The invention provides a semiconductor package assembly. The semiconductor package assembly includes a first semiconductor package including a first semiconductor die. A first redistribution layer (RDL) structure is coupled to the first semiconductor die. The first redistribution layer (RDL) structure includes a first conductive trace disposed at a first layer-level. A second conductive trace is disposed at a second layer-level. 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, are disposed between the first conductive trace and the second conductive trace.