Oca25htv

The wettability of the solders was conducted by a high-temperature wettability angle tester (OCA25HTV, Data Physics Instruments, Stuttgart, Germany), during which the temperature was increased from room temperature to 500 °C at a heating rate of 5 °C/min with a holding time of 1 h, and then decreased to room temperature with the same rate of 5 °C/min. In the wettability test, the mass of the solder ball was 0.3 g, and the size of the copper plate used as the substrate was 3 × 3 × 3 mm³. The solder flux of RMA218 from Seamark ZM was used for the wettability test. The wettability tests were performed three times for each alloy composition.

SEM (GeminiSEM 500, China) and TEM (JEOL JEM2100, Japan) were used to characterize the samples’ morphology. X-ray diffraction (XRD) patterns were acquired on a PANalytical X’pert MPDPro (The Netherlands) using a Cu Kα radiation source (40 kV, 40 mA). The AXIS ULtrabld (UK) instrument was used to obtain X-ray photoelectron spectroscopy (XPS) using a monochromatic Al Kα radiation source (15 kV, 1486.6 eV). Fourier-transform infrared spectroscopy (Bruker Tensor 37 spectrometer, China) was used to determine surface functional groups and chemical bonds of samples. An HR800 Raman spectrometer (France) was used for Raman scattering, and excitation was carried out with 532 nm laser light. The specific surface area and pore sizes of the samples were detected with N₂ adsorption/desorption using an SSA-4300 (China) instrument. Sessile drops were measured using the optical contact angle meter (OCA25HTV, DataPhysics, China), where distilled water drops were placed on solid surfaces using a dispenser.