Comparison of Differential Scanning Calorimetry and Energy Dispersive X-ray Microanalysis for Measuring Low Gold Concentrations in Sn/Pb Solder Bumps

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.