Ryszard Pawlak

Thermokinetic processes in laser welding of current leads

The aim of this study was to investigate the usefulness of the laser welding technology for the realization of wire connections: semiconductor structure-outer leading in power devices. Laser technology can be alternative to the traditional ultrasonic method of bonding, applied in power devices (for example IGBT transistors). The bondings made by ultrasonic method have adhesive nature and therefore are more susceptible for the damage than laser welded joints.A laser beam of a wavelength of 1.06 μm was applied in the new method of leads joining. Nickel was used as a material for wire leads and an intermediate plate (Molybdenum) between semiconductor structure and wire was placed additionally. The wire was welded directly to this plate. In this paper the thermo-mechanical properties of these bonding will be presented. Two fundamental problems will be discussed: thermal stresses, induced during laser welding, which have influence on the behaviour of the joints, and thermal state of the finished leads during conducting great currents, typical for the work of the power devices. The results of experiment investigations and results of computer modeling will be also presented.The aim of this study was to investigate the usefulness of the laser welding technology for the realization of wire connections: semiconductor structure-outer leading in power devices. Laser technology can be alternative to the traditional ultrasonic method of bonding, applied in power devices (for example IGBT transistors). The bondings made by ultrasonic method have adhesive nature and therefore are more susceptible for the damage than laser welded joints.A laser beam of a wavelength of 1.06 μm was applied in the new method of leads joining. Nickel was used as a material for wire leads and an intermediate plate (Molybdenum) between semiconductor structure and wire was placed additionally. The wire was welded directly to this plate. In this paper the thermo-mechanical properties of these bonding will be presented. Two fundamental problems will be discussed: thermal stresses, induced during laser welding, which have influence on the behaviour of the joints, and thermal state of the finished leads during c...

Laser-induced change of electrical resistivity of metals and its applications

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 (Cu-Au, Cu-Ni) or partial solubility (Mo-Ni, W-Ni, Cu-Al, Ag-Sn), insoluble (Mo-Au and Cu-Cr) and immiscible (Ag-Ni and Ni-Au) 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 10-8 Ωm (Cu-Cr) to 128 x 10-8 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 -- producing micro-areas with extremely high resistivity -- have been presented.

Laser microtechnologies for passive elements of electronic circuits

Varied innovative laser-technologies introduced to manufacturing process of electronic circuits and devices were applied to semiconductor and dielectric materials. As distinct from this we have investigated some laser microtechnologies concerning electrically conductive materials and elements made of them. Laser technologies such as microremelting and microalloying of thin wires and metallic foils as well as microwelding and material removing were applied for creating of a new type of conductive elements. These elements containing micro-areas of form, dimensions and materials properties, especially high electrical resistivity, determined by applying of laser microtechnology, could be use as new generation of miniature fuse links. The problems of heat and mass transfer specific to remelting and alloying of elements of microscopic dimensions were investigated by computer modeling. The results of investigations into materials, electrical and thermal properties of modified elements are discussed with reference to results of experimental utilization of elements manufactured by means of laser technologies.Varied innovative laser-technologies introduced to manufacturing process of electronic circuits and devices were applied to semiconductor and dielectric materials. As distinct from this we have investigated some laser microtechnologies concerning electrically conductive materials and elements made of them. Laser technologies such as microremelting and microalloying of thin wires and metallic foils as well as microwelding and material removing were applied for creating of a new type of conductive elements. These elements containing micro-areas of form, dimensions and materials properties, especially high electrical resistivity, determined by applying of laser microtechnology, could be use as new generation of miniature fuse links. The problems of heat and mass transfer specific to remelting and alloying of elements of microscopic dimensions were investigated by computer modeling. The results of investigations into materials, electrical and thermal properties of modified elements are discussed with referenc...

Three-dimensional flow-field measurements in multistage turbomachinery using a computer-aided system

In order to measure a complicated unsteady 3D subsonic turbomachinery flow field by use of five-hole pressure probes and a multisensor hot-wire probe, a computer aided measurement system was built up and developed. Long experiences acquired by us and by other research institutes in various experimental studies were taken into consideration as measurement rules in the system. Using the present measurement system, the 3D unsteady flow fields in turbumachinery were determined. The automatic measurements were performed satisfactorily even in the downstream rotor flow region. From the experiments, it is concluded that the quality of the measurements of the unsteady 3D flow field behind a rotor is improved greatly by means of the proposed computer aided multisensor system.

Laser-remelted plasma coatings

In this article, changes in structural and electrical properties of surface coatings were investigated after laser remelting. The surface Ni-coating under investigation has been obtained by plasma spraying. Surface remelting was carried out under a pulse Nd:YAG laser. Microstructure evolution and phase identification was investigated by means of optical and scanning microscopy and X-ray microanalysis. Laser remelting eliminated defects and porosity of a surface layer and suppressed the oxide phase. The electrical resistivity of a plasma sprayed layer was decreased and the temperature resistivity coefficient was increased due to these structural changes.

Structure and properties of resistive micro-areas made using a pulsed and continuous laser beam

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 mm3). 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.

Laser-Textured Rubbers with Carbon Nanotube Fillers

This paper describes a method of laser ablation for improving the hydrophobic properties of vulcanized rubber. The treatment was tested on acrylonitrile rubber (NBR) and styrene butadiene rubber (SBR) containing carbon nanotubes and soot as fillers. The surface layer of the vulcanizates was modified using a nanosecond-pulsed laser at 1060 nm wavelength. The parameters of the ablation process were congruent, so no chemical changes in the polymeric material were observed. Evaluation of the surface condition of the laser-textured samples was performed using a Leica MZ6 stereoscopic microscope, operating with MultiScan 8.0 image analysis software. The contact angles were determined for all the samples before and after the surface modification process. Following modification of the surface morphology, with the best parameters of laser ablation, the contact angle increased, reaching 147°, which is very close to the threshold of superhydrophobicity (150°). On the basis of the results from several tests, laser ablation with a fiber-pulsed laser can be considered a very useful method for producing rubbers with superhydrophobic surfaces.

Precise laser cutting of narrowings in miniature fuse links by use of fiber laser and YAG (355 nm) laser

Laser cutting is widely used in many manufacturing processes with high requirements for accuracy, reliability and reproducibility. In the paper there are discussed some results of our research into precise laser cutting of different shapes in thin metallic foil strips that could play a role of a new type of miniature fuse links. In the study the Cu/Ag foil strips of width of 600 μm and thickness of 50 μm (outer layer of Ag about 3 μm) were used. The holes were cut by use of two different lasers: Nd:YAG laser (355 nm), duration of pulses 25 ns (AVIA 355-10 Coherent) and fiber laser (1070 nm) (SPI redENERGY 20W) duration of pulses 9 - 200 ns. The influence of beam power, pulse repetition frequency and scanning velocity on quality and efficiency of micromachining were investigated. The main advantage of applying Nd:YAG laser (355 nm) was better quality of cutting edges of holes. The experiments have shown that results of micro-cutting by use of pulsed (ns) fiber laser beam, despite of lower absorption by Cu/Ag foil are also to be accepted. The results of investigation confirmed expected electrical and thermal properties of elements created by laser technology.Laser cutting is widely used in many manufacturing processes with high requirements for accuracy, reliability and reproducibility. In the paper there are discussed some results of our research into precise laser cutting of different shapes in thin metallic foil strips that could play a role of a new type of miniature fuse links. In the study the Cu/Ag foil strips of width of 600 μm and thickness of 50 μm (outer layer of Ag about 3 μm) were used. The holes were cut by use of two different lasers: Nd:YAG laser (355 nm), duration of pulses 25 ns (AVIA 355-10 Coherent) and fiber laser (1070 nm) (SPI redENERGY 20W) duration of pulses 9 - 200 ns. The influence of beam power, pulse repetition frequency and scanning velocity on quality and efficiency of micromachining were investigated. The main advantage of applying Nd:YAG laser (355 nm) was better quality of cutting edges of holes. The experiments have shown that results of micro-cutting by use of pulsed (ns) fiber laser beam, despite of lower absorption by Cu/...

Laser modification of properties of materials and elements for electronics

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.

Laser modification of properties of the surface layer of conducting materials

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.