A New Two-Step Process for Obtaining Thin Copper Flakes and Their Utilization in Conductive Inks

Fabrication of devices by printing conductive interconnections on plastic substrates is of growing interest. Metal flakes are an excellent component for conductive inks due to their favorable tight packing in printed layers. Currently silver flakes are wildly used; however the high cost of silver prevents their wide use in many electrical devices, and there is an unmet need for metal flakes with a cheaper metal such as copper. A new two-step process for obtaining thin copper flakes and their utilization in conductive inks is presented. In the first step, submicron copper particles were formed by thermal decomposition and self-reduction of copper formate. These copper particles were than milled in a wet bead mill that resulted in their transformation into thin flakes with an average thickness of 48 nm. XRD results indicated that the copper particles undergo plastic deformation in a mechanism similar to cold rolling. We have studied the effect of various process parameters and type of carboxylic acid as a dispersing agent on the morphology and electrical performance of the obtained particles. The flakes were used for ink formulations that after printing and thermal sintering, resulted in copper patterns with 22% of bulk copper conductivity. The copper flake ink was used to print functioning NFC antennas on Kapton, which were found to have a high bending durability.