Provided is a package structure including a substrate, a metal pad, a first polymer layer, a second polymer layer, a redistribution layer (RDL), and a third polymer layer. The metal pad is located on the substrate. The first polymer layer is located on the substrate. The first polymer layer has a first opening which exposes a portion of a top surface of the metal pad. The second polymer layer is located on the first polymer layer. The second polymer layer has a second opening which exposes the portion of the top surface of the metal pad and a first top surface of the first polymer layer. The RDL covers the portion of the top surface of the metal pad and extends onto a portion of the first top surface of the first polymer layer and the second polymer layer. The third polymer layer is located on the RDL.