Influence of Bi on IMC of Sn-0.3Ag-0.7Cu-xBi/Ni Solder
The growth of intermetallic compounds(IMC) between lead-free solder and pad has an important influence on the reliability of primary device.Ni substrate was welded by Sn-0.3Ag-0.7Cu-xBi lead-free solder,and the joints were aging-treated at 180℃,aging time was 0,24,95,216 and 384 h respectively,The growth and morphology characteristics of the IMCs were investigated by metallographic microscope,SEM and EDX.The content change of Ni in the IMC was also analysed,meanwhile,the IMC growth rates were fitted by experimental data.The results show that the IMC between Sn-0.3Ag-0.7Cu-xBi and Ni substrate is(CuxNi1-x)6Sn5.The effect of controlling the thickness of IMC is not very good after the addition of Bi,with the increase of Bi content,the thickness of IMC firstly increases,then decreases,when the content of Bi is more than 1.0%.And there are two regions whose average content of Ni in the Sn-0.3Ag-0.7Cu/Ni solder IMC is respectively 15wt% and 5wt%,which show a descending tend from the near Ni substrate side to the bulk solder side.But the average content of Ni in Sn-0.3Ag-0.7Cu-3.0Bi/Ni solder IMC is 7%.After aging,the thickness of IMC increases as aging time prolonging.But the growth speed of Sn-0.3Ag-0.7Cu-3.0Bi/Ni IMC is slower than Sn-0.3Ag-0.7Cu/Ni IMC,because of the precipitation of Bi.Besides,the content of Ni in the(CuxNi1-x)6Sn5 decreases from 15% to 5%,but the average content of Ni in Sn-0.3Ag-0.7Cu-xBi/Ni IMC increases from 7% to 9%.According to the calculation,the growth rate of Sn-0.3Ag-0.7Cu-xBi/Ni IMC decreases as Bi content increasing.