MEANS FOR ELECTRICALLY CONNECTING ELECTRODES ON DIFFERENT SURFACES OF PIEZOELECTRIC POLYMERIC FILMS

Abstract: Electrodes with leads deposited on different surfaces of a piezoelectric polymeric film or films are easily and quickly electrically connected by forming a continuous channel through the film and lead to form a pierced lead, and then applying an electrically conductive material, by any one of several known processes, onto the film over the channel to thereby form a connecting lead, the conductive material being permitted to penetrate the channel to effect a continuity of conductive material between the pierced lead and connecting lead.

Description: The present invention relates to a piezoelectric transducer comprising: (a) a first lead deposited on one side of a piezoelectric sheet; (b) a second lead deposited on the opposite side of said piezoelectric sheet and opposite to said first lead; (c) a channel provided through said piezoelectric sheet and connecting said first and second leads; and (d) a conductor extending through said channel and electrically connecting said first and second leads. Furthermore the present invention relates to a process for producing a piezoelectric transducer, comprising: (a) depositing a first lead on one side of a piezoelectric sheet; (b) depositing a second lead on the opposite side of said piezoelectric sheet and opposite to said first lead; (c) providing a channel through said piezoelectric sheet, which connects said first and second leads; and (d) providing a conductor within said channel, which electrically connects said first and second leads. More particularly this invention relates to piezoelectric transducers employing a polymeric film as the piezoelectric element wherein an electrode on one surface of the film is quickly and easily electrically connected to an electrode on the opposite surface of the film or to an electrode deposited on a surface of another film, or to allow an electrical connection to be made to the opposite surface of the film. In the vast area of piezo film applications, it is necessary to have a means of detecting the charge or voltage produced by a piezo or pyro event. An electrode is needed on each side of the film for any application. Most such applications require the electrodes on opposite surfaces of the film to be electrically isolated from each other. Thus, care must be observed when depositing the electrodes on film surfaces to insure that metal migration does not occur over the edges of the film to result in possible shorting out of the electrodes. It is sometimes necessary however to electrically connect an electrode on one film surface with an electrode on the opposing film surface or to an electrode on the surface of another film to control capacitance or impedance; to effect a common electrical connection; to "move", i.e. guide a conductor, from one film surface to another surface; to permit ease of lead attachment for termination, and the like. A piezoelectric transducer and a process of the types mentioned in the beginning are known from JP-A-60-41272 and JP-A-55-156376. In these transducers a lead conductor or wire is provided through a hole in a piezoelectric sheet to connect electrodes or leads on opposite sides of the piezoelectric sheet. However, it is troublesome and time-consuming to provide such electrical connection. Furthermore from the document "Lexikon der Elektronik", O. Neufang, Vieweg, Braunschweig 1983, S. 272, it is known to connect a lead path on one side of a printed circuit board with a lead path on the opposite side of such board by chemically plating a hole leading through the board. However, chemically plating such holes is also a relatively complicated process, which is not suited when the holes are provided in thin piezoelectric films of e.g. 6 µm to 110 µm. According to the invention there is provided a piezoelectric transducer of the type mentioned in the beginning, which is characterized in that: (1) said conductor being a conductive material of a polymer matrix having a conductive metal embedded therein selected from the group consisting of silver, nickel and copper; (2) said channel piercing said first lead; (3) said conductive material coating the sidewalls of said channel; (4) said conductive material being affixed to said piezoelectric sheet over said channel and forming said second lead; and (5) said piezoelectric sheet being a piezoelectric polymer film. Furthermore the invention provides a process of the type mentioned in the beginning, which is characterized in that: (1) said channel is provided such that it pierces said first lead; (2) said conductor is provided by silk-screening, electrostatic printing, xerography technique, ink jet printing, carbon particle deposition, spraying or painting a conductive material over and into said channel so that said conductive material coats the sidewalls of said channel and said second lead is formed by said conductive material; (3) using as said conductive material a finely divided electrically conductive metal, embedded within a polymer matrix; and (4) using as said piezoelectric sheet a piezoelectric polymer film. The present invention provides a facile and convenient method for electrically connecting electrodes on opposing surfaces of a piezoelectric film by forming at least one hole or channel through the film as well as the lead to be electrically connected or linked to another surface. The hole may be formed by pin, punch, or laser, for example. Then, by depositing conductive ink over the hole by silk-screening, for example, a portion of the ink will adhere to the hole sidewalls while penetrating the hole to effect the electrical connection with the pierced electrode. If it is desired to electrically "move" an electrode from the surface of one film to the surface of another film, it is only necessary to align the films, pierce the film whose surface is to be linked to the already deposited electrode, and silk-screen conductive ink over the pierced hole or channel. The invention is not intended to be limited to silk-screening processes for depositing a conductive ink over the hole, but may employ electrostatic printing and xerography techniques, spraying, painting, ink jet printing, carbon particle deposition, and the like. Brief Description of the Drawings FIG. 1 is a sectional view through a piezoelectric acoustic or vibration pick-up transducing device employing the "plated-through-hole" technique of the present invention. FIG. 2 is a sectional view of FIG. 1 looking in the direction of arrows 2-2. FIG. 3 is a sectional view of a portion of FIG. 2 taken along line 3-3 thereof and including a plated-through-hole and resultant electrical connection made in accordance with the present invention. FIG. 4 is a perspective view, part in phantom, of a piezoelectric transducer employing the plated-through-hole technique of the present invention. FIGS. 5 and 6 are sectional views of FIG. 4 taken along lines 5-5 and 6-6 respectively, including components FIG. 7 is a view similar to FIG. 3 illustrating the electral "moving" of an electrode from one film to the surface of another film. Detailed Description of the Invention Referring to FIGS 1, 2 and 3, a piezoelectric acoustic or vibration pickup transducing device 10 is affixed to a guitar 12, for example, in vibration receiving relationship. Vibration pick-up 10 comprises a piezoelectric polymeric film 14, typically Kynar®, a polyvinylidene fluoride (PVDF) product of Pennwalt Corporation, Philadelphia, Pennsylvania, assignee of the present invention. The piezoelectric film 14 is provided with a ground electrode 16 and termination lead 18, both simultaneously deposited on an upper surface of the film, and a signal generating or detecting electrode 20 with termination lead 22 deposited on its lower surface. The electrodes 16 and 20 are deposited in substantial superposed relationship, unlike leads 18 and 22 which are staggered. An insulating film or sheet 24, typically Mylar, a polyethylene terephthalate resin film product of duPont, separates the signal generating electrode 20 from a grounding shield 26. A plastic protection laminate 28 embraces pick-up 10 except at its front end, i.e., where termination leads 18 and 22 extend. Ground electrode 16, signal generating electrode 20, and leads 18 and 22 are preferably deposited on film 14 by a silk-screening process. The silk-screening conductive ink comprises a finely divided electrically conductive metal, suitably silver, nickel or copper, embedded within a polymer matrix. Shield 26 may be deposited on the undersurface of insulating sheet 24 by a silk-screening process, or by an electroplating process, vacuum deposition by evaporation or sputtering, and the like. Shield 26 insures against spurious voltages or radiation being picked up by acoustic transducer 10. The laminated acoustic pick-up 10 may have a total thickness of about 0.1524 to 0.2032 mm (6 to 8 mils). Thickness of piezoelectric film 14 may range between 6 µm to 110 µm, and preferably 20 to 50 µm. The insulating film 24 thickness may range between about 6 to 25 µm while the electrodes 16 and 20 and shield 26 thicknesses will typically be about 6 to 8 µm. In order to facilitate connections to be made to leads 18 and 22, i.e., to permit connections to be readily made on the same film surface, reference is made to FIGS. 2 and 3 of the drawings wherein an electrically linking or connecting electrode 30 is formed on the upper surface of film 14, as is ground electrode 16 and lead 18. Linking electrode 30 is caused to become electrically connected to signal generating electrode 20 (FIG. 1) deposited on the lower surface of piezoelectric film 14. To that end, a hole or channel 32, typically a pin hole or punched-out hole, is provided through film 14 and lead 22. Linking electrode 30 is then formed over channel 32 by depositing or applying conductive ink 33 thereon by silk-screening, or spraying, painting, and the like. More specifically, by silk-screening, spraying or printing, the linking electrode 30 on the film, a portion of the conductive ink or material 33 will penetrate hole 32 to contact lead 22 to fill, or partially fill hole 32, or at least to coat the walls thereof to thereby form an electrical connection between the signal generating electrode 20 on the lower surface of film 14 and the linking electrode 30 formed on the film's upper surface. The invention may be practiced by forming a plurality of pin holes and the like in lieu of a single hole and then plating through the holes as abovedescribed. Larger hole sizes, i.e., those approaching 6.35 mm (1/4 inch) in diameter, which expose more film 14 sidewall area than the area exposed by one or more pin holes result in electrical connections which are at least equally reliable to connections formed by the single pin hole method. Ground electrode 16 and shield 26 are led to ground (not shown) by conventional means. Referring now to FIG. 4 of the drawings, a piezoelectric transducer 40, such as an acoustic pick-up, includes an electrode deposited on each surface of a piezoelectric film, the electrodes being connected in series for controlling or matching impedance of the system. More specifically, transducer 40 includes a signal generating electrode 42 with termination lead 44 and connecting lead 46 deposited on an upper surface of piezoelectric film 14'. An identical electrode 48 with termination lead 50 and connecting lead 52 is deposited on the lower surface of film 14', shown by dotted lines. Electrodes 42 and 48 are deposited in staggered relationship and include shoulder portions 54 and 56 respectively. Connecting leads 46 and 52 are similarly staggered but turn inwardly in order that end portions of each become aligned and superimposed. Termination leads 44 and 50 may be brought to the same surface of film 14' by means described hereinabove. A hole or channel 60 is provided through the end portions of connecting leads 46 and 52 as well as film 14', and a conductive ink 62 silk-screened, for example, over the upper signal generating electrode 42. Ink 62 penetrates hole 60 to contact lead 52 of electrode 48 on the lower surface of film 14' to effect a series connection between the electrodes. As mentioned above, ink 62 or suitable conductive material may be applied by spraying, painting, and the like, and may fill, partially fill, or only coat the walls of hole or channel 60 to thereby effect the desired electrical connection. Similarly, a plurality of holes 60 may be provided along the end portions of the connecting leads as aforementioned. In FIG. 7, PVDF films 70 and 72 have electrodes 74 and 76 deposited on upper surfaces thereof respectively and it is desired to electrically "move" electrode 76 to the same surface of film 70 as is electrode 74. A hole or channel 78 is provided through film 70 and electrode 76 which may then be coated or filled with a conductive ink or electrode material 80. While the preferred piezoelectric polymeric film is PVDF, films made from copolymers of vinylidene fluoride and copolymerizable comonomers of tetrafluoroethylene and trifluoroethylene, for example, may be used advantageously with the present invention.

Claims: A piezoelectric transducer comprising: (a) a first lead (22, 52, 76) deposited on one side of a piezoelectric sheet; (b) a second lead (30, 62, 80) deposited on the opposite side of said piezoelectric sheet and opposite to said first lead (22, 52, 76); (c) a channel (32, 60, 78) provided through said piezoelectric sheet and connecting said first and second leads (22, 52, 76; 30, 62, 80); and (d) a conductor extending through said channel (32, 60, 78) and electrically connecting said first and second leads (22, 52, 76; 30, 62, 80), characterized in that (1) said conductor being a conductive material of a polymer matrix having a conductive metal embedded therein selected from the group consisting of silver, nickel and copper; (2) said channel (32, 60, 78) piercing said first lead (22, 52, 76); (3) said conductive material coating the sidewalls of said channel (32, 60, 78); (4) said conductive material being affixed to said piezoelectric sheet over said channel (32, 60, 78) and forming said second lead (30, 62, 80); and (5) said piezoelectric sheet being a piezoelectric polymer film (14, 14', 70). A piezoelectric transducer according to claim 1, characterized in that said conductor fills said channel (32, 60, 78) completely. A piezoelectric transducer according to claim 1 or 2, characterized in that it further comprises: (a) a ground electrode (16) with a third lead (18) deposited on one side of said film (14); (b) a signal generating electrode (20) provided with said first lead (22) and deposited on the other side of said film (14), said first lead (22) extending substantially parallel to said third lead (18) but being laterally offset from said third lead (18); and (c) said second lead (30) provided on the same side of said film (14) as said third lead (18). A piezoelectric transducer according to claim 3, characterized in that said ground electrode (16) with said third lead (18) and said signal generating electrode with said first lead (22) consist of said conductive material of which said second lead (30) consists. A piezoelectric transducer according to claim 1 or 2, characterized in that it further comprises: (a) a first signal generating electrode (42) deposited on one side of said film (14') and a third lead (46) attached to said first signal generating electrode (42); (b) a second signal generating electrode (48) deposited on the other side of said film (14'), said first lead (52) being attached to said second signal generating electrode (48); (c) said third lead (46) having a portion positioned over said channel (60) and being pierced by said channel (60); and (d) said second lead (62) being affixed to said film (14') through said portion of said third lead (46). A piezoelectric transducer according to claim 5, characterized in that said signal generating electrodes (42, 48) and said first and third leads (52, 46) consist of said conductive material of which said second lead (62) consists. A piezoelectric transducer according to claim 5 or 6, characterized in that said signal generating electrodes (42, 48) are deposited in non-aligned positions. A piezoelectric transducer according to claim 1 or 2, characterized in that it comprises an upper and a lower piezoelectric polymer film (70, 72), said first lead (76) being deposited on the upper surface of said lower piezoelectric film (72), said channel (78) being provided through said upper piezoelectric film (70), and said second lead (80) being deposited on the upper surface of said upper piezoelectric film (70). A piezoelectric transducer according to claim 8, characterized in that said electrodes, said first lead (78) and said other lead (74) consist of said conductive material of which said second lead (62) consists. A piezoelectric transducer according to any one of claims 1 to 9, characterized in that a plurality of channels (32, 60, 78) is provided. A piezoelectric transducer according to any one of claims 1 to 10, characterized in that said piezoelectric polymer film (14, 14', 70, 72) is selected from the group consisting of polyvinylidene fluoride, copolymers of vinylidene fluoride, and copolymerizable comonomers of tetrafluoroethylene and trifluoroethylene. A process for producing a piezoelectric transducer comprising: (a) depositing a first lead (22, 52, 76) on one side of a piezoelectric sheet; (b) depositing a second lead (30, 62, 80) on the opposite side of said piezoelectric sheet and opposite to said first lead (22, 52, 76); (c) providing a channel (32, 60, 78) through said piezoelectric sheet, which connects said first and second leads (22, 52, 76; 30, 62, 80); and (d) providing a conductor within said channel (32, 60, 78), which electrically connects said first and second leads (22, 52, 76; 30, 62, 80); characterized in that (1) said channel (32, 60, 78) is provided such that it pierces said first lead (22, 52, 76); (2) said conductor is provided by silk-screening, electrostatic printing, xerography technique, ink jet printing, carbon particle deposition, spraying or painting a conductive material over and into said channel (33, 60, 78) so that said conductive material coats the sidewalls of said channel (32, 60, 78) and said second lead (30, 62, 80) is formed by said conductive material; (3) using as said conductive material a finely divided electrically conductive metal, embedded within a polymer matrix; and (4) using as said piezoelectric sheet a piezoelectric polymer film (14, 14', 70). A process according to claim 12, characterized said second lead (62) is formed on a third lead (46) which is also pierced by said channel (60). A process according to claim 12 or 13, characterized in that said polymer film (14, 14', 70, 72) has a thickness in the range between 6 µm and 110 µm. A process according to claim 12, characterized in that said metal is silver, nickel or copper.

Inventors: RADICE, PETER FRANCIS
Applicants: ATOCHEM NORTH AMERICA, INC. (A PENNSYLVANIA CORP.)
Application year: 1986
Main classification: H01L41
IPC codes: H01L41