Abstract
Tin–indium alloys represent attractive lead-free solder candidates. They show lower values of melting point than pure indium, so that they are investigated as materials with significant applications potential in the electronic industry. Electrodeposition is a very convenient route to prepare Sn–In alloys. The paper presents several experimental results regarding the electrodeposition of Sn–In alloy coatings involving deep eutectic solvents (DESs), namely using choline chloride-ethylene glycol eutectic mixtures. The influence of the main operating parameters on the Sn–In alloy composition and characteristics are presented. Adherent and uniform Sn–In alloy deposits containing 10–65 wt % In have been obtained on Cu substrates. The In content was found to increase as both the In:Sn molar concentration ratio of ionic species in the electrolyte and the applied temperature increased. The use of pulsed current allowed the use of higher current densities leading to slightly higher values of In content in the alloy deposit. X-ray diffraction (XRD) analysis revealed the presence of InSn4 and In3Sn phases in agreement with the phase diagram. According to thermogravimetric analysis (TGA) measurements, values of melting points in the range of 118.6 and 127.5 °C were obtained depending on the alloy composition. The solder joints’ behavior and alloy coatings corrosion performance were also discussed.
Highlights
Several years back and motivated by environmental and health concerns, the legislation regarding the end-of-life disposal and the European Union’s (EU) Restriction of Hazardous Substances (RoHS)Directive determined the elimination of SnPb solder from all electronic applications in the EU and other countries’ markets, including China, Japan, South Korea, Turkey and the United States [1,2]
Considering the above, the present paper aims to explore the feasibility of the co-electrodeposition of Sn–In alloy coatings involving deep eutectic solvents (DESs), mainly using choline chloride-ethylene glycol eutectic mixtures
Viscosity values between 35 and 7 mPa·s have been determined for the same range of temperature, quite comparable with those of the pure ILEG solvent
Summary
Directive determined the elimination of SnPb solder from all electronic applications in the EU and other countries’ markets, including China, Japan, South Korea, Turkey and the United States [1,2]. Under these circumstances, the development of lead-free solder alloys attracted increased interest. A major problem affecting reliability aspects in long-life electronic applications is represented by the tin whiskers They represent crystalline filaments 1–10 μm thick and up to hundreds of microns long, which can grow from any high-Sn solder or coating, causing short circuits. Various substitute approaches that mitigate the whiskers growth of Sn include the use of Bi, of Ni underlayer or of conformal coatings [9,10,11,12]
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