Abstract
Addition of lead into tin based solders represents a serious health risk and environmental problem. Lead-free solders represent one of the ways to remove pollution of lead into environment, nevertheless, new advanced joining methods have to be considered. Aggregation effect of nanoparticles studied in this work seems to be an interesting alternative. It was found experimentally that Ag nanopowder annealed at temperatures above silver oxide decomposition forms continuous Ag layer and yields a firm junction between copper plates. Oxide layer is observed at the Cu-Ag interface. The oxide interlayer thickness reflects the temperature and annealing time. Microstructure of prepared experimental joints, composition profiles and local mechanical properties were studied on cross-sectional samples by analytical electron microscopy and depth-sensing indentation technique.
Highlights
Lead containing materials represent health risk and serious environmental problem
The silver nanoparticles were investigated by means of DSC technique in slightly oxidizing 4.7N Ar atmosphere
Three groups of indentation response curves corresponding to Cu, Cu2O and sintered nano-silver layer are clearly distinguishable at low indentation loads on both samples
Summary
Lead containing materials represent health risk and serious environmental problem. Electronic devices are remarkable sources of lead pollution. Since 2006, when regulations enforcing lead-free solders were implemented into the EU legislation, there is an ongoing strong drive to find the best lead-free solder alternatives Those presently used have often reliability problems caused by worse mechanical properties, higher tendency to oxidation, higher occurrence of undesirable intermetallic phases and higher melting temperature. The use of environmentally friendly nano-sized metallic particles [8,9] as a solder material seems to be very promising because this green nanosolder can melt at low temperature (best at temperature close to melting temperature 183oC of Pb-Sn eutectic solder) and form a stable joint, which can be used up to bulk melting. The source can be oxidation or addition of soldering flux They disable growth of melted metal nano-sized particles and formation of bulk and joint with the substrate. This effect does not vent itself in the case of silver, which is in the focus of the presented paper
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