Polarity effect of electromigration on intermetallic compound (IMC) formation in lead-free solder V-groove samples

With the trend of further miniaturization of very-large-scale-integration (VLSI) of circuits, electromigration becomes a reliability concern in solder alloys. The polarity effect of electromigration on intermetallic compound (IMC) formation at the anode and the cathode in solder V-groove samples has been investigated.; The V-groove solder line samples, with width of about 100 mum and length of 500--700 mum, were used to study the change in thickness and morphology of interfacial IMC at anode and cathode in the SnAg 3.8Cu0.7/Cu system under different current density and temperature settings. The current densities were in the range of 103 to 104A/ cm2 and the temperature settings were 120° C, 150°C and 180°C. The samples were formed by flowing molten lead-free solder SnAg 3.8Cu0.7 into V-grooves etched on (001) silicon wafers, and two copper wires were used as electrodes.; We observed that IMC transformed from initial scallop-type into layer-type morphology with or without applying current. Due to the polarity of electric current and the local current crowding, IMC transformed from scallop-type into layer-type morphology differently from cathode to anode. We also found that the same IMCs of Cu6Sn 5 and Cu3Sn formed at solder/Cu interfaces with or without the passage of electric current. The growth of IMC has been enhanced by electric current at the anode and inhibited at the cathode, comparing with samples without applying current. A kinetic theory is derived, based on the Cu mass flux transport in the sample, to model the growth rate of IMC at anode and cathode.