Rheology and Processing of Ni Based Nano-Composite Pastes for Electronic Assembly

Abstract

Lead-free solder paste printing process accounts for majority of the assembly defects in the electronic manufacturing industry. In the stencil printing process, the solder paste must be able to withstand low and high shear rates, which results in continuous structural breakdown and build-up. The study investigates the effect of nickel additional to the thixotropic behaviour of lead-free Sn/Ag/Cu solder pastes using the structural kinetic model. A hysteresis loop test and constant shear test is utilized to investigate the thixotropic behaviour of the pastes using parallel plate rheometry in temperature 30 oC. In this study, the shear rates were increased from 0.01 s-1 to 10s-1 and the second curve was a result of decreasing shear rate from 10s-1 to 0.01s-1. For the constant shear test, the samples were subjected to two constant shear rates of 0.1s-1 and 1s-1. The constant shear rate test was designed to study the structural breakdown and build-up of the paste materials. From this investigation, hysteresis loop test was shown to be an effective test method to differentiate the extent of structural recovery in the solder pastes. The results of the structural parameter values obtained from the kinetic model showed a good correlation to the breakdown and build-up of the paste structure.