Partial Thermal Resistance Research Articles

Structural Analysis of Power Devices and Assemblies by Thermal Transient Measurements

Power modules composed of semiconductor dice, thermal interface layers, and cooling mounts can be characterized by thermal transient testing at their actual position (in situ). This paper demonstrates that transient testing enables tracking of changes in material quality and structural details on the raw heating or cooling curves. Higher precision can be achieved with the structure function technique where absolute and partial thermal resistance and capacitance values can be used for unambiguous identification of structural elements in a heat conducting path. Measurement techniques are presented to characterize the self-heating of a die and heat transfer between dice. Change of the thermal interface material layers in assembly during test sequences is also highlighted by the structure function concept. The power distribution between dice and wiring is analyzed by the newly introduced “accordion” principle.

Oxidation behavior of C/C composites with SiC/ZrSiO4–SiO2 coating

A SiC/ZrSiO4–SiO2 (SZS) coating was successfully fabricated on the carbon/carbon (C/C) composites by pack cementation, slurry painting and sintering to improve the anti-oxidation property and thermal shock resistance. The anti-oxidation properties under different oxygen partial pressures (OPP) and thermal shock resistance of the SZS coating were investigated. The results show that the SZS coated sample under low OPP, corresponding to the ambient air, during isothermal oxidation was 0.54% in mass gain after 111 h oxidation at 1500 °C and less than 0.03% in mass loss after 50 h oxidation in high OPP, corresponding to the air flow rate of 36 L/h. Additionally, the residual compressive strengths (RCS) of the SZS coated samples after oxidation for 50 h in high OPP and 80 h in low OPP remain about 70% and 72.5% of those of original C/C samples, respectively. Moreover, the mass loss of SZS coated samples subjected to the thermal cycle from 1500 °C in high OPP to boiling water for 30 times was merely 1.61%.

Analysis on partial thermal resistances of packaged SiC schottky barrier diodes at elevated temperatures

This paper investigates the temperature dependence of partial thermal resistances of a packaged SiC schottky barrier diode (SBD) for high temperature applications. Transient thermal resistances of the packaged SiC SBD were measured and characterized in temperature range from 27 to 275 °C. The partial thermal resistances were extracted and analyzed using the cumulative and differential thermal structure functions. The extracted partial thermal resistances were compared to the results from the finite difference thermal model, and both results were in good agreement. The temperature dependence of the partial thermal resistance of the SiC device and the Si3N4 substrate contributes to the overall thermal characteristics variation of the packaged SiC SBD.

Modelling of the flow-rate dependent partial thermal resistance of integrated microscale cooling structures

As microscale cooling structures are integral parts of modern chip level cooling concepts, the understanding of the behavior of different assemblies is desirable to create a novel co-design concepts where the thermal design is embedded into the conventional IC design flow. The first step of understanding is to create a general formula which describes the heat transfer mechanism and can be implemented in IC CAD environments. This paper presents an analytical study of this mechanism in microscale channel based cooling structures. A closed analytical formula is also given to calculate the partial thermal resistance. Numerical analyses are also conducted and the results are compared against the analytical ones.

Improved thermal characterization method of integrated microscale heat sinks

The thermal management of semiconductor devices is still a hot topic. Most designers, who are aware of the thermal aspects of IC design, know that new, cheaper and more efficient methods are required to keep the temperature of electronic systems low. Research by different teams regarding the cooling of stacked die structures is in progress.In this paper an improved thermal characterization method will be presented to determine the flow dependent partial thermal resistance of integrated microchannel based heat sinks. This reliable characterization method does not demand thermal isolation during the measurements, only constant environment conditions. The measurements are based on the industrial standard thermal transient testing method.On the other hand we present an approach to realize an integrated microfluidic channel based heat sink, which can be realized in the backside of the silicon chip itself. The approach is based on a cheap wet etching process instead of reactive ion etching or LIGA technologies, which enables batch processing.

Thermo-hydraulic behavior of ice slurry in an offset strip-fin plate heat exchanger

Ice slurry is a promising alternative to conventional single-phase coolants in indirect refrigeration systems. In this paper, an experimental analysis of an offset strip-fin heat exchanger operating with ice slurry as working fluid is presented. The pressure drop and thermal performance have been determined. In order to obtain the partial thermal resistance in the ice slurry side an empirical correlation for the secondary fluid side was determined by applying the Wilson plot method in a set of tests performed previously. An empirical correlation in terms of the Colburn j-factor to describe the thermal behavior of the heat exchanger with ice slurry was obtained. On the other hand, the direct pressure drop measurements operating with different flow rates and ice fractions are shown and compared with values obtained with single-phase fluids. Pressure drop instabilities have been observed for flow rates lower than the nominal value provided by the manufacturer.

Thermal Analysis of GaN-Based Light Emitting Diodes With Different Chip Sizes

In this paper, we present the thermal, electrical, and optical analyses of light emitting diode (LED) packages with different chip sizes. The LED packages under investigation employed the same configuration of package components, except for the chip sizes. The forward current was found to increase with the chip size at the same forward voltage due to the area increase of current spreading. The luminous flux and optical power were found to increase with the chip size at the same current density. The thermal analysis was made by the transient thermal measurement and thermal simulation using the finite volume method. It was demonstrated that the thermal resistance decreased with the chip size under the same package conditions both by simulation and experiment. The bulk thermal resistance and spreading thermal resistance were combined together to give out a quantitative investigation of the partial thermal resistance variation. Moreover, the spreading thermal resistance was found to have a great effect on the total thermal resistance of LED packages.

Thermal Analysis of GaN-Based Light Emitting Diodes With Different Chip Sizes

In this paper, we present the thermal, electrical, and optical analyses of light emitting diode (LED) packages with different chip sizes. The LED packages under investigation employed the same configuration of package components, except for the chip sizes. The forward current was found to increase with the chip size at the same forward voltage due to the area increase of current spreading. The luminous flux and optical power were found to increase with the chip size at the same current density. The thermal analysis was made by the transient thermal measurement and thermal simulation using the finite volume method. It was demonstrated that the thermal resistance decreased with the chip size under the same package conditions both by simulation and experiment. The bulk thermal resistance and spreading thermal resistance were combined together to give out a quantitative investigation of the partial thermal resistance variation. Moreover, the spreading thermal resistance was found to have a great effect on the total thermal resistance of LED packages.

Thermal Resistance Measurement of LED Package with Multichips

Thermal transient measurements of high power GaN-based light-emitting diodes (LEDs) with multichip designs are presented and discussed in the paper. Once transient cooling curve was obtained, the structure function theory was applied to determine the thermal resistance of packages. The total thermal resistance from junction to ambient considering optical power is 19.87 K/W, 10.78 K/W, 6.77 K/W for the one-chip, two-chip and four-chip packages, respectively. The contribution of each component to the total thermal resistance of the package can be determined from the cumulative structure function and differential structure function. The total thermal resistance of multichip packages is found to decrease with the number of chips due to parallel heat dissipation. However, the effect of the number of chips on thermal resistance of package strongly depends on the ratio of partial thermal resistance of chip and that of slug. Therefore, an important thermal design rule for packaging of high power multichip LEDs has been analogized.

Cross-Verification of Thermal Characterization of a Microcooler

Abstract The thermal behavior of a microcooler has been investigated using two different measurement methods to verify their feasibility. On the one hand structure function derived from the thermal measurements was used, while on the other hand, characterization was done with a heat-flux sensor array. The measurement sample was a square nickel plate microcooler holding 128 microchannels in radial arrangement. In our previous studies it was attached to a power transistor which was used as a dissipator and a temperature sensor. The thermal transient response to a dissipation step of the transistor was recorded in the measurement. The measured transients (cooling curves) were transformed into structure functions from which the partial thermal resistance corresponding to the cooling assembly was identified. In the current study the measurement setup was completed by a heat-flux sensor inbetween the dissipator and the microcooler to be able to verify the results extracted via structure functions. In this way we could compare the heat-transfer coefficient (HTC) values obtained from the identified thermal resistances to those calculated directly from the measured heat-flux values. Good matching of the HTC values resulting from the two different methods was found.

Thermal analysis of GaN‐based laser diode package

AbstractThis paper reports on the thermal behavior of GaN‐based laser diode (LD) package as functions of cool‐ing systems, die attaching materials, and chip loading conditions. Thermal resistance and junction tem‐perature was determined by electrical‐thermal transient method. Significant change of thermal resistance with input current was observed under natural cooling condition due to the sensitive change of heat trans‐fer coefficient (h ) with temperature. Employment of PbSn as a die attachment was more advantageous over Ag‐paste in thermal behavior of LD package. Compare the thermal resistance of LD packages epi‐down and epi‐up structures. The partial thermal resistance from junction to submount is 4.68 K/W for epi‐down structure, and 9.65 K/W to epi‐up structure. The results demonstrate that the total thermal resistance of LD package be controlled mainly by the packaging design rather than the chip structure itself. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

B-4 衣服による部位別抵抗値に関する実験研究

B-4 衣服による部位別抵抗値に関する実験研究

Measuring partial thermal resistances in a heat-flow path

The paper presents techniques of measuring partial steady state thermal resistance values in a heat flow path with the help of thermal transient measurements and the subsequent numerical evaluation. The method is based on the further evaluation of the structure functions of the heat flow path. After presenting the theoretical background of the evaluation two different practical examples are presented to demonstrate the use of the method. The first example presents a series of experiments on how to use the method to detect die attach and/or soldering failures in packaged devices. The second example demonstrates that the method can be applied to measure the very small R/sub th/ values of thin conducting layers. Various practical solutions are discussed and demonstrated by simulations. The chances and the limits of the methodology are discussed in detail in the conclusion section.

放射冷房による居住熱環境の改善に関する研究 : 第2報 熱放射環境評価のための居室者の簡易型モデル

In this paper, the simplified model of occupant for evaluating a radiant cooled space was proposed. The model was constructed by combining some kinds of cylindrical and rectangular parts to simulate a shape of the real subject accurately. The geometrical validity of the model was examined. As a result, an effective body surface area which contributes to a radiation and convection heat transfer and an effective radiation area of the real subject agreed well with those of the model. Furthermore, a skin temperature at some typical positions on the body surface and a partial thermal resistance of clothing were defined respectively on the basis of measured values and they were added to the model as thermal properties. Finally, the model was applied to an analysis of thermal environment in the radiant cooled space and a local thermal environment around the model was evaluated quantitatively. The analyzed value of a mean surface temperature on the body agreed well with that on the real subject. The practical validity of the model was verified.