Narrow Results

A quick and relatively simple technique for stripping off Si wafers of its native oxide and carbon impurities, using pulsed laser ablation at room temperature, is presented. In a chamber at 10^-10 Torr, an oxidized Si(100) surface is ablated with 248 nm UV radiation from a KrF excimer laser. Experiments using 200 pulses of different laser energy densities were performed until a clean surface, at 600 mJ/cm², was obtained as determined by Auger electron spectroscopy and ellipsometry measurements. The slightly out of focus laser beam is scanned over the selected area leaving an atomically 1×1 feceted Si surface, as shown by RHEED. The familiar 1×2 reconstructed Si surface may be obtained through a post annealing process.

During the manufacturing of tires, surface pollutants on tire mould will lead to the production of unqualified tires. Tire moulds need to be regularly cleaned. Laser cleaning is recognized as a non-destructive, effective, precise and environmental friendly method. In this paper, laser cleaning was used to remove contaminants on tire mould surface. First, laser induced damage experiments were performed. The results showed that the roughness and hardness of the cast steel sample surface seldom changed under the energy range of 140.1–580.2 mJ laser irradiation 1 pulse and the energy range of 44.7–168.9 mJ laser irradiation 100 pulses. In the laser cleaning experiments, the cleaning thresholds and the optimal cleaning parameters were obtained. Results indicated that laser cleaning was safe and effective for tire mould contamination removal.

A pulsed fiber laser was used to conduct laser cleaning experiments on the composite paint layer on the surface of carbon fiber composite materials (carbon fiber-reinforced plastic (CFRP)). The influence of laser energy density and laser travel speed on the cleaning effect was studied. The surface morphology, surface roughness and phase composition of the cleaned sample were analyzed. After bonding, tensile testing was conducted on the bonding part to verify the impact of laser cleaning on the bonding performance. The research results indicate that the cleaning effect gradually improves with the increase of laser energy density or the decrease of travel speed. In this experiment, when the laser energy density is 4.00J/cm² and the travel speed is 6.5mm/s, the phase composition of the cleaned substrate surface is only C, without TiO₂ and BaSO₄. This indicates that the paint layer has been completely removed under this process parameter. By selecting reasonable process parameters, the surface paint layer of CFRP can be effectively removed, and a good surface morphology can be obtained without damage to the carbon fiber. Meanwhile, the mechanical properties after bonding can be improved.

Interference ring marks were observed on a copper substrate consisting of plated layers of Au, Pd and Ni after laser ablation of epoxy material from the top surface. These ring marks are the result of laser-induced surface oxidation and need to be avoided or minimized in order to improve the solder wettability on the treated surface. Studies of laser-induced thermal diffusion through the plated layers were carried out using a 532 nm Q-switch Nd:YAG laser. The major process variables investigated were the beam profile, pulse repetition rate and beam scan pattern. Secondary ion mass spectroscopy (SIMS) was used to obtain a depth profile of the laser-treated layers. It revealed that interfusion of Pd and Ni by diffusion occurred during laser irradiation. Calculations of thermal diffusion length and temperature rise of the metal layers without considering the accumulated thermal effect of overlapping pulses are presented in this article. The study results are useful for a better understanding of the process of laser removal of epoxy flashes on leadframe heatsink surfaces.

Laser ablation is a rapid-material removal technique with potential application in remanufacturing of bearings to clean damaged surfaces. This study reports the ablation morphology and change in surface composition of 52100 bearing steel irradiated with a femtosecond laser. A smooth ablated surface was achieved by operating the laser at fluence just above the ablation threshold, but higher fluences resulted in roughened surfaces with recast formation. Such coarse morphology is believed to result from higher energy deposition and surface melting. Minimal oxidation occurred at lower fluences. Periodic ripple patterns formed in the ablated area at low fluence; their morphology and possible formation mechanism is discussed.

The occurrence of flux residue is a manufacturing and reliability concern for flip chip assemblies. In this paper, removal of flux residue by laser cleaning before chip attachment to board is carried out. In the flip chip process, 63%Sn37%Pb solder paste with a water soluble flux was printed on wafer by stencil and subjected to infrared reflow. Instead of washing with water, flux residue on the chips after wafer sawing was removed by ablation of pulsed ultraviolet (UV) lasers with wavelengths of 248 nm and 355 nm respectively. Some parameters in the cleaning process such as the energy density of laser and number of pulses irradiated on the chips had been optimized. It was found that the laser beams also etched polyimide passivation on the chips. After laser etching, the passivation surface became cleaner. The rate of etching was measured by a surface profilometer. To conclude, we discuss the advantages of laser cleaning over wet chemical cleaning in the removal of flux residue.

The main focus of laser cleaning research at Macquarie University, Sydney, Australia, has been developing techniques for cleaning applications in the optics, optoelectronics and photonics industries. Dry/raised humidity cleaning techniques are favoured for small scale optical, integrated-optic and photonic devices. All of wet, damp and dry laser-cleaning methods are applicable to larger scale optics. All of our studies to date have measured the laser cleaning result effected by a single laser pulse. Excellent removal efficiencies of alumina particles (0.3 µm −tens of microns) from glass surfaces have been obtained. Also we have used “dry” particles rather than particles in suspension. Use of dry particles leads to significant agglomeration, thus, our studies evaluate the impact of particle agglomeration on laser cleaning results. In the sections that follow we firstly present some tables summarizing the results from experimental laser cleaning studies, from the research literature published at the time of writing. Then, secondly, we review our own laser cleaning research from the perspectives of development and critical evaluation of the experimental and analysis methods, contrasting laser cleaning results achieved with different UV pulsed laser systems, and accurately measuring laser cleaning threshold fluence.

Laser cleaning of FEA (field emitter array) surfaces with four different wavelengths has been performed to improve the emission characteristics of FEAs. Wavelength dependent (i.e., energy dependent) cleaning effect was found to take place for Si FEAs, when the FEAs were irradiated by a Nd: YLF laser.

Conservation has an important role in bringing the past to life and minimizing the effects of deterioration on the material. There is a range of different treatments for conservation, but it is important to take into consideration to choose suitable techniques and methods for conservation to avoid damage and to use good monitoring, controlling techniques and skilled operators with experience of the process to achieve the most satisfactory results. Cleaning is one of conservation techniques and process, which involve removal of materials from an object or building and to reveal its true conditions, so that appropriate action can be taken to ensure that it survives for many future generations to enjoy. One of the promising Technology-Aided Heritage Conservation (TAHC) for buildings among the cleaning techniques can be Laser cleaning. This research work may address laser uses, techniques, methods, advantages and disadvantages. In addition, it discusses lasers as a method of cleaning architectural detail on historic buildings, rather than large areas of plain stonework.

Ancient artifacts excavated from archaeological site were covered with different soil contaminates and stains which changed their chemical composition and aesthetic appearance. Ancient inorganic materials such as bronze, glass and pottery covered with different contaminates such as corrosion products, soil deposits, organic stains and gray white encrustations. Lasers are currently being tested for a wide range of conservation applications. Since they are highly controllable and can be selectively applied, lasers can be used to achieve more effective and safer cleaning of archaeological artifacts and protect their surface details. In the present work we investigated in a general way the laser cleaning of bronze corrosion products, glass, and pottery by Q-switched Nd:YAG Lasers. The results were compared with conventional methods. The artifact samples were examined by Light Optical Microscope (LOM) and showed no noticeable damage.