Effect Of Cu Content On The Interfacial Reaction And Mechenical Properties Of Low-Ag Lead-free Brazing

As the connection material of electronic components, solder plays an important role on electrical connection among components. SnAgCu Pb-free is considered the best solder which can replace Sn-Pb solder because of its good performance, but there are some problem in application though. So, improving the performance of solder by adding trace elements has got more and more attentions. this paper was based on a new low-Ag Sn-Ag-Cu-Ni-Bi solder and analysed it's interfacial reaction and mechanical properties on Cu/Ni pad, which was studied by thermal-aging and deep etching method using electron microscopy and bonding strength and indentation hardness tester equipment.The results show that: on Cu pad, when the Cu content is 0.3wt%-1.5wt%, with the Cu content changing, Significant changes occurred on the thickness,morphology and Composition of Sn-Ag-xCu-Ni-Bi intermetallic compounds (IMC) layer. with the increase of Cu content in these low-Ag Pb-free solders, the thickness of IMC layer decrease obviously after reflowing,and the sizes of grains become larger. At the same time , a large amount of granule-like (Cu,Ni)6Sn₅ IMC were observed at interfaces while the Cu content below 0.5wt%,and there are a few granule-like (Cu,Ni)6Sn₅ IMC and a large number of prism-like Cu₆Sn₅ IMC appeared at interfaces while the Cu content is 0.7wt%. However, the IMC between Cu pad and solder became cobble-like Cu₆Sn₅ IMC instead of (Cu,Ni)6Sn₅ when the Cu content is 1.0wt%-1.5wt%. In aging test,the thinkness increment is minimum when the Cu content is 1.0wt%. the shear strength is highest when Cu content is 0.5wt%. Indentation hardness increase with the increasing of Cu content.On Ni pad, the thickness of IMC layer increasing with the increase of Cu content. A large amount of lamellar-like (Ni,Cu)3Sn4 IMC were observed at interfaces while the Cu content below 0.3wt%; There are a few lamellar-like (Ni,Cu)3Sn4 IMC around a large number of Polyhedron-like (Cu,Ni)₆Sn₅ IMC while the Cu content is 0.5wt%; Strip-like(Cu,Ni)₆Sn₅ IMC were observed at interfaces while the Cu content more than 0.7wt%. After aging, the thinkness increment is minimum when the Cu content is 1.0wt%. The shear strength is highest when Cu content is 1.0wt%. Indentation hardness increase with the increasing of Cu content.