Pulse-resolved LIBS for real-time control of laser microvia drilling

We present a high-speed laser-induced breakdown spectroscopy (LIBS) sensor enabling per-pulse material identification during laser microvia drilling in printed circuit boards at repetition rates exceeding 1 MHz. Existing LIBS approaches are fundamentally limited in acquisition speed, precluding their use for inline monitoring and closed-loop control at industrial laser drilling rates. The present system overcomes this bottleneck by replacing broadband spectral acquisition with single-line detection: the copper atomic emission line of the conduction layer at 521.8 nm is isolated using a narrow bandpass filter (FWHM = 0.6 nm) and detected by a silicon photomultiplier with custom analog signal processing, delivering per-pulse analog and digital outputs within 500 ns after the laser trigger. Temporal gating suppresses the broadband plasma continuum while preserving the atomic line signal. Microvia drilling experiments on a 130 μm diameter via demonstrate position-resolved material tracking throughout the drilling sequence, establishing the feasibility of closed-loop termination control with a potential reduction in pulse count of 22.9% on average compared to fixed-pulse protocols, with savings reaching up to 34.4% in favorable cases.