Abstract:
An integrated circuit (IC) package, such as a Quad Flat Pack (QFP), has at least one lead with a tip that extends substantially perpendicular to the ends of two or more bondwires, so that there is room for more than one bondwire to be attached to it along its length. Thus, bondwires leading from die bondpads that are not adjacent to one another can be efficiently connected to the same lead in a bus-like manner.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     Electronic packaging is essentially the final step in the process of fabricating an integrated circuit (IC) or “chip.” In the packaging step, the semiconductor die is mounted on a leadframe, and electrical connections are made between the die and the leads of the leadframe, before encapsulating the assembly in the component body. The leadframe is typically made from a thin sheet of metal by stamping or etching. The majority of IC packages use a method known as wirebonding to make the electrical connections between the die and the leads. In wirebonding, one end of a very fine gold or aluminum bondwire (on the order of 10-100 micrometers in diameter) is attached to a bondpad on the die, and the other end is attached to an end of a lead. The end of the lead to which the bondwire is attached is sometimes referred to as a bondfinger and sometimes as a lead tip. The bondwire ends are typically attached by applying some combination of pressure and heat. The resulting weld-like or solder-like attachment or bond is commonly referred to as a wirebond. The other end of the lead extends externally to the package (component body) for connection to other circuitry when the IC is used as a circuit component. This external portion of the lead may have a stepped shape or other features to facilitate mounting it to a circuit board, but such features are not relevant to the present invention.  
         [0002]     Many common ICs, including many application-specific integrated circuits (ASICs), are in the form of a package known as a Quad Flat Pack (QFP). As illustrated in  FIG. 1 , a QFP package  100  has four sides with leads  102  extending from the component body  104  on all four sides. As illustrated in  FIG. 2 , inside a QFP package  100  the electrical connections between the die  106  and the leads  102  are made by wirebonding with bondwires  108 . (Some leads  102  and other grouped elements are not shown individually for purposes of clarity, and their omission is indicated collectively by an ellipsis (“ . . . ”) symbol.) Typically, one wirebond (i.e., the weld-like attachment or bond) connects or attaches one bondpad  110  to one lead  102 . In general, the number of bondpads  110  dictates the number of corresponding QFP leads  102 . Nevertheless, in instances in which adjacent or proximate bondpads are intended to carry the same electrical signal (e.g., device ground and power), more than one bondpad may be wirebonded to a single lead. Typically, there are numerous electrically common bondpads that lie along each of the four sides of the die, such as device ground (“VSS”) and core power (“VDD”).  
         [0003]     In some packages, ground bondpads are wirebonded to diepaddle  112 , which is a metal plate-like portion of the leadframe underneath the die that physically supports the die and acts as an electrical ground plane. (The leadframe is the entire stamped or etched area comprising all leads  102 .) The diepaddle  112  effectively combines and consolidates the ground connections from the die and redistributes ground to a number of package lead tips. A similar structure, sometimes referred to as an interposer (not shown), can be used for distributing core power. Such structures add significant manufacturing cost and increase the size and weight of the package.  
         [0004]     The more leads in a QFP package, the greater its size, weight, cost and complexity. Thus, it would be advantageous to minimize the number of package leads. In some instances, a package for which a component manufacturer or customer indicates a preference has too few leads to accommodate the number of bondpads of the die to be packaged. In such an instance, a larger, more complex, less economical package must be selected. Note in the QFP package  100  of  FIG. 2  that a few bondpads  110   a,    110   b  and  110   c  cannot be accommodated and thus have been left unattached. While in this exemplary QFP package  100  it may be that bondpads  110   a,    100   b  and  100   c  are not utilized by the die  106 , i.e., carry no signal in operation, and thus are not to be accommodated by any leads  102 , it would be desirable to provide the option of accommodating them.  
         [0005]     It would be desirable to provide an IC package that maximizes the number of bondpads that a given number of leads can accommodate. The present invention addresses the above-described problems and deficiencies and others in the manner described below.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention relates to an integrated circuit (IC) package, such as a Quad Flat Pack (QFP), in which at least one lead has a lead tip with an extended shape, extending substantially perpendicular to the ends of two or more bondwires, so that there is room for more than one bondwire to be attached to it along its length. Thus, bondwires leading from die bondpads that are not adjacent to one another can be efficiently connected to the same lead in a bus-like manner.  
         [0007]     The elongated lead portions of leads along one edge of the package are substantially parallel to one another (and perpendicular to the package edge) as in a conventional QFP or similar package. In an exemplary embodiment of the invention, a lead tip having the extended shape and orientation described above is also substantially perpendicular to the elongated lead portion of a lead, thus defining an L-shaped lead. Nevertheless, in other embodiments the lead tip can have any suitable shape and orientation with respect to the elongated lead portion of the lead.  
         [0008]     In some embodiments of the invention, the elongated lead tips can interconnect two or more leads, thereby defining a loop-like lead structure. For example, in an embodiment in which the lead tip is also substantially perpendicular to the elongated lead portions of two leads, a U-shaped loop-like lead structure is defined. As noted above, in other embodiments the lead tip can have any suitable shape and orientation with respect to the elongated lead portion of the lead. Lead structures (loops) can be nested, with one loop being within another loop.  
         [0009]     Bondwires can be attached at any point along the lead tips, thereby maximizing the number of die bondpads that a given number of leads can accommodate. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a top plan view of the exterior of a prior art Quad Flat Pack (QFP) IC package.  
         [0011]      FIG. 2  is a generalized top plan view of the interior of the QFP package of  FIG. 1 .  
         [0012]      FIG. 3  is a generalized top plan view of the interior of a QFP package in accordance with an exemplary embodiment of the present invention.  
         [0013]      FIG. 4  illustrates a lead having an extended shape in accordance with the embodiment illustrated in  FIG. 3 .  
         [0014]      FIG. 5  is a generalized top plan view of the interior of a QFP package in accordance with another exemplary embodiment of the present invention.  
         [0015]      FIG. 6  is a detail view of a portion of  FIG. 5 .  
         [0016]      FIG. 7  is a detail view, similar to  FIG. 6 , of another portion of  FIG. 5 .  
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0017]     In the following description, like reference numerals indicate like components to enhance the understanding of the invention through the description of the drawings. The drawing figures are not to scale. Also, although specific features, configurations, arrangements and steps are discussed below, it should be understood that such specificity is for illustrative purposes only. A person skilled in the relevant art will recognize that other features, configurations, arrangements and steps are useful without departing from the spirit and scope of the invention.  
         [0018]     As illustrated in  FIG. 3 , in an exemplary embodiment of the present invention, a Quad Flat Pack (QFP) package  300  has four sides with leads  302  extending from the component body  304  (shown in dashed line in this interior view) on all four sides. The electrical connections between the die  306  and the leads  302  of the package are made by wirebonding with bondwires  308 . (Some leads  302  and other grouped elements are not shown individually for purposes of clarity, and their omission is indicated collectively by an ellipsis (“ . . . ”) symbol.) The first end of each bondwire  308  is attached to one of the bondpads  310  of die  306 . The second end of each bondwire  308  is attached to either a lead  302  or a point on the diepaddle  312 .  
         [0019]     Each of leads  302  has an elongated lead portion  314  integrally formed with a lead tip  316 . The elongated lead portions  314  are substantially parallel to one another and perpendicular to the edge of the component body  304  from which they extend. In other embodiments of the invention there can be additional leads that are not arranged in this manner.  
         [0020]     Note that each of the two lead tips  316  encircled in dashed line for emphasis has an elongated or extended shape and essentially acts as an electrical bus to which a plurality of bondwires  308  are attached at points along its length. Note that each of those bondwires  308  is substantially perpendicular to the lead tip  316  at the point at which it is attached. The term “substantially perpendicular” is intended not to be limiting with geometric precision but rather only to evoke the bus-like structure, in which two or more bondwires  308  branch off from a lead tip  316  at points along its length in directions substantially at right angles (i.e., perpendicular) to the direction in which lead tip  316  extends, even though some or all bondwires  308  may deviate somewhat from precise right angle attachments.  
         [0021]     As best illustrated by the solid-line portions of  FIG. 4 , a lead  302  can comprise a single elongated lead portion  314  integrally formed with a single lead tip  316 , defining an L-shaped structure (or, similarly, a T-shaped structure, 7-shaped structure (not shown), etc.). Nevertheless, a lead tip  316  can also be integrally formed with more than one elongated lead portion  314 , as in  FIG. 3  (and, in  FIG. 4  with the inclusion of the dashed-line portion). As illustrated in  FIGS. 3 and 4 , a U-shaped structure can be defined by two elongated lead portions  314  and a lead tip  316  extending between and perpendicular to them. The U-shaped structures can be nested, with one inside the other, as shown on the right side of package  300 . The U-shaped structures define a type of looped lead or loop between leads, but as described below with regard to another embodiment of the invention, such loops can have shapes other than a “U”.  
         [0022]     As illustrated in  FIG. 5 , the invention can be very useful embodied as a System-In-Package (SIP), which is a complex type of QFP. A SIP includes two or more components within a package. The components can include not only one or more dies but also one or more other components, such as passive components, filters, amplifiers and other discrete circuit elements. The exemplary SIP  500  shown in  FIG. 5  includes multiple leads  502  extending from four sides of the body  504 , a die  506 , and another component  508 . The novel lead structures in two exemplary regions  510  and  512  (indicated in dashed line) are discussed below in further detail with regard to  FIGS. 6 and 7 , respectively. (The lead structures are shown with hatching in  FIG. 5  for clarity and not to indicate a cross-sectional view or for other reasons.)  
         [0023]     As illustrated in  FIG. 6 , in region  510  ( FIG. 5 ) the lead tip  516  of the lead  502  that is encircled in dashed line for emphasis has an extended shape and essentially acts as an electrical bus to which a plurality of bondwires  508  are attached at points along its length. Note that each of those bondwires  508  is substantially perpendicular to the lead tip  516  at the point at which it is attached. As noted above, the term “substantially perpendicular” is intended not to be limiting with geometric precision but rather only to evoke the bus-like structure, in which two or more bondwires  508  branch off from a lead tip  516  at points along its length in directions substantially at right angles (i.e., perpendicular) to the direction in which lead tip  516  extends, even though some or all bondwires  508  may deviate somewhat from precise right angle attachments. An axis  518 , parallel to the distal edge of that lead tip  516  and thus oriented in the direction in which it extends, is shown for reference purposes.  
         [0024]     As in the embodiment described above with regard to  FIG. 3 , each of leads  502  has an elongated lead portion  514  integrally formed with a lead tip  516 . The elongated lead portions  514  are parallel to one another and perpendicular to the edge of the component body  504  from which they extend. Between each elongated lead portion  514  and lead tip  516  is the remaining or intermediate portion of that lead  502 . Note that in the embodiment illustrated in  FIGS. 5-7 , this portion is actually longer than elongated lead portions  514 , and some are bent or elbowed in one or more places for routing purposes. This portion is not critical to the present invention and can have any suitable shape and be routed in any suitable manner.  
         [0025]     As illustrated in  FIG. 7 , in region  512  ( FIG. 5 ) a lead tip  516  (encircled in dashed line for emphasis) similarly has an extended shape and essentially acts as an electrical bus to which a plurality of bondwires  508  are attached at points along its length. An axis  520 , parallel to the distal edge of that lead tip  516  and thus oriented in the direction in which it extends, is shown for reference purposes. Note that each of those bondwires  508  is substantially perpendicular to the lead tip  516  at the point at which it is attached. As  FIGS. 5-7  should suggest to those skilled in the art, a lead tip  516  can have essentially any suitable shape that allows two or more bondwires  508  to be attached to it in a bus-like manner along its length.  
         [0026]     Note that the lead tip  516  to which the plurality of bondwires  508  are attached is integrally formed with four elongated lead portions  514 . A loop structure, analogous to the U-shaped structure described above with regard to  FIG. 3 , can be defined by any two of those elongated lead portions  314  and the portion of lead tip  316  extending between them. In the U-shaped structure described above, the right angles between the elongated lead portions  314  and the lead tip  316  characterize the loop as U-shaped. Nevertheless, a loop structure can have any other suitable shape, such as the irregular comb-like shape of  FIG. 7  in which four finger-like portions extend toward lead tip  516 . In view of the teachings herein, other such loop structures will readily occur to those skilled in the art.  
         [0027]     It will be apparent to those skilled in the art that various modifications and variations can be made to this invention without departing from the spirit or scope of the invention. For example, although in the illustrated embodiments of the invention the IC package is a QFP, the invention can be embodied in other suitable package types. Thus, it is intended that the present invention cover all modifications and variations of this invention that come within the scope of one or more claims and their equivalents. With regard to the claims, no claim is intended to invoke the sixth paragraph of 35 U.S.C. Section 112 unless it includes the term “means for” followed by a participle.