Development of novel electroless nickel for Selective electroless nickel immersion gold applications

There are a number of final finishing technologies available in the market, each with different cost and performance attributes. The unique attributes of the Selective ENIG process have made it a popular choice for mobile device and high density interconnect (HDI) applications. This hybrid final finishing process combines the benefits of both ENIG and organic solderability preservative (OSP) processes. ENIG surfaces typically exhibit excellent planarity, electrical contact performance, solderability, wire bondability and wear/abrasion resistance, while OSP shows excellent solder joint reliability. However, the OSP process, applied after the ENIG step, induces a great stress on the corrosion resistance of the ENIG deposit. Attack of the aggressive process chemistries used in the OSP process on an ENIG deposit with insufficient corrosion resistance might cause nickel corrosion, gold peel-off or solder joint failure, which could affect the reliability of final product. Appropriate corrosion protection against multiple passes through an OSP process is therefore required. A new electroless nickel, which is compatible with a low gold immersion gold process, has been developed to protect ENIG deposits from corrosion after multiple OSP exposures, and to minimize the potential for galvanic corrosion during immersion gold plating. In this article, the characteristics of this newly developed electroless nickel process are described. Corrosion resistance capability to OSP is compared with currently available ENIG processes. The solder joint intermetallic compound structure and reliability performance are also discussed.