A package-on-package (PoP) assembly includes a bottom die package and a top die package. The bottom die package includes an interposer having a first side and a second side, an active chip mounted on the first side within a chip mounting area through first bumps, and a dummy chip mounted on the first side within a peripheral area. The dummy chip is directly mounted on a passivation layer of the interposer. A dielectric layer covers the active chip and the dummy chip. At least one TSV connecter penetrates through the dielectric layer and the dummy chip. A molding compound is disposed on the first side. The molding compound covers the active chip and the TSV chip. Solder bumps are mounted on the second side.