A substrate for packaging a semiconductor device is disclosed. The substrate includes a first dielectric layer having a first surface and a second surface opposite to the first surface, a first patterned conductive layer adjacent to the first surface of the first dielectric layer, and a second patterned conductive layer adjacent to the second surface of the first dielectric layer. The first dielectric layer includes a first portion adjacent to the first surface, a second portion adjacent to the second surface, and a reinforcement structure between the first portion and the second portion. A thickness of the first portion of the first dielectric layer is different from a thickness of the second portion of the first dielectric layer.