Abstract
This article reports on the design and implementation of a miniaturized impression creep apparatus for characterizing the creep behavior of tiny solder balls attached to a ball grid array (BGA) microelectronic packaging substrate. The technique requires no special sample preparation, can probe individual solder balls, and proffers high data throughput by allowing numerous creep curves to be obtained from one substrate, as well as by minimizing the time required to achieve steady state creep. The apparatus reported here uses a 100-μm-diameter cylindrical WC punch to characterize the creep behavior of 750-μm-diameter BGA solder balls from ambient temperature to 423 K. A video imaging system facilitates precise alignment and placement of the indenter on the specimen at the test temperature. The possible effect of substrate curvature on the experimental solder creep curves was evaluated and was deemed to be insignificant. Example creep curves and data based on 90Pb-10Sn BGA solder balls are presented. The test is further scalable for testing of smaller flip-chip joints, using a smaller punch. The present work reports on the implementation of impression creep for testing nonbulk specimens.
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