US 3453711 A
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Description (OCR text may contain errors)
July 8, 1969 c. MILLER 3,453,711
. METHOD OF CONNECTING TOGETHER A PLURALITY OF TRANSDUCER SEGMENTS Filed Aug. 24, 1966 Sheet I of 2 0H Transducers IPolurizution L J J 1 i J 46 54 58 42 50 92 82 e as 84 \V I I I r I 4 I I I I 70 I 5 &\\
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' Irving 6. Miller 44%, i
July 8, 1969 c, WLLER 3,453,711
METHOD OF CONNECTING TOGETHER A PLURALITY OF TRANSDUCER SEGMENTS Filed Aug. 24, 1966 Sheet ,8 of 2 PROVIDE SUBSTRATE, TRANSDUCERS, APERTURED MASK AND LEAD WIRES APPLY A PLURALITY OF FIRST ELECTRODES TO SUBSTRATE BOND A TRANSDUCER TO EACH ELECTRODE APPLY A BACK ELECTRODE TO EACH TRANSDUCER PLACE APERTUFIED MASK OVER BACK ELECTRODES OF THE TRANSDUCERS DEPOSIT AN ELECTRICALLY CONDUCTIVE FILM THROUGH APERTURES ONTO ELECTRODES REMOVE APERTURED MASK 1 ATTACH LEAD wIREs To INPUT AND OUTPUT ELECTRODES F g. 6 INVENT OR.
Irving C. Miller BY f ga w fi A 7' TORNE Y United States Patent O METHOD OF CONNECTING TOGETHER A PLURALITY OF TRANSDUCER SEGMENTS Irving C. Miller, Bradford, Pa., assignor to Corning Glass Works, Corning, N.Y., a corporation of New York Filed Aug. 24, 1966, Ser. No. 574,697 Int. Cl. B01j 17/00; H01l 1 5/ 02; H01c 7/08 U.S. Cl. 29--25.35 10 Claims ABSTRACT OF THE DISCLOSURE A method for making improved connections between a plurality of adjacent, but separate, transducers or transducer segments. The transducers are bonded to a substrate by electrodes which extend beyond the transducers so that terminals can be connected to the extended portions of the electrodes. Adjacent transducers are interconnected by first applying a layer of insulating material therebetween and thereafter applying an electrically conductive material over the insulating material so that it contacts electrodes on the surface of the adjacent transducers.
The word transducer will hereinafter be used to designate a device made from a piezoelectric material; that is, a material which is capable of transforming electrical energy into mechanical energy and which, conversely, is capable of transforming mechanical energy into electrical energy. Transducers may be made from naturally occurring or artificial-1y produced crystalline materials. Titanates, zirconates, metaniobates and the like, in combination with various metal earth elements, are numbered among suitable artificial transducer materials. Broadly, such materials are known as ferroelectric ceramics. Crystals of Rochelle salts, quartz and the like are found to be suitable, naturally occurring, transducer materials. In recent art, artificially produced transducer materials have assumed precedence over the natural crystalline materials, for reasons of improved efficiency, economy, reliability, and reproducibility.
A transducer must be electrically polarized before being placed in service. Such polarization may be accomplished by several methods well known to one familiar with the art. One such method, for example, is to apply a direct current to a pair of electrodes deposited on opposite broad faces of a slab of piezoelectric material, thereafter slices may be removed from the slab and transducers fabricated therefrom.
In use, transducers must carry a pair of electrodes which serve as electrical signal input or output means. Various methods of forming such electrodes are known, and, ordinarily, each electrode comprises one or more thin, highly conductive, metallic films deposited on a substrate of piezoelectric material. One method of forming electrodes is taught in U.S. Patent No. 3,206,698 in the name of Richard E. Allen and George M. Deegan.
A transducer, with electrodes formed thereon, is usually bonded to a body of material through which it is desired to transmit, or from which it is desired to receive, an acoustic energy wave. Such a body, for example, may be a solid, plate type, acoustic delay line, with the trans ducer bonded to a facet there-of, but is not necessarily limited thereto. Commonly, transducer electrodes play a part in the bonding process, which part is also described in the above-identified patent. Briefly, an electrode is used to for-m a portion of the mechanical bond between a transducer and a substrate. Electrical excitation of the transducer is provided by attaching a polarized signal source, through a pair of signal input terminals, to a corresponding pair of electrodes on the transducer. In some instances, it is desirable to connect a plurality of transducers in electrical series with each other and with the input signal source. For example, U.S. Patent 3,150,- 275, in the name of C. J. Lucy, teaches a sectional, series connected transducer which provides improved signal transfer capabilities, together with higher eificieney, lower input terminal capacitance, and increased radiation resistance.
In a power transducer, such as may be used on a photoelastic delay line, power and eificiency at the transducer are of prime importance. Since acoustic backings result in up to 50 percent power loss in the backing itself, which power loss is converted to heat that may deleteriously affect the components, such power transducers are backed by employing a thin metal film back electrode without any other backing material thereby enabling virtually all of the energy being transmitted to be launched into the delay line medium and be utilized. When a plurality of such transducers have been employed it has been necessary to interconnect them by soldering wires to the thin metal film electrodes. Such a solder forms spot acoustic backing thus resulting in lower transducer efiiciency, heating and the like, in the area of the spot. When a plurality of connections have been made the effect is multiplied. Other transducers, however, have been intentionally backed when power transmission is of secondary importance to performance parameters such as band width, pulse characteristics and the like.
By acoustic loading of a transducer is meant the mechanical impedance seen by either surface thereof. By acoustic backing is meant a material applied to a transducer, which material has the property of absorbing energy.
In prior art transducer connection, the connecting wires provided weak mechanical connections and required careful handling. Furthermore, in power transducers the solder would form spot backings that produced heating and resulted in transducer inefiiciency as heretofore described. In addition, with respect to some transducers, such connections would be costly, result in an unreliable product, and have an impractical input impedance.
It is therefore an object of the present invention to provide a method whereby the difficulties and problems hereinabove briefly described are overcome.
Another object of the present invention is to provide a means for eificiently interconnecting transducers, or segments thereof, to each other and to a signal source.
Still another object of the present invention is to reduce spot loading of transducers.
A further object of the present invention is to provide a means and method of coupling electrical energy to a transducer without causing large energy losses therein.
A still further object of the present invention is to provide a method for connecting together a plurality of transducer electrodes in a predetermined pattern,
These, together with other objects, features and advantages of the present invention will be more apparent from the following detailed description and drawing.
The present invention is a method of electrically connecting together in a predetermined manner a plurality of transducer electrodes comprising the following steps: providing a suitable substrate, and a plurality of transducers; applying to said substrate a plurality of first electrodes, in adjacent spaced-apart relationship, said electrodes including a signal input electrode and a signal output electrode; bonding a transducer to each of said first electrodes and to said substrate; applying a back electrode to each of said transducers; depositing an electrical insulating material between adjacent transducers to electrically separate the electrodes of one transducer from the electrodes of an adjacent transducer; selectively depositing an electrically conductive material onto portions of the electrodes and the insulating material thereby forming electrical connections between pairs of the electrodes in said predetermined manner; providing a pair of lead wires, and thereafter attaching one lead wire of said pair of lead wires to said input electrode and the other lead Wire to said output electrode, thereby forming an array of electrically connected transducers.
FIGURE 1 is a fragmentary plan view of a pair of transducers bonded to a suitable substrate and electrically connected in series according to the present invention.
FIGURE 2 is a fragmentary, longitudinal cross section view of the delay line and transducers taken along line 2--2 of FIGURE 1.
FIGURE 3 is a plan view of a delay line facet showing a plurality of transducers bonded thereto and electrically connected together in series in accordance with another embodiment of the present invention.
FIGURE 4 is a lateral cross section view of the delay line and a transducer taken along line 44 of FIG- URE 3.
FIGURE 5 is a fragmentary, cross-sectional view of a pair of transducers bonded to the facet of a delay line and electrically connected together in parallel in accordance with a further embodiment of the present invention.
FIGURE 6 is a flow diagram of the method of connecting together a plurality of transducers in accordance with the present invention.
In FIGURES 1 and 2 transducers 12 and 14 are bonded to a suitable substrate, such as facet 15 of delay line 16, by means of facet electrodes 17 and 18. Back electrodes and 22, partially cut away in FIGURE 1 to reveal transducers 12 and 14 beneath, are electrically connected together by means of an electrically conducting film 24. Signal terminals 28 and 30 are attached to electrodes 17 and 18 by means of lead wires 32 and 34 respectively. As may be seen in FIGURE 2, transducers 12 and 14 are separated by electrical insulating material 26 which serves to electrically separate the transducers and also to support conducting film 24, which electrically connects the electrodes together. Lead wires 32 and 34 are attached by any convenient means, such as soldering for example, to facet electrodes 17 and 18 respectively.
The transducers may be made from suitable piezoelectric materials, such for example as one of the lead zirconate-titanate ceramics hereinbefore briefly described. Delay line 16 may be a solid, plate type delay line made from glass or fused silica, for example. Suitable transducer and delay line materials may be readily selected by one familiar with the art. Facet 15 may be a signal input facet or a signal output facet of the delay line. Facet electrodes 17 and 18, and back electrodes 20 and 22 are formed from one or more thin layers of metal film such as has been described in the aforementioned Allen-Deegan patent. In addition, the back electrodes may have acoustic energy absorbing material bonded thereto for improved transducer response, as is well known to one familiar with the art.
Electrical insulation 26 is deposited on facet 15 of delay line 16, filling the gap between adjacent transducers 12 and 14. Electrical insulation 26 is a material which adheres to the delay line and to the transducers, is easily applied, and provides a solid mechanical connection between the transducers. Examples of suitable insulating materials are organic coatings and lacquers, which may be applied by spraying, painting, flowing and similar methods, and which will dry in air at room temperature or upon baking at low temperature into tough, adhesive films. It has been found that a preferable material for electrical insulation is an organic lacquer marketed by Bee Chemical Company, Lansing, 111., and known as Logo Clear ET 179 or M 5972. This particular material is especially suitable for use with the process of vacuum depositing metal films, since it does not outgas in vacuum and metallic films readily adhere to it. It may be applied as a thin sprayed coating, but is preferably applied by painting, to provide a relatively thick base for the vacuum evaporation of thin metallic films thereon.
Electrically conducting film 24 may be made from at least one layer of highly conductive material such as metal for example, but is preferably made from a plurality of metallic layers vacuum evaporated on portions of back electrodes 20 and 22, and on the surface of electrical insulation 26, thereby electrically connecting electrode 20 to electrode 22.
Examples of suitable metals for electrically conducting film 24 are gold, aluminum, combinations of nickel and chrome, and layered combinations thereof which provide high electrical conductivity and resistance to atmospheric oxidation. Signal input terminals 28 and 30 are connected in series with transducers 12 and 14 by means of lead wires 32 and 34, facet electrodes 17 and 18, back electrodes 20 and 22, and electrically conducting film 24. Lead wires 32 and 34 may be soldered directly to their corresponding facet electrodes.
In FIGURE 3 a plurality of back electrodes including electrodes 40, 42, and 44 are series connected in a particular pattern on transducers which are bonded to delay line 46 by means of conducting films 48, 50, and 52 and facet electrodes 54, 56, and 58. Lead wires 60 and 62 are attached to the input and output electrodes respectively. Dotted line 63 illustrates the current flow path between input lead wire 60 and output lead wire 62 through the various electrodes and transducers.
In FIGURE 4 back electrode 42 is bonded to transducer 43 which in turn is bonded to delay line 46 by means of facet electrode 54. Conducting film 50 is applied by vacuum evaporation, for example, to back electrode 42, electrical insulation 64, and facet electrode 56, thereby electrically connecting back electrode 42 of transducer 43 to facet electrode 56 of an adjacent transducer. As will be immediately apparent by comparing the embodiment of FIGURE 4 with the embodiment shown in FIGURE 2, the electrical connection of FIGURE 4 provides another means of series connecting transducer segments. Instead of electrical insulation 64 filling a gap between transducers, it provides a sloping surface, or ramp, to support an electrically conductive film such as film 50, for example, which joins the back electrode of one transducer to the facet electrode of an adjacent transducer.
FIGURE 5 illustrates a pair of transducers 70 and 72 electrically connected in parallel, and bonded to delay line 76. A common facet electrode 74 is bonded to facet 75 of delay line 76. Signal input lead wire 78 is attached directly to facet electrode 74 at point 80. Back electrodes 82 and 84 are bonded to transducers 70 and 72 respectively. Electrical insulation 86 mechanically joins, but electrically insulates, the transducers, providing a suitable base for application of electrical conducting film 88 which connects back electrode 82 to back electrode 84. Output lead wire 90 is attached to back electrode 82 at point 92 by any convenient means such as soldering, for example. It should be noted that when desired, electrodes 82 and 84 as well as film 88 could be of integral construction.
Series connection between transducers in the manner of the present invention has several major advantages which may be divided into mechanical advantages and electrical advantages. It will be seen in FIGURES 1, 2 and 3, for example, that the lead wires are attached directly to the facet electrodes bonded to the delay line, rather than to the back electrodes bonded to the more fragile transducers. One distinct mechanical advantage is that the lead wires are more solidly attached, are only two in number, and at their points of attachment do not provide spot loading of the transducers. Heretofore, it has been necessary to connect electrodes together by soldering connecting lead Wires therebetween, thus creating the problem of spot loading at each point of attachment to a back electrode. The reliability of electrical and mechanical connection between transducer electrodes is enhanced by the present invention. A further mechanical advantage lies in the fact that a plurality of conducting films may be applied simnltaneously between a plurality of electrodes, in a predetermined pattern, by vacuum evaporating a metallic film through, for example, a suitably apertured mask whose apertures correspond to the desired location of the conducting films.
Electrically, a series connection between transducer electrodes effectively lowers the terminal capacitance and effectively raises the terminal impedance of a delay line transducer as will hereinafter be described in a typical example. It is not intended that the present invention be limited to series connections, however, since parallel con-= nections may be desired for other purposes.
As shown in the flow diagram of FIGURE 6 which illustrates the steps of the method of the present invention, there is provided a delay line having a suitable facet to receive a plurality of transducers, and a pair of lead wires. A plurality of electrically conducting facet electrodes are deposited on the delay line facet in adjacent side-by-side relationship by a process of vacuum evaporation of one or more metallic films. The transducers are bonded to the delay line facets by means of the facet electrodes, each facet electrode having one transducer bonded thereto. A back electrode is next applied to each transducer. =Electrical insulation is next deposited in the gap between adjacent transducers, or between a back electrode of one transducer and a facet electrode of adjacent transducer, whichever may be desired, as has been heretofore described. A suitably apertured mask is next placed over the plurality of transducers in such a manner that the apertures are disposed directly over the areas where the electrically conducting films are to be deposited. A plurality of electrically conducting films are simultaneously vacuum evaporated in the desired pattern through the apertures of the apertured mask, directly onto the surfaces of the electrodes and the insulating material. Thereafter, a lead wire is attached to the signal input electrode and another lead wire is attached to a signal output electrode, completing the connections.
In a typical example of the present invention, eighteen transducers, each about 0.1 inch wide, 0.6 inch long and 0.004 inch thick, are arranged in adjaent side-by-side relationship along the input facet of a fused silica, plate type, ultrasonic delay line and are bonded thereto by corresponding facet electrodes formed of thin films of gold, chrome-nickel, nickel and indium. The transducers are made from a ferroelectric ceramic material consisting essentially of about 45% PbTiO and 55% PbZrO by weight. The transducer electrodes are formed of thin films of nickel, chrome and gold to which the transducer back electrode material consisting essentially of 60% tin and 40% lead, is bonded to the transducers by solder consisting essentially of 65% indium and 35% tin. Insulating material formed of the heretofore noted preferred organic lacquer made by Bee Chemical Company is deposited between the transducers by means of a small paint brush with a thin, pointed tip for painting the material in place. A highly conductive nickel-chrome alloy film and a gold 6 film are successively vacuum evaporated onto the back electrode through an apertured mask whose apertures are arranged in such a manner as to provide a patterned deposit of conductive film on the electrodes and on the surface of the insulating material, thereby connecting the electrodes to each other and to the input terminals. The pattern is similar to that shown in FIGURES 3 and 4 of the drawings. A signal input lead wire is spot soldered to a first facet electrode at one end of the array of eighteen adjacently deposited electrodes, and an output lead wire is spot soldered to a last facet electrode at the opposite end of the array from the input electrode.
The terminal impedance of each transducer is about of an ohm, and the terminal capacitance of each electrode is about 166,000 picofarads. Connected in series as hereinabove described, the overall impedance of the array is about 12 ohms, while the terminal capacitance of the array is about 5 12picofarads.
Although the present invention has been described with respect to specific details of certain embodiments thereof, it is not intended that such details be limitations upon the scope of the invention except insofar as set forth in the following claims.
What is claimed is: 1. A method of electrically connecting together, in a predetermined pattern, a plurality of transducer electrodes comprising the following steps:
providing a suitable substrate, a plurality of transducers, an apertured mask whose apertures are disposed therein according to a predetermined pattern,
applying to said substrate a plurality of first electrodes in adjacent spaced-apart relationship, said electrodes including a signal input electrode and a signal out: put electrode,
bonding a transducer to each of said first electrodes and to said substrate,
applying a back electrode to each of said transducers,
depositing an electrical insulating material between adjacent transducers to electrically separate the electrodes of one transducer from the electrodes of an adjacent transducer,
placing said apertured mask over said transducers and the respective back electrode thereof so that said predetermined pattern of apertures corresponds to a desired location on said back electrodes and said first electrodes,
depositing an electrically conductive material through said apertures onto said electrodes, thereby forming electrical connections between said electrodes in ac=- cordance with said predetermined pattern,
removing said apertured mask,
providing a pair of lead wires, and
attaching one lead wire to said pair to said input electrode and the other lead wire to said output electrode, thereby forming an array of electrically connected transducers.
2. The method of claim 1 wherein said substrate is a signal input facet of an acoustic delay line.
3. The method of claim 2 wherein said first electrodes are metallic films deposited on said signal input facet.
4. The method of claim 3 wherein said back electrodes include acoustic absorbing material.
5. The method of claim 4 wherein said electrically insulating material is deposited by painting.
6. The method of claim 4 wherein said electrically insulating material is deposited by spraying.
7. The method of claim 5 wherein said electrically conductive material is deposited through said apertures by vacuum evaporation.
8. A method of electrically connecting a plurality of transducers comprising the steps of:
providing a substrate and a plurality of transducers,
applying to said substrate a plurality of first electrodes in adjacent spaced relationship,
bonding one of said transducers to each of said electrodes respectively,
disposing electrical insulating material between adjacent transducers,
applying a back electrode to each of said transducers,
applying an electrically conductive material over a predetermined portion of said electrically insulating material in electrical contact with the back electrodes of adjacent transducers.
9. The method of claim 8 wherein said back electrodes and said electrically conductive material are integral.
10. The method of claim 8 wherein said electrically insulating material is disposed between adjacent transducers by filling the gap between adjacent transducers with a liquid insulating material and drying said insulating material to form a tough, adhesive film, and wherein said electrically conductive material is applied by placing an apertured mask over said transducers and electrodes and thereafter depositing said electrically conductive material through the apertures in said mask to form electrical connections between the electrodes in accordance with a predetermined pattern.
References Cited UNITED STATES PATENTS CHARLIE T. MOON, Primary Examiner.
D. C. REILEY, Assistant Examiner.
US. Cl. X.R. 29572, 578; 3108