Electroless Plating Cycle Process for High-Conductivity Flexible Printed Circuits

In this work, a non-formaldehyde electroless plating cycle process was successfully applied to prepare the flexible copper printed circuits on poly (ethylene terephtalate) (PET) films. Copper nanoparticles (Cu NPs) were employed as catalytic seeds, and dimethylaminoborane (DMAB) was used as the reductant. Cu NPs were directly printed on the PET surface modified by 3-mercaptopropyltriethoxysilane (MPTES) to serve as the seeds to trigger the electroless deposition. MPTES modification can dramatically improve the adhesion of the PET and Cu layer. Cu NPs can ideally substitute noble metals Ag, Pt, and Pd to catalyze electroless deposition. DMAB, as an innocuous reductant can replace formaldehyde in an alkalescent plating bath. The amount of Cu NPs with different sizes on the per area of the PET surface was investigated to determine its appropriate dosage. Various times, temperatures, concentrations of reactants in the electroless plating process were researched to obtain optimal deposition. The minimal sheet resistance of the copper pattern was 6 mΩ/sq with a resistivity of 2.01 μΩ·cm, which is 1.18 times that of bulk copper. These results demonstrated that the prepared Cu pattern had excellent conductivity. The kinetics of the electroless plating process was researched to quantify the thickness of the Cu layer and the consumption of reactants. The electroless plating bath can well be cycled after compensating reactants, while the sheet resistance of the Cu pattern fluctuated very little. The cycling electroless plating bath will greatly reduce the discharge of waste and is of vital significance for the large-scale and cheap manufacturing of flexible printed electronics.