A lead frame substrate includes a circuitry layer, terminals, a warpage inhibiting dielectric layer and a stiffening dielectric layer. The circuitry layer extends laterally from the terminals and has an external surface facing away from the stiffening dielectric layer and an inner surface facing in and spaced from a top surface of the stiffening dielectric layer by the warpage inhibiting dielectric layer. The stiffening dielectric layer can serve as a robust platform to support the lateral extension of a circuitry layer and avoid crack propagation through the stiffening dielectric layer into the circuitry layer. The warpage inhibiting dielectric layer can absorb stress and alleviate warpage of the structure during bonding the stiffening dielectric layer to a lead frame with the terminals.