Improve Interconnect Reliability of BGA Substrate with Stacked Vias by Reducing Carbon Inclusion in the Interface Between Via and Land Pad

In this paper, an investigation was carried out on how to improve bonding of electroless copper (Cu) to electroplated Cu by optimizing the activation process. First, interfacial structure between via and land pad was analyzed to identify the normal and abnormal features. Carbon inclusion was determined as an anomaly of Pd seed layer. Second, an experiment was performed to characterize the impact of activation dipping time and rinse time on the formation of carbon inclusions. A procedure was developed to quantitatively evaluate carbon inclusions in the via interface. It was found that, as expected, combination of shorter dipping time and longer rinse time resulted in fewer carbon inclusions in the Pd seed layer. Finally, based on the mechanism of Cu-Cu bonding and data from the experimental study, the quantity of carbon inclusions and the coverage of carbon on the interface are proposed for monitoring the quality of via/pad interface.