High-Temperature Reliability of Direct-Bond-Copper Substrates with Sealed Edges

Recent reports have shown the reliability of direct-bond-copper (DBC) substrates was significantly improved by sealing their edges with polymeric materials. In this work, DBC substrates with and without sealed edges had been prepared. Parylene HT and Nusil R-2188 had been chosen as sealing materials. Parylene HT was applied to the edges of the DBC by chemical vapor deposition (CVD), and Nusil R-2188 by programmable fluid dispensing. The DBC substrates with and without sealed edges were cycled between −55°C to 200°C. The cycled substrates were monitored by optical microscope and scanning electron. DBC substrates whose edges were not sealed were found to fail in approximately 100 cycles. No failure was observed in DBC substrates coated with parylene HT before 300 cycles. Samples whose edges were sealed with Nusil R-2188 exhibited the highest lifetime under the thermal cycling condition of −55°C – 200°C. After 300 cycles, neither detachment of Nusil from DBC surfaces nor failure at Cu/Al2O3 interface was detected. After 900 cycles, 30 μm – 60 μm cracks appeared at the edges of Cu/Al2O3 interface, which are signaling the early stage of substrate failure. Additionally, Nusil was found to be partially detached from DBC surfaces. The improvement in reliability is attributed to the release of thermo-mechanical stress concentrated at the edges of the Cu/Al2O3 interface.