Journal of Applied Science and Engineering

Published by Tamkang University Press

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Accumulated-Energy-Controlled Nanosecond UV Laser Microvia Drilling in Cu–PI Copper-Clad Laminates

 2026

 Volume 35

Duong Duc Tai1,2, Vu Van Quang1

1Precision Engineering & Smart Measurement Lab, School of Mechanical Engineering, Hanoi University of Science and Technology, No. 1 Dai Co Viet Street, Hanoi 100000, Vietnam.

2Sumitomo Electronic Components (Vietnam) Co., Ltd

Received: June 20, 2026
Accepted: August 03, 2026
Publication Date: September 06, 2026

上傳圖片

Schematic of the experimental machining process.

 Copyright The Author(s). This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are cited.

Download Citation: BibTeX | http://dx.doi.org/10.6180/jase.202612_35.022

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Conductive microvias in flexible printed circuits (FPCs) play a critical role in establishing electrical interconnections between circuit layers and directly affect the reliability of electronic systems. However, microvia drilling in flexible copper-clad laminate (FCCL) substrates with heterogeneous Cu-PI structures remain challenging because copper and polyimide exhibit significantly different optical, thermal, and ablation characteristics. This study proposes an integrated nanosecond UV laser machining strategy in which laser power, pulse repetition rate, scanning speed, and pressure-assisted debris extraction are coordinated to control the accumulated energy distribution and improve microvia quality. The hole-formation and material-removal mechanisms are analyzed based on laser-material interaction theory and an accumulated-energy model to guide parameter selection. Experiments were conducted using an industrial 355 nm UV Nd:YAG laser system with spiral and circular drilling strategies[cite: 15]. The results show that the optimized processing conditions, combining lower laser power, lower pulse repetition rate, higher scanning speed, and pressure-assisted debris removal, improved the taper ratio by 18.94 percentage points for spiral drilling and 6.42 percentage points for circular drilling compared with the baseline conditions. EDX analysis indicated a reduction in carbon-containing residues on the microvia sidewalls, with the carbon content decreasing from 11.87% to 9.29% for spiral drilling and from 8.86% to 7.54% for circular drilling. Meanwhile, SEM observations and laser microscopy confirmed improvements in hole geometry, surface quality, and taper control. These findings demonstrate the potential of the proposed strategy for stable and industrially compatible microvia fabrication in flexible electronic circuits.

Keywords: Conductive microvias; Flexible printed circuits/FPCs; Nanosecond UV laser machining; microvia quality; Cu-PI structures.

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