52 July/August 2026 | E-Mobility Engineering Developments in EVs are increasing the demands made of thermal interface materials. Peter Donaldson investigates what’s hot and what’s not The heat is on A thermal interface material (TIM) has a deceptively simple job: to fill the microscopic air gaps between a heat source and a heat sink and allow thermal energy to flow. For decades, this was typically done by a simple material selected from a catalogue based on a single number for bulk thermal conductivity. This is no longer the case. Three converging developments in EVs are driving fundamental changes in these materials. The first is the shift toward cellto-pack and cell-to-chassis battery architectures. This means that a TIM can no longer be just a thermal conductor between a module and a cooling plate. Instead, it must be a large-area structural adhesive, a high-voltage electrical insulator and a critical line of defence in a thermal runaway event. It must also be dispensed rapidly and guaranteed for the life of the vehicle. The second is the adoption of widebandgap semiconductors such as SiC and GaN in traction inverters, which is pushing junction temperatures beyond 200 C into a realm where traditional organic TIMs fail and even high-lead solders reach their limits. Solutions include sintered silver and copper pastes that transform the interface into a solid metallic bond. Third, the industry is now thinking beyond initial performance and grappling with the full life cycle. The need is now for TIMs that will hold up for 15 years or more on bumpy roads in salty humidity, yet will cleanly debond so that the battery pack can be repaired, remanufactured or recycled. The simple watts-per-metre-kelvin (W/mK) number denoting thermal conductivity on a datasheet is no longer sufficient. Key initiatives to balance high thermal performance and thermomechanical reliability include polymers designed with either semi-bonding properties, such as next-generation gap fillers, or high-bonding-strength thermally conductive adhesives (TCAs). Depending on the temperature resistance, resin technologies such as polyurethane, epoxy or even silicone could be employed to tackle the different requirements of battery systems, power conversion applications and battery management electronics. Thermal dielectric trade-off One challenge is that increasing thermal conductivity often comes at the expense of electrical insulation performance in a TIM. In many cases, a single material may no longer be able to optimise both properties simultaneously, making hybrid concepts attractive. Such a hybrid might, for example, combine highly thermally conductive ceramic layers with a very thin thermal interface layer, such as thermal grease or a gap filler – the latter used only to compensate for tolerances and ensure good thermal contact. The exact solution would depend strongly on the tolerance chain and overall layer design, but multilayer approaches could Cell-to-pack battery designs, such as BYD’s Blade 2.0 used in the latest Seal and other models need TIMs that also provide structural strength (Image: BYD)
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