Sn–Bi–Fe thermodynamic modeling and Sn–Bi/Fe interfacial reactions

Phase Diagrams and Their Applications in Pb‐Free Soldering

“…Since Fe is the major constituent of steels used in lead frames and solder pots [71,72], understanding the Sn-Bi/Fe interfacial reactions is important. As shown in Figure 2.28, the growth rates of the intermetallic compounds in the Sn-57 wt%Bi/Fe couples reacted at 390 C are higher than those at 500 C [33]. Further examination reveals that the different reaction rates are results of formation of different reaction phases at different temperatures.…”

“…Both experimental and thermodynamic modeling results are usually available for most of the binary solder-related phase diagrams; however, information regarding the ternary and higherordersystemsisrelativelylimited.Experimentalphaseequilibriummeasurementsareavailable for Sn-Ag-Au [19][20][21][22], Sn-Ag-Cu [23][24][25][26][27], Sn-Ag-Ni [28], Sn-Bi-Au [29], Sn-Bi-Ag [30,31], Sn-Bi-Cu [32], Sn-Bi-Fe [33], Sn-Bi-Ni [34], Sn-Cu-Au [35], Sn-Cu-Ni [36,37], Sn-In-Au [38], Sn-In-Cu [39], Sn-In-Ag [40], Sn-In-Ni [41], Sn-Sb-Ag [12,[42][43][44], Sn-Sb-Au [45], Sn-Zn-Ag [46], Sn-Zn-Bi [47], and Sn-Zn-Cu [48], and Sn-Ag-Cu-Ni [49,50] systems. As for lead-free soldering, there are some commercial thermodynamics databases, such as COST531 database [51], NIST solder database [52] and ADAMIS database [53].…”

“…A schematic diagram illustrating the composition profile through an A-B reaction couple is shown in Figure 2.25. Although the reaction couple is not in thermodynamic equilibrium, the local equilibrium condition usually holds at the interfaces [11,28,33,66,74,85]. When the local equilibrium condition is followed, the kinds and compositions of the IMCs can be determined from the phase diagrams.…”

“…However, for ternary or higher-order systems, there are diverse possibilities of reaction and solidification paths. An isothermal section of phase equilibria in a ternary system is a useful tool for illustrating interfacial reactions at a binary solder/substrate joint [11,28,33,66,74,85]. It must be mentioned that interfacial reactions and the IMC formation are not only governed by thermodynamics but also kinetics, and it is risky to predict the interfacial reactions using phase diagrams alone.…”

“…The remaining question is what drives the changing of FeSn 2 into FeSn phase at reaction temperatures of 390 C and 500 C, respectively. Figures 2.29-2.31 are the isothermal sections of the Sn-Bi-Fe ternary system at 390 C, 395 C and 500 C, respectively [33]. For reaction temperatures lower than 395 C, there are tie lines between the FeSn 2 and molten Sn-Bi eutectic alloy, and the formation of the FeSn 2 phase is thermodynamically feasible.…”