A flexible circuitized interposer (50) and method of making same wherein the interposer includes at least one flexible circuitized substrate (53) having a dielectric (e.g., polyimide) layer (54) with a conductor (55) and plated elements (56), e.g., copper pad, including possibly with dendrites (57) thereon for enhanced connection, an apertured support member (58) aligning with the conductor, and a support member (60) having the apertured member thereon. When the interposer is engaged, the flexible circuitized substrate (53) is depressed within the aperture (59). Various alternatives, including a support (60") formed with compressible portions (69) that extend into respective apertures (59) in the support member (58), and an interim, compressible support (60""), are disclosed. The support member may also be metallic, e.g., for use as an electrical ground shield. Flexure is also enhanced by utilization of patterns of one or more apertures (64) in the flexible substrate relative to and substantially surrounding the positioned conductors (56). Electrical assemblies including a pair of circuitized substrates electrically interconnected by the defined interposers are also described.