Nickel-based surface finishes offer a major benefit in terms of inhibiting copper dissolution. Palladium-enhancement has been shown to improve Ni-based surface finishes for substrate and PWB applications; Based on these investigations, NiPd was found to achieve equivalent performance to NiPdAu by: Improved reliability demonstrated by both high-speed ball shear and cold ball pull investigations, Reduced nickel corrosion and formation of desired IMCs; Thickness of the palladium deposit is critical to achieve performance Improvements; The presence of (Cu, Ni)6Sn5 IMC correlates directly to the occurrence of interfacial fracture of nickel-based surface finishes; Test vehicle design is critical to evaluating solder joint reliability by high-speed shear and cold ball pull test metrologies; High-speed shear and cold ball pull test results reflect physical and mechanical relationships that are strongly influenced by: Shear and pull speeds, Ball diameter and solder resist opening, Solder volume : pad area ratio, Solder alloy properties, Time delay from reflow until testing; Changes to any one of these parameters may cause significantly different results, particularly in terms of failure mode; The investigations presented in this paper are part of a continuing comprehensive DOE focused on enhancement of surface finishes for high-density first and second level interconnects.
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