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What is the function of thermal interface materials and why are they used?
In the design of modern electronic devices, from high-performance AI servers to electric vehicle battery packs, heat is the primary enemy of reliability. Even the most advanced heat sinks or liquid cooling systems will fail if heat cannot be effectively transferred from components to the cooler. Thermal interface materials (TIM) address the most common thermal challenge: they fill microscopic air gaps between contacting surfaces with a thermally conductive medium, thereby reducing thermal resistance (Rth) and enabling reliable heat transfer from components to heat sinks and ultimately to the environment.
Fundamentals of Thermal Interface Materials: Reducing Thermal Resistance and Optimizing Heat Transfer
The Invisible Barrier: Understanding Contact Thermal Resistance
Electronic components that appear smooth and flat to the naked eye reveal uneven surfaces at the microscopic level. This results in heat dissipation devices and electronic components only appearing to fit perfectly, while in reality numerous gaps trap air (thermal conductivity k ≈ 0.026 W/m·K), creating significant contact thermal resistance. Thermal interface materials (TIM) are specifically designed to fill these invisible interfacial gaps, thereby reducing the contact thermal resistance within the overall heat transfer path.
Microscopic Surface Roughness and Air Gaps
Without thermal interface material, these microscopic protrusions would only make contact at a few discrete points. The remaining interface gaps would be filled with air, which is a poor conductor of heat (essentially a thermal insulator). This creates a barrier to heat flow, explaining why in practice, even when the heatsink is tightly secured, a CPU without thermal paste will overheat within seconds.
Definition of Thermal Resistance
Engineers use thermal resistance (Rth) to quantify this obstruction. The goal of any thermal interface material (TIM) is to minimize the total thermal resistance (θ), which consists of three components:
- Contact resistance 1: The interface between the component and the thermal interface material.
- Contact resistance 2: The interface between the thermal interface material and the heat sink.
The Role of Surface Wetting
To minimize contact resistance, a material must possess excellent "wet-out" properties. This refers to the material's ability to flow under pressure into those microscopic valleys, displacing the air and creating a continuous thermal path. Soft materials generally offer better wet-out, which is why compressibility is a key specification.Classification of Thermal Interface Materials: From Thermal Grease to Phase Change Materials
Thermal Grease and Thermal Paste
.webp "Thermal Grease")
Sheen Technology's SG560 series thermal grease achieves an ultra-low thermal resistance with a minimum interface thickness of 0.02mm. Its viscous, non-curing compound exhibits excellent wettability.
| Properties | Thermal Conductivity(W/m·K) | Thermal Impedance (℃*in2/W) @30psi | Density(g/cm³) | Operating Temp(℃) |
| SG560-10 | 1.0 | 0.04 | 2.0 | -50~150 |
| SG560-20 | 2.0 | 0.035 | 2.2 | -50~150 |
| SG560-25 | 2.5 | 0.025 | 2.4 | -50~150 |
| SG560-30 | 3.0 | 0.02 | 2.5 | -50~150 |
| SG560-35 | 3.5 | 0.02 | 2.6 | -50~150 |
| SG560-40 | 4.0 | 0.017 | 2.6 | -50~150 |
| SG560-50 | 5.0 | 0.015 | 2.8 | -50~150 |
Thermal Gap Filler Pads
Sheen Technology offers compressible sheet thermal gap filler pads:- Carbon Fiber Thermal Pads
- Silicone Thermal Pads
- Silicone-Free Thermal Pads
- Thermal Insulation Sheets
Thermal Gels and Dispensable Materials
.webp "Thermal Gels")
Sheen Technology's SE Series thermal gel is a flexible gap-filling material. It extrudes like grease but cures into a soft rubber-like substance that won't flow out of the pump.
| Properties | Thermal Conductivity(W/m·K) | Thermal Impedance (℃*in2/W) @30psi | Density(g/cm³) |
| SE10 | 1.0 | 0.13 | 2.0 |
| SE20 | 2.0 | 0.10 | 2.5 |
| SE30 | 3.0 | 0.08 | 3.0 |
| SE40 | 4.0 | 0.06 | 3.1 |
| SE50 | 5.0 | 0.06 | 3.1 |
| SE60 | 6.0 | 0.045 | 3.3 |
| SE80 | 8.0 | 0.05 | 3.4 |
| SE100 | 10.0 | 0.045 | 3.4 |
Phase Change Material (PCM)
.webp "Phase Change Materials")
Sheen Technology's SP Series thermal phase change material remains solid at room temperature for easy assembly and handling. It softens/flows at operating temperatures to form a thin contact layer.
| Properties | Thermal Impedance (℃*in2/W) @30psi | Thermal Conductivity(W/m·K) | Thickness(mm) | Density(g/cm³) | Operating Temp(℃) | Phase Change Temp(℃) |
| SP205A-30 | 0.05 | 3.0 | 0.2 | 2.85 | -40~125 | 45 ~ 55 |
| SP205A-35 | 0.04 | 3.5 | 0.2 | 2.75 | -40~125 | 45 ~ 55 |
| SP205A-40 | 0.03 | 4.0 | 0.2 | 2.75 | -40~125 | 45 ~ 55 |
| SP205A-50 | 0.02 | 5.0 | 0.3 | 2.9 | -40~125 | 45 ~ 55 |
| SP205A-60 | 0.015 | 6..0 | 0.3 | 3.0 | -40~125 | 45 ~ 55 |
| SP205A-L-80 | 0.007 | 8.0 | 0.3 | 2.8 | -20~100 | 45 ~ 55 |
| SP350P | 0.4 | 1.8 | 0.13~0.5 | - | -40~125 | 45 ~ 55 |
| Test Method | - | ASTM D5470 | ASTM D5470 | ASTM D751 | ASTM D3418 | ASTM D3418 |
Engineering Selection Criteria: How to Choose the Right Thermal Interface Material
Thermal Conductivity and Thermal Resistance
Don’t chase k alone — compute R″ = t / k for your expected BLT.Request vendor k at specified thickness & pressure (ASTM D5470 style) — apples-to-apples comparison is essential.
Bond Line Thickness (BLT) and Compressibility
Target BLT: paste/grease ~30–100 µm; pads >300 µm.Higher compression lowers BLT for pads but may cause compression set over time — include compression-set tests in qualification.
Electrical Insulation (Dielectric Strength)
For applications near PCBs, thermally conductive and insulating interface materials should be selected for power electronic devices such as MOSFETs, UPS uninterruptible power supplies, and IGBTs to prevent short circuits that could damage electronic components.Reworkability and Service Life
When selecting thermal interface materials, engineers should also consider repairability and product lifespan. For electronic devices and industrial/automotive applications, repairable thermal pads or pastes facilitate maintenance. For extended service life requirements, thermal gels or phase change materials may be more suitable.
Practical Applications of Advanced Thermal Interface Materials
New Energy Vehicle Electronic Battery Modules
Use case: equalize module temps and manage local hot spots. Gap fillers and PCMs often used; for module balancing, lower Rth at module interface reduces peak cell temperatures and extends life.
Consumer Electronics
SoC cooling: paste + heat spreader or PCM; example: swapping a 1 mm pad for controlled paste/PCM can reduce junction temp by ~5–8°C in lab comparisons, improving performance headroom.
5G Base Stations and Telecommunication Equipment
High duty cycles and outdoor environments require TIMs with stable Rth over humidity and thermal cycling (85°C/85% RH tests recommended).
Artificial Intelligence (AI) Accelerators
AI chips feature extremely high power density, demanding exceptionally precise bonding layer thickness (BLT) for thermal interface materials. Manufacturers increasingly adopt high-performance thermal interface materials (TIMs), such as liquid metals or high-performance metal-filled thermal pastes, to meet ultra-high thermal conductivity requirements.
Frequently Asked Questions
Q: Can I reuse thermal pads?
A: Generally no. Thermal pads compressed for extended periods may experience reduced resilience, affecting performance. However, Sheen Technology's thermal silicone sheets and carbon fiber thermal sheets offer limited reusability. Case studies:
Q: What's the difference between W/m·K and thermal resistance?
A: W/m·K is a material property (similar to a speed limit). Thermal resistance represents the actual heat transfer time, which depends on distance (thickness) and contact conditions (contact resistance).
Q: Why use silicone-free thermal pads?
A: Silicone oil can migrate and contaminate sensitive optical components or electrical contacts. In optical sensors and automotive paint shops, silicone-free thermal pads are mandatory.
Q: Is higher thermal conductivity always better?
A: No—high thermal conductivity only benefits when bonded layer thickness (BLT) is controlled; calculate your stack-up's thermal impedance (R″).
Q: How often should thermal interface materials be replaced?
A: Consumer PCs: 2–5 years; Industrial equipment: Recertify based on thermal drift or perform scheduled maintenance.
Q: Which is better: thermal paste or thermal pads?
A: Each has advantages and disadvantages, requiring consideration of specific application scenarios. Thermal paste is more suitable for extremely small thermal gaps, but thermal pads offer better stability.
Thermal interface materials do far more than simply fill gaps; they serve as critical bridges enabling high-power electronics to operate safely and efficiently. When selecting thermal interface materials, engineers should focus on thermal resistance, control bond layer thickness during assembly, and validate performance through practical testing.
Sheen Technology is a specialized provider of thermal management solutions and manufacturer of thermal interface materials. Whether you're designing rugged 5G base stations or sleek consumer wearables, contact us today for complimentary material consultations and expert application-specific thermal management solutions.
