A self-made solidification controlling facility was developed in accordance with the principle of directional solidification to study the solidification behavior of SAC305 solder alloy and the effect of directional solidification on the alloy microstructure. The microstructure of the tin-rich phase grows with significant orientation under the rapid cooling conditions. Increasing the cooling rate can enhance the continuity of columnar tin-rich phase and is likely to inhibit the secondary dendrite growth. Rapid cooling reduces the size and disperses intermetallic compounds significantly, resulting in the increase of the microhardness of the solder.