中國(guó)有色金屬學(xué)報(bào)(英文版)
Transactions of Nonferrous Metals Society of China
| Vol. 26 No. 4 April 2016 |
（1. Corrosion and Protection Center, University of Science and Technology Beijing, Beijing 100083, China;
2. State Key Laboratory for Marine Corrosion and Protection,
Luoyang Ship Material Research Institute, Qingdao 266101, China;
3. Ningbo Institute of Material Technology & Engineering, Chinese Academy of Sciences, Ningbo 315201, China）
Abstract:The effects of relative humidity (RH) on a printed circuit board finished with electroless nickel immersion gold (PCB-ENIG) under an adsorbed thin electrolyte layer (ATEL) were investigated in situ via the measurement of cathodic polarization curves, electrochemical impedance spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy to clearly elaborate the corrosion behavior of PCB-ENIG in the atmospheric environment. Results indicated that the cathodic process of PCB-ENIG under ATEL was dominated by the reduction of dissolved oxygen, corrosion products, and H2O. The cathodic current density of PCB-ENIG increased progressively with increasing RH. Moreover, its cathodic current density in the solution was greater than that under ATEL. This result demonstrated that the diffusion process was not the controlling step during the limiting reduction of cathodic oxygen. When the polarization potentials were located in a more negative region, the cathodic polarization current density gradually decreased under 75% and 85% RH. Notably, the anodic process became the controlling step in the extremely thin liquid film during the remainder of the experiment.
Key words: electronic materials; adsorbed thin electrolyte layer; cathodic polarization curve; electrochemical impedance spectroscopy; relative humidity
