Predictive Modelling of UV Laser Penetration Depth in Copper Foil for PCB Microvia Drilling Using Design of Experiments

Precise microvia formation is a critical requirement in printed circuit board manufacturing. This study develops predictive mathematical models for the penetration depth of a Coherent AVIA LX Q-switched diode-pumped nanosecond laser in the copper foil of PCB laminates. The laser operated at a fixed pulse repetition frequency of 100 kHz, with a wavelength of 355 nm and a pulse duration of 30 ns. A comprehensive Design of Experiments methodology was employed to investigate the influence of key operational parameters on the minimum (hmin) and maximum (hmax) penetration depths. Three distinct microvia diameter ranges were considered: 50–70 μm, 70–100 μm, and 100–200 μm. Empirical relationships were established through full factorial and fractional factorial DoEs, identifying the significant factors and interactions governing UV laser ablation. The models showed reasonably consistent predictive performance in the overlapping diameter region (100 μm), with discrepancies of approximately 2–3 μm. Validation experiments, using parameter combinations not tested in the DoEs, showed deviations below 1 μm between predicted and measured penetration depths in copper, and the parameter sets selected through the models achieved complete copper opening on the production panels and copper-foil thicknesses tested. Within their calibrated domains, the models can support the selection of UV laser microdrilling parameters, reducing parameter identification time and scrap generation. Since they are specific to the material and laser system investigated, their transfer to other conditions may require recalibration, whereas the methodology remains transferable.