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Reducing Thermal Impedance with LORD Gap Fillers

( 08/23/2018 ) Written by: Dr. Tim Fornes

With the trend toward electric vehicles (EV), increased battery range and performance is needed to allow competition with combustion engines. Battery manufacturers are feeling the pressure to increase battery density, which in turn creates more heat in the battery pack – making thermal management a key issue for battery performance and design. A cooler battery equals better efficiency and longer life. Batteries for EVs must not overheat, yet should run longer. Better performance and lower costs are going to be critical for market attractiveness and market consumer adoption.

To effectively transfer heat from the battery pack’s hot substrate to a cooler one, it is necessary to use a thermal interface material (TIM), such as a cure-in-place, liquid-dispensable gap filler. LORD’s CoolTherm® gap filler promotes conduction by displacing any air that resides in both the large gaps and the microscopic rough surfaces that exist between the substrates to be bridged. This is crucial to producing a longer lasting battery pack.

The ability for heat to transfer from a hot substrate to a cooler one will be governed by the thermal impedance of the TIM. Thermal impedance is the measured heat flow through the TIM assembly, as opposed to a being a property of a single material. In addition to the bulk thermal resistance of the thermal management material, thermal impedance across the assembly is influenced by the ability or inability of heat to transfer across the interfaces of the substrates – see picture below. The materials under consideration, and the boundaries between them, reflect multiple discrete areas, each with its own conductive (or resistant) properties. Given these multiple zones that heat must transfer across, a thermal management assembly may have a high thermal impedance even though it has a high thermal conductivity and thin bond line. One situation that causes this is when the TIM has poor physical contact with one or both substrates, failing to provide a proper bridge for energy transfer and creating a high interfacial resistance. Because of their comparatively poor contact with substrates at a microscopic level, thermal pads (one form of thermal interface material) are known to have significantly higher impedance values as compared to gap fillers.  

Our gap fillers readily flow into surface imperfections and create a more complete thermal bridge, which allows a more efficient transfer of heat between upper and lower substrates. Better flowability accommodates macroscopic variations in thickness across the length of a bond line and, since it is not uncommon for bond lines to vary by several millimeters across the length of a battery pack, results in lower thermal interfacial impedance. Liquid-dispensable gap fillers can bridge large gaps without the need to apply forces that add stress to the design, while maintaining a more consistent interfacial interface and in turn, minimizing hot spots.

Contact us today for the thermal management material that will help your battery packs meet the needs of the EV market. LORD’s CoolTherm® gap filler will provide the low thermal impedance needed to produce a cooler battery, longer battery life, less hot spots and overall better performance.



Dr. Tim Fornes

Dr. Tim Fornes is a Principal Scientist within the Chemical Research Department of LORD Corporation. Since joining LORD in 2005, Tim has focused on creating new adhesive and coating products and technologies that have commercial relevance in the electronics, aerospace, and automotive industries. Tim is the author or co-author on 19 peer-reviewed technical publications and is a co-inventor on numerous US and international patents.

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