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By using the first principles cluster calculation together with the band calculation, we identified that (a) Ru or Rh substitution for Fe and (b) Zr, Nb and Mo substitution for V are presumably useful for decreasing the lattice thermal conductivity without greatly affecting the electron transport properties. The Fe2V1� xZrxAl0:9� xSi0:1þx (x ¼ 0, 0.02, 0.04, 0.06, and 0.1) alloys indeed possessed the effective reduction in lattice thermal conductivity with increasing Zr concentration while the Seebeck coefficient showed very weak Zr concentration dependence. The Fe2� yIryV0:9� yTi0:1þyAl (y ¼ 0, 0.02, 0.04, 0.06, and 0.1) alloys, on the other hand, possessed drastic reduction of Seebeck coefficient most likely due to the newly introduced Ir 5d states. These experimental facts agree with the present theoretical-prediction, and it was clearly proved that the combinational use of cluster calculation and band calculation is very useful in developing new thermoelectric material. [doi:10.2320/matertrans.M2010224]

Electroless Ni/Au plating is often performed on a surface of a Cu pad to improve the wettability of lead-free solders on such a pad. Generally, electroless Au plating is performed by an immersion plating method. Since a substitution reaction of Ni and Au occurs selectively on the surface of a Ni layer in immersion plating, the Au layer does not uniformly form on the Ni layer and microvoids or microcracks easily form at the Ni/Au interface. Such defects induce void formation at the joint interface in soldering, and consequently degrade the reliability of the lead-free solder joint. In this study, the influences of immersion plating time on microvoid formation at the joint interface and the reliability of a solder ball joint with a Sn-3 mass%Ag-0.5 mass%Cu lead-free solder were investigated.

Electroless Ni/Au plating is presently in use with high-density Jisso technology in the manufacture of electrical appliances. Electroless Ni/Au plating is said to be less satisfactory than conventional electrolytic plating with respect to the quality of solder joints and lead-free solder in particular. The reason for this is considered the P-rich layer which forms at the interface of solder bulk and Ni layer but this has yet to be fully confirmed. Solder joints made by electroless Ni/Au plating and Sn-3 mass%Ag-0.5 mass%Cu lead-free solder balls were examined here for reliability assessment under high temperature storage, using an electroless Ni/Au layer made by autocatalytical deposition and another made by immersion Au plating. Interfacial structure and solder pull strength data for the two layers were compared as basis for this assessment and confirm if solder joints made by electrolytic plating is actually superior. At the interface of both layers, cavity formation was found to have occurred by Ni corrosion during Au plating and the number of which appeared to be a factor determining solder joint reliability. Electrolytic Au plating not accompanied by Ni corrosion should provide solder joints with reliability exceeding that by electroless Au plating.