Multi-scale study of the electrical properties of organic layers grafted on gold surfaces

Many studies have been performed on the corrosion and fretting degradation mechanisms of gold plated contacts for low level applications. Reliability requirements constantly increase and finding new solutions able to postpone degradations is still a challenge. A large study has led to the elaboration of a fluorinated organic film grafted to the surface and allowing outstanding protection of the gold surfaces. These organic films involved new thiol functionalized perfluoro polyethers, deposited as mixed layers. Back-panel connector systems coated with various fluorinated organic films were submitted to a four gases corrosion test (Bellcore uncontrolled environment test). High values of the contact resistance Rc were found for the contacts coated with some of the films. The present study is aimed at understanding the electrical properties of these films. The electrical behavior of model contacts (dimple on flat) was investigated in static and in dynamic modes. Fretting experiments showed the combined influence of friction and of the surface roughness. Finally the electrical properties were investigated at a more microscopic scale. An experiment performed with a modified AFM microscope with a conducting probe (CP-AFM) showed the particular behavior of functionalized PFPE lubricant on gold. Results are discussed in order to have an insight into the conduction mechanisms involved.