Capillary FBG temperature sensor packaging method based on ultrasonic-assisted brazing

Abstract

The invention discloses a capillary FBG temperature sensor packaging method based on ultrasonic-assisted brazing. The capillary FBG temperature sensor packaging method comprises the steps that an optical fiber coating layer is removed, and an optical fiber, a metal capillary and brazing filler metal are subjected to ultrasonic cleaning; an optical fiber penetrates through a metal capillary tube, the metal capillary tube is placed on a heating platform, it is ensured that an optical fiber grid region is located in the center of the metal capillary tube, an ultrasonic welding amplitude-change pole is vertically pressed down on the metal capillary tube, and limiting and fixing are achieved by matching an arc groove in the lower end of the ultrasonic welding amplitude-change pole with the metal capillary tube. Brazing filler metal is placed at two ends of the metal capillary; starting a heating platform to melt the brazing filler metal, and continuously stirring the brazing filler metal to uniformly distribute the brazing filler metal at the end part of the metal capillary tube; an ultrasonic welding amplitude-change pole is started, and ultrasonic vibration is vertically applied to the metal capillary tube; and after ultrasonic vibration is finished, heating is stopped, and the metal capillary tube is taken out after the brazing filler metal at the end is completely solidified. According to the method, long-term stability and reliability of the capillary FBG temperature sensor can be ensured, and the measurement range is expanded.

Description

Technical Field

[0001] The invention belongs to the field of fiber optic sensor packaging, and particularly relates to a capillary FBG temperature sensor packaging method based on ultrasonic-assisted brazing. Background Art

[0002] The packaging steps of an FBG (fiber Bragg grating) temperature sensor are important steps to ensure its normal and stable operation. The quality of the packaging directly affects the performance and lifespan of the FBG temperature sensor. The capillary FBG temperature sensor encapsulates the FBG in a metal capillary. This packaging structure can greatly improve the mechanical strength of the FBG temperature sensor, and at the same time has a certain sensitivity enhancement effect. It is simple to operate and convenient to install, can achieve the lightweight of the sensor, and has the potential to be embedded inside the component to be measured to form an intelligent component. Therefore, it is widely used.

[0003] Currently, the packaging of FBG temperature sensors mainly includes mechanical fixation, gluing, welding, etc. Among them: mechanical fixation requires many components and is not suitable for miniature and lightweight capillary sensors; adhesives usually use epoxy resin, 353ND, ultraviolet glue, etc. These adhesives have characteristics such as high-temperature creep and low-temperature deterioration. They often show different bonding effects at different temperatures, resulting in inaccurate measurement of the sensor. Therefore, adhesive packaging is not suitable for the packaging of temperature sensors.

[0004] In contrast, for capillary FBG temperature sensors, welding packaging is superior to mechanical fixation and gluing. However: traditional fusion welding methods such as electric welding, argon arc welding, and laser welding require relatively high temperatures and need to reach the melting point of the substrate. This will cause a large loss of optical transmission power, resulting in problems such as a small measurement range and low lifespan of the capillary FBG temperature sensor. In severe cases, it may cause the failure of the capillary FBG temperature sensor; moreover, these traditional fusion welding methods do not have obvious advantages in the welding of dissimilar materials, especially the welding of metal and non-metal materials. Summary of the Invention

[0005] The purpose of the invention is to provide a capillary FBG temperature sensor packaging method based on ultrasonic-assisted brazing, which can ensure the long-term stability and reliability of the capillary FBG temperature sensor and expand the measurement range of the sensor.

[0006] The technical solution adopted by the invention is as follows: A packaging method for a capillary FBG temperature sensor based on ultrasonic-assisted soldering. First, remove the optical fiber coating layer, and perform ultrasonic cleaning on the optical fiber, metal capillary, and solder to remove surface impurities. Then, pass the optical fiber through the metal capillary, place the metal capillary on the heating platform, ensure that the fiber grating area is located at the center of the metal capillary, vertically press the ultrasonic welding horn down on the metal capillary, and use the arc groove at the lower end of the ultrasonic welding horn to match the metal capillary to achieve limit fixation. Place solder at both ends of the metal capillary. Then, turn on the heating platform to only melt the solder, and continuously stir the solder to make it evenly distributed at the ends of the metal capillary. Then, turn on the ultrasonic welding horn and apply ultrasonic vibration vertically to the metal capillary. After the ultrasonic vibration ends, stop heating. After the solder at the ends of the metal capillary completely solidifies, take it out to complete the packaging.

[0007] Preferably, the inner diameter of the metal capillary is 0.2 mm - 0.4 mm, the outer diameter is 0.4 mm - 0.6 mm, and the length is 12 mm - 20 mm.

[0008] Preferably, the metal capillary is made of copper alloy material.

[0009] Preferably, the metal capillary is made of Invar material.

[0010] Preferably, the solder is a tin-based solder.

[0011] Preferably, during soldering, the heating temperature applied by the heating platform is 330 °C, the vibration frequency of the ultrasonic vibration applied by the ultrasonic welding horn is 60 KHz, and the ultrasonic power is 15 W.

[0012] Preferably, there are multiple arc grooves with different sizes at the lower end of the ultrasonic welding horn to match metal capillaries with different outer diameters.

[0013] Preferably, after packaging, a protective tube is sleeved on the optical fiber pigtail at the soldering joint. The protective tube is made of a high-performance polyester elastomer material to prevent the optical fiber pigtail from breaking and affecting the input and output of signals.

[0014] Preferably, after packaging, connect the optical fiber pigtail to a jumper to transmit optical signals, and connect the jumper to a wavelength demodulator and a host computer to obtain temperature signals.

[0015] The beneficial effects of the present invention are: This method applies ultrasonic-assisted soldering to the encapsulation process of capillary FBG temperature sensors. Compared with mechanical fixed encapsulation, it has the advantages of small structural size and light weight, and can be installed in airborne systems with limited space or embedded inside electromechanical components to achieve real-time temperature measurement of the object to be measured. Compared with adhesive encapsulation, it has the advantages of reliable connection and stable operation under high and low temperature conditions, avoiding the problem of temperature measurement uncertainty caused by adhesive creep at high temperatures. Compared with fusion welding encapsulation, it can ensure the integrity of the optical fiber, thereby ensuring the normal and high-quality transmission of optical signals, and avoiding the problems of optical signal loss or fiber fracture caused by fusion welding encapsulation. Compared with ordinary soldering, the cavitation effect of ultrasonic waves promotes the wetting and uniform distribution of the solder on the surfaces of the optical fiber and the metal capillary. Therefore, it can ensure the long-term stability and reliability of capillary FBG temperature sensors and expand the measurement range of the sensors. Description of the Drawings

[0016] Figure 1 It is a schematic diagram of the encapsulation of a capillary FBG temperature sensor based on ultrasonic-assisted soldering in the present invention.

[0017] Figure 2 It is a schematic diagram of the structure of the capillary FBG temperature sensor after encapsulation in the present invention.

[0018] Figure 3 It is a physical diagram of the capillary FBG temperature sensor after encapsulation in the present invention, and the metal capillary is made of copper alloy material.

[0019] Figure 4 For Figure 3 the sensitivity curve of the capillary FBG temperature sensor in

[0020] Figure 5 It is a physical diagram of the capillary FBG temperature sensor after encapsulation in the present invention, and the metal capillary is made of invar material.

[0021] Figure 6 For Figure 5 the sensitivity curve of the capillary FBG temperature sensor in

[0022] Figure 7 It is a physical diagram of the capillary FBG temperature sensor after encapsulation in the present invention with a protective sleeve at the soldering joint.

[0023] Figure 8 It is a comparison diagram of the response characteristics of the capillary FBG temperature sensor after encapsulation in the present invention at high temperatures.

[0024] Figure 9 It is a comparison diagram of the response characteristics of the capillary FBG temperature sensor after encapsulation in the present invention at low temperatures.

[0025] In the figure: 1 - optical fiber; 2 - metal capillary; 3 - heating platform; 4 - filler metal; 5 - stirring rod; 6 - ultrasonic generator; 7 - ultrasonic welding horn; 71 - arc groove; 8 - grating area; 9 - brazed joint; 10 - protection tube; 11 - optical fiber pigtail; 12 - jumper wire. Specific implementation manner

[0026] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. Usually, the components of the embodiments of the present application described and illustrated herein can be arranged and designed in various different configurations.

[0027] Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed present application, but merely represents selected embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts fall within the scope of protection of the present application.

[0028] The features and performance of the present application will be further described in detail below in conjunction with the embodiments.

[0029] This embodiment discloses a packaging method for a capillary FBG temperature sensor based on ultrasonic-assisted brazing, including the following steps: S1. Pretreatment: First, remove the coating layer of the optical fiber 1, and ultrasonically clean the optical fiber 1, metal capillary 2, and filler metal 4 through an ultrasonic cleaner to remove surface impurities; S2. Assembly: As Figure 1 shown, pass the optical fiber 1 through the metal capillary 2, place the metal capillary 2 on the heating platform 3, ensure that the grating area 8 of the optical fiber 1 is located at the center position of the metal capillary 2, vertically press the ultrasonic welding horn 7 downward on the metal capillary 2, and use the arc groove 71 at the lower end of the ultrasonic welding horn 7 to match the metal capillary 2 to achieve limit fixation, and place the filler metal 4 at both ends of the metal capillary 2; S3. Ultrasonic-assisted brazing: First, turn on the heating platform 3 to only melt the filler metal 4, and continuously stir the filler metal 4 through the stirring rod 5 to make it evenly distributed at the end of the metal capillary 2, then turn on the ultrasonic welding horn 7, vertically apply ultrasonic vibration to the metal capillary 2, after the ultrasonic vibration ends, stop heating, and take it out after the filler metal 4 at the end of the metal capillary 2 is completely solidified, that is, the packaging is completed.

[0030] Brazing is a welding method in which the filler metal 4 and the workpiece to be welded are heated simultaneously to the melting temperature of the filler metal below the melting point of the workpiece to be welded, and the liquid filler metal 4 is used to fill the gaps of the solid workpiece to achieve metal connection. Brazing requires a relatively low temperature, the joints are smooth and have little deformation, and reliable connection of dissimilar materials can be achieved. Ultrasonic-assisted brazing is based on brazing and integrates the high-frequency vibration of ultrasound. The filler metal 4 is vibrated at a high frequency in a molten state to break the oxide film of the substrate to achieve welding. This method applies ultrasonic-assisted brazing to the encapsulation process of capillary FBG temperature sensors. Compared with mechanical fixed encapsulation, it has the advantages of small structural size and light weight, and can be installed in an airborne system with a small space or embedded inside electromechanical components to achieve real-time temperature measurement of the measured object. Compared with adhesive encapsulation, it has the advantages of reliable connection and stable operation under high and low temperature conditions, avoiding the problem of temperature measurement uncertainty caused by the high-temperature creep of the adhesive. Compared with fusion welding encapsulation, it can ensure the integrity of the optical fiber 1, thereby ensuring the normal and high-quality transmission of optical signals, and avoiding the problems of optical signal loss or optical fiber fracture caused by fusion welding encapsulation. Compared with ordinary brazing, the cavitation effect of ultrasound promotes the wetting and uniform distribution of the filler metal 4 on the surfaces of the optical fiber 1 and the metal capillary 2. Therefore, it can ensure the long-term stability and reliability of capillary FBG temperature sensors and expand the measurement range of the sensors.

[0031] Regarding the optical fiber 1: The optical fiber 1 is used as a temperature-sensing element, and its material is quartz glass (SiO2). As Figure 2 shown, a grating region 8 is arranged at the central position of the optical fiber 1.

[0032] Regarding the metal capillary 2: In order to ensure the light weight and miniaturization of the capillary FBG temperature sensor, in this embodiment, the inner diameter of the metal capillary 2 is 0.2 mm - 0.4 mm, the outer diameter is 0.4 mm - 0.6 mm, and the length is 12 mm - 20 mm.

[0033] For the purpose of the feasibility and high connection strength of the connection of dissimilar materials under the ultrasonic-assisted brazing process, the metal capillary 2 can be made of titanium alloy, aluminum alloy, copper alloy, stainless steel, invar (4J36), etc. Considering the relevant characteristics and uses of the capillary FBG temperature sensor, in this embodiment, the metal capillary 2 is preferably made of copper alloy and invar (4J36) materials.

[0034] The metal capillaries 2 made of copper alloy and invar (4J36) materials can both protect the FBG from external interference and damage, and: As Figure 3 and Figure 4As shown, the metal capillary 2 is made of a copper alloy material with an extremely high coefficient of thermal expansion, which can significantly increase the sensitivity of the capillary FBG temperature sensor. The sensitivity calculation formula of the capillary FBG temperature sensor is as follows:

[0035] In the formula, and are the initial central wavelength and the drift amount of the central wavelength of the FBG, respectively; represent the coefficient of thermal expansion, the thermo-optic coefficient, and the elasto-optic coefficient of the optical fiber 1, respectively; is the coefficient of thermal expansion of the material of the metal capillary 2; After calculation, when the grating wavelength of the optical fiber 1 is 1550 nm, the sensitivity of the temperature sensor encapsulated with copper alloy reaches 31.04 pm / °C, which is about three times the temperature measurement sensitivity of the bare grating of 11.2 pm / °C.

[0036] As Figure 5 and Figure 6 shown, the metal capillary 2 is made of invar (4J36) material with an extremely low coefficient of thermal expansion, which can reduce the risk of the optical fiber 1 detaching from the metal capillary 2 at high and low temperatures.

[0037] Regarding the solder 4: As Figure 3 , Figure 5 and Figure 7 shown, the solder 4 therein uses a tin-based solder. The tin-based solder has a low melting point. For example, the tin-based solder of model CS297 has a melting point of 297°C. The solder composition of this model contains elements with solid chemical affinity for oxygen, such as zinc, titanium, silicon, aluminum, and rare earths. These elements form relatively stable compounds at the welding interface, which is an important reason for realizing welding. The solder 4 has stable chemical properties, can not only ensure the reliability of welding, improve the temperature measurement range, but also has the ability of corrosion resistance and can work stably in the airborne system.

[0038] Regarding the parameters of ultrasonic-assisted soldering: In this embodiment, during soldering, the heating temperature applied by the heating platform 6 is 330°C, the vibration frequency of the ultrasonic vibration applied by the ultrasonic welding horn 7 is 60KHz, and the ultrasonic power is 15W. The USS-9210Mkll type ultrasonic vibration-assisted soldering vibration system can be selected as the ultrasonic-assisted soldering equipment. This equipment is mainly composed of an ultrasonic generator 9, a heating platform 7, a pressurizing device (including the ultrasonic welding horn 7), and a support structure. The heating temperature of this equipment is 150°C - 480°C, the temperature control accuracy is 1°C, the frequency of the ultrasonic drive power supply is 60KHz, and the output range of the amplitude is 3μm - 10μm.

[0039] Regarding the ultrasonic welding horn 7: As Figure 1 shown, in this embodiment, a plurality of arc grooves 71 with different sizes are provided at the lower end of the ultrasonic welding horn 7 to match metal capillary tubes 2 with different outer diameters.

[0040] Regarding the subsequent processing after encapsulation: As Figure 2 and Figure 7 shown, after encapsulation, a protective tube 10 can be sleeved on the fiber optic pigtail 11 at the brazed joint 9. The protective tube 10 is made of a high-performance polyester elastomer material to prevent the fiber optic pigtail 11 from breaking and affecting the input and output of signals. The material of the protective tube 10 has excellent high-temperature resistance, ultraviolet resistance, antistatic performance, and abrasion resistance, and has elasticity, which can play a good protective role for the fiber optic pigtail 11 that is easily broken at the brazed joint 9.

[0041] As Figure 5 shown, after encapsulation, the fiber optic pigtail 11 can be connected to the jumper wire 12 to transmit optical signals, and the jumper wire 12 can be connected to the wavelength demodulator and the upper computer to obtain temperature signals.

[0042] Test comparison: Figure 8 is a comparison chart of the response characteristics of the capillary FBG temperature sensor after brazing encapsulation with ultrasonic-assisted tin-based solder at high temperatures. Both the bare FBG temperature sensor and the capillary FBG temperature sensor after brazing encapsulation with ultrasonic-assisted tin-based solder have good continuity between 70 °C and 280 °C. The capillary FBG temperature sensor encapsulated with epoxy resin shows poor high-temperature resistance. At about 115 °C, due to the failure of the epoxy resin in a high-temperature environment, the real-time curve shows a distortion phenomenon.

[0043] Figure 9 is a comparison chart of the response characteristics of the capillary FBG temperature sensor after brazing encapsulation with ultrasonic-assisted tin-based solder at low temperatures. The capillary FBG temperature sensor after brazing encapsulation with ultrasonic-assisted tin-based solder has a better temperature sensing effect between -50 °C and 20 °C, while the capillary FBG temperature sensor encapsulated with epoxy resin starts to show abnormalities near -25 °C.

[0044] The embodiments described above are some, but not all, of the embodiments of the present application. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application claimed, but merely represents the selected embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without making creative efforts fall within the scope of protection of the present application.

Claims

1. A packaging method for a capillary FBG temperature sensor based on ultrasonic-assisted soldering, characterized in that: First, remove the optical fiber coating, and perform ultrasonic cleaning on the optical fiber, metal capillary, and solder to remove surface impurities; Then, pass the optical fiber through the metal capillary, place the metal capillary on the heating platform, ensure that the fiber grating area is located at the center of the metal capillary, vertically press the ultrasonic welding horn down on the metal capillary, and use the arc groove at the lower end of the ultrasonic welding horn to match the metal capillary to achieve limit fixation. Place solder at both ends of the metal capillary; then turn on the heating platform to only melt the solder, and continuously stir the solder to make it evenly distributed at the ends of the metal capillary; then turn on the ultrasonic welding horn and apply ultrasonic vibration vertically to the metal capillary; after the ultrasonic vibration ends, stop heating, and take it out after the solder at the ends of the metal capillary has completely solidified, that is, the encapsulation is completed.

2. The capillary FBG temperature sensor packaging method based on ultrasonic-assisted brazing according to claim 1, wherein: The inner diameter of the metal capillary is 0.2 mm - 0.4 mm, the outer diameter is 0.4 mm - 0.6 mm, and the length is 12 mm - 20 mm.

3. The capillary FBG temperature sensor packaging method based on ultrasonic-assisted soldering as claimed in claim 1, wherein: The metal capillary is made of copper alloy material.

4. The capillary FBG temperature sensor packaging method based on ultrasonic-assisted soldering according to claim 1, characterized in that: The metal capillary is made of invar material.

5. The capillary FBG temperature sensor packaging method based on ultrasonic-assisted soldering according to claim 1, wherein: The solder uses tin-based solder.

6. The capillary FBG temperature sensor packaging method based on ultrasonic-assisted soldering according to claim 1, characterized in that: During brazing, the heating temperature applied by the heating platform is 330 °C, the vibration frequency of the ultrasonic vibration applied by the ultrasonic welding horn is 60 KHz, and the ultrasonic power is 15 W.

7. The capillary FBG temperature sensor packaging method based on ultrasonic-assisted soldering according to claim 1, characterized in that: There are multiple arc grooves with different sizes at the lower end of the ultrasonic welding horn to match metal capillaries with different outer diameters.

8. The capillary FBG temperature sensor packaging method based on ultrasonic-assisted soldering according to claim 1, wherein: After encapsulation, a protective tube is sleeved on the optical fiber pigtail at the brazed joint. The protective tube is made of high-performance polyester elastomer material to prevent the optical fiber pigtail from breaking and affecting the input and output of signals.

9. The capillary FBG temperature sensor packaging method based on ultrasonic-assisted brazing according to claim 1, characterized in that: After encapsulation, connect the optical fiber pigtail to the jumper to transmit the optical signal, and connect the jumper to the wavelength demodulator and the host computer to obtain the temperature signal.

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