Abstract
High-entropy alloys (HEAs) are promising materials for next-generation applications because of their mechanical properties, excellent high-temperature stability, and resistance against oxidation and corrosion. Although many researchers have investigated high-temperature HEA applications, few have considered low-temperature applications. Here we demonstrate an unprecedented intermetallic compound of (Fe, Cr, Co, Ni, Cu)Sn2 at the interface between Sn-3.0Ag-0.5Cu (SAC) solder and FeCoNiCrCu0.5 HEA substrate after reflow at 400 °C. Significantly suppressed growth of intermetallic compound without detachment from the substrate was observed during thermal aging at 150 °C for 150 h. Sn grains with an average grain size of at least 380 μm are observed. The results reveal a completely new application for the fields of Sn-Ag-Cu solder and HEA materials.
Highlights
Various studies indicate that high-entropy alloy (HEA), which is composed of at least five principal elements, has excellent mechanical properties and offers the advantages of high-temperature stability and resistance to oxidation and corrosion[1,2,3,4,5]
Using a scanning electron microscope (SEM, JOEL 7800, Japan) to observe the cross-sectional back-scattered images (BEIs), we find that the reflow temperature was 400 °C, the thickness of intermetallic compound (IMC) of (Fe, Cr, Co, Ni, Cu)Sn2, which is identified by energy dispersive X-ray spectrometer (EDS) and electron probe microanalyzer (EPMA, JOEL JXA-8530F, Japan), in SAC-HEA is approximately equal to the thickness of Cu-Sn IMC in SAC-Cu (Fig. 1b,e)
There are few Sn grain boundaries in SAC-HEA, those that are present are mostly cyclic twin boundary (CTB) which could prevent SAC solder from experiencing crack propagation and electromigration. These findings provide a method to fabricate SAC-HEA, and shed light on the reactions of SAC solder with HEA and the Sn microstructures in the SAC solder
Summary
These findings provide a method to fabricate SAC-HEA, and shed light on the reactions of SAC solder with HEA and the Sn microstructures in the SAC solder. The IMC formation of (Fe, Cr, Co, Ni, Cu)Sn2 at the interface is key to the SAC-HEA samples, and its excellent stability suppressed IMC growth at 150 °C. The average grain size is approximately 380 μm and CTBs are found in the Sn solder on the HEA substrate. Each sample was reversed and re-melted four times to assure chemical homogeneity. Fabricated Cu substrates 16 mm × 16 mm × 0.5 mm in dimension, and ball-shaped Sn-3.0Ag-0.5Cu solders with a diameter of 0.76 mm, were used. We used software to measure the areas of interface between Sn-3.0Ag-0.5Cu solder balls and the substrates. The equation can be expressed as follows: T= A , 18 μm where T is the IMC thickness, A is the measured area of IMC at the interface, and 18 μm is the measured width
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