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Thermomechanical Reliability Evaluation of Direct Bonded Aluminum (DBA) as a Substrate for High-Temperature Electronics Packaging
Keywords: Direct bonded aluminum (DBA), nanoscale silver paste, thermomechanical reliability
This study is focused on the evaluation of direct bonded aluminum (DBA) substrate for high-temperature electronics packaging applications. The state of the art direct bond copper (DBC) substrate is susceptible to large temperature cycling range, delamination of copper from the ceramic base-plate caused by the thermomechanical stress is often observed. In this work, effects of large temperature cycling range on direct bond aluminum (DBA) substrate reliability have been investigated. DBA substrates with different metallizations are thermally cycled between -55oC and 250oC. Unlike the failure mode of the DBC substrate, no delamination of aluminum from ceramic base-plate is found for the DBA substrate. However, the substrates suffer the increased surface roughness after the thermal cycling test. It is believed that in the high temperature regime, due to the significant amount of thermal stress and grain-scale deformation, recrystallization and grain-boundary sliding become very active in the aluminum layer, and thus cause the microstructural evolution. Besides the reliability evaluation of DBA substrate, the process of using nanoscale silver paste is also designed, which is further used to investigate the effects of the surface roughened DBA substrate to the die-attachment performance. Results are shown that the DBA surface roughness could greatly weaken the die-attach bonding strength, and could further degrade the die-attach thermomechanical reliability.
Thomas G. Lei, Student
Virginia Tech - Center for power electronics systems (CPES)
Blacksburg, VA

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