The influence of silver content on structure and properties of Sn-Bi-Ag solder and Cu/solder/Cu joints

The effect of silver content on structure and properties of Sn100−xBi10Agx (x=3-10 at%) lead-free solder and Cu-solder-Cu joints was investigated. The microstructure of the solder in both bulk and rapidly solidified ribbon forms was analyzed by scanning electron microscopy (SEM) and X-ray diffraction. The peculiarities in melting kinetic, studied by differential scanning calorimetry (DSC), and silver influence on it are described and discussed. The wetting of a copper substrate was examined by the sessile drop method in the temperature range of 553-673 K in air and deoxidizing gas (N2+10%H2) at atmospheric pressure. Cu-solder-Cu joints were also prepared in both atmospheres, and their shear strength was measured by the push-off method. The produced solders consisted of tin, bismuth and Ag3Sn phases. The product of the interaction between the solder and the copper substrate consists of two phases: Cu3Sn, which is adjacent to the substrate, and a Cu6Sn5 phase. The wetting angle in air increased slightly as the silver concentration in the solder increased. Wetting of the copper substrate in N2+10H2 gas shows the opposite tendency: the wetting angle slightly decreased as the silver content in the solder increased. The shear strength of the joints prepared in air (using flux) tends to decrease with increasing production temperature and increasing silver content in the solder. The equivalent decrease in the shear strength of the joints prepared in N2+10H2 is more apparent.