Sensor Package Design Improvements Using Computer Simulation and Experimental Testing

The Motorola micro-machined 50G accelerometer sensor and control chips are packaged in a Single In-line Package (SIP) configuration. The package requires an housing or saddle for positioning the SIP sensor perpendicular to the Printed Circuit Board (PCB). Development tests of the prototype accelerometer assembly determined the first resonant frequency was in the operating range. Analytical and experimental methods, consisting of finite element analysis, holographic modal testing, and device electrical output monitoring were applied to identify the natural frequencies and mode shapes. Good agreements were obtained in the methods. Design changes for raising the package natural frequency were incorporated in the finite element model. Follow-up testing confirmed that the new package design was acceptable. The methodology of incorporating both analysis and experimental testing was found to be valuable in design process. The integration of these methods facilitated understanding of the resonance problem, for evaluating potential solutions to raise the fundamental frequency, and to assure first time success upon design change implementation.