Ion track lithography: novel low-cost process to form deep vertical and high aspect ratio MEMS in flexible laminates

High aspect ratio microstructures are today of utterly importance in MEMS. The process described in this paper can be used to produce deep, vertical microstructures in polyimide based materials, used in e.g. flexible printed circuit boards (FPCBs). Stacked polyimide and metal layers have the potential of integrating microelectronic circuits with above applications. The process is capable of producing regions with perpendicular sub-micron metal wire connections at numerous, arbitrarily specified locations. The flexible laminate is irradiated with heavy ions creating a vertical damage anisotropy (ion tracks) in the polymer layer. Lithographically defined apertures in the metallic layer define the geometry. The tracks exposed are selectively developed forming nanometer-wide pores. Metallic structures have been replicated in these pores by electrodeposition of metals. Demonstrator microstructures and highly vertical, through hole microvias have been fabricated. Ion track technology is promising for ultra-high density via batch production and has a potential of further miniaturizing via dimensions.