Hybrid package for high performance Inertial Measurement Units

Abstract

In the field of MEMS sensors, package plays a primary role since it strongly affects device behavior and performance. Depending on the application and mission profile, design and package technology need to be targeted in order to fit the best the given requirements.When sensors work in harsh environments like in automotive applications, system is subject to very aggressive thermal cycles. Neglecting cost aspects, main and conflicting features are electrical performance stability and package board level reliability.Due to the high mechanical stiffness and due to the coefficient of thermal expansion matched versus that of silicon, ceramic cavity packages limit the stress transfer to the MEMS sensor ensuring high performance in terms of stability. However, the substantial mechanical proprieties discrepancy compared to that of PCB, implies stress absorption at solder joint level causing reduced board level reliability performance. Cavity packages based on organic substrate, show opposite behavior. If on the one hand they shift the stress concentration toward the substrate increasing board level reliability, on the other they worsen package-to-MEMS decoupling and thus the stability performance.In this paper a hybrid package is presented to achieve optimal trade-off between stability and reliability requirements. Proposed solution is based on a Si-interposer glue-bonded on the substrate, ASIC and MEMS dice are attached on top of it. Si-interposer provides stiff substrate with low coefficient of thermal expansion ensuring package-to-MEMS decoupling. Organic substrate shifts stress concentration to the interposer DA material increasing board level reliability performance.Numerical analysis has been performed to properly design the package. Focus is given to solder joint reliability at the thermal cycles. Experimental solder joint reliability test and electrical performance characterization are finally presented to confirm the effectiveness of the proposed approach.