A CIRCUIT BOARD ASSEMBLY, A HANDSET AND A METHOD OF PRODUCING A CIRCUIT BOARD ASSEMBLY FOR A HANDSET

Abstract: In a handset (10) comprising two housing parts (12 and 14) and a circuit board assembly (16) which includes substantially all electronic components of the handset including a first transducer or microphone (32) for converting audio energy into electrical energy and a second transducer or loudspeaker (34) for converting electrical energy into audio energy, the transducers (32 and 34) are implemented in accordance with the piezo-electric transducer principle. Thus, the transducers comprise a transducer foil, i.e. a piezo-electric sheet having metallic layers arranged on opposite side surfaces of the sheet, and a resilient element imparting mechanical tension to the transducer foil. An impedance matching or transforming element such as a field effect transistor (36) may be interconnected between the microphones and a transmission circuit for the telephone line. As the handset is assembled from two housing parts enclosing a finished circuit board assembly (16) which is prefabricated by employing conventional circuit board production techniques from low cost and light weight materials, a handset of extremely low weight and low cost, yet fulfilling telephone line requirements is provided (e.g. CEPT-specifications The European Conference of Postal and Telecommunications Administrations).

Description: A CI RCU IT BOARD ASSEMBLY, A HANDSET AND A METHOD OF PRODUCI NG A CI RCU IT BOARD ASSEMBLY FOR A HANDSET The present invention relates to the communication field and generally to the telecommunication field . More particularly, the present inven¬ tion relates to a handset, a circuit board assembly for a handset and a method of producing a circuit board assembly for a handset. Conventionally, a handset includes a first transducer or microphone for converting audio energy into electrical energy and a second transducer or loudspeaker for converting electrical energy into audio energy. The transducers are normally connected through conductors of a multi-core cable to a telephone apparatus. Alternatively, the transducers may be connected through individual cores to electronic circuits included in the handset and comprising amplifier, filtering, switching, dialling or tone burst signalling circuits and, furthermore, transmitter and receiver circuits . Although the field of electronic circuits has been highly developed throughout the past decades due to the appearance of novel tech¬ niques, eg . printed circuit board technique, thin-film and thick-film layer techniques and further the semi-conductor techniques involving planar, integration and large-scale integration ( LSI ) technique, the handset has not been altered or developed by employing or adapting these novel techniques . Basically, the conventional handset is assembled from individual or discrete components such as a handset housing, a discrete microphone unit or microphone cartridge, a telephone or loudspeaker unit, a multi-core cable for connecting the handset to the telephone apparatus and a printed circuit board including the above electronic circuits, if any. Although the novel electronic circuitry techniques have been employed for printed circuit boards little attention has been directed to the transducers of the handset. Conventionally, the transducers are still provided as discrete components, e. g. as an electric cartridge or a moving coil microphone cartridge and an electro- dynamic loudspeaker unit mounted in the handset housing individually by employing fastening means such as screws, springs, etc. , or the microphone cartridge is, " provided the cartridge is of a fairly low weight, mounted on a conventional printed circuit bord, which is in turn mounted in the handset housing. As will be appreciated, the total price of the handset becomes ex¬ tremely high, first, due to the relatively expensive components em¬ ployed, i . e. the discrete microphone cartridge and the discrete loud¬ speaker unit, and second, due to a highly elaborate and time con- suming assembling procedure necessitated by the number of individual or discrete components and some of the components being heavy, viz. the electro-dynamic loudspeaker unit. It is therefore an object of the present invention to provide extremely simple and extremely light circuit board assemblies integrally compris- ing substantially all of the above electronic components and all of the above electronic circuits, including at least one of the transducers of the handset. A further object of the present invention is to provide , novel tech¬ niques of producing extremely simple and extremely light circuit board assemblies, however, still at extremely low costs and integrally comprising basically all of the above electronic components and all of the above electronic circuits of the handset, including at least one of the transducers of the handset. The above objects are fulfilled by a circuit board assembly according to the invention comprising a circuit board including an electrically insulating base board, at ' least one pair of conductors, and at least one of said conductors included in the handset, said transducer being a foil-type transducer having a pair of terminals and being arranged on the circuit board substantially parallel therewith having its termi- nals arranged in electrically conductive connection with said one pair of conductors. Fundamentally, the concept of the present invention is based on the realisation that, contrary to conventional handsets in which individual or discrete components constitute the transducers, i . e. the micro¬ phone and the loudspeaker, the novel techniques developed within the transducer field renders it possible to integrate the active transducer element or the active transducer elements into the circuit board assembly. This integration concept of the present invention renders it possible, on the one hand, to provide a finished circuit board assem¬ bly while employing techniques well known within the electronic field involving printed circuit board technique and layer techniques such as thick-film and thin-film technique, and on the other hand, to mount a finished circuit board assembly in the handset housing, thus reducing the number of components involved in the process of assem¬ bling the handset and, furthermore, reducing the complexity of the techniques involved in this assembling process . A further aspect of the present invention is the concept of integra¬ ting a foil-type transducer into the circuit board assembly which is adapted to be mounted as a finished component into a handset housing thus rendering it possible to tune the finished handset within specific acoustic and electronic limits in a manner completely different from the conventional acoustic and electronic tuning technique. While, in the conventional handset in which discrete transducer elements are employed, the overall specifications of the finished handset is deter¬ mined by the specifications and properties of the individual compo- nents employed, i . e. of the microphone cartridge, the loudspeaker unit, the handset housing and the electronics employed in the hand¬ set, the acoustic and electronic characteristics of the handset pro¬ vided in accordance with the teaching of the present invention are solely determined by the specifications and properties of the finished circuit board assembly and the acoustic properties of the handset housing. Furthermore, due to the fact that the overall acoustic characteristics and properties of the handset are determined as a combination of the specifications and properties of the finished circuit board assembly according to the invention and the acoustic properties of the handset housing, and due to the fact that the acoustic characteristics of the foil-type transducer employed in the ci rcuit board assembly according to the invention and further included in the handset highly surpasses the conventional telephone line specifica¬ tions, e. g. the CEPT-specifications (The European Conference of Postal and Telecommunications Administrations) , the overall acoustic. characteristics and properties of the finished handset may be tuned to these telephone line specifications by the acoustic properties of the handset housing exclusively, i . e. by adapting cavities in the handset housing in front of and behind the transducer of the circuit board assembly in accordance with well-known acoustic tuning principles. Apart from the highly desirable feature that merely two components, viz. the finished circuit board assembly and the handset housing are to be manufactured fulfilling specific characteristics or qualities, it is further realized that the concept of providing a finished board assem¬ bly renders it possible to test the finished circuit board assembly while employing automatic testing techniques developed within the electronic circuit testing field. The foil-type transducer of the present invention may be implemented in accordance with the piezo-electric transducer principle, the elec¬ trostatic transducer principle and the electrodynamic transducer prin- ciple. I n the presently preferred embodiment of the circuit board assembly according to the invention, the foil-type transducer is implemented in accordance with the piezo-electric transducer principle. Consequently, in accordance with this embodiment of the invention the foil-type transducer comprises a piezo-electric sheet or film having metallic layers arranged on opposite side surfaces thereof, parts of the metal¬ lic layers constituting the terminals of the piezo-electric foil-type transducer, the foil being supported by the circuit board along at least part of the edge of the foil, and mechanical tension or resiliency being imparted to the foil . I n accordance with an alternative embodiment of the circuit board assembly according to the invention, the foil-type transducer is implemented in accordance with the electrostatic transducer principle, and, consequently, the foil-type transducer comprises an electret sheet or film having metallic layers arranged on opposite side surfaces thereof, the metallic layers constituting electrodes of the electret foil type transducer, parts of the layers constituting the terminals of said transducer, and the foil being supported by the circuit board along at least part of the edge of the foil . In a further alternative embodiment of the circuit board assembly according to the invention , the foil-type transducer is implemented in accordance with the electrodynamic transducer principle. Consequent- ly, the foil-type transducer comprises a sheet or film having a metal¬ lic conductor embedded therein or fastened to a side surface of the foil, the conductor defining a coiled configu ration and being adapted to cooperate with a magnetic field generating source in an electro- dynamic transducer, the terminals of the transducer being constituted by the ends of the conductor, and the foil being supported by the circuit board along at least part of the edge of the foil and mechanic¬ al tension or resiliency being imparted to the foil . I n order to reduce the harmonic distorsion produced by the trans¬ ducer element in its conversion of audio energy into electric energy or in its conversion of electric energy into audio energy, in particu¬ lar harmonic distorsion of even order, mechanical tension or resiliency has to be imparted to the foil , as is well known in the art. The mechanical tension or resiliency may be imparted by tensioning the foil in a curved or dome-shaped configuration or by suspending the foil over a tensioning element, e. g . a rod, a bar or the like. I n the presently preferred embodiment of the invention the mechanical ten¬ sion is provided by a resilient element supporting one of the side surfaces of the foil . I n a further implementation of this preferred embodiment of the invention , the resilient element is arranged in a recess of the circuit board . The base board of the circuit board may be an inflexible base board of a conventional single- or double-sided printed circuit board or an inflexible substrate employed in accordance with conventional thick- or thin-film technique. For some applications, the inflexible base board may cause limitations to the overall construction and design of the handset housing and on the one hand unfavourably influence the acoustic properties of the finished handset, and on the other hand make the mechanical construction and fixation of the circuit board assembly in the handset housing complex . Therefore, in the presently preferred embodiment of the invention, the base board or the circuit board is a flexible sheet providing a handset construction in which the circuit board layout is by no means limited by the handset housing design . The flexible sheet may be a polyester sheet, an epoxy fibreglass sheet or a Kapton® sheet of a thickness of 50-200 μm. The provision of electrically conductive connection between the ter¬ minals of the foil-type transducer and the circuit board assembly may be provided in accordance with techniques well known within the circuit board mounting and thick-film layer or thin-film layer field . Thus, the technique may involve soldering, sintering, bonding, wire-wrapping, rolling or any other step of providing electrically conductive connection between a pair of terminals and a pair of con¬ ductors of a circuit board . Fu rthermore, the pair of conductors may be arranged on one of the side surfaces of the circuit board or on opposite side surfaces of the circuit board, i . e. basically provide a single-sided circuit board or a double-sided circuit board, respective- ly. I n accordance with the presently preferred embodiment of the ci rcuit board assembly according to the invention, a very simple, yet very reliable electrically conductive connection between the pair of termi¬ nals of the foil-type transducer and the pair of conductors of the circuit board is provided requiring no additional components such as soldering or bonding material, wire connections, etc. I n this embodi- ment of the circuit board assembly, the pair of conductors are ar¬ ranged on one side surface of the circuit board, i . e. the circuit board is a single-sided circuit board, a first metallic layer of a first side surface of the foil being arranged in direct electrically con¬ ductive connection with a first conductor of said pair of conductors, and a second conductor of said pair of conductors being arranged on a turned-in part of the circuit board providing direct electrically conductive connection between said second conductor and a second metallic layer of a second side surface of the foil . Although the turned-in part of the circuit board providing direct electrically conductive connection between the second conductor and the second side surface of the foil may constitute a contact flap only contacting a minor portion of the second metallic layer, the foil is preferably sandwiched between the circuit board and the turned-in part thereof, and an aperture of the circuit board exposes at least part of one of the metallic layers of the foil. In this embodiment, the transducer element constituted by the foil is so to speak clamped between the circuit board and the turned-in part thereof. The aper¬ ture exposing at least part of one of the metallic layers of the foil may be provided in the turned-in part of the circuit board so that at least part of the second metallic layer of the foil is exposed or alter¬ natively be provided in the circuit board itself so that at least part of the firs " metallic layer of the foil is exposed. I n this embodiment, the foil is preferably fixed to the circuit board and/or the turned-in part thereof along the edge of the aperture of the circuit board. The foil-type transducer may be of any configu ation, e.g . be of a circular, elliptical or any other configuration comprising curved or linear segments. However, since a circular or elliptical configuration provides a highly resonant transducer, the foil-type transducer is preferably of a substantially rectangular configuration . Apart from the acoustic advantage of producing the resonancy of the transducer element by providing a transducer of a rectangular configuration, a rectangularly shaped foil may very easily be provided from a length of a foil material by simply dividing the length of foil material into rectangular segments, e. g . by cutting the foil material length, as will be described below. Apart from providing electrically conductive connection through its conductors to the terminals of the foil-type transducer, the circuit board may, like a conventional circuit board, i . e. as a conventional single-sided or double-sided printed circuit board or a thick-film or thin-film substrate, comprise electronic components cooperating with the transducer. I n case the foil-type transducer constitutes a trans¬ ducer for converting audio energy into electric energy, i . e. con¬ stitutes a microphone, the transducer is preferably connected to impedance transforming or impedance matching circuits, which may further provide gain, if desired. As is well-known in the art, high impedance microphones such as high impedance piezo-electric, high impedance electrostatic or electric microphones and even high impedance dynamic microphones are preferably connected through a high-impedance-input/low-impedance-output circuit, such as a trans¬ former or an active circuit such as a field effect transistor (FET) or an operational amplifier (OP-Amp) . I n case the foil-type transducer of the circuit board assembly according to the invention is adapted to convert electrical energy into audio energy, i. e. the transducer constitutes a loudspeaker unit, the signal supplied to the circuit board assembly included in the handset from the telephone line or from the receiver output, etc. , may have a signal level or power level too low or too high fn relation to the signal level or power level required by the transducer. Therefore, the electronic components of the circuit board assembly may constitute signal level transforming circuits or power level increasing or power level reducing circuits. Apart from electronic components cooperating with the transducer, the circuit board may comprise electronic components serving different purposes, e. g . constituting dialling circuits including tone burst signalling ci rcuits and keyboard switches, etc. In the above described presently preferred embodiment of the inven¬ tion, the piezo-electric foil is a Polyvinylidene Fluoride Film (PVDF) of a thickness of 6-120 μm, preferably 40 μm. I n a further aspect of the present invention, the circuit board assembly comprises two foil-type transducers having any of the above characteristics or any combination of the above characteristics, one foil-type transducer constituting the first transducer of the handset, i . e. the microphone, and another foil-type transducer constituting the second transducer of the handset, i . e. the loudspeaker. Although the first and second foil-type transducers may be implemented in accord¬ ance with different transducer principles, i . e. the microphone trans¬ ducer implemented in accordance with a piezo-electric transducer principle, and the loudspeaker transducer implemented in accordance with the electrodynamic transducer principle, the first and second foil-type transducers of the circuit board assembly are, however, implemented in accordance with the same transducer principle. I n a presently preferred embodiment of the invention, the foil-type trans¬ ducers of the circuit board assembly are of the above described piezo-electric foil concept. The present invention further relates to a handset including a first transducer for converting audio energy into electrical energy, a second transducer for converting electrical energy into audio energy, a handset housing and fu rther a circuit board assembly having any of the above described characteristics and mounted in the handset housing. The present invention also relates to a method of producing a circuit board assembly for a handset which includes a first transducer for converting audio energy into electrical energy and a second trans- ducer for converting electrical energy into audio energy, and com¬ prising the following steps : providing a circuit board including an electrically insulating base board and at least one pair of conductors, and arranging at least one foil-type transducer constituting one of the transducers included in the handset and having a pair of terminals on the ci rcuit board substantially parallel therewith and having its termi¬ nals arranged in electrically conductive connection with said one pair of conductors. The invention will now be fu rther described with reference to the drawings, wherein, Fig. 1 is an exploded and perspective view of a handset comprising a presently preferred embodiment of the ci rcuit board assembly accord¬ ing to the invention , disclosing a first side surface of the circuit board assembly, Fig . 2 is a perspective and schematical view of a circuit board blank constituting the circuit board of the circuit board assembly shown in Fig . 1 , disclosing a second side surface of the circuit board, Fig . 3 is a perspective and partly broken away view of a lower hand- set housing part comprising a inflexible circuit board embodiment of the circuit board assembly according to the invention. Fig. 4 is an exploded, perspective and partly broken-away view of an alternative embodiment of a circuit board assembly according to the invention comprising a transducer of the electrodynamic transducer type, Fig. 5 is a perspective view of a slightly modified embodiment of the presently preferred embodiment of the circuit board assembly shown in Figs . 1 and 2 and comprising additional electronic components, and Figs . 6-11 are schematical and perspective views illustrating different production steps in the process of producing the presently preferred embodiment of the circuit board assembly shown in Figs. 1 and 2. In Fig . 1 a handset is shown designated the reference numeral 10 in its entirety. The handset 10 comprises a handset housing constituted by two handset housing parts, a top part 12 and a bottom part 14, which are glued or welded or otherwise fixed to each other, e.g. by means of screws or the like. Within the handset housing, a circuit board assembly 16 is arranged . The circuit board assembly 16 com¬ prises a flexible base board 18 of a flexible material such as a flexible polyester or epoxy fibreglass sheet. On a first side surface of the base board 18, the upper side surface shown in Fig . 1 , electrical conductors 20 and 21 are arranged. The conductors 20 and 21 may be provided in accordance with well-known printed circuit board tech¬ niques i . e. by techniques involving masking areas of a metallic layer and etching uncovered metallic surface areas, or in accordance with thin-film or thick-film layer techniques, e. g. a technique involving silk screen printing electrically conductive surface areas unto a base board or substrate. As evident from Fig . 1 , the flexible circuit board assembly is shaped into a configuration basically in conformity with the overall shape of the handset housing . At one end of the housing top part 12, an aperture 22 is provided for providing access to a multi-pin plug 24, which is connected to a coiled multi-core cable 26. The multi-pin plug 24 is adapted to cooperate with a mating plug 28 when the circuit board assembly 16 is ar.ranged in the handset housing and the handset housing parts 12 and 14 are fixed to each other. The coiled multi-core cable 26 is adapted to provide electrically conductive connection between a first transducer or microphone of the handset and a second transducer or loudspeaker and a telephone apparatus, a wireless transceiver (transmitter/ receiver) , an intercom terminal, etc. The plug 28 is fastened to a flap 30 of the flexible circuit board assembly 16 and the individual pins of the plug 28 are connected to conductors of the circuit board assembly for providing electrically conductive connection between the pins of the plug and the transducers of the handset. The first transducer or microphone is designated the reference numeral 32 and is provided at a first end of the circuit board assembly 16 adapted to be received at the end of the handset housing from which end the coiled multi-core cable .26 extends from the multi- pin plug 24 received in the aperture 22. The second transducer or loudspeaker is designated the reference numeral 34 and is provided at a second end of the circuit board assembly 16 and adapted to be received in the handset housing at the end thereof remote from the above end . The microphone 32 and the loudspeaker 34 are basically of identical construction involving a piezo-electric transducer and com¬ prise a polymer sheet which exhibits piezo-electric characteristics such as a polyvinylidene fluoride film ( PVDF) having metallic layers applied on opposite side su rfaces of the PVDF sheet. The microphone 32 which is a piezo-electric microphone, is connected to an impedance matching component, e. g. a field effect transistor (FET) 36 which has a very high input impedance and a very low output impedance. The FET is connected in a source-follower mode or in a source-grounded mode. Alternatively, the active impedance matching element may be constituted by an integrated amplifier, e. g. an operational amplifier (OP-Amp) , also providing a high input impedance and a low output impedance. The microphone 32 of the circuit board assembly 16 is adapted to be mounted between fixation elements 38 protruding from the housing part 14 into the inner space defined within the handset housing and to be maintained in position so that the lower side surface of the microphone 32, not shown in Fig. 1 , which provides an exposed transducer membrane, is retained in contact with an inner surface 39 of the housing part 14. The microphone 32 may be retained in posi¬ tion, i . e. in contact with the inner surface 39, by means of mechanic¬ al fixation means, not shown in Fig. 1 , protruding from the housing part 12 into the inner space of the handset housing, and imparting mechanical pressure to the transducer 32 along the outer edge of the transducer. Acoustic communication is provided from the surroundings to the above mentioned exposed transducer membrane through a plurality of apertures 40 and a cavity 41 of the housing part 14. Analogously, the loudspeaker 34 is adapted to be retained between fixation elements protruding from an inner surface 43 at the other end of the handset housing, and a plurality of apertures 44 and a cavity 45 provide acoustic communication from an exposed transducer membrane, not shown in Fig . 1 , to the surroundings . Now turning to Fig . 2, the above described circuit board assembly 16 is viewed from below and at a production step prior to the mounting of the plug 28. I n Fig. 2, the above mentioned exposed transducer membranes of the microphone 32 and of the loudspeaker 34 are shown designated 46 and 48, respectively. The transducer elements 32 and 34, the production of which is to be described in greater detail below with reference to Figs. 6-11 , each comprises an active foil-type transducer element, constituted by the above described PVDF foil having metallic layers arranged on opposite side surfaces of the PVDF sheet. The active transducer element of each of the transducers is sandwiched between a first section 49 of the circuit board 18 which is further provided with the above mentioned aperture exposing a first side surface of the active transducer element constituting the exposed transducer membrane 46, and a second section 50 of the circuit board 18, which is dome-shaped and folded so that the active transducer element is sandwiched between the two sections . Within the inner space defined between the second side surface of the active trans- ducer element and the dome-shaped surface of the section 50, a resilient element is confined which imparts mechanical tension to the transducer element as will be described in greater detail below. I n Fig. 3, a slightly modified embodiment of the above described handset 10 is shown . Whereas in Figs . 1 and 2 the ci rcuit board assembly 16 comprises a flexible base board 18, the handset shown in Fig. 3 comprises a circuit board assembly 52 including an inflexible base board 54, such as a base board of a conventional single-sided or double-sided printed circuit board . Furthermore, the circuit board assembly 52 includes electronic components 56 and 58 which are soldered onto printed circuit tracks or conductors of the printed circuit board. The electronic components may constitute audio circuits connected to the transducers 32 and 34 of the handset, i . e. con¬ stitute a microphone amplifier circuit and a loudspeaker driver circuit or may, alternatively, constitute dialling means, wireless transmitter or receiver means or the like. In the embodiments of the circuit board assemblies shown in Figs. . 1 , 2 and 3, the transducers are implemented in accordance with the piezo-electric transducer principle. It is, however, to be understood that the foil-type transducer concept of the present invention may also be implemented in accordance with the electrostatic or electret transducer principle by employing an electric foil having metallic electrodes arranged on opposite side surfaces of an electret sheet and further in accordance with the electrodynamic transducer principle as will be discussed below with reference to Fig . 4. I n the embodiment of the handset 10 shown in Fig . 4, a magnetic assembly 60 is received in a fixation ring 62 protruding from the lower side surface of the housing part 12 and generates a magnetic field below its lower side surface. Adjacent to the lower side surface of the magnetic assembly 60, a foil-type transducer implemented in accordance with the electrodynamic transducer principle is arranged comprising a membrane sheet 64 in which a coiled conductor 66 is embedded constituting a voice coil . The membrane sheet 64 is included in a circuit board assembly 68 basically identical to the circuit board assembly 16 which is received in the housing part 14 and comprises two conductors 69 and 70 which are connected to a respective end of the voice coil conductor 66. I n . Fig . 5, a slightly modified embodiment of the above described circuit board assembly 16 shown in Figs . 1 and 2 is shown . Apart from the base board 18 of the circuit board assembly 16, the embodi¬ ment shown in Fig. 5 includes two circuit board flaps 72 and 74 which are hinged to the main body of the base board 18. On the main body of the base board 18, a plurality of switches 80 are provided con¬ stituting dialling switches of the handset. On the circuit board flap 72 a plurality of electronic components 56 and 58 are mounted con¬ stituting a dialling circuit operable by means of the switches 80. The circuit board flap 72 further includes a display 76 which is adaptd to be arranged in an aperture 78 of the main body of the base board 18. The circuit board flap 74 constitutes a distance plate serving the purpose of maintaining the switches 80 in a predetermined distance from the front surface of the handset housing in which the circuit board assembly is adapted to be mounted . I n Fig. 5 the handset housing in which the circuit board assembly is adapted to be mounted is not shown . However, the circuit board assembly is, as will be understood, of a construction providing an integrated handset and telephone apparatus . In Figs . 6-11 a number of steps of a method according to the present invention for producing a circuit board assembly for a handset are shown . I n Fig. 6, a circuit board blan k is shown comprising the base board 18 having the conductors 20 and 21 arranged on one side surface of the board, or on the top surface of the board . I n the section 50 of the base board 18 the conductor 20 is shaped into a quadratic ring 82, and in the section 49 of the base board 18, the conductor 21 is shaped into a quadratic ring 83. I n -Fig . 7, the area defined within the quadratic ring 82 of the sec¬ tion 50 is shaped into a dome by means of a dome-shaped pressing die 84 which is brought into contact with the upper side surface of the base board 18 from above. The pressing die 84 may be a preheated die or a cold die, dependent on the material of the base board 18. I n Fig . 8 an aperture 85 is provided within the area defined within the quadratic ring 83 of the section 49 by means of a punching die 86 which is also brought into contact with the upper side surface of the base board 18 from above. Between the sections 49 and 50, a weaken¬ ing line 88 is further provided . It should be mentioned that the pressing of the area defined within the ring 82 and the punching of the aperture 85 may be carried out in one and the same production step together with the stamping, of the weakening line 88. Alternative¬ ly, the weakening line 88 may be stamped in a separate production step and the pressing of the dome, the punching of the aperture, and the stamping of the weakening line may be carried out in any sequence. In Fig. 9, two strips 89 and 90 of an adhesive material are applied to the upper side surface of the circuit board assembly along the longi¬ tudinal outer edges of the board within the sections 49 and 50. I n- Fig . 10, the active transducer element constituted by a foil 92 comprising a piezo-electric sheet or en electret sheet having metallic layers arranged on opposite side surfaces of the piezo-electric sheet or electret sheet is brought into contact with the upper side surface of the circuit board assembly within the section 49. Preferably prior to or after its arrangement on top of the circuit board assembly, the transducer element or transducer foil 92 is cut from a length of the foil material . A resilient backing element constituted by a block 94 of foam rubber or foam plastics material is also arranged in the dome- shaped recess within the quadratic ring 82 of the section 50. Like the transducer element .or foil-transducer 92, the block 94 is preferably cut from a length of foam rubber or foam plastics material . In Fig . 11 , the section 50 is folded along the weakening line 88 so that the section 50 is arranged on top of the section 49 and the strips 89 and 90 of adhesive material retain the sections in position in relation to the transducer foil 92 sandwiched between the sections and in relation to each other. After this folding step, the transducer is finished . It should be mentioned that the microphone 32 as well as the loudspeaker 34 of the circuit board assembly 16 shown in Figs . 1 and 2 may be produced simultaneously in a production process involving the above described pressing, stamping, punching, adhesive strip applying, foil and block arranging, and folding step. Furthermore, the active elements of the transducers, i . e. of the microphone and the loudspeaker may be made from the same foil material . EXAMPLE In a proto type implementation of the handset shown in Fig. 1 includ¬ ing a circuit board assembly also shown in Fig. 1 comprising a micro¬ phone and a telephone implement in accordance with the piezo-electric transducer principle, the handset housing comprising the part 12 and the bottom part 14 was composed of housing components of the appli- cant's danMark 1® and danMark 2® handsets, and the circuit board assembly 16 was made from a 100 μm polyester sheet having printed circuit tracks arranged on one side surface only. The transducer foil used in the microphone and in the telephone was one and the same and was a 40 μm PVDF-foil . The microphone foil measured 15 mm x 15 mm and the loudspeaker foil measured 30 mm x 30 mm. The active or exposed surface areas of the transducers constituted 43 per cent and 59 per cent of the microphone foil area and of the loudspeaker foil area, respectively. The resilient blocks imparting mechanical tension to the foils were constructed from combined soft (15 kg) foam rubber and hard (50 kg) foam rubber bodies, the hard foam rubber body imparting the rear side of the foil . The bodies had areas identical to the respective areas of the foils, and the soft foam rubber body had a height of 3 cm, and the hard foam rubber body had a height of 0.5 cm. Cavities behind the transducers constituted 0.5 cm 3 and 2 cm 2 , respectively. The active impedance matching element 36 was constituted by a microphone amplifier of the type RI FA PBL 3747. The microphone had a 1 kHz sensitivity of -63 dB re 1 V/μbar, and _. th.e Joudspeaker had a 1 kHz sensitivity of 76 dB re 20μPa/mVA. The microphone and the loudspeaker fulfilled the CEPT-specifications regarding microphones and telephones for use in telephone handsets .

Claims: CLAIMS 1 . A ci rcuit board assembly for a handset which includes a fi rst transducer for converting audio energy into electrical energy and a second transducer for converting electrical energy into audio energy, said assembly comprising a ci rcuit board including an electrically insulating base board and at least one pair of conductors, and at least one of said transducers included in the handset, - said transducer being a foil-type transducer having a pair of terminals and being arranged on the circuit board substantially parallel therewith having its terminals arranged in electrically conductive connection with said one pair of conductors . 2. A circuit board assembly according to claim 1 , the foil-type trans¬ ducer comprising a piezo-electric sheet having metallic layers ar¬ ranged on opposite side surfaces thereof, parts of the metallic layers constituting the terminals of the piezo-electric foil-type transducer, the foil being supported by the circuit board along at least part of the edge of the foil , and mechanical tension or resiliency being imparted to the foil . 3. A circuit board assembly according to claim 1 , the foil-type trans- ducer comprising an electret sheet having metallic layers arranged on opposite side surfaces thereof, the metallic layers constituting elec¬ trodes of the electret foil type transducer, parts of the layers con¬ stituting the terminals of said transducer, the foil being supported by the ci rcuit board along at least part of the edge of the foil , and mechanical tension or resiliency being imparted to the foil . 4. A circuit board assembly according to claim 1 , the foil-type trans¬ ducer comprising a sheet having a metallic conductor embedded there¬ in or fastened to a side surface of the foil, the conductor defining a coiled configuration and being adapted to cooperate with a magnetic field generating source in an electrodynamic transducer, the terminals of the transducer being constituted by the ends of the conductor, and the foil being supported by the circuit board along at least part of the edge of the foil, and mechanical tension or resiliency being imparted to the foil . 5. A circuit board assembly according to any of the claims 2-4, the mechanical tension being provided by a resilient element supporting one of the side surfaces of the foil . 6. A circuit board assembly according to claim 5, the resilient element being arranged in a recess of the circuit board. 7. A circuit board assembly according to any of the preceding claims, the base board of the circuit board being a flexible sheet. 8. A circuit board assembly according to claim 7, the flexible sheet being a polyester sheet, an epoxy fiberglass sheet, or a Kapton® sheet of a thickness of 50-200 μm. 9. A circuit board assembly according to claim 2 or 3 and any of the claims 5-7, the pair of conductors being arranged on one side surface of the circuit board, a first metallic layer of a first side surface of the foil being arranged in direct electrically conductive connection with a first conductor of said pair of conductors, and a second con¬ ductor of said pair of conductors being arranged on a turned-in part of the circuit board providing direct electrically conductive connection between said second conductor and a second metallic layer of a second side surface of the foil . 10. A circuit board assembly according to claim 9, the foil being sandwiched between the circuit board and the turned-in part thereof, and an aperture of the circuit board exposing at least part of one of the metallic layers of the foil . 11 . A circuit board assembly according to . any of the preceding claims, the foil-type transducer being of a substantially rectangular configuration . 12. A circuit board assembly according to any of the preceding claims, the circuit board further comprising electronic components co¬ operating with the transducer. 13. A ci rcuit board assembly according to claim 2 and any of the claims 5-11 the piezo-electric foil being a Polyvinylidene Fluoride Film (PVDF) of a thickness of 6-120 μm, preferably 40 μm. 14. A circuit board assembly according to any of the preceding claims, the circuit board assembly comprising two foil-type trans¬ ducers having any of the characteristics of the claims 1 -13, or any combination of the characteristics of the claims 1 -13, one of the foil-type transducers constituting the first transducer of the handset, and another one of the foil-type transducers constituting the second transducer of the handset. 15. A handset including a fi rst transducer for converting audio energy into electrical energy, a second transducer for converting electrical energy into audio energy, a handset housing, and further a circuit board assembly having any of the characteristics of the claims 1 -14 and mounted in the handset housing . 16. A method σf producing a circuit board assembly for a handset which includes a first transducer for converting audio energy into electrical energy and a second transducer for converting electrical energy into audio energy, comprising the following steps : providing a circuit board including an electrically insulating base board and at least one pai r of conductors, and arranging at least one foil-type transducer constituting one of the transducers included in the handset and having a pair of terminals on the ci rcuit board substantially parallel therewith and having its termi- nals arranged in electrically conductive connection with said one pair of conductors . 17. A method according to claim 16, the foil-type transducer compris¬ ing a piezo-electric sheet having metallic layers arranged on opposite side surfaces thereof, parts of the metallic layers constituting the terminals of the piezo-electric foil-type transducer, the foil being arranged on the circuit board so that the foil is supported by the circuit board along at least part of the edge of the foil , the method further comprising the step of permanently imparting mechanical tension or resiliency to the foil . 18. A method according to claim 17, the method further comprising the step of arranging a resilient element supporting one of the side surfaces of the foil so as to permanently impart mechanical tension to the foil . 19. A method according to claim 18, the method further comprising the introductory step of providing a recess in the circuit board and arranging the resilient element in that recess . 20. A method according to any of- the claims 17-19, the pair of con¬ ductors being provided on one side surface of the circuit board, a first metallic layer of a first side surface of the foil being arranged in direct electrically conductive connection with a first conductor of said pair of conductors, the method further comprising the step of folding a part of the circuit board, a second conductor of the pair of conductors being arranged on said part so as to provide direct elec- trically conductive connection between said second conductor and a second metallic layer of a second side surface of the foil . 21 . A method according to claim 20, the method further comprising the step of providing an aperture of the circuit board and sandwich¬ ing the piezo-electric foil-type transducer between the circuit board. and said part of the circuit board so as to make the aperture expose at least part of said first metallic layer of the foil . 22. A method according to any of the claims 17-21 , the pjezo-electric sheet having metallic layers arranged on opposite side su rfaces there¬ of being cut from a length of the piezo-electric foil material having metallic layers arranged on opposite side surfaces thereof. 23. A method according to any of the claims 16-22 and of manufactur¬ ing a circuit board assembly comprising said first and second trans¬ ducers, comprising the step of arranging two foil-type transducers on the circuit board.

Inventors: BUUR JACOB, BUUR, JACOB
Applicants: GNT AUTOMATIC AS, GNT AUTOMATIC A/S
Application year: 1985
Main classification: H04M1
IPC codes: H04M1, H04R17