Laser processing of printed copper interconnects on polymer substrates

With the increasing demand for integration of electronics embedded within devices there has been a consequent increase in the requirement for the deposition of electrically conductive materials to form connecting tracks on or within non-traditional substrate materials, such as temperature sensitive polymers, that may also have non-planar surfaces. In this work, micron scale copper powder based materials were deposited onto acrylic and glass substrates and then selectively laser processed to form electrically conductive copper tracks. Before deposition, the copper powder was chemically treated to remove the surface oxide and subsequently protected with a self-assembled monolayer coating. The copper was then patterned onto the substrate either as a dry powder confined within pre-formed grooves, or was combined with a binder to be printed as a paste. A CO2 laser was then used to heat the copper powder in air, leading to tracks that showed good electrical conductivity. At low laser power levels, the tracks appeared largely unchanged from the original material, but showed measureable conductivity. With higher laser power levels the tracks showed evidence of partial melting of the surface layers and further reductions in resistivity, to values approximately 30 times those of bulk copper, were obtained