Abstract:
A semiconductor package structure including a conductive adhesive material which is used to form an electromagnetic interference shield-forming Faraday cage. The Faraday cage incorporates a module lid as the top surface thereof, the conductive material as the sides and a laminate ground plane(s) or substrate as its bottom. Also disclosed is a method for fabricating the foregoing semiconductor package structure.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a semiconductor package structure comprising a conductive tape which is used to form an electromagnetic interference shield-forming Faraday cage, wherein the Faraday cage incorporates a module lid as the top surface thereof, the conductive tape as the sides and a laminate ground plane(s) or substrate as its bottom. The present invention also discloses a method for fabricating the foregoing semiconductor package structure. 
         [0003]    2. Description of the Related Art 
         [0004]    Currently, the Federal Communications Commission (FCC) requires that electronics products, which are commercialized, and used in the United States, meet rigorous standards in limiting their emissions of electromagnetic interference (EMI). Hereby, the spectrum of regulated electromagnetic emissions reaches up to 40 GHz; whereby on-chip and on-module signal speeds of 3, 5 and 8 GHz are fairly common. These high-speed signals radiate at up to 10× their signal rates. Semiconductor products evince a larger amount of GHz frequency emissions than ever before; whereby a wide range of chips, extending from server systems to consumer chips, has encountered costly release or approval delays because they have failed the requisite EMI standards. 
         [0005]    Normally, electromagnetic radiation (EM) can be contained inside a hermetically-sealed conductive enclosure, however, in the presence of any holes in that enclosure, they will radiate wavelengths less than or equal to twice the length of the opening, such that higher frequencies can escape from smaller holes. Thus, a 10 GHz signal will radiate from holes, which are larger than 15 mm. A bare die or chip on a module has essentially no enclosure, and will radiate freely in an unobstructed manner. Heretofore, a commonly employed solution has been to position a conductive lid upon the chip, and then connect the lid to the ground for the chip. More recently, conductive posts have been introduced between the surface of the laminate substrate and the lid, whereby an 8-post design is employable and halves the size of the aperture, such that a 40 mm package with 8 posts provides a partial shielding for EMI of up to 7.5 GHz. The laminate may be equipped with surface ground pads, whereby the pads are required to have a BGA (ball grid array) located directly beneath wired to ground. In that case, the posts are made of a conductive adhesive material. 
         [0006]    Various consumers for the electronic packages are insisting on protection against EMI to levels above and beyond this 7.5 GHz because of the increased frequency content on their chips inside the package and are requesting a solution with an increased number of posts, such as 16. This, however, is problematic on several levels, inasmuch as firstly, each post requires a specific lateral clearance, which makes tighter placement increasingly difficult and driving adhesive and dispense development, while secondly, each post requires a signal BGA to be converted to ground, thereby reducing the allowed signal count for a given package. Finally, discrete posts with gaps between them create a permeable barrier to EM radiation. 
         [0007]    Thus, Chung, U.S. Pat. No. 6,136,128, discloses a method of making an adhesive pre-formed lid for electronic devices, which is adapted to reduce or potentially even eliminate EM radiation. However, Chung does not disclose the structure and method pursuant to the present invention, wherein a novel Faraday cage serves as a two-way EM barrier. 
       SUMMARY OF THE INVENTION 
       [0008]    Accordingly, pursuant to the invention, a unique and novel barrier structure shields the gap between the lid and laminate substrate with a solid strip of a conductor, such as of copper or aluminum. The conductor adheres to both the lid and the laminate, completely sealing the periphery, or at most leaving a small breathing gap. Hereby, a barrier of this type will provide a strong degree of shielding of up to 150 GHz, which is deemed to be adequate for multiple generations of modules and is well beyond both the theoretical and practical shielding capability of prior art post systems. The size and completeness of the inventive solid shield will allow some relaxation of the resistance requirement compared to the presently employed post solution, and, resultingly, will free up more BGA pins for signals. 
         [0009]    The inventive shielding utilizes existing technology components in essentially new and inventive configurations. Pressure sensitive adhesive backed Cu and Al tapes are commercially available, which eliminates the need for developing enhanced adhesives and adhesive dispensing systems. Additionally, the EMI shield can be attached to lids, which are designed using present lid and module ground rules. The laminate or substrate designs need to be modified only to the extent to expose ground contacts on the top surface thereof. Moreover, the invention does not increase the height, length or width of the overall module. 
         [0010]    In particular detail, the present invention is directed to forming a novel structure, which reduces or meliorates to a significant extent the effects of external electromagnetic radiation, which would adversely affect the functioning of the semiconductor package. In essence, this contemplates the provision of a Faraday cage with the module lid as its top surface, the solid conductor as the sides thereof and the laminate ground plane(s) or substrate as its bottom. The Faraday cage serves as a 2-way EM barrier, whereby the chip and laminate EM radiation magnitude and bandwidth will be reduced, and, additionally, the chip will be protected from the effects of external EMI. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Reference may now be made to the following detailed description of an exemplary embodiment of the present invention, taken in conjunction with the accompanying drawings; in which: 
           [0012]      FIG. 1  illustrates, generally diagrammatically, a lidless module, pursuant to the present state-of-the-technology; 
           [0013]      FIG. 2  illustrates, generally diagrammatically, a lidded module which is constructed pursuant to the present state-of-the-technology; 
           [0014]      FIG. 3  illustrates, generally diagrammatically, a lidded module including posts, in accordance with the present state-of-the-technology; 
           [0015]      FIG. 4  illustrates, generally diagrammatically, a side view of the grounded lid with posts, pursuant to the present state-of-the-technology; and 
           [0016]      FIG. 5  illustrates, generally diagrammatically, a cross-sectional representation of the inventive shield configuration in the form of a Faraday cage, forming a protective structure against EM radiation. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    Referring in particular to detailed aspects, diagrammatically illustrated in  FIG. 1  is a lidless module  10 , pursuant to the prior art, including a chip  12  mounted on a laminate or substrate  14 , representing an unshielded EMI structure, wherein no EMI protection is afforded. In that instance, EMI radiation radiates from the electrical components  16  in multiple wavelengths and directions, as shown by the arrows  18 , in the absence of any protection. 
         [0018]    Similarly, pursuant to the prior art, in the event of utilizing a lidded module  20  where the lid  22  is electrically grounded, as shown in  FIG. 2  of the drawings, the laminate  26  with the lid having an aperture  27  equal in size to the package, including the chip structure thereon, there is produced radiation by the chip and electrical components  24  along arrows  28  in fewer wavelengths and directions, although still not affording an adequate shielding against EMI. 
         [0019]    As shown in the prior art configuration of  FIG. 3 , representing a lidded module  30  with (conductive) posts  32 , which are aligned with grounded BGAs  34 , in that instance, eight (8) posts  32  grounded in nature are shown for the chip on laminate structure. This structure blocks radiation of shorter wavelengths than the configuration of  FIG. 2 , as shown by arrows  36 , but still does not provide for full protection against unwanted EMI radiation. 
         [0020]    Pursuant to the known technology, as also shown in  FIG. 4 , only applicable components are described hereinbelow, a side view of a module  50  shows the lid  52  with a grounded electrical connection  54  between the lid and a stiffener, a die or chip structure  58  being supported on a laminate carrier  60  having an adhesive  62  interposed thereon, and where the lid is grounded to an adhesive, which is of a thermal nature. Again, there is inadequate structure provided in that module to implement a solid barrier against EMI radiation, particularly that derived from external sources. 
         [0021]    Pursuant to the present invention, as illustrated in  FIG. 5  of the drawings, a module  70  has a laminate or substrate  72  with a die or chip  74  positioned thereon. A lid bond  76  connects a one-piece lid  78 , which is superimposed thereon, and is encompassed, or partially encompassed, by a conductive shield  80 . Adhesive conductive material  82  interposed between the conductive shield  80 , the laminate  72 , and the lid  78 , so to sealingly form, or partially sealingly form, a closed structure. 
         [0022]    The adhesive conductive material  82  may be in the form of a tape, creates a Faraday cage, wherein the maximum frequency is limited by the size of the gap, or gaps, in the conductive shield  80 . Thus, a 1 mm gap in the conductive shield will block radiation of wavelength longer than 2 mm, or 150 GHz in air. 
         [0023]    Any electrically conductive lid  78  can be used, such as a one-piece lid. 
         [0024]    The sides of the Faraday cage can be made with a precut adhesive-backed conductive tape. For example, these tapes are available from 3M in ⅛ inch widths; commercially designated as Material 1126, 35 μm Cu, 88 μm with adhesive, Material 1170, 50 μm Al, 81 μm with adhesive, Material 1181, 35 μm Cu, 66 μm with adhesive, or alternatively, Fabric-backed materials are readily available for providing an enhanced durability. Moreover, the sides of the Faraday cage can also be produced by being dispensed as a viscous fluid that cures into a conductive solid state. Also, tape-based conductors can be cut and then placed into position with a rolling toolhead. 
         [0025]    The sides of the Faraday cage contact the laminate electrically through landing pads or strips on the laminate surface. These sides can be connected locally to the ground plane of the card or a third-level package through local package vias and the package-card interconnect. 
         [0026]    Even with a 1 mm gap, there is obtained a shielding, which extends well beyond 100 GHz, in effect, more than an order of magnitude improvement in bandwidth. From the foregoing, it becomes readily apparent that there is provided an advantageous structure in EM protection and forming an EMI barrier. 
         [0027]    While the present invention has been particularly shown and described with respect to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in forms and details may be made without departing from the scope and spirit of the present invention. It is therefore intended that the present invention not be limited to the exact forms and details described and illustrated, but fall within the scope of the appended claims.