A semiconductor device with a first (101) and a second (111) semiconductor chip assembled on an insulating flexible interposer (120). The interposer, preferably about 25 to 50 μm thick, has conductive traces (121), a central planar rectangular area and on each side of the rectangle a wing bent at an angle from the central plane. The central area has metal studs (122, 123) on the top and the bottom surface, which match the terminals of the chips, further conductive vias of a pitch center-to-center about 50 μm or less. The side wings have contact pads (130) with metallic connectors (131) on the bottom surface; the connectors may be solder balls, metal studs, or anisotropic conductive films. The second chip is adhesively attached to a substrate, whereby the interposer faces away from the substrate. The interposer side wings have a convex bending (150) downwardly along the second chip and a concave bending (151) over the substrate; the side wing connectors are attached to the matching substrate sites.