Investigation of reactions between lead/tin solder and palladium surface finishes

• Published in: Acta materialia Vol. 50; no. 18; pp. 4667 - 4676
• Main Authors: Kobe, B, McIntyre, N.S
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 28.10.2002; Elsevier Science
• Subjects: Applied sciences; Brazing. Soldering; Composite materials; Diffusion; Exact sciences and technology; Growth kinetics; Intermetallics; Joining, thermal cutting: metallurgical aspects; Lead; Metallurgy; Metals. Metallurgy; Palladium; Solder; Thin films; Tin; X ray analysis; Solder; Intermetallics; Palladium; Diffusion; Growth kinetics; Scanning electron microscopy; Intermetallic compound; Tin; Lead; Solder metal; Experimental study; Soldering; Thin film
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/S1359-6454(02)00319-1

The role of palladium as a surface finish for the electronics industry was investigated. Of particular interest were the metallurgical phases that form during and following soldering operations of palladium thin films. The formation of PdSn 4 intermetallics on composite substrates (gold/palladium/nickel) with varying palladium chemistry and layer thickness were soldered at 220 °C and observed using scanning electron microscope combined with energy dispersive X-ray (SEM/EDX) analysis. Thin layers of palladium approximately 1 μm thick, combined with a fast dissolution rate also resulted in the formation of Ni 3Sn 4 intermetallics. The role of phosphorus in palladium thin films was also investigated. Its presence was found to increase the solubility of palladium in molten solder producing intermetallic crystals that are confined to the bulk. A thin gold layer, used to protect the palladium was found to dissolve rapidly into the solder and to redeposit, forming a thin layer just outside the PdSn 4 intermetallic structure.