Anna Andonova

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.

Modeling NMOS snapback characteristic using PSpice

Gate-grounded NMOS is often used as ESD protection for circuit design. The ESD behavior of the NMOS transistor is based on the snapback action of its parasitic, lateral NPN BJT. Modeling this behavior of NMOS devices is very important for design of ICs, because there are no standard models, which can be used for describing high current regions in the NMOS snapback characteristic. In this paper an approach of modeling snapback characteristic of NMOS device, intended for use as ESD clamp in IC I/O cells, is proposed. The modeled snapback characteristic is simulated and evaluated using PSPICE.

Study of high power COB LED modules with respect to topology of chips

The thermal influence of the topology of the COB (Chip-on-Board) LED modules is examined. For this purpose CFD simulations of a powerful COB LED module thermal model are carried out and the thermal distribution at different locations of LED chips is analyzed. Simulation experiments are designed, using the substrates of ceramic materials - Alumina (Typical), Alumina (94 %), Alumina (96 %) and AlN. The thermal efficiency of four different structures of COB LED modules with different modes of operation and environment is examined. The simulation results are verified with thermal measurements.

Problems of noncontact thermography measurements of HICs

The temperature is an important physical parameter influencing hybrid integrated circuit (HIC) performance and reliability. Different interesting techniques using infrared thermography have been proposed. However, they do not give an absolute temperature, require an electronic system to synchronize the camera and the electronic device or have difficulties to obtain relevant thermograms because of the problem of low emissivity on the one hand and the poor spatial resolution on the other hand. In the paper are analyzed the specialties of HICs under thermography inspection. A HIC consists components with different geometry that are made of materials with strongly varying radiation properties. Therefore almost each of the point in the thermal image has to be considered with individual emissivity value. In most cases the general knowledge concerning emissivity coefficient e in function of angle of view, temperature and surface property is unknown. The lack of knowledge on the mentioned parameters values can results in a measurement error in tens or even hundreds percent of the true temperature. One approach for quantitative temperature measurements of HICs using infrared thermography with experimental set up is presented.

Thermal stability analysis of power LED during aging

The aim of this work is therefore to analyze the thermal stability by lifetime accelerated tests for three different constructions of LED lighting fixtures. In result of studied we believe to provide information on the role of temperature in determining devices degradation, since in most of the cases high current and high temperatures acted as degradation driving forces. In order to high light the influence of the ageing tests on the LEDs, we firstly measured their characteristics at the initial state and than the measurements were carried out in a cyclical way after every ageing step. The accelerated current test implied a faster degradation than the constant thermal stress: even if the degradation modes were similar for both stress and appeared to be thermally activated, the high carrier flow acted as an acceleration factor on the failure of devices. These results underline that package design in terms of heat dissipation is significant for devices with longer lifetime, and essential requirement for solid state lightning market. Thermal modeling of the LED packages was done in FLOTHERM. Using an IR camera, we measured the die surface temperature of the high-power single dies in LED packages, which are heat sunk at the case.

Quality control of chip on board LED packaging by transient thermography

A new methodology of infrared thermography (IRT) measurements for quality control of chip on board light emitting diode (COB LED) package is studied and presented. For this goal information measuring system and appropriate additional software is developed and used. COB LED samples are prepared with different kind of defects are prepared. Results from using some suitable IRT methods of passive-, pulsed-, lock in-, FMTWI-thermography are shown and relevant image processing methods are used and discussed.

LED PCB thermal simulation using FLOEFD

This paper presents work done to create a high power light emitted diode (LED) package on a PCB and a double layer FR4. First ly , a detailed model of an LED package-on-substrate is created. Then the model is optimized with respect to kind, number and location of the thermal vias, width of thermal paths and LED power dissipation. The method CFD (computational fluid dynamics) via the software Mentor Graphics FLOEFD is used as a tool to assist in the design of the power LED for the real application. The results show that the models agree well with the actual measured value. A major advantage is saving time and money for the development of reliable design of LED modules

Provoking and organizing discussion and gathering information and feedback on message boards regarding MCM design and use

The following paper aims to present work done towards provoking and organizing discussion and gathering information and feedback on message boards regarding MCM design and use. In order to accomplish that, information was presented on the Internet allowing the creation of a virtual community, dedicated to discussing specific topics on MCM design and use. Through discussion it was possible to obtain feedback from users of various age, gender and education level. The goal was to present the information in an accessible and interesting way and obtain the opinions of various people throughout the Web. The provided information provoked interest and intrigued the users, resulting in a lot of positive feedback and comments.

Thermal difference investigation of the boundary surfaces of Hall element

The aim of the presented paper is an investigation of the influence of the current IS and the magnetic induction B over the temperature difference Δ between the both boundary surfaces of t Hall sensor Σ=f(IS,B). A new method of surface temperature distribution on Hall sensor by using infrared thermovision approach is presented. The correlation between the current and the value and direction of the magnetic induction, at which a maximum temperature difference is obtained, is investigated. The results obtained from this experimental method may lead to more refined and accurate computer simulation techniques for studies of the thermal behavior of Hall elements.

Development and investigation of horizontal elements in 3D micro-contacts and structures

The present article describes the development and production of horizontal elements in 3D micro-contacts, implemented in IC package to PCB assembly and micro mechanical actuators. Instead of the standard vacuum deposition of metal films onto dielectric interfaces and lift-off stripping, an alternative method aiming at simplicity and lower-cost, relative to the technology roadmap is proposed. This method employs chemical activation and pre-treatment of the dielectric photoresist surfaces with fluid carbon content substance, thus providing also electrical conductivity for direct metal electroplating. A special regime of reverse electrochemical deposition is applied in order to enhance the adhesion of the layer, deposited onto the activated surface. This paper presents experimental results of the horizontal elements investigation, relative to the 3D micro-contacts. Thermal simulations of the proposed structures are also included. This issue is of a great importance, due to the nature of the horizontal elements - actuator type and bending features.