Study of interfacial reactions in Sn-3.5Ag-3.0Bi sandwich structure solder joint with Ni(P)/Cu metallization on Cu substrate

摘要

This paper studied the coupling effect in Sn-3.5Ag-3.0Bi solder joint with sandwich structure by long time reflow soldering. It was found that the interfacial compound at the Cu substrate was binary Cu-Sn compound on Cu substrate and the ternary (Cu,Ni)_6Sn_5 compound formed at the Sn-Ag-Bi/Ni(P)-Cu metallization interface. It was observed that Cu atoms could diffuse from the Cu substrate through the solder matrix to the Ni(P)-Cu metallization within lmin reflow soldering time for both solder systems, indicating that just 30 second was long enough for Cu to go through 250um diffusion length in the Sn-Ag-Bi solder joint at 250℃. The coupling effect between Ni(P)/Cu metallization and Cu substrate was confirmed as the type of IMCs at Ni(P) layer had been changed from Ni-Sn system to Cu-Sn system apparently by the diffusion effect of Cu atoms. The (Cu,Ni)_6Sn_5 layer at the Ni(P)/Cu metallization grew significantly and its thickness was even greater than that of the Cu-Sn compound on the opposite Cu substrate.