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The needs for novel, miniaturized, high performance and multi-functional electronics have necessitated high density and precise assembles between the IC chip and substrate, which is achieved by flip chip bonding (FCB) technologies using the solder bump and adhesives such as anisotropic conductive adhesive and non conductive adhesive. The excessive growth of intermetallic compounds at the joint interface degrades the performance and reliability of the solder bumps during bonding and system operation. The adhesives show poor electrical property and low reliability. Recently, interest in ultrasonic FCB technologies has been growing, due to the potential advantages such as fast bonding time, low bonding temperature, low bonding pressure, environment-friendly process, high electrical and mechanical performance and good reliability. However, the joint strength is sensitive to the morphology and cleanness of the bump surface. Wet cleaning effectively cleans the surface with advantages such as low cost and high reproducibility. However, the use of wet chemicals raises environmental problems and maintenance costs. Dry cleaning is an environment-friendly process with low operating cost, although it suffers disadvantages such as the high cost and low productivity. Therefore, the atmospheric pressure plasma cleaning technique may be an effective method to clean the bump surface because of its simple structure, high productivity and applicability throughout the in-line process. However, plasma cleaning without the appropriate set up can do more harm than good. Although many researchers have investigated the effect of atmospheric pressure plasma on the surface modification of polymers and metals, research on the atmospheric pressure plasma for ultrasonic FCB has remained limited. Cu bump has advantages such as low cost, excellent conductivity, and good ductility. Therefore, the aims of our study were to determine the optimum conditions of atmospheric pressure plasma cleaning for ultrasonic FCB of Cu bump and to understand the surface phenomena using atomic force microscopy, Auger electron microscopy, X-ray photoelectron spectroscopy in order to increase the bondability of the bump. The cleaning conditions strongly affected the bonding strength of the bumps.
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