Initial interfacial reaction layers formed in Sn–3.5Ag solder/electroless Ni–P plated Cu substrate system

• Published in: Journal of materials research 2008-08, Vol.23 (8), p.2195-2201
• Main Authors: Kang, Han-Byul, Lee, Jae-Wook, Bae, Jee-Hwan, Park, Min-Ho, Yoon, Jeong-Won, Jung, Seung-Boo, Ju, Jae-Seon, Yang, Cheol-Woong
• Format: Article
• Language: English
• Subjects: Applied and Technical Physics; Biomaterials; Inorganic Chemistry; Materials Engineering; Materials Science; Nanotechnology; Packaging; Soldering; Transmission electron microscopy (TEM)
• ISSN: 0884-2914; 2044-5326
• DOI: 10.1557/JMR.2008.0266

Analytical electron microscopy (AEM) was used to examine the initial interfacial reaction layers between a eutectic Sn–3.5Ag solder and an electroless nickel-immersion gold-plated (ENIG) Cu substrate during reflow at 255 °C for 1 s. AEM confirmed that a thick upper (Au,Ni)Sn2 layer and a thin Ni3Sn4 layer had formed through the reaction between the solder and ENIG. The amorphous electroless Ni(P) plated layer transformed into two P-rich Ni layers. One is a crystallized P-rich Ni layer, and the other is an intermediate state P-rich Ni layer before the crystallization. The crystallized P-rich layer consisted of Ni2P and Ni12P5. A thin Ni2P layer had formed underneath the Ni3Sn4 layer and is believed to be a predecessor of the Ni2SnP ternary phase. A Ni12P5 phase was observed beneath the Ni2P thin layer. In addition, nanocrystalline Ni was found to coexist with the amorphous Ni(P) phase in the intermediate state P-rich Ni layer.