Conoscopy as a Failure Analysis Method for Single Crystals.

Conoscopy is widely used to evaluate single crystals used as substrates on which epitaxial layers are grown in the LED industry, where the quality of the single crystal affects the reliability of the final product, the LED chip, and the package. However, the application of this method is currently restricted to characterizing birefringence. We performed conoscopy measurements on single crystals with failure modes (e.g., birefringence, lineages, dislocations, polycrystallinity, and amorphousness) and examined whether it was possible to inspect such failures using conoscopy. Sapphire (α-Al2O3) and silicon carbide (6H­SiC) single crystals containing failures were investigated. X-ray diffraction and transmission electron microscopy analyses were also performed; their results were compared with the conoscopy results. Conoscopy was shown to inspect birefringence as well as other failure modes. Comparison of the conoscopic patterns obtained via simulation and experiment shows that quantitative evaluation of the failure level is possible. These results show that conoscopy can be used to quickly and easily investigate various failure mechanisms in single crystals.

Failure Analysis of a Nickel-Plated Electronic Connector Due to Salt-Induced Corrosion (ENGE 2014).

When electronic connectors in mobile devices are miniaturized, the thickness of plating decreases. However, this thin plating is expected to decrease the life of the connector due to problems with corrosion. In this study, salt spray aging tests were performed on miniaturized nickel-plated stainless steel electronic connectors to observe failure mechanisms in realistic environments. The tests were performed three times using a 5% NaCl solution in an atmosphere of 45 °C; each test included several cycles where one cycle was one 24-h period consisting of 8 h of salt spray and 16 h without salt spray. The nickel-plating layers were periodically observed by electron probe X-ray micro-analyzer, wavelength dispersive spectroscopy, and field-emission scanning electron microscopy to analyze and identify the corrosion mechanism. We found that the primary failure mode of the nickel plating is blistering and delamination. The corrosion mechanism is typically a chain reaction of several corrosion mechanisms: pitting corrosion --> stress corrosion cracking --> hydrogen-induced cracking --> blistering and delamination. Finally, we discuss countermeasures to prevent corrosion of the nickel layer based on the corrosion mechanisms identified in this study.

Thermal stability of gallium-doped zinc oxide thin film on glass substrates by an RF sputtering process.

The effects of a heat treatment on the structural and electrical properties of GZO thin films grown by RF magnetron sputtering were investigated. The heat treatment involved temperatures in the range from 200 degrees C to 500 degrees C under air. As the temperature was increased, the electrical properties of GZO thin films increased exponentially and the surface morphology was drastically altered. The effect of temperature is discussed based on electrical and structural characterization of the materials.

Interfacial structure and electrical properties of transparent conducting ZnO thin films on polymer substrates.

The effects of polymer substrates on the interfacial structure and the thermal stability of Ga-doped ZnO (GZO) thin films were investigated. The GZO thin films were deposited on polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) substrates by rf-magnetron sputtering at room temperature, and thermal stability tests of the GZO thin films on the polymer substrates were performed at 150°C up to 8 h in air. Electrical and structural characterizations of the GZO thin films on the PET and the PEN substrates were carried out, and the origins of the stable interfacial structure and the improved thermal stability of the GZO thin film on the PEN substrate were discussed.