A Computational Thermodynamics-Assisted Development of Sn-Bi-In-Ga Quaternary Alloys as Low-Temperature Pb-Free Solders

Abstract

Low-temperature lead (Pb)-free solders are demanding in the electronic packaging industry, because it would open the door for various economic choices of polymeric materials as substrates and also revives the lower cost processes. Here, we proposed a tin–bismuth–indium–gallium (Sn-52.5Bi-2.68In-1Ga, SBIG (in wt.%)) quaternary low-temperature solder, designed based on systematic CALPHAD (CALculation of PHAse Diagram)-type thermodynamic calculations and corresponding key experiments. The solidification behavior of SBIG was carefully elaborated based on the computations using the lever rule and the Scheil model, and the experiments in terms of thermal analyses and microstructures of sample produced with step-quenching and various cooling rates. The mechanical properties of as-cast and 80 °C-annealed SBIG as well as their microstructures and fracture surfaces were evaluated in the tensile tests. The proposed SBIG solder is with a low liquidus temperature of 141.9 °C and is typically composed of the primary (Sn) phase, the (Sn) + (Bi) eutectic structure and a small amount of (Ga) phase. Air cooling has been identified as a satisfactory cooling rate, which would not lead to the formation of the brittle BiIn intermetallic compound. The as-cast SBIG solder exhibited high yield strength (YS) of 43.7 MPa, high ultimate tensile strength (UTS) of 53.3 MPa and an extremely large elongation of 97.3% as comparing to the conventional eutectic Sn-58Bi solder (YS: 43.1 MPa, UTS: 49.5 MPa, and elongation: 37.5%). However, the proposed SBIG solder does not possess qualified thermal stability, that significant degradation in both strength and elongation were observed after being subjected to extensive thermal ageing at 80 °C for 504 h.

Ultrasonic-Assisted Dispersion of ZnO Nanoparticles to Sn-Bi Solder: A Study on Microstructure, Spreading, and Mechanical Properties

“…In general, fracture in eutectic SnBi alloy balances the toughness of ductile Sn-rich phase and the brittle Bi phase. The bulge fracture occurs in the ductile Sn-rich phase and cleavage fracture occurs in the brittle Bi phase (Ref 22 ). Sn57Bi alloy with 0.05 wt.% ZnO (Figure 4 c) shows a dominant bulge fracture mode with dimples.…”

On the Direct Extrusion of Solder Wire from 52In-48Sn Alloy

“…It always has a melting point lower than the parts to be joined [1]. To date, a large number of solder alloys have been created, which differ in composition, material ratio, and the presence of impurities [2,3,4,5,6,7,8]. According to the melting temperature, the solders are subdivided into solders for low-temperature soldering with a melting point of not more than 450 ° C [9] and soldering alloys for high-temperature soldering with a melting point of more than 450 ° C [10].…”

“…In 2006, the European Union's RoHS (Restriction of the Use of Certain Hazardous Substances) Directive on the Environment restricted the use of lead in new electrical and electronic equipment to a maximum of 0.01% [12]. Several environmental-friendly Sn-based alloys such as Sn-3.0Ag-0.5Cu [13], Sn-14Bi-5In [14], Sn-0.7Cu [15], Sn-9Zn [8], Sn-8Zn-3Bi [16], Sn-58Bi [17], Sn-52.5Bi-2.68In-1Ga [18], Sn-In [6] have been considered the most promising candidates to replace the toxic Sn-Pb alloy from electronic packaging systems [2].…”

Analysis of Sn-Bi Solders: X-ray Micro Computed Tomography Imaging and Microstructure Characterization in Relation to Properties and Liquid Phase Healing Potential

“…Efforts to reduce the environmental impact of microelectronic products led to the development of lead-free solder alloys with varying content of Ag, Bi, In, Cu, Ga and Zn among other alloying elements [ 1 , 2 , 3 , 4 , 5 , 6 ]. The effort to reduce the environmental impact of Pb containing solders led to several alloys of varying Sn, Ag and Cu content [ 7 ].…”