Insight into the surface behavior and dynamic absorptivity of laser removal of multilayer materials.

Laser-materials interaction is the fascinating nexus where laser optics, physical/ chemistry, and materials science intersect. Exploring the dynamic interaction process and mechanism of laser pulses with materials is of great significance for analyzing laser processing. Laser micro/nano processing of multilayer materials is not an invariable state, but rather a dynamic reaction with unbalanced and multi-scale, which involves multiple physical states including laser ablation, heat accumulation and conduction, plasma excitation and shielding evolution. Among them, several physical characteristics interact and couple with each other, including the surface micromorphology of the ablated material, laser absorption characteristics, substrate temperature, and plasma shielding effects. In this paper, we propose an in-situ monitoring system for laser scanning processing with coaxial spectral detection, online monitoring and identification of the characteristic spectral signals of multilayer heterogeneous materials during repeated scanning removal by laser-induced breakdown spectroscopy. Additionally, we have developed an equivalent roughness model to quantitatively analyze the influence of surface morphology changes on laser absorptivity. The influence of substrate temperature on material electrical conductivity and laser absorptivity was calculated theoretically. This reveals the physical mechanism of dynamic variations in laser absorptivity caused by changes in plasma characteristics, surface roughness, and substrate temperature, and it provides valuable guidance for understanding the dynamic process and interaction mechanism of laser with multilayer materials.

High-quality and efficient large-area copper removal utilizing laser-induced active mechanical peeling.

Large-area copper layer removal is one of the essential processes in manufacturing printed circuit boards (PCB) and frequency selective surfaces (FSS). However, laser direct ablation (LDA) with one-step scanning is challenging in resolving excessive substrate damage and material residue. Here, this study proposes a laser scanning strategy based on the laser-induced active mechanical peeling (LIAMP) effect generated by resin decomposition. This scanning strategy allows the removal of large-area copper layers from FR-4 copper-clad laminates (FR-4 CCL) in one-step scanning without additional manual intervention. During the removal process, the resin decomposition in the laser-irradiated area provides the mechanical tearing force, while the resin decomposition in the laser-unirradiated area reduces the interfacial adhesion force and provides recoil pressure. By optimizing scanning parameters to control the laser energy deposition, the substrate damage and copper residue can be effectively avoided. In our work, the maximum removal efficiency with different energy densities, pulse duration, and repetition frequency are 31.8 mm2/ms, 30.25 mm2/ms, and 82.8 mm2/ms, respectively. Compared with the reported copper removal using laser direct write lithography technology combined with wet chemical etching (LDWL+WCE) and LDA, the efficiency improved by 8.3 times and 66 times. Predictably, the laser scanning strategy and the peeling mechanism are simple and controllable, which have potential in electronics, communications, and aerospace.

Laser adaptive processing technology for multilayer dissimilar materials.

We report a laser adaptive processing technology (LAPT) for the selective removal of Cu/Al multilayer dissimilar materials. Using the wavelength range and intensity distribution of the characteristic spectrum, the properties and content of multilayer dissimilar materials can be analyzed online based on laser-induced breakdown spectroscopy. The traditional low-speed spectral detection mode was transformed into a high-speed photoelectric detection method by using a scheme consisting of a bandpass filter with an avalanche photodetector (APD), and the in situ online detection of a 30 ns, 40 kHz high-frequency pulse signal during laser scanning was realized. Combined with a field programmable gate array (FPGA) digital control unit, online feedback and closed-loop control were achieved at the kHz level, and the adaptive intelligent control of material interfaces and laser processing parameters was achieved. This excellently demonstrated the feasibility and flexibility of LAPT for processing arbitrary multilayer dissimilar materials.