A Novel Packaging Method for FBG Temperature Sensors Based on Ultrasonic-assisted Soldering Technology

The packaging technology of fiber Bragg grating (FBG) sensors is the key to determining their operational performance. A method for encapsulating FBG temperature sensors using ultrasonic-assisted soldering technology has been proposed and attempted. This packaging method is based on the successful connection between SiO2 quartz glass and Invar alloy. Implementing this soldering connection depends on the active components in the solder, which are dispersed into SiO2 and metal alloys to form more stable substances. The FBG with the removed coating is reliably connected to the metal capillary through ultrasonic soldering. The fragile FBG is adequately protected in the capillary. Sn-based solder with a melting point of 297 ℃ has been selected. The soldering temperature of 330 ℃ avoids significant residual stress caused by the difference in the thermal expansion coefficient of the material at the joint. Excellent bonding strength between optical fibers, solder, and capillaries is necessary for encapsulating sensors. Compared to adhesive, solder packaging is no longer affected by the creep of the sealant. The results show that the working range of FBG temperature sensors encapsulated in epoxy resin is -25 ℃ -115 ℃, while temperature sensors encapsulated by welding can operate stably at -50 ℃ -280 ℃. Sensors packaged using ultrasonic-assisted soldering technology have the potential to be embedded in metal substrates, creating favorable conditions for the development of intelligent electromechanical components.