The introduction of the high performance T**2L device technology for the IBM 4300 Systems and the System/38 required extensions of the 24-mm metallized ceramic module used in prior IBM systems. The extension of the metallized ceramic technology into a physically larger 28-mm module, electrically enhanced with a reference plane and with fine line (0. 025-mm) wiring, is described. The reliability of this module was evaluated with particular emphasis on corrosion and metal migration in humid environments and on exposure to atmospheric contaminants.