A flexible membrane includes a horizontal central portion, a vertical portion coupled to the central portion, a thick rim portion coupled to the vertical portion, and an extension coupled to the thick rim portion. An outer surface of the horizontal central portion provides a mounting surface configured to receive a substrate. The thick rim portion has a thickness that is greater than a portion directly adjacent to the thick rim portion. The thick rim portion is between the extension and the vertical portion and a greatest dimension of the extension is less than the thickness of the thick rim portion.
