JPH1022777A - Crystal vibrator and manufacture therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide crystal vibrator with less dispersion by soldering an electrode formed crystal vibration piece to an airtight terminal, turning it to a half-complete crystal vibrator, then washing it, performing a heat treatment in nitrogen atmosphere, then adjusting a vibration frequency and performing sealing. SOLUTION: An electrode formation process (11), an assembling process (12) and a washing process (13) are the same as a conventional technique. A nitrogen atmosphere heat treatment (14) is then performed to the washed half-complete crystal vibrator. Temperature distribution in a heating tank is easily uniformized by the convection of gaseous nitrogen, heat transmission to the half-complete crystal vibrator is quick and moisture absorbed to the half-complete crystal vibrator is sufficiently removed in a short time. After the nitrogen atmosphere heat treatment (14), leaving time in atmosphere is shortened as much as possible and an (f) adjustment process (15) is started. In the (f) adjustment process (15), silver is vapor-deposited to the surface of the crystal vibrator inside a vacuum tank. A vibration frequency is adjusted by the (f) adjustment process and the next sealing process (16) is immediately started. Thus, since frequency adjustment and sealing are performed in the state of less moisture absorption, the difference of an (f) adjustment target value and a complete vibration frequency is made small and the dispersion is made small as well.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crystal resonator and a method for manufacturing the same.

[0002]

2. Description of the Related Art Quartz resonators are employed as clock sources in many fields. In particular, as the crystal resonator, a cylinder type using a tuning fork type crystal resonator element and a cylinder type using an AT-cut crystal resonator element having a rectangular resonator element are frequently used. In the description of the present invention, a rectangular AT-cut quartz resonator is taken as an example, but the present invention can be applied regardless of the shape of the quartz resonator blank.

FIG. 1 is a perspective view of a cylinder-type crystal resonator in which a rectangular crystal resonator element according to the prior art is fixed to two leads. The crystal resonator element 1 is fixed by solder 7 to two leads 4, 4 of an airtight terminal in which two leads 4, 4 are hermetically sealed to a metal ring 2 with an insulating material (glass) 3. The sealing tube 5 covers the quartz vibrating piece 1 and the metal ring 2
Is press-fitted to the outer periphery.

[0004] Generally, a soft metal is interposed between the press-fitting portion of the sealing tube 5 and the metal ring 2 in order to ensure the airtightness of the press-fitting portion. To manufacture a crystal resonator, artificial quartz is processed into a desired rectangular AT-cut crystal resonator element, and (1) a quartz resonator element 1
The electrode 6 is formed by a thin film forming method such as vapor deposition or sputtering, and (2) the crystal vibrating piece 1 on which the electrode 6 is formed is soldered to a hermetic terminal to form a semi-finished crystal vibrator. And (4) adjusting the vibration frequency of the semi-finished crystal unit (hereinafter referred to as f-adjustment), and then (5) heat treating in a vacuum atmosphere, (9) soldering or nickel plating, and (10) in vacuum. The heat-treated sealing tube 5 is (6) press-fitted and sealed around the outer periphery of the metal ring 2, and further (7) heat-treated and (8) inspected. The heat treatment of the semi-finished crystal unit and the sealing tube in a vacuum atmosphere before the sealing is for desorbing moisture adsorbed on the respective surfaces.

FIG. 2 shows a flowchart of the above process.
The washing step (3) is for removing soldering flux and deposits, and generally uses an organic solvent (for example, methylene chloride). The f-adjustment step (4) is a step of adjusting the oscillation frequency by forming a metal film on the surface of the quartz-crystal vibrating piece, and generally deposits silver in a vacuum chamber. (5)
The vacuum heat treatment step is a step of heating the semi-finished quartz resonator in a vacuum chamber to desorb water. It is desirable to perform the treatment for as long as possible at a temperature as high as possible. However, there is a limitation due to the type of solder and the equipment capacity.
2 hours at 200 ° C. and about 2 hours at 200 ° C. when a Pb-based high-temperature solder is used. The sealing step (6) is a step of press-fitting a sealing tube to the outer periphery of the metal ring of the semi-finished crystal unit, and is performed in a vacuum chamber. The heat treatment step (7) is a step for preventing the vibration frequency of the completed crystal unit from changing due to temperature rise such as high-temperature storage or solder reflow. In the case where eutectic solder is used. Is 1 hour when using Pb-based high-temperature solder at 100 ° C for 24 hours.
It is about 24 hours at 70 ° C.

[0006]

The vibration frequency is adjusted in the f-adjustment step (4), but the process proceeds, and the variation in the completed vibration frequency becomes large in the inspection step (8). FIG. 3 is a graph in which changes in the vibration frequency median value and the standard deviation after each process are investigated in summer (humidity 70%) and winter (humidity 30%) assuming that the vibration frequency variation at the end of the f adjustment is zero. The vertical axis is the vibration frequency change (Δf / f),
The horizontal axis represents a process. Arrows extending up and down from the points in the graph are standard deviations (3σ) indicating variations in the vibration frequency at each point. The causes of fluctuations in the vibration frequency are that water is physically adsorbed on the surface of the crystal vibrating piece when exposed to room air between processes, and trace substances contained in room air (for example, hydrogen sulfide, chlorine, carbon dioxide, methane gas, etc.). Etc.) and an electrode (generally made of silver) undergo a chemical reaction, and the vibration frequency shifts to a negative value due to the adhesion of dust contained in room air.

The amount of physical adsorption of water to the crystal resonator element depends on the surface roughness of the crystal resonator element, the state of the electrode film, the environment in which the semi-finished crystal resonator is placed, and the like, but is higher in summer when the humidity is higher. . In particular, the capillary condensation phenomenon, which is multi-layered adsorption, is said to increase sharply when the relative humidity is 60% or more, and the physical adsorption amount of water is larger and more uneven when placed in a place with high humidity. The cleaning removes moisture and dust physically adsorbed on the surface, but does not remove moisture or chemically reactive substances that have entered the inside of the electrode film. The turn from the deposition of the electrode film to the f adjustment is 2-3 days, during which the vibration frequency shift is 20 days.
It is 20 to 30 ppm on a yearly average for a crystal oscillator of MHz. Of course, in summer the vibration frequency shift is 20-30ppm
Bigger and smaller in winter. The vibration frequency returned by washing is about half of the shift amount. When the f-adjustment is performed in this state, the vibration frequency further shifts to a negative value due to the adhesion of water during evacuation. The shift amount also varies. In the next vacuum heat treatment, the average value and the variation of the vibration frequency hardly change as a result.

In the vacuum heat treatment, heat is not transferred by air molecules, so that radiation or heat conduction by a solid must be used. However, semi-finished quartz resonators are chipped when they come into contact with each other, so they must be placed apart from each other.Therefore, there is a temperature difference between the place where solid heat conduction occurs and the place where heat conduction does not occur, resulting in variations in moisture desorption. You. In addition, in order to use radiant heat, semi-finished quartz oscillators must be arranged in a line, and the number of semi-finished quartz oscillators that can be heat-treated (degassed) in an expensive vacuum furnace is reduced, and the cost is reduced. Disadvantageous. For this reason, even if a large number of semi-finished quartz oscillators are put into a vacuum furnace and subjected to heat treatment, the heat is not sufficiently transmitted, so that the moisture is not sufficiently removed. Of course, if it takes more than several tens of hours, heat is transmitted and the temperature rises, but it is disadvantageous in terms of delivery. Therefore, moisture is desorbed from the crystal vibrating piece by performing heat treatment after sealing, and the vibration frequency changes (shifts). The amount of change in the vibration frequency varies depending on the amount of water held by the quartz vibrating piece, the sealed tube, and the amount of moisture held by the hermetic terminal. The variation in the water content is equivalent to the variation in the vibration frequency variation due to the heat treatment.

Since it is impossible to make the adsorption of water zero, it is necessary to reduce the adsorption of water and how to uniformly desorb the adsorbed water. This is important in manufacturing a crystal resonator with less noise.

As a method for desorbing water, heating in a vacuum chamber is considered effective. However, at the moment when the vacuum chamber is evacuated, the air in the vacuum chamber instantaneously expands adiabatically. As the relative humidity in the air drops suddenly and rises above the saturated vapor pressure, it condenses on the surface of the crystal vibrating piece. Such factors are intertwined and cause fluctuation of the vibration frequency shift after the vacuum heat treatment. Since there is a vacuum heat treatment step between the f-adjustment step and the sealing step, there are two opportunities for the semi-finished crystal unit to come into contact with the atmosphere from the f-adjustment step to the sealing step. It is technically possible to make the humidity in summer and winter constant, but it is not economically suitable for producing low-cost products.

[0011]

At least a step of forming an electrode on a crystal vibrating piece, a step of soldering the crystal vibrating piece on which the electrode is formed to an airtight terminal to form a semi-finished crystal vibrator, A method of manufacturing a crystal resonator includes a step of cleaning, a step of heat treatment in a nitrogen atmosphere, a step of adjusting the vibration frequency of the semi-finished crystal resonator, and a step of sealing. The step of sealing is a step of performing solder plating or nickel plating on the sealing tube, heat treating in a nitrogen atmosphere, and then sealing.

After washing the semi-finished quartz oscillator, it is immediately put into a heating tank in a nitrogen atmosphere. Since the speed at which moisture is adsorbed on a clean surface is high, the shorter the standing time in the air, the better. The heat treatment in a nitrogen atmosphere is preferably performed at as high a temperature as possible for a long time to remove moisture. When the f-adjustment step is performed after completion of the heat treatment step, it is better that the leaving time in the air before the introduction is shorter, and it is preferable to store the apparatus in a dry nitrogen atmosphere. After the f-adjustment step, it is preferable to seal immediately after the end of the f-adjustment process for the same reason. It is even better to keep it inside.

Although the sealing is performed in a vacuum chamber, the influence of the heat treatment after the sealing is not limited to the quartz vibrating reed, but also to the moisture or other gas adsorbed on the inner side of the hermetic terminal and the inner wall of the sealing tube. Affected. Therefore, after the sealing tube is also plated and cleaned, a heat treatment is performed in a nitrogen atmosphere. For plating the sealing tube, nickel or copper plating is applied to the base in the case of solder plating, and copper plating is applied directly or to the base in the case of nickel plating.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 4 is a flow chart of a manufacturing process of a quartz oscillator for explaining the present invention. The electrode forming step of (11), the assembling step of (12), and the cleaning step of (13) are the same as in the prior art. (14) is a nitrogen atmosphere heat treatment, which is a characteristic step of the present invention. (15) is f
It is a feature of the present invention that the preparation step is performed after heat treatment in a nitrogen atmosphere. (16) is a sealing step, (17) is a heat treatment step,
(18) is an inspection step. (19) is a plating step of the sealing tube, and (20) is a nitrogen atmosphere heat treatment. It is also a feature of the present invention that the sealing step (16) is immediately after the f-adjustment step and that the sealing tube is heat-treated in a nitrogen atmosphere.

After the cleaning step (13), a heat treatment is performed in a nitrogen atmosphere, and then the f-tone is adjusted. 13 if the solder is eutectic
Heat treatment is performed at 0 ° C. for 2 hours, and in the case of Pb-based high-temperature solder at 200 ° C. for about 2 hours. The heat treatment temperature and time are the same in the case of the sealed tube, but the longer the time, the more reliably the water can be eliminated (72 hours in this example). By performing a heat treatment in a nitrogen atmosphere after the cleaning, the moisture adsorbed on the semi-finished quartz oscillator can be uniformly desorbed. This is because the convection of nitrogen tends to make the temperature distribution in the heating tank uniform. The heat transfer to the semi-finished quartz oscillator is fast, and the heating tank can be forcibly stirred with a fan because of the presence of nitrogen as a medium for heat conduction. Since a vacuum exhaust system is not required, there is no backflow of oil from an oil pump or the like, and maintenance of the heating tank is easy.

After the heat treatment in the nitrogen atmosphere, the vibration frequency is adjusted by the f-adjustment step, and the process proceeds to the next sealing step. Vibration frequency is adjusted immediately after moisture is desorbed by nitrogen atmosphere heat treatment, and sealing is performed. Vibration frequency can be adjusted with less moisture adsorption, and sealing is performed with less moisture adsorption after vibration frequency adjustment. become. Decrease in frequency change amount and variation due to uniform desorption before f-adjustment process, decrease in frequency change amount and variation due to decrease in adsorption due to reduced chance of coming into contact with air after vibration frequency adjustment (one time). The effect of reduction is obtained.

FIG. 5 shows the transition of the median vibration frequency and the standard deviation after each step in the summer (humidity 70
%) And winter (30% humidity). The vertical axis indicates the vibration frequency change amount, and the horizontal axis indicates the process.
Arrows extending up and down from the points in the graph are standard deviations (3σ) indicating variations in the vibration frequency at each point. Compared to FIG. 3, which is a graph of a quartz oscillator according to the prior art, the change in the median vibration frequency and the standard deviation is reduced to less than half. Since the moisture adsorbed on the crystal vibrating piece before the f adjustment is sufficiently removed in a short time by heat treatment in a nitrogen atmosphere, the amount of moisture desorbed during vacuum sealing is small and the dispersion is small. The frequency change between the sealing steps is small, and the variation in the vibration frequency after the sealing is small. Similarly, since the absolute amount of water desorbed from the quartz vibrating piece, the sealing tube, and the airtight terminal by the heat treatment is small, the change in the vibration frequency is small and the variation is not increased. As a result, since the difference between the target f-tuning value and the completed vibration frequency is small, it is sufficient to aim at a value as close as possible to the completed vibration frequency in the f-adjustment step, and the workability is improved.

[0018]

The quartz resonator manufactured according to the present invention has the following advantages. 1) Even after a heat treatment step after completion of sealing, the shift of the center vibration frequency is small and the dispersion is small. 2) Due to the above effects, the heat treatment step (17) can be omitted. 3) Since desorption of water is made effective, a long-term vibration frequency change after sealing is small, and a stable and high-precision vibrator can be manufactured. 4) Since a vacuum exhaust system is not used for the heat treatment apparatus, the heat treatment apparatus can be procured at low cost, and maintenance is easy. 5) Since a vacuum exhaust system is not used in the heat treatment apparatus, there is no risk of quality deterioration due to backflow of oil from the pump system. 6) Since the influence of a change in humidity can be reduced, a stable quality quartz resonator can be manufactured with little difference between summer and winter.

[Brief description of the drawings]

FIG. 1 is a perspective view of a crystal unit.

FIG. 2 is a manufacturing flowchart of a quartz resonator according to the related art.

FIG. 3 shows the transition of the median vibration frequency and the standard deviation after each process in summer (humidity 70%) and winter (humidity), assuming that the oscillation frequency variation at the end of the f-adjustment of the quartz oscillator manufactured by the prior art is zero. 30%)

FIG. 4 is a flowchart for manufacturing a quartz oscillator according to the present invention.

FIG. 5 is a graph showing the transition between the median vibration frequency and the standard deviation after each process in summer (humidity 70%) and winter (humidity), with the vibration frequency variation at the end of f-tuning of the quartz resonator manufactured according to the present invention as zero. 30%)

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Crystal vibrating piece 2 Metal ring 3 Insulating material 4 Lead 5 Sealing tube 6 Electrode 7 Solder

Claims (4)

[Claims] An electrode is formed on a crystal vibrating piece, and the crystal vibrating piece on which the electrode is formed is soldered to an airtight terminal to form a semi-finished crystal vibrator. A crystal unit wherein the vibration frequency of a completed crystal unit is adjusted and sealed. 2. The crystal unit according to claim 1, wherein the sealing tube is solder-plated or nickel-plated, and then heat-treated in a nitrogen atmosphere for sealing. 3. At least a step of forming an electrode on the quartz-crystal vibrating piece, a step of soldering the quartz-crystal vibrating piece on which the electrode is formed to an airtight terminal to obtain a semi-finished quartz-crystal vibrator, and a step of cleaning after soldering. Heat treating in a nitrogen atmosphere, and adjusting the vibration frequency of the semi-finished quartz resonator,
A method for manufacturing a crystal resonator, comprising a sealing step. 4. The method according to claim 3, wherein the step of sealing is a step of performing solder plating or nickel plating on the sealing tube and then performing heat treatment in a nitrogen atmosphere for sealing.