Jiri Jakovenko

Thermal resistance investigations on new leadframe-based LED packages and boards

In Solid State Lighting, thermal management is a key issue. Within the C-SSL consortium, we have developed an advanced leadframe based package to reduce the thermal resistance of the component. Numerical simulations have been implemented using Ansys® software and thermal measurements have been carried out using the forward voltage method to derive the thermal resistance. The T3ster® transient thermal analysis has been used to determine the different thermal resistance contributions in the package and in the board showing good correlation between experimental and simulation results. Low thermal resistances of 5.5 K/W have been obtained on our advanced leadframe based package and have been compared with standard Rebel LEDs on board.

Thermal Analysis of LED Lamps for Optimal Driver Integration

This paper studies the thermal influence of a light-emitting diode (LED) driver on a retrofit LED lamp, also reporting on a procedure for its thermal characterization and multiscale modeling. In this analysis, temperature is measured by infrared thermography and monitoring specific locations with thermocouples. Experimental results point out that temperature increases considerably in all lamp parts when the driver is installed in the lamp (up to 15% for LED board). The multiscale simulation approach is set with thermal parameters (thermal conductivity, emissivity, and LED board thermal resistance) measured from several parts of the lamp, reaching an agreement between experiment and simulation smaller than 10%. With this model, the driver temperature is investigated under operational conditions accounting for two alternative thermal designs. First, the driver is completely surrounded with a filling material (air completely removed, Case A), and, second, only the thermal contact between the board and the lamp is improved (air is kept, Case B). In both cases, the heat removal from the driver to the ambient by conduction is enhanced, observing that temperature decreases in its most heated components up to 10 °C in Case A, and up to 7 °C in Case B.

Design for reliability of solid state lighting systems

This work presents a methodology to design an SSL system for reliability. An LED lamp is thermally characterised and its model thermally simulated, indicating that the LED board (FR4 board with thermal vias, copper tracks and LED package) is the thermally most stressed part. Therefore, a thermo-mechanical analysis is performed from a detailed LED board model to study reliability and lifetime limits, using thermal boundary conditions deduced from the thermal simulation of the whole LED lamp. Based on this analysis the weakest spots are identified as the metal vias in the LED package and the interconnection area between the LED package and copper tracks on the FR4 board.

Design methodologies for reliability of SSL LED boards

This work presents a comparison of various LED board technologies from thermal, mechanical and reliability point of view provided by an accurate 3-D modelling. LED boards are proposed as a possible technology replacement of FR4 LED boards used in 400 lumen retrofit SSL lamps. Presented design methodology can be used for other high power SSL lamp designs. The performance of new LED board designs were evaluated by numerical modeling. Modeling methodology was proven by measurement on reference FR4 LED board. Thermal performance was compared by extracting of LED boards thermal resistances and thermal stress has been inspected considering the widest temperature operating range according to standards (-40 to +125 C). Thermo-mechanical and reliability analysis have been performed to study parameters of each LED board technology, using thermal boundary conditions extracted from the thermal simulation of a whole LED lamp. Elastic-plastic analysis with temperature dependent stress-strain material properties has been performed. The objective of the work is to optimize not only the thermal management by thermal simulation of LED boards, but also to find potential problems from mechanical failure point of view and to present a methodology to design SSL LED boards for reliability.

Design and simulation of micromechanical thermal converter for RF power sensor microsystem

Abstract This paper discusses the thermo-mechanical simulations performed with the aim to optimize the temperature distribution of the microwave power sensor (MPS) microsystem keeping the thermal stress as low as possible. The concept of the absorbed power measurement is based on a thermal conversion, where the dissipated or absorbed RF power is converted into the thermal power, inside a thermally isolated system, so-called the micromechanical thermal converter (MTC) device. A new MTC approach uses a GaAs with an active high electron mobility transistor (HEMT) heater. New technology of low stress polyimide has been used for MTC thermal isolation. By means of thermo-mechanical simulations, we propose a GaAs micromechanical thermal converter design and a layout of the active sensor elements (HEMT heater and a temperature sensor TS) placed on the MTC structure. Spatial temperature distribution, thermal time constant, thermal stress and displacement and the power to temperature characteristics are calculated from the heat distribution. These findings are compared with results of thermo-mechanical measurement of real micromachined MTC devices. The 3-D thermal and thermo-mechanical simulations were performed, using the CoventorWare simulator.

MICROMECHANICAL THERMAL CONVERTER DEVICE BASED ON POLYIMIDE-FIXED ISLAND STRUCTURE

Design technology and characterization of new GaAs island based Micromechanical Thermal Converter (MTC) device are presented. The MTC device introduced consists of pHEMT as a microwave heater and thin film polySi/Ni resistor as a temperature sensor monolithically integrated on polyimide-fixed 1 μm thick GaAs/AlGaAs island structure. The preliminary experimental results in the device electro-thermal conversion evaluation are demonstrated.

Differential evolutionary optimization algorithm applied to ESD MOSFET model fitting problem

The aim of this paper is to present the utilization of modern optimization algorithm called Differential Evolution to automatically fit the appropriate Electrostatic discharge (ESD) model to the measured data from a test chip without the need of manual model-parameter tuning, which presents very time and resource-consuming process. In this paper, the optimization procedure and the results of fitting the generic process NMOST model to the piece-wise linear I-V characteristic are presented.

Use of barometric sensor for vertical velocity measurement

The measure system is based on the principle of evaluating the change of an atmospheric pressure. The vertical velocity is derived from the exponential form of the barometric equation which relates the air pressure versus the altitude. The relatively simple method has some drawbacks (a nonlinearity of the exponential dependency of the pressure versus altitude, the air temperature plays a significant role). There are used the compensated methods for measuring the vertical velocity. The correction is calculated from the horizontal velocity change which induces another vertical velocity change. The solution is based on the altitude equation, including the effects of temperature. The acceleration is evaluated in the horizontal direction using the information about the dynamic pressure. The possibility of nonlinearity compensation and temperature compensation are used.

Design of strain gauge structure

The paper describes the design of a strain gauge on a cantilever with implanted layers. In the paper, the physical model of implanted strain gauges is characterized and basic technological steps are described. Simulation using CoventorWare (MEMCAD) program is used to verify the mechanical properties and temperature distribution in cantilever structures. A suitable electric bridge connection of the structure for evaluation of electric parameters of strain gauges at mechanic deformation and different temperatures has been designed. On realized structures, basic parameters have been measured such as the dependence of electric parameters of strain gauges on mechanical deformation, temperature dependence at different mechanical load, temperature stability of output parameters, and temperature dependence of pn junctions in the structure. From the measured data, piezoresistive coefficients of deformation sensitivity, linearity, hysteresis, temperature coefficients of resistance, etc. have been calculated. The measured characteristics show very good linearity, small hysteresis and very good sensitivity.

Automated pre-placement phase as a part of robust analog-mixed signal physical design flow

Abstract A new pre-placement phase of integrated circuits (IC) analog-mixed-signal (AMS) physical design flow, introduced in this paper, automatically sorts electrical devices used in planar IC technologies according to their topological, structural and electrical properties. The presented design phase replaces human labour and allows to save design time and prevent human mistakes. Software implementation of the proposed method works with virtual objects of layout instances which are moved only once at the end of the script when creating the final pre-placement matrix. Algorithm complexity is decreased by a new way of virtual objects matrix indexing. The automatic pre-placement phase has been used during design of AMS circuits in 160u202fnm BCD8sP and SOIBCD8S technologies from STMicroelectronics and has been faster in the range of 3164 to 20099 times compared to manual sorting. The estimation of ratio between manual sorting time and automatic pre-placement time shows a growing time saving with increasing circuit complexity compared to standard layout flow. The introduced enhanced layout flow is able to prevent a creation of hardly detectable errors occurring at the beginning of AMS physical design, especially the wrong bulk connection errors of semiconductor devices. The automatic pre-placement phase saves hours of reworks and speeds up the entire design process.