Cutting – Processes – Cut advances across work surface
Reexamination Certificate
1998-03-04
2001-02-06
Rachuba, M. (Department: 3724)
Cutting
Processes
Cut advances across work surface
C083S076000, C083S365000, C083S675000, C083S676000
Reexamination Certificate
active
06182546
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to microelectronic packages and more specifically relates to devices and methods for separating one or more microelectronic packages from a common substrate.
BACKGROUND OF THE INVENTION
A semiconductor chip is generally connected to an external circuit element, such as a printed circuit board, through contacts on the front face of the chip. For example, in the tape automated bonding process (hereinafter referred to as the “TAB” process), a flexible dielectric sheet, such as a thin foil of polyimide, is provided with one or more bond windows and an array of metallic leads on one surface thereof. Each lead has one end integrally connected to terminals on a dielectric sheet and an opposite end extending from the dielectric sheet so that the outermost ends of the leads project beyond the bond windows. The dielectric sheet is then juxtaposed with the semiconductor chip so that the bond windows are aligned with the contacts on the chip and so that the outermost ends of the leads overlie the front face of the chip. The leads are then bonded to the contacts of the chips using bonding techniques, such as ultrasonic or thermocompression bonding. After the bonding step, the terminals may be connected to an external circuit element.
Certain embodiments of commonly assigned U.S. Pat. No. 5,659,952, the disclosure of which is hereby incorporated by reference herein, disclose methods of manufacturing a plurality of semiconductor chip packages by assembling a plurality of semiconductor chips on a common substrate, such as a substantially continuous sheet of flexible dielectric material. The common substrate preferably has a plurality of connection components which are spaced lengthwise or in a matrix arrangement on the common substrate. Each connection component preferably includes terminals and flexible leads extending therefrom for electrically connecting the terminals with contacts on a front face of a semi-conductor chip. Before semiconductor chips are assembled to respective connection components on the common substrate, a plurality of compliant pads are attached to a top surface of each connection component whereby any two adjacent compliant pads define a channel therebetween. The compliant pads preferably include a resilient material such as a silicone elastomer. Next, the front contact bearing faces of the respective semiconductor chips are abutted against the array of compliant pads and the contacts are electrically connected to the terminals by bonding the flexible leads to the contacts. A compliant filler, such a curable liquid elastomer, may then be provided in the channels between the front face of the semiconductor chips and the top surface of the common substrate while the semiconductor chips and the common substrate are held in place. The curable liquid elastomer is then cured to form a substantially uniform planar compliant layer between the chip and the dielectric film.
After a plurality of semiconductor chip packages have been manufactured using the techniques described above, the individual microelectronic packages must be separated from the common substrate, such as by severing the common substrate to free the individual packages. As used herein, the term semiconductor chip package means a semiconductor chip which has been assembled to a portion of the common substrate, whereby an individual chip package includes the semiconductor chip and a portion of the common substrate which has been severed.
A number of methods have been used for severing or cutting the common substrate so as to separate the one or more microelectronic packages therefrom. One effort involves using a stationary rotating cutting wheel, such as a wafer saw which is colloquially referred to as a “salami slicer”. However, the results achieved using salami slicers have proven to be disappointing because the common substrate material and the encapsulant material tend to act as brake pads which squeeze on the lateral sides of the rotating cutting wheel. This occurrence slows rotation of the cutting wheel and heats the cutting wheel and the package elements. The salami slicer also can move the common substrate out of planarity which results in the formation of an irregular cut line. Another method for separating microelectronic packages from a common substrate includes using a circular saw. This method has proven to be very fast and the cuts are generally straight and reasonably smooth. However, this particular method produces debris, thereby requiring another process step to clean the separated microelectronic packages. Further methods include using ultrasonic knives having cutting edges which are symmetrical or asymmetrical in configuration. However, none of the various blades and cutting speeds yield an acceptable straight cut line. Routers have also proven to be somewhat effective at separating microelectronic packages from common substrates, however, the method typically leaves the encapsulant layer torn and frazzled.
Thus, there is a need for improvement in cutting apparatus and methods for efficiently and reliably separating microelectronic packages from a common substrate after they have been manufactured in a plurality of rows and/or columns on the common substrate.
SUMMARY OF THE INVENTION
In one preferred embodiment of the present invention, an apparatus for separating one or more microelectronic packages which are assembled to a common substrate includes a mechanical element which travels over a path defined on the common substrate. Each microelectronic package preferably includes one or more microelectronic elements, such as semiconductor chips, assembled to a section of the common substrate. The common substrate may include a flexible dielectric sheet, such as a flexible polymeric film having a plurality of conductive terminals thereon with a plurality of conductive traces integrally connected to and extending from the terminals. Typically, the microelectronic elements are electrically interconnected with the flexible dielectric sheet by electrically interconnecting the conductive traces with contacts on front faces of the respective microelectronic elements. Each microelectronic package may also include a plurality of compliant pads which space the chips from the common substrate and an encapsulant, such as a cured silicone elastomer between the chips and the common substrate.
The cutting apparatus preferably includes a mechanical element, such as a robotic arm, which travels over a path defined on the common substrate. The mechanical element may be connected to a moving element for moving the mechanical element over the defined path. The moving element may include an electro-mechanical element such as a robotic device or may include a series of cams. The cutting apparatus also includes a castor element pivotally mounted to the mechanical element for movement about a pivot axis and a cutting wheel rotatably mounted to the castor element, thereby providing a castoring action for the cutting wheel so that the cutting wheel follows the track of the mechanical element. In certain embodiments the castor element includes a pivoting shaft having an upper end pivotally mounted to the castor element and a lower end remote therefrom, the lower end including a connecting assembly for rotatably mounting the cutting wheel to the castor element. The lower end of the castor element may be angled with respect to the longitudinal axis of the shaft so that the cutting wheel trails the shaft as the shaft travels along the path defined over the flexible dielectric sheet, thereby further facilitating the castoring action of the cutting wheel. The cutting wheel is rotatably mounted to the castor element so that it is free to rotate about an axis of rotation and within a rotary plane. The axis of rotation of the cutting wheel is preferably offset from the pivot axis of the castor element. The periphery of the cutting wheel is sharpened to provide a cutting edge. In certain embodiments the cutting edge of the cutting wheel is formed symmetrically with res
Lerner David Littenberg Krumholz & Mentlik LLP
Rachuba M.
Tessera Inc.
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