JP6029345B2 - Small acoustic sensor - Google Patents

Description

  The present invention relates to a small acoustic sensor.

  A small acoustic sensor mounted on an electronic device such as a mobile phone or a digital camera is a minute sensor having a diameter of 3 to 10 mm and a thickness of about 1 mm, and includes a support ring, a vibrating membrane, a spacer, and a back electrode. Etc. are very small, and various troubles may occur in the assembly work.

  Therefore, in order to facilitate the assembly work, for example, in Patent Document 1, a back electrode is molded into a cup shape, and a small size is adopted in which an electret dielectric film is formed on the outer surface of the cup-shaped back electrode. Acoustic sensors have been proposed.

JP 2000-50394 A

  By the way, the cup-shaped back electrode proposed in Patent Document 1 is manufactured as follows. First, a tetrafluoroethylene-hexafluoropropylene copolymer (FEP) film is formed on one main surface of the back electrode plate, and the back electrode plate is drawn into a cup shape so that the FEP film is on the outside. To do. Then, the FEP film is irradiated with an electron beam or corona discharge to make the FEP film an electret. In this way, a cup-like back electrode having an electret dielectric film formed on the outer surface is obtained.

  However, if the adhesion between the back electrode plate and the FEP film is not sufficient, when the back electrode plate is molded into a cup shape, the FEP film does not follow the deformation of the back electrode plate, and the electret dielectric finally obtained There is a problem in that a short circuit occurs as a circuit when the body membrane is peeled off from the cup-shaped back electrode.

  The present invention has been made to solve the above problems, and provides a small acoustic sensor excellent in reliability.

The small acoustic sensor of the present invention has a cup-shaped back electrode made of a metal material and an electret dielectric film formed on the outer surface of the cup-shaped back electrode . An insulating layer is formed on the side surface and the inner surface by anodizing treatment or chemical conversion treatment.

  ADVANTAGE OF THE INVENTION According to this invention, the small acoustic sensor excellent in reliability can be provided.

It is a schematic sectional drawing which shows an example of the small acoustic sensor of this invention. It is a schematic sectional drawing which shows the other example of the small acoustic sensor of this invention. It is a figure which shows an example of the planar view shape of the small acoustic sensor of this invention. It is a figure which shows the other example of the planar view shape of the small acoustic sensor of this invention. It is a figure which shows the other example of the planar view shape of the small acoustic sensor of this invention. It is a figure which shows the other example of the planar view shape of the small acoustic sensor of this invention. It is a figure which shows the other example of the planar view shape of the small acoustic sensor of this invention.

  The small acoustic sensor of the present invention has a cup-shaped back electrode made of a metal material and an electret dielectric film formed on the outer surface of the cup-shaped back electrode, and at least the cup-shaped back electrode An insulating layer is formed on the outer surface by anodizing treatment or chemical conversion treatment. As a result, since an insulating layer is formed on the outer surface of the cup-shaped back electrode, the problem that a short circuit occurs as a result of peeling of the electret dielectric film can be avoided, and a small acoustic sensor with excellent reliability can be obtained. It is feasible. Further, since the insulating layer is formed by oxidizing the back electrode itself by anodizing treatment or chemical conversion treatment, the thickness of the cup-shaped back electrode does not change before and after the anodizing treatment or chemical conversion treatment, and the small acoustic sensor It can meet the demand for further miniaturization.

  The small acoustic sensor of the present invention will be described below with reference to FIGS. FIG. 1 is a schematic cross-sectional view showing an example of a small acoustic sensor of the present invention. FIG. 3 is a diagram showing an example of a planar view shape of the small acoustic sensor of the present invention.

  The small acoustic sensor of the present invention shown in FIG. 1 includes a capsule 11, a support ring 15, a vibrating membrane 16, a spacer 17, a back electrode 18, and a wiring board 14.

  The capsule 11 is made of a metal member such as aluminum and has a bottomed cylindrical shape with one end face closed. A sound hole 13 through which a sound wave passes is formed at the center of the closed end surface (hereinafter referred to as the top surface) 12 of the capsule 11. In this capsule 11, the support ring 15, the vibration film 16, the spacer 17, the back electrode 18, and the wiring substrate 14 are accommodated in this order from the top surface 12 side, and then the rear end is caulked to fix the whole, thereby FIG. The small acoustic sensor shown in FIG. In this specification, a case where there is one sound hole 13 will be described, but a plurality of sound holes 13 may be provided.

  The capsule 11 has a circular plan view shape as shown in FIG. Note that the shape of the capsule 11 in plan view is not limited to the circular shape shown in FIG. 3. For example, the capsule 11 has an elliptical shape shown in FIG. 4, a square shape shown in FIG. 5, a rectangular shape shown in FIG. It may be.

  The support ring 15 is made of a metal material. Examples of the metal material include brass and stainless steel. The size and shape of the support ring 15 are not particularly limited as long as they can support the vibration film 16. As the support ring 15, when the capsule 11 has a circular shape as shown in FIG. 3, for example, a ring shape having an outer diameter of 3 mm to 10 mm and an inner diameter of 2 mm to 9 mm when viewed in plan can be used. The thickness can be arbitrarily set according to the size (thickness) of the small acoustic sensor to be manufactured. The ring-shaped support ring 15 has a circular outer shape when viewed in plan, but the outer shape when the support ring 15 is viewed in plan is not limited to a circular shape, but is elliptical, square, rectangular. Shape, diamond shape, and the like, and may be appropriately selected according to the shape of the capsule 11 in plan view.

  The vibration film 16 is vibrated by sound waves. As the vibration film 16, a polymer film having heat resistance and high strength can be used. Specific examples of the material include super engineering plastics such as polyphenylene sulfide (PPS), polyether ether ketone (PEEK), and polytetrafluoroethylene (PTFE). Moreover, as the vibrating membrane 16, when the planar view shape of the capsule 11 is the circular shape shown in FIG. 3, for example, it has a circular planar view shape with a diameter of 3 mm to 10 mm and a thickness of 2 μm to 4 μm. Can be used. The planar view shape of the vibration film 16 is not limited to a circular shape, and may be an elliptical shape, a square shape, a rectangular shape, a rhombus shape, or the like, and may be appropriately selected according to the planar view shape of the capsule 11.

  The spacer 17 is made of an insulating material. Examples of the insulating material include insulating materials such as polyethylene terephthalate (PET), thermosetting polyimide (PI), and polyether ether ketone (PEEK). The size and shape of the spacer 17 are not particularly limited. As the spacer 17, when the capsule 11 has a circular shape as shown in FIG. 3, for example, a ring shape having an outer diameter of 3 mm to 10 mm and an inner diameter of 2 mm to 9 mm when viewed in plan can be used. The thickness can be set to 20 μm to 30 μm, for example. Note that the ring-shaped spacer 17 has a circular outer shape when viewed in plan, but the outer shape when the spacer 17 is viewed in plan is not limited to a circular shape, but is oval, square, rectangular, A rhombus shape etc. are mentioned, What is necessary is just to select suitably according to the planar view shape of the said capsule 11. FIG.

  The back electrode 18 forms a capacitor together with the diaphragm 16 and converts an audio signal into a current. The back electrode 18 is made of a metal material and has a thickness of 0.1 mm to 0.5 mm, for example. The shape of the back electrode 18 may be the same as that of the capsule 11 and is a bottomed cylindrical shape (cup shape) in FIG. 1. Hereinafter, the back electrode 18 is referred to as a cup-shaped back electrode. Moreover, the planar view shape of the cup-shaped back pole 18 is circular when the planar view shape of the capsule 11 is the circular shape shown in FIG. In addition, the planar view shape of the cup-shaped back pole 18 is not limited to a circular shape, and includes an elliptical shape, a square shape, a rectangular shape, a rhombus shape, and the like, and may be appropriately selected according to the planar view shape of the capsule 11. Good.

  On the outer surface of the cup-shaped back electrode 18, an insulating layer 18 a which is an oxide film generated by anodizing treatment or chemical conversion treatment is formed. Here, the anodic oxidation treatment is a treatment in which a metal material is placed in an electrolytic solution and a weak current is passed as an anode to oxidize the surface of the metal material to generate an oxide film. As a specific example, May be anodized. Further, the chemical conversion treatment is a treatment for producing an oxide film by chemically oxidizing the surface of a metal material using an oxidizing agent without electrolysis, and specific examples include boehmite treatment and phosphate treatment. And chromate treatment. These treatments are appropriately selected according to the type of metal material to be treated. For example, when the metal material is aluminum, an oxide film can be formed on the aluminum surface by performing an alumite treatment. Usually, aluminum combines with oxygen in the atmosphere to naturally form a thin oxide film (thickness: about 0.0053 μm) on the surface, but an artificially formed oxide film by anodizing has a thickness of 1 μm or more. And thick and strong.

  The insulating layer 18a preferably has a thickness of 1 μm to 5 μm, more preferably 3 μm to 5 μm. If the thickness of the insulating layer becomes too thin, there will be problems such as cracking or unevenness of anodizing treatment or chemical conversion treatment, resulting in a short circuit. On the other hand, if the insulating layer is too thick, cracks and cracks are likely to occur, resulting in a problem of short circuit.

  Examples of the metal material constituting the cup-shaped back electrode 18 include aluminum, titanium, and magnesium, and aluminum is particularly preferable. This is because aluminum is excellent in drawability.

  An electret dielectric film 19 is formed on the outer surface of the cup-shaped back electrode 18. In order to reduce the thickness of the small acoustic sensor, the thickness of the electret dielectric film 19 is preferably 50 μm or less. However, if the thickness is too thin, it is difficult to form the electret dielectric film 19, and the thickness is preferably 10 μm or more.

  Examples of the electret material constituting the electret dielectric film 19 include tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polytetrafluoroethylene (PTFE), and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer. (PFA), tetrafluoroethylene-perfluoromethyl vinyl ether (MFA) and the like.

  Here, a method for producing the cup-shaped back electrode 18 on which the electret dielectric film 19 is formed will be described. First, an anodizing process or a chemical conversion process is performed on one main surface of the substrate to form an insulating layer. Next, a film made of an electret material is heat-sealed on the insulating layer forming surface of the substrate. Next, the substrate is drawn into a cup shape so that the film made of the electret material is on the outside. Thereafter, the film made of the material for electret is irradiated with an electron beam or corona discharge, so that the film made of the material for electret becomes an electret and becomes an electret dielectric film. In this way, the cup-shaped back electrode 18 used in the present invention is obtained.

  Further, by forming a plurality of back electrode holes 20 on the top surface of the cup-shaped back electrode 18 on which the electret dielectric film 19 is formed, it becomes easy to transmit sound to the vibration film 16.

  An IC element 22, a gate 25, and a contact piece 21 are disposed on one main surface (upper surface in FIG. 1) of the wiring board 14, and an output terminal 23, on the other main surface (lower surface in FIG. 1). A ground terminal 24 is disposed. The gate 25 is electrically connected to the cup-shaped back electrode 18 through the contact piece 21.

  FIG. 1 shows the case where the insulating layer 18a is provided only on the outer surface of the cup-shaped back electrode 18. However, the inner surface of the cup-shaped back electrode 18 is also subjected to anodizing treatment or chemical conversion treatment. May be provided. FIG. 2 shows a schematic cross-sectional view of a small acoustic sensor when insulating layers are provided on both surfaces of the cup-shaped back electrode 18. In FIG. 2, the same components as those in FIG. In the case of the small acoustic sensor shown in FIG. 2, since the insulating layer 18b is also formed on the inner surface of the cup-shaped back electrode 18 by anodizing treatment or chemical conversion treatment, the distance between the IC element 22 and the cup-shaped back electrode 18 is increased. Contact failure does not occur even if they are close to each other, and the thin acoustic sensor can be made thinner. The thickness of the insulating layer 18b is preferably in the same range as the insulating layer 18a.

  Hereinafter, effects of the small acoustic sensor of the present invention will be described in detail based on examples.

Example 1
First, a substrate (here, an aluminum thin plate) having a thickness of 0.2 mm was prepared, and an alumite treatment as an anodizing treatment was performed on one main surface of the aluminum thin plate to form an alumite layer as an insulating layer. The thickness of the alumite layer was 3 μm. Here, in the alumite treatment, aluminum was used as an anode, electrolysis was performed in a sulfuric acid electrolyte solution, an oxide film was formed by a chemical reaction, and then an alumite layer was formed by performing a sealing treatment with water vapor. Moreover, the thickness of the alumite layer was measured using the eddy current type nondestructive measuring method prescribed | regulated to Japanese Industrial Standard (JIS) 8680.

  Next, an FEP film having a thickness of 25 μm was thermally fused on the alumite layer forming surface of the aluminum thin plate. Next, the aluminum thin plate was drawn so that the FEP film was on the outside and molded into a cup shape. Next, the FEP film was irradiated with an electron beam to obtain a cup-shaped back electrode having an electret dielectric film formed on the outer surface. Using this cup-shaped back electrode, a small acoustic sensor shown in FIG. 1 was produced.

(Example 2)
A cup-shaped back electrode was prepared in the same manner as in Example 1 except that the thickness of the alumite layer as the insulating layer was changed to 1 μm, and a small acoustic sensor was manufactured using the cup-shaped back electrode.

Example 3
A cup-shaped back electrode was prepared in the same manner as in Example 1 except that the thickness of the alumite layer, which was an insulating layer, was changed to 5 μm, and a small acoustic sensor was manufactured using this cup-shaped back electrode.

Example 4
A cup-shaped back electrode was prepared in the same manner as in Example 1 except that an alumite layer (thickness: 3 μm) as an insulating layer was formed on the outer surface and the inner surface of the cup-shaped back electrode. A small acoustic sensor was produced using this.

(Comparative Example 1)
A cup-shaped back electrode was produced in the same manner as in Example 1 except that the alumite layer as an insulating layer was not formed on the outer surface of the cup-shaped back electrode, and a small acoustic sensor was manufactured using this cup-shaped back electrode. Produced.

(Comparative Example 2)
A small acoustic sensor was produced in the same manner as in Example 1 except that brass was used as the cup-shaped back electrode and that no insulating layer was formed on the outer surface of the cup-shaped back electrode.

(Comparative Example 3)
A small acoustic sensor was produced in the same manner as in Example 1 except that the FEP film was not used.

  Next, evaluation of the electrical insulation, adhesiveness, and drawability of the small acoustic sensors of Examples 1 to 4 and Comparative Examples 1 to 3 was performed as follows.

  The electrical insulation was evaluated by placing a cup-shaped back electrode in a capsule, and then contacting a tester terminal between the outside of the capsule and the inside of the cup-shaped back electrode to confirm the presence or absence of energization. When energized, it was evaluated as x. When not energized, it was evaluated as o.

  The evaluation of the adhesion between the substrate and the electret dielectric film is performed by performing a peel test (180 degree peel test) based on JIS K6894 8.6 and then visually confirming whether the electret dielectric film is peeled off. went. When the peeling of the electret dielectric film was observed at one or more places, it was evaluated as x, and when no peeling was observed at all, it was evaluated as ◯. Since Comparative Example 3 does not use an FEP film, that is, does not have an electret dielectric film, the evaluation of adhesiveness is not performed.

  The drawing workability is evaluated based on whether there is damage, peeling of the electret dielectric film, flatness, etc. at the open end of the cup-shaped back electrode, that is, the portion of the cup-shaped back electrode in contact with the wiring substrate 14 (FIG. 1). Was carried out by visual observation. When damage or peeling was observed at one or more places, or when the flatness was insufficient, x was evaluated. When damage or peeling was not observed at all and the flatness was good, it was evaluated as ◯. .

  From Table 1, the small acoustic sensors of Examples 1 to 4 in which the insulating layer is formed on at least the outer surface of the cup-shaped back electrode are Comparative Examples 1 to 4 in which the insulating layer is not formed on the outer surface of the cup-shaped back electrode. It can be seen that all of the electrical insulation, adhesiveness, and drawability are better than 2.

  In addition, the small acoustic sensor of Comparative Example 3 that does not have an electret dielectric film but has an insulating layer formed on the outer surface of the cup-shaped back electrode has good electrical insulation and drawing workability. It can be seen that electrical insulation and drawing workability can be improved by providing an insulating layer on the outer surface of the cup-shaped back electrode.

  The small acoustic sensor of the present invention can be used for a wide range of electronic devices such as a mobile phone, a digital camera, a video camera, and a PDA (Personal Digital Assistant).

DESCRIPTION OF SYMBOLS 11 Capsule 12 Top surface 13 Sound hole 14 Wiring board 15 Support ring 16 Vibration film 17 Spacer 18 Back electrode (cup-shaped back electrode)
18a, 18b Insulating layer 19 Electret dielectric film 20 Back electrode hole 21 Contact piece 22 IC element 23 Output terminal 24 Ground terminal 25 Gate

Claims (7)

A cup-shaped back electrode made of a metal material;
An electret dielectric film formed on the outer surface of the cup-shaped back electrode,
Small acoustic sensor, characterized in that the outside surface and the inner surface of the cup-shaped back electrode, an insulating layer is formed by anodic oxidation treatment or chemical treatment.   The small acoustic sensor according to claim 1, wherein the metal material is aluminum, titanium, or magnesium.   The small acoustic sensor according to claim 1, wherein the anodizing treatment is an alumite treatment.   The small acoustic sensor according to claim 1, wherein the chemical conversion treatment is a boehmite treatment. The thickness of the insulating layer is a small acoustic sensor according to any one of claims 1 to 4, which is 1 m to 5 m. The electret dielectric film is formed by electretizing a film made of tetrafluoroethylene-hexafluoropropylene copolymer, polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, or tetrafluoroethylene-perfluoromethyl vinyl ether. The small acoustic sensor according to any one of claims 1 to 5 . The thickness of the electret dielectric layer is a small acoustic sensor according to any one of claims 1 to 6, which is 10 m to 50 m.

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