US 2302024 A
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Description (OCR text may contain errors)
Nov, 17, 1942. F, 5655, JR 2,362,024:
METHOD OF CUT'I ING Filed May 23, 1941 2 Sheets-Sheet 1 F/G. I
QUARTZ p/szoa cm/c PLA 7E APPLY ELECTRODE COATINGS 0F SILVER SEPARATE ELECTRODE COATINGS INTO ELECTRICAL DISTINCT SECTIONS BY HEATED STYLUS RINSE IN HYPO BATH TOv REMOVE SILVER OXIDE WASH IN TAP WATER AND CARBON TETRA- CHLORIDE HN/SHED P/E ZOE LE C TR/C PL ,4 TE 0F D/V/DED ELECTRODE TYPE lNl/E/VTOR F A. 6055, JR
ATTORNEY Nov. E7, 1942.- A. sass, JR 2,302,024
METHOD OF CUTTING Filgd May 23, 1941 2 Sheets-Sheet 2 //5 82 FIG. 2
' lNVE/VTOR E A 6055, JR.
ATTORNEY Patented Nov. 17, 1942 UNITED STATES PATENT OFFICE METHOD OF CUTTING Frank A. Goss, Jr., Morris Plains, N. 1., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application May 23, 1941, Serial No. 394,780
' tallic coatings of objects.
Another object of the invention is to facilitate the production of piezoelectric plates.
A more specific object of the invention is to remove predetermined, narrowly defined portions of the silver electrode coating of a quartz piezoelectric crystal plate and to remove at the same -time any silver oxide formed during the process.
To facilitate the use of piezoelectric crystals in electrical circuits, it is common practice, as is well known, to provide a coating of suitable conductive material on one or more of the electrode surfaces of the crystal plate, the necessary circuit lead wires then being electrically connected to the coating by a suitable method. It has been proposed, for example, to provide a quartz piezoelectric crystal plate with electrode coatings of silver and to attach the lead wires directly to the electrode coatings by soldering; the present invention is particularly applicable to such a crystal plate.
In connection, with the preparation of certain types of piezoelectric crystal plates, for example the so-called harmonic crystals described in Patent 2,185,599 issued January 2, 1940, to W. P. Mason, it is desirable to divide the metallic coatings into a plurality of electrically distinct portions or patches. It has been proposed heretofore to divide the metallic coatings by means of an electrically energized stylus, the point of which is moved over the electrode coating along a predetermined path. A device of this nature is described in Patent 2,248,057 issued July 8, 1941, to W. L. Bond, entitled Electrical cutting device.
Use of a movable stylus arrangement of the nature referred to above offers many worthwhile advantages over other available methods of dividing the electrode coatings such as the acid etching method or the use 01' abrasive wheels. It has been found, however, that when electrode coatings of silver are subjected to the electrically energized stylus, silver oxide is formed in the out which establishes an undesirable low resistance connection between the "divided areas.
A feature of the present invention is a method 171-327) division of silver electrode'coatings by the electrically energized stylus method.
In accordance with a specific embodiment of the invention, the quartz piezoelectric plate, after the silver electrode coatings thereof have been divided by the electrically energized stylus method, is rinsed in a bath of photographer's hypo (sodium thiosulphate) in order to remove the silver oxide formed during the dividing process.
A complete understanding of the method contemplated by the invention as well as appreciation of the various valuable features thereof may be had by consideration of the subsequent detailed description in connection with the drawings, in which:
Fig. 1"is an operational diagram of one form of the method contemplated by the invention;
Fig. 2 is a perspective view of a suitable device for removing predetermined portions of the metallic electrode coatings;
Fig. 3 is a schematic of the electrical circuit I involved in the device of Fig. 2; and
Fig. 4 is a perspective, enlarged view of a third harmonic crystal, the coating of which has been divided into electrically distinct portions by the method contemplated by the present invention.
One method in accordance with the present invention whereby a piezoelectric plate of the divided electrode type is produced is outlined in four steps in Fig. 1. As a first step, electrode coatings of silver are applied to the quartz piezoelectric plate by suitable means, for example, the coatings may be applied by means of evaporation apparatus similar to that disclosed in Patent 2,241,228 issued May 6, 1941, to H. W. Weinhart, entitled Coating machine.
' As a second step, the electrode coatings are separated into the desired electrically distinct sections by suitable dividing apparatus such as, for example, the device illustrated in Fig. 2 which is generally similar to that disclosed in the W. L. Bond patent referred to above.
vAs a third step, the plate is immersed for a period of not less than one minute in a solution of photographers hypo preferably made up by dissolving one pound of plain hypo crystals (sodium thiosulphate) in two quarts of distilled water. Applicant has discovered that the hypo is'eifective in completely dissolving the silver oxide found in the dividing tracks but that it has no deleterious effect on the silver electrode coatings. Applicant has observed that it is particularly important that the hypo solution used in of removing silver oxide films formed during the the above process be free from contamination.
As a fourth and final step the plate is thoroughly washed, first in tap water and then in carbon tetrachloride.
It may occasionally happen that, during testing of the finished crystal plates, oxides may be formed in the dividing paths by the high testing voltages; in such event steps three and four of the above process may be repeated in order to dissolve and remove all traces of oxide.
It has been found that a process of the nature outlined above is particularly effective in dividing silver electrode coatings of quartz piezoelectric plates; the process is an economical one and entails no perplexing or uncertain operations and the resulting product is entirely satisfactory both electrically and mechanically.
Referring now to Fig. 2, there is illustrated a device which may be used advantageously in connection with step 2 of the process referred to above, i. e., the step of separating the electrode coatings into electrically distinct sections. The device illustrated comprises a rectangular base I I upon which are mounted two carriages I2 and I3, these carriages being movable with respect to the base and to each other.
Carriage I 2 is movable along slide I4 in a direction parallel to the longer axis of base II; feed screw I5 when rotated by crank I6 causes movement of this carriage backward or forward depending upon the direction of rotation of the U crank. Graduated scale 2| and index 22 serve to gauge movement of carriage I2 while rotation of crank I6 may be gauged by friction micrometer dial 23.
Carriage I3 is movable along slide 24 in a direcb tion generally at right angles to the direction of movement of carriage I2. Feed screw 25 when rotated by crank 26 causes movement of this carriage backward or forward depending upon the direction of rotation of crank 26. Graduated scale II and index 42 serve to gauge movement of carriage I3 while rotation of crank 26 may be gauged by friction micrometer dial 43.
Slide 24 is rotatable, within limits, with respect to base I I and slide I4 thereby varying somewhat the right angular relationship between the movements of the two carriages. Scale 44 serves to gauge this rotational movement of slide 24; the slide after angular adjustment may be rigidly clamped in position by means of a suitable bind- U ing lever (not shown).
Work table 5I is supported upon carriage I3. A piezoelectric plate 52, the electrode coating of which is to be divided, is shown on the work table being positioned within tray 53 which is mounted thereon. The plate is held in position on the work table by spring fingers 54 and 55; these fingers, as will be described subsequently, serve also as electrically contacting members and are specially designed both to hold the crystal firmly in place and to provide wide electrically contacting surfaces on the coating of the crystal plate. Spring finger 54 is mounted on block 56 which in turn is supported on rod 51; similarly, springfinger 55 is mounted on block H which in turn is supported on rod "I2. Springs 13 and I4, acting respectively through blocks 56 and II, supply a proper bias to spring fingers 54 and 55. Blocks 56 and II may be moved laterally along their supporting rods thereby adjusting the posi-- tion of the respective spring fingers. Rod 51 may be rotated in a clockwise direction against the bias of spring 13 in order to raise the spring finger 54 from its contacting position on plate 52; similarly rod I2 may be rotated in a counterclockwise direction in order to raise spring finger 55 from its contacting position.
An inverted U-shaped member 8I is mounted on base II and supports upright shaft member 82. Stylus supporting block 83 is, in turn, supported by upright member 82 through angular arms 84 and 85.
Stylus IOI of suitable hard material, for example a tungsten-carbon-cobalt alloy is positioned within a cylindrical sleeve I02 of suitable insulating material which sleeve, in turn, is positioned within stylus supporting block 83 being held therein by screw I03.
The stylus supporting assembly is normally held in the position illustrated through engagement of projecting tab I04 with grooves I 05 which is provided onthe upper surface of stop I06. Upon occasion, however, for example when a plate is being positioned on the work table, angle arms 84 and 85 may be raised slightly on upright shaft 82 in order to free tab I04 from groove I05 after which the stylus assembly may be rotated to a position away from work table 5I.
The electrical circuit involved is indicated schematically in Fig. 3 to which figure we will now refer for the moment. A suitable power source III, preferably a source of 60 volts alternating current, is connected through a suitable transformer II2 to leads H3 and H4. Applicant has observed that it is preferable to energize stylus IOI with voltage of a value that is as low as is consistent with a complete removal of silver in the division area. Use of voltage of a value higher than this ideal" value has been found to result in a rough edged division. For the thickness of silver electrode coatings normally specified at present for quartz piezoelectric plates, applicant has found that 2.5 volts is the ideal value. We will asume, therefore, that transformer H2 is designed to deliver 2.5 volts across the secondary winding and that the transformer is capable of delivering at least 10 amperes when connected to a 0.2 ohm load. The circuit across the secondary of transformer II2 may be traced through lead II3 to conductive stylus IOI, through the stylus to the conductive coating of silver on quartz' plate 52, through this silver coating to work table 5| of the divider mechanism and to lead II4.
Referring again now to Fig. 2, one external lead (II3 of Fig. 3) may be connected directly to stylus IN by screw H5 or it may be connected to binding post II6, which is floating, i. e., insulated from member BI and the rest of the machine, in which event a suitable local conductor would be run from binding post II6 to screw I I5. The other external lead (I I4 of Fig. 3) is connected to binding post I II which is electrically connected to support 8|. It might be pointed out here that all metal portions of the machine are bonded together electrically with the exception of stylus IOI which, it will be recalled. is insulated electrically from the rest of the machine by insulating sleeve I02. We have, therefore, (as indicated schematically in Fig. 3) one side of the circuit brought through stylus IN to the silver coatings of plate 52, through the coatings to spring fingers 54 and 55 which are in contact with said coatings, and through the spring fingers and other metal parts of the machine to binding post II! and the other side of the circuit.
In order to further describe the machine of Fig. 2 let us assume that it is to be used to divide the silver coating of quartz piezoelectric plate 52 in the mannerillustrated by Fig. 4. As shown in Fig. 4 the silver coating on the front surface of the plate has been divided into two electrically distinct sections by cutting a thin line across the coating, this line comprising three straight portions, I3 I, I33 and I34 extending in one direction joined by straight portions I32 and I35 which extend in a direction at right angles thereto. Referring again to Fig. 2, we will see just how such a line is cut.
Work table 5|, upon which plate 52 is carried, is first positioned so that the point of stylus I3I contacts the coating of the plate at the exact point where section I3I of the cut is to be started. The electrical circuit is completed and crank I6 is rotated in the proper direction to cause forward horizontal motion of carriage I2 and the assembly, including work table 5|, which moves therewith. As plate 52 is moved along under the point of stylus IDI, the electrode coating is burned away in the form of a thin, distinct line.
Upon completion of section I3I, rotation of crank I6 is stopped and crank 26 is rotated in order to cause the transverse movement of carriage I3 and the work table necessary to produce section I32. Upon completion of section I32, crank I6 is again rotated in the first direction to produce section I33 and so on.
It will be understood that in an instance such as described above where the two directions of 'the line sections to be out are at right angles to each other, the angular adjustment of slide 24 with respect to slide I4 is such that their longer axes are at right angles.
In the process described above care should be exercised to insure that the work table is in motion when the electrical circuit is completed in order to prevent the formation of silver islands at the point of contact of stylus and coating.
The piezo electric plate should be moved at a rate of approximately A" per second and a continuous pressure of the order of one pound should be applied to the stylus. The width of the cut" may well be regulated by varying the dimension of the point of the stylus which should be ground to a small flat circular surface perpendicular to the longer axis of the stylus. As an illustration, applicant has observed the following relationships between the dimension of the stylus tip and the width of the cut:
Diameter of stylus tip: Width of cut,
- millimeters .204 mm .32 to .35
.127 mm .22 to .25
.089 mm .12 to .15
After division of the electrode coatings as described above, plate 52 is then subjected to steps 3 and 4 of the process in order to remove any traces of silver oxide that may have been formed in the cuts and to thoroughly clean the plate.
While a specific embodiment of the invention has been described and illustrated, the invention is not, of course, limited in its application to such specific embodiment. The embodiment described of conducting material on a quartz plate, divid-' ing the electrode coating into electrically distinct sections by removal of certain predetermined portions of the conducting coating by means of an electrically energized stylus, and dissolving the oxides of the conducting material formed during the removal process.
2. The method of producing a piezoelectric plate of the divided electrode type which comprises the steps of forming an electrode coating of silver on a quartz plate, dividing the electrode coating into electrically distinct sections by removal of certain predetermined portions of the silver coating by means of an electrically energized stylus, and dissolving the silver oxide.
formed during the removal process.
3. In a method of producing a quartz piezoelectric plate of the divided electrode type which is productive of od of removing the silver oxide which comprises the steps of rinsing the plate after division of the electrode in a solution containing sodium thiosulphate and thereafter washing the plate with water and carbon tetrachloride.
4. The method of producing a piezoelectric plate of the divided electrode type which comprises the steps of forming an electrode coating of silver on a quartz plate, dividing the electrode coating into a plurality of electrically distinct sections by removal of certain predetermined portions of the silver coating by means of an electrically energized stylus, rinsing the plate in a solution of sodium thiosulphate and water and washing the plate in water and carbon tetrachloride.
5. In a method of producing a quartz piezoelectric plate of the type provided with divided electrode coatings of silver which is productive of undesired silver oxide, the method of removing the silver oxide without disturbing the required silver electrode coating which comprises the steps of rinsing the plate after division of the electrode in a material which is effective to dissolve silver oxide but which has no deleterious 'eifect on substantially pure silver and thereafter washing the plate in water and carbon tetrachloride.
6. In a method of producing a piezoelectric plate of the type provided with divided electrode coatings of a conductive metal which is productive of undesired oxides of said metal, the meth- A. GOSS, JR.
undesired silver oxide, the meth-.