András Poppe

Thermal investigation of high power Optical Devices by transient testing

In case of opto-electronic devices, the power applied on the device leaves in a parallel heat and light transport, the interpretation of R/sub th/ is not obvious. The paper shows results of a combined optical and thermal measurement for the characterization of power light emitting diodes (LEDs). A model explaining R/sub th/ changes at different current levels is proposed.

Thermal management for LED applications

In this chapter, after a generic discussion of thermal testing techniques used to characterize packaged semiconductor devices; the latest practical test methods widespread in thermal testing of LED components and SSL luminaires are discussed. Thus, the focus is on the latest, power semiconductor and LED-specific test procedures, environments and thermal metrics—all derived from the classical JEDEC JESD51 family of testing standards. Detailed discussion is devoted to the transient extension of the so-called static test method and the differential measurement principle in its practical realization. Different representations of the thermal impedance are presented starting from the classical Zth(t) functions ending with the so-called structure functions. These are discussed in depth because they became the de facto standard in laboratory testing of thermal properties of LED components, in reliability analysis and in quality assurance at leading LED manufacturers. The basic concepts are introduced through practical examples.

THERMAN: a thermal simulation tool for IC chips, microstructures and PW boards

Abstract This article presents THERMAN: the renewed version of the μS-THERMANAL simulation program. The program was rewritten last year, in order to include algorithmic novelties such as time-constant analysis. The new code is fully transportable providing the same user interface on PCs and on Unix-based workstations. The graphical interface allows a fast problem definition and easy, many-sided evaluation of the results.

Multi-domain simulation and measurement of power LED-s and power LED assemblies

Besides their electrical properties the optical parameters of LEDs also depend on junction temperature. For this reason thermal characterization and thermal management plays important role in case of power LEDs, necessitating tools both for physical measurements and simulation. The focus of this paper is a combined electrical, thermal and optical characterization of such devices. In terms of simulation a novel approach of board-level electro-thermal simulation is presented whereas in terms of measurement, a combined thermal and radiometric characterization method is discussed

Electro-thermal simulation: a realization by simultaneous iteration

After a comparison of major strategies of electro-thermal simulation (the relaxation method and the method of simultaneous iteration) a detailed description of the fundamentals and realization issues of the simultaneous iteration method is given. The paper introduces the SISSSI electro-thermal simulation package which is a recent realization of the latter method, fully integrated into the Cadence Opus design framework. The use of the package as an analogue circuit layout design verification tool is demonstrated through a detailed case study.

High-aspect-ratio metal microchannel plates for microelectronic cooling applications

A new manufacturing process and the characterization of high-aspect-ratio metal microchannel plates for microelectronic cooling applications are reported in this article. A nickel-based microchannel cooling plate, with channels of width 20 µm and aspect ratio up to 3.6:1, has been successfully fabricated using a modified UV-LIGA process. Similar metal microstructures, based on electroplated copper, have also been obtained with a width of 15 µm and an aspect ratio of up to 5:1. In both cases, an over-plate technology was used to electroform the metallic microchannel plates in a single manufacturing step. Hydrodynamic and cooling characteristics of the microchannel plates such as flow rate and heat resistance have been measured. A heat transfer coefficient of 511 W m−2 K−1 for a flow rate of 120 l h−1 has been obtained for the 20 µm wide nickel-based microchannel.

Multi-domain compact modeling of LEDs

Operating parameters of power LEDs are strongly coupled and are mutually dependent. There have been lots of attempts to provide different kinds of multi-domain LED models with different complexity. This paper gives an overview of recently published models and suggests a practical approach in which the forward current is split into two parts in a straightforward manner. One current component is derived from the LEDs measured radiant flux directly, the other component is calculated as the difference of the net forward current and the previously mentioned current component associated with light emission. Parameters of the proposed model can be identified from isothermal LED characteristics measured in industry standard LED test setups using textbook techniques. Temperature dependence of the model parameters is discussed in detail; including comparison of different models for the temperature dependence of the saturation current in Shockleys diode equation.

Electro-thermal and Logi-thermal Simulators aimed at the Temperature-aware Design of Complex Integrated Circuits

With the increasing power dissipation increasing attention has been paid to the thermal issues in electronics design on system, board, package and chip level, including electrothermal simulation of even rather complex integrated circuits. Two distinct algorithmic directions can be distinguished in electro-thermal simulation: the simulator coupling and the simultaneous iteration or direct method. In our view the direct method is well suited for electro-thermal simulation of analog circuit blocks while simulator coupling can be used to implement logi-thermal simulation. In case of complex designs containing digital and analog blocks the two approaches can also be combined. Ideally thermal, electro-thermal and logi-thermal simulation of a circuit is performed already in the phase of conceptual design when only a rough idea exists about the final physical realization of the circuit. In any case, effect of the thermal boundary conditions of the die+package, cooling via the electrical connections to the die and the granularity of the simulation should be carefully considered.

Electro-thermal simulation for the prediction of chip operation within the package

The device level electro-thermal simulation of analog circuits and the logical gate level logi-thermal simulation of digital circuits are addressed in the paper. After presenting the main algorithms, realization questions are also discussed. For both the electro-thermal cases, simulated results of realized structures are presented. These are compared with benchmark results, proving the applicability and the accuracy of the methods.

Nonlinear electro-thermal modeling and field-simulation of OLEDs for lighting applications I: Algorithmic fundamentals

Large area OLEDs aimed at lighting applications should provide homogeneous luminance-homogeneity is one of the quality metrics of such devices. Local light generation depends on both the local temperature and the local voltage drop across the light emitting polymer(s) in the device. Therefore the thermal and electrical engineering of OLEDs aimed at lighting applications is critical. Due to the large area of these devices the coupled electrical and the thermal simulation problem is of distributed nature. Electrical characteristics of organic semiconductor materials used in OLED devices are highly nonlinear, and their nonlinear temperature-dependence is significant. In our present approach to distributed electro-thermal field simulation we address special needs of OLEDs, which is not yet the case with widely used, commercially available simulation tools. In this paper we present the latest version of our SUNRED electro-thermal field solver algorithm capable of handling coupled, non-linear electro-thermal problems. The new features of the algorithm are demonstrated by modeling some research OLED samples available to us in the Fast2Light project-this way simulation results are compared against measured data.