We report on a comprehensive study of laser percussion microvia drilling of FR-4 printed circuit board material using ultrashort pulse lasers with emission in the green spectral region. Laser pulse durations in the pico- and femtosecond regime, laser pulse repetition rates up to 400 kHz and laser fluences up to 11.5 J/cm2 are applied to optimize the quality of microvias, as being evaluated by the generated taper, the extension of glass fiber protrusions and damage of inner lying copper layers using materialography. The results are discussed in terms of the ablation threshold for FR-4 and copper, heat accumulation and pulse shielding effects as a result of pulse to pulse interactions. As a specific result, using a laser pulse duration of 2 ps appears beneficial, resulting in small glass fiber protrusions and high precision in the stopping process at inner copper layer. If laser pulse repetition rates larger than 100 kHz are applied, we find that the processing quality can be increased by heat accumulation effects.
We report on the characterization of a hybrid laser scanning system using acousto-optical deflectors in combination with galvanometer scanners for ultra-short pulse laser material processing. The hybrid scanning system is characterized by the roundness of static pulsed ablations of metal thin film on a transparent substrate within the acousto-optical scanning field at different galvanometer scanner deflection angles and laser focal positions. An ablation roundness of more than 90% is reached in a defocusing range of 200 $$\upmu \text{m}$$ μ m within a galvanometer scanfield of 900 $$\text{mm}^2$$ mm 2 , corresponding to approximately 74% of the usable scan area of the f-theta lens. A high maximum positioning speed of 843 m/s is pointed out within an acousto-optical scanfield of 0.4 $$\text{mm}^{2}$$ mm 2 by applying positioning frequencies of up to 1 MHz across a distance of 843 $$\upmu \text{m}$$ μ m . Consequently, the hybrid scanning system combines the advantages of optical and mirror-based scanners, enabling a highly dynamic and extremely precise laser beam positioning in a large processing area.
Advanced packaging technologies like wafer-level fan-out and 3-D system-in-package (3-D SIP) are rapidly penetrating the market of electronic components. For cost reduction, one approach is the migration of processes from wafer to panel format, called panel-level packaging (PLP). In a consortium of partners from industry and research, advanced technologies for PLP are developed. The project aims for an integrated process flow for 3-D SIPs with chips embedded into an organic laminate matrix. At first, 6 mm × 6 mm chips (100 µm thickness) with Cu bumps (25-µm height, 110-µm pitch) are placed into cavities of a printed circuit board (PCB) core layer. They are embedded by vacuum lamination of thin organic films. The core is equipped with fiducials for local alignment and provides handling robustness. Developments aim for a final panel size of 600 mm × 600 mm (here 227 mm × 305 mm demonstrated). Onto the contact side of embedded chips, a 25-µm dielectric film is applied. The copper bumps are subsequently opened by plasma etching. By sputtering and electroplating of Cu, electrical contacts to the chips are formed without via opening. Highaspect-ratio vias as an element for vertical interconnects are formed by UV laser drilling. At via diameters of 17 µm, a drill hole depth of 74 µm was achieved (aspect ratio 4.4:1). Using a newly developed electrolyte, microvia filling was achieved for aspect ratios up to 4:1. With a newly developed direct imaging (DI) machine, 4-µm structures in a 7-µm dry film photoresist are formed. Adaptive imaging of a redistribution layer was realized.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.