The conformation of 2,2,2-trifluoroethanol (TFE) in the 2-fluoropyridine-(TFE) m -(H 2 O) n clusters in a supersonic jet has been investigated with fluorescence-detected infrared spectroscopy and quantum chemical calculations. It is common to the observed clusters that they form chain structures containing the weak interaction of the pyridyl CH with the fluorine or oxygen atom in the terminal TFE. The detectable conformation of TFE is gauche only even in the case of the existence of the strong base such as 2-fluoropyridine. This result is explained by the change in hyperconjugation among several dominant orbitals. The preference of the terminal TFE in the mixed clusters with TFE and water solvents is observed, which is ascribed to the stronger cooperative effect of TFE than water.

Sn-Bi alloy is one of the representative low temperature type lead-free solders. However, the bonding properties of the Sn-Bi solder are not good. The reason for such properties is related to Bi microcrystallines that segregate at the interface between the solder and a Cu substrate. We found that ultrasound improves the bonding strength for the Sn-Bi alloy system solders by dispersing and miniaturizing the Bi crystals. To achieve such dispersion, we invented a novel ultrasonic soldering technique. By using this technique, ultrasound can be applied to printed wiring boards (PWB). Besides the improved bonding strength, we found that the temperature of a PWB is increased by the application of ultrasound to the PWB. Sn-58 mass%Bi solder is melted by the vibrational energy of ultrasound without other heating methods. Moreover, the interfacial layer between the Sn-58Bi solder and the Cu land is homogenized by ultrasound. Also, the interfacial layer between the Sn-8Zn-3Bi solder and a Cu land becomes thinner by ultrasound. We believe that these changes in the interfacial structure improve the mechanical properties of the solders. Therefore, ultrasonic soldering technique will improve the usability and reliability of Sn-Bi alloy system solders.

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