Patent Publication Number: US-2009227048-A1

Title: Method for die bonding having pick-and-probing feature

Description:
FIELD OF THE INVENTION 
     The present invention relates to fabrication technologies of semiconductor devices about a die-bonding method after wafer sawing, especially to a die-bonding method with pick-and-probe features after wafer sawing. 
     BACKGROUND OF THE INVENTION 
     In semiconductor front-end fabrication, the process flow is IC design, wafer fabrication, wafer probing, and wafer sawing. After wafer probing and wafer sawing processes, individual IC dice are formed for semiconductor packaging. 
     Whether the electrical performance and characteristics of each IC die have met the design specifications are confirmed by testers and probe cards to probe every die on a wafer. The probes of a probe card mounted on the tester head of a tester keep in contact with the bonding pads of a die to test its electrical characteristics and then failed dice will be marked. After wafer sawing, a wafer is diced into a plurality of individual dice where some of the dice with marks are scrapped without proceeding to the sequent packaging processes to save unnecessary packaging costs. Moreover; multiple wafer probing is necessary to ensure all the dice before packaging are known good dies (KGD) to avoid yield loss due to stacking or assembling of in multiple dice such as multi-die module, MCM, or system-in-package, SIP. 
     Generally speaking, the first step in semiconductor packaging is die bonding or die attaching performed after wafer probing and wafer sawing. After wafer probing and wafer sawing, different grades or different types of individual dice are sorted and stored at different die trays or die carrier tapes before die bonding. Then, individual dice are picked from the die trays or die carrier tapes by a suction nozzle then die bonded to die carriers which is the most time consuming step and greatly reduces the productivity. If die bonding is performed right after wafer sawing, higher graded dies and lower graded dies may easily be mixed in a die carrier, especially in multi-die package applications. If different graded dice are packaged in the same semiconductor package, then the overall operation frequency will base on the die with the lowest grade leading to lower electrical performance of the semiconductor packages. Moreover, the yield and productivity of semiconductor packages with higher grades are reduced leading to decrease of revenue. 
     SUMMARY OF THE INVENTION 
     The main purpose of the present invention is to provide a die-bonding method with pick-and-probe features after wafer sawing where die probing and sorting are performed at the same time as picking the dice during die bonding processes without extra sorting steps to reduce processing time. Moreover, higher graded dice and lower graded dice are not mixed together in the same semiconductor packages leading to better productivity of different graded semiconductor packages. 
     The second purpose of the present invention is to provide a die-bonding method with pick-and-probe features after wafer sawing to reduce particle contaminations of bonding pads during wafer probing to keep wafers clean. 
     The third purpose of the present invention is to provide a die-bonding method with pick-and-probe features after wafer sawing to screen out bad dies during die-bonding processes according to the sorting results to eliminate the risk of probing or sorting errors to maintain higher packaging yields. 
     According to the present invention, a die-bonding method with pick-and-probe features after wafer sawing is revealed. Firstly, at least a die is provided, having a plurality of electrical terminals where the die is loaded in a loading area. Additionally, a plurality of die carriers are loaded in a plurality of die-bonding areas where the die-bonding areas are sorted for different graded dice. Then, the die is picked by a suction nozzle where the suction nozzle has a plurality of probes to contact the electrical terminals of the die. The die is tested and moved to a corresponding one of the die-bonding areas through the suction nozzle during a pick-and-place step. Moreover, the suction nozzle is working in a plurality of sorting paths from the loading area to the die-bonding areas. Then, according to the sorting results, a corresponding one of the sorting paths is chosen so that the die is moved to the corresponding die-bonding area and is bonded onto a die carrier in the corresponding die-bonding area. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows operation processes of dice moved on a plurality of sorting paths of the die-bonding method with pick-and-probe features after wafer sawing according to the preferred embodiment of the present invention. 
         FIG. 2  shows a side view at the loading area illustrating the die-bonding method with pick-and-probe features after wafer sawing according to the preferred embodiment of the present invention. 
     
    
    
     DETAIL DESCRIPTION OF THE INVENTION 
     Please refer to the attached drawings, the present invention will be described by means of embodiments below. 
     According to the first embodiment of the present invention, a die-bonding method with pick-and-probe features after wafer sawing comprises the following steps. As shown in  FIG. 1 , firstly, at least a die  10  is provided where the dice  10  are taken from a singulated wafer. As shown in  FIGS. 1 and 2 , a plurality of electrical terminals  11  are disposed on the active surface  12  of the die  10 . A die-bonding equipment, also known as a die bonder, includes at least a suction nozzle  30 , a loading area  40 , a plurality of die-bonding areas  51 ,  52 , and  53 , and a plurality of sorting paths  61 ,  62 , and  63 . Therein, the die-bonding areas  51 ,  52 , and  53  are graded according to a plurality of different die grades, and the sorting paths  61 ,  62 , and  63  is connected from a common moving path  70  connecting the loading area  40  to the corresponding die-bonding areas  51 ,  52 , and  53 . 
     By choosing an appropriate sorting path  61 ,  62 , or  63 , the suction nozzle  30  can move from the loading area  40  optionally to one of the die-bonding areas  51 ,  52 , and  53 . In one embodiment, the die grades for sorting the die-bonding areas  51 ,  52 , and  53  are the sorting of DDR2 dice so that the die-bonding areas  51 ,  52 , and  53  are defined as a 533 MHz area, a 667 MHz area, and an 800 MHz area, or preferably, by more die-bonding areas of a 1066 MHz area or/and a scrapped area. However, without any limitations, the die-bonding method according to the present invention can also be implemented in flash memories and other ASIC. The dice  10  are located at the loading area  40 . As shown in  FIG. 1  and  FIG. 2 , the dice  10  are loaded in the loading area  40  by attached to a wafer-saw tape  80  or the other method so that die-bonding processes can be performed right after wafer sawing. Some of the dice  10  with marks on the wafer-saw tape  80  are lower graded dice or bad dice such as the dice marked with circles in  FIG. 1 . 
     According to the method, a plurality of die carriers  20  are loaded in the plurality of die-bonding areas  51 ,  52 , and  53 . In one embodiment, the die carriers  20  are substrates for multi-die packages or for multi-die stacked memory cards. Alternatively, the die carriers  20  can be semiconductor dice  10  to form multi-die module packages. 
     The die-bonding method includes a pick-and-place step. The suction nozzle  30  is working among the sorting paths  61 ,  62 , and  63  connecting the loading area  40  to the die-bonding areas  51 ,  52 , and  53 . Firstly, the suction nozzle  30  moves to the loading area  40  to pick up a die  10  where the suction nozzle  30  has a plurality of probes  31  to probe the electrical terminals  11  of the die, as shown in  FIG. 2 . After picking Lip the die  10 , the functions of the die  10  are tested and the die  10  is moved on the common moving path  70 , then one of the sorting paths  61 ,  62 , and  63  is chosen according to the testing result. The die  10  picked by the suction nozzle  30  is moved on the chosen sorting paths  61 ,  62 , or  63  and then bonded onto the corresponding die carrier  20  in the corresponding die-bonding area  51 ,  52 , or  53 . Accordingly, different grades of probed dice can be placed to different die-bonding areas  51 ,  52 , and  53  to avoid any waste of sorting materials such as die trays or die carrier tapes and to simplify processing steps. 
     To be more specific, as shown in  FIG. 2 , the suction nozzle  30  picks the die  10  in contact with the active surface  12  of the die  10  to probe the electrical terminals  11  of the die  10  by the probes  31 . Preferably, the probes  31  of the suction nozzle  30  are formed in the vacuum holes  32  of the suction nozzle  30  where the vacuum holes  32  are connected to a vacuum source such as a vacuum pump by a vacuum tube, not shown in the figure, so that the suction nozzle  30  has a suction force to hold the die  10  and to probe the electrical terminals  11  of the die  10  at the same time. Moreover, the electrical terminals  11  of the die  10  are not be contaminated during probing the die  10  so that the die  10  is kept clean. 
     As shown in  FIG. 1 , according to the different grades of the probed dice  10 , a corresponding sorting path  61 ,  62 , or  63  of the suction nozzle  30  is chosen, and then the probed die  10  is moved on the chosen sorting path  61 ,  62 , or  63  to the corresponding die-bonding areas  51 ,  52 , or  53  without manually sorted the dice  10  to save processing time. In the present embodiment, the suction nozzle  30  can work along the common moving path  70  connecting the loading area  40  to the sorting path  61 ,  62 , or  63 . The step of testing the picked die  10  by the suction nozzle  30  is completed when the suction nozzle  30  is moved on the common moving path  70 . 
     Finally, the probed die  10  is bonded to the corresponding die-bonding areas  51 ,  52 , or  53  by the suction nozzle  30 . A die-attaching material can be disposed on the die carrier  20  such as epoxy, silver paste, B-stage paste, or double-sided adhesive P1 tapes. Accordingly, the suction nozzle  30  picks the die  10  from the loading area  40 , work in a corresponding sorting path  61 ,  62 , or  63 , and die bond the die  10  to the die carrier  20 . The die-bonding method according to the present invention includes the pick-and-place step, the testing step, the sorting step and the die bonding step by the operation of the suction nozzle  30 . 
     Therefore, the die-bonding method with pick-and-probe features after wafer sawing according to the present invention can pick, probe, and sort the dice at the same time without extra sorting steps to save processing time. Moreover, there is no chance of mixing the higher graded dice with the lower graded dice on a same die carrier to form an inferior semiconductor package. The productivity of higher graded packages is increased. 
     The above description of embodiments of this invention is intended to be illustrative and not limiting. Other embodiments of this invention will be obvious to those skilled in the art in view of the above disclosure.