Photoimageable silver paste for high density interconnection technology

We have formulated aqueous developable photoimageable thick film conductor pastes, which comprised of in-house processed submicron-sized silver powder (functional material), micron-sized lead borosilicate glass frit (permanent binder), epoxy acrylate resin with pendant -COOH group (base photoimageable polymer/temporary binder/organic vehicle) and 2,2′-dimethoxy-2-phenylacetophenone (photoinitiator). The conductor paste thus formulated was manually screen-printed on alumina substrate, dried, exposed to ultraviolet light through the desired test pattern, developed in 1% aqueous sodium carbonate solution and subjected to standard 1 h thick film firing cycle. The resultant samples were investigated for surface morphology, thermal behavior and electrical conductivity. Solid content of the polymer appears to influence the paste performance. Prima facie observations indicate that the paste corresponding to polymer solid content of 89.9% and organic:inorganic ratio of 28:72 exhibits better electrical conductivity, thermal stability, relatively smooth surface finish and line/space resolution of 100 μm with ±5 μm accuracy.