Conclusions

The subtractive processing of glass substrates represents a diverse and interdisciplinary field that bridges material science, precision engineering, and microsystem integration. Through this book, we have explored a wide spectrum of subtractive micromachining techniques tailored for glass, a material that, while mechanically robust and chemically inert, presents significant challenges in fabrication due to its brittleness, hardness, and resistance to conventional etching. From a holistic perspective, the subtractive techniques covered in this book can be broadly classified into five major categories: mechanical, chemical, plasma-based, thermal, and hybrid/sequential approaches. Each class serves specific roles in shaping glass at micro- and sub-microscales, offering trade-offs in terms of feature resolution, material removal rate, aspect ratio, surface finish, and process complexity. Mechanical techniques , such as micro-grinding, ultrasonic machining, and sandblasting, are well-suited for bulk shaping and surface patterning, particularly in applications where rapid prototyping and cost-effectiveness are essential. However, these methods are often constrained by tool wear and limited precision when targeting fine features. Chemical and electrochemical methods , including wet etching with hydrofluoric acid and Electrochemical Discharge Machining, enable smoother surfaces and complex three-dimensional structures. Their effectiveness, however, depends heavily on precise control of etchant dynamics, masking strategies, and electrolyte conditions. Plasma-based processes , most notably Reactive Ion Etching, offer exceptional anisotropy and dimensional accuracy, making them indispensable for fabricating high-aspect-ratio features and for applications requiring CMOS compatibility. Thermal and photonic approaches , such as glass reflow, microwave-assisted machining, and laser micromachining, allow for localized, non-contact material removal with minimal mechanical stress. These methods are particularly suitable for creating micro-optical features, through-glass vias, and hermetic cavities. Hybrid strategies have emerged as powerful solutions to address the limitations of individual processes. By integrating multiple energy modalities, such as laser-ultrasonic-ECDM combinations, these approaches enhance machining depth control, minimize thermal or mechanical damage, and broaden the range of achievable geometries. While post-processing techniques are not strictly categorized as subtractive methods, they play a vital complementary role in transforming micromachined substrates into functional devices. Processes such as surface activation, thin-film deposition, photolithography, and wafer bonding enable the integration of sensing materials, the definition of circuit patterns, and the realization of complete MEMS and microfluidic systems. Taken together, the subtractive techniques presented in this book, when considered alongside essential post-fabrication workflows, constitute a robust and versatile toolkit for engineering next-generation microdevices on glass platforms. This integrated perspective emphasizes not only individual process performance but also their synergistic potential in enabling high-performance, application-specific microsystems.