MEMS Sensor Package Decoupling Structure for Stress Isolation
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Solution Overview
Problem
Microelectromechanical systems (MEMS) sensors face challenges in maintaining long-term stability and performance due to mechanical stresses during manufacturing and thermal expansion mismatches between sensors and their ceramic packages, which can lead to performance drifting and reduced lifespan.
Innovation Solution
A sensor package design featuring a ceramic package with stair-stepped sidewalls and a ceramic plate that decouples sensors from mechanical stresses by using metal lids and wire bondings to connect sensors and an ASIC, reducing stress transmission from the package to the sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If sensors are directly attached to the package bottom, then device complexity is reduced, but mechanical stresses from soldering and thermal expansion are transmitted to the sensors, causing performance drift and reduced reliability
Solution Approach 1:
The package structure is segmented into distinct functional zones: a stress-isolating cavity formed by sidewalls, a sensor mounting platform elevated from the package bottom, and separate attachment points for sensors and ASIC. This segmentation physically separates sensors from stress sources while maintaining electrical connectivity through the cavity structure.
Solution Approach 2:
The cavity and sidewall structure act as an intermediary element between the package bottom and the sensors. This intermediary absorbs and isolates mechanical stresses from soldering and thermal expansion, preventing direct transmission to the sensors while still allowing electrical connections through wire bondings.
2Reliability
If ceramic packaging materials with matched CTE are used, then sensor stability is improved, but mechanical stress levels on the package during soldering are still high and are coupled through to the sensors
Solution Approach 1:
The cavity structure is designed beforehand to cushion and absorb mechanical stresses before they reach the sensors. The sidewalls and elevated platform configuration pre-establish a stress-isolating environment that protects sensors during subsequent soldering and thermal cycling operations.
Solution Approach 2:
The sensors are extracted from the direct stress path by elevating them on a platform within the cavity, separating them from the package bottom where stresses are concentrated. This extraction removes sensors from the harmful stress field while maintaining their functional integration.
3Manufacturing precision
If sensors are calibrated after final test, then manufacturing precision is improved, but soldering-induced stresses still cause performance drift after calibration
Solution Approach 1:
The stress-isolating cavity structure is prepared in advance before soldering operations, creating a protected environment for the sensors. This preliminary structural preparation ensures that when sensors are calibrated and then subjected to soldering, the pre-built cavity prevents stress transmission that would otherwise cause calibration drift.
4Ease of manufacture
If a simple package structure is used, then ease of manufacture is improved, but the ability to decouple sensors from package stresses is reduced
Solution Approach 1:
The package structure transitions from a two-dimensional planar attachment to a three-dimensional elevated cavity structure. The sidewalls and platform create vertical separation between sensors and the package bottom, adding a dimensional aspect that provides stress isolation while remaining compatible with standard ceramic fabrication processes.
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 design significantly reduces mechanical stresses on sensors by 40.34% to 49.4%, enhancing their service life and performance stability, similar to standalone operation, and minimizes the need for additional testing.
Implementation Method 1
Wire bondings electrically connect pads on a top face of the sensor to corresponding pads on a top face of the ASIC
Implementation Method 2
mismatches in the coefficient of thermal expansion (CTE) between the sensors and the package
Data Source
AI summary
A sensor package includes a packaging formed by a package bottom, first and second sidewalls extending upwardly from first and second opposite sides of the package bottom, and third and fourth sidewalls extending upwardly from third and fourth opposite sides of the package bottom, the sidewalls and package bottom defining a cavity. An integrated circuit is attached to the package bottom. A plate extends between two of the sidewalls within the cavity and is spaced apart from the package bottom. Sensors are attached to a top surface of the plate on opposite sides of an opening. Wire bondings electrically connect pads on a top face of the sensor to corresponding pads on a top face of the integrated circuit, for example by passing through the opening in the plate or passing past a side end of the plate. A lid extends across and between the sidewalls to close the cavity.