting LEDs according to electrostatic resistance  100 . The detecting path P′ extends through the electrostatic discharging zone  2 , the electrostatic eliminating zone  5 , the lightening evaluating zone  3 , and the sorting zone  4  in sequence. The LEDs  200  is transported by the transport carrier  1  along the detecting path P′ (step  12 ). The transport carrier  1  is transported from the electrostatic discharging zone  2  to the electrostatic eliminating zone  5  (step  23 ). The electrostatic eliminating device  51  can generate the high density positive ions and the high density negative ions for stabilize the electrical potential to eliminate the electrostatic existing in the LEDs  200 . The electrostatic eliminating member  511  of the electrostatic eliminating device  51  is electrically connected with the LEDs  200 , and is for eliminating the electrostatic existing in the LEDs  200  via the electric conducting member  11 (step  24 ). The electrostatic eliminating device  51  can be replaced by other device with electrostatic eliminating function, such as, a electrostatic elimination blower and so on. 
     The second difference between the second embodiment and the first embodiment is that the electrostatic discharging zone  2  of the system for automatically sorting LEDs according to electrostatic resistance  100   a  is further provided with an electrode arranging member  22 , and the lightening evaluating zone  3  do not provide with the electrode arranging member  32 . 
     While the transport carrier  1  is moved to the electrostatic discharging zone  2 (step  20 ), the electrode arranging member  22  is provided to arrange the electrode of the LEDs  200  according to the direction of electrical flow corresponding to the lighting device  31 (step  21 ). As previously mentioned, the electrode of the LEDs  200  can be previously known in various ways, so the electrode arranging member  22  is not a necessary member, and the step  21  is not a necessary step. Thereafter, an electrostatic is discharged to the LEDs  200  on the transport carrier  1  in a way for keeping the electrostatic existing in the LEDs (step  22 ). Therefore, after step  30 , there is not necessary to repeatedly eliminate electrostatic within the LEDs (step  31 ), and to arrange the electrode of the LEDs (step  32 ) as in the second embodiment. The subsequent steps, such as the aforementioned in first embodiment, are the same. 
     As can be appreciated from the above embodiments, the system for automatically sorting LED according to electrostatic resistance  100 ,  100   a  are able to detect the electrostatic resistance of the LEDs more efficiently than the prior art, and thus the reliability of both the failure rate and the detection rate is improved. 
     The above description should be considered as only the discussion of the preferred embodiments of the present invention. However, a person skilled in the art may make various modifications to the present invention. Those modifications still fall within the spirit and scope defined by the appended claims.