Finite Element Analysis of Silicone Rubber Spacers Used in Automotive Engine Control Modules

Silicone Rubber Spacers in the shape of truncated cones are used in automotive electronic applications to ensure thermal or electrical contact between different components. In one such application, the “cones” are used in Engine Control Modules (ECM) to press flip chip Integrated Circuits (IC) against metal heat sinks to provide a conduction heat transfer path. The spacer size and height has to be specified in order to exert sufficient pressure on the face of the flip chips. The silicone rubber material exhibits a nonlinear force deflection curve and assuming linear behavior would lead to designing incorrectly sized spacers which would either not provide enough pressure for efficient heat transfer or excessive force which may cause damage to the system. This paper describes an effort undertaken at Delphi Electronics and Safety to characterize the silicone rubber material and simulate its behavior using finite element analysis and the Mooney Rivlin material model. Cubic and Cylindrical spacers were built and tested to establish force-deflection and stress-strain curves for the material and to calculate the Mooney Rivlin constants. Since the material is used in compression only, only uniaxial compression tests were performed. The finite element models using the Mooney Rivlin constants were validated by reproducing the measured data for the cylindrical and cubic samples before they were used to model truncated cone and pyramid shape spacers.

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