US2763050A

US2763050A - Crystal unit inductance adjustment

Info

Publication number: US2763050A
Application number: US137243A
Authority: US
Inventors: David F Ciccolella
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1950-01-06
Filing date: 1950-01-06
Publication date: 1956-09-18
Anticipated expiration: 1973-09-18

Description

Sept. 18, 1956 D. F. CICCOLELLA CRYSTAL UNIT INDUCTANCE ADJUSTMENT Filed Jan. 6. 1950 w/o TH 0F s ur m 7, OF CRYSTAL BLANK WIDTH M) VEN 70/? D. E C/CCOLELLA A T TORNEV nited States CRYSTAL UNIT INDUCTANCE ADJUSTMENT Application January 6, 1950, S'eri'alNo. 137,243

1 Claim. (Cl. 29-4535);

This invention relates to the production of piezoelectric crystals having divided coatings and, more particularly, to a method and apparatus for improving the inductance adjustment of such crystals.

It is known that adjustment of the impedance of coated piezoelectric crystals can be made. by separating portions of the coatings from each other and by connecting, the divided sections in certain preferred manners. The factors involved in such impedance adjustments are. described in Patent 2,194,539, issued March 26, 1940, to J- F. Barry and H. G. Och, which. explains how a variety of circuit arrangements and crystalconstants can be. obtained by appropriate divisions of the coating and interconnections of the separate sections.

The means by which such separations between various coating areas were obtained in the prior art included methods of removing the coating, such as grinding with a sharp-bladed wheel or chemical etching, which were likely to change the characteristics of the crystalline material along the division path. For example, chemical etching frequently removed a portion of the surface of the crystal as well as the plating, and thus changedthe frequency or introduced spurious vibration. Similarly, grinding may disturb the crystalline structure adjacent the ground portion and thus change the vibrational characteristics of the crystal blank.

The present invention pertains to means and methods for adjusting the inductance and dividing; the coating which avoids interference with the surface structureof the crystal blank and reduces the number of steps required improduction. It contemplates removing: a desired width. of the coating along the intended line of division: by means of a fine air jet loaded with a mild abrasive and directed against the line of division through a carefully dimensioned mask.

Apart from the method used. to remove; the coating along the intended division line, the prior art has involved two steps in the adjustment of inductance in. splitplated crystals. The inductance adjustment has commonly been made commercially only in substantially rectangular crystals. In such crystals, usually the coating is divided along either the longitudinal or transverse axis of a major face or faces. The initial step has been that of making a transverse split near one end to" adjust the inductance, followed by a second step comprising the longitudinal or transverse dividing of the main coatings. Each of these operations has had to' be carried on with the use of a separate set of jigs and fixtures, and involved handling the crystal a number of times during theproduction. The inductance adjustment had to account for the change in inductance value which would subsequently be produced by the second step, that is, the longitudinal or transverse division of the main coatings.

The fact that two operations, both of which were held to the same tolerances in accuracy, were required raised the cost of production and led to a doubled possibility of rejection. The method hereafter described reduces atent 2. thisv possibility, and the cost, by requiring only asingle operation to accomplish both the splitting and inductance adjustment.

The present invention contemplates the attainment in one operation of the inductance adjustment and the longitudinal or transverse division of the coatings through careful predetermination of the adjustment in the width of the longitudinal or transverse division. This eliminates several steps in handling and several sources of inaccuracy, inasmuch as the entire adjustment tov the proper value of inductance is obtained during the single step, and it is unnecessary to allow separately, inv adjusting inductance, for the subsequent dividing operation, which might again change the inductance value of the crystal.

The method of providing the entire adjustment for inductance by controlling the. width of the longitudinal or transverse division in the coating is facilitated by the use of a fixture comprising a stand on which the crystal may be securely held, and a masking plate having the width of the aperture therein accurately predetermined.

When it is desired to adjust the inductance of a coated crystal blank, the proper width of coating to be removed in order to obtain the desired inductance is determined. From a group of masking plates having sharply defined apertures formed therein, in a series covering all necessary removal area widths, the proper masking plate is selected and placed over the crystal on its stand. A finely pointed air brush arranged to be fed by a mixture of air and a mild abrasive, such as finely powdered pumice, stone or pounce, is directed against the coating through the mask. It has been found that by this method, it is possible to remove the desired width of line accurately and quickly without in any way damaging or changing the character of the surface of the quartz immediately therebeneath.

The determination of the width of the division necessary to accomplish the desired change in the value of inductance has been determined empirically, and graphs made for the guidance of an operator which show the inductance step-up which will be obtained by removing any particular width of coating.

A primary object of the invention is to improve the technique of manufacturing coated crystals by combining in one operation the adjustment of crystal inductance, and the dividing of the coating.

A further object is the reduction of the cost of manufacture of crystals having divided coatings.

Another object is reduction of possible errors in acl justment by reducing the number of steps in which separateerrors may appear.

Yet another object is the elimination of the necessity for applying, in one step, a correctional factor to take account of alater step-in production.

A still further object is toprovide a simple and inexpem sive fixture for use in carrying out the dividing operation.

An additionalobject is to provide such a fixture in a form which will permit dividing a coating either longitudinally or transversely.

Another object is the provision of a form of fixture which will allow the division process to be accomplished on crystals to which connecting wires have already been attached, without disturbing the electrical continuitybetween the coating and the wires.

A further object is the improving of the technique of dividing the coating on. piezoelectric crystals Still another object is the provision of a method of dividing crystal coatings without deleteriously affecting the surface of the crystal.

An additional object is the provision of a method of inductance adjustment which is applicable to machinery in which the width of the masking aperture may be ice adjusted as needed over a continuous range, by an operator.

These and other objects are achieved by means of the embodiments illustrated and described hereafter. .lt-is to be understood that these embodiments are exemplary only, and it is contemplated that other forms and shapes of fixtures, other materials, and variations in the method of producing the divided coatings are included within the scope of the invention.

The invention may be better understood from the following detailed description with reference to the drawings in which:

Fig. l is an exploded perspective view of a stand for holding the crystal, a crystal blank and a masking plate, separated from their normal assembled position for clarity in illustrating the relation of the parts;

Fig. 2 is a fragmentary sectional view taken along line 2-2 of Fig. l to show the masking plate in cross section;

Fig. 3 is a top elevation of a coated crystal in which the inductance has been adjusted and a longitudinal division in the coating made by the use of the method and apparatus hereinafter described.

Fig. 4 is a perspective view of a fixture for use in practicing the invention; and

Fig. 5 is a graphical representation showing the change in inductance as a function of the width of the division in terms of percentage of the width of the crystal blank.

Referring now to Fig. l of the drawings, there is disclosed a stand 1 comprising a bed plate 2 and supporting legs 4. Bed plate 2 is longitudinally and transversely grooved at 5 and 6 respectively to receive a coated crystal 7 in either of two alternative positions. Alignment pins 9 extend upwardly from the surface of plate 2. A cover plate 10 is aligned properly on the stand 1 by bores 11, which cooperate with and fit over pins 9. Plate 10 fits snugly over the crystal 7, and serves by virtue of its weight to retain the crystal in place during the dividing operation. The cover or mask plate 10 is provided with a beveled slot 12 carefully machined to have exactly the width of opening desired. It is to be understood that a complete fixture set includes a number of plates 10, each having a slot 12 of different width and the slot widths being graduated to cover the necessary range by small increments. Slot 12 is cut parallel to the longitudinal axis of plate 10, so that when a crystal is held in recess 5, a longitudinal division of the coat ing may be obtained, and when the crystal is set in recess 6, a transverse division may be produced.

The masking plate 10, as shown in detailed section in Fig. 2, has, in addition to the slot 12, a number of bores 13, extending along the transverse midline of the plate. The bores 13 are recessed or countersunk at 14 on the underside of the mask to permit use with blanks to which connecting and supporting leads 15 have already been attached. These recessed portions 14, which may be conical as shown in Fig. 2, provide clearance between the mask and the areas of attachment of the connecting wires. Where such means for connecting the crystal in the circuit are to be used, the inductance adjustment is normally made after the connecting wires have been attached to the crystal plate.

The techniques commonly used for the attachment of ered temporarily by strips of a pressure-sensitive or ad hesive tape 16. Clearance for the connecting wires ex tending from the lower side of the crystal as it rests on bed plate 2 may be obtained by providing large clearance bore 17 centrally of the bed plate.

A considerable variation in crystal length is possible with the stand and cover shown in Fig. l, as indicated by the dotted outline 8. The maximum length of a particular division line is of course the length of the slot 12. lt'will be obvious, however, that with varying widths and thicknesses of crystals, additional means must be used to obtain proper alignment and a snug fit between the crystal andthe masking plate. ,7

An adapter'20 suitable for this purpose is shown in Fig. 4, and it is contemplated that it-will be used with a stand similar to the type shown in Fig. 1, but in which the bed plate 2 is substantially thicker, and the recesses 5 and 6 correspondingly deeper and wider than in that showing. I

There will befrequired a set of adapters, 20, one for each width and thickness of crystal to be processed. All the adapters in the series will have identical outer dimensions in width 21 and thickness 22, so they may fit interchangeably in the stand recesses 5 and 6. Each will have the wires involve a contact area greater than the diameter of the wire. Whether this increased area is obtained by upsetting the wire end, using a relatively large amount of solder or cement, or by other means, it is desirable to protect the bond. Different connecting wire spacings are provided for by making a series of clearance bores a central bore 26 for the accommodation of connecting leads.

Each, however, will have a difierent combination of seat width 24 and seat depth 25, tailored to fit the anticipated dimensions of the different crystals to be processed, so that the mask will fit snugly against the crystal surface, and the crystal will be accurately aligned with the intended division line.

The actual removal of the coating along the intended line of division is then accomplished by directing a fine air jet, loaded with a pumice or other mild abrasive, against the mask along the aperture 12.

An air gun of the type known commercially as the Paasch air brush is satisfactory for this use, although any other means of providing a concentrated air jet may be used.

A crystal blank 7 is shown in Fig. 3 after the coating has been removed along the intended division line 27.

By eliminating the separate inductance and splitting operation, a saving is achieved in manufacture which amounts to about 50 per cent of the present cost of splitting and adjusting the inductance, and the use of prepared graphs to select the width of plating to be removed simplifies and expedites the operation, especially since this eliminates the necessity for providing in the adjustment of inductance step for the change in inductance produced by the longitudinal splitting operation. In prior methods, this was of necessity an approximation, since the width of the inductance adjustment determined the length of the longitudinal plating division, and hence in turn introduced a possible second order error in the final provision for inductance adjustment.

In processing two groups of Y-cut EDT crystals by the method herein disclosed, it was found that in one group which required an inductance step-up of 9 per cent, the final inductance measurements indicated that all units in'the group were within -1.5 per cent of the desired normal inductance. The second group which required an inductance step-up of 20 per cent gave a final measurement within :L-Z per cent of the desired normal inductance for all of the units in the group.

It will be apparent that the method described of adjusting the inductance by a single step could be applied to machinery in which the width of the mask slot could be easily adjusted by an operator to provide the desired change in inductance so that the method is well adapted to mass-production technique.

What is claimed is:

The method of simultaneously dividing the metallic electrode coating and adjusting the inductance of an e ect o s tsd P zoel ct sr alw p s h d n all of the metallic coated area of a major face of a piezoelectric crystal except for a strip across the full length of the metallic coating, said strip of a Width directly proportional to the inductance step up desired, and directing a stream of compressed air and mild abrasive toward the exposed portion of the metallic coating to remove said exposed portion Without interference with the underlying crystal structure.

References Cited in the file of this patent UNITED STATES PATENTS 6 Fritsche Dec. 19, 1933 Beard Oct. 22, 1935 Barry Mar. 26, 1940 Prange Oct. 20, 1942 Lindenmeyer Aug. 31, 1943 Wolfskill Apr. 4, 1944 Fruth Oct. 16, 1945 Williams June 10, 1947 Thompson Sept. 28, 1948 FOREIGN PATENTS Australia Feb. 21, 1946