A wafer level package and a manufacturing method thereof capable of reducing stress between an under bump metal and a bump. The wafer level package includes a substrate provided with a plurality of chip pads on a top surface; a first passivation layer to expose the chip pads; vias connected to the chip pads by passing through the first passivation layer; a metal wiring layer formed on the first passivation layer and connected to the vias; an under bump metal formed on the first passivation layer to be connected to the metal wiring layer and having a buffer pattern separated through a trench on a center; a second passivation layer formed on the first passivation layer to expose the under bump metal; a first bump formed on the buffer pattern; and a second bump filling the trench and formed on the first bump and the under bump metal.