Apparatus and methods for flattening thin substrate surfaces by stretching thin flexible substrates to which ICs can be bonded. Various embodiments beneficially maintain the substrate flatness during the assembly process through singulation. According to one embodiment, the use of a window frame type component carrier allows processing of thin laminates and flex films through various manufacturing processes. The flexible substrate is bonded to a rigid carrier. The carrier is placed into a specialized fixture comprising a bottom plate and a top plate. The bottom plate with raised regions is created that allows the windowed region of the flex film to be pressed flat. After aligning the top plate, the bottom plate, and the middle structure, the plates are pressed together causing the raised regions to push the flex film substrate upward and around the carrier. By pressing the thin substrate upward, the substrate is stretched like a drum head over the raised sections of the bottom plate, thereby flattening the substrate. The die assembly site is held flat overtop of the raised portion of the carrier to provide a stable vase for placement of the die.