Mechanisms for interfacial reactions between liquid Sn-3.5Ag solders and cu substrates

Abstract

Intermetallic compounds formed during the soldering reactions between Sn-3.5Ag and Cu at temperatures ranging from 250°C to 375°C are investigated.The results indicate that scallop-shaped η-Cu 6 (Sn 0.933 Ag 0.007 ) 5 intermetallics grow from the Sn-3.5Ag/Cu interface toward the solder matrix accompanied by Cu dissolution. Following prolonged or higher temperature reactions, ε-Cu 3 (Sn 0.996 Ag 0.004 ) intermetallic layers appear behind the Cu 6 (Sn 0.933 Ag 0.007 ) 5 scallops. The growth of these interfacial intermetallics is governed by a kinetic relation: ∆X ϭ t n , where the n values for η and ε intermetallics are 0.75 and 0.96, respectively. The mechanisms for such nonparabolic growth of interfacial intermetallics during the liquid/solid reactions between Sn-3.5Ag solders and Cu substrates are probed.

Effect of thermal aging on the interfacial reactions of tin-based solder alloys and copper substrates and kinetics of formation and growth of intermetallic compounds

“…Some areas of this interface (growth front) developed into elongated, needlelike morphologies such as the one shown in the micrograph. In other areas, the initiation of the needle-like morphologies, "A", and the formation of the scalloped structures [16], "B", were observed, Figure 4(a). In addition, Ag 3 Sn was found in the form of small particles at the Cu 6 Sn 5 /solder interface.…”

Mechanisms for the intermetallic formation during the Sn-20In-2.8Ag/Ni soldering reactions

“…These islandlike precipitates possess a composition (at.%) of Ag : In ϭ 67.7 : 32.3, which corresponds to the Ag 2 In phase. A previous study indicated the appearance of fine Ag 3 Sn particles in large quantities in an as-cast Sn-3.5Ag solder, 15 but those particles are absent in this Sn-20In-2.8Ag solder. The EDX analysis also shows that the formation of Ag 2 In precipitates causes the composition (wt.%) of the matrix to deviate from Sn-20In-2.8Ag to Sn-22.6In-1.2Ag.…”

Interfacial reactions of Cu-containing lead-free solders with Au/NiP metallization

“…The EDX analysis established that the medium-Cu containing QIMCs have formed at the interface. 14,17 The atomic percentage of the QIMCs was Sn 0.51 Cu 0.26 Ni 0.20 In 0.03 . A small amount of InSn-Au IMCs have been entrapped into the QIMCs (Figs.…”

“…The growth rates of TIMCs in the solder joints are diffusion controlled. 14 Figure 5a shows that Cu 6 Sn 5 compounds have formed with a specific shape in the Sn-Cu solder. The formation of high-Cu containing TIMCs is insufficiently fast to consume all the Cu atoms from the liquid of Sn-Cu solder.…”

“…11 Cheng et al reported that the strength of Sn-3.8Ag-0.7Cu solder joints were higher than that of Sn-20In-2Ag-0.5Cu solder joints. 14 The formation of AuIn 2 compounds prevents the formation of more brittle intermetallic compounds such as AuSn 4 in the bulk solder. 15 In15Pb-5Ag solder has a higher strength and a lower thermal coefficient of expansion than those of pure In and it reduces the embitterment by Au.…”