Stannum-silver-copper three-part alloy leadless solder paste

The invention relates to a tin-silver-copper ternary alloy lead-free soldering paste. Alloy welding powder is made to the soldering paste through bismuth-tin binary eutectic alloy welding powder Bi48Sn42 and Sn-Ag-Cu ternary alloy welding powder with a melting point between 200 to 230 DEG C as well as scaling powder; wherein, the bismuth-tin binary eutectic alloy welding powder takes the 80 to 90 percent of mass percent; the tin-copper binary eutectic alloy welding powder takes 9.6 to 19.5 percent of mass percent; the scaling powder takes 0.1 to 0.5 percent of mass percent. The tin-silver-copper ternary alloy lead-free soldering paste keeps the peak value temperature in reflow soldering process between 210 to 215 DEG C, greatly reducing the peak value temperature and the possibility of damaging a breadboard and an element device.