Effect Of Solvent Type And Resin Molecular Weight On The Performance Of Low Temperature Curing Silver Pastes

With the electronic products develop rapidly toward smaller, lighter, thinner, and softer in recent years, flexible circuits which have both the characteristic of light and soft enjoyed great popularity. And as a key material to the production of flexible circuits, low temperature curing silver pastes also enjoying a sound momentum of development. Because of its large content, conductive phase and binder phase were mainly studied concerning low temperature curing silver pastes. However, for the same kind of resin, it may have different molecular weight, and it can be dissolved in many solvents. In order to more fully develop better conductive silver paste products, polyester resin were used as binder phase in this paper, and the effect of solvent type and resin molecular weight on the performance of low temperature curing silver pastes were studied. The specific contents are as follows:Cyclohexanone, butyl acetate, ethylene glycol ethyl ether acetate, propylene glycol monomethyl ether acetate, diethyl carbonate and dibasic acid ester mixture were chosen as the solvent to dissolve polyester resin, and silver pastes were prepared under the same process condition. The effect of solvent type on the performance of electrical conductivity, flexural resistance, adhesion to the substrate and stability of low temperature curing silver pastes were studied. The results show that, silver pastes prepared by using cyclohexanone as solvent has the best comprehensive performance, with the smallest sheet resistance, good flexural resistance, with an adhesion grade of 5B and good stability. In addition, thermogravimetric analysis and scanning electron microscopy(SEM) observation were made to determine the curing temperature of the sample and analyze the reasons of conductivity differentiation.4 polyester resins with different molecular weight were selected as binder phase to prepare silver pastes under the same process condition; the average molecular weight of polyester resin were measured and the effect of resin molecular weight on the performance of electrical conductivity, flexural resistance, adhesion to the substrate and stability of low temperature curing silver pastes were studied. The results show that, silver pastes prepared by using polyester resin with an weight average molecular weight of approximately 150000 has the best comprehensive performance, with the lowest sheet resistance of 36.73 m?/?, good flexural resistance, good adhesion and good stability. By observing the cross section SEM photograph of the samples before and after bending, the reason why sheet resistance becomes smaller after bending and smoothing were analyzed.Through optimizing the formulation, experimental verification, the best recipe of silver paste which has lowest silver content and sheet resistance lower than 100 m?/? was obtained as follow: polyester resin C, 7.5 wt%; CAC, 30 wt%; micron-sized flake silver and nano-scale silver particles: 51 wt%, and additives: 11.5 wt%.