Thermal pastes are known by many names, thermal grease, thermal compound and CPU grease to name a few. All of these are essentially the same thing, they are all substances that are used to promote better heat conduction between two surfaces. They are commonly used in computers and electronic equipment between microprocessors and heatsinks.
Before you buy a thermal compound though it is worth understanding in mind that there two different types of thermal compound. These are;
Conductive -These include silver, copper and Aluminium based compounds. These are not ideal for circuit boards and CPU's.
Non-conductive - These are silicones and zinc compounds. These are ideal for CPU's.
How do they work?
The top of most microprocessors are not flat, some have small grooves and others may even be curved, this allows for air gaps which reduce cooling performance of the heatsink. By applying a thin layer of thermal grease you fill these gaps making for better cooling performance.
Above diagram shows how a thermal paste is used.
Conclusion: Why do I need to use one?
When working with items like microprocessors and heatsinks cooling performance is crucial to how the heatsink performs. In computers thermal pastes are a pivotal part of cooling by helping with the transfer of heat between the CPU and the CPU cooler.