Oscillatory and Creep Recovery Test on Nano-Composite Lead-Free Solder Pastes (Nickel and Platinum Powder)

This study investigates the relationship of rheological properties of nanoparticles added to lead-free solders paste. For lead-free solder paste, a large number of combinations can be made from different elements. Every ingredient plays a role of the paste and the rheological properties. The effect of filler concentration was studied in this present investigation. Creep recovery, stress is applied on samples for a period of time and later release in order for it to recovery itself. In the other words, creep recovery involves a tensile specimen under constant load maintained at a constant temperature. Oscillatory tests were carried out to study the visco-elastic behaviour and paste stability. The visco-elastic behaviour of the paste lies between solid and liquid characteristic of the paste, which could be used to study the flow behaviour of paste during stencil printing process. From this study, it was found that the solid characteristic, G' is higher than liquid characteristic, G'' for all the samples. In addition, the results from the study showed that the 0.06 volume fraction sample system with a large yield point which G'= G'' has a higher cohesiveness and hence resulting in poor withdrawal of the paste during stencil printing process. The phase angle, δ was used to correlate the quality of the dense suspensions to the formulation of solder paste materials. Lower value of phase angle for 0.06 volume fraction sample system may indicating that the paste is very tacky compare to the other samples. As the demand for lead-free pastes increases rheological measurements can assist with the formulation of new pastes.