Dos and don’ts in mounting ZERODUR

Abstract

Because of its extremely low thermal expansion glass ceramic ZERODUR ® is widely used as mirror substrate material in earth-bound and space-borne astronomy or as structural parts in integrated-circuit and flat panel display lithography (to name only some of its wide applications). In all its applications it needs to be mounted in some way to a support structure to enable its functionality. Common examples used in astronomical telescopes are epoxy bonding of invar pads to the ZERODUR ® mirror blanks or epoxy-free mechanical clamping of ZERODUR ® parts to support frames.The mounting should not influence the functionality by inducing thermo-mechanical deformation on the ZERODUR ® part. But even more important the bonding procedure should prevent inducing high stresses to the mounting interface that potentially reduces the lifetime of the mount.The achievable strength of ZERODUR ® strongly depends on its surface treatment. Generally, mechanical strengths of around 100 MPa are achieved on fine ground and acid etched ZERODUR ® surfaces. When becoming interfaces, the reliability of the mount is not only influenced by the initial strength of these surfaces but also on the choice of the epoxy, the mounting material and even the geometrical configuration of the bonding.This paper gives a guideline on the "dos" and "don'ts" in mounting ZERODUR ® supplemented by practical examples from literature.