Effect of particle size distribution (PSD) and flux medium on the creep recovery performance of lead-free solder pastes

Purpose - The purpose of this paper is to investigate how the formulation of a solder paste (with regards to the flux and particle size distribution (PSD)), can influence its creep and recovery performance.Design methodology approach - New lead-free paste formulations were characterised utilising viscometry and oscillatory methods, after which creep recovery investigations were conducted to determine the recovery performance. Measurements were recorded using a rheometer with a parallel plate geometry of 40 mm and a sample height of 1 mm.Findings - Results from the study highlighted that the formulation of a solder paste can have a significant impact on the creep recovery measurements. Variations in flux and PSD highlighted a considerable difference in the recoverability of the solder pastes, in one instance demonstrating more than a 20 per cent increase in structural recovery.Research limitations implications - More extensive research is needed relating to reduced PSDs, such as type 6 and 7 solder pastes, to fully understand their influence on the creep recovery performance.Practical implications - The results presented in this paper emphasise important information and investigational methods for research and development, and quality control.Originality value - The paper highlights how the composition of new paste formulations can influence the creep recovery behaviour. It was found that the recoverability can be increased by careful selection of the flux and PSD, which in turn could reduce slumping influences in the print process. If used as a quality control tool, this paper may allow for the reduction in print defect occurrence.