AU1943988A

AU1943988A - Improvements in and relating to electrical components

Info

Publication number: AU1943988A
Application number: AU19439/88A
Authority: AU
Inventors: Edwin Thomas Webb
Original assignee: PED Ltd
Current assignee: PED Ltd
Priority date: 1987-06-16
Filing date: 1988-06-08
Publication date: 1989-01-19
Also published as: EP0363410A1; WO1988010505A1; JPH02503844A

Description

Title: Improvements in and relating to Electrical Components

Field of the invention

This invention concerns the construction of electrical components particularly components for mounting on printed circuit boards and the like. Whilst aspects of the invention have general applicability to the design and construction of electrical components, the invention is particularly concerned with the design and construction of miniature switches and relays for printed circuit board mounting.

Background to the invention

A miniature electro-magnetically operated relay suitable for circuit board mounting is described in US Patent 4587501. The particular relay described therein is a polarised electromagnetic relay having an armature assembly at each end with related contacts and permanent magnets. Energisation of the core by the passage of current through the coil produces appropriate movement of the armatures and appropriate opening and closing of the contact sets.

The relay is designed to fit on an insulating base through which conductive pins extend and protrude on the underside thereof. The unit is thereby readily securable to a printed circuit board having an appropriate pattern of holes formed therein through which the pins extend for soldering to conductive tracks normally on the underside of the printed circuit board-

Figure 1 of the Patent illustrates how the relay is constructed from a large number of separate items whose juxtaposition and spacing has to be determined and controlled during manufacture.- ..Where .tiny, distances are concerned as between the pole pieces in the working gaps at opposite ends of core, manufacturing tolerances can produce wide variations in the operating characteristics of the final product and high reject rates. In addition this type of construction does not lend itself to automated assembly line techniques.

It is therefore an object of the present invention to provide an alternative and improved form of construction and method of assembly of electrical components and in particular miniaturised switches and relays for printed circuit board mounting, more appropriate to automated methods of. construction and assembly.

It is another object to provide a method of assembly which is less prone to introduce variation in operating characteristics and parameters of the final product due to manufacturing tolerances.

Summary of the invention

According to one aspect of the present invention an insulating base on which an electrical device is to be carried is moulded onto a sheet of conductive material which has previously been stamped or otherwise cut away so as to define a plurality of components which after being partially embedded in the base material, can be cut to length and formed as by bending in one direction so as to comprise conductive pins extending from the underside of the base for attachment to a printed circuit board or the like and by bending in another direction to provide conductive members protruding from at least one other face of the moulded base, for the attachment thereto of other electrical components or parts thereof, or which can themselves form structural elements of said component.

Preferably the conductive sheet material is sheet metal, such as phosphor bronze, copper or brass.

The base may be moulded from plastics material, typically by injection moulding.

By adopting this method of construction and by using a stable material for the sheet, the position of the conductive pins (and more particularly the positions of the conductive members upstanding from the base) can be determined very precisely by means of a stamping process or the like, working on the conductive sheet material, and no reliance is placed on the moulded material for determining the relative positions of these conductive members. In this case the moulding merely serves as a support for holding the prepositioned and preformed conductive members in place.

The invention enables precise relative positioning of the electrically conductive members which greatly facilitates the subsequent attachment of electrical components, parts or devices to the assembly, particularly where automated assembly is to be employed. Furthermore the precise positioning of the conductive upstanding members removes one area of uncertainty as regards dimensioning, so that a wider range of tolerance on components to be mounted and connected thereto can be accommodated, if desired.

What is more important however is that where the conductive members are themselves to form part of or to carry other members, which themselves must be precisely located relative to other parts of the assembly, the final position of the members and supports is dictated solely by the original stamping or cutting process and the bending of the members after severance, and no reliance is placed on relative positioning of the conductive members by the moulding of the base. This is of considerable importance since it is generally accepted that moulded components suffer from large manufacturing tolerances and by utilising a stable material in sheet form, it can be cut and bent to very precise limits allowing accurate spacing of a few thousandths of an inch to be achieved.

The invention is thus of great importance in the construction of miniature switches particularly magnetically operated switches where, because of other manufacturing restraints, the working gaps between contacts must be very small and typically require accuracies of the order of a thousandth of an inch. Thus for example conductive supports for fixed contacts at one end of the device and a support for a magnetically attractable arm which is to extend between the two first mentioned supports, can be positioned very accurately, and the accuracy maintained during and after manufacture, so that working gaps of the order of a thousandth of an inch or so can be readily achieved using automated metal bending and cropping techniques, without the need (except perhaps for final setting up) for manual adjustment.

In a preferred arrangement a separate sub-assembly is also formed from the sheet of conductive material, and has further components attached thereto (for example by the use of jigs) before being severed from the sheet for subsequent assembly with the main .component. The sub- assembly, which may for example comprise the armature/actuator of a relay, may also have a plastics part formed thereon during moulding of the insulating base.

Since such a sub-assembly may be comparatively small, it can be accurately manufactured from the same sheet and without requiring a separate fabrication process.

A comparison of the method of assembly and construction envisaged by the present invention with the construction described in US Patent 4587501 will immediately demonstrate the advantage of the invention, if only in that the present invention does not require a large number of separate, tiny loose piece parts to be fitted together.

What is more important however is that in this prior art method of construction a contact set is made up of two separate metal elements 15 and 15' between which is located an armature 14, which itself has to be carried by a further element 16. The elements such as 15 and 16 include downwardly depending pin sections such as 17 which protrude through and are secured in slots in the base 12. The positions of the upstanding sections 15, 15' etc. is thus determined by the positions of the slots in the base 12 and are therefore susceptible to manufacturing tolerances in the moulding of the base. This approach has been found by the applicants to be highly undesirable in practice and has made it very difficult to assemble a miniature relay using automated assembly techniques. Invariably a very considerable human input to fine tune the positions of the elements and contact sets has been necessary before a relay constructed in this general way ^! can be made to work.

According to another apsect of the present invention a method of constructing an electrical switch having at least one movable contact and at least one fixed contact and which is adapted for mounting on a printed circuit board comprises the steps ofs-

1. forming a plurality of conductive fingers by removal of material from a sheet of conductive material,

2. moulding plastics material in the form of a base so as to envelop part of the conductive fingers in the conductive sheet material,

3. severing at least some of the fingers from the remainder of the conductive sheet material,

4. bending some of the conductive fingers in a downward direction relative to the base to provide conductive pins for attachment to a printed circuit board or the like,

5. bending others of the conductive fingers in a generally upward direction so as to form (or form supports for) fixed and movable switch contacts, the working gap therebetween being determined solely by the relative position of the conductive fingers in the original sheet material and on the bends in the fingers after moulding, and

6. finally severing the sub-assembly from the sheet by severing all remaining fingers joining the sub-assembly thereto.

Where different conductive material is to be incorporated as contacts for the switching members, such material may be applied as by riveting, brazing or the like, to appropriate regions of the conductive fingers before the latter are bent upwardly from the base, thus enabling the addition of the contact material to be performed in the flat.

Where a further conductive member, such as an elongate conductive arm bearing a switch contact at one end, is to extend for example from one end of the base to the other, or across the base, it may be advantageous to secure the elongate arm to one of the conductive fingers which is to be bent up relative to the base, whilst the finger is still "in the flat", and thereafter to bend the finger relative to the base so as to bring the attached arm thereon into its correct working position relative to other conductive fingers or other components similarly mounted on other fingers associated with the base.

In order to further facilitate automated assembly and construction of such devices, where such additional conductive components, (such as elongate resiliently deformable contact bearing arms), are to be attached to conductive support fingers associated with a moulded base as aforesaid, the components which are to be secured to the fingers may themselves be formed by stamping (or other processes for material removal) from a second sheet of conductive material, so that the components are left joined to the sheet by severable limbs, and so that the second sheet can be positioned as an overlay to the first mentioned sheet, either before or after moulding of the base material, and the components which are to be secured to the conductive- fingers-in the first sheet ma be secured thereto as by riveting, brazing, welding or the like, and thereafter removed from the second sheet by severance of the joining limbs, so that the overlay can be removed to enable the first sheet to be further processed.

Where the first and second sheets are in the form of elongate strips drawn from two rolls, and severable components are formed at regular intervals along the length thereof, the two lengths of sheet material may be fed to, overlaid at and indexed through a single work station at which at least one component in the first sheet is secured to at least one component in the second sheet, and is thereafter severed from the first mentioned sheet, to enable the second sheet subsequently to be indexed beyond the station with the component (or components) from the first sheet now attached thereto.

This aspect of the invention is of particular advantage where the material from which the one component is to be formed differs from that from which the other component (to which it is to be attached) is formed_

Preferably at least at the position of overlaying, the direction of feed of the one sheet is not parallel to the direction of feed of the other sheet. Typically the two sheets are overlaid orthogonally.

A manufacturing process incorporating the invention may include two or more such stations by which different components from two or more sources can be added to the components in a primary sheet by simply indexing the latter through a series of work stations at each' ofwhich a different sheet is overlaid and a component therein is secured to the appropriate component in the primary sheet before the now joined component is severed from the overlaid sheet to enable the primary sheet to be indexed to a further work station.

Each sheet may be in the form of a so-called lead frame having sprocket holes (for engagement by indexing means) at intervals along the length thereof. Such sheets which have also been stamped or otherwise treated to provide appropriate patterns of components at intervals along their length, may be drawn from the roll by engagement with appropriate sprocket drive means, and, at each work station, locating pins may be employed, to engage in the sprocket holes in both sheets of material, so as to accurately position the two sheets relative the one to the other at the work station.

According to a particularly preferred feature of this aspect of the invention, the indexing sprocket holes are spaced,apart by the same distance along the length of each sheet as they are spaced apart transverse to the length direction thereof, so that at a work station at which one length of sheet material is overlaid at right angles by another length of sheet material, there is a unique position at which four indexing holes in the two lengths of sheet material are aligned at the four corners of a square, and can be engaged by four locating pins to hold the assembly of overlaid sheet material accurately in this unique position whilst a manufacturing process is performed.

It is an advantage of the invention that during the manufacturing process, the moulded base and intermediate assemblies of the final device are maintained in position along the length of the so-called lead frame so as to obviate the need for handling individual sub-assemblies. It is thus possible to index the moulded base and growing component structure through an automated assembly line by simply indexing the lead frame along the line through a series of work stations. To this end at least some of the components embedded in the moulded base simply comprise fingers for attaching the base to the lead frame during the manufacturing process. At the end of the process, the assembly can be removed from the lead frame by simply cutting the now redundant attachment fingers and allowing the component to become separated from the lead frame. Since it may be difficult to cut the attachment fingers flush with the moulded base, it is advantageous if the fingers are cut at a position some distance from the edge of the base, and the sections of the fingers which remain protruding from the base are bent up (as a further operation) into recesses conveniently provided within the moulding, so as not to constitute unwanted conductive protrusions along edges of the base. This is of particular importance where a cover is to be fitted to the base and is of even greater importance where the cover is to be sealed to the base as in the case of a miniature relay where it is desirable that the device is sealed within a controlled environment. In general, where the moulded base is to be contained within the lead frame and supported therein by means of a plurality of severable attachment fingers, the latter are preferably provided on at least three edges of the base so as to reduce the risk of twisting and bending of the base relative to the lead frame.

According to a further aspect of the invention, in a method of assembly of an electrical switch or relay, a cover is fitted to the base and sealed thereto by means of a suitable adhesive.

Where the final component is to be remotely actuable as by means of an electromagnetic actuator, an electromagnet and associated armature assembly may be secured to the base during assembly.

The invention also lies in the construction of an electrical device fabricated within a lead frame comprising a moulded base attached to the lead frame by severable elongate links, which incorporates a first set of elongate conductive members formed by severing and bending in a downward direction selected links for example for connecting and mounting the device on a printed circuit board, and a second set of elongate conductive members formed by severing other of the links, which are bent upwardly from the base to serve as structural elements of the device or supports for components forming, the device.

According to a further aspect of the invention in the assembly of a miniature electromagnetically operated relay comprising a base having mounted thereon an electromagnet, an armature and at least one contact set operable from a closed to open position (or vice versa) by movement of the armature, at least the contact set is formed by or carried on upstanding conductive components whose spacing and position during manufacture are determined by a lead frame, within which the base is supported by severable attachment tabs, the upstanding components being formed during manufacture by cutting and^'-bending elongate links of the lead frame which have been embedded in part in the moulded base.

Conductive pins for attachment of the relay to a printed circuit board or the like preferably extend from the underside of the base and may also be formed by cutting and bending elongate links of the lead frame which have been partially embedded in the moulded base.

According to another aspect of the present invention such an electrical component comprises a sub-assembly to be mounted on the base having at least one conductive pin which after final assembly is to protrude through a hole in the base so as to provide for electrical connection to the sub-assembly, the base being provided with an oversize aperture through which the pin can protrude having a diameter which decreases from the top of the base to the underside of the base and the sub-assembly is provided with a downwardly directed spigot having a similar decreasing diameter for insertion into the aperture in the base, the spigot itself surrounding the conductive pin which is a tight fit therein but can be pushed therethrough to protrude below the base to provide the electrical connection as aforesaid during assembly of the device. - 13 -

The spigot provides for location of the sub-assembly relative to the base and avoids the need for the conductive pin to provide mechanical support between the sub-assembly.

An adhesive may be employed to secure the sub-assembly in the base by smearing or otherwise coating some or all of the surface of the spigot before it is inserted into the hole (or smearing the wall of the hole) before the spigot is inserted.

A particular advantage of this aspect of the present invention is that the conductive pins cannot be guaranteed straight and therefore hole clearances in the base through which they have to protrude would normally have to be large to accommodate manufacturing tolerances etc. By mounting the pins themselves in a sub-assembly which itself is locatable by way of a tapering fit between a spigot and a tapering hole, so problems associated with location and manufacturing tolerances can be obviated and a reliable sealed joint can be provided through which the conductive pin can protrude. This is of particular importance where the device is a relay which itself is to be sealed within a casing. In such a device, it is important that the conductive pins for example associated with the relay coil can penetrate through the base but nevertheless must be sealed to the base so as to prevent the seal being broken, and the present invention allows this.

The invention is thus particularly applicable to a coil bobbin sub-assembly forming part of a electromagnetic relay which is moulded on a moulded base wherein the coil bobbin includes tapering spigots protruding from its underside through which conductive pins can pass for providing electrical connection to the relay coil and wherein the spigots can be sealed into their cooperating holes in the base by means of an appropriate adhesive to provide a good seal.

Brief description of the drawings

The invention will now be described by way of example with reference to the accompanying drawings in whic ^~ —

Figure 1 is a plan view of one section of a sheet metal lead frame, after a stamping operation to remove metal from the lead frame sheet.

Figure 2 shows the same lead frame section after a plastics base has been moulded into position.

Figure 3 illustrates how a second lead frame can overlie the first to allow the superposition of components and permit components in one lead frame to be secured to components in the other before separation from their host frame.

Figure 4 is a perspective view of a primary lead frame with a moulded base in position and certain of the conductive fingers bent up to form structural elements of the final device in accordance with the invention,

Figure 5 is a perspective view of an armature/actuator sub-assembly forming part of the device of Figure 4,

Figure 6 is a perspective view of a coil bobbin suitable for attachment to the base of Figure 4 between the various upstanding components thereon,

Figure 7 is a perspective view of a central core for use with the coil former of Figure 6,

Figure 8 is a perspective view of a U-shaped yoke which cooperates with the central core of Figure 7 to form an electromagnet core assembly,

Figure 9 is a perspective view of the assembled coil ^* former, core and yoke with a coil shown wound on the former,

Figure 10 is a rear end view of the assembly of Figure 9,

Figure 11 is a perspective view of the base assembly shown in Figure 4 after separation from its lead frame, with the electromagnet assembly of Figure 9 mounted thereon, and illustrates how the overall assembly can be encompassed within a lid, and

Figure 12 is an internal view of the lid of Figure 11.

Detailed description of the drawings

Figure 1 shows part of a lead frame 10 having pairs of indexing sprocket holes 12, 14 and 16, 18 at regular intervals along its length. The lead frame is formed from thin sheet metal such as phosphor bronze, and typically can be coiled.

Intermediate sprocket holes 15 are shown which may be used for indexing but are not necessarily used for locating the lead frame at work stations. The two pairs of sprocket holes 12 and 14 and 16 and 18 define a square on the lead frame having apertures formed therein as by stamping. Similar patterns of apertures are formed at regular intervals along the length of the lead frame between corresponding spaced apart pairs of sprocket holes. In this context the two large substantially rectangular apertures 20, 22 of the next pattern of _ -.. - apertures along the length of the lead frame can just be seen at the bottom of Figure 1 as denoted by 20' and 22' . Extending into the apertures 20, 22 is a transverse strip 208, which is again repeated at 208" between the apertures 20' and 22' .

Electrical contacts of appropriate metal, typically of a precious metal are formed at 24 and 26 as by riveting or brazing- and on the underside at 28 and 30 in a similar way.

The material which has not been cut away in the lead frame of Figure 1-comprises conductive links which are to form pins on the one hand, adapted for securing to a printed circuit board or the like, and on the other hand, structural elements or supports for the final device. Such devices require an insulated base and this is most conveniently formed by plastics injection moulding in the central region of the lead frame to form a substantially rectangular plastics base 32 as shown in Figure 2, in which the same reference numerals have been used to denote corresponding parts as in Figure 1. The plastics material of base 32 is also shaped around the ends of the strip 208 to form end pieces 210, 212.

Pole pieces 202, 204 (to be described with reference to Figure 5) are now attached to the strip 208 as by welding or soldering, the pole pieces being correctly aligned by means of a jig (not shown). A permanent magnet 206 (see Figure 5), as yet unmagnetised, may also be welded or soldered to the strip 208 at this time to form an armature/actuator sub-assembly 102. This sub-assembly, is then severed and removed from the lead frame by a die tool which cuts- or crops along the lines 101 and 103. The waste portion adjacent the crop line 103 may at the same time also be severed along a line 105.

In this manner this separate sub-assembly can be made from the same lead frame 10, and without the complication and expense of fabricating the sub-assembly on a separate production machine. Also the pole pieces and magnet can be accurately positioned for attachment to the strip 208.

Whilst still in the flat, additional components can be secured to the conductive links of the lead frame as shown in Figure 3. Here a second lead frame 34 is laid over the first lead frame 10 at right angles to the general direction of the latter so that elongate spring arms 36 and 38 in the second lead frame are correctly positioned relative to appropriate links in the first lead frame to allow the components to be joined as by riveting, brazing or welding at 40 and 42 respectively. After joining in this way, the arms 36 and 38 can be severed from the remainder of the lead frame 34 by means of cuts at 44, 46, 48 and 50 whereafter the second lead frame 34 can be lifted and indexed relative to the lower lead frame 10. The latter may then also be indexed away from the work station.

Circular holes in the second lead frame 34 are aligned with the sprocket holes 12, 14 and 16, 18 of the first lead frame to enable locating pins 52, 54, 56 and 58 to protrude therethrough and accurately align the two lead frames at the work stations.

The spring arms 36 and 38 also include rectangular lugs 55 and 57 (see Figure 4) which are formed by stamping and severing cuts along .the^* lines.44 land 50 shown in- igure 3.

The moulded base 32 includes two tapered circular apertures 60 and 62, the purpose of which will be described later.

By severing and selectively folding some of the links which secure the moulded base assembly 32 to the first lead frame 10, so the sub-assembly of Figure 4 can be formed. By way of illustration the fingers 64 and 66 shown in Figures 2 and 3 have been folded down to form two of the pins by which the device can be secured to a printed circuit board or the like, whilst fingers such as 68 and 70 to which the components 36 and 38 are attached, have been folded in an upward sense so as to provide structural elements of the final component.

Although not shown clearly in Figures 2 and 3, the moulded base includes recesses and slots as at 72 and 74 (Figure 4) to facilitate the bending of the severed links such as 68 and 64 to their final positions.

Whilst some of the links joining the moulding to the lead frame are shown as having been severed and bent in Figure 4, others remain as at 76 to 80, by way of example. These remaining links serve to support the moulding within the lead frame for the remaining stages of manufature and after the component has been fully manufactured and assembled, these remaining but now redundant links can likewise be severed and as appropriate bent up into slots such as 86 for link 78, so as to be well clear of the edges of the base and enable, if appropriate, a lid or cover to be sealingly engaged over the base.

The sub-assembly shown in Figure 4 actually comprises the spring contact assembly of a miniature relay. Thus the arms 36 and 38 are the springs on which the moving contacts are carried whilst the bent up severed links 68 and 70 provide the supports for the fixed ends of the springs. The bent up severed links 88, 90, 92 and 94 comprise the fixed contact supports which cooperate with the two springs 36 and 38 to form two change-over contact sets.

Within the sub-assembly of Figure 4 is mounted the electromagnetic actuator made up of a coil 104 and magnet assembly and attention is now directed to the manner of manufacture of this internal sub-assembly of actuator and magnet.

Reference will first of all be made to Figure 11 which is a perspective view of the base sub-assembly of Figure 4 (after separation from the lead frame) having the actuator sub-assembly mounted therein. The latter comprises a U- shaped yoke 100 and the armature/actuator sub-assembly 102 the construction of which is further described below.

The armature/actuator sub-assembly carries the actuator strip 208 and end pieces 210, 212 which act on the two elongate spring arms 36 and 38 and by biasing the armature in one direction opposite to the direction in which it will move when the coil 104 is energised, so the contact sets can be made to change over in response to energisation of the coil.

Having described the overall relay in general terms, the construction of the actuator sub-assembly 102 will now be described briefly -with, reference to Figure 5. The armature essentially comprises three parts, the pair of magnetiseable cheeks or pole pieces 202, 204 held separated by the strip 208, the very powerful permanent magnet 206 between the two cheeks and actuator strip, and end pieces 210, 212 for determining the initial and actuated position of the two spring sets, as previously referred to. The two side cheeks or pole pieces 202, 204 are formed from the flat and are made of soft iron, such as Swedish iron.

It should here be noted the actuator strip 208 and the end pieces 210 and 212 are shown chain-dotted in Figures 3 and 4. In fact at this stage they are no longer in those positions, as previously referred to.

The electromagnet is formed from a number of different constituent parts one of which is shown in Figure 6. This comprises a bobbin 156 having end cheeks 158 and 160 the latter including legs 162 and 164 having tapering spigots 166 and 168 on their undersides respectively. Conductive pins 170 and 172 protrude through and are embedded in the legs 162, 164. The lower protruding ends of the pins comprise further conductive devices for attaching the component to a printed circuit board or the like, and the upper protruding ends provide terminations for the coil 104, which is wound on the bobbin 156 in a manner known per se and may comprise a single or double wound coil. If the latter, then additional leads and terminations are required.

A magnetiseable core 174 shown in Figure 7, is fitted through the rectangular section hollow interior 176 of the bobbin 156 with a central pole 178 at the end remote from the end having the legs.,.162 and 164.

The U-shaped yoke 100 is fitted around the bobbin after the coil 104 has been wound thereon and is shown in Figure 8. The two pole pieces which are to cooperate with the central pole 178 are shown at 180 and 182 respectively.

Figure 9 shows the assembly of the coil and yoke and illustrates how the coil wire can be terminated on the conductive pins, one of which is shown at 172.

A rear view of the electromagnetic assembly of Figure 9 is shown in Figure 10. This clearly shows the two spigots 166 and 168 which are designed to fit into the tapering holes 60 and 62 previously referred to with reference to Figure 3. The location of the spigots in the holes 60 and 62 is sufficiently accurate to position the bobbin and electromagnetic assembly relative to the fixed contacts formed by bending up the severed links 88, 90 etc. as shown in Figure 4. To ensure a good seal, the spigots 166 and 168 are adhesively secured within the holes 60 and 62.

The conductive pins 170 and 172, to which opposite ends of the winding are attached, are themselves a tight fit in the base of the sub-assembly shown in Figure 10 and can be pushed through holes which extend through the base and the spigots 166 and 168 so as to protrude beyond and below the base of the device after assembly. By providing a good tight fit between the pins and the base of the sub- assembly, so there is little chance of any ingress of moisture into the otherwise sealed interior of the relay assembly after construction.

Referring again to Figure 11, the U-=shaped armature*-and actuator assembly of Figure 5 is fitted over the central pole 178 with the cheeks 202 and 204 between the two pole pieces 180 and 182 and the central pole 178.

The assembly of Figure 11 is protected by means of a lid or cover of generally rectangular proportions, denoted by reference numeral 184, the interior of which is generally rectangular but includes pairs of moulded bosses 186 at the upper corners and towards the centre thereof (see Figure 12) . These extend to a depth within the cover 184 such that the latter is caused to just fit snugly on the base 10 with the lower ends of the bases 186 contacting the upper edges of the U-shaped yoke 100 (Figure 11).

The height of the cover 184, at least internally, is thus controlled so that when fitted the cover prevents the U-¬ shaped yoke 100 from lifting off the base and the armature actuator from lifting relative to the spring arms 36 and 38.

Figure 11 also shows how the unwanted support links can be folded up after severing so as to be wholly contained within the cover 184 when the latter has been fitted. In this way they do not constitute unwanted conductive protrusions on the underside or along the edge of the base. Two of the folded up links are denoted by reference numerals 186 and 188 in Figure 11.

The conductive pins such as 190, 192 and 194 provide electrical connection to the moving contacts and fixed contacts of the nearest contact set shown in Figure 11, whilst a similar set of conductive pins on the other side of the base, (of which one can be seen at 196) provide similar contacts to the other contact set on the other side of the assembly.

Since the actuator strip 208 is non-symmetrical, and both of the spring arms 36 and 38 are biased inwardly towards on another, the insertion of the armature/actuator assembly of Figure 5 will cause the spring arm 36 to be -displaced outwardly, leaving spring arm 38 in the position dictated by its natural resilience. Energisation of the coil 104 will result in interaction between the powerful static field due to the permanent magnet and the induced electromagnet field, thereby causing the armature assembly to move in the direction of the spring 38 thus allowing spring 36 to relax inwardly and cause spring 38 to be displaced. The contacts on the ends of the springs 36 and 38 will thus change-over, and in the case of the nearest spring set, the spring contact will change-over from being in contact with the outboard fixed contact to the inboard fixed contact, upon energisation of the coil, and vice versa on denergisation. The opposite is the case with regard to spring 38.

It will be seen that by constructing the contact and spring carrying structure by folding up severed links of metal sheet material, which have been cut from the flat in a metal stamping or other fabricating process, and always ensuring that folds are made in a non-critical direction, so it is possible to achieve very high assembly accuracies and extremely small tolerances.

Claims

- 25 -C AIMS

1. An electrical component fabricated from a sheet of conductive material to provide a plurality of conductive members and comprising an insulating base moulded onto said sheet to envelop part of said conducting members, said conductive members including a first set of members bent downwardly from the base for connection with and mounting on a printed circuit board or the like, and a second set of members bent upwardly from the base to serve as structural elements or supports for additional components.

2. An electrical component according to claim 1 in which some of said second set of members comprise supports for fixed and movable electrical contacts, the working gap therebetween being determined by the relative position of said supports in said original sheet and on the upward bending of said supports from said base.

3. An electrical component according to claim 2 in which said base has mounted thereon an electromagnet and an armature, said electrical contacts being operable between a closed position and an open position by movement of said armature.

4. An electrical component according to claim 1 in which said base has mounted thereon a sub-assembly having at least one conductive pin to provide for electrical connection to the sub-assembly, the base being provided with an oversize hole through which the pin can protrude and having a diameter which decreases from the top to the underside of the base, the sub-assembly comprising a downwardly directed spigot having a similar decreasing diameter for insertion into said hole, the spigot itself surrounding the conductive pin which is a tight fit therein but can be pushed therethrough to protrude below the base to provide said electrical connection.

55 An electrical component according to claim A , in which the sub-assembly is secured to the base by the application o_ adhesive between the spigot and the hole of the base.

6. An electrical component according to claim 1, further comprising a cover fitted to said base and secured thereto by adhesive.

7. A method of constructing an electrical component having fixed and movable contacts and adapted for mounting on a printed circuit board or the like, comprising the steps of forming a plurality of conductive fingers from a sheet of conductive material by removal of material therefrom; moulding an insulating base on to said sheet so as to envelop part of said conductive fingers; bending some of the conductive fingers in a downward direction relative to the base to provide conductive pins for attachment to the printed circuit board; bending others of the conductive fingers in a generally upward direction, so as to form or provide supports for said contacts, the working gap therebetween being determined by the relative position of the conductive fingers in the original sheet and on the bends in the fingers after moulding; and severing the component from the sheet by severing all remaining attachment fingers.

8. A method according to claim 7 in which a conductive contact material different from said sheet is incorporated -an - in said contacts, and further comprising the step of applying said contact material by riveting, brazing or the like to appropriate regions of the conductive fingers before the latter are bent upwardly from the base, thus enabling the addition of the contact material to be performed in the flat.

9. A method according to claim 7 in which an additional component is attached to conductive support fingers associated with said moulded base, and said additional component itself is formed by material removal from a second sheet of conductive material, so that the component is left joined to the second sheet by severable arms, wherein the second sheet is positioned as an overlay to the first mentioned sheet and the additional component is secured to the conductive fingers in the first sheet and thereafter removed from the second sheet by severing said arms to enable the first sheet to be further processed.

10. A method according to claim 9, in which the first and second sheets are in the form of elongate strips drawn from two rolls, and severable components are formed at regular intervals along the lengths thereof, the two lengths of sheet material being fed to, overlaid at and indexed through a single work station at which at least one component in the second sheet is secured to at least one component in the first sheet, and is thereafter severed from the second sheet, to enable the first sheet subsequently to be indexed beyond the station with the component from the second sheet now attached thereto.

11. A method according to claim 9 in which, at least at the position of overlaying, the direction of feed of the one sheet is orthogonal to the direction of feed of the -73 - other sheet.

12. A method according to claim 10 further comprising two or more such stations by which different additional components from two or more sources can be added to the main component in the first sheet by indexing the latter through a series of work stations at each of whic a different sheet- is overlaid and- a component therein- is secured to the main component in the first sheet before the now joined component is severed from the overlaid sheet to enable the first sheet to be indexed to a further work station.

13. A method according to claim 10 in which each sheet is in the form of a lead frame having sprocket holes at regular intervals along the length thereof.

14. A method according to claim 13 in which said sheets are drawn from respective rolls by engagement with appropriate sprocket drive means, and at each work station locating pins are employed to engage in the sprocket holes in both sheets of material, so as to accurately position the two sheets one relative the other at the work station.

15. A method according to claim 14 in which the indexing sprocket holes are spaced apart by the same distance along the length of each sheet as they are spaced apart transverse to the length direction thereof, so that at a work station at which one length of sheet material is overlaid at right angles by another length of sheet material, there is a unique position at which four indexing holes in the two lengths of sheet material are aligned at the four corners of a square, and can be -2*1- engaged by four locating pins to hold the assembly of overlaid sheet material accurately in this unique position whilst a manufacturing process is performed.

16. A method according to claim 7 in which said attachment fingers are severed at a position spaced from the edge of the base, and further comprising the step of bending the severed fingers which remain protruding from the base into recesses provided within the insulating base, so as not to constitute unwanted conductive protrusions along edges of the base.

17. A method according to claim 7 in which said attachment fingers are provided on at least three edges of the base, so as to reduce the risk of twisting and bending of the base relative to the conductive sheet.

18. A method according to claim 7 in which said conductive sheet is made of phorphor bronze, copper or brass.

19. A method according to claim 7 in which said insulating base is made of plastics material and is formed by injection moulding.

20. A method according to claim 7, in which a separate sub-assembly is also formed from said conductive sheet, and further comprising the step of attaching electrical parts thereto before the sub-assembly is removed from said sheet for subsequent assembly with the main component.

21. A method according to claim 20 in which said sub- assembly has a separate plastics part formed thereon during the step of moulding said base.