PIM housing

Abstract

In a process for producing a hearing aid, comprising a housing made out, at least partially, of a metallic or ceramic part using powder injection molding technique (PIM) within the housing (1) at least one additional element (3) made out of a polymeric material is arranged for placing functional parts (5, 7, 13) within or at the housing (1) to reduce complexity of P parts and/or to compensate any tolerances due to the PIM process.

Claims

1. A process for producing a hearing aid, comprising a housing made out, at least partially, of a metallic or ceramic part using powder injection molding technique (PIM), wherein within the housing at least one additional element made out of a polymer material is arranged for placing functional parts within or at the housing to reduce complexity of PIM parts and/or to compensate any tolerances due to the PIM process, wherein at least a main part of the housing design is made with an integral tubular cross section, wherein at least two ceramic or metal parts are used for the housing of the hearing aid, and wherein the hearing aid comprises at least one intermediate part made out of a polymeric material to ensure a stress free connection between the at least two parts.

2. A process for producing a hearing aid, comprising a housing made out, at least partially, of a metallic or ceramic part using powder injection molding technique (PIM), wherein within the housing at least one additional element made out of a polymer material is arranged for placing functional parts within or at the housing to reduce complexity of PIM parts and/or to compensate any tolerances due to the PIM process, wherein at least a main part of the housing design is made with an integral tubular cross section, and wherein in case two or more metal or ceramic housing parts are made with PIM technique and a wide gap between the housing parts occurs, the wide gap is compensated by an arrangement of compression ribs at the at least one additional element that can deform to adjust and fasten the distance between the assembled metal or ceramic parts.

3. A hearing aid comprising at least two metal or ceramic parts made using powder injection molding technique (PIM), wherein at least one additional element is arranged within the housing for placing functional parts to compensate any tolerances due to the PIM process, wherein at least a main part of the housing design comprises an integral tubular cross section, and wherein the hearing aid comprises an arrangement of compression ribs that are deformed to compensate for a gap between the assembled metal or ceramic parts.

4. A process according to claim 1, wherein electronic components are placed within the housing, using a frame made out of a polymeric material.

5. A process according to claim 1, wherein supplement parts, are carried by the additional element and/or a further additional element made of a polymeric material.

6. A process according to claim 1, wherein for assembling the hearing aid, fastening elements are used together with respective counterparts for fixation of the fastening elements, wherein the counterparts are made out of a polymeric material.

7. A process according to claim 1, wherein in case of the use of a metal injection molded part a non-conductive lacquer (coating or another non-conductive encapsulation part) is applied to the metal injection molded part to ensure separation from electronic components.

8. A process according to claim 1, wherein the hearing aid includes a battery door comprising a ceramic or metal cover and a counterpart made of a polymer material, being integrated in the battery door for holding a battery, the counterpart being connected to the PIM made ceramic or metal cover by a fastening element, snap-fit, adhesive bonding, welding or press-fit.

9. A process according to claim 1, wherein in case polymeric parts are connected to metal or ceramic parts, the connection is achieved by adhesive bonding, the adhesive bonding can also be used to seal already connected parts.

10. A process according to claim 1, wherein the at least one additional element is designed with an integral hinge or spring characteristic to be used as an elastic structure and to compensate a larger tolerance range with metal or ceramic parts.

11. A process according to claim 1, wherein the at least two ceramic or metal parts are coated with a hydrophobic coating.

12. A process according to claim 1, wherein a microphone protection and/or sound port are directly integrated into a ceramic or metal housing part by means of laser or conventional milling and drilling.

13. A process according to claim 1, wherein the housing is labelled or serialized with means of a laser engraving process.

14. A process according to claim 9, wherein the PIM part is subjected to a laser treatment prior to a bonding process in order to increase surface roughness.

15. A hearing aid according to claim 3, wherein the at least two metal or ceramic parts are relatively movable against each other.

16. A hearing aid according to one of the claim 3 or 15, wherein the additional element is made out of a polymeric material.

17. A hearing aid according to claim 3, wherein electronic components are arranged in a separate frame made of a polymeric material.

Description

WITHIN THE FIGURES

(1) FIG. 1 shows in perspective and cut cross sectional view of a tubular design of a hearing aid housing,

(2) FIG. 2 in perspective view a hearing aid housing with functional elements to be placed within the housing according to the present invention,

(3) FIG. 3 the battery door in perspective view with a PIM made part connected to a polymeric part,

(4) FIG. 4 in cross sectional view, a part of the hearing aid assembly with so called compression ribs,

(5) FIG. 5 in top view on a battery door showing the adhesive bonding,

(6) FIG. 6 in cross sectional view the polymeric element according to the present invention with an integrated spring, and

(7) FIG. 7 in top view a hearing aid housing with integrated microphone protection and sound port.

(8) Due to the small size of a hearing aid in general, the wall thickness of a housing has to be as thin as possible. When using a material with a relatively low breaking elongation, such as sintered ceramic or metal, the structure of the part itself has to be rigid, since increasing the wall thickness is usually not possible due to the space and size limitations. Therefore, a housing design 1 with a tubular cross section as shown in FIG. 1 is an appropriate solution to get a rigid structure.

(9) Parts produced with PIM technology suffer from relatively large tolerances when compared to parts produced in plastic injection molding. Furthermore, the achievable complexity of PIM parts is considerably limited. In particular, ceramic parts do not allow delicate structures, because of material cracking risk. The approach to overcome these limitations is the use of specifically designed plastic parts in combination with the metal or ceramic parts.

(10) In the hearing aid housing 1, as shown in FIG. 2, it is necessary to place the electronic components in an accurately defined position. Due to the above mentioned limitations, this is hardly possible with a PIM part. This can be solved by placing the electronic components in a separate frame 7, preferably made of a plastic material for a more accurate positioning. The frame can also compensate tolerances and allows certain absorption of accelerating forces in case the device is dropped accidentally by the user. An additional plastic part 3 inside or mounted to the PIM housing parts can be used to carry supplementary parts such as a microphone protection and/or sound port 5/13 or user control elements such as e.g. a program switch or volume control.

(11) To assemble the hearing aid, fastening elements like pins 9, cones or snap-fit elements are required. The large tolerances and low ductility of PIM materials, except some metals, do not allow the realization of press-fit or snap-fit connections. Therefore, a polymeric counterpart for the fixation of the fastening element is necessary.

(12) In case the hearing aid housing consists of more than two ceramic parts, such as e.g. a housing comprising two half-shells, direct contact between the two parts is critical because of the possibility of pre-stressed assembly due to no relaxation of the material. This can result in crack formation during usage of the device. Furthermore, a tight sealing of the contact surface between ceramic housing parts is hardly feasible. An intermediate part made of plastic or rubber can secure a close and stress free connection between two ceramic housing parts.

(13) Metal injection molded parts are conductive and therefore need to be separated from the electronic components, wires and battery contacts as well as the battery itself by using lacquer, coating or another non-conductive encapsulation part.

(14) The typical mechanical solution for hearing aids to lock the battery door is realized by designing a snap-fit element into the battery door that can engage in a counterpart in the main housing of the hearing aid or the internal electronic module. This function cannot be realized with ceramic or metal parts due to the significantly higher stiffness and low ductility of these materials. To still realize a snap-fit battery door containing a ceramic or metal part, a counterpart 17 made of plastic with integrated snap and fit element 21, as shown in FIG. 3, can be integrated into the battery door and/or the housing parts and/or the internal electronic module. This counterpart 17 can be connected to the PIM part 19 by a fastening element, snap-fit, adhesive bonding, welding or press-fit.

(15) As a result of the large tolerance range of PIM parts, compared to injection molded plastic parts, wide gaps 20 between the housing parts 1 and 19 can occur as shown in FIG. 4. In most cases it is necessary to reduce or compensate to some extent these gaps for technical reasons in order to prevent, e.g. acoustical instability, reliability or assembling issues.

(16) To ensure a connection between a PIM part 1 and a plastic part 3 free from float, compression ribs 23 can be added to the plastic part. These compression ribs allow to be deformed during assembling with a small amount of force. The deformed compression ribs will adjust and fasten the distance between the assembled parts as shown in FIG. 4.

(17) To fill tolerance related gaps and connect a PIM part to a plastic part or a second PIM part, adhesive bonding can be used as shown in principal in FIG. 5. The adhesive connection can be designed to compensate the occurring dimension differences with a variable adhesive gap 27. It is also possible using an adhesive to seal already connected parts.

(18) If adhesive bonding is used to connect PIM parts to other PIM or polymeric parts, the PIM part can be subjected to a laser treatment prior to the bonding in order to increase surface roughness and thus improving the strength of the adhesive bond.

(19) A further solution to compensate the larger tolerance range with PIM parts is to use a plastic part 3 with an elastic structure 31. The plastic part 3 is designed with an integral hinge or spring 31 and adapts to the ceramic or metal part without being irreversibly deformed.

(20) It is possible to reduce the number of parts by directly integrating the microphone protection and/or sound port into a ceramic or metal housing part, as shown in FIG. 7. The typical microphone openings are very small and split up in several holes or grooves. Only simple openings can be integrated directly into the part during the PIM forming process. More complex and very fine openings can be integrated after the PIM process by laser or conventional milling and drilling.

(21) A further requirement for hearing aid devices is the environmental resistance over long periods of time. Especially the highly corrosive human sweat is known to severely affect the hearing aid function once it reached the inside of the housing getting in contact with the sensitive electronic components. Also, hearing aid batteries are attacked resulting in corrosion of the battery and soiled battery compartment. Ceramic and metals both are materials with high surface energies compared to plastics. This leads to a different wetting behaviour: high energy liquids, such as water or sweat, will readily wet metal and ceramic. This problem can be solved with the deposition of a hydrophobic coating. Such a treatment will alter the surface energy considerably, thereby changing the wetting characteristics of the underlying metal or ceramic completely. The general coating requirements are a contact angle with water of higher than 90° (preferably higher than) 95°, resistance against mechanical abrasion, resistance against environmental influences such as low pH (sweat), fatty substances (skin, sun-cream), UV light exposure and alcoholic cleaning agents. For highly polished metal or ceramic parts, the coating has to be very thin (<50 nm, preferably <30 nm).

(22) Silicon or fluorine based chemistries are possible for hydrophobic coatings on metal or ceramic parts. The coating process can be a gas phase process (with or without plasma), or liquid based coating (spraying, dipping, brushing). If ceramic or metal parts previously joined to plastic parts have to be coated, the process temperature should not exceed the glass transition point of the respective polymer material.

(23) Moreover, the coating should be biocompatible for long term skin contact (non toxic, non irritating, non sensitizing).

(24) Further, a hearing aid housing is required to feature some kind of labelling for identification of brand and product name. Ceramic or metal housings can be labelled with different techniques, such as pad printing and laser engraving. In order to emphasize the high value appeal, laser structuring is the preferred method. This method can also be used for serialization purposes.

(25) The present invention is not at all limited to the shown examples within the figures and the respective above description. The basic idea of the figures is to give a better understanding of the present invention. According to the present invention, it becomes possible to produce hearing aids and in particular hearing aid housing with metallic and/or ceramic appearance by using PIM technique in an easy and costly manner, nevertheless taking the high quality requirements of a hearing aid into consideration.