DCB substrates: solution for high temperature applications

Abstract

Summary form only given. DBC (Direct Bonded Copper) substrates have been proved over many years to be the most cost effective and reliable solution for circuits in power electronics. The bases of these substrates are ceramics, either alumina or aluminium nitride. The metallisation consists of copper layers bonded to ceramic at high temperature. DBC differs from thick film metallisation in that the copper layers consist of pure metal with high electric conductivity whereas the DBC process is carried out at temperatures above 1065/spl deg/C; the working temperature of DBC substrates can be up to 900/spl deg/C. DBC substrates are successfully brazed to covar at temperatures of 850/spl deg/C to 900/spl deg/C without affecting their functionality. At temperatures above 500/spl deg/C in hydrogen atmosphere the copper/ceramic interface peel strength is reduced. The copper surface of DBC substrates can be protected against oxidation by plating (Ni+Au) as a standard process. The range thickness of DCB is between 0.2 and 0.7 mm. Standard thicknesses are 0.2 mm and 0.3 mm. The reliability of DBC substrate temperature cycling is dependent on the absolute temperature and the temperature range. For military and automotive specifications the reliability could be improved by reducing the copper thickness at the copper edges by a simple low cost etching process.