Gold/tin soldering of flexible silicon chips onto polymer tapes

A novel method for biocompatible gold/tin soldering of ultrathin silicon chips onto flexible polyimide tapes is presented. Apart from substantial weight and volume reductions, flexible silicon chips enable the fabrication of flexible microsystems with the advantage of good adaptability to the geometry of the place of use. Silicon chips with thicknesses between 16 and 25 µm were fabricated and bonded onto 5 µm thick polyimide tapes using eutectic Au80Sn20 solder. The contact resistance per bond was of the order of 1 mΩ. A finite element method (FEM) model predicts deformations in the soldered system with an accuracy of ±13%.