Design of a Vibration-Sensitive Electronics Module with Glass-Filled Plastics

Plastics provide lightweight, low-cost, versatile designs in automotive electronics applications. However, their low stiffness and strength in comparison with metal structures leads to questions regarding their suitability to perform well in harsh automotive environments. This paper discusses the evolution of a design for a vibration-sensitive automotive electronics module using a glass filled plastic (30% glass-fiber filled PBT). As a key sensing and diagnostic module for automotive safety, the plastic-encased unit is required to demonstrate high rigidity in the 10 - 5000 Hz vibration frequency range, at all temperatures. A complicating factor in the study of glass-filled plastics is the importance of direction-dependent material properties, since mechanical properties along the glass-fiber direction are significantly different from that perpendicular to the fibers. The paper indicates the importance of considering high-temperature, direction-dependent properties of glass-filled plastics in guiding the design to acceptable vibration performance. Minimizing gain due to resonance of the module requires structural design optimization using finite element analysis and experimental measurements to corroborate the results, both of which are discussed in detail in this study. Uncertainties surrounding boundary conditions and damping are highlighted as critical to the limitations of up-front predictive methods in guiding the design