Highly Reliable CO2 Laser VIA Hole Drilling Technology by In-site Process Monitoring

Abstract

For VIA hole drilling into printed-wiring boards using a CO 2 laser, one of the critical issues is some insu cient electrical conduction by the thin layer of residual resin, so-called smear, on the inner circuits a er the drilling. In general, smear over 2 μm thick cannot be removed by a chemical etching process. In this study, a novel in-situ process monitoring technology for laser drilling was developed to overcome this issue. During the laser drilling process, the amount of smear can be estimated by detecting the light emission generated from the reductive reaction of copper oxide on the inner circuits. Depending on the thickness of the smear, the number of laser pulses is controlled to keep it below 2 μm. is technology enables a VIA hole drilling system with high reliability.