Thermal interfaces – thermal interface materialsMüller Ahlhorn
Ahlhorn | 17.12.2020
Function of thermal interface materials
Thermally conductive materials, called Thermal Interface Material (TIM), are used in many areas of electronics where fast and efficient heat conduction is important. TIMS fill in unevenness and thus enable better heat transfer from the component to the heat sink. Typical areas of application are heat-sensitive components where an active or passive cooler is used. It serves as an assembly aid for electronics, measurement and control technology and for improved heat dissipation from electronic components such as power transistors.
Types of thermal interface materials
Phase change materials
What is special about phase change materials (PCMs) is that they transition from a solid to a semi-solid phase using heat from the operating processor and a slight clamping pressure. The semi-solid phase has the property of adapting to both surfaces very easily. The ability to completely fill the interfacial air gaps and surface cavities under slight clamping pressure enables this material to perform as well as thermal paste.
Thermally conductive pastes are usually made of silicone, which is enriched with thermally conductive fillers. Curing is usually not necessary and they can flow and adapt perfectly to the interfaces. The thermal interfaces can be reworked without any problems. However, it must be ensured that sufficient paste or grease has been applied before installing the heat sink.
One of the largest market segments of the TIMs is Gap filler. These can be supplied in different strengths. These efficient, soft and highly thermally conductive materials can cover gaps up to 15 mm. The practical gap fillers can cover several components of different heights and then transfer the heat to a common heat distributor.
Thermally conductive foils not only do the heat transfer, but also provide electrical insulation. In terms of tear resistance and puncture resistance, the thermal films offer excellent durability. This category includes silicone-containing and silicone-free (e.g. polyurethane filled with ceramics) thermal conductive foils and graphite materials. The range of thermal conductivities and price ranges is wide, so that everyone can find a good solution.
Thermal pads usually consist of molding unreinforced silicone with conductive fillers. Reinforcements for thermal pads are typically woven glass, metal foils, or polymer films. The practical thermal pads are usually pre-cut in different sizes to accommodate components of different sizes. In terms of conduction, while phase change materials and thermal paste are clearly superior, the thermal pads have the advantage of being an inexpensive and convenient option for applications with less cooling requirements.
This cost-effective option has been used for a long time. The foils are electrically conductive and can be used at very high temperatures of up to 500ºC. Some providers align the fibers horizontally. This results in very different thermal conductivity measurements. There is material that shows 7.0 W / mK on the x-axis and 150.0 W / mK on the yz-axis – a clear difference.
Double-sided thermally conductive adhesive tapes
Thermal tape can consist of a finely woven, nickel-coated copper mesh that adapts tightly to irregular mounting surfaces. Thermally conductive double-sided adhesive tapes made from PSA are very often used to attach small heat sinks to components. Important factors here are the peel strength, the overlap and punching shear strength, the holding force and the thermal resistance. As far as the performance in terms of heat conduction of the double-sided adhesive tapes is concerned, it is in the middle range. You save additional assembly parts, but the belts have problems with irregular surfaces of the components and can therefore only be used to a limited extent. Plastic ICs are typically concave in the middle and the heat sink surfaces also vary, which can result in air gaps in the interface.
Thermal adhesives – also known as thermally conductive adhesives – can be either one-component or two-component systems. These are equipped with conductive fillers. The application is usually done by metering or stencil printing. A hardening of the adhesive is necessary in order to make a reliable crosslinking of the polymer possible, which offers the adhesive property. The fact that the thermal adhesives provide structural support and thus no mechanical clamping is required is certainly the greatest advantage of this TIM.
Gels are a material similar to fats that is slightly cross-linked. The behavior is correspondingly similar, whereby the bleeding of the material is reduced.
TIMs made of metal
Thermally conductive materials made of metal can be produced in all possible forms and are currently no longer limited to use with soldering. In numerous applications, the metal TIMs can be reworked very well and can also be easily recycled.
Areas of application of thermal paste
The main area of application of thermal paste is in the field of electronics. In addition, thermal pastes are used in the following industries, among others:
- Plastic industry
- Shoe machine industry
- Apparatus construction and laboratory industry
- Wood machine industry
- Packaging machine industry
- Medical technology
- General Engineering
Preserved by expanding electromobility Thermal pasten also increasingly entering the automotive sector in the field of power electronics.
Our brochure on thermal interface materials
When it comes to choosing the correct thermal material, many people are unsure of what exactly to look out for. In our brochure “Choosing the right thermal interface material” we would like to give you everything you need to know about heating materials.