Effect Of La Addition On Interfacial Reaction And Properties Of Sn0.3Ag0.7Cu Solder

With the improvement of brazing technology and progress of people's environmental protection consciousness, Which exploiting ideal cost and property of the new green lead-free solder had become a hot study. The good performance of SnAgCu solder had the most promising alternative to SnPb solder alloy, but widely used SnAgCu Pb-free solders still have some deficiency such as relatively high melting point, poor wettability, etc. The paper was based on Sn0.3Ag0.7Cu low silver solders, then adding element La (0⁰.25wt%) to alloys system study solder microstructure, melting properties, wettability, grain morphology growth rate in the interfacial IMC and shear performance.The results showed that melting point of Sn0.3Ag0.7Cu almost unchanged with the La content changing, the melting range minimum when w(La) was 0.05%. In addition, the appropriate La adding in SAC0307 solder made spread area lager, better surface quality and enhanced wettability of solder joints. At the same time, a little addition of La could refine the microtructure of SAC0307 solder alloy, Sn dendrite fractal addition polymerization resulting in secondary dendrite spacing reduction, promoted the development of high-dendrite by deepening constitutional supercooling. Adding 0.25% to SAC0307 solder alloy could form primary LaSn3 dendrite phases gathered in the grain boundary.The analysis of variation regular pattern of the interface IMC in SAC0307-xLa/Ni and SAC0307-xLa/Cu indicated that the total IMC thickness increased with aging time,and decreased as increasing La content under the same aging condition. On the Ni pad, the IMC (Cu_1-xNi_x)₆Sn₅ was storm-like. After aging, SAC0307-xLa/Ni interface IMC is (Cu_1-xNi_x)₆Sn₅ the morphology of IMC transform jagged to storm-like. SAC0307-xLa/Cu interface IMC after reflowing is Cu6Sn5, after aging 96h, a new Cu3Sn layer appears between Cu and Cu6Sn5. The thickness of IMC and the growth rate are smallest of all at aging process when adding 0.07Lawt.%.According to jointing strength tester PTR1100 analysis shear strength SAC0307/Cu adding to elements La. The results showed that the shear strength of Sn0.3Ag0.7Cu-xLa/Cu decrease along with increasing of aging time and rises then decreases with the increasing of La content, when it is 0.07 La wt%, the shear strength is still highest. The fracture types of solder joint change from ductile fracture to ductile-brittle fracture SAC0307-xLa/Cu. The fracture position of solder joints changes from solders to between sloders and IMC. Solder joint shear strength with a significant volume of solder volume effect. The shear strengths of SAC0307/Cu after as-reflowed solder joints decrease with increasing the solder joints volumes.