Increasing the temperature in power electronic applications usually causes a decreasing lifetime and reliability. This study shows that packaging materials and technologies like silver sintering or gold germanium solders can easily deal with temperatures above 150°C. Furthermore the power cycling capability at increased temperatures can be much better than at room temperature. Active power cycling tests with 240 devices offered more cycles to failure at 120°C cooling temperature than at 40°C. The three tested sample groups consisted of silicon carbide diodes which were soldered (gold germanium/ tin lead) or silver sinter to copper-ceramic-substrates (DBCs). The reason behind this effect is the decreasing of Youngs modulus, yield strength and ultimate strain over temperature. The materials are getting much more ductile and robust against load cycling at higher temperatures. The three mentioned material properties were measured by nano-indentation and tensile tests up to 200°C. In summary, packaging materials and their properties should be adopted to the intended application and its requirements, starting with a temperature-dependent analysis
Increasing the temperature in power electronic applications usually causes a decreasing lifetime and reliability. This study shows that packaging materials and technologies, such as silver-sintering or gold germanium solders combined with silicon-carbide devices, can easily deal with temperatures above 200 °C/392 °F. Furthermore, lifetime tests (active power cycling) with 300 devices offered more cycles to failure at 120 °C/248 °F heat sink temperature than at 40 °C/104 °F (same ΔT) for silver-sintered samples and goldgermanium solders. SAC305 and tin-lead solders were also tested for comparison but could not withstand the harsh conditions. The samples were silicon carbide diodes attached to copper-ceramic-substrates (DBCs). For testing, the devices were heated up by current to ach ieve a 130 K temperature swing at different coolant temperatures (250 °C/482 °F maximum temperature). The reason behind the higher lifetime at elevated temperatures is the increasing ductility over temperature. The materials capability against thermomechanical stress is better at higher temperatures, while creep effects are not dominating. This effect can be used especially for high temperature application with extraordinary requirements on lifetime and reliability. Analytical models based on stress strain calculations can explain this material behavior. Together with an in-situ measurement of the thermal impedance the models can predict the lifetime consumption of the application and thereby upcoming maintenance
Modelling was undertaken to investigate the role of bond wire size on reliability in power electronic converters. Experiments have shown that thin 125 µm Al wires used in place of 375 µm Al wires alleviate bond wire lift-off and further outlast other sources of failure such as solder degradation in a power module. To investigate the role of bond-wire size on wire lift-off, the effective plastic strain was estimated through thermo-mechanical simulation. Three-dimensional models were constructed for the thin and thick bond wires, respectively. For the critical deformation of the aluminium bond wires during thermal cycling, a temperature-dependent bi-linear plasticity model was used. The effect of a difference in yield strength for the thin wires was also investigated. Maximum as well as volumetrically averaged values of the effective plastic strain showed significant differences between the thick and thin wires and wires with different yield strengths. The modelling results show higher effective plastic strain for the thick wires - supporting the experimental findings
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