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Ultrathin AlN barrier coatings for enhancing surface chemical stability and suppressing electrochemical migration in immersion silver–finished printed circuit boards
Author(s)
Kaewbuadee, Woraprach
Theekhasuk, Nattharika
Khumtong, Thanakorn
Date Issued
August 15, 2026
Type
Article
Abstract
Immersion silver-finished printed circuit boards (PCB-ImAg) provide low contact resistance and excellent solderability, but their chemical instability in humid and sulfur-containing environments can compromise long-term reliability. In this study, ultrathin aluminum nitride (AlN) films (20–60 nm) were deposited on PCB-ImAg substrates by reactive DC magnetron sputtering as inorganic barrier layers. Their protective performance was evaluated by accelerated H2S exposure, long-term ambient air exposure, tape testing, electrical resistance measurements, electrochemical migration (ECM) testing under a 3 V bias at 30 °C and 80% RH, and surface characterization. Uncoated PCB-ImAg samples showed severe tarnishing, Ag2S formation, dendritic corrosion, and a marked increase in electrical resistance after both H2S and prolonged air exposure. In contrast, AlN-coated samples retained a cleaner surface, remained adherent after the tape test, and showed much smaller resistance changes. X-ray photoelectron spectroscopy detected sulfur-related chemical states only on the uncoated surfaces, indicating suppression of sulfide formation by the AlN layer. A 20 nm AlN coating was sufficient for anti-tarnish and ambient air stability, whereas coatings of 40 nm or greater were required for robust ECM suppression. These results demonstrate that ultrathin AlN films effectively improve the corrosion resistance and ECM reliability of PCB-ImAg surfaces.
Citation
Applied Surface Science, 737, 2026