Design trade-offs and reliability of power circuit substrates with respect to varying geometrical parameters of direct copper bonded Al2O3 and BeO

This paper describes preliminary work performed to develop adhesion as well as thermal cycle reliability data for the DBC-Al₂ O₃ and DBC-BeO substrates. Samples of direct copper bonded Al₂O₃ and BeO were prepared with varying copper as well as ceramic thickness combinations including those which are found to give optimum thermal performance. This study was targeted to evaluate adhesion of the copper metallization as well as crack sensitivity of ceramic as a function of thermal cycling as well as soldering and brazing cycles with different blends of inert and reducing atmospheres, commonly used in power circuit assembly. The results indicate that peel strength of the copper metallization is related to the copper thickness. There is a strong effect of varying thickness combinations on thermal cracking of DBC-Al₂O₃ and DBC-BeO substrates. Thermal cycling study indicates that a ceramic to copper thickness ratio of 2 and higher is more resistant to thermal cracking. Soldering and brazing cycles strongly influence the peel strength. Regardless of atmosphere (H₂ or H₂+N₂) 350°C has been determined to be the safe temperature below which the bond integrity degradation is minimal