标题: 提高晶控片使用寿命的要点 [打印本页] 作者: 李伟华 时间: 2004-2-8 23:47 标题: 提高晶控片使用寿命的要点 In order to get the maximum life out of Zens quartz crystals we recommend the following guidelines:
Always use plastic tweezers around the edge of the crystal during handling. Do not touch the center of a quartz crystal, as any oil, dirt, dust, or scratches will quickly degrade the ability of the crystal to vibrate.
Keep the crystal holder clean. Do not allow flakes of material to come into contact with the center of the crystal, front or back. Any burrs or particulate that come between the crystal and cap will interfere with the electrical contact and develop stress points, affecting the crystal’s vibrational pattern.
After the crystal is mounted in the cap, if possible, blow off the crystal surface with a low-pressure jet of dry, filtered nitrogen or oil-free air. This will remove any dust or flakes of loose coating that may have come in contact with the crystal during installation.
In order to promote better film adhesion, maintain the cooling water to the sensor head in the 20 to 40 degree Centigrade range. The hotter the deposition, the closer the crystal should run to 40 degrees Centigrade. Additionally, whatever your temperature, keeping it stable to within 1-2 degrees will give superior results.
文字作者: 李伟华 时间: 2004-2-8 23:52 标题: 提高晶控片使用寿命的要点 In order to use a quartz crystal in the coating chamber, a device had to be developed that could be electrically activated to vibrate the crystals in vacuum, allow only a portion of the crystal to be coated with evaporated material, and permit the crystal to be changed easily. Furthermore, the device would have to shield the crystal from the high temperatures inherent in the coating processes. Thus, the “sensor head” was created.
In currently available sensor head designs, the crystal rests in the “crystal holder” a metal cap with a hole drilled through the center of the cap. The holder serves as one half of the electrical circuit that causes the crystal to vibrate. This hole allows the evaporating film to coat a circular region of approximately 0.3 diameter (7.6 mm) on the crystal face. The crystal is held in place in the holder by a spring. In some models, the spring is located around the inside of the holder and presses against the crystal edge. In other designs, a “ceramic retainer with a gold-coated spring in the center presses against the outer back edge of the crystal.
In both designs, the crystal holder is inserted into the sensor head (a metal block), where a second gold coated spring presses against the back of the crystal or retainer to complete the crystal electrical circuit. The head often contains another spring for holding the crystal holder in place and providing electrical contact between the holder and the head.
On the outside of the sensor head is a screw-on miniature connector, a “Microdot Connector”. At this point, a thin microcoaxial (two wires in one body) cable connects the sensor head to the feedthrough, interfacing the inside of the chamber and atmosphere. The feedthrough then connects in atmosphere to the oscillator and on to the thin film monitor.
The sensor head also has two small metal tubes, “water lines” extending from one ento to provide water cooling to the crystal. The water lines feed either an internal passageway drilled through the sensor head or simply connect to a tubing bend that rests in the back of the head. Both water lines connect to the feedthrough.
When new, a sensor head allows easy insertion of the crystal snug mounting of the crystal holder, uninterrupted electrical connection to the feedthrough and unimpeded water cooling. After repeated use, however, this system can break down and lead to erratic or failed crystal readings. Several of the most common modes of failure are:
The contact springs in the crystal holder or sensor head break or bend sufficiently, interrupting the electrical circuit;
The wires inside the sensor head connecting to the microcoaxial cable fitting break, interrupting the electrical circuit;
The microcoaxial cable connecting the sensor head to the feedthrough cracks or loosens, interrupting the electrical circuit; and ,
The water lines clog due to high mineral content of the water, causing the sensor head to overheat. 作者: royyang 时间: 2012-6-19 22:21
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