The normative study of acoustic parameters in normal Egyptian children aged 4–12 years

The study of normative data of childhood voice is very important to aid in the identification of pathological voices in this age group. Objectives: The aim of this study was to establish a database of the normal acoustic parameters in children aged 4–12 years. Methods: The study was carried out at the Unit of Phoniatrics, Faculty of Medicine, Alexandria Main University Hospital, on one hundred normal children of both sexes aged from 4 to 12 years, all children were subjected to computerized acoustic analysis using Multidimensional voice program software. The vocal samples were obtained from the children by holding a microphone 10 cm in front of their mouth and producing sustained phonation. The analyses of the vocal parameters were carried out with the sustained/a/vowel, with elimination of the irregularities in the beginning and end of utterance .The studied acoustic parameters were the fundamental frequency, shimmer and jitter disturbance measures, and the harmonic/noise ratios.A full informed consent was taken from all subjects contributing to the study. Results: The mean Fundamental frequency was around 260.46 Hz. Jitter and jitter % were around 81.8% and 1.9% in boys and 62.8% and 1.6% in girls. Conclusion: The inclusion of computerized acoustic analyses makes the vocal assessment more accurate and less subjective, thus representing an important tool for vocal screening, for it is a simple, fast and reliable method.To construct a representative database of normal children, we recommend the recruitment of large number of subjects, inclusion of younger age group, and covering other acoustic parameters. KEYWORDS: Childhood voice, Normative values, Computerized acoustic vocal analysi

Thermal characterization of highly conductive die attach materials

This paper deals with the development of a new test stand for determination the thermal conductivity of metals, semiconductors, highly conductive die attaches and substrates using the steady state technique. We designed the test stand and optimized it by FE simulation to have flexibility for the selection of the sample size and measurement parameters. We determine the thermal conductivity from the measured thermal resistance and the geometries of the measured samples. To measure the thermal resistance by steady state techniques one need a hot source and a heat sink. Putting the sample between these hot source and sink, so the sample will be flowed by heat and temperature gradient across the sample will be generated. The temperature gradient across the sample is measured by a thermal imaging system. The input and the output heat flow are measured by metal based heat flow sensors (HFS) which is a metal socket with integrated high precise temperature sensors. To determine the exact heat flow through the sample we analysed the heat loss by radiation and convection by a case study and calculated a correction factor for the heat flow. Different solder and die attach materials as well as metals and highly conductive substrates have been measured by the new test stand. Selected results will be presented in this paper in order to demonstrate the functionality and the accuracy of the new test stand

In-situ monitoring of interface delamination by local thermal transducers exemplified for a flip-chip package

We have developed a novel, rapid, robust and non-destructive experimental technique for in-situ monitoring of delamination of interfaces for electronic packages. The method is based on a simple thermal transducer matrix of so-called THIXELS (thermal pixels) which allows a spatially resolved real-time image of the current status of delamination. The transducers are small metal wire meanders which are driven and electrically read out using the well-known 3-omega method. This method has special advantages over other thermal contrast methods with respect to robustness, sensitivity and signal-to-noise ratio. Notable is the absence of cross-effects. The proof of concept has been furnished on an industry-grade flip-chip package with underfill on an organic substrate. The technique is especially powerful for buried interfaces, where time-honoured methods like scanning acoustic microscopy (SAM) cannot be applied. As the technique effectively performs a thermal diffusivity sensitive scan, it may not only be useful for stress testing during package qualification, but sensor applications on other fields of health monitoring seem also possible

Effective thermal modelling evaluation and non-destructive tests for thermal via-structures in organic multi layer PCBs

This paper derives and evaluates an effective thermal material simulation model in simula-tion and experiment as well as proposes a non-destructive failure analysis for multi-layer sub-strates with thermal or electrical vias to derive exact failure data to supplement existing life-time models. The effective thermal material simulation model is investigated for a test matrix of repre-sentative structures. It results in a via structure class-dependent correction factor. As non-destructive failure test the pulse IR thermography using electrical and laser excita-tion was chosen as an analytic method to ob-serve and quantify crack growths in vias. The method shows that cracks are detectable un-ambiguously and its advantage over the ohmic test. The electrical excitation correlates well with the FE-simulation for different crack length in the cylindrical via structure. The laser excitation shows also a good agreement with the FE-simulation and has in contrast to the electrical excitation a good potential for large-scale screening as the board can be stepwise thermally excited and screened in one go with-out having any additional measuring lines. The results were validated with a 3D computer tomography analysis

Limitations and accuracy of steady state technique for thermal characterization of thermal interface materials and substrates

The steady state method is a commonly used and in principle simple way to measure thermal resistance and conductivity of thermal interface materials (TIMs). The sample must be positioned between a hot and a cold plate with constant temperatures, whereby a heat flow through the sample and temperature gradient across the sample are generated. To determine the thermal resistance of the sample the heat flow and the temperature gradient have to be measured. This is also defined by the ASTM standard ASTM D5470 [4]. However, for the new generation of highly conductive and thin TIMs, die attach materials and substrate the resolution of the common steady state technique often reaches its limit. To increase the resolution of the steady state equipment beyond the state-of-the-art the test systems must be analyzed and parasitic effects be studied. Some options for increasing the resolution of the steady state method will be studied analytically and by FE simulation within this paper. Accuracy and resolution depend not only on the precision of the setup, but decisively on the selection and execution of the measuring method conformed to the specific measurement task. We will also present our test stand TIMA Tester for thermal characterization of TIMs, die attach materials and substrates based on the mentioned steady state method. It has been developed as a platform which allows the integration of various modules for characterization of different materials under different conditions, e.g. mated surface, finish, operation temperature, pressure, aging etc. Finally, selected studies of different materials will be presented in order to demonstrate the functionality and the accuracy of the test stand

Phase change based thermal buffering of transient loads for power converter

This paper deals with the system design, technology and test of a novel concept of integrating silicon power dies along with thermo-electric coolers and a phase change heat buffer in order to thermally manage transients occurring during operation. The innovative power-electronics concept features double-sided cooling as well as new materials and joining technologies to integrate the dies such as transient liquid phase bonding/soldering and sintering. To avoid a cold plate at the backside, a new low-cost, low-footprint thermal storage device has been developed and optimized by simulation to meet the requirements given by this application. Coupled-field simulations are used to predict thermal performance and are being verified by especially designed test stands

Double-sided cooling and transient thermo-electrical management of silicon on DCB assemblies for power converter modules: Design, technology and test

This paper deals with the system design, technology and test of a novel concept of integrating Silicon power dies along with thermo-electric coolers and a phase change heat buffer in order to thermally manage transients occurring during operation. The concept features double-sided cooling as well as new materials and joining technologies to integrate the dies such as transient liquid phase bonding/soldering and sintering. Coupled-field simulations are used to predict thermal performance and are verified by especially designed test stands to very good agreement

Reliability investigation on SiC based diode and MOSFET modules developed for high power conversion in medical X-ray applications

For the sake of compactness and mass reduction, the high power converter modules for x-ray generators in medical applications have been developed utilizing novel SiC diodes and SiC MOSFETs for the first time. The paper discusses the results of comprehensive investigations on the thermal per-formance as well as on the reliability of these modules - as found by power cycling tests supplemented by electro-thermo-mechanical simulations

Measurement and modeling of the effective thermal conductivity of sintered silver pastes

The effective thermal conductivity of sintered porous pastes of silver is modeled through two theoretical methods and measured by means of three experimental techniques. The first model is based on the differential effective medium theory and provides a simple analytical description considering the air\u3cbr/\u3epores like ellipsoidal voids of different sizes, while the second one arises from the analysis of the scanning-electron-microscope images of the paste cross-sections through the finite element method. The predictions of both approaches are consistent with each other and show that the reduction of the\u3cbr/\u3ethermal conductivity of porous pastes can be minimized with spherical pores and maximized with pancake-shaped ones, which are the most efficient to block the thermal conducting pathways. A thermal conductivity of 151.6 W/m K is numerically determined for a sintered silver sample with 22% of porosity.\u3cbr/\u3eThis thermal conductivity agrees quite well with the one measured by the Lateral Thermal Interface Material Analysis for a suspended sample and matches, within an experimental uncertainty smaller than 16%, with the values obtained by means of Raman thermometry and the 3\omega technique, for two samples buried in a silicon chip. The consistence between our theoretical and experimental results demonstrates the good predictive performance of our theoretical models to describe the thermal behavior of porous thermal interface materials and to guide their engineering with a desired thermal conductivity