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What is a quartz crystal? The role and production process of quartz crystal

What is a quartz crystal? The role and production process of quartz crystal


Quartz crystal components have a high quality factor (ie "Q value") and a small frequency deviation caused by temperature. They are more accurate and stable than other oscillator components, and are especially suitable for higher frequency accuracy requirements. Communication products. Products are widely used in communications, information, networks, automotive electronics and household appliances, etc. The specifications are usually differentiated by frequency (MHz), accuracy (PPM), size (mm×mm) and packaging methods.

Quartz crystal component products can be divided into the following three categories:

1. Quartz crystal resonator

The quartz crystal resonator is composed of a quartz wafer with a certain shape, size and cut type, electrodes, and a package shell that meet a certain frequency standard. It uses the piezoelectric effect and the inverse piezoelectric effect of the quartz crystal itself to generate frequency and play a role in frequency control. Any circuit that requires a frequency signal can be obtained within a certain range by using the piezoelectric effect of quartz crystal, so it is an indispensable and important component for most electronic products.

2. Quartz crystal oscillator

The quartz crystal oscillator is composed of a resonator with a very high quality factor and a special oscillator circuit. Crystal oscillators are widely used in information, communications and consumer electronics products.

3. Quartz crystal filter

The quartz crystal filter is packaged with a combination of quartz crystal, coil, capacitor, and resistance. Filters can pass specific frequencies, or pass frequencies within a specific range, and are mainly used in the communications field.

As the core component of frequency control and frequency selection, quartz crystal resonators are widely used in communication fields (mobile phones, cordless phones, PHS, walkie-talkies); information fields (laptop computers, desktop computers, servers, printers, mobile hard drives, optical drives, Fax machine); network products (network control, network interface and adapter, network connector, network testing equipment); household appliances (LCD TV, digital video camera, digital camera, set-top box, DVD, MP3, CD burner, home audio); In terms of automotive electronics and aerospace products, in recent years, the development of emerging products such as automotive electronics, GPS, digital cameras, LCD TVs, Bluetooth products, and MP3 has expanded the application areas of quartz crystal components.

SMD quartz crystal oscillator, as the source of frequency signal, is manufactured by adding feedback amplifier circuit on the basis of quartz crystal resonator. Based on the manufacturing technology of the quartz crystal resonator, the key to the manufacturing technology of the SMD quartz crystal oscillator is the circuit design, the selection of the matching parameters of the quartz resonator and the circuit, and the testing technology.

The process flow chart of SMD resonator is as follows:

Design and manufacturing technology of wafers for small-size SMD resonators

The chip of the SMD resonator is quite small, because the main vibration of the quartz crystal resonator adopts the thickness shear vibration of the quartz crystal, but at the same time, the quartz crystal has parasitic vibration modes such as width bending vibration. For SMD resonators, width bending vibration is particularly easy to produce. When the width-to-thickness ratio of the wafer reaches a certain value, the parasitic vibration will be very close to the required main vibration. When the crystal is working, its output frequency signal will be unstable. Since the frequency of the crystal is inversely proportional to the thickness of the wafer, in order to avoid these values ​​for the width-to-thickness ratio of the wafer, the width dimension processing of the wafer is very important. The chip size of other domestic counterparts is usually accurate to 0.01mm, and its measuring instrument generally uses a micrometer with a measurement accuracy of 0.001mm.

In order for the crystal to work stably at 0.01μW, the equivalent resistance of the crystal must be reduced. The equivalent resistance of the crystal is related to the smoothness and cleanliness of the wafer surface and the stress generated during crystal processing. The company adopts fine polishing process and new cleaning process and cleaning agent to improve the smoothness and cleanliness of the wafer surface; adopts electric cleaning process and high temperature annealing process to reduce stress.

Production considerations

Due to the implementation of the EU RoHS directive, all electronic products are soldered with lead-free solder, and lead-free soldering requires a soldering temperature of up to 260°C. Because the expansion coefficient of the crystal and the electrode material silver in the quartz crystal are different, at such a high welding temperature, the bonding force between the silver electrode and the crystal will be greatly reduced, which will seriously affect the performance of the quartz crystal resonator, and in severe cases, it will cause the quartz Failure of the crystal resonator. Adopting double-layer electrode film sputtering technology and adding a layer of different metal film between the silver electrode and the crystal can solve the problem that the electrode bonding force decreases when the welding temperature increases.

In the conventional quartz crystal resonator production process, the method of adding silver to the silver electrode is usually used to adjust the frequency accuracy. This technology can be used for products with larger product sizes. If it is used in miniaturized SMD products, it will bring two defects: one is that the shape of the newly added silver sometimes cannot overlap with the original silver electrode; the other is that there is one after the silver electrode is sputtered and before the frequency is adjusted. The high temperature baking process will produce oxide film on the silver electrode due to the influence of high temperature. If silver is added to adjust the frequency accuracy at this time, the electrode oxide film will be wrapped in the electrode, resulting in deterioration of the performance of the quartz crystal resonator.

The ion etching frequency fine-tuning technology uses the opposite method, reducing the silver on the silver electrode to adjust the frequency accuracy. Ion etching technology can just solve the above two shortcomings.

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