High-precision and ultrafast UV laser system for next-generation flexible PCB drilling

•We prepared 36 mm thickness of FPCB composed of copper and polyimide.•We successfully fabricated micro via-hole diameter of 15 mm, 35 mm, 50 mm and 85 mm by using AWAVE-355(Advanced Optowave).•We especially achieved the size of via-hole that is less than 15 mm of diameter, which has 95% of roundness and 80° of taper angle.•The drilling speed of 2800 holes per second is faster than current industry one which is 2000 holes per second.•We applied modified the Greedy 2-opt algorithm to UV-laser drilling to reduce the time of hole fabrication.•We successfully reduced the production time approximately 23%.•In order to get accurate via-hole, the Canny edge detection algorithm and pattern matching algorithm were used to detect the defective micro via-holes automatically.•We could detect defective or mis-fabricated holes using the pattern matching and Canny edge detection algorithms.•We successfully fabricate tiny via-hole by using UV laser system as well as quickly exact via-hole was formed with algorithms.

Since conventional mechanical punching technology for Flexible Printed Circuit Board (FPCB) drilling has restricted via-hole size and depth control for multi-layer circuit boards, CO2 and Ultra Violet (UV) laser drilling technologies have been developed. However, the FPCBs for mobile phones and Personal Digital Assistants (PDAs) require smaller via-hole diameters, since the development of thinner and higher circuit density devices is demanded. Currently, UV laser systems are widely used for FPCB drilling of 75–105 μm diameter via-holes and inspectors performs quality test manually using microscopes. We developed a high-precision UV laser microfabrication system for next-generation FPCB drilling of 15 μm diameter via-holes. The degrees of the precision of the microfabricated via-holes of 15, 35, 50 and 85 μm were mean absolute error rate of 4.4, 2.2, 2.3, and 2.2 which was fully satisfied with industrial inspection specification ±10%. The drilling speed of the system of 2800 via-holes per second at stationary state was achieved. In addition, we applied modified Greedy 2-opt algorithm to find out optimal drilling path which reduced the total time of via-hole fabrication. We successfully reduced the production time by 25% compared with the result obtained in the normal Greedy 2-opt algorithm. Moreover, we designed very accurate inspection method using Canny edge detection and geometric pattern matching algorithms and successfully applied it to the Automated Optical Inspection (AOI) module for the inspections of 15 μm diameter via-hole which was required for the fabrication of high density FPCB.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slide