Femtosecond lasers are known to cut almost any material, and they are used in the processing and manufacturing of displays, semiconductors, and other electronic components or custom parts. In fact, femtosecond laser micromachining is more precise and minimizes the thermal impact on the material, resulting in higher quality parts. the Amplitude team has worked for years on one application for femtosecond lasers: glass processing.
How can femtosecond lasers improve glass cutting?
The distinguishing characteristic of glass is its hard and brittle nature, which poses a significant processing challenge. Traditional mechanical glass cutting techniques such as diamond wheel cutting, sandblasting or water jet processes cut imprecisely, lack regularity in the edges, and have large and asymmetrical residual edge stresses during the cutting process, resulting in micro-cracks, dust, and debris on the edges of glass processed in this manner. For many applications, tiny cracks caused by chips and localized stresses will cause device failure, and thus post-pass edge grinding and polishing must be performed to strengthen the edges to achieve acceptable quality. In addition, mechanical knife wheel processing also requires some auxiliary agents to assist in cutting, which may stick to the finished edge and require treatment such as water cleaning or ultrasonic cleaning. Subsequent treatment processes and low yields will increase the cost of the finished glass product.
In addition, when the single piece of glass is thinned to the micron level (UTG glass), these traditional mechanical cutting methods will no longer be applicable. The unique advantages of ultrafast lasers make it possible to process these hard, brittle and ultra-thin glass materials, and a femtosecond laser with appropriate parameters can cut effectively with a very limited number of edges in a single pass. This is true even for thick glass, and femtosecond lasers offer an alternative to other glass cutting techniques.
Femtosecond laser glass cutting: How does it work?
Ultrashort laser pulses combined with a Bezier-like beam can be used for glass processing. The Bessel beam has a thinner beam waist and longer focal depth than a Gaussian beam, and is able to simultaneously absorb the energy of ultrashort pulses along the entire thickness of the glass. The use of Pulse Bursts allows the glass to be absorbed more efficiently by the laser and results in the cracks needed to cut through the glass from top to bottom. This femtosecond laser with a Bessel-like beam can be used, for example, to cut glass in either straight or curved trajectories.
The Amplitude applications team has developed a femtosecond laser-based process to precisely control the direction of the fracture and the accompanying glass processing optics, and to use extended fracture generation to improve the processing efficiency of the glass cutting process. The process can be used to cut thin and ultra-thin glass (<200μm), thick glass (>2mm) and even multi-layer glass or a variety of easily separated brittle transparent materials with low surface roughness (<1μm) and no chips and chipping.
The key feature of the process is that the femtosecond laser energy absorbed by the glass produces an extended crack that far exceeds the size of the actual impact point. This feature significantly speeds up the processing time and increases the efficiency of laser power usage. For a range of glass types and thicknesses (<1 mm nanolaminate glass, for example), the use of sub-picosecond or femtosecond pulses can produce longer extended cracks for more efficient processing. For cutting thin glass, cutting speeds in excess of ~1 m/s along a straight line and in excess of 100 mm/s for curved parts can be achieved with laser power of only 10 W. For ultra-thin glass, cutting energy of no more than 40 μJ can result in a chipped edge of less than 1 μm.
The process can also be used to cut thick glass or multilayer glass (>1 mm) in one pass. experimental studies performed by the Amplitude process team have shown that the most efficient processing parameter is to generate a pulse train (Burst) of 4 to 6 pulses with a flat sub-pulse energy distribution. In combination with certain optical configurations, glass thicker than 2 mm can be processed in a single pass. For this study, an Amplitude Tangor laser was used, equipped with the Femtoburst ™️ feature, which allows the user to program the individual sub-pulse amplitudes in the burst pattern to precisely modulate the burst energy distribution for a detailed study of customized material energy absorption.
Who is femtosecond laser glass cutting for?
This process can be used in a variety of applications such as mobile device display manufacturers who use thinner glass or multi-layer glass (e.g. LCD), and in consumer electronics where coated glass is often used and must often be processed with curved corners, contoured shapes and cuts, and the short pulse processing characteristics of the femtosecond pulses can effectively reduce the heat affected zone of the coated layer. Many mechanical or other laser methods cannot provide the level of precision and quality required for such products. Our technology can also be used to cut thicker glass for the medical industry or even tempered glass for screen protection or the automotive industry.
In addition, with the development of glass through-hole technology (TGV) in recent years, it will be the direction and trend to use glass through-hole substrates in 3D integrated package adapter boards, MEMS and Mini LED/Micro LED, etc. In addition, there is also a special demand for high depth-to-diameter ratio hole types in optical communication, consumer electronics, bio-chips, etc. In TGV technology, Bessel beam processing module is an indispensable tool, using this technology can achieve micron or even sub-micron, super 250,000 per square centimeter ultra-high density through-hole, so dense and high-speed processing of glass through-hole requires 1. micro-hole between the laser processing can not appear in the thermal stress caused by micro-crack, 2. hole spacing must be precisely controlled. Femtosecond lasers offer a narrow pulse width to control microcracking (<350fs) while providing an excellent solution to precisely control the position accuracy of the trigger pulse on the material using the FemtoTrig® feature developed by Amplitude's technical team, synchronized with the oscillator clock (fosc:40Mhz, jitter. 25ns) to achieve higher machining position accuracy (100m/ s, Position Error: 2.5um) while maintaining a constant single pulse energy (RMS <1% energy fluctuation) for high speed pulse machining.
