Jing Dong Guo

Dependence of electromigration damage on Sn grain orientation in Sn-Ag-Cu solder joints

The relationship between the “polarity effect” of electromigration on interfacial intermetallic growth and the Sn grain orientation was investigated in Sn-Ag-Cu solder joints. The growth of the interfacial intermetallic compound was found to depend strongly on the Sn grain orientation. When the c-axes of the Sn grains were closely aligned to the current flow direction, a severe polarity effect was observed in which the anode interface was covered with a thick layer of Cu-Sn intermetallic while the intermetallic layer at the cathode interface was almost depleted. If the c-axes of the Sn grains were rotated away from the current direction, the polarity effect became less pronounced. When the c-axis was perpendicular to the current direction, the polarity effect essentially disappeared. The difference in the intermetallic layer thickness between the anode and the cathode, Δd, followed a parabolic function of the cosine of the angle, α, between the c-axis and the current direction. A kinetic model based on th...

Evolution of microstructure in TiC/NiCr cermet induced by electropulsing

Microstructures of a TiC/Ni80Cr20 cermet, subjected to single high-current-density electropulsing, were characterized by x-ray diffraction, transmission electron microscopy, and high-resolution transmission electron microscopy. Under the electropulsing, the shift of NiCr peaks versus the reverse change of TiC counterparts illustrates that the treatment gives rise to strong thermal stress impacting on the cermet. The stress, accompanied by the transient rise of temperature, led to microstructural evolutions of the cermet. Some nanostructured TiC grains, consisting of many nanocrystallites with small-angle grain boundaries, developed during electropulsing. Also, many regions teemed with coexisting nanosized TiC and NiCr crystallites, which possessed good bonding. Within the NiCr regions, large amounts of deformation twins were produced by the electropulsing.

The reliability of through silicon via under thermal cycling

Through silicon via (TSV) is a critical element for three-dimensional (3D) integration of devices in vertically multilevel stack-die microelectronic packages. In this paper, the microstructure evolution of TSV-Cu under thermal cycling was studied and the topography of TSVs under thermal cycling tests was examined by white light interferometer. It was found that the Cu was intrude inside the Si die during the test, and the intrusion height increased with cycle time and leveled off at 0.72μm and 0.53μm for upside and backside after 210 cycles, respectively. Besides, the Cu intrusion height at the Cu/Si interface is greater than that in the middle of Cu bar. in addition, cracks were observed at SiO2/Ta barrier interface and between BEOL line and Cu vias. It suggests that diffusional creep of the interface is the key for Cu via intrusion, the residual stress and thermal stress drive the interfacial sliding at interfaces.

Electromigration behavior of the Ni/SnZn/Cu solder interconnect

Electromigration in the Ni/SnZn/Cu solder interconnect was studied with an average current density of 4.1times10⁴A/cm² for 168.5h at 150degC. When the electrons flowed from the Ni side to the Cu side, uniform layers of Ni₅Zn₂₁ and Cu₅Zn₈ were formed at the Ni/SnZn and Cu/SnZn interfaces. The results are similar to those without passage of an electric current. However, upon reversing the current direction where electron flow was from the Cu side to the Ni side, thicker Cu₆Sn₅ phase replaced Ni₅Zn₂₁ phase at the Ni/SnZn interface, whereas at the Cu/SnZn interface, thicker beta-CuZn phase replaced Cu₅Zn₈ phase. Meanwhile, Cu-Sn phases also appeared at the Cu/SnZn interface. A kinetic model, based on the Zn and Cu mass transport in the sample, was presented to explain the growth of the intermetallic compound at the anode and cathode.

Electromigration In Cu/Sn-58Bi/Cu Interconnects

The microstructural changes on the surface of Cu/Sn-58Bi/Cu interconnects, under current stressing of 2.7 times 104A/cm2 95degC for 60 hrs, are examined in this paper. At the anode side, the Bi phase accumulated in front of the intermetallic compound (IMC), and bumps of Bi rich solder extruded out of the surface along the IMC/solder interface. At the cathode side, a Bi depleted zone appeared, which was composed of Sn rich particles and tiny Bi-rich particles. After grinding and polishing, a continuous Bi layer was observed accumulated in front of the IMC at the anode side, which caused a reliability concern in the solder joints.