Laser Direct Writing (LDW) are used in the manufacture of electronic circuits, pads, and paths in sub millimeter scale. They can also be used in the sensors systems. Ablative laser writing in a thin functional layer of material deposited on the dielectric substrate is one of the LDW methods. Nowadays functional conductive layers are composed from graphene paint or nanosilver paint, indium tin oxide (ITO), AgHT<sup>TM</sup> and layers containing carbon nanotubes. Creating conducting structures in transparent layers (ITO, AgHT and carbon nanotubes layers) may have special importance e.g. for flexi electronics. The paper presents research on the fabrication of systems of paths and appropriate pattern systems of paths and selected electronic circuits in AgHT<sup>TM</sup> and ITO layers deposited on glass and polymer substrates. An influence of parameters of ablative fiber laser treatment in nanosecond regime as well as an influence of scanning mode of laser beam on the pattern fidelity and on electrical parameters of a generated circuit was investigated.
Set of different physical processes has crucial influence on the required precision in case of shaping of elements with
dimensions less than tenths millimeter by means of a laser beam, both in terms of the 3D geometry and the structure of
the material in micro-volume. Many issues in the field of micrometer scale materials can be solved and used in practice
by modeling processes. This article presents some selected examples of accomplished laser microtechnologies, using
beam of nanosecond pulses of fiber laser, successfully supported by computer modeling. Using a pulsed fiber laser beam
in the process of a thermal ablation spatial structures of micro elements in ceramic and semiconductor materials were
produced. Optimum range of process parameters to ensure efficient removal of material, and acceptable quality of a
surface of made elements was set by modeling. In micro-technologies, where structures with submillimeter dimensions
are formed, modeling of the process with the phase transition phenomena requires taking into account the energy
coupling of a beam – material, nonlinear thermal phenomena and the difficult to modeling problems associated with
moving phase boundary as well as latent heat of phase transition.
Applying of laser technologies offer many new possibilities for achieving conducting materials with modified properties. Laser processes also allow microfabrication of elements of dimension in micrometer scale. The modified materials and elements were obtained by special using of such a laser technologies as rapid remelting, microalloying, removing of material. For some cases, the required energetic parameters of the laser beam have been established and especially developed technological ideas have been presented. Microstructure evolution and phase identification of treated
materials was investigated by means of optical and scanning microscopy and X-ray microanalysis. It has been shown that in these technological processes it was possible to achieve conducting materials with changed properties, among other things with modified electrical resistivity. In selected cases it was also possible 3_D shaping of modified elements. The results of investigations were applied for laser welding of joints in power devices, laser microsoldering of IC on PC-board, producing some contact materials.
Applying of laser alloying for modification of electrical resistivity of metals with significant importance in electrical and electronic engineering and utilization of this method for producing passive elements of electric circuit have been presented. The alloyed metals were obtained by means of laser beams with different wave length and various mode of working (cw or pulse), by different methods for the supplying of alloying elements. It was possible to form alloyed layers of metals forming different types of metallurgical systems: with full (<b><i>Cu-Au</i></b>, <b><i>Cu-Ni</i></b>) or partial solubility (<i><b>Mo-Ni</b></i>, <b><i>W-Ni</i></b>, <b><i>Cu-Al</i></b>, <b><i>Ag-Sn</i></b>), insoluble (<b><i>Mo-Au</i></b> and <b><i>Cu-Cr</i></b>) and immiscible (<i><b>Ag-Ni</b></i> and <b><i>Ni-Au</i></b>) metals, with metallic as well as non-metallic additions (oxide). It has been shown as well that it is possible to achieve resistive elements modified in whole cross section, in a single technological process. The results of systematic investigations into the resistivity of alloyed metals in the temperature range of 77-450 K have been presented. The alloyed layers, obtained, were characterised by a range of resistivity from 2.8 x 10<sup>-8</sup> Ωm (Cu-Cr) to 128 x 10<sup>-8</sup> Ωm (W-Ni). The microstructure and composition of alloyed layers were examined by means of SEM-microscopy and EDX analyser. In selected cases it was shown how results of investigations could be utilized for modification of surface layer of contact materials or to optimize the resistance of laser welded joints. In addition the results of investigations of new developed microtechnology -- <i>producing micro-areas with extremely high resistivity</i> -- have been presented.
This paper presents the results of modification of surface layer properties, obtained the optimised laser alloying of metals insignificant in electrical engineering. Systems with continous, quasi-continuous and pulsed laser beams and different wave lengths were used in the experiments. The structure and composition of the alloyed layers were examined by means of SEM-microscopy and an EDX analyser. The changes of electrical resistivity after laser alloying were measured in a temperature range of 77-450 K.
It has been shown that the formation of alloyed lasers for metals with limited solubility (Ag-Sn), insoluable (Mo-Au, Cu-Cr), and even immiscible metals (Ni-Au, Ag-Ni) is possible. It is also possible to obtain alloyed layers with non-metallic additions (oxide).
The investigations have shown how alloyed layers with strongly modified properites, especially electrical resistivity, can be obtained by means of different laser beams and various methods for the supplying of alloying elements.
This article presents some investigations of a laser alloyed surface layer of nickel doped with gold and of copper doped with aluminum. The velocity of the convectino flow in the laser pool predicted by computation implies that there may exist good miscibility for the range of components different from those obtained by the conventional method. This indicates a predominant role of the Marangoni convection for mixing elements. Some metallurgical cross-sections of Ni-Au; Mo-Au; Cu-Al; Cu-Au layers, alloyed by an Nd-YAG laser, for different contents of doping elements are presented. They may be interesting information about miscibility of these metals during laser pulse τ<sub>1</sub>=4ms.
In the paper a laser method for producing micro-areas of a high resistivity has been presented. To obtain such areas, a local character of the pulsed radiation beam interaction was used, which - in the laser alloying process - allowed the generation of an alloy in a limited spatial area (of a volume of 0.01 - 1 mm<SUP>3</SUP>). In the case of thin wire and foils the alloyed micro-areas comprise the whole section of the element subjected to treatment. For some cases, the required energetic parameters of the beam have been established. The conditions for obtaining the homogeneity of an alloyed area for different lasers (pulse or cw) have been determined. The results of investigations into electrical properties of the elements have been presented. The use of such areas for fuse-links has been suggested. Using the microscopic infrared thermography method, the heating of the elements containing resistive areas with the flow of current of a fixed value and with jump changes in current intensity has been determined.
The work deals with selected problems of modification of metal surface layer parameters, which parameters are significant for the use of these metals in electrical engineering. The first part of the paper is devoted to selected questions of technology of metal surface layer properties, based on the doping of these layers with foreign elements. The second part of the work contains selected results of the authors' own studies. Special attention has been paid to the modification of resistivity and microhardness of surface layers.
The paper presents the results of analysis of thermocapillary phenomena in the liquid phase of a laser fusion. Making use of the FIDAP program the authors modelled the phenomena of convection using silver as an example. Silver was subjected to the action of a laser radiation pulse of the duration (tau) equals 4 ms and the Gaussian distribution of the power density q<SUB>o</SUB> approximately 10<SUP>9</SUP> . . . 10<SUP>11</SUP> W/m<SUP>2</SUP>, of the radius r<SUB>o</SUB> equals 150 micrometer. The axis symmetry of the model was assumed. Thermal coefficients were assumed to be constant for each phase, while the values of the surface tension as a function of temperature. With such assumptions the Marangoni convection is the primary cause of convection motion. The velocity field and the shape of the interfacial surface were determined on the basis of calculations performed using the FIDAP program. The shape coefficient (K equals d/h - width by depth) of the fusion is in good agreement with the real value. The paper indicates some possibilities of using a model built with the help of the FIDAP program for predicting some results of laser melting.
The paper deals with stresses induced in the alloyed layers of high-melting metals in the laser treatment process with a continuous beam and a pulse of a duration (tau) equals 4 ms. It has been found that the threshold power densities of laser radiation resulting in the permanent plastic strain of the metal under treatment are greater than the ones used during treatment. Making use of an analysis of the temperature field, the cooling rates of the treated zone have been determined by the finite difference method and an analytical method. The spatial non-uniformity of the heating and cooling rate of tungsten and molybdenum can be the cause of plastic strain and fractures on the metal surface. Experimental investigations were carried out for the optimal parameters of a laser radiation beam (the maximum depth of the alloyed layer, possibly with the smallest number of fractures). A privileged direction of fractures at an angle of 45 degrees in relation to the direction of scanning was observed (basing on the microscopic observations of 2 mm by 2 mm layers made on the surface of 10 specimens). Experiments showed a considerable effect of the type of the metals treated on the likelihood of occurrence of fractures; these are distinct and numerous in the case of molybdenum alloyed with nickel, whereas they cannot be observed in tungsten alloyed with nickel at a magnification of X 20,000. The smaller concentration of stresses in tungsten is also confirmed by the results of microhardness measurements (Table 2). The different behavior of the metals under treatment may be caused by volumetric changes brought about by metallurgical phase transitions.
Modern methods of treatment of the surface layer allow improvement in mechanical properties of metals (an increase in the life and resistance to wear of mechanical elements as well as other properties, e.g., electrical ones). Owing to the very large temperature gradients (approximately 10<SUP>8</SUP> K/m) and great rates of crystallization obtained, the laser treatment method is the most efficient of them all. The range of changes in mechanical properties obtained through such treatment cannot be achieved by other methods. The method of laser doping of metal surface layers offers especially distinct advantages. This is related to obtaining various and atypical heterogeneous systems in these layers. In the paper the results have been discussed of the treatment of the surface layer using a Nd-YAG pulsed laser. Studies have been carried out for metals of significance in electrical engineering: Ag, W, Mo -- as base metals and Sn, Ni, Pd and Au -- as a doping material. Special attention has been paid to changes in the microhardness of the layers obtained compared with the properties of base metals and doping metals. The results point to strong possibilities of modification of microhardness through laser doping.
Laser treatment of the surface of materials is of major importance for many fields technology. One of the latest and most significant methods of this treatment is laser alloying consisting of introducing foreign atoms into the metal surface layer during the reaction of laser radiation with the surface. This opens up vast possibilities for the modification of properties of such a layer (obtaining layers of increased microhardness, increased resistance to electroerosion in an electric arc, etc.). Conductivity of the material is a very important parameter in case of conductive materials used for electrical contacts. The paper presents the results of studies on change in electrical conductivity of the surface layer of metals alloyed with a laser. A comparative analysis of conductivity of base metal surface layers prior to and following laser treatment has been performed. Depending on the base metal and the alloying element, optical treatment parameters allowing a required change in the surface layer conductivity have been selected. A very important property of the contact material is its resistance to plastic strain. It affects the real value of contact surface coming into contact and, along with the material conductivity, determines contact resistance and the amount of heat generated in place of contact. These quantities are directly related to the initiation and the course of an arc discharge, hence they also affect resistance to electroerosion. The parameter that reflects plastic properties with loads concentrated on a small surface, as is the case with a reciprocal contact force of two real surfaces with their irregularities being in contact, is microhardness. In the paper, the results of investigations into microhardness of modified surface layers compared with base metal microhardness have been presented.