Abstract:
A method of forming a semiconductor package is provided. The method includes forming a leadframe wherein the conductors or leads of the leadframe extend from a first end to a second end such that a portion of each lead exhibits a generally arcuate shape. The first end may be coupled with a printed circuit board and the second end may be coupled with a semiconductor die. The generally arcuately shaped portion of the leads may include a portion which exhibits a constant radius. The generally arcuately shaped portion may also be formed from a plurality of conductor segments including, for example, at least one generally arcuately shaped segment. The semiconductor die and at least a portion of the leads may be encapsulated with an insulating material.

Description:
[0001]    CROSS-REFERENCE TO RELATED APPLICATION  
         [0002]    This application is a divisional of application Ser. No. 10/972,743, filed Feb. 7, 2002, pending, which is a continuation of application Ser. No. 09/004,214, filed Jan. 9, 1998, now U.S. Pat. No. 6,362,426 issued Mar. 26, 2002. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0003]    Field of the Invention The present invention relates generally to integrated circuit semiconductor chips. More particularly, the present invention pertains to leadframes for bonding with the integrated circuits.  
           [0004]    Integrated circuit manufacturers face many design challenges, including reducing the amount of noise in the integrated circuit. Resistance, capacitance and inductance, parasitics of an integrated circuit package, can result in increased signal delays and signal distortions in the electrical signals transmitted to and from the integrated circuit.  
           [0005]    Two sources of noise in an integrated circuit package are switching noise and cross-coupling noise, or cross-talk. Switching noise may be an inductive voltage spike that occurs on a conductive path as the result of rapid current switching in the conductive path. Cross-talk is the undesirable appearance of an electrical current in a conductive path as a result of mutual capacitance and inductance between the conductive path and other nearby conductive paths. At higher frequencies, the integrated circuit is even more susceptible to noise.  
           [0006]    One approach to reduce noise in an integrated circuit is to increase spacing between transmission lines, such as leads of a leadframe  100  as shown in FIG. 1. The individual leads  110  forming a right angle are curved in a small portion of the lead and have tightly radiused corners  118 . However, as integrated circuits and electronic equipment become smaller and more complex, spacing transmission lines farther apart becomes increasingly difficult, if not impossible.  
           [0007]    Another approach to reduce noise is to reduce the length of the transmission line on a leadframe by using diagonal leads. While diagonal leads minimize the length of the leads, the spacing between the leads would also be decreased. The decreased spacing would increase the overall cross-talk between the leads, and would therefore be undesirable.  
           [0008]    Accordingly, there is a need for an integrated circuit package in which the above benefits are achieved and the above problems are overcome.  
         BRIEF SUMMARY OF THE INVENTION  
         [0009]    The present invention solves the above-mentioned needs in the art and other needs which will be understood by those skilled in the art upon reading and understanding the present specification.  
           [0010]    A leadframe is provided comprising, in part, a first and second set of conductors. The leadframe is adapted for coupling with a semiconductor integrated circuit. The conductors of the leadframe extend radially from a first end to a second end such that a portion of each conductor has a generally arcuate shape between the first and second end. In one embodiment, the first end of the conductor is for coupling with a printed circuit board, and the second end is for coupling with a semiconductor die. Alternatively, each conductor is sized and spaced such that the line spacing remains constant.  
           [0011]    In another embodiment, the conductors have a plurality of segments. Each conductor has at least three segments disposed between the first end and the second end. The segments forming the conductors are disposed such that a portion of each conductor generally has an arcuate shape. In another embodiment, the segments each have substantially the same length. Alternatively, the segments have varying lengths.  
           [0012]    In one embodiment, an integrated circuit package is provided comprising a leadframe having a plurality of leads, at least one semiconductor die coupled with the plurality of leads, and an insulating enclosure encapsulating the die and a portion of the leadframe. The leads each extend radially from a first end to a second end such that a portion of each lead has a generally arcuate shape. Alternatively, in another embodiment, the leads each have at least three segments disposed between the first end and the second end.  
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is a top plan view illustrating a conventional leadframe having leads with tightly radiused corners;  
         [0014]    [0014]FIG. 2 is a top plan view illustrating a leadframe constructed in accordance with one embodiment of the present invention;  
         [0015]    [0015]FIG. 3 is a top plan view illustrating a leadframe constructed in accordance with another embodiment of the present invention;  
         [0016]    [0016]FIG. 4 is a top plan view illustrating an integrated circuit package constructed in accordance with one embodiment of the present invention; and  
         [0017]    [0017]FIG. 5 is a top plan view illustrating a leadframe constructed in accordance with another embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]    In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and in which is shown, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural changes may be made without departing from the spirit and scope of the present invention. Therefore, the following detailed description is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims.  
         [0019]    A portion of a leadframe  200  is illustrated in FIG. 2. The leadframe  200  has first and second sets of leads  210 ,  215 . Although leads are discussed, other conductors can be used, such as lead fingers, and are considered within the scope of the invention. The first set of leads  210  extends from a first end  220  to a second end  230 , and the second set of leads  215  extends from the first end  220  to a third end  225 . For the first set of leads  210 , the first end  220  is substantially perpendicular to the second end  230 . For the first and second set of leads  210 ,  215 , the first end  220  is for electrically coupling with an electronic system, such as a printed circuit board. The first end  220  can be coupled using reflow solder and other methods as known by those skilled in the art. The second end  230  of the first set of leads  210  and the third end  225  of the second set of leads  215  are adapted for coupling with a semiconductor die, as will be discussed further below.  
         [0020]    In one embodiment, a portion of each lead of the first set of leads  210  has a generally arcuate shape, as the lead  210  extends radially from the first end  220  to the second end  230 . For some of the first set of leads  210 , a substantial portion of the lead has a generally arcuate shape. The arcuate shape of each lead of the first set of leads  210  has a different arc length than the other leads of the first set of leads  210 . In another embodiment, each lead of the first set of leads  210  is spaced and sized such that the line spacing between at least one lead, or alternatively each lead, remains constant from the first end  220  to the second end  230 . Each lead of the second set of leads  215  extends substantially straight from the first end  220  to the third end  225 .  
         [0021]    Another embodiment is illustrated in FIG. 3. A leadframe  300  has first and second sets of leads  310 ,  315 . The first set of leads  310  extends from a first end  320  to a second end  330 , and the second set of leads  315  extends from the first end  320  to a third end  325 . In one embodiment, the first end  320  of each lead of the first set of leads  310  is substantially perpendicular to the second end  330 . For both the first and second sets of leads  310 ,  315 , the first end  320  of each lead is for electrically coupling with a printed circuit board. The second end  330  of the first set of leads  310  and the third end  325  of the second set of leads  315  are adapted for coupling with a semiconductor die, as will be discussed further below.  
         [0022]    In one embodiment, each lead of the first set of leads  310  has at least three segments  340 . The segments  340  are disposed such that a portion of each lead of the first set of leads  310  has a generally arcuate shape between the first end  320  and the second end  330 . The arcuate shape of each lead of the first set of leads  310  has a different arc length than the other leads of the first set of leads  310 . The segments  340  are substantially straight, and are each substantially the same length and substantially the same width. In one embodiment, at least one of the segments  340  is substantially straight and has a different length. In another embodiment, at least one of the segments  340 ′ has an arcuate shape as shown in FIG. 5. Each lead of the second set of leads  315  extends substantially straight from the first end  320  to the third end  325 . The segmented leads provide a significant advantage since they are stamped, which is easier and less expensive to manufacture.  
         [0023]    The leadframe  200  of FIG. 2 and the leadframe  300  of FIG. 3 are formed from a single sheet of material or thin strip which is etched or stamped into a predetermined shape for connection with a selected chip design. The leads off the die are substantially flat. However, the leads or sections of the leadframe that extend over the die may need to be upset or downset, depending upon where the parting line of the mold is formed. After encapsulation in plastic, portions of the leadframe extend out of the respective chip packages. In one embodiment, the leadframe extends out of the sides ,of the packages at a selected elevation which is determined in advance. These outwardly extending portions include the ends of the leads of a package. These leads may be ultimately bent for insertion into a suitable connector device.  
         [0024]    As shown in FIG. 4, a leadframe  400  is assembled into an integrated circuit package  405 . A semiconductor die  460  comprises circuitry (not shown) formed centrally on the die  460  and a plurality of bond pads  465  formed around the periphery of the die  460 . The semiconductor die  460  is mounted using LOC technology with additional support from the leadframe at the edge of the die opposite the bond pad (not shown). Electrically conductive wire bonding  480  is used to connect selected bond pads  465  on the die  460  to selected leads of the leadframe  400 . A portion of each lead of the first set of leads  410  of the leadframe  400  is formed in a generally arcuate shape. In one embodiment, a portion of the first set of leads  410  extends radially from a first end  420  to a second end  430 . Alternatively, the first set of leads  410  includes a plurality of segments for forming the arcuate shape.  
         [0025]    In one embodiment, the leadframe  400 , semiconductor die  460  and wire bonding  480  are enclosed in protective, electrically insulative material such that ends of the leads are exposed to allow connection to be made to other electrical components. In another embodiment, leadframe  400 , semiconductor die  460  and wire bonding  480  are encapsulated in plastic, thereby forming the integrated circuit package  405 .  
         [0026]    An integrated circuit package including the leadframe according to the invention has reduced effective inductance and cross-talk relative to existing integrated circuit packages. Below are simulated inductances and resistances for the tightly radiused leads of the conventional right angle leadframe shown in FIG. 1 and the leads of the arcuate leadframe shown in FIG. 2. The lead number refers to leads shown in FIGS. 1 and 2. Like numbers in the figures indicate leads connecting between same locations on the die and same exterior connection.  
                       TABLE 1                           Prior Art   Radiused           Lead   Lead                       Lead No.   (nH|Ohms)   (nH|Ohms)                   1   10.30|.514   9.62|.452       2    9.38|.522   8.85|.466       3    8.71|.506   8.29|.451       4    8.08|.476   7.83|.432       5    7.32|.423   7.39|.409                  
 
         [0027]    The results in Table 1 reveal the decreased inductance for the present invention. The inductance and resistance of each lead is less for the arcuate leadframe and the segmented leadframe than in the tightly radiused leadframe. In particular, the longer leads experience the greatest improvement in using the arcuate leadframe and the segmented leadframe versus the tightly radiused leadframe.  
         [0028]    Advantageously, the radiused leadframe provides for lower inductance, resistance, and capacitance of leads in a leadframe, as opposed to leads with tightly radiused corners. The factors are important when the leads are carrying high-frequency signals, or signal having high-frequency harmonics, such as sub-nanosecond rise times. The continuous arcuate shape of the leads and the constant width of the leads maintains line spacing between the leads. This consistency maximizes layout space of the leadframe without increasing cross-talk. In addition, a single leadframe strip or assembly can comprise leadframes for any number of a predetermined number of chips.  
         [0029]    It is to be understood that the above description is intended to be illustrative, and not restrictive. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.