Reliability assessment of sintered nano-silver die attachment for power semiconductors

For decades soldering has been the technology of choice in die bonding. However, due to worldwide health protection regulations, the most common solder alloys, which contain lead, have been banned. Furthermore, standard solders cannot fulfil the reliability requirements of future power electronic devices. New interconnection technologies have to be developed. One of them is pressure sintering (p=30..50 MPa) of silver flakes below 300°C. It forms a strong, highly electrically and thermally conductive bond. In order to lower the level of pressure, silver nanoparticles can be used. Shear tests have shown that even 5 s of sintering, a temperature of 225°C, or a pressure as low as 2 MPa is sufficient to generate bonds comparable to solder and high pressure sinter joints if the remaining parameters (p, t and T, respectively) are set correctly. However, strength is only a necessary criterion as aging comes into play. Therefore, reliability tests using thermal cycling and power cycling were run. These returned superior reliability of the sintered samples. 160 million of the power cycles between +45 and +175°C run in this work can be extrapolated using a Coffin-Manson model. Solder joints failed at about 40,000 cycles.