Influence Of Trace Rare-earth On Properties And Structure Of SnAgCu Lead-free Solders

SnPb solders have been widely used in electronic packing industrybecause of many benefits, such as low cost, low melting temperatures, excellentductility and wetting properties. However, in respect of environmental and healthconcerns, the EU has issued banning mandate which prohibit the use of lead andsome other hazardous materials in household electrical appliances since July1,2006,significant research of Lead-free solder is in use stage. SnAgCu Lead-free solderalloys are expected to be one of the most promising alternatives of SnPb solderalloys due to the excellent mechanical properties. Taking Sn0.3Ag0.7Cu andSn1.0Ag0.5Cu Lead-free solders that added trace rare earth element Ce, Er and Y asthe research object, study on the influence of different rare earth element on thephysical properties, mechanical properties and antioxidant. Effects of different rareearth on the wetting properties were studied by the spreading test. Finally observedand analyzed their microstructures by SEM.The results show that the doping of rare earth element has a little effect on thedensity and melting temperature of Sn0.3Ag0.7Cu and Sn1.0Ag0.5Cu Lead-freesolders. The spreading area, shear strength and antioxidant of soldered joints can beimproved by adding small amount of rare earth element. With the increase of rareearth element content, the microstructure of the solder alloy was fir-tree crystal toequiaxed crystal and refined. According to the testing on the properties, the mostsuitable content of rare earth in SnAgCu solder is within0.05～0.15wt%. As shownin the testing results, the rare earth Cerium can improve the composite properties ofSnAgCu Lead-free solder better, followed by Er, the effect of rare earth Y on theproperties of solder is not obvious.The microstructures of Sn0.3Ag0.7Cu and Sn1.0Ag0.5Cu solders with differentrare earth were analyzed by means of SEM. The results show that theMicrostructures can be refined and the intermetallic compounds can be suppresseddue to the adding of small amounts of rare earth. The microstructures of solderedjoint were further analyzed by using SEM. It is turned that adding small amount ofrare earth to the Lead-free solder, the mechanical properties of the soldered joint are enhanced by refining the microstructure. But mechanical properties of the solderedjoint are decreased.