A fine-tuning method for a surface mount crystal

Abstract

The present invention discloses a fine-tuning method for surface acoustic wave crystals. After taking the whole-board surface acoustic wave crystal resonators after rough tuning, measure the frequency of each surface acoustic wave crystal under vacuum and upload it to the server for recording. During fine-tuning, measure the frequency of each surface acoustic wave crystal again in an atmospheric environment. Based on the difference between the measured value of each surface acoustic wave crystal under vacuum and the measured value under atmospheric pressure, calculate the fine-tuning frequency target value of each surface acoustic wave crystal in the atmospheric environment; then use a laser & galvanometer to perform fine-tuning in the atmospheric environment, and use high-purity nitrogen for cooling during the fine-tuning process to avoid cracking of the crystal oscillator; this method has low cost and high efficiency, and the frequency consistency of the products after sealing and soldering is good.

Description

Technical Field

[0001] This solution relates to the field of the production process of quartz crystal oscillators, and specifically relates to a fine-tuning method for surface-mounted crystals. Background Art

[0002] The quartz crystal oscillator in a quartz clock is of the tuning fork type, and its most commonly used standard frequency is 32.768 kHz. The accuracy of the crystal oscillator frequency determines the accuracy of the clock's timekeeping.

[0003] During the processing of a quartz crystal oscillator, generally after the wafer is fixed to the base, a fine-tuning is performed before the final encapsulation to ensure the accuracy of the frequency of the final product.

[0004] The existing fine-tuning methods mainly include the following two methods:

[0005] Measurement under atmospheric pressure and laser fine-tuning;

[0006] 1.1 Principle: A high-energy laser beam irradiates the silver layer surface at the end of the surface-mounted crystal, causing it to melt and vaporize, forming a groove with a certain depth to achieve the purpose of etching the material. The divergence angle of the laser beam can be less than 1 milliradian, the spot diameter reaches the micron level, the action time is as short as nanoseconds and picoseconds, it can output power continuously, is easy to control, and is easy to combine with precision machinery, precision measurement technology, and electronic computers to meet the requirements of high automation and high precision in processing.

[0007] 1.2 Advantages are: a High frequency modulation efficiency. The reason is that a laser + galvanometer device is used for frequency adjustment: the laser + galvanometer moves fast and the power is adjustable. A high-frequency short-pulse laser is used for laser etching, which can focus the laser beam into a spot with a diameter of several hundred nanometers to 20 microns through optical fiber focusing. After focusing, the spot reaches the material removal energy value, and through the high-speed scanning galvanometer system for precise and rapid scanning, the etching process is simplified, the cost is reduced, and the accuracy is improved. b Pollution-free. An air suction and collection pollution device is added to blow and suck the laser etching position under atmospheric pressure to avoid the gaseous substances generated by laser etching from contaminating and adsorbing on the silver layers of other wafers that have been adjusted.

[0008] 1.3 Disadvantages are: Poor frequency consistency after pressure sealing. The reason is that the frequency of the surface-mounted crystal under vacuum is different from that under atmospheric pressure, and the frequency difference between the vacuum and atmospheric pressure tests for each product is also different. For example, for products with a test value of 0 ppm under atmospheric pressure, the frequency (in vacuum state) dispersion after pressure sealing can reach 0 to ±50 ppm, and the smaller the product, the greater the frequency dispersion after pressure sealing.

[0009] 1.4 Since there is thermal stress concentration in laser etching, cracks are likely to occur. When etching in an atmospheric environment, inert gas can be blown while etching to cool down, and the maximum adjustment amount can reach 2000 ppm. However, if laser etching is carried out in a vacuum, since heat cannot be removed by the purge of inert gas, the adjustment amount can only be limited within 500 ppm, otherwise cracks are extremely likely to occur.

[0010] II. Measurement and ion etching under vacuum;

[0011] 2.1 Principle: Ion etching is an etching method based on a pure physical process. It uses a high-energy ion beam to directly bombard the material surface and removes the material through sputtering. The principle is as follows: a Ion generation: The gas (such as argon) is ionized through the principle of glow discharge to form ions. b Ion acceleration: Under the action of an electric field, the ions are accelerated and form a beam of ion current. c Ion bombardment: The high-energy ion beam bombards the material surface, causing the kinetic energy of the atoms on the material surface to increase and finally be sputtered out. d Material removal: The sputtered material atoms or molecules are pumped out by a vacuum pump and removed from the reaction chamber.

[0012] 2.2 The advantage is that the frequency consistency is good after pressure sealing. The reason is that both etching and sealing are measured under vacuum. For products with an etching frequency test value of 0 ppm, the frequency (in a vacuum state) after pressure sealing is discrete within 0 to ±5 ppm.

[0013] 2.3 The disadvantage is that the equipment cost is high, which is 3 - 4 times that of the laser etching equipment in the atmosphere, but the working efficiency is only about 50% of the laser etching solution under the atmosphere.

[0014] The frequency consistency of a crystal oscillator with a high frequency (MHz) is better in a vacuum environment than in an atmospheric environment. However, the frequency of a tuning fork crystal oscillator is only 32 KHz. After testing, its frequency characteristics in a vacuum are not consistent with those in an atmospheric environment, and the discreteness is very large. The existing fine-tuning solutions cannot efficiently and accurately fine-tune the tuning fork crystal oscillator. Summary of the Invention

[0015] The technical problem to be solved by the present invention is to provide an efficient, low-cost, and high-precision fine-tuning method for a tuning fork crystal oscillator.

[0016] The specific technical solution of the present invention to solve the above technical problems is:

[0017] S1. Take the crystal resonator on the whole board after coarse adjustment, read the substrate ID of the crystal resonator on the whole board, measure it in a vacuum environment to obtain the frequency of each crystal in the vacuum environment, which is abbreviated as the vacuum frequency after coarse adjustment and denoted as F3, and record the substrate ID, the position of the crystal on the whole board, and their respective vacuum frequencies F3 after coarse adjustment in the server. The crystal resonator on the whole board is processed based on the whole board base, each whole board base has a unique substrate ID, and the position of each crystal resonator on the whole board base is recorded. Therefore, each crystal and its vacuum frequency after coarse adjustment are accurately recorded in the server;

[0018] S2. Place the crystal resonator on the whole board into the fine-tuning machine, and use the measuring device in the fine-tuning machine to measure the crystal resonator on the whole board again in the atmospheric pressure environment to obtain the frequency of each crystal in the atmospheric environment, which is abbreviated as the standard pressure frequency after coarse adjustment and denoted as F2, and upload it to the server for recording;

[0019] S3. Based on the data recorded in the server, compare the differences between the vacuum frequency F3 after coarse adjustment and the standard pressure frequency F2 after coarse adjustment of each crystal resonator one by one to obtain the difference between the vacuum frequency after coarse adjustment and the standard pressure frequency after coarse adjustment of each crystal resonator, which is abbreviated as the deviation frequency and denoted as ΔF2, that is, ΔF2 = F3 - F2; write it into the server;

[0020] S4. Calculate the fine-tuning target value F1 of the process ID. The expected accurate frequency F0 of each crystal resonator in the vacuum environment after vacuum pressure sealing is 32.768 KHz, and the target value F1 of the fine-tuning frequency under atmospheric pressure. Then, the fine-tuning amount ΔF1 under atmospheric pressure = F1 - F2;

[0021] Then: F1 = F0 - ΔF2

[0022] = F0 - F3 + F2;

[0023] S5. Based on the target value F1 of the fine-tuning frequency under atmospheric pressure of each crystal obtained from the above calculation, upload it to the server. In the atmospheric pressure environment, the fine-tuning machine fine-tunes each crystal resonator one by one in the way of laser and galvanometer according to the target value F1 recorded in the server.

[0024] Furthermore, the crystal resonator on the whole board refers to the semi-finished product in which the wafer has been fixed on the base but has not been encapsulated. It can be the semi-finished product obtained by processing based on a whole intact and un-split base whole board, or the single semi-finished product processed one by one, or the crystal resonator with the "workbench" as the "whole board" obtained by fixing several single semi-finished products on the workbench.

[0025] Further, while fine-tuning with a laser and a galvanometer at atmospheric pressure, use N2 to blow the laser etching position to prevent cracks in the wafer caused by heat concentration; at the same time, add an air suction device to the N2 air duct to collect the etched substances, avoid contaminating the wafer, and prevent affecting the stability of frequency testing.

[0026] Further, the fine-tuning amount ΔF1 = F1 - F2 under atmospheric pressure is within 2000 ppm, that is, the deviation of the coarse tuning is controlled within 2000 ppm of the target frequency. Specific embodiments

[0027] The following is a description in conjunction with examples. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0028] A method for fine-tuning a surface acoustic wave resonator crystal includes the following steps:

[0029] S1. Take the whole-board surface acoustic wave resonator crystal after coarse tuning, read the substrate ID of the whole-board surface acoustic wave resonator crystal, measure it in a vacuum environment to obtain the frequency of each surface acoustic wave resonator crystal in the vacuum environment, abbreviated as the vacuum frequency after coarse tuning, denoted as F3, and record the substrate ID, the position of the surface acoustic wave resonator crystal on the whole board, and its respective vacuum frequency after coarse tuning F3 in the server. The whole-board surface acoustic wave resonator crystal is processed based on the whole-board base, each whole-board base has a unique substrate ID, and the position of each surface acoustic wave resonator crystal on the whole-board base is recorded, so the server accurately records each surface acoustic wave resonator crystal and its vacuum frequency after coarse tuning;

[0030] S2. Place the whole-board surface acoustic wave resonator crystal into the fine-tuning machine, and use the measuring device in the fine-tuning machine to measure the whole-board surface acoustic wave resonator crystal again in the atmospheric environment to obtain the frequency of each surface acoustic wave resonator crystal in the atmospheric environment, abbreviated as the standard pressure frequency after coarse tuning, denoted as F2, and upload it to the server for recording;

[0031] S3. Based on the data recorded in the server, compare the difference between the vacuum frequency after coarse tuning F3 and the standard pressure frequency after coarse tuning F2 of each surface acoustic wave resonator crystal one by one to obtain the difference between the vacuum frequency after coarse tuning and the standard pressure frequency after coarse tuning of each surface acoustic wave resonator crystal, abbreviated as the deviation frequency, denoted as ΔF2, that is, ΔF2 = F3 - F2; write it into the server;

[0032] Here, it is assumed that the measuring devices used in the vacuum environment and in the fine-tuning machine are both accurate. Because in steps S1 and S2, the measured whole-board surface acoustic wave resonator crystals are the same piece and no other processing is done after step S1, the difference between F3 measured in S1 and the value F2 measured in the fine-tuning machine is only caused by the difference in the operation of the corresponding crystal oscillator resonator crystal in the vacuum environment and the atmospheric environment.

[0033] S4. Calculate the fine-tuning target value F1 for each surface-mounted crystal resonator. The expected precise frequency F0 of each surface-mounted crystal resonator in a vacuum environment after vacuum encapsulation is 32.768 KHz. Let the target value of the fine-tuning frequency under atmospheric pressure be F1. Then, the fine-tuning amount ΔF1 under atmospheric pressure is ΔF1 = F1 - F2;

[0034] Then: F1 = F0 - ΔF2

[0035] = F0 - F3 + F2;

[0036] S5. Based on the above calculations, obtain the target value F1 of the fine-tuning frequency under atmospheric pressure for each surface-mounted crystal on the whole-board surface-mounted crystal resonator, and upload it to the server. In an atmospheric environment, the fine-tuning machine adjusts each surface-mounted crystal resonator one by one in the way of laser and galvanometer according to the target value F1 of each surface-mounted crystal resonator recorded by the server. After completion, the fine-tuned whole-board surface-mounted crystal resonator is obtained.

[0037] Subsequently, encapsulation, testing, etc. are carried out to obtain the final product.

[0038] Furthermore, the whole-board surface-mounted crystal resonator refers to the semi-finished product in which the wafer has been fixed on the base but has not been encapsulated. It can be a semi-finished product obtained by processing the whole intact and un-split base board, or a single semi-finished product processed one by one, or a semi-finished product with the "tooling" as the "whole board" obtained by fixing several single semi-finished products on the tooling.

[0039] Furthermore, while performing fine-tuning with laser and galvanometer under atmospheric pressure, continuously blow the laser etching position with N2 to prevent cracks in the wafer caused by heat concentration; at the same time, add a negative pressure collection device to the N2 air duct to collect the etched material debris to avoid contaminating the wafer and preventing it from affecting the stability of frequency testing.

[0040] This solution is based on the whole-board processing technology of crystal oscillators. Based on the real-time recording and calculation of the server, it fully considers the factor that the measurement values of surface-mounted crystals in the atmospheric environment and the vacuum environment are quite different. It finely tunes each surface-mounted crystal at low cost, and finally makes the working frequencies of the processed surface-mounted crystals highly consistent and have low dispersion, improving the product quality.

[0041] For example, a certain whole-board surface-mounted crystal has a total of 168 single surface-mounted crystal resonators. In the past, fine-tuning was carried out in the atmospheric environment to make the measured values of all surface-mounted crystal resonators consistent in the atmospheric environment, with a dispersion of 0 ppm. After vacuum encapsulation, the actual working frequency was measured again, and its dispersion reached ±50 ppm. The smaller the product, the greater the frequency dispersion after encapsulation.

[0042] For the whole-board surface-mounted crystal processed by this solution, when fine-tuning is carried out in the atmospheric environment, the frequency difference ΔF2 measured in the vacuum environment and the atmospheric environment is considered one by one. After fine-tuning, the dispersion of the frequency measured in the atmospheric environment is ±50 ppm. However, after vacuum encapsulation, the dispersion of its actual operating frequency is compressed to ±5 ppm. And we ultimately pursue a higher consistency of the actual operating frequency. Therefore, for the products processed by this solution, the frequency consistency during actual operation is better.

[0043] The maximum fine-tuning amount ΔF1 in the atmospheric pressure environment can reach 2000 ppm. According to actual experience statistics, F0 = 62768 HZ (deviation ±10 ppm), F1 = 32757 HZ (deviation about 15 ppm), F2 = 32738 HZ (deviation within about 300 ppm), and the frequency difference ΔF2 measured in the vacuum environment and the atmospheric environment is around 300 ppm.

[0044] For the same fine-tuning amount, if the ion etching method is used, the one-time fine-tuning amount can only reach within 500 ppm. Multiple etching operations are required or the rough-tuning amount needs to be controlled within 500 ppm in advance. Moreover, the processing efficiency is only about 50% of that of the laser and galvanometer methods, and the equipment cost is 3 - 4 times that of the laser and galvanometer method equipment. Therefore, the processing cost is very high.

[0045] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A fine-tuning method for a surface crystal, characterized in that, It includes the following steps: S1. Take the trimmed whole-board surface crystal resonator, read the substrate ID of the whole-board surface crystal resonator, measure it in a vacuum environment to obtain the frequency of each surface crystal in the vacuum environment, abbreviated as the trimmed vacuum frequency, denoted as F3, and record the substrate ID, the position of the surface crystal on the whole board, and their respective trimmed vacuum frequencies F3 in the server. The whole-board surface crystal is processed based on the whole-board base, each whole-board base has a unique substrate ID, and the position of each surface crystal resonator on the whole-board base is recorded. Therefore, each surface crystal and its trimmed vacuum frequency are accurately recorded in the server; S2. Place the whole-board surface crystal resonator into the fine-tuning machine, and use the measuring device in the fine-tuning machine to measure the whole-board surface crystal resonator again in the atmospheric pressure environment to obtain the frequency of each surface crystal in the atmospheric environment, abbreviated as the trimmed standard pressure frequency, denoted as F2, and upload it to the server for recording; S3. Based on the data recorded in the server, compare the difference between the trimmed vacuum frequency F3 and the trimmed standard pressure frequency F2 of each surface crystal resonator one by one to obtain the difference between the trimmed vacuum frequency and the trimmed standard pressure frequency of each surface crystal resonator, abbreviated as the deviation frequency, denoted as ΔF2, that is, ΔF2 = F3 - F2; write it into the server; S4. Calculate the fine-tuning target value F1 of the process ID. The expected accurate frequency F0 of each surface crystal resonator after vacuum pressure sealing in the vacuum environment is 32.768 KHz, and the target value F1 of the fine-tuning frequency under atmospheric pressure is as follows: F1 = F0 - ΔF2 = F0 - F3 + F2; S5. Based on the target value F1 of the fine-tuning frequency under atmospheric pressure of each surface crystal obtained from the above calculation, upload it to the server. In the atmospheric pressure environment, the fine-tuning machine fine-tunes each surface crystal resonator one by one in the way of laser and galvanometer according to the target value F1 recorded in the server.

2. The fine-tuning method of the surface acoustic wave crystal according to claim 1, characterized in that, The whole-board surface crystal resonator refers to the crystal oscillator semi-finished product obtained by processing based on a whole and un-split base whole board.

3. The fine-tuning method of the surface acoustic wave crystal according to claim 1, characterized in that, The whole-board surface crystal resonator refers to the single surface crystal resonator processed one by one, and it is also the crystal oscillator semi-finished product with the "workbench" as the "whole board" obtained by fixing several single crystal oscillator semi-finished products on the workbench.

4. The fine-tuning method of the surface acoustic wave crystal according to any one of claims 1-3, characterized in that, While fine-tuning with laser and galvanometer under atmospheric pressure, use N2 to blow the laser etching position to prevent the wafer from cracking due to heat concentration.

5. The fine-tuning method of the surface-mounted crystal according to claim 4, characterized in that An air suction device is provided on the N2 air duct, and the air suction device is used to recover the etched substances.

6. The fine-tuning method of the surface acoustic wave crystal according to any one of claims 1-3, characterized in that, The deviation of the rough adjustment is controlled within 2000 ppm of the target frequency.