Thermal interface materialsMüller Ahlhorn
Ahlhorn | 17.12.2020
Function of thermal interface materials
Thermal interface materials (TIM) are used in many areas of electronics where fast and efficient heat conduction is important. TIMS fill in irregularities and thus enable better heat transfer from the component to the heat sink. Typical applications are heat sensitive components where an active or passive cooler is used. It is used as an assembly aid of electronics, measurement and control equipment and for improved heat dissipation of electronic components such as power transistors.
Types of thermal interface materials
Phase change materials
The unique feature of phase change materials (PCMs) is that they undergo a transition – from a solid to a semi-solid phase – with the application of heat from the operating processor and light clamping pressure. In this process, the semi-solid phase has the property of conforming very easily to both surfaces. The ability to completely fill the interfacial air gaps and surface voids under light clamping pressure allows this material to perform like thermal paste.
Thermal conductive pastes are usually silicone enriched with thermally conductive fillers. Curing is usually not necessary and they can flow and conform to the interfaces excellently. The thermal interfaces can be reworked without any problems. However, it is important to ensure that sufficient paste or grease has been applied before installing the heat sink.
One of the largest market segments of TIMs is gap fillers. These can come in a variety of thicknesses. 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 into a common heat distributor.
Heat conducting foils
Thermal conductive films not only take care of heat transfer, but also provide electrical insulation. In terms of tear resistance and puncture resistance, thermal films offer excellent durability. This category includes silicone-containing and silicone-free (e.g., ceramic-filled polyurethane) thermal foils and graphite materials. The spectrum of thermal conductivities and also price ranges is wide, so 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 convenient thermal pads are typically pre-cut in various sizes to accommodate components of different sizes. In terms of conduction, phase change materials and thermal paste are clearly superior; however, thermal pads have the advantage of being an inexpensive and convenient option for applications with a lower cooling requirement.
This cost-effective option has been used for a long time. The films are electrically conductive and perform well at very high temperatures up to 500 ºC. Some suppliers align the fibers horizontally. This results in very different thermal conductivity measurements. Thus, there is material that shows on the x-axis with 7.0 W / mK and on the y-z axis with 150.0 W / mK – a significant difference.
Double-sided thermal adhesive tapes
A thermal tape can consist of a finely woven, nickel-coated copper mesh that conforms tightly to irregular mounting surfaces. Thermally conductive double-sided adhesive tapes made of PSA are very commonly used to attach small heat sinks to components. Important factors here are peel strength, overlap and punch shear strength, holding power and thermal resistance. As far as the performance in terms of heat conduction of the double-sided adhesive tapes is concerned, it is in the medium range. There is no need for additional mounting parts, but the tapes have problems with irregular surfaces of the components and are therefore of limited use. For example, plastic ICs are typically concave in the middle, and heat sink surfaces also vary, which can cause air gaps in the interface.
Thermal adhesives – also called heat adhesives – can be either one- or two-component systems. These are equipped with conductive fillers. Application is usually by dispensing or stencil printing. Curing of the adhesive is necessary to enable reliable crosslinking of the polymer, which provides the adhesive property. The fact that the thermal adhesives provide structural support, thus eliminating the need for mechanical clamping, is certainly the greatest advantage of this TIM.
Gels are a similar material to greases, being slightly cross-linked. The behavior is correspondingly similar, with reduced bleeding of the material.
TIMs made of metal
Thermal conductive materials made of metal can be produced in all kinds of forms and are currently no longer limited to applications with soldering. In numerous applications, metal TIMs are very easy to rework and can also be easily recycled.
Application areas of thermal conductive pastes
The main application area of thermal conductive pastes is in the field of electronics. In addition, thermal conductive pastes are used in the following industries, among others:
- IT hardware
- Plastics industry
- Shoe machine industry
- Apparatus engineering and laboratory industry
- Wood machinery industry
- Packaging machinery industry
- Medical engineering
- General mechanical engineering
Due to the expansion of electromobility, thermal conductive pastes are also increasingly entering the automotive sector in the field of power electronics.
Our brochure on thermal interface materials
When it comes to selecting the correct thermal material, many people are unsure of what exactly to look for. In our brochure “Thermal interface materials“, we would like to provide you with all the essentials on the subject of thermal materials.