Evaluation on the characteristics of tin-silver-bismuth solder

Abstract

Tin-silver-bismuth solder is characterized by its lower melting point, good wetting behavior, and good mechanical property for which it is expected to be a new lead-free solder to replace tin-lead solder. In this article, Sn-3.33Ag-4.83Bi solder was investigated concerning its physical, spreading, and mechanical properties under specific conditions. Cooling curves and DSC results showed that it was close to eutectic composition (m.p. 210°-212°C). Coefficiency of thermal expansion (CTE) of this solder, between that of PCBs and copper substrates, was beneficial to alleviate the thermal mismatch of the substrates. It was also a good electrical and thermal conductor. Using a rosin-based, mildly activated (RMA) flux, a spreading test indicated that SnAgBi solder paste had good solderability. Meanwhile, the solder had high tensile strength and fracture energy. Its fracture mechanism was a mixture of ductile and brittle fracture morphology. The metallographic and EDAX analyses indicated that it was composed of a tin-based solid solution and some intermetallic compound (IMC) that could strengthen the substrate. However, these large needle-like IMCs would cut the substrate and this resulted in the decreasing of the toughness of the solder.

Effect of thin gold/nickel coating on the microstructure, wettability and hardness of lead-free tin–bismuth–silver solder

“…The better wettability and good mechanical properties environmental-friendly Sn-35Bi-1Ag (wt%) based solder alloy (187°C), with a melting temperature close to the eutectic Sn-Pb solder (183°C) has been considered as a suitable replacement for the traditional Sn-Pb solder alloy used in electronic packaging industries [33,34]. Some fundamental research works are available in the literature [33][34][35], but the knowledge of interfacial reaction kinetics and wettability of the Sn-35Bi-1Ag solder on Au/Ni-plated Cu substrate is insufficient. However, for widely industrial application it is a fundamental issue to clearly demonstrate their microstructure, chemical kinetics and material properties on different surface-finished Cu substrates.…”

Interfacial microstructure, wettability and material properties of nickel (Ni) nanoparticle doped tin–bismuth–silver (Sn–Bi–Ag) solder on copper (Cu) substrate

“…For instance, the high melting point lead-free Sn-based interconnect materials may damage the polymer-based substrates having a low glass transition temperature, hot tearing due to the formation of large size Sn dendrites, non-homogeneous distribution of strain, excessive growth of IMC layers and relatively poor wettability as compared to the eutectic SnPb solder alloys [15]. Among the Sn-based lead-free solder alloys, the superior wettability and good mechanical properties of Sn-Bi-Ag based solder alloy, with the melting temperatures close to the eutectic Sn-38Pb solder have been regarded as a possible replacement for the conventional Sn-Pb solder alloy used in electronic packaging systems [16][17][18].…”

Effect of aluminium additions on wettability and intermetallic compound (IMC) growth of lead free Sn (2 wt. % Ag, 5 wt. % Bi) soldered joints

“…%, huge platelets of Ag 3 Sn are generated, and they impair solderability. [19] On the other hand, if the Ag content in the Sn-Ag alloy is lower than 2 wt. %, finer Ag 3 Sn particles will be uniformly dispersed in the Sn-Ag solder.…”