An automotive electronic controller starting on a winter morning, a server running at full load in summer, a power module energized for long shifts: in each case the thermal interface between component and heat sink swings repeatedly between low and high temperatures. A common question on the shop floor is why a component runs at a normal temperature right after assembly, yet creeps warmer after a period of thermal cycling. This article follows two threads, thermal expansion and interface thermal impedance, to outline how to judge a thermal grease for wide-temperature-range service.
Product Confirmation
The product discussed here is Lixing Thermal Grease (導熱硅酯/導熱膏), product key high-performance-thermal-grease-paste. According to the official product page, it is a grey, silicone-based thermal grease with a stated operating temperature of -40°C to 250°C and a momentary temperature resistance of -50°C to 340°C. Data checked on 2026-09-24.
The Engineering Problem: Temperature Swings Make the Interface Move
Component packages, metal lids, heat sinks and circuit boards are usually made from different materials. As temperature changes, each material expands or contracts by a different amount, so the thermal interface sandwiched between them experiences relative displacement and gap variation. If the grease is squeezed out of the contact zone by repeated compression and release, or dries at high temperature, voids can form. Air conducts heat far less effectively than thermal grease, so heat must detour and the component temperature rises. Such issues often do not appear in end-of-line testing; they emerge after long-term thermal cycling.
Mechanism 1: Different Materials Expand Differently
How much a solid expands when heated is governed by its coefficient of linear expansion. When a heat sink and a component lid have different coefficients, they grow by different amounts over the same temperature change. The difference becomes lateral relative displacement at the interface; if the parts are clamped, it turns into thermal stress and warpage that make the bond line thickness vary with temperature. The wider the temperature range, the more pronounced the effect, so an interface material for wide-temperature service needs to follow that movement while keeping continuous coverage.
Theory: Linear Thermal Expansion
Equation: ΔL = α × L × ΔT
- ΔL: change in length, in m or mm
- α: coefficient of linear expansion, in 1/°C or 1/K
- L: original length, in m or mm
- ΔT: change in temperature, in °C or K
How to use it: apply the equation separately to the heat sink and to the component lid; the difference between the two ΔL values gives a rough estimate of relative displacement at the interface. For the same L and ΔT, the part with the larger α grows more, and a wider temperature span widens the gap between the two.
Applicability and limits: as described in OpenStax University Physics Volume 2, 1.3 Thermal Expansion, α varies slightly with temperature; treating it as constant is accurate for small temperature changes, and an average value can be used for larger ones. The equation is limited to one-dimensional free expansion. It excludes clamping restraint, warpage, viscoelasticity and the rheology of the grease itself. It is an engineering model for understanding interface displacement, not a specification or performance guarantee for this product.
Mechanism 2: Interface Thermal Impedance Depends on a Continuous Thin Layer
Thermal grease fills the microscopic peaks and valleys between two contact surfaces, replacing air with a conductive material. ASTM D5470 is the standard test method for measuring thermal impedance and calculating apparent thermal conductivity of thermally conductive electrical insulation materials, ranging from liquid compounds to hard solids. The official product page lists a thermal conductivity of 2–10 W/m-K (multiple grades) and a thermal impedance of < 0.126 °C-in²/W, both per ASTM D5470. These values come from standard test conditions. In a real assembly, thermal resistance also depends on contact pressure, surface flatness and applied thickness, and voids created by thermal cycling can shift interface resistance away from its initial value.
Mechanism 3: Non-Flowing Paste and Low Evaporation Help the Interface Stay in Place
In an interface that moves repeatedly, a paste that is too fluid is easily squeezed out, while excessive evaporation can lead to dry-out. The official data describes this product as a silicone-based, high-viscosity, non-flowing paste with very low evaporation; both characteristics help the grease maintain coverage through thermal cycling. Actual retention should still be confirmed with thermal cycling tests on representative samples of the specific assembly.
Key Technical Points
- Grey silicone-based thermal grease for filling the interface between electronic components and heat sinks.
- Thermal conductivity of 2–10 W/m-K, available in multiple grades (ASTM D5470).
- Thermal impedance of < 0.126 °C-in²/W (ASTM D5470).
- Operating temperature of -40°C to 250°C; momentary temperature resistance of -50°C to 340°C.
- Volume resistivity of 10^14 Ohm-cm (ASTM D257), with non-flowing and low-evaporation characteristics.
Civil Industrial Applications
- Thermal interfaces between server CPUs, GPUs and other high-power processors and their heat sinks.
- Thermal filling between power modules, diodes, transistors and heat spreaders.
- Automotive electronics and other precision electronics exposed to hot and cold swings.
- Thermal management in laptops, game consoles and high-power LED lighting.
Selection and Design Reminders
- Judge by the actual interface temperature rather than ambient temperature; component surfaces can run noticeably hotter than the enclosure air.
- The momentary range of -50°C to 340°C describes short temperature excursions; use -40°C to 250°C as the basis for continuous operation.
- Choose a grade by power density, applied thickness and contact pressure; a higher-conductivity grade does not automatically mean lower assembled thermal resistance.
- Use ΔL = α × L × ΔT to estimate the expansion difference between the two mating parts; for long interfaces or strongly mismatched materials, plan thermal cycling and thermal resistance measurements on representative samples.
- Contact Lixing to confirm the exact grade, packaging and specifications for your model.
Conclusion
A wide temperature range tests a thermal interface in more ways than heat resistance alone: the question is whether the interface stays continuous and low in resistance through cycle after cycle. Understanding expansion mismatch, reading thermal impedance data in the context of a standard method, and validating in the real assembly form a sound selection path. To evaluate grades or application conditions, see the Lixing Thermal Grease product page and get in touch with our team.
Sources and Review Status
Author: Lixing Compound Material technical content team. This article was drafted by AI from official product data and public engineering references and is pending human review (ai_draft_pending_human_review); data checked on 2026-09-24. Product data: Lixing Thermal Grease official product page. Theory: OpenStax University Physics Volume 2, 1.3 Thermal Expansion. Test method scope: ASTM D5470. The equation and mechanisms are engineering explanations, not product guarantees, and this article does not include Lixing in-house thermal cycling test data.
Tags: #ThermalGrease #ThermalInterfaceMaterial #WideTemperatureRange #ThermalManagement #ThermalExpansion #PowerElectronics #Lixing
