Correlations of Long-Term Reliability and Irregularly Electrodeposited Metal Surface Induced Corrosion on Module Tabs

摘要

One of the most common chemical failures to reduce long-term reliability of electronic devices is the corrosion. A particular factor causing it is the local heterogeneity either in metal or in electrolyte. In this study,we will discuss the extremely accelerated local attack that results in holes in electrodeposited Au/Ni/Cu substrates and electroless nickel immersion gold pads. The driving force for this local corrosion is roughly deposited metal surfaces which make the galvanic potential difference at the interface of Au and Ni. Although it is not easy to detect pits at the initial state of corrosion because of their small size,once the hole is formed the rate of metal erosion incredibly increases. In case of ENIG pads,we observed not only even large pores penetrating into the underlying Cu substrates but also the oxidized Ni depositing on the top Au layer,indicating that the Au/Ni/Cu layered structure was transformed to the NiO/Au/Cu structure through such pores. In order to accelerate ion assisted surface restructuring or surface breakdown ascribed to the heterogeneous electrodeposition and to measure the corrosion phenomena,we employed electrochemical approaches such as potential cycling and potential steps. Using scanning electron microscopy and optical microscopy,the modified surface structures could be revealed. We expect that this study will help the improved reliability in solder joints or wire bonding on ENIG pads and package substrates as well as give a clue for producing anticorrosive substrates. In respect to this,we suggest the potential pulse method in which the electrochemical potential goes toward negative and positive direction repeatedly to obtain a homogeneously electrodeposited substrate.