Boride Coatings on Steel Protecting it Against Corrosion by a Liquid Lead-Free Solder Alloy

The goal of this research is to study the applicability of the diffusion boriding process as a high-temperature thermochemical heat treatment to enhance the lifetime of steel selective soldering tools. The main purpose of the work is to discuss the behavior of double-phase (FeB/Fe2B) iron-boride coating on the surface of different steels (DC04, C45, CK60, and C105U) against the stationary SAC309 lead-free solder liquid alloy. The boride coating was formed on the surface of the steel samples through the powder pack boriding technique. The microstructure of the formed layer was examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The borided samples were first cut in half and then immersed into a stationary SAC309 lead-free solder liquid alloy (Sn–3Ag–0.9Cu) for 40 days. Microstructure examinations were performed by SEM with energy-dispersive spectroscopy and an elemental distribution map after the dissolution test. Excessive dissolution/corrosion of the original steel surface was observed at the steel/SAC interfaces, leading also to the formation of Fe–Sn intermetallic phases. This was found to be the major reason for the failure of selective soldering tools made of steel. On the contrary, no dissolution and no intermetallic compounds were observed at the FeB/SAC and at the Fe2B/SAC interfaces; as a result, the thicknesses of the FeB and Fe2B phases remained the same during the 40-day dissolution tests. Thus, it was concluded that both FeB and Fe2B phases show excellent resistance against the aggressive liquid solder alloy. The results of the dissolution tests show a good agreement with the thermodynamic calculations.

Study of mechanical properties of indium-based solder alloys for cryogenic applications

Purpose This study aims to develop indium-based solders for cryogenic applications. Design/methodology/approach This paper aims to investigate mechanical properties of indium-based solder formulations at room temperature (RT, 27 °C) as well as at cryogenic temperature (CT, −196 °C) and subsequently to find out their suitability for cryogenic applications. After developing these alloys, mechanical properties such as tensile and impact strength were measured as per American Society for Testing and Materials standards at RT and at CT. Charpy impact test results were used to find out ductile to brittle transition temperature (DBTT). These properties were also evaluated after thermal cycling (TC) to find out effect of thermal stress. Scanning electron microscope analysis was performed to understand fracture mechanism. Results indicate that amongst the solder alloys that have been studied in this work, In-34Bi solder alloy has the best all-round mechanical properties at RT, CT and after TC. Findings It can be concluded from the results of this work that In-34Bi solder alloy has best all-round mechanical properties at RT, CT and after TC and therefore is the most appropriate solder alloy amongst the alloys that have been studied in this work for cryogenic applications Originality/value DBTT of indium-based solder alloys has not been found out in the work done so far in this category. DBTT is necessary to decide safe working temperature range of the alloy. Also the effect of TC, which is one of the major reasons of failure, was not studied so far. These parameters are studied in this work.

Effect of Temperature Cycling on IMC Growth and Solder Joint Strength of SAC305 Solder Alloy and Low Silver Alloy REL61

This work deals with the comparison of the standard SAC305 (Sn 96.5 %; Ag 3 %; Cu 0.5 %) solder alloy with melting temperature between 217 - 220 °C and an alternative alloy REL61 (SnBiAgCu) with lower silver content and melting temperature in the range of 208 - 215 °C in terms of IMC layer growth during thermal cycling and its effect on the shear strength of the solder joints. The test PCBs were soldered using two different temperature profiles and the temperature cycling was performed under two different conditions. No negative effect of REL61 solder alloy on the growth of the IMC layer under thermal stress and on the subsequent shear strength of the solder joint was found. From this point of view, the REL61 solder alloy can be used as a replacement for the SAC305 solder alloy.

Thermal and Mechanical Properties of Sn-8Zn-3Bi Solder Alloy

Thermal and mechanical properties of Sn-8Zn-3Bi solder alloy on copper substrate were evaluated via measuring the melting temperature, the coefficient of thermal expansion (CTE), the tensile and shear strength of the solder joint. The measured properties of the alloy were then compared to the properties of the traditional and widely used eutectic Sn-37Pb solder alloy. The results show that the melting (liquidus) temperature of Sn-8Zn-3Bi was 195 °C, the CTE of Sn-8Zn-3Bi was 22.2´10-6 K-1 in the temperature range of 30-130 °C. At the same testing condition, both tensile and shear strength of Sn-8Zn-3Bi joints were higher than those of Sn-37Pb. The stress-strain curve indicated that the Sn-8Zn-3Bi joints were brittle whilst the Sn-37Pb joints were ductile.

Low Temperature Material Characterization of Lead-Free SAC Solder Alloy at High Strain Rate After Prolonged High Temperature Storage

During operations, handling, and storage in extreme environmental applications including aerospace, defense and automotive, the electronics may be exposed to high and low operating temperatures. In automotive underhood applications, the temperature can vary especially from −65 to +200 °C. Under prolonged storage, SnAgCu solder materials have been shown to continually evolve in the mechanical properties. New doped SAC solder alloys have recently been introduced with the addition of Ni, Co, Au, P, Ga, Cu and Sb to SAC solder alloy to increase the robustness under prolonged thermal exposure. High strain-rate data on SAC solder alloys after prolonged storage operating at low operating temperatures is not available in published literature. In this paper, materials characterization of SAC (SAC105 and SAC-Q) solder after prolonged storage at low operating temperatures (−65°C–0 °C) and at high strain rates (10–75 per sec) has been studied. The fabricated SAC leadfree solder specimens were isothermally aged up to 12 months at 50°C before testing. Anand Viscoplastic model has been used to compute 9 anand parameters from measured Tensile data to describe the material constitutive behavior. The computed 9 anand parameters were used to verify the accuracy of the Anand model. A good correlation was found between experimental data and Anand predicted data.