Correlation between microstructure and mechanical properties of Sn–Bi–X solders

Low Melting Temperature Solder Materials for Use in Flexible Microelectronic Packaging Applications

“…To be specific, two types of Bi-based micropowders, composed of binary Bi-Sn and ternary merits, including high wetting behavior, large creep resistance, and low coefficient of thermal expansion [12][13][14]. However, the relatively low mechanical strength and melting temperature (138°C) of these materials require improvement for their more effective use in flexible interconnection applications [3,15]. Comparatively, Sn-In solder, which has a low melting temperature (118 °C), has excellent electrical and thermal properties [12,16].…”

“…The microstructure reflects the mechanical properties of a solder [15][16][17][18][19][20][21]. Based on the microstructural analysis of low melting point solders, specific phases and their distribution in the microstructure can be observed, and these characteristics can be used to describe intended properties [15][16][17][18][19][20][21].…”

“…Based on the microstructural analysis of low melting point solders, specific phases and their distribution in the microstructure can be observed, and these characteristics can be used to describe intended properties [15][16][17][18][19][20][21]. In this section, we show how the microstructure of low melting point solders is altered by the incorporation of an additive, especially with regard to grain size and solid solution.…”

“…Usually, a plausible explanation for this is that Sn-and Bi-rich grains are heterogeneously nucleated in the formation of certain IMCs. For example, Mokhtari et al demonstrated that the addition of In or Ni can modify the microstructure of Sn-Bi solder; in particular, the addition of 0.5 wt.% In was able to suppress the coarsening of the Bi-rich phase, which means that the Sn-Bi-0.5In solder comprised primary Sn dendrites and eutectic phases [13,15]. Comparatively, Ni appears to have been included in the Sn phase since Ni-containing Sn-Bi solder exhibited eutectic phases and the Ni 3 Sn 4 IMC but did not show any sign of coarsening due to the Bi-rich phase.…”

“…For the cooling (solidification) process of the Sn-40Bi-2Zn-0.1Cu solder alloy from the liquid state, the following procedure took place: L (liquid) → L + primary Sn → primary Sn + eutectic (β-Sn + Bi-rich) + eutectic (β-Sn + Zn-rich) → primary Sn + secondary precipitated Bi + eutectic (β-Sn + secondary precipitated Bi + Bi-rich) + eutectic Figure 1. SEM micrographs of (a) eutectic Sn-Bi, (b) Sn-Bi-0.5In, and (c) Sn-Bi-0.5Ni [15].…”