Behavior of Hydrogen in Electrolessly Deposited Ni/Au and Ni/Pd/Au Films

Abstract

This study was conducted to investigate changes in hydrogen amounts in metal films obtained using electroless nickel/immersion gold (Ni-P/ Au) and electroless nickel/electroless palladium/immersion gold (Ni-P/Pd/Au and Ni-P/Pd-P/Au) surface finishes used for microelectronic solder joints. Thermal desorption spectroscopy revealed that the Ni-P films contained large amounts of diffusible hydrogen that desorbs at room temperature. During electroless deposition of Pd and Pd-P on Ni-P films, the greater part of the hydrogen in the Ni-P films desorbed. Although no hydrogen evolution accompanied immersion gold deposition, the hydrogen amounts in Ni-P/Au, Ni-P/Pd/Au, and Ni-P/Pd-P/Au films were much greater than in films without a Au layer. Moreover, at room temperature, they remained almost unchanged for one month after deposition, indicating that the thin Au layer (＜0.1 μm) prevents hydrogen desorption from the metal films. The high hydrogen concentration in Ni-P/Au films improved solder wettability.