Patent ID: 8375559

Claim:
A method for manufacturing a quartz crystal unit, comprising the steps of: providing a case having a mounting portion and a through-hole; providing a metal lid or a glass lid for covering an open end of the case; providing a quartz crystal wafer having opposite surfaces; disposing at least one metal film on at least one of the opposite surfaces of the quartz crystal wafer; forming a quartz crystal tuning fork resonator having an overall length and capable of vibrating in a flexural mode of an inverse phase by etching the quartz crystal wafer to form a quartz crystal tuning fork base, and first and second quartz crystal tuning fork tines connected to the quartz crystal tuning fork base, each of the first and second quartz crystal tuning fork tines having opposite main surfaces and opposite side surfaces; forming at least one groove having a length and a surface opposite at least one of the opposite side surfaces in at least one of the opposite main surfaces of each of the first and second quartz crystal tuning fork tines so that a width of the at least one groove formed in the at least one of the opposite main surfaces of each of the first and second quartz crystal tuning fork tines is greater than a distance in the width direction of the at least one groove measured from an outer edge of the surface of the at least one groove to an outer edge of the at least one side surface of the corresponding one of the first and second quartz crystal tuning fork tines; determining each of the overall length of the quartz crystal tuning fork resonator and the length of the at least one groove formed in the at least one of the opposite main surfaces of each of the first and second quartz crystal tuning fork tines so that a series resistance R 1 of a fundamental mode of vibration of the quartz crystal tuning fork resonator is less than a series resistance R 2 of a second overtone mode of vibration thereof; mounting the quartz crystal tuning fork resonator on the mounting portion of the case; adjusting an oscillation frequency of the quartz crystal tuning fork resonator; connecting the metal lid or the glass lid to the case to cover the open end of the case; and disposing a metal or a glass into the through-hole of the case to close the through-hole thereof in a vacuum after the connecting step.