Flexible PET Substrate for High-Definition Printing of Polymer Thick-Film Conductive Pastes

A major obstacle in screen printing conductive low-temperature curing polymer thick-film (PTF) pastes onto common flexible PET substrate materials is the substantial spread of the pastes beyond the designed line width after printing. Industry observation and controlled testing have shown this spread can be as much as 80% over the circuit design's intended line width. This phenomenon prevents designers from increasing circuit density and/or reducing circuit real estate without incorporating other more involved and higher cost patterning methods. In many cases, flexible circuit fabricators, desiring more accurate high-definition circuit elements, may have to subcontract parts out of house to incorporate alternate patterning methods. This subcontracting, in turn, leads to a loss of control of both cost and lead time. This article will provide results of numerous in-house and field testings, comparing printed line width control, edge definition, and improved conductivity of printed polymer Ag conductors on different flexible PET substrates.