Laser Processing of Thin Borosilicate Glass with UV Nanosecond Laser Radiation for Display and Interposer Applications

The application of thin and ultra thin borosilicate glass as smartphone and tablet cover or interposer material in microelectronic devices requires methods for separation and drilling. Laser processing with short and ultra-short laser pulses have proven to enable high quality cuts by either direct ablation or internal glass modification and cleavage. A recently developed high power UV nanosecond laser source allows for pulse shaping of individual laser pulses and bursts. Thus, the pulse duration, pulse bursts and the repetition rate can be set individually at a maximum output power of up to 60 W. In this study, the novel pulsed UV laser system was used to study the laser ablation and drilling process on 400 μm and 50 μm thick borosilicate glass at different pulse durations ranging from 2 – 10 ns and a pulse burst with two 10 ns laser pulses with a separation of 10 ns. Single line scan and multiscan experiments were performed to correlate the process parameters and the laser pulse shape with the ablation depth and cutting edge chipping. Increasing the pulse duration within the single pulse experiments from 2 ns to longer pulse durations led to a moderate increase in ablation depth and a significant increase in chipping. The highest material removal was achieved with the 2x10 ns pulse burst. Experimental data also suggest that chipping could be reduced while maintaining a high ablation depth by selecting an adequate pulse overlap. In addition, the real-time combination of different pulse patterns during drilling thin borosilicate glass produced holes with low overall chipping at a high throughput rate. Finally, a temperature characterization was conducted with a thermographic camera while hole arrays were drilled in borosilicate glass at different repetition rates, in order to identify a damage generation threshold.