Abstract:
A method for fabricating a low cost integrated circuit package ( 600 ) includes separating a processed silicon wafer into a plurality of individual die ( 601 ) and then positioning the die ( 603 ) on a secondary substrate in a face down position for allowing an increased die I/O connection area. The die is covered ( 605 ) with one or more epoxy materials to form a group of embedded die packages. One or more pads on the die are then exposed ( 615 ) and subsequently connected ( 617 ) to an I/O connection in a die I/O connection area. Each of the die are then separated ( 619 ) forming singular embedded die packages from the secondary substrate. The method provides a manufacturing process to form a low cost, very high density integrated circuit package using a combination of both wafer scale packaging and wafer level packaging processes.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to a method of manufacturing integrated circuit (ICs) packages and more particularly to improvements to wafer level IC packaging techniques. 
       BACKGROUND 
       [0002]    Many types of integrated circuit packaging techniques are currently used to increase the yield and efficiency in making highly cost effective electronic components. One such packaging technique that is commonly used is referred to as chip scale packaging. Chip scale packaging involves cutting individual chips from a silicon wafer after the chip has been processed to form an integrated circuit. Each chip is then individually placed one at a time in a package. The package provides mechanical and environmental protection for the chip and enables electrical connections to be made from the chip to other electronic components. In a chip scale package, the chip and the package are substantially the same size with the package typically 0% to 15% larger than the chip by area. 
         [0003]    Another process used to package an integrated circuit chip is known as wafer level packaging. Wafer level packaging involves forming the package on the chip before it is cut from the silicon wafer. This process reduces the time needed to package a chip because an entire silicon wafer of chips can be packaged at once prior to cutting the individual chips from the silicon wafer. Thus, a wafer level packaging process reduces the time needed to individually package each chip making it much less costly than chip scale packaging. 
         [0004]      FIG. 1  illustrates a silicon wafer  100  comprised of like integrated circuit chips  101 ,  101 ′,  101 ″ and so forth such that the surface of the silicon wafer  100  is as densely populated with integrated circuit chips as possible. Each integrated circuit chip contains input/output (I/O) pads  102  that enable electrical connection to and from the chip to other devices that are not part of either the chip  101  or the silicon wafer  100 . The input output pads  102  must be contained within the surface area of the IC for which they are associated. For ICs with many input/output pads, the pitch or distance  103  between pads can be small and not compatible with the electrical connection capability of other devices such as resistors, capacitors, or printed circuit boards. 
         [0005]    Prior art  FIG. 2A  illustrates a flow chart diagram describing the processes upon which the chip scale package addresses the input/output compatibility with other devices. The flow chart  200  defines the process flow for a chip scale package. The process includes fabricating the IC chips on a silicon wafer  251 . The silicon wafer is then cut  253  into individual IC chips and placed onto an interposer substrate  255 . An interposer substrate is typically fabricated in 8-up strips using commonly known PCB processes  257 . Wire is then bonded from the IC input/output pad to the interposer I/O pad  259 . An epoxy mold compound is then overmolded on the IC interposer  261  and the IC and package are then singulated from the strip  263 . 
         [0006]      FIG. 2B  illustrates a prior art diagram of the cross-section the device  201  where an integrated circuit chip  202  uses a wire  203  bonded to the chip. A substrate  204  is used to make electrical connection to interposer substrate  205 . The interposer substrate  205  is larger than the chip  202  and redistributes the pitch of the integrated circuit input output pads to a larger pitch that is compatible with electrical connection requirements of resistors, capacitors, or printed circuit boards. 
         [0007]    Similarly, prior art  FIGS. 3A and 3B  illustrate how a wafer level package addresses the input/output compatibility with other devices. Specifically,  FIG. 3A  is a prior art flow chart  300  that defines the process flow for a wafer level package. This process begins where the IC chips are fabricated on a silicon wafer  351 . The silicon wafer is then coated with epoxy dielectric  353  and vias are formed in the epoxy dielectric to expose the IC input/output pad  355 . Next, the vias are metalized  357  and the metal input/output pads are formed on the silicon wafer using vias to connect to the IC input/output pads  359 . Finally, the IC and package are singulated from the wafer  361 . 
         [0008]      FIG. 3B  illustrates a top view of the device silicon wafer  303 . The process as defined in  FIG. 3A  produces input/output pads  301  compatible with resistors, capacitors, and printed circuit boards. In order to obtain compatible input/output pads  301 , the integrated circuits  302 ,  302 ′, and  302 ″ on silicon wafer  303  are spaced at a distance or pitch  304  such that pitch  304  is greater than pitch  103 . The increased pitch  304  requires more silicon area for integrated circuit  302  on silicon wafer  303  than for the same integrated circuit  101  on silicon wafer  100 . 
         [0009]    Thus, those skilled in the art will recognize that the number of integrated circuits processed on a given silicon wafer will be less for a wafer level package because of the extra space required for the input/output pad pitch. This reduces the overall processing cost since fewer steps are required to make a wafer level packaged integrated circuit as compared with a chip scale packaged IC. Hence, cost saving with few processing steps is negated by the increase in cost associated with the decrease in the total number of ICs processed on the silicon wafer. 
         [0010]    In light of the shortcomings of the prior art, the need exists to provide an integrated circuit package processing technique that will yield a substantially high density of integrated circuit chips on the silicon substrate and still provide reduced processing steps for making input/output connections to each individual chip and package. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0011]    The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views and which together with the detailed description below are incorporated in and form part of the specification, serve to further illustrate various embodiments and to explain various principles and advantages all in accordance with the present invention. 
           [0012]      FIG. 1  is a prior art diagram of an integrated circuit chip on a silicon wafer. 
           [0013]      FIG. 2A  is a prior art flow chart diagram describing the processes upon which the chip scale IC package addresses the input/output compatibility with other devices. 
           [0014]      FIG. 2B  is a prior art diagram of a chip scale IC package. 
           [0015]      FIG. 3A  is a prior art flow chart diagram defining the process flow for a wafer level IC package. 
           [0016]      FIG. 3B  is a prior art diagram of a wafer scale package 
           [0017]      FIG. 4  is a diagram illustrating a plurality of IC chips cut from a silicon wafer and placed on a secondary substrate where secondary substrate is used for subsequent processing and does not become part of the finished IC and package in accordance with an embodiment of the invention. 
           [0018]      FIG. 5  is a diagram illustrating a cross-sectional view of the IC chip and package where input/output pads extend beyond the die surface area in accordance with an embodiment of the invention. 
           [0019]      FIGS. 6A ,  6 B and  6 C are flow chart diagrams illustrating the method for manufacturing the IC circuit packaging in accordance with an embodiment of the invention. 
       
    
    
       [0020]    Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention. 
       DETAILED DESCRIPTION 
       [0021]    Before describing in detail embodiments that are in accordance with the present invention, it should be observed that the embodiments reside primarily in combinations of method steps and apparatus components related to integrated circuit packaging. Accordingly, the apparatus components and method steps have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein. 
         [0022]    In this document, relational terms such as first and second, top and bottom, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms “comprises,” “comprising,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by “comprises . . . a” does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element. 
         [0023]    As will be described in more detail herein, the method of the present invention improves on the current state of integrated circuit (IC) packaging by integrating wafer level packaging with traditional printed circuit board substrate technologies. The preferred methods enable gang processing of the ICs into their respective package much like wafer level packaging while maximizing IC silicon wafer utilization and maintaining input/output pad compatibility with other devices such as resistors, capacitors, and printed circuit board substrates. Therefore, the methods of the present invention, extend the current art for IC packaging by providing a low cost solution to process chip scale packages in a wafer level format using printed circuit board processing. 
         [0024]      FIG. 4  is a diagram illustrating an IC chip utilizing the manufacturing method where input/output leads can be extended beyond the die surface area in accordance with preferred methods of the invention. As will be described herein, the manufacturing process begins by cutting or “dicing” the IC chips in the silicon wafer and then placing each die  101  front-side down on a second substrate  400 . Thus, the original silicon wafer (not shown) is reconstituted on the second substrate  400  for package processing. As will be evident to those skilled in the art, the second substrate  400  does not become an integral part of the package but only serves to facilitate subsequent processing. As such, the substrate  400  may be manufactured as a metal substrate such as aluminum or stainless steel, a glass material or a high temperature polymer. By way of example, the substrate  400  might be a polished aluminum where a release film is attached. Hence the surface area of the second substrate  400  is relatively greater than the surface area of the silicon wafer the chips were diced from. The greater surface area enables the chips that are reconstituted on  400  to have a greater space between them. Therefore, input output pads  401 ,  401 ′,  401 ″ will have a pitch  402 . The pitch  402  is greater than the pitch  103  enabling more surface area for input/output connections of the packaged chip. 
         [0025]      FIG. 5  is a diagram illustrating a cross-sectional view of the IC chip using an extended substrate. The chip package  500  includes the chip  501  which is positioned upside down so its bottom  502  faces toward the copper clad surface  503  of the substrate. As will be described herein, the package around the chip  501  is formed using a first epoxy material  504  which surrounds the bottom  502  and side  504  of the die  501 . A second epoxy material  505  is used on the top  504  of the chip  501 . One or more I/O pins  506  are used to access and distribute electric circuits on the IC within the package  500 . 
         [0026]      FIGS. 6A ,  6 B and  6 C are flow chart diagrams illustrating the method for manufacturing the integrated circuit and packaging in accordance with an embodiment of the invention. As seen in  FIG. 6A , the method for providing increased input/output pad pitch in IC package  600  includes the steps of initially singulating processed chips on a silicon wafer  601 . As known to those skilled in the art, the processed chips include discrete semi-conductor components or IC type devices. The chips are picked from the wafer and placed  603  on the substrate and released and/or positioned face down such that the bottom of the die faces away from the substrate. Once all the die are in position the package can be formed for each die in mass where a first epoxy is placed  605  on a secondary substrate. The first epoxy is typically a pre-impregnated (prepreg) release film with or without copper clad that is used to cover the die. As well known in the art, pre-impregnation film includes a combination of mat, fabric, non-woven material or roving with resin that is typically cured at which point is ready for molding. Thus, after placing the chip on the substrate, an epoxy resin film such as resin coated copper foil (RCC) or 1080 prepreg is placed on top of the die  605  and press-cured  607  in a traditional printed circuit board (PCB) lamination press. The pressing process works to press the epoxy between the gaps between each die. Thereafter, the cured epoxy sheet with the embedded chips are removed  609  from the substrate. 
         [0027]    In a first embodiment shown in the flow chart of  FIG. 6B , a second sheet of epoxy prepreg clad with copper foil is placed  611  and then pressed  613  on the front side of the die and cured to harden. Vias are subsequently laser ablated  615  to expose the input/output pads on the IC. The ablated vias are plated with electroless/electroplated copper, and formed into circuit traces and pads using typical PCB process techniques  617 . Thereafter, each of the embedded chips is singulated  619  from the substrate to provide individual finished IC packages. 
         [0028]    In the second embodiment shown in the flow chart of  FIG. 6C , either an epoxy prepreg (without copper clad) or a liquid dielectric (such as Dow Chemical CYCLOTENE or Polyimide) is applied  621  to the front side of the die and cured  623 . Thereafter, vias are typically laser ablated or photo-defined  625  to expose the input/output pads on the IC chip and subsequent via connections. Input/output circuit trace and pad formation is accomplished  627  using traditional thin film metallization processing techniques for providing wired connections to components in the IC chip. The final step is to singulate  629  the array for each embedded IC using routing, scoring, sawing, or punching techniques. 
         [0029]    Thus, the invention improves on the manufacturing process for integrated circuit packaging. Integrated circuits are cut from the wafer and placed with the die front-side down on a second substrate in a manner where more I/O chip area is available. Epoxy materials are then applied, input/output pads are accessed and wire connections made to the IC. Thus, the original die on the silicon wafer is reconstituted on the second substrate for package processing which does not become an integral part of the package and only serves to facilitate more rapid chip packaging. The invention as described herein enables low cost, very high density integrated circuit package manufacturing since the chip scale packaging and wafer level packaging processes are both used in combination. 
         [0030]    In the foregoing specification, specific embodiments of the present invention have been described. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of present invention. The benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential features or elements of any or all the claims. The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued.