Clock wafer vacuum measurement system and test method thereof

Abstract

The embodiment of the invention discloses a clock wafer vacuum measurement system and a test method thereof.The system comprises a water-cooling radiator, a vacuum cavity, a probe module and a measurement device, the probe module and the measurement device are arranged in the vacuum cavity, the system further comprises a TEC module and a heat conduction piece, and the water-cooling radiator is in heat conduction connection with the hot end of the TEC module; the heat conduction piece is in heat conduction connection with the probe module and the cold end of the TEC module, and the probe module conducts heat to the cold end of the TEC module through the heat conduction piece. According to the invention, the frequency and impedance of the 32.768 KHz clock wafer can be accurately measured in a high-vacuum environment, and an in-situ trimming function is realized.

Description

Technical Field

[0001] This invention relates to the field of crystal oscillator technology, and in particular to a vacuum measurement system for clock wafers and its testing method. Background Technology

[0002] Currently, parameter testing of 32.768kHz crystal oscillators in a vacuum environment (such as equivalent series resistance (ESR) and resonant frequency (Fr)) mainly relies on vector network analyzers or impedance analyzers from companies like Keysight and Agilent Technologies. These devices are expensive (typically ranging from 500,000 to 1,000,000 RMB), and their core technologies are subject to export controls, posing a risk of technological bottlenecks. After-sales maintenance and calibration are also difficult.

[0003] Traditional crystal oscillator testing is conducted under standard atmospheric pressure. However, the interior of the 3215 crystal oscillator after sealing is in a high vacuum state. The loss of air damping causes an increase in the Q value and a frequency shift. Test data under normal pressure cannot accurately reflect the performance of the crystal oscillator in its final operating environment, resulting in frequency exceeding the standard after sealing and low yield.

[0004] In a high vacuum environment, gas convection disappears, and heat cannot be dissipated through the air. When the test probes of the probe module contact the crystal oscillator or the circuit operates, the resulting Joule heat accumulates within the cavity, causing a localized temperature rise. Because the crystal oscillator frequency is temperature-sensitive, this temperature rise can lead to severe frequency drift (thermal drift). Most existing vacuum testing equipment lacks an active cooling mechanism for the small test areas. Summary of the Invention

[0005] The technical problem to be solved by the embodiments of the present invention is to provide a clock chip vacuum measurement system and testing method to achieve active cooling of the probe module and solve the thermal drift problem in a vacuum environment.

[0006] To address the aforementioned technical problems, this invention provides a clock chip vacuum measurement system, comprising a water-cooled heat sink, a vacuum chamber, a probe module and a measuring device disposed within the vacuum chamber, and a TEC module and a heat-conducting component. The water-cooled heat sink is thermally connected to the hot end of the TEC module, and the heat-conducting component is thermally connected to the probe module and the cold end of the TEC module. The probe module conducts heat to the cold end of the TEC module through the heat-conducting component.

[0007] Furthermore, the water-cooled radiator is located on the wall of the vacuum chamber, and the TEC module is located inside the water-cooled radiator.

[0008] Furthermore, both the cold water outlet and the cold water inlet of the water-cooled radiator are located outside the vacuum chamber.

[0009] Furthermore, the outer wall of the vacuum chamber is wrapped with a water-cooled jacket.

[0010] Furthermore, the heat-conducting component is composed of multiple thin copper sheets stacked together.

[0011] Furthermore, the probe module consists of a probe and a probe holder, with a temperature sensor mounted on the probe holder.

[0012] Furthermore, a Z-axis assembly is provided inside the vacuum chamber, and a probe holder fixing block is provided on the Z-axis assembly, with the probe module located on the probe holder fixing block.

[0013] Furthermore, it also includes a laser assembly for adjusting the crystal oscillator inside the vacuum chamber, with a corresponding glass window on the vacuum chamber, and the probe module connected to a frequency testing device that detects the crystal oscillator frequency via a coaxial line.

[0014] Furthermore, the system adjusts the crystal oscillator according to the following steps: Detect the current resonant frequency F of the crystal oscillator real and impedance R esr ; If |F real -F target |>δ,F target Given the target resonant frequency and δ as a preset threshold, the laser component is controlled to emit a single pulse to remove the electrode material on the crystal oscillator in a single laser pulse. Measure the crystal oscillator frequency again, if |F real -F target If |≤δ, then the crystal oscillator adjustment is complete; if |F real -F target If |>δ, then continue with a single laser removal, repeating this cycle until |F real -F target |≤δ.

[0015] Accordingly, this invention also provides a testing method for a clock wafer vacuum measurement system, which adjusts the power P of the TEC module based on the real-time temperature of the probe module: P = K p e + K i ∫ EDT + K d dt / de ; e =T A - T target ; in, e T represents the temperature difference between the real-time temperature of the probe module and the target temperature. target For the target temperature, T A This represents the real-time temperature of the probe module. dtRepresents the integral variable. dt / de This represents the derivative of the temperature difference with respect to time. K p , K i , K d These are the proportional, integral, and derivative control parameters, respectively.

[0016] The beneficial effects of this invention are as follows: 1) This invention breaks the technological monopoly and significantly reduces costs and increases efficiency: It can use a self-developed circuit based on FPGA and lock-in amplification principle to replace imported network analyzers, reducing hardware costs by about 90%, and ensuring that the supply chain is secure, independent and controllable, and is not affected by the international situation.

[0017] 2) This invention completely solves the problem of vacuum thermal drift: It innovatively adopts a dual temperature control scheme of TEC local forced cooling + cavity water cooling. Under high vacuum insulation environment, the temperature fluctuation of the test point can still be controlled within ±0.5°C, thereby controlling the thermal error of frequency measurement to below 0.05PPM, realizing true vacuum and true constant temperature measurement.

[0018] 3) Extremely high test authenticity and accuracy: The measurement is performed directly under high vacuum, eliminating the influence of air damping on the Q value. The measured ESR and Fr are the true parameters after the crystal oscillator is sealed and soldered, without the need for subsequent estimation and compensation, which greatly improves the product yield.

[0019] 4) Integrated measurement and adjustment improves efficiency: It integrates a laser adjustment window, realizing the closed-loop completion of the entire process of measurement-calculation-adjustment-retest in a vacuum environment, avoiding the huge waste of traditional processes of atmospheric measurement -> sealing welding -> vacuum retest -> unqualified scrapping. Attached Figure Description

[0020] Picture 1 This is a schematic diagram of the structure of the clock chip vacuum measurement system according to an embodiment of the present invention.

[0021] Picture 2 This is a top view of the probe module according to an embodiment of the present invention.

[0022] Explanation of icon numbers 1. Vacuum chamber; 2. Heat-conducting component; 3. Water-cooled radiator; 4. TEC module; 5. Cold water outlet; 6. Cold water inlet; 7. Laser assembly; 8. Glass window; 9. Crystal oscillator fixture; 10. Probe; 11. Probe holder; 12. Coaxial cable connector; 13. Coaxial cable; 14. Z-axis assembly; 15. Probe holder fixing block; 16. Temperature sensor. Detailed Implementation

[0023] 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.

[0024] 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.

[0025] 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.

[0026] Please refer to Picture 1 ~ Picture 2 The clock chip vacuum measurement system of this invention includes a water-cooled heat sink, a vacuum chamber, a probe module, a measuring device, a TEC (Thermo Electric Cooler) module, and a heat-conducting component. The probe module and measuring device are housed within the vacuum chamber. The vacuum chamber consists of a stainless steel main chamber, a molecular pump, a backing pump, and a high-vacuum gauge tube, used to provide a vacuum level superior to... The extreme vacuum environment was used to simulate the actual working state of the crystal oscillator.

[0027] The water-cooled radiator is thermally connected (in contact) to the hot end of the TEC module, and is connected to an external circulating chiller. The water-cooled radiator removes the heat generated by the TEC module during operation. The thermally conductive component is thermally connected (in contact) to the probe module and the cold end of the TEC module, allowing the probe module to conduct heat to the cold end of the TEC module via the thermally conductive component.

[0028] In one implementation, the water-cooled radiator is mounted on the wall of the vacuum chamber, and the TEC module is located inside the water-cooled radiator. Both the cold water outlet and the cold water inlet of the water-cooled radiator are outside the vacuum chamber to avoid water leakage at the pipe joints (in a high vacuum environment, micro-leakage is easy to occur at the joints, and even a small leak can produce water vapor, which can easily reduce the vacuum level).

[0029] In one implementation, the outer wall of the vacuum chamber is wrapped with a water-cooled jacket, which is connected to an external circulating chiller to remove radiant heat from the chamber wall, serving as primary cooling (macroscopic). The TEC module serves as secondary cooling (microscopic / core).

[0030] In one implementation, the heat-conducting component is made of multiple thin copper sheets stacked together.

[0031] In one implementation, the probe module consists of a probe and a probe holder, with a temperature sensor mounted on the probe holder. The temperature sensor is a PT1000 high-precision temperature sensor that collects temperature data in real time. A PID algorithm is used to dynamically adjust the cooling power of the TEC module, locking the test point temperature at 20.0 ± 0.5°C.

[0032] The probe is directly integrated inside the vacuum chamber and connected to the external circuit via a coaxial cable, greatly shortening the signal path and reducing the interference of parasitic capacitance on weak pA-level signals. Preferably, a coaxial cable connector is provided on the vacuum chamber, and the probe is connected to the external circuit via a coaxial cable and the coaxial cable connector.

[0033] In one embodiment, a Z-axis assembly is provided inside the vacuum chamber, a probe holder fixing block is provided on the Z-axis assembly, and a probe module is provided on the probe holder fixing block.

[0034] The clock chip vacuum measurement system also includes a laser assembly for adjusting the crystal oscillator (fixed by a crystal oscillator clamp within the vacuum chamber) inside the vacuum chamber. A corresponding glass window is provided on the vacuum chamber. The glass window is made of quartz glass and is located at the top of the vacuum chamber. The laser assembly uses an optical focusing system to direct a laser beam into the electrode mass load layer on the surface of the crystal oscillator within the chamber, achieving in-situ adjustment without breaking the vacuum. This part is a common technical solution in the field and will not be described in detail here.

[0035] The probe module is connected to an external frequency testing device via a coaxial cable to detect the crystal oscillator frequency. The frequency testing device uses FPGA+DDS (Direct Digital Synthesis) technology to generate a highly stable 32.768kHz sweep excitation signal. The frequency testing device employs a lock-in amplifier (LSI) detection circuit: it acquires the crystal oscillator response current through a high-precision I / V conversion chip, extracts the in-phase and quadrature components using a quadrature LSI algorithm, and directly calculates the resonant frequency (Fr) and equivalent series resistance (ESR). This circuit eliminates the need for expensive imported network analyzers, reducing costs to 1 / 10 of their cost. This part is a common technical solution in this field and will not be elaborated further here.

[0036] As one implementation method, the clock wafer vacuum measurement system adjusts the crystal oscillator according to the following steps: Pre-cooling and vacuuming: Start the water chiller and TEC module for cooling. After the probe holder cools down to the set low temperature (e.g., 20°C), start the molecular pump to evacuate the air in the vacuum chamber to a high vacuum state.

[0037] Probe contact: The Z-axis assembly pushes the probe to contact the 3215 crystal oscillator electrode. At this time, the TEC module continues to work to counteract the frictional heat at the moment of contact and the Joule heat of the subsequent power-on test.

[0038] Frequency sweep measurement: The DDS outputs a frequency sweep signal to excite the crystal oscillator, the lock-in amplifier circuit acquires the response, and the current resonant frequency F of the crystal oscillator is determined by FFT spectrum analysis. real and impedance R esr ; Drift compensation judgment: The system monitors the temperature sensor in real time. If the temperature rises due to the vacuum insulation effect, the PID algorithm immediately increases the TEC power to force the temperature to stabilize, ensuring that the change in Freal is caused only by the characteristics of the crystal oscillator itself, rather than thermal drift.

[0039] Closed-loop adjustment: If |F real -F target |>δ,F target The target resonant frequency is δ, which is a preset threshold (e.g., 0.5 PPM). The laser component is then controlled to emit a single pulse to remove (vaporize) the electrode material on the crystal oscillator in a single laser pulse. In-situ retest: Within 50ms after the laser is turned off, measure the crystal oscillator frequency again. If |F real -F target If |≤δ, then the crystal oscillator adjustment is complete; if |F real -F target If |>δ, then continue with a single laser removal, repeating this cycle until the frequency reaches the target value, i.e., |F. real -F target |≤δ.

[0040] This invention measures crystal oscillator parameters, controls laser adjustment based on the results, and performs secondary measurements and verifications without disrupting the vacuum until the parameters are within acceptable limits. This invention enables precise frequency and impedance measurement of a 32.768kHz clock chip in a high vacuum environment, and provides in-situ adjustment capabilities. This invention introduces an active temperature-controlled cooling system to solve the thermal drift problem in a vacuum environment, achieving an integrated process of realistic environment simulation, precise temperature control, domestically produced alternative circuitry, and online laser adjustment.

[0041] The testing method of the clock wafer vacuum measurement system of this invention adjusts the power P of the TEC module according to the real-time temperature of the probe module. P = K p e + K i ∫ EDT + K d dt / de ; e =T A - T target ; in, eT represents the temperature difference between the real-time temperature of the probe module and the target temperature. target For the target temperature, T A This represents the real-time temperature of the probe module. dt Represents the integral variable. dt / de This represents the derivative of the temperature difference with respect to time. K p , K i , K d These are the proportional, integral, and derivative control parameters, respectively.

[0042] This invention converts the calculated power P into the input voltage or current of the TEC module to achieve power regulation. This PID-based testing method effectively overcomes the delay caused by thermal inertia and improves temperature stability.

[0043] Example: The vacuum chamber is made of 304 stainless steel, with the inner surface electropolished to reduce outgassing. It is equipped with a turbomolecular pump (pumping speed 50 L / s) and a rotary vane backing pump, achieving an ultimate vacuum of 1 × 10⁻⁶. -5 Pa.

[0044] The probe holder is made of pure iron and is pressed tightly against the heat-conducting component. The heat-conducting component is composed of multiple stacked thin copper sheets. The heat-conducting component is pressed tightly against the probe holder and moved up and down by a Z-axis assembly while ensuring good thermal conductivity. The other side of the heat-conducting component is connected to the cold side of the TEC module (model: TEC1-12706). The hot side of the TEC module is attached to the water-cooled radiator at the water-cooling window of the vacuum chamber. Cooling is achieved through the cold water inlet and outlet of the water-cooled radiator to an external chiller (set water temperature 15℃). A temperature sensor on the probe holder can collect temperature data in real time. A PID algorithm dynamically adjusts the cooling power of the TEC module to lock the test point temperature at 20.0±0.5°C.

[0045] Circuit System: The main control chip is a Xilinx Artix-7 FPGA. The DDS module generates a 32768Hz sweep frequency signal with 1Hz steps. The detection front end uses an Analog Devices AD8628 high-precision operational amplifier to perform I / V conversion, and the subsequent stage extracts the signal through a software phase-locked loop algorithm.

[0046] The testing process is as follows: Place the unsealed 32.768kHz crystal oscillator die onto the crystal oscillator fixture inside the vacuum chamber. Close the chamber and start the vacuum system. Simultaneously, operate the TEC module at maximum power to pre-cool the probe holder to 18°C. The vacuum level is reached. At that time, the probe rises and contacts the crystal oscillator electrode.

[0047] Self-developed circuit testing: The FPGA controls the DDS to scan between 32760Hz and 32776Hz. The lock-in amplifier detects a phase zero-crossing frequency of 32768.5Hz and an impedance of 85kΩ. At this time, the temperature sensor displays a probe temperature of 18.2℃ (slightly higher than the set temperature due to vacuum insulation; the PID is adjusting).

[0048] Data correction: Based on the built-in frequency-temperature curve algorithm, the system calculates the equivalent frequency of the crystal oscillator in a standard environment of 25℃ to be 32768.1Hz (10PPM higher).

[0049] Laser tuning: The system calculates the mass load to be removed, controls the laser component (YAG laser) to output a single pulse with an energy of 0.5mJ, and irradiates the tuning point at the edge of the crystal oscillator.

[0050] Vacuum retest: After waiting 200ms, measure again; the frequency will now be 32768.02Hz. The test ends when the deviation is within the allowable range.

[0051] The probe descends, breaking the vacuum and completing the wafer production.

[0052] 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 vacuum measurement system for a clock chip, comprising a water-cooled heat sink, a vacuum chamber, and a probe module and a measuring device disposed within the vacuum chamber, characterized in that, It also includes a TEC module and a heat-conducting component. The water-cooled radiator is thermally connected to the hot end of the TEC module, and the heat-conducting component is thermally connected to the probe module and the cold end of the TEC module. The probe module conducts heat to the cold end of the TEC module through the heat-conducting component.

2. The clock wafer vacuum measurement system as described in claim 1, characterized in that, The water-cooled radiator is located on the wall of the vacuum chamber, and the TEC module is located inside the water-cooled radiator.

3. The clock wafer vacuum measurement system as described in claim 2, characterized in that, The cold water outlet and cold water inlet of the water-cooled radiator are both outside the vacuum chamber.

4. The clock wafer vacuum measurement system as described in claim 1, characterized in that, The outer wall of the vacuum chamber is wrapped with a water-cooled jacket.

5. The clock wafer vacuum measurement system as described in claim 1, characterized in that, The heat-conducting component is made up of multiple thin copper sheets stacked together.

6. The clock wafer vacuum measurement system as described in claim 1, characterized in that, The probe module consists of a probe and a probe holder, with a temperature sensor mounted on the probe holder.

7. The clock wafer vacuum measurement system as described in claim 1, characterized in that, The vacuum chamber contains a Z-axis assembly, on which a probe holder fixing block is mounted, and the probe module is mounted on the probe holder fixing block.

8. The clock wafer vacuum measurement system as described in claim 1, characterized in that, It also includes a laser assembly for adjusting the crystal oscillator inside the vacuum chamber. The vacuum chamber has a corresponding glass window, and the probe module is connected to a frequency testing device that detects the crystal oscillator frequency via a coaxial line.

9. The clock wafer vacuum measurement system as described in claim 8, characterized in that, The system adjusts the crystal oscillator according to the following steps: Detect the current resonant frequency F of the crystal oscillator real and impedance R esr ; If |F real -F target |>δ,F target Given the target resonant frequency and δ as a preset threshold, the laser component is controlled to emit a single pulse to remove the electrode material on the crystal oscillator in a single laser pulse. Measure the crystal oscillator frequency again, if |F real -F target If |≤δ, then the crystal oscillator adjustment is complete; if |F real -F target If |>δ, then continue with a single laser removal, repeating this cycle until |F real -F target |≤δ.

10. A test method for a clock wafer vacuum measurement system as described in any one of claims 1 to 9, characterized in that, Adjust the power P of the TEC module based on the real-time temperature of the probe module: P = K p e + K i ∫ edt + K d dt / de ； e =T A - T target ; in, e T represents the temperature difference between the real-time temperature of the probe module and the target temperature. target For the target temperature, T A This represents the real-time temperature of the probe module. dt Represents the integral variable. dt / de This represents the derivative of the temperature difference with respect to time. K p , K i , K d These are the proportional, integral, and derivative control parameters, respectively.

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