The interface between the components and the heat sink is one of the most critical factors in determining system thermal management performance. Standard machined surfaces are often rough and wavy, leading to multiple insulating gaps that fill with air of low thermal conductivity. Thermally conductive gap pads can improve performance by filling these gaps and promoting good contact between mating surfaces.
There are a variety of thermal gap pads available, each with its own unique properties and advantages. Some of the most common include gels, greases, thermal tapes and shaped pad materials.
Gels are a relatively new TIM option that offer fluidic properties and a high level of flexibility. Generally easy to work with at room temperature, they soften when heated and flow into the micro-gaps to reduce the interfacial resistance. However, this flexible nature may make them more susceptible to pump-out during vibration or thermal cycling.
Greases are the oldest class of TIMs and are generally easy to work with. They are used to fill the microscopic air gaps in a gap-filling application and can be augmented with metal particles for improved performance. They are more sensitive to voids and pump-out than other TIMs, but can provide significant improvements in performance.
Adhesives are a sometimes overlooked TIM option that can offer superior mechanical bonding to minimize vibrations. Usually epoxy or silicone based formulations with fillers, they can also help to reduce the overall size and weight of the assembly. Although they can be difficult to rework, they offer the benefit of a compact package and a good thermal interface with long term reliability. Thermal Interface Material