Thermal Management Materials
There are many different types of Thermal Interface Materials (TIMs). Generally, TIMs are manufactured from Silicone loaded with various fillers that enhance the thermal coefficient of the Silicone. There are non-silicone versions available.
Thermal interface material is crucial to every thermal management solution. It’s also important to know the characteristics of various thermal interface material types so you’re well equipped to make the right choice for your application. Depending upon your application, you may want to use one type of TIM over another to help facilitate better performance. Some are rigid, others flexible. Some TIMs are solid, and others can change between phases. There’s a wide range of thermal interface material types available for improving heat transfer between surfaces, but it’s crucial to spec in the right type
Thermal Interface Material Types
For anyone who’s built their own PC, thermal grease is probably the first of the thermal interface material types that comes to mind. Thermal grease, as you can guess, is a grease specially designed to have a high thermal conductivity. Most thermal greases are silicone based with tiny thermally conductive filler particles that increase the overall conductivity of the mixture. There are silicone-free greases on the market for applications that are sensitive to silicone. Applications that are concerned with the wettability and adhesion of surfaces that may come in contact with a thermal grease would benefit from using a silicone-free compound.
Thermal grease is easy to acquire, making it popular for DIY projects or smaller quantity prototype or production runs. For applications that require consistency from one product to the next, it’s relatively simple to create a template for screening on thermal grease. This makes application specific grease patterns simple and cost effective. Other thermal interface materials require die cutting to produce custom shapes, which are typically more expensive than a grease screen.
Gap fillers are another popular interface material type. Gap fillers are elastomeric sheets, typically made from silicone, that contain specialized thermal filler material to increase the overall thermal conductivity of the material. These materials come with a wide range of options, so it’s fairly easy to find a suitable gap filler for a specific application. Gap fillers are typically cut to standard device sizes or customised shapes for specific applications.
Gap fillers are probably the most diverse major thermal interface material type. All gap fillers have a base elastomer and a thermal filler mixed in, which include silicone and silicone free materials. These are just a fraction of options available when selecting a gap filler. Within the same elastomer and filler mix, there are multiple sheet thicknesses, tacky or adhesive options for each side of the sheet, reinforcement materials like fibreglass, and carrier options for protecting the material before application. Some materials can electrically isolate hot devices. Other gap fillers have the ability to absorb electromagnetic interference (EMI). Between all of these options, you could have a hundred options with one material type. This range of options is what makes gap fillers a popular selection when it comes to thermal interface material.
Thermal Pads & Films
Thermal pads and films are thin materials used to conduct heat from one surface to another. These interface materials are also ideal for heat dissipation away from hot spots. All but a few thermal pads and films are flexible materials. Like gap fillers, thermal pads, films and foils are typically cut to standard device sizes or customised shapes for specific applications.
Pads are typically made from a higher durometer silicone based material than gap fillers. Like gap fillers, silicone pads also doped with more conductive materials like aluminium oxide or boron nitride. Additionally, thermal pads are reinforced by fibreglass or another material to increase tear resistance of the material. This makes thermal pads a robust and compliant replacement for thermal interface hardware.
Thermal films are commonly made of polyimide, a transparent thermoset polymer that has great electrical isolation properties. You’ll also hear it referred to as its brand name Kapton. Films can be made from other materials, like graphite, which we’ll get into in a moment.
Phase Change Material
Phase change material is an interesting thermal interface material type. It’s composed of a wax like substance that has a specific melting temperature, typically between 50-65°C. While the material is transitioning from a solid to a liquid, the temperature of the material stays consistently at its melting temperature as is absorbs heat. This provides excellent temperature control between surfaces. Once the phase change material absorbs its latent heat of fusion, the energy it takes to completely melt the solid, then the phase change material will start to increase temperature while in its liquid state.
Many phase change material are deposited onto a highly thermally conductive base material that is also installed in the application. Some use a thermal film or aluminium foil to hold the material before and while it’s installed. Other phase change materials have films on both sides so as you install the waxy material, the films from both sides are removed, leaving just the phase change material between the surfaces.
Thermal epoxy is the most robust thermal interface material. What sets thermal epoxy apart from other epoxies is the thermally conductive fillers mixed in with the resins. Some epoxies use thermally conductive ceramic particles and others use small metallic particles. Like other epoxies, there are one part and two part resins that can be mixed and applied to join surfaces together. The type of epoxy used is typically dependent on the materials being joined together.