Abstract:
Disclosed is a method of forming a support structure for supporting multiple dies and resulting structure. The support structure has a cavity with an upper die support surface, sidewalls providing the upper die support surface, and a lower die support bottom surface connected with the sidewalls. The support structure can be formed of a plurality of layers. A first semiconductor die is secured on the lower die support surface and a second semiconductor die is secured to the upper die support surface. An aperture can be formed from the structure bottom surface to the cavity to facilitate electrical connections between the first die and electrical contact areas on the support structure. An encapsulating material is formed around the dies, the electrical connections, and the vacant cavity space to form a packaged semiconductor device.

Description:
This application is a divisional of application Ser. No. 09/803,045, filed Mar. 12, 2001, the subject matter of which is incorporated by reference herein now U.S. Pat. No. 6,469,376. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to a method of forming a packaged semiconductor device and the resulting structure. 
     DESCRIPTION OF RELATED ART 
     In some types of semiconductor die packaging a die is secured to the surface of a die support structure. Electrical connections are made between the die and the support structure. The die, electrical connections, and at least a part of the support structure are covered with an encapsulating material to form a semiconductor package. Leads extend from the package for electrical connection to any external circuit. The package is generally secured to a printed circuit board or other mounting substrate when in use. One method of reducing the thickness of a conventional semiconductor device package is to use a thin die support structure. A thin support structure is generally about 50 microns to 75 microns thick while a conventional support structure is typically about 200 microns thick. However, a thin support structure is typically about 100% more expensive than a conventional thicker structure and thus increases the cost of packaged semiconductor devices. Another disadvantage of a thin support structure is that during fabrication the thin structure flexes and/or bows more than a thicker structure. This bowing or flexing can weaken the strength of the die&#39;s attachment to the structure as well as damage fragile electrical contacts between the die and support structure. 
     Yet another disadvantage of a thin support structure is its limited ability to secure and support multiple dice on a single support structure. One method of constructing multiple die assemblies on a conventional support structure is to stack dice vertically. U.S. Pat. No. 5,994,166 issued Nov. 30, 1999, to Salman Akram and Jerry M. Brooks discloses a semiconductor package with two die vertically stacked on opposing sides of a substrate. However, if multiple semiconductor dice are vertically stacked on a substrate the height of the packaged semiconductor devices increases. If on the other hand, multiple semiconductor dice are mounted horizontally side by side on a support structure, both the thickness and area of the support structure must be increased to support the multiple dice which results in larger packaged semiconductor devices. Thus, conventional techniques for securing multiple dice to a single support structure increase the dimensions of packaged semiconductor devices. It would be advantageous to have a semiconductor support structure that can secure and support multiple semiconductor dice which will results in a smaller dimensions semiconductor packages than conventional techniques while reducing the cost of the die support structure. 
     SUMMARY OF THE INVENTION 
     The invention provides a packaged semiconductor structure in which multiple semiconductor dice are secured to a common support structure. In an exemplary embodiment, a multi-layered support structure is formed. The support structure has a central cavity with an open surface at the top and a die support bottom surface. An aperture with a perimeter smaller than that of the central cavity is formed from the bottom exterior of the support structure to the central cavity. A first semiconductor die is supported and secured to the cavity bottom surface. The first die is electrically connected to the bottom surface of the support structure by electrical connections, e.g., wire bonds, which extend from the die through the aperture to electrical contact areas on the bottom exterior surface of the support structure. A second semiconductor die is secured on the top surface of the support structure and electrical connections are made between the second die and electrical contact areas on the bottom exterior surface of the support structure. The dice, electrical connections and structure cavity are encapsulated with encapsulating material to form a packaged semiconductor assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other advantages and features of the invention will be more readily understood from the following detailed description of the invention which is provided in connection with the accompanying drawings. 
         FIG. 1  is a top view of a semiconductor support structure of the invention; 
         FIG. 2  is a cross-sectional view of  FIG. 1 ; 
         FIG. 3  is a top view of a semiconductor support structure of the invention after a first semiconductor die has been secured inside a cavity of the support structure; 
         FIG. 4  is an cross-sectional view of  FIG. 3 ; 
         FIG. 5  is a top view of a semiconductor support structure of the invention after a second semiconductor die has been secured to the top of surface of the support structure; 
         FIG. 6  is a cross-sectional view of  FIG. 5 ; and 
         FIG. 7  is a cross-sectional view of a semiconductor support structure of the invention after the semiconductor dice have been encapsulated. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     The invention will be described as set forth in the exemplary embodiments illustrated in  FIGS. 1-7 . Other embodiments may be utilized and structural changes may be made without departing from the spirit or scope of the invention. 
       FIG. 1  illustrates a top view of a semiconductor support structure  100  of the invention.  FIG. 2  is an cross-sectional view of  FIG. 1  taken at line II—II. The support structure  100  has a top surface  20 , exterior perimeter  22 , a cavity  42  with interior perimeter  35  and bottom surface  40 . An aperture  50  with interior perimeter  36  is provided in bottom surface  40 . The interior perimeter  36  of aperture  50  is smaller in size that the interior perimeter of cavity  42  to form bottom surface  40 . The support structure  100  is formed of five thin stacked layers  30 - 34  as shown in FIG.  2 . In an exemplary embodiment, the structure  100  is formed of stacked layers of any suitable semiconductor die support material, such as, for example, Bismaleimide Triazine (BT) which may be used for all five layers  30 - 34 . 
     It is to be understood that the illustration of a five-layer structure  100  is exemplary and that the support structure  100  could be constructed with less than or more than five layers. The support structure  100  is fabricated by securing the five layers  30 - 34  to each other using techniques well known in the art, for example, with adhesives. The total structure thickness and number of layers is based on the thickness of a die which will be mounted within cavity  42  and the required spacing for various electrical contacts. The support structure  100  can be of any dimension (height, length, or width) suitable for mounting semiconductor dice. An exemplary thickness T for support structure  100  is about 500 microns or less and an exemplary depth D of cavity  42  is 400 microns or less. It is to be understood that each layer as shown in  FIG. 2  could be made of a multi-layer laminate as well. 
     One technique for fabrication of the support structure  100  is described below. Central layer  32  is formed of film of about 200 microns thickness, but larger and smaller thickness are possible. Central layer  32  can also be made of multiple layers, such as a multi-layer laminates. The other layers  30 - 31 ,  33 - 34  thickness can be sized based on the dimensions of the die  60  ( FIGS. 3 and 4 ) and the desired overall package thickness. It is to be understood that the exemplary layers  30 - 34  can comprise similar or different material and can vary in thickness from each other. Second layer  33  is secured above central layer  32 . Fourth layer  31  is secured below central layer  32 . First layer  34  is secured above second layer  33 . Finally fifth layer  30  is secured to fourth layer  31 . It is to be understood that the method of stacking or fabricating the support structure  100  layers  30 - 34  and/or method of securing the layers  30 - 34  can vary without limiting the scope of the invention. 
     One advantage of using a conventional layer thickness of, for example, 200 microns for central layer  32  is that such a conventional layer thickness is commonly available at a lower cost than a thinner material layer. In an exemplary embodiment, the layers  30 - 34  contain interior electrical paths  90  through the various layers and providing electrical paths  90  for the semiconductor dice  60 ,  80  ( FIG. 7 ) from the structure&#39;s top surface  20  down to the structure&#39;s bottom surface  37 . It is to be understood that external electrical paths (not shown) located on the surface of layers  30 - 34  are also possible either adjacent to the cavity&#39;s interior perimeter  35  or along the exterior perimeter  22  of the structure  100 . Also the die  60  (FIG.  4 ), while shown as connected by wire bottom to electrical contact areas  76  provided on layer  30 , can also connect to the electrical contact areas  76  through conductive vias internal to the layer  30 . 
     An open cavity  42  is formed by layers  30 - 34  which define a cavity perimeter  35  and a bottom surface  40 . The cavity  42  can be any suitable shape. An aperture  50  is shown formed in the fifth layer  30 , i.e., which extends from bottom surface  37  to the cavity  42 . The aperture  50  has an aperture perimeter  36  which is smaller than the cavity perimeter  35  to provide a mounting surface for die  60 . The cavity  42  and aperture  50  can be formed using techniques well known in the art, such as milling. Alternatively preformed layers having holes therein can be stacked to form the support structure  100 , having cavity  42  and aperture  50 . It is to be understood that the cavity depth D could be varied without limiting the scope of the invention. The cavity depth D is sized based on the thickness of the semiconductor die  60  ( FIG. 4 ) secured inside the cavity  42 . An exemplary dimension for cavity depth D is about 250 microns or less. Aperture  50  can be any suitable shape. Aperture  50  is sized to provide a die support surface  40 . The dimensions of aperture  50  will vary depending on the dimension of the first semiconductor die  60  and the necessary clearance for proper die  60  operation or for electrical connection. It is to be understood that aperture  50  is optional and is an exemplary way of providing an electrical contact path between the die  60  and structure  100 . 
     After support structure  100  is fabricated as shown in  FIGS. 1 and 2 , a semiconductor die  60 , shown in  FIGS. 3 and 4 , is secured to bottom layer  30 , such as, for example, by adhesive layer, bonding tape or solder balls  70 , using techniques well known in the art. It is to be understood that more than one semiconductor die  60  can be secured inside the cavity  42 , such as two dies  60  stacked on top of each other or side-by-side on the bottom surface  40 . In an exemplary embodiment, semiconductor die  60  is a board-on-chip (BOC), where a chip has electrical contact areas formed on the chip surface and the chip is directly bonded to a support surface, such as, a printed circuit. The semiconductor die  60  is electrically connected  74  to electrical contact areas  76 , such as, for example, bond pads, on the bottom surface  37  of support structure  100 . In an exemplary embodiment, wire bonds  74  extend from the die  60  electrical contact areas  72  through aperture  50  to the support structure electrical contact areas  76 . It is to be understood that various materials, types, methods, techniques, and locations for electrical contact areas  72 ,  76  and electrical connections  74  are possible and that the wire bonds disclosed above and shown in  FIG. 4  are only exemplary of one way of electrically connecting die  60  to electrical contact areas  76  provided on the bottom surface  37 . 
     After semiconductor  60  is electrically connected to the support structure  100 , a second semiconductor die  80  ( FIGS. 5-6 ) is secured to the top surface  20  of the support structure  100  by connections  83 . In an exemplary embodiment the second die  80  is a flip chip, a chip or package where bumps or connecting metal are formed on the chip surface and the chip is flipped over for soldering to a support surface, and is secured by a solder ball connections  83  to electrical contact areas  84  located on the top surface  20  of support structure  100 . The second die  80  is arranged to align with various electrical contact areas  84  which are in electrical communication through electrical vias  90  through layers  30 - 34  to electrical contact areas  76  on the structure bottom surface  37 . It is to be understood that the electrical contact areas between die  80  and the structure bottom surface  37  could also be by external conductors on the sidewalls  22 ,  35  of the support structure  100 . 
       FIG. 7  shows a packaged semiconductor assembly  110  after an encapsulation material  94  has been deposited in cavity  42  and aperture  50  and beneath die  80 . The encapsulation material  94  can be any well known material suitable for semiconductor assemblies. The encapsulation material  94  can be selected to provide under fill support for the second semiconductor die  80  as well as to reduce the coefficient of thermal expansion between the dies  60 ,  80  and structure  100 . The encapsulation material  94  is shown covering electrical contacts  74 ,  83  of the die  60 ,  80 . It is to be further understood that the encapsulation process could be broken into two steps, a first step after the first semiconductor die  60  is secured to the structure  100  and before the second die  80  is secured. And a second step after the second semiconductor die  80  is secured to the structure  100 . After the encapsulation material  94  is deposited, additional electrical contact areas  92  can be added to the semiconductor assembly  110 , on electrical contact areas  76  such as a fine ball grid array along the bottom surface  37  of the structure  100 . It is to be understood that multiple packaged semiconductor assemblies  110  can be formed in a large structure and singulated after fabrication, or at any intermediate stage of fabrication. 
     Having thus described in detail the exemplary embodiments of the invention, it is to be understood that the invention defined by the appended claims is not to be limited by particular details set forth in the above description as many apparent variations thereof are possible without departing from the spirit or scope of the invention. Accordingly, the above description and accompanying drawings are only illustrative of exemplary embodiments which can achieve the features and advantages of the invention. It is not intended that the invention be limited to the embodiments shown and described in detail herein. The invention is only limited by the scope of the following claims.