In this work we investigate the influence of self-affine roughness parameters on the pull-in voltage in capacitive microelectromechanical devices. The capacitor plate roughness is considered as self-affine type, which is described by the roughness amplitude w, the lateral correlation length , and the roughness exponent H. By comparing the influence of the three parameters, we confirm that not only the long-wavelength roughness parameters w and , but also the short-wavelength fine roughness details, as described by the roughness exponent H, play a major role. Therefore, the proper characterization of the involved surface roughness and its evolution at all relevant length scales are necessary to gauge properly the performance of associated devices.