Low-temperature lead-free solder paste and preparation method thereof

The invention discloses a low-temperature lead-free solder paste and a preparation method thereof. The low-temperature lead-free solder paste is prepared from the following raw materials according tomass percent: 86% to 91% of low-temperature tin-bismuth-silver-copper quaternary lead-free solder powder and 9% to 14% of scaling powder, wherein the low-temperature tin-bismuth-silver-copper quaternary lead-free solder powder is composed of four elements including tin, bismuth, silver and copper, the mass percent of bismuth is 46% to 52%, the mass percent of copper is 0.3% to 1.2% of copper, themass percent of silver is 0.4% to 1.2%, and the mass percent of tin is 45.6% to 53.3%. The solder paste is prepared by adopting the formula and the method, the bismuth content is in a relatively highreasonable range, so that the solidus temperature of the product is increased from 138 DEG C to 151 DEG C, the solder paste is suitable for a low-temperature packaging process, the welding peak temperature does not exceed 200 D