While reflection phenomena are well-established in optics, their influence on laser direct patterning processes has largely been neglected. In this study, we demonstrate that internal laser reflection plays a critical role in pattern formation and reaction kinetics during copper precursor sintering. Our findings reveal two key factors governing the process. First, internal reflections significantly enhance the patterning process at low-energy beams, challenging the conventional assumption that thinner films pattern more readily due to higher energy absorption per unit thickness. Second, internal laser reflections sustain the concentration of reaction intermediates, stabilizing the sintering process and enabling efficient patterning, even at lower laser power. Furthermore, we demonstrate the crucial influence of water adsorption on both the film thickness and electrical properties. Water not only increases the film thickness─enhancing reflection effects─but also alters electron transport within the precursor, accelerating intermediate dissolution. This interplay between internal reflection and water-mediated electron dynamics provides a deeper understanding of laser direct patterning mechanisms. Additionally, by implementing laser patterning on an affordable 3D printer platform, we showcase its potential for scientific applications. Our findings emphasize the need to reconsider laser reflection effects, particularly in low-power laser systems, to optimize factors for achieving fine patterns.
Keywords: 3D printer platform; internal laser reflection; laser direct copper patterning; reaction kinetics; water adsorption effect.