PREPARATION OF LEAD FRAME

PURPOSE:To resolve a problem of slight dimensional change and to prevent the occurrence of various deformations such as strain, distortion, warp, and dislocation and so on of the tip of inner lead by removing the internal residual stress completely leaving the internal residual strain as it is. CONSTITUTION:When forming wire member C for lead frame, wire member B for lead frame is molded leaving part of the area to be removed unpunched so as to reduce the stress of the cross section where a stress exceeding an allowable range for an added tension. Next, a tension that the apparent internal stress falls in a range of 0.2-1.2kg/mm is applied to wire member B in the longitudinal direction, the wire member B is then heated in a furnace with an atmospheric temperature of 400 deg.C-800 deg.C to remove the internal residual stress from wire member B leaving a resident internal residual strain as it is. Furthermore, after heat treatment, the area of the front part marked with slanting lines is punched out to mold wire member A for final lead frame.