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Title: Laser-assisted plating of printed circuit board (PCB) microvias
Authors: Leung, Sau-wai Esther
Degree: M.Phil.
Issue Date: 2002
Abstract: In conventional plated-through-hole (PTH) process, plating microvias with high aspect ratio may not be feasible due to the limited access of electro-chemical solution to the hole wall surface. This research project aims to investigate a new process - laser-assisted plating (LAP) of printed circuit board (PCB) microvias. The LAP mechanism has potential to replace the conventional PTH process since it combines the steps of laser drilling and plating into one single process. Firstly, the feasibility of LAP was investigated, by performing experiments to investigate the factors and the parameters affecting LAP, with the aim of identifying whether copper deposition is feasible, and to determine the feasible range of processing parameters for this new process. Secondly, quality evaluation of the quality and thickness of copper deposition was carried out. Thirdly, the thermal reliability stress on microvias by the LAP process and by the conventional PTH process were studied and compared. Fourthly, the thickness of LAP copper was determined by resistance measurement. Finally, microvias formed by LAP and the conventional PTH process were compared. It was found that a 3-stage approach should be used in performing the LAP process. Factors such as z offset, laser power, bite size, repetition rate and number of repetitions were tested in the experimental work. The feasible process window or parameter range is z offset of 2mm, laser power of 0.2W, bite size of 1 um to 5um, repetition rate of 8kHz to 12kHz and repetition steps of 600. Results of the thermal cycling reliability test showed that the reliability of microvias produced by the LAP process are acceptable under the specification. IPC-TM-650 Moreover, the LAP copper thickness is also sufficient for subsequent electro-plating process and complies with IPC-6012 The LAP process is more successful when plating high aspect ratio microvias when compared with the conventional plated-through-hole (PTH) process. To enable PCB industry to adopt the LAP developed in this research, a patent application and filing process is underway.
Subjects: Hong Kong Polytechnic University -- Dissertations
Printed circuits
Lasers -- Industrial applications
Pages: xvii, 237 leaves : ill. ; 30 cm
Appears in Collections:Thesis

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