Laser-assisted plating of printed circuit board (PCB) microvias

Pao Yue-kong Library Electronic Theses Database

Laser-assisted plating of printed circuit board (PCB) microvias

 

Author: Leung, Sau-wai Esther
Title: Laser-assisted plating of printed circuit board (PCB) microvias
Degree: M.Phil.
Year: 2002
Subject: Hong Kong Polytechnic University -- Dissertations
Printed circuits
Plating
Lasers -- Industrial applications
Department: Dept. of Industrial and Systems Engineering
Pages: xvii, 237 leaves : ill. ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1641641
URI: http://theses.lib.polyu.edu.hk/handle/200/525
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 2.6.7.2. Moreover, the LAP copper thickness is also sufficient for subsequent electro-plating process and complies with IPC-6012 3.2.6.1. 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.

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