Abstract:
A lead-frame method and assembly for interconnecting circuits within a circuit module allows a circuit module to be fabricated without a circuit board substrate. Integrated circuit dies are attached to a metal lead-frame assembly and the die interconnects are wire-bonded to interconnect points on the lead-frame assembly. An extension of the lead-frame assembly out of the circuit interconnect plane provides external electrical contacts for connection of the circuit module to a socket.

Description:
RELATED APPLICATION 
     The present application is a divisional of U.S. application Ser. No. 09/956,190 entitled LEAD-FRAME METHOD AND ASSEMBLY FOR INTERCONNECTING CIRCUITS WITHIN A CIRCUIT MODULE filed Sep. 19, 2001 now U.S. Pat. No. 6,900,527. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to circuit modules, and more specifically, to a method and assembly for interconnecting circuits within a circuit module. 
     BACKGROUND OF THE INVENTION 
     Circuit modules or cards are increasing in use to provide storage and other electronic functions for devices such as digital cameras, personal computing devices and personal digital assistants (PDAs). New uses for circuit modules include multimedia cards and secure digital cards. 
     Typically, circuit modules contain multiple integrated circuit devices or “dies”. The dies are interconnected using a circuit board substrate, which adds to the weight, thickness and complexity of the module. Circuit modules also have electrical contacts for providing an external interface to the insertion point or socket, and these electrical contacts are typically circuit areas on the backside of the circuit board substrate, and the connection to the dies are provided through vias through the circuit board substrate. Producing vias in the substrate adds several process steps to the fabrication of the circuit board substrate, with consequent additional costs. 
     Therefore, it would be desirable to provide a method and assembly for interconnecting circuits within modules that require no circuit board substrate. 
     SUMMARY OF THE INVENTION 
     A circuit module assembly and method for interconnecting circuits within modules to provide a circuit module that may be fabricated without a circuit board substrate. A lead-frame assembly is connected to one or more dies and external contacts may be provided by an extension of the lead-frame assembly out of the plane of the die interconnect. 
     The present invention is best understood by reference to the following detailed description when read in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a pictorial diagram depicting a top view and  FIG. 1B  is a pictorial diagram depicting a cross section of a prior art circuit module; 
         FIG. 2A  is a pictorial diagram depicting a top view and  FIG. 2B  is a pictorial diagram depicting a cross section of a lead-frame in accordance with an embodiment of the invention; and 
         FIG. 3A  is a pictorial diagram depicting a top view and  FIG. 3B  is a pictorial diagram depicting a cross section of a circuit module in accordance with an embodiment of the invention. 
     
    
    
     Common reference numerals are used throughout the drawings and detailed description to indicate like elements. 
     DETAILED DESCRIPTION 
     Referring now to the figures and in particular to  FIG. 1A  a top view of a prior art circuit module  10  is depicted. Circuit module  10  is depicted as a circuit module as used in various multimedia card memory applications. The present invention is also applicable to cards and modules having other outlines such as secure digital cards and to peripheral device cards (I/O cards), as well. 
     A carrier  14  to which the integrated circuit dies  12  are attached and circuit contacts  13  are included on the bottom side, is covered by a cover  11  that is bonded to carrier  14 . The circuit module housing may be completely formed from an encapsulant, or the circuit may be encapsulated and a lid  19  applied over the encapsulant. Dies  12  are coupled to each other and to circuit contacts  13  by circuit traces  16 , which are typically etched from a metal layer on the top of carrier  14 . Circuit contacts  13  are coupled by means of plated-through holes  15  that pass through carrier  14 . The bottom side of carrier  14  is also typically etched from a metal layer on the bottom side forming electrical contacts  13  that are generally plated with a corrosion resistant material such as gold and circuit contacts  13  connect on the bottom side of carrier  14  to plated-through holes  15  by circuit traces on the bottom side of carrier  14 . Circuit traces  16  include wire bonding areas  17  that may also be plated, permitting a wire bonding apparatus to electrically couple dies  12  by wires  18 . 
     Referring now to  FIG. 1B , a cross section end view of circuit module  10  is depicted. Dies  12  are covered by cover  11  and are bonded to carrier  14 . Circuit contacts  13  are disposed on the bottom side of carrier  14  to provide electrical connections to the external circuits via a socket in which circuit module  10  is inserted. 
     The present invention provides a circuit module that does not require a separate carrier, wherein the circuit paths between dies  12  and electrical contacts  13  are provided by a conductive lead-frame to which dies  12  are bonded and an encapsulant applied surrounding the lead-frame to provide support and electrical insulation. 
     Referring now to  FIG. 2A , a top view of a lead-frame  20  in accordance with an embodiment of the invention is depicted. Circuit traces  16 A are supported by a dam bar  22  that surrounds the periphery of the lead-frame, providing rigidity during the fabrication and integration processes. Lead-frame  20  is generally stamped from a metal, such as copper, and integrated circuit dies are bonded to lead-frame in die bonding areas  21 . Wire bonding pads  17 A are provided on circuit traces  16 A to permit attachment of wires from dies to the lead-frame. The lead-frame is then encapsulated and portions of dam bar  22  are cut, resulting in electrical isolation of circuit traces  16 A, after mechanical rigidity has been provided by the encapsulant. 
     In addition or in alternative to wire bonding pads  17 A, pads may be included for attachment of surface mounted passive components by soldering or conductive adhesive attachment, and pad grids may be included for attachment of pre-packaged integrated circuits. 
     Referring now to  FIG. 2B , a cross-section side view of lead-frame  20  is depicted. Dam bar  22  is shown at ends of the lead-frame and is cut-away along the sides in the figure to illustrate that circuit traces  17 A are a half-thickness of metal with respect to dam bar  22 . This half-thickness may be produced by etching the bottom side of lead-frame after applying an etchant resistant coating to dam bar and circuit contacts  13 A. Circuit contacts  13 A are also partially a half-thickness of metal, produced by etching the top side of lead-frame after applying an etchant resistive coating to circuit traces  16 A and dam bar  22 . The etching of both sides of lead-frame  20  results in a circuit that has circuit contacts  13 A disposed as an extension out of the plane of circuit traces  16 A, while the full thickness portion of the electrical contacts/circuit trace combination produces a continuous conductive and mechanically rigid connection from circuit traces  16 A to circuit contacts  13 A. Thus, encapsulant may be applied beneath circuit traces and the circuit contact  13 A surfaces may protrude from the encapsulant, providing an interface connection external to a circuit module. 
     As an alternative, circuit contacts  13 A may be fabricated in the same plane as circuit traces  16 A and additional length supplied so that the circuit traces may be bent to provide an extension out of the plane of circuit traces  16 A so that circuit contacts  13 A may protrude from an encapsulant applied beneath lead-frame  20 . 
     The illustrative embodiments herein depict an etched lead-frame, but lead-frames may also be stamped in accordance with an embodiment of the present invention. The alternative embodiment depicted, wherein circuit traces are bent to provide circuit contacts especially lends itself to stamping, because the circuit traces may be formed and bent in a single stamping operation. 
     Referring now to  FIG. 3A , a top view of a circuit module  30 , in accordance with an embodiment of the invention is depicted. The depiction shows the internal features after dies  12  have been bonded to lead-frame  20 , an encapsulant cover  11 A applied and the dam bar  22  is singulated from circuit module  30 . The resulting circuit module  30  has circuit traces  16 A that are isolated (but supported by the encapsulant) and wires  18  have been bonded from dies  12  to bonding pads  17 A. Circuit contacts  13 A are located at the bottom surface of encapsulant cover  11 A and protrude from or are conformal to the bottom surface to provide an external electrical connection. 
     Referring now to  FIG. 3B , a cross-section end view of a circuit module  30 , in accordance with an embodiment of the invention is depicted. The plane of circuit traces  16 A adjacent to the plane of electrical contacts  13 A may be seen from the figure. Die  12  is shown as mounted above the plane of circuit traces  16 A, but a mounting within the plane of circuit traces is also possible. Additionally, circuit contacts  13 A may be attached using plating techniques to attach to circuit traces  16 A rather than including the circuit contacts within the lead-frame. 
     This disclosure provides exemplary embodiments of the present invention. The scope of the present invention is not limited by these exemplary embodiments. Numerous variations, whether explicitly provided for by the specification or implied by the specification, such as variations in structure, dimension, type of material and manufacturing process may be implemented by one of skill in the art in view of this disclosure.