Thermal Interface Materials

gap filler · grease · fillers

A TIM fills the air gaps between two clamped surfaces. In inverters the best TIM is increasingly none at all; in battery packs, kilograms of dispensed gap filler are now a standard part.

Heat path from chip to coolant in two power module designs. Conventional module on a cold plate, top to bottom: SiC die, solder or sinter, DBC or AMB substrate, baseplate, a thermal interface layer of grease or phase-change material (highlighted), cold plate, coolant. Direct-cooled pin-fin module: SiC die, silver sinter, AMB substrate, pin-fin baseplate wetted directly by coolant - no TIM layer - as in Infineon's HybridPACK Drive and Tesla's inverters. HEAT PATH, CHIP TO COOLANT Conventional module on a cold plate Direct-cooled pin-fin module SiC die Solder or sinter Substrate (DBC / AMB) Baseplate TIM: grease or PCM Cold plate Coolant SiC die Silver sinter Substrate (AMB) Pin-fin baseplate Coolant No TIM layer: coolant wets the baseplate directly (Infineon HybridPACK Drive, Tesla)
Air conductivity
~0.026 W/m-K
Typical gap filler
2-4 W/m-K
Battery use
Dispensed gap filler
Leaders
Henkel, Dow, Shin-Etsu
Hub
Supply Chain

Finding

The TIM is often the weakest link in a power-electronics heat path, which is why traction inverters are designing it out while battery packs consume more of it than ever

Air conducts heat at about 0.026 W/m-K; a dispensed silicone gap filler reaches 2-4 W/m-K and a good grease or phase-change material higher still, against more than 200 W/m-K for the aluminum on either side. In a conventional power module, the grease between baseplate and cold plate can be one of the largest thermal resistances in the stack, and it degrades through pump-out and dry-out over thousands of thermal cycles.

Traction inverters are removing that layer. Infineon's HybridPACK Drive and most current silicon carbide (SiC) inverters, including Tesla's, use pin-fin baseplates that coolant wets directly, with silver-sintered die attach replacing solder. Battery packs move the other way: cell-to-pack and cell-to-body designs bond cells to a cooling plate with dispensed thermally conductive adhesive or gap filler over the full pack area, several kilograms per vehicle, and the dispensing line becomes part of the pack process.

Formulators are Henkel (Bergquist and Loctite), Dow, Shin-Etsu, Momentive, Parker (Chomerics), 3M, Honeywell and Laird; Chinese suppliers such as Shenzhen FRD and Jones Tech are scaling with domestic battery and electronics makers. The deeper dependency is filler: alumina, boron nitride and aluminum nitride powders from Denka, Showa Denko (Resonac), Saint-Gobain and 3M, and specialty silicone polymers concentrated at Shin-Etsu, Dow, Wacker and Momentive. Requalifying a TIM on a validated platform takes months, so suppliers rarely change mid-program.

Types

TIM types

The choice follows gap size, clamp pressure, electrical isolation, rework needs and process.

TIM types
TypeWhere usedStrengthTradeoff
Thermal greasePower module to cold plate; computeThinnest bond line, lowest resistancePump-out and dry-out over cycling
Phase-change materialPower modules, pre-appliedClean assembly, low resistance after first heatNeeds activation temperature and clamp
Dispensed gap fillerBattery cells or modules to cold plateFills large uneven gaps; automatedHigher resistance; mass adds up
Thermally conductive adhesiveCell-to-pack and cell-to-body structuresBonds and conducts in one stepPack is hard to rework or repair
Gap padOnboard chargers, DC-DC, ECUsEasy assembly, electrical isolationHigher resistance than grease
Graphite sheetCompute, displays, spreadingHigh in-plane conductivityPoor through-plane conduction

By application

Requirements by application

TIM requirements
ApplicationPriorityRequirementTrend
Traction inverterLowest junction-to-coolant resistanceStable over thermal cycling; dielectric where neededDirect-cooled pin-fin, sintered die, no TIM
Battery packUniform contact over large areaIsolation, dispensable at line rate, low densityStructural adhesive in cell-to-body packs
Autonomy computeDense local heat in small packagesLow resistance within pressure limitsLiquid cold plates and metal TIMs on top parts

Supply

Supplier base and constraints

TIM supply
ElementLeading suppliersConstraint
Formulated TIMsHenkel, Dow, Shin-Etsu, Momentive, Parker, 3M, Honeywell, Laird; Shenzhen FRD, Jones TechLong requalification cycles
Conductive fillersDenka, Resonac, Saint-Gobain, 3M (boron nitride, alumina, aluminum nitride)Spherical alumina and BN grades concentrated in Japan
Silicone base polymersShin-Etsu, Dow, Wacker, Momentive; HoshineSiloxane supply increasingly Chinese
Dispensing equipmentGraco, Nordson, Scheugenpflug, ViscoTecAbrasive fillers wear pumps

Sources

Sources and scope

Scope
Thermal Interface Materials
Sources
Infineon HybridPACK Drive documentation; supplier datasheets; ElectronsX thermal research
Updated
October 2026