Morphology and Growth Kinetics of Intermetallic Compounds in Solid-State Interfacial Reaction of Electroless Ni-P with Sn-Based Lead-Free Solders

摘要

A comparative study of solid/solid interfacial reactions of electroless Ni-P (15 at.% P) with lead-free solders,Sn-0.7Cu,Sn-3.5Ag,Sn-3.8Ag-0.7Cu,and pure Sn,was carried out by performing thermal aging at 150 deg C up to 1000 h.For pure Sn and Sn-3.5Ag solder,three distinctive layers,Ni_3Sn_4,SnNiP,and Ni_3P,were observed in between the solder and electroless Ni-P;while for Sn-0.7Cu and Sn-3.8Ag-0.7Cu solders,two distinctive layers,(CuNi)_6Sn_5 and Ni_3P,were observed.The differences in morphology and growth kinetics of the intermetallic compounds (IMCs) at the interfaces between electroless Ni-P and lead-free solders were investigated,as well as the growth kinetics of the P-enriched layers underneath the interfacial IMC layers.With increasing aging time,the coarsening of interfacial Ni_3Sn_4 IMC grains for pure Sn and Sn-3.5Ag solder was significantly greater than that of the interfacial (CuNi)_6Sn_5 IMC grains for Sn-0.7Cu and Sn-3.8Ag-0.7Cu solders.Furthermore,the Ni content in interfacial (CuNi)_6Sn_5 phase slightly increased during aging.A small addition of Cu (0.7 wt.%) resulted in differences in the type,morphology,and growth kinetics of interfacial IMCs.By comparing the metallurgical aspects and growth kinetics of the interfacial IMCs and the underneath P-enriched layers,the role of initial Cu and Ag in lead-free solders is better understood.