A synchrotron radiation real-time in situ imaging study on the reverse polarity effect in Cu/Sn–9Zn/Cu interconnect during liquid–solid electromigration

Effect of Ni on the Formation and Growth of Primary Cu6Sn5 Intermetallics in Sn-0.7 wt.%Cu Solder Pastes on Cu Substrates During the Soldering Process

“…[19], Qu et al [20,21] and Huang et al [22]. Recently we have successfully developed [23] a synchrotron based in-situ method to observe, in real time, the entire soldering process of a solder paste on a Cu substrate, including the solid-liquid-solid transition to provide an understanding on the real-time primary intermetallic growth.…”

Different diffusion behavior of Cu, Ni and Zn atoms in Cu/Sn-9Zn/Ni interconnects during liquid-solid electromigration

“…Therefore, the supply of Cu atoms for the growth of Cu 5 Zn 8 at Ni interface was limited by the continued growth Cu 5 Zn 8 IMC at Cu interface. Second, the effective charge number of Zn atoms (Z*) was positive during the L-S EM at 230 o C [15], resulting in the migration of Zn atoms from Ni side to Cu side in the liquid solder. Under this condition, the Zn concentration in the liquid solder near the Ni interface continuously decreased, which would break the local equilibrium.…”

In situ study on reverse polarity effect in Cu/Sn–9Zn/Ni interconnect undergoing liquid–solid electromigration

“…It is known that the Zn atomic flux is the major contributor to the growth of interfacial Cu-Zn IMCs, since Zn atoms are the dominant diffusing species for the interfacial reaction in Zn/Cu system [10]. As there is no back stress in liquid solder, the Zn atomic flux J Zn undergoing L-S EM can be expressed as [17] …”

“…6. However, when electrons flowed from the Ni to the Cu, Zn atoms in the liquid solder was continuously consumed till depleted, since Cu atoms would preferentially migrated to the cathode Ni interface and reacted with Zn atoms to form interfacial Cu 5 Zn 8 IMC [10]. Since the thin interfacial IMC at the anode Cu ensures the dissolution of Cu substrate into the molten solder through grain boundaries and the continuous consumption of Cu atoms by the growth of Cu 5 Zn 8 at the cathode, there exists a chemical potential gradient across the solder from the anode to the cathode.…”

“…It was proposed that the reverse polarity effect undergoing L-S EM was induced by the positive effective charge number (Z ⁄ ) of Zn atoms [10,11]. However, when Cu/Sn-9Zn/Ni interconnects were current stressed under 5.0 Â 10 3 A/cm 2 at 230°C, Zn atoms only directionally diffused toward the solder/Cu interface but not the solder/Ni interface despite the flowing direction of electrons [12].…”