MEMS Microphone Housing Design for Acoustic Rear Volume Optimization
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Solution Overview
Problem
Miniaturized MEMS microphones face challenges in maintaining acoustic sensitivity and noise properties due to reduced rear volume, leading to increased counter pressure that prevents membrane deflection and affects performance.
Innovation Solution
A housing design that utilizes a large cavity as the rear volume by positioning the MEMS chip above a sound inlet opening, with electrically conductive connections to the housing terminals, and maintaining a passage between the chip and housing to form a common rear volume, while using elastic compounds or spring elements for mechanical and electrical contact to minimize stress and ensure efficient sound transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the MEMS chip surface area is reduced for miniaturization and cost reasons, then the component size and cost are improved, but the rear volume available for microphone function is reduced, leading to increased counter pressure and reduced sensitivity
Solution Approach 1:
The patent transitions from a two-dimensional planar arrangement to a three-dimensional vertical stacking configuration. The MEMS chip is positioned above the sound inlet opening on the circuit board, utilizing the vertical dimension to create acoustic passages through the chip structure. This dimensional change allows the sound wave path to extend through multiple layers (housing → sound inlet opening → MEMS chip passages → rear volume), effectively increasing the acoustic path length and rear volume without increasing the footprint area on the circuit board.
Solution Approach 2:
The patent implements nested structures where passages are formed within the MEMS chip itself, and the chip is nested within the housing structure. The sound inlet opening is positioned within the housing, and the MEMS chip with internal passages is positioned within the housing above the opening. This nesting creates efficient use of space, allowing acoustic pathways to be embedded within the chip structure while maintaining compact overall dimensions.
2Manufacturing precision
If the MEMS chip is positioned to maximize rear volume usage, then acoustic sensitivity is improved, but mechanical stress and connection complexity increase
Solution Approach 1:
The electrically conductive connections serve dual functions: providing electrical connectivity between the MEMS chip and circuit board, and forming mechanical support structures that define acoustic passages. The same conductive elements that carry electrical signals also structurally define the sound pathways from the inlet opening through the chip to the rear volume, eliminating the need for separate acoustic channel structures.
Solution Approach 2:
The patent introduces an elastic compound as an intermediary material between the MEMS chip and the housing/circuit board. This elastic compound serves multiple purposes: providing mechanical cushioning to reduce stress on the MEMS chip, maintaining acoustic seal integrity, and allowing for thermal expansion differences. The intermediary layer decouples the rigid mechanical connections while preserving acoustic functionality.
3Strength
If elastic compounds are used for mechanical contact to reduce stress, then mechanical stress is reduced, but acoustic transmission efficiency may be affected
Solution Approach 1:
The patent applies different material properties to different regions: rigid electrically conductive connections are used where structural support and electrical connectivity are needed, while elastic compounds are applied specifically in regions requiring stress absorption and acoustic sealing. The local application of elastic materials at critical stress points allows the majority of the acoustic pathway to maintain rigid, acoustically efficient boundaries.
Solution Approach 2:
The patent employs composite construction combining rigid materials (housing, MEMS chip, electrically conductive connections) with elastic materials (elastic compound). This composite approach allows the system to simultaneously achieve rigid acoustic boundaries for efficient sound transmission and elastic elements for stress absorption and sealing. The combination of material properties resolves the contradiction between mechanical stress resistance and acoustic transmission efficiency.
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 enhances acoustic properties and sensitivity of MEMS microphones by optimizing the rear volume and reducing mechanical stress, allowing for improved performance without increasing component size.
Implementation Method 1
A known operating principle consists in the measurement of a capacitance between a membrane excited into vibration by sound and an adjacent fixed counter electrode.
Implementation Method 2
An elastic compound has the advantage that mechanical stresses cannot be formed between the MEMS chip and the top inside of the housing.
Data Source
AI summary
A component with a housing for a MEMS microphone is proposed that has a cavity with terminals arranged in the cavity, a sound inlet opening, and SMT contacts on an outer side. The MEMS chip installed in this housing closes the sound inlet opening from the inside and is connected by means of electrically conductive connections to the terminals of the housing. Opposite the electrically conductive connections, the MEMS chip is in mechanically intimate contact with the housing. The dimensioning of the housing relative to the MEMS chip allows the cavity at the sides of the MEMS chip to be used as an acoustic rear volume.