Authored By:
Dr. Lei Jin, Dr. Jun Nable, Dr. Kesheng Feng, Lenora Toscano, Dr. Ernie Long
Electronics Solutions, MacDermid, Inc.
Waterbury, CT USA
Summary
An electroless nickel (EN) layer is frequently used in various industrial applications. Commonly it is used as the barrier layer in electroless nickel/immersion gold (ENIG) as a solderability preservative for the electronics industry. The finish provides excellent corrosion resistance and good solderability. A shortcoming of this process is the potential for a hyperactive corrosion of the nickel surface during immersion gold plating. The resultant defect displays itself as a gray or black appearance at the nickel/gold interface, known as "Black Pad" or "Black Line Nickel".
It is important to determine and control the corrosion properties of an EN deposit during an ENIG process to obtain high quality products. Unfortunately, quantitative analysis of corrosion resistance of the EN layer has not been established in the field of PCB. In this paper, an electrochemical method via sequential electrochemical reduction analysis (SERA) instrument to quantify the corrosion resistance of the EN deposit is proposed. The data obtained via the electrochemical method was analyzed and correlated to the deposit properties of the EN. The method is easy to use and can be applied for quantitative analysis in industrial EN processes.
Conclusions
Results presented here show that the new SERA test method can be applied on a routine basis to assess the corrosion resistance behavior of EN deposit. This method is a relatively simple, fast, and quantitative analysis. Within the same EN bath, this method can even be used to determine P% at different points on a PCB boards. This proposed method can also been applied on other applications, such as EN quality control, product screening, and formulation comparisons on a simple and quantitative basis.
Initially Published in the IPC Proceedings
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