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Thermal interface materials (TIMs) are generally thermally conductive and used in the construction of electronic and optical devices in order to provide a degree of heat transfer between dissimilar surfaces. TIMs in thermal management applications can reduce the size and weight of heat sinks or heat spreaders, and can also reduce airflow constraints for cooling fans. The use of TIMs in chip packaging is an emerging technology that promises to address current limitations, such as insufficient thermal conductivity and low mechanical durability.
Thermal interface material manufacturers offer a wide variety of materials with different requirements for usage. The user should be aware of the key characteristics in order to choose the right product for the job. This paper is intended to give a broad overview of TIMs and their various uses, with an emphasis on how such materials influence semiconductor device performance. (The authors gratefully acknowledge the contributions from members of Dow Electronic Materials’ Thermal Interface Material group.
Types of thermal interface materials
There are a large variety of thermal interface materials available but a few of them are listed below:
Thermal grease
Thermal grease is typically made up of particles in a thermally conductive base fluid, mixed with processing aid chemicals to achieve the desired viscosity. Viscosity reduction can be achieved by adding larger particles or incorporating fillers into the base fluid. Fillers are inert particles that provide bulk and do not actively take part in the thermal conductivity of the grease. Fillers are typically metal oxides but fumed silica particles are also used in some greases.
Grease ingredients can be subdivided into two categories: thermally conductive particles and viscosity-reducing chemicals.
Thermally conductive particles
The thermally conductive particles in thermal grease also called “thermally conductive fillers” or simply “conductive fillers”, are the main ingredients that contribute to the thermal conductivity. Their primary function is to move heat; they do not rely on fluid for this process (whereas, for instance, copper and alloys of beryllium and magnesium do).
Thermally conductive particles can be divided into two general groups: metal-based and ceramic-based. Metal-based particles typically consist of metallic powders such as silver, aluminum, gold, and copper alloy with traces of other elements to improve processing properties. Ceramic-based particles include boron nitride, alumina, and diamond.
The choice of thermally conductive particles varies depending on the application requirements. With regard to size distribution, in general, metal-based particles are available in a much wider particle size range than ceramic particles; however, ceramic materials can achieve very low bulk densities (by adding very small-sized fines). Also, ceramic materials tend to offer better wear resistance.
Surface treatment is used to increase particle adhesion, wettability, or lubricity of the particles with the base fluid. The surface treatments include adhesive coatings (e.g., using organofunctional silanes), shape anisotropy (i.e., spherically shaped or cylindrical particles), and ion implantation.
Viscosity-reducing chemicals
The viscosity-reducing chemicals provide the bonding mechanism between the thermally conductive filler particles and base fluid. These chemicals can be divided into two groups: reactive (curing agents such as organofunctional silanes or anhydrides) and non-reactive (e.g., polydimethylsiloxane).
The viscosity-reducing chemicals can also be divided into two subgroups based on the functionality of the base fluid: reactive or non-reactive. Reactive fluids must be cured with a curing agent, which will react with the fluids and thicken the base fluid. The most commonly used reactive fluids are based on anhydrides or silicones. However, reactive fluids do not possess good thermal stability at high temperatures. Non-reactive fluids will not react with the curing agent and thus give the advantage of excellent thermal stability over a wide range of temperatures; however, the base fluid must be chosen carefully as thermal stability, volatility and other process requirements can vary significantly from application to application.
Why you should use a thermal interface material in your system:
If your computer or other electronic equipment is producing an excessive amount of heat it has the potential to shut itself down in order to save itself from damage. An overheated computer can cause significant and sometimes irreversible damage such as warping motherboards, melting plastic, and even melting circuit boards. This is especially true for gaming computers or media centers with powerful graphics cards and processors.
If your computer or other electronic equipment is producing an excessive amount of heat it has the potential to shut itself down in order to save itself from damage. An overheated computer can cause significant and sometimes irreversible damage such as warping motherboards, melting plastic, and even melting circuit boards. This is especially true for gaming computers or media centers with powerful graphics cards and processors.
Conclusion:
Choose the right thermal interface material for your project by knowing what it is supposed to do and what you want out of a good thermal solution. Read about the different types of materials available on the market, learn what they are made from, how they work with your system, and see if any have been used in similar applications that might inform your choice.
