Constructing a heterogeneous interlayer in relieving the residual stresses for the AlN/Cu brazed joint used in IGBT

The aluminum nitride (AlN) ceramic is a underlying substrate material for high-voltage/power insulated gate bipolar transistors (IGBT), due to its excellent thermal conductivity and low coefficient of thermal expansion (CTE). The high-quality joining between AlN and Cu, which have a huge CTE mismatch and large residual stress remained in the joint, is the prerequisite for the application of AlN in IGBT. In this work, a AgCuTi-Al brazing filler was designed to connect the AlN and pure Cu. The element Al with a low melting point of 660 °C would decrease the brazing temperature, alleviating the residual stress level in the joints. In addition, Al could react with Cu and Ti in the liquid filler to in situ produce AlCu2Ti intermetallic compounds (IMCs), contributing to the mitigation of CTE mismatch and amelioration of joint bond strength. A heterogeneous structure in relieving the residual stresses would be driven based on the modulation of filler composition and joining condition, while the microstructural optimization and enhancement in mechanical properties could be achieved. Based on this, effects of Al content, brazing temperature, and soaking duration on the microstructure and mechanical properties of the AlN/Cu joints were investigated. The formation process and strengthening mechanism of the joints were also discussed. The work performed may provide useful strategies for the manufacture of high-performance packaged substrates in IGBT.