Study On Preparation And Performance Of Conductive Films Based On Free-particles Of Silver Conductive Ink By Inkjet Printing

Printed electronics refers to the newly-developing technology that sprays the functional inks onto different substrates to prepare circuits and other kinds of electronic components by some follow-up steps without contacting with the substrates.When it comes to printed electronics,a film with conductivity by printing ink on it is called a printed conductive film.It is currently the most widely studied and the most basic application of printed electronic products.In this technology,electrical conductivity of printed circuits,anti-bend performance of circuits on the flexible substrates,combining capacity between printed circuits and substrates and welding properties of printed circuits are not only the key problems in the development of printed electronics but also the hot issue in the field of material and science both at home and abroad.Hence carrying out researches on the properties of printed circuits plays a significant role in the development of printed electronics.In this paper,silver acetate and formic acid function as the metal precursor and the reducing agent and ammonia water serves as the aqueous solution.Particle-free conductive silver ink can be prepared with the materials mentioned above.Making use of the modified flatbed ink jet printer and spraying ink onto the flexible polyethylene terephthalate polyester film?PET?and fiber glass board?FGB?,samples with good film-forming property are obtained.When the factors which may have influence on the electrical conductivity of printed circuits are being studied,the growth of crystal during the heat treatment and annealing is affected by both two growth mechanisms,Oriented Attachment?OA?and Ostwald Ripening?OR?.The mixture of two crystal growth mechanisms makes the particle arrangement more closely,which ensures the good conductivity of printed circuits.After carrying on research on the different layers of the printed circuit,the distribution of ink particles on the substrate is relatively uniform and compact when the printer prints 11 layers on the substrate,and stable conductivity can be found in the conductive film.The research on the annealing process shows that when the annealing process is carrying out at90? for 15 min,the electrical resistance can be as low as 4.1??·cm which is 2.5times that of massive siver.Additionally,the higher the temperature of annealing process is,the lower the electrical resistance will be,not varying greatly though.In consideration of the range of temperatures within which the flexible substrates can cope,annealing at 90? for 15 min is the optimal technological parameter.Then,researches have been carried out on the ultimate bending radius of curvature ofprinted circuits produced by printing 11 layers on the flexible PET substrates and annealing at 90? for 15 min.The adhesion between nano-silver and PET substrates has also been studied.The results show that upon the bending radius of curvature of flexible circuits reaches 1.5mm,the electrical resistance starts to change and the nano-silver layer in the printed circuits breaks completely as soon as the bending radius of curvature of flexible circuits reaches 0.5mm.In addition,the form and morphology of bending fracture are analyzed.The crack appears in the space between the ink droplets and develops along the outline of the droplets till the crack goes through the whole conductive film.Finally,ductile fracture happened.When the nano-silver layer breaks away from the PET substrate,the maximum shear force is 0.624 MPa and the stretching force is 0.15 MPa.Based on the morphology of the fractures,the result shows that most fractures occur between the nano-silver layer and the PET substrate while few occur within the nano-silver layer.Besides,experiments have been carried out on the weld ability of the printed circuits produced printing 11 layers on the rigid FGB which functions as the substrate and annealing at 90? for 15 min,tin-base brazing filler metals being the solder paste.Studies have been done to explore the growth process of metallurgy products and intermetallic compounds?IMC?layer during the welding process.The researches indicate that tin-base brazing filler metals react quickly with nano-silver layer with a high pore density.Good Ag₃Sn intermetallic compounds can be generated if the sintering temperature is 225? and the holding time is 5min.