Microphone unit
View Patent ↗Disclosed is a microphone unit comprising a film substrate ( 1 ), electrically conductive layers ( 15, 16 ) which are formed on both substrate surfaces of the film substrate ( 11 ), and an electrical acoustic transducer unit ( 12 ) which is provided on the film substrate ( 11 ) and comprises a diaphragm capable of converting a sound pressure to an electrical signal. In the microphone unit, the linear expansion coefficient of the film substrate ( 11 ), including the electrically conductive layers ( 15, 16 ), falls within the range of 0.8 to 2.5 times, inclusive, the linear expansion coefficient of the diaphragm.
1. A microphone unit comprising:
a base board;
an electrically conductive layer formed on a first surface of the base board; and
a transducer that is mounted on the base board, includes a diaphragm, and transduces a sound pressure into an electrical signal,
wherein a coefficient of thermal expansion of the diaphragm is larger than a coefficient of thermal expansion of the base board and is smaller than a coefficient of thermal expansion of the electrically conductive layer, and
a coefficient β of thermal expansion of the combination of the base board and the electrically conductive layer given by the following formula is in a range 0.8 to 2.5 times as large as the coefficient of thermal expansion of the diaphragm:
β=( ax+bry )/( x+ry ),
where:
a is the coefficient of thermal expansion of the base board,
b is the coefficient of thermal expansion of the electrically conductive layer,
x is a thickness of the base board,
y is a thickness of the electrically conductive layer, and
r is a formation area ratio of the electrically conductive layer.
2. The microphone unit according to claim 1 , wherein the electrically conductive layer is a mesh-shaped electrically conductive layer.
3. The microphone unit according to claim 2 , wherein the mesh-shaped electrically conductive layer has a structure in which a metal thin line is formed into a net shape.
4. The microphone unit according to claim 3 , wherein a ratio of the metal thin line is 50% or smaller in a region where the mesh-shaped electrically conductive layer is formed.
5. The microphone unit according to claim 3 , wherein:
the mesh-shaped electrically conductive layer is further formed on a second surface opposite to the first surface of the base board; and
the metal thin line of the mesh-shaped electrically conductive layer formed on the first surface and the metal thin line of the mesh-shaped electrically conductive layer formed on the second surface are deviated from each other in position when viewed from a direction perpendicular to the first surface and the second surface.
6. The microphone unit according to claim 2 , wherein a connection pad for securing electric connection with a component mounted on the base board is formed on the first surface separately from the mesh-shaped electrically conductive layer.
7. The microphone unit according to claim 1 , wherein the electrically conductive layer is formed on a region that does not overlap a region where the transducer is disposed.
8. The microphone unit according to claim 7 , wherein the electrically conductive layer is further formed on at least a portion of a region that overlaps the region where the transducer is disposed.
9. The microphone unit according to claim 1 , wherein the first surface is a surface where the transducer is disposed.
10. The microphone unit according to claim 1 , wherein the electrically conductive layer is a wiring pattern for ground connection.
11. The microphone unit according to claim 1 , wherein the electrically conductive layer is formed on a wide area of the first surface.
12. The microphone unit according to claim 1 , wherein the electrically conductive layer is further formed on the second surface opposite to the first surface of the base board.
13. The microphone unit according to claim 1 , wherein the base board is composed of a film.
14. The microphone unit according to claim 1 , wherein the transducer is disposed on the base board by flip chip mounting.
15. A microphone unit comprising:
a base board;
an electrically conductive layer formed on a first surface of the base board; and
a transducer that is mounted on the base board, includes a diaphragm, and transduces a sound pressure into an electrical signal,
wherein a coefficient of thermal expansion of the diaphragm is larger than a coefficient of thermal expansion of the base board and is smaller than a coefficient of thermal expansion of the electrically conductive layer,
the electrically conductive layer is a mesh-shaped electrically conductive layer that has a structure in which a metal thin line is formed into a net shape,
the mesh-shaped electrically layer is further formed on a second surface opposite to the first surface of the base board, and
the metal thin line of the mesh-shaped electrically conductive layer formed on the first surface and the metal thin line of the mesh-like electrically conductive layer formed on the second surface are deviated from each other in position when viewed from a direction perpendicular to the first surface and the second surface.