Preparation of solder bumps incorporating electroless nickel-boron deposit and investigation on the interfacial interaction behaviour and wetting kinetics

Investigation of a method for preparing solder bumps on Al pads incorporating electroless nickel deposition and soldering for solder bumps was undertaken. The experimental variables included bath temperature and dipping velocity. The formation of intermetallic compounds and wetting kinetics between electroless Ni-B deposit and molten solder was also investigated. The interfacial interaction behaviour was studied with the aid of Auger depth profile and scanning electron microscopy. Intermetallic compounds Ni3Sn4 and Ni3Sn2 were formed between the Ni-B deposit and solder. Aluminium atoms diffuse through the intermetallic compound layer and dissolve in the solder when the electroless Ni-B deposit is entirely consumed. The contact angles of molten solder on a Ni-B deposit, measured with the sessile drop method, decrease with increasing temperature and time. The activation energy for wetting of molten solder on a Ni-B deposit was estimated to be 208.27 kcal mol(-1).