Mechanistic study of copper wire-bonding failures on packaging devices in acidic chloride environments

Abstract

Microelectronic reliability requirements are tightening to a standard of near zero ppb defects due to the evolution of self-driving cars and wearable electronics. The successful transition from gold (Au) to copper (Cu) in wire-bonding introduces corrosion related reliability concerns to wire-bonded devices in integrated circuit (IC) packaging. This report studies the effect of bimetallic contact, Cu wire vs. aluminum (Al) bond pad, on the corrosion failure of Al bond pads when exposed to low ppm levels of chloride (Cl−) contamination. Real time corrosion screening was carried out on simulating Cu/Al micro patterns for time-dependent observation of corrosion progression in 5–20 ppm Cl− solutions at pH 5. Al in Cu/Al bimetallic couple corroded at accelerated rate compared to Al without bimetallic contact. Cathodic hydrogen evolution was found to be the key factor driving this aggressive Al bond pad corrosion under the influence of the peripheral Cu/Al bimetallic contact in acidic chloride solution. Chemically modifying the surface of Cu wires to prevent this H2 evolution reaction resulted in the inhibition of Al bond pad corrosion.