Early stage soldering reaction and interfacial microstructure formed between molten Sn–Zn–Ag solder and Cu substrate

Abstract

The soldering reaction and interfacial microstructure formed between liquid Sn–Zn–Ag solder and Cu at the early stage of soldering at 250 °C for 15 s were studied primarily with the aid of transmission electron microscope (TEM). To achieve the early stage reaction information, the soldered specimens, 5 mm × 5 mm × 500 μm solder on 10 mm × 10 mm × 20 μm Cu, were rapidly quenched in liquid nitrogen after soldering. The results of TEM interfacial analysis show that a Cu–Zn reaction zone, consisting of β′–CuZn and γ–Cu5Zn8, formed near Cu while a Ag–Zn zone, consisting of γ–Ag5Zn8 and ϵ–AgZn3, formed near solder. The innermost layer adjacent to the Cu substrate is an amorphous Cu-Zn diffusion region that contains dispersed β′–CuZn nanocrystalline cells. The β′–CuZn also precipitates in the γ–Ag5Zn8 and ϵ–AgZn3 layer due to the supersaturation of Cu.

Role of Ag in the formation of interfacial intermetallic phases in Sn-Zn soldering

“…That is, the former one is formed through diffusion involving Al, and the AgZn 3 is likely to be formed during solidification. A recent transmission electron microscopy study by Yu et al 20 reveals that residual Ag 5 Zn 8 can be observed between Cu 5 Zn 8 and AgZn 3 at the Sn-Zn-Ag/Cu interface of liquid nitrogen-quenched sample. Those observations support the occurrence of peritectic transformation of Ag-Zn intermetallics illustrated in Fig.…”

Interfacial Reaction and Mechanical Characterization of Eutectic Sn–Zn/ENIG Solder Joints during Reflow and Aging

“…Therefore, the pursuit of Pb-free solder has become an important issue for electronic material research, and has led to extensive research and development work. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] Many different solder alloys have been proposed as potential Pbfree solders and the most promising of these falls into the category of the Sn-Ag, Sn-Ag-Cu and Sn-Cu family of alloys. 13,14) Recently, compared with Sn-Ag solders, Sn-Zn solders have been highly recommended as a substitute for eutectic Sn-Pb solder due to their low melting point, excellent mechanical properties and low cost.…”

“…7) Many studies have been performed on the interfacial reaction between Sn-Zn solders and the various surface finish layers (Cu, Au/Ni/Cu and electroless Nickel-immersion Gold [ENIG]) during reflow or aging. [8][9][10][11][12][16][17][18][19] According to these previous studies, 10,20) unlike the general reaction layer formed in a Sn-base solder (solder without Zn), stable binary Cu-Zn, Au-Zn, and Ni-Zn IMCs are formed between the Sn-Zn solder and various substrates. Nevertheless, our knowledge of the mechanical properties and joint reliabilities of Sn-Zn solder joints is still insufficient.…”

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

“…However, Cu 5 Zn 8 was the most stable phase under solidstate in the Cu-Zn binary system [20]. Usually, it was the dominant IMC formed at the interface between the Sn-Zn eutectic solder and the Cu substrate [23,24]. Nevertheless, in this study, Cu 5 Zn 8 was not found at both the Sn/Cu15Zn and Sn/Cu-30Zn interfaces.…”