Lead-free tin solder paste and preparation method thereof

The invention discloses a lead-free tin solder paste and a preparation method thereof. The lead-free tin solder paste comprises the raw materials by mass percent: 80-90% of tin-silver-copper alloy tinpowder and 10-20% of lead-free flux, wherein the tin-silver-copper alloy tin powder comprises the componentsby mass percent: 0.3-3.0% of silver, 0.5-0.7% of copper and 96.5-99.0% of tin, and the lead-free flux comprises the componentsby mass percent: 20-35% of solvent, 30-45% of rosin, 5-10% of surface active agent, 10-20% of organic acid, 3-10% of antioxidant and 2-8% of thixotropic agent. The rosin which is a mixture of hydrogenated rosin and polymerized rosin according to a weight ratio of 1:(1-3) is adopted, so that the prepared lead-free tin solder paste is good in adhesive force and stability; by adjusting a ratio of the solvent to the rosin, the prepared lead-free tin solder paste has a wider viscosity range and good printing performance; with the compounding of various organic acid, the prepared lead-free tin solder paste is halogen-free, and the activity of the lead-free tin solder paste is improved greatly; the surface active agent is compounded with the solvent with high boiling point, low viscosity and low volatility, so that the prepared lead-free tin solder paste is long in printing time, and excellent in insulating property.