National Science Foundation
Cooling Technologies Research Center
Purdue University - School of Mechanical Engineering logo

CTRC Breakthroughs

Thermal Materials R&D

PCM - Optimizing Material Properties: Enthalpy and Conductivity

Enthalpy PCM breakthroughs figure

Phase change materials (PCM) are an attractive technology for the passive dissipation of power during peak processing loads in portable electronics. However, proper implementation of PCMs into a device requires optimization of not only the PCM itself, but also the heatsink/packaging. This project expanded/updated a database for selection of PCMs, constructed numerical models investigating the behavior of the PCM composite structure during melting/solidification, and developed an improved experimental platform for enhanced testing at higher heat fluxes while incorporating cycling. The project resulted in the design of composite PCM heat exchangers tunable to power maps of individual chips, and then testing of these PCM composite structures.

Foil Based Transient Liquid Phase Bonding Systems

Transient liquid phase bonding (TLPB) has been suggested as an alternative to high-Pb solders, Ag paste, and sintered silver bonds in die-attach and heat rail applications. This project developed a thermodynamic framework for identifying multicomponent formulations for TLPB and associated processing requirements. Composition and processing temperature requirements for a Cu-Sn-Bi TLPB system were identified. Experimental observations of phase transformation were used to develop processing guidelines for specific formulations.

Cooling Paint

Cooling Paint breakthroughs figure

We designed, fabricated, and tested cooling paints using nanoparticle composites, in order to achieve radiative cooling of outdoor equipment such as antennas, RRUs, or even buildings. Previous solutions in literatures either involve multilayer structures which are expensive to fabricate or include metallic components that are prohibitive in equipment in telecomm systems like antennas. Our analysis indicated that it is feasible to achieve emissivity higher than 0.9 in the 8-13m “sky window” and reflectivity higher than 0.9 in the solar spectrum with a paint-form solution without metallic components. The CaCO3-acrylic paint is fabricated and demonstrates full-daytime cooling, along with an average of 55W/m2 cooling power. Due to its phonon resonance at 9m, a thin film of BaSO4 particles is capable of emitting in the “sky window” while reflecting the solar irradiation. The results show more than 117W/m2 cooling power continuously throughout 24 hours, among the highest ever achieved. Our paints are compatible with commercial paint fabrication, low cost, scalable and providing considerable cooling

PCM: Optimizing Material Properties: Enthalpy and Conductivity

Phase change materials (PCM) are an attractive technology for the passive dissipation of power during peak processing loads in portable electronics. Insertion of a PCM into a device requires optimization of not only the PCM itself, but also the heatsink and surrounding packaging. The first year of this project expanded and updated a database for selection of PCMs, constructed numerical models investigating the behavior of PCM composite structures during melting/solidification, and developed a testing platform for characterized at high heat fluxes while incorporating cycling. The second phase of the project will see the design of a modular heat exchanger for the PCM, tunable to power maps of individual chips, and experimental testing of PCM composite structures.

Effects of Nanoparticle Size and Aggregation on Metal Nanoparticle-Polymer Thermal Interface Materials

The ultimate goal is to understand how the factors, such as metal types, nanoparticle size, concentration, aggregation effects, interfacial resistance, affect the overall thermal conductivity of thermal interface materials. By both fabricating nanocomposites and developing new EMA models to include aggregation effect, we can predict thermal conductivity of TIMs more accurately and design thermal interface materials with higher thermal conductivity. This will allow better thermal management in modern electronic devices, thus further improve the performance of those high-power electronics.

Passive Thermal Management using Phase Change Materials

Passive PCM breakthroughs figure

The ultimate goal of the project is to advance the understanding of the impact of phase change materials on thermal performance of mobile devices. The development of design metrics enables rapid determination of the feasibility of PCMs for this application and increase the operating time of the electronic processor / package especially during transient power spikes. In situ on-chip and system level measurements will aid industry in the design and implementation of PCMs primarily in the cooling of mobile devices. The developed dry PCM synthesis techniques enable probing of the fundamental relationship between polymer structure and thermal response. Additionally, the accomplishments to date in this project have improved thermal and material characterization techniques and chip and system level modeling capabilities that may be used in future research projects for a wide variety of applications.

Foil Based Transient Liquid Phase Bonding Systems

Liquid Phase Bonding breakthroughs figure

The ultimate goal of the project is to create the thermodynamic and kinetic basis for rational alloy design, without relying on heuristics to limit the candidate compositions. While we have developed Improved thermodynamic and kinetic models for alloy design in the Sn-Bi-Cu system, new microstructure evolution factors will now have to be created to identify improved alloys, in terms of both processing conditions and thermal and mechanical performance. By applying these in a systematic, yet creative way, the electronics industry will have the tools to increase the thermal and mechanical performance of bonding systems as chip and operating temperatures increase. 

Thermal Design of Multilayer/Stacked Structures

This project developed a computational tool for optimal thermal design of multi-layered electronic structures and assemblies was developed. This computational tool is capable of efficient, systematic and automated thermal design of through-silicon-vias (TSV), heat spreaders and thermal interface materials (TIM) in 3D packages. The strategy is to couple a steady state heat conduction finite element analysis (FEA) code with a nonlinear optimization function implementing sequential quadratic programming (SQP) algorithm that allows topology optimization of multilayer structures. The developed tool was demonstrated to be two orders of magnitude more efficient for thermal design of multilayer stacked structures as compared to a popular commercial tool.

Optimized Porous Media-Based Heat Exchanger Surfaces

Porous Exchanger breakthroughs figureHeat exchange surfaces that provide improved efficiency in compact spaces have the potential for significant reduction in energy consumption. Tools were developed for simulation-based characterization and design of three dimensional heat exchange surfaces for more compact, lightweight, and efficient cars, airplanes, and electronics. Porous media provide high surface area to volume ratios thereby enabling them to be used as effective cooling solutions in many thermal applications. These porous media often provide other secondary desirable features like low weight-to-volume ratio, making them suitable for heat exchangers. Simulations, validated against experiments, evaluated the transport properties of a lattice frame material (LFM) fin structure and optimize the geometry based on performance factors.

Designing Transient Liquid Phase Sintering Systems for Power Electronics

Liquid Sintering breakthroughs figure In transient liquid phase sintering, a low melting temperature metal powder and an organic flux are mixed with high melting point alloys in particle form. When the temperature is increased above the melting temperature of the low melting point phase, a new compound begins to form at the interface between the liquid and the solid. This project developed model paste formulations for the development of new electrical and thermal technology based on transient liquid phase sintering for attaching cooling systems to chips, semiconductor dies, and substrates in power electronics. Thermodynamic software and down-selection criteria for specific applications were developed and applied to evaluate novel alloy formulations for these uses.

Variable Conductivity Material Based on Topologically Interlocked Assembly

VCM breakthroughs figure The designed material (based on topologically interlocked assembly) is able to change its thermal conductivity under different ambient temperature, therefore allows for precise and reliable control on temperature. Numerical simulation was conducted to investigate the thermal conductivity of the designed material. Prototypes were manufactured with a 3D printing method. The figure shows a prototype of variable thermal conductivity material and predicted thermal conductivity-temperature curve.

High-Performance, Low Cost Thermoelectric Materials

Thermo Materials Thin Films breakthroughs figure Waste heat is generated ubiquitously in domestic and industrial applications. By implementing thermoelectric devices, waste heat can be utilized to generate electricity instead of being directly emitted to the environment. This project developed and optimized a method to synthesize ultra-small Bi2Te3nanoparticles with various morphologies, and have fabricated bulk nanocomposite based on them. Our material system can be potentially high-performance thermoelectric materials. The effects of different ligand levels (i.e., the levels of leftover carbon-based compounds needed for nanocrystal synthesis) within the composites was studied and the composite oxidation as a function of depth into the pellet.

Optimal Porous Microstructures for Enhanced Thermal Management

Porous Exchanger breakthroughs figure The porous structures formed by sintering powders are commonly employed as capillary wicks in two-phase heat transport devices such as heat pipes. The effect of sintering conditions such as sintering time, temperature, particle size, and porosity on the transport characteristics of interest may be directly analyzed to design intricate sintered porous structures with desired properties tailored to specific applications. A cellular automata model, which determines mass transport during sintering based on curvature gradients in digital images, is employed to predict the sintering dynamics of two- and three-dimensional packed beds. Further, transport characteristics, viz., effective thermal conductivity and permeability are predicted as a function of sintering time, along with morphological properties such as change in surface area. The figure shows 3-Dimensional views of synthetic microstructure produced employing the developed sintering algorithm. Also shown on the right is a 3-Dimensional view of a real sintered wick microstructure.

Transport in Porous Structures and Metal Foams

Foams breakthroughs figure A novel computational methodology for direct numerical simulation of open-cell foams and heat pipe wicking structures has been developed.  This comprehensive model predicts the thermal and flow characteristics of foams and particle beds, which are in excellent agreement with published measurements. The results show the capability of the developed methodology and presents opportunities to explore other problems such as thermal dispersion, particulate fouling and foam structure optimization.