GB2255688A

GB2255688A - Telephone station set with flexible and rigid circuit boards

Info

Publication number: GB2255688A
Application number: GB9209077A
Authority: GB
Inventors: Michael Eugene Berry; Alan Patrick Westfall
Original assignee: Northern Telecom Ltd
Current assignee: Nortel Networks Ltd
Priority date: 1991-05-10
Filing date: 1992-04-27
Publication date: 1992-11-11
Anticipated expiration: 2012-04-27
Also published as: GB9209077D0; GB2255688B

Abstract

The structure of a telephone set is configured so as to capture a rigid circuit conductor substrate 30 and a more economical flexible circuit conductor substrate 40 in predetermined juxtaposition with a compressed elastomeric element 58 to facilitate an economical and reliable electrical connection between overlapping portions of the conductor substrates, and thereby reduce the cost of the telephone set. <IMAGE>

Description

TELEPHONE STATION SET WITH FLEXIBLE AND RIGID CIRCUIT BOARDS The invention is in the field of electronic apparatus including telephone terminal apparatus, and more particularly relates to apparatus including rigid and resilient circuit path carriers.

One of the trends in telephony has been an enhancement of the numbers and variations of call management services and features now available to the user of the telephone system. By way of example some of these features include: calling party identification provided at a small liquid crystal display at a called party's telephone terminal; speed call reperatory dialling; and simultaneous plural directory number access; to name but a few.

In small telephone systems, often referred to as key telephone systems, the provision of each additional feature and additional line access usually requires a similar assignment of a key or push button to enable user access to the feature or line. A few years ago very sophisticated telephone systems became available in small line sizes as exemplified in United States Patent No. 4,873,682 entitled "Digital Key Telephone System" issued 10 October 1989 in the name G. Irwin et al, and in United States Patent No. 4,893,310, also entitled "Digital Key Telephone System", issued 9 January 1990 in the name D. Robertson et al. Each of the telephone sets or terminal apparatus used in one of these systems includes a microprocessor and ancillary circuitry for communicating via a proprietary digital signal telephone line.The most basic of these telephone sets includes many more push buttons than the minimum of twelve required for a dial pad. Hence it was convenient that the face of the telephone be of ample dimensions to provide sufficient space for the buttons and the display. These dimensions were found to be convenient for circuit designers and implementors as there was usually sufficient space beneath the face and within the body of the telephone set to contain all the button electrical contact areas, the microprocessor, memory, codec and ancillary circuit elements upon one plural layered rigid circuit board, including a multitude of copper and/or nickel conductor paths extending across most of the space beneath the face of the telephone set.One example of a telephone set is that which is disclosed in United States Patent No. 4,654,488 entitled "Push and Rocker Action Switch" issued 31 March 1987 to A. P. Westfall. A more recent example of a key telephone set is found in United States Patent Application Serial No. 630,580 entitled "Private Telephone System with Simplified Command Feature" filed on December 20, 1990 by A. G. Offers et al and issued with Patent No. 5,073,923 on 17 December 1991. In these telephone sets the rigid circuit board has traditionally been in the form of a rigid epoxy glass board which includes two or more layers of metallic conductor patterns formed thereupon and is usually referred to as a printed circuit board (PCB).Part of each push button switch or key is provided by a conductive carbon pattern located on a surface of the PCB beneath each of the push button switches and keys whereby depression of the switch or key closes a circuit across the carbon pattern. Usually there is only one PCB extending beneath all the push button switches and keys, with attendant electronic circuits and devices being distributed among the carbon patterns as convenient. However, it has been determined that operational malfunctions may occur in proportion to the circuit board size and the lengths and numbers of metallic conductors, particularly during operation in areas of extreme electromagnetic interference.

Accordingly this problem can be reduced by reducing the total area of the circuit board. In some cases this consideration and/or other design constraints have required the use of two or more PCBs. In such cases the printed circuit boards are interconnected by cables and connectors. One of the penalities of having more than one circuit board is that of the cost of providing reliable connections between the circuit boards. Recently cost reduction design activities have reduced the bulk of the electronic circuitry such that the area of the circuit board required for this purpose is substantially less than the area required for the electrical contact areas.Consequently the circuit board might be of reduced size and expense and provide for more error free operation, were it not for the requirement of providing each of the conductive carbon patterns at the required push button locations within the telephone set.

It is an object of the invention to provide an electronic apparatus of a structure so configured as to capture a rigid circuit conductor substrate and a more economical flexible circuit conductor substrate in predetermined justaposition with a compressed elastomeric element to facilitate an economical and reliable electrical connection between overlapping portions of the conductor substrates, and thereby reduce the cost of providing the electronic apparatus without sacrificing functionality.

It is another object of the invention to provide a telephone set having electronic circuitry therein being carried by a circuit substrate of reduced area, whereby sensitivity to electromagnetic interference (EMI) is reduced.

It is another object of the invention to provide a telephone set having electronic circuitry therein being coupled to switch elements by conductor paths consisting of non-metallic material, whereby the conductor paths are of a greater resistance than that of a metallic path of similar proportions, whereby sensitivities to EMI and electrostatic discharge are reduced.

In accordance with the invention, an electronic apparatus includes a plurality of push button switches accessible for user actuation, and a flexible substrate carrying push button contact patterns underlying the push buttons. At least one of the contact patterns is connected with an electrode supported by the flexible substrate and being held under a welt of elastomeric material, in compression, against a corresponding electrode on a rigid substrate.

More specifically the electronic apparatus includes a plurality of push buttons being retained by apertures provided in a face portion, for access by a user. A base portion includes a peripheral wall carrying the face portion, a floor including a platform associated with at least some of the plurality of push buttons, and a plurality of support pillars extending from the floor.

A rigid circuit substrate is fixed to the plurality of support pillars and includes a first electrically conductive contact pad near an edge of the rigid circuit substrate, adjacent an edge of the platform. Advantageously, a flexible circuit substrate of relatively lesser cost per unit area than the rigid circuit substrate is used in conjunction with some of the plurality of push buttons. The flexible circuit substrate is positioned against the platform and carries an electrically conductive push button contacting formation thereupon, in association with each of the last mentioned push buttons. A portion of the flexible circuit substrate includes a second electrically conductive contact pad lying in contact with the first electrically conductive contact pad, and a circuit path being carried by the flexible circuit substrate between one of the push button contacting formation and the second electrically conductive contact pad. A welt of resilient material is retained by either one of the face portion and the base portion in compression relationship with the flexible circuit substrate, whereby electrical continuity is maintained between the first and second electrically conductive contact pads.

In an example, a telephone terminal apparatus, including a base portion fixedly supporting a face member for receiving a handset, comprises; rigid and flexible circuit substrates, each including an edge overlapping a corresponding edge of the other, each edge including a plurality of electrically conductive contact pads being arranged in a row for mechanical contact with the row of pads of the other edge; an elastomeric body lying along the overlapping edge of the flexible circuit substrate, remote from the rigid circuit substrate; and means integral with one of the base portion and the face portion, for retaining the elastomeric body in compression relationship with the overlapping edge of the flexible circuit substrate, whereby corresponding pads of the rigid and flexible circuit substrates are maintained in electrically conductive contact one with another.

An example embodiment is described with reference to the accompanying drawings in which; Figure 1 is a plan view diagram of an electronic apparatus, in the form of a key telephone station set, wherein the invention is useful; Figure 2 is a partial plan view of an interior portion of the key telephone station set in figure 1, as seen with an upper portion of the key telephone station set having been removed; Figure 3 is a partial plan view of a rigid circuit substrate used within the key telephone station set in figure 1, in accordance with the invention; Figure 4 is a partial plan view of a flexible circuit substrate used within the key telephone station set in figure 1, in accordance with the invention;; Figure 5 is a top view of a portion of an elastomeric sheet having push button contact members formed therein for use in conjunction with the rigid circuit substrate illustrated in figure 3; Figure 6 is a bottom view of a portion of the elastomeric sheet illustrated in Figure 5; Figure 7 is a partial cross sectional view taken along a line 7 - 7 in figure 5; Figure 8 is a diagram of a partial assembly of some elements illustrated in the preceding figures, in accordance with the example embodiment of the invention; and Figure 9 is an exploded assembly view of the telephone station set illustrated in the Figures 1 - 8; The key telephone station set is provided by: a body having a face portion 10 which carries a hand set 11 thereupon while the key telephone station set is in an idle or ON HOOK condition, as shown in figure 1; and a base portion 20, the interior of which is illustrated in figure 2, and which supports the face portion 10. The face and base portions 10 and 20 coact to contain electronic components and mechanical elements therebetween, for the purpose of providing a functioning key telephone station set.

However only those components and elements which are convenient for an understanding of the example embodiment of the invention are shown in the accompanying drawings.

In the description, specific reference of any of the drawings is taken in context with figure 9, which shows the relationship of the elements illustrated in each of the drawings 1 8; Referring to Figure 1, the face portion 10 includes apertures for viewing display devices 15 and 16, and many more apertures for user accessible confinement of a dial pad 12, feature access push button 13 and line access push buttons 14. Each of the push buttons is part of a push to make electrical switch which includes a contact pattern carried by a substrate and connectable by an associated conductor carried by an elastomeric membrane, a configuration well known to persons of typical skill in the technology of push button switch apparatus.

In Figure 2, the base portion 20 is shown with the face portion having been removed. The base portion 20 includes a floor 29 bounded by a peripheral wall 28 extending therefrom. Five tubular recesses 26 receive screw fasteners, not shown, for fixing the face portion upon the peripheral wall 28. A cavity is provided in the underside of the floor 29 by a raised portion 22, at a position which lies beneath the location at which the dial pad 12 is shown in figure 1. The raised portion 22 is at an elevation below that of an upper edge of the wall 28 and provides for a cavity, not visible beneath the base 20. Three openings 22a are provided in the raised portion 22, each of which may receive a telephone connector, not shown, with the cavity providing space for convenient physical access for insertion or withdrawal of one or more of the telephone connectors.Support pillars 24 extend from the floor 29 to an elevation beyond that of the raised portion 22 and provide fastening positions 24a, 24b and 24c, which may be threaded, for mounting a rigid circuit substrate 30, as exemplified in figure 3, directly beneath the dial pad 12. In addition to the fastening positions, alignment pillars 25, 25b and 25c each protrude beyond the elevation of the fastening positions 24a, 24b and 24c. A platform 23 is supported by the floor 29 at a position which lies beneath the feature and line access push buttons 13 and 14 in figure 1. The platform 23 has a flat surface being at an elevation greater than that of the fastening positions 24a, 24b and 24c, by an amount corresponding to a thickness of the rigid circuit substrate.

However this elevation is less than that to which the alignment pillars 25b and 25c protrude. A shelf 27 extends from one side of the platform 23, and at the same elevation as that of the fastening positions 24a, 24b and 24c; an edge of the rigid circuit substrate 30 shown in figure 3, being supportable thereupon. A resilient or flexible circuit substrate 40, as shown in figure 4, is supported by the platform 23 and is arranged to protrude at least over the shelf 27.

Referring to figure 3 the rigid circuit substrate 30 is provided by a plural circuit layer fiber epoxy circuit board 30, wherein connector electrodes 31 provide for connections with conductor paths 32. As a matter of convenience in this example, the circuit board 30 carries a plurality of switch contact conductive patterns, as exemplified at 33a and 33b, at locations such that when assembled in the key telephone set of figure 1, there is a switch contact pattern in alignment with each of the dial pad push buttons. The switch contact pattern 33a is exemplified as being connected to conductors in at least one circuit layer, not visible, via two plated through hole structures 36.An opposite side of the circuit board 30 is available to carry various electronic circuit packages and components which may be connected to conductors in any of the circuit layers in a manner familiar to persons of typical skill in the design and manufacture of printed circuit board assemblies. The circuit board 30 also includes two alignment openings 35, one of which is shown. The alignment openings are of diameters for slidably receiving the alignment pillars 25a and 25b, whereby the substrate 30 is positioned upon and supported by the fastenings positions 24a, 24b and 24c. Electronic components 38 and 39 are connected to the opposite side of the rigid circuit substrate, as represented in dotted outline.

Referring to figure 4, plastic sheet material, for example a polyester sheet material of about 0.005 of an inch thick, provides the flexible circuit substrate 40. The flexible circuit substrate 40 carries connector electrodes 41 which provide for connections via conductor paths 42 with switch contact conductor patterns, as exemplified at 43a - 43d. In this example switch contact conductor patterns at 43a - 43d are bifurcated. The switch contact conductive patterns are positioned at locations such that when assembled in the key telephone set of figure 1, there is a switch contact pattern in alignment with each of the feature and line push buttons 13 and 14. In this example the conductor elements are printed with a carbon ink by a silk screening process.

The flexible circuit substrate 40 includes two alignment opening 45, one of which is shown. The alignment openings are of diameters for slidably receiving the alignment pillars 25b and 25c, whereby the flexible circuit substrate 40 is positioned upon and supported by the platform 23. As the plastic sheet material circuit substrate 40 is limited to providing for conductor paths and switch contact conductor patterns it is providable at a small fraction of the cost of a typical rigid printed circuit board of similar area.

Although not shown, both sides of the flexible circuit substrate 40 are useful for supporting conductor paths.

In Figure 5, a portion of a top surface 51 of an elastomeric sheet 50 is shown with resilient depressible push button contact members 53a and 53b formed therein. In figure 6, a bottom surface 52 of the same portion of the same elastomeric sheet 50 is shown with the resilient depressible push button contact members 53a and 53b. In assembly the elastomeric sheet 50 is positioned via alignment openings 55, one only shown, and sandwiched between the rigid circuit board 30 and the push buttons of the dial pad 12. A somewhat similar elastomeric sheet, not shown, with resilient depressible push button contact members formed therein is likewise sandwiched between the flexible circuit substrate 40 and the feature and line push button 13 and 14. In this example the elastomeric sheet 50 is combined with an elastomeric flange 54 extending along part of one edge of the sheet.A top edge of the flange is visible in figure 5, and a bottom edge 56 of the flange is visible in figure 6. In figure 7 a partial cross sectional view, taken along a line 7 - 7 in figure 5, is more illustrative of detail showing the bottom edge 56 to be at an apex of convergent surfaces 58 and 59.

As before mentioned, it is an object of the invention to provide reliable electrical connections, between the rigid and flexible circuit substrates, at small cost, such that the cost advantage of using the flexible circuit substrate 40, instead of a rigid PCB, is preserved. An arrangement which provides for economical and reliable electrical connections is shown in figure 8, wherein the structure of the telephone terminal apparatus, namely that of the face and base portions 10 and 20, are utilised as containment members for a sandwich-like construction. Part of the face portion 10 in figure 1 is viewed in cross section along a line 8 - 8, in figure 8, to illustrate a retaining formation, in the form of a groove 19, which is provided by walls 17 and 18 depending from an underside of the face portion 10.The walls 17 and 19 need not be continuous and may include one or more gaps, as may be convenient along the length of the flange 54. Part of the flange 54 is lodged within the retaining formation with its end position or apex being compressed against the flexible circuit substrate 40, immediately adjacent the connector electrodes 41.

The flexible circuit substrate 40 lies upon the platform 23 being positioned- by the alignment pillars 25b and 25c and in a similar manner the rigid circuit substrate 30 lies upon the step 27, positioned by the alignment pillars 25a and 25b and being retained upon the fastening positions 24a, 24b and 24c. By this arrangement each of the connector electrodes 41 is maintained in physical and electrical pressure contact with a corresponding one of the connector electrodes 31.

With reference to the example embodiment, it should be noted that the combination of the flange 54 extending from the elastomeric sheet 50 has advantages of stabilising the flange in the desired assembly, desirably reducing the part count and cost of the assembly, and ultimately reducing structural rigidity and continuity requirements of the retaining formation 19. Particularly with reference to the illustration in figure 8, the end portion or apex 58 is shown to be distorted under compressive force, as is part of the flange 54 to resemble a thickened welt. It should be noted that the distortion of compression may not be of the same exact form as that illustrated. Alternate embodiments of the invention may include structures wherein the support pillars or the alignment pillars depend from the underside of the face portion 10 or the retaining formation for the welt may just as well be supported by the base portion 20.

Claims

CLAIMS:

1. An electronic apparatus including a plurality of push buttons being accessible to a user, the electronic apparatus comprising: a face portion having apertures defined therein for retaining the plurality of push buttons; a base portion carrying the face portion, the base portion having a floor including a platform beneath the plurality of push buttons, and a plurality of support pillars extending from the floor; a rigid circuit substrate including an electrically conductive contact pad near an edge of the rigid circuit substrate, adjacent an edge of the platform;; a flexible circuit substrate, being positioned against the platform and carrying an electrically conductive push button contacting formation, a portion of the flexible circuit substrate including an electrically conductive contact pad and a circuit path being carried by the resilient circuit substrate between the push button contacting formation and the electrically conductive contact pad; the electrically conductive contact pads of the rigid and flexible circuit substrates lying in contact with one another; a welt of resilient material being retained by one of the face portion and the base portion in compression relationship with the resilient circuit substrate, whereby electrical continuity is maintained between the first and second electrically conductive contact pads.

2. A telephone terminal apparatus including a base portion fixedly supporting a face member for receiving a handset, the telephone terminal apparatus comprising: rigid and flexible circuit substrates, each including a plurality of conductive circuit paths, an edge for overlapping a corresponding edge of the other, each edge including a plurality of electrically conductive contact pads terminating some of the conductive circuit paths and being arranged in a row for mechanical contact with the row of electrically conductive contact pads of the other edge; an elastomeric body lying along the overlapping edge of the flexible circuit substrate; and means, integral with one of the base portion and the face portion, for retaining the elastomeric body in compression relationship with the overlapping edge of the flexible circuit substrate, whereby corresponding pads of the rigid and flexible circuit substrates are maintained in electrically conductive contact one with another.

3. A telephone terminal apparatus as defined in claim 2 wherein the flexible circuit substrate includes electrical contacting formations being supported by a platform in justaposition with a plurality of push button switch means, each push button switch means including a resiliently deformable contact carrier being integral with an elastomeric sheet, the elastomeric sheet overlying the flexible circuit substrate and including an edge portion which provides said elastomeric body.

4. A telephone terminal apparatus as defined in claim 3 wherein said elastomeric body is of the form of a thickened welt.

5. A telephone terminal apparatus as defined in claim 3 wherein said elastomeric body comprises an elastomeric flange extending along part of the edge of the elastomeric sheet, the flange including parallel sides extending to a top edge and convergent surfaces extending to an apex, providing a bottom edge for deformable contact with the flexible circuit substrate.

6. A telephone terminal apparatus as defined in claim 3 wherein the rigid and flexible circuit substrates each include a plurality of alignment openings for slidably receiving corresponding alignment pillars each extending from one of the face and base portions.

7. A telephone terminal apparatus as defined in claim 2 wherein the conductive circuit paths of the flexible circuit substrate are primarily of a carbon material.

8. A key telephone station set, including a body for receiving a hand set, the body comprising: a face portion having an outer surface for carrying the hand set thereupon while the key telephone station set is in an idle condition, an underside including a groove being defined by walls depending from the underside and apertures extending through the face portion between the outer surface and the underside; a display device being viewable through one of the apertures; dial pad push buttons being accessible through corresponding ones of the apertures; line and feature selection push buttons being accessible through corresponding ones of the apertures;; a base portion which supports the face portion, the face and base portions being arranged in combination to contain electronic components and mechanical elements of the key telephone station set in operable assembly therebetween, the base portion including, a floor bounded by a peripheral wall extending therefore, fastening positions being provided by support pillars extending from the floor to a predetermined elevation, a platform being supported by the floor at a position which lies beneath the feature and line access push buttons, the platform having a flat surface being of an elevation greater than that of the fastening positions, a shelf extending from a side of the platform next to the dial pad push buttons at an elevation corresponding to that of the fastening positions, a rigid substrate including a surface, the surface carrying the connector electrodes connected with conductor paths leading to a plurality of switch contact conductive patterns, and an opposite surface, the rigid substrate being fastened such that each switch contact conductive pattern is aligned with a corresponding one of the dial pad push buttons and a portion of the opposite surface, beneath the conductor electrodes, lies against the shelf; a flexible substrate being supported upon the flat surface of the platform and including a surface, the surface carrying connector electrodes connected with conductor paths leading to a plurality of switch contact conductive patterns, the connector electrodes of the flexible substrate being aligned and in contact with the connector electrodes of the rigid substrate; ; an elastomeric sheet being sandwiched between one of the rigid and the flexible substrates and corresponding ones of the push buttons, including resiliently deformable push button contact members, and an elastomeric flange extending along part of one edge of the sheet, the elastomeric flange having a top edge occupying said groove, and a bottom edge positioned in contact against the flexible substrate along a line adjacent the connector electrodes and held in compression there against by the assembly of the face portion with the base portion.

9. A telephone terminal apparatus substantially as described with reference to the accompanying drawings.