In this study, the interface reactions between eutectic SnPb solder and two Ni-based UBM systems are reported, namely the sputtered Cu/Ni(V)/Al and the electroless Au/Ni(P) systems. Comparisons are made to the conventional Au/Al ball bonding system in terms of microstructure evolution, and metallurgical stability. TEM sample preparation is critical in this analysis. The capability of TEM in UBM microstructure studies is demonstrated.

The presence of gold within a Sn/Pb solder joint accelerates diffusion between the Sn and Ni of the Ni- V/Cu underlying bump metallurgy (UBM), generating early failures. A concentration of 1.2 wt% gold in the solder joint can accelerate time to failure by a factor of 400 [3]. The EDS x-ray microanalysis detection limit for gold in tin / lead solder of about 1.2 wt% gold was found to be above the concentration range of interest (0.1 – 0.5 wt% gold). Due to the reliability impact that even a low concentration of gold can have on solder joints employing Ni-V/Cu UBM, a method using differential scanning calorimetry (DSC) was developed to accurately measure gold concentrations of less than 1 wt% in solder bumps.

Very highly purified water such as De-ionized (DI) water tends to become very corrosive once exposed to the atmosphere. This “Hungry Water” as known in the water purification world is known to be a major source of corrosion [1]. The DI water was responsible for corrosion of tin during autoclave (pressure cooker) testing of Integrated Circuit (IC) devices assembled in plastic Quad Flat Package (QFP) with fine pitch leads. The copper leads of these packages are plated with solder. The copper leads of the packages are plated with solder composed of Lead and Tin. Due to the effect of corrosive water, Tin from solder corroded during the autoclave testing and formed thin whiskers of solder. These whiskers created a leakage path between the leads causing the devices to fail for pin to pin leakage.