Thermal interface

In all cooled appliances, the heat from the device s heat sources must first arrive via thermal conduction at the surfaces exposed to the cooling fluid before it can be transferred to the coolant. For example, as shown in Fig. 2.2, it must be conducted from the chip through the lid to the heat sink before it can be discharged to the ambient air. As can be seen, thermal interface materials (TIMs) may be used to facilitate this process. In many cases a heat spreader in the form of a flat plate with high thermal conductivity may be placed between the chip and the lid. 

Launay S, Fedorov AG, Joshi Y, Cao A, Ajayan PM (2006) Hybrid micro-nano structured thermal interfaces for pool boiling heat transfer enhancement. Microelectronics Journal 37 1158-1164. 

In some applications, low modulus materials are desirable. In high-power semiconductor components, for example, heat is conducted away from a sUicon die (which has a coefficient of thermal expansion (CTE) of 2.49 x 10 K ) to a copper heat sink (CTE = 16.5 X 10 K ) via a thermal interface material, or TIM, which is often... 

Fig. 14.1 Schematic diagram of a microprocessor assembly showing different levels of packaging and thermal management solution using a heat sink. TIM thermal interface material, BGA ball grid array...

Only up to 10% of heat can be removed with the cathode airflow since the water balance must be maintained. To remove the waste heat from the system additional heat sinks are needed. It was established that heat can be transferred very efficiently at the stack sides. Commercially available heat sinks were mounted at the sides using electrically isolating thermal interface materials. To add as little extra weight and volume as possible to the system, high performance pin fin coolers were used. The heat sinks are made of pure aluminum with a thermal conductivity of above 220 W m" by means of impact extrusion. 

Bond line thickness and flow out shape often fluids are compressed between two surfaces to create a mechanical bond, electrical interface, and/or thermal interface. When this is the case, the shape of the fluid as dispensed can significantly affect the bond line thickness, flow out, and coverage of the interface. Any part geometries that cause variation in the bond line thickness will likewise influence the volumetric tolerances of the material to be dispensed. 

Thermal interface materials are slurries of thermally conductive particles, usually diamond or metallic oxides, suspended in liquid or low modulus adhesive. They are designed to be flexible or slightly fluid to maintain good thermal contact during temperature cycling. 

Thermal interface compounds conduct heat from a part to a heat sink or lid (Figure 10-13). In fuel cell assemblies they could be used to remove heat from reaction sites. 

Time-pressure dispensing is often used in thermal interface applications, but lacks accuracy compared with other available technologies, with typical tolerances of 20%... 

Care must be taken so that the thermal interface material does not conduct stress to the die. 

High viscosity combined with high-solids content of most thermal interface fluids causes abrasion of mechanical components of dispense equipment. Worn dispense components affect overall dispense quality,... 

Yu, A, Ramesh, P., Itkls, M. E., Belq arova, E., and Haddon, R C. (2007], Graphite nanoplatelet-epoxy composite thermal interface materials. J. Phys. Chem. C, 21, pp. 7565-7569. 

Liu, Y Zhang, L.-Q. Wang, W.-C. Yu, H.-T. Lu, Y.-L., Preparation of Polydimethylsiloxane-Coated a-Alumina Filler with Cold Plasma for Elastomer Thermal Interface Materials. J.Appl. Polym. Sci. 2012,123, 2875-2882. Fang, C. Shao, L. Zhao, Y Wang, J. Wu, H., A Gold Nanocrystal/ Poly(dimethylsiloxane) Composite for Plasmonic Heating on Microfluidic Chips. Adv Mater. 2012,24,94-98. 

The liquid-based thermal management system of the Voltec battery system is fully integrated into the vehicle s heating, ventilation, and air conditioning system (HVAC) via its thermal interface, a coolant-in and coolant-out hose [2]. The coolant is normally... 

Chung, D.D.L., 2012. Carbon materials for structural self-sensing, electromagnetic shielding and thermal interfacing. Carbon 50, 3342—3353. 

In order to predict temperature rises in electronic components, a thermal model needs to be created, which shows all of the dissipating elements and the entire heat path. Starting at the junction of each dissipating semiconductor, the model needs to include all layers in the thermal path the die attach, substrate (if used and its attachment), package, thermal interface materials (if used), heat sink and circuit card assembly (CCA). The heat dissipated in each component, physical layout, and availability of cooling air are required to calculate the temperature-rise predictions. 

The thermal resistances for many discrete components, both active and passive, have been characterized, and their values published in data sheets. Table 3.2 lists the properties of various thermal interface materials. For custom components, a thermal model needs to be created. 

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