Interfacial Reactions Between Pb-Free Solders and In/Ni/Cu Multilayer Substrates

Abstract

This study investigates the interfacial reactions between Sn-3.0wt.% Ag-0.5wt.%Cu (SAC) and Sn-0.7wt.%Cu (SC) on In/Ni/Cu multilayer substrates using the solid-liquid interdiffusion bonding technique. Samples were reflowed first at 160°C, 180°C, and 200°C for various periods, and then aged at 100°C for 100 h to 500 h. The scalloped Cu 6 Sn 5 phase was formed at the SAC/In/Ni/Cu and SC/In/Ni/Cu interfaces. When the reflowing temperatures were 160°C and 180°C, a ternary Ni-In-Sn intermetallic compound (IMC) was formed when the samples were further aged at 100°C. This ternary Ni-In-Sn IMC could be the binary Ni 3 Sn 4 phase with extensive Cu and In solubilities, or the ternary Sn-In-Ni compound with Cu solubility, or even a quaternary compound. As the reflow temperature was increased to 200°C, only one Cu 6 Sn 5 phase was formed at the solder/substrate interface with the heat treatment at 100°C for 500 h. Mechanical test results indicated that the formation of the Ni-In-Sn ternary IMC weakened the mechanical strength of the solder joints. Furthermore, the solid-liquid interdiffusion (SLID) technique in this work effectively reduced the reflow temperature.Key words: Sn-3.0wt.%Ag-0.5wt.%Cu and Sn-0.7wt.%Cu, lead-free solder, In/Ni/Cu multilayer substrates, solid-liquid interdiffusion bonding technique

A Novel Electronic Packaging Method to Replace High-Temperature Sn-Pb Solders

“…This method is accepted by most people in the soldering society and the results remain convincing. 3,5,7,11,12 The data reveal that a considerable amount of In and Ni atoms are incorporated into the Sn and Cu sublattices of the Cu 6 Sn 5 phase. The micro-island shaped and the light region dispersed among the (Cu,Ni) 6 (Sn,In) 5 phase with a unique Cu-1.0 at.% Ni-14.6 at.% Sn-52.8 at.% In composition is likely the Cu 2 In 3 Sn phase.…”

“…[2][3][4] The In/Sn/Metal multilayer structure substrate bonded with Pb-free solders has been successfully adopted in electronic packaging. [5][6][7] Yan et al concluded that the In-48Sn solder bonded strongly with a Cu substrate, which was proven by fractures occurring at solders instead of at interfacial regions in shear testing. The In-Sn/Cu interfacial reaction revealed the Cu/In/Sn/Cu joints bonded with the chip at low temperatures formed intermetallic compounds (IMCs), having melting temperature higher than 300°C.…”

“…The SLID technique can be used to connect the low-temperature solder and the high-temperature metallic substrate. 7,8 This In/Ni/Cu/Ni/In multi-layer structure is projected to match the qualities of high-temperature Sn-Pb solders and could therefore replace them.…”

Stable interconnections for LTCC micro-heater using isothermal solidification technique

“…Search for alternative solders and Pb-free soldering techniques, the intermetallic-based Pb-free solders development received a great deal of attention over past few decades because of its high-temperature stability, good electrical conductivity and thermal conductivity. The solid-liquid interdiffusion (SLID) (Liu et al , 2012; Yen et al , 2009) or transient liquid phase (Tollefsen et al , 2012; Venkatraman et al , 1997) followed by isothermal solidification (Kang et al , 2002; Sharma et al , 2010; Khanna et al , 1999a, 1999b; Sommadossi et al , 2002) are the prominent methods developed as Pb-free alternative solder joint formations. These methods based on the diffusion of atoms into an intermediate soft solder to form intermetallic compounds between two dissimilar metal surfaces and establish strong Pb-free interconnections for high-temperature microelectronic assemblies.…”