Patent Publication Number: US-2005130497-A1

Title: Stress dispersing lead and stress dispersing method of lead

Description:
BACKGROUND OF THE INVENTION  
      The present invention relates to a lead to which a stress in a tape carrier package is dispersed, and a method of dispersing a stress generated in the lead.  
      A description will be given of a relevant structure of a lead and a printed circuit board in a conventional tape carrier package with reference to  FIGS. 1A and 1B .  FIG. 1A  is a cross sectional view of a whole structure, and  FIG. 1B  is an enlarged cross sectional view of a portion within an oval in  FIG. 1A . A structure within a broken line oval in  FIG. 1B  shows a main portion of the lead.  
      As shown in  FIG. 1B , electrodes  22   a  provided in both right and left sides of a semiconductor device  22  such as an IC chip or the like are connected onto semiconductor device connecting terminal portions  21   a  of a pair of small leads  21  arranged in a lower side, respectively. A leading end of an intermediate slope portion  21   b  of each of the leads  21  is bent to an outer side, whereby a substrate connecting terminal portion  21   c  is structured.  
      Electrodes  24   a  provided in both right and left sides of a semiconductor device  24  are connected onto semiconductor device connecting terminal portions  23   a  of a pair of large leads  23  arranged in an upper side, respectively. A leading end of an intermediate slope portion  23   b  of each of the leads  23  is bent to an outer side, whereby a substrate connecting terminal portion  23   c  is structured.  
      The substrate connecting terminal portion  21   c  of each of the leads  21  and the substrate connecting terminal portion  23   c  of each of the leads  23  are connected by solder to pads  25   a  of a printed circuit board  25 , respectively.  
      An upper surface of the semiconductor device  24  is in contact with a silicone sheet  27  which is attached to a copper cover  26 . A heat radiation is executed from an inner side of the tape carrier package to an outer side thereof by the means mentioned above.  
      A structure and a function of a lower half portion of the tape carrier package are the same as the structure and the function of an upper half portion.  
      A length of the lower lead  21  is short. Since the length of the lead is bounded by a width of the tape carrier package and a thickness of a module, it is estimated that the length is going to be further shorter. If the length of the lead is short, the lead can not absorb a repeated bending stress generated at a time of a temperature cycle. Accordingly, the lead is ruptured.  
      In this case, there has been proposed a structure for preventing an excessive stress from being generated in a connection portion of a bump and an inner lead, by arranging an R-bent portion depressed to a side of the semiconductor device in the inner lead connected to the bump formed on the semiconductor device, in the taper carrier package on which the semiconductor is mounted (for example, refer to JP-A-11-40622).  
      Further, there has been proposed a structure for lowering a stress generated by a base film applied to an inner lead so as to prevent the inner lead from being ruptured, by supporting the inner lead suspending an IC chip by a stress relaxation portion of a base film, and elastically deforming the stress relaxation portion (for example, refer to JP-A-10-178052).  
      Since the conventional lead can not absorb the repeated bending stress generated at a time of the temperature cycle due to its short length, the lead is ruptured.  
     SUMMARY OF THE INVENTION  
      An object of the present invention is to provide a lead which can absorb a repeated bending stress generated at a time of a temperature cycle, and a stress treating method of the same.  
      The object can be achieved by the following stress dispersing lead and lead stress dispersing method.  
      1. A stress dispersing lead in which a lead is continuously and integrally structured by a semiconductor device connecting terminal portion, an intermediate slope portion and a substrate connecting terminal portion, the semiconductor device connecting terminal portion extends to an outer side from a semiconductor device, and the substrate connecting terminal portion is bent to an inner side from one end of the intermediate slope portion.  
      2. A stress dispersing lead in which a lead is continuously and integrally structured by a semiconductor device connecting terminal portion, an intermediate slope portion and a substrate connecting terminal portion, a semiconductor device is arranged between the semiconductor device connecting terminal portion and a substrate, and an electrode of the semiconductor device is connected to the semiconductor device connecting terminal portion.  
      3. A stress dispersing lead in which a lead is continuously and integrally structured by a semiconductor device connecting terminal portion, an intermediate slope portion and a substrate connecting terminal portion, a semiconductor device is provided with an electrode near a center thereof, and the semiconductor device connecting terminal portion is connected to the electrode.  
      4. A stress dispersing lead in which a lead is continuously and integrally structured by a semiconductor device connecting terminal portion, an intermediate slope portion and a substrate connecting terminal portion, the semiconductor device connecting terminal portion, the intermediate slope portion and the substrate connecting terminal portion are formed approximately in an S-shape as a whole. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1A  is a cross sectional view of a whole of a lead in a conventional tape carrier package;  
       FIG. 1B  is an enlarged cross sectional view of a part surrounded by an oval in  FIG. 1A ;  
       FIG. 2  is a cross sectional view of an embodiment 1 of a stress dispersing lead in a taper carrier package and a method of dispersing a stress of a lead in accordance with the present invention;  
       FIG. 3  is a cross sectional view of an embodiment 2 in accordance with the present invention;  
       FIG. 4  is a cross sectional view of an embodiment 3 in accordance with the present invention; and  
       FIG. 5  is a cross sectional view of an embodiment 4 in accordance with the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
      A description will be given of a stress dispersing lead and a lead stress dispersing method in accordance with four embodiments of the present invention.  
      A description will be given of an embodiment 1 in accordance with the present invention with reference to  FIG. 2 .  
       FIG. 2  is a cross sectional view of a whole of a relevant structure of a lead and a printed circuit board in a tape carrier package, and a structure within a broken oval corresponds to a main portion of the lead.  
      Electrodes  2   a  provided in both right and left sides of a semiconductor device  2  such as an IC chip or the like are connected onto semiconductor device connecting terminal portions  1   a  of a pair of small leads  1  arranged in a lower side, respectively. The semiconductor connecting terminal portion  1   a  of each of the leads  1  extends to an outer side from the semiconductor device  2 . One end of an intermediate slope portion  1   b  of each of the leads  1  is bent to an inner side, whereby a substrate connecting terminal portion  1   c  is structured.  
      Electrodes  4   a  provided in both right and left sides of a semiconductor device  4  are connected onto semiconductor device connecting terminal portions  3   a  of a pair of large leads  3  arranged in an upper side, respectively. One end of an intermediate slope portion  3   b  of each of the leads  3  is bent to an outer side, whereby a substrate connecting terminal portion  3   c  is structured.  
      The substrate connecting terminal portion  1   c  of each of the leads  1  and the substrate connecting terminal portion  3   c  of each of the leads  3  are connected by solder to pads  5   a  of a printed circuit board  5 , respectively.  
      An upper surface of the semiconductor device  4  is in contact with a silicone sheet  7  which is attached to a copper cover  6 . In this case, a portion between the semiconductor device  4  and the silicone sheet  7  is shown in a spaced manner in the drawing. A heat radiation is executed from an inner side of the tape carrier package to an outer portion by the means mentioned above.  
      In the embodiment 1, the semiconductor device connecting terminal portion  1   a  of the lead  1  extends to the outer side from the semiconductor device  2 , and the one end of the intermediate slope portion  1   b  of the lead  1  is bent to the inner side, whereby the substrate connecting terminal portion  1   c  is structured. Accordingly, since an entire length of the lead  1  is elongated, the stress is absorbed dispersedly, and the tape carrier package is made compact.  
      A description will be given of an embodiment 2 in accordance with the present invention with reference to  FIG. 3 .  
      In the description of the embodiments 2 to 4, a description of the same points as those of the embodiment 1 is omitted and is given only of different points.  
      An intermediate slope portion  1   e  in accordance with the embodiment 2 is structured by extending the intermediate slope portion  1   b  in the embodiment 1. Electrodes  2   a  provided in both right and left sides of the reversed semiconductor device  2  are connected to a lower side of a semiconductor device connecting portion id, respectively. The semiconductor device connecting terminal portion  1   d  may be changed in design such that the semiconductor device connecting terminal portion  1   d  does not extend to the outer side from the semiconductor device  2 . Further, a substrate connecting terminal portion  1   f  may be structured by bending one end of the intermediate slope portion  1   e  to the outer side.  
      The electrodes  4   a  provided in both right and left sides of the reversed semiconductor device  4  are connected to a lower side of the semiconductor device connecting terminal portion  3   d,  respectively.  
      In the embodiment 2, an entire length of the lead  1  is elongated by extending the intermediate connecting portion  1   e  and connecting the electrodes  2   a  provided in both right and left sides of the reversed semiconductor device  2  to the lower side of the semiconductor device connecting terminal portion  1   d.    
      A description will be given of an embodiment 3 in accordance with the present invention with reference to  FIG. 4 .  
      Each of the electrodes  2   a  and  4   a  in accordance with the embodiment 1 are provided in both right and left sides of the semiconductor devices  2  and  4 , respectively, however, electrodes  2   b  and  4   b  in accordance with the embodiment 3 are provided near center portions of the semiconductor devices  2  and  4 , respectively. Lengths of semiconductor device connecting terminal portions  1   g  and  3   g  of the leads  1  and  3  are structured long in correspondence to arrangements of the respective electrodes  2   b  and  4   b.  The semiconductor device connecting terminal portion  1   g  may be changed in design such that the semiconductor device connecting terminal portion does not extend to the outer side from the semiconductor device  2 . Further, a substrate connecting terminal portion  1   i  is structured by bending one end of an intermediate slope portion  1   h  to an outer side.  
      In the embodiment 3, an entire length of the lead  1  is elongated on the basis of the structure of the leads  1  and  3  and the semiconductor devices  2  and  4  mentioned above.  
      A description will be given of an embodiment 4 in accordance with the present invention with reference to  FIG. 5 .  
      The lead  1  in accordance with the embodiment 4 is structured by modifying a whole of the lead  1  constituted by the semiconductor device connecting terminal portion  1   a,  the intermediate slope portion  1   b  and the substrate connecting terminal portion  1   c  in accordance with the embodiment 1, in an approximately S shape.  
      In the embodiment 4, an entire length of the lead  1  is elongated by a simple structure in which the lead  1  is simply curved at two times.  
      As is apparent from the description in the specification, the following effects can be achieved by the present invention.  
      1. Since the entire length of the lead is elongated, the stress is absorbed dispersedly, and the tape carrier package is made compact.  
      2. It is possible to elongate the entire length of the lead by simply modifying the lead, changing the attitude of the semiconductor device, and changing the arrangement of the electrode in the semiconductor device.