Svetozar Andreev

Investigation of thermal conductivity of PCB

The thermal conductivity of PCB structures variations according to the position of the metal layers as a function of the local copper contents and distribution are studied. The value of the parallel and serial thermal conductivity coefficient of PCB have been calculated by usage of the corresponding electrical analogs of parallel and serial resistive systems. Solutions were obtained for two PCB thicknesses. Cases with and without a copper layer on the component side were investigated. Simulated results are verified with infrared thermovision measurements.

Novel microcontacts in microwave chip carriers developed by UV-liga process part II

This paper presents the design and development of novel type microcontacts in monolithic microwave integrated circuit (MMIC) chip-carriers to printed circuit board (PCB) assembly. Several new concepts of microcontacts for packaging solutions of microwave and millimeter-wave MMIC are depicted. Simulation and vector network analyzer (VNA) measurement results for these microcontact transitions are discussed. The results show that the electrical parameters are highly dependent on the transition dimensions and substrate features. These contacts are based on male stud (bump) and female (ring) concept. When mating each other, there are clips effect and self-alignment features. Special attention is paid to the shape of the microcontacts in order to facilitate assembly and strengthen the connection. Equivalent electrical circuit is proposed for PSPICE simulation of the dc contact resistance. Finally, the article discusses the technological implementation of the proposed new microcontact stud-ring through low-cost ultraviolet electroplating, lithography, and molding (UV-LIGA) process and the regime influence on the shape, geometry, and mating capabilities. Results from mechanical pull and adhesion tests are also discussed

Effect of anodization conditions on the breakdown voltage of nanoporous aluminium oxide

Within the work presented the effect of voltage, electrolyte nature and time of anodization on breakdown voltage of nanoporous aluminium oxide layers are investigated. The dielectric layers formed under various conditions feature a pore diameter from 20 to 90nm, and the thickness lies within 1÷14μm. The results reveal that reanodization up to 300V significantly enhances the breakdown voltage. For Al/Al2O3 structure, it is found out that breakdown voltage depends mainly on the layer thickness and significantly less on the pore diameter.

Programmable setup for Peltier element control with fine smooth regulation of the temperature about testing of semiconductor structures

This article presents the design of non-standard equipment for obtaining experimental data about defects in thin film semiconductor structures. The idea of using low-powered Peltier element programmed to cause small temperature changes in semiconductor structures is scanning of the energy bandgap and thermal stimulation of the trapped charge carriers for defects analysis. Block diagram, control algorithm and PCB layout of the testing stand are given. Samples consisting of organic semiconductor and aluminum electrodes are examined for demonstration of the device working capacity. Energy distribution and concentration of the existing defects are determined.

Engineering of III-Nitride Semiconductors on Low Temperature Co-fired Ceramics

This work presents results in the field of advanced substrate solutions in order to achieve high crystalline quality group-III nitrides based heterostructures for high frequency and power devices or for sensor applications. With that objective, Low Temperature Co-fired Ceramics has been used, as a non-crystalline substrate. Structures like these have never been developed before, and for economic reasons will represent a groundbreaking material in these fields of Electronic. In this sense, the report presents the characterization through various techniques of three series of specimens where GaN was deposited on this ceramic composite, using different buffer layers, and a singular metal-organic chemical vapor deposition related technique for low temperature deposition. Other single crystalline ceramic-based templates were also utilized as substrate materials, for comparison purposes.

Investigation of the dielectric permittivity of anodic aluminum oxide substrates for multi-chip modules

The present article describes the investigations, performed in order to determine some dielectric characteristics of anodic aluminum oxide (AAO), obtained by electrochemical anodization process. The AAO layer is grown directly on aluminum substrates, considered as suitable carriers for multi-chip modules (MCM). Test samples for measurements of the dielectric permittivity and loss tangent were elaborated by anodization in 5% oxalic acid electrolyte. The chosen measurement technique is based on the ring resonator method. The values, obtained for the S21 parameter of a two-port ring resonator, were used to determine the permittivity of the board substrate.

Study of thermal conductivity of nanoporous anodic alumina layer formed in sulphuric acid using steady-state heat flow technique

The paper presents the results of studies of thermal characteristics of nanoporous anodic alumina layer formed in sulphuric acid. One-sided heating of aluminum boards by heating element from carbon filament was used. The temperature of the back side of the board was kept constant by using an aluminum heatsink. Thermograms of aluminum board surface were taken by thermal imaging camera MobIR M4.

Kinetics of reanodization of porous anodic oxide films on aluminium formed in pore-forming solutions of various acids

Investigations are carried out towards reanodization of porous anodic oxide films on aluminium formed in aqueous solutions of sulphuric, oxalic and chromic acid. These films are prepared in a way to have one and the same porosity. It is found out that in case of equal porosity the slopes of the kinetic voltage-time curves recorded during reanodization are different. The effect of the anionic species incorporated from electrolyte solution into the porous template could be a probable explanation for the dissimilar rates of barrier layer growth.

Spray deposition of organic electroluminescent coatings for application in flexible light emitting devices

Abstract Organic electroluminescent (EL) films of tris(8-hydroxyquinolinato)aluminum (Alq3) mixed with polystyrene (PS) binder were produced by spray deposition. The influence of the substrate temperature on the layer’s morphology and uniformity was investigated. The deposition conditions were optimized and simple flexible light-emitting devices consisting of indium-tin oxide/Alq3:PS/aluminum were fabricated on polyethylene terephthalate (PET) foil to demonstrate the advantages of the sprayed organic coatings. Same structure was produced by thermal evaporation of Alq3 film as a reference. The influence of the deposition method on the film roughness and contact resistance at the electrode interfaces for both types of structures was estimated. The results were related to the devices’ efficiency. It was found that the samples with sprayed films turn on at 4 V, which is 2 V lower in comparison to the device with thermal evaporated Alq3. The current through the sprayed device is six times higher as well (17 mA vs. 2.8 mA at 6.5 V), which can be ascribed to the lower contact resistance at the EL film/electrode interfaces. This is due to the lower surface roughness of the pulverized layers.

Some aspects of novel micro-contacts in Microwave Chip Carriers

Design and development of novel type micro-contacts in Microwave Chip Carriers to Printed Circuit Board (PCB) assembly are presented in this paper. A new concept of micro-contacts for packaging solutions of microwave and mm-wave MMICs is depicted. Simulation and Vector Network Analyzer (VNA) measurement results for these micro-contact transitions are discussed. The results show that electrical parameters are highly dependent on the transition dimensions and substrate features. These contacts are based on male stud (bump) and female (ring) approach. When mating each other, clips effect and self-alignment features appear. Special attention is paid to the shape of the micro-contacts in order to facilitate assembly and strengthen the connection. Equivalent electrical circuit is proposed for SPICE simulation of the DC contact resistance. Finally, the article discusses technological development of the proposed new micro-contact stud/ring pair by means of low cost Ultra-violet electroplating, lithography and molding (UV-LIGA) process.