Hermetic chip-scale packaging using Au:Sn eutectic bonding for implantable devices

Abstract: Advancements in miniaturisation and new capabilities of implantable devices impose a need for the development of compact, hermetic, and CMOS-compatible micro packaging methods. Gold-tin-based eutectic bonding presents the potential for achieving low-footprint seals with low permeability to moisture at process temperatures below 350\degree C. In this paper, a method for the deposition of gold-tin eutectic alloy frames via sequential electroplating from commercially available solutions, with no special fabrication process, is described in detail. Bond quality was characterised through shear force measurements, scanning electron microscopy, visual inspection, and immersion tests. Characterisation of seals geometry, solder thickness, and bonding process parameters were evaluated, along with toxicity assessment of bonding layers to the human fibroblast cells. With a successful bond yield of over 70\% and no cytotoxic effect, AuSn eutectic bonding appears as a suitable method for the protection of integrated circuitry in implantable applications.