Optimal Gold-Ball Bonding Parameters Determined from Ball Shear and Wire Pull Tests

In microelectronic packaging, wire bonding is the preferred method used to form electrical interconnections between integrated circuit chips and a substrate. However, ball lift (i.e., when a ball bond becomes completely detached from the chip) and wire breaking are critical problems that degrade the quality of a wire bond. In this study we considered three parameters of gold-ball bonding—ball bond thickness (7–22μm), gold-wire loop height (180–300μm), and gold-wire loop length (1050–2100μm)—and tried to determine the most suitable bond parameters to realize high-quality gold-ball bonding. For this, we experimented with four different values for each parameter considered. Ball shear and wire pull strength between chip and bond pad were used as parameters to evaluate the quality of the gold-ball bond. Experimental results revealed that the ball shear and wire pull initially increase with an increase in the gold-ball thickness up to 12μm and then starts decreasing gradually with further increases in the gold-ball thickness. Further, ball shear and wire pull between chip and bond pad were found to decrease with increasing gold-wire loop height and loop length. For achieving good-quality gold-ball bonding, a gold-ball thickness of about 12μm, and assuming that the cost of the gold consumed is a major concern, a gold-wire loop height of 180μm and loop length of 1050μm are suggested.