JP2006025384A - Highly stable crystal vibrator and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To remove deterioration factors in a sealed structure of a crystal vibrator and to break through a manufacture limit of frequency stability where a long-term aging property is at a 10<SP>-6</SP>/year level. <P>SOLUTION: As a process of manufacturing a highly stable crystal vibrator, a crystal element formed with an electrode is fixed at a predetermined position inside a container body by conductive adhesives, and then dried or die-bonded by a gold bump in a process S11, and the inside of the container body is cleaned by decomposing a contaminant inside the container body by far ultraviolet ray radiation or low ion radiation in a process S12. An electrolytically polished stainless steel holder or cap is used to suppress generation of gas from the stainless steel cap as much as possible in a process S13, and the holder is sealed in vacuum or with inert gases using the electrolytically polished stainless steel cap in a process S14. Distortions in the respective processes are removed by thermal aging in a process S15, and unnecessary gas which can not be removed in the process S11 to the process S14, are discharged, so that a highly stable crystal vibrator can be manufactured. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

INDUSTRIAL APPLICABILITY The present invention is used for a mobile phone in the field of mobile communication where high stability and high quality are required, and for a crystal oscillator which is the heart of an electromechanical functional part used as various reference signal sources in the field of optical communication. The present invention relates to a highly stable crystal resonator having excellent long-term aging characteristics and a method for manufacturing the same. A highly stable crystal resonator manufactured by applying the present invention has a fundamental wave of 10 MHz to 30 MHz by removing distortion generated in a crystal piece by a series of crystal resonator manufacturing processes and contamination applied to the crystal piece. High-stable and high-performance crystal vibration with a frequency stability of 10 ⁻⁷ / year level or less for a crystal resonator up to about 200 MHz with 3rd, 5th, and 7th harmonics, which are the frequency bands and harmonic components of Its greatest feature is that it can produce a large number of children with high reproducibility.

In fields such as mobile communication devices and optical communication devices that require ultra-compact and high stability, crystal oscillators have established themselves as essential devices. Conventional crystal oscillators include temperature compensated crystal oscillator (TCXO), digital temperature compensated crystal oscillator (D-TCXO), voltage controlled crystal oscillator (VCXO), etc. A crystal resonator is manufactured by sorting, and this high-performance crystal oscillator is realized by combining this crystal resonator with LSI and passive components such as resistors and capacitors. As the quartz plate, flat plate processing is the mainstream because of its ease of manufacture, and the long-term aging characteristics of the flat plate quartz resonator have a production limit of 10 ⁻⁶ / year level frequency stability. A 2.5 MHz to 5 MHz convex crystal resonator using a fifth harmonic is realized as a highly stable crystal resonator at a low frequency. The frequency stability is a frequency stability of a level of 10 ⁻⁸ / year to 10 ⁻⁹ / year. However, further improvement in frequency stability is desired as a reference signal generation source in recent digitalization. By the way, if you can roughly divide the items that can be considered as the determinants of the time-varying characteristics of crystal units,
It can be classified into two types: (A) one caused by distortion generated in the crystal piece and (B) one caused by contamination applied to the crystal piece. (A) is based on a change in the compliance compliance of the vibrating body, and a frequency shift occurs due to distortion applied during processing or distortion caused by temperature change, and the distortion disappears with time and returns to a stable state. Frequency drift occurs in the process. What can be thought of as this specific factor is
(1) Strain due to the residual processed layer on the crystal piece surface (2) Interfacial strain between the crystal piece surface and the electrode (3) Strain due to the lever operation of the crystal piece mount (4) Mount adhesive Distortion due to fixation of the crystal piece surface Conceivable.
(B) is based on the “mass” change, and it is considered that frequency drift occurs in the process in which the “mass” change occurs with the elapsed time. What is considered to be this type of factor is
(1) Adsorption and desorption of gas molecules to the crystal piece (2) Oxidation of the vapor deposition electrode (3) Recrystallization of the vapor deposition electrode (4) Diffusion of electrode metal or the like into the crystal blank is conceivable. In general crystal oscillators, a negative tendency of “mass” increase generally appears.

The adsorption / desorption of gas molecules to the crystal piece will be described with reference to FIGS. 7, 8, 9, and 10. FIG. 7 shows a stainless steel cap wall 702 of a stainless steel cap 701 that constitutes a metal holder of a high-frequency quartz crystal resonator UM-1, which is widely used. The surface of the metal subjected to machining such as fine buffing is as follows: Work-affected layers such as a Bailby layer, a crushed crystal layer, and a plastically deformed layer remain from the surface in order to form a residual stress layer. The gas molecules 702 taken into the scratches on the outer wall made of stainless steel are not easily removed by the cleaning, and are gradually sucked into and removed from the UM-1 holder to contaminate the quartz element mounted inside. Further, the gas 703 is also released from the inside of the stainless steel. The holding portions 704 and 705 of the base portion 708 of the UM-1 holder are electrically connected to the external lead terminals 706 and 707. The generation of gas from the inner and outer walls of the stainless steel cap, which is a long-term deterioration factor, is extremely serious. FIG. 8 is a three-terminal holding metal cage for a master ultra-stable crystal resonator. This cage has a structure for holding a planar convex quartz plate at three locations. The inner wall 802 of the stainless steel cap 801 has a mechanically altered layer such as a Bailby layer, a crushed crystal layer, and a plastically deformed layer in order from the surface on the surface of the metal subjected to machining such as fine buffing, and a residual stress layer is formed. Is formed. Holding portions 804, 805, and 806 from the base portion 810 of the three-terminal holding metal cage are electrically connected to the external lead terminals 807, 808, and 809. As with the UM-1 cage in FIG. 7, the generation of gas from the inner and outer walls of the stainless steel cap, which is a long-term deterioration factor, is extremely serious. FIG. 9 is a cross-sectional view of a ceramic package 901 (1002) obtained by dividing the surface mount ceramic package formed in the sheet shape 1001 of FIG. Reference numeral 1003 in FIG. 10 denotes a crystal element. On the surfaces of the flat plate caps 902 and 903 made of stainless steel, work-affected layers such as a Bailby layer, a crushed crystal layer, and a plastic deformation layer remain in order from the surface, and a residual stress layer is formed. Similarly, in the surface mount ceramic package, the influence of the release gas 904 from the stainless cap wall and the release gas 905 from the stainless steel is that the physical distance between the electrode formed on the crystal piece, which is a crystal element, and the stainless cap. Since it is as narrow as 0.1 mm to 0.2 mm, the influence of outgas on the aging characteristics is the most serious in the holding structure of FIG. 9 among the holders of FIGS.

Usually, in the electrode film forming step, the formed electrode film cannot avoid reaction with the oily gas discharged from the exhaust system in a vacuum atmosphere. In particular, even when an oil-free exhaust system is used, reaction products with H ₂ , N ₂ , H ₂ O, O ₂ , and CO ₂ are formed on the surface of the electrode film, and the influence on long-term aging characteristics is ignored. Can not. Improvement in the quality of the film formed in vacuum can be achieved by drying the exhaust system of the film formation process of the crystal unit. FIGS. 11 and 12 show the mass analysis results 1101 and 1201 of the residual gas on the suction side of the oil rotary pump and the dry pump. When the oil rotary pump is combined with a mechanical booster pump (using mineral oil), the dry pump is an ERD type multistage dry pump (using fluorine-based lubricating oil). As for the oil rotary pump, C3 to C5 hydrocarbons, which are components of mineral oil, are found. As can be seen from this analysis result, the back-diffusion of the oil vapor into the reaction chamber is eliminated by the drying, and the contamination of the crystal and the vacuum vessel are prevented. Furthermore, since moisture taken into the oil does not diffuse back during operation, moisture remaining in the reaction chamber is also reduced. Accordingly, the electrodes used in the quartz resonator are mainly gold electrodes or silver electrodes, and aluminum electrodes that are likely to be oxidized are highly active, and therefore are rarely used. Regarding the oxidation of the vapor deposition electrode, the recrystallization of the vapor deposition electrode, and the diffusion problem of the electrode metal inside the crystal piece, the problem of long-term aging can be concerned.
(Non-patent Document 1) Norio Kikuta “Multistage Dry Vacuum Pump” Vacuum, Vol. 33, No. 7, 1990 p. 634 FIG.

The problem to be solved by the present invention is that the long-term aging characteristic of the current crystal resonator breaks through the manufacturing limit of the frequency stability of the 10 ⁻⁶ / year level. Since the crystal oscillator is used as a crystal oscillator, the stability of the oscillation frequency always depends on the stability of the crystal oscillator. Since the oscillation current always flows through the crystal resonator, the crystal oscillator is operating in the accelerated aging state. A systematic view of the sealed structure that makes up the crystal unit reveals that it is surrounded by many deterioration factors. Until now, it has not been easy to remove this deterioration factor. In particular, the absorption and desorption of gas adsorbed on the stainless steel outer wall, which is a long-term deterioration factor, and the release of gas from the inside of the stainless steel contaminate the quartz crystal housed inside the container, resulting in a change in the oscillation frequency. It was. The long-term aging characteristics of the crystal resonator have a manufacturing limit of frequency stability of 10 ⁻⁶ / year level. The quartz industry has never used an electropolished material. Of course, neither a stainless steel holder nor a cap that had been electropolished was used for the master crystal unit that had been subjected to convex processing. The reason is that, in the case of a crystal resonator of 5 MHz or less, since the thickness of the crystal resonator is relatively large with respect to the thickness of the molecular layer of the gas adsorbed to the electrode film, the amount of frequency fluctuation is extremely small. However, in a crystal resonator up to about 200 MHz that uses a third harmonic, a fifth harmonic, and a seventh harmonic which are frequency bands and harmonic components in a fundamental wave of 10 MHz to 30 MHz, Since the thickness is small, the amount of frequency fluctuation increases.
The characteristics of the electropolishing method applied to the metallic material in the present invention are as follows.
1. There is no work-affected layer.
The original stainless steel is a metal that has been subjected to mechanical processing such as buffing, and a deformed layer such as a Bailby layer, a crushed crystal layer, and a plastic deformation layer remains from the surface, forming a residual stress layer. Organization is lost. This may cause deformation and corrosion after aging.
2. Because it is in a low temperature processing solution, it is not affected by heat.
In buffing, the polished surface becomes hot, so deformation is often caused by thermal expansion, especially for thin workpieces. In addition, this heat deforms the original metal structure of stainless steel near the surface and causes a decrease in corrosion resistance.
3. It is composed of a smooth curve that has excellent smoothness and does not easily retain dirt.
The buffed surface looks like a specular surface without scratches, but the entire surface is an aggregate of fine scratches. Contaminants embedded in these scratches are not easily removed by cleaning.
4). Excellent corrosion resistance.
Chromium is concentrated more than the normal surface of stainless steel, and a strong passive film is formed, so it has excellent corrosion resistance.

The electropolishing method will be described with reference to FIGS. FIG. 5 shows a method of electrolytic polishing a stainless steel cap of a UM-1 cage and a stainless steel cap 501 for a metal cage of a three-terminal holding for a master ultra-stable crystal resonator. It is immersed in the electrolytic polishing bath 502 and the power terminals are connected to the anode electrode and the cathode electrode, respectively. To electropolish the stainless steel cap 501, the cathode electrodes 504 and 505 are used as counter electrodes, and the surface of the stainless steel cap 501 is electrochemically dissolved in units of microns through a direct current from a power source 505. A cathode electrode 503 is provided inside a stainless steel cap 501 for electrolytic polishing treatment on the inner wall of the deep drawing structure. FIG. 6 shows a method of electrolytic polishing a stainless steel plate cap 601 for surface mounting type. It is immersed in the electrolytic polishing bath 602 and the power terminals are connected to the anode electrode and the cathode electrode, respectively. To electrolytically polish the stainless steel cap 601, the cathode electrodes 603 and 604 are used as counter electrodes, and the surface of the stainless steel cap 601 is electrochemically dissolved in units of microns through a direct current from a power source 605.

  The highly stable crystal resonator according to the present invention includes a step of housing a crystal element in a main body of an electropolished metal container or ceramic container, and a contaminant such as an organic solvent or an attached gas existing in the container main body. A step of cleaning with ultraviolet (UV) irradiation or ion irradiation, a step of sealing the electropolished lid placed on the container body with a vacuum or an inert gas (N2, Ar, He); A highly stable crystal unit comprising a process of releasing distortion of a container body and discharging unnecessary gas by thermal aging, and a method for manufacturing the same.

The highly stable crystal unit of the present invention includes a step of housing a crystal element in a retainer body of a sheet-like surface-mount (SMD) ceramic container, and a contaminant such as an organic solvent or an adhering gas present in the container body. And the step of cleaning the electropolished lid placed on the container body with vacuum or inert gas (N2, Ar, He) And a highly stable quartz crystal resonator and a method of manufacturing the crystal resonator comprising the steps of releasing distortion of the container body and discharging unnecessary gas by thermal aging. The most important thing is that a highly stable and high performance SMD crystal resonator having a frequency stability of 10 ⁻⁷ / year level or less can be transferred to mass production at a low cost by applying a hybrid IC manufacturing process.

As described above, the highly stable crystal resonator according to the present invention has the third harmonic, the fifth harmonic, and the seventh harmonic, which are the frequency bands and harmonic components of the fundamental wave of 10 MHz to 30 MHz, which has not been achieved by the quartz industry until now. The greatest feature is that it is possible to produce a high-stability and high-performance crystal resonator having a frequency stability of 10 ⁻⁷ levels / year or less with high reproducibility and in large quantities. Since the highly stable crystal resonator of the present invention can keep the amount of gas generated extremely small, the master ultra-stable crystal resonator having a frequency stability of 10 ⁻⁹ / year to 10 ⁻¹⁰ / year level or less is provided. It is feasible. The highly stable crystal resonator according to the present invention has a very high industrial value because a further highly stable crystal resonator can be obtained by suppressing contaminants and distortion inherent in the crystal element.

The absorption and desorption of gas adsorbed on the stainless steel outer wall and the release of gas from inside the stainless steel, which are long-term deterioration factors, contaminate the quartz crystal housed in the container, resulting in a change in the oscillation frequency. It was. As a method of removing this deterioration factor, the quartz crystal element is stored in an electropolished metal container or ceramic container, and then contaminants such as an organic solvent or attached gas in the container body are irradiated with deep ultraviolet (UV) or ions. After cleaning by irradiation, a process of sealing the electrolytically polished stainless steel cap placed on the container body with vacuum or an inert gas (N2, Ar, He) and release of distortion of the crystal resonator A highly stable crystal unit is realized by a systematic approach that discharges unnecessary gas by thermal aging.

FIG. 1 is a manufacturing process flowchart of a highly stable crystal unit that is the basis of the present invention. In the process S11, a crystal element in which an Ag electrode or an Au electrode is formed on a crystal piece is fixed at a predetermined position in the container body with a conductive adhesive and then dried or die-bonded with a gold bump. In the process S12, the organic solvent component generated in the drying process when the crystal element is fixed with the conductive adhesive in the container body, the outgas from the exhaust system, and unnecessary gas in the atmosphere contaminate the crystal element and the container body. Therefore, the inside of the container body is cleaned by decomposing the contaminants by using a low temperature irradiation method such as deep ultraviolet irradiation or low ion irradiation such as Ar gas. Process S13 is an auxiliary procedure for process S14. The adsorption / desorption of gas adsorbed on the outer wall of the stainless steel, which is a long-term deterioration factor from the cap, and the release of gas from the inside of the stainless steel contaminate the quartz crystal housed in the container, resulting in a change in the oscillation frequency. It will be. By using an electrolytically polished stainless steel cage or cap, the generation of gas from the stainless steel cap, which is a long-term deterioration factor, can be suppressed as much as possible. By forming the silicon film on the stainless steel cap that has been electropolished, the amount of gas released from the stainless steel wall can be lowered by an order of magnitude more than the stainless steel cap that has been electropolished. Process S14 is a step of sealing the cage with vacuum or an inert gas (N2, Ar, He) with an electropolished stainless steel cap. As a sealing method, there are a cold pressure welding method and an electron beam welding method in vacuum sealing. As a method for sealing with an inert gas (N2, Ar, He), there are a resistance welding method for a metal cage and a seam welding method applied to an SMD ceramic package. Process S15 is a process of removing strain due to the residual processed layer on the surface of the crystal piece, removing interfacial strain between the surface of the crystal piece and the electrode, removing strain due to the lever operation of the crystal piece mount, and fixing distortion of the mount adhesive crystal piece surface. By removing the unnecessary gas that could not be removed in the processes S11 to S14 by heat aging, a highly stable crystal resonator can be manufactured by the processes S11 to S15.

FIG. 2 shows a case where the present invention is applied to a metal cage such as a high-frequency crystal resonator UM-1 that is widely used. In the UM-1 holder, a thickness vibration excitation electrode 202 is formed on the surface of the crystal plate 201, and the stainless cap 203 subjected to electrolytic polishing is mirror-polished on the inner wall 204 of the stainless cap. The holding parts 205 and 206 from the UM-1 holder base part 209 are electrically connected to the external lead terminals 207 and 208. A lead electrode portion from an electrode formed on the crystal plate 201 is held and fixed by holding portions 205 and 206 to constitute a high-frequency crystal resonator UM-1. As a method of processing a large amount of the stainless cap 203 by electrolytic polishing, an electrolytic polishing method using a barrel tank is applied. Since the amount of gas generated from the stainless steel cap, which is a long-term deterioration factor, can be suppressed to a very low level, a highly stable crystal resonator is realized.

FIG. 3 shows an example in which the present invention is applied to a three-terminal holding metal cage of a master ultra-stable crystal resonator. In this cage, the planar convex quartz plate 301 is held at three locations. In the electrolytically polished stainless steel cap 302, the stainless steel cap inner wall 303 is mirror-polished. The holding portions 304, 305, and 306 from the base portion 306 of the three-terminal holding metal cage are electrically connected to the external lead terminals 307, 308, and 309. A lead electrode portion from the electrode formed on the crystal plate 301 is held and fixed by holding portions 304, 305, and 306 to constitute a master ultra-stable crystal resonator. The stainless steel cap 302 is electrolytically polished by the connection method shown in FIG. Since the amount of gas generated from the stainless steel cap, which is a long-term deterioration factor, can be suppressed to an extremely low level, a master ultra-stable crystal vibration having a frequency stability of 10 ⁻⁹ / year to 10 ⁻¹⁰ / year level or less. A child is realized.

In FIG. 4, the present invention is applied to a ceramic package for surface mounting. In an SMD ceramic package having an outer dimension of 7 × 5 × 1 mm, thickness vibration excitation electrodes 402 and 403 facing each other are formed on a quartz plate 401 having a resonance frequency of 10 MHz (thickness 160 microns) to 30 MHz (thickness 53 microns). A quartz crystal element is formed, and the quartz crystal element is held and fixed by die bonding with a conductive adhesive or gold bumps at two locations of the quartz plate holding portions 409 and 410. The stainless steel caps 404 and 405 that have been electropolished are mirror polished by the electropolishing wire connection method shown in FIG. The electrolytically polished stainless steel cap is hermetically sealed with a vacuum or an inert gas such as N ₂ gas via a lead frame for welding. Since the stainless steel flat cap is mirror-polished and a passive film is formed, the amount of gas generated from the stainless steel cap, which is a long-term deterioration factor, can be kept extremely low, and the distortion applied to the crystal piece SMD high-stability crystal resonators having a frequency stability of 10 ⁻⁷ / year level or less are realized by thermal aging (heating temperature: 145 ° C., aging time: 20 hours).

It is a manufacturing process flowchart of a highly stable crystal unit. It is sectional drawing of the high frequency crystal resonator of the metal holder of UM-1. It is sectional drawing of the ultra high stability crystal oscillator for masters of the metal holder | retainer of 3 terminal holding | maintenance. It is sectional drawing of the SMD highly stable crystal oscillator of the ceramic package for surface mounting. It is sectional drawing of the conventional UM-1 metal cage. It is sectional drawing of the conventional metal cage for masters. It is sectional drawing of the conventional ceramic package for surface mounting. It is a top view of the conventional ceramic package for surface-like surface mounting. This is an electropolishing method for a stainless steel cap for a metal cage with three terminals. This is an electrolytic polishing method for a stainless steel cap for a ceramic package for sheet-like surface mounting. It is a mass spectrometry result of the residual gas in the suction side of an oil rotary pump. It is a mass spectrometry result of the residual gas in the suction side of a dry pump.

Explanation of symbols

201 Crystal plate 202 Electrode 203 Cap 204 Cap wall 205 Support column 206 Support column 207 Lead terminal 208 Lead terminal 209 Cage base

301 Plano convex quartz plate 302 Cap 303 Cap wall 304 Holding part 305 Holding part 306 Holding part 307 Lead terminal 308 Lead terminal 309 Lead terminal

401 Crystal plate 402 Electrode 403 Electrode 404 Flat plate cap 405 Cap wall 406 Metal lead frame for welding 407 Metal lead frame for welding 408 Ceramic substrate 409 Crystal plate holder 410 Crystal plate holder

501 Cap 502 Electrolytic polishing treatment liquid layer 503 Cathode electrode 504 Cathode electrode 505 Cathode electrode 506 Power supply

601 Cap 602 Electrolytic polishing treatment liquid layer 603 Cathode electrode 604 Cathode electrode 605 Power supply

701 Cap 702 Emission gas from cap wall 703 Emission gas from inside cap 704 Support column 705 Support column 705 Lead terminal 706 Lead terminal 707 Cage base

801 Cap 802 Emission gas from cap wall 803 Emission gas from inside cap 804 Support strut 805 Support strut 805 Support strut 806 Lead terminal 807 Lead terminal 808 Lead terminal 809 Cage base

901 Ceramic substrate 902 Cap wall 903 Cap wall 904 Emission gas from cap wall 905 Emission gas from inside cap 906 Crystal plate holder 907 Crystal plate holder

1001 Sheet-like ceramic substrate 1002 Ceramic package 1003 Crystal element

    1101 Mass analysis result of residual gas of oil rotary pump

    1201 Mass analysis results of residual gas in dry pump

Claims (2)

A step of storing a crystal element in a surface-treated container body, a step of cleaning contaminants in the container body by irradiation with deep ultraviolet rays or ions, and a surface-treated lid placed on the container body A method for producing a highly stable crystal resonator comprising the steps of: sealing a part with a vacuum or an inert gas; and thermally aging the container body. The highly stable crystal resonator according to claim 1, wherein the electrolytically polished container body is sealed with an electrolytically polished metal lid.

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