Time-dependent thixotropic behaviours of lead-free Sn-Ag-Cu (SAC) solder pastes and flux mediums used in electronic assemblies
AbstractSolder pastes are widely used as crucial joining material in microelectronic assemblies. This study investigates time-depended behaviours of paste materials (solder pastes and flux mediums) in relation to their transportation, storage, handling and applications. Two fluxes and four commercially available lead-free solder pastes prepared from those fluxes were evaluated. Two rheological test methods – ‘hysteresis loop test’ and ‘step shear test’ were adapted, taking account of actual shear profile of solder pastes and flux mediums. Within hysteresis loop tests, samples were sheared for both single and multiple cycles, with increasing and decreasing shear rates. These tests provided a quick and straightforward way of benchmarking time-depended structural breakdown and build-up of paste materials. The test results also provided an effective means of predicting how the pastes will behave during their use, such as at various stages of the stencil printing process. Step shear tests were performed by applying a sequence of stepwise increase in shear rates. The step-wise increase in shear rate has influenced the timedependent behaviours of solder paste samples and flux mediums. The result from the stepshear-test implies that the build-up of solder paste structure depends mainly on both the previous shear history and the intensity of structural break-down.
CitationMallick, S., Ekere, N. and Depiver, J. (in press) Time-dependent thixotropic behaviours of lead-free Sn-Ag-Cu (SAC) solder pastes and flux mediums used in electronic assemblies, Journal of Materials Science and Engineering B.
JournalJournal of Materials Science and Engineering B
DescriptionThis is an accepted manuscript of an article published by David Publishing in Journal of Materials Science and Engineering B (in press). The accepted version of the publication may differ from the final published version.
Except where otherwise noted, this item's license is described as https://creativecommons.org/licenses/by-nc-nd/4.0/