Flow rate sensor

A flow rate sensor comprising:

• a sensing portion in a plate form, the sensing portion configured to detect a flow rate of a fluid;
• and
• a resin seal sealing the sensing portion, wherein
• the sensing portion includes
• a semiconductor substrate including a thin portion, the thin portion having a smaller thickness in the thickness direction as compared to other portions of the semiconductor substrate, and
• an oil soluble film attached to the semiconductor substrate to cover the thin portion and having water repellency,
• the semiconductor substrate includes
• a first surface including an exposed portion that includes a specified area corresponding to the thin portion and a peripheral area corresponding to an outer periphery of the thin portion, and
• a second surface facing the first surface in a thickness direction of the sensing portion, the second surface including a portion that is recessed toward the first surface along the thickness direction to form the thin portion,
• the oil soluble film includes a recessed portion within a portion corresponding to the peripheral area and between the thin portion and a rim of the first surface,
• the recessed portion extends to surround the thin portion and is recessed toward the second surface, and
• the sensing portion is configured to detect the flow rate of the fluid flowing along the thin portion.

A flow rate sensor comprising:

• a sensing portion in a plate form, the sensing portion configured to detect a flow rate of a fluid;
• and
• a resin seal sealing the sensing portion, wherein
• the sensing portion includes
• a semiconductor substrate including a thin portion, the thin portion having a smaller thickness in the thickness direction as compared to other portions of the semiconductor substrate, and
• an oil soluble film having water repellency,
• the semiconductor substrate includes
• a first surface including an exposed portion that includes a specified area corresponding to the thin portion and a peripheral area corresponding to an outer periphery of the thin portion,
• a second surface facing the first surface in a thickness direction of the sensing portion, the second surface including a portion that is recessed toward the first surface along the thickness direction to form the thin portion, and
• a recessed portion formed within the peripheral area of the first surface and between the thin portion and a rim of the first surface,
• the recessed portion extends to surround the thin portion and is recessed toward the second surface, and
• the oil soluble film covers the first surface of the semiconductor substrate and an inner surface of the recessed portion and includes a rough surface at least in a portion corresponding to the peripheral area of the first surface, and
• the sensing portion is configured to detect the flow rate of the fluid flowing along the thin portion.