Franciszek Kostrubiec

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...

Laser modification of macroscopic properties of metal surface layer

Surface laser treatment of metals comprises a number of diversified technological operations out of which the following can be considered the most common: oxidation and rendering surfaces amorphous, surface hardening of steel, modification of selected physical properties of metal surface layers. In the paper basic results of laser treatment of a group of metals used as base materials for electric contacts have been presented. The aim of the study was to test the usability of laser treatment from the viewpoint of requirements imposed on materials for electric contacts. The results presented in the paper refer to two different surface treatment technologies: (1) modification of infusible metal surface layer: tungsten and molybdenum through laser fusing of their surface layer and its crystallization, and (2) modification of surface layer properties of other metals through laser doping of their surface layer with foreign elements. In the paper a number of results of experimental investigations obtained by the team under the authors supervision are presented.

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.

Laser wire bonding in power transistors

Attempts at increasing the reliability of assembly of power transistors the authors have proposed a new method for thick wire bonding. Bonding produced in this technology has the form of weld made by the pulsed laser beam. The results of some investigations into the proposed method are presented. The results of studies on semiconductor test structures bring the hope for the positive solution to the problem of increasing the reliability of assembly of such structures.

Laser technologies of production of electric-current-conducting layers

At present, in electrical and electronic engineering, conductive materials are applied in the form of thin and thick films. Their properties are different from the properties of those materials in the bulk form, and are dependent on technological processes and substrate properties. Some materials are obtained using laser technologies. This paper presents the results of the research on laser modification of conductivity of surface layers, and the synthesis of conductive films on metallic and non-metallic substrates. Physical and technological conditions as well as a possible range of modification of properties and synthesis of conductive materials with their applications or practical prognosis.

Multifiber laser Doppler velocimeter with backward scattering

A laser Doppler velocimeter (LDV) using a multi-fiber optic pickup was designed. A single fiber directs the beam to the moving surface. The back scattered signals were received by ten optical fibers. A multi-fiber laser Doppler velocimeter is (MFLDV) capable of determining the value of velocity as high as 10 mm/sec and as low as 0.031 mm/sec. A good linearity is obtained between Doppler shifted frequency (Delta) f and the velocity of a moving surface with a correlation factor of 0.999. LDV using fiber optics has important advantages over conventional systems, it is simpler, easier to align, and non-invasive i.e., the surface does not need to be touched or physically contacted.

Changes of electrical conductivity of the metal surface layer by the laser alloying with foreign elements

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.

Thermocapillary mechanism of laser pulse alloying of a metal surface layer

Laser doping mechanism with the aid of the one pulse of the radiation has been described in this paper . Experiments have proved that mechan isin of the thennocapilary waves of melted metal is the fundamental effect influencing the final distrilution of dope in the dopir area.