temperature_controlled

 

Application of Design of the Experiment (DoE) in modelling and investigation of properties of cooling systems and temperature controllers fabricated using Low Temperature Cofired Ceramics (LTCC) technology

Project leader: Dominik Jurków

project duration: VII 2012 - II 2015

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Summary
The increase of electronics components integration and miniaturization affect the heat dissipation problem. Too high temperature of electronic components decrease their performance and life. Hence, heat dissipation is one of the key issues in the designing of new electronic systems. The most common method of thermal management is integration of electronic systems with external heat sinks or fans.


Practical goals
The possibility of integration of cooling systems or temperature control directly with electronic substrates is developed in the frame of this project. The direct integration of both systems in the frame of one technology enables the elimination of costs of systems joining and increase the reliability (the same thermal expansion of the whole system). The integrated cooling and thermal controlling systems is developed in the frame of this project. Moreover, the technological complexity of this solution and its disadvantages are analyzed.

 

Scientific goals
The development of a mathematical model describing LTCC ceramic firing process as well as numerical models of selected cooling and temperature regulating (using heating and cooling) systems fabricated using LTCC technique is not so far described in the literature. The scientific goal of this project is a determination of the influences of different input parameters (e.g. firing process parameters, geometry or construction of structures) on properties of sintered LTCC modules, properties of screen printed thick film electronic components, cooling systems and temperature controllers.


Results
At first initial verification of co-firing process conditions of both Low Temperature Co-fired Ceramics (LTCC) and High Temperature Co-fired Ceramics (HTCC) was conducted. Moreover, the influence of lamination process conditions of HTCC (alumina based) on properties of sintered ceramics was investigated. Both these inspection were carried out using Design of the Experiment (DoE) methodology. The obtained results showed that if DoE is utilized the interpretation of results can be much easier, however, the experimenter has to be very careful at interpretation of findings stage and has to extend his/her knowledge about DoE methods and their drawbacks. Otherwise his or her conclusions can be wrong. The precision of DoE depends on the methodology which was utilized for experiment design. The investigations of co-firing conditions of LTCC and HTCC tapes were described more precisely in three papers indexed at JCR list. Next paper about investigation of lamination properties of HTCC tapes is under preparation.


Meanwhile it was also developed possibility of deposition thick-films through stencil instead of screens. It was proved that such solution can be applied to reduce the variability of thick-film resistors resistance and to provide finer tolerance of thick-film components. The results were published as an open access publication.

In the next stage the development, modeling and fabrication of passive LTCC coolers were carried out. The exemplary structure is presented below. This version was fabricated as a reference for active cooling system. The cooling efficacy as it could be expected is very low (low thermal conductivity of LTCC), moreover, the technological complexity of this solution was high. Hence, these devices will be not further developed. The exemplary structure is presented in Fig. 1. The results were presented at two international conferences. Please have a look at these papers:

 LTCC passive cooler

Fig. 1. Passive LTCC cooler

In the frame of next part of the investigations liquid LTCC cooling systems were developed. The devices consist of LTCC chip with integrated buried gas flow channels. Such solution permits to conduct much more efficient cooling of electronic components. This solution has following main advantages:

  • Possibility of an integration of a multilayer electronic substrate directly with a liquid cooling system (one technological process)
  • Higher thermal conductivity of LTCC in the comparison with PCB
  • Possibility using external fans, liquid cooling system (copper ones) and heat sinks additionally if needed

Thanks to simple optimization it was possible to decrease component maximal temperature by 40 K, when liquid LTCC cooling system was utilized. The exemplary cooler photos are presented in Fig. 2. The final structure consists also top cover which make the fluid channles invisible from user. In the comparison to LTCC coolers without cooling fluid flow this reduction was around 75 K. This presents very good potential of this solution and its usefulness in the field of power and/or highly integrated electronics. The results which were achieved shows that such cooling systems can be directly integrated with electronic substrate and thanks to this it can increase the reliability of whole systems. The results were presented in at IMPAS EDS International Conference in Brno (Czech Republic):

  • Jurków, D. (2014). Low Temperature Co-fired Ceramic (LTCC) active cooling systems analysis using Taguchi Design of the Experiment (DoE). Electronic Devices and Systems IMAPS CS International Conference 2014, pp. 48-53

LTCC active fluid flow cooler
Fig. 2. Active fluid flow cooling system - view of buried channels

Meanwhile a possibility of an integration of LTCC with AlN and alumina substrates were investigated. It was estimated that if cooled component would be isolated from cooling gas channels using material with higher thermal conductivity the efficiency of cooling can be even higher. However, such solution introduce many technological problems and will be much less reliable in the comparison to monolithic liquid LTCC cooling system.

The last stage of the project was the development and fabrication of temperature controllers (integrated coolers and heaters). The work was successfully finalized and results are presented in the Journal paper (see below). It was proved that integration of heaters and cooling channels with LTCC housing is possible and enables good properties of such complex packages. The package permits the temperature reduction of cooled components by 60 K. This temperature reduction  was possible thanks to the application of both numerical modeling and design of the experiment during designing and validation of the cooler function performances.

Conclusions

Sophisticate cooling components (fluidic channels) with heaters were successfully integrated with LTCC packages. The cooling and heating properties of such packages are very good.