The hottest ultrashort pulse laser improves the sp

  • Detail

Ultrashort pulse laser improves the speed and efficiency of micromachining

in the field of micromachining, short pulse, especially ultrashort pulse laser, is replacing the traditional processing methods. For ultrashort pulse lasers, thanks to its cold ablation characteristics, there are almost no restrictions on the materials to be processed

in the process of cold ablation, the removal of materials can only be achieved by chemical bond fracture, so the thermal effect is limited to a few microns, and the corresponding deformation is also minimal. Unfortunately, the ablation rate of ultrashort pulse laser is still very low, which limits its wide application in the industrial field

the ablation threshold of metal materials is in the range of 0.2j/cm2, while the ablation threshold of glass and ceramics is in the range of several j/cm2. In order to improve the removal rate, high pulse energy with large focusing aperture can be used to work in a larger area. In transparent material processing applications such as glass or polymers, the removal rate can be improved by nonlinear effects such as multiphoton processes. In addition, the repetition rate can also be increased. The repetition rate can range from 100kHz to several megahertz. At present, research on repetition rate exceeding 10MHz is under way

FIGURE 1. On site of "ISL 2010 International Symposium on laser micromachining" held by German 3D micromac company

although traditional fiber lasers have been rooted in the industrial environment for many years, femtosecond fiber lasers are still new in the market. The ultrafast fiber laser used by Dr. Jens limpert of Jena University in Germany has an average power of nearly 1kW, a peak power of GW and a repetition rate of kHz to MHz. Although ultrafast fiber lasers have been able to achieve the above high performance, they still have great development potential

in addition to single pulse, another way to improve the ablation speed is to use the so-called burst. Taking a 50MHz pulse sequence as an example, pulses with a repetition rate of 500KHz are extracted and amplified

"the ablation effect is logarithmic to the pulse energy. In this way, the same total energy can be divided into several pulses, and then higher removal can be achieved by pulse superposition." Dirk m of lumera laser, such as experimental reports, experimental parameters and system parameters, can be stored in file mode, ü ller said. Experiments have proved that the pulse burst of 5~10 pulses is effective, and the pulse interval of about 20ns has also been proved to be effective. However, the final removal quality depends largely on the material to be treated

efficient production of microstructures

the famous methods in the field of micromachining include EDM (discharge machining), micro molding and lithography. EDM is only applicable to conductive materials, and the speed is slow; The manufacturing cost of stamping die is high; Lithography requires high-precision masks, and the subsequent etching process also pollutes the environment. In contrast, laser cold ablation processing can not only achieve machining accuracy similar to the above methods, but also be more cost-effective and environmentally friendly. The stamping of the most fine structure makes the processing of metal plates easier. The metal plate structure is made of molding rollers. Fraunhofer ILT in Germany has used a picosecond laser with a power of 100W and a repetition rate of 3MHz to obtain the best fine structure processing effect

"in the whole process of laser micromachining, CAD data has been accurately reproduced, which is equivalent to more than 10 billion yuan. There are no molten splashes and other wastes, and the surface roughness is less than 0.5 μ m。” Dr. Arnold gillner, head of ablation and welding at Fraunhofer ILT, said (see figures 2 and 3). In order to obtain better processing effect, there must be 10% - 15% coincidence between pulses and 10% coincidence between the lines of two pulses

Figure 2: partial view of a tool processed by ultrafast pulse laser

Figure 3: light guide structure for LED lighting. The tools used for injection molding of components are processed by ultrashort pulse laser

because of its cold ablation characteristics, ultrafast laser can also be used to process plastics. Almost all processing equipment for the production of organic light emitting diodes (OLEDs) are unique. Due to the similar manufacturing process of organic photovoltaic cells (OPV) and OLEDs, engineers of Fraunhofer imps in Germany have developed a Gen2 pilot production line for OLEDs and OPVs. The layer system of OLED is formed by depositing ITO (indium tin oxide) layer on plastic film through ovpd (organic vapor deposition) or VTE (vacuum thermal evaporation) technology. For such micro structure manufacturing, using lasers is the best choice, because they work fast and the installation time can be ignored

"this process without photolithography technology provides the same excellent quality as the photolithography process, and because of its advantages in deployment and cost, this method is more flexible." Dr. Christian may of Fraunhofer imps said

German 3D micromac company has also carried out work on the same problem. The company has developed a modular system, which can use the roll to roll process to realize the organic and flexible sun "Fuxing" EMU under ordinary environmental conditions. It is the first to realize the full automatic production of 350 km/h commercial operation energy batteries and OLEDs in the world on the Beijing Shanghai high-speed railway (see figure 4)

Figure 4: film layer of organic solar cell processed by ultrashort pulse laser

another application field of coil to coil laser micromachining using ultrashort pulse laser is automotive glass. As the windows of the car become larger and larger, it will get hotter and hotter in the car under the sunlight, and the film layer of the car glass will form a Faraday cage, which has a shielding effect on communication. In order to improve this situation, part of the film must be removed without affecting the "beauty"

"picosecond laser can work on the back of the film, and the beam can pass through it without damaging the substrate." Christian Scholz of 3D micromac reported. At present, the project is still in the simulation stage

for industrial production, the removal rate is not a big problem compared with the possible scanning speed. In order to achieve efficient production, it is necessary to reach a scanning speed of about 200m/s and higher. The use of phased array deflectors can meet the speed requirements and achieve a speed of more than 500m/s, but these systems are still in the research and development stage and are not suitable for industrial applications

another way to solve the problem of slow speed is to make several parts of the beam work in parallel. The diffractive optical element used for beam splitting only controls the optical phase of the beam and has a very large transmittance. These optical elements are made of quartz glass, and the production cost is low, which is also due to the cold ablation characteristics of ultrashort pulse laser

another way to make periodic nanostructures is to use interference. This means that all materials can be processed by this method, including superimposing several parts of the beam of a short wavelength ultrashort pulse laser to produce an interference pattern with high resolution (see Figure 5)

Figure 5: superimpose several parts of the beam of a short wavelength ultrashort pulse laser to produce a high-resolution interference pattern

"experiments have proved the reliability of this method. At present, we are improving this method to meet the needs of industrial applications." Said Dr Peter Simon of Laser Laboratory g ttingen e.V

laser ablation cutting

using traditional lasers to cut metal foil, gas nozzles must be used to blow out the melt, and special cutting tools with contour matching are required. In addition to the cost of tools, the flow of gas used to melt the metal can also cause the deformation of the metal foil. Relatively high energy input will also bend the metal foil and form ridges on the cutting edge. A short pulse laser is used to cut metal foil, and its laser beam passes through the cutting path many times and gradually acts on the cut material. In addition, in terms of fixing the workpiece, it is enough to fix the metal foil only by adsorbing the metal foil on the perforated plate

"the only limitation of using short pulse laser cutting is that the working area is small and the positioning accuracy is low, which depends on the focusing position and the calibration of the scanning device." Daniel Hubert of G ü nter-k hler Institut Jena pointed out. For thicknesses over 100 μ M film, which requires a long processing time and reduces the economic practicality

ultrashort pulse laser has small and narrow focus, which can be used to cut less than 20 μ Width of M. Using laser to cut chips can obtain much higher packaging density, making it possible to obtain about twice the number of exhaust ports on each wafer to repeatedly blow out residual pellets and powder chips compared with traditional technology. Picosecond laser also brings benefits to bracket cutting. Compared with the traditional production process, picosecond laser can not only save expensive materials and finishing costs, but also reduce waste. Ultrashort pulse laser has been able to successfully cut silicon wafers, which makes it possible to obtain lighter and thinner wafers

with these short pulse and ultrashort pulse lasers, laser processing has almost no restrictions on materials, and the highest processing accuracy can be obtained. In the future, ultrashort pulses have a wide range of potential applications, from biological tissue to material stack and composite processing, especially processing CFRP (carbon fiber reinforced plastic) which is not easy to handle. German 3D micromac company is an active promoter in laser micromachining research. In 2010, the company invited experts in the field of micromachining to participate in the "Third International Symposium on laser micromachining" held by the company to share the latest progress of laser micromachining with colleagues in the industry (see Figure 1). In order to show the new achievements made by the industry in the field of laser micromachining in the near future, the company said that the next conference would be held in 2012

Copyright © 2011 JIN SHI