Growth mechanisms of interfacial intermetallic compounds in Sn/Cu–Zn solder joints during aging

Abstract

The interfacial reactions of Sn/Cu-xZn (x = 15 and 30 at.%) solder joints were investigated. Before aging, [Cu 6 (Sn,Zn) 5 ] and [Cu 6 (Sn,Zn) 5 /Cu-Zn-Sn] intermetallic compounds (IMCs) formed at the [Sn/Cu-15Zn] and [Sn/Cu30Zn] interfaces, respectively. After thermal aging at 150°C for 80 days, [Cu 6 (Sn,Zn) 5 /Cu 3 (Sn,Zn)/Cu(Zn,Sn)/CuZn] and [Cu 6 (Sn,Zn) 5 /Cu(Zn,Sn)/CuZn] IMCs, respectively, formed at the [Sn/Cu-15Zn] and [Sn/Cu-30Zn] interfaces. Increasing the amount of Zn in the Cu-Zn substrates evidently suppresses the growth of Cu 3 Sn and Kirkendall voids at the solder joint interfaces. Transmission electron microscopy images show the different microstructure of CuZn and Cu-Zn-Sn phases in Sn/Cu-Zn joints. These Cu-Zn phases act to inhibit the growth of Cu 6 Sn 5 and Cu 3 Sn IMCs. As the content of Zn increased in Cu-Zn substrates, both CuZn and Cu(Zn,Sn) grew significantly. In addition, the growth of the Cu 6 (Sn,Zn) 5 / Cu 3 Sn IMCs approached a reaction-controlled process. The formation mechanisms of the CuZn and Cu(Zn,Sn) phases were probed and proposed with regard to the interfacial microstructure, elemental distribution, and the compositional variation at Sn/Cu-xZn interfaces.

An eco-friendly Cu-Zn wetting layer for highly reliable solder joints

“…While, the elongated scallop-type Cu 6 (Sn, Zn) 5 IMC layer formed in the Sn-2.5Ag solder/Cu-Zn interfaces. This Cu 6 (Sn, Zn) 5 IMC phase is generally observed in the SAC solder/Cu-Zn interfaces [9,13,14]. During reflow, Cu and Zn atoms dissolved from the CuZn layer into the solder, reacting with Sn to form scallop-type Cu 6 (Sn, Zn) 5 .…”

“…Previously, Cu-Zn solder wetting layers have been developed as an alternative solder wetting layer for Pb-free solders [9,[11][12][13][14][15][16] by replacing the conventional pure Cu wetting layer. Cu-Zn wetting layers have several advantages since Zn addition supressed the formation of large Ag 3 Sn plates in the Sn-Ag-Cu (SAC) solder [13], and slowed interfacial IMC growth [9,[11][12][13][14][15][16].…”

“…Cu-Zn wetting layers have several advantages since Zn addition supressed the formation of large Ag 3 Sn plates in the Sn-Ag-Cu (SAC) solder [13], and slowed interfacial IMC growth [9,[11][12][13][14][15][16]. Also, Cu 3 Sn and microvoids did not form in the SAC solder/Cu-Zn interfaces during aging [11,13,15].…”

Interfacial reactions in the Sn-9.0 wt.% Zn/Cu-Ti alloy (C1990 HP) couple

“…No Cu-Sn IMCs were found at the interface. The Gibbs formation energy of the Cu-Zn IMCs is lower (−10.8 kJ/mol to −11.2 kJ/mol) than the Cu-Sn IMCs (−6.2 kJ/mol to −7.0 kJ/mol) (Yu and Duh, 2012). Thus, the Cu atom initially reacts with the Zn atom to form the Cu-Zn IMCs at the interface.…”

Linear growth behaviour of intermetallic compound layer in electronic interconnections

“…20 Other studies speculate that n = 0.5 indicates lattice diffusion-controlled layer growth. 21 According to Schaefer et al, 22 there are a few basic assumptions regarding IMC layer growth: (a) the diffusion coefficients are independent of material compositions; (b) equilibrium is maintained at the phase boundaries; (c) the phase boundaries are flat and parallel; and (d) volume diffusion through the IMC layer is the predominant diffusion mechanism. Despite the inconsistencies associated with the n values for IMC layer growth, the parabolic growth law is mostly used for analysing the growth behaviour.…”