Frequency modulation method of quartz crystal tuning fork and resonator

Abstract

This invention discloses a frequency tuning method and resonator for a quartz crystal tuning fork oscillator. The method includes: a coating step: cleaning the quartz crystal blank and depositing a base metal layer after cleaning; a coarse tuning step: repeatedly printing conductive paste in the tuning area of ​​the tuning fork arm and curing it to form a printed tuning layer, adjusting the frequency of the tuning fork oscillator to a preset frequency range; and a fine tuning step: performing an excitation test to obtain the current frequency F1, using a laser to perform targeted ablation on the printed tuning layer, stopping when the frequency reaches the target value F2, thus completing the frequency tuning of the quartz crystal tuning fork oscillator. This invention adopts a layered coating architecture, abandoning the full vacuum process, and using a stacked structure of "one-time vacuum coating (base conductive / reflective layer) + two-time printed coating (tuning weight-adding layer)," which solves the problem of material waste and achieves nanometer-level precise frequency locking.

Description

Technical Field

[0001] This invention relates to the field of crystal oscillator technology, and in particular to a method for tuning a quartz crystal tuning fork oscillator and a resonator. Background Technology

[0002] In the process of evolving from the 32.768kHz tuning fork quartz crystal resonator to the 3215 (3.2×1.5mm) ultra-miniaturization, the control of frequency accuracy has become the core bottleneck.

[0003] Existing technologies suffer from two major problems: 1. Extremely low material utilization: Traditional secondary frequency modulation coating uses vacuum evaporation or magnetron sputtering. Metal atoms disperse spherically in a vacuum, with only a small portion adhering to the tiny 3215 crystal surface; over 60% of the precious metals (gold, silver) are deposited on the vacuum chamber walls. This not only results in enormous material waste but also leads to vacuum pump oil contamination and high maintenance costs.

[0004] 2. Limited and irreversible frequency tuning methods: Vacuum coating is a process that "only adds, never subtracts." If the coating is too thick in one step, resulting in a low frequency, the material often has to be scrapped. Although laser adjustment can be performed later, directly ablating the hard vacuum-coated layer with a laser can easily damage the quartz substrate or cause the coating to peel off, and the adjustment amount is extremely difficult to control.

[0005] Therefore, the industry urgently needs a composite frequency modulation process that "first increases weight at low cost (printing), then reduces weight with high precision (laser)," which can solve the problem of material waste and achieve nanometer-level precise locking of frequency. Summary of the Invention

[0006] The technical problem to be solved by the embodiments of the present invention is to provide a frequency modulation method and resonator for a quartz crystal tuning fork oscillator, so as to achieve accurate frequency modulation while avoiding material waste.

[0007] To address the aforementioned technical problems, this invention provides a method for tuning a quartz crystal tuning fork oscillator, comprising: Coating step: Prepare a quartz crystal blank for the tuning fork oscillator and clean it. After cleaning, deposit a base metal layer on the surface of the quartz crystal blank to obtain a pretreated quartz crystal tuning fork oscillator. Coarse adjustment step: Conductive paste is printed multiple times on the tuning area of ​​the tuning fork arm of the pre-treated quartz crystal tuning fork oscillator and cured to form a printed tuning layer. The frequency of the tuning fork oscillator is adjusted to the preset frequency range to obtain the printed and cured quartz crystal tuning fork oscillator. Fine-tuning steps: Excite the quartz crystal tuning fork oscillator after printing and curing to obtain the current frequency F1. Use a laser to perform targeted ablation on the printed tuning layer. Stop when the frequency reaches the target value F2 to complete the tuning of the quartz crystal tuning fork oscillator.

[0008] Furthermore, the thickness of the base metal layer is 50 nm - 100 nm.

[0009] Furthermore, the base metal layer is one or more of Cr, Au, or Al, and is deposited using magnetron sputtering.

[0010] Furthermore, the conductive paste is a precious metal conductive paste with a solid content of 80%-90%.

[0011] Furthermore, an organic resin binder is added to the conductive paste.

[0012] Furthermore, the metal in the precious metal conductive paste is one or more of silver, palladium, and gold.

[0013] Furthermore, in the coarse adjustment step, the paste is printed onto the tuning area of ​​the tuning fork arm through a 300-400 mesh steel mesh.

[0014] Furthermore, in the coarse adjustment step, the curing temperature is 150℃-200℃.

[0015] Furthermore, in the fine-tuning step, ultraviolet laser or fiber laser ablation is used.

[0016] Accordingly, embodiments of the present invention also provide a resonator, including a quartz crystal tuning fork oscillator obtained by frequency modulation using the above-described frequency modulation method for a quartz crystal tuning fork oscillator.

[0017] The beneficial effects of this invention are as follows: 1. Extreme cost control: This invention completely eliminates the waste of "material flying walls" in vacuum coating, reduces the consumption of precious metals by 70%-90%, and the cost of printing equipment is only 1 / 10 of that of vacuum machines.

[0018] 2. Significantly improved frequency modulation tolerance: Traditional vacuum coating is unusable if it is too thick; in the process of this invention, the printing layer can be printed thicker, and then the excess part is burned off with a laser. This "reversible" operation logic greatly improves the production yield of 3215 crystals.

[0019] 3. Higher adjustment accuracy and speed: The printed layer of this invention is composed of metal particles and resin, which is a "soft film". It is easily vaporized and removed by laser, and the adjustment linearity is good (the laser energy and frequency change are linearly related), avoiding the cracking or sputtering problems of hard metal film during adjustment.

[0020] 4. Improved high-frequency characteristics: The micro-roughness of the printed layer surface in this invention helps to increase the effective electrode area, which to a certain extent reduces the equivalent resistance (ESR) and facilitates oscillation. Attached Figure Description

[0021] Figure 1 This is a schematic flowchart of the frequency modulation method for a quartz crystal tuning fork oscillator according to an embodiment of the present invention.

[0022] Figure 2 This is a schematic diagram of the structure of a quartz crystal tuning fork oscillator that has completed frequency modulation according to an embodiment of the present invention.

[0023] Explanation of icon numbers 1. Quartz crystal substrate, 2. Base metal layer, 3. Printed frequency modulation layer, 4. Laser ablation pits. Detailed Implementation

[0024] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0025] In this embodiment of the invention, directional indicators (such as up, down, left, right, front, back, etc.) are only used to explain the relative positional relationship and movement of each component in a specific posture (as shown in the figure). If the specific posture changes, the directional indicator will also change accordingly.

[0026] Furthermore, in this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features.

[0027] The frequency tuning method for a quartz crystal tuning fork oscillator according to this invention includes a coating step, a coarse tuning step, and a fine tuning step. Please refer to [link / reference]. Figure 1 The process is as follows: preform cleaning → first vacuum coating → frequency measurement (too high) → second printing coating (weight increase and frequency reduction) → frequency measurement (close to target) → laser adjustment (weight reduction and frequency increase) → frequency measurement (locked) → packaging.

[0028] Coating steps: Substrate pretreatment and a single vacuum coating are performed to prepare a quartz crystal blank (3215 quartz crystal blank) for the tuning fork oscillator. After cleaning, a base metal layer is deposited on the surface of the quartz crystal blank to obtain the pretreated quartz crystal tuning fork oscillator. The main function of this base metal layer is to ensure the conductivity and reflectivity of the tuning fork oscillator substrate, and it is not used as the main frequency modulation method.

[0029] Coarse adjustment step: Secondary printing coating (coarse adjustment / weighting), paste preparation: Use a high solids content (80%-90%) precious metal (silver, palladium, gold) conductive paste, with added organic resin binder. That is, the mass percentage of the organic resin binder is 10%–15%; the mass percentage of the metal conductive phase is 85%–90%. (If the mass percentage of the organic resin binder is less than 8%: the resin cannot effectively encapsulate the metal powder, the bonding force between the printed layer and the quartz crystal substrate is insufficient, and the thermal shock or airflow impact during subsequent laser trimming will cause the coating to peel off or flake, affecting oscillation. If the mass percentage of the organic resin binder is greater than 18%: there is too much resin residue. The principle of laser trimming is to ablate the metal. If the resin content is too high, the laser energy will be absorbed by the resin for carbonization or volatilization, rather than effectively removing metal particles, resulting in low frequency modulation efficiency, and even micro-cracks in the coating due to the gas produced by resin combustion.)

[0030] Conductive paste is repeatedly printed onto the tuning area (the front section of the tuning fork, i.e., the tuning zone) of a pre-treated quartz crystal tuning fork oscillator using a high-mesh stencil, and then cured to form a printed tuning layer. This adjusts the frequency of the tuning fork oscillator to a preset frequency range, resulting in a printed and cured quartz crystal tuning fork oscillator. This invention dynamically adjusts the number of printing cycles based on the frequency deviation after the initial coating. Each printed layer and cured (150℃-200℃) causes a frequency decrease of approximately 1-3 ppm. Through multiple printing cycles, the frequency is rapidly brought closer to the target value (with a laser adjustment margin, such as +2 ppm).

[0031] This invention utilizes the physical shielding principle of screen printing or gravure printing to directly transfer conductive paste containing metal particles to the crystal surface of a quartz crystal tuning fork oscillator, increasing material utilization from <50% in vacuum coating to >95%, with almost zero waste.

[0032] The printed frequency modulation layer, serving as the frequency modulation mass load layer, is specifically designed to support laser trimming. The presence of this layer makes laser trimming highly efficient and does not damage the substrate. The conductive paste is a thermosetting conductive polymer paste with a metal content between 70% and 95%.

[0033] Fine-tuning steps: Laser adjustment (fine-tuning / weight reduction) is performed on the printed and cured quartz crystal tuning fork oscillator for a final excitation test to obtain the current frequency F1. The printed tuning layer is then ablated at specific points using a laser. The laser energy instantly vaporizes some metal particles and resin, reducing the effective mass of the crystal arm and thus restoring the frequency. Frequency changes are monitored in real time. When the frequency reaches the target value F2 (e.g., 32768.00Hz ±0.5ppm), laser ablation is stopped, completing the tuning of the quartz crystal tuning fork oscillator. Vacuum sealing is then performed. The structure of the tuned quartz crystal tuning fork oscillator is shown below. Figure 2As shown, the bottom layer is a quartz crystal substrate 1, on which a vacuum base metal layer 2 is plated. The tuning fork arm tuning area has a secondary printed tuning layer 3, and the printed tuning layer 3 has laser ablation pits 4.

[0034] This invention utilizes the relatively soft nature and organic content of printed frequency modulation layers to remove a portion of the printed layer through laser ablation. Compared to directly ablating vacuum metal films, laser ablation offers higher removal efficiency, a smaller heat-affected zone, and extremely high tuning resolution (up to 0.1 ppm / pulse) for printed frequency modulation layers.

[0035] This invention employs a layered coating architecture, abandoning the all-vacuum process and adopting a stacked structure of "one-stage vacuum coating (basic conductive / reflective layer) + two-stage printed coating (frequency modulation weight-adding layer)". First, weight is added (frequency reduction) through printing, and then weight is removed (frequency increase) through laser. The printed layer serves as the main source of frequency modulation mass load.

[0036] In one embodiment, the thickness of the base metal layer is 50 nm to 100 nm. The metal of the base metal layer is one or more of Cr, Au, or Al, and is deposited by magnetron sputtering.

[0037] In one embodiment, the conductive paste is a precious metal conductive paste with a solid content of 80%-90%. The metal in the precious metal conductive paste is one or more of silver, palladium, and gold.

[0038] In one implementation, during the coarse adjustment step, the paste is printed onto the tuning area of ​​the tuning fork arm using a 300-400 mesh steel mesh. The curing temperature is 150℃-200℃. Preferably, ultraviolet laser or fiber laser ablation is used.

[0039] The resonator in this embodiment of the invention includes a quartz crystal tuning fork oscillator obtained by frequency modulation using a quartz crystal tuning fork oscillator method. Example:

[0040] Initial state: A batch of 3215 preforms was selected, with a designed frequency of 32.768kHz. After one vacuum sputtering of silver electrodes, the measured frequency was 32.775kHz (5ppm too high, requiring weight increase to reduce frequency).

[0041] Secondary printing increases weight: Silver-palladium alloy paste (85% solid content) was selected.

[0042] A 350-mesh stencil was used for the first printing and curing process (curing temperature 180℃, curing time 20 min). The measured frequency dropped to 32.771 kHz.

[0043] A second printing and curing process was performed. The measured frequency dropped to 32.769kHz (at this point, it was very close to the target, with a margin of +1.2ppm).

[0044] Cost accounting: Compared with vacuum coating, which increases weight for the same mass, printing process saves about 80% of the cost of silver paste.

[0045] Laser retouching and fine-tuning: Place the crystal into the laser frequency modulator and start the automatic frequency measurement.

[0046] Calculate the number of laser pulses required to remove the required amount of silver paste (e.g., approximately 5 ng of silver paste needs to be removed).

[0047] The laser beam is focused on the printed layer at the root of the tuning fork arm, performing microsecond-level pulse ablation. As the paste is ejected, the frequency begins to rise from 32.769 kHz.

[0048] The laser immediately stopped when the frequency was monitored at 32.768.05 kHz.

[0049] Results: The final product has an extremely narrow frequency distribution, concentrated at 32.768kHz ±0.2ppm, and the printed layer has good adhesion to the quartz substrate with no peeling.

[0050] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for tuning the frequency of a quartz crystal tuning fork oscillator, characterized in that, include: Coating step: Prepare a quartz crystal blank for the tuning fork oscillator and clean it. After cleaning, deposit a base metal layer on the surface of the quartz crystal blank to obtain a pretreated quartz crystal tuning fork oscillator. Coarse adjustment step: Conductive paste is printed multiple times on the tuning area of ​​the tuning fork arm of the pre-treated quartz crystal tuning fork oscillator and cured to form a printed tuning layer. The frequency of the tuning fork oscillator is adjusted to the preset frequency range to obtain the printed and cured quartz crystal tuning fork oscillator. Fine-tuning steps: Excite the quartz crystal tuning fork oscillator after printing and curing to obtain the current frequency F1. Use a laser to perform targeted ablation on the printed tuning layer. Stop when the frequency reaches the target value F2 to complete the tuning of the quartz crystal tuning fork oscillator.

2. The frequency modulation method for a quartz crystal tuning fork oscillator as described in claim 1, characterized in that, The thickness of the base metal layer is 50 nm - 100 nm.

3. The frequency modulation method for a quartz crystal tuning fork oscillator as described in claim 1, characterized in that, The base metal layer is one or more of Cr, Au, or Al, and is deposited by magnetron sputtering.

4. The frequency modulation method for a quartz crystal tuning fork oscillator as described in claim 1, characterized in that, The conductive paste is a precious metal conductive paste with a solid content of 80%-90%.

5. The frequency modulation method for a quartz crystal tuning fork oscillator as described in claim 4, characterized in that, An organic resin binder is added to the conductive paste.

6. The frequency modulation method for a quartz crystal tuning fork oscillator as described in claim 4, characterized in that, The precious metal conductive paste contains one or more of silver, palladium, and gold.

7. The frequency modulation method for a quartz crystal tuning fork oscillator as described in claim 1, characterized in that, In the coarse adjustment step, the paste is printed onto the tuning area of ​​the tuning fork arm through a 300-400 mesh steel mesh.

8. The frequency modulation method for a quartz crystal tuning fork oscillator as described in claim 1, characterized in that, In the roughing step, the curing temperature is 150℃-200℃.

9. The frequency modulation method for a quartz crystal tuning fork oscillator as described in claim 1, characterized in that, In the fine-tuning step, ultraviolet laser or fiber laser ablation is used.

10. A resonator, characterized in that, This includes a quartz crystal tuning fork oscillator obtained by frequency modulation using the frequency modulation method of the quartz crystal tuning fork oscillator as described in any one of claims 1-9.

Images