Thermal Interface Materials: Everything You Need to Know
Thermal Interface Materials or TIMs are products that conduct heat between two or more solid mating surfaces. For example, these materials can aid in the thermal management involving semiconductor devices and a heat sink by serving as gap fillers between the two mating surfaces. By doing so, these materials improve heat transfer between the two surfaces and enhance the efficiency of the thermal management system.
This guide provides an overview of thermal interface materials, the types of materials you can choose from, and important factors you should consider when selecting the right TIM for your unique application.
Why Do Electronic Devices Get Hot?
Electronic devices become hot due to a physical phenomenon called electrical resistance or simply resistance. When voltage is applied to a conductor, the free electrons start moving. These free electrons, while flowing, collide with the atomic particles of the conductor material. This collision results in friction (resistance) between the flowing electrons and the atomic particles of the conductor, generating an excessive amount of heat.
The highest thermal energy generating devices among modern electronic devices include Light-emitting Diodes (LEDs) and computer processing units such as GPUs, CPUs, and TPUs. The voltage-changing devices such as transformers, resistors, converters, and inverters also release high thermal energy. Therefore, it is critical to keep these devices cool to ensure optimum performance and reliability. As a result, thermal management systems are usually employed which maintain the device temperature within specified limits.
Electronics cooling techniques can be passive and active. The passive cooling method utilizes natural conduction, radiation, and convection to cool down an electronic device. On the other hand, an active cooling method requires external energy to cool down an electronic device or component.
Evidently, active cooling is more effective but a costly method compared to active cooling. However, it is possible to enhance the efficiency of passive cooling using thermal interface materials instead of air.
What are Thermal Interface Materials?
Thermal Interface Materials or TIMs are cost-effective and energy-efficient passive thermal management solutions that help maintain recommended operating temperatures in electronic devices or components. In addition, they aid in thermal conduction between a semiconductor device and a heat sink.
The surfaces of these two mating components may appear flat. However, a closer inspection will reveal some choppiness or imperfections such as pores or tool marks. These tiny cracks and scratches prevent actual physical contact between the two parts. The resulting gap gets filled with low thermal conductivity air, which leads to higher thermal resistance between the interfacing surfaces.
The primary purpose of passive cooling with TIMs is to fill those gaps between mating surfaces with a substance that possesses better thermal conductivity than the air. A typical TIM conducts heat roughly 100 times more than the air displaced.
Applications of Thermal Interface Materials
Thermal interface materials are considered a significant element of any efficient thermal management system. These materials are widely used in consumer and industrial electronic systems to ensure efficient heat dissipation and prevent overloads of local temperature. Some industries where TIMs find applications include telecommunications, servers, gaming, automotive, and aerospace.
Types of Thermal Interface Materials
There are several thermal interface materials available to suit different electronics thermal management requirements. The most common ones include:
Thermal Tapes
As a heat sink attachment method, thermal tapes eliminate the need for external clamps, bringing down the overall hardware requirement. They are filled with Pressure Sensitive Adhesives (PSAs) coated on a support material such as polyimide film, fiberglass, aluminum foil, or mat. They are commonly found on ‘sticky’ note paper and bandages. PSAs, when slight pressure is applied on them, stick to surfaces by contact.
More than the thermal performance, it is their adhesive property that drives the use of thermal tapes. However, these tapes have limited applications and are generally not suitable for Ball Grid Array (BGA) packages that come with concave top surfaces.
Greases
Greases, also known as thermal compounds, are the oldest class of TIMs as they are the easiest way to fill microscopic air pockets. Due to their high viscosity, greases are often characterized as messy and difficult to apply on surfaces. The viscosity can be brought down by heating during usage. Heating lets the greases further wet the contact surfaces, lowers the interfacial resistance, and improves performance. Greases, with their low viscosity, are very good for filling very thin interface areas.
Gels
Gels are a recently developed thermal interface option. Gels are used like grease, but they are cured to a partially cross-linked structure to reduce chances of pump-out issues.. Thermal resistance levels of gels are comparable to grease.
Thermal Adhesives
Although thermal conductive adhesives such as epoxy and silicone-based formulations are overlooked TIM options, they can reduce the size and weight of a system by offering a superior mechanical bond. Fundamentally, the thermal adhesive is a high-performing compact thermal interface material package that comes with long-term reliability.
Dielectric Pads
Dielectric pads, because of their high demand, are offered in a wide array of thermal conductivity and dielectric capabilities. These thermal interface materials possess ‘good’ to ‘very good’ thermal conductivity. Most dielectric pads are available with PSA on one side to allow easier manufacturing of the mating components. These pads come with a thickness range of 5 to 15 mil. They are used in either smaller size interfaces or very strong, larger interfaces, owing to their relatively hard nature.
Phase Change Materials or PCMs
At relatively low temperatures ranging from 55-65°C, PCMs can change from a solid-state to a viscous liquid. They are generally used as an alternative to grease-type thermal interface materials. Their unique phase-changing characteristic allows easier handling and processing of the materials as solids at room temperature. While at higher operating temperatures, they can maintain the conformability and wetting properties of a fluid. In manual assembly processes, PCMs are much neater to handle, generally don’t have dry-out issues, and can be pre-applied for an assembling process in the future.
Advanced Materials
Advanced materials consist of a relatively new type of thermal materials based on pyrolytic graphite. It has the interesting property of being thermally anisotropic (a quality that allows the material to assume different properties in different directions). Because of their unique qualities, these graphite-based thermal interface materials can move heat around in the tight confines of portable consumer devices. They can also be used in other devices or components where an efficient thermal management solution is needed.
Selecting the Right TIM for Your Application
TIMs improve heat transfer across the interface, but they also account for a major part of the thermal resistance of the entire system. While choosing the right TIM for your application, here are some of the characteristics you should consider.
Thermal Conductivity/Thermal Resistance
Thermal conductivity determines the amount of heat TIMs can transfer across the interface, impacting its thermal performance. A material with higher thermal conductivity will offer a better heat transfer rate and is an important metric when comparing different materials.
Ease of Application and Installation
The overall cost of your thermal management system based on TIMs will also depend on the cost associated with application and assembly. For example, with grease as a TIM, you will require additional processes such as clamping, secondary curing operation, and mechanical attachment. These requirements not only add to the cost but also increase the assembly time. However, if the thermal management requirements are minimal, you can benefit from adhesive thermal tape instead of grease.
Reliability in Performance
TIMs should perform consistently and reliably throughout the lifespan of an electronics device. Electronic devices are designed to last up to a decade, while avionics and telecommunication devices are built to last through decades. The dwindling size of electronics devices and components, along with an increase in power densities, turned thermal management into a major concern in electronics. It also ensures optimum performance and reliability of the devices and components.
Compatibility with Heat Sink Material
Compatibility is an easily overlooked factor as it’s not a major issue in most electronics applications. However, there are a number of use cases in which it can bring significant issues. For instance, exposure to silicone vapors damages many gases and humidity sensors, restricting them from using silicone-based TIMs in the same components. Therefore, it is always a good idea to verify the compatibility of TIMs with any thermal adhesives or heat sink materials before implementation.
Environmental Factors
There are a good number of environmental factors you must consider along with thermal changes before using TIMs. You may check the resistance of a gap filler or a TIM against environmental conditions such as salt mist, corrosive gases, and high humidity. Since TIM layers are usually very thin and placed between two surfaces, it is not likely to be completely exposed to these adverse environmental conditions. But, with gap filling material, it may be more likely to be affected by challenging environments.
What Makes Laird’s Thermal Interface Materials Different?
Laird Performance Materials is an IATF 16949 certified industry-leading gap filler company. We have a wide array of gap filler materials that suits almost any application. We also offer various TIM and enclosure solutions. Our premium quality products gained us the highest ratings on major customer qualification audits.
At Laird Performance Materials, our customers consistently rank us among the top suppliers of premium quality and high-performing products at affordable prices. We partner with our customers to evaluate their preferences for the types of materials and applications. We conduct testing for the customers and never hesitate to get down deep into helping them to find the right TIM for their needs.
Need to learn more about our TIMs? Feel free to get in touch with us