Reliability of die attached AlN-DBC module using Zn-Sn high temperature lead-free solders

Interfacial reaction and reliability of Si die attached joints with Zn-xSn (chi= 20, 30, 40 wt%) were investigated, and Pb-5wt%Sn, and Au-20wt% were compared as a typical high temperature solder alloy. The joining strength of Cu/solder/Cu joints was investigated using the as soldered joints and thermal cycled joints up to 2000 cycles. At the interface with Si die coated with Au/TiN thin layers, the TiN layer did not react with the solder and worked as a good protective layer. At the interface with Cu, for Zn-Sn solders, CuZn5 and Cu5Zn8 IMC layers was confirmed. Au-20Sn and Pb-5Sn solder forms zeta-Au5Sn and Cu3Sn IMC layers at the interface with Cu, respectively. For improving the joint reliability, TiN layer was proposed as a protective layer and was applied to the DBC substrates. For the die attached joints on DBC substrates coated with Au/TiN thin layers, no fatigue crack has been found until 1000 cycles of thermal cycling test. The joining strength of the Cu/solder/Cu joints with Zn-Sn solder was about 30~34 MPa, which was higher than that of Pb-5Sn solder (26.2 MPa). For the thermal cycled Cu/solder/Cu joints up to 2000cycles, Zn-Sn solder also shows the higher joining strength than that of Pb-5Sn solder.