Optimisation of silver paste for flexography printing on LTCC substrate

The originality of this work consists in printing on ceramic tapes conductive silver tracks that reach a low resistivity by flexography process. Flexography is a solution for the mass production of multimaterial microdevices offering a huge potential of commercialisation in the near future. In order to test the flexography printing process for microelectronic application on Low Temperature Cofired Ceramic (LTCC) tapes, a screen printing paste was optimised to reach flexography printing requirements. Ink with 30% silver per weight was prepared and printed by flexography, roll to roll (R2R) process, on LTCC substrates. Three to five print passes were performed. Printed lines were sintered during 10 min at a peak temperature of 850 °C under normal air atmosphere. Conductive lines, with a mean width of 190 μm, a mean thickness of 1.50 μm and a resistivity of 2.8 × 10−8 Ω m close to bulk silver resistivity, were achieved after sintering.

► 30% Ag ink with 36 mPa s viscosity was prepared.
► Conductive Ag lines were printed by R2R on LTCC.
► Sintering under normal atmosphere −850 °C – 15 min.
► Narrowest line width = 150 μm. Maximum line thickness = 3.47 μm.
► A minimum resistivity of 28 nΩ m was obtained.