Abstract:
A multi-chip module (MCM) includes a plurality of semiconductor dies within a single package. RF transceivers on two or more of the dies provide inter-chip communications between the dies permitting the establishment of communications without requiring that hardwire connections be established for each signal connection.

Description:
CROSS REFERENCE TO RELATED APPLICATION(S)  
       [0001]     This application claims priority from U.S. Provisional Patent Application No. 60/507,971, filed Oct. 2, 2003, which is incorporated herein by reference. 
     
    
     FIELD OF INVENTION  
       [0002]     The present invention relates to semiconductor packaging and to stacked semiconductors. More particularly the invention relates to the interconnection of semiconductor dies in a stacked relationship, either within a single package or in discreet packages in a stacked or closely adjacent configuration.  
       BACKGROUND  
       [0003]     One of the problems with stacked semiconductor dies is a requirement for interconnection. Typically such interconnection is achieved by wirebonding, because techniques used for direct bondpad-to-leadframe connections, such as flip chip and bump connections, are difficult to achieve in the situation of multiple dies. In addition, if a multi-chip module (MCM) is to be pre-characterized and tested, dies which are inoperative must be disconnected and then re-connected to the package substrate. In addition, the transfer of data at high speeds creates problems with respect to lead wires, in that the lead wires tend to have significant inductance, particularly at high frequencies. Accordingly, it is desired to provide a multi-chip module (MCM) in which communication is effected in a manner which bypasses the requirement for lead wires.  
         [0004]     Another problem with stacked dies is that, if it is desired to communicate between the dies, then some form of a connection must be made between the dies. There are two ways to accomplish this: 1) direct interconnection from one die to another die; and 2) connection from one die to a lead frame or a connection on a package substrate and a second connection from the lead frame or substrate to a second die. In the case of a direct connection, it becomes necessary to provide wirebonding from die to die. In the case of an interconnection through the lead frame or substrate, a double connection is required, thereby a creating a potential for more signal loss. Accordingly, it is desired to provide a signal communications system for semiconductors in which multiple semiconductors in a vertically spaced relationship or in a closely-spaced relationship are able to communicate. It is further desired to reduce the number of internal connections for a semiconductor package, and if possible, not greatly exceed the lead count for the package.  
       SUMMARY  
       [0005]     In accordance with the present invention, semiconductor dies which are closely positioned are provided with an RF link in order to effect communications between the dies. In the case of stacked semiconductor dies, in which multiple dies are stacked within a single package, RF communication is established between the dies. This permits communications between the dies in the package to be effected without wirebond connections between the dies, or with a reduced number of wirebond connections between dies.  
         [0006]     In another aspect of the invention, multiple dies in a single package are provided with RF transceivers and communications between the dies are effected through RF links through the transceivers. This configuration can be used for either stacked or planar multi-chip modules, thereby reducing the number of physical signal connections between dies.  
         [0007]     In yet another aspect of the invention, the RF transceivers are used to establish links between dies which are either within a single package or within separate packages. This enables the use of multiple semiconductor dies in a manner which reduces a necessity for physical connections between the dies.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a side view of a stacked semiconductor package, schematically showing the use of RF transceivers to establish communication links between stacked dies.  
         [0009]      FIG. 2  is a top view of a multi chip module, schematically showing the use of RF transceivers to establish communications links between semiconductor dies. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0010]      FIG. 1  is a side view of a multi-chip module  10  in which a plurality of dies  1 l 1 ,  11   2 ,  11   3 ,  11   N  are shown in a stacked relationship. The bottom of the die  11   N  is shown as mounted on a package substrate  21 . As depicted, the specific number, N, of dies  11   1 ,  11   2 ,  11   3 ,  11   N  can vary. Although, the stacking of the dies  11   1 ,  11   2 ,  11   3 ,  11   N  is shown as precluding mounting more than one of the dies  11   1 ,  11   2 ,  11   3 ,  11   N  directly on the same package substrate  21 . In other embodiments, multiple dies can be stacked directly on the substrate  21 . A plurality of wirebond connections  31   1 ,  31   2 ,  31   3 ,  31   N  are shown, in which the stacked dies  11   1 ,  11   2 ,  11   3 ,  11   N  are wire connected to the package substrate  21 . The wirebond connections  31   1 ,  31   2 ,  31   3 ,  31   N  are established at some point during assembly, so that if for some reason one of the dies  11   1 ,  11   2 ,  11   3 ,  11   N  is changed, the wirebonding must be re-executed.  
         [0011]     Some dies  11   1 ,  11   3 ,  11   N  include an RF transceiver  41   1 ,  41   3 ,  41   N . For simplicity, the transceivers  41   1 ,  41   3 ,  41   N  are depicted on an opposite side of each die  11   1 ,  11   2 ,  11   3 ,  11   N  from the bond pads. In practice, typically, the transceivers  41   1 ,  41   3 ,  41   N  will be on a surface of each die  11   1 ,  11   2 ,  11   3 ,  11   N  adjacent to the bondpads as well as separate from the bondpads. As illustratively shown, not all the dies  11   2  may include RF transceivers.  
         [0012]     The RF transceivers  41   1 ,  41   3 ,  41   N  are capable of RF communication with closely adjacent transceivers, such as the other transceivers  41   1 ,  41   3 ,  41   N  on the nearby dies  11   1 ,  11   3 ,  11   N . The transceivers  41   1 ,  41   3 ,  41   N  include modulator/demodulator circuits, which facilitate communications between the dies  11   1 ,  11   3 ,  11   N .  
         [0013]     In the configuration shown, the bottom die  11   N , while equipped with RF transceiver  41   N , is not able to communicate with the package substrate  21  by use of RF transmissions, although in other embodiments the substrate may have the RF transceiver or both may have the transceiver. Conveniently as shown, this die  11   N  is mounted adjacent to the substrate  21  and is able to use hardwire connections for communications with the substrate  21 . Such hardwire connections can be the wirebond connections  31   1 ,  31   2 ,  31   3 ,  31   N  shown, or can be any other convenient form of connection. In the case of the communication between the substrate  21  and the adjacent die  11   N  being hardwired connections, the RF transceivers  41   1 ,  41   3 ,  41   N  are used to establish further communication links with other dies  11   1 ,  11   3 ,  11   N .  
         [0014]      FIG. 2  is top view of a multi-chip module (MCM), in which a semiconductor package  100  is used to hold a plurality of semiconductor dies  101 - 113 . Each die  101 - 113  may include an RF transceiver  119 . The dies  101 - 113  are each depicted as mounted directly onto a substrate  121  of the MCM  100 , although it is one or more of the dies may be positioned in a stacked arrangement. As a result of the direct mounting of the dies  101 - 113 , it is possible to provide direct connections to the mounting substrate  121 , and this direct mounting is used for power connections (such as v SS , v CC ). It is also possible to directly connect the signal connections for each individual die  101 - 113  by use of hardwire techniques. Such connection requires the connection configuration of the dies  101 - 113  to be established prior to configuring such hardwire connections.  
         [0015]     Unused spaces  131 - 134  are illustratively depicted in the configuration of the MCM  100 . It is possible to provide additional dies in those spaces  131 - 134 . The use of RF transceivers permits the additional dies to communicate with the original set of dies  101 - 113  for which the module  100  was configured, thereby eliminating a requirement to provide separate configurations for the additional dies. The use of RF connections between the dies allows added flexibility in the interaction facilitating more flexible hardware designs. Additionally, the flexible hardware design is more readily software configurable, since the RF connections can be more readily changed than traditional hardware connections. In alternate embodiments, the RF transceivers on the dies can be utilized to provide RF links between multi-chip modules or even single chip modules (module sets). Preferably, the RF transceivers have a limited range to maintain a small footprint and low power consumption. Accordingly, typically, the modules are in close proximity. However, by sacrificing the small footprint and low power consumption, these distances between the module sets can be increased.