Effects of Cu contents in flux on microstructure and joint strength of Sn–3.5Ag soldering with electroless Ni–P/Au surface finish

Microstructure and morphology of interfacial intermetallic compound CoSn3 in Sn–Pb/Co–P solder joints

“…Ni-based UBM has been intensely investigated as a diffusion barrier between Sn and Cu, including electroless nickel immersion gold (ENIG), electroplated Ni-P, Ni-Cu-P, and Ni-Zn-P [14][15][16][17][18][19][20][21][22][23][24][25]. During soldering with Ni-based UBM, the formation of columnar Ni 3 P accelerates interfacial reaction, and voids appear in Ni 3 P. Due to the voids, the interface is weakened and reliability of solder joints is degraded [14,16,17,25].…”