| abstract |
Lead-free solder balls having a smooth surface and no shrinkage cavities or wrinkles are made of a lead-free solder which comprises, by atomic percent, 3%-6% of Ag, 1%-4% of Cu, 0.01%-2% of at least one element of the iron group and preferably Co, optionally 0.04%-4% of P, and a balance of Sn. |