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|Reliability of Multilayered Molybdenum-Copper-Composites for Thermal Management Applications|
|Keywords: Molybdenum copper composite, Reliability, GaN package|
|With the increasing success of Gallium Nitride (GaN) based radio-frequency devices, the thermal management of these devices is gaining more and more attention . Multilayered molybdenum-copper-composites are promising materials in this field due to their variable layer structure and thus adjustable coefficient of thermal expansion and thermal conductivity . However, a major concern on these composites is their reliability especially in terms of fatigue and delamination at the molybdenum-copper-interfaces. Such defects would lead to a total failure of the device. Furthermore, if the composites are showing a hysteresis upon heating and cooling, remaining stresses could be induced after thermal loading. In order to check the reliability of the molybdenum-copper-interfaces thermal cycling was performed according to the European standard EN 600068-2-14. Three-layered copper-molybdenum-copper-composites were alternatingly transferred from a chamber at -40°C to a chamber at +125°C and kept in each chamber for 30 minutes. The total number of cycles was 2000 and samples were taken after 100, 500, 1000 and 2000 cycles. The material was examined for interface defects and delamination by scanning electron microscopy and the results will be discussed. Furthermore, samples were repeatedly heated in a dilatometer from -150°C to +200°C, -150°C to +400°C and -150°C to +600°C. The dilatometer curves give information on a possible hysteresis. Moreover, the different temperature ranges may indicate if the hysteresis is suppressed above a threshold temperature. In summary, the presentation will give a general picture on the reliability of multilayered molybdenum-copper-composites.|