Investigation of low cost flip chip under bump metallization (UBM) systems on Cu pads

Cu is considered as a promising alternative interconnection material to Al-based interconnection materials in Si-based integrated circuits due to its low resistivity and superior resistance to the electromigration. New bumping and UBM material systems for solder flip chip interconnection of Cu pads were investigated using electroless-plated copper (E-Cu) and electroless-plated nickel (E-Ni) plating methods as low cost alternatives. Optimally designed E-Ni/E-Cu UBM bilayer material system can be used not only as UBMs for solder bumps but also as bump itself. Electroless-plated E-Ni/E-Cu bumps assembled using anisotropic conductive adhesives on an organic substrate is successfully demonstrated and characterized in this study.