A method includes forming a package, which includes forming a plurality of redistribution lines over a carrier, and forming a thermal dissipation block over the carrier. The plurality of redistribution lines and the thermal dissipation block are formed by common processes. The thermal dissipation block has a first metal density, and the plurality of redistribution lines have a second metal density smaller than the first metal density. The method further includes forming a metal post over the carrier, placing a device die directly over the thermal dissipation block, and encapsulating the device die and the metal post in an encapsulant. The package is then de-bonded from the carrier.