Method of manufacturing a quartz crystal unit

Abstract

In a method for manufacturing a quartz crystal unit, a quartz crystal tuning fork resonator is formed by etching a quartz crystal wafer to form a quartz crystal tuning fork base, quartz crystal tuning fork tines connected to the quartz crystal tuning fork base, and a groove having stepped portions in at least one of opposite main surfaces of each of the quartz crystal tuning fork tines. A first electrode is disposed on at least one of the stepped portions of each of the grooves and a second electrode is disposed on each of side surfaces of each of the quartz crystal tuning fork tines. A frequency of oscillation of the quartz crystal tuning fork resonator is adjusted at least twice and in different steps. The quartz crystal tuning fork resonator is then mounted in a case and an open end of the case is covered with a lid.

What is claimed is: 
     
       1. A method for manufacturing a quartz crystal unit, comprising the steps of:
 forming at least one quartz crystal tuning fork resonator by etching a quartz crystal wafer to form a quartz crystal tuning fork base, a plurality of quartz crystal tuning fork tines connected to the quartz crystal tuning fork base, and at least one groove having a plurality of stepped portions in at least one of opposite main surfaces of each of two of the quartz crystal tuning fork tines, and disposing a first electrode on at least one of the stepped portions of at least one of the grooves and a second electrode on at least one side surface of each so that a width of the at least one groove formed in the at least one of the main surfaces of each of the two of the 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 at least one groove to an outer edge of the corresponding one of the two of the quartz crystal tuning fork tines; 
 adjusting at least twice and in different steps a frequency of oscillation of the quartz crystal tuning fork resonator;disposing an electrode on a surface of the at least one groove formed in the at least one of the main surfaces of one of the two of the quartz crystal tuning fork tines and disposing an electrode on a surface of the at least one groove formed in the at least one of the main surfaces of the other of the two of the quartz crystal tuning fork tines so that the electrode disposed on the surface of the at least one groove formed in the at least one of the main surfaces of the one of the two quartz crystal tuning fork tines has an electrical polarity opposite to an electrical polarity of the electrode disposed on the surface of the at least one groove formed in the at least one of the main surfaces of the other of the two quartz crystal tuning fork tines; 
 providing a case having an interior space and an open end communicating with the interior space a mounting portion; 
 providing a lid for covering the open end of the case; 
 after the disposing step, mounting the quartz crystal tuning fork resonator in the interior spaceon the mounting portion of the case; and 
 connecting the lid to the case to cover the open end thereofafter the mounting step, adjusting at least once a frequency of oscillation of the quartz crystal tuning fork resonator. 
 
     
     
       2. A method according to  claim 1 ; wherein the step of forming the groove comprises the step of forming a throughhole in each of the quartz crystal tuning fork tines extending through the opposite main surfaces thereof. 
     
     
       3. A method according to  claim 1 ; wherein the step of forming a plurality of quartz crystal tuning fork tines comprises the step of forming a first quartz crystal tuning fork tine and a second quartz crystal tuning fork tine; wherein the step of forming the first and second electrodes comprises the steps of forming the first electrode on each of two of the stepped portions of the groove in at least one of the opposite main surfaces of each of the first and second quartz crystal tuning fork tines and forming the second electrode on each of two of the side surfaces of each of the first and second quartz crystal tuning fork tines; and wherein the first electrode disposed on each of two of the stepped portions of the groove of the first quartz crystal tuning fork tine is connected to the second electrode disposed on each of two of the side surfaces of the second quartz crystal tuning fork tine to form a first electrode terminal, and the second electrode disposed on each of two of the side surfaces of the first quartz crystal tuning fork tine is connected to the first electrode disposed on each of two of the stepped portions of the groove of the second quartz crystal tuning fork tine to form a second electrode terminal so that the quartz crystal tuning fork resonator vibrates in a flexural mode of an inverse phase when an alternating current voltage is applied between the first electrode terminal and the second electrode terminal. 
     
     
       4. A method according to  claim 3 ; wherein the at least one groove is formed in each of the first main surface and the second main surface of each of the quartz crystal tuning fork tines so that a ratio W 2 /W is in the range of 0.35 to 0.85, where W 2  represents a width of the groove and W represents a width of each of the quartz crystal tuning fork tines. 
     
     
       5. A method according to  claim 3 ; wherein the adjusting step comprises the step of adjusting the frequency of oscillation of the quartz crystal tuning fork resonator by at least one of a laser method and evaporation and etching methods so that the frequency of oscillation of the quartz crystal tuning fork resonator is about 32.768 Hz with a frequency deviation within the range of −9000 PPM to +5000 PPM. 
     
     
       6. A method according to  claim 3 ; wherein the side surfaces of the first and second quartz crystal tuning fork tines comprise a first side surface and a second side surface, the first side surface of the first quartz crystal tuning fork tine confronting the first side surface of the second quartz crystal tuning fork tine; and wherein the stepped portions of the groove comprises a first stepped portion, a second stepped portion, and a third stepped portion connecting the first stepped portion to the second stepped portion, each of the first and second stepped portions being formed opposite to the first side surface of each of the first and second quartz crystal tuning fork tines. 
     
     
       7. A method according to  claim 3 ; wherein the step of forming at least one quartz crystal tuning fork resonator comprises the steps of forming two of the quartz crystal tuning fork resonators and integrally connecting together the two quartz crystal tuning fork resonators at their respective quartz crystal tuning fork bases at an angle of 30° or less. 
     
     
       8. A method according to  claim 3 ; wherein the adjusting step comprises the step of adjusting the frequency of oscillation of the quartz crystal tuning fork resonator by at least one of a laser method and evaporation and etching methods after the quartz crystal tuning fork resonator is mounted in the interior space of the case so that the frequency of oscillation of the resonator is about 32.768 kHz with a frequency deviation within the range of −100 PPM to +100 PPM. 
     
     
       9. A method according to  claim 8 ; wherein the step of forming at least one quartz crystal tuning fork resonator comprises the step of forming one quartz crystal tuning fork resonator capable of vibrating in a flexural mode of an inverse phase; and further comprising the step of forming one quartz crystal resonator capable of vibrating in a mode different from the flexural mode of an inverse phase. 
     
     
       10. A method according to  claim 8 ; wherein the connecting step comprises the step of connecting the lid to the case using at least one of a metal and a glass with a low melting point. 
     
     
       11. A method according to  claim 10 ; wherein the adjusting step comprises the step of adjusting the frequency of oscillation of the quartz crystal tuning fork resonator by a laser method after the connecting step so that the frequency of oscillation of the quartz crystal tuning fork resonator is about 32.768 kHz with a frequency deviation within the range of −30 ppm to +30 ppm. 
     
     
       12. A method according to  claim 10 ; wherein the adjusting step comprises the step of adjusting the frequency of oscillation of the quartz crystal tuning fork resonator by a laser method after the connecting step so that the frequency of oscillation of the resonator is about 32.768 kHz with a frequency deviation within the range of −50 ppm to +50 ppm. 
     
     
       13. A method according to  claim 12 ; wherein one of the case and the lid has a through-hole; and further comprising the step of disposing at least one of a metal and a glass into the through hole to maintain the interior space of the case in a vacuum. 
     
     
       14. A method according to  claim 13 ; wherein the adjusting step comprises the step of adjusting the frequency of oscillation of the quartz crystal tuning fork resonator by a laser method after the disposing step so that the frequency of oscillation of the resonator is about 32.768 kHz with a frequency deviation within the range of −30 ppm to +30 ppm. 
     
     
       15. A method according to  claim 3 ; wherein the forming step comprises the steps of forming the quartz crystal tuning fork tines in a first etching process and forming the corresponding grooves in a second etching process different from the first etching process; and wherein the step of forming the quartz crystal tuning fork tines is performed before the step of forming the corresponding grooves. 
     
     
       16. A method according to  claim 3 ; wherein the forming step comprises the steps of forming the quartz crystal tuning fork tines in a first etching process and forming the corresponding grooves in a second etching process different from the first etching process; and wherein the step of forming the corresponding grooves is performed before the step of forming the quartz crystal tuning fork tines. 
     
     
       17. A method according to  claim 1 ; wherein the adjusting step comprises the step of adjusting a frequency of oscillation of the quartz crystal tuning fork resonator to a preselected frequency with a frequency deviation within the range of −100 ppm to +100 ppm. 
     
     
       18. A method according to  claim 17 ; wherein the preselected frequency is about 32.768 kHz. 
     
     
       19. A method according to  claim 17 ; wherein a width of the groove formed in at least one of the opposite main surfaces of each of the quartz crystal tuning fork tines is greater than a distance in the width direction of the groove measured from an outer edge of the groove to an outer edge of the quartz crystal tuning fork tine. 
     
     
       20. A method according to  claim 19 ; wherein the forming step comprises the steps of forming the quartz crystal tuning fork tines in a first etching process and forming the corresponding grooves in a second etching process different from the first etching process; and wherein the step of forming the quartz crystal tuning fork tines is performed before the step of forming the corresponding grooves. 
     
     
       21. A method according to  claim 19 ; wherein the forming step comprises the steps of forming the quartz crystal tuning fork tines in a first etching process and forming the corresponding grooves in a second etching process different from the first etching process; and wherein the step of forming the corresponding grooves is performed before the step of forming the quartz crystal tuning fork tines. 
     
     
       22. A method according to  claim 19 ; wherein the groove formed in at least one of the main surfaces of each of the quartz crystal tuning fork tines comprises a through hole. 
     
     
       23. A method according to  claim 19 ; wherein the forming step comprises the steps of forming the quartz crystal tuning fork tines into a first quartz crystal tuning fork tine and a second quartz crystal tuning fork tine; forming a groove in each of opposite main surfaces of each of the first and second quartz crystal tuning fork tines; forming a first electrode on each of at least two of the stepped portions of the groove in each of the opposite main surfaces of the first and second quartz crystal tuning fork tines; forming a second electrode on each of two of side surfaces of each of the first and second quartz crystal tuning fork tines; connecting the first electrodes disposed on at least two of the stepped portions of the groove of the first quartz crystal tuning fork tine to the second electrodes disposed on two of the side surfaces of the second quartz crystal tuning fork tine to form a first electrode terminal; and connecting the second electrodes disposed on two of the side surfaces of the first quartz crystal tuning fork tine to the first electrodes disposed on at least two of the stepped portions of the groove of the second quartz crystal tuning fork tine to form a second electrode terminal; and further comprising the step of applying an alternating current voltage between the first electrode terminal and the second electrode terminal to vibrate the quartz crystal tuning fork resonator in a flexural mode of an inverse phase. 
     
     
       24. A method according to  claim 23 ; wherein the forming step comprises the step of forming the first and second quartz crystal tuning fork tines simultaneously with the corresponding grooves. 
     
     
       25. A method according to  claim 23 ; wherein a ratio W 2 /W is in the range of 0.35 to 0.85, where W 2  represents a width of the groove and W represents a width of each of the first and second quartz crystal tuning fork tines. 
     
     
       26. A method according to  claim 25 ; wherein the connecting step comprises the step of connecting the lid to the case using at least one of a metal and a glass with a low melting point. 
     
     
       27. A method according to  claim 25 ; wherein the quartz crystal tuning fork resonator has a fundamental mode of vibration and a second overtone mode of vibration; and wherein a series resistance R 1  of the fundamental mode of vibration is less than a series resistance R 2  of the second overtone mode of vibration. 
     
     
       28. A method according to  claim 27 ; wherein one of the case and the lid has a through-hole; and further comprising the step of disposing at least one of a metal and a glass into the through-hole to maintain the interior space of the case in a vacuum. 
     
     
       29. A method according to  claim 27 ; further comprising the step of providing a CMOS inverter, a plurality of capacitors, and a plurality of resistors to form an oscillator having the quartz crystal tuning fork resonator. 
     
     
       30. A method according to  claim 1 ; wherein the adjusting step comprises the steps of adjusting a frequency of oscillation of the quartz crystal tuning fork resonator to a first preselected frequency of oscillation, and adjusting the frequency of oscillation of the quartz crystal tuning fork resonator to a second preselected frequency of oscillation different from the first preselected frequency of oscillation. 
     
     
       31. A method according to  claim 30 ; wherein the first preselected frequency of oscillation is about 32.768 kHz with a frequency deviation within the range of −9000 ppm to +5000 ppm; and wherein the second preselected frequency of oscillation is about 32.768 kHz with a frequency deviation within the range of −100 ppm to +100 ppm. 
     
     
       32. A method according to  claim 30 ; wherein the at least one groove is formed in each of the opposite main surfaces of each of the quartz crystal tuning fork tines so that a ratio W 2 /W is in the range of 0.35 to 0.85, where W 2  represents a width of the groove and W represents a width of each of the first and second quartz crystal tuning fork tines. 
     
     
       33. A method according to  claim 30 , further comprising the step of etching the quartz crystal wafer to simultaneously form the quartz crystal tuning fork tines and the corresponding grooves by a single etching process. 
     
     
       34. A method according to  claim 30 , wherein the quartz crystal tuning fork resonator has a fundamental mode of vibration and a second overtone mode of vibration; and wherein a series resistance R 1  of the fundamental mode of vibration is less than a series resistance R 2  of the second overtone mode of vibration. 
     
     
       35. A method according to  claim 34 ; wherein the at least one groove is formed in each of the opposite main surfaces of each of the quartz crystal tuning fork tines so that a width of at least one of the grooves in each of the opposite main surfaces of each of the quartz crystal tuning fork tines is greater than a distance in the width direction of the groove measured from an outer edge of the groove to an outer edge of the quartz crystal tuning fork tine; and wherein the forming step comprises the steps of forming the quartz crystal tuning fork tines into a first quartz crystal tuning fork tine and a second quartz crystal tuning fork tine; forming at least one groove in each of opposite main surfaces of each of the first and second quartz crystal tuning fork tines; forming a plurality of first electrodes on at least two of the stepped portions of the grooves in the opposite main surfaces of the first and second quartz crystal tuning fork tines; forming a plurality of second electrodes on side surfaces of each of the first and second quartz crystal tuning fork tines; connecting the first electrodes disposed on at least two of the stepped portions of the grooves of the first quartz crystal tuning fork tine to the second electrodes disposed on the side surfaces of the second quartz crystal tuning fork tine to form a first electrode terminal; and connecting the second electrodes disposed on the side surfaces of the first quartz crystal tuning fork tine to the first electrodes disposed on at least two of the stepped portions of the grooves of the second quartz crystal tuning fork tine to form a second electrode terminal; and further comprising the step of applying an alternating current voltage between the first electrode terminal and the second electrode terminal to vibrate the quartz crystal tuning fork resonator in a flexural mode of an inverse phase. 
     
     
       36. A method according to  claim 35 ; wherein the forming step comprises the steps of forming the quartz crystal tuning fork tines in a first etching process and forming the corresponding grooves in a second etching process different from the first etching process; and wherein the step of forming the quartz crystal tuning fork tines is performed before the step of forming the corresponding grooves. 
     
     
       37. A method according to claim 1; wherein the quartz crystal tuning fork resonator has an overall length and the at least one groove formed in the at least one of the main surfaces of each of the two of the quartz crystal tuning fork tines has a length; and further comprising the step of determining 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 main surfaces of each of the two of the 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. 
     
     
       38. A method according to claim 1; wherein the two of the quartz crystal tuning fork tines comprise first and second quartz crystal tuning fork tines, and the main surfaces of each of the first and second quartz crystal tuning fork tines comprise a first main surface and a second main surface opposite the first main surface; wherein each of the first and second quartz crystal tuning fork tines has a first side surface and a second side surface opposite the first side surface, the first side surface of the first quartz crystal tuning fork tine confronting the first side surface of the second quartz crystal tuning fork tine; wherein the quartz crystal wafer has a first surface and a second surface opposite the first surface, each of the first main surfaces of the first and second quartz crystal tuning fork tines being formed at the first surface of the quartz crystal wafer; wherein the at least one groove is formed in the first main surface of each of the first and second quartz crystal tuning fork tines with a first stepped portion and a second stepped portion connected to the first stepped portion through a third stepped portion so that each of the first and second stepped portions of the at least one groove formed in the first main surface of the first quartz crystal tuning fork tine is formed opposite the first side surface of the first quartz crystal tuning fork tine and is directly connected to the third stepped portion, and so that each of the first and second stepped portions of the at least one groove formed in the first main surface of the second quartz crystal tuning fork and is directly connected to the third stepped portion; wherein the at least one groove formed in the first main surface of each of the first and second quartz crystal tuning fork tines has a fourth stepped portion directly oposite a fifth stepped portion in the length direction, the fourth stepped portion being directly connected to the first stepped portion and the fifth stepped portion being directly connected to the second stepped portion. 
     
     
       39. A method according to claim 38; further comprising the steps of providing a lid for covering an open end of the case, one of the lid and the case having a throughhole and the case having an interior space containing the mounting portion; forming the at least one groove in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines so that a ratio W 2 /W is in the range of 0.35 to 0.85, where W 2  represents a width of the groove and W represents a width of each of the first and second quartz crystal tuning fork tines; adjusting the frequency of oscillation of the quartz crystal tuning fork resonator so that the frequency of oscillation thereof is about 32.768 kHz with a frequency deviation within the range of −100 ppm to +100 ppm; connecting the lid to the case to cover the open end thereof; and disposing a metal or a glass in the through hole to close the through hole in a vacuum. 
     
     
       40. A method according to claim 38; further comprising the step of providing a lid for covering an open end of the case, one of the lid and the case having a through hole, and the case having an interior space containing the mounting portion; wherein the adjusting step comprises adjusting in a vacuum the frequency of oscillation of the quartz crystal tuning fork resonator; and further comprising, after the mounting, and adjusting steps, the sequential steps of connecting the lid to the case to cover the open end thereof and disposing a metal or a glass in the through hole to close the through hole in a vacuum. 
     
     
       41. A method according to claim 38; further comprising the step of providing a lid for covering an open end of the case, one of the lid and the case having a through hole, and the case having an interior space containing the mounting portion; wherein the adjusting step comprises adjusting the frequency of oscillation of the quartz crystal tuning fork resonator so that the frequency of oscillation thereof is about 32.768 kHz with a frequency deviation within the range of −30 ppm to +30 ppm; and further comprising, after the mounting and adjusting steps, the sequential steps of connecting the lid to the case to cover the open end thereof and disposing a metal or glass in the through hole to close the through hole in a vacuum. 
     
     
       42. A method according to claim 38; wherein the step of forming the at least one groove comprises the step of forming a groove in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines so that a ratio W 2 /W is in the range of 0.35 to 0.85, where W 2  represents a width of the groove and W represents a width of each of the first and second quartz crystal tuning fork tines; wherein the adjusting step comprises adjusting the frequency of oscillation of the quartz crystal tuning fork resonator so that the frequency of oscillation thereof is about 32.768 kHz with a frequency deviation within the range of −100 ppm to +100 ppm; and further comprising, after the mounting and adjusting steps, the step of connecting a lid to the case to maintain the quartz crystal tuning fork resonator in a vacuum. 
     
     
       43. A method according to claim 1; wherein the two of the quartz crystal tuning fork tines comprise first and second quartz crystal tuning fork tines each having a length, and the main surfaces of each of the first and second quartz crystal tuning fork tines comprise a first main surface and a second main surface opposite the first main surface; wherein the step of forming the at least one groove comprises the steps of forming a groove having at least two stepped portions including a first stepped portion and a second stepped portion in the first main surface of each of the first and second quartz crystal tuning fork tines so that each of the first and second stepped portions is formed along the length of each of the first and second quartz crystal tuning fork tines, and forming a groove having at least three stepped portions including a first stepped portion, a second stepped portion and a third stepped portion in the second main surface of each of the first and second quartz crystal tuning fork tines so that each of the first, second and third stepped portions is formed along the length of each of the first and second quartz crystal tuning fork tines and the first stepped portion is connected to the second stepped portion through a stepped portion, and so that each of the first and second stepped portions is directly connected to the stepped portion; and wherein the groove having the at least three stepped portions formed in the second main surface of each of the first and second quartz crystal tuning fork tines has a fourth stepped portion directly opposite a fifth stepped portion in the length direction, the fourth stepped portion being directly connected to the first stepped portion and the fifth stepped portion being directly connected to the second stepped portion. 
     
     
       44. A method according to claim 38; wherein the step of forming the at least one groove comprises forming a groove in at least one of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines; wherein the step of disposing the electrode comprises forming a first electrode on a surface of the groove formed in the at least one of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines and forming a second electrode on each of the first and second side surfaces of each of the first and second quartz crystal tuning fork tines so that the first electrode formed on the surface of the groove formed in the at least one of the first and second main surfaces of the first quartz crystal tuning fork tine is connected to the second electrode formed on each of the first and second side surfaces of the second quartz crystal tuning fork tine, and the second electrode formed on each of the first and second side surfaces of the first quartz crystal tuning fork tine is connected to the first electrode formed on the surface of the groove formed in the at least one of the first and second main surfaces of the second quartz crystal tuning fork tine; and further comprising the steps of providing a lid for covering an open end of the case, connecting the lid to the case to cover the open end of the case, and disposing a metal or a glass in a through hole formed in one of the case and the lid to close the through hole in a vacuum after the connecting step. 
     
     
       45. A method according to claim 44; wherein the step of forming the at least one groove comprises the step of forming a groove having a first stepped portion, a second stepped portion and a third stepped portion connecting the first stepped portion to the second stepped portion in the second main surface of each of the first and second quartz crystal tuning fork tines, each of the first and second stepped portions being formed opposite the first side surface of each of the first and second quartz crystal tuning fork tines and being directly connected to the third stepped portion; and wherein the groove formed in the second main surface of each of the first and second quartz crystal tuning fork tines has a fourth stepped portion directly opposite a fifth stepped portion in the length direction, the fourth stepped portion being directly connected to the first stepped portion and the fifth stepped portion being directly connected to the second stepped portion. 
     
     
       46. A method according to claim 45; wherein the adjusting step comprises the step of adjusting in a vacuum the frequency of oscillation of the quartz crystal tuning fork resonator after the connecting step and before the disposing step. 
     
     
       47. A method according to claim 45; wherein the adjusting step comprises the step of adjusting the frequency of oscillation of the quartz crystal tuning fork resonator after the disposing step so that the frequency of oscillation thereof is about 32.768 kHz with a frequency deviation within the range of −30 ppm to +30 ppm. 
     
     
       48. A method according to claim 45; wherein the adjusting step comprises adjusting the frequency of oscillation of the quartz crystal tuning fork resonator before the connecting step. 
     
     
       49. A method according to claim 45; wherein the adjusting step comprises the step of adjusting the frequency of oscillation of the quartz crystal tuning fork resonator so that the frequency of oscillation thereof is about 32.768 kHz with a frequency deviation within the range of −9000 ppm to +5000 ppm. 
     
     
       50. A method according to claim 44; wherein the adjusting step comprises a first step of adjusting the frequency of oscillation of the quartz crystal tuning fork resonator to a first preselected frequency of oscillation after the disposing step of the first and second electrodes and before the mounting step; and a second step of adjusting the frequency of oscillation of the quartz crystal tuning fork resonator to a second preselected frequency of oscillation after the mounting step and before the connecting step. 
     
     
       51. A method according to claim 50; wherein the first preselected frequency of oscillation is about 32.768 kHz with a frequency deviation within the range of −9000 ppm to +5000 ppm; and wherein the second preselected frequency of oscillation is about 32.768 kHz with a frequency deviation within the range of −100 ppm to +100 ppm. 
     
     
       52. A method according to claim 44; wherein the adjusting step comprises the step of adjusting in a vacuum the frequency of oscillation of the quartz crystal tuning fork resonator after the connecting step and before the disposing step of the metal or the glass. 
     
     
       53. A method according to claim 44; wherein the adjusting step comprises adjusting the frequency of oscillation of the quartz crystal tuning fork resonator after the disposing step of the metal or the glass so that the frequency of oscillation thereof is about 32.768 kHz with a frequency deviation within the range of −30 ppm to +30 ppm. 
     
     
       54. A method according to claim 1; wherein the two of the quartz crystal tuning fork tines comprise first and second quartz crystal tuning fork tines, the main surfaces of each of the first and second quartz crystal tuning fork tines comprise a first main surface and a second main surface opposite the first main surface, and each of the first and second quartz crystal tuning fork tines has a first side surface and a second side surface opposite the first side surface; wherein the step of forming the at least one groove comprises forming a groove in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines so that a width of the groove formed in each of the first and second 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 groove measured from an outer edge of the groove to an outer edge of the corresponding one of the first and second quartz crystal tuning fork tines; wherein the disposing step comprises forming a first electrode on a surface of the groove formed in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines and forming a second electrode on each of the first and second side surfaces of each of the first and second quartz crystal tuning fork tines so that the first electrode formed on the surface of the groove formed in each of the first and second main surfaces of the first quartz crystal tuning fork tine is connected to the second electrode formed on each of the first and second side surfaces of the second quartz crystal tuning fork tine, and the second electrode formed on each of the first and second side surfaces of the first quartz crystal tuning fork tine is connected to the first electrode formed on the surface of the groove formed in each of the first and second main surfaces of the second quartz crystal tuning fork tine; wherein the case has an interior space containing the mounting portion and an open end through which the quartz crystal tuning fork resonator is mounted on the mounting portion; and after the adjusting step, further comprising the step of connecting a lid to the open end of the case to cover the open end of the case. 
     
     
       55. A method according to claim 54; wherein the first side surface of the first quartz crystal tuning fork tine confronts the first side surface of the second quartz crystal tuning fork tine; wherein the step of forming the at least one groove comprises forming the groove having a first stepped portion including a first width and a second groove portion including a second width different from the first width in at least one of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines so that a first distance in the width direction of the first groove portion measured from a first outer edge of the first groove portion to a first outer edge of the first side surface of the corresponding one of the first and second quartz crystal tuning fork tines is greater than a second distance in the width direction of the second groove portion measured from a second outer edge of the second groove portion to a second outer edge of the first side surface of the corresponding one of the first and second quartz tuning fork tines; wherein the first width of the first groove portion of the groove formed in the at least one of the first and second main surfaces of the first quartz cystal tuning fork tine is greater than the first distance in the width direction of the first groove portion of the first quartz crystal tuning fork tine; wherein the first width of the first groove portion of the groove formed in the at least one of the first and second main surfaces of the second quartz crystal tuning fork tine is greater than the first distance in the width direction of the first groove portion of the second quartz crystal tuning fork tine; wherein the case has a through hole; and further comprising the step of disposing a metal or a glass in the through hole of the case to close the through hole thereof in a vacuum; wherein the lid is a metal lid or a glass lid; and wherein the connecting step comprises the step of connecting the metal lid or the glass lid to the open end of the case. 
     
     
       56. A method according to claim 54; wherein the adjusting step comprises the step of adjusting the frequency of oscillation of the quartz crystal tuning fork resonator so that the frequency of oscillation thereof is about 32.768 kHz with a frequency deviation within the range of −100 ppm to +100 ppm; and wherein the connecting step comprises the step of connecting the lid to the open end of the case so that the interior space of the case is in a vacuum. 
     
     
       57. A method according to claim 54; further comprising the step of adjusting the frequency of oscillation of the quartz crystal tuning fork resonator after the forming step of the first and second electrodes and before the mounting step so that the frequency of oscillation thereof is about 32.768 kHz with a frequency deviation within the range of −9000 ppm to +5000 ppm. 
     
     
       58. A method according to claim 54; wherein the first side surface of the first quartz crystal tuning fork tine confronts the first side surface of the second quartz crystal tuning fork tine; wherein the step of forming the at least one groove includes the step of forming a groove having a first and a second surface connected to the first surface through a third surface in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines so that a ratio W 2 /W is in the range of 0.35 to 0.85, where W 2  represents a width of the groove and W represents a width of each of the first and second quartz crystal tuning fork tines, and so that each of the first and second surfaces of the groove formed in each of the first and second main surfaces of the first quartz crystal tuning fork tine is formed opposite the first side surface of the first quartz tuning fork tine and each of the first and second surfaces of the groove formed in each of the first and second main surfaces of the second quartz crystal tuning fork tine is formed opposite the first side surface of the second quartz crystal tuning fork tine, each of the first, second and third surfaces having a first end and a second end portion, the first end portion of the first surface being directly connected to the first end portion of the third surface and the first end portion of the second surface being directly connected to the second end portion of the third surface; wherein the groove having the first, second and third surfaces formed in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines has a fourth surfaces directly opposite a fifth surface in the length direction, an end portion of the fourth surface being directly connected to the second end portion of the first surface and an end portion of the fifth surface being directly connected to the second end portion of the second surface. 
     
     
       59. A method according to claim 1; wherein the two of the quartz crystal tuning fork tines comprise first and second quartz crystal tuning fork tines, the main surfaces of each of the first and second quartz crystal tuning fork tines comprise a first main surface and a second main surface opposite the first main surface, and each of the first and second quartz crystal tuning fork tines has a first side surface and a second side surface opposite the first side surface; wherein the step of forming the at least one groove comprises forming at least one groove in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines; wherein the step of disposing an electrode comprises the steps of forming a first electrode on a surface of the at least one groove formed in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines and forming a second electrode on each of the first and second side surfaces of each of the first and second quartz crystal tuning fork tines; and further comprising the steps of connecting the first electrode formed on the surface of the at least one groove formed in each of the first and second main surfaces of the first quartz crystal tuning fork tine to the second electrode formed on each of the first and second side surfaces of the second quartz crystal tuning fork tine to form a first electrode terminal, and connecting the second electrode formed on each of the first and second side surfaces of the first quartz crystal tuning fork tine to the first electrode formed on the surface of the at least one groove formed in each of the first and second main surfaces of the second quartz crystal tuning fork tine to form a second electrode terminal so that the quartz crystal tuning fork resonator vibrates in a flexural mode of an inverse phase when an alternating current voltage is applied between the first electrode terminal and the second electrode terminal. 
     
     
       60. A method according to claim 59; wherein the step of forming the at least one groove comprises the step of forming the at least one groove in each of the first and second 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 each of the first and second 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 at least one groove to an outer edge of the corresponding one of the first and second quartz crystal tuning fork tines; and wherein the forming step of the at least one groove is performed before the forming step of the second electrode. 
     
     
       61. A method according to claim 60; wherein the case comprises a ceramics case having a through hole and an interior space containing the mounting portion; and further comprising the steps of adjusting in a vacuum the frequency of oscillation of the quartz crystal tuning fork resonator, covering an open end of the ceramics case with a glass lid after the mounting step and before the adjusting step and thereafter disposing a metal or a glass in the through hole of the ceramics case to close the through hole thereof in a vacuum. 
     
     
       62. A method according to claim 61; wherein the adjusting step comprises the step of adjusting in the vacuum the frequency of oscillation of the quartz crystal tuning fork resonator after the connecting step and before the disposing step of the metal or the glass so that the frequency of oscillation thereof is about 32.768 kHz with a frequency deviation within the range of −50 ppm to +50 ppm. 
     
     
       63. A method according to claim 60; wherein the case comprises a ceramics case having a through hole and an interior space containing the mounting portion; and further comprising the steps of covering an open end of the ceramics case with a glass lid after the mounting step, disposing a metal or a glass in the through hole of the ceramics case to close the through hole thereof in a vacuum, and performing the adjusting step after the step of disposing the metal or the glass in the through hole of the ceramics case so that the frequency of oscillation thereof is about 32.768 kHz with a frequency deviation within the range of −30 ppm to +30 ppm. 
     
     
       64. A method according to claim 60; wherein the case comprises a ceramics case having an open end an interior space containing the mounting portion; wherein the adjusting step comprises adjusting the frequency of oscillation of the quartz crystal tuning fork resonator after the mounting step so that the frequency of oscillation thereof is about 32.768 kHz with a frequency deviation within the range of −100 ppm to +100 ppm; and further comprising the step of connecting a metal lid to the ceramics case after the adjusting step to cover the open end thereof so that the interior space is placed in a vacuum. 
     
     
       65. A method according to claim 60; wherein the case comprises a ceramics case having a through hole, an open end, and an interior space containing the mounting portion; wherein the adjusting step comprises adjusting the frequency of oscillation of the quartz crystal tuning fork resonator so that the frequency of oscillation thereof is about 32.768 kHz with a frequency deviation within the range of −100 ppm to +100 ppm; and further comprising the steps of covering the open end of the ceramics case with a metal lid after the adjusting step and thereafter disposing a metal or a glass in the through hole of the ceramics case to close the through hole thereof in a vacuum. 
     
     
       66. A method according to claim 50; wherein the first side surface of the first quartz crystal tuning fork tine confronts the first side surface of the second quartz crystal tuning fork tine; wherein the step of forming the at least one groove comprises the step of forming a groove having a first stepped portion and a second stepped portion connected to the first stepped portion through a third stepped portion in at least one of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines, each of the first and second stepped portions of the groove formed in the at least one of the first and second main surfaces of the first quartz crystal tuning fork tine being formed opposite the first side surface of the first quartz crystal tuning fork tine and being directly connected to the third stepped portion, and each of the first and second stepped portions of the groove formed in the at least one of the first and second main surfaces of the second quartz crystal tuning fork tine being formed opposite the first side surface of the second quartz crystal tuning fork tine and being directly connected to the third stepped portion; wherein the groove formed in the at least one of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines has a length, and a fourth stepped portion directly opposite a fifth stepped portion in the length direction, the fourth stepped portion being directly connected to the first stepped portion and the fifth stepped portion being directly connected to the second stepped portion; wherein the quartz crystal tuning fork resonator has an overall length; wherein each of the overall length of the quartz crystal tuning fork resonator and the length of the groove formed in the at least one of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines is determined 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; wherein the adjusting step comprises adjusting the frequency of oscillation of the quartz crystal tuning fork resonator so that the frequency of oscillation thereof is about 32.768 kHz with a frequency deviation within the range of −100 ppm to +100 ppm; wherein the case has a through hole; and further comprising the step of disposing a metal or a glass in the through hole of the case to close the through hole thereof in a vacuum. 
     
     
       67. A method according to claim 59; wherein the quartz crystal wafer has a first surface and a second surface opposite the first surface; and further comprising the sequential steps of forming a plurality of grooves in the first and second surfaces of the quartz crystal wafer; forming the first and second quartz crystal tuning fork tines so that a groove having a first surface opposite the first side surface and a second surface opposite the second side surface is located in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines, a width of the groove located in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines being greater than a distance in the width direction of the groove measured from an outer edge of the groove to an outer edge of the corresponding one of the first and second quartz crystal tuning fork tines; and wherein the disposing step comprises disposing the electrode on each of the first and second surfaces of the groove located in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines so that the electrode formed on each of the first and second surfaces of the groove located in each of the first and second main surfaces of the first quartz crystal tuning fork tine has an electrical polarity opposite to an electrical polarity of the electrode formed on each of the first and second surfaces of the groove located in each of the first and second main surfaces of the second quartz crystal tuning fork tine. 
     
     
       68. A method according to claim 59; wherein the at least one groove formed in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines comprises a plurality of grooves formed in at least one of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines, the grooves being divided in the length direction; and further comprising the step of forming simultaneously the first and second quartz crystal tuning fork tines and the grooves formed in the at least one of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines so that a width of at least one of the grooves formed in the at least one of the first and second 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 at least one groove to an outer edge of the corresponding one of the first and second quartz crystal tuning fork tines. 
     
     
       69. A method according to claim 59; wherein the quartz crystal wafer has a first surface and a second surface opposite the first surface; wherein the quartz crystal tuning fork base has a third main surface and a fourth main surface opposite the third main surface, each of the third main surface of the quartz crystal tuning fork base and the first main surface of each of the first and second quartz crystal tuning fork tines being formed at the first surface of the quartz crystal wafer, and each of the fourth main surface of the quartz crystal tuning fork base and the second main surface of each of the first and second quartz crystal tuning fork tines being formed at the second surface of the quartz crystal wafer; wherein each of the third and fourth main surfaces of the quartz crystal tuning fork base has a third electrode and a fourth electrode, the third electrode having an electrical polarity opposite to an electrical polarity of the fourth electrode; wherein the third electrode formed on each of the third and fourth main surfaces of the quartz crystal tuning fork base is connected to the second electrode formed on each of the first and second side surfaces of one of the first and second quartz crystal tuning fork tines; wherein the fourth electrode formed on each of the third and fourth main surfaces of the quartz crystal tuning fork base is connected to the second electrode formed on each of the first and second side surfaces of the other of the first and second quartz crystal tuning fork tines; wherein the first electrode formed on the surface of the at least one groove formed in one of the first and second main surfaces of the first quartz crystal tuning fork tine is connected to the second electrode formed on each of the first and second side surfaces of the second quartz crystal tuning fork tine through one of the third and fourth electrodes formed on one of the third and fourth main surfaces of the quartz crystal tuning fork base; and wherein the third electrode formed on the third main surface of the quartz crystal tuning fork base is formed opposite the third electrode formed on the fourth main surface thereof, the third electrode formed on the third main surface of the quartz crystal tuning fork base having the same electrical polarity as the third electrode formed on the fourth main surface of the quartz crystal tuning fork base. 
     
     
       70. A method according to claim 1; wherein the two quartz crystal tuning fork tines comprise first and second quartz crystal tuning fork tines, the main surfaces of each of the first and second quartz crystal tuning fork tines comprising a first main surface and a second main surface opposite the first main surface, and each of the first and second quartz crystal tuning fork tines having a first side surface and a second side surface opposite the first side surface; wherein the quartz crystal wafer has a first surface and a second surface opposite the first surface; further comprising the step of providing a lid for covering an open end of the case, one of the lid and the case having a through hole and the case having an interior space containing the mounting portion; and further comprising the sequential steps of disposing at least one first metal film on each of the first and second surfaces of the quartz crystal wafer; disposing a first resist on the at least one first metal film; removing a part of each of the first resist and the at least one first metal film to form a pattern of a tuning fork shape; forming the quartz crystal tuning fork base, and the first and second quartz crystal tuning fork tines; forming a groove in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines so that a width of the groove formed in each of the first and second 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 groove measured from an outer edge of the groove to an outer edge of the corresponding one of the first and second quartz crystal tuning fork tines; disposing at least one second metal film on each of the first and second main surfaces and the first and second side surfaces of each of the first and second quartz crystal tuning fork tines, and a surface of the groove formed in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines; disposing a second resist on the at least one second metal film; forming a first electrode on the surface of the groove formed in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines and a second electrode on each of the first and second side surfaces of each of the first and second quartz crystal tuning fork tines so that the first electrode formed on the surface of the groove formed in each of the first and second main surfaces of the first quartz crystal tuning fork tine is connected to the second electrode formed on each of the first and second side surfaces of the second quartz crystal tuning fork tine, and the second electrode formed on each of the first and second side surfaces of the first quartz crystal tuning fork tine is connected to the first electrode formed on the surface of the groove formed in each of the first and second main surfaces of the second quartz crystal tuning fork tine; mounting the quartz crystal tuning fork resonator on the mounting portion in the interior space of the case; connecting the lid to the case to cover the open end thereof; and disposing a metal or a glass in the through hole to close the through hole in a vacuum after the connecting step of the lid and the case. 
     
     
       71. A method according to claim 70; wherein the first side surface of the first quartz crystal tuning fork tine confronts the first side surface of the second quartz crystal tuning fork tine; wherein the forming step of the groove includes the step of forming the groove having a first stepped portion, a second stepped portion, and a third stepped portion connecting the first stepped portion to the second stepped portion in at least one of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines, each of the first and second stepped portions of the groove formed in the at least one of the first and second main surfaces of the first quartz crystal tuning fork tine being formed opposite the first side surface of the first quartz crystal tuning fork tine and being directly connected to the third stepped portion, and each of the first and second stepped portions of the groove formed in the at least one of the first and second main surfaces of the second quartz crystal tuning fork tine being formed opposite the first side surface of the second quartz crystal tuning fork tine and being directly connected to the third stepped portion; and wherein the groove having the first, second and third stepped portions formed in the at least one of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines has a fourth stepped portion directly opposite a fifth stepped portion in the length direction, the fourth stepped portion being directly connected to the first stepped portion and the fifth stepped portion being directly connected to the second stepped portion. 
     
     
       72. A method according to claim 70; wherein the quartz crystal tuning fork resonator has an overall length and the groove formed in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines has a length; and further comprising the step of determining the overall length of the quartz crystal tuning fork resonator and the length of the groove formed in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines before the disposing step of the at least one first metal film 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. 
     
     
       73. A method according to claim 70; further comprising the steps of adjusting the frequency of oscillation of the quartz crystal tuning fork resonator to a first preselected frequency of oscillation after the forming step of the first and second electrodes and before the mounting step; and adjusting the frequency of oscillation of the quartz crystal tuning fork resonator to a second preselected frequency of oscillation after the mounting step and before the connecting step of the lid and the case. 
     
     
       74. A method according to claim 73; wherein the first preselected frequency of oscillation is about 32.768 kHz with a frequency deviation in the range of −9000 ppm to +5000 ppm; and wherein the second frequency of oscillation is about 32.768 kHz with a frequency deviation within the range of −100 ppm to +100 ppm. 
     
     
       75. A method according to claim 70; further comprising the step of adjusting in a vacuum the frequency of oscillation of the quartz crystal tuning fork resonator after the connecting step of the lid and the case and before the disposing step of the metal or the glass. 
     
     
       76. A method according to claim 70; further comprising the step of adjusting the frequency of oscillation of the quartz crystal tuning fork resonator after the disposing step of the metal or the glass so that the frequency of oscillation thereof is about 32.768 kHz with a frequency deviation within the range of −30 ppm to +30 ppm. 
     
     
       77. A method according to claim 70; wherein the first electrode formed on the surface of the groove formed in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines extends on a surface in the width direction adjoining the groove; wherein the groove formed in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines has a first surface and a second surface, the first surface having a first outer edge and the second surface having a second outer edge; wherein the first surface of the groove formed in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines is opposite the first side surface of the corresponding one of the first and second quartz crystal tuning fork tines; wherein the second surface of the groove formed in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines is opposite the second side surface of the corresponding one of the first and second quartz crystal tuning fork tines; wherein each of the first and second side surfaces of each of the first and second quartz crystal tuning fork tines has a first outer edge and a second outer edge, a distance in the width direction of the groove measured from the first outer edge of the first surface of the groove to the first outer edge of the first side surface of the corresponding one of the first and second quartz crystal tuning fork tines being defined by W 1  and a distance in the width direction of the groove measured from the second outer edge of the second surface of the groove to the second outer edge of the second side surface of the corresponding one of the first and second quartz crystal tuning fork tines being defined by W 3 ; wherein the first main surface of each of the first and second quartz crystal tuning fork tines is formed at the first surface of the quartz crystal wafer; and further comprising the step of forming the groove in the first main surface of each of the first and second quartz crystal tuning fork tines so that W 1  is greater than W 3 . 
     
     
       78. A method according to claim 70; further comprising the step of removing all of each of the first resist disposed on the at least one first metal film and the at least one first metal film before the disposing step of the at least one second metal film. 
     
     
       79. A method according to claim 70; wherein the first side surface of the first quartz crystal tuning fork tine confronts the first side surface of the second quartz crystal tuning fork tine; wherein the step of forming the groove comprises forming a groove having a first groove portion including a first width and a second groove portion including a second width different from the first width in at least one of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines so that a first distance in the width direction of the first groove portion measured from a first outer edge of the first groove portion to a first outer edge of the first side surface of the corresponding one of the first and second quartz crystal tuning fork tines is greater than a second distance in the width direction of the second groove portion measured from a second outer edge of the second groove portion to a second outer edge of the first side surface of the corresponding one of the first and second quartz crystal tuning fork tines; wherein the first width of the first groove portion of the groove formed in the at least one of the first and second main surfaces of the first quartz crystal tuning fork tine is greater than the first distance in the width direction of the first groove portion of the first quartz crystal tuning fork tine; and wherein the first width of the first groove portion of the groove formed in the at least one of the first and second main surfaces of the second quartz crystal tuning fork tine is greater than the first distance in the width direction of the first groove portion of the second quartz crystal tuning fork tine. 
     
     
       80. A method according to claim 1; wherein the quartz crystal tuning fork tines has first and second quartz crystal tuning fork tines, each of the first and second quartz crystal tuning fork tines having a first main surface and a second main surface opposite the first main surface, and a first side surface and a second side surface opposite the first side surface; wherein the quartz crystal wafer has a first surface and a second surface opposite the first surface; and further comprising the sequential steps of disposing at least one first metal film on each of the first and second surfaces of the quartz crystal wafer; disposing a first resist on the at least one first metal film; removing a part of each of the first resist and the at least one first metal film to form a pattern of a tuning fork shape; forming the quartz crystal tuning fork base, and the first and second quartz crystal tuning fork tines; forming a groove in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines so that a width of the groove formed in each of the first and second 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 groove measured from an outer edge of the groove to an outer edge of the corresponding one of the first and second quartz crystal tuning fork tines; disposing at least one second metal film on each of the first and second main surfaces and the first and second side surfaces of each of the first and second quartz crystal tuning fork tines, and a surface of the groove formed in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines; disposing a second resist on the at least one second metal film; forming a first electrode on the surface of the groove formed in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines and a second electrode on each of the first and second side surfaces of each of the first and second quartz crystal tuning fork tines so that the first electrode formed on the surface of the groove formed in each of the first and second main surfaces of the first quartz crystal tuning fork tine is connected to the second electrode formed on each of the first and second side surfaces of the second quartz crystal tuning fork tine, and the second electrode formed on each of the first and second side surfaces of the first quartz crystal tuning fork tine is connected to the first electrode formed on the surface of the groove formed in each of the first and second main surfaces of the second quartz crystal tuning fork tine; mounting the quartz crystal tuning fork resonator on the mounting portion of the case; adjusting the frequency of oscillation of the quartz crystal tuning fork resonator; and connecting a lid to the case after the adjusting step. 
     
     
       81. A method according to claim 80; wherein the forming step of the groove includes the step of forming the groove in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines so that a ratio W 2 /W is in the range of 0.35 to 0.85, where W 2  represents a width of the groove and W represents a width of each of the first and second quartz crystal tuning fork tines; wherein the adjusting step includes the step of adjusting the frequency of oscillation of the quartz crystal tuning fork resonator so that the frequency of oscillation thereof is about 32.768 kHz with a frequency deviation within the range of −100 ppm to +100 ppm; wherein the connecting step of the lid and the case includes the step of connecting the lid to the case in a vacuum; and further comprising the step of adjusting the frequency of oscillation of the quartz crystal tuning fork resonator after the forming step of the first and second electrodes and before the mounting step so that the frequency of oscillation thereof is about 32.768 kHz with a frequency deviation within the range of −9000 ppm to +5000 ppm. 
     
     
       82. A method according to claim 1; wherein the two quartz crystal tuning fork tines comprise first and second quartz crystal tuning fork tines, each of the first and second quartz crystal tuning fork tines having a first main surface and a second main surface opposite the first main surface, and a first side surface and a second side surface opposite the first side surface, the first side surface of the first quartz crystal tuning fork tine confronting the first side surface of the second quartz crystal tuning fork tine; wherein the step of forming the at least one groove includes the step of forming a groove having at least two surfaces in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines; and further comprising the sequential steps of forming the quartz crystal tuning fork base and the first and second quartz crystal tuning fork tines; and forming the groove having the at least two surfaces with a first surface opposite the first side surface and a second surface opposite the second side surface in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines so that a width of the groove formed in each of the first and second 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 groove measured from an outer edge of the groove to an outer edge of the corresponding one of the first and second quartz crystal tuning fork tines, a first electrode being formed on each of the first and second surfaces of the groove formed in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines; wherein the quartz crystal tuning fork resonator has an overall length and the groove formed in each of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines has a length; and further comprising the step of determining the overall length of the quartz crystal tuning fork resonator and the length of the groove formed in each of the first and second 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. 
     
     
       83. A method according to claim 82; wherein the quartz crystal tuning fork resonator has the series resistance R 1  of the fundamental mode of vibration less than the series resistance R 2  of the second overtone mode of vibration; wherein the forming step of the groove includes the step of forming the groove having a first stepped portion, a second stepped portion and a third stepped portion connecting the first stepped portion to the second stepped portion in at least one of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines, each of the first and second stepped portions of the groove formed in the at least one of the first and second main surfaces of the first quartz crystal tuning fork tine being formed opposite the first side surface of the first quartz crystal tuning fork tine, and being directly connected to the third stepped portion, and each of the first and second stepped portions of the groove formed in the at least one of the first and second main surfaces of the second quartz crystal tuning fork tine being formed opposite the first side surface of the second quartz crystal tuning fork tine and being directly connected to the third stepped portion; and wherein the groove having the first, second and third stepped portions formed in the at least one of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines has a fourth stepped portion directly opposite a fifth stepped portion in the length direction, the fourth stepped portion being directly connected to the first stepped portion and the fifth stepped portion being directly connected to the second stepped portion. 
     
     
       84. A method according to claim l; wherein the two quartz crystal tuning fork tines comprise first and second quartz crystal tuning fork tines, each of the first and second quartz crystal tuning fork tines having a first main surface and a second main surface opposite the first main surface, and a first side surface and a second side surface opposite the first side surface, the first side surface of the first quartz crystal tuning fork tine confronting the first side surface of the second quartz crystal tuning fork tine; wherein the step of forming the at least one groove comprises forming a groove having a first groove portion including a first width and a second groove portion including a second width different from the first width in at least one of the first and second main surfaces of each of the first and second quartz crystal tuning fork tines so that a first distance in the width direction of the first groove portion measured from a first outer edge of the first groove portion to a first outer edge of the first side surface of the corresponding one of the first and second quartz crystal tuning fork tines is greater than a second distance in the width direction of the second groove portion measured from a second outer edge of the second groove portion to a second outer edge of the first side surface of the corresponding one of the first and second quartz crystal tuning fork tines; wherein the first width of the first groove portion of the groove formed in the at least one of the first and second main surfaces of the first quartz crystal tuning fork tine is greater than the first distance in the width direction of the first groove portion of the first quartz crystal tuning fork tine; and wherein the first width of the first groove portion of the groove formed in the at least one of the first and second main surfaces of the second quartz crystal tuning fork tine is greater than the first distance in the width direction of the first groove portion of the second quartz crystal tuning fork tine.