Abstract
Abstract
It is expected that more power electronic systems will be used in future vehicles. This is the case for hybrid vehicles where power devices are used in order to drive electrical motors in the power range of 30kW to 50kW [Toy03]. The corresponding nominal voltage supply network is about 500V and requires power electronic devices which must satisfy both the constraints of cost and reliability during the expected lifetime of the vehicle which is estimated at about 8000h to 10 000h. For these applications, fully integrated inverters power modules are necessary. The component of choice is the IGBT, but technologies must still be improved so that this device can operate in a reliable way over all the vehicle lifespan. Improvements are awaited in particular in the field of thermics, assembly, interconnections and bonding technologies. Hybrid traction will be able to emerge only if the cost, the weight and the volume of the electronics devices are not crippling. In particular, on assumption of mass production, the costs will be fixed by the competition with the traditional propulsion systems and the cost of the fuels. Electronic devices will be used in a nominal thermal environment of 90°C being able to go up until 120°C and will have to undergo a very high number of power cycles as well as passive thermal cycles. In order to meet the cost objectives, the cooling system of these devices may use the same coolant circuit than the ICE (Internal Combustion Engine). However, the high temperatures values of the coolant liquid (90°C to 120°C) combined to high power cycling due to traffic conditions imposes significant constraints on the electronic devices. Thus, chips and packaging are highly stressed and the goal achievement for reliability is a real challenge. It appears that the most fragile element with the thermal environment and the constraints of cyclings remains the device assembly. In particular, the bonding wires which tend to lift-up and the delamination of solders between the ceramic substrate (DCB) and the base-plate.