MEMS Microphone Ceramic Package for Harsh Environments
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Solution Overview
Problem
MEMS condenser microphones in harsh environments face contamination and thermal expansion mismatches, which compromise their operation due to aperture vulnerabilities and material incompatibilities, especially in extreme temperatures and high RF/EMI conditions.
Innovation Solution
A silicon MEMS microphone system with a ceramic package base and metal lids forming an acoustic chamber, equipped with a filter to prevent contaminants and an EMI shield to reduce interference, and thermally matched to extend the operating temperature range, while using vias to minimize RFI.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If an aperture is provided in the microphone package to allow acoustic signals to reach the microphone, then acoustic signal reception is improved, but contaminants such as particles and moisture can enter the interior and interfere with microphone operation
Solution Approach 1:
A filter is introduced as an intermediary component between the aperture and the microphone interior. The filter allows acoustic signals to pass through while blocking contaminants such as particles and moisture, thus resolving the contradiction between maintaining acoustic signal reception and preventing contaminant intrusion.
2Ease of manufacture
If standard package materials are used for the microphone package, then manufacturing ease is improved, but thermal expansion mismatches between the microphone die and package materials limit the operating temperature range
Solution Approach 1:
The package base material is changed from standard materials to a ceramic material with a coefficient of thermal expansion matched to silicon. This parameter change in material selection eliminates thermal expansion mismatches, allowing the microphone to operate reliably across an extended temperature range from -55°C to +215°C while maintaining manufacturability through established ceramic packaging processes.
3Reliability
If the microphone package provides shielding from environmental conditions, then reliability in harsh environments is improved, but electromagnetic interference can affect microphone signals
Solution Approach 1:
Metal lids are added to the package structure, which inadvertently provide electromagnetic shielding. The metal lids, initially intended primarily for mechanical protection and sealing, are configured to electrically connect and form an EMI shield, thus converting a potential source of interference into a protective feature that blocks electromagnetic interference from affecting microphone signals.
4Object-affected harmful factors
If a filter is added to cover the aperture to prevent contaminants, then contamination prevention is improved, but acoustic signal transmission may be affected
Solution Approach 1:
A porous filter material is selected that allows acoustic signals to pass through while blocking contaminants. The porous structure provides sufficient open area to maintain acoustic signal transmission while the pore size is small enough to prevent particles and moisture from entering the microphone interior, thus resolving the contradiction between contaminant blocking and acoustic signal transmission.
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
The solution enables reliable operation in harsh environments by preventing contamination, reducing electromagnetic interference, and expanding the temperature range for MEMS microphone systems.
Implementation Method 1
A filter covers the aperture in the second face of the package base to prevent contaminants from reaching the microphone
Implementation Method 2
A second metal lid encloses the second face of the base and the filter; includes an opening for allowing the audio signal to reach the acoustic chamber; and is electrically connected to the first metal lid, forming an EMI shield
Implementation Method 3
The package base is a ceramic material providing a good thermal expansion match for the silicon microphone and any silicon processing elements attached to the package base
Data Source
AI summary
A MEMS microphone system suited for harsh environments. The system uses an integrated circuit package. A first, solid metal lid covers one face of a ceramic package base that includes a cavity, forming an acoustic chamber. The base includes an aperture through the opposing face of the base for receiving audio signals into the chamber. A MEMS microphone is attached within the chamber about the aperture. A filter covers the aperture opening in the opposing face of the base to prevent contaminants from entering the acoustic chamber. A second metal lid encloses the opposing face of the base and may attach the filter to this face of the base. The lids are electrically connected with vias forming a radio frequency interference shield. The ceramic base material is thermally matched to the silicon microphone material to allow operation over an extended temperature range.