Development of Sn-Ag-Cu and Sn-Ag-Cu-X alloys for Pb-free electronic solder applications

‘Effects of Minor Alloying Additions on the Properties and Reliability of Pb‐Free Solders and Joints’

“…These minor alloying elements reported include such as Al, Be, Bi, Co, Fe, Hf, Mg, Mn, Mo, Ni, Pt, Ti, Zn, Zr, W, and others [9,12,14,18,25,26,35,[41][42][43][44][45]. Among them, Zn has been extensively investigated, because it is most effective and practical to be used with Sn or alloys [14,25,26,43,44].…”

“…The reduced growth of Cu 3 Sn was regarded to be beneficial to suppress the Kirkendall voids and thereby to improve the impact strength of the corresponding joint. However, in a search for the fourth element addition to Sn-Ag-Cu solders to improve the high-temperature aging resistance, the Ni addition was not favorably recommended, because it could cause a brittle failure or reduction in the impact strength after hightemperature aging [61]. The beneficial effects of minor Ti or Mn addition were reported with SAC joints by controlling their microstructure, improving drop impact strength as well as suppressing the interfacial IMC growth [62].…”

“…Accordingly, several approaches have been proposed to improve the impact reliability of Sn-rich solder joints. Among these are the placement of a diffusion barrier layer over Cu, such as electroless Ni(P) or electroplated Ni [22], and additions of minor alloying elements into the SAC alloys to control the IMC growth [18,22] or to suppress the interfacial void formation [17,25,26,52].…”

“…By the early 2000s, the near-ternary eutectic Sn-Ag-Cu (SAC) alloy compositions of melting temperatures around 217 C became a consensus candidate in the US as well as abroad [10][11][12][13][14][15][16][17][18]. Some variations of SAC solders are included in Table 5.1.…”

“…A few examples are listed here, such as severe interfacial reactions during reflow or thermal aging [6,19], large Ag 3 Sn plate formation [14], large undercooling during Sn solidification [17,18], unique twining microstructure in Sn-Ag or Sn-Ag-Cu [28], anisotropic physical/mechanical properties of Sn crystals [28], fast diffusions of Cu, Ag and Ni solute atoms along the c-axis of b-Sn crystal [30][31][32], only a few grains in BGA or flip-chip joints [15] and others. These new findings have also closely related with the reliability issues of Sn-rich solder joints.…”