Electromigration-induced interfacial reactions in line-type Cu/Sn/ENIG interconnect

The effect of electromigration (EM) on the solid state interfacial reactions in line-type Cu/Sn/ENIG interconnect was investigated under the current density of 5.0×10³ A/cm² at 150 °C for 100 h and 200 h. The Cu/Sn/ENIG specimens were also aged at the same temperature and durations for comparison. After soldering, Cu₆Sn₅ and Ni₃Sn₄ IMCs formed at the Cu/Sn and ENIG/Sn interfaces, respectively. During aging time, a thin Cu₃Sn layer formed beneath the Cu6Sn5 at the Cu/Sn interface, and the original Ni₃Sn₄ transformed into (Cu,Ni)₆Sn₅ IMC at the ENIG/Sn interface. A thin Ni₃P film was detected at the ENIG/Sn interface after aging for 200 h. During EM, when the electrons flowed from the Cu side to the ENIG side, the type of interfacial IMCs kept unchanged at Cu/Sn interface for 100 h and 200h, while the origin Ni₃Sn₄ transformed into (Cu,Ni)₆Sn₅ IMC at the ENIG/Sn interface for 100 h and 200h. When the electrons flowed toward the Cu side, high current density induced Ni-P consumption and EM-induced the formation of nearly all (Ni,Cu)₃Sn₄ IMC in solder near the ENIG/Sn interface were observed. The EM-assisted crystallization of electroless Ni-P was more noticeable with increasing time, and a thin NiSnP layer formed on the thick Ni₃P layer at the ENIG/Sn interface for 200 h. Little Ni was detected at the Cu/Sn interface when it acted as the anode side.