A printed wiring board includes a substrate having first and second cavities, first electronic components accommodated in the first cavity, second electronic components accommodated in the second cavity, and a build-up layer formed on the substrate and including an insulating interlayer such that the interlayer is covering the first and second cavities. The substrate has a first projection structure partitioning the first components in the first cavity and a second projection structure partitioning the second components in the second cavity, and the first and second cavities and the first and second projection structures are formed in the substrate such that T1