“…40,41 The samples were cut using a sawing machine (Buehler, Isomet 1000), cold mounted in a mixture of epoxy resin and hardener, grounded (PM-1V) with SiC abrasive paper from 800, 1000, 1200, 2000, and 4000 grit with a speed of 50–100 rpm, and polished (PM-1V) using Dp-Nap polishing cloth and diamond sprays of 6 and 1 µm with a speed of 50 rpm. The microstructure of the solder joint, which consists of Cu substrate, IMC layer, and solder matrix, was observed and analysed qualitatively and quantitatively using focus variation microscopy (Alicona, G4) 38,42 and a field emission scanning electron microscope equipped with energy dispersive spectroscopy (ZEISS, MERLIN COMPACT) for morphology and elemental characterisation. The average IMC layer thickness has been estimated from 300 measurement points for each HTS time.…”