NiW-micro springs for chip connection

The characterisation of planar electroplated NiW micro springs for temporary connection of Flip Chips is presented. Four micro spring types with different properties were designed. FEM-analysis was used to simulate the spring characteristics for a force of 20 mN at a vertical displacement up to 50 μm. Micro springs were fabricated using electroplating of NiW and a sacrificial copper layer etching process. Three versions of elliptically shaped contacts elements with self-alignment capabilities for Flip Chip bumps were realised on top of the micro springs. At the required contact force of 20 mN a contact resistance of 400 mΩ was observed using a Au80Sn20 solder ball as a probe.