US3031804A - Ultrasonic slicing tool and method - Google Patents

Description

y 1962 c. J. THATCHER ETAL 3,031,804

ULTRASONIC SLICING TOOL AND METHOD Filed June 2, 1958 2 Sheets-Sheet 1 INVENTOR. C.J.Thofcher. E. Q. M0 5 e s.

I I By ATTORNEY.

y 1962 c. J. THATCHER ETAL 3,031,804

ULTRASONIC SLICING TOOL AND METHOD Filed June 2, 1958 2 Sheets-Sheet 2 IllIllllIll||||IlllllllllllllllllllmllllllllllIll llllflllmlllllllllllllIIWIIWIJIWIIIlliifllii |nmmmunmummnnmu INVENTORS C. J. Thatcher .Q- M oses- MMA @wM/w;

ATTORNEY.

United States Patent 3,031,304 ULTRASUNHC SLHQBING T001, ANT METHOD Charles 3. Thatcher, 132 E. lilth and Edmund Quincy Moses, 11 W. 42nd gt, both of New York, Filed June 2, 1958, Ser. No. 739,335

8 Claims. ('Cl. 51-59) This invention relates to a means and method for producing thin uniform slices or dices from hard or brittle material, such as semiconductors or quartz, by the use of ultrasonic cutting. In recent years it has often been desirable to produce a large number of thin, fragile slices of work pieces of hard material, a particularly important example of this being the cutting of thin slices of germanium or silicon, or other hard and brittle metals from elongated ingots or crystals including quartz or the like, for use in transistors, frequency stabilizers, or other electrical devices. As an example, in the manufacture of transistors, single crystal ingots of germanium have to be cut into standardized even slices on the order of 0.01 thick, these slices being later diced into small squares or pellets for use in the transistor. It is important to have the slices of uniform thickness and also to cut as many slices as possible from a block or ingot of the germanium, thereby avoiding waste of the costly material.

The usual practice has been to use diamond saws for forming these slices but industrial diamonds are limited in supply, particularly during wars, and expensive, and furthermore, even using saws of the minimum thickness there is a very substantial waste of material, both of the work and diamonds. It has also been attempted to slice hard materials of this character by means of ultrasonic tools having a plurality of blades, but one difficulty has been to remove the detritus from the locus of abrasion and to eject the slices themselves from between the embracing blades after they were cut. The slices are very fragile and easily broken and a very small clearance exists between the slices and the cutting blades. The U.S. Patent to Thatcher 2,774,194 illustrates an improved tool for this purpose, one form of the tool in FIGS. 8, 9 and showing the use of a plurality of blades separated by spacers. These blades are mounted so that they cause scavenaging of the detritus and also that they may be separated if necessary and thereby facilitate the removal of the slices. Moreover, the cutting blades and spacers may be so moved relatively so as to eject the severed slices intact from the tool blades.

The present invention contemplates a method of slicing a hard and brittle material in which a series of closely parallel wires or narrow blades are used as the cutting elements; and these are mounted in such a way that they are passed entirely through the block or ingot to be sliced thereby freeing them entirely from the slices once the cutting operation has been completed. Preferably the block or ingot is mounted on a supporting table by means of an underlying layer of paraffin, wax or a plastic. The cutting elements of the cutting tool are mounted in the tool body in such a manner that a clear space is provided above, around and behind the cutting elements of such size as to permit the cutting elements to be passed cross-wise entirely through the block or ingot (usually vertically) while leaving the slices formed entirely free from contact with the body of the tool and the cutting elements. Thus the ingot will be formed into a plurality of slices which may be either detached or temporarily supported by the Patented May 1, less "ice paraffin, wax or plastic, which is then melted or chemically dissolved permitting the slices to be removed Without any interference whatever from the cutting elements.

By the use of the method and tool described not only is the removal of the slices from the tool Without breakage made easy but during the cutting operation it is possible to flow over the slices and cutting elements an ample supply of a slurry containing the necessary abrasive ingredients which also is free to fiow under and out from between the slices so as to instantly remove all detritus. Thus efective and rapid cutting is possible. Also an ample sup ply of the slurry may be utilized to keep the cutting ele ments cool. Prior to recent inventions of C. J. Thatcher (e.g. US. No. 2,804,724), ultrasonic cutting has been so slow that it was claimed to be a cold process, no cooling being deemed necessary. However, by the utilization of the improved patented methods whereby all detritus is removed, such rapid cutting has become possible as to cause a substantial generation of heat. This can be taken care of by providing a copious supply of cooling liquid, preferably in the form of a simple flow of the slurry over the horn amplifier or the holder of the cutting elements.

In the accompanying drawings illustrating preferred forms of the invention and modes of practicing same,

FIG. 1 is a side elevation showing an adjustable sup porting table with the ingot or work piece mounted thereon above which is mounted a transducer of the magneto striction type of piezoelectric type carrying an energy amplfying horn at the lower end of which is mounted a tool holder carrying one form of the tool;

FIG. 2 is an end elevation of the tool shown in FIG. 1;

FIG. 3 is a perspective view of the tool shown in FIGS. 1 and 2;

FIG. 4 is a side elevation of a modified form of tool having narrow bars as cutting elements;

FIG. 5 is an end elevation of the tool shown in FIG. 4;

FIG. 6 is a side elevation similar to FIG. 1 showing a modified form of tool;

FIG. 7 is an end elevation of the tool shown in FIG. 6, and

FIG. 8 is a plan view of the underside of the tool shown in FIGS. 6 and 7.

Referring to the drawings in detail, a transducer is illustrated diagrammatically at 10. Atfixed to this is the head of the energy amplifier 12 shown of a conventional horn shape. Secured to the lower end of the horn is a tool head 14 having a threaded hole 16 therein to screw it on a stud at the smaller end of the horn and having four spaced legs 18 so as to provide a longitudinal passage 20 and a transverse passage 22 between the legs. in the form of the invention shown in FIGS. 1 2 and 3, the cutting element comprises a plurality of stretched Wires 24 which may be of stainless steel, Monel metal, or other suitable metal. A convenient way of mounting the wires is that shown which comprises a pair of spools 26, one mounted between each of the pairs of legs and which are uniformly grooved at 27 as by means of having a fine thread cut therein, each cutting element 24 forming part of a continuous wire winding about the spools. The threads or grooves keep the wires properly and uniformly spaced so that the spacing between the cutting elements 24 will be just wide enough to form slices of the proper thickness. Means are preferably provided for applying uniform tensioning to the wires. As shown one of the in spools is mounted on a bolt Ell passing through eccentric bushings 23. The bushings 28 are mounted in holes in a pair of legs 18 and may be rotated by heads 32 and held firmly in adjusted position by set screws 34. By rotating the bushings more or less it can be seen that a sufficient degree of tension may be applied to the wires.

For locking the wires firmly to the spools so as to pre vent loosening of the continuous wire in case of a breakage, suitable means are provided such as the transverse members 36 carrying fibre blocks 38 which are pressed firmly against the wires on the spool by means of clamping screws 44 The illustrations of the tool body, the legs or holders for the cutting elements, etc. are intended only to suggest one form thereof; but they and all parts of the slicing tool may of course be altered in shape, size and configuration and in accordance with the laws and practice of ultrasonic technology. Instead of the head and legs being straight sided and with angular corners as shown, the head of the tool may be round or oval and the legs conical or tapered cylinders 18a (FIGS. 6, 7 or 8); and the legs may be separate from the head and attached thereto by suitable countersunk screws 80 or otherwise, whereby assembly of the wire of strip cutting elements is facilitated.

The work piece or ingot 42 may be carried on an adjustable table 44. This may be adjusted by screws or otherwise, a convenient mechanism for forcing the ingot upwardly against the cutting elements consisting of a lever 4-6 having a slotted end 48 engaging a pin 50, the lever being pivoted at 52 and having an adjustable weight 54 on its end. The ingot 42 may obviously be of any shape but it is shown as a conventional elongated cylindrical single crystal block. This may be mounted upon the table 44 so that the slices will be cut across the cylinder. A suitable method consists in mounting the ingot on a supporting block or body 56 of hard Wax such as hard parafiin or sealing wax or a low melting point plastic material.

The transverse space 22 between the legs of the tool body is sufilciently large to receive at least one end of the entire ingot or work piece. The spools 26 are also of a greater diameter than the maximum diameter of the work piece; wherefore the cutting elements 24- may pass entirely across and through the work piece without bringing the upper or return runs of the wire indicated at E8 into contact with the upper surface of the ingot or work piece. With this construction it is possible for the work piece to be moved, as slices, past and between the cutting elements 24 which pass down through the work piece and into the part of the wax or plastic holding material 56, thereby completely severing the work piece into a plurality of uniform slices which may be either temporarily retained by adhesion to the wax or plastic body 56 or become entirely detached and floating in the slurry. The slices are readily detached if necessary by heating the wax or chemically dissolving the same so as to separate the slices from the wax. The slices can now be taken right out from the tool without any interference as heretofore from the cutting elements which have been passed completely through the ingot and have no contact therewith. By this method and means slices may be rapidly cut and removed without any loss from breakage. Also great uniformity in the thickness of the slices is attained because the narrow cutting elements pass into and through the ingot or work pieces and the detritus of the kerfs which are formed thereby is continually flushed out as the cutting proceeds by the forced flow of slurry. As the cutting elements are narrow and are supported between the legs of the tool body which is open, an ample supply of slurry may be flowed over the work piece at all times through a suitable jet, forcing the slurry into the upper part of the space between the legs of the tool body and around and underneath the cutting elements. One such method of supplying the slurry is by means of a hole 60 11 passing through the tool holder 12, the slurry being forced into this passage through a pipe s2.

FIGS. 4 and 5 show a modified construction of the tool in which the cutting elements comprise a plurality of thin strips '76 which may be of stainless steel or other metal and which are provided at their ends with eyes 72 fitting transverse bolts 74. The strips are separated by spacers '76 also having eyes and of suitable thickness so as to space the cutting element far enough apart to produce slices of the desired thickness. The cutting elements or blades itl may be placed under tension if desired, preferably by the use of eccentric bushings 25 as described above. The blades 7% are narrow enough so as to leave the transverse passage 22 through the tool body unobstructed for a height greater than the vertical dimension of the ingot or Work piece. Thus the cutting elements may pass entirely through the ingot leaving the slices free to be removed without interference.

While certain specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.

What is claimed is: V

1. A method of producing thin slices of hard brittle materials by ultrasonic abrasive cutting which consists in supporting a work ingot piece below cutting tool means, flowing an abrasive slurry thereover, ultrasonically vibrating a plurality of parallel narrow cutting elements and passing the same through and entirely across the work piece so as to free themselves from the slices formed by their passage through the Work piece scavenging the detritus as formed from the abrasion locus and removing the slices back of the cutting elements without returning the cutting elements back through the cuts formed between the slices.

2. A method of forming a work piece of hard brittle material into a plurality of thin uniform slices which comprises mounting the work piece in a body of relatively soft, removable material, ultrasonically vibrating a plurality of narrow parallel cutting elements held in a tool body in such manner as to provide a free space. between the back of the cutting elements and the tool body of suihcient dimensions to receive the entire ness of the piece, passing an abrasive slurry and the cutting elements entirely through and across the work piece so as to scavenge the abrasion locus and to form the work piece into a plurality of thin slices which are temporarily held only by the removable material and then separating the slices from the removable material and removing them from within the tool body back of the cutting elements.

3. An apparatus for ultrasonically cutting fragile thin slices of hard material comprising a means for producing ultrasonic vibrations, a tool mounte thereon comprising a plurality of narrow parallel cutting elements, sup ported on the tool under longitudinal tension in such manner as to provide a free space between the backs of the cutting elements and the tool body of sufficient dimensions as to receive the entire work piece and means for moving the Work piece and tool relatively to one an other for a suilicient distance to pass the cutting elements entirely through the work piece so that the sliced work piece is received within the tool body back of the cutting elements and free therefrom.

4. An apparatus for the ultrasonic slicing or dicing of hard and brittle material comprising a tool body, having a transverse space therethrough and cutting elements extending across the front of such space so as to leave the space within the tool body back of said cutting elements unobstructed, said cutting elements comprising a plurality of thin parallel members held under longitudinal tension, and means for producing ultrasonic vibrations between the cutting elements and the material to be sliced.

th ck 5. A construction as claimed in claim 4 in which the cutting elements are stretched Wires.

6. A construction as claimed in claim 4 in which the cutting elements are thin strips of metal.

7. A construction as claimed in claim 4 in which the cutting elements are held tight by bolts mounted in eccentric bushings by which the tension on the cutting elements may be adjusted.

8. A construction as claimed in claim 4 in which means are provided to introduce a stream of liquid abrasive slurry into the space within the tool body back of the cutting elements to scavenge detritus from the locus of abrasion.

References Cited in the file of this patent UNITED STATES PATENTS

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