Contact properties of Ni micro-springs for MEMS probe card

We have developed MEMS probe cards consisting of micro-springs arranged in a 250-μm-pitch array. Three-dimensional spring structures were designed and Ni micro-springs were directly fabricated on a circuit board by a multi-layer electroplating process. ´S shaped´ springs consisting of seven electroplated layers and ´folded lever´ springs of five layers were designed and fabricated. Mechanical properties of the micro-springs were measured and no fracture or deformation were found after applying force of 10 mN for 10,000 times to 7-layer springs, while deformation of 1 μm were found in 5-layer springs. Low force electric contacts of smaller than 5 Ω for Al, and 3 Ω for Cu electrodes were obtained. Difference of the contact resistance in different types of spring structure was found.