Thermal Interface Materials (TIMs)

Thermal conductivity is a material’s ability to transfer heat, measured in W/mK. For thermal interface materials — gap pads, greases, pastes, phase change materials, and adhesives — it is a primary performance indicator. A TIM with insufficient thermal conductivity creates a thermal bottleneck between a heat source and a heat sink, leading to elevated operating temperatures, reduced component lifespan, and potential system failure. Accurate characterization is therefore essential at every stage of TIM development and qualification.

There are several established methods for testing TIMs, and the best choice depends on your specific requirements.

MTPS (Modified Transient Plane Source) is the simplest, fastest, and most automated method for TIM thermal conductivity characterization. C-Therm’s patented MTPS technology, available on the Trident Thermal Conductivity Platform, is widely used for rapid screening and formulation development. It is particularly effective for identifying filler sedimentation and agglomeration, which can significantly impact TIM performance, and is well suited for material selection and quality control where repeatability and ease of use are critical. MTPS supports a wide range of formats, including pads, tapes, pastes, adhesives, and phase change materials.

TPS (Transient Plane Source) is the double-sided ‘hot disc’ method and is compliant with ISO 22007-2, ISO 22007-7 and E3088. It is one of the most widely referenced methods on TIM datasheets and is well suited for advanced users requiring greater control over test parameters such as power and measurement time. TPS can also be used to evaluate anisotropic thermal conductivity when density and heat capacity are known. MTPS and TPS are complementary techniques available on the C-Therm Trident platform, offering both rapid measurements within a single system.

THW (Transient Hot Wire) is well suited for testing coolants and heat transfer fluids, where convective stability and low-viscosity behavior are important, providing reliable thermal conductivity measurements for fluid-based thermal management systems.

ASTM D5470 (ZFW TIM-Tester) is a steady-state comparative method used to measure thermal resistance (thermal impedance) of thermal interface materials. The ZFW TIM-Tester enables direct evaluation of through-plane thermal transport under controlled temperature and pressure conditions, making it highly relevant for electronics cooling applications. The method captures the combined effects of material thermal conductivity, thickness, surface roughness, and interfacial contact resistance, all of which strongly influence real-world heat transfer performance.

Each method provides distinct and complementary insights, together forming a comprehensive toolkit for evaluating thermal performance in TIMs and thermal management fluids.

TIM testing refers to the thermal characterization of thermal interface materials, including measurements such as thermal conductivity, thermal resistance (or thermal impedance), and interfacial heat transfer performance. These properties are used to evaluate how effectively a TIM facilitates heat flow between mating surfaces under applied pressure and temperature conditions. Accurate thermal characterization helps predict in-use performance, reduce thermal bottlenecks, and improve reliability and efficiency in electronics, EV batteries, telecommunications systems, and other high-power applications.

TIM performance is influenced by:

• Compression state / applied pressure
• Temperature
• Quality of interface contact
• Filler type, size, and loading
• Dispersion quality (agglomeration/sedimentation)
• Polymer matrix composition
• Cure state (for adhesives)
• Thickness. and
• Mechanical properties

Yes. The MTPS sensor is designed to accommodate pastes, greases, and other semi-solid TIM formats without specialized sample preparation. Liquid and low-viscosity TIMs can be tested using the MTPS Liquids & Powders Cell or the THW sensor. The single-sided nature of the MTPS sensor makes it particularly practical for sticky or non-self-supporting materials that are difficult to handle with double-sided sensor techniques.

Yes. Anisotropy (in-plane vs. through-plane conductivity) can be measured using TPS (ISO 22007-2) when density and heat capacity are known.

Yes. MTPS and TPS can test PCMs, greases, gels, and adhesives. Additional sample containment may be recommended depending on viscosity.

TIMs are often compressible, and applied pressure affects their:

• Thickness
  Density
  Contact quality
  Measured thermal conductivity/impedance
  To obtain representative and repeatable results, the TIM must be tested under controlled, application-relevant compression conditions.

C-Therm’s Compression Test Accessory (CTA) provides adjustable, reproducible loading and is compatible with both MTPS and FLEX TPS (Hot Disc) test methods.

The Compression Test Accessory (CTA) enables users to precisely control the level of compression applied to a sample during MTPS testing. Since many TIMs — including gap pads, greases, and pastes — exhibit pressure-dependent thermal conductivity, the CTA ensures that measurements are taken under conditions representative of actual application use. It is compatible with solid, paste, grease, and powder TIM formats and is particularly valuable for benchmarking competing products under standardized compressive loads.

The ZFW TIM-Tester, developed by the Zentrum für Wärmemanagement (ZFW) in Stuttgart and has been the market benchmark for TIM characterization since 2012. It is distinguished by its high-precision optical gap measurement — with a resolution of 0.1 μm and absolute accuracy of ±4 μm — which accounts for material compression and thermal expansion during testing. This results in reproducibility of less than 1 mm²K/W, the best available in the market. It supports both gap-controlled and pressure-controlled measurement modes (up to 2 N/mm²), making it suitable for the full range of TIM forms, from low-viscosity pastes to rigid gap pads.

Thermal contact resistance (TCR) is the resistance to heat flow at the interface between a TIM and the mating surfaces it contacts. It arises from microscopic surface roughness, air gaps, and wettability effects. The ZFW TIM-Tester isolates TCR by measuring thermal resistance at multiple bondline thicknesses and extrapolating the interface contribution. This enables engineers to distinguish between the TIM’s intrinsic bulk thermal conductivity and the additional resistance introduced at the interface — a critical distinction for accurate thermal stack modeling.

The Trident MTPS sensor operates from -50°C to +200°C, and the Flex TPS sensor from -200°C to +600°C, making it suitable for characterizing TIMs across a wide range of operating environments. The ZFW TIM-Tester supports sample temperatures from 10°C to 150°C, with a hot-side capacity up to 175°C, covering typical electronics and EV operating conditions. Temperature-dependent measurements can reveal how TIM performance changes under real-use thermal cycling conditions.