Reliability in Mechatronics Systems from TEM, SEM and SE Material Analysis
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1195-B07-04
Reliability in Mechatronics Systems from TEM, SEM and SE Material Analysis P.R. Dahoo 1, 3 , N. Alayli 1,2,, 3 , A. Girard 1,2 , P. Pougnet 4 K.L Tan5 and J.M. Morelle5 1 Physics & Engineering Science Department, University of Versailles St Quentin en Yvelines, Versailles, France 2 Laboratoire d'étude des Microstructures (LEM), CNRS/ONERA,BP72, 92320 Chatillon cedex France 3 Université Versailles St-Quentin; CNRS/INSU, LATMOS-IPSL, BP3, 91371, Verrières-leBuisson, France 4 Valeo VEES, 14 avenue des Béguines - BP 68532 Cergy, 95892 Cergy Pontoise Cedex, France 5 Valeo VECS, 5 avenue Newton - BP 214 F-78180 Montigny Le Bretonneux, France ABSTRACT Mechatronic systems designed to meet new EU directives are studied through interconnections by means of electronic and photonic probes, that is, SEM, TEM, SE or 3D Xray tomography. The modules assembled by interconnection technologies using leaded or leadfree solders are studied for their robustness by subjecting them to accelerated life thermal tests. The results obtained with JEOL 6060LV SEM and with an optical microscope show that although the slow rate of growth of inter-metallic compounds (IMC) is compliant with the expected reliability goals, IMC growth is nevertheless responsible for the propagation of cracks, in particular when gold is present on the PCB side. Innovative Low Temperature Joining (LTJ) technology applied to nano or micro silver pastes which should reduce IMC effects were tested on mechatronic systems. Results obtained from studies by above mentioned electronic and photonic probes of samples are shown. Pressureless LTJ technology is shown to be unsuitable for robust interconnections. INTRODUCTION There is a growing interest in materials for power electronics for electric power steering, hybrid or electric vehicles. These systems need to be adapted to face different challenges such as the reduction of green house effect gases and the development of ecologically friendly strategies. Mechatronic systems for vehicles require reliable lead-free connections. This can be achieved using new technologies and new materials which enable the design of more compact and robust mechatronic systems in which embedded electronic systems are integrated with increased 3D capabilities while maintaining cost reduction, size and weight. To manufacture robust systems [1], special assembly know-how is required as well as new design methodologies.. In this context, the present study focuses on interconnections and device packages of Power Mechatronics sub-systems which are part of the vehicle system. The most delicate step in packaging technology is die attachment. This process needs to be closely controlled in order to ensure robustness of mechatronic systems [2] as wires can lift-up and solder joints can delaminate: these are the main causes of failure [3]. Two principal studies related to interconnections, either by standard technology soldering with lead-free solder alloys or by silver sintering from Low Temperature Joining (LTJ) technology [4], are described in
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