Monitoring Method for Laser Via Hole Processing of Printed Circuit Boards Based on Two-Color Method With a High-Speed Video Camera

Abstract

A build-up process is used to manufacture printed wiring boards (PWBs) for high-density circuits. Presently, CO2 laser beams are used to drill blind via holes (BVHs) that connect copper foils. The Cu-direct drilling process has received considerable attention but is problematic because it produces a copper overhang due to the complex processing phenomena. This report focuses on monitoring scattered matter by Cu-direct laser drilling with a high-speed camera and clarifying the factors related to processing quality while verifying the results by CFD (Computational Fluid Dinamics) analysis. Previous research has shown that processing progress can be made from temperature information using the two-color image method that can measure temperature without contact. However, the two-color image method generates noise in the temperature range (500–3000 °C) which is treated in this research. Filtering was possible by using the RGB data of each pixel on the image. By focusing on laser fluence, it became possible to estimate the laser irradiation time that can guarantee the quality in the drilled hole (BVH) in single pulse continuous irradiation.