Material interactions of solder bumps produced with fluxless wave soldering

A fluxless wave soldering process was attempted for producing solder bumps of 100 /spl mu/m/spl times/100 /spl mu/m, on silicon wafers containing 8/spl times/8 chips with 20/spl times/20 bumps on each chip. The solder bump structure, Al/Mo,(Mo-N)/Pd/Pb-Sn, was produced by fluxless wave soldering. The sputtering deposited Mo or MoN film was applied as a diffusion barrier between Al and solder. The Pd layer, also produced by sputtering deposition, was applied for wetting purposes. Interactions between materials during wave soldering and subsequent heat treatment of this structure were investigated. The interactions, investigated using SEM and XRD, within the multilayers occured rapidly between Pd and solder elements during wave soldering.