Lithography based Metal Manufacturing (LMM): Influence of particle size and composition of copper powder on UV light penetration

In this study, a Mie-theory-based computation was used to investigate the influence of two main factors (the particle size and the particle oxidation) affecting UV light transmission in copper loaded suspensions. The behavior of UV light penetration was then compared with highly loaded copper photocurable formulation used in 3D printing. According to the model, large particles (diameter > 2 µm) should be selected to afford UV transmission in a diluted (<10 vol%) copper suspension regardless of the oxidation of copper particles. For loading rate higher than 20 vol% transmission dramatically drops but the photopolymerization process remains efficient within the cured layer. This might confirm the hypothesis of UV light penetration through light scattering. Additional results on oxidized copper powders exhibited curing depths and curing kinetics that might be correlated to the less important light scattering compared to oxide-free powders. Solutions are proposed to tune curing depth by modifying the oxidation state of copper particles. The wise selection of copper powders and the application of thermal pre-treatment offers the opportunity to fabricate copper parts by Lithography based Metal Manufacturing (LMM).