Abstract:
Conventional configuration of a lead frame, particularly a lead frame in a Lead-on-Chip package, is substituted by one having inward ends of leads thereof arranged in unprecedented ways, resulting in bigger gap between any two adjacent inward ends of inner leads, leading to bigger Inner Lead Pitch of a lead frame in which the space available is inherently limited. It is by the new configuration that an IC packaging process can be immunized against the difficulty resulting from too small Inner Lead Pitch of a lead frame, and the bottle neck in the process of packaging an IC subject to the tendency of minimizing the size of an IC can thus be overcome.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an art of configuring the leads of a Lead Frame used in packaging integrated circuits, particularly for LOC (Lead on Chip) packages. 
     BACKGROUND OF THE INVENTION 
     In conventional processes of packaging an IC (integrated circuit), a lead frame  1  as shown in FIG. 1 usually includes a plurality of leads separated into two groups respectively represented by reference numerals  11  and  12 , the group represented by reference numeral  11  including a line of outward ends represented by reference numeral  13  and a line of inward ends represented by reference numeral  15 , the group represented by reference numeral  12  including a line of outward ends represented by reference numeral  14  and a line of inward ends represented by reference numeral  16 , the leads in the two groups stretching to the outside of the lead frame  1  in opposite directions. The two lines of inward ends  15  and  16 , in order to match the size of an IC (under the lead frame  1 , not shown in the figure), must be inside a quadrilateral region  17 , and opposite to each other with a space  18  therebetween so that bonding wires  20  can be connected between bonding pad  100  of the IC and inward ends  15  or  16 . As shown in FIG. 1, the two lines of inward ends  15  and  16  are inside a quadrilateral region  17  which is located in the central portion of lead frame  1 , and are evenly dispersed between two parallel edges  171  and  173  of quadrilateral region  17  in two lines both perpendicular to the edges  171  and  173  while separated from each other by a distance  18 . The distance  18  is to let bonding wire  20  pass therethrough so that the inward ends  15  and  16  can be connected to bonding pads  100  of an IC. 
     For more information about structures of a conventional lead frame used in Lead on Chip packages, reference to U.S. Pat. Nos. 5,545,920 and 5,872,398 shall be made. 
     To keep pace with the tendency of minimizing the size of an IC, the space available for accommodating leads  11  and  12  (also inward ends  15  an  16 ) in lead frame  1  is decreasing. For example, the pitch of bonding pads of an IC is reduced as a result of size reduction of the IC, and the pitch of leads as well as the gap  191  between adjacent inward ends of leads must be reduced accordingly, resulting in significant difficulty in packaging an IC subject to the tendency of minimizing the size of the IC, leading to higher failure rate and higher manufacturing cost. To respond to the tendency of minimizing the size of ICs (integrated circuits), the present invention provides schemes of changing the configuration of inward ends  15  and  16 , so that the difficulty in the process of packaging ICs of smaller size arising from the requirement of smaller pitch of leads  11  or  12  (also smaller gap between adjacent inward ends  15  or  16 ) of a lead frame  1  can be avoided. 
     To keep pace with the tendency of increasing number of electrical connections with an IC, the space of a lead frame must be capable of accommodating more leads, resulting in significant difficulty in packaging an IC due to the inevitable reduction of inner lead pitch of a lead frame if size remains on the same scale, leading to higher failure rate and higher manufacturing cost. To respond to the tendency of requiring more electrical connections with an IC, the present invention provides schemes of changing the configuration of inward ends  15  and  16 , so that the difficulty in the process of packaging an IC providing more electrical connections can be avoided. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide new configurations of a lead frame by which bigger inner lead pitches can be achieved without need of increasing the size of the lead frame, thereby the failure rate and manufacturing cost in the process of packaging ICs can be lowered, particularly the difficulty in packaging ICs of smaller size can be significantly eased. 
     Another object of the present invention is to immunize an IC packaging process against the difficulty resulting from smaller size of the lead frame or the IC to be packaged, or from larger number of leads/electrical connections of the lead frame or the IC to be packaged. 
     The present invention is characterized by arranging the inward ends of leads of a lead frame in unprecedented ways in order to realize bigger inner lead pitch (or bigger gap between adjacent inward ends) of a lead frame compared to a conventional one of equivalent size. 
     The word “IC” in this disclosure means “integrated circuit”, and the word “ICs” means “integrated circuits”. 
     What is represented by the words “lead frame” in this disclosure is not limited to the popularly known lead frame. The lead frame in this disclosure represents any means capable of providing or supporting electrical conduction between at least an IC in a package and any device outside the package. A bonding surface of an IC in this disclosure means a surface from which the IC is electrically connected. For example, a bonding surface of an IC in the form of a chip is a surface having bonding pads thereon for electrical connection with the IC. What is represented by the word “disperse” in this disclosure includes the meaning of “be disposed”. 
     A first aspect of the present invention may be represented by a lead frame for a process of packaging at least an IC, which comprises: a first group of leads; a second group of leads; and an IC corresponding region enclosed by a polygon (a quadrilateral corresponding to the pattern of an IC, or equivalent to the size or shape of a bonding surface of an IC, for example); wherein the lead includes at least an outward end and an inward end, the inward end being inside the IC corresponding region, the inward ends of the first group of leads facing and being spaced from the inward ends of the second group of leads; and wherein the first edge of the polygon is perpendicular to the second edge of the polygon, the third edge of the polygon parallels the first edge of the polygon, the inward ends disperse one by one between the first edge of the polygon and the third edge of the polygon (i.e., disperse one by one from the first edge of the polygon to the third edge of the polygon, or from the third edge of the polygon to the first edge of the polygon) in such a way that the further an arbitrary one of the inward ends is from the first edge of the polygon than another one of the inward ends, the nearer the arbitrary one of the inward ends is from the second edge of the polygon than the another one of the inward ends. 
     It can be seen the gap between any adjacent two of the inward ends of leads of either the first group or the second group in the lead frame according to the first aspect of the present invention can be significantly bigger than a corresponding gap ( 191  in FIG. 1) in a conventional lead frame of the same size scale, and the inner lead pitch of leads of either the first group or the second group according to the present invention can thus be significantly bigger. It is obvious the inner lead pitch of any two arbitrary leads of either the first group or the second group can be bigger than or at least equal to the gap between the inward ends of the two arbitrary leads. 
     If used in LOC packages, the inward ends of the first group of leads in the lead frame according to the first aspect of the present invention are spaced from those of the second group of leads by distances adequate for making electrical connection between the IC and the leads of the lead frame. For example, the bonding wires connecting the bonding pads of the IC and the leads of the lead frame must pass the space between the inward ends of the first group of leads and those of the second group of leads, therefore the distances between the inward ends of the first group of leads and those of the second group of leads are usually adequate for the bonding wires to be connected between the inward ends of the leads and the bonding pads of the IC. The distances between the inward ends of the first group of leads and those of the second group of leads may be uniform or vary with the locations of the inward ends, subject to the only condition that the space between the inward ends of the first group of leads and those of the second group of leads is adequate for electrically connecting therethrough the IC and the leads. 
     In the lead frame according to the first aspect of the present invention, the first group of leads may stretch to the outside of the lead frame in a first direction, and the second group of leads may stretch to the outside of the lead frame in a second direction different from or opposite to the first direction. 
     In the lead frame according to the first aspect of the present invention, the inward ends of the first group of leads may disperse along a first straight line, and the inward ends of the second group of leads may disperse along a second straight line either paralleling or not paralleling the first straight line. However, in the lead frame according to the first aspect of the present invention, the inward ends of the first group of leads do not necessarily disperse along a straight line, neither do the inward ends of the second group of leads necessarily disperse along a straight line. 
     In the lead frame according to the first aspect of the present invention, the IC corresponding region may be a plane matching the pattern of the IC or a bonding surface of the IC. 
     A second aspect of the present invention may be represented by a lead frame for a process of packaging at least an IC, which comprises: a first group of leads; a second group of leads; and an IC corresponding region (a 3-dimensional space) enclosed by a hexahedron which, for example, has a bottom surface corresponding to a bonding surface of an IC, and is rather small in height; wherein the lead includes at least an outward end and an inward end, the inward ends being inside the IC corresponding region, the inward ends of the first group of leads facing and being spaced from the inward ends of the second group of leads; and wherein the first surface of the hexahedron is perpendicular to the second surface of the hexahedron, the third surface of the hexahedron parallels the first surface of the hexahedron, the inward ends disperse one by one between the first surface and the third surface (i.e., disperse one by one from the first edge of the polygon to the third edge of the polygon, or from the third edge of the polygon to the first edge of the polygon) in such a way that the further an arbitrary one of the inward ends is from the first surface of the hexahedron than another one of the inward ends, the nearer the arbitrary one of the inward ends is from the second surface of the hexahedron than the another one of the inward ends. 
     It can be seen the gap between any adjacent two of the inward ends of leads of either the first group or the second group in the lead frame according to the second aspect of the present invention can be significantly bigger than a corresponding gap ( 191  in FIG. 1) in a conventional lead frame of the same size scale, and the inner lead pitch of leads of either group according to the present invention can thus be significantly bigger. Again it is obvious the inner lead pitch of any two arbitrary leads of either group can be bigger than or at least equal to the gap between the inward ends of the two arbitrary leads. 
     If used in LOC packages, the inward ends of the first group of leads in the lead frame according to the second aspect of the present invention, similar to those in the lead frame according to the first aspect of the present invention, are spaced from the inward ends of the second group of leads by distances adequate for making electrical connection between the IC and the leads of the lead frame. For example, the bonding wires between the bonding pads of the IC and the leads of the lead frame must pass the space between the inward ends of the first group of leads and those of the second group of leads, therefore the distances between the inward ends of the first group of leads and those of the second group of leads are usually adequate for the bonding wires to be connected between the inward ends and of leads and the bonding pads of the IC. The distances between the inward ends of the first group of leads and those of the second group of leads, similar to those according to the first aspect of the present invention, may be uniform or vary with the locations of the inward ends, subject to the only condition that the space (not limited to two dimensions here) between the inward ends of the first group of leads and those of the second group of leads is adequate for electrically connecting therethrough the IC and the leads. 
     In the lead frame according to the second aspect of the present invention, the first group of leads may stretch to the outside of the lead frame in a first direction, and the second group of leads may stretch to the outside of the lead frame in a second direction different from or opposite to the first direction. 
     In the lead frame according to the second aspect of the present invention, the inward ends of the first group of leads may disperse along a first plane, and the inward ends of the second group of leads may disperse along a second plane either paralleling or not paralleling the first plane. However, in the lead frame according to the second aspect of the present invention, the inward ends of the first group of leads do not necessarily disperse along a plane, neither do the inward ends of the second group of leads necessarily disperse along a plane. 
     In the lead frame according to the second aspect of the present invention, any surface of the IC corresponding region may be a plane. For example, the first, the second, and the third surfaces as well as and the aforementioned “bottom surface” of the IC corresponding region are planes, wherein the aforementioned “bottom surface” may be perpendicular to the second surface and be a plane facing a bonding surface of an IC, with its size or pattern or shape equivalent to the bonding surface of an IC. The aforementioned “bottom surface” may even be the bonding surface of an IC. 
     A third aspect of the present invention may be represented by a lead frame for a process of packaging at least an IC, which comprises: a plurality of leads each including at least an outward end and an inward end; and an IC corresponding region (a region enclosed by a polygon such as a quadrilateral corresponding to the pattern of an IC, or equivalent to the size or shape of a bonding surface of an IC, for example); wherein the inward ends are inside the IC corresponding region, the first edge of the polygon is perpendicular to the second edge of the polygon, the third edge of the polygon parallels the first edge of the polygon, and the inward ends disperse one by one between the first edge and the third edge (i.e., disperse one by one from the first edge of the polygon to the third edge of the polygon, or from the third edge of the polygon to the first edge of the polygon) in such a way that the further an arbitrary one of the inward ends is from the first edge of the polygon than another one of the inward ends, the nearer the arbitrary one of the inward ends is from the second edge of the polygon than the another one of the inward ends. 
     According to the third aspect of the present invention, the difficulty to provide a lead frame with all leads thereof stretch in the same direction to the outside of the lead frame can be significantly eased. This is because the gap between any two adjacent inward ends of the leads according to the present invention can be significantly augmented under the condition the size of the lead frame and the number of leads of the lead frame remain the same. The inner lead pitch, as a result, can be significantly augmented for a lead frame with the same size and the same number of leads. All of the leads of the lead frame according to the third aspect of the present invention may stretch to the outside of the lead frame in the same direction without suffering the difficulty of dealing with smaller inner lead pitch, and without need of bigger size of lead frame. All of the leads of the lead frame according to the third aspect of the present invention may stretch to the outside of the lead frame in a direction perpendicular to the second edge of the polygon, for example. 
     It must be noted the IC corresponding region according to the third aspect of the present invention is not limited to a 2-dimensional space, and can be a 3-dimensional space enclosed by a hexahedron such as the one defined in the second aspect of the present invention, i.e., the inward ends of leads of the lead frame do not necessarily disperse along a line, nor do they necessarily disperse along a plane. Actually the lead frame according to the second aspect of the present invention may include one instead of two groups of leads, all the leads stretching to the outside of the leads frame in the same direction, the inward ends of the leads being configured in the same way as the third aspect of the present invention. 
     A fourth aspect of the present invention may be represented by a lead frame for a process of packaging at least an IC, which comprises: a plurality of leads each including at least an outward end and an inward end; and an IC corresponding region enclosed by a polygon (a quadrilateral, for example) including a first edge, a second edge, a third edge, and a fourth edge, the first edge paralleling the third edge, the second edge paralleling the fourth edge, the first edge and the second edge constituting an obtuse angle (an angle smaller than 180° while larger than 90°); wherein the leads are separated into two groups respectively having the inward ends thereof dispersing along the second edge and the fourth edge. 
     As can be understood from the first aspect of the present invention, the gap between any adjacent two inward ends of leads of each of the two groups in the lead frame according to the fourth aspect of the present invention can be significantly bigger than a corresponding gap ( 191  in FIG. 1) in a conventional lead frame of the same size scale, and the inner lead pitch of leads of each group according to the present invention can thus be significantly bigger. 
     Obviously the two groups of leads in the lead frame according to the fourth aspect of the present invention may respectively stretch to the outside of the lead frame in different or opposite directions. 
    
    
     The present invention may best be understood through the following description with reference to the accompanying drawings, in which: 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a top view of a lead frame for a process of packaging an IC in LOC configuration. 
     FIG. 2 shows a top view of a lead frame according to a first embodiment of the present invention. 
     FIG. 3 shows a top view of a lead frame according to a second embodiment of the present invention. 
     FIG. 4 shows a top view of a lead frame according to a third embodiment of the-present invention. 
     FIG. 5 shows a top view of a lead frame according to a fourth embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in FIG. 2 for its top view, a lead frame  2  according to a first embodiment of the present invention comprises: a first group of leads represented by  21 ; a second group of leads represented by  22 ; and an IC corresponding region enclosed by a polygon  27 . The polygon  27  may be a quadrilateral corresponding to the pattern of an IC which is under the lead frame  2  and not shown in FIG.  2 ). For example, the polygon  27  may be a quadrilateral equivalent to the size or shape of a bonding surface of an IC, or may even be a bonding surface of an IC. Each lead, no matter it is in group  21  or  22 , includes at least an outward end and an inward end, i.e., the first group of leads  21  include a first group of outward ends represented by  23  and a first group of inward ends represented by  25 , and the second group of leads  22  include a second group of outward ends represented by  24  and a second group of inward end  26 . All the inward ends  25  and  26  are inside the IC corresponding region, with inward ends  25  of the first group of leads  21  facing and being spaced from the inward ends  26  of the second group of leads  22  by a distance  28  or by various distances represented by  28 . The first edge  271  of the polygon  27  is perpendicular to the second edge  272  of the polygon  27 , the third edge  273  of the polygon  27  parallels the first edge  271  of the polygon  27 . The inward ends, no matter they are the first group  25  or the second group  26 , disperse one by one between the first edge  271  of the polygon  27  and the third edge  273  of the polygon  27  in such a way that the further an arbitrary one of the inward ends in a group (either group  25  or  26 ) is from the first edge  271  of the polygon  27  than another one of the inward ends in the group, the nearer the arbitrary one of the inward ends is from the second edge  272  of the polygon  27  than the another one of the inward ends. In other words, the inward ends  25  disperse, one by one from the first edge  271  of the polygon  27  to the third edge  273  of the polygon  27  or from the third edge  273  of the polygon  27  to the first edge  271  of the polygon  27 , in such a way that the further an arbitrary one of the inward ends  25  is from the first edge  271  of the polygon  27  than another one of the inward ends  25 , the nearer the arbitrary one of the inward ends  25  is from the second edge  272  of the polygon  27  than the another one of the inward ends  25 . The pitch of inward ends  25 , i.e., the gap between adjacent two of inward ends  25 , may be uniform or not uniform. Similarly, the inward ends  26  disperse, one by one from the first edge  271  of the inwards polygon  27  to the third edge  273  of the polygon  27  or from the third edge  273  of the polygon  27  to the first edge  271  of the polygon  27 , in such a way that the further an arbitrary one of the inward ends  26  is from the first edge  271  of the polygon  27  than another one of the inward ends  26 , the nearer the arbitrary one of the inward ends  26  is from the second edge  272  of the polygon  27  than the another one of the inward ends  26 . The pitch of inward ends  26 , i.e., the gap between adjacent two of inward ends  26 , may be uniform or not uniform. 
     It can be seen the gap  291  or  292  between any adjacent two of the inward ends for each group ( 25  or  26 ) in the lead frame  2  of FIG. 2 according to the present invention can be significantly bigger than a corresponding gap ( 191  in FIG. 1) in a conventional lead frame ( 1  in FIG. 1) of the same size scale, and the inner lead pitch  293  or  294  of leads (group  21  or  22 ) according to the present invention can thus be significantly bigger, because the inner lead pitch  293  or  294  of any two arbitrary leads (group  21  or  22 ) can be bigger than or at least equal to the gap  291  or  292  between the inward ends of the two arbitrary leads. 
     If used in LOC packages, the inward ends  25  of the first group of leads  21  in the lead frame  2  of FIG. 2 are spaced from the inward ends  26  of the second group of leads  22  by distances (represented by  28  in FIG. 2, but not necessarily uniform) which are adequate for making electrical connection between the IC and the leads (both groups  21  and  22 ) of the lead frame  2 . For example, the bonding wires  20  connecting the bonding pad  100  of an IC to the inward ends  25  or  26  must pass the space between the inward ends  25  (or  26 ) of the first (or second) group of leads  21  (or  22 ) and the bonding pads  100  of the IC, therefore the distances  28  between the inward ends  25  and inward ends  26  are usually adequate for the bonding wires  20  to be connected between the inward ends  25  (or  26 ) and the bonding pads  100  of the IC. The distances  28  between the inward ends of the first group of leads  21  and those of the second group of leads  22  may be uniform or vary with the locations of the inward ends, subject to the only condition that the space between the inward ends of the first group of leads  21  and those of the second group of leads  22  is adequate for electrically connecting therethrough the IC (or bonding pads  100  of the IC) and the leads. One way to design the distances  28  is to keep it always in a specified distance range which has proved satisfactory according to experience or experiments. 
     In the lead frame  2  according to the first embodiment of the present invention shown in FIG. 2, the space between any adjacent inward ends  25  of the first group of leads  21  and the space between any adjacent inward ends  26  of the second group of leads  22  are in a specified gap range which has proved satisfactory in view of lowering failure rate, minimizing cost, simplifying manufacturing process, or any relevant factors. 
     In the lead frame  2  according to the first embodiment of the present invention shown in FIG. 2, the first group of leads  21  may stretch to the outside of the lead frame  2  in a first direction  111 , and the second group of leads  22  may stretch to the outside of the lead frame  2  in a second direction  112  different from or opposite to the first direction  111 . For example, the first direction  111  and/or the second direction  112  may be perpendicular to the second edge  272  of the polygon  27 . 
     In the lead frame  2  according to the first embodiment of the present invention shown in FIG. 2, the inward ends  25  of the first group of leads  21  may disperse along a first straight line (numeral reference not shown), and the inward ends  26  of the second group of leads  22  may disperse along a second straight line (numeral reference not shown) either paralleling or not paralleling the first straight line. However, in the lead frame  2  according to the first embodiment of the present invention shown in FIG. 2, the inward ends  25  of the first group of leads  21  do not necessarily disperse along a straight line, neither do the inward ends  26  of the second group of leads  22  necessarily disperse along a straight line. 
     As shown in FIG. 3 for its top view, a lead frame  3  according to a second embodiment of the present invention comprises: a first group of leads represented by  31 ; a second group of leads represented by  32 ; and an IC corresponding region enclosed by a polyhedron  37  (3 dimensions, with only top view shown in FIG.  3 ). The IC corresponding region may be a space enclosed by the polyhedron  37  which includes a first surface represented by a top view edge  371 , a second surface represented by a top view edge  372 , a third surface represented by a top view edge  373 , and a certain surface (not shown in FIG. 3) corresponding to a bonding surface of an IC that is under the lead frame  3  and not shown in FIG.  3 . For example, the IC corresponding region is a space enclosed by polyhedron  37  having a certain surface equivalent to the size or shape of a bonding surface of an IC, or being a bonding surface of an IC. Each lead, no matter it is in group  31  or  32 , includes at least an outward end and an inward end, i.e., the first group of leads  31  include a first group of outward ends represented by  33  and a first group of inward ends represented by  35 , and the second group of leads  32  include a second group of outward ends represented by  34  and a second group of inward end  36 . All the inward ends  35  and  36  are inside the IC corresponding region, with inward ends  35  of the first group of leads  31  facing and being spaced from the inward ends  36  of the second group of leads  32  by a distance  38  or by various distances represented by  38 . The first surface represented by top view edge  371  is perpendicular to the second surface represented by top view edge  372 , the third surface represented by top view edge  373  parallels the first surface represented by top view edge  371 . The inward ends, no matter they are the first group  35  or the second group  36 , disperse one by one between the first surface represented by top view edge  371  and the third surface represented by top view edge  373 , in such a way that the further an arbitrary one of the inward ends in a group (either group  35  or  36 ) is from the first surface represented by top view edge  371  than another one of the inward ends in the group, the nearer the arbitrary one of the inward ends is from the second surface represented by top view edge  372  than the another one of the inward ends. In other words, the inward ends  35  disperse, one by one from the first surface represented by top view edge  371  to the third surface represented by top view edge  373  or from the third surface represented by top view edge  373  to the first surface represented by top view edge  371 , in such a way that the further an arbitrary one of the inward ends  35  is from the first surface represented by top view edge  371  than another one of the inward ends  35 , the nearer the arbitrary one of the inward ends  35  is from the second surface represented by top view edge  372  than the another one of the inward ends  35 . Similarly, the inward ends  36  disperse, one by one from the first surface represented by top view edge  371  to the third surface represented by top view edge  373  or from the third surface represented by top view edge  373  to the first surface represented by top view edge  371 , in such a way that the further an arbitrary one of the inward ends  36  is from the first surface represented by top view edge  371  than another one of the inward ends  36 , the nearer the arbitrary one of the inward ends  36  is from the second surface represented by top view edge  372  than the another one of the inward ends  36 . The pitch of inward ends  35 , i.e., the gap between adjacent two of inward ends  35 , may be uniform or not uniform, and the pitch of inward ends  36 , i.e., the gap between adjacent two of inward ends  36 , may be uniform or not uniform. 
     It can be seen the gap  391  or  392  between any adjacent two of the inward ends for each group ( 35  or  36 ) in the lead frame  3  of FIG. 3 according to the present invention can be significantly bigger than a corresponding gap ( 191  in FIG. 1) in a conventional lead frame ( 1  in FIG. 1) of the same size scale, and the inner lead pitch  393  or  394  of leads (group  31  or  32 ) according to the present invention can thus be significantly bigger, because the inner lead pitch  393  or  394  of any two arbitrary leads group  31  or  32 ) can be bigger than or at least equal to the gap  391  or  392  between the inward ends of the two arbitrary leads. 
     If used in LOC packages, the inward ends  35  of the first group of leads  31  in the lead frame  3  of FIG. 3 are spaced from the inward ends  36  of the second group of leads  32  by distances (represented by  38  in FIG. 3, but not necessarily uniform) which are adequate for making electrical connection between the IC and the leads (both groups  31  and  32 ) of the lead frame  3 . For example, the bonding wires (not shown in FIG. 3) connecting the bonding pad  100  of an IC to the inward ends  35  or  36  must pass the space between the inward ends  35  (or  36 ) of the first (or second) group of leads  31  (or  32 ) and the bonding pads  100  of the IC, therefore the distances  38  between the inward ends  35  and inward ends  36  are usually adequate for the bonding wires to be connected between the inward ends  35  (or  36 ) and the bonding pads  100  of the IC. The distances  38  between the inward ends of the first group of leads  31  and those of the second group of leads  32  may be uniform or vary with the locations of the inward ends, subject to the only condition that the space between the inward ends  35  of the first group of leads  31  and those ( 36 ) of the second group of leads  32  is adequate for electrically connecting therethrough the IC (or bonding pads  100  of the IC) and the leads. One way to design the distances  38  is to keep it always in a specified distance range which has proved satisfactory according to experience or experiments. 
     In the lead frame  3  according to the second embodiment of the present invention shown in FIG. 3, the space (gap  391 ) between any adjacent inward ends  35  of the first group of leads  31  and the space (gap  392 ) between any adjacent inward ends  36  of the second group of leads  32  are in a specified gap range which has proved satisfactory in view of lowering failure rate, minimizing cost, simplifying manufacturing process, or any relevant factors. 
     In the lead frame  3  according to the second embodiment of the present invention shown in FIG. 3, the first group of leads  31  may stretch to the outside of the lead frame  3  in a first direction, and the second group of leads  32  may stretch to the outside of the lead frame  3  in a second direction different from or opposite to the first direction. For example, the first direction and/or the second direction may be perpendicular to the second surface represented by top view edge  372 . 
     In the lead frame  3  according to the second embodiment of the present invention shown in FIG. 3, the inward ends  35  of the first group of leads  31  may disperse along a first plane (numeral reference not shown), and the inward ends  36  of the second group of leads  32  may disperse along a second plane (numeral reference not shown) either paralleling or not paralleling the first plane. However, in the lead frame  3  according to the second embodiment of the present invention shown in FIG. 3, the inward ends  35  of the first group of leads  31  do not necessarily disperse along a plane, and neither do the inward ends  36  of the second group of leads  32  necessarily disperse along a plane. 
     As shown in FIG. 4 for its top view, a lead frame  4  according to a third embodiment of the present invention comprises: a plurality of leads represented by  41 ; and an IC corresponding region  47  of 2 dimensions or 3 dimensions. The IC corresponding region  47 , for example, may be a 2-dimensional space enclosed by a polygon such as a quadrilateral corresponding to the pattern of an IC (an IC under the lead frame  4  and not shown in FIG.  4 ), or a quadrilateral equivalent to the size or shape of a bonding surface of an IC, or a quadrilateral being a bonding surface of an IC. To simplify descriptions, FIG. 4 is illustrated as follows by an arbitrary example with the IC corresponding region  47  enclosed by a quadrilateral. Each lead  41  includes at least an outward end represented by  43  and an inward end represented by  45 . All the inward ends  45  are inside the IC corresponding region  47 . The first edge  471  of the IC corresponding region  47  is perpendicular to the second edge  472  of the IC corresponding region  47 , the third edge  473  of the IC corresponding region  47  parallels the first edge  471  of the IC corresponding region  47 . The inward ends  45  disperse one by one between the first edge  471  of the IC corresponding region  47  and the third edge  473  of the IC corresponding region  47  in such a way that the further an arbitrary one of the inward ends  45  is from the first edge  471  of the IC corresponding region  47  than another one of the inward ends  45 , the nearer the arbitrary one of the inward ends  45  is from the second edge  472  of the IC corresponding region  47  than the another one of the inward ends  45 . In other words, the inward ends  45  disperse, one by one from the first edge  471  of the IC corresponding region  47  to the third edge  473  of the IC corresponding region  47  or from the third edge  473  of the IC corresponding region  47  to the first edge  471  of the IC corresponding region  47 , in such a way that the further an arbitrary one of the inward ends  45  is from the first edge  471  of the IC corresponding region  47  than another one of the inward ends  45 , the nearer the arbitrary one of the inward ends  45  is from the second edge  472  of the IC corresponding region  47  than the another one of the inward ends  45 . The pitch of inward ends  45 , i.e., the gap between adjacent two of inward ends  45 , may be uniform or not uniform. 
     According to the third embodiment of the present invention, the difficulty to provide a lead frame  4  with all leads  41  thereof stretch in the same direction to the outside of the lead frame  4  can be significantly eased. This is because the gap  491  between any two adjacent ones of inward ends  45  according to the present invention can be significantly augmented under the condition the size of the lead frame and the number of leads of the lead frame remain the same, the inner lead pitch  493 , as a result, can be significantly augmented for a lead frame with the same size and the same number of leads. All of the leads  41  of the lead frame  4  according to the third embodiment of the present invention shown in FIG. 4 may stretch to the outside of the lead frame  4  in a direction perpendicular, for example, to the second edge  472  of the IC corresponding region. 
     It is obvious the IC corresponding region  47  according to the third embodiment of the present invention shown in FIG. 4 can also be a 3-dimensional space enclosed by a hexahedron as defined in the second aspect of the present invention, i.e., the inward ends  45  of leads  41  of the lead frame  4  do not necessarily disperse along a line, nor do they necessarily disperse along a plane. Actually the lead frame  3  according to the second embodiment of the present invention shown in FIG. 3 may include one group ( 31  or  32 ) instead of two groups ( 31  and  32 ) of leads, with the only one group ( 31  or  32 ) of leads thereof stretching to the outside of lead frame  3  in the same direction, and with the only one group ( 35  or  36 ) of inward ends thereof being configured in the same way as the third embodiment of the present invention shown in FIG.  4 . 
     As shown in FIG. 5 for its top view, a lead frame  5  according to a fourth embodiment of the present invention comprises: a plurality of leads represented by  51  and  52  each including at least an outward end (represented by  53  and  54 ) and an inward end (represented by  55  and  56 ); and an IC corresponding region enclosed by a polygon  57  (a quadrilateral, for example) including a first edge  571 , a second edge  572 , a third edge  573 , and a fourth edge  574 , the first edge  571  paralleling the third edge  573 , the second edge  572  paralleling the fourth edge  574 , the first edge  571  and the second edge  572  constituting an obtuse angle (an angle smaller than 180° while larger than 90°); wherein the leads are separated into two groups (represented by  51  and  52 ) respectively having the inward ends (represented by  55  and  56 ) thereof dispersing along the second edge  572  and the fourth edge  574 . The pitch of inward ends  55 , i.e., the gap between adjacent two of inward ends  55 , may be uniform or not uniform, and the pitch of inward ends  56 , i.e., the gap between adjacent two of inward ends  56 , may be uniform or not uniform. 
     The gap  591  or  592  between any adjacent two of inward ends  55  or  56  of leads  51  or  52  in the lead frame  5  according to the fourth embodiment of the present invention can be significantly bigger than a corresponding gap ( 191  in FIG. 1) in a conventional lead frame of the same size scale, and the inner lead pitch  593  or  594  of leads  51  or  52  according to the present invention can thus be significantly bigger. 
     Obviously the two groups of leads  51  and  52  in the lead frame  5  according to the fourth aspect of the present invention may respectively stretch to the outside of the lead frame  5  in different or opposite directions. 
     While the invention has been described in terms of what are presently considered to be the most practical or preferred embodiments, it shall be understood that the invention is not limited to the disclosed embodiment. The spirit and scope of the invention shall cover any modifications or similar arrangements.