Flip-chip bonding of fine-pitch ultra-thin chips for SiF applications

This paper describes the successful process investigations on ultrathin flip-chip bonding for fine-pitch applications on foil, using a novel bonding process involving Isotropic Conductive Adhesives (ICA). A Ag-based B-stage curing ICA was printed using state-of-the-art electroformed stencil on printed Ag circuitry, pre-cured and flip-chip bonded at low bonding force and short duration. The interconnection resistance measurements, performed before and after a stabilizing underfilling step, revealed low interconnect resistances down to 150 μm bond pad pitch. Finally, the reliability of the specimens prepared using this process was successfully evaluated by means of standard reliability test procedures such as thermal shock testing and accelerated humidity testing.