Study On Picosecond Laser Induced Forward Transfer And Laser Sintering Of Silver Paste

With the development of laser technology,laser micro processing has been applied in many fields,such as laser etching,surface modification,and additive manufacturing.Laser induced forward transfer(LIFT)is one of the micro processing technology which has a good development prospect in manufacturing process of microelectronic products for the unique advantages like strong adaptability,high processing accuracy,low cost,environmental protection and wide application range.LIFT is mainly used for processing high-resolution micro patterns or micro devices with solid and metal ink.When metal patterns are fabricated with metal ink,sintering process will be applied to evaporate the solvent and obtain better conductivity.As an efficient and high selective curing process,laser sintering has been applied in the production process of sensors,electronic components and integrated circuits.In this project,the technological parameters of LIFT and laser sintering technology were studied in order to prove the feasibility of the combination of LIFT and laser sintering technology.Picosecond laser was employed to study the procession of silver paste lines:1.Silver deposition points were processed by picosecond laser based on LIFT.The experimental platform for LIFT and laser sintering was established.Single deposited points were processed with single pulse laser based on LIFT.Laser pulse energy,film thickness and the gap were changed to analyze the variation of diameter and height of deposition points systematically.High-speed camera was applied to observe transfer process at different energies for further analysis of dynamical behaviors of jet.The silver deposition point with uniform morphology is fabricated when single pulse laser energy,film thickness and gap is 20 ?J,20 ?m and 150 ?m,respectively.2.Continuous silver lines were processed with multiple-pulse based on LIFT.The influence of different laser energies and scanning speeds on the morphology of deposited silver lines were studied.Continuous and uniform silver lines were successfully processed under the laser energy of 20 ?J and scanning speed of 25 mm/s.Then,silver lines were placed in an oven and sintered at different temperatures.The resistivity of silver lines was measured with four-point probe method by digital multimeter.The morphology of silver lines was further analyzed with the help of confocal laser scanning microscopy(CLSM)and scanning electron microscope(SEM).It is learned that the silver line sintered in an oven with the temperature of 448 K for 30 minutes achieves the best conductivity of 2.35×10-7?m.3.The experiment and simulation of laser sintering were carried out.Silver lines were sintered by picosecond laser with different laser energies,laser frequencies and scanning speeds.The finite element model and two-temperature model based on COMSOL were established to calculate the temperature distribution of silver lines.T The resistivity of silver lines was measured with four-point probe method by digital multimeter,and the morphology was analyzed with CLSM and SEM images.It can be learned that the lowest resistivity of silver lines is 1.42×10-7?m(sintered at laser pulse energy of 1.3 ?J,laser frequency of 0.8 MHz and scanning speed of 9 mm/s),which is about 9 times of the resistivity of silver.4.Micro patterns were manufactured based on LIFT and laser sintering.On the basis of manufacturing continuous and uniform silver lines with good electrical conductivity,three simple applications were processed.Firstly,LED circuit was processed and the LED was successfully lighted up after accessing to the 5 V voltage source.Secondly,humidity micro sensor was fabricated.The capacitance response value of the humidity micro sensor in different humidity environments was measured,and the main character like sensitivity and stability of the sensor were further analyzed.The capacitance value of humidity micro sensor increases with the increase of relative humidity.The stability and sensitivity keeps quite good in low humidity range and high humidity range respectively.Thirdly,heavy metal ion micro sensor was printed.The volt-ampere characteristic curves of heavy metal ion micro sensor were analyzed by cyclic volt-ampere method and the detection effect of heavy metal ions was further studied by square wave anodic stripping voltammetry.The reversibility of heavy metal ion micro sensor is quite good,and the concentration of heavy metal ions in the solution can be detected approximately.