Abstract:
The present invention relates to a packaging method for segregating die paddles of a leadframe. The method comprising: (a) providing a leadframe having a top surface, a bottom surface and a die paddle region, the die paddle region having a plurality of die paddles, wherein at least two of the die paddles are connected to each other by at least one connecting bar; (b) attaching a plurality of dies onto the die paddles; (c) forming a molding compound to encapsulating the dies on the die paddles, and exposing the bottom surface of the connecting bar outside the molding compound; and (d) removing part of the connecting bar so as to segregate the die paddles, Whereby the die paddles are stable during the steps of die attaching, wire bonding and molding, and the yield is raised.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the invention  
         [0002]     The present invention relates to a packaging method, particularly for segregating die paddles of a leadframe.  
         [0003]     2. Description of the Related Art  
         [0004]      FIG. 1  shows a top view of the die paddles region of a leadframe before molding. The die paddles region  1  of the leadframe comprises a first die paddle  11 , a second die paddle  12  and a third die paddle  13  so as to carry dice  14 ,  15 ,  16  respectively, wherein each of the die paddles  11 ,  12 ,  13  is segregated from the others. In addition, the die paddles  11 ,  12 ,  13  and the dice  14 ,  15 ,  16  are electrically connected by a plurality of conducting wires  18 .  
         [0005]     Since the left end of the third die paddle  13  is a free end, the third paddle  13  is unstable during the steps of die attaching, bonding and molding, such as shaking problem, to cause a failure of packaging. In order to improve the shortcoming, the stability of the third die paddle  13  in prior art is increased by using a connecting bar  17  to link the left end of the third die paddle  13  to the left end of the die paddle region  1 . However, the connecting bar  17  is so long that a weak point is formed at the connecting region between the right end of the connecting bar  17  and the third die paddle  13 . The weak point probably sways and bends, even cracks and thus causes defects of products. Besides, the connecting bar  17  decreases the usage area of surface of the die paddle region  1 .  
         [0006]     Consequently, there is an existing need for a packaging method to solve the above-mentioned problems.  
       SUMMARY OF THE INVENTION  
       [0007]     One objective of the present invention is to provide a packaging method. Firstly, a plurality of die paddles are connected to each other by connecting bars. Afterwards, the connecting bars are cut or removed after die attaching, bonding and molding method. Whereby, the die paddles are stable during the steps of die attaching, wire bonding and molding, and the yield is raised.  
         [0008]     Another objective of the present invention is to provide a packaging method that reduces the area of the surface of connecting bars and increases the usage area of die paddle region by using the connecting bars to connect the die paddle.  
         [0009]     Still another objective of the present invention is to provide a packaging method for segregating die paddles of a leadframe. The packaging method of the invention comprises the steps of: 
        (a) providing a leadframe having a top surface, a bottom surface and a die paddle region, the die paddle region having a plurality of die paddles, at least two die paddles connected to each other by a connecting bar;     (b) attaching a plurality of dies onto the die paddles;     (c) forming a molding compound to encapsulate the dies on the die paddles and to expose a bottom surface of the connecting bar outside the molding compound; and     (d) removing part of the connecting bar so as to segregate the connected die paddles.       
 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  shows a top view of the die paddles region of a conventional leadframe before a molding step;  
         [0015]      FIG. 2  shows flow chart of the packaging method for segregating die paddles of a leadframe according to a first embodiment of the present invention;  
         [0016]      FIG. 3  shows a top view of die paddle region of the leadframe according to the first embodiment of the present invention;  
         [0017]      FIG. 4  shows a partial sectional view along line  4 - 4  of the  FIG. 3 ;  
         [0018]      FIG. 5  shows a top view of the die paddle region after the die attaching step according to the first embodiment of the present invention;  
         [0019]      FIG. 6  shows a top view of the die paddle region after the bonding step according to the first embodiment of the present invention;  
         [0020]      FIG. 7  shows the molding step according to the first embodiment of the present invention;  
         [0021]     FIGS.  8  to  11  show the segregating step according to the first embodiment of the present invention;  
         [0022]      FIG. 12  shows a bottom view of the die paddle region of the first embodiment by omitting the compound after the molding step according to the first embodiment of the present invention;  
         [0023]     FIGS.  13  to  15  show the segregating step according to a second embodiment of the present invention;  
         [0024]      FIG. 16  shows a top view of die paddles of the leadframe according to a third embodiment of the present invention;  
         [0025]      FIG. 17  shows a partial sectional view of die paddle region of the leadframe according to the third embodiment of the present invention;  
         [0026]      FIG. 18  shows the molding step according to the third embodiment of the present invention;  
         [0027]     FIGS.  19  to  22  show the segregating step according to the third embodiment of the present invention;  
         [0028]     FIGS.  23  to  26  show the segregating step according to a fourth embodiment of the present invention;  
         [0029]      FIG. 27  shows a partial sectional view of die paddle region of the leadframe according to a fifth embodiment of the present invention;  
         [0030]      FIG. 28  shows the molding step according to the fifth embodiment of the present invention;  
         [0031]     FIGS.  29  to  32  show the segregating step according to the fifth embodiment of the present invention; and  
         [0032]     FIGS.  33  to  36  show the segregating step according to a sixth embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0033]      FIG. 2  shows flow chart of the packaging method for segregating die paddles of a leadframe according to a first embodiment of the present invention.  FIG. 3  shows a top view of die paddle region of the leadframe according to the first embodiment of the present invention.  FIG. 4  shows a sectional view of the  FIG. 3  along line  4 - 4  according to the present invention. The packaging method of the present invention comprises the following steps. Firstly, referring to  FIG. 3  and  FIG. 4 , as shown in step S 201  of  FIG. 2 , a leadframe is provided. The leadframe comprises a top surface  31 , a bottom surface  32  and a die paddle region  2 . The die paddle region  2  has a first die paddle  21 , a second die paddle  22  and a third die paddle  23 . The second die paddle  22  and the third die paddle  23  connect to each other by a connecting bar  27 . The first die paddle  21  and the third die paddle  23  connect to each other by a connecting bar  29 . Except the connecting bars  27 ,  29 , the first die paddle  21 , the second die paddle  22  and the third die paddle  23  do not connect to each other. It should be noted in the embodiment that the die paddle region  2  has three die paddles, but the die paddle region of the invention may not be limited to have three die paddles. The die paddle region also can have two, four, five, six or more die paddles.  
         [0034]     The left side of the third die paddle  23  connects to the first die paddle  21  and the second die paddle  22  by using the connecting bars  27 ,  29 , respectively. Therefore, the left side of the third die paddle  23  is not a free end, and it will be stable in the following processes. Compared with the conventional connecting bar  17 , the present invention is better for fastening the third die paddle  23 . In addition, the present invention omits the conventional connecting bar  17  so as to increase the areas of the first die paddle  21  and the second die paddle  22 .  
         [0035]     In the embodiment, because the connecting bars  27 ,  29  are finally cut off, the thickness of the connecting bars  27 ,  29  are designed to be thinner than that of the die paddles  22 ,  23 , as shown in  FIG. 4 , so as to facilitate the following step of cutting. In the embodiment, the left side of the third die paddle  23  connects to the first die paddle  21  and the second die paddle  22  by using the connecting bars  27 ,  29 , respectively; however, it is understood that the third die paddle  23  can only connect to the first die paddle  21  or only connect to the second die paddle  22 . In addition, the third die paddle  23  can also connect to the first die paddle  21  by using a plurality of connecting bars.  
         [0036]     Referring to  FIG. 5 , the step S 202  in  FIG. 2  is a die attaching step. A plurality of dice  24 ,  25 ,  26  are attached onto the die paddles  21 ,  22 ,  23 .  
         [0037]     Referring to  FIG. 6 , the step S 203  in  FIG. 2  is a bonding step. A plurality of conducting wires  28  are formed to electrically connect the dice  24 ,  25 ,  26  and the die paddles  21 ,  22 ,  23  or somewhere that should be electrically connected. It is to be understood that the step S 203  is not necessary; in other words, the step S 203  is an optional step.  
         [0038]     Referring to  FIG. 6 , the step S 204  in  FIG. 2  is a molding step. A molding compound  30  is formed to encapsulating the dies  24 ,  25 ,  26  on the die paddles  21 ,  22 ,  23 , and the bottom surface of the connecting bar  27  is exposed outside the molding compound  30 .  
         [0039]     Finally, the step S 205  in  FIG. 2  is a segregating step. Part of the connecting bar  27  is removed to segregate the die paddles  21 ,  22 ,  23 . Perfectly, the connecting bar  27  is totally removed. In the embodiment, the connecting bar  27  is cut off at the bottom surface by etching method. It is noted that the connecting bar  27  can also be cut off in another method. The etching method of the embodiment is described as follows. Firstly, referring to  FIG. 8 , a photo resist layer  40  is formed under the connecting bar  27 , wherein the photo resist layer  40  does not fully cover the bottom surface of the connecting bar  27  so as to expose part of the connecting bar  27 . Referring to  FIG. 9 , the exposed part of the connecting bar  27  is etched so as to completely cut off the connecting bar  27 . Referring to  FIG. 10 , the photo resist layer  40  is removed. Finally, the bottom surface of the connecting bar  27  is plated to form a plating layer  41 , as shown in  FIG. 11 , and the segregating steps are therefore performd.  
         [0040]      FIG. 12  shows a bottom view of the die paddle region without the compound after the molding step according to the first embodiment of the present invention. It can be observed that the connecting bars  27 ,  29  (as shown in  FIG. 3 ) are totally removed. In the die paddle region  2 , the die paddles  21 ,  22 ,  23  have already been segregated and are disconnected from each other.  
         [0041]     FIGS.  13  to  15  show the segregating step according to a second embodiment of the present invention. In the embodiment, the steps of providing a leadframe, die attaching, bonding and molding are the same as those of the first embodiment, however, there is difference in the segregating step. In the embodiment, the connecting bar  27  is the same cut off at the bottom surface by etching method. The etching method of the embodiment is described as follows. Firstly, referring to  FIG. 13 , the bottom surface of the connecting bar  27  is plated to form a plating layer  42 , wherein the plating layer  42  does not fully cover the bottom surface of the connecting bar  27  so as to expose part of the connecting bar  27 . It is to be understood that the plating step may be performed after the step S 201  in  FIG. 2 , i.e. the bottom surface of the leadframe has a plating layer  42  in the beginning. Referring to  FIG. 14 , the exposed part of the connecting bar  27  is etched so as to completely cut off the connecting bar  27  to form a cavity. It is to be noted that the etching step must be performed after the molding step. Finally, the cavity of the bottom surface of the connecting bar  27  is plated, shown in  FIG. 15 , and the segregating step is therefore performed.  
         [0042]     Referring to  FIG. 16  and  FIG. 17 , they show a top view and a sectional view of die paddle region of the leadframe respectively according to a third embodiment of the present invention. The difference between the leadframe of the third embodiment and the leadframe of the first embodiment is the type of the connecting bars  57 ,  59  in the die paddle region. In the embodiment, taking the connecting bar  57  for an example, at least one top cavity  571  is preformed on the top surface of the connecting bar  57  because the connecting bar  57  is to be finally cut off, i.e. the top surface of the connecting bar  57  have already had the top cavity  571  in the step S 201  in  FIG. 2 . The die attaching step and the bonding step are the same as those of the first embodiment. Afterwards, the step S 204  is a molding step. The molding step utilizes a molding compound  30  to encapsulate the dice  24 ,  25 ,  26  on surfaces of the die paddles  21 ,  22 ,  23 , and the bottom surface of the connecting bar  57  is exposed outside the molding compound  30 , as shown in  FIG. 18 . Furthermore, the top cavity  571  is filled up with the molding compound  30 .  
         [0043]     Finally, the step S 205  in  FIG. 2  is a segregating step. In the segregating step, part of the connecting bar  57  is removed so as to segregate the die paddles  21 ,  22 ,  23 . Perfectly, the connecting bar  57  is to be totally removed. In the embodiment, the connecting bar  57  is to be cut off at the bottom surface of the connecting bar  57  by etching method. The etching method of the embodiment is described as follows. Firstly, referring to  FIG. 19 , a photo resist layer  60  is formed on the bottom surface of the connecting bar  57 , wherein the photo resist layer  60  does not fully cover the bottom surface of the connecting bar  57  so as to expose part of the connecting bar  57 . Referring to  FIG. 20 , the part of the connecting bar  57  is etched to be completely cut off. Referring to  FIG. 21 , the photo resist layer  60  is removed. Finally, the bottom surface of the connecting bar  57  is plated to form a plating layer  61 , as shown in  FIG. 22 , and the segregating step is therefore performed.  
         [0044]     Referring to  FIG. 23  to  FIG. 26 , they show the segregating step according to a fourth embodiment of the present invention. In the embodiment, the steps of providing a leadframe, die attaching, bonding and molding are the same as those of the third embodiment; however, there is difference in the step of segregating. In the embodiment, similarly, the connecting bar  57  is the same cut off at the bottom surface by etching. The etching method of the embodiment is described as follows. Firstly, referring to  FIG. 23 , the bottom surface of the connecting bar  57  is plated to form a plating layer  62 , wherein the plating layer  62  does not fully cover the bottom surface of the connecting bar  57  so as to expose part of the connecting bar  57 . It is to be understood that the plating step may be performed after the step S 201  in  FIG. 2 , i.e. the bottom surface of the leadframe has a plating layer  62  in the beginning.  FIG. 24  shows the molding step. Referring to  FIG. 25 , the exposed part of the connecting bar  57  is etched to be completely cut off to form a cavity. It should be noted that the etching step must be performed after the molding step. Finally, the cavity of the bottom surface of the connecting bar  57  is plated, as shown in  FIG. 26 , and the segregating step is therefore performed.  
         [0045]     Referring to  FIG. 27 , it shows a sectional view of die paddle region of the leadframe according to a fifth embodiment of the present invention. In the fifth embodiment, the type of the connecting bars  57 ,  59  in the die paddle region is different from the third embodiment. In the embodiment, taking the connecting bars  57  for an example, at least one top cavity  571  is preformed on the top surface of the connecting bar  57  and two bottom cavities  572  are performed on the bottom surface of the connecting bar  57  because the connecting bar  57  is to be finally cut off, i.e. the top surface of the connecting bar  57  have already had the top cavity  571  and the bottom surface of the connecting bar  57  have already had the bottom cavities  572  in the step S 201  in  FIG. 2 . Wherein the bottom cavities  572  disconnects from the top cavity  571 .  
         [0046]     Afterwards, steps of attaching die and bonding are the same as the third embodiment. The step S 204  is a molding step. A molding compound  30  is formed to encapsulating the dice  24 ,  25 ,  26  on surfaces of the die paddles  21 ,  22 ,  23 , and exposing the bottom surface of the connecting bar  57  outside the molding compound  30 , as shown in  FIG. 28 . Furthermore, the top cavity  571  and the bottom cavities  572  are filled up with the molding compound  30 .  
         [0047]     Finally, the step S 205  in  FIG. 2  is a segregating step. In the step, part of the connecting bar  57  is removed to segregate the die paddles  21 ,  22 ,  23 . Perfectly, the connecting bar  57  is totally removed. In the embodiment, the connecting bar  57  is to be cut off at the bottom surface by etching method. The etching method of the embodiment is described as follows. Firstly, referring to  FIG. 29 , a photo resist layer  70  is formed under the connecting bar  57 , wherein the photo resist layer  70  covers the bottom cavities  572  but does not fully cover the bottom surface of the connecting bar  57  so as to expose part of the connecting bar  57 . Referring to  FIG. 30 , the part of the connecting bar  57  is etched to be completely cut off. Referring to  FIG. 31 , the photo resist layer  70  is removed. Finally, the bottom surface of the connecting bar  57  is plated to form a plating layer  72 , as shown in  FIG. 32 , and the segregating step is therefore performed.  
         [0048]     Referring to  FIG. 33  to  FIG. 36 , they show the segregating step according to a sixth embodiment of the present invention. In the embodiment, the steps of providing a leadframe, die attaching, bonding and molding are the same as those of the fifth embodiment; however, there is difference in the segregating step. In the embodiment, the connecting bar  57  is the same cut off at the bottom surface by etching method. The etching method of the embodiment is described as follows. Firstly, referring to  FIG. 33 , the bottom surface of the connecting bar  57  is plated to form a plating layer  72 , wherein the plating layer  72  does not fully cover the bottom surface of the connecting bar  57  so as to expose part of the connecting bar  57  and the bottom cavities  572 . It is to be understood that the plating step may be performed after the step S 201  in  FIG. 2 , i.e. the bottom surface of the leadframe has a plating layer  72  in the beginning.  FIG. 34  shows the molding step. Referring to  FIG. 35 , the exposed part of the connecting bar  57  is etched to be completely cut off to form a cavity. It should be noted that the etching step must be performed after the molding step. Finally, the cavity of the bottom surface of the connecting bar  57  is plated, as shown in  FIG. 36 , and the segregating step is therefore performed.  
         [0049]     While several embodiments of the present invention have been illustrated and described, various modifications and improvements can be made by those skilled in the art. The embodiments of the present invention are therefore described in an illustrative but not restrictive sense. It is intended that the present invention may not be limited to the particular forms as illustrated, and that all modifications which maintain the spirit and scope of the present invention are within the scope as defined in the appended claims.