Wire diameter and length effects on wire sweep performance of multi-tier copper and gold wire bonding in plastic ball grid array packages

As the semiconductor packaging industry continues to lower its manufacturing costs, concerted efforts in the supply chain focusing on using copper (Cu) as wire bond interconnects has intensified to an unprecedented level. In our previous study we showed that Cu wire has significantly higher wire sweep compared to gold (Au) wire after molding. In this study, wire sweep performance was further evaluated using various wire lengths and diameters of both Au and Cu wires in plastic ball grid array (PBGA) packages. In general, wire sweep increases with wire length increase and reduces with increasing wire diameter. It was accepted that wire sweeps are influenced by wire length, wire diameter, and density of wire which can be further explained with the cantilever deflection formula. In this study, a screening design of experiment was conducted on 18µm copper wire using thermally enhanced PBGA package to identify key molding parameter factors affecting wire sweep during mold encapsulation process. Based on JMP analysis, pellets preheat time, package pressure, and transfer speed are found to be the key factors to reducing the wire sweep percentage. Moreover, it was also found that the interaction of pellet preheat time and package pressure is also a significant factor to reduce overall Cu wire sweeping.