Valentin Videkov

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

New assembling technique for BGA packages without thermal processes

Abstract A new assembling technique for flip-chip mounting without heating processes was developed. The proposed construction is an FR4 substrate with ring shaped connectors. It is a typical flip-chip technology. The chip is placed, with its active part face-down, directly on to the connecting areas of the substrate. The electrical connection is obtained through a mechanical contact between the ring-shaped clips and the chip bumps. The main advantage of the ring-clip-bump attachment technique is the possibility for multi-chip modules repairing without thermal processes. It is a lead-free assembling technology involving only “conventional” processes.

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.

Influence of geometry on the applied solder paste in technology Pin in Paste(PiP)

PiP (Pin in Paste) is a technology for soldering with the least expenses and high quality because it is carried out fast (in one step for all components) and without human intervention. In the report it is shown the influence of geometry of the laid paste on the quality of soldering. It is examined in what geometry and in what ways of laying a reliable and repeated soldering can be achieved. There are some rules for successful laying of solder paste which are fixed by the experiments. The most important conclusions are: after a precise estimation of the quantity of paste for every point of soldering it is necessary to define the type, the dimensions and the place of the figure of the laid paste on PCB, which is connected to the design of the stencils aperture, the place of laying of PCB, the way of laying and the qualities of the solder paste. Some producers of pastes for soldering created and offer special designed pastes for PiP. This process is used by EMS (electronic manufacturing services) producers more and more, especially by decreasing the dimensions of the components and increasing the degree of integration. More and more producers of electronic components offer such ones for PiP technology.

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.

Systems for electronic support of the educational process as a behavioural analyst

This paper discusses the application of e-learning systems as a tool for indirect survey. Different modules from the electronic systems used at the Technical University of Sofia for control and assessment of the educational process are presented. The possibilities to summarise data from the application of the electronic means for education as a tool for assessing the behaviour of students are presented. Practical results from such studies are shown.

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 efficiency of the heat dissipation for the heat-conducting circuit boards made of aluminum with the nanoporous alumina layer

The results of the investigation of the efficiency of the heat dissipation from the circuit board made of aluminum with the nanoporous alumina layer and conducting copper layer. In the construction of these circuit boards nanoporous alumina was used as insulator, which provided heat transfer from topology elements to the aluminum substrate. The conducting copper layer was formed by electroplating followed by chemical deposition of thin nickel layer. The diode MBRB16H60 was used as an element possessing high level of heat release. The temperature on the surface of the circuit board was measured by the thermocouple and the infrared images of the samples were studied by the thermal imaging camera. It was shown that proposed circuit boards allow significantly increasing the efficiency of the heat dissipation from the circuit board elements and reducing their operating temperature. The thermal conductivity of the nanoporous anodic alumina layer was determined to be 1.56 W K−1 m−1.

Improved soldering of components with different thermal masses by hybrid printing of solder pastes

In this work are shown the results of an improved Pin in Paste (PiP) technique. With the purpose of soldering of SMD and PTH (Pinthrough Hole) components, the PiP technique is making use of solder paste printing. The problematic PtP soldering due to thermal shading of areas under large size connectors, which results from their big thermal masses, has been considered. The actual temperatures under such connectors differ from the optimum thermal profile needed for the particular solder paste which profile can be monitored by a KIC instrument. A solution of this problem is suggested by making use of a solder paste, whose optimum thermal profile corresponds to the actual thermal profile under the connector components. For that purpose are used two different kinds of solder pastes. The proposed method, named Hybrid Printing, of two kinds of SMD pastes is based on the special design of a rakel which allows depositing of more than one kind of solder paste within one processing step. The effect of the use of Bi containing, Pb containing and Pb-free solder pastes has been investigated. The application of hybrid printing in a real production line has been demonstrated. The results of the X-ray and metallographic assessment of the fabricated solder joints are presented.