Abstract:
Disclosed embodiments include a manufacturing method for an LED assembly. Providing a first carrier, wherein several LED chips are formed on the first carrier, and providing a second carrier. Attaching the second carrier to the LED chips and detaching the first carrier from the LED chips but leaving the LED chips on the second carrier.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and claims the benefit of Taiwan Patent Application Serial Number 102136175 filed on Oct. 7, 2013, which is incorporated by reference in its entirety. 
     FIELD OF THE INVENTION 
     Embodiments of the application relate to a method for fabricating LED (light emitting diode) assemblies. 
     BACKGROUND 
     Applications of various LED goods, such as traffic signs, motorcycle tail lights, automobile head lights, street lamps, computer indicators, flashlights, LED backlight sources, etc., can now be seen in daily life. In addition to the chip process, almost all of these products are gone through packaging procedure as well. 
       FIG. 1  shows a conventional process of LED assemblies. First, a sapphire substrate  10  is provided. Subsequently, semiconductor fabrication processes like epitaxial process, thin film deposition, lithography and etching are performed to form multiple LED chips on the sapphire substrate  10 , as the wafer  12  shows. Each LED chip may have one or more LED units, and each LED unit comprises a light-emitting layer. In the light-emitting layer, light is emitted due to recombination of electrons and holes. Each wafer  12  is examined by the wafer acceptance test (WAT) first, and then the qualified wafer  12  is cut to form individual LED chips. The LED chip is also referred as LED die. Each LED chip is inspected and classified according to the photoelectric characteristics thereof, such as forward voltage, dominant wavelength, luminous intensity, etc. LED chips have same photoelectric characteristic are picked and placed on a temporary carrier film, and the temporary carrier film may be a blue tape or a tape-on-reel having a surface for the chips to be mounted thereon. In  FIG. 1 , three different kinds of LED chips are placed on the temporary carrier films B 1 , B 2  and B 3 , respectively. LED packaging manufacturers purchase temporary carrier films with LED chips and produce LED assemblies after appropriate packaging process. For example, the LED assembly  14  in  FIG. 1  comprises an LED chip  16 , a cooling base  18 , bonding wires  20 , silicone  22  and a lens  24 . 
     Nevertheless, the process of removing LED chips one by one from a temporary carrier film and to fix them to the base of a LED product is usually very time consuming. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a fabrication process of an LED assembly. 
         FIG. 2  shows a fabrication method of an LED assembly according to an embodiment of the present application. 
         FIG. 3  shows a temporary carrier film according to an embodiment of the present application. 
         FIG. 4  shows a transparent carrier according to another embodiment of the present application. 
         FIG. 5A  and  FIG. 5B  show a transparent carrier and a temporary carrier film before bonding according to an embodiment of the present application. 
         FIG. 6  shows a transparent carrier and a temporary carrier film after bonding according to an embodiment of the present application. 
         FIG. 7  shows a temporary carrier film is separated from the LED chip according to an embodiment of the present application. 
         FIG. 8  shows that an LED assembly having a region C 1  after the cutting process is completed according to an embodiment of the present application. 
         FIG. 9  shows a transparent carrier film and a temporary carrier prior to bonding according to an embodiment of the present application. 
         FIG. 10  shows a transparent carrier film and a temporary carrier that have been bonded according to an embodiment of the present application. 
         FIG. 11  shows that a temporary carrier film is separated from the LED chip according to an embodiment of the present application. 
         FIG. 12  shows bonding wires are formed on an LED chip according to an embodiment of the present application. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       FIG. 2  shows a fabrication method of LED assemblies according to the present application. In step  102 , a wafer acceptance test (WAT) is performed on the wafer  12  that comprises chips to determine if the wafer meets the specifications. In step  104 , a cutting process is applied on the qualified wafer  12  to form individual LED chips. Each LED chip is inspected to be classified according to the photoelectric characteristics thereof, such as forward voltage, dominant wavelength, luminous intensity, etc. and the LED chips have same photoelectric characteristic are placed on a temporary carrier film in step  106 . The temporary carrier film may be a blue tape.  FIG. 3  shows a temporary carrier film BB 1  according to the present application, which LED chips  120  of the same photoelectric characteristic are mounted thereon. The LED chips  120  on the temporary carrier film BB 1  can be roughly divided into  4  groups of G 1 , G 2 , G 3  and G 4  based on the locations. The locations of all LED chips  120  within each group form a pattern, and the patterns are substantially the same for all groups as shown in  FIG. 3 . 
     In  FIG. 2 , a transparent carrier is provided in step  108  as an example of carriers, wherein the transparent carrier comprises a material that is transparent to the light emitted by the LED chips, such as sapphire, glass or transparent silicon carbide sheets. In step  110 , a printed circuit is formed on the transparent carrier.  FIG. 4  shows a transparent carrier CC in an embodiment of the present application, with printed circuits PC formed thereon. The transparent carrier CC comprises a number of grooves  130  thereon to facilitate the subsequent cutting process. The grooves  130  substantially define eight regions C 1 ˜C 8 , and each region has a printed circuit PC of same pattern as shown in  FIG. 4 . 
     In the step  112  shown in  FIG. 2 , an anisotropic conductive film (ACF) is formed on the printed circuits PC. 
       FIG. 5A  shows a transparent carrier CC and a temporary carrier film BB 1  prior to a bonding process. As shown in  FIG. 5A , the LED chip  120  in the group G 1  is attached to the region C 1  of the transparent carrier CC while the LED chip  120  in the group G 2  is attached to the region C 2  of the transparent carrier CC; and so on.  FIG. 5B  shows that the LED chip  120  is bonded to the temporary carrier film BB 1 , and the transparent carrier CC has printed circuits PC and an ACF  132  thereon. In  FIG. 5B , the LED chip  120  is not connected to the transparent carrier CC. 
     As the step  11  shows in  FIG. 2 , the LED chip  120  on the temporary carrier film BB 1  are bonded with the transparent carrier CC like  FIG. 6  shows. In  FIG. 6 , the LED chip  120  is bonded to the temporary carrier film BB 1 , and the LED chip  120  is bonded to the transparent carrier CC via the ACF  132 . 
     According to the step  116  in  FIG. 2 , the temporary carrier film BB 1  and the LED chip  120  are separated as shown in  FIG. 7 . For example, the temporary carrier film BB 1  may be torn apart directly or after being heated. The heating process may be realized by baking the temporary carrier film BB 1 , the LED chip  12  and the transparent carrier CC simultaneously or only heating the side of the temporary carrier film BB 1  opposing to the LED chip  12 . In  FIG. 7 , the temporary carrier film BB 1  and the LED chip  120  are separated while the LED chip  120  remains on the transparent carrier CC and is fixed by the ACF  132 . 
     In  FIG. 3 , the LED chips  120  of four groups G 1 ˜G 4  on the temporary carrier film BB 1  are respectively fixed to four regions (C 1 ˜C 4 ) among eight regions in the transparent carrier CC. In another embodiment, another temporary carrier film that is identical to the temporary carrier film BB 1  and has a plurality of LED chips  120  formed thereon may be fixed to the other four regions (C 5 ˜C 8 ) in the transparent carrier CC. 
     According to step  118  in  FIG. 2 , the transparent carrier CC can be divided along the grooves  130  to separate the eight regions (C 1 ˜C 8 ) to be eight LED assemblies.  FIG. 8  shows an LED assembly  140  having a region C 1  after the cutting process. As shown in  FIG. 8 , the LED assembly  140  comprises the region C 1 , which is a part of the transparent carrier CC, and the region C 1  comprises the printed circuit PC and the LED chips  120  of the group G 1 . In  FIG. 8 , each LED chip  120  is fixed to the transparent carrier CC in a form of flip chip. The electrical connection between every two LED chips  120  is provided by the printed circuit PC and the ACF  132 . The printed circuit PC can transmit electrical energy to enable LED chips  120  to emit light. 
     According to the embodiments in  FIGS. 2 ˜ 8 , regardless of the amount of LED chips  120  on the temporary carrier film BB 1 , all the LED chips  120  can be bonded to the transparent carrier CC in the same time, and all of the LED chips  120  can be separated from the temporary carrier film BB 1  in the same time. Compared with a conventional process that moves one LED chip from a carrier film to another carrier a time, the process shown in the embodiments in  FIGS. 2 ˜ 8  greatly simplifies the fabrication steps and improves the throughput. 
     Although the LED assembly  140  in  FIG. 8  is fixed to the transparent carrier CC in a form of flip chip, the present invention is not limited by the embodiment.  FIG. 9  shows that the LED chips  120  are bonded to the temporary carrier film BB 1 , and a bonding layer  134  is provided on the transparent carrier CC without printed circuit PC. Referring to  FIG. 9 , the LED chips  120  have not yet been attached to the transparent carrier CC. 
       FIG. 10  shows a cross-sectional view of an LED assembly in the fabrication process after  FIG. 9 , wherein the LED chips  120  on the temporary carrier film BB 1  are simultaneously bonded to the transparent carrier CC via the bonding layer  134 . 
       FIG. 11  shows a cross-sectional view of an LED assembly in the fabrication process after  FIG. 10 , which shows that the temporary carrier film BB 1  is separated from the LED chips  120 , while the LED chips  120  are bonded to the transparent carrier CC via the bonding layer  134 . 
     Before the LED chips  120  is bonded to the transparent carrier CC as shown in  FIG. 9 , or after the LED chips  120  are bonded to the transparent carrier CC as shown in  FIG. 10 , a conductive electrode plate  138  can be attached to the transparent carrier CC in  FIG. 9  or in  FIG. 10 . As  FIG. 11  shows, the temporary carrier film BB 1  has been separated from the LED chips  120 . As shown in  FIG. 12 , the bonding wires  136  are formed on the LED chips  120 . The bonding wires  136  not only provide electrical connection between the LED chips  120 , but also provide electrical connection between the LED chips  120  and the conductive electrode plates  138 . As shown in  FIG. 12 , the electrical connection region of the LED chips  120  (i.e. the region where the conductive electrode plate  138  is located) is different from the region where the LED chips  120  are bonded to the transparent carrier CC; namely, the position, on the transparent carrier CC, of the conductive electrode plate  138  is not overlapped with the position of the LED chip  120 , and the LED chips  120  are electrically connected to the conductive electrode plate  138  via the bonding wires  136 . Therefore, the LED chips  120  are fixed to the transparent carrier CC not in a form of flip chip. Nevertheless, in order to bond the LED chips  120  to the transparent carrier CC with the front side facing upward, as indicated in  FIG. 8 , the LED chips  120  are bonded to the transparent carrier CC in a form of flip chip. 
     The embodiments in  FIGS. 2 ˜ 8  are similar with the embodiments in  FIGS. 9 ˜ 12 , that is, regardless of the amount of LED chips  120  on the temporary carrier film BB 1 , all of the LED chips  120  can be bonded to the transparent carrier CC in the same time, and all of the LED chips  120  can be separated from the temporary carrier film BB 1  in the same time. As a result, the fabrication steps can be greatly simplified and the throughput can be improved. 
     While the disclosure has been described by way of example and in terms of preferred embodiment, it is to be understood that the disclosure is not limited thereto. 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.