Thermal grease, or thermally conductive adhesive, is used in the semiconductor industry to assist a heat sink to draw heat away from semiconductor components like transistors or integrated circuits. The thermal grease fills air gaps that occur when a heat generating component is pressed against the surface of a heatsink. Surface imperfections come from the limitations of the mechanics of the manufacturing process and can be anywhere in size from visible flaws like casting irregularities, to sub-microscopic flaws invisible to the naked eye.
Thermally conductive adhesives and greases work in part because they conform to the surface. They are useful in any electronic application in which heat is generated. However, excess thermally conductive adhesive or grease will degrade conductivity and actually increase the risk of overheating. Also, over time, some thermal grease will dry out, reducing their heat sinking capabilities, and making removal difficult.
Composition of Thermally Conductive Adhesives
Thermally conductive adhesives are made of polymerizable liquid matrix and large volume fractions of electronically insulating, thermally conductive filler. Some of the matrix materials typically used are epoxies, silicones, urethanes and acrylates, while most thermally conductive adhesives use silicone as a medium, which itself is a heat conductor. Thermal greases and conductive adhesives are ideal primary interface materials.
The Role of Thermal Phase Change Material
Thermal phase change material is used in cases where increased thermal management is desired. Like thermally conductive greases and adhesives, it works excellently on non-uniform surfaces, like substrates with multiple chip packages.
Thermal phase change material, or PCM, conducts heat in a more complex manner. A thermal phase change material is a substance with high heat fusion. It solidifies and melts at specific temperatures, and has the capability of storing and releasing energy. Heat is conducted—stored or released—when the material changes form. They are therefore considered latent heat storage units.
Thermal Phase Change Packaging
Thermal phase change materials work best in small containers and so are usually divided into cells. However, the packaging material should conduct heat well and be durable enough to withstand volume changes in the cell as the phase changes occur. The packaging must also resist corrosion and leakage. In fact, it should restrict andy water passage through the package walls. If the phase change material looses water it will dry out, or water out if the material is hygroscopic. PCM are being used in thermal regulation of electronics.