Formation of intermetallic reaction layer and joining strength in nano-composite solder joint

In this study, the effects of CeO₂ nanoparticle addition on tensile strength and formation of interfacial intermetallic compound layer for lead-free Sn-3.5Ag-0.7Cu solder joint were investigated. The results showed that the thickness of intermetallic layer was decreased with increasing weight percentages of CeO₂ reinforcements, and the growth of the intermetallic layer was remarkably suppressed during isothermal aging at 150 °C. It was also found that the tensile strength of the solder joint gradually increased with the addition of CeO₂ particles, reached to the maximum value at 0.5 wt% CeO₂ and then decreased drastically with further increase in CeO₂ content. Microstructural investigation of 1 wt% CeO₂ reinforced solder joint revealed that due to particle pushing under the influence of interfacial tension between the particles and the matrix, the brittle cluster-like regions with high concentration of CeO₂ particles were formed inside the joint. These brittle clusters act as preferential site for crack initiation during tensile test which would degrade the tensile strength. Hence, based on the results obtained in this study, addition of CeO₂ particles up to 0.5 wt% provide an optimized solder joint with improved strength together with suppressed intermetallic growth and long-term reliability.     

Ceria reinforced nanocomposite solder foils fabricated by accumulative roll bonding process

As one of the key technologies for high performance electronic devices, composite solders have been recently developed to improve thermal and mechanical properties of solder joints. In this study, accumulative roll bonding process was used as an effective alternative method for manufacturing high-strength, finely dispersed, void-free and highly uniform Sn–Ag–Cu/CeO₂ nanocomposite solders. Microstructural investigation of nanocomposite solders revealed that homogenous distribution of CeO₂ nanoparticle has been achieved and the eutectic as-cast morphology of the solder changed to recrystallized fine grained structure. As a result of severe plastic deformation during rolling, brittle and elongated intermetallics crushed into fine particles with an average diameter of a few hundred nanometers and dispersed uniformly in the solder matrix. Mechanical test results showed that the microhardness, 0.2% yield stress, and ultimate tensile strength of the composite solder increased with addition of CeO₂ nanoparticles, while the ductility of the composite was decreased.     

Flexible LCDs fabricated with a slit coater: Not requiring an alignment film

A homogeneously aligned liquid crystal layer on a substrate film on which it is not necessary to form a liquid crystal alignment film can be assembled by a slit coater. Types of twisted nematic and in‐plane switching flexible liquid crystal displays were demonstrated. The production time can be considerably shortened because of the lack of need for an alignment film. The slit coater method is also applicable to the roll‐to‐roll process.