Date of Graduation

8-2025

Document Type

Thesis

Degree Name

Master of Science in Mechanical Engineering (MSME)

Degree Level

Graduate

Department

Mechanical Engineering

Advisor/Mentor

Shou, Wan

Committee Member

Wang, Dongyi

Second Committee Member

Hu, Han

Keywords

Laser Sintering; Manufacturing; Nanoparticle

Abstract

Copper (Cu) is widely utilized in electronics and photonics applications due to its outstanding electrical and thermal conductivity. With increasing demand for miniaturization and higher precision in modern manufacturing, traditional selective laser sintering (SLS) techniques designed primarily for high-throughput production are becoming insufficient. These conventional methods struggle to deliver the resolution required for micro-scale fabrication and often cause thermal damage to sensitive substrates. Therefore, there is a growing necessity to develop compact and high-resolution laser sintering systems capable of precise microfabrication with minimal thermal influence. This study addresses this challenge by investigating nanosecond pulsed laser sintering as a method to achieve precise and energy-efficient fabrication of copper nanoparticles (Cu NPs) structures. Specifically, 70 nm Cu NPs were uniformly deposited onto aluminum foil substrates using a dry electrostatic powder coating method, avoiding solvent-related complications common in ink-based printing. A UV laser with a fixed wavelength of 355 nm was employed, and systematic experiments were conducted by exploring multiple key variables, including laser average power, repetition rate, scanning speed, focal spot location, and powder packaging density. Through careful optimization of these parameters, appropriate laser fluence conditions were identified, enabling effective sintering with minimal thermal damage and improved control over the morphology and quality of the fabricated microstructures. Experiments were conducted to selectively sinter Cu NPs into 2D microstructure. The sintered samples were thoroughly analyzed using scanning electron microscopy (SEM) to evaluate their microstructure and porosity. Results indicated that optimized parameter control enabled the formation of dense, smooth copper features with linewidths below 20 µm and minimal thermal impact on surrounding areas. Furthermore, short-wavelength UV laser processing showed significantly enhanced absorption by copper nanoparticles compared to conventional infrared lasers commonly used in commercial metal 3D printing, thereby improving overall energy efficiency. This work provides insights into the fundamental mechanisms underlying UV nanosecond laser-matter interactions during metallic nanoparticle sintering. By establishing optimized processing conditions, our findings support the advancement of precise and energy-efficient additive manufacturing techniques for copper and other metal nanopowders. The outcomes hold promises for broad applications, including flexible electronics, biomedical sensors, aerospace components, and microscale devices, ultimately contributing to innovation in precision manufacturing.

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