Effects of Nd substitution with Bi on the microwave dielectric properties of BiNbO4 were studied. Bi1−xNdxNbO4 ceramics sintered at 920–980 °C consisted of orthorhombic and triclinic phases. The amount of triclinic phase increased with the increase in the Nd content, x, and sintering temperature. The apparent density and the dielectric constant decreased with the Nd content, but increased with sintering temperature, reached the peak values at 960 °C and then rapidly decreased. The Q × f0 value was between 11,000 and 13,000 GHz over all sintering temperatures for x < 0.05, but for x ≥ 0.05 it reached the peak value at 950 °C and then rapidly decreased. The temperature coefficient of resonance frequency increased in the positive direction with the Nd content and showed the minimum value of −1.82 ppm/°C for x = 0.025 sintered at 940 °C. However, it rapidly increased in the negative direction for sintering temperature over 960 °C.

The microstructure and adhesion strength of the Sn–0.7Cu/Cu solder joints were examined. The acicular η(Cu6Sn5)-phase was formed inside the solder and at the solder/Cu interface, mostly in the direction normal to the interface. Compared to the Sn–3.5Ag alloy, the Sn–0.7Cu solder showed comparable wettability, but lower microhardness and joint strength. After aging, the acicular η-phase grew into a round and scallop-shaped morphology, thin є(Cu3Sn)-phase evolved just above the Cu substrate, and the joint strength decreased linearly with aging time.

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