Ultrashort pulsed laser ablation of stainless steel using MHz bursts

Background: Ultrashort pulsed laser burst ablation has attracted considerable attention in micromachining, offering notable advantages over traditional single-pulse ablation, including enhanced efficiency and reduced thermal damage. In electronics manufacturing, achieving ultrasmooth surfaces while minimizing defects and maintaining material integrity is critical for ensuring high device performance. Aim: We aim to investigate the influences of burst ablation on the surface processing of stainless steel using an ultrashort pulsed laser and explore the feasibility of laser burst ablation to achieve smooth surfaces and precise patterning for advanced electronics applications, including semiconductor packaging and micro/nanoelectronic device fabrication. Approach: We examine stainless steel ablation using an ultrashort pulsed laser with an intra-burst repetition rate of 82 MHz. Primary laser ablation parameters, including pulse fluence and pulse number per burst, are varied to study their influences on the ablation efficiency, surface roughness, and morphology. In addition, the effects of the scanning strategy on the surface quality are analyzed. Results: Compared with single-pulse ablation, burst-mode ablation shows a 30% reduction in the maximum ablation efficiency. However, surface quality can be significantly enhanced, with ultrasmooth surfaces achieving roughness below 0.2 μm using four pulses per burst. The key factor to control surface structures is the surface melting layer. A thin melting layer can prevent cone formation, yielding smooth surfaces, whereas an overly thick melting layer results in rough textures. Interlacing maintains good dimensional accuracy by providing sufficient cooling time between scanning lines, whereas hatch distance and burst overlap ratio show limited impacts on ablated surfaces. Conclusions: We highlight the advantages of burst-mode ablation in ultra-fine surface processing and demonstrate the significant potential in electronics manufacturing. The ability to achieve precise, smooth surfaces with minimal thermal damage opens up opportunities for electronics applications, facilitating the continued miniaturization and performance enhancement of electronic devices.