A high-quality graphene transparent conductive film was fabricated by roll-to-roll chemical vapor deposition (CVD) synthesis on a suspended copper foil and subsequent transfer. While the high temperature required for the CVD synthesis of high-quality graphene has prevented efficient roll-to-roll production thus far, we used selective Joule heating of the copper foil to achieve this. Low pressure thermal CVD synthesis and a direct roll-to-roll transfer process using photocurable epoxy resin allowed us to fabricate a 100-m-long graphene transparent conductive film with a sheet resistance as low as 150 Ω/sq, which is comparable to that of state-of-the-art CVD-grown graphene films.

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Mechanically induced Sn whiskers are a serious problem in the electronics industry because they can cause electrical short circuits in narrow gaps between electrodes such as fine pitch connector pins. The authors tried to prevent the formation of them by using one of the typical Pb-free solder materials, SnAgCu alloy, as a plating material on connector pins. It was found that reflowed SnAgCu plating was whiskerfree even under mechanical stress. Scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) analyses revealed that Sn grains of reflowed SnAgCu plating were extremely larger than those of whisker-prone pure Sn or SnCu platings that have columnar structures. The notable feature was no obvious microstructural changes in reflowed SnAgCu plating even after applying mechanical stress for 38 days. The present study demonstrates that reflowed SnAgCu plating is one of the best candidates as whisker-free plating.