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Display Omitted Co-Sn intermetallics growth is faster than Cu-Sn IMC which is faster than Ni-Sn IMC.Co-Sn intermetallics growth is inhibited by the presence of Cu dopants/additives.Co oxides are cleanable with Ar/H2 microwave plasma or Rosin-based soldering fluxes.CoSn2 and CoSn3 IMC phases were confirmed with Energy Dispersive X-ray Spectroscopy.CoSn3 IMC's are ~20% more compliant and ~30% softer than Cu-Sn IMC's. Cobalt exhibits good wetting by lead-free solders (Humpston, 2010) 1], generates Sn-rich intermetallic compounds (IMC's) and has lower dissolution in solders than Cu and Ni, thus potentially being a more effective solder diffusion barrier with improved electro- and thermo-migration resistance in interconnect applications (Ishida et al., 1991; Okamoto et al., 2006; Wang et al., 2013; Kanatzidis et al., 2005; Liu et al., 2004; Labie, 2007) 5-7]. In this work, we extend prior data (Vakanas et al., 2013; M.O. et al., 2012; Vakanas et al., 2014) on formation, processing, characterization and quantification of Co-Sn IMC phases generated upon deposition, reflow and aging of electroplated and solder paste screen printed samples. Cobalt oxides growth (vs. Cu) was characterized by X-ray Photoelectron Spectroscopy (XPS) as a function of multiple reflows. Cobalt oxides cleaning by microwave Ar/H2 plasma was also demonstrated. Co-Sn IMC growth rate (vs. Cu-Sn and Ni-Sn) was quantified after one reflow cycle and aging in solid-state temperature range of 180-220?C. Relevant kinetic parameters were calculated assuming a diffusion-driven, parabolic growth model. IMC phases were identified by Energy-Dispersive X-ray Spectroscopy (EDS) verifying Sn-rich Co IMC's. Young's modulus (E) and hardness (H) were measured by nanoindentation indicating that Co-Sn IMC's are more compliant and softer than Cu-Sn IMC's. Implications of the findings for material selection in 3D micro-bumping and stacking integration are discussed with a future outlook and recommendations to improve interconnect reliability.

The aim of the research described in this paper is to develop a low-cost, roll-to-roll compatible process for the realization of electronic systems in foil using chip embedding. The small cost makes these systems suitable for disposable applications as food labels, medicine packages or smart bandages. Surface mount attaching of components on foils is a well-known process for building systems-in-foil. When using low-cost films like PEN and PET, there are serious restrictions on the maximum temperatures that can be used for the surface mounting process (soldering, adhesive bonding). Surface mounting has the additional disadvantage that the components are on the surface of the foil and are therefore not well protected mechanically and physically. The proposed process flow for embedding thin chips in PET foils overcomes these limitations. A key aspect of this technology is the application of a suitable adhesive to encapsulate the chips. The resulting product is based on full-metal copper which has a good thermal and electrical conductivity and allows for fine pitches. The process is compatible with several metal foils (Cu, Al …), offering further possibilities in cost reduction, and does not rely on bumping of the chips or plating of the interconnections to the chips.