Discrete Stress Isolators for MEMS Sensor Packages
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Solution Overview
Problem
MEMS inertial sensor devices face performance irregularities and potential damage due to thermal expansion mismatches between disparate package materials and the silicon or glass die, as well as stress from vibrations and shocks, which existing isolation materials fail to adequately address.
Innovation Solution
A discrete stress isolation structure is implemented, where multiple stress isolation structures are interposed between the mechanism die and package substrate, allowing for electrical and mechanical coupling through metallized bond pads, and a capacitive device mechanism is attached to the die with a moveable portion for measuring differential capacitance, using gold stud bump flip chip techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If isolation materials with intermediate CTE are used between die and substrate, then thermal stress is reduced, but residual stress and performance irregularities remain due to CTE mismatch
Solution Approach 1:
The patent introduces discrete stress isolator structures as intermediary elements between the mechanism die and package substrate. These isolators serve as mechanical mediators that decouple the thermal expansion paths of the die and substrate, allowing each to expand and contract independently without transmitting stress to the other. The isolators are positioned at specific locations rather than providing continuous isolation, enabling targeted stress relief while maintaining structural integrity.
Solution Approach 2:
The isolation function is segmented into discrete, spatially distributed stress isolator structures rather than using a continuous isolation material layer. Each isolator is a separate element that can be independently positioned and sized, allowing optimization of stress relief at critical locations while minimizing overall package volume and maintaining mechanical stability.
2Strength
If die mounting is performed at high temperature, then bonding strength is achieved, but thermal expansion mismatch causes stress and potential damage during cooling
Solution Approach 1:
The stress isolator structures are pre-positioned between the mechanism die and package substrate before final bonding. These isolators act as pre-installed cushioning elements that accommodate thermal expansion differences during the high-temperature bonding process and subsequent cooling, preventing stress concentration that would otherwise occur at the bonding interfaces.
3Reliability
If isolation material is positioned between die and substrate, then mechanical isolation is provided, but electrical coupling requires additional complex interconnection structures
Solution Approach 1:
The stress isolator structures serve multiple functions simultaneously: they provide mechanical isolation to decouple thermal stresses, act as spacing elements to maintain proper z-direction positioning, and function as electrical interconnection carriers through metallized bond pads. This multi-functionality eliminates the need for separate electrical interconnection structures, reducing overall device complexity.
Solution Approach 2:
The patent merges the mechanical isolation function with the electrical interconnection function into a single integrated structure. The stress isolators are metallized to provide both mechanical support and electrical pathways, combining what would traditionally require separate components into one unified element that simplifies the overall package architecture.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively reduces thermal expansion-related biases and mechanical stresses, enhancing the reliability and performance of MEMS inertial sensor devices by spacing the device mechanism away from the package substrate and allowing for precise motion measurements.
Implementation Method 1
The mechanism die and package substrate are formed of different materials having substantially different coefficients of thermal expansion (CTE)
Implementation Method 2
The mechanism die is electrically and mechanically coupled through metallized bond pads on the respective isolation structures to metallized bond pads provided on the surface of the package substrate
Implementation Method 3
A capacitive device mechanism is attached to the mechanism die between the mechanism die and package substrate. The device mechanism is spaced away from the surface of the mechanism die facing toward the package substrate and is attached thereto through one or more anchors
Data Source
AI summary
A discrete stress isolation apparatus for a Micro Electro-Mechanical System (MEMS) inertial sensor device having a mechanism die and a package. A capacitive device mechanism is formed in a substrate layer positioned between the mechanism die and package substrate. A discrete stress isolation structure is formed in the same substrate layer with but physically separated from the capacitive device mechanism. The discrete stress isolation structure is interposed between the mechanism die and the package substrate and provides the mechanical and electrical attachment therebetween.