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Step 1: Growth of as-grown quartz crystals
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There are various types and sizes of synthetic quartz crystals which are to be used depending upon applications. The time required for the growth is different if the dimensions of synthetic quartz crystals are different. As grown quartz crystals are shaped into crystal lumbers by means of a surface grinder.
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*Crystal seedsThere are two kinds of crystal seeds, such as. Y-bars and Z-plates. they are set in a seed growth hardware, which is to be put at the upper part of an autoclave.
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*Crystal seedsThere are two kinds of crystal seeds, such as. Y-bars and Z-plates. they are set in a seed growth hardware, which is to be put at the upper part of an autoclave.
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*Crystal seedsThere are two kinds of crystal seeds, such as. Y-bars and Z-plates. they are set in a seed growth hardware, which is to be put at the upper part of an autoclave.
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*Crystal seedsThere are two kinds of crystal seeds, such as. Y-bars and Z-plates. they are set in a seed growth hardware, which is to be put at the upper part of an autoclave.
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Step 2: Cutting and Cutting-angle measurement
Purpose
To cut crystal lumbers and make crystal wafers which have specified cutting angles and thickness. Crystal wafers are classified according to their cutting angles.
Operation
Crystal wafers are cut by means of a multiblade saw and the cutting angles are measured by a high-precision X-ray cut angle inspection instrument.
Work Procedure
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Using an X-ray cut angle inspection instrument, an as-grown crystal is set on a multiblade saw so that crystal wafers having specified cutting angles will be obtained.
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Crystal lumbers are cut by means of a multiblade saw. The cutting speed is approximately 0.5 to 2.0mm/h. The blade saw is pulled by the force of 40 to 50 tons.
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X-rays are applied onto a crystal wafer through a filter so that X-rays are adjusted in terms of phase and wave length.
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The reading of the rate meter becomes the highest if the X-ray incident angle against the lattice plane is equal to the Bragg reflection angle. At this time, the cutting angle is to be read for the classification of crystal wafers.
(Measurement accuracy: 10 sec. max. )
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Step 3: External waver processing
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Purpose
To process crystal wafers so as to provide specified outline, dimension and surface finish.
Operation
Round wafer / Cylindrical grinder and cylindrical lapping machine used. Square wafer / Squaring machine used.
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Step 4: Lapping and polishing
Purpose
To allow crystal wafers to have specified thickness, surface roughness, flatness and parallelism.
Operation
Dual-face lapping machine is used. Surface roughness required determines the kind of abrasives to be used.
Work Procedure
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[Dual-face lapping machine]
The internal gear and the peripheral gear of a carrier cause each crystal wafer to move planetarily, thus leading to extremely effective wafer flattening.
[Types of abrasives]
Lapping: AIO3Sic Polishing: Cerium oxide.
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*Principle of polishing
As compared with the lapping. wafer grinding force is less due to the fact that the soft material used for the polisher absorbs the force generated by abrasive level irregularity. Crystal wafers are removed little by little without being broken. |
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*Principle of lapping
Between lapping plate and crystal wafer abrasives grind crystal wafer surface little by little during the rolling. Abrasive size determines surface finish. Smaller abrasives make surface smoother although lapping ability becomes lower. |
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Step 5: Etching and cleaning
Purpose
To remove the dirt and damaged layer caused by wafer lapping.
Operation
Etching / By etching process, the distorted layer on the crystal wafer is removed. Cleaning / To be cleaned by acid or alkalin solution.
Work Procedure
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*Frequency classification
Prior to the etching process, crystal wafers which have undergone lapping and polishing process are classified according to the individual frequency.
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The whole surface of a crystal wafer is distorted after the lapping process.
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*Etching
The distortion caused by the cutting and lapping is removed by the chemical etching. Fig.1 shows the crystal wafers put in a jig and Fig.2 shows the crystal wafers being etched.
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By etching process, the distorted layer on the crystal wafer is removed.
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*Cleaning
Cleaning by means of ultrasonic waves or chemicals allows crystal wafers to be cleaned in terms of one micron(1/1000mm)
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Step 6: Vacuum evaporation
Purpose
To form the electrode on a crystal wafer for oscillation.
Operation
The vacuum evaporation method is used to form the evaporation film on a crystal wafer.
Work Procedure
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*Masking
To form electrodes, various types of evaporation masks are used according to required Specification.
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| The evaporation film thickness is monitored by the frequency of the monitor crystal unit to control the film thickness and evaporation speed. The exhaust system uses a cryopump or an oil diffusion pump. The cryopomp is used in combination with a mechanical pump, and provides clean and high vacuum by trapping gas molecules on the adsorption surface chilled down. |
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*Vacuum evaporation
In a vacuum evaporation chamber, the heated metal vapor reaches crystal wafer without any barriers, and forms strong metal films. Various techniques such as wafer plasma cleaning and wafer heating are used for the formation of excellent film.
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*Taking out from masking
For electrodes used are the metals having good electrical conductivility such as gold, silver and aluminum. In general, silver is used. Aluminum which has light specific gravity is used for high overtone and high frequency products. For severe aging requesting product. gold is used because gold is chemically stable.
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Step 7: Assembly
Purpose
To mount a crystal wafer on the base and connect it electrically to lead wires.
Operation
A crystal wafer is mounted on a base and fixed with conductive epoxy.
Work Procedure
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*Support
Due to the fact a crystal unit vibrates mechanically, the edges of the crystal wafers are fixed so as not to prevent vibration.
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Distribution of vibration
The displacement of vibration is the greatest around midrange and is less at both ends. |
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| Tunnel-oven temperature profile |
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*Adhesion
Conductive adhesive is applied to the crystal wafer to fix it.
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*Cure
Conductive adhesives are cured in a tunnel oven.
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To fabricate a surface-mounted crystal unit, a crystal wafer is bonded directly to the base with an adhesive.
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Step 8: Frequency Adjustment
Purpose
To adjust the frequency of each crystal unit finely so that its frequency, which disperses due to the dispersion of crystal wafer thickness or evaporation film thickness, falls between the range specified by the customer.
Operation
Additional evaporation of gold or silver onto the electrode during the actual oscillation.
Work Procedure
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*Masking
Due to the fact that the secondary adjustment pattern position or size causes an equivalent circuit constant and the spurious characteristics of a crystal unit to change, positional and quantitative control is important.
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| Sectional diagram of crystal wafer after frequency adjustment |
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| Functional diagram of frequency adjustment machine |
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*Vacuum evaporation
Metal is evaporated onto the oscillating crystal wafer until its frequency decreases down to the target frequency. The evaporation shutter is closed when the frequency of the crystal unit is equal to the target value. Frequency adjustment in terms of +-3ppm is possible.
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Step 9: Sealing
Step 10: Inspection
Purpose
To make sure that characteristics of manufactured crystal units meet the requirements.
Operation
Inspection of mechanical and electronical characteristics.
Mechanical Inspection |
| 1. Leakage |
Insufficient sealing causes oxygen and moisture to intrude into a holder, thus leading to inferior aging characteristics. A helium-leak-detector is used for sealing inspection.
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| 2. Visual Inspection |
Visual inspection is performed according to Specification
in terms of marking, flaw, dirt and lead bend.
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Helium-leak-detector
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| Mechanical Inspection |
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| 1. Insulation |
Insulation resistance is measured by means of a megohmmeter due to the fact that insufficient insulation may result in non oscillation and excessive current flaw.
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| 2. Co and C1 |
These values determine the changeability of the frequency due to the load capacitance. lmproper value causes the failure to tune the frequency to the target value when set in circuit.
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| 3. CI (Crystal Impedance) |
The increase in CI value results in the decrease in output of oscillation circuit voltage and if it exceeds the circuit negative resisitance causes non-oscillation.
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| 4. Frequency |
An inspection is perfomed to make sure that the frequency of a crystal unit, which is the most important inspection item, is within the specified range. To measure the frequency, ci meter or ?I-network system are applied.
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| 5. Spurious Response |
To prevent the spurious-mode oscillation, spurious frequency and attenuation are measured by means of an equivalent constants measuring system.
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| 6. Temperature Characteristics |
Frequency change is inspected within the operating temperature range by an automated frequency temperature characteristics measuring system.
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Megohmmeter
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Equivalent constants measuring system
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Automated frequency Temperature characteristicsmeasuring system
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Technical 
