GB2349598A

GB2349598A - Moulded electrical components

Info

Publication number: GB2349598A
Application number: GB9901299A
Authority: GB
Inventors: Howard Frank Bottomley; John Garvey
Original assignee: FINGLAS TECHNOLOGIES Ltd
Current assignee: FINGLAS TECHNOLOGIES Ltd
Priority date: 1999-01-22
Filing date: 1999-01-22
Publication date: 2000-11-08
Also published as: GB9901299D0

Abstract

An electrical component (e.g. a mobile telephone antenna) is produced by moulding a core 20 from a metallically plateable polymer, over moulding on the core with a non-plateable polymer 26 so as to leave portions 22 of the core exposed and then applying a metallic plating process to plate metal only on the exposed portions 22. The antenna is completed by a moulded or snap-fitting cap 28. A two-shot injection moulding process may be employed. The plateable polymer may be a PC/ABS blend and non-plateable polymer may be PBT. The metallic plating may be copper. A list of other polymeric material, for use as plateable and non-plateable polymers, are disclosed.

Description

ELECTRICAL COMPONENTS SUCH AS MOBILE TELEPHONE ANTENNAS AND MANUFACTURE THEREOF Field of the Invention This invention relates to electrical components such as mobile telephone antennas and also to a method of manufacture thereof and generally to electrical components produced by said method.

Prior Art In one known method of manufacturing an antenna for a mobile telephone, an electrical coil is assembled to a plastics core and moulded therearound is a non-conductive polymer which bonds to the core to form a substrate supporting the coil.

In another known method, an antenna core of plastics material, moulded with an external helical rib, is wholly plated with metal and the rib crest is machined away to leave a helical conductive path on the core.

Object of the Invention In one aspect, the invention has for its aim to provide a method of manufacturing electrical components, applicable more especially but not exclusively to mobile telephone antennas.

In another aspect, the invention has for its aim to provide an improved construction of mobile telephone antenna, for example but not necessarily produced by the aforesaid method of manufacture in accordance with the first aspect of the invention.

The Invention According to one aspect of the invention, therefore, there is provided a method of manufacturing an electrical component comprising the steps of moulding a core from a metallically plateable polymer, overmoulding the core from a metallically non-plateable polymer, leaving one or more regions of the core exposed, whereby to form a component substrate, and subjecting the substrate to a metallic plating process which plates metal only on the exposed region or regions of the core.

The electrical component may be an inductor or a mobile telephone antenna, for example a single and/or multi-band personal communications device antenna.

Preferably, the metallically plateable core is moulded with one or more raised surface portions creating one or more recessed surface portions, and the non-plateable polymer is moulded into said recessed surface portions to provide a flush surface on the component substrate.

While it is not essential to mould and overmould the component substrate in any particular way, a preferred method is a so-called two shot moulding process, in which the core is moulded and the overmould produced in a single mould tool on a single injection moulding machine. This machine preferably incorporates two injection units, and a rotary unit on which the movable part of the mould tool is positioned. Thus, the plateable core may initially be created in a first mould cavity using the first injection unit in a first working position and then the moulded core transferred to the second working position by opening the mould and rotating the movable part of the mould tool through 180 degrees, whereafter the non-plateble overmould is produced in a second mould cavity using the second injection unit. Conveniently, while the overmould is being produced, another plateable core may be produced in the first mould cavity.

The shape and dimensions of the plateable core and of its raised portion or portions will depend on the nature of the electrical component being produced.

In one arrangement, the component substrate may be cylindrical and the exposed surface portion of the plateable core may follow a helical path. On plating, an electrical component such as an inductor or electrical winding, may be produced.

In one embodiment, however, the helical path is of such dimensions that, after plating, the component can be used as a mobile telephone antenna operable in a particular or chosen wavelength band.

According to another aspect of the invention, therefore, there is provided an antenna for a mobile telephone, comprising a non-conducting antenna substrate bearing on its surface interleaved conductive helical paths of differing lengths, whereby to provide dual waveband performance.

Preferably, the longer helical path has a first part of wider pitch interleaved with the shorter helical path of the same wider pitch, and an extension beyond its interleaved portion of relatively narrower pitch. The longer helical path having parts of differing pitches serves for one wavelength band and the shorter helical path interleaved with the wider pitch portion of the first helical path serves for the second wavelength band.

The antenna may be produced (without machining of the antenna parts) using the aforedescribed manufacturing method in accordance with the invention to produce a selectively plated cylindrical antenna substrate, which is completed for incorporation in a mobile telephone by either moulding on or snapping on a protective cover.

The use of a variety of polymers is possible in production of the antenna or other electrical component. For example, the core may be of suitable plateable polymers such as PP, a PES/ABS blend or PA, although a PC/ABS blend may be preferred.

The non-plateable overmould is preferably produced of PBT, but alternatively PET, PC, PVC or PMMA may be suitable.

The essential requirements are for the core polymer to be plateable and the overmould polymer non-plateable when subjected to the particular plating process used. Electrolytic plating is preferred. The two polymers should most desirably also bond together effectively, in order to prevent possible accumulation of chemicals between them during subsequent plating. Moreover, the heat distortion temperature of the core polymer should most preferably be higher than the melt processing temperature of the overmould polymer in order to prevent distortion of the core, whilst washing and intermixing of the two polymers during production of the overmould is undesirable. The relative permittivity and dissipation factors of both polymers must be taken into account in production of an antenna, as these properties have a significant effect on radiation efficiency, which can also be influenced by the addition of colour dyes.

As above-mentioned, an electrolytic plating process is preferred, electroless plating being very time consuming. Copper is a preferred plating metal, deposited to a thickness of the order of 10 microns in the case of a mobile telephone antenna. A minimum thickness of this order is desirable because of the effects of"skin depth"when transmitting a high frequency signal. As copper corrodes if left exposed, and is also not very hard wearing, a protective coating is desirable. Nickel can be used for some electrical components, but in the case of an antenna a hard gold plate of 1 to 2 microns thickness is preferred, because nickel can have a detrimental effect on radiating efficiency.

The invention is further described with reference to the accompanying drawings, in which: Description of Drawings Figure 1 illustrates a prior art method of making a mobile telephone antenna; Figure 2 shows one embodiment of mobile telephone antenna produced by the method according to the first aspect of the invention; Figure 3 shows a mobile telephone antenna in accordance with the second aspect of the invention, also produced by the method in accordance with the first aspect of the invention; and Figures 4A and 4B show a two station mould, respectively when closed and when open, for use in carrying out the method according to the first aspect of the invention.

Description of Embodiments Referring first to Figure 1, a known method of making a mobile telephone antenna comprises assembling an electrical coil 10 to a metal stud 12, and assembling a nonconductive plastics material 14 therearound to form a substrate supporting the coil. The antenna is completed by a moulded or snap-on cap 16.

Figure 2 illustrates a first embodiment of antenna made by the method in accordance with the invention.

A core 20 is moulded of a metalically plateable first polymer. This core 20 is moulded with a raised surface portion 22 following a helical path of uniform pitch. The core is then overmoulded with a non-plateable second polymer to form an antenna substrate 24 with a flush cylindrical surface on which the helical raised surface portion 22 of the core is exposed.

The substrate 24 is then subjected to an electrolytic plating process which plates only the helical raised surface portion 22 of the core, the main surface portion 26 of the substrate being formed by the non-plateable second polymer.

The antenna is completed by a moulded or snap-fitting cap 28.

A preferred plateable first polymer is a PC/ABS blend and a preferred non-plateable second polymer is PBT. A preferred plating material is copper, deposited to 10 microns thickness. A protective coating of gold plate, of 1 to 2 microns thickness is applied over the copper plate.

For performing the moulding and overmoulding steps in production of the antenna substrate, a two-shot moulding tool such as that illustrated in Figures 4A and 4B may be employed.

This mould 30 has two stations in the first of which the antenna core is produced and in the second of which the overmould is produced. Figure 4A shows the mould closed while the antenna core is being produced. Subsequently, the mould is opened and its movable part rotated through 180 degrees to transfer the moulded core to the second station, as indicated in Figure 4B. The mould is then closed and the overmould produced.

The mobile antenna shown in Figure 2 is suitable for operation on a single wavelength band.

Figure 3 shows that the same method of production may be used to produce a dual wavelength band antenna.

For this purpose, the core 40 is moulded with dual, interleaved, helical, raised surface portions 42,44, one portion 42 longer than the other 44 and having beyond its interleaved portion of relatively wider pitch 46 a part of relatively narrower pitch 48. Ultimately, in use, the complete helical path 42 having parts of differing pitches serves for one wavelength band and the complete helical path 44 interleaved with the wider pitch portion of the first path 42 serves for the second wavelength band.

The above-described method of producing a mobile telephone antenna can also be employed in the production of other electrical components, such as inductors and electrical windings. Equally, it is possible to produce the dual wavelength band antenna of Figure 3 by methods other than that described with reference to Figure 4, such as the prior art method described with reference to Figure 1.

Claims

CLAIMS 1. A method of manufacturing an electrical component comprising the steps of moulding a core with a metallically plateable polymer, overmoulding the core with a metallically non-plateable polymer, leaving one or more regions of the core exposed, whereby to form a component substrate, and subjecting the substrate to a metallic plating process which plates metal only on the exposed region or regions of the core.
2. A method according to claim 1, wherein the metallically plateable core is moulded with one or more raised surface portions creating one or more recessed surface portions, and the non-plateable polymer is moulded into said recessed surface portions to provide a flush surface on the component substrate.
3. A method according to claim 1 or claim 2, wherein the substrate is produced by a two shot moulding process, in which the core is moulded and the overmould produced in a single mould tool on a single injection moulding machine.
4. A method according to claim 3, wherein the machine incorporates two injection units, and a rotary unit on which the movable part of the mould tool is positioned, whereby the plateable core is initially created in a first mould cavity using the first injection unit in a first working position and then the moulded core is transferred to the second working position by opening the mould and rotating the movable part of the mould tool through 180 degrees, whereafter the non-plateable overmould is produced in a second mould cavity using the second injection unit.
5. A method according to claim 4, wherein, while the overmould is being produced, another plateable core may be produced in the first mould cavity.
6. A method according to any of claims 1 to 5, wherein the component substrate is cylindrical and the exposed surface of the plateable core is overmoulded with non-plateable material along a helical path, whereby, on plating, a cylindrical component such as an inductor or electrical winding, is produced.
7. A method according to claim 6, wherein the helical path is formed with such dimensions that, after plating, the component serves as a mobile telephone antenna operable in a particular or chosen wavelength band.
8. A method according to any of claims 1 to 7, wherein the core is moulded of PP, a PESiABS blend, PA or a PC/ABS blend.
9. method according to claim 8, wherein the non-plateable overmould is produced of PBT, PET, PC, PVC or PMMA.
10. A method according to any of claims 1 to 9, wherein the substrate is plated by electrolytic plating.
11. A method according to any of claims 1 to 10, wherein the two polymers are selected to bond together effectively, whereby to prevent possible accumulation of chemicals between them during subsequent plating.
12. A method according to any of claims 1 to 11, wherein the heat distortion temperature cf the core polymer is higher than the melt processing temperature of the overmould polymer, whereby to prevent distortion of the core.
13. A method according to any of claims 1 to 12, wherein copper is used as the plating metal.
14. A method according to claim 13, wherein the copper is deposited to a thickness of the order of 10 microns for production of a mobile telephone antenna.
15. An antenna for a mobile telephone, comprising a non-conducting antenna substrate bearing on its surface interleaved conductive helical paths of differing lengths, whereby to provide dual waveband performance.
16. An antenna according to claim 15, wherein the longer helical path has a first part of wider pitch interleaved with the shorter helical path of the same wider pitch, and an extension beyond its interleaved portion of relatively narrower pitch, whereby the longer helical path having parts of differing pitches serves for one wavelength band and the shorter helical path interleaved with the wider pitch portion of the first helical path serves for the second wavelength band.
17. An antenna according to claim 15 or 16, produced by the method of any of claims 1 to 14.
18. An antenna according to claim 17, when completed for incorporation in a mobile telephone by either moulding on or snapping on a protective cover.
19. A mobile telephone antenna substantially as hereinbefore described with reference to Figure 2 or 3 of the accompanying drawings.

19. A method of manufacturing an electrical component substantially as hereinbefore described with reference to Figures 4A and 4B of the accompanying drawings.