Intermetallic compound surfaces effect characteristics

In section 3 the phenomenon of hydrogen sorption in intermetallic compounds is described. Topics dealt with in this section are activation treatment, pressure-composition isotherms, miscibility gap, sorption hysteresis, lattice expansion, diffusion, sorption kinetics, surface effects, poisoning, impurity effects and decomposition of ternary hydrides. The sorption characteristics of all ternary rare-earth hydrides investigated are listed in several tables given in the appendix. For comparison the sorption characteristics of some selected ternary hydrides based on non-rare-earth metals are given in a separate table. 

A detailed study on the wetting characteristics of eutectic Bi-Sn solder has been reported in terms of impurity effects, fluxes, base metals, and soldering temperature [18]. It was determined that eutectic Bi n solder is far less tolerant of impurities than eutectic Plr n [19]. In particular, the presence of impurity elements which form intermetallic compounds with Bi-Sn solder, such as Cu, Ni, Fe, and Pd, is especially critical, while Sb and Pb appear to be beneficial in terms of promoting wetting characteristics. Table 1 compares the solderabihty of several low-melting-point solders on various surface metallizations [20]. Only the Au/Ni-plated metallization is considered acceptable for Bi n solder, while the Cu, Ni, and Au/Ni metallizations are all acceptable for eutectic Sn Pb solder when a rosin-base flux is used. Another study confirmed that Bi Sn solder does not wet Cu-base metallizations as well as eutectic Sn-Pb solder does when a rosin-base flux is used [21]. However, if the Cu surface is pre-tirmed, then Bi-Sn wetting is acceptable even with a rosin-base flux [22]. Based on the wettabihty studies, eutectic Bi-Sn solder can only be considered a viable candidate if a suitable flux system is developed which allows it to be utilized for metallizations other than a Au/Ni overplate. 

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