Anisotropic conductive films (ACFs) consist of conducting particles and adhesive resins, and have been widely used for packaging technologies in flat panel displays (FPDs) such as liquid crystal displays (LCDs) and plasma display panels (PDPs). Various packaging technologies such as film on glass (FOG), chip on flex (COF) and Chip on glass (COG) using ACFs have been currently carried out by using a hot plate as a heat source for cure. But this method is difficult to meet the requirement of fine pitch capability and to make the flat panel displays smaller, lighter and thinner because of inhomogeneous thermal distribution of hot plate and thermal expansion of a film. New ACF bonding processes by making use of high power diode laser have been proposed and investigated experimentally. Laser ACF bonding is worthy of attention because of a considerable reduction of the total process time due to the rapid reach of curing temperature. Laser ACF bonding also eliminates problem associated with a deterioration of contact reliability due to the thermal expansion caused by the hot plate surface, when temperature is rising

Laser joining is a promising technique for wafer-level bonding. It avoids subjecting the complete MEMS package to a high temperature and/or the high electric field associated with conventional wafer-level bonding processes, using the laser to provide only localized heating. We demonstrate that a benzo-cyclo-butene (BCB) polymer, used as an intermediate bonding layer in packaging of MEMS devices, can be satisfactorily cured with a substantial reduction of curing time compared with an oven-based process by using laser heating. A glass-on-silicon cavity bonded with a BCB ring can be produced in few seconds at typical laser intensity of 1 W/mm2 resulting in a local temperature of ~ 300°C. Hermeticity and bond strength tests show that such cavities have similar or better performance than cavities sealed by a commercial substrate bonders which require a minimum curing time of 10 minutes. The influence of exposure time, laser power and pressure on degree of cure, bond strength and hermeticity is investigated. The concept of using a large area, uniform laser beam together with a simple mirror mask is tested, demonstrating that such a mask is capable of protecting the centre of the cavity from the laser beam; however to prevent lateral heating via conduction through the silicon a high conductivity heat sink is required to be in good thermal contact with the rear of the silicon.

Aluminum combines comparably good thermal and electrical properties with a low price and a low material weight. These properties make aluminum a promising alternative to copper for a large number of electronic applications, especially when manufacturing high volume components. However, a main obstacle for a wide use of this material is the lack of a reliable joining process for the interconnection of copper and aluminum. The reasons for this are a large misalignment in the physical properties and even more a poor metallurgical affinity of both materials that cause high crack sensitivity and the formation of brittle intermetallic phases during fusion welding. This paper presents investigations on laser micro welding of copper and aluminum with the objective to eliminate brittle intermetallic phases in the welding structure. For these purposes a combination of spot welding, a proper beam offset and special filler material are applied. The effect of silver, nickel and tin filler materials in the form of thin foils and coatings in a thickness range 3-100 μm has been investigated. Use of silver and tin filler materials yields to a considerable improvement of the static and dynamic mechanical stability of welded joints. The analysis of the weld microstructure shows that an application even of small amounts of suitable filler materials helps to avoid critical, very brittle intermetallic phases on the interface between copper and solidified melt in the welded joints.

Laser transmission welding in recent years has been established as a versatile method for interconnection of thermoplastics, at least for macroscopic parts. The technology also offers interesting possibilities for packaging of transparent, micro-structured polymer chips, as used for life science or biotechnology applications. A method for transmission welding, based on a diode laser bar in combination with a thin layer of IR-absorbing dye, is introduced, that allows for fast, mask-less welding of two thermoplastic substrates, at least one of which contains micro structures. The process strongly depends on the ratio of the IR-absorbing dye layer thickness to the depth of the microstructures and should be <<1. Detailed results of the absorption of the dye layers as a function of the spin coating parameters used for preparation of the films are presented, including depth profile analysis. It is demonstrated that the formation of good quality weld seams mainly depends on the energy per unit length coupled to the substrate, which is adjustable by the feed rate and the laser power applied. As an example the process window for welding CGE chips made of PMMA, containing 50 μm wide and deep channels, separated by 100 μm wide webs is shown. The applicability of the technology to other polymer chip geometries together with concepts for further improvement is demonstrated.

CO₂-laser-assisted micro-patterning of polymethylmethacrylate (PMMA) or cyclo-olefin copolymer (COC) has a great potential for the rapid manufacturing of polymeric devices including cutting and structuring. Channel widths of about 50 μm as well as large area patterning of reservoir structures or drilling of vias are established. For this purpose a high quality laser beam is necessary as well as an appropriate beam forming system. In combination with laser transmission welding a fast fabrication of two- and three-dimensional micro-fluidic devices was possible. Welding as well as multilayer welding of transparent polymers was investigated for different polymers such as PMMA, polyvinylidene fluoride (PVDF), COC, and polystyrene (PS). The laser transmission welding process is performed with a high-power diode laser (wavelength 940 nm). An absorption layer with a thickness of several nanometers is deposited onto the polymer surfaces. The welding process has been established for the welding of polymeric parts containing microchannels, if the width of the channels is equal or larger than 100μm. For smaller feature sizes the absorption layer is structured by UV-laser radiation in order to get a highly localized welding seam, e.g., for the limitation of thermal penetration and thermal damaging of functional features such as channels, thin walls or temperature-sensitive substances often contained in micro-fluidic devices. This process strategy was investigated for the welding of capillary electrophoresis chips and capillary blood separation chips, including channel widths of 100 μm and 30 μm. Analysis of the thickness of the absorption layer was carried out with optical transmission spectroscopy.

In dental prosthodontics, miniaturized unit assembly systems are increasingly used in order to enable the optimized adaptation of the prosthesis to the individual anatomic situation. To manufacture these miniaturized systems, there is the need to cover the complete device, in the reported case made of polycarbonate, comprising among others springs that apply pressure to fix and adjust the prosthesis. The laser is a suitable joining tool for applications in micro technology. Therefore, laser transmission welding was investigated for joining the specific miniaturized components, so-called retention modules. The housing was made of PC with carbon black. The cover consisted of transparent PC with a thickness of 400 μm along the joining contour. The wall thickness of the joining partners amounted to 400 μm. The investigations presented in this paper include detailed examinations of the welding process with and without laser mask. For both process variants, the influence of the main process parameters laser output power, welding speed and focal position was studied. The process was qualified especially with regard to joining strength, swelling, process time, reproducibility, accuracy and functionality of the complete assembly. It was examined how the positioning of the mask determines the formation of the weld seam. The geometry of the retention module and the clamping were optimized. It turned out that the clamping of the components is crucial for a reliable process. Optimized process conditions enable the micro welding of plastic components for dental products considering the high requirements regarding functionality, biocompatibility, lifetime, and esthetics. Laser transmission micro welding proved to be a suitable method to package the final assembly without any refinishing operation.

The phenomenological model of laser joining at so called boundary kitetic is developed. The criteria of microjoints strength is suggested. As a result of kinetics of computer simulation of soldered joints forming, practical investigations of soldering modes influence at the joints strength and analysis of micro section metallographic specimens fulfilled with the aid of electronic microscope, the possibility of two-three fold enhancement of soldered joints strength in comparison with manual soldering. Technological process and automated equipment are developed for laser soldering of electronic components with planar leads at the printed circuit boards.

The results of numerical simulation of laser drilling of aluminum, copper and steel samples using femtosecond and nanosecond pulses are presented. The drilling rates were predicted for a wide range of laser beam irradiance. The theoretical model utilized for the simulation was upgraded to include phase transition at the critical temperature. In the new theoretical approach the latent heat of evaporation was assumed to be temperature dependent, such that in the range below the critical temperature its value is practically constant, decreases rapidly as the temperature approaches the critical temperature and is zero at the temperatures exceeding the critical temperature. The computed drilling rates for 4 ns and 200 fs laser pulses are in agreement with the experimental data. The upgraded model provides explanation to the observed saturation of drilling rate dependence on laser pulse energy. A new method of determining critical temperatures of metals and metallic alloys is proposed.

A new mechanism of ultra-deep (up to tens of microns per pulse, sub-mm total hole depths) plasma-assisted ablative drilling of optically opaque and transparent materials by high-power nanosecond lasers proposed by Kudryashov et al. has been studied experimentally using average drilling rate and photoacoustic measurements. In the drilling experiments, average multi-micron crater depth per laser shot and instantaneous recoil pressure of ablated products have been measured as a function of laser energy at constant focusing conditions using optical transmission and contact photo acoustic techniques, respectively. Experimental results of this work support the theoretical explanation of the ultra-deep drilling mechanism as a number of stages including ultra-deep "non-thermal" energy delivery by a short-wavelength radiation of the surface high-temperature ablative plasma, bulk heating and melting of these materials, accompanied by the following subsurface boiling in the melt pool and resulting melt expulsion off of the target.

CO₂ gas dissociation through optical and plasma collision breakdown was investigated by optical emission spectroscopy (OES), using an Andor Mechelle monochromator with an iStar intensified charge coupled device (ICCD). A pulsed Nd:YAG laser was used to provide energy for the gas breakdown processes. The evolution of the luminous plasmas was examined by time-resolved optical spectroscopy. Emission lines of carbon and oxygen species, such as atomic C (I), ionic C (II) and atomic O (I), were observed to understand the process of CO₂ dissociation. Effects of background gas pressure on plasma propagation in the experiments were studied. Some emission lines could be obviously distinguished, indicating that the emitting species had different behaviors in the evolution. They were frequently ionized and excited after the laser irradiation.

Laser processing offers an attractive way of manufacturing both optical and biomedical devices including microfluidic channels and biochips. Laser processing is also promising for the fabrication and trimming of silica-based planar lightwave circuits (PLCs). PLCs are key functional components for use in optical telecommunication systems since they offer compactness and high functionality in addition to excellent stability. A laser light that strongly interacts with glass, such as ultraviolet (UV) light or femtosecond pulses, can increase the refractive index of glass. This phenomenon can be used to improve the performance of PLCs as well as to enhance their functionality. UV laser trimming is useful in that it can be used to change the refractive index of fabricated waveguides and thus compensate for fabrication errors. Fabrication errors have various detrimental effects on PLC performance including deviation from the designed wavelength, polarization dependence and crosstalk degradation. UV laser trimming can greatly improve PLC performance by compensating for these errors. In addition, laser processing can provide PLCs with new functionalities. For example, a UV laser can be used to produce band-reflection mirrors in external cavity lasers in PLCs. Direct waveguide writing is also an attractive way to enhance circuit layout flexibility. Recently, a femtosecond laser was found to be effective for writing 3-dimensional waveguides, and it can also be used to interconnect waveguides flexibly. This enables us to expand PLC geometry from two to three dimensions. This talk will review trends in laser processing for PLC fabrication and recent R and D topics.

We present recent results on experimental micro-fabrication and numerical modeling of advanced photonic devices by means of direct writing by femtosecond laser. Transverse inscription geometry was routinely used to inscribe and modify photonic devices based on waveguiding structures. Typically, standard commercially available fibers were used as a template with a pre-fabricated waveguide. Using a direct, point-by-point inscription by infrared femtosecond laser, a range of fiber-based photonic devices was fabricated including Fiber Bragg Gratings (FBG) and Long Period Gratings (LPG). Waveguides with a core of a couple of microns, periodic structures, and couplers have been also fabricated in planar geometry using the same method.

As a means to accomplish high-throughput and damage-free processes, non-digitized diffractive beam splitters are effectual: they can afford to fully suppress undesired diffraction beams by containing as much light energy as possible in a fan-out of beams meant for the process. The surface-relief structures of the splitters are designed using a Fourier- iterative algorithm and are formed on high-quality fused silica substrates using direct laser writing and reactive ion etching. For a 13-beam splitter, for example, a non-digitized element gives an efficiency of 97% with SN=38, whereas a binary counterpart is as efficient as 78% with SN=5, where SN is defined as the ratio between the minimum of the fanout beam intensities and the maximum of higher-order diffraction intensities. We have tested these two types of elements in laser-cutting experiments and verified that the non-digitized element is far superior to the binary element.

Three-dimensional (3-D) photonic crystals were fabricated by laser-assisted imprinting of self-assembled silica particles into silicon substrates. The multilayer self-assembly of silica particles were formed on the silicon substrates using isothermal heating evaporation approach. A KrF excimer laser pulse with a wavelength of 248 nm and a duration of 23 ns was used to melt the silicon substrate surface, which infiltrated and solidified over the assembled silica particles. By removing the silica particles embedded in the silicon using hydrofluoric (HF) acid, inverse-opal photonic crystals were fabricated This technique is capable of fabricating structures with complete photonic bandgaps (PBG), and engineering the photonic bandgaps by flexibly varying the silica particle size.

An aggressive pursuit for ever decreasing the minimum feature size in modern integrated circuit has lead to various challenges in nanofabrication. Finer feature size is very desirable in microelectronics and other applications for higher performance. However, it is difficult to achieve critical dimensions at sub-wavelength scale using traditional optical lithography techniques due to the optical diffraction limit. We developed several techniques to overcome this diffraction limit and simultaneously achieve massive, parallel patterning. One of the methods involves the principle of optical near-field enhancement between the spheres and substrate when irradiated by a laser beam, for obtaining the nano-features. Nonlinear absorption of the enhanced optical field between the spheres and substrate sample was believed to be the primary reason for the creation of nano-features. Also, we utilized the near-field enhancement around nanoridges and nanotips upon pulsed laser irradiation to produce line or dot patterns in nanoscale on gold thin films deposited on glass substrates. We demonstrated that the photolithography can be extended to a sub-wavelength resolution for patterning any substrate by exciting the surface plasmons on both metallic mask and a shield layer covering the substrate. We used laser-assisted photothermal imprinting method for directly nanopatterning carbon nanofiber-reinforced polyethylene nanocomposite.

In this paper the current state of the art and new trends in excimer laser processing of polymer materials are presented. Two processing regimes are of general interest: below and above the ablation threshold. The modification of polymer surface can be carried out by laser processing below ablation threshold. This is successfully demonstrated for the fabrication of optical singlemode waveguides in PMMA for the visible optical range and for 1550 nm. The obtained structures reveal absorption losses in the order of 1.4 dB/cm up to 5 dB/cm. Laser exposure using contact masks or direct scanning of planar structures are appropriate methods for the integration of optical waveguides in PMMA sensor devices (Y-branch). Above the ablation threshold excimer laser micromachining is a powerful tool for a rapid manufacturing of complex three-dimensional micro-structures in polymer surfaces with depths between 0.1 μm and 1000 μm and aspect ratios up to 10. Typical application fields are presented in micro-optics, micro-fluidics and rapid tooling. Micro-Laser-LIGA is established in order to fabricate nebulizer membranes, micro-fluidic devices and integrated single mode waveguides. Furthermore, the fabrication of 3d-shapes in metallic mold inserts is successfully demonstrated. Debris formation is completely suppressed. Polymer structuring with a low power short pulse excimer laser with high repetition rates up to 500 Hz is compared to the structuring with a "conventional" high power excimer laser with a repetition rate of about 10-100Hz as well as with a UV-Nd:YAG (1-2 kHz). These "high-repetition-rateexcimer lasers" with relatively small pulse energies but with much shorter laser pulse duration (< 6 ns) provide a significant improvement of pattern quality. Furthermore, the high repetition rate enables a fast material processing which is discussed in detail for several application fields.

The laser cleaving process is a new method to cut brittle materials such as glass, silicon and ceramics. In this dry process, the material is diced only by the thermal stress induced by the laser irradiation. Therefore, the material is not contaminated with the coolant generally used in the mechanical dicing process, but teh thermal damages are caused on the irradiated surface. The objective of this paper is the prevention of thermal damages in the laser cleaving process of silicon wafer. The cleavin experiments are conducted with pulsed ND:YAG laser and cw Nd:YAG laser. In the cleaving with pulsed laser, the temperature required for crack propagation is investigated by measuring with a two-color pyrometer developed. The critical temperature at which the stress intensity factor slightly exceeds the fracture toughness depends on the pulse frequency, the pulse width, the scanning velocity of laser spot and the material properties. The temperature is also confirmed by the thermal stress analysis. And then, for the cleaving with cd laser, a refrigerating-chuck system is developed to reduce the thermal damage of workpiece. The system refrigerates the working table below the freezing point of water, and the material is fixed on the table by the frozen water between the material and the table. While the silicon oxide is caused on the surface of wafer in the room temperature, the refrigerating-chuch can prevent the thermal damage and improve the linearity of the cleaving trajectory and the reliability of the cleaving process.

Inside inkjet-printer heads, a silicon chip is used as a barrier between the orifice plate, which contains hundreds of nozzles, and the ink reservoir. The silicon chips used to create the barriers have to be drilled. The conventional manufacturing technique (sandblasting) does not anymore provide satisfactory results for the new generation of printers. The water-jet-guided laser, a hybrid technology which uses a water jet to guide a laser beam, has recently been adapted to this application, showing very promising results combining high processing speed and quality.

In view of the need to obtain high-efficiency and low-cost photovoltaic power generation systems, the electrical series connection of multiple solar cells by laser patterning is a key issue for thin-film silicon solar cells. For a series connection with no thermal damage to the photovoltaic layers, a theoretical analysis of glass-side laser patterning, in which a laser beam is irradiated from the side of a glass substrate, and the optimization of the structure of the solar cells are conducted for a-Si:H/a-SiGe:H stacked solar cells deposited on glass substrates. As a result, an a-Si:H/a-SiGe:H module with both a large area (8,252 cm²) and a conversion efficiency of 11.2% is obtained. Then, to improve efficiency and to reduce cost, the minute structure of microcrystalline silicon (μ c-Si:H) and film-side laser patterning, in which a laser beam is irradiated from the side of the deposited film, are investigated for a-Si:H/μ c-Si:H stacked solar cells deposited on insulator/metal substrates. It is proved that the discontinuity of the doped and photovoltaic layer may cause a reduction in the path density of the leak current, and that this contributes to an improvement in the efficiency of the solar cells. Based on the developed structure, an initial efficiency of 12.6% is obtained in a small-size solar cell. An a-Si:H/μ c-Si:H module (Aperture area = 56.1cm²) with three segments has also been fabricated with an initial efficiency of 11.7% as a first try.

Since the development of layered freeform manufacturing processes some technologies have emerged such as the Selective Laser Melting process (SLM) which uses layers of metal powder to manufacture 3D-objects from CAD-data by melting targeted geometries. The main goal using this process is to obtain functional products from engineering materials that feature desired properties such as given strength, hardness, surface roughness and residual stress behaviour. Rapid production with short throughput times due to only few process steps, a high individuality and a high degree of geometric freedom are considered to be its major advantages. However one disadvantage to all laser-based freeform manufacturing is the immense consumption of time since only considerably small quantities of material can be processed per time unit. Therefore it is desirable to review oldfashioned engineering design rules and develop part geometries that allow for hollow shaped parts with interior lattice structures providing the part with virtually the same stiffness and strength. Thus the process cost could be massively cut down due to reduced production time and less need for costly powder material. The SLM-process is meeting the requirements to fulfil this intention. Based on using fiber laser technology that delivers high beam quality the process is capable of producing thin walled structures of high tensile strength. Here development, production and testing of such lightweight yet sustainable SLM-parts will be presented along with their possible applications.

With recent advances in the aligned growth of carbon nanotubes (CNTs), there are great interests in CNT-based field-emission and electronic applications. In conventional thermal chemical vapor deposition, substrates as well as chambers need to be globally heated to a sufficiently-high reaction temperature. In this paper, we report a method for direct synthesis of CNTs on pre-defined electrodes using laser-assisted chemical vapor deposition. A CW CO₂ laser (wavelength 10.6 μm, beam diameter 2 mm) was used to irradiate the pre-defined structures for CNT growth. The temperature of the substrate was measured by a pyrometer, ranging from 850-1000 °C. By varying catalysts and laser parameters, carbon nanostructures including carbon nanofiber, multi-walled and single-walled CNTs can be controllably synthesized.

Poly(amic acid) (PAA), a precursor to polyimide, was successfully deposited on substrates without reaching curing temperature, by resonant infrared pulsed laser ablation. The PAA was prepared by dissolving pyromellitic dianhydride and 4, 4' oxidianiline in the polar solvent N-methyl pyrrolidinone (NMP). RIR-PLD transferred material showed two distinct geometries, droplets and string-like moieties. The unaltered nature of the deposited PAA was confirmed by Fourier transform infrared spectroscopy (FTIR). Thermal curing was achieved by heating for one hour on a 250°C hotplate, and the transformation to polyimide was demonstrated from changes in the FTIR spectrum following curing. Plume shadowgraphy showed very clear contrasts in the ablation mechanism between ablation of the solvent alone and the ablation of the PAA, with additional contrast shown between the various resonant frequencies used.

We report an apparatus designed to characterize two-dimensional (2D) surfaces of carbon films based on the principle of inelastic light scattering (Raman scattering). The design and construction details are presented. The system with a backscattering configuration, is constructed using a high power argon ion laser with a wavelength of 514.5 nm, an XYZ motorized stage with a step resolution of 3.175 μm, a microscope objective lens, a confocal spatial filter and a holographic notch filter, to achieve extremely low crosstalk and maximum resolution in spectroscopy. The radial resolution for film surface is much enhanced by confocal spatial filter due to its stray light suppression capability. A large depth of sampling field is achieved using an objective lens with a middle NA of 0.55 and a long working distance of 8 mm, thus the requirement of using auto-focusing can be avoided. A specific algorithm is designed to decide the film boundaries as well as the outline of surface structures from pre-defined spectral windows. Control software on Labview^TM platform has been developed for controlling movement of the sample stage, spectral acquisition and data visualization. Single-walled carbon nanotubes (SWCNTs) and patterned silicon were used to evaluate the sensitivity, 1D profile and 2D mapping functionality of the designed system. Diamond-like amorphous carbon (DLC) films prepared by pulsed-laser deposition (PLD) were studied using the developed instrument. The results from this approach are compared with those using general scanning tunneling microscope (STM). This comparable low-cost system with high performance is suitable to characterize semiconductors and other materials both for industrial applications and academic research.

Diamond-like carbon (DLC) films were synthesized by KrF excimer laser irradiation of single-crystal Si substrates immersed in a cyclohexane liquid. The deposition process was performed with a peak laser power density of about 10⁸ W/cm² in open atmosphere at room temperature. Scanning electron microscopy (SEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) studies showed diamond-like characteristics of the deposited films. Optical emission spectroscopy (OES) of laser-induced plasmas of cyclohexane indicated decomposition of the cyclohexane molecules. A mechanism based on the dissociation of the cyclohexane molecules and condensation of energetic carbon atoms into diamond-like films was proposed to explain the process.

We present an adaptive mesh approach to high performance comprehensive investigation of dynamics of light and plasma pattens during the process of direct laser inscription. The results reveal extreme variations of spatial and temporal scales and tremendous complexity of these patterns which was not feasible to study previously.

Selective laser removal of micro-particles of one chemical composition from their mixture with micro-particles of another chemical type pre-deposited on hydrophobic or hydrophilic surfaces have been demonstrated by means of steam laser cleaning method realized with nanosecond IR laser and various liquid energy transfer media (ETM). Microscopic imaging of particle mixture deposition, ETM dosing and final particle removal has been performed with the help of timeresolved optical microscopy. Optimal ETM/particle combinations for selective targeting and removal of specific particles from their mixture on the surfaces have been revealed.

Several types of center-symmetrical (elliptical) microstructures of multi-nanometer heights are fabricated on a surface of quasi-crystalline graphite ablated by single femtosecond laser pulses with peak intensities in the range of 1-10²TW/cm². Potential underlying physical mechanisms for these high-intensity micro-structuring ablative phenomena are discussed.