| Summary: | 碩士 === 國立中興大學 === 機械工程學系所 === 106 === In this study, the microscale bubble formation and dynamics in the Laser Direct Synthesis and Patterning (LDSP) process for patterning and fabricating micro silver structure on flexible substrate was investigated experimentally. A method to effectively remove the bubbles thus to improve the tield and properties of the silver structure fabricated by the LDSP process was also proposed and demonstrated. In the LDSP process, continuous blue laser was used as light source to be focused on the polyimide (PI) substrate, where a certain amount of transparent non-toxic reactive silverionic solution was coated on the flexible substrate. The solution near the laser focal spot was chemically reduced to form silver structure in-situ due to the elevated temperature after the PI absorbed the energy from the laser. The LDSP process can be operated under normal temperature and pressure without any toxic solution and expensive equipment. In addition, the expensive mask used in the traditional semiconductor process was not required in the LDSP process. Therefore, it is a rapid, economic, environmental friendly process for fabricating micro-elecronics, especially for flexible and wearable electronics where low temperature and highly reconfigurable process is needed. However, in the LDSP process, gas bubbles form near the laser focus spot mainly owing to the byproduct, carbon dioxide, being generated from the chemical reaction. These bubbles adversely affect the continuity and robustness of the fabricated silver patterns, and thus the electrical resistance of the resulted silver lines increases.
In this study, the formation and dynamics of the gas bubbles in the LDSP process with a variety of process parameters were investigated using a high-speed camera system in conjunction with image process technique. The mechanism for the formation of the ring-like structure of the firstly synthesized and deposited silver line during the LDSP process was also analyzed and discussed based on experimental measurements. To reduce the damage on the synthesized and patterned silver line due to gas bubbles, an actuator was used to induced micro-vibration of the substrate during the LDSP process, which in turn resulted bubble sliding, collision, merging and departing from the substrate surface. The effectiveness of the bubble removal by a variety of vibration frequencies were tested and analyzed. It is demonstrated that the gas bubble generated on the substrate surface from chemical reaction during the LDSP process can be effectively removed with micro-vibrating of the substrate, and this greatly improves the mechanical and electrical properties of the silver micro structures.
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