A tuning fork blade processing method
By using online frequency monitoring and closed-loop control of laser processing, the problem of inconsistent resonant frequencies in tuning fork plate processing was solved, achieving improved frequency consistency and production efficiency, and reducing additional frequency fine-tuning steps.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- NINGBO ZHONGLEI LASER TECHNOLOGY CO LTD
- Filing Date
- 2026-05-20
- Publication Date
- 2026-06-19
Abstract
Description
Technical Field
[0001] This invention belongs to the field of quartz resonator manufacturing technology, specifically relating to a method for processing tuning fork plates. Background Technology
[0002] As the core component of a quartz resonator, the resonant frequency of the tuning fork plate is primarily determined by its geometry, electrode configuration, and mass. In traditional manufacturing processes, fixed design drawings are typically used, and pre-defined grooves are machined onto the tuning fork plate surface using photolithography or laser etching. Although the machining accuracy of the geometry can be improved through high-precision visual positioning and parameter optimization, this "open-loop" machining method has a fundamental flaw: Perfect reproduction of geometric dimensions does not guarantee a high degree of consistency in electrical performance (especially resonant frequency).
[0003] This is because quartz crystals inherently possess anisotropy, and wafers from different batches and at different wafer locations exhibit subtle differences in microscopic physical properties such as elastic constants and density. Even when the exact groove geometry is fabricated, the resulting changes in equivalent mass and stiffness will vary slightly, leading to dispersion in the final resonant frequency. To compensate for this difference, the industry has to add a cumbersome, inefficient, and expensive "frequency fine-tuning" process after photolithography, adjusting the electrode quality by evaporating or sputtering trace amounts of metal to correct the frequency to the target value.
[0004] Therefore, how to move the frequency adjustment function forward and integrate it into the main processing steps to achieve integrated and intelligent processing and frequency modulation is a major technical problem that has not yet been solved in this field. Summary of the Invention
[0005] To address the problems in the prior art, the present invention aims to provide a method for processing tuning fork plates that can dynamically adjust processing parameters based on real-time frequency response. This method abandons the traditional "rigid" fixed-size processing mode and instead adopts a closed-loop intelligent processing strategy with the final frequency performance as the direct control target. By monitoring the resonant frequency of the tuning fork plate in situ and in real time during processing, and using the frequency deviation to dynamically correct the depth or length of laser processing, adaptive and precise frequency control is achieved, resulting in a finished product with highly consistent frequency in a single process.
[0006] To achieve the above objectives and technical effects, the technical solution adopted by this invention is as follows: A method for processing a tuning fork plate includes the following steps: Step 1: Pre-processing and initial clamping: Select a tuning fork plate substrate and perform surface cleaning and activation pretreatment on it; then clamp the pretreated tuning fork plate onto a processing platform with online frequency monitoring function. Step 2: Determination of reference frequency and generation of initial photolithography parameters: The online frequency monitoring unit of the processing platform applies an excitation signal to the tuning fork and collects its response signal to determine the initial resonant frequency f0 of the tuning fork in its unprocessed state; based on the target resonant frequency f0... target The difference Δf between the initial resonant frequency f0 and the preset frequency-lithography depth mapping model are used to calculate and generate the first set of adaptive lithography parameters for front-side processing. Step 3: Front-side adaptive laser lithography and frequency closed-loop control: A processing coordinate system is established using a high-resolution vision positioning system, and the lithography path for the front groove is planned based on the first set of adaptive lithography parameters. The laser lithography equipment is started to process the groove on the front of the tuning fork sheet, and during the processing, the following frequency closed-loop control steps are repeatedly executed at a set sampling interval until the first processing termination condition is reached: S31. Pause photolithography and measure the current resonant frequency f of the tuning fork plate in real time using the online frequency monitoring unit. current ; S32. Calculate the current frequency deviation Δf current =f target -f current ; S33, If |Δf current If the frequency is less than the preset frequency tolerance threshold ε, then the front-side photolithography is terminated; otherwise, according to Δf current With a frequency-lithography depth mapping model, the depth or length of subsequent lithography paths is adjusted in real time, and lithography continues; Step 4: Precise alignment and collaborative photolithography on the reverse side: After the front lithography is completed, the tuning fork is flipped over. A high-resolution visual positioning system is used to identify the reference feature points on the back side, and the positional deviation introduced by the flipping operation is calculated and compensated. Based on the compensated coordinate system, a second set of parameters that is the same as or proportional to the first set of adaptive lithography parameters is used to plan the lithography path of the back groove and perform lithography, so as to achieve the alignment of the front and back grooves and the coordinated control of frequency characteristics.
[0007] Furthermore, in step one, the surface cleaning and activation pretreatment steps include: The process involves sequential ultrasonic cleaning at 40-100kHz, oxygen plasma cleaning at 80-150W, and baking and drying at 60-80℃.
[0008] Furthermore, in step one, the processing platform with online frequency monitoring function includes a vacuum adsorption stage, which integrates an excitation electrode and a pickup electrode for coupling with the tuning fork plate electrode area in a non-contact or probe-contact manner to achieve in-situ frequency testing.
[0009] Furthermore, in step two, the frequency-lithography depth mapping model is established through prior experiments. It describes the frequency change caused by a unit lithography depth or a unit lithography length under a specific frequency band and packaging specification, and is stored in the database of the control system.
[0010] Furthermore, in step three, the first processing termination condition is: |Δf current |≤ε, where ε takes the value of 10-100ppm.
[0011] Furthermore, in step three, adjusting the depth or length of subsequent photolithography paths in real time includes the following steps: According to Δf current The sign and absolute value of Δf current If Δf > 0, then the photolithography depth or length is increased proportionally. current If the value is less than 0, the photolithography depth or length will be reduced proportionally, or the processing will be terminated and an alarm will be issued.
[0012] Furthermore, in steps three and four, the laser lithography equipment used for lithography is an ultraviolet picosecond or femtosecond laser, and an inert protective gas is introduced during the lithography process.
[0013] Furthermore, step five follows step four: ultrasonic-assisted chemical etching to remove residues, specifically as follows: The tuning fork plate is placed in a fluorine-containing etching solution. Under the combined action of an ultrasonic field of 60-150kHz and mechanical stirring at 30-150r / min, the residual powder in the groove is selectively removed. The etching time is 10-90s.
[0014] Furthermore, the concentration of the etching solution is selected based on the frequency band of the tuning fork plate: For the kilohertz frequency band, an etching solution with a volume fraction of 8-12% is selected; For the megahertz frequency band, an etching solution with a volume fraction of 5-9% is selected; For the terahertz frequency band, an etching solution with a volume fraction of 2-6% is selected; The ultrasonic corrosion process parameters are: corrosion temperature 15-35℃, ultrasonic power 30-120W; The corrosive solution is a fluoroboric acid solution, an ammonium fluoride-ammonium hydrogen fluoride buffer solution, or an organic acid complex fluoride solution, with a toxicity LD50. 50 >500mg / kg; or, The etching solution is a diluted hydrofluoric acid solution or a fluorine-containing composite etching solution.
[0015] Furthermore, following step five, there is also step six: multi-stage cleaning, drying, and final testing, specifically as follows: Remove the ultrasonically etched tuning fork plates and place them in a container with a resistivity ≥18MΩ. Clean with 60-100kHz ultrasonic waves for 5-10 minutes in ultrapure water. Then place it in a 2-6% concentration of dilute hydrochloric acid solution, dilute sulfuric acid solution, or sodium bicarbonate solution, and allow it to neutralize for 5-25 seconds. Rinse again with ultrapure water 2-3 times, 3-5 minutes each time, to ensure that there are no chemical residues on the surface; Use 0.3-0.5 MPa nitrogen gas to dry the surface moisture of the tuning fork plate; Place in an oven at 70-90℃ and bake for 20-30 minutes until thoroughly dried to obtain a clean tuning fork plate. The dimensional accuracy and surface roughness of the groove are detected by laser confocal microscopy or atomic force microscopy. The surface roughness Ra is required to be ≤0.2μm and the size is within the broad generalization range of the corresponding frequency band. The resonance performance was tested using frequency band-adaptive testing equipment: kilohertz band ESR≤80Ω, oscillation start-up time≤1.2ms; megahertz band ESR≤50Ω, oscillation start-up time≤0.8ms; terahertz band ESR≤40Ω, oscillation start-up time≤0.5ms; frequency drift≤1ppm; Defective products are removed, and qualified products proceed to the next process.
[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1) Pioneering performance closed-loop control: This invention is the first to link online frequency monitoring with laser processing in real time, shifting the control target from the "intermediate quantity" of geometric dimensions to the "final quantity" of electrical performance, realizing a fundamental conceptual shift from "what to process" to "how to process it", which has extremely high non-obviousness; 2) It solves the frequency consistency problem at its root: Through in-chip closed-loop control, it effectively compensates for the intrinsic differences of quartz crystal materials and process disturbances, and can control the frequency deviation after one photolithography process to within 100ppm, greatly reducing or even completely eliminating the subsequent frequency fine-tuning process, significantly shortening the production cycle and reducing costs. 3) It endows the processing system with intelligent adaptive capabilities: it can automatically adjust the corresponding processing parameters according to each tuning fork piece, realizing flexible manufacturing and intelligent manufacturing, and greatly improving the robustness of the process and the product yield. 4) Ingenious hardware integration design: The frequency testing function is integrated into the vacuum adsorption stage of the processing platform, realizing "zero distance" between processing and testing, and providing reliable hardware support for in-situ closed-loop control. Detailed Implementation
[0017] The present invention will now be described in detail so that its advantages and features can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.
[0018] The following provides a brief overview of one or more aspects to offer a basic understanding of them. This overview is not an exhaustive summary of all conceived aspects, nor is it intended to identify key or decisive elements of all aspects, nor to define the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form to prepare for the more detailed descriptions that follow.
[0019] This invention discloses a method for processing tuning fork plates, comprising the following steps: Step 1: Pre-processing and initial clamping: Select tuning fork plate substrates with corresponding frequency bands (kilohertz / megahertz / terahertz) and package specifications (0402-4025), and perform surface cleaning and activation pretreatment on them; then clamp the pretreated tuning fork plate onto a processing platform with online frequency monitoring function. The innovation of this step lies in the fact that the processing platform itself integrates frequency testing function, which makes subsequent in-situ monitoring possible and avoids the positioning error and time loss caused by repeatedly transferring the workpiece between different workstations. Step 2: Determination of reference frequency and generation of initial photolithography parameters: The online frequency monitoring unit of the processing platform applies an excitation signal to the tuning fork plate and collects its response signal to determine the initial resonant frequency f0 of the tuning fork plate in its unprocessed state; based on the target resonant frequency f0... target The difference Δf between the initial resonant frequency f0 and the preset frequency-lithography depth mapping model are used to calculate and generate the first set of adaptive lithography parameters for front-side processing. The core value of this step lies in first performing a "physical examination" on each tuning fork crystal to obtain its unique initial resonant frequency f0. Since the initial resonant frequency f0 already reflects the intrinsic characteristics of this specific crystal, the subsequent processing amount calculated based on Δf has taken into account the variable of material difference, thus realizing personalized initial path planning for this crystal. Step 3: Front-side adaptive laser lithography and frequency closed-loop control: A processing coordinate system is established using a high-resolution vision positioning system, and the lithography path of the front groove is planned according to the first set of adaptive lithography parameters. Based on the frequency band, packaging specifications, and vibration mode requirements of the tuning fork plate, the generalized dimension parameters of the front groove are input into the control system: kilohertz band: slot edge distance d=10-50μm, depth h=1-10μm, width w=5-25μm, length L is 10%-80% of the effective length of the fork arm; Megahertz band: d=2-30μm, h=0.3-8μm, w=1-20μm, L is 15%-75% of the effective length of the fork arm; Terahertz band: d=0.5-20μm, h=0.1-5μm, w=0.5-15μm, L is 20%-70% of the effective length of the fork arm; It also satisfies the following requirements: length-to-width ratio (L / w) of 2:1-20:1 and depth-to-width ratio (h / w) of 0.1:1-2:1; Start the laser lithography equipment to process grooves on the front side of the tuning fork plate, and repeat the following frequency closed-loop control steps at a set sampling interval during the processing until the first processing termination condition is reached: S31. Pause photolithography and measure the current resonant frequency f of the tuning fork plate in real time using the online frequency monitoring unit. current ; S32. Calculate the current frequency deviation Δf current =f target -f current ; S33, If |Δf current If the frequency is less than the preset frequency tolerance threshold ε, then the front-side photolithography is terminated; otherwise, according to Δf current With a frequency-lithography depth mapping model, the depth or length of subsequent lithography paths is adjusted in real time, and lithography continues; This is the most core and creative step of the invention. It breaks with the conventional "one-step" approach of laser processing and innovatively introduces a cyclical iterative logic of "processing-measurement-decision-reprocessing". This closed-loop control mechanism can effectively compensate for all random interference factors such as heat accumulation effect and nonlinearity of material removal rate during laser processing, ensuring that the processing endpoint accurately falls on the target frequency point; Step 4: Precise alignment and collaborative photolithography on the reverse side: After the front lithography is completed, the tuning fork plate is flipped over. A high-resolution visual positioning system is used to identify the reference feature points on the back side, calculate and compensate for the positional deviation introduced by the flipping operation. Based on the compensated coordinate system, a second set of parameters that is the same as or proportional to the first set of adaptive lithography parameters is used to plan the lithography path of the groove on the back side and perform lithography, so as to achieve the alignment of the grooves on the front and back sides and the coordinated control of the frequency characteristics. Since the closed-loop machining on the front side has already adjusted the frequency to near the target value, the machining on the back side is mainly to maintain the symmetry of the structure in order to suppress stray modes and reduce ESR. Therefore, the machining parameters on the back side directly reference or refer to the final results of the front side, which can ensure both symmetry and frequency stability.
[0020] In some embodiments, step one, the surface cleaning and activation pretreatment step, includes: The surface is cleaned sequentially using ultrasonic cleaning at 40-100kHz (to remove surface oil, large particles and dust), oxygen plasma cleaning at 80-150W and vacuum degree 0.5-1.0Pa (to remove surface organic contaminants and oxide layer, improve surface hydrophilicity, and lay the foundation for subsequent photolithography positioning and processing quality), and baking and drying at 60-80℃.
[0021] In some embodiments, in step one, the processing platform with online frequency monitoring function includes a vacuum adsorption stage. The vacuum adsorption stage integrates excitation electrodes and pickup electrodes for coupling with the tuning fork plate electrode area in a non-contact or probe-contact manner to achieve in-situ frequency testing. This structural design combines the processing platform and the testing platform into one, which is the key hardware foundation for implementing the method of the present invention.
[0022] In some implementations, in step two, the frequency-lithography depth mapping model is established through prior experiments. It describes the frequency change caused by a unit lithography depth or a unit lithography length under a specific frequency band and packaging specification, and is stored in the database of the control system.
[0023] In some implementations, in step three, a corresponding high-resolution visual positioning system is selected based on the tuning fork plate's frequency band and packaging specifications. The terahertz band / micro-package (0402 / 0603) uses coaxial vision and is paired with a 20-50 megapixel camera to meet the high-precision imaging requirements of microstructures. The megahertz band / standard package (1610 / 2016) uses pseudo-coaxial vision and is paired with a 10-30 megapixel camera to optimize costs while ensuring imaging accuracy. The kilohertz band / large package (3215 / 4025) uses a rangefinder vision system and is equipped with a 5-20 megapixel camera to meet the wide field-of-view imaging needs of large workpieces.
[0024] In some implementations, in step three, the first processing termination condition is: |Δf current |≤ε, where ε ranges from 10 to 100 ppm, thus enabling extremely high-precision frequency consistency control.
[0025] In some implementations, step three, adjusting the depth or length of subsequent photolithography paths in real time, includes the following steps: According to Δf current The sign and absolute value of Δf current If Δf > 0, it indicates that the current frequency is too low and needs to be increased. Therefore, the lithography depth or length should be increased proportionally. currentIf the value is less than 0, it indicates that the current frequency is too high and needs to be reduced. In this case, the photolithography depth or length will be reduced proportionally, or the processing will be terminated and an alarm will be issued to prevent overprocessing from causing scrap.
[0026] In some implementations, in steps three and four, the laser lithography equipment used for lithography is an ultraviolet picosecond or femtosecond laser to reduce the heat-affected zone, and an inert protective gas is introduced during the lithography process to prevent material oxidation.
[0027] In some embodiments, step five is included after step four: ultrasonic-assisted chemical etching to remove residues, specifically: The tuning fork plate is placed in a fluorine-containing etching solution. Under the combined action of an ultrasonic field of 60-150kHz and mechanical stirring at 30-150r / min, the residual powder in the groove is selectively removed. The etching time is 10-90s.
[0028] In some specific implementations, the concentration of the etching solution is selected based on the frequency band of the tuning fork plate: For the kilohertz frequency band, an etching solution with a volume fraction of 8-12% is selected; For the megahertz frequency band, an etching solution with a volume fraction of 5-9% is selected; For the terahertz frequency band, an etching solution with a volume fraction of 2-6% is selected; The ultrasonic corrosion process parameters are: corrosion temperature 15-35℃, ultrasonic power 30-120W; The corrosive solution is a fluoroboric acid solution, an ammonium fluoride-ammonium bifluoride buffer solution, or an organic acid complex fluoride solution. Its toxicity LD50 is... 50 >500mg / kg; or, the corrosive solution is a diluted hydrofluoric acid solution or a fluorine-containing composite corrosive solution.
[0029] In some implementations, after step five, a sixth step is included: multi-stage cleaning, drying, and final testing, specifically: Remove the ultrasonically etched tuning fork plates and place them in a container with a resistivity ≥18MΩ. Clean with 60-100kHz ultrasonic waves for 5-10 minutes in ultrapure water. Then place it in a 2-6% concentration of dilute hydrochloric acid solution, dilute sulfuric acid solution, or sodium bicarbonate solution, and allow it to neutralize for 5-25 seconds. Rinse again with ultrapure water 2-3 times, 3-5 minutes each time, to ensure that there are no chemical residues on the surface; Use 0.3-0.5 MPa nitrogen gas to dry the surface moisture of the tuning fork plate; Place in an oven at 70-90℃ and bake for 20-30 minutes until thoroughly dried to obtain a clean tuning fork plate. The dimensional accuracy and surface roughness of the groove are detected by laser confocal microscopy or atomic force microscopy. The surface roughness Ra is required to be ≤0.2μm and the size is within the broad generalization range of the corresponding frequency band. The resonance performance was tested using frequency band-adaptive testing equipment: kilohertz band ESR≤80Ω, oscillation start-up time≤1.2ms; megahertz band ESR≤50Ω, oscillation start-up time≤0.8ms; terahertz band ESR≤40Ω, oscillation start-up time≤0.5ms; frequency drift≤1ppm; Defective products are removed, and qualified products proceed to the next process.
[0030] Example 1
[0031] A method for manufacturing tuning fork plates, specifically for tuning fork plates in the 32.768 kHz kilohertz frequency band, includes the following steps: Step 1: Pre-processing and initial clamping: Tuning fork substrates with a 3215 package specification were selected and subjected to surface cleaning and activation pretreatment, specifically: ultrasonic cleaning at 50kHz for 10 minutes (to remove surface oil, large particles and dust), oxygen plasma cleaning at 100W and 0.5Pa vacuum for 5 minutes (to remove surface organic contaminants and oxide layer, improve surface hydrophilicity, and lay the foundation for subsequent photolithography positioning and processing quality), and baking and drying at 80℃ for 15 minutes. The pre-treated tuning fork plate is clamped onto a processing platform (model VSP-600) with online frequency monitoring capabilities. The platform's vacuum adsorption stage integrates excitation and pickup electrodes. The frequency test probe is coupled to the tuning fork plate's electrode area via contact, enabling in-situ frequency testing. The processing platform's vacuum adsorption pressure is 0.4 MPa, and combined with a three-point mechanical positioning structure, ensures stable clamping of the tuning fork plate without loosening, with a positioning reference repeatability better than ±0.2 μm. Step 2: Determination of reference frequency and generation of initial photolithography parameters: The online frequency monitoring unit of the processing platform applies an excitation signal to the tuning fork plate and collects its response signal to determine the initial resonant frequency f0 = 32.760 kHz of the tuning fork plate in its unprocessed state. This is achieved by measuring the frequency through a frequency test probe contacting the electrodes of the tuning fork plate. The target resonant frequency f0 is also measured. target The frequency is 32.768 kHz, and the difference between it and the initial resonant frequency f0 is Δf = +8 Hz; Based on the frequency-lithography depth mapping model established in advance through a large number of calibration experiments, for a tuning fork chip with a 32.768 kHz kilohertz frequency band and a 3215 package specification, the frequency change caused by a unit lithography depth (per 1 μm) is approximately +6.67 Hz / μm within the commonly used processing range. To compensate for the +8Hz frequency deviation, the required increase in lithography depth correction is calculated as follows: 8Hz / 6.67Hz / μm ≈ 1.2μm; Based on the generalized groove size parameter range of this frequency band and packaging specifications, the initial photolithography parameters are set as follows: groove edge distance d = 32μm, width w = 15μm, reference depth h0 = 4.0μm. After adding the correction amount, the target depth h target =4.0+1.2=5.2μm; groove length L=80μm (80% of the effective length of the fork arm 100μm); length-to-width ratio is approximately 5.3:1, depth-to-width ratio is approximately 0.35:1, both of which are within the generalization scope defined by the claims; Step 3: Front-side adaptive laser lithography and frequency closed-loop control: Based on the frequency band (kilohertz) and packaging specifications (3215 large size) of the tuning fork plate, a rangefinder vision positioning system was selected, paired with a 12-megapixel CCD camera with a frame rate of 60fps, to meet the wide field of view imaging requirements of large-sized workpieces. The rangefinder vision positioning system identifies the edges and endpoints of the tuning fork forks as reference feature points, and performs the following sub-pixel level recognition and distortion correction steps: 1) The Canny edge detection algorithm is used to extract sub-pixel level edge point sets. By performing quadratic polynomial fitting along the gradient direction, the edge positioning accuracy is improved to 0.1 pixels. 2) The least squares method is used to fit a straight line to the edge point set of the fork arm, and the fitting residual is controlled within 0.05 pixels to obtain high-precision reference feature coordinates; 3) The Zhang calibration method is introduced to perform global correction of camera lens distortion. A machining coordinate system is established with the intersection of the center lines of the two forks as the origin, the length direction of the forks as the X-axis, and the vertical direction as the Y-axis, ultimately achieving a comprehensive positioning accuracy of ±0.5μm. The ultraviolet picosecond laser (wavelength 355nm, pulse energy 8μJ, repetition rate 80kHz) was activated, and front-side groove lithography began along the planned path at a scanning speed of 200mm / s. Nitrogen gas at a flow rate of 8L / min was introduced as a protective gas during the lithography process to prevent surface oxidation of the processed area. The groove shape was set as a rectangular groove. During the processing, the system is set to pause photolithography once after removing approximately 1.0 μm of depth, and then execute a frequency closed-loop control step. The specific process is as follows: First pause (processed depth approximately 1.0 μm): The current resonant frequency f of the tuning fork is measured in real time using an online frequency monitoring unit. current =32.762kHz (32762Hz); Calculate the current frequency deviation Δf current =ftarget -f current =32768-32762=+6Hz,|Δf current |>ε (ε=1Hz, approximately equivalent to 30ppm), termination condition not met. According to the mapping model, the remaining deviation of 6Hz corresponds to a depth of approximately 0.9μm, so processing continues; Second pause (processed depth approximately 2.0 μm): Determine f current =32.764kHz (32764Hz); Calculate Δf current =32768-32764=+4Hz; the remaining deviation of 4Hz corresponds to a depth of approximately 0.6μm, continue processing; Third pause (processed depth approximately 3.0 μm): Determine f current =32.7658kHz (32765.8 Hz); Calculate Δf current =32768-32765.8=+2.2Hz; The remaining deviation of 2.2Hz corresponds to a depth of approximately 0.33μm, continue processing; Fourth pause (processed depth approximately 3.8μm): Determine f current =32.7673kHz (32767.3Hz); Calculate Δf current =32768-32767.3=+0.7Hz; The remaining deviation of 0.7Hz corresponds to a depth of approximately 0.1μm, continue processing; Fifth pause (processed depth approximately 4.2μm): Determine f current =32.7682kHz (32768.2Hz); Calculate Δf current =f target -f current =32768-32768.2=-0.2Hz; at this time |Δf current |=0.2Hz, this deviation is equivalent to 6.1ppm (0.2 / 32768×1000000≈6.1ppm), which is less than the preset frequency tolerance threshold ε. Therefore, the first processing termination condition is met, and the front-side photolithography is automatically terminated. The final actual machining depth on the front side is approximately 4.2 μm. Due to the real-time correction effect of the closed-loop control, there is a difference between the actual machining depth and the theoretical calculated value (5.2 μm), which reflects the adaptive compensation capability of closed-loop control for material properties and process disturbances. Step 4: Precise alignment and collaborative photolithography on the reverse side: After the front photolithography is completed, an automated robotic arm flips the tuning fork plate over and re-fixes it to the processing platform; The high-resolution visual positioning system is restarted to identify three sets of cross alignment marks on the reverse side of the tuning fork plate as reference feature points. These reverse reference point coordinates are then compared point-to-point with the corresponding reference point coordinate data stored during the front-side photolithography process to automatically calculate the positional deviation introduced during the flipping process. Translational deviation calculation: Let the coordinates of a reference point on the front be (x1, y1), and the coordinates of the corresponding reference point after flipping be (x2, y2). We measure Δx = x2 - x1 = 0.15 μm and Δy = y2 - y1 = 0.12 μm. Rotational deviation calculation: Select two reference points, calculate the angle θ1=0.00° between the two points on the front side, and the angle θ2=0.08° between the two points after flipping. The rotational deviation Δθ=θ2-θ1=0.08° is then measured. Based on the calculated deviation value, the lithography machine stage is dynamically compensated in real time. Translation compensation: Control the machining platform to move -0.15μm along the X-axis and -0.12μm along the Y-axis to compensate for positional offset; Rotational compensation: The machining platform's built-in rotation mechanism rotates in the opposite direction by -0.08° to correct angular deviations; The overall alignment accuracy after compensation is controlled within ±0.15 μm; Based on the compensated coordinate system, the final lithography parameters of the front groove (depth 4.2μm, edge distance 32μm, width 15μm, length 80μm) are read. Combined with the deviation compensation parameters, the path is transformed (translation and rotation correction) to generate the lithography path of the back groove composed of continuous straight line segments. This adapts to the scanning motion mode of the lithography machine and ensures that the front and back grooves are accurately aligned. The same ultraviolet picosecond laser was used to complete the reverse side groove lithography according to the above parameters. Nitrogen gas protection was also introduced during the lithography process. The final alignment deviation of the front and back grooves was controlled within ±0.3μm, which is far better than the ±2μm level of traditional processes; Step 5: Ultrasonic-assisted chemical etching to remove residues, specifically: The tuning fork plate was placed in an 8% (v / v) fluoroboric acid solution. Under the combined action of a 60kHz ultrasonic field and 100r / min mechanical stirring, the residual powder in the groove was selectively removed. The etching time was 50s, the etching temperature was 25℃, and the ultrasonic power was 80W. The corrosive solution is an ammonium fluoride-ammonium bifluoride buffer solution or an organic acid complex fluoride solution; toxicity LD50. 50 >500mg / kg; or, the corrosive solution is a diluted hydrofluoric acid solution or a fluorine-containing composite corrosive solution; Step Six: Multi-stage cleaning, drying, and final testing, specifically as follows: Remove the ultrasonically etched tuning fork plate and place it in a 18 MΩ resistivity diaphragm. Cleaned for 5 minutes with 100kHz ultrasonic waves in cm of ultrapure water; Then place it in a 4% dilute hydrochloric acid solution and allow it to neutralize for 15 seconds. Rinse twice more with ultrapure water, 5 minutes each time, to ensure that there are no chemical residues on the surface; Use 0.3 MPa nitrogen gas to dry the surface moisture of the tuning fork plate; Place in a 70℃ oven and bake for 30 minutes to dry completely to obtain a clean tuning fork plate. The dimensional accuracy and surface roughness of the groove are detected by laser confocal microscopy or atomic force microscopy. The surface roughness Ra is required to be 0.08 μm and the size is within the broad generalization range of the corresponding frequency band. The resonant performance was tested using frequency band-adapted testing equipment: ESR 52Ω in the kilohertz band, oscillation start-up time 0.7ms; frequency drift 0.8ppm; Defective products are removed, and qualified products proceed to the next process.
[0032] The frequency consistency of the tuning fork plates processed in this batch is better than ±15ppm, and the alignment deviation of the grooves on the front and back is within ±0.3μm, with a product qualification rate of 97.5%. Since the closed-loop control has precisely controlled the frequency near the target value, this batch of products does not need to undergo a subsequent frequency fine-tuning process and can directly enter the electrode preparation stage.
[0033] Example 2
[0034] A method for processing tuning fork plates, specifically for tuning fork plates in the 26MHz band and packaged in 2016, includes the following steps: Step 1: Pre-processing and initial clamping: The tuning fork substrate of the 3215 package was selected and subjected to surface cleaning and activation pretreatment, specifically: ultrasonic cleaning at 50kHz for 10min (to remove surface oil, large particles and dust), oxygen plasma cleaning at 100W and 0.5Pa vacuum for 5min (to remove surface organic contaminants and oxide layer, improve surface hydrophilicity, and lay the foundation for subsequent photolithography positioning and processing quality), and baking and drying at 80℃ for 15min. The pre-treated tuning fork plate is clamped onto a processing platform with online frequency monitoring function; Step 2: Determination of reference frequency and generation of initial photolithography parameters: The online frequency monitoring unit of the processing platform applies an excitation signal to the tuning fork plate and collects its response signal to determine the initial resonant frequency f0 = 25.996850MHz of the tuning fork plate in its unprocessed state. This is achieved by measuring the frequency through a frequency test probe contacting the electrodes of the tuning fork plate. The target resonant frequency f0 is also measured. target The frequency is 26.000000MHz, and the difference between it and the initial resonant frequency f0 is Δf = +3150Hz. According to the preset frequency-lithography depth mapping model (established through prior experiments, under this frequency band and packaging conditions, the resonant frequency increases by approximately 420Hz for every 1μm increase in lithography depth), the frequency needs to be increased, and the corresponding lithography depth needs to be increased by approximately 3150 / 420 = 7.5μm. Based on the generalized groove parameter range of this frequency band, the initial photolithography parameters are set as follows: edge distance d = 18μm, width w = 10μm, reference depth 3.5μm. After adding the correction amount, the target depth is 3.5 + 7.5 = 11μm, and the length L is 70% of the effective length of the fork arm. Step 3: Front-side adaptive laser lithography and frequency closed-loop control: A pseudo-coaxial vision positioning system was selected, paired with a 20-megapixel CMOS camera, to identify the reference feature points on the edge of the tuning fork fork. A processing coordinate system was established through sub-pixel edge extraction and distortion correction algorithms, achieving a positioning accuracy of ±0.5μm. The ultraviolet picosecond laser (wavelength 355nm, pulse energy 4μJ, repetition frequency 180kHz) was activated to begin front-side groove photolithography at a scanning speed of 300mm / s, while nitrogen gas with a flow rate of 10L / min was introduced as a protective gas. During processing, the system is set to pause once after removing approximately 1.5 μm of depth, and then perform closed-loop frequency control. First pause (processed depth approximately 1.5μm): Online measurement of the current resonant frequency f. current =25.997520MHz, deviation Δf current =26.000000-25.997520=+2480Hz, |Δf current |>20ppm (approximately 520Hz), continue processing and fine-tune the number of scans for subsequent paths based on the remaining deviation; Second pause (processed depth approximately 3.0 μm): f current =25.998150MHz, Δf current =+1850Hz; Third pause (processed depth approximately 4.5μm): f current =25.998820MHz, Δf current =+1180Hz; Fourth pause (processed depth approximately 6.0 μm): f current=25.999460MHz, Δf current =+540Hz; Fifth pause (processed depth approximately 7.5μm): f current =25.999910MHz, Δf current =+90Hz. At this point, the deviation has entered the preset frequency tolerance threshold ε, and the system determines that the first processing termination condition has been met, automatically terminating the front-side photolithography. The final actual machining depth on the front side is approximately 7.6 μm; Step 4: Precise alignment and collaborative photolithography on the reverse side: The tuning fork plates are flipped over and re-vacuum-adhesive fixed. The vision system identifies the corresponding reference feature points on the reverse side and calculates the translational deviation (Δx, Δy) = (-0.12μm, 0.09μm) and rotational deviation Δθ = -0.06°. The control system drives the worktable to perform reverse compensation, with a compensation accuracy of ±0.1μm. Based on the compensated coordinate system, the reverse side uses the same final lithography parameters as the front side (depth 7.6μm, edge distance 18μm, width 10μm) to plan the path and perform lithography, ensuring the symmetry of the front and back structures and suppressing stray modes. The final alignment deviation of the grooves on the front and back sides is controlled within ±0.2μm. Step 5: Ultrasonic-assisted chemical etching to remove residues, specifically: The tuning fork plate was placed in a 9% (v / v) fluoroboric acid solution. Under the combined action of a 150 kHz ultrasonic field and a 150 r / min mechanical stirring, the residual powder in the groove was selectively removed. The etching time was 10 s, the etching temperature was 35 ℃, and the ultrasonic power was 30 W. Step Six: Multi-stage cleaning, drying, and final testing, specifically as follows: Remove the ultrasonically etched tuning fork plate and place it in a 18 MΩ resistivity diaphragm. Cleaned for 5 minutes with 100kHz ultrasonic waves in cm of ultrapure water; Then place it in a 2% dilute hydrochloric acid solution and allow it to neutralize for 25 seconds. Rinse three more times with ultrapure water for three minutes each time to ensure that there are no chemical residues on the surface; Use 0.3 MPa nitrogen gas to dry the surface moisture of the tuning fork plate; Place in a 70℃ oven and bake for 30 minutes to dry completely to obtain a clean tuning fork plate. The dimensional accuracy and surface roughness of the groove are detected by laser confocal microscopy or atomic force microscopy. The surface roughness Ra is required to be 0.06 μm and the size is within the broad generalization range of the corresponding frequency band. The resonance performance was tested using frequency band-adapted testing equipment: ESR of 38Ω and oscillation start-up time of 0.4ms in the megahertz band; frequency drift of 0.8ppm. Defective products are removed, and qualified products proceed to the next process.
[0035] Comparative Example 1 The difference between this comparative example and Example 1 is that this comparative example uses a tuning fork plate of the same specification processed by traditional fixed-parameter open-loop machining. Under the same initial frequency deviation (+8Hz) condition, after machining at a fixed depth of 5.0μm, the final frequency distribution is in the range of 32.766kHz to 32.773kHz, with a frequency dispersion of more than ±100ppm. All of them need to enter the frequency fine-tuning process, and the alignment deviation of the grooves on the front and back is usually more than ±2μm. The average ESR is 68Ω.
[0036] This embodiment fully demonstrates the significant advantages of the adaptive closed-loop machining method based on online frequency feedback in terms of frequency consistency control, improved machining accuracy, and simplified processes.
[0037] Any parts or structures not specifically described in this invention can be made using existing technologies or products, and will not be elaborated upon here.
[0038] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.
Claims
1. A method for processing tuning fork plates, characterized in that, Includes the following steps: Step 1: Pre-processing and initial clamping: Select a tuning fork plate substrate and perform surface cleaning and activation pretreatment on it; then clamp the pretreated tuning fork plate onto a processing platform with online frequency monitoring function. Step 2: Determination of reference frequency and generation of initial photolithography parameters: The online frequency monitoring unit of the processing platform applies an excitation signal to the tuning fork and collects its response signal to determine the initial resonant frequency f0 of the tuning fork in its unprocessed state; based on the target resonant frequency f0... target The difference Δf between the initial resonant frequency f0 and the preset frequency-lithography depth mapping model are used to calculate and generate the first set of adaptive lithography parameters for front-side processing. Step 3: Front-side adaptive laser lithography and frequency closed-loop control: A processing coordinate system is established using a high-resolution vision positioning system, and the lithography path for the front groove is planned based on the first set of adaptive lithography parameters. The laser lithography equipment is started to process the groove on the front of the tuning fork sheet, and during the processing, the following frequency closed-loop control steps are repeatedly executed at a set sampling interval until the first processing termination condition is reached: S31. Pause photolithography and measure the current resonant frequency f of the tuning fork plate in real time using the online frequency monitoring unit. current ; S32. Calculate the current frequency deviation Δf current =f target -f current ; S33, If |Δf current If the frequency is less than the preset frequency tolerance threshold ε, the front-side photolithography will be terminated. Otherwise, according to Δf current With a frequency-lithography depth mapping model, the depth or length of subsequent lithography paths is adjusted in real time, and lithography continues; Step 4: Precise alignment and collaborative photolithography on the reverse side: After the front lithography is completed, the tuning fork is flipped over. A high-resolution visual positioning system is used to identify the reference feature points on the back side, and the positional deviation introduced by the flipping operation is calculated and compensated. Based on the compensated coordinate system, a second set of parameters that is the same as or proportional to the first set of adaptive lithography parameters is used to plan the lithography path of the back groove and perform lithography, so as to achieve the alignment of the front and back grooves and the coordinated control of frequency characteristics.
2. The method for processing a tuning fork plate according to claim 1, characterized in that, Step one, the surface cleaning and activation pretreatment steps include: The process involves sequential ultrasonic cleaning at 40-100kHz, oxygen plasma cleaning at 80-150W, and baking and drying at 60-80℃.
3. The method for processing a tuning fork plate according to claim 1, characterized in that, In step one, the processing platform with online frequency monitoring function includes a vacuum adsorption stage. The vacuum adsorption stage integrates an excitation electrode and a pickup electrode, which are used to couple with the tuning fork plate electrode area in a non-contact or probe contact manner to realize in-situ frequency testing.
4. The method for processing a tuning fork plate according to claim 1, characterized in that, In step two, the frequency-lithography depth mapping model is established through prior experiments. It describes the frequency change caused by a unit lithography depth or a unit lithography length under a specific frequency band and packaging specification, and is stored in the database of the control system.
5. A method for processing a tuning fork plate according to claim 1, characterized in that, In step three, the first processing termination condition is: |Δf current |≤ε, where ε takes the value of 10-100ppm.
6. The method for processing a tuning fork plate according to claim 1, characterized in that, Step three, adjusting the depth or length of subsequent photolithography paths in real time, includes the following steps: According to Δf current The sign and absolute value of Δf current If Δf > 0, then the photolithography depth or length is increased proportionally. current If the value is less than 0, the photolithography depth or length will be reduced proportionally, or the processing will be terminated and an alarm will be issued.
7. A method for processing a tuning fork plate according to claim 1, characterized in that, In steps three and four, the laser lithography equipment used is an ultraviolet picosecond or femtosecond laser, and an inert protective gas is introduced during the lithography process.
8. A method for processing a tuning fork plate according to any one of claims 1-7, characterized in that, Step four is followed by step five: ultrasonic-assisted chemical etching to remove residues, specifically: The tuning fork plate is placed in a fluorine-containing etching solution. Under the combined action of an ultrasonic field of 60-150kHz and mechanical stirring at 30-150r / min, the residual powder in the groove is selectively removed. The etching time is 10-90s.
9. A method for processing a tuning fork plate according to claim 8, characterized in that, Select the concentration of the etching solution based on the frequency band of the tuning fork plate: For the kilohertz frequency band, an etching solution with a volume fraction of 8-12% is selected; For the megahertz frequency band, an etching solution with a volume fraction of 5-9% is selected; For the terahertz frequency band, an etching solution with a volume fraction of 2-6% is selected; The ultrasonic corrosion process parameters are: corrosion temperature 15-35℃, ultrasonic power 30-120W; The corrosive solution is a fluoroboric acid solution, an ammonium fluoride-ammonium hydrogen fluoride buffer solution, or an organic acid complex fluoride solution, with a toxicity LD50. 50 >500mg / kg; or, The etching solution is a diluted hydrofluoric acid solution or a fluorine-containing composite etching solution.
10. A method for processing a tuning fork plate according to claim 8, characterized in that, Following step five, there is also step six: multi-stage cleaning, drying, and final testing, which specifically includes: Remove the ultrasonically etched tuning fork plates and place them in a container with a resistivity ≥18MΩ. Clean with 60-100kHz ultrasonic waves for 5-10 minutes in ultrapure water. Then place it in a 2-6% concentration of dilute hydrochloric acid solution, dilute sulfuric acid solution, or sodium bicarbonate solution, and allow it to neutralize for 5-25 seconds. Rinse again with ultrapure water 2-3 times, 3-5 minutes each time, to ensure that there are no chemical residues on the surface; Use 0.3-0.5 MPa nitrogen gas to dry the surface moisture of the tuning fork plate; Place in an oven at 70-90℃ and bake for 20-30 minutes until thoroughly dried to obtain a clean tuning fork plate. The dimensional accuracy and surface roughness of the groove are detected by laser confocal microscopy or atomic force microscopy. The surface roughness Ra is required to be ≤0.2μm and the size is within the broad generalization range of the corresponding frequency band. The resonant performance was tested using frequency band-adaptive testing equipment: kilohertz band ESR≤80Ω, oscillation start-up time≤1.2ms; megahertz band ESR≤50Ω, oscillation start-up time≤0.8ms; terahertz band ESR≤40Ω, oscillation start-up time≤0.5ms; frequency drift≤1ppm; Defective products are removed, and qualified products proceed to the next process.