Corrosion study of electrodeposited Co-Ni-Fe protective coating on Electroless Nickel Immersion Gold (ENIG) flexible printed circuit

摘要

Flexible Printed Circuits (FPCs) have been vastly used in electronic devices such as mobile phones and sensors. This multi-layer polymer is used in electronic packaging to interconnect high performance devices. Electroless Nickel Immersion Gold (ENIG) is the final finishing method commonly applied on FPCs due to its excellent planarity, wear or abrasion resistance and electrical contact performance. However, corrosion problem on FPCs surface may influence the electrical conductivity, performance and thus affect the functionality of the end product. Previous published literature showed that Co-Ni-Fe enhanced the corrosion behavior of metals. Therefore, ternary Cobalt alloys (Co-Ni-Fe) have been synthesized as the protective coating on ENIG FPCs in this research. A low cost electrodeposition method is applied to produce a Co-Ni-Fe protective coating to improve the corrosion resistance of ENIG FPCs. The result will be compared between FPCs with and without protective coating. Co-Ni-Fe solution for electrodeposition process was prepared at pH 1. The current applied to coat the FPCs is 0.6 ± 0.05 A. The experiment conducted at 50°C ± 0.5 and performed at 30s and 60s of deposition time. Irregular shape of microstructure with grain size range from 46 nm to 88 nm was observed under FESEM micrographs. Corrosion test was performed by using Potentiodynamic Polarization technique under acidic environment. The corrosion rate per year of the FPCs after coated with electrodeposited Co-Ni-Fe showed lower corrosion rate than ENIG FPC. The corrosion behavior and surface morphology studies have shown that the electrodeposited Co-Ni-Fe coating improved the corrosion rate of ENIG FPCs.