Method of manufacturing a resin encapsulated semiconductor device to provide a vent hole in a base substrate

This invention relates to a technique that is applied to a semiconductor device, especially to a semiconductor device having a base substrate that comprises flexible films. In a ball grid array type semiconductor package, a semiconductor chip is mounted through an adhesive material on a surface of a flexible film substrate. Plural bump electrodes are arranged in an array on the opposite side of said substrate and the semiconductor chip is sealed by a resin. In this regard, an insulation layer is formed to cover an electric conductor layer pattern formed on the surface of the substrate, and the semiconductor chip is mounted through an adhesive material on the insulation layer. The insulation layer is divided into a plural number of parts that are mutually discontinuous in the area under the semiconductor chip. By this divided insulation layer, a short circuit between the semiconductor chip and the electric conductor layer pattern is prevented and a deformation of the substrate that comprises the flexible films is suppressed.