In one implementation, a semiconductor package assembly includes a first semiconductor package having a first semiconductor die and a first redistribution layer (RDL) structure coupled to the first semiconductor die. The first redistribution layer (RDL) structure includes a first conductive trace at a first layer-level, a second conductive trace at a second layer-level, and a first inter-metal dielectric (IMD) layer and a second inter-metal dielectric (IMD) layer, which is beside the first inter-metal dielectric (IMD) layer, wherein the second inter-metal dielectric (IMD) layer is disposed between the first conductive trace and the second conductive trace, and the second inter-metal dielectric (IMD) layer is zigzag shape in a cross-sectional view.