What does Thermal Interface Material do?
This is where using thermal interface material comes in. TIM replaces most of these air pockets with a material optimized for better thermal conductivity. By using thermal interface material, we increase how much heat is transferred away from the heat source and into the heat sink.
In the diagram below, dark blue represents thermal interface material. Most of the light blue air pockets have been eliminated and replaced with a more conductive material. Heat is now efficiently conducting across the entire surface. This improves heat transfer away from the heat source significantly. It’s nearly impossible to remove 100% of air in most cases so there are still small air pockets in little nooks and crannies. But the thermal performance in this instance is greatly improved to the scenario with no TIM present.
Thermal interface material comes in many different formats and options: electrically isolating or electrically conductive, silicone base or silicone free, compliant or hard, solid or liquid or both, etc. TIM selection is a very application specific decision.