Laser marking method for crystal oscillator circuits

Abstract

This invention discloses a laser marking method for crystal oscillator circuits, comprising: Step 1: fixing the crystal oscillator to be marked; Step 2: obtaining the coordinates of the area to be marked on the crystal oscillator; Step 3: using a laser at a first preset power to etch and remove the marking layer on the crystal oscillator according to the obtained coordinates; Step 4: using a laser at a second preset power to etch the circuit layer on the crystal oscillator according to the obtained coordinates, and capturing the spectral / acoustic characteristics of the etching product in real time. When it is detected that the nickel layer is about to be etched through, the laser is controlled to etch intermittently in a single-pulse manner until a preset adjustment amount is reached, and then the etching is stopped to complete the marking. This invention utilizes the high absorption rate of 355nm ultraviolet light to metals and the high transmittance of quartz, combined with picosecond ultrashort pulses, to directly vaporize and sublimate the metal material, achieving coating etching without damaging the quartz substrate; the heat-affected zone is strictly controlled within 2μm, completely eliminating burrs and recast layers.

Description

Technical Field

[0001] This invention relates to the field of crystal oscillator technology, and in particular to a method for laser marking crystal oscillator circuits. Background Technology

[0002] With the miniaturization of 5G communication and IoT devices, the demand for 3215 package (3.2mm × 1.5mm) crystal oscillators has surged. The surface of the internal quartz wafer needs to be covered with multiple layers of metal plating such as Au / Ni / Cr as electrodes. Traditional processes face significant bottlenecks when producing frequency trimming circuits or customized markings. Traditional photolithography processes are costly and polluting: they require photoresist, developer, and etchant, resulting in expensive mask fabrication and generating large amounts of chemical waste. Infrared or nanosecond lasers have long pulse widths, and energy diffuses through heat conduction, causing melting at the plating edges and severe recasting, with a heat-affected zone >10μm, which easily leads to microcracks or frequency drift in the quartz substrate. Summary of the Invention

[0003] The technical problem to be solved by the embodiments of the present invention is to provide a laser marking method for crystal oscillator circuits, so as to achieve coating etching without damaging the quartz substrate and avoid microcracks or frequency drift in the quartz substrate.

[0004] To address the aforementioned technical problems, this invention provides a method for laser marking crystal oscillator circuits, comprising: Step 1: Fix the crystal oscillator to be marked; Step 2: Obtain the coordinates of the area to be marked on the crystal oscillator; Step 3: Use a laser at a first preset power to etch and remove the marking layer on the crystal oscillator according to the obtained coordinates; Step 4: Use a laser to etch the circuit layer on the crystal oscillator at the second preset power according to the obtained coordinates, and capture the spectral / acoustic characteristics of the etched product in real time. When it is detected that the nickel layer is about to be etched through, control the laser to etch intermittently in a single pulse mode until the preset adjustment amount is reached, and stop etching to complete the marking.

[0005] Furthermore, the laser wavelength is 355nm or 532nm, and the pulse width is <20ps.

[0006] Furthermore, the first preset power is 3W.

[0007] Furthermore, in step 3, the laser scanning speed is 500 mm / s and the pulse frequency is 100 kHz.

[0008] Furthermore, the second preset power is 6W.

[0009] Furthermore, in step 4, the laser scanning speed is 100 mm / s.

[0010] Furthermore, in step 4, the energy density of the single-pulse laser during intermittent etching in a single-pulse manner is 0.1 mJ / cm² - 0.5 mJ / cm².

[0011] Furthermore, in step 4, when the Si signal intensity is detected to exceed the set threshold, the laser is immediately cut off.

[0012] Furthermore, the crystal oscillator to be marked is fixed by negative pressure adsorption using a negative pressure adsorption fixture. The negative pressure adsorption fixture is provided with an air suction groove on its edge, and during etching, airflow is sprayed obliquely towards the etching point to blow molten metal droplets horizontally towards the air suction groove on the edge of the negative pressure adsorption fixture.

[0013] Furthermore, the airflow direction is at a 45° angle to the surface of the crystal oscillator.

[0014] The beneficial effects of this invention are: 1) Replacement of photolithography, reducing costs and increasing efficiency: This invention eliminates the need for photomasks and chemicals, achieving the effect of maskless photolithography, which greatly reduces NRE costs and production cycles, and is particularly suitable for customized crystal oscillator production.

[0015] 2) Extreme precision, no damage to the substrate: The ultra-fast cold processing of this invention compresses the heat-affected zone to within 2μm, protecting the crystal structure of the quartz crystal and ensuring the crystal oscillator's extremely high Q value and frequency stability.

[0016] 3) Intelligent error prevention and soaring yield: The plasma endpoint detection scheme of this invention is like putting brakes on the laser, completely solving the over-etching problem; the unique airflow field design reduces the short circuit risk to below 0.05%, and improves the overall yield to over 99.2%.

[0017] 4) Green manufacturing: The dry processing of this invention produces no wastewater or exhaust gas emissions, which greatly reduces the cost of environmental protection treatment. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the crystal oscillator etching process according to an embodiment of the present invention.

[0019] Figure 2 This is a schematic flowchart of the laser marking method for crystal oscillator circuits according to an embodiment of the present invention.

[0020] Explanation of icon numbers 1. Airflow, 2. Negative pressure adsorption fixture, 3. Negative pressure airway, 4. Crystal oscillator to be marked, 5. Suction groove, 6. Suction hole. Detailed Implementation

[0021] 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.

[0022] 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.

[0023] 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.

[0024] Please refer to Figure 2 The laser marking method for crystal oscillator circuits in this embodiment of the invention includes steps 1 to 4.

[0025] Step 1: Fix the crystal oscillator to be marked. Please refer to... Figure 1 The crystal oscillator to be marked is fixed by negative pressure adsorption fixture. The fixture has a negative pressure air channel and an air suction groove at its edge. During etching, airflow is sprayed obliquely towards the etching point, horizontally blowing molten metal droplets towards the air suction groove at the edge of the fixture. Preferably, the airflow direction is at a 45° angle to the crystal oscillator surface. This embodiment of the invention, considering the small size and narrow spacing of the 3215 crystal, designs a vacuum adsorption + coaxial side blowing + bottom negative pressure structure. At the moment of etching, high-pressure airflow blows away molten metal residue, which is then sucked away by negative pressure, completely eliminating the risk of electrode short circuits caused by secondary particle deposition.

[0026] In practice, the negative pressure adsorption fixture uses an anti-static ceramic suction cup with a vacuum degree of -0.08MPa. The nozzle of the jet airflow is designed as a ring-shaped air knife structure, which sprays high-pressure nitrogen gas (0.3-0.5MPa) at a 45° angle towards the etching point. At the same time, an air suction hole is set in the center of the fixture to form a blowing-suction airflow field.

[0027] Step 2: Obtain the coordinates of the area to be marked on the crystal oscillator. The scanning system of this invention uses a high-precision digital galvanometer in conjunction with an F-theta flat lens, with a focused spot diameter ≤15μm. The optical path of this invention integrates a narrowband filter and a photomultiplier tube (for plasma monitoring) or a piezo-acoustic sensor (for acoustic wave monitoring), connected to a high-speed data acquisition card (response time <50μs). In specific implementation, the vision system can use a coaxial high-frame-rate CCD linked with the digital galvanometer to identify the crystal oscillator mark point and the coating edge, achieving a positioning accuracy of ±3μm, ensuring precise etching on the tiny pads.

[0028] Step 3: Using a laser at a first preset power, the marking layer on the crystal oscillator is etched away according to the obtained coordinates, removing only the gold and not damaging the nickel. The laser wavelength is 355nm or 532nm, and the pulse width is <20ps. Preferably, this invention can use a high repetition rate (50-200kHz) ultraviolet picosecond laser with a wavelength of 355nm, a pulse width <10ps, an adjustable single pulse energy of 0.1-5mJ, and a beam quality M² <1.2. M² is a dimensionless parameter that measures how close the laser beam is to an ideal perfect beam (Gaussian beam).

[0029] Step 4: Use a laser at the second preset power to etch the circuit layer on the crystal oscillator according to the obtained coordinates (only remove nickel without damaging chromium), and capture the spectral / acoustic characteristics of the etched product in real time.

[0030] The physical mechanism of this invention is the switching from explosive to precise etching. In laser etching, the single-pulse energy directly determines the thickness of material removed in a single impact (i.e., the single-pulse etching rate).

[0031] Rough processing stage (high energy): Energy range: for example, 2.0 mJ - 5.0 mJ.

[0032] Physical phenomenon: High energy density causes metal to vaporize instantaneously, producing micro-explosions, and peeling off relatively thick materials in one go (e.g., single-pulse removal of 0.1μm - 0.2μm).

[0033] Disadvantages: Although it is fast, when approaching the base, energy fluctuations or uneven material thickness can easily cause the shovel to dig through the foundation with a single shovel.

[0034] When the nickel layer is detected to be about to be etched through, the laser is controlled to etch intermittently in a single-pulse manner while maintaining high-frequency sampling until the preset adjustment amount is reached, at which point etching stops and marking is completed. When the Si signal intensity is detected to exceed a set threshold, the laser is immediately cut off. This stage of the invention is the fine-tuning stage (low energy). Energy range: automatically reduced to 0.1 mJ - 0.5 mJ (close to the minimum stable output of the laser).

[0035] Physical phenomenon: The energy density is just near the ablation threshold of the metal. At this point, it is no longer a violent micro-explosion, but rather a process of non-thermal photochemical ablation or very shallow sublimation, where each pulse removes only a few nanometers to tens of nanometers of material.

[0036] Effect: It's like replacing smashing a wall with a scalpel with scraping it, achieving the effect of peeling away layers without damaging the underlying structure.

[0037] This invention employs plasma flash or high-frequency acoustic sensors to capture the spectral / acoustic characteristics of the etched product in real time and perform microsecond-level response. Once the quartz substrate element (Si) signal is detected, the laser is immediately cut off, achieving "atomic layer" level depth control and preventing over-etching.

[0038] This invention utilizes the high absorption rate of 355nm ultraviolet light for metals (Au / Ni / Cr) and its high transmittance for quartz, combined with picosecond (<10ps) ultrashort pulses, to directly vaporize and sublimate the metal material, achieving coating etching without damaging the quartz substrate. The heat-affected zone is strictly controlled within 2μm, completely eliminating burrs and recast layers.

[0039] The fine-tuning in this invention is not an arbitrary energy reduction, but rather triggered by trend analysis of the plasma flash spectrum. Trigger condition: Real-time monitoring of the intensity of characteristic spectral lines of nickel (Ni) I Ni and attenuation slope .

[0040] when The descent rate accelerates, or a signal of intermediate chromium (Cr) is detected. When it starts to rise significantly (meaning the nickel layer is almost gone). Or, a quartz (Si) signal. The appearance of slight fluctuations (meaning that the laser field has begun to affect the substrate surface).

[0041] Action execution: The controller sends a command to the acousto-optic modulator (AOM) or power control module to transfer the single-pulse energy E from E high (e.g., 3mJ) decreased stepwise or linearly to E low (e.g., 0.3mJ).

[0042] Continuous monitoring: Etching continues at low energy while maintaining high-frequency sampling. Once the preset tuning depth (or frequency tuning amount) is reached, etching is stopped immediately.

[0043] Once in the fine-tuning region, the system no longer uses a constant high energy, but instead reduces the energy to the edge of the ablation threshold. At this point, each laser pulse removes only the thickness at the atomic level. This invention employs a high-frequency iterative process of firing a pulse, collecting a spectrum, and estimating the removal depth until the cumulative removal reaches the tuning target (e.g., removing exactly 0.5 μm of nickel layer to increase the frequency by 5 ppm).

[0044] In one implementation, the first preset power is 3W. In step 3, the laser scanning speed is 500mm / s and the pulse frequency is 100kHz. The second preset power is 6W. In step 4, the laser scanning speed is 100mm / s.

[0045] In step 4, the energy density of the single-pulse laser during intermittent etching is 0.1 mJ / cm²-0.5 mJ / cm².

[0046] This invention targets the Au / Ni / Cr three-layer structure and presets different laser energy density thresholds (e.g., 0.5 J / cm² for the gold layer, 1.2 J / cm² for the nickel layer, and >5 J / cm² for the quartz damage threshold).

[0047] Experiments showed that: when the laser pulse energy is 0.1mJ, a single pass can remove 10-20 nanometers of thickness (for final finishing without damaging the quartz); when the laser pulse energy is 1-2mJ, a single pass can remove 100-200 nanometers (for etching the crystal oscillator body); when the laser pulse energy is 5mJ, a single pass can remove 300-500 nanometers (for rapid removal of the marking layer, but microcracks must be prevented).

[0048] Example:

[0049] Tape feeding and vacuum holding: The 3215 crystal oscillator tape is fed into the feeding track and conveyed by a stepper motor at a fixed length. When the crystal oscillator reaches the processing position, the cylinder presses down and the vacuum pump starts (vacuum degree -0.08MPa). The crystal oscillator is tightly adsorbed through the micro-holes of the fixture to ensure vibration-free processing.

[0050] Visual edge detection and coordinate mapping: A CCD camera captures an image of the top of the crystal oscillator, and an edge detection algorithm identifies the pins and plating areas. The system automatically calculates the offset, generates a processing coordinate matrix, compensates for incoming material tolerances, and achieves ±3μm positioning.

[0051] Layered laser etching: (1) Marking layer (gold removal): Adjust the laser parameters to an average power of 3W, a scanning speed of 500mm / s, and a pulse frequency of 100kHz. The laser removes approximately 0.1μm of gold layer from the surface, exposing the nickel layer to form high-contrast characters / QR codes. The energy at this stage is strictly controlled below the quartz damage threshold.

[0052] (2) Circuit layer (nickel removal / adjustment): For electrode edges where frequency adjustment is required, the system switches to high energy mode (power 6W, speed 100mm / s).

[0053] (3) Real-time monitoring: The plasma sensor collects the spark spectrum in real time.

[0054] (4) Closed-loop control: When it is detected that the nickel layer is about to be etched through (Ni signal decays in the spectrum, Cr signal appears, or Si signal shows slight fluctuations), the single pulse energy is automatically reduced for "fine-tuning" until the preset adjustment amount is reached (such as removing 0.5 μm nickel layer to increase the frequency by 5 ppm). Once the Si signal intensity suddenly exceeds the set threshold, the system cuts off the laser within 50 microseconds to prevent damage to the quartz.

[0055] Particle removal and airflow protection: While the laser is irradiating, nitrogen gas (0.4MPa) is sprayed from the coaxial side nozzle, which blows the molten metal droplets horizontally toward the suction groove on the edge of the fixture. The droplets are captured by the high-efficiency filter, preventing the metal from splashing into the insulation gap after cooling and causing a short circuit.

[0056] Online inspection and unloading: After etching, machine vision is used again to check the circuit connectivity and marking clarity. Qualified products are lifted by a cylinder and fall into the unloading tape; unqualified products are diverted to the waste box.

[0057] The test metrics are shown in Table 1.

[0058] Table 1

[0059] 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 laser marking a crystal oscillator circuit, characterized in that, include: Step 1: Fix the crystal oscillator to be marked; Step 2: Obtain the coordinates of the area to be marked on the crystal oscillator; Step 3: Use a laser with the first preset power to etch and remove the marking layer on the crystal oscillator according to the obtained coordinates; Step 4: Use a laser to etch the circuit layer on the crystal oscillator at the second preset power according to the obtained coordinates, and capture the spectral / acoustic characteristics of the etched product in real time. When it is detected that the nickel layer is about to be etched through, control the laser to etch intermittently in a single pulse mode until the preset adjustment amount is reached, and stop etching to complete the marking.

2. The laser marking method for crystal oscillator circuits as described in claim 1, characterized in that, The laser wavelength is 355nm or 532nm, and the pulse width is <20ps.

3. The laser marking method for crystal oscillator circuits as described in claim 1, characterized in that, The first preset power is 3W.

4. The laser marking method for crystal oscillator circuits as described in claim 3, characterized in that, In step 3, the laser scanning speed is 500 mm / s and the pulse frequency is 100 kHz.

5. The laser marking method for crystal oscillator circuits as described in claim 1, characterized in that, The second preset power is 6W.

6. The laser marking method for crystal oscillator circuits as described in claim 5, characterized in that, In step 4, the laser scanning speed is 100 mm / s.

7. The laser marking method for crystal oscillator circuits as described in claim 1, characterized in that, In step 4, the energy density of the single-pulse laser during intermittent etching is 0.1 mJ / cm² - 0.5 mJ / cm².

8. The laser marking method for crystal oscillator circuits as described in claim 1, characterized in that, In step 4, when the intensity of the Si signal is detected to exceed the set threshold, the laser is immediately cut off.

9. The laser marking method for crystal oscillator circuits as described in claim 1, characterized in that, The crystal oscillator to be marked is fixed by negative pressure adsorption using a negative pressure adsorption fixture. The negative pressure adsorption fixture is provided with an air suction groove on its edge, and during etching, airflow is sprayed obliquely towards the etching point to blow molten metal droplets horizontally towards the air suction groove on the edge of the negative pressure adsorption fixture.

10. The laser marking method for crystal oscillator circuits as described in claim 9, characterized in that, The airflow direction is at a 45° angle to the surface of the crystal oscillator.

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