Silicone vs Silicone Free Thermal interface materials

Silicone vs. Silicone-Free Thermal Interface Materials

The development of high frequency, speed, power, performance, and integration of electronic devices greatly increases the risk of overheating problems. That’s why effective thermal management is extremely important for various electronics, and the key objective of thermal management is to remove excess heat from electronic devices to the ambient environment. 

As an advanced materials supplier, CAPLINQ has been meeting the application needs of electronic device manufacturers. We provide vital materials for thermal management solutions across multiple industries which work closely with Honeywell’s Thermal Interface Materials on their thermal solution strategy.

Thermal interface materials (TIMs) play a crucial role in managing heat dissipation between electronic components and heat sinks. One key factor in choosing a suitable TIM is the composition of the material. TIM’s material composition is dependent on the application and the desired thermal conductivity. As new technologies and materials are created, the precise formulation and composition of a thermal interface material may also change over time.

In recent years, there has been a growing debate about silicone-free and silicone-based TIMs. In this article, we define the characteristics, advantages, and disadvantages of both silicone-free and silicone-based TIMs to make an informed decision when selecting a thermal interface material.

Silicone-based Thermal Interface materials

Silicone-based chemical formulations are widely employed in electronic applications due to their enhancing properties. Silicone has several features that make it appropriate for extreme operating conditions, including the ability to cope with vibration, chemicals, and extreme temperatures. They are typically formulated using silicone polymers, such as silicone oils or greases, with added fillers for improved thermal conductivity. Given these characteristics, silicone is popular as the foundation chemical for thermal interface materials (TIMs). 

High Thermal Conductivity: Silicone-based TIMs generally offer higher thermal conductivity of 6-12 W/mK (Honeywell’s Quick Thermal Conductivity Overview), enabling efficient heat transfer across the interface. This characteristic makes them suitable for applications with demanding thermal management requirements such as eMobility, Power Systems, and LED Lighting

Excellent Compressibility: Silicone-based TIMs often exhibit better compressibility with highlights on Honeywell’s Thermal Putty Pads 90% compressibility, allowing for effective filling of microscopic surface imperfections, air gaps, and large dimension variations. This ensures optimal thermal contact and improved heat dissipation. We can see in the figures below the Thermal Performance of TGP3510PT in terms of deflection and decreased thermal impedance in increasing pressure.

Nevertheless, there are certain limitations when using silicone-based TIMs:

Electrical Conductivity: Silicon-based materials are electrically conductive at high temperatures because silicon electrons can break loose from the silicon covalent bond. Electrical conduction is enabled by their movement across the lattice. As a result, caution must be exercised to avoid short circuits when employed in applications with exposed electrical connections or sensitive circuitry. 

Honeywell’s silicone-based TIMs range from Thermal Greases, Thermal Gap Pads, Thermal Putty Pads, One-Part & Two-Part Hybrid, and Thermal Insulators with both high thermal conductivity and high compressibility.

Silicone-Free Thermal Interface Materials: Efficient Alternatives for Heat Dissipation  

Silicone-free TIMs are formulations that do not contain silicone compounds. Instead, they are typically based on non-silicone polymers, such as acrylics, polyimides, or ceramics. Honeywell offers silicone-free, thermally conductive Phase Change Materials (PCM) in both pad and paste formats. Based on a robust polymer PCM structure, these materials exhibit effective wetting properties during typical operating temperature ranges, resulting in very low surface contact resistance which makes them desirable for high-performance semiconductor, and automotive applications. These silicone-free materials offer several distinct advantages:

Low Outgassing: With the absence of silicone, TIMs typically exhibit lower outgassing characteristics, minimizing the risk of contamination or degradation of nearby components. This makes Honeywell’s carbon hydride based PCM important for high-vacuum applications, such as aerospace or semiconductor manufacturing. In the graph below you will see the Outgassing testing of one of Honeywell’s in-demand PCM, the PTM7950. A minimal 0.052% weight loss was observed during temperature ramping up and 0.060% weight loss was observed when the sample was baking at 200°C for 30 min wherein the weight loss represents the volatiles evaporated during testing.

PTM 7950 TGA Report

% Outgassing for PTM 7950
Figure 2. % Outgassing for PTM 7950

Electrical Insulation: Non-silicone polymers possess inherently high dielectric strength, minimizing the risk of short circuits between sensitive electronic components. One example of non-silicone TIMs is the study of Demko et. al.: Thermal and Mechanical Properties of Electrically Insulating Thermal Interface Materials. In this paper, a new polyimide-based thermal interface material is introduced. A polyimide film is loaded with inorganic particles in such a way as to increase thermal conductivity, producing three grades of TIM films but still maintaining the dielectric breakdown voltage (Figure 4).

Thermal Conductivity and breakdown voltage for three grades of polyimide films
Figure 3. Thermal Conductivity and breakdown voltage for three grades of polyimide films

Thin Bond Line Thickness (BLT). Honeywell’s Phase change materials come in thicknesses ranging from 0.2-1mm. Those are the initial values that are adjusted after you heat up (>45°C) and pressure the material. Their silicone-free chemistry enables them to achieve a bondline of 20~30μm making it the thinnest, cleanest, and most reliable bondline in the market.

However, silicone-free TIMs also have some limitations:

Lower Thermal Conductivity & Compressibility: Non-silicone materials have lower thermal conductivity, resulting in less efficient heat transfer. They are also less compressible, which makes it difficult to achieve optimal surface contact and remove air gaps between the heat source and heat sink. These constraints can have an impact on overall thermal performance. 

Despite these constraints, Honeywell’s unique PCM offer thermally conductive TIMs of 6-12 W/mK (PTM7000 | PTM7900 | PTM7950) in both pad and paste formats.

Choosing the right thermal interface material is critical for improving heat dissipation in electronic devices so an application-specific assessment should be conducted. Contact us and our application engineers and in-house thermal experts will help you out with product selection for your application requirements.

About Darlene Pudolin

Darlene Pudolin is one of CAPLINQ's Application Engineers specializes in Thermal Interface Materials, Fine & Specialty Chemicals, and Soldering Materials within the company's Technical Marketing unit. Darlene recently joined CAPLINQ in early 2023 but has been an experienced materials quality engineer for 5+ years. She has a broad range of experience in materials solution from Thermal Interface Materials, Cement Chemistry, and Hydrogen Renewable Technology. With a long history of serving customers in Industrial and Research academe, Darlene is passionate on driving solutions about troubleshooting points that best fit the market requirements. Based in the Philippines, Darlene holds a Bachelor's degree in Chemical Engineering from Mapua University and currently doing her Master's degree in Energy Engineering at University of the Philippines Diliman.

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