Abstract:
A packaged integrated circuit for installation on a printed wiring board (PWB) or other type of circuit mounting structure, that allows for the routing of high-speed signals out from high-speed leads on an underside of the packaged integrated circuit. The packaged integrated circuit comprises a die and a package body formed from encapsulant that at least partially encloses the die. A leadframe is also connected to the die and partially enclosed in the package body. Leads extend out from the package body and a subset of these leads are separated by a lead-to-lead pitch. At least two adjacent leads of the leadframe are separated by a space larger than the pitch. An additional lead is also connected to the die and disposed on an underside of the package. The additional lead is connectable to a circuit mounting structure trace passing between the adjacent leads separated by the space larger than the pitch.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to integrated circuits, and more particularly to integrated circuit packages and packaging techniques.  
       BACKGROUND OF THE INVENTION  
       [0002]     With the continued anticipation of higher speed requirements in the computer hard drive industry, a transition from Parallel Advanced Technology Attachment (PATA) interfaces to Serial Advanced Technology Attachment (SATA) interfaces is currently underway. See, e.g., J. Donovan, “Here Comes Serial ATA,” E. E. Times, April 2003; and L. Wood, “SATA: Evolutionary or Revolutionary Disk Technology,” EnterpriseStorageForum.com, March 2003. SATA meets the rising hard drive performance requirements without significant increases in price. Further, SATA improves airflow and cuts power consumption by replacing PATA ribbon cables with low voltage serial cables. A SATA interface is typically integrated in a System-on-Chip (SOC) configuration. Such SOCs are frequently utilized in desktop computers. Due to extreme cost pressure in the industry, package solutions for SOCs that offer the right level of performance, while having the lowest cost, will be sought for use in the higher speed systems. Thus, the increased performance demands of the systems have not stopped production and use of traditional leadframe-based packaging. Recent innovations have allowed the more traditional package structures to reach into the markets of the more demanding applications. See, e.g., S. Jewler, “Current Challenges Dictated by Today&#39;s IC Packaging Trends,” Solid State Technology, April 2003.  
         [0003]     A standard SOC is a Thin Quad Flat Package (TQFP) which provides a space efficient packaging solution, resulting in smaller PWB space requirements. The TQFP includes a central die upon which an integrated circuit device is disposed. The central die is electrically connected to a plurality of leads that extend outward from the die and beyond the packaging, or the material which encapsulates the die and the leads. The ends of the leads may then be soldered to traces on a PWB. The reduced height and body dimensions of the TQFP are ideal for space-constrained applications, such as laptop PCs, video/audio devices, data acquisition devices, office equipment, disc drives, and communication boards.  
         [0004]     A preferred SOC package is the Exposed Pad Thin Quad Flat Package (ETQFP). A more particular example of such a package is the ExposedPad L/TQFP commercially available from Amkor Technology of West Chester, Pa., U.S.A. In this type of package, the integrated circuit die is shifted downward and an associated die pad is exposed on the underside of the package. The exposed die pad significantly increases the thermal efficiency of the package. The ETQFP can increase heat dissipation by as much as 110% over a standard TQFP, thereby expanding operating parameter margins. Additionally, the exposed pad can be connected to ground, thereby reducing loop inductance for high-frequency applications. The exposed pad is soldered directly to the PWB to realize the thermal and electrical benefits.  
         [0005]     An additional product also available from Amkor Technology is the MicroLeadFrame, which replaces all the traditional leadframe leads on the perimeter of the integrated circuit package with lands on an underside of the package. The lands are used to provide electrical connection of the integrated circuit package to the PWB. This modification allows package size to be reduced, while also reducing lead inductance for high-frequency applications. This technology also incorporates the exposed pad on the bottom surface of the package to provide an efficient heat path.  
         [0006]     The adaptation of these packages is intended to extend the useful life of the low-cost TQFP, so that it may comply with anticipated higher speed requirements of the systems, while remaining inexpensive. However, a problem exists in that users generally prefer a circuit board arrangement having high-speed lines that may be routed to an integrated circuit on a top surface of a PWB, while maintaining the traditional properties of TQFPs, such as leadframe leads. Conventional TQFPs, including the above-noted ETQFP, typically do not include high-speed leads, and instead have leadframe leads with a tight pitch preventing trace access to the underside of the packaged integrated circuit from the top surface of the PWB. The MicroLeadFrame is smaller in size than traditional TQFPs and does not provide leadframe leads. Thus, a need exists for an improved package that addresses the drawbacks of the conventional arrangements.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention in accordance with one aspect thereof provides a packaged integrated circuit that allows for the routing of high-speed signals out from high-speed leads on an underside of the packaged integrated circuit, across the top surface of a PWB or other type of circuit mounting structure, to a high-speed connector on the circuit mounting structure.  
         [0008]     For example, one aspect of the invention is a packaged integrated circuit comprising a die. A package body is formed from encapsulant and at least partially encloses the die. A leadframe is also connected to the die and partially enclosed in the package body. Leads extend out from the package body and a subset of these leads are separated by a lead-to-lead pitch. At least two adjacent leads of the leadframe are separated by a space larger than the pitch. An additional lead, not part of the lead frame, is also connected to the die and disposed on an underside of the package. The additional lead is connectable to a PWB trace or other circuit mounting structure trace passing between the adjacent leads separated by the space larger than the pitch.  
         [0009]     The present invention may further comprise a PWB, or other type of circuit mounting structure, having at least one electrical connector, a plurality of traces, and at least one packaged integrated circuit, as described above, mounted thereon. At least one trace is routed on the top surface of the circuit mounting structure, from the electrical connector, passing between the adjacent leads separated by the space larger than pitch, to an additional lead on the underside of the packaged integrated circuit.  
         [0010]     The present invention may also comprise a leadframe for use in a packaged integrated circuit having a plurality of leads. At least two adjacent leads of the leadframe are separated by a space larger than the pitch, so that when the leadframe is used in a packaged integrated circuit, a trace on a circuit mounting structure is connectable to an additional lead on an underside of the package body.  
         [0011]     Advantageously, the packaged integrated circuit allows high-speed traces to be routed on a top surface of a circuit mounting structure, through the space that is larger than the pitch, to the exposed surface of the additional lead. Additionally, such an arrangement may extend the useful life of a low-cost package solution by allowing it to be incorporated into systems that have higher speed requirements.  
         [0012]     These and other objects, features, and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a diagram illustrating a bottom view of a packaged integrated circuit, according to an embodiment of the present invention;  
         [0014]      FIG. 2A  is a diagram illustrating a partial view of a leadframe for an integrated circuit, according to an embodiment of the present invention;  
         [0015]      FIG. 2B  is a diagram illustrating a magnified view of the leadframe of  FIG. 2A  showing a locking mechanism, according to an embodiment of the present invention; and  
         [0016]      FIG. 3  is a diagram illustrating a top view of a PWB having a packaged integrated circuit mounted thereon, according to an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]     As will be illustrated in detail below, the present invention in an illustrative embodiment provides a packaged integrated circuit that allows for the routing of high-speed signals out from high-speed leads on an underside of the packaged integrated circuit. The high-speed signals may then be routed across a top surface of a PWB, or other type of circuit mounting structure, to a high-speed connector.  
         [0018]     Referring initially to  FIG. 1 , a diagram illustrates a bottom view of a packaged integrated circuit  100 , according to an embodiment of the present invention.  
         [0019]     Packaged integrated circuit  100  is suitable for mounting on a PWB or other type of circuit mounting structure. It will be assumed for the remaining description that the circuit mounting structure in the illustrative embodiment is a PWB.  
         [0020]     At the center of packaged integrated circuit  100  is a die  102 . Die  102  generally includes at least one integrated circuit device. Packaged integrated circuit  100  comprises a package body  104 , formed from encapsulant. Die  102  is substantially surrounded by package body  104 , but a portion of its bottom surface is exposed through the bottom surface of package body  104 . Additional leads  106  are also substantially surrounded by package body  104 , with portions of additional leads  106  exposed through the bottom surface of package body  104 . Additional leads  106  are electrically connected to the integrated circuit device within package body  104 . Die  102  significantly increases the thermal efficiency of packaged integrated circuit  100  and may be connected to ground, reducing loop inductance for high-frequency applications. In such a case, die  102  is soldered directly to a PWB, to realize the thermal and electrical benefits. While the present embodiment shows die  102  exposed on the bottom surface for thermal purposes, it is also possible to have a packaged integrated circuit without an exposed die  102 . In such a case die  102  would be completely surrounded by package body  104  and would not be visible when viewing packaged integrated circuit  100 .  
         [0021]     Additional leads  106  are preferably disposed on an underside of packaged integrated circuit  100  a short distance from die  102  so that they have the shortest trace length from the integrated circuit device. Additional leads  106  are connected to die  102  in a conventional manner, preferably through wire bonding. The shorter the trace length, the lower the lead inductance, and the higher the speed that may be achieved at additional leads  106 . In the present embodiment, four additional leads  106  are disposed on a single side of die  102 . However, any number of additional leads  106  may be disposed on any or all of the sides of die  102 . Further, while it is preferable for additional leads  106  to be disposed adjacent to die  102 , they may be disposed anywhere on the underside of packaged integrated circuit  100 . However, the shortest distance from die  102  is most preferable due to the reasons specified above.  
         [0022]     In the illustrative embodiment of  FIG. 1 , leadframe leads  108  run through and project out from package body  104  along the perimeter of packaged integrated circuit  100 . This is similar to a traditional TQFP arrangement. However, the invention can be implemented using a wide variety of other packaging arrangements. Leadframe leads  108  are formed and shaped from a leadframe, an example of which is shown in  FIG. 2A . Leadframe leads  108  are also electrically connected to the integrated circuit device mounted on die  102  within package body  104 . This electrical connection is preferably implemented using a wire bonding technique.  
         [0023]     The spacing between leadframe leads  108  at the perimeter of packaged integrated circuit  100  is defined as the pitch. For example, the pitch of leadframe leads  108  in the illustrative embodiment may be approximately 0.4 mm to 0.5 mm. Other lead pitches may be used in alternative embodiments. Leadframe leads  108  in the illustrative embodiment are, by way of example, approximately 0.13 to 0.27 mm in width. Also, in accordance with the invention, a large pitch  110  exists between a pair of adjacent leadframe leads  108 . The width of large pitch  110  may be determined by adding a combination of lead widths and pitches. When packaged integrated circuit  100  is mounted on a PWB, large pitch  110  permits high-speed lines to be routed between this pair of adjacent leadframe leads  108 , providing access to additional leads  106  on an underside of packaged integrated circuit  100 .  
         [0024]     In the present embodiment a single large pitch  110  is shown. However, multiple large pitches  110  may exist along the perimeter of packaged integrated circuit  100 . The number and placement of large pitches  110  along the perimeter of packaged integrated circuit  100  may correspond to the number and placement of additional leads  106  surrounding die  102  on the underside of package body  104 .  
         [0025]     Large pitch  110  is preferably disposed at the nearest point along the perimeter of packaged integrated circuit  100  from additional leads  106 . Thus, large pitch  110  may be disposed along any side of packaged integrated circuit  100 .  
         [0026]     Referring now to  FIG. 2A , a diagram illustrates a partial view of a leadframe  200  for a packaged integrated circuit  100 , according to an embodiment of the present invention. Leadframe  200  shows leadframe leads  208  before they are trimmed and formed, before connection to die  102 , and before encapsulating material is applied. A locking mechanism  212  is disposed at a specific point along the perimeter of leadframe  200 , and in place of at least one leadframe lead  208 . Locking mechanism  212 , in the illustrative embodiment, creates a large pitch between two neighboring leadframe leads  208 . Large pitch  210  is greater than the pitch between the remaining pairs of leadframe leads  208 . The width of large pitch  210  is determined by the number of leadframe leads  208  locking mechanism  212  replaces. The present embodiment shows locking mechanism  212  replacing two leadframe leads  208 . Therefore, the width of large pitch  210  may be determined by the equation: 
 
 LP=wx+p ( x+ 1) 
 
 where LP represents the large pitch, w represents the width of leadframe leads  208 , p represents the pitch between leadframe leads  208 , and x represents the number of leadframe leads  208  replaced by locking mechanism  212 . 
 
         [0028]     Referring now to  FIG. 2B , a diagram illustrates a magnified view of leadframe  200  of  FIG. 2A  showing locking mechanism  212 , according to an embodiment of the present invention. Locking mechanism  212  is connected to leadframe  200  and leadframe leads  208 A and  208 B by dambar  214 . Dambar  214  represents the individual sections of leadframe between leadframe leads  208  and locking mechanism  212 . Locking mechanism  212  and dambar  214  keep leadframe  200  stable during manufacturing in place of the depopulated leadframe leads replaced by locking mechanism  212 . Therefore, the manufacturing process of leadframe  200  does not require existing manufacturing equipment to be changed.  
         [0029]     During manufacturing, after leadframe  200  is wire-bonded to the die, encapsulant material is formed over leadframe  200  to form package body  104 . Dambar  214  is a portion of leadframe  200  that prevents encapsulating material from flowing to the ends of leadframe  200 , thus forming perimeter  216  of package body  104  and permitting portions of leadframe leads  208  to remain exposed. Locking mechanism  212  is partially covered by the encapsulating material leaving only a small extension of its legs exposed beyond perimeter  216 . This small exposure of the legs of locking mechanism  212  is not shown, but each exposed leg represents where a leadframe lead would normally protrude from package body  104 . Leadframe leads  208  are then trimmed and formed and portions of dambar  214  between each leadframe lead  208  and leg of locking mechanism  212  are punched out. The horseshoe shape of locking mechanism  212  prevents it from being pulled out during the trimming and forming of leadframe leads  208  and the removal of dambar  214 . If locking mechanism  212  were to be pulled out it would result in holes in package body  104  on a perimeter  216  of the packaged integrated circuit.  
         [0030]     Locking mechanism  212  may take other shapes. For example, in accordance with the current embodiment, if locking mechanism  212  were to replace an additional leadframe lead  208 , locking mechanism  212  would comprise three prongs, forming an M-shape. While the present embodiment shows locking mechanism  212  having a shape with prongs, different forms are also possible that achieve the same result.  
         [0031]     Referring now to  FIG. 3 , a diagram illustrates a top view of a PWB  318  having mounted thereon a packaged integrated circuit  300 , according to an embodiment of the present invention. Leadframe leads  308  of packaged integrated circuit  300  are soldered to corresponding traces  320  on PWB  318 . Traces  320  are routed on a top surface of PWB  318  from a connector  324  to leadframe leads  308 . High-speed traces  322  may be routed on the top surface of PWB  318  from connector  324  through a large pitch, beneath packaged integrated circuit  300 , to additional leads  306  on an underside of packaged integrated circuit  300 . Critical signals may be routed through high-speed traces  322  on the top surface of PWB  318 , while less critical signals may be routed through leadframe leads  308  or in lower layers of PWB  318 . For example, lower-speed data and control signals may be carried by leadframe leads  308  and traces  320 , while additional leads  306  and high-speed traces  322  may carry higher-speed signals, such as signals having a frequency of at least 2 GHz.  
         [0032]     Packaged integrated circuit  300  may be disposed anywhere on PWB  318 . The present embodiment shows a single packaged integrated circuit  300  on PWB  318 , however a plurality of packaged integrated circuits  300  may be disposed thereon. Further, the present invention shows a single connector  324  on PWB  318 , however, a plurality of connectors  324  may be disposed thereon. Connectors  324  may also be disposed in a multitude of positions on PWB  318 . The present embodiment shows traces  320  and  322  taking specific paths from connectors  324  to packaged integrated circuit  300 , however, traces  320  and  322  can take any path on PWB  318  to reach their destination. Traces  320  and  322  are shown to be routed on a top surface of PWB  318 , which is preferred for high-speed traces  322 . However, traces  320  and  322  may also be routed on a different layer of PWB  318 .  FIG. 3  shows packaged integrated circuit  300  having a plurality of additional leads  306  and leadframe leads  308 . As described above, additional leads  306  and leadframe leads  308  may vary in number and placement in packaged integrated circuit  300 . Finally,  FIG. 3  shows an embodiment of the present invention on a PWB, however, it is also possible to mount the present invention on other circuit mounting structures.  
         [0033]     Accordingly, as described herein, the present invention in the illustrative embodiment provides a high-speed packaged integrated circuit for installation on a PWB or other type of circuit mounting structure. More particularly, the present invention provides an improved packaged integrated circuit that allows for routing of high-speed traces on the top surface of the PWB from high-speed leads to a high-speed connector.  
         [0034]     Although illustrative embodiments of the present invention have been described herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various other changes and modification may be made by one skilled in the art without departing from the scope or spirit of the invention.