Effects of Cu Contents in Pb-Free Solder Alloys on Interfacial Reactions and Bump Reliability of Pb-Free Solder Bumps on Electroless Ni-P Under-Bump Metallurgy

摘要

Using the screen-printed solder-bumping technique on the electroless plated Ni-P under-bump metallurgy (UBM) is potentially a good method because of cost effectiveness.As SnAgCu Pb-free solders become popular,demands for understanding of interfacial reactions between electroless Ni-P UBMs and Cu-containing Pb-free solder bumps are increasing.It was found that typical Ni-Sn reactions between the electroless Ni-P UBM and Sn-based solders were substantially changed by adding small amounts of Cu in Sn-based Pb-free solder alloys.In Cu-containing solder bumps,the (Cu,Ni)_6Sn_5 phase formed during initial reflow,followed by (Ni,Cu)_3Sn_4 phase formation during further reflow and aging.The Sn3.5Ag solder bumps showed a much faster electroless Ni-P UBM consumption rate than Cu-containing solder bumps:Sn4.OAgO.5Cu and Sn0.7Cu.The initial formation of the (Cu,Ni)_6Sn_5 phase in SnAgCu and SnCu solders significantly reduced the consumption of the Ni-P UBM.The more Cu-containing solder showed slower consumption rate of the Ni-P UBM than the less Cu-containing solder below 300 deg C heat treatments.The growth rate of the (Cu,Ni)_6Sn_5 intermetallic compound (IMC) should be determined by substitution of Ni atoms into the Cu sublattice in the solid (Cu,Ni)_6Sn_5 IMC.The Cu contents in solder alloys only affected the total amount of the (Cu,Ni)_6Sn_5 IMC.More Cu-containing solders were recommended to reduce consumption of the Ni-based UBM.In addition,bump shear strength and failure analysis were performed using bump shear test.