Properties Of Thermal Interface Materials Research Articles

Numerical study on the polydispersive effect of filler size distribution on the properties of thermal interface materials

Abstract Advanced thermal interface materials (TIMs) are indispensable for work reliability and lifespan assurance of high-power density electronic systems by facilitating timely and effective heat dissipation. A random algorithm consisting of diluting, dropping, and stirring processes is first proposed to simulate microstructures of TIMs with continuous particle size distribution, with an accessible maximum volume fraction of 55 vol%. Then the size polydispersity impact on the thermal performance and the fluidity of TIMs is numerically investigated. Simulation results reveal that as the particle size polydispersity increases, the thermal conductivity of TIMs improves, along with the improved fluidity. Therefore, it is necessary to consider the polydispersive impact of filler size distribution in actual production and optimize the material preparation process based on the actual distribution of particles. This work provides a deeper understanding of the influence of particle polydispersity on the co-optimization of the desired attributes of TIMs.

Boron Nitride/Carbon Fiber High-Oriented Thermal Conductivity Material with Leaves-Branches Structure.

In the realm of thermal interface materials (TIMs), high thermal conductivity and low density are key for effective thermal management and are particularly vital due to the growing compactness and lightweight nature of electronic devices. Efficient directional arrangement is a key control strategy to significantly improve thermal conductivity and comprehensive properties of thermal interface materials. In the present work, drawing inspiration from natural leaf and branch structures, a simple-to-implement approach for fabricating oriented thermal conductivity composites is introduced. Utilizing carbon fibers (CFs), known for their ultra-high thermal conductivity, as branches, this design ensures robust thermal conduction channels. Concurrently, boron nitride (BN) platelets, characterized by their substantial in-plane thermal conductivity, act as leaves. These components not only support the branches but also serve as junctions in the thermal conduction network. Remarkably, the composite achieves a thermal conductivity of 11.08 W/(m·K) with just an 11.1 wt% CF content and a 1.86 g/cm3 density. This study expands the methodologies for achieving highly oriented configurations of fibrous and flake materials, which provides a new design idea for preparing high-thermal conductivity and low-density thermal interface materials.

Improving the heat conduction and mechanical properties of thermal interface materials by constructing diphase continuous structure reinforced by liquid metal

Based on the existence of self-gap and bridging effect during powder compaction, chromium-coated diamond particles and gallium-based liquid metal are selected to prepare an inter-connective porous structure, and then polydimethylsiloxane is filled into this porous medium by vacuum infiltration to fabricate co-continuous thermal pads. The results show that the reinforcing phase of diamond particles bridged by liquid metal is responsible for ensuring heat-transfer performance, while the polymer matrix imparts a certain degree of softness, elasticity, and strength. The thermal conductivity of composites with great conformability can go as high as 29 W/(m·K). Furthermore, once thermal pads are applied on substrates under pressure, a small amount of liquid metal will seep out from the composite surfaces, which is beneficial to obtaining a low interface thermal resistance. This work provides a novel approach for fabricating high-performance composites which may further advance their applications in thermal management of electronic industry.

Unveiling the role of filler surface energy in enhancing thermal conductivity and mechanical properties of thermal interface materials

With heat-flux density of electronics drastically increase polymer-based thermal interface materials play a critical role in the performance of electronics. Although surface energy of fillers has been recognized as a crucial parameter, the exploitation of the filler surface energy-dependent properties is still unclear. Herein, we report on unveiling the effect of the surface energy of aluminum on thermal and mechanical properties in thermal interface materials consisted of polydimethylsiloxane and modified aluminum with silane-coupling agents containing varied chain lengths. The results show that reducing the surface energy of aluminum is beneficial to improve the aluminum fillers dispersibility in polydimethylsiloxane, leading to improved macroscopic properties, including rheology, mechanical properties, and thermal properties. Furthermore, based on the thermodynamic prediction, a winding hypothesis was proposed to explain the interaction between the modified aluminum and polydimethylsiloxane. This work provides valuable guidance for rationally designing the surface energy of fillers in thermal interface materials.

Thermal Evaluation of 2.5-D Integration Using Bridge-Chip Technology: Challenges and Opportunities

In this paper, 2.5-D integrated circuits (ICs) using bridge-chip technology are thermally evaluated to investigate thermal challenges and opportunities for such multi-die packages. To this end, the objectives of this paper are twofold. First, thermal benchmarking of a number of 2.5-D integration approaches is performed and compared to 3-D ICs for completeness. Thermal modeling shows that the evaluated 2.5-D integration approaches exhibit similar thermal characteristics, but show significant improvements compared to 3-D IC solutions with the same power consumption. Second, this paper explores bridge-chip-based 2.5-D integrated systems as a function of bridge-chip thickness, thermal interface material properties, microbump properties, die thickness, die thickness mismatch, and die-to-die spacing along with transient analysis to investigate time-domain thermal coupling. Results suggest that a die thickness mismatch of 100 $\mu \text{m}$ can increase the maximum temperature by 25.8% Therefore, the die thickness mismatch should be kept as small as possible, and the hottest die should be the thickest. Moreover, reducing die-to-die space from 1 to 0 mm increases thermal coupling, and the low-power dice, such as DRAM, can have a temperature increase of 6.1%.

Basic Study on Reduction of Measurement Time for Evaluating Thermophysical Properties of Thermal Interface Materials by Steady Temperature Prediction Method

Basic Study on Reduction of Measurement Time for Evaluating Thermophysical Properties of Thermal Interface Materials by Steady Temperature Prediction Method

Magnetically-functionalized self-aligning graphene fillers for high-efficiency thermal management applications

We report on heat conduction properties of thermal interface materials with self-aligning “magnetic graphene” fillers. Graphene enhanced nano-composites were synthesized by an inexpensive and scalable technique based on liquid-phase exfoliation. Functionalization of graphene and few-layer-graphene flakes with Fe3O4 nanoparticles allowed us to align the fillers in an external magnetic field during dispersion of the thermal paste to the connecting surfaces. The filler alignment results in a strong increase of the apparent thermal conductivity and thermal diffusivity through the layer of nano-composite inserted between two metallic surfaces. The self-aligning “magnetic graphene” fillers improve heat conduction in composites with both curing and non-curing matrix materials. The thermal conductivity enhancement with the oriented fillers is a factor of two larger than that with the random fillers even at the low ~ 1 wt.% of graphene loading. The real-life testing with computer chips demonstrated the temperature rise decrease by as much as 10 °C with use of the non-curing thermal interface material with ~ 1 wt.% of the oriented fillers. Our proof-of-concept experiments suggest that the thermal interface materials with functionalized graphene and few-layer-graphene fillers, which can be oriented during the composite application to the surfaces, can lead to a new method of thermal management of advanced electronics.

Design of a Static TIM Tester

Testing the thermal properties of thermal interface material (TIM) has been a big challenge for decades. Recent development trends made this challenge even bigger, as now the values that have to be measured are extremely small. In this paper, we present a newly developed TIM tester equipment that is targeting to overcome all the problems that present industrial TIM testing methods face. The main idea behind our design is to use the capabilities of microelectronics in order to make small sized sensors both for temperature and heat-flux sensings. This way it is possible to place these sensors in the closest proximity of the measured sample. This paper presents details of all the technical solutions of the newly developed static TIM tester that is capable to measure Rth of unit area values in the order of 0.01 K cm2/W with good accuracy. Special attention is made to analyze and eliminate the possible sources of measurement inaccuracy. A number of measurement examples prove the usability of the developed measuring instrument.