Modifiable Silicones for Harsh Environments

Abstract

Silicones have been used for decades in aerospace and other harsh environments where temperature extremes are common. As the level of sophistication increases for electronic devices to serve these industries where failure is not an option, the material supplier has to also be able to meet these needs. Silicones are polymeric materials composed primarily of repeating silicon and oxygen bonds, known as siloxanes, which can be optimized for various chemical and physical properties by incorporating different organic groups onto the silicon atom. Employing advanced processing techniques to the siloxane system can also greatly reduce mobile siloxane molecules to reduce contamination that can cause electronic failures during assembly or operation. Siloxane based polymeric systems are also unique polymers compared to standard organic based materials in that they have a large free volume that imparts a low modulus which absorbs stresses during thermal cycling as well as not degrading at continuous operating temperatures up to 250 C. They are also slightly polar which allows the incorporation of fillers to impart a variety of unique properties. Filler technology is also a rapidly growing enterprise where fillers with various particle sizes and shapes can be added to silicones to impart key properties such as maintaining electric conductivity at elevated temperatures. This paper will explain fundamentals of silicone chemistry and processing related to getting the optimal performance in harsh environments. A case study comparing two different electrically conductive fillers and how they can influence the electrical conductivity at elevated temperatures will be presented.