EFFECT OF ELECTROMIGRATION ON INTERFACIAL REACTION IN Ni/Sn3.0Ag0.5Cu/Cu FLIP CHIP SOLDER JOINTS
HUANG Mingliang, CHEN Leida, ZHOU Shaoming
School of Materials Science & Engineering, Dalian University of Technology, Dalian 116024
Cite this article:
HUANG Mingliang CHEN Leida ZHOU Shaoming. EFFECT OF ELECTROMIGRATION ON INTERFACIAL REACTION IN Ni/Sn3.0Ag0.5Cu/Cu FLIP CHIP SOLDER JOINTS. Acta Metall Sin, 2012, 48(3): 321-328.
Abstract The effect of electromigration (EM) on the interfacial reaction in Ni/Sn3.0Ag0.5Cu/Cu solder joints was investigated under a current density of 5.0×103 A/cm2 at 150 ℃. All solder joints were aged at 150 ℃ for comparison purpose. It has been found that the (Cu, Ni)6Sn5 intermetallic compounds (IMCs) form at both solder/Ni and solder/Cu interfaces in the as-reflowed state. During aging at 150 ℃, the thickness of interfacial IMC increases with increasing aging time, and no interfacial IMC transformation occurs even after aging for 800 h. The flowing direction of electrons plays an important role in Cu consumption. When electrons flow from printed circuit board (PCB) to chip, the current crowding effect induces a rapid and localized dissolution of Cu pad on PCB and a formation of microcrack at the Sn3.0Ag0.5Cu/(Cu, Ni)6Sn5 interface. The dissolved Cu atoms are driven towards anode by EM, and a large amount of Cu6Sn5 IMC particles form in solder matrix along the flowing direction of electrons. When electrons flow from chip to PCB, no obvious consumption of Ni underbump metallogy (UBM) has been observed and few Cu6Sn5 IMC particles form in solder matrix near the anode interface. There is no evidence of failure induced by EM in solder joints even after EM for 800 h. To sum up, EM enhances the growth of interfacial (Cu, Ni)6Sn5 at anode side, no matter how the direction of electrons is. The interfacial IMC at anode side is thicker than that at cathode side. The Ni/Sn3.0Ag0.5Cu/Cu solder joint is prone to fail when electrons flowing from Cu to Ni.