Electret condenser microphone

1. An electret condenser microphone, comprising:

a substrate in which an opening is formed;

an electret condenser connected to one face of the substrate so as to close the opening and having an acoustic hole and a cavity;

a drive circuit element connected to the one face of the substrate; and

a case mounted over the substrate so as to cover the electret condenser and the drive circuit element,

wherein electric contact is established at a joint part between the electret condenser and the substrate,

the acoustic hole communicates with an external space through the opening, and

the cavity and an internal region of the case serve as a back air chamber for the electret condenser.

2. The electret condenser microphone of claim 1 ,

wherein the acoustic hole includes a plurality of acoustic holes each having a diameter of 3 μm or smaller.

3. The electret condenser microphone of claim 1 ,

wherein the substrate is formed of a multilayer substrate.

4. The electret condenser microphone of claim 3 ,

wherein the multilayer substrate is made of ceramic.

5. The electret condenser microphone of claim 3 ,

wherein the opening is a hollow formed in the multilayer substrate so that the acoustic hole is not seen directly from the external space.

6. The electret condenser microphone of claim 1 ,

wherein the electret condenser and the substrate are joined to each other with the use of a metal protrusion and an anisotropic conductive resin.