Abstract:
A semiconductor integrated circuit (IC) device is defined by a low-profile package without a die attach pad (DAP). In place of the DAP, an adhesive element is used to retain a die relative to a lead frame during processing. In one example, a method of manufacturing the device includes sealing the lead frame on one side using an adhesive tape and exposing a portion of the tape within a die attach region. The die is secured onto the tape adhesive and held in place during subsequent processing, such as a wire bonding procedure to couple the die to external portions of the frame.

Description:
TECHNICAL FIELD 
     The invention relates to semiconductor chip packages and more particularly to systems and methods for lowering the profile of semiconductor devices using lead frames. 
     BACKGROUND OF THE INVENTION 
     Leadframes are used to provide a stable support structure for positioning a semiconductor die during semiconductor manufacturing. Typical leadframes include a centrally located die attach pad (DAP) surrounded by a plurality of conductive lead segments used to attach various electrical conductors in close proximity to the die. The remaining gaps between the lead segments and conductor pads on the die surface are typically bridged by thin metallic wires. In application, the other ends of the lead segments can be electrically connected to other structures, for example, a printed circuit board. 
     Limitations of typical lead frame-based IC manufacturing technologies include delamination defects, relatively large product size, relatively large product thickness (high profile) and limited thermal and electrical conductivity of the product. Typical lead frame design presents size constraints which limit the opportunity to reduce overall device volume. Delamination defects are often associated with the epoxy/device interface at the DAP. Additionally, electrical conductivity may be impaired as the layers of epoxy and DAP each have associated impedances. The combined impedance of the epoxy and DAP often degrades overall device performance. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is directed to systems and methods for manufacturing a semiconductor integrated circuit (IC) device without use of a die attach pad (DAP). In place of a DAP, an adhesive element is used to temporarily secure a die within a lead frame opening during processing. In one embodiment, a method includes applying an adhesive tape to one side of a lead frame. At the opposite side, adhesive is exposed within an opening of the lead frame. The opening and exposed adhesive define a region used to secure a die. The die is placed on the adhesive surface within the die attach region and is held by the adhesive tape during subsequent processing, including for example, a wire bonding procedure which couples the die to external portions of the frame. Wire bonding, such as bond stitch on ball (BSOB), may be used to connect the die to external portions of the frame prior to an encapsulation process. Chip packages can be separated from the lead frame via a singulation process including, for example, punch or saw procedures. 
     The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which: 
         FIG. 1  shows a perspective view of one embodiment of a lead frame semiconductor device; 
         FIGS. 2 through 5  show perspective views of a lead frame assembly using the lead frame of  FIG. 1 ; 
         FIG. 6  shows a cross-sectional view of a lead frame assembly of  FIG. 5  taken along lines  6 - 6 ; 
         FIG. 7  shows a flow chart of a manufacturing process using the lead frame of  FIG. 1 ; 
         FIG. 8  is a perspective exploded view of components of a prior art package. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Prior to a detailed description of the inventive concepts, it might be helpful to review prior art technology with respect to  FIG. 8 . Assembly  80  in  FIG. 8  depicts bonding of die  800  to die attach pad  802  of lead frame  804  during a manufacturing process. Die attach pad  802  is secured relative to side rails  803  of lead frame  804  via a pair of arms  805 . Once die  800  is bonded thereto, die attach pad  802  provides a relatively stable base for die  800  during a subsequent wiring process. Die  800  is electrically connected to a plurality of leads  808  through bonding wires which connect bonding pads  812  on an upper surface of die  800  to respective corresponding leads  808 . Die  800 , die attach pad  802  and bonding wires  810  are encapsulated to provide a package body. 
       FIG. 1  shows a perspective view of one embodiment  10  of a semiconductor device having frame  11  suitable for employment with a method according to an embodiment of the invention. In the embodiment shown, frame  11  is a lead frame and has a pair of opposing side rails  12  and a pair of rows of leads  14 . Frame  11  may be a half-etched frame. Side rails  12  are disposed so that one is opposed to the other, and, in one example, have plural through-holes  16  formed at regular intervals. Side rails  12 , in this embodiment, are in mechanical contact with rails (not shown) having a plurality of projections when transferring lead frame  11  within a semiconductor chip packaging line. The rail projections engage through-holes  16  of side rail  12 . Thus, when the rail moves, lead frame  11  is transferred accordingly. 
     Frame  11  does not have a die attach pad (DAP) located between side rail  12  and leads  14 , unlike conventional lead frames as shown in  FIG. 8 . In place of a DAP, die attach region  18  is defined generally as the region between side rails  12  and leads  14  into which a die will be subsequently placed. In one embodiment, die attach region  18  is defined within a lead frame aperture. 
       FIG. 2  is an exploded perspective view showing assembly  20  including tape  22  applied to an under surface of lead frame  11 . In the illustrated embodiment, tape  22  extends between the side rails  12  and adheres across the surface of lead frame  11 . Tape  22  in alternative embodiments may be larger or smaller in width as compared to the width of lead frame  11 . Tape  22  may be applied using any of a variety of assembly processes. In this example, tape  22  is a high temperature polyimide adhesive tape. However, other inventive methods may employ one or more other kinds of tape. 
     Assembly  20  depicts silicon die  23  being brought into contact with adhesive tape  22  within die attach region  18  of frame  11 . Silicon die  23  includes a plurality of bonding pads or terminals  24  on a top surface and a plurality of contact pads or terminals  25  on an opposite lower surface. Tape  22  maintains die  23  within die attach region  18  during a subsequent wiring process. Note that die  23  can be attached to adhesive tape  22  before tape  22  is positioned on frame  11 . 
       FIG. 3  shows assembly  30  subsequent to a wire bonding process wherein individual wires  36  are connected between the row of leads  14  and bonding pads  34  so as to electrically and mechanically connect die  23  to device  10 . A variety of different wire bonding techniques may be utilized to perform this step. Advanced bonding techniques, such as bond stitch on ball (BSOB), may be utilized to provide low profile loop heights. 
       FIG. 4  shows assembly  40  subsequent to an encapsulation process. The encapsulation process includes, for example, resin compound  42  placed so as to cover the die  23 , wires  36  and inner portions of leads  14 . A liquid resin compound, such as a polyimide compound, can be used. After the encapsulation process, tape  22  is removed, either partially or fully, to expose lower contact terminals  25  of die  23 . At this point individual packages can be defined through a separation process utilizing, for example, sawing, forming or punching techniques. Tape  22  can be removed from die  23  prior to or subsequent to the separation process. 
       FIG. 5  shows assembly  50  and depicts a separation process wherein encapsulant  42  containing die  23  is separated from lead frame  11 . Typical punch or sawing processes may be utilized. 
       FIG. 6  shows a cross-sectional view of die  23  within encapsulant  42  forming part of device  60 . Device  60  includes printed circuit board  62 . Contact pads  25  of die  23  are directly connected to traces  63  of printed circuit board  62 . Pads  14  are also connected to traces  63  of printed circuit board  62  or to other devices. 
       FIG. 7  shows process flow chart  70  in accordance with an embodiment of the invention. In an initial step  71 , lead frame  11  is provided, for example, in roll form. At step  72 , adhesive tape  22  is brought into contact with a surface of lead frame  11  covering the openings and providing an adhesive surface at an opposite side of lead frame  11  within die attach region  18 . At step  73 , die  23  is brought into contact with the adhesive surface of tape  22  within die attach region  18 . Die  23  was previously processed through, for example, wafer sawing process  74 . At step  75 , tape  22  adhesively retains die  23  within region  18  during a wiring process. The wiring process connects bonding pads  24  of die  23  to leads  14  of frame  11 . At step  76 , die  23  and portions of lead frame  11  are encapsulated using an encapsulation processes. Subsequent to encapsulation, tape  22  is removed at step  77  to exposed contacts  25 . At step  78 , a singulation process separates encapsulated dies  23  from lead frame  11 . Further processing can be employed to yield a discrete package suitable for applications, such as direct connection to a printed circuit board. 
     Chip fabrication processes according to various embodiments of the present invention eliminate lamination defects of epoxy/die attach pad interface. A reduction of overall device size can be attained. For example, overall profiles of 4-5 mm may be achieved. Additionally, chip performance can be increased through an impedance reduction achieved by elimination of a DAP and direct solder contact of the lower die pads  25  to corresponding pads on a printed circuit board. Note, during fabrication, pads  25  can be covered to prevent contamination from the adhesive of tape  22 . For purposes of this application, such pads will be considered in contact with the adhesive of tape  22 . 
     Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.