Study On Curing Silver Paste For High-Resolution And High-Conductivity

The conductive silver paste is one of the key basic materials of thick film electronic components by printing, which has been widely used as electric wiring for the field of electronic information and has a large of requirement. At present, the electronic and information technology has put forward higher requirements for the miniaturization and integration of products. That forces the wiring to have smaller width and spacing, and minor resistance. Therefore, studying on curing silver paste for high-resolution and high-conductivity is very important. The paper mainly studies on the curable conductive silver paste used for screen printing. Through analyzing the basic factors and their mechanics which have notable impact on the resolution and conductivity of the printed pattern, this work seeks for providing theoretic references and technical supporting of fabricating silver paste with high resolution and conductivity simultaneously.By adopting control variate method, silver pastes of different components are screen printed onto PET substrates and then cured to make samples with certain shapes and sizes. Optical microscope is used for obtaining surface morphology for further analyzing. Additionally, the resistance and thickness of the single patterns are tested to estimate the sheet resistance and its relevant factors. The results of this work show that the printing parameters, wettability between silver paste and substrate and the rheological behaviors of the silver paste are the three fundamental factors that influence the resolution of screen printed patterns; Meanwhile, the component and curing process.Comparing the photos of the conductive patterns taken by the microscope, we conclude that overall broadening, scalloped edges, satellite drops, spikes and local bulging are five major forms resulting in the deteriorating of pattern's resolution. Among them overall broadening and scalloped edges have the biggest impact on pattern's resolution. Results show that increasing speed, angle of the slicker as well as the separate distance can decrease the broadening to some degree; Advisably decrease the surface tension of the substrate or increase that of the paste could also alleviate the broadening; Relatively speaking, silver pastes with high viscosity, low yield strength, rapid structural recovery and relatively weak wire-drawing ability could also benefit the resolution.Experiments were carried to figure out the relationship between the sheet resistance of the pattern and the component of the paste. By constructing mathematical models, mechanism and principles are made to clarify the factors that are responsible to the conductivity of membrane forming. Consequently, schistose silver powders ball milled by spherical powders and highly schistosed powders with large diameter-thickness ratio, clean and cureless surface are generally highly conductive. Moreover, resins with appropriate molar weight and high polarity also avail low sheet resistance.