Abstract:
A semiconductor package including a top-surface metal layer for implementing circuit features provides improvements in top-surface interconnect density, more flexible routing and mounting of top surface semiconductor packages, dies and passive components or a conformal shield cap implementation. The metal layer interconnected with an internal substrate of the semiconductor package by blind vias laser-ablated through the encapsulation and filled with metal. The vias extend from the top surface to an internal package substrate or through the encapsulation to form bottom-side terminals. The metal layer may be formed by circuit patterns and/or terminals embedded within the encapsulation conformal to the top surface by laser-ablating channels in the top surface of the encapsulation and filling the channels with metal. A conformal coating may be applied to the top surface of the semiconductor package over the metal layer to prevent solder bridging to circuit patterns of the metal layer.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation-in-part of U.S. Patent Application “SEMICONDUCTOR PACKAGE INCLUDING TOP-SURFACE TERMINALS FOR MOUNTING ANOTHER SEMICONDUCTOR PACKAGE”, Ser. No. 10/806,640 filed on Mar. 23, 2004 now U.S. Pat. No. 7,185,426. The above-referenced application has at least one common inventor and assigned to the same assignee. The specification of the above-referenced U.S. Patent Application is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to semiconductor packaging, and more specifically, to a semiconductor package having blind vias for interconnecting a metal layer atop the semiconductor package to internal circuits of the semiconductor package. 
     BACKGROUND OF THE INVENTION 
     Semiconductor packages that provide mechanical mounting and electrical interconnection of a semiconductor die are commonly provided in ball grid array and land grid array configurations. A semiconductor die is electrically connected to a substrate with grid array terminals disposed on the “bottom” side of the semiconductor package and solder balls are attached for connection to a system substrate, typically a printed circuit board (PCB) having lands located to attach the solder balls of the semiconductor package (referred to as ball grid array or BGA attach). Alternatively, conductive paste, a socket or “interposer” may be used to provide contacts between lands of the semiconductor package and lands on the system substrate (referred to as land grid array or LGA connection). 
     The above-incorporated Parent U.S. Patent Application discloses a top-surface mounting terminal structure for attaching a second semiconductor package or die to the top of a first semiconductor package. While the packaging density of the combined devices is increased, the location of the terminals is dictated by the design of the die or semiconductor package mounted on the first semiconductor package, which typically increases the interconnect density of the substrate in the first semiconductor package. 
     Also, it is often desirable to provide a metal shield cap atop a semiconductor package. Such shields are usually connected to a ground terminal or other reference voltage level by a through via extending through the semiconductor package to one or more terminals. 
     Therefore, it would be desirable improve upon the techniques of the above-incorporated parent U.S. Patent Application to provide a semiconductor package and a method of manufacturing such a semiconductor package that facilitates stacking of grid arrays and other components while reducing interconnect densities in the semiconductor package and increases flexibility of design. It would further be desirable to improve the techniques of the above-incorporated parent U.S. Patent Application to provide a semiconductor package and method of manufacture that provides a metal shield cap without requiring additional through vias. 
     SUMMARY OF THE INVENTION 
     The above objectives are accomplished in a semiconductor package having one or more metal patterns conformal to the top surface of an encapsulation of the semiconductor package. The one or more metal patterns are electrically connected to an interconnect substrate within the semiconductor package or terminals on the bottom of the semiconductor package by blind vias laser-ablated through the to the substrate or through the circuit package and subsequently filled with metal. 
     The top-surface metal circuit patterns may include via capture lands, interconnect patterns, terminals for connection of semiconductor package or dies and/or passive components or may implement a single contiguous shield cap. The blind vias may be filled with conductive paste or a low melting-temperature alloy or plated. The vias may have a conical profile to improved plating uniformity. The vias may terminate on the internal substrate circuit pattern, or may pass through the encapsulation and the substrate to provide lands for bottom-side terminals. A conformal coating (solder mask) may be applied to the top surface of the semiconductor package exclusive of terminal areas of the one or more metal patterns to prevent solder flow to circuit patterns implemented by the one or more metal patterns. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-1H  are pictorial diagrams depicting stages in preparation of a semiconductor package in accordance with an embodiment of the present invention; 
         FIGS. 2A-2D  are pictorial diagrams depicting further stages in assembly of a semiconductor package in accordance with another embodiment of the present invention; 
         FIG. 3A  is a pictorial diagram depicting a semiconductor package in accordance with another embodiment of the present invention; and 
         FIGS. 3B-3C  are pictorial diagrams depicting stages in fabrication of a semiconductor package in accordance with yet another embodiment of the present invention. 
     
    
    
     The invention, as well as a preferred mode of use and advantages thereof, will best be understood by reference to the following detailed description of illustrative embodiments when read in conjunction with the accompanying drawings, wherein like reference numerals indicate like parts throughout. 
     DETAILED DESCRIPTION 
     The present invention concerns a semiconductor package and a method for manufacturing a semiconductor package that include a metal layer formed atop a semiconductor package encapsulation and connected to an internal substrate of the semiconductor package by blind vias and/or terminals on the bottom side of the encapsulation by through vias. 
     While the exemplary embodiments depict ball grid array packages, it will be understood by those skilled in the art, that the techniques of the present invention can be extended to other types of semiconductor packages. The exemplary embodiments also show wirebond die connections within the semiconductor package, but it will be understood that any type of internal die and die mounting can be used within the semiconductor package embodiments of the present invention. 
     Referring now to  FIG. 1A , a semiconductor package  10 A for forming a semiconductor package in accordance with an embodiment of the invention and corresponding to a first illustrated step of manufacture is depicted. Semiconductor package  10 A is in the form of a ball grid array (BGA) or land grid array (LGA) package as is commonly known in the art, except that particular circuit features are positioned for providing vias to the top side of semiconductor package  10 A in subsequent manufacturing steps, so that connections may be made to features to be formed in subsequent steps. 
     Semiconductor package  10 A includes a die  16  mounted to a substrate  14 A that includes lands  18  to which solder ball terminals may be attached or that may be connected with a conductive paste to form a LGA mounted semiconductor package. Encapsulation  12 A surrounds die  16  and substrate  14 A, although substrate  14 A may alternatively be exposed on a bottom side of semiconductor package  10 A. Electrical connections  15  of die  16  are connected to circuit patterns  17  on substrate  14 A via wires  19 , but the type of die mounting is not limiting, but exemplary and other die mounting types may be used such as flip-chip die mounting. Additionally, while substrate  14 A is depicted as a film or laminate-type mounting structure, lead frame and other substrate technologies may be used within the structures of the present invention. 
     Referring now to  FIG. 1B , a first modification to semiconductor package  10 A that illustrates a second step in the manufacturing process to form semiconductor package  10 B is shown. Semiconductor package  10 B includes a plurality of via holes  20 A,  20 B and  20 C laser-ablated through encapsulation  12 A of  FIG. 1A  to form encapsulation  12 B. While only three via holes are shown, many via holes may be provided. The three via holes shown and as disclosed in the above-incorporated parent U.S. Patent Application illustrate the three different types of via holes that may be provided through control of laser energy and exposure time. The first via hole type, illustrated as via  20 A, is fabricated by laser-ablating either completely through semiconductor package  10 B or by laser-ablating through encapsulation  12 A to the top side of lands  18 , so that a connection is provided through from the top side of semiconductor package  10 B to the bottom side of semiconductor package  10 B when the via is filled. If via  20 A is ablated completely through, then the corresponding land  18  is provided by the bottom surface of a via formed in hole  20 A. 
     The next type of via hole is provided by laser-ablating through encapsulation  12 A to reach circuit pattern  17  so that connection may be made through substrate  14 A circuit patterns to die  16  electrical terminals, to lands  18  or both. The last type of via is provided by laser-ablating through encapsulation  12 A to reach electrical connections  15  of die  16  so that direct connection to the circuits of die  16  can be made from a piggybacked semiconductor package. Each of via holes  20 A,  20 B and  20 C is depicted as a via hole having a conical cross-section, which is desirable for providing uniform plating current density during a plating process. However, via holes  20 A,  20 B and  20 C may alternatively be made cylindrical in shape if the advantage of conical cross-section is not needed, for example if a conductive paste is used to fill the via holes. 
     Referring now to  FIG. 1C , a semiconductor package step  10 C is illustrated. Conductive material applied within via holes  20 A,  20 B and  20 C to form conductive vias  22 A,  22 B and  22 C through encapsulation  12 C and optionally substrate  14 C for vias that are formed completely through substrate  14 C. The conductive material used form vias  22 A,  22 B and  22 C may be electroplated or electro-less plated metal, conductive paste such as copper or silver epoxy compounds, or a low melting temperature high-wicking solder alloy such as SUPER SOLDER. 
     Referring now to  FIG. 1D , a next step of preparation of a semiconductor package  10 D is illustrated. Channels  24  are laser-ablated in the top surface of encapsulation  12 C to form encapsulation  12 D. Channels  24  may define circuit traces, terminals and other features that either provide complete interconnection at the top surface of encapsulation  12 D or connect top-side features such as circuit traces and terminals to one or more of vias  22 A,  22 B and  22 C. 
     Next, as shown in  FIG. 1E , channels  24  are filled to provide a metal layer  26  in a semiconductor package step  10 E. Channels  24  may be filled by electroplating, filling with conductive paste with planarization if required, or electro-less plating after treating channels  24  with an activating compound. Further, the top surface of encapsulation  12 D may be overplated or over-pasted and then etched to isolate the circuit features of metal layer  26 . 
     After formation of metal layer  26 , plating  28  may be applied as shown in  FIG. 1F , yielding semiconductor package step  10 F to protect the surface of metal layer and/or to prepare terminal areas defined by the top surface of metal layer  26  for further processing such as wire bond attach or soldering. 
     Then, as shown in  FIG. 1G , a solder mask  30  may be applied over the top of encapsulation  12 D and portions of the metal layer  26 , yielding semiconductor package step  10 G. Solder mask  30  is useful in operations where reflow solder operations will be used to attach components to metal layer  26 . 
     Solder balls  34  may be attached to bottom-side terminals  18  of semiconductor package step  10 G to yield a completed ball-grid-array (BGA) package  10 H that is ready for mounting on a circuit board or other mounting location. Alternatively, as with all depicted final semiconductor packages described herein below, the step illustrated in  FIG. 1H  may be omitted and bottom side terminals  18  plated, yielding a land-grid-array (LGA) package. 
     A “tinning” coat of solder  32  may be applied to the top side of semiconductor package  10 H as illustrated by  FIG. 2A  to prepare for mounting of top side components. The solder may be selectively applied to only solder mounting terminal areas via a mask. 
     Next, components are mounted on the top side of semiconductor package  10 H and attached to metal layer  26  as illustrated in  FIG. 2B . It will be apparent that the steps of attaching solder balls depicted in  FIG. 1H  can be performed after this step and that in general, various steps in formation of structures above encapsulation  12 D may be performed at different times.  FIG. 2B  illustrates mounting of another semiconductor die  16 A that is wire-bonded via wires  19 A to plated terminals of metal layer  26  and also mounting of discrete surface-mount components  36  via reflow soldering. 
     After attachment and interconnection of die  16 A, a second encapsulation  12 E may be applied over die  16 A, wires  19 A and part of the top surface of encapsulation  12 D to form a completed assembly. 
     Another alternative embodiment of the present invention is shown in  FIG. 2D . In  FIG. 2D , another semiconductor package  38  may be ball-mounted to terminals formed on metal layer  26 . The depicted embodiment provides for redistribution of terminals at virtually any position atop semiconductor package  10 H 2 , since metal layer  26  can provide routing of circuits from vias such as  22 A-C to solder balls  34 A at virtually any position atop semiconductor package  10 H 2 . 
       FIG. 3A  illustrates another embodiment of the present invention that includes a metal layer  40  that provides a shield cap for semiconductor package  10 I. Metal layer  40  may be electro-less plated atop encapsulation  12 C (See  FIGS. 1A-1C  for formation steps prior to  FIG. 3A ) by applying a seed layer or may be paste screened to form metal layer  40 . Metal layer may be solid layer, or a continuous pattern such as a mesh screen to reduce separation and required metal to improve the plating process. Metal layer  40  is electrically connected to vias  22 A and/or  22 B to provide a return path for the shield. 
       FIG. 3B  illustrates another shield embodiment of the present invention. A shield cavity is laser-ablated in the top surface of encapsulation  12 E to form a semiconductor package step  10 J having a cavity  24 A. Cavity  24 A is then filled to form a metal shield layer  40 A as shown in  FIG. 3C . Metal layer  40 A may be applied by paste screening or plating (and possible subsequent etching process) to yield a shield that is contained within the sides of semiconductor package  10 K. 
     The above description of embodiments of the invention is intended to be illustrative and not limiting. Other embodiments of this invention will be obvious to those skilled in the art in view of the above disclosure and fall within the scope of the present invention.