The use of Micro Electro-Mechanical Systems (MEMS) for measuring accelerations, pressure, gyroscopic yaw rate and humidity in engine controls, inflatable restraint, braking, stability and other safety critical vehicle systems is increasing. Their use in these safety critical systems in high stress automotive environments makes ensuring their reliability and durability essential tasks, especially as the Vehicle System Functional Safety requirements of ISO-26262 are being implemented across the industry. A Design for Reliability (DfR) approach that applies Physics of Failure methods to evaluate and eliminate or mitigate susceptibilities to failure modes of a device during the design of a product is the most effective and efficient way to achieve Functional Safety levels of reliability-durability.
MEMS packages exhibit several failure modes that can be predicted as a device is designed using modern Computer Aided Engineering (CAE) software tools. This paper provides a methodology for using the Sherlock ADA CAE APP to rapidly create a high-fidelity model of a MEMS interposer with all the conductor geometries. The two failure modes that are explored with this model are:
Package warpage due to copper imbalance between the two sides of the MEMS interposer. If a Coefficient of Thermal Expansion (CTE) mismatch due to copper imbalance exists between the two sides, bending of the package can occur to such a degree that it becomes impossible to assemble the solder interconnects.
Filled microvia delamination that can occur when the filled microvias have copper structures that can delaminate from the copper traces in the conductor layers.
High-fidelity CAE modeling where each layer can be meshed based on the actual geometry of the layout of a MEMS device provides a predictive tool that allows designers to optimize the design to balance the layout without the need for costly and time consuming manufacture and testing of prototype parts.