Microphone unit

1. A microphone unit comprising:

an electroacoustic conversion portion that includes a diaphragm vibrated by sound pressure and that converts the sound pressure into an electrical signal; and

a first board that is placed and joined on a second board;

the second board on which the electroacoustic conversion portion is mounted;

a cover portion that includes a first opening portion and a second opening portion formed in one surface of the cover portion and that is arranged on the second board to cover the electroacoustic conversion portion;

a first sound passage that leads from an outside through the first opening portion of the cover portion to a first surface of the diaphragm; and

a second sound passage that leads from the outside through the second opening portion of the cover portion to a second surface which is a back surface of the diaphragm,

wherein the first board includes a groove portion, and the second board includes a first board opening portion communicating with the first opening portion of the cover portion, and the groove portion and a second board opening portion provided opposite to the diaphragm and a locating wall that is provided around the second board opening portion and that comes in contact with the electroacoustic conversion portion to locate the electroacoustic conversion portion.

2. The microphone unit of claim 1 ,

wherein the locating wall is included in a projection portion provided on the second board.

3. The microphone unit of claim 1 ,

wherein the locating wall is included in a recess portion provided in the second board.

4. The microphone unit of claim 1 ,

wherein the electroacoustic conversion portion is a MEMS (micro electro mechanical system) chip.

5. The microphone unit of claim 1

wherein the first sound passage leads from the outside to the first opening portion of the cover portion to the first board opening portion to the groove portion, and to the second board opening portion, and to the first surface of the diaphragm, and

the second sound passage leads from the outside to the second opening portion of the cover portion to an inner space formed between the cover portion and the second board and to the second surface of the diaphragm.

6. The microphone unit of claim 5 ,

wherein the locating wall is included in a projection portion provided on the second board.

7. The microphone unit of claim 5 ,

wherein the locating wall is included in a recess portion provided in the second board.

8. The microphone unit of claim 6 ,

wherein the electroacoustic conversion portion is a MEMS (micro electro mechanical system) chip.

9. The microphone unit of claim 7 ,

wherein the electroacoustic conversion portion is a MEMS (micro electro mechanical system) chip.

10. The microphone unit of claim 1 ,

wherein the groove portion is substantially rectangular in a plan view.

11. The microphone unit of claim 1 ,

wherein the first board opening portion, formed on the second board, is substantially oval in a plan view.

12. The microphone unit of claim 4 ,

wherein the first board further comprises an electrode pad for feeding electrical power from the outside to the electroacoustic conversion portion; an electrode pad for outputting the electrical signals amplified by the electroacoustic conversion portion to the outside; or an electrode pad for GND (ground) connection of the electroacoustic conversion portion.

13. The microphone unit of claim 5 ,

wherein the locating wall is included in a frame-shaped projection portion that is formed around the second board opening portion of the second board.

14. The microphone unit of claim 13 ,

wherein the frame-shaped projection portion is substantially C-shaped in a plan view.

15. The microphone unit of claim 13 ,

wherein the frame-shaped projection portion is substantially L-shaped in a plan view.