A preformed lead frame includes multiple lead frame units, a connecting member connecting the lead frame units, a molding layer molded over the lead frame units and the connecting member, and a solder layer. The molding layer has opposite upper and lower surfaces, a plurality of side surfaces each extending therebetween, and a plurality of spaced-apart elongated grooves indented from the lower surface towards the upper surface. Each of the lead frame units includes a row of spaced-apart leads each having a grooved surface and a grooved soldering surface indented from the grooved surface towards the upper surface. The solder unit includes multiple solder layers for filling the elongated grooves. A lead frame package formed from the preformed lead frame is also disclosed.