Effect Of Sm On Microstructures And Properties Of SnAgCu Solder

With the development of utilizing electronic packaging technology, micro lead-free solder joints has become the main topic in the electronic packaging area. Sn-Ag-Cu is recognized as the best product to take the place of traditional solder and putinto practice because of its low melting point and high reliability. But we can stillfind its weakness in its application. Then the addition of the forth small amount ofalloy element has become an efficient way to improve the solder’s property.To improve the property of Sn3.0Ag0.5Cu, small amount of Sm is added. Thisreport studied Sn-3.0Ag-0.5Cu-XSm（X=0,0.025,0.05,0.1,0.2wt.%）property,micro structure, and shear strength systematically, and analyzed Sm.Different Sm amount’s influence on SnAgCu melting temperature is studied.The results show that certain Sm’s addition can decrease SnAgCu’s melting point.With the increase of Sm, SnAgCu’s melting point will increase after decreasing. Thelowest melting point comes when Sm takes up0.1wt.%in the solder, which is217.19℃.Different Sm amounts’ influence on SnAgCu wetting property is studied byspreading area. The results show that certain Sm can improve SnAgCu’s wettingproperty. The best wetting property comes when Sm is0.05wt.%, but because ofSm’s oxidizing, too much Sm can decrease the wetting property.Different Sm amounts’ influence on interface morphology and thickness ofsolder’s IMC are studied before and after ageing. When Sm is0.05%, IMCmorphology turns to be plain. The transition between solder and IMC is ease. WhenSm is0.025-0.1%, IMC is thin. After ageing, the interface with Sm is plainer thanthe interface without Sm. With the increase of Sm, the interface’s thickness willincrease after decreasing. With Sm in the solder, the growth of IMC’s thickness issmaller after ageing.Different Sm amount’s influence on1000μm lead-free micro-solder’s shearing strength on PCB board is studied and ageing experiments for400h isconducted. The results show that, when Sm is0.05%, shearing strength reaches thehighest before ageing. After ageing, with Sm’s increase, shearing strength willdecrease after increasing. With Sm, the solder’s shearing strength reaches the highest.