No abstract

The Ba(Ce 0.8 Zr 0.2 ) 0.95 Yb 0.05 O 2.975 ceramics electrolyte was prepared via a Pechini method using metal nitrate salts as starting materials. An optimum annealing temperature of 1,400°C was needed to obtain a pure perovskite-like phase with orthorhombic structure. Particle size distribution showed a bimodal distribution that corresponds to the loose powders and agglomerates size. Scanning electron micrograph revealed that the loose powders were in the nanosize range (70-200 nm). These ultrafine loose powders enhanced the densification of a pellet with relative density ∼95% obtained at 1,400°C. The sample formed clear and compact grains with submicron sizes. Impedance results showed that the impedance semicircle of the grain was observed only at T≤250°C. The introduction of 20 mol% Zr improved the chemical stability of BaCe 0.95 Yb 0.05 O 2.975 sample in atmosphere containing carbon dioxide at 600°C. The sample also exhibited high proton conductivity in wet hydrogen.

This study investigated the effect of Ag addition on the morphology and growth rate of Cu5Zn8, Cu6Sn5 and Cu3Sn intermetallics in the Sn-8Zn-3Bi solder. The solder was prepared by mixing 1wt% of Ag into 99wt% of Sn-8Zn-3Bi solder. The intermetallics were formed by liquid-state aging, whereby the solders were reacted on Cu substrate above the melting temperature of the solder. The reflow was done at 250°C and 270°C at various soldering times. A scanning electron microscope (SEM) was used to observe the morphology of the intermetallic phase and energy dispersive X-ray (EDX) was used to identify the elemental composition. The Sn-8Zn-3Bi solder reacting with Cu substrate formed a single Cu5Zn8 intermetallic layer with a flat structure. On the other hand, the reaction between (Sn-8Zn-3Bi)-1Ag solder and Cu substrate produces Cu6Sn5 intermetallic. This Cu6Sn5 intermetallic has a scallop structure. As the soldering time increases, a second layer, identified as Cu3Sn starts to grow. The thickness of the intermetallics increases with aging temperatures and time. The addition of Ag into the Sn-8Zn-3Bi solder has significantly suppressed the formation of Cu5Zn8 intermetallic and promoted the growth of Cu6Sn5 intermetallic.

Due to environmental concerns, lead-free solders were introduced in replacing the lead-based solders in microelectronics devices technology. Although there are many lead-free solder available, the Sn-Ag-Cu is considered the best choice. But the solder has its draw backs in terms of melting temperature and intermetallic formations. To improve the solder, a fourth element Zn was added into the solder. The new composite solders were synthesized via powder metallurgy route. This research studies the effect of 0.1wt% Zn addition on the hardness and intermetallic formation on Cu substrate. For the hardness results, the micro Vickers values were reported. For intermetallic, the solders were melted at 250°C and aged at 150°C until 400 hours. The microhardness value for Zn based composites solder shows higher micro Vickers hardness compared to un-doped counterparts. The phases formed and its growth was studied under SEM and by energy dispensive x-ray (EDX). The SEM results show the presence of Cu6Sn5and Cu3Sn intermetallics and the Cu5Zn8intermetallic was not detected. The addition of 0.1wt% Zn has retarded the growth of the Cu3Sn intermetallic but not the total intermetallic thickness.

This study investigated the effect of Ag addition on the formation of intermetallic compounds and joint strength of the Sn-Zn-Bi based alloys under liquid state aging. The intermetallic compounds were formed by reacting Sn-8Zn-3Bi and (Sn-8Zn-3Bi)-IAg lead free solders on copper substrate. Scanning electron microscope (SEM) was used to see the morphology of the phases and energy dispersive x ray (EDX) was used to estimate the elemental compositions of the phases. It was found that for Sn-8Zn-3Bi solder reacting with Cu substrate, the Cu5Zn8 intermetallic was formed. On the other hand, when 1 % Ag was added into the solder, the CU3Sn and CU6SnS IMC were formed. The morphology of the CusZng intermetallic was flat whereas for CU3Sn and CU6SnS were rather scallop. The addition of Ag into the Sn-Zn-Bi solder increases the shear strength of the solder joint. It is believed the scallop morphology of Cu Sn contribute to strengthening the (Sn-8Zn-3Bi)-IAg/Cu joints.