Semiconductor packages that use metallization and lead-free solders are increasingly being used in electronic products. In this study, interface reactions and joint-strength reliability were investigated for Sn-3W%Ag-0.5W%Cu solder ball joints joined to Cr/Cu and Cr/Ni-40W% metallization layers that were heat treated at 260°C. The strength of the joint with the Cr/Cu metallization layer decreased as the duration of the heat treatment increased. Sn and Cr interface reactive layers were generated after the loss of Cu in the Cr/Cu metallization layer, but the connection was maintained. By contrast, the connection of the joint to the Cr/Ni-40W metallization layer was relatively stable under the heat treatment conditions investigated.