WO2014090282A1

WO2014090282A1 - Magnetically-shielding housing

Info

Publication number: WO2014090282A1
Application number: PCT/EP2012/075025
Authority: WO
Inventors: David Waeckerlin; Erdal Karamuk; Paul Portmann
Original assignee: Phonak Ag
Priority date: 2012-12-11
Filing date: 2012-12-11
Publication date: 2014-06-19

Abstract

A magnetically-shielding housing for an electronic component, the housing being formed from a plurality of mating parts (1a, 1b), at least one of the mating parts (1a, 1b) being fabricated in a two-part injection moulding process from a harder material (3a, 3b) and a soft material (4a, 4b). The magnetic shielding is provided by a plating (7a, 7b) of a suitable magnetically-soft metallic material on the surface of the harder material (3a, 3b) of the said at least one of the mating parts (1a, 1b). The invention has particular application in miniaturised electronic devices such as hearing devices.

Description

MAGNETICALLY-SHIELDING HOUSING

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a magnetically-shielding housing for an electronic component, such as a transducer, such as more specifically a receiver of a hearing device, but is not limited thereto. The term "hearing device" incorporates hearing aids, tinnitus reduction devices, active hearing protection for gunfire and other loud noises, earpieces for communication devices, and so on. Such hearing devices may be worn behind-the-ear, in-the- ear, or may be implanted.

BACKGROUND OF THE INVENTION

Although the present invention is described in relation to hearing devices, it self-evidently has a wider application in other miniaturised electronic devices.

The close proximity of different electronic components in miniaturised electronic devices such as hearing aids can lead to problems with electromagnetic interference between the various electronic components making up such devices. For instance, hearing aid receivers (i.e. loudspeakers) generate a magnetic field which can cause disturbance on other components such as a telephone coil. Therefore, ofte: a magnetic shielding has to be applied by using suitable high-permeability, low-coercivity materials, such as soft iron, Ni-Fe alloys (e.g. uMetal or Permalloy), or

amorphous magnetic metals (e.g. amorphous cobalt-based alloys, such as described in US2011/0235837 Al) .

Magnetic shielding, particularly but not limited to low- frequency magnetic shielding, in hearing aids is an issue which has been extensively considered in the prior art. A common approach is to use foils, sheets / shields of high magnetic permeability material between the source of the interference, such as the receiver, and the component which is affected, e.g. a telephone coil. An example of such a solution is given in EP2229009A1. However, these types of shielding are not very effective, since they work not so much by the absorption of the magnetic field in the metal but rather by deflecting it away from the sensitive

component .

Various prior art solutions to the problem of improving the poor magnetic shielding associated with the above-mentioned approach have been considered. For instance, US 6,813,364

Bl describes a deep-drawn or metal-in ection-moulded beaker of MuMetal, inside which the receiver is encapsulated, and US 2011/044485 describes a tubular-shaped shielding made of drawn or metal-injection-moulded MuMetal, as well as a similarly-shaped plastic part plated with a MuMetal-like material. However, such solutions are bulky and require bulky support structures, complicating assembly and adding to the manufacturing cost. Furthermore, metal-injection- moulded parts are subject to minimum practical wall- thickness constraints.

An additional consideration in hearing device design is the mechanical isolation of the receiver from the shell of the hearing device, so as to protect the receiver from

vibration and mechanical shocks, and also to prevent a mechanical feedback path from the receiver to the

microphone. As a result, the receiver is usually suspended in the shell of the hearing device. The beaker-type or tube-type shielding essentially requires a complicated and bulky external suspension system, since due to the rather large tolerances on such parts, the application of a compact integrated suspension such as that described in US 2008/112584 is difficult or impossible to implement. In consequence, until now, the quality of magnetic shielding has been proportional to the bulk of the receiver housing and its accompanying suspension.

SUMMARY OF THE INVENTION

The aim of the present invention is thus to overcome at least one of the above-mentioned drawbacks of the prior art, and thereby to propose a housing for an electrical component exhibiting excellent magnetic shielding and small size, and a corresponding method of manufacturing the same.

This object is attained by a housing defining a cavity for the electronic component, the housing comprising a plurality of mating parts. Normally, these mating parts would number two, however three, four, or even more parts are not excluded. At least one mating part comprises a first component made of a first material, which defines at least part of a suspension for the electronic component, and a second component made of a second material, which defines at least part of a structural element of the housing, i.e. (at least part of) a housing shell.

Naturally, each mating part may be so constructed. These two components are integral with each other. Each component presents at least one surface. The first material is a softer, resilient material, so as to serve as suspension for the electronic component and for shock protection and vibration isolation therefor. The second material is a harder, i.e. stiffer, material, so as to serve for the structural strength of the housing. Furthermore, the harder material is capable of being plated with a metallic plating, either directly, or indirectly via one or more intermediate layers. A plating of a magnetically-soft material is provided on the exposed surface of the second component. By magnetically-soft material we understand a material capable of absorbing magnetic fields, so as to shield the electronic component from other components, and vice versa. This is achieved by a material having a low coercivity, i.e. lA/cm or less. This permits excellent magnetic shielding to be implemented with a housing with integrated suspension, which results in a compact housing with no requirement for an external suspension system, nor any requirement for complex and bulky metal injection moulded parts. In an embodiment, each mating part is an integrally-moulded two-component injection moulded part, rendering cheap, fast, high-precision manufacture possible.

In an embodiment, the first material is a thermoplastic elastomer or silicone rubber, giving excellent suspension, shock absorbing, and vibration-isolating and absorbing properties to the first component, and/or the second material is ABS (acrylonitrile butadiene styrene) , PA

(polyamide), PC (polycarbonate) , PC/ABS

(polycarbonate/acrylonitrile butadiene styrene blend) , PP (polypropylene), PPS ( Poly (p-phenylene sulfide)), PEEK (Polyetheretherketone) , LCP (liquid crystal polymer) , or PPA (Polyphthalamide) , giving plateability and structural strength to the second component.

In an embodiment, the first material is not suitable for receiving a metallic plating. This obviates any requirement for conventional masking of the first component during its production to prevent it from being plated. Such plating will stiffen the first component and thus reduce its suspension, shock-absorbing and vibration-absorbing

properties.

In an embodiment, the magnetically soft material comprises a nickel-iron alloy such as MuMetal or permalloy. Nickel- iron alloys are particularly suited for plating, and can be directly plated in a form exhibiting the low coercivity required for good magnetic shielding properties. The magnetically soft material may exhibit a coercivity of no more than 1 A/cm, or no more than 0. lA/cm, or no more than O.OlA/cm, providing excellent magnetic shielding properties. The magnetically soft material may also exhibit a nanocrystalline grain structure with a grain size of not larger than 30 nm, which enables a low coercivity without requiring thermal annealing, which is essentially

impossible with injection-moulded plastic parts due to their temperature sensitivity.

In an embodiment, the electronic component is a receiver (i.e. a loudspeaker) for a hearing device.

The object of the invention is further attained by a hearing device comprising a housing according to any of the above-mentioned embodiments.

The object of the invention is likewise attained by a method of manufacturing a housing for an electronic

component, the housing defining a cavity for the electronic component and comprising a plurality of mating parts. At least one of the mating parts is produced by two-component injection moulding, the at least one mating part comprising a first component of a first material, defining a

suspension of the electronic component, and a second component of a second material, defining a structural element of the housing. The two components are formed integrally will each other by the two-component injection moulding, and each component presents at least one surface. The first material is a softer, resilient material and the second material is a harder, i.e. stiffer, material

suitable for receiving a metallic plating. The exposed surface of the second component is then plated either directly, or indirectly via one or more intermediate layers, with a magnetically-soft material. By magnetically- soft material we understand a material capable of absorbing magnetic fields, so as to shield the electronic component from other components, and vice versa. This is achieved by having a low coercivity and a high magnetic permeability. This permits the simple, cost-effective production of a housing with integrated suspension, which exhibits

excellent magnetic shielding, resulting in a compact housing with no requirement for an external suspension system, nor any requirement for complex and bulky metal injection moulded parts. Naturally, each mating part may be so manufactured.

Subsequently, the housing is formed by assembling the plurality of mating parts, one or more of which are

produced as described above, e.g. after positioning of an electronic component in the housing. A housing with the above-mentioned properties is thus produced.

In an embodiment of the method, the first material is not suitable for receiving a metallic plating. In consequence a conventional masking step is not required, significantly simplifying the method. In a variation of this method, portions of the surface of the second component which should not receive the metallic plating, such as for instance clips or other fixing means, are masked with the first material. This completely eliminates any requirement for masking of portions of the surface of the second component, thereby resulting in simple production with a minimum number of steps. In an embodiment of the method, the first material is a thermoplastic elastomer or silicone rubber, giving

excellent suspension, shock absorbing, and vibration- absorbing properties to the first component, and/or the second material is ABS (acrylonitrile butadiene styrene) , PA (polyamide) , PC (polycarbonate) , PC/ABS

(polycarbonate/acrylonitrile butadiene styrene blend) , PP (polypropylene), PPS ( Poly (p-phenylene sulfide)), PEEK (Polyetheretherketone) , LCP (liquid crystal polymer) , or PPA ( Polyphthalamide ) , giving good plateability and

structural strength to the second component.

In an embodiment of the method, the magnetically soft material comprises a nickel-iron alloy such as uMetal or Permalloy. Nickel-iron alloys are particularly suited for plating, and can be directly plated in a form exhibiting the low coercivity required for excellent magnetic

shielding properties. The magnetically soft material may exhibit a coercivity of no more than 1 A/cm, or no more than O.lA/cm, or no more than 0.0lA/cm, providing excellent magnetic shielding properties. The magnetically soft material may also be deposited with a nanocrystalline grain structure with a grain size of not larger than 30 nm, which enables a low coercivity without requiring additional treatment step such as thermal annealing, which is

essentially impossible with injection-moulded plastic parts due to their temperature sensitivity. Thus, the plating can be directly deposited with excellent magnetic shielding properties, minimising the number of manufacturing steps. The object of the invention is further attained by a method of manufacturing a hearing device comprising manufacturing a hearing device receiver, a hearing device shell, and a housing according to any of the above-mentioned method embodiments. The hearing device receiver is then assembled into the housing, and the thus assembled hearing device receiver and housing is assembled into the hearing device shell. This incorporation of the above-mentioned housing into a hearing device results in a compact hearing device with excellent shielding of the electronic component.

BRIEF DESCRIPTION OF FIGURES

The invention will be further elaborated by means of specific nonlimiting embodiments in the accompanying figures, which show:

Figure 1 - a perspective view of two halves of a housing according to the invention;

Figure 2 - a cross-section on line A-A of Figure 1;

Figure 3 - a graph of the correlation between crystalline grain size and coercivity in soft magnetic materials;

Figure 4 - a flowchart of a method of manufacturing a housing according to the invention; and

Figure 5 - a flow chart of a further method of

manufacturing a housing according to the invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

Figure 1 shows a perspective view of a base part la and a cover part lb which, when assembled, form a housing for containing an electrical component such as a transducer, e.g. a receiver. Base part la and cover part lb are both mating parts, and are mutually attached by means of fixing means 5a, 5b, as illustrated comprising resilient catches 5a on base part la cooperating with corresponding recesses 5b on cover part lb. Other arrangements of fixing means are naturally possible, such as for instance arranging catches 5a on cover part lb, and recesses 5b on base part la, or the fixing means may be by glueing, welding, soldering, or fastening with one or more pins or screws. Furthermore, although only two mating parts la, lb are illustrated in figure 1, three, four, or even more mating parts are also foreseeable .

On assembly, the interior of the housing formed of mating parts la, lb defines a cavity for receiving and supporting an electronic component, such as a receiver.

In the illustrated embodiment, each mating part la, lb comprises two components: a first component 4a, 4b made of a softer, shock- and vibration-absorbing material, and a second component 3a, 3b made of a harder material. Each mating part is produced in a conventional two-component injection moulding process (also known as a two-shot injection moulding process) that need not be described further. However, it may be adequate or even desirable that only one of the mating parts exhibits these features, one or more other mating parts being single-component, or a two-component moulded component without plating, as is conventional .

The first component 4a, 4b of each mating part la, lb comprises a soft, resilient material such as a

thermoplastic elastomer material or silicone rubber, and serves as a vibration- and shock-damping element, and also suspends the receiver inside the housing: as such, the first components 4a, 4b of the two mating parts la, lb form an integrated suspension system within the housing for the electronic component, comprising protuberances 2a, 2b, analogous to those described in US 2008/0112584, herein incorporated by reference in its entirety. A suitable hardness for the first material is a Shore hardness of greater than 10, ideally between 20 and 60. Block

copolymers such as styrene elastomers (TPE-S) or polymer blends such as a polyolefin elastomer (TPE-O) have been found to be particularly well-suited. However, depending on the application, other TPE types may be equally suitable, for instance thermoplastic polyurethane (TPE-U) ,

thermoplastic SEBS-based elastomers ( styrene-ethylene- butylene-styrene ) , or vulcanized materials such as silicone rubber etc.

Each first component 4a, 4b of each mating part la, lb is partially surrounded by a second component 3a, 3b, made of a harder material such as ABS (acrylonitrile butadiene styrene) , PA (polyamide) , PC (polycarbonate) , PC/ABS

(polycarbonate/acrylonitrile butadiene styrene blend) , PP (polypropylene), PPS ( Poly (p-phenylene sulfide)), PEEK ( Polyetheretherketone ) , LCP (liquid crystal polymer) , or PPA ( Polyphthalamide ) . The second components 4a, 4b, on assembling the two mating parts la, lb together around and electronic components such as a receiver (not illustrated) so as to form a housing therefor, form the structural strength of the housing for supporting the receiver. For mounting the assembled housing to a hearing aid shell, base part la is provided with a mounting bracket 6 formed integrally with its second component 3a.

The arrangement for magnetically shielding the receiver will now be described. The magnetic shielding is provided by plating the surface of the second component 3a, 3b of at least one mating part la, lb, which in the present

embodiment is illustrated as being the case for each mating part la, lb, with a suitable metallic material plating 7a, 7b. This is illustrated in figure 2 in a cross-section on line A-A of figure 1, not to scale. Plating 7b is

illustrated in solid block colour for clarity, and is provided only on the exposed surface of second component 3B. First component 4b is situated on the concave side of second component 3b, and is not plated.

The material selected for the second components 3a, 3b must be suitable for plating with a metallic material either directly, or via one or more intermediate adhesion layers. The above-mentioned polymers ABS, PA, PC, PC/ABS, PP, PPS, PEEK, LCP, and PPA are examples of such suitable materials, having a good strength and stiffness and also being plateable with a metallic plating, however other materials are foreseeable.

The first material from which each first component 4a, 4b of each mating part la, lb is made should not receive metallic plating, since it adds stiffness to the first components 4a, 4b, lowering their elastic properties and thereby having a deleterious effect upon the effectiveness of the first components 4a, 4b as suspension, shock- absorbing, and vibration-absorbing elements. This can simply be achieved with conventional masking techniques. However, it is advantageous that the first material from which each first component 4a, 4b of each mating part la, lb is made, is a non-plateable material, i.e. exhibits an extremely low adhesion with the plating material such that the plating does not adhere thereto. This eliminates any requirement for conventional masking of the first

components 4a, 4b during the plating process, keeping costs and processing time down. As an additional advantage, any areas of the surface of each second component 3a, 3b which should not receive the plating, such as fixing means 5a, 5b, can be masked with the said first material during injection moulding, eliminating again the requirement for a separate masking step. If required, however, a conventional separate mask may be used. The plating is usually applied galvanically . However, other plating processes such as physical vapour deposition with or without plasma enhancement are also forseeable.

Thickness of the plating is typically 20-200 μπι, however thicker or thinner platings are forseeable. If using a conventional mask, after coating, any metallic material which has been deposited upon upon the mask can then easily be removed by removing the mask conventionally, taking the undesired deposited material with it.

The metallic plating, to have good magnetic shielding properties, is of a material exhibiting low coercivity (typically less than 1 A/cm) , and corresponding high permeability. Suitable materials include alloys based on nickel and iron, such as MuMetal and Permalloy, or

amorphous cobalt-based alloys such as those described in US 2011/0235837.

Traditional MuMetal parts achieve magnetic shielding through very large crystalline grain structure. This structure is traditionally obtained by annealing the part at over 1100°C in a specific atmosphere (usually pure hydrogen) for several hours. This is naturally not possible with injection-moulded plastic housing parts, since the high temperatures would destroy the parts. Since plastic deformation of traditional MuMetal lowers the grain size, MuMetal parts which have been subject to such deformation

(for instance during the process of applying a MuMetal foil to a housing part) have increased coercivity and therefore reduced magnetic shielding properties. The only way to regain good magnetic shielding properties would be to re- anneal the foil, which is impossible in the present case for the reasons given above.

However, many Ni-Fe alloys with nanocrystalline grain structure also exhibit low coercivity and high permeability which is required for effective magnetic shielding, and can be deposited as a coating. (G. Herzer, In: Handbook of Magnetic Materials, ed. By K.H.J. Bushchow, Elsevier

Science, Amsterdam Vol 10, Chap 3, 1997; G. Herzer,

Magnetization process in nanocrystalline ferromagnets , Materials Science and Engineering, A33 (1991) 1-5). This effect in certain nanocrystalline materials can be observed when the average grain size is in the range of a magnetic domain wall thickness. (Rev. Adv. Mater . Sci . 5 (2003) 252- 258) . An illustration of the correlation between

crystalline grain size and coercivity in such materials is shown in Figure 3, taken from Herzer 1991 op cit, which demonstrates nanocrystalline crystal structures in

ferromagnets having low coercivity. Since a Ni-Fe plating with nanocrystalline grain structure can be applied as a coating, thus taking immediately its final form without being subject to mechanical deformation, no additional annealing step is required to achieve good magnetic

shielding characteristics. In addition, mechanical shock or deformation of the part will not alter the shielding properties, whereas a significant drop in shielding

properties of conventional MuMetal parts can be observed and usually requires re-annealing.

Figure 4 illustrates a flow diagram of a method of

manufacturing a housing according to the invention, comprising at least two mating parts, at least one of which comprises a metallic plating. In this embodiment of the method, the soft, first component of the at least one mating part is produced of a non-plateable material. In a first step 31, the at least one of the mating parts

destined to form at least part of the housing is/are produced by two-component injection moulding. The total number of mating parts would normally number two as

disclosed above, however may number three, four, or even more as appropriate. Any number of these mating parts may be two-component plated mating parts as described herein. Any remaining mating parts may be single-piece, or co- moulded as is conventional.

Since the first material is non-plateable , in step 32, the at least one mating part is plated with a suitable

magnetically soft metallic material as discussed above, e.g. galvanically . If required, during the two-component injection moulding step, regions of the second component which should not be plated, such as clips or other fixing means, can be masked with the first material during this integral moulding step, thus eliminating the requirement for separate masking. In step 33, if required, any metallic material which has plated accidentally onto the first component is removed, e.g. mechanically. If no, or

substantially no, metallic material has deposited on the first component, step 33 is redundant and may be omitted. Finally, in step 34, the housing is assembled.

Figure 5 illustrates an alternative embodiment of

manufacturing a housing according to the invention, which does not rely on the softer, first material being non- plateable. As such, the method incorporates conventional masking techniques. In a first step 41, at least one of the mating parts destined to form at least part of the housing is/are produced by two-component injection moulding as above. In step 42, masks are applied to the portions of the at least one mating part which are not to receive the plating, i.e. the surfaces of the first component and any parts of the second component such as clips or other fixing means. Subsequently, the at least one mating part is plated in step 43 as above, and in step 44 the masks are removed so as to remove undesired plating material. Finally, as above, the housing is assembled in step 45. Although this process comprises more steps than that of figure 4, it allows a wider choice of materials for the first material, since this method is not contingent upon the first material being non-plateable . On the other hand, the method of figure 4 is not subject to mask alignment issues, hence the non-plated areas can be defined more precisely in that method.

It must be noted that in either of the methods of figures 3 and 4, it is not necessary that the plating be applied directly on the surface of the second component. It may be desirable to incorporate an intermediate adhesion layer between the surface of the second component and the plating so as to improve adhesion of the plating, if this becomes necessary as a result of the choice of second material and metallic plating material. If this is the case, this intermediate layer may be applied conventionally, utilising masks if required to prevent its deposition on portions upon which coating is undesired. If not all of the mating parts are of the inventive plated two-part construction, the remaining conventional mating parts are produced as is conventional.

Furthermore, different shapes and arrangements of the mating parts are naturally conceivable, such as for instance a large beaker and a small cover place

longitudinally along the large beaker.

Although the invention has been explained in terms of specific embodiments, these are not to be construed as limiting: the invention includes all embodiments falling within the scope of the appended claims.

Claims

1. Housing for an electronic component, the housing defining a cavity for receiving the electronic component and comprising a plurality of mating parts, at least one mating part comprising:

- a first component of a first material, the first

component defining at least part of a suspension for the electronic component;

- a second component of a second material, the second component defining at least part of a structural element of the housing;

wherein the first component is integral with the second component, each of the first and second components

presenting at least one surface, and wherein the first material is a softer, resilient material and the second material is a harder material suitable for receiving a metallic plating;

characterised in that said at least one mating part

comprises a metallic plating of a magnetically-soft

metallic material on at least one surface of the second component .

2. Housing according to the preceding claim, wherein each mating part is an integrally-moulded two-component

injection moulded part.

3. Housing according to any preceding claim, wherein the first material is a thermoplastic elastomer or silicone rubber, and/or the second material is at least one of ABS, PA, PC, PC/ABS, PP, PPS, PEEK, LCP, PPA.

4. Housing according to any preceding claim, wherein the first material is not suitable for receiving a metallic plating.

5. Housing according to any preceding claim, wherein the magnetically soft material comprises a Ni-Fi alloy such as MuMetal or Permalloy.

6. Housing according to the preceding claim, wherein the magnetically soft material has a coercivity of no more than

1 A/cm, or no more than 0.1 A/cm, or no more than 0.01 A/cm.

7. Housing according to claim 5, wherein the magnetically soft material exhibits a nanocrystalline grain structure with a grain size of not larger than 30 nm.

8. Housing according to any preceding claim, wherein the electronic component is a receiver for a hearing device.

9. Hearing device comprising a housing according to any proceeding claim.

10. Method of manufacturing a housing for an electronic component, the housing defining a cavity for receiving the electronic component and comprising a plurality of mating parts, the method comprising:

- forming a plurality of mating parts, at least one mating part being formed by two-component injection moulding, said at least one mating part comprising a first component of a first material, the first component defining at least part of a suspension for the electronic component, and a second component of a second material, the second component defining at least part of a structural element of the housing, the first component being formed integrally with the second component and each component presenting at least one surface, the first material being a softer, resilient material and the second material being a harder material suitable for receiving a metallic plating;

- plating at least one surface of the second component of said at least one mating part with a magnetically soft material;

- forming the housing by assembling the plurality of mating parts.

11. Method according to the preceding claim, wherein the first material is not suitable for receiving a metallic plating.

12. Method according to the preceding claim, wherein portions of the surface of the second component which are not intended to be plated are masked with the first material .

13. Method according to any of claims 10-12, wherein the first material is a thermoplastic elastomer or silicone rubber, and/or the second material is at least one of ABS, PA, PC, PC/ABS, PP, PPS, PEEK, LCP, PPA.

14. Method according to any of claims 10-13, wherein the magnetically soft material comprises a Ni-Fe alloy such as MuMetal or Permalloy.

15. Method according to any of claims 10-14, wherein the magnetically soft material has a coercivity of no more than 1 A/cm, or no more than O.lA/cm, or no more than 0.0lA/cm.

16. Method according to any of claims 10-15, wherein the magnetically soft material is deposited with a

nanocrystalline grain structure with a grain size of no larger than 30 nm.

17. Method of manufacturing a hearing device comprising:

- manufacturing a hearing device receiver;

- manufacturing a hearing device shell;

- manufacturing a housing according to any of claims 1-16;

- assembling the hearing device receiver into the housing;

- assembling the thus-assembled hearing device receiver and housing into the hearing device shell.