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Parametric Simulation of the Mechanical Behavior of a DBA Substrate Directly Joined to an Aluminum Heat Exchanger

FEA (Finite Element Analysis) method is employed to identify the structures and dimensions of the Heat Exchanger by lowering the maximum thermal stress in the joint material and the whole structure, as well as the deflection of DBA substrate. SAC305 solder, TS3601-35 silver epoxy and conductive adhesive are selected as the joint material between the DBA substrate and the Heat Exchanger. Two structures of the Heat Exchanger, Structure 1 without the target plate and Structure 2 with the target plate, are involved in to identify a more reliable structure. We can see that the maximum thermal stress and deformation can be relieved while the wall of the Heating Exchanger getting thinner in Structure 1 compared to that in Structure 2. When the wall becomes 1 mm thick, the maximum thermal stress Structure 1 will be almost half of that in Structure 2. Meanwhile, the bending of Al on the top of DBA in Structure 1 will be less than that in Structure 2. Therefore, Structure 1 will be selected as a better and more compliant structure combined considering the difficulty to achieve larger area-bonding in Structure 2. Parametric study of special parameters, such as the thickness of the wall in the Heating Exchanger and the height of joining material, will be preformed. It is found that the maximum thermal stress in SAC305 solder joint is much smaller than that in silver epoxy and conductive adhesive when temperature load applied on both the Power Module and the Heat Exchanger increases from 25°C to 80°C, although the maximum thermal stress in the whole structure and deflection of DBA substrate are comparable no matter what kinds of joint material has been used in both structures. Structure 1 without target plate is more potentially reliable than Structure by decreasing the thickness of the wall in the Heat Exchanger. Structure 1 with 2mm thick wall in the Heating Exchanger and 0.5 mm high joint is identified in the Cooling System.

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