Impact of Thermal Aging on the Microstructure Evolution and Mechanical Properties of Lanthanum-Doped Tin-Silver-Copper Lead-Free Solders

Abstract

is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. An extensive study is made to analyze the impact of pure lanthanum on the microstructure and mechanical properties of Sn-Ag-Cu (SAC) alloys at high temperatures. Different compositions are tested; the temperature applied for the isothermal aging is 150°C, and aging times of 10 h, 25 h, 50 h, 100 h, and 200 h are studied. Optical microscopy with cross-polarized light is used to follow the grain size, which is refined from 8 mm to 1 mm for as-cast samples and is maintained during thermal aging. Intermetallic compounds (IMCs) present inside the bulk Sn matrix affect the mechanical properties of the SAC alloys. Due to high-temperature exposure, these IMCs grow and hence their impact on mechanical properties becomes more significant. This growth is followed by scanning electron microscopy, and energy-dispersive spectroscopy is used for elemental mapping of each phase. A significant refinement in the average size of IMCs of up to 40% is identified for the as-cast samples, and the coarsening rate of these IMCs is slowed by up to 70% with no change in the interparticle spacing. Yield stress and tensile strength are determined through tensile testing at 20°C for as-cast samples and after thermal aging at 150°C for 100 h and 200 h. Both yield stress and tensile strength are increased by up to 20% by minute lanthanum doping.

Effect of Lanthanum Doping on the Microstructure Evolution and Intermetallic Compound (IMC) Growth during Thermal Aging of SAC305 Solder Alloy

“…Also grain size decreases significantly up to 0.05% of La doping and then increase slightly with increasing amount of La doping. This is consistent with the previous studies conducted by Min et al [25] and Sadiq et al [94] for Sn-3.5Ag and SAC305 alloy respectively with similar La doping. Also a slight change in the grain size for La-doped alloy has been observed with thermal aging.…”

“…Also a slight change in the grain size for La-doped alloy has been observed with thermal aging. This demonstrates that La-doping refines the grains which comply to [25] and Sadiq et al [94]. The philosophy of this refinement is because of the particular effect of La adsorption at different planes in the Sn-Ag-Cu alloys.…”

Study on coarsening of Ag3Sn intermetallic compound in the Fe-modified Sn–1Ag–0.5Cu solder alloys

“…Maleki et al [16] reported that a considerable coarsening of Ag 3 Sn IMC particles occurs in the Sn-4Ag-0.5Cu solder alloy during ageing and therefore the mechanical behavior of solder shows a continuous reduction in the yield resistance. The impact of pure La on the microstructure and mechanical properties of Sn-3Ag-0.5Cu alloy at high temperatures was studied by Sadiq et al [17]. According to them, the addition of La refined the microstructure, and reduced the size of particles of Ag 3 Sn IMC up to 40% for the as-cast samples, and drastically reduced the coarsening rate of these particles by up to 70% with no changes in the particle spacing, which in turn improved the mechanical properties of Sn-3Ag-0.5Cu alloy.…”

A review: microstructure and properties of tin-silver-copper lead-free solder series for the applications of electronics

“…In SAC, the near eutectic composition consists of a high volume of β-Tin (Sn) matrix and intermetallic compounds (IMCs) namely Ag 3 Sn, Cu 6 Sn 5 and Cu 3 Sn (El-Daly et al, 2013). In comparison to the Snmatrix, IMCs are brittle in nature and represent the properties of solder alloys (Sadiq et al, 2013). It is worth noting that the formation of Ag 3 Sn is due to the reaction between Sn and Silver (Ag) whereas Cu 6 Sn 5 is possibly formed by the reaction between Sn and Copper (Cu).…”