Stone working – Sawing – Reciprocating
Reexamination Certificate
1998-09-10
2001-05-22
Hail, III, Joseph J. (Department: 3723)
Stone working
Sawing
Reciprocating
C125S021000, C125S016010, C451S435000, C451S309000
Reexamination Certificate
active
06234159
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a wire saw and a process for cutting shaped articles from a workpiece.
2. The Prior Art
Wire saws are used to cut a multiplicity of semiconductor wafers from a crystal in one operation. Wire saws of this kind have a wire web, which is formed by a sawing wire wound round two or more wire-guide rollers. The sawing wire may be covered with a coating. With wire saws having a sawing wire which does not have fixedly bonded abrasive grain, abrasive grain is supplied during the cutting operation in the form of a suspension or slurry. During the cutting operation, the workpiece passes through the wire web, in which the sawing wire is arranged in the form of parallel adjacent wire segments. The workpiece is made to pass through the wire web by a feed device which guides the workpiece onto the wire web or the wire web onto the workpiece. It is advantageous for the direction of movement of the wire segments to be changed constantly by periodically changing the direction of rotation of the wire-guide rollers, i.e., the oscillating operation, in order to allow the cutting slurry to be supplied from both sides. In this way, it is possible to produce wafers of improved geometry (TTV, warp).
The thickness of the cut shaped articles is fixed by selecting the distance between the parallel wire segments. This distance is limited as one moves toward smaller amounts by the fact that the sawing wire runs in grooves formed in the wire-guide rollers. The grooves require comparatively large amounts of space and cannot be arranged as close together as desired without impairing their wire-guiding properties. The thickness of semiconductor wafers should therefore not fall below a certain minimum thickness, even though this might be useful to conserve material. Furthermore, the wire saws described can generally only be used to produce disk-like shaped articles having parallel side faces.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a wire saw which can be used without the abovementioned limitations.
The invention relates to a wire saw for cutting shaped articles from a workpiece, having at least two wire webs made from sawing wire, which are used for cutting off the shaped articles. The wire webs lie one above the other at a distance h and are tensioned between wire-guide rollers. The wire webs are formed by one or more adjacent and parallel wire segments, wherein no wire segment covers any other wire segment congruently when the wire webs are viewed from above.
The invention also relates to a process for cutting shaped articles from a workpiece, using a wire saw having at least two wire webs made from sawing wire. The wire webs lie one above the other at a distance h and are tensioned between wire-guide rollers. The wire webs are formed by one or more adjacent and parallel wire segments. The shaped articles are shaped in a single operation by the action of the wire webs.
With the present invention, it is possible to divide crystals of semiconductor material into comparatively thin semiconductor wafers. However, it is also possible to produce shaped articles of different shapes from these crystals. These shaped articles may also consist of a different material. A wide variety of possibilities are available when selecting the shape of the shaped articles.
According to the invention, two or more wire webs are stacked one above the other at a short distance from one another. It is possible to move one or more of the wire webs before and during the cutting operation, if desired. The wire webs are intended to longitudinally displace and rotate the wire-guide rollers of the wire webs, while preferably remaining in the planes in which they are arranged while the movements take place.
Moreover, it is also possible for tilting movements to be provided, causing the wire segments to leave these planes entirely or partially. The rotation of a wire web can be achieved by rotating the wire-guide rollers that tension the wire webs. Wire segments can also be rotated through a small angle of rotation by axially displacing one wire-guide roller. Correspondingly, the wire segments of a wire web may also be tilted by displacing only one wire-guide roller of the wire web perpendicular to the plane of the wire web.
A wire web generally comprises a plurality of wire segments which lie parallel to one another and are tensioned between two wire-guide rollers and intersect the wire-guide rollers perpendicularly in the longitudinal direction. Furthermore, the invention also relates to wire saws with wire webs which are formed by only one single wire segment.
The wire segments in the wire webs lying one above the other are arranged in such a manner that at most only one wire segment of a wire web lies completely in a plane which perpendicularly intersects the planes of the wire webs. This means that the wire segments of different wire webs, when the wire webs are viewed from above, either lie parallel to one another or run at a certain angle toward one another or intersect one another. However, one wire segment never lies congruently above another wire segment. During the cutting operation, the workpiece is divided into the planned shaped articles in a single operation with the wire segments of the superposed wire webs engaging in the workpiece.
Wire saws according to the invention may comprise one or more roller systems, with one roller system comprising two or more wire-guide rollers around which a sawing wire is wound.
REFERENCES:
patent: 4903682 (1990-02-01), Kurokawa
patent: 5609148 (1997-03-01), Mitwalsky et al.
patent: 5628301 (1997-05-01), Katamachi
patent: 5839425 (1998-11-01), Toyama et al.
patent: 5944007 (1999-08-01), Miyoshi et al.
Berry Jr. Willie
Collard & Roe P.C.
Hail III Joseph J.
Wacker Siltronic Gesellschaft fur Halbleitermaterialien AG
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