The study explores the effects of adding silver (Ag) to a Sn0.7Cu solder alloy on its mechanical properties and microstructures. Ag was introduced at concentrations of 3 wt. %, 4 wt. %, and 5 wt. %. The solder alloy was melted at 330 ℃ for bulk samples and 217 ℃ for solder sheets on aluminium plates. After cleaning with acetone and ultrasonic treatment, the solder sheets were rolled to 30 µm thickness and cut into 12 mm2 pieces. Copper substrates were prepared by etching, rinsing, and drying, and then solder flux paste was applied. The solder sheets were placed on the substrates, covered with another layer of flux paste, and reflowed in an oven to complete the process. After reflow, samples were mounted for observation of intermetallic compounds (IMC) and analysed for microstructure using an optical microscope. The hardness of bulk samples was evaluated using a micro-Vickers tester. Results showed that silver addition increased hardness progressively with higher concentrations in the solder alloy. Microstructural analysis revealed that while the original Sn0.7Cu alloy had mainly eutectic networks, the addition of silver introduced a combination of eutectic networks and β-Sn grains. The spacing between these structures decreased with 3 wt. % silver and increased with higher concentrations (4 wt. %, 5 wt. %). Overall, the study highlights how silver modification alters the microstructure and mechanical properties of Sn0.7Cu solder alloys, enhancing solder joint performance through a dispersion-strengthening mechanism.