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Flow characteristics of underfill encapsulant were evaluated to improve the flow of encapsulation resin into small gap between LSI chip and substrate so as to achieve uniform and void-free underfill encapsulant for high-reliability flip-chip interconnection. Encapsulant flow was observed through crystal TEG LSI chips using a video camera and its flow characteristics were evaluated using the Newtonian laminar flow model. The relationships between flow rate of underfill encapsulant and the bump stand-off height, the bump pitch and the bump gap of the adjoining bumps were obtained. The flow rate and flow distance were found to be functions of these bump design parameters. The bump design parameters for encapsulation to be perfectly complete and the maximum chip size permitting encapsulation were obtained from the results for high-reliability flip-chip interconnection. This paper describes the flow characteristics of underfill encapsulant that are necessary to achieve the uniform and void-free underfill encapsulant for LSI which has large chip size, small bump pitch and high I/O number.