Gy. Bognár

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.

Cross-Verification of Thermal Characterization of a Microcooler

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.

Fabrication and Characterization of a Low-Cost, Wafer-Scale Radial Microchannel Cooling Plate

The modeling, simulation, fabrication, and testing of a microchannel cooling plate for microelectronic packaging applications are described in this paper. The cooling component uses forced convection of gas injected inside 128 microchannels of 100-mu m width and 70-mu m height. The nickel-based plate is fabricated on a glass substrate using a two-layer electroforming process using UV-LIGA technology. The thermal behavior of the microchannel cooling device is investigated by using the measurement of partial thermal resistances through the use of the structure functions method. Heat transfer coefficient values of 300 W/m2 K have been measured for a nitrogen flow rate of 120 l/h.

Thermal characterization of a radial micro-channel cooling plate

The thermal behavior of a square nickel plate micro-cooler holding 128 micro-channels in radial arrangement has been investigated. The device is to be used in microelectronic packaging cooling applications. In our study 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. The measurement and the partial thermal resistance identification was carried out at different flow-rates of nitrogen gas forced through the micro-channels. This way thermal resistance versus flow-rate and heat-transfer coefficient versus flowrate characteristics of the investigated micro-channel cooler were derived.

Contactless thermal characterization of high temperature test chamber

In this paper the methodology and the results of a contactless thermal characterization of a high temperature test chamber will be introduced. The test chamber is used for fatigue testing of different MEMS devices where the homogenous temperature distribution within the close proximity from the heating filaments is very important. Our aim was to characterize the evolving temperature distribution inside the test chamber. In order to achieve smaller time constant a new contactless sensor card was developed. The contactless thermal characterization method introduced in this paper enables in situ heat distribution measurement inside the test chamber during operation, with the detection of potentially uneven heat distribution.

Experimental study of a radial micro-channel cooling plate

The thermal behavior of a micro-channel cooling device has been investigated by using two different, complementary measurement methods. The measured sample was a square nickel plate micro-cooler holding 128 micro-channels in radial arrangement. In our previous studies we used only thermal transient measurements and the structure functions method to identify the partial thermal resistance corresponding to the cooler. In the current study the measurement setup was completed by a heat-flux sensor array placed under the micro-cooler. This way we could compare the heat-transfer coefficient values obtained: (1) from the identified thermal resistance value; and (2) calculated directly from the measured heat-flux values. Good matching of the values obtained the different methods was found

Enhanced thermal characterization method of microscale heatsink structures

In the frame of thermal management of electronic devices, finding efficient cooling solutions of the next generation equipment is a hot topic. If a new or improved solution is presented it always requires efficient characterization methods to prove the benefits compared to its predecessor. In case of microscale heatsink structures which are integral parts of modern chip or package level cooling concepts, an efficient measurement method is needed to analyse the performance of structures with different layouts and/or manufacturing technologies. This paper presents an enhanced thermal characterization method of microchannel based cooling structures, determining relevant partial thermal resistances from structure functions obtained by thermal transient testing. Our prior microscale heatsink characterization method was recently improved, accounting e.g. for possible nonlinearities of the heat transfer processes. This paper presents how we have improved our measurements setup in detail to deal with these phenomena compared to the previous setup.

Integrating chip-level microfluidics cooling into system level design of digital circuits

In this paper, a novel tool and a methodology are introduced to create a thermally driven digital cell placement capability that considers the cooling capability of the integrated microscale heatsink structures. Normally, the realization of this kind of placement would require time-consuming computation fluid dynamics (CFD) simulations. With the presented solution, the CFD tool can be replaced by a thermal simulator, which incorporates analytical fluid dynamics compact models. By this approach, the determination of the precise local heat transfer coefficient(s) (thus cooling efficiency) can be realized. In addition, the temperature distribution along the microchannels can also be obtained depending on the channel geometries, the thermal properties of the fluid and the wall temperature(s). While this model is integrated into the thermal simulator, it is still needed to be connected to commercial digital IC design tools to unleash its full potential. Therefore, the interfacing tool is also developed that launches either the thermal, the electrical, or logical simulators and placement programs by using the outputs (results) of the other programs as the inputs.

Thermal model generalization of infrared radiation sensors

In many theories and applications, generalized models can give a good head start for further researches where the implementation of new elements and/or boundary conditions could become quite complex. In this paper the development of a compact thermal model of an infrared sensor will be presented. This thermal model includes not just the thermal resistances and capacitances of the sensor but the radiative and convective thermal resistances to the ambient (acts as thermal ground) and between the sensor plate and the heat source (thermal transfer impedance). The article deals with the limitation of the linearization and applicability of this model. Further aim is to present the generalization and creation of a well applicable compact model which can be used in modelling of different thermal radiation sensors (e.g.: MEMS based sensor).

Powerful tools for thermal characterisation of MEMS

Thermal aspects of the design and fabrication of sensor structures based on thermally isolated heater filaments (Ducso, Cs. et al., Sensors and Actuators, vol.A60, p.235-9, 1997) were investigated with special attention to their dynamic properties. Thermal engineering was aided by high performance simulation methods, such as finite element modelling (COSMOS) and thermal equivalent circuit simulation using successive network reduction (SUNRED) method. The detailed static and dynamic thermal behaviour of the structure was experimentally characterised applying the high resolution thermography system of Thermosensorik GmbH and the thermal transient tester (T3Ster) of MicReD Ltd.