Two-Medium Model for the Bond Line Thickness of Particle Filled Thermal Interface Materials

2004 ◽  
Author(s):  
Xuejiao Hu ◽  
Senthil Govindasamy ◽  
Kenneth E. Goodson
Keyword(s):  
Filler Particle ◽  
Bond Line ◽  
Thermal Interface Materials ◽  
Heterogeneous Structure ◽  
Thermal Interface ◽  
Line Thickness ◽  
Medium Model ◽  
Bond Line Thickness ◽  
The Impact ◽  
Interface Materials

Thermal interface materials (TIMs) are widely used in electronics packaging. Increasing heat generation rates require lower values of the TIM thermal resistance, which depends on the material thermal conductivity and the TIM thickness, or the bond line thickness (BLT). The variation of the TIM thickness is not well understood. The major difficulty comes from the complexity of TIMs as condensed particle systems, especially when the TIM thickness is squeezed to several multiples of the filler particle diameter. This confined heterogeneous structure makes the behavior of TIMs different from that of homogeneous fluids. In this study, we propose a two-medium model for the BLT. The variation of BLT with attachment pressure is modeled using two parameters: the viscidity of the fluids and the interactions of particles. The predictions are compared with the measurements for TIMs made of aluminum oxide particles (sizes: 0.6–6 microns, volume fractions: 30%–50%) and silicon oil (kinematic viscosity: 100 cst and 1000 cst). Reasonable agreement is obtained for different applied pressures. Results indicate that the impact of the particle interactions is an important factor governing the variation of the TIM BLT, especially when the BLT is small.

Bond Line Thickness of Thermal Interface Materials With Carbon Nanotubes

2005 ◽  
Author(s):  
Senthil A. G. Singaravelu ◽  
Xuejiao Hu ◽  
Kenneth E. Goodson
Keyword(s):  
Thermal Conductivity ◽  
Carbon Nanotubes ◽  
Volume Fraction ◽  
Bond Line ◽  
Thermal Interface Materials ◽  
Thermal Interface ◽  
Line Thickness ◽  
Bond Line Thickness ◽  
The Impact ◽  
Interface Materials

Increasing power dissipation in today’s microprocessors demands thermal interface materials (TIMs) with lower thermal resistances. The TIM thermal resistance depends on the TIM thermal conductivity and the bond line thickness (BLT). Carbon Nanotubes (CNTs) have been proposed to improve the TIM thermal conductivity. However, the rheological properties of TIMs with CNT inclusions are not well understood. In this paper, the transient behavior of the BLT of the TIMs with CNT inclusions has been measured under controlled attachment pressures. The experimental results show that the impact of CNT inclusions on the BLT at low volume fractions (up to 2 vol%) is small; however, higher volume fraction of CNT inclusions (5 vol%) can cause huge increase in TIM thickness. Although thermal conductivities are higher for higher CNT fractions, a minimum TIM resistance exists at some optimum CNT fraction for a given attachment pressure.

Thermal Resistance of Bond-Lines Formed With Composite Thermal Interface Materials

2005 ◽  
Author(s):  
Gary Lehmann ◽  
Hao Zhang ◽  
Arun Gowda ◽  
David Esler
Keyword(s):  
Thermal Conductivity ◽  
Particle Size ◽  
Thermal Resistance ◽  
Bond Line ◽  
Surface Conductance ◽  
Thermal Interface Materials ◽  
Thermal Interface ◽  
Bond Line Thickness ◽  
Matrix Surface ◽  
Interface Materials

Measurements and modeling of the thermal resistance of thin (< 100 microns) bond-lines are reported for composite thermal interface materials (TIMs). The composite TIMs consist of alumina particles dispersed in a polymer matrix to form six different adhesive materials. These model TIMs have a common matrix material and are distinguished by their particle size distributions. Bond-lines are formed in a three-layer assembly consisting of a substrate-TIM-substrate structure. The thermal resistance of the bond-line is measured, as a function of bond-line thickness, using the laser flash-technique. A linear variation of resistance with bond-line thickness is observed; Rbl = β · Lbl + Ro. A model is presented that predicts the effective thermal conductivity of the composite as a function of the particle and matrix conductivity, the particle-matrix surface conductance, the particle volume fraction and the particle size distribution. Specifically a method is introduced to account for a broad, continuous size distribution. A particle-matrix surface conductance value of ∼10W/mm2K is found to give good agreement between the measured and predicted effective thermal conductivity values of the composite TIMs.

Rheological Study of Micro Particle Laden Polymeric Thermal Interface Materials: Part 1 — Experimental

2002 ◽  
Author(s):  
Ravi S. Prasher ◽  
Jim Shipley ◽  
Suzana Prstic ◽  
Paul Koning ◽  
Jin-Lin Wang
Keyword(s):  
Thermal Conductivity ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Electronics Cooling ◽  
Bond Line ◽  
Rheological Parameters ◽  
Thermal Interface Materials ◽  
Particle Volume ◽  
Thermal Interface ◽  
Interface Materials

Particle laden polymers are one of the most prominent thermal interface materials (TIM) used in electronics cooling. Most of the research groups have primarily dealt with the understanding of the thermal conductivity of these types of TIMs. Thermal resistance is not only dependent on the thermal conductivity but also on the bond line thickness (BLT) of these TIMs. It is not clear that which material property(s) of these particle laden TIMs affects the BLT. This paper discusses the experimental measurement of rheological parameters such as non-Newtonian strain rate dependent viscosity and yield stress for 3 different particle volume fraction and 3 different base polymer viscosity materials. These rheological and BLT measurements vs. pressure will be used to model the BLT of particle-laden systems for factors such as volume fraction.

Silicone Phase Change Thermal Interface Materials: Properties and Applications

2003 ◽  
Author(s):  
S. Mark Zhang ◽  
Diane Swarthout ◽  
Thomas Noll ◽  
Susan Gelderbloom ◽  
Douglas Houtman ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Thermal Resistance ◽  
Mechanical Strength ◽  
Phase Change ◽  
Bond Line ◽  
Thermal Interface Materials ◽  
Thermal Interface ◽  
Interface Materials ◽  
Change Material ◽  
Aluminum Mesh

Thermal interface materials (TIM) play a very important role in effectively dissipating unwanted heat generated in electronic devices. This requires that the TIM should have a high bulk thermal conductivity, intimate contact with the substrate surfaces, and the capability to form a thin bond line. In designing new TIMs to meet these industry needs, alkyl methyl siloxane (AMS) waxes have been studied as phase change matrices. AMS waxes are synthesized by grafting long chain alpha-olefins on siloxane polymers. The melting point range of the silicone wax is determined by the hydrocarbon chain length and the siloxane structure. When the AMS wax is mixed with thermally conductive fillers such as alumina, a phase change compound is created. The bulk thermal conductivities of the phase change material (PCM) are reduced as they go through the phase change transition from solid to liquid. By coating the PCM onto an aluminum mesh, both the mechanical strength and the thermal conductivity are drastically improved. The thermal conductivity increases from 4.5 W/mK for the PCM without aluminum support to 7.5 W/mK with the supporting mesh. The thermal resistance of the aluminum-supported sheet at a bond line thickness of 115 microns has been found to be ∼0.24 cm2-C/W. Applying pressure at the time of application has a positive effect on the thermal performance of the PCM. Between contact pressures of 5–80 psi, the thermal resistance decreases as the pressure increases. The weak mechanical strength of the phase change material turns out to be a benefit when ease of rework and the effects of shock and vibration during shipping and handling are considered. A stud pull test of the aluminum mesh-supported PCM shows an average of 13 psi stress at the peak of the break.

Thermoelectric Heat Recovery From a Tankless Water Heating System

2008 ◽  
Author(s):  
S. A. LeBlanc ◽  
Y. Gao ◽  
K. E. Goodson
Keyword(s):  
Thermoelectric Material ◽  
System Integration ◽  
Waste Heat ◽  
Thermal Interface Materials ◽  
Water Heater ◽  
Thermal Interface ◽  
System Parameters ◽  
Material Parameters ◽  
The Impact ◽  
Interface Materials

Thermoelectric cogeneration promises to recover waste heat energy from a variety of combustion systems. There is a need for computationally efficient simulations of practical systems that allow optimization and illustrate the impact of key material and system parameters. Previous research investigated thermoelectric material enhancement and thermoelectric system integration separately. This work connects material parameters and system integration. We develop a thermal simulation for a 15kW tankless, methane-fueled water heater with thermoelectric modules embedded within a cross-flow heat exchanger. The simulation employs a finite volume method for the two fluids. It links external convection with a surface efficiency of 85%, internal convection for laminar flow, and conduction through the system in order to determine power generation within the thermoelectric. For a single pipe in the water heater system, 126 W of electrical power can be generated, and a typical system could yield 370 W. Realization of effective cogeneration systems hinges on investigating the impact of thermoelectric material parameters coupled with system parameters, so the impact of varying flow rate, convection coefficient, TEM thermal conductivity, Seebeck coefficient, and thermal interface materials are investigated. While varying parameters can improve thermoelectric output by over 50%, thermal interface materials can severely limit cogeneration system power output.

Parametric and Sensitivity Analysis of Power Module Design

2019 ◽  
Author(s):  
L. M. Boteler ◽  
M. C. Fish ◽  
M. S. Berman
Keyword(s):  
Sensitivity Analysis ◽  
Heat Sink ◽  
Thermal Interface Materials ◽  
Power Module ◽  
Thermal Interface ◽  
Module Design ◽  
Die Attach ◽  
Power Modules ◽  
The Impact ◽  
Interface Materials

Abstract As technology becomes more electrified, thermal and power engineers need to know how to improve power modules to realize their full potential. Current power module technology involves planar ceramic-based substrates with wirebond interconnects and a detached heat sink. There are a number of well-known challenges with the current configuration including heat removal, reliability due to coefficient of thermal expansion (CTE) mismatch, and parasitic inductance. Various solutions have been proposed in literature to help solve many of these issues: alternate substrates, advanced thermal interface materials, compliant die attach, thermal ground planes, high performing heat sinks, superconducting copper, wirebondless configurations, etc. While each of these technologies have their merits, this paper will perform a holistic analysis on a power module and identify the impact of improving various technologies on the device temperature. Parametric simulations were performed to assess the impact of many aspects of power module design including material selection, device layout, and heat sink choice. Materials that have been investigated include die attach, substrate, heat spreader, and thermal interface materials. In all cases, the industry standard was compared to the state of the art to quantify the advantages and/or disadvantages of adopting the new technologies. A sensitivity analysis is also performed which shows how and where the biggest benefits could be realized when redesigning power modules and determining whether to integrate novel technologies.

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