Semiconductor device manufacturing: process – Packaging or treatment of packaged semiconductor – Making plural separate devices
Reexamination Certificate
1999-05-10
2001-09-04
Chaudhuri, Olik (Department: 2814)
Semiconductor device manufacturing: process
Packaging or treatment of packaged semiconductor
Making plural separate devices
C438S124000, C438S126000, C438S127000
Reexamination Certificate
active
06284569
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to integrated circuit packaging technology. In particular, the present invention relates to an integrated carrier and stiffener for an integrated circuit package, and a method for manufacturing such a package.
2. Discussion of the Related Art
Flexible circuits, including ball grid array packages, and semi-rigid circuits, such as those using a printed circuit board material as a substrate, are small-footprint and high pin-count packages. Various techniques for making these circuits are disclosed, for example, in (1) U.S. Pat. No. 5,614,443 to Nakashima et al., entitled “METHOD FOR PRODUCING A FRAME MADE OF CONNECTED SEMICONDUCTOR DIE MOUNTING SUBSTRATE,” issued on Mar. 25, 1997, and (2) U.S. Pat. No. 5,652,185 to Lee, entitled “MAXIMIZED SUBSTRATE DESIGN FOR GRID ARRAY BASED ASSEMBLIES,” issued on Jul. 29, 1997.
In a tape-automated bonding ball grid array (“TBGA”) package, for example, a semiconductor die is attached and conventionally bonded (e.g., using wire bonding, direct chip attach, or tape-automated bonding) to a polyimide substrate embedded with photolithographically developed conductive traces provided for interconnecting the input and output terminals of the semiconductor die to external terminals provided on the package. Typically, these external terminals are provided by an array of solder balls, or other conductive terminals (e.g., terminals suitable for eutectic reflow). In one implementation of a TBGA, the substrate, wire bonds and the semiconductor die are encapsulated in a resin using a transfer molding process or an encapsulation dispensed in the liquid form.
In the prior art, to maximize the benefits of automation in the assembly process, and to minimize retooling requirements, standard assembly process flows provide highly automated assembly for packages of a few standard size packages. The sizes of these standard size packages, however, do not bear a close relationship with the size of the actual semiconductor die, and hence increase the packaging material cost by incurring waste, and provide larger footprints when incorporated in systems. There is a need to minimize material costs, to accommodate a greater range of package sizes and at the same time, without compromising the advantages of standard assembly processes and tooling.
SUMMARY OF THE INVENTION
The present invention provides a carrier ring and a method for using such a carrier ring for assembling integrated circuits. The carrier can act as a stiffener for flexible or semi-rigid circuits during the assembly process. The same carrier can be used to manufacture integrated circuits packages of any size, so that retooling or customizing of conventional assembly equipment is not required. The carrier provide alignment and index holes or marks which can be used with conventional assembly equipment.
In one embodiment, the carrier includes a stiff carrier frame, provided in a strip form, which includes a row of annular portions each enclosing a cavity sized to accommodate an array of semiconductor dies. Included on the carrier are distinctive marks for use in automatic alignment and indexing operations of conventional assembly equipment in subsequent assembly steps. The stiff carrier frame can be provided by high temperature plastic capable of withstanding the temperature of a transfer molding process, when used in such transfer molding process, or low temperature plastic, when used in a liquid encapsulation process. Alternatively, the stiff carrier frame can also be machined from a metal of the requisite strength.
During a first step in the assembly process the stiff carrier frame is attached to a substrate by adhesive, which can be a thermal set adhesive dispensed in liquid, semi-liquid or preformed formats. Alternatively, the stiff carrier frame can be attached using other suitable adhesives, such as pressure sensitive or liquid adhesives. A conductive pattern can be provided on the substrate to which terminals of the semiconductor dies can be wire-bonded or directly attached, and external terminals or pins, such as solder balls or a lead frame coupled to the conductive pattern can be provided for external connections.
Suitable substrates to be used under the present invention includes single or multi-layer polyimide tapes, such as those used in tape-automated bonding applications, or-semi-rigid printed circuit boards.
In one embodiment of the present invention, the stiff carrier frame is designed for use with a transfer molding process. For that application, a protruding portion is provided on the annular portion of the stiff carrier frame. This protruding portion is adapted to provide a seal of the enclosed cavity against a transfer mold. In addition, the stiff carrier frame also provides a mold gate and a mold vent, wherein a mold gate to act as a conduit for introducing an encapsulation material and a mold vent to allow passage for air from the cavity during the transfer molding step.
The present invention also provides a method for assembling integrated circuits using the carrier provided above. In one embodiment, the stiff carrier frame provided above is attached to a substrate, aligned according to the corresponding distinctive marks on both the stiff carrier frame and the substrate. Thereafter, single or multiple semiconductor dies are attached to the substrate. The semiconductor dies can then be wire-bonded or direct chip attached, and then encapsulated. In one embodiment, the thickness of the stiff carrier frame is used to define a thickness of the encapsulation.
As mentioned above, when a transfer molding step is used, the protruding portion of the stiff carrier frame can be used to provide a seal for the cavity against a transfer mold. In addition, the mold gates and the mold vents built into the stiff carrier frame can be used to provide a conduit for introducing an encapsulation material and to provide a passage for air exuded from the cavity during the transfer molding step.
The semiconductor dies can be singulated from the carrier assembly without removing the stiff carrier frame. In one embodiment, the semiconductor dies are singulated by sawing through the stiff carrier frame using a wafer saw.
The present invention is better understood upon consideration of the detailed description below and the accompanying drawings.
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Combs Edward G.
Sheppard Robert P.
ASAT Limited
Chambliss Alonzo
Chaudhuri Olik
Gallagher Thomas A.
Gallagher & Lathrop
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