Laser frequency modulation method of crystal oscillator

Abstract

The invention discloses a laser frequency modulation method for a crystal oscillator, and the method comprises the following steps: 101) determining the position and volume of a region where materials need to be removed according to the frequency deviation value of the crystal oscillator; 102) performing laser treatment on the composite frequency modulation region at the top end of the crystal oscillator tuning fork arm by using ultrafast laser, and removing a coating material and / or a quartz matrix material according to the region position and volume determined in the step 101 to adjust the frequency; 103) the composite frequency modulation area comprises at least one frequency modulation unit, and the frequency modulation unit comprises a frequency modulation function structure formed by at least one laser ablation point according to a set diagram.The frequency modulation efficiency is high, the frequency concentration after frequency modulation is good, and the frequency precision is high.

Description

Technical Field

[0001] This invention relates to the field of crystal oscillator manufacturing, and more particularly to a laser frequency modulation method for crystal oscillators. Background Technology

[0002] With the rapid development of the microelectronics industry, the demand for crystal oscillators is constantly increasing, especially for low-frequency kHz crystal oscillators. A mere 10nW of excitation power is sufficient to start them. Compared to traditional MHz crystals, kHz crystal oscillators operate with less than 100 times the power, significantly reducing power consumption in circuits. Electronic products requiring extended standby time but also needing to enter a sleep state when not in use, such as electronic door locks, smart remote controls, mobile phones, and computers, rely heavily on low-frequency crystal oscillators. These oscillators allow the device to transmit signals to the RTC (Real-Time Clock) module within the MCU (Microcontroller Unit) through low-frequency oscillations, enabling it to continue timing and wake up other functions. Therefore, the requirements for low frequencies are more stringent, leading to the technological breakthrough of precision frequency modulation.

[0003] The traditional method of frequency modulation is to spray silver powder onto the bottom of the wafer to change the crystal frequency. However, this method is difficult to control precisely, and it is easy to overspray or underspray. This process also causes a lot of pollution to the surrounding photomasks during production, making it difficult to obtain a large number of crystal oscillators with frequencies in the 32.768kHz range. The low production yield leads to a surge in costs, which inevitably prevents its use in a wider market.

[0004] Application number CN201610784196.7 discloses a laser-based crystal oscillator frequency modulation processing device and method. It includes a worktable and a monitoring device, a control system, an adsorption positioning device, a laser generating system, a driving device, and a dust extraction device mounted on the worktable. The monitoring device, laser generating system, driving device, and dust extraction device are electrically connected to the control system. The output end of the driving device is connected to the adsorption positioning device. The laser in the laser generating system outputs a laser with a center wavelength of 532 nm, a pulse width range of 1-2 ns, and a spot diameter of 3.5 mm. The volume of the product to be processed ranges from 0.47*0.13*0.07 to 0.53*0.19*0.13 mm. 3 This invention is suitable for processing small-sized crystal oscillator products. It limits the parameters of the laser output in the laser generation system, using a laser wavelength of 532nm, which is easily absorbed by the silver layer, causing the material to vaporize instantly. This reduces the heat-affected zone and burrs generated at the edges, thus ensuring product precision and consistency.

[0005] However, this invention has the following drawbacks: 1) Using a 532nm wavelength laser (pulse width 1-2ns) is suitable for absorption by the silver layer, but it has a significant thermal impact on the quartz matrix material, which can easily cause thermal burning and affect the stability of the crystal oscillator.

[0006] 2) The spot diameter is fixed at 3.5mm, which limits the processing accuracy and makes it difficult to meet the high-precision frequency tuning requirements of small-sized crystal oscillators (such as 3215 and 1610).

[0007] 3) Frequency tuning using laser evaporation coating alone cannot flexibly address the fine adjustments required for different frequency deviations.

[0008] 4) It is only applicable to crystal oscillators with a volume of 0.47-0.53mm³, and cannot cover the high-yield production needs of smaller sizes (such as 1210) or low-frequency crystal oscillators (such as 32.768KHz). Summary of the Invention

[0009] The technical problem to be solved by the present invention is to provide a laser frequency modulation method for a crystal oscillator with high frequency modulation accuracy and efficiency.

[0010] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is a laser frequency modulation method for a crystal oscillator, comprising the following steps: 101) Determine the location and volume of the area where material needs to be removed based on the frequency deviation of the crystal oscillator; 102) Use an ultrafast laser to perform laser treatment on the composite frequency tuning region at the top of the crystal oscillator tuning fork arm, and remove the coating material and / or quartz substrate material according to the region position and volume determined in step 101 to adjust the frequency. 103) The composite frequency modulation zone includes at least one frequency modulation unit, and the frequency modulation unit includes a frequency modulation functional structure formed by at least one laser ablation point according to a set diagram.

[0011] The laser frequency modulation method for crystal oscillators described above includes the following steps: 201) In step 101, based on the frequency deviation value of the crystal oscillator, the software system automatically retrieves the data of the corresponding composite frequency modulation zone. The data of the composite frequency modulation zone includes the parameters of the composite frequency modulation zone, which include geometric feature parameters and material removal parameters. 202) The position of the composite frequency modulation zone is adjusted according to the frequency deviation value. The larger the absolute value of the frequency deviation value, the closer the composite frequency modulation zone is to the top of the tuning fork arm.

[0012] The laser frequency modulation method for crystal oscillators described above includes a frequency modulation unit with a shape that is rectangular, square, circular, triangular, or elliptical. The frequency modulation function structure of the frequency modulation unit is a through hole or a blind hole.

[0013] The laser frequency modulation method for crystal oscillators described above includes geometric characteristic parameters such as frequency modulation unit-level parameters and composite frequency modulation zone-level parameters. The frequency modulation unit-level parameters include unit shape, unit size, and unit spacing; the composite frequency modulation zone-level parameters include zone arrangement pattern, total zone area, and zone location.

[0014] The laser frequency modulation method for crystal oscillators described above includes material removal parameters such as the type of material to be removed, the volume of material to be removed, and the material removal rate.

[0015] The laser frequency modulation method for crystal oscillators described above, wherein the composite frequency modulation region is composed of a plurality of frequency modulation units.

[0016] The laser frequency modulation method for the crystal oscillator described above uses a 355nm ultrafast ultraviolet picosecond laser.

[0017] In the laser frequency modulation method for crystal oscillators described above, before laser processing of the composite frequency modulation area at the top of the tuning fork arms using an ultrafast laser in step 102, the position coordinates of the left and right arms of the tuning fork are located using a visual capture system; the frequencies of the left and right arms are measured in real time using a frequency testing system, and the deviation value is calculated; differentiated frequency modulation unit parameters and laser processing parameters are generated based on the deviation value, wherein the unit density on the high deviation side is greater than that on the low deviation side; the composite frequency modulation area is processed using an ultraviolet picosecond laser according to a planned path; after each frequency test, laser frequency modulation is performed once until the frequency is adjusted to the specified value.

[0018] The laser frequency modulation method for the crystal oscillator described above adjusts the frequency deviation value of the crystal oscillator to a negative value before step 101.

[0019] The laser frequency modulation method using a crystal oscillator employed in this invention has high frequency modulation efficiency, good frequency concentration after modulation, and high frequency accuracy. Attached Figure Description

[0020] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0021] Figure 1 This is a schematic diagram of four composite frequency modulation zones according to embodiments of the present invention.

[0022] Figure 2 This is a schematic diagram of four composite frequency modulation zones according to embodiments of the present invention.

[0023] Figure 3 This is a schematic diagram of four composite frequency modulation zones according to embodiments of the present invention.

[0024] Figure 4 This is a schematic diagram of four composite frequency modulation zones according to embodiments of the present invention.

[0025] Figure 5 This is a schematic diagram of four composite frequency modulation zones according to embodiments of the present invention.

[0026] Figure 6 This is a schematic diagram of five composite frequency modulation zones according to embodiments of the present invention.

[0027] Figure 7 This is a schematic diagram of four composite frequency modulation zones according to embodiments of the present invention.

[0028] Figure 8 This is a schematic diagram of five composite frequency modulation zones according to embodiments of the present invention.

[0029] Figure 9 This is a schematic diagram of five composite frequency modulation zones according to embodiments of the present invention.

[0030] Figure 10 This is a schematic diagram of two composite frequency modulation zones according to an embodiment of the present invention. Detailed Implementation

[0031] This invention employs ultrafast laser to remove material from the tip of the tuning fork arm of a crystal oscillator to increase its frequency, achieving laser frequency modulation. The standard frequency of a 3215 crystal oscillator is 32.768 kHz, with 1 Hz equal to 30.5 PPM. Before modulation, the frequency deviation is adjusted to a negative value, such as -20,000 PPM, which is 32.112 kHz. Due to errors in wafer cutting, etching, and coating processes, the frequency is not concentrated, requiring material removal to raise the frequency to zero PPM. This removed material includes the coating material and / or the quartz substrate material. Traditional frequency modulation methods involve grinding the tuning fork arm of the crystal oscillator to increase the frequency. Another traditional method is to first make the frequency deviation of the crystal oscillator positive, and then spray metal onto the tuning fork arm to reduce the frequency. These two traditional methods are suitable for tuning large-size crystal oscillators, but they are no longer applicable for tuning small-size surface-mount crystal oscillators such as 3215, 1610, and 1210. Laser frequency modulation is a suitable method for tuning small-size crystal oscillators. The present invention discloses a frequency modulation method for the laser composite frequency modulation region of a crystal oscillator. The frequency modulation unit patterns in the composite frequency modulation region can be rectangular, square, circular, triangular, or elliptical, etc. Each pattern's laser aperture constitutes a frequency modulation unit, and multiple frequency modulation units (multiple circular laser apertures) form a composite frequency modulation region. The larger the absolute value of the negative PPM of the crystal oscillator frequency deviation, the closer the composite frequency modulation region composed of the frequency modulation units should be to the top of the tuning fork arm. For example, if the same volume of plating area or quartz substrate area is removed near and far from the top of the tuning fork arm, the increase in frequency due to proximity to the top of the tuning fork arm will be greater.

[0032] This invention utilizes a composite frequency modulation zone composed of one or more frequency modulation units for laser frequency modulation, resulting in high modulation efficiency, good frequency concentration after modulation, and high frequency accuracy. The frequency modulation units can have uniform or gradually varying dimensions, providing greater flexibility in the modulation method and resolving over-frequency or under-frequency issues that easily arise during the modulation process.

[0033] This invention increases the frequency of a crystal oscillator tuning fork by removing material from the top of the arms using ultrafast laser. The laser frequency modulation method requires a vision-based imaging system. The vision-based imaging area covers the entire area of ​​both arms of the tuning fork. The system determines the position coordinates of the two arms, extracts their edge contours, calculates the centerline coordinates, establishes a processing coordinate system based on these coordinates, and calibrates the sensitive areas. The processing path is then planned using the centerline coordinates as a reference, and the location of the sensitive area at the top of the tuning fork arm is calibrated. 。 Next, the high-frequency probe of the crystal oscillator frequency testing system contacts the tuning fork arm electrodes to measure the frequencies of the left and right arms respectively, and calculates the deviation value from the target frequency. Based on the frequency deviation values ​​of the left and right arms, the system dynamically generates the frequency modulation unit parameters by calling the pre-stored image files in the image library, and determines the location of the composite frequency modulation zone and the parameter values ​​of the composite frequency modulation zone. Using a Galvo galvanometer and dynamic focusing system, the shortest processing path is planned to perform differentiated frequency modulation processing on the left and right arms using laser. After the differentiated frequency modulation processing of the left and right arms is completed, the frequency is retested within 3 seconds. If it does not meet the target, a second frequency modulation is initiated until the target frequency is reached.

[0034] The parameter system of the composite frequency modulation region is quantitatively defined from the perspective of geometric characteristics and material properties: 1. Geometric characteristic parameters (1) Frequency modulation unit level parameters Unit shapes: circle, square, rectangle, triangle, etc. (specific geometric tolerances need to be defined, such as roundness ≤ 5%).

[0035] Unit size: diameter / side length (e.g., circular unit diameter 10-50μm, square unit side length 20-60μm); depth (blind hole: 5-30μm; through hole: penetrating the substrate).

[0036] Element spacing: the center distance between adjacent elements (e.g., 20-100μm, which affects the linearity of frequency adjustment).

[0037] (2) Composite frequency modulation zone level parameters Regional layout pattern: array type (rectangular array, circular array, gradually spaced array, etc.) and overlap rate (the percentage of overlapping area of ​​partially overlapping units, such as 0%-50%).

[0038] Total area of ​​the region: The area covered by the composite FM zone on the tuning fork arm (e.g., 0.1mm²-0.5mm²).

[0039] Region location: distance from the top of the tuning fork arm (sensitive area: ≤200μm); asymmetrical distribution parameters of the left and right arms (e.g., the area of ​​the left arm region is 10%-30% larger than that of the right arm).

[0040] 2. Material removal parameters Material types removed: coating materials (such as Ag layer thickness 0.1-1μm) and / or quartz substrate (SiO2 removal depth 5-30μm).

[0041] Material removal volume: unit removal volume (e.g., volume of a circular blind hole = π × radius² × depth) and total removal volume of the region (i.e., the sum of all unit removal volumes). The total removal volume of the region is positively correlated with the frequency increase.

[0042] Material removal rate: the volume removed per unit time (mm³ / s), reflecting processing efficiency.

[0043] The crystal oscillator frequency testing system can test the frequency of a crystal oscillator hundreds of times per second. Each time the frequency is tested, it is tuned by laser until the frequency is adjusted to the specified value.

[0044] The vibration frequencies of the left and right arms of a tuning fork may be different, so the tuning values ​​of the left and right arms are different, and therefore the volume and position of the material removed from the left and right arms of the tuning fork are different.

[0045] In the composite frequency modulation zone, the frequency modulation unit that removes material by laser can be combined in various ways, such as rectangular, square, circular, triangular, elliptical or a combination thereof.

[0046] The frequency modulation unit for laser material removal can also be formed by a mixture of rectangular, square, circular, triangular and / or elliptical shapes.

[0047] Among them, the composite frequency modulation zone composed of frequency modulation units can have a variety of transformation forms, and the frequency modulation units in the composite frequency modulation zone can be arranged in the form of circles, rectangles, squares, triangles, or ellipses.

[0048] The frequency modulation units in the composite frequency modulation zone can be a combination of frequency modulation units of different sizes.

[0049] The novel laser frequency-modulated drilling method will be described in further detail below with reference to the accompanying drawings and examples: The standard frequency of the 3215 crystal oscillator is 32.768 kHz, with 1 Hz equal to 30.5 PPM. Before tuning, the frequency deviation of the crystal oscillator is made negative, such as -20,000 PPM, which is 32.112 kHz. Due to errors in processes such as wafer cutting, etching, and coating, the frequency is not concentrated. It is necessary to raise the frequency to zero PPM by removing material from the tips of the left and right arms of the tuning fork. This removed material includes coating material and / or quartz substrate material. If the same volume of coating area or quartz substrate area is removed near and away from the tips of the tuning fork arms, the increase in frequency is greater near the tips of the tuning fork arms. In other words, the crystal oscillator frequency is more sensitive to changes in material near the tips of the tuning fork arms.

[0050] Figures 1-10The shape of the frequency modulation unit can be rectangular, square or circular. The laser aperture of the frequency modulation unit can be a through hole or a blind hole. Multiple frequency modulation units form a large composite frequency modulation zone, which is located near the top of the tuning fork arm.

[0051] Figure 1 China A- Figure 1 The frequency modulation unit of D is rectangular. Figure 1 In section A, multiple rectangular frequency modulation units are arranged to form a large circular composite frequency modulation zone 1. Figure 1 In section B, multiple rectangular frequency modulation units are arranged to form a large square composite frequency modulation zone 2. Figure 1 In section C, multiple rectangular frequency modulation units are arranged to form a large triangular composite frequency modulation zone 3. Figure 1 In section D, multiple rectangular frequency modulation units are arranged to form a large inverted triangular composite frequency modulation zone 4.

[0052] Figure 2 China A- Figure 2 The frequency modulation unit of the middle D is square, in Figure 2 In section A, multiple square frequency modulation units are arranged to form a large circular composite frequency modulation zone 5. Figure 2 In section B, multiple square FM units are arranged to form a large square composite FM zone 6. Figure 2 In section C, multiple square frequency modulation units are arranged to form a large triangular composite frequency modulation zone 7. Figure 2 In section D, multiple square frequency modulation units are arranged to form a large inverted triangular composite frequency modulation zone 8.

[0053] Figure 3 China A- Figure 3 The frequency modulation unit of the middle D is circular. Figure 3 In section A, multiple circular FM units are arranged to form a large circular composite FM zone 9. Figure 3 In section B, multiple circular FM units are arranged to form a large square composite FM zone 10. Figure 3 In section C, multiple circular FM units are arranged to form a large triangular composite FM zone 11. Figure 3 In section D, multiple circular frequency modulation units are arranged to form a large inverted triangular composite frequency modulation zone 12.

[0054] Figure 4 China A- Figure 4 The frequency modulation unit of the middle D is a triangle, in Figure 4 In section A, multiple triangular frequency modulation units are arranged to form a large circular composite frequency modulation zone 13. Figure 4 In section B, multiple triangular frequency modulation units are arranged to form a large square composite frequency modulation zone 14. Figure 4In section C, multiple triangular frequency modulation units are arranged to form a large triangular composite frequency modulation zone 15. Figure 4 In the middle D, multiple triangular frequency modulation units are arranged to form a large inverted triangular composite frequency modulation zone 16.

[0055] Figure 5 China A- Figure 5 The frequency modulation unit of the middle D is elliptical. Figure 5 In section A, multiple elliptical frequency modulation units are arranged to form a large circular composite frequency modulation zone 17. Figure 5 In section B, multiple elliptical frequency modulation units are arranged to form a large square composite frequency modulation zone 18. Figure 5 In section C, multiple elliptical frequency modulation units are arranged to form a large triangular composite frequency modulation zone 19. Figure 5 In the middle D, multiple elliptical frequency modulation units are arranged to form a large inverted triangular composite frequency modulation zone 20.

[0056] Figure 6 China A- Figure 6 The frequency modulation unit of the CM-E is a long rectangular shape, and the width of each rectangular strip can be the same or different. Figure 6 In section A, multiple long rectangular bars of the same size form a square composite frequency modulation zone 21. Figure 6 In section B, multiple rectangular strips of varying sizes form a square composite frequency modulation zone 22. The width of the rectangular strips gradually changes and increases towards the connecting bridge. Figure 6 In section C, multiple long rectangular bars of varying sizes form a square composite frequency modulation zone 23. The width of the long rectangular bars gradually changes and decreases towards the connecting bridge. Figure 6 In section D, multiple rectangular strips of varying sizes form a square composite frequency modulation zone 24. The width of the rectangular strips gradually changes towards both ends, with the middle strip being the widest and the end strips being the narrowest. Figure 6 In the middle E, multiple long rectangles of different sizes form a square composite frequency modulation zone 25. The width of the long rectangles gradually changes towards both ends, that is, the width of the middle long rectangle is the smallest, and the width of the long rectangles at both ends is the largest.

[0057] Figure 7 26. Composite frequency modulation zone of A in the middle Figure 7 27. Composite frequency modulation zone of B in the middle Figure 7 28. Composite frequency modulation range of C. Figure 7 29. Composite frequency modulation zone of D Figure 8 The composite frequency modulation zone 30 of A in the middle Figure 8 31. Composite frequency modulation zone of B in the middle Figure 8 32. Composite frequency modulation range of C Figure 8 33. Composite frequency modulation zone of D Figure 8 34. Composite frequency modulation zone of E in the middle Figure 9 35. Composite frequency modulation zone of A in the middle Figure 9 36. Composite frequency modulation zone of B in the middle Figure 9 37. Composite frequency modulation range of C Figure 9 The composite frequency modulation zone 38 of D and Figure 9 In the composite frequency modulation zone 39 of the middle E, the frequency modulation unit is square or circular. The long and short sides of the square frequency modulation unit can be arranged in different gradient patterns, and the outer diameter of the circular frequency modulation unit can also be arranged in different gradient patterns.

[0058] The frequency modulation units within the composite frequency modulation zone may or may not overlap. Figure 10 Image A shows the composite frequency modulation zone 40 where the frequency modulation units do not overlap. Figure 10 Figure B shows a composite frequency modulation zone 41 in which frequency modulation units overlap. The frequency modulation units in this composite frequency modulation zone can be circular, or they can be square, rectangular, triangular or elliptical.

[0059] The present invention has the following beneficial effects: (1) Select composite frequency modulation zone graphics for processing according to different frequency bands. The frequency modulation accuracy is high and the frequency concentration can reach 99.5%.

[0060] (2) The composite frequency modulation zone uses different combinations of frequency modulation units, which can effectively avoid the frequency modulation result from over-frequency or under-frequency.

[0061] (3) Using a short-wavelength 355nm ultrafast ultraviolet picosecond laser to perform cold processing and frequency modulation on the crystal oscillator will not cause thermal burning of the crystal body, thus avoiding thermal damage.

Claims

1. A laser frequency modulation method for a crystal oscillator, characterized in that, Includes the following steps: 101) Determine the location and volume of the area where material needs to be removed based on the frequency deviation of the crystal oscillator; 102) Use an ultrafast laser to perform laser treatment on the composite frequency tuning region at the top of the crystal oscillator tuning fork arm, and remove the coating material and / or quartz substrate material according to the region position and volume determined in step 101 to adjust the frequency. 103) The composite frequency modulation zone includes at least one frequency modulation unit, and the frequency modulation unit includes a frequency modulation functional structure formed by at least one laser ablation point according to a set diagram.

2. The laser frequency modulation method for a crystal oscillator according to claim 1, characterized in that, Includes the following steps: 201) In step 101, based on the frequency deviation value of the crystal oscillator, the software system automatically retrieves the data of the corresponding composite frequency modulation zone. The data of the composite frequency modulation zone includes the parameters of the composite frequency modulation zone, which include geometric feature parameters and material removal parameters. 202) The position of the composite frequency modulation zone is adjusted according to the frequency deviation value. The larger the absolute value of the frequency deviation value, the closer the composite frequency modulation zone is to the top of the tuning fork arm.

3. The laser frequency modulation method for a crystal oscillator according to claim 1, characterized in that, The shape of the frequency modulation unit includes rectangle, square, circle, triangle or ellipse, and the frequency modulation function structure of the frequency modulation unit is through hole or blind hole.

4. The laser frequency modulation method for a crystal oscillator according to claim 2, characterized in that, The geometric feature parameters include frequency modulation unit-level parameters and composite frequency modulation zone-level parameters. The frequency modulation unit-level parameters include unit shape, unit size, and unit spacing; the composite frequency modulation zone-level parameters include zone layout pattern, total zone area, and zone location.

5. The laser frequency modulation method for a crystal oscillator according to claim 2, characterized in that, The material removal parameters include the type of material to be removed, the volume of material to be removed, and the material removal rate.

6. The laser frequency modulation method for a crystal oscillator according to claim 1, characterized in that, The composite frequency modulation zone consists of a plurality of frequency modulation units.

7. The laser frequency modulation method for a crystal oscillator according to claim 1, characterized in that, The ultrafast laser is a 355nm ultrafast ultraviolet picosecond laser.

8. The laser frequency modulation method for a crystal oscillator according to claim 1, characterized in that, Step 102: Before using an ultrafast laser to perform laser processing on the composite frequency modulation area at the top of the crystal tuning fork arms, the position coordinates of the left and right arms of the tuning fork are located using a vision capture system; the frequencies of the left and right arms are measured in real time using a frequency testing system, and the deviation values ​​are calculated; differentiated frequency modulation unit parameters and laser processing parameters are generated based on the deviation values, with the unit density on the high deviation side being greater than that on the low deviation side; the composite frequency modulation area is processed using an ultraviolet picosecond laser according to the planned path; after each frequency test, the laser is used for frequency modulation once until the frequency is adjusted to the specified value.

9. The laser frequency modulation method for a crystal oscillator according to claim 1, characterized in that, Before step 101, the frequency deviation value of the crystal oscillator is adjusted to a negative value.

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