Seong-jae Jeon

A Study on the Bonding Process of Cu Bump/Sn/Cu Bump Bonding Structure for 3D Packaging Applications

This study reports the kinetics of the bonding process of a Cu bump/10 μm thick Sn bonding layer/Cu bump bonding structure, popularly adopted for three-dimensional (3D) packaging, and the mechanical properties of the joints. Characterizing the bonding morphologies of the joints using scanning electron microscopy disclosed that a drastic intermetallic phase transformation occurred around the melting temperature of Sn in a manner similar to the wetting process of SnPb solder on Cu. We also delved into the mechanical behavior of the joints using lap-shear testing to illuminate that a unique feature of the joints is a lack of ductility. In addition, the samples exhibited a sensitive dependence of the joint strength on the bonding conditions (temperature and pressure).

A hybridized graphene carrier highway for enhanced thermoelectric power generation

The decoupling and enhancement of both Seebeck coefficient and electrical conductivity were achieved by constructing the c-axis preferentially oriented nanoscale Sb(2)Te(3) film on monolayer graphene. The external graphene layer provided a highway for charge carriers, which were stored in the thicker binary telluride film, due to the extremely high mobility.

A Study on the Breakdown Mechanism of an Electroless-Plated Ni(P) Diffusion Barrier for Cu/Sn/Cu 3D InterconnectBonding Structures

This study examined the thermal stability of an electroless-plated Ni(P) barrier layer inserted between Sn and Cu in the bonding structure of Cu/Sn/Cu for three-dimensional (3D) interconnect applications. A combination of transmission electron microscopy (TEM) and scanning electron microscopy allowed us to fully characterize the bonding morphology of the Cu/Ni(P)/Sn/Ni(P)/Cu joints bonded at various temperatures. The barrier suppressed Cu and Sn interdiffusion very effectively up to 300°C; however, an interfacial reaction between Ni(P) and Sn led to gradual decomposition into Ni3P and Ni3Sn4. Upon 350°C bonding, the interfacial reaction brought about complete disintegration of the barrier in local areas, which allowed unhindered interdiffusion between Cu and Sn.

Study on the contact resistance of various metals (Au, Ti, and Sb) on Bi–Te and Sb–Te thermoelectric films

In this study, we explore various electrode materials (Au, Ti, and Sb) for use as contact materials on Bi2Te3 and Sb2Te3 thermoelectric films. Using the transmission line method (TLM), we measured the specific resistivity of the contacts, which showed that Au has the lowest contact resistivity for both the thermoelectric films (after annealing): 2.7 × 10−10 Ω m2 for Bi2Te3 and 2.9 × 10−11 Ω m2 for Sb2Te3. The specific contact resistivity data suggest that the dominant factor for the contact properties is interface states. After annealing, the contact resistivity does not change much for the Bi2Te3 contacts while it drops greatly for the Sb2Te3 ones. Analysis of the carrier transport mechanism across the contacts discloses that changes in the carrier concentration in the thermoelectric films after annealing are responsible for the different behaviors.

Mechanical Reliability Evaluation of Sn-37Pb/Cu and Sn-37Pb/ENIG Solder Joints by using High Speed Lap-shear Test

This study utilized out high speed lap-shear tests at various strain rates (0.01 mm/s ~ 500 mm/s) for Sn-37Pb/Cu and Sn-37Pb/ENIG solder joints to evaluate the drop reliability. The samples aged for 120 h at different temperatures (150°C and 170°C) were also tested to examine the effects of aging on the drop reliability. We thoroughly analyzed the stress-strain curves obtained from the lap-shear tests and the fractured surfaces. This analysis generated insightful information that reveals three fracture surface types active in our samples. This study also elucidates different fracture mode for the Sn-37Pb/Cu and Sn-37Pb/ENIG solder joints. This study successfully demonstrates that the analysis based on a high speed lap-shear test could be critically used to evaluate the drop reliability of solder joints.