Fabrication and Characterization of Double Helix Structures for Compliant and Reworkable Electrical Interconnects

Microelectromechanical systems (MEMS)-type double helix chip-level electrical interconnect structures are fabricated and characterized in this paper. Due to their springlike structure, double helix interconnects have the potential to provide large mechanical compliance to compensate for nonidealities, such as nonplanarity and thermal expansion mismatch between silicon chips and substrates. A double helix configuration provides for structures with a high volumetric density of conductor for enhanced current carrying capability. The fabrication process is compatible with wafer-level fabrication and packaging. Instead of using solder to form semipermanent interconnections, the double helix interconnects use pressure to make electrical connection and provide sufficiently low resistance (~35 ± 15 mΩ). Large arrays of double helix structures have been fabricated and characterized with excellent yield. The mechanical and electrical models of the structures are presented. Reworkability tests were performed and the structures show a consistent resistance over 50 remating cycles.