High quality laser microcutting of difficult-to-cut materials - Copper and silicon wafer

Advances in microelectronics and Micro-Electro-Mechanical Systems (MEMS) technologies have spurred a need for high precision, flexible cutting and hole opening of thin silicon wafers and high electrical conductivity copper-alloys substrates. Previous publications indicated that laser cutting of these materials generally resulted in poor quality due to excessive heat effects, deposition of resolidified debris, and formation of burrs or recasts at the cut edges. The cutting speed was also very low compared with conventional methods. This paper will demonstrate the feasibility of laser micro-cutting that overcomes many of these disadvantages. High quality laser beams of appropriate temporal and spatial characteristics were used to cut silicon wafers that were uncoated and coated (with passivation and metallisation layers) and copper-alloys such as bronze and brass sheets. The thickness of these substrates was in the range between 150 µm to 650 µm. Kerf widths of 50 µm were achieved on substrates up to 300 µm thick. Respectable cutting speed of 0.25 m/min for copper and 2 m/min for silicon wafers were achieved. It is believed that higher cutting speed is possible with higher power and better quality laser beam. Optical and scanning electron microscopes were used to examine the cut-edges. The results showed virtually no heat-affected zone and negligible burr formation.