Anna V Andonova Stoynova | Technical University - Sofia (original) (raw)

Uploads

Papers by Anna V Andonova Stoynova

The investigation deals with quality improvement of wave soldering joints for printed circuit boa... more The investigation deals with quality improvement of wave soldering joints for printed circuit boards (PCB) by using DOE approach. Using DOE pro XL capabilities, DOE and statistic process control an effective way to approach and evaluate wave soldering process development is ...

The investigation deals with the numerical solution of the 3D heat conduction equatioin and study... more The investigation deals with the numerical solution of the 3D heat conduction equatioin and study variation of the effective conductivity of PCB with different component size. Cases with and without a copper layer on the component side and different PCB thicknesses were investigated. It was shown that the effective thermal conductivity of a PCB with/without a copper layer on the component side would be larger/smaller than the values given by the onedimensional effective thermal conductivity model if the components mounted on the PCB were smaller than the PCB itself. The difference was more pronounced for smaller components. Correlations were obtained for the effective thermal conductivity of PCBs.

The thermal conductivity of PCB structures variations according to the position of the metal laye... more 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.

This paper presents an approach to evaluate the design limits of integrated circuits. The basis o... more This paper presents an approach to evaluate the design limits of integrated circuits. The basis of that approach is a destructive evaluation performed on a small number of test items to measure their design limits. Results from applying it demonstrate that the approach can be quite effective for ALT experiments

In order to investigate parameters and design methods of SAW stabilized microwave generators a me... more In order to investigate parameters and design methods of SAW stabilized microwave generators a methodology is elaborated. The generator is divided into four different blocks: SAW resonator, power divider, attenuator, and amplifier. This solution allows each block to be measured and analyzed separately. The amplitude and phase condition for generation can be calculated and the resonant frequency of the oscillator can be predicted. The measurements of the microwave oscillator are done in time and frequency domain by frequency meter and spectrum analyzer. The jitter and the spectrum are observed. The output signal is analyzed, observing the frequency, phase noise (at given offset) and power of the main harmonic and the magnitude and frequency of the other harmonics.

This article deals with numerical simulation of air flow and heat transfer in an electric junctio... more This article deals with numerical simulation of air flow and heat transfer in an electric junction box comprising conductive metal wire rods each having a cylinder shape in cross section. Results obtained by a commercial CFD package widely used for electronic system temperature predictions. The paper gives considerable insight into the nature of the enclosure heat transfer and an indication of the accuracy of a widely used predictive code.

Simulation and analysis of the electromagnetic behavior of 3D-MCM (multichip module) carrier stru... more Simulation and analysis of the electromagnetic behavior of 3D-MCM (multichip module) carrier structures by means of investigation on symmetric folded microstrip filters realised on their basis is proposed in the present paper. The technology for building multilayer high-speed MCM structures, based on Al carriers enables the development of multiple and multilayered interconnections combined with thin film integrated passive components-resistors and MIM capacitors-embedded in the whole structure. In order to study these material systems of interconnections, constructions of multilevel folded symmetric microstrip filters for 1.7 GHz were developed. An electromagnetic simulation of the various filter constructions was performed. RF measurements by means of a vector analyzer were carried out and compared with the simulated characteristics. The obtained measurement and simulation results were used to study successfully the electromagnetic characteristic as well as the parasitic high-frequency effect of interconnection, in order to achieve a reliable practical realisation of high rate production quality

This paper presents a fully-integrated voltage controlled oscillator working in the 2.45GHz ISM b... more This paper presents a fully-integrated voltage controlled oscillator working in the 2.45GHz ISM band. It uses the standard differential design as it gives major advantageshigh suppression of noise on the power supply lines, better start-up for a given power consumption. The oscillator achieves very low phase noise of -123dBc/Hz at 1MHz offset from the carrier. Emitter degeneration technique is used to improve the phase noise over the standard design. The power consumption of the oscillator is 8mA from a 3V power supply. The output voltage amplitude is 800mV. The tuning frequency range is 2.38-2.68GHz and the tuning voltage is from 2V to 3 V.

Pick-and-place of micro/nano sized objects means handling of very tiny and very different in prop... more Pick-and-place of micro/nano sized objects means handling of very tiny and very different in properties objects having specific behavior. Besides formal requirements of assembly processes, the tools for controllable manipulation with these objects should not affect the examined micro/nano environment, i.e. should be “small and passive” in any sense. Despite of the recent progress, most available micro-grippers are still suffering of high voltage power supply required, short lifetime, low detection sensitivity and high price. Prototypes of a newly designed micro-gripper, having advantages over the existing analogues, have been developed, experimentally studied, and presented in this paper. The envisaged microgripper is of normally-closed type with thermo-mechanically driven actuator and piezoresistive arm-displacement feedback. The thermo actuator is placed between gripper’s arms and consists of double-folded highly-doped compliant silicon beam. As low average voltage vs. arm displacement value as 1V/μm, was experimentally measured.

This paper describes a model for accelerated reliability growth (ARG) analysis. It provides targe... more This paper describes a model for accelerated reliability growth (ARG) analysis. It provides target accelerated test times and aids in the estimation of the expected number of failures for each phase of the subsystem's qualification program. Tools such as Microsoft® Excel are used to program a spreadsheet and graphically display growth curves. An input/output table form is created in this program, and a graphical output is made. An example illustrates the idealized curves for a subsystem using the ARG equations. The MTBF at each point of a test-analyze-and-fix reliability growth phase is shown. After each phase, corrective actions are incorporated into the subsystem, yielding a jump in MTBF. The acceleration factor (AF) is estimated from accelerated conditions and expected typical failure modes.

Degradation analysis is an important method of assessing the reliability of highly reliable compo... more Degradation analysis is an important method of assessing the reliability of highly reliable components and especially microsystems. Its application constantly increases due to the continuous efforts to produce increasingly reliable electronic products. The presented methodology is an effective way to estimate the component's reliability by monitoring performance degradation. The main advantage is that the time-to-failure is not directly observed but the degradation can be accurately measured. Consequently, the test time can be significantly shorter than if the times-to-failure are recorded

The proliferation of system-on-chip designs is forcing us to consider the possibility of doing al... more The proliferation of system-on-chip designs is forcing us to consider the possibility of doing all design phases at the highest possible levels of abstraction. Behavioral-level design tools are today commercially available, and offer a solution to this problem. Conversely, test issues are usually addressed at the lowest levels of abstraction and, although in recent years many efforts have been devoted to the definition of strategies for addressing test at the high level, a global solution is yet to come. We present preliminary experimental results about some of the available high-level fault models working at the register-transfer (RT) level. The experimental procedure we adopted is presented and some preliminary results are discussed.