Microscale selective laser sintering of Cu nanoparticles with a short-wavelength nanosecond laser

TL;DR

This study demonstrates that using a short-wavelength UV nanosecond laser enables high-resolution microscale additive manufacturing of copper nanoparticles, achieving sub-20 micron features with improved energy efficiency and morphology.

Contribution

It introduces the use of UV nanosecond lasers for copper nanoparticle sintering, achieving sub-20 micron resolution and providing insights into laser-metal nanoparticle interactions.

Findings

Short-wavelength laser reduces energy requirements for sintering.

Densified nanoparticle beds favor continuous melting.

Sub-20 micron printing is achievable with UV ns laser.

Abstract

Microscale additive manufacturing of reflective copper is becoming increasingly important for microelectronics and microcomputers, due to its excellent electrical and thermal conductivity. Yet, it remains challenging for state-of-the-art commercial metal 3D printers to achieve sub-100-micron manufacturing. Two aspects are sub-optimal using commercial laser powder bed fusion systems with infrared (IR) lasers (wavelength of 1060-1070 nm): (1) IR laser has a low absorption rate for Cu, which is energy-inefficient for manufacturing; (2) short wavelength lasers can potentially offer higher resolution processing due to the diffraction-limited processing. On the other hand, laser sintering or melting typically uses continuous wave (CW) lasers, which may reduce the manufacturing resolution due to a large heat-affected zone. Based on these facts, this study investigates the UV (wavelength of 355 nm) nanosecond (ns) laser sintering of Cu nanoparticles. Different laser processing parameters, as well as different nanoparticle packing densities, are studied. Our results show that a short-wavelength laser can reduce the required energy for sintering with decent morphology, and a densified nanoparticle powder bed favors continuous melting. We further show that sub-20 micron printing can be readily achieved with a UV ns laser. These findings provide new insights into short-wavelength laser-metal nanoparticle interactions, which may pave the way to achieve high-resolution micro and nano-scale additive manufacturing.