Laser Micromachining

Beat Neuenschwander

CONTENTS
5.1 Introduction
5.2 Basics
5.2.1 Energy Transfer
5.2.2 Absorption of Light
5.2.3 Heat Transfer for Long (Nanosecond) Pulses
5.2.3.1 Heat Diffusion Equation
5.2.3.2 Point Source in Infinite Homogeneous 3D Body
5.2.3.3 Linear Heat Conduction
5.2.3.4 Enthalpy Model
5.2.4 Heat Transfer for Ultra-short Pulses
5.2.4.1 Two-temperature Model
5.2.4.2 Metals
5.2.4.3 Dielectrics and Semiconductors
5.2.5 Heat Accumulation
5.3 Optimized Material Removal
5.3.1 Problem
5.3.2 Ablation Efficiency
5.3.2.1 Top Hat Intensity Distribution
5.3.2.2 Gaussian Beam
5.3.3 Specific Removal Rate
5.3.4 Consequences from the Model
5.3.5 Incubation
5.3.6 Influence of the Pulse Duration
5.3.7 Influence on the Machining Quality
5.3.7.1 Metals
5.3.7.2 Semiconductors: Silicon and Germanium
5.4 Power Scale-up for Surface Structuring: Demands, Solutions and Limiting Factors
5.4.1 Surface Structuring
5.4.2 Marking Speed and Power Scale-up
5.4.3 Limiting Factors
5.4.3.1 Heat Accumulation
5.4.3.2 Plasma and Particle Shielding
5.4.4 Pulse Bursts
5.4.5 Alternative Approaches
5.5 Summary and Future Challenges
References